A polyacrylonitrile-based graphite film induced by in-situ nitrogen-doped graphene and a preparation method thereof

Abstract

The application relates to a polyacrylonitrile-based graphite film induced by in-situ nitrogen-doped graphene and a preparation method thereof, and relates to the technical field of graphene film materials.The preparation method comprises the following steps: mixing an oxidized graphene solution and a polyacrylonitrile solution to obtain a GO / PAN mixed slurry; coating and first drying the GO / PAN mixed slurry to obtain a GO / PAN composite film; suspending the GO / PAN composite film above ammonia liquid, and then performing fumigation treatment and second drying and the like.The application promotes the conversion of linear polyacrylonitrile into a graphite structure and improves the formation of a long-range ordered graphite structure in a two-dimensional space, and simultaneously solves the gas expansion problem of GO in the warm treatment process in the composite film, so that the heat conduction performance of the obtained polyacrylonitrile-based graphite film is significantly improved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of graphene film materials, and particularly relates to a polyacrylonitrile-based graphene film induced by in-situ nitrogen doping and a preparation method thereof. BACKGROUND

[0002] In recent years, graphene heat-conducting films have won wide praise in the scientific research and industrial fields as the best in the field of thermal management materials, with excellent heat transfer efficiency, extraordinary mechanical strength and excellent low-temperature resistance. In many high-tech fields such as electronics, communications and aerospace, especially in microelectronics, integrated circuits and high-performance computing devices, graphene heat-conducting films have become a key technical approach to improve the reliability and performance of devices due to their excellent heat distribution and dissipation performance. In addition, their light weight characteristics also show unique charm in meeting the strict weight reduction requirements, further expanding the application scope in modern high-end technologies.

[0003] The preparation process of graphene heat-conducting films is rich and varied, and is mainly realized through inorganic and organic paths. The inorganic method usually involves the steps of expansion, exfoliation, oxidation, reassembly and high-temperature carbonization of natural flake graphite to obtain graphene heat-conducting films with excellent heat-conducting performance. Among them, graphene oxide (GO) prepared by the Hummers method is particularly classic as a building unit to prepare graphene heat-conducting films. In this process, graphene oxide is assembled into a highly oriented film material, and then undergoes complex and strict temperature rising treatment to remove impurity atoms, thereby obtaining a graphene film with high crystallinity.

[0004] To cope with the challenges of processing cost and performance optimization, researchers and engineers continue to explore and expand new ways of preparing graphene films. In recent years, organic carbonization, as a mature field accompanied by the development of petrochemical industry, has attracted wide attention. However, there are not many materials in the organic system that can be graphitized, and many organic materials can only produce products containing a large amount of sp 3 defect carbon after carbonization, which is difficult to form ordered sp 2 sheet graphite structure, which is mainly due to the difference in carbonization mechanism of different organic precursors.

[0005] From the perspective of processability, polymer-based and asphalt-based precursors have become research hotspots. Among them, polyacrylonitrile (PAN), as a mature and widely used carbonizable organic precursor, has demonstrated its unique advantages in the preparation of carbon fibers. PAN has a unique carbonization mechanism, and its linear main chain structure is gradually transformed into a ladder, multi-condensed ring and even graphite structure through pre-oxidation and cyclization of cyano groups. Despite this, there are few reports on the preparation of two-dimensional ordered carbon films using PAN as a precursor. The reason is that although the orientation and cyclization of linear PAN molecules in one dimension are easy to achieve, it is extremely challenging to achieve ordered cyclization and carbonization and graphitization in two dimensions. Carbon films prepared by traditional methods are often difficult to form, and the preparation of continuous and dense two-dimensional carbon films has become a technical problem that needs to be solved urgently.

[0006] To solve this problem, researchers tried to cast the PAN solution, introduce a porous structure through a coagulation bath, form a fiber-like network, and obtain a loose carbon film after carbonization. Furthermore, Gao Chao's team innovatively introduced GO into PAN as an effective inducer to promote the graphitization process of PAN. After multiple pressing heat treatments and slow heating processes, a polyacrylonitrile-based high thermal conductivity graphite film was successfully prepared. However, although the porous structure introduced by the coagulation bath method increases the movable space and is conducive to the overflow of small molecules during the cyclization process, it also leads to a loose structure of the carbon film. The presence of a large number of pores is not conducive to the effective transfer of heat. Although the direct introduction of graphite oxide contributes to the densification of the film during high-temperature treatment due to its high intrinsic oxygen content, there is a contradiction between the overflow of small molecules and the densification of the film.

[0007] Therefore, the key to preparing high-performance polyacrylonitrile-based graphene thermally conductive films lies in balancing high crystallinity and dense structure, optimizing processing methods, improving the ordered cyclization and carbonization of PAN, and selecting the right materials for carbonization. It is against this backdrop that the present invention proposes a polyacrylonitrile-based graphene film induced by in-situ nitrogen doping of graphene and its preparation method. This innovative approach aims to address these challenges and pave a new path for the preparation and application of graphene thermally conductive films. Summary of the Invention

[0008] To solve the above problems, the present invention provides a polyacrylonitrile-based graphite film induced by in-situ nitrogen-doped graphene and a preparation method thereof.

[0009] In a first aspect, the present invention provides a method for preparing a polyacrylonitrile-based graphite film induced by in-situ nitrogen-doped graphene, the preparation method comprising the following steps:

[0010] Mixing the graphene oxide solution and the polyacrylonitrile solution to obtain a GO / PAN mixed slurry;

[0011] The GO / PAN mixed slurry is coated and dried to obtain a GO / PAN composite membrane;

[0012] The GO / PAN composite membrane is suspended above an ammonia solution, and then subjected to fumigation treatment and secondary drying to obtain an in-situ nitrogen-doped N-rGO / PAN composite membrane;

[0013] The N-rGO / PAN composite film is subjected to carbonization and graphitization treatment and pressing treatment to obtain the polyacrylonitrile-based graphite film.

[0014] Furthermore, the graphene oxide solution and the polyacrylonitrile solution have the same solvent, which includes at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone and dimethyl sulfoxide; the flake diameter of the graphene oxide is 8 to 25 microns.

[0015] Furthermore, the weight ratio of graphene oxide to polyacrylonitrile in the GO / PAN mixed slurry is (5-50):(50-95).

[0016] Furthermore, the working condition parameters of the coating include: a coating thickness of 0.5 to 2 mm; the working condition parameters of the first drying include: a temperature of 45 to 75° C. and a time of 4 to 6 hours.

[0017] Furthermore, the GO / PAN composite membrane is suspended above an ammonia solution, and then subjected to fumigation treatment and secondary drying to obtain an in-situ nitrogen-doped N-rGO / PAN composite membrane, comprising the following steps:

[0018] The GO / PAN composite film is placed in a mold frame and fixed, and then the mold frame fixture is suspended above a container filled with ammonia liquid through a bracket to build a thin film in-situ nitrogen doping device;

[0019] The thin film in-situ nitrogen doping device is placed in a 95-100° C. environment for fumigation treatment for 3-16 hours, and then a second drying is performed at 45-75° C. for 4-6 hours to obtain the N-rGO / PAN composite film.

[0020] Furthermore, the ammonia solution is an aqueous solution of nitrogen-containing compounds with a pH of 9 to 11, and the nitrogen-containing compounds include at least one of liquid ammonia, hydrazine, urea, triethylamine, ethylenediamine, hexamethylenediamine, pyridine, pyrrole and N-methylpyrrolidone.

[0021] Furthermore, the ammonia solution is composed of liquid ammonia, hydrazine and water in a weight ratio of (5-10):(0.05-5):(50-80).

[0022] Furthermore, the step of subjecting the N-rGO / PAN composite film to carbonization and graphitization treatment and pressing treatment to obtain the polyacrylonitrile-based graphite film includes the following process:

[0023] Pre-oxidize the N-rGO / PAN composite film under the condition of air atmosphere and 250-300 DEG C for 30-60 min to obtain a pre-oxidized N-rGO / PAN composite film;

[0024] Carbonize and graphitize the pre-oxidized N-rGO / PAN composite film under inert gas atmosphere by using a gradient constant temperature mode, and then press under the pressure of 250-350 Mpa to obtain the polyacrylonitrile-based graphite film.

[0025] The temperature rising procedure of the gradient constant temperature mode comprises: rising the temperature to 480-520 DEG C at the temperature rising rate of 2-5 DEG C / min and keeping constant temperature for 25-35 min; then rising the temperature to 650-750 DEG C at the temperature rising rate of 1-2 DEG C / min and keeping constant temperature for 25-35 min; subsequently rising the temperature to 1450-1550 DEG C at the temperature rising rate of 1-2 DEG C / min and keeping constant temperature for 1.5-2.5 h; finally rising the temperature to 2800-3200 DEG C at the temperature rising rate of 4-7 DEG C / min and keeping constant temperature for 1.5-2.5 h, and cooling to room temperature.

[0026] In the second aspect, the application provides a polyacrylonitrile-based graphite film induced by in-situ nitrogen-doped graphene, which is prepared by the method of any one of the first aspect.

[0027] Further, the thermal conductivity of the polyacrylonitrile-based graphite film induced by in-situ nitrogen-doped graphene is 771.9-1164.7 W / m K.

[0028] Compared with the prior art, the above technical solution provided by the embodiments of the application has at least the following advantages:

[0029] The embodiments of the application provide a preparation method of a polyacrylonitrile-based graphite film induced by in-situ nitrogen-doped graphene, which promotes the conversion of linear polyacrylonitrile to graphite structure and improves the formation of long-range ordered graphite structure in two-dimensional space, and solves the problem of gas expansion of GO in the warm treatment process in the composite film, thereby significantly improving the thermal conductivity of the obtained polyacrylonitrile-based graphite film. BRIEF DESCRIPTION OF DRAWINGS

[0030] The accompanying drawings, which are incorporated into and form part of the specification, illustrate embodiments consistent with the application and, together with the specification, serve to explain the principles of the application.

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0032] Figure 1 A schematic flow chart of a method for preparing a polyacrylonitrile-based graphite film induced by in-situ nitrogen-doped graphene is provided in an embodiment of the present invention.

[0033] Figure 2 Schematic diagram of the structure of a thin film in-situ nitrogen doping device in a method for preparing a polyacrylonitrile-based graphite film based on in-situ nitrogen-doped graphene induced by an embodiment of the present invention.

[0034] Figure 3 A front schematic diagram of a thin film in-situ nitrogen doping device in a method for preparing a polyacrylonitrile-based graphite film induced by in-situ nitrogen doping of graphene provided in an embodiment of the present invention.

[0035] Figure 4 Schematic diagram of the chemical structure of graphene oxide and nitrogen-doped graphene oxide in an embodiment of the present invention.

[0036] Figure 5 These are the scanning electron microscope and elemental scanning results of graphene oxide nanosheets before and after in situ nitrogen doping.

[0037] Figure 6 2 is a cross-sectional view of the in-situ nitrogen-doped and undoped pre-oxidation films of the present invention.

[0038] Figure 7 These are SEM images of the cross-section of the carbonized polyacrylonitrile membrane before and after the addition of nitrogen-doped graphene in the present invention.

[0039] Figure 8 These are the XRD and Raman spectra of the polyacrylonitrile carbonized film before and after adding nitrogen-doped graphene in the present invention.

[0040] Figure 9 These are cross-sectional SEM images of the polyacrylonitrile graphitized film before and after the addition of nitrogen-doped graphene in the present invention.

[0041] Figure 10 These are the XRD and Raman spectra of the pure PAN graphitized film and the rGO / PAN graphitized film before and after nitrogen doping in the present invention.

[0042] Figure 11 The thermal conductivity results of the polyacrylonitrile graphitized film according to the present invention are as the amount of nitrogen-doped graphene is added, the thermal conductivity comparison of the graphitized film before and after in-situ nitrogen doping, and the comparison results with graphene films prepared by other nitrogen-doping and composite methods.

[0043] wherein, Figure 2 Fig. 1 is a schematic diagram of a preparation process of a polyacrylonitrile-based graphite film according to an embodiment of the present application. DETAILED DESCRIPTION

[0044] In order to make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0045] Unless otherwise specifically indicated, all the various raw materials, reagents, instruments and equipment and the like used in the present application can be purchased from the market or can be prepared by the existing methods.

[0046] In a first aspect, the present application provides a preparation method of a polyacrylonitrile-based graphite film induced by in-situ nitrogen-doped graphene, as shown in Figure 1 The preparation method comprises the following steps:

[0047] Mixing the graphene oxide solution and the polyacrylonitrile solution to obtain a GO / PAN mixed slurry;

[0048] Coating and first drying the GO / PAN mixed slurry to obtain a GO / PAN composite film;

[0049] Suspended the GO / PAN composite film above an ammonia solution, and then performing fumigation treatment and second drying to obtain an N-rGO / PAN composite film doped with in-situ nitrogen;

[0050] Carbonizing and graphitizing the N-rGO / PAN composite film and performing pressing treatment to obtain the polyacrylonitrile-based graphite film.

[0051] The embodiments of the present application provide a preparation method of a polyacrylonitrile-based graphite film induced by in-situ nitrogen-doped graphene. The preparation method of the graphene film induced by in-situ nitrogen-doped graphene promotes the conversion of linear polyacrylonitrile to a graphite structure and improves the formation of long-range ordered graphite structures in two-dimensional space. Meanwhile, the gas expansion problem of GO in the warm treatment process in the composite film is solved, thereby significantly improving the thermal conductivity of the obtained polyacrylonitrile-based graphite film.

[0052] As an embodiment of the present application, the solvent of the graphene oxide solution and the polyacrylonitrile solution is the same, and the solvent includes at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone and dimethyl sulfoxide; and the flake diameter of the graphene oxide is 8-25 microns.

[0053] The present application can ensure that the large flake GO with a flake diameter of 8-25 microns can be stably dispersed in the GO / PAN mixed slurry to form a uniform and stable GO / PAN mixed slurry system by mixing the graphene oxide solution and the polyacrylonitrile solution with the same solvent. In some embodiments, the graphene oxide solution with the same solvent as the polyacrylonitrile solution can be obtained by solvent replacement, which includes the following process: the large flake graphene oxide aqueous dispersion is centrifuged at a speed of 5000-10000 rpm for 30 min-60 min, and the supernatant is replaced with a replacement solvent such as N,N-dimethylformamide after centrifugation, and the high-speed centrifugation and replacement of the solvent are cycled for 3-5 times; preferably, the centrifugal speed is 10000 rpm, the single time is 1 h, the replacement times of centrifugation is 5 times, and the replacement solvent is N,N-dimethylformamide (DMF).

[0054] As an embodiment of the present application, the stirring speed for mixing the graphene oxide solution and the polyacrylonitrile solution is 8000-150000 rpm, and the time is 30 min-1 h.

[0055] As an embodiment of the present application, the weight ratio of the graphene oxide and the polyacrylonitrile in the GO / PAN mixed slurry is (5-50):(50-95), and preferably, the weight ratio of the graphene oxide and the polyacrylonitrile in the GO / PAN mixed slurry is 50:50.

[0056] As an embodiment of the present application, the working condition parameters of the coating include: the coating thickness is 0.5-2 mm; the working condition parameters of the first drying include: the temperature is 45-75℃, preferably 60℃; and the time is 4-6 hours. In some embodiments, the GO / PAN composite film can be obtained by uniformly coating the GO / PAN mixed slurry on a dust-free glass plate with a thickness of 0.5-2 mm, then slowly drying in a vacuum oven at 60℃ for 4-6 hours, and cooling to room temperature.

[0057] As an embodiment of the present application, the steps of suspending the GO / PAN composite film above the ammonia liquid, then carrying out fumigation treatment and second drying to obtain the in-situ nitrogen-doped N-rGO / PAN composite film include the following process:

[0058] The GO / PAN composite film is fixed in a mold frame, and then the mold frame clamp is suspended above a container filled with ammonia liquid through a support, and a thin film in-situ nitrogen doping device is built;

[0059] The thin film in-situ nitrogen doping device is placed in an environment of 95-100°C for fumigation treatment for 3-16 hours, and then second drying is performed at 45-75°C for 3-16 hours, to obtain the N-rGO / PAN composite film.

[0060] The in-situ nitrogen doping method is adopted, as shown in Figure 2 ( Figure 2 from top to bottom, which are: 1-GO / PAN composite film; 2-mold frame; 3-support; 4-container filled with ammonia liquid), and Figure 3 as shown in the figure, at this time, the GO is uniformly compounded in the internal part of the PAN film, and the NH3 and N2H4 and other nitrogen-containing small molecules vapor are allowed to enter the film internal part through fumigation, to react with the GO (such as the defects in the graphite and the oxygen-containing functional groups), to realize in-situ nitrogen doping, which can ensure that the GO is uniformly dispersed in the PAN, and in the process of in-situ nitrogen doping, the GO can be partially reduced and nitrogen atoms maintaining the graphite aromatic ring structure are introduced at a lower heat treatment temperature, a small amount of nitrogen doping can maintain the two-dimensional flatness of the GO nanosheet, and the chemical structure difference between the nitrogen-doped graphene and the graphene oxide is as shown in Figure 4 In some specific embodiments, the GO / PAN composite film is fixed by a carbon fiber mold frame clamp, the film is in a natural stretched state and is not taut, and the film is suspended and supported by a metal hollow support, so that the upper and lower surfaces of the film are exposed. The entire support and mold frame are placed in a closed container filled with ammonia liquid, the upper end of the support is suspended, and the film is ensured not to be in direct contact with the liquid surface. The entire container is placed in a 98°C oven for fumigation treatment for 3-16 hours. After fumigation, the film is dried to obtain the N-rGO / PAN composite film.

[0061] As an embodiment of the present application, the ammonia liquid is a nitrogen-containing compound aqueous solution with pH=9-11, and the nitrogen-containing compound includes at least one of liquid ammonia (NH3), hydrazine (N2H4), urea, triethylamine, ethylenediamine, hexanediamine, pyridine, pyrrole and N-methyl pyrrolidone (NMP); preferably, the ammonia liquid is composed of liquid ammonia, hydrazine and water with a weight ratio of (5-10):(0.05-5):(50-80).

[0062] As an embodiment of the present application, the N-rGO / PAN composite film is subjected to carbonization and graphitization treatment and pressing treatment, to obtain the polyacrylonitrile-based graphite film, and the steps include the following processes:

[0063] Pre-oxidize the N-rGO / PAN composite film under air atmosphere and at 250-300 DEG C for 30-60 min to obtain a pre-oxidized N-rGO / PAN composite film;

[0064] Carbonize and graphitize the pre-oxidized N-rGO / PAN composite film under inert gas atmosphere by using a gradient constant temperature mode, and then press the film under a pressure of 250-350 MPa to obtain the polyacrylonitrile-based graphite film.

[0065] The temperature rising procedure of the gradient constant temperature mode comprises: rising the temperature to 480-520 DEG C at a temperature rising rate of 2-5 DEG C / min and keeping the temperature for 25-35 min; then rising the temperature to 650-750 DEG C at a temperature rising rate of 1-2 DEG C / min and keeping the temperature for 25-35 min; subsequently rising the temperature to 1450-1550 DEG C at a temperature rising rate of 1-2 DEG C / min and keeping the temperature for 1.5-2.5 h; finally rising the temperature to 2800-3200 DEG C at a temperature rising rate of 4-7 DEG C / min and keeping the temperature for 1.5-2.5 h, and cooling to room temperature.

[0066] In the carbonization and graphitization process of the N-rGO / PAN composite film, the linear PAN molecular chain is first changed into a ladder-shaped molecule through pre-oxidation, and the ladder-shaped molecule has a certain planar structure, which prepares for the subsequent carbonization and graphitization, and this is one of the key steps in the carbonization and graphitization process. In some specific embodiments, the above process specifically comprises: 1) placing the N-rGO / PAN composite film into a muffle furnace, introducing air, and rising the temperature to 250-300 DEG C and keeping the temperature for 30 min-1 h to obtain a pre-oxidized N-rGO / PAN composite film; 2) placing the pre-oxidized N-rGO / PAN composite film into a graphite furnace, introducing inert gas, rising the temperature to 500 DEG C at a temperature rising rate of 3 DEG C / min, keeping the temperature for 30 min, then rising the temperature to 700 DEG C at a temperature rising rate of 1 DEG C / min, keeping the temperature for 30 min, subsequently rising the temperature to 1500 DEG C at a temperature rising rate of 1 DEG C / min and keeping the temperature for 2 h, finally rising the temperature to 3000 DEG C at a temperature rising rate of 5 DEG C / min and keeping the temperature for 2 h, slowly cooling to room temperature, and taking out the sample; 3) the obtained graphite film is pressed at a pressure of 300 MPa to obtain a polyacrylonitrile-based graphite film product.

[0067] In a second aspect, based on the same inventive concept, the present application provides a polyacrylonitrile-based graphite film induced by in-situ nitrogen-doped graphene, which is prepared by the method of any one of the first aspect.

[0068] The polyacrylonitrile-based graphite film induced by the in-situ nitrogen-doped graphene provided by the embodiment of the present application can effectively guide the two-dimensional cyclization and graphite growth of linear polyacrylonitrile, and compared with graphene oxide, the nitrogen-doped graphene can maintain the graphite benzene ring conjugated structure and planar structure and reduce thermal expansion in the low and medium temperature treatment process, thereby obtaining a high-thermal-conductivity polyacrylonitrile-based graphite film. With the increase of the content of the nitrogen-doped graphene, the thermal conductivity of the graphitized film of the polyacrylonitrile-based graphite film at a content of 50wt% can reach 1164.7W / m K.

[0069] As an embodiment of the present application, the thermal conductivity of the polyacrylonitrile-based graphite film induced by the in-situ nitrogen-doped graphene is 771.9-1164.7W / m K.

[0070] It should be noted that the raw material components involved in the polyacrylonitrile-based graphite film induced by the in-situ nitrogen-doped graphene and the preparation method thereof provided by the embodiment of the present application can be directly purchased from the market or self-made according to the existing preparation method if there is no special limitation or specific description; at the same time, the operation steps involved in the preparation method can be performed according to the existing polyacrylonitrile-based graphite film preparation method or using the existing equipment if there is no special limitation or specific description, and the present application document will not be described in detail.

[0071] The present application will be further described in combination with specific examples. It should be understood that these examples are only used to illustrate the present application and not used to limit the scope of the present application. The experimental methods in the following examples without specific conditions are generally determined according to the national standards. If there is no corresponding national standard, the general international standards, conventional conditions, or the conditions suggested by the manufacturers are used.

[0072] Example 1

[0073] The present example provides a polyacrylonitrile-based graphite film induced by in-situ nitrogen-doped graphene, and a preparation method of the polyacrylonitrile-based graphite film induced by in-situ nitrogen-doped graphene includes the following steps:

[0074] Step (1), preparation of GO / PAN composite film: the graphene oxide water dispersion with a sheet diameter of 22 microns was prepared by ultracentrifugation-solvent replacement, the centrifugal speed was 10000 rpm, the time was 1 h / time, after centrifugation, the upper clear liquid was replaced with DMF to prepare the GO DMF dispersion; stirring and ultrasonic centrifugation again, and so on for 4 times, the GO DMF dispersion with a weight percentage of 1% was obtained; then the GO DMF dispersion was mixed with a 15% PAN DMF solution according to the weight ratio of graphene oxide to polyacrylonitrile of 50:50, and a mixed slurry with a GO content of 50% of the GO / PAN composite material was prepared; the mixed slurry was uniformly dispersed by homogenizing stirring at a stirring speed of 150000 rpm for 1 h; then the GO / PAN mixed slurry was uniformly coated on a clean glass plate, and was dried slowly in a vacuum oven at 60°C for 5 hours by simple blade coating, and a GO / PAN composite film was obtained;

[0075] Step (2), in-situ nitrogen-doped GO / PAN composite film: the GO / PAN composite film obtained in step (1) was fixed in a hollow carbon fiber mold frame, and the GO / PAN composite film was in a natural stretched state without tension; then a metal hollow support was used to suspend the GO / PAN composite film, and the middle part of the GO / PAN composite film was suspended; the entire support device was placed in a sealed container, water was added at the bottom, and then ammonia and hydrazine were added according to the weight ratio of liquid ammonia: hydrazine: water of 5:1:80 to obtain an ammonia solution with a pH of 9-11, and the liquid surface was at a certain distance (specifically 3 cm) from the GO / PAN composite film; the container was placed in a 98°C oven for fumigation treatment for 15 hours, and then was dried at 55°C for 5 hours to obtain the N-rGO / PAN composite film;

[0076] Step (3), carbonization and graphitization treatment and pressing treatment of N-rGO / PAN composite film: the N-rGO / PAN composite film obtained in step (2) is placed in a muffle furnace and heated to 300℃ for 1h to obtain a pre-oxidized N-rGO / PAN composite film; then the pre-oxidized N-rGO / PAN composite film is placed in a graphite furnace, inert gas is introduced, heated to 500℃ at a heating rate of 3℃ / min and kept for 30min, then heated to 700℃ at a heating rate of 1℃ / min and kept for 30min, then heated to 1500℃ at a heating rate of 1℃ / min and kept for 2h (the composite film at this time in this example is marked as C-N-rGO / PAN); finally, heated to 3000℃ at a heating rate of 5℃ / min and kept for 2h, slowly cooled to room temperature, and the sample was taken out; the obtained composite film is pressed at 300Mpa for 10min to obtain a polyacrylonitrile-based graphite film product (the composite film at this time in this example is marked as G-N-rGO / PAN-1).

[0077] Example 2

[0078] This example provides a polyacrylonitrile-based graphite film induced by in-situ nitrogen-doped graphene and a preparation method thereof, which is different from example 1 only in that in step (1) of preparing the GO / PAN composite film, the GO DMF dispersion liquid and the DMF solution of PAN with a weight percentage of 15% are mixed according to a weight ratio of graphene oxide to polyacrylonitrile of 40:60 to prepare a mixed slurry with a GO content of 40% in the GO / PAN composite material; the rest of the steps and parameters are the same.

[0079] The above preparation method of the polyacrylonitrile-based graphite film induced by in-situ nitrogen-doped graphene includes the following steps:

[0080] Step (1), preparation of GO / PAN composite film: the graphene oxide water dispersion liquid with a sheet diameter of 22 microns is prepared into a GO DMF dispersion liquid by ultracentrifugation-solvent displacement, with a centrifugal speed of 10000 revolutions / min and a time of 1h / once; after centrifugation, the upper clear liquid is replaced with DMF; the GO DMF dispersion liquid is stirred and ultrasonically centrifuged again, and this cycle of centrifugation is repeated 4 times to obtain a GO DMF dispersion liquid with a weight percentage of 1%; then the GO DMF dispersion liquid and the DMF solution of PAN with a weight percentage of 15% are mixed according to a weight ratio of graphene oxide to polyacrylonitrile of 40:60 to prepare a mixed slurry with a GO content of 40% in the GO / PAN composite material; the mixed slurry is uniformly dispersed by homogenizing stirring at a stirring speed of 150000 revolutions / min for 1h; then the GO / PAN mixed slurry is uniformly coated on a clean glass plate and simply blade-coated to a thickness of 1.5mm, and then slowly dried in a vacuum oven at 60℃ for 5 hours to obtain a GO / PAN composite film;

[0081] Step (2), in-situ nitrogen-doping of GO / PAN composite film: the GO / PAN composite film obtained in step (1) is fixed in a hollow carbon fiber mold frame in a natural stretched state without tension; a metal hollow support is used to suspend the GO / PAN composite film, with the middle part of the GO / PAN composite film suspended; the entire support device is placed in a sealed container, water is first added to the bottom, and then ammonia water and hydrazine hydrate are added according to the weight ratio of liquid ammonia:hydrazine:water of 5:1:80 to obtain ammonia solution with pH of 9-11, with a certain distance (specifically 3 cm) from the liquid surface to the GO / PAN composite film; the container is placed in a 98℃ oven for fumigation treatment for 15 hours, and then dried at 55℃ for 5 hours to obtain the N-rGO / PAN composite film;

[0082] Step (3), carbonization and graphitization treatment and pressing treatment of N-rGO / PAN composite film: the N-rGO / PAN composite film obtained in step (2) is placed in a muffle furnace and heated to 300℃ for 1h to obtain a pre-oxidized N-rGO / PAN composite film; then the pre-oxidized N-rGO / PAN composite film is placed in a graphite furnace, inert gas is introduced, and the temperature is raised to 500℃ at a rate of 3℃ / min and kept constant for 30min, then the temperature is raised to 700℃ at a rate of 1℃ / min and kept constant for 30min, then the temperature is raised to 1500℃ at a rate of 1℃ / min and kept constant for 2h; finally, the temperature is raised to 3000℃ at a rate of 5℃ / min and kept constant for 2h, and then slowly cooled to room temperature, and the sample is taken out; the obtained composite film is pressed at 300Mpa for 10min to obtain a polyacrylonitrile-based graphite film product.

[0083] Example 3

[0084] This example provides a polyacrylonitrile-based graphite film based on in-situ nitrogen-doped graphene and a preparation method thereof, which is different from example 1 only in that in step (1) for preparing the GO / PAN composite film, the GO DMF dispersion liquid and the 15% PAN DMF solution are mixed according to the weight ratio of graphene oxide to polyacrylonitrile of 30:70 to prepare a mixed slurry with GO content of 30% of the GO / PAN composite material; the rest of the steps and parameters are the same.

[0085] The above preparation method of the polyacrylonitrile-based graphite film based on in-situ nitrogen-doped graphene includes the following steps:

[0086] Step (1), preparation of GO / PAN composite film: the graphene oxide water dispersion with a sheet diameter of 22 microns was prepared by ultracentrifugation-solvent replacement, the centrifugal speed was 10000 r / min, the time was 1 h / time, after centrifugation, the supernatant was replaced with DMF to prepare a GO DMF dispersion; stirring and ultrasonic centrifugation were repeated 4 times to obtain a GO DMF dispersion with a weight percentage of 1%; then the GO DMF dispersion was mixed with a 15% PAN DMF solution according to the weight ratio of graphene oxide to polyacrylonitrile of 30:70, and a mixed slurry with a GO content of 30% of the GO / PAN composite material was prepared; the mixed slurry was uniformly dispersed by homogenizing stirring at a stirring speed of 150000 r / min for 1 h; then the GO / PAN mixed slurry was uniformly coated on a clean glass plate, and a simple doctor blade coating was performed with a coating thickness of 1.5 mm; the coated glass plate was placed in a vacuum oven at 60°C and slowly dried for 5 hours to obtain a GO / PAN composite film.

[0087] Step (2), in-situ nitrogen doping of GO / PAN composite film: the GO / PAN composite film obtained in step (1) was fixed in a hollow carbon fiber mold frame in a natural stretched state; a metal hollow support was used to suspend the GO / PAN composite film, and the middle part of the GO / PAN composite film was suspended; the entire support device was placed in a sealed container, water was added at the bottom, and then ammonia water and hydrazine hydrate were added according to the weight ratio of liquid ammonia: hydrazine: water of 5:1:80 to obtain an ammonia solution with a pH of 9-11, the liquid surface was at a distance (specifically 3 cm) from the GO / PAN composite film; the container was placed in a 98°C oven and fumigated for 15 hours, and then dried at 55°C for 5 hours to obtain the N-rGO / PAN composite film.

[0088] Step (3), carbonization and graphitization treatment and pressing treatment of N-rGO / PAN composite film: the N-rGO / PAN composite film obtained in step (2) was placed in a muffle furnace and heated to 300°C for 1 h to obtain a pre-oxidized N-rGO / PAN composite film; then the pre-oxidized N-rGO / PAN composite film was placed in a graphite furnace, inert gas was introduced, the temperature was raised to 500°C at a rate of 3°C / min and kept constant for 30 min, then the temperature was raised to 700°C at a rate of 1°C / min and kept constant for 30 min, then the temperature was raised to 1500°C at a rate of 1°C / min and kept constant for 2 h; finally, the temperature was raised to 3000°C at a rate of 5°C / min and kept constant for 2 h, and then the sample was taken out after slow cooling to room temperature; the obtained composite film was pressed at 300Mpa for 10 min to obtain a polyacrylonitrile-based graphite film product.

[0089] Example 4

[0090] The example provides a polyacrylonitrile-based graphite film induced by in-situ nitrogen-doped graphene and a preparation method thereof, which is different from the example 1 only in that: in the in-situ nitrogen-doped graphene of the GO / PAN composite film, the ammonia solution is composed of urea, ethylenediamine, hydrazine hydrate and water with a weight ratio of 5:5:1:80; the rest of the steps and parameters are the same.

[0091] The preparation method of the polyacrylonitrile-based graphite film induced by in-situ nitrogen-doped graphene includes the following steps:

[0092] Step (1), preparation of GO / PAN composite film: the graphene oxide water dispersion with a sheet diameter of 22 microns is prepared into GO DMF dispersion by ultracentrifugation-solvent displacement, the centrifugal speed is 10000 revolutions / min, the time is 1h / time, and the supernatant is replaced with DMF after centrifugation; stirring and ultrasonic centrifugation are repeated for 4 times to obtain a GO DMF dispersion with a weight percentage of 1%; then the GO DMF dispersion is mixed with a 15% PAN DMF solution according to a weight ratio of graphene oxide to polyacrylonitrile of 50:50, and a mixed slurry with a GO content of 50% of the GO / PAN composite material is prepared; the mixed slurry is uniformly dispersed by homogenizing stirring at a stirring speed of 150000 revolutions / min for 1h; then the GO / PAN mixed slurry is uniformly coated on a clean glass plate and is simply scraped to a thickness of 1.5mm, and is slowly dried in a vacuum oven at 60℃ for 5 hours to obtain a GO / PAN composite film;

[0093] Step (2), in-situ nitrogen-doped GO / PAN composite film: the GO / PAN composite film obtained in step (1) is fixed in a hollow carbon fiber mold frame in a natural stretched state; a metal hollow support is used to suspend the GO / PAN composite film, and the middle part of the GO / PAN composite film is suspended; the entire support device is placed in a sealed container, water is first added at the bottom, and then urea, ethylenediamine and hydrazine hydrate are added according to a weight ratio of 5:5:1:80 to obtain an ammonia solution with a pH of 9-11, and the liquid surface is at a certain distance (specifically 3cm) from the GO / PAN composite film; the container is placed in a 98℃ oven for fumigation treatment for 15 hours, and then second drying is carried out at 55℃ for 5 hours to obtain the N-rGO / PAN composite film;

[0094] Step (3), carbonization and graphitization treatment and pressing treatment of the N-rGO / PAN composite film: the N-rGO / PAN composite film obtained in step (2) is placed in a muffle furnace and heated to 300℃ for 1h to obtain a pre-oxidized N-rGO / PAN composite film; then the pre-oxidized N-rGO / PAN composite film is placed in a graphite furnace, inert gas is introduced, heated to 500℃ at a heating rate of 3℃ / min and kept for 30min, then heated to 700℃ at a heating rate of 1℃ / min and kept for 30min, then heated to 1500℃ at a heating rate of 1℃ / min and kept for 2h; finally, heated to 3000℃ at a heating rate of 5℃ / min and kept for 2h, slowly cooled to room temperature, and the sample was taken out; the obtained composite film is pressed at 300Mpa for 10min to obtain a polyacrylonitrile-based graphite film product (in this example, the composite film at this time is marked as G-N-rGO / PAN-2).

[0095] Example 5

[0096] This example provides a polyacrylonitrile-based graphite film induced by in-situ nitrogen-doped graphene and a preparation method thereof, which is different from example 1 only in that in the in-situ nitrogen-doping of the GO / PAN composite film in step (2), the ammonia solution is composed of pyridine, pyrrole, hydrazine hydrate and water in a weight ratio of 5:5:1:80; the rest of the steps and parameters are the same.

[0097] The above preparation method of the polyacrylonitrile-based graphite film induced by in-situ nitrogen-doped graphene includes the following steps:

[0098] Step (1), preparation of GO / PAN composite film: the graphene oxide water dispersion with a sheet diameter of 22 microns is prepared into GO DMF dispersion by ultracentrifugation-solvent displacement, the centrifugal speed is 10000 revolutions / min, the time is 1h / time, after centrifugation, the upper clear liquid is replaced with DMF; stirring and ultrasonic centrifugation are repeated for 4 times to obtain a GO DMF dispersion with a weight percentage of 1%; then the GO DMF dispersion is mixed with a 15% PAN DMF solution according to a weight ratio of graphene oxide to polyacrylonitrile of 50:50 to prepare a mixed slurry with a GO content of 50% in GO / PAN composite material; the mixed slurry is uniformly dispersed by homogenizing stirring at a stirring speed of 150000 revolutions / min for 1h; then the GO / PAN mixed slurry is uniformly coated on a clean glass plate by simple doctor blading, the doctor blading thickness is controlled at 1.5mm, and the glass plate is placed in a vacuum oven at 60℃ for slow drying for 5 hours to obtain a GO / PAN composite film;

[0099] Step (2), in-situ nitrogen doping of GO / PAN composite film: the GO / PAN composite film obtained in step (1) is fixed in a hollow carbon fiber mold frame, and the GO / PAN composite film is in a natural stretched state without tension; a metal hollow support is used to suspend the GO / PAN composite film, and the middle part of the GO / PAN composite film is suspended; the entire support device is placed in a sealed container, water is added at the bottom, and pyridine, pyrrole and hydrazine hydrate are added in a weight ratