Preparation method of high-quality graphene conductive and heat-conductive film

Abstract

The application belongs to the field of functional films, and particularly relates to a preparation method of high-quality graphene heat-conducting and electricity-conducting film. The preparation method uses weakly oxidized graphene or graphene doped with heteroatoms in a covalent lattice as raw material, obtains a layered film through liquid-phase assembly, and obtains the high-quality graphene heat-conducting and electricity-conducting film through high-temperature graphitization heat treatment. The vacancies and defects generated by the covalent doping atoms from the graphene lattice at high temperature promote the interlayer migration of carbon atoms, effectively promote the three-dimensional rearrangement and crystallization of the graphite crystal in the graphitization process, thereby greatly improving the graphitization efficiency, the grain size, the order and the crystallization quality of the graphene film, and the heat-conducting and electricity-conducting performance. The application has the characteristics of simple preparation process, high efficiency, easy scale-up, high quality and performance of the obtained graphene film, lays a foundation for the application of graphene in the fields of heat management, electromagnetic shielding, energy storage, nuclear technology and the like, and is expected to be used for efficient graphitization of carbon materials such as graphene fibers.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of functional films, and particularly relates to a preparation method of high-quality graphene heat-conducting and electricity-conducting film. BACKGROUND

[0002] Graphene refers to a two-dimensional carbon material with a single-atom thickness, which is formed by sp 2 Hybridized carbon atoms are tightly packed in a honeycomb lattice structure in the plane direction, and has extremely high thermal conductivity (5300 W / mK) and carrier mobility (2x10 4 cm 2 / Vs), excellent thermal stability and chemical stability, and its two-dimensional structure characteristics make it easy to assemble into macro-ordered films, which has broad application prospects in the fields of thermal management, electromagnetic shielding, energy storage, etc. However, it is extremely difficult to transfer the excellent performance of graphene at the microscale to macro materials. Studies have shown that the transmission of electrons and phonons in graphene film is affected by many structural factors such as pores, defects, grain boundaries and stacking structure, and therefore, it is the key to the application of graphene film in the field of heat and electricity conduction to obtain highly dense, high crystallinity and highly ordered graphene film.

[0003] At present, graphene heat-conducting and electricity-conducting film is mainly prepared by using graphene oxide (GO) as an assembly unit, assembling the dispersion liquid into a film, and then performing chemical reduction, heat treatment and graphitization. Studies have shown that during the heat treatment process, the GO film mainly exists in three evolution stages: (1) 100-1000℃, in which stage, thermal decomposition of oxygen-containing functional groups mainly occurs, accompanied by carbon loss and serious interlayer expansion; (2) 1000-2000℃, in which stage, the in-plane lattice structure of graphene is mainly repaired; (3) 2000-3000℃, in which stage, the formation of three-dimensional crystal structure of graphite, i.e. the graphitization process, mainly occurs, including the migration and rearrangement of carbon atoms, and the transition from disordered stacking to AB stacking. However, at the graphitization temperature, the migration energy barrier of carbon atoms and vacancies in the in-plane repaired graphene is high, and the interlayer expansion also inhibits the further growth of the grain size, thus resulting in small grain size of the graphene film and containing a large amount of disordered arrangement and stacking, which greatly limits the heat and electricity conduction performance of the graphene film. Although the use of reduced graphene oxide or graphene with less oxygen content can reduce the expansion of the graphene film during heating, the obtained graphene film still has the problems of small grain size, low graphitization degree and disordered stacking. Moreover, for the above raw materials, even if a high-temperature graphitization of up to 4 hours is adopted, the grain size and order of the graphene film cannot be effectively improved. Therefore, it is urgent to develop a new graphene film preparation method which can realize efficient graphitization, and obtain high-performance graphene heat-conducting and electricity-conducting film with large grain size, high crystallinity and high order. SUMMARY

[0004] The application aims to provide a preparation method of high-quality graphene heat-conducting and electricity-conducting film, which can efficiently prepare graphene film with large grain size, high crystallinity and high order, and solve the problems of low efficiency, small grain size, high disorder degree and poor performance of the existing preparation method.

[0005] The technical scheme of the application is:

[0006] The application discloses a preparation method of high-quality graphene heat-conducting and electricity-conducting film, which uses heteroatom covalent lattice doped weakly oxidized graphene or graphene as raw material, obtains a layered film through liquid phase assembly, and uses defects and vacancies generated by covalent doped atoms at high temperature to promote the migration of carbon atoms between graphene layers, effectively promotes the three-dimensional rearrangement and crystallization of graphite crystals in the subsequent high-temperature graphitization process, and greatly improves the grain size, crystallization quality and order of the graphene film, so that the graphene film with high heat conduction and electricity conduction is prepared.

[0007] The preparation method of the high-quality graphene heat-conducting and electricity-conducting film, the doped elements of the heteroatom covalent lattice doping effectively prevent the defects of the graphene from healing during the heating process below 2000 DEG C, the doped elements are one or more than two kinds of nitrogen, boron, silicon, phosphorus, sulfur and fluorine, and the doped element / carbon atom ratio is between 0.01 and 0.5.

[0008] The preparation method of the high-quality graphene heat-conducting and electricity-conducting film, the weakly oxidized graphene or graphene has a layer number of between 1 and 10, a flake size of between 0.1 mu m and 1000 mu m, and a carbon / oxygen atom ratio of between 1 and 100.

[0009] The preparation method of the high-quality graphene heat-conducting and electricity-conducting film, preferably, the weakly oxidized graphene or graphene has a layer number of 1, a flake size of between 0.5 mu m and 100 mu m, and a carbon / oxygen atom ratio of between 4 and 40.

[0010] The preparation method of the high-quality graphene heat-conducting and electricity-conducting film, the weakly oxidized graphene or graphene is directly prepared; or the weakly oxidized graphene or graphene is prepared by using an oxidized graphene, a reduced oxidized graphene, a fluorinated graphene or graphene as raw material, and using a dopant containing a hetero element through a solvothermal treatment or a gas phase heat treatment.

[0011] The preparation method of the high-quality graphene heat-conducting and electricity-conducting film, the weakly oxidized graphene or graphene raw material needs to be configured into a dispersion liquid for liquid phase assembly, the dispersion liquid has a concentration range of 0.001-100 mg / mL, and a solvent includes but is not limited to one or more than two kinds of water, N-methyl pyrrolidone, N,N-dimethylformamide, formamide, acetonitrile, methanol and ethyl acetate.

[0012] The preparation method of the high-quality graphene conductive and heat-conductive film, preferably, the concentration of the dispersion liquid ranges from 0.01 mg / mL to 10 mg / mL.

[0013] The preparation method of the high-quality graphene conductive and heat-conductive film, and the method for obtaining the layered film through liquid-phase assembly includes but is not limited to a centrifugal casting film preparation method, a pressure-driven film preparation method, a coating method, a blade coating method, a spraying method, a spin coating method or a suction filtration method.

[0014] The preparation method of the high-quality graphene conductive and heat-conductive film, in the high-temperature graphitization process, an atmosphere of argon or nitrogen is used, the heating rate ranges from 1 ℃ / min to 20 ℃ / min, the graphitization temperature ranges from 2000 ℃ to 3000 ℃, the processing time ranges from 0.1 h to 5 h, and after natural cooling, a high-crystallinity high-heat-conductivity and high-conductivity graphene film is obtained through pressing, the pressure ranges from 1 MPa to 50 MPa, and the pressing time ranges from 0.01 h to 10 h.

[0015] The design idea of the application is:

[0016] The application proposes to use weakly oxidized graphene or graphene with hetero-element covalent lattice doping as raw materials to prepare graphene films, to use the characteristics of high-temperature decomposition of heteroatoms covalently doped into the lattice of graphene to generate vacancies and defects, to promote the migration of carbon atoms between graphene layers and the three-dimensional rearrangement and crystallization of graphite crystals in the graphitization process through vacancies and defects, and to greatly improve the graphitization efficiency and the grain size, crystallization quality, order and heat-conductivity and conductivity of the graphene film.

[0017] The application has the following advantages and beneficial effects:

[0018] 1. The application uses in-plane covalent lattice doping of graphene to generate activated vacancies and defects at high temperatures, promotes the migration and rearrangement of carbon atoms in the graphitization process, greatly improves the graphitization efficiency and the grain size, order and crystallinity of the graphene film, and the grain size of the graphene film prepared by using oxidized graphene as raw materials is increased by more than 100 times, the structural disorder degree is reduced from >30% to <5%, and the interlayer is mainly AB-stacked.

[0019] 2. The high-heat-conductivity and high-conductivity high-crystallinity graphene film obtained by the application has conductivity and heat-conductivity close to the limit of single-crystal graphite, and the conductivity and heat-conductivity can reach 20000-25000 S / cm and 1700-2000 W / mK, respectively, the high crystallinity is reflected in that the in-plane grain size reaches 10-100 mu m, the grain size perpendicular to the in-plane direction can reach 50-200 nm, the grain texture size is >500 nm, the graphitization degree can reach 0.9-1.0, and the interlayer spacing can reach 0.3354-0.336 nm.

[0020] 3、The method has high graphitization efficiency, and large crystal size, high order and high crystallinity can be realized in 10 minutes of graphitization, and the method is suitable for preparing graphene films with different thicknesses, including preparation and performance improvement of ultra-thick high-quality graphene films, and lays a foundation for application of graphene as heat-conducting film, conductive film, electromagnetic shielding film, neutron filter and monochromator, X-ray monochromator, etc. in the fields of electronic information, 5G communication, thermal management, nuclear technology, high-end instrument equipment, etc.

[0021] 4、The defect-promoted efficient graphitization method has universality, and is expected to be used for efficient graphitization of graphene films, graphene fibers, aerogels, carbon nanotube fibers, films, aerogels, carbon fibers, graphite and other carbon materials, and significantly improves the crystallization quality, order and thermal and electrical conductivity of the materials. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 : Schematic diagram for preparing high-crystalline graphene film by introducing defects through doping.

[0023] Figure 2 : Cross-sectional TEM photo of graphene film obtained by heat treatment at 3000 DEG C in Example 1.

[0024] Figure 3 : Cross-sectional STEM photo of graphene film obtained by heat treatment at 3000 DEG C in Example 1.

[0025] Figure 4 : Surface morphology photo of graphene film obtained by heat treatment at 3000 DEG C in Example 1.

[0026] Figure 5 : Surface orientation structure photo of graphene film obtained by heat treatment at 3000 DEG C in Example 1.

[0027] Figure 6 : XRD spectrum of graphene film obtained by heat treatment at 3000 DEG C in Example 1, the horizontal coordinate 2theta is the diffraction angle, and the unit is degree (°); the vertical coordinate Intensity is the diffraction peak intensity, and the unit (a.u.). Among them, the (002) peak position of graphene film obtained by heat treatment at 3000 DEG C is 26.539°, and the half peak width is 0.102, and the (002) peak position of high-oriented pyrolytic graphite HOPG is 26.541°, and the half peak width is 0.150.

[0028] Figure 7 : Raman spectrum of graphene film obtained by heat treatment at 3000 DEG C in Example 1, the horizontal coordinate Raman Shift is wave number, and the unit is cm -1: Cross-section high-magnification TEM image of graphene film obtained by heat treatment at 2000 °C in Example 1. T

[0029] Figure 8 : Cross-section high-magnification TEM image of graphene film obtained by heat treatment at 2500 °C in Example 1.

[0030] Figure 9 : Cross-section high-magnification TEM image of graphene film obtained by heat treatment at 2500 °C in Example 1.

[0031] Figure 10 : Cross-section low-magnification TEM image of graphene film obtained by heat treatment at 2500 °C in Example 1.

[0032] Figure 11 : Cross-section STEM image of graphene film obtained by heat treatment at 2500 °C in Example 1.

[0033] Figure 12 : XRD pattern of graphene film obtained by heat treatment at different temperatures in Example 1, horizontal axis 2theta is diffraction angle, unit is degree (°); vertical axis Intensity is diffraction peak intensity, unit is (a.u.).

[0034] Figure 13 : Raman spectrum of graphene film obtained by heat treatment at different temperatures in Example 1, horizontal axis Raman Shift is wave number, unit is cm -1 ; vertical axis Intensity is signal peak intensity, unit is (a.u.).

[0035] Figure 14 : Cross-section TEM image of graphene film obtained by heat treatment at 3000 °C in Comparative Example 1.

[0036] Figure 15 : Cross-section STEM image of graphene film obtained by heat treatment at 3000 °C in Comparative Example 1.

[0037] Figure 16 : Surface morphology image of graphene film obtained by heat treatment at 3000 °C in Comparative Example 1.

[0038] Figure 17 : Surface orientation structure image of graphene film obtained by heat treatment at 3000 °C in Comparative Example 1.

[0039] Figure 18 ​: XRD pattern of graphene film obtained in Comparative Example 1 at 3000°C, abscissa 2theta is diffraction angle, unit is degree (°); ordinate Intensity is diffraction peak intensity, unit (a.u.). Among them, graphene film (002) peak position = 26.521°, half peak width = 0.158, highly oriented pyrolytic graphite HOPG (002) peak position = 26.541°, half peak width = 0.150.

[0040] Figure 19 : Raman spectrum of graphene film obtained in Comparative Example 1, abscissa Raman Shift is wave number, unit is cm -1 ; ordinate Intensity is signal peak intensity, unit (a.u.). The small box is the fine peak spectrum of 2D peak, which shows that the AB stacking ratio (2D2 / (2D2+2D T ) in the structure of the graphene film is about 65%.

[0041] Figure 20 : Cross-sectional TEM photograph of graphene film obtained in Comparative Example 1 at 2000°C.

[0042] Figure 21 : Cross-sectional TEM photograph of graphene film obtained in Comparative Example 1 at 2500°C.

[0043] Figure 22 : XRD pattern of graphene film obtained in Comparative Example 1 at different temperatures, abscissa 2theta is diffraction angle, unit is degree (°); ordinate Intensity is diffraction peak intensity, unit (a.u.).

[0044] Figure 23 : Raman spectrum of graphene film obtained in Comparative Example 1 at different temperatures, abscissa Raman Shift is wave number, unit is cm -1 ; ordinate Intensity is signal peak intensity, unit (a.u.).

[0045] Figure 24 : Cross-sectional TEM photograph of graphene film obtained in Comparative Example 2 at 3000°C.

[0046] Figure 25 : Cross-sectional STEM photograph of graphene film obtained in Comparative Example 2 at 3000°C.

[0047] Figure 26 : Surface morphology photograph of graphene film obtained in Comparative Example 2 at 3000°C.

[0048] Figure 27: The surface orientation structure photograph of the graphene film obtained by heat treatment at 3000°C in Comparative Example 2.

[0049] Figure 28 : The XRD pattern of the graphene film obtained by heat treatment at 3000°C in Comparative Example 2, the horizontal axis 2theta is the diffraction angle, unit: degree (°); the vertical axis Intensity is the diffraction peak intensity, unit (a.u.). Wherein the graphene film (002) peak position = 26.461°, half peak width = 0.178, highly oriented pyrolytic graphite HOPG (002) peak position = 26.521°, half peak width = 0.158.

[0050] Figure 29 : The Raman spectrum of the graphene film obtained by heat treatment at 3000°C in Comparative Example 2, the horizontal axis Raman Shift is the wave number, unit: cm -1 ; the vertical axis Intensity is the signal peak intensity, unit (a.u.). The fine peak spectrum of 2D peak in the small box shows that the AB stacking ratio (2D2 / (2D2+2D T ) of the graphene film structure is about 79%. DETAILED DESCRIPTION

[0051] As shown in Figure 1 , the process for preparing the high-crystalline graphene film by introducing defects through doping is as follows: taking the graphene doped with heteroatoms (or weakly oxidized graphene) as raw material, using the dispersion liquid thereof to obtain a layered film through liquid phase assembly, heating to 2000°C to form a graphene film rich in defects (or a weakly oxidized graphene film rich in defects), and further heating to 3000°C to prepare a graphene film with excellent thermal and electrical conductivity, large grain size, high crystallinity and high order through high-temperature graphitization heat treatment. The electrical conductivity ranges from 20000 to 25000 S / cm, the thermal conductivity ranges from 1700 to 2000 W / mK, the in-plane grain size ranges from 10 to 100 μm, the grain size perpendicular to the in-plane direction ranges from 50 to 200 nm, the grain texture size is > 500 nm, the interlayer spacing ranges from 0.3354 to 0.336 nm, the graphitization degree ranges from 0.9 to 1.0, the AB stacking structure ratio ranges from 98 to 100%, and the density of the graphene film ranges from 2.20 to 2.25 g / cm 3 .

[0052] Hereinafter, the present application is further described in detail through examples and drawings.

[0053] Example 1

[0054] In this embodiment, the preparation method of the high-quality graphene thermal and electrical conductive film comprises the following steps:

[0055] (1) A dispersion of graphene oxide with an average sheet diameter of 1.5 μm was prepared using water as a solvent to a concentration of 0.2 mg / mL. Ammonia water with a volume fraction of 0.3% was added to the dispersion, and the mixture was stirred until homogeneous. The mixture was then placed in a reaction vessel with a filling degree of 75 vol%. The reaction vessel was sealed and placed in an oven at 150 °C for 16 h. Elemental analysis revealed that the nitrogen content of the nitrogen-doped graphene oxide was approximately 10.5 wt%, the carbon content was approximately 70 wt%, the oxygen content was approximately 18.5 wt%, the hydrogen content was approximately 1%, and the C / O atomic ratio was approximately 5.4.

[0056] (2) The nitrogen-doped graphene oxide dispersion after hydrothermal reaction was assembled into a membrane on a substrate by pressure-driven filtration. The substrate filter membrane material used was polyethersulfone with a pore size of 0.22 μm, and the filtration pressure was 6 bar. After drying, the substrate was peeled off to obtain a self-supporting nitrogen-doped graphene oxide membrane.

[0057] (3) A highly crystalline, conductive and thermally conductive graphene film was obtained by heating a nitrogen-doped graphene oxide film to 3000℃ at a rate of 10℃ / min under an inert atmosphere, holding it at that temperature for 10 min, allowing it to cool naturally, and then pressing it under a pressure of 30 MPa for 10 min. Additionally, nitrogen-doped graphene films were heated to 2000℃ and 2500℃ at a rate of 10℃ / min under an inert atmosphere and held for 1 h, respectively, as a comparison.

[0058] (4) The thermal conductivity and electrical conductivity of the graphene film obtained by heat treatment at 3000℃ were tested. The electrical conductivity was 20000 S / cm, and the thermal conductivity was 1700 W / mK. The corresponding TEM and STEM cross-sectional structures of the graphene film are shown below. Figure 2 and Figure 3 As shown, the SEM surface morphology and orientation structure of the graphene film are as follows. Figure 4 and Figure 5 As shown, it exhibits a highly regular, highly crystalline layered structure, with an in-plane grain size of approximately 20 μm, a grain size perpendicular to the in-plane direction of approximately 50 nm, and a grain texture size of approximately 700 nm. XRD and Raman spectra are shown below. Figure 6 and Figure 7 As shown, the graphene film exhibits high order, high graphitization degree, and high crystallinity, with an interlayer spacing of approximately 0.3558 nm, a graphitization degree of 0.93, an AB stacking structure ratio of 99%, and a graphene film density of approximately 2.22 g / cm³. 3 .

[0059] (5) The thermal conductivity and electrical conductivity of the graphene film obtained by heat treatment at 2000℃ were tested. The electrical conductivity was 310 S / cm and the thermal conductivity was 60 W / mK. The corresponding TEM cross-sectional structure of the graphene film is shown below. Figure 8As shown in FIG. 1, the graphene film prepared by the method of the present application exhibits a short-range ordered layered structure with defects. The graphene film obtained by heat treatment at 2000°C was tested for thermal conductivity and electrical conductivity, and the graphene film had an electrical conductivity of 8120 S / cm and a thermal conductivity of 1000 W / mK. The TEM and STEM cross-sectional structure of the graphene film are shown in FIGS. 2 and 3, respectively. Figure 9 、 Figure 10 and Figure 11 As shown in FIG. 1, the graphene film prepared by the method of the present application exhibits a short-range ordered layered structure with defects. The graphene film obtained by heat treatment at 2000°C was tested for thermal conductivity and electrical conductivity, and the graphene film had an electrical conductivity of 8120 S / cm and a thermal conductivity of 1000 W / mK. The TEM and STEM cross-sectional structure of the graphene film are shown in FIGS. 2 and 3, respectively. Figure 12 and Figure 13 As shown in FIG. 1, the graphene film prepared by the method of the present application exhibits a short-range ordered layered structure with defects. The graphene film obtained by heat treatment at 2000°C was tested for thermal conductivity and electrical conductivity, and the graphene film had an electrical conductivity of 8120 S / cm and a thermal conductivity of 1000 W / mK. The TEM and STEM cross-sectional structure of the graphene film are shown in FIGS. 2 and 3, respectively. 3 3

[0060] Comparative Example 1

[0061] In the present comparative example, the graphene thermally and electrically conductive film was prepared by the following steps:

[0062] (1) The graphene oxide with an average flake size of 2 μm was configured into a 0.2 mg / mL dispersion using water as the solvent. The elemental analysis showed that the content of carbon element in the graphene oxide was about 48 wt%, the content of oxygen element was about 47 wt%, the content of hydrogen element was 5 wt%, and the C / O atomic ratio was about 1.4.

[0063] (2) The graphene oxide dispersion was assembled into a film on a substrate by a centrifugal casting film formation method. The substrate film material used was a copper foil, and a rotating roller with an inner diameter of 100 mm and a width of 100 mm was used. The rotating roller had a rotation speed of 5000 rpm, the needle moving speed was 800 mm / min, the moving distance was 70 mm, and the flow rate of the graphene oxide dispersion was 60 ml / min. The number of repeated scans was 1000 times.

[0064] ​​(3) The obtained assembled film is dried and peeled off from the substrate to obtain a self-supporting graphene oxide film. The graphene oxide film is heated to 3000°C at a rate of 10°C / min in an inert atmosphere, and held for 10 min. After natural cooling, the graphene film is obtained by pressing under a pressure of 30 MPa for 10 min. In addition, the graphene oxide film is heated to 2000°C and 2500°C, respectively, at a rate of 10°C / min in an inert atmosphere, and held for 1 h as a comparison.

[0065] (4) The graphene film obtained by heat treatment at 3000°C is tested for thermal conductivity and electrical conductivity, and the electrical conductivity is 3250 S / cm and the thermal conductivity is 880 W / mK. The TEM and STEM cross-sectional structures of the corresponding graphene film are shown in Figure 14 and Figure 15 , and there are pores and wrinkles between the layers, and the degree of crystallization is low. The SEM surface morphology and orientation structure of the graphene film are shown in Figure 16 and Figure 17 , and the in-plane grain size is about 2 μm, the grain size perpendicular to the in-plane direction is about 12 nm, and the grain texture size is about 200 nm. The XRD and Raman spectra are shown in Figure 18 and Figure 19 . Compared with Example 1, the graphene film prepared from graphene with a higher oxidation degree exhibits low order degree, low graphitization degree and low crystalline quality, the interlayer spacing is about 0.3565 nm, the graphitization degree is only 0.70, and the proportion of AB stacking structure is only 65%. The density of the graphene film is about 1.7 g / cm 3 .

[0066] (5) The graphene film obtained by heat treatment at 2000°C is tested for thermal conductivity and electrical conductivity, and the electrical conductivity is 1330 S / cm and the thermal conductivity is 450 W / mK. The TEM cross-sectional structure of the corresponding graphene film is shown in Figure 20 . The graphene in-plane lattice defects are repaired and perfect, and the structure is complete. The graphene film obtained by heat treatment at 2500°C is tested for thermal conductivity and electrical conductivity, and the electrical conductivity is 2450 S / cm and the thermal conductivity is 740 W / mK. The TEM cross-sectional structure of the corresponding graphene film is shown in Figure 21 . It exhibits a similar layered structure to the graphene film heat-treated at 2000°C. The XRD and Raman spectra of the graphene films heat-treated at 2000°C and 2500°C are shown in Figure 22 and Figure 23As shown, the interlayer spacing of the graphene film obtained by 2000℃ heat treatment is about 0.3418 nm, and the graphitization degree is 0.14. The interlayer spacing of the graphene film obtained by 2500℃ heat treatment is about 0.3370 nm, and the graphitization degree is 0.62. It can be found from the peak shape of the 2D peak in the Raman spectrum that the graphene films obtained by 2000℃ and 2500℃ heat treatment are both non-AB stacking structures. The density of the graphene film obtained by 2000℃ heat treatment is about 0.80 g / cm 3 , and the density of the graphene film obtained by 2500℃ heat treatment is about 1.60 g / cm 3 .

[0067] Comparative Example 2

[0068] In the present comparative example, the preparation method of the high-quality graphene conductive and heat-conductive film comprises the following steps:

[0069] (1) The graphene oxide with an average flake size of 10 μm was configured into a 0.2 mg / mL dispersion solution with water as the solvent, and was placed in a reaction kettle with a filling degree of 75 vol%. The reaction kettle was sealed and placed in a 150℃ oven for 20 h. The element analysis showed that the content of carbon element in the graphene oxide was about 75 wt%, the content of oxygen element was about 22 wt%, the content of hydrogen element was about 3 wt%, and the C / O atomic ratio was about 4.6.

[0070] (2) The graphene oxide dispersion solution was assembled into a film on a substrate by a centrifugal casting film forming method. The substrate film material used was a copper foil, and a rotating drum with an inner diameter of 100 mm and a width of 100 mm was used. The rotating drum speed was 2000 rpm, the needle moving speed was 500 mm / min, the moving distance was 90 mm, and the flow rate of the graphene oxide dispersion solution was 70 ml / min. The number of repeated scans was 1000 times.

[0071] (3) After drying, the obtained self-supporting graphene oxide film was peeled off from the substrate film, and was heated to 3000℃ at a rate of 10℃ / min under an inert atmosphere, and was kept for 2 h. After natural cooling, the graphene film was obtained by pressing under a pressure of 30 MPa for 10 minutes.

[0072] (4) The obtained graphene film was tested for thermal conductivity and electrical conductivity. The electrical conductivity was 9400 S / cm, and the thermal conductivity was 1000 W / mK. The TEM and STEM cross-sectional structure of the corresponding graphene film is shown in Figure 24 and Figure 25 , and the SEM surface morphology and orientation structure of the graphene film are shown in Figure 26 and Figure 27The in-plane grain size is about 3.2 μm, the grain size perpendicular to the in-plane direction is about 17 nm, and the grain texture size is about 410 nm. The XRD and Raman spectra are shown in Figure 28 and Figure 29 As shown in the figure, compared with Example 1, the graphene film prepared by using undoped graphene as raw material exhibits low order degree and low graphitization degree, and the density of the graphene film is about 1.90 g / cm 3 .

[0073] Example 2

[0074] In this embodiment, the preparation method of the high-quality graphene conductive and heat-conductive film comprises the following steps:

[0075] (1) The graphene oxide with an average flake size of 10 μm is configured into a dispersion liquid with a concentration of 0.1 mg / mL by using water as a solvent, ammonia water with a volume fraction of 0.2% of the dispersion liquid is added, and the mixture is stirred and mixed uniformly. The reaction kettle is filled to 75 vol%, and the reaction kettle is sealed and placed in an oven at 180°C for 20 h. The nitrogen element content of the nitrogen-doped graphene oxide is about 13 wt%, the carbon element content is about 74 wt%, the oxygen element content is about 11 wt%, the hydrogen element content is about 2%, and the C / O atomic ratio is about 9, which is measured by elemental analysis.

[0076] (2) The nitrogen-doped graphene oxide dispersion liquid after the hydrothermal reaction is assembled into a film on a substrate by a centrifugal casting film forming method. The substrate film material used is a copper foil, a rotating roller with an inner diameter of 100 mm and a width of 100 mm is used, the rotating speed of the rotating roller is 1000 rpm, the moving speed of the needle is 400 mm / min, the moving distance is 50 mm, and the flow rate of the nitrogen-doped graphene oxide dispersion liquid is 50 ml / min. The number of repeated scanning is 1000 times.

[0077] (3) After the layer-by-layer assembled film is dried, a self-supporting nitrogen-doped graphene oxide film is obtained. The film is heated to 3000°C at a rate of 10°C / min in an inert atmosphere, and then heat preserved for 2 h. After natural cooling, the film is pressed under a pressure of 30 MPa for 10 minutes to obtain a high-crystallinity conductive and heat-conductive graphene film.

[0078] (4) The obtained graphene film is tested for thermal conductivity and electrical conductivity. The electrical conductivity is 25000 S / cm, and the thermal conductivity is 2000 W / mK. The in-plane grain size is about 50 μm, the grain size perpendicular to the in-plane direction is about 80 nm, and the grain texture size is about 1080 nm. The graphene film exhibits high order degree, high graphitization degree and high crystalline quality. The interlayer spacing is about 0.3556 nm, the graphitization degree is 0.98, the proportion of AB stacking structure is 99.5%, and the density of the graphene film is about 2.25 g / cm 3 .

[0079] Example 3

[0080] In this embodiment, the preparation method of high-quality graphene thermally and electrically conductive film includes the following steps:

[0081] (1) The average flake size of 1 μm graphene oxide is configured into a 0.1 mg / mL dispersion solution with DMF as the solvent and ultrasonic dispersion. 0.5% volume fraction of ammonia borane solution is added, mixed and stirred uniformly, placed in a reaction kettle, the filling degree of the reaction kettle is 60 vol%, the reaction kettle is sealed and placed in a 200°C oven, and the reaction is carried out for 20 h. The nitrogen content of boron-nitrogen co-doped graphene oxide is about 8 wt%, the boron content is about 6 wt%, the carbon content is about 82 wt%, the oxygen content is about 4 wt%, and the carbon-oxygen ratio is about 27, measured by elemental analysis.

[0082] (2) The boron-nitrogen co-doped graphene oxide dispersion solution is assembled into a film on the substrate by pressure-driven film forming method, the pressure is 6 bar, and the filter membrane is polyether sulfone.

[0083] (3) After drying the boron-nitrogen co-doped graphene oxide film obtained by assembly, it is heated to 3000°C at a rate of 10°C / min in an inert atmosphere, and kept for 0.5 h. After natural cooling, it is pressed under a pressure of 50 MPa for 10 minutes to obtain a graphene film.

[0084] (4) The thermal conductivity and electrical conductivity of the obtained graphene film are tested, the electrical conductivity is 22000 S / cm, the thermal conductivity is 2000 W / mK. The in-plane grain size is about 35 μm, the grain size perpendicular to the in-plane direction is about 72 nm, the grain texture size is about 1500 nm, the interlayer spacing is about 0.3560 nm, the graphitization degree reaches 0.98, and the proportion of AB stacking structure reaches 99.7%. The graphene film shows similar highly ordered and highly crystallized structure as in Example 1, and the density of the graphene film is about 2.25 g / cm 3 .

[0085] Example 4

[0086] In this embodiment, the preparation method of high-quality graphene thermally and electrically conductive film includes the following steps:

[0087] (1) The average flake size of 1 μm graphene oxide was configured into a 0.2 mg / mL dispersion with water as the solvent, 0.5% volume fraction of ammonia borane solution was added to the dispersion, and the mixture was stirred uniformly and placed in a hydrothermal reactor. The reactor filling degree was 60 vol%, and the reactor was sealed and placed in a 180°C oven. The reaction was carried out for 15 h. The nitrogen content of the boron-nitrogen co-doped graphene oxide was about 7 wt%, the boron content was about 4 wt%, the carbon content was about 81 wt%, the oxygen content was about 8 wt%, and the C / O atomic ratio was about 13.5, as measured by elemental analysis.

[0088] (2) The boron-nitrogen co-doped graphene oxide dispersion was assembled into a film on a substrate by pressure-driven film formation method, with a pressure of 5 bar and a filter membrane of polyether sulfone.

[0089] (3) After drying the assembled boron-nitrogen co-doped graphene oxide film, it was heated to 2500°C at a rate of 10°C / min in an inert atmosphere, and held for 1 h. After natural cooling, the graphene film was pressed at a pressure of 50 MPa for 10 minutes.

[0090] (4) The obtained graphene film was tested for thermal conductivity and electrical conductivity, with an electrical conductivity of 5000 S / cm and a thermal conductivity of 1000 W / mK. Compared with Examples 1, 2 and 3, the crystallinity, order and graphitization degree of the graphene film were lower, and the difference in electrical conductivity and thermal conductivity mainly came from the difference in graphitization treatment temperature. The density of the graphene film was about 2.0 g / cm 3 .

[0091] Example 5

[0092] In this embodiment, the method for preparing high-quality graphene heat-conducting and electricity-conducting film comprises the following steps:

[0093] (1) The average flake size of 10 μm graphene oxide was configured into a 0.4 mg / mL dispersion with methanol as the solvent, 0.5 g of diphenyl disulfide was added and stirred uniformly, and placed in a reactor. The reactor filling degree was 75 vol%, and the reactor was sealed and placed in a 150°C oven. The reaction was carried out for 10 h. The sulfur content of the sulfur-doped graphene oxide was about 10 wt%, the carbon content was about 80 wt%, the oxygen content was about 10 wt%, and the C / O atomic ratio was about 11, as measured by elemental analysis.

[0094] (2) The sulfur-doped graphene oxide dispersion was assembled into a film by pressure-driven film formation method, with a pressure of 7 bar and a filter membrane of polyvinylidene fluoride film.

[0095] (3) The assembled sulfur-doped graphene oxide film is dried, and then heated to 3000°C at a rate of 10°C / min under inert atmosphere, and kept for 0.5 h. After natural cooling, the graphene film is obtained by pressing under a pressure of 50 MPa for 5 min.

[0096] (4) The obtained graphene film is tested for thermal conductivity and electrical conductivity. The electrical conductivity is 19500 S / cm, the thermal conductivity is 1800 W / mK, and the density of the graphene film is about 2.2 g / cm 3 .

[0097] Example 6

[0098] In this embodiment, the method for preparing a high-quality graphene film with thermal and electrical conductivity comprises the following steps:

[0099] (1) Oxidized graphene with an average flake size of 10 μm is configured into a 0.4 mg / mL dispersion solution using formamide as a solvent, and is placed in a reaction kettle with a filling degree of 75 vol%. The reaction kettle is sealed and placed in an oven at 150°C for 20 h. Elemental analysis shows that the nitrogen-doped graphene oxide contains about 15 wt% of nitrogen, about 75 wt% of carbon, and about 10 wt% of oxygen, and the C / O atomic ratio is about 10. The solvent can be directly used as a dopant to achieve doping.

[0100] (2) The nitrogen-doped graphene oxide dispersion solution is assembled into a film by pressure-driven film formation method, and the pressure is 6 bar. The filter membrane is a polyvinylidene fluoride membrane.

[0101] (3) The assembled nitrogen-doped graphene oxide film is dried, and then heated to 3000°C at a rate of 10°C / min under inert atmosphere, and kept for 0.5 h. After natural cooling, the graphene film is obtained by pressing under a pressure of 50 MPa for 5 min.

[0102] (4) The obtained graphene film is tested for thermal conductivity and electrical conductivity. The electrical conductivity is 21000 S / cm, the thermal conductivity is 1800 W / mK, and the density of the graphene film is about 2.21 g / cm 3 .

[0103] Example 7

[0104] In this embodiment, the method for preparing a high-quality graphene film with thermal and electrical conductivity comprises the following steps:

[0105] (1) Oxidized graphene with an average flake size of 1 μm is configured into a 0.2 mg / mL dispersion solution using water as a solvent, and is freeze-dried to obtain graphene oxide powder. The graphene oxide powder is mixed with thiourea and placed in a tube furnace for heat treatment at 600°C for 1 h. Elemental analysis shows that the nitrogen-sulfur co-doped graphene oxide contains 12 wt% of nitrogen, 3 wt% of sulfur, and 85 wt% of carbon.

[0106] (2) The nitrogen-sulfur co-doped graphene oxide powder is dispersed in N-methyl pyrrolidone (NMP) solvent, and a film is assembled on a substrate by a pressure-driven film forming method, the pressure is 4 bar, and the filter membrane is a polyether sulfone membrane.

[0107] (3) After the assembled nitrogen-sulfur co-doped graphene oxide film is dried, the temperature is increased to 3000 DEG C at a rate of 10 DEG C / min under an inert atmosphere, and the temperature is kept for 0.5 h, and after natural cooling, a high-crystallinity conductive and heat-conductive graphene film is obtained.

[0108] (4) The obtained graphene film is tested for thermal conductivity and electrical conductivity, the electrical conductivity is 20000 S / cm, and the thermal conductivity is 1800 W / mK. The density of the graphene film is about 2.21 g / cm 3 .

[0109] The implementation results show that, by using covalent lattice-doped graphene or weakly oxidized graphene as raw material, vacancies and defects generated by covalent doping atoms from the graphene lattice at high temperature promote the interlayer migration of carbon atoms, effectively promote the three-dimensional rearrangement and crystallization of graphite crystals in the graphitization process, and thus greatly improve the graphitization efficiency, grain size, order and crystallization quality of the graphene film, and the thermal and electrical conductivity.

Claims

1. A method for preparing a high-quality graphene thermally and electrically conductive film, characterized in that, Using weakly doped graphene oxide or graphene with heteroatom covalent lattice as raw material, layered films are obtained through liquid-phase assembly. The defects and vacancies generated by the decomposition of covalent doped atoms from the graphene lattice at high temperature promote the migration of carbon atoms between graphene layers, effectively promoting the three-dimensional rearrangement and crystallization of graphite crystals during the subsequent high-temperature graphitization process. This significantly improves the grain size, crystal quality and order of the graphene film, resulting in a graphene film with high thermal and electrical conductivity. The dopant elements of heteroatom covalent lattice doping effectively prevent the healing of defects in graphene during the heating process below 2000℃. The dopant elements are one or a mixture of two of nitrogen, boron, and sulfur, and the ratio of dopant elements to carbon atoms is between 0.01 and 0.

5.

2. The method for preparing a high-quality graphene thermally and electrically conductive film according to claim 1, characterized in that, Weakly oxidized graphene or graphene has 1 to 10 layers, a sheet size of 0.1 μm to 1000 μm, and a carbon / oxygen atom ratio of 1 to 100.

3. The method for preparing a high-quality graphene thermally and electrically conductive film according to claim 2, characterized in that, Weakly oxidized graphene or graphene with one layer, a sheet diameter ranging from 0.5 μm to 100 μm, and a carbon / oxygen atom ratio ranging from 4 to 40.

4. The method for preparing a high-quality graphene thermally and electrically conductive film according to claim 1, characterized in that, It can be prepared directly from weakly doped graphene oxide or graphene with heteroatom covalent lattice; or it can be prepared by using graphene oxide, reduced graphene oxide, fluorinated graphene or graphene as raw materials and employing dopants containing heterogeneous elements through solvothermal treatment or gas-phase heat treatment.

5. The method for preparing a high-quality graphene thermally and electrically conductive film according to claim 1, characterized in that, The weakly doped graphene oxide or graphene raw material with heteroatom covalent lattice needs to be prepared into a dispersion for liquid phase assembly. The concentration of the dispersion ranges from 0.001 to 100 mg / mL. The solvent used includes one or more of the following: water, N-methylpyrrolidone, N,N-dimethylformamide, formamide, acetonitrile, methanol, and ethyl acetate.

6. The method for preparing a high-quality graphene thermally and electrically conductive film according to claim 5, characterized in that, The concentration range of the dispersion is 0.01~10 mg / mL.

7. The method for preparing a high-quality graphene thermally and electrically conductive film according to claim 1, characterized in that, Methods for obtaining layered thin films by liquid phase assembly include centrifugal casting, pressure-driven film formation, coating, blade coating, spray coating, spin coating, or vacuum filtration.

8. The method for preparing a high-quality graphene thermally and electrically conductive film according to claim 1, characterized in that, During the high-temperature graphitization process, argon or nitrogen atmosphere is used, the heating rate is between 1 and 20℃ / min, the graphitization temperature is between 2000 and 3000℃, the processing time is between 0.1 and 5h, and after natural cooling, a highly crystalline, highly thermally and electrically conductive graphene film is obtained by pressing at a pressure of 1 to 50MPa for a pressing time of 0.01 to 10h.

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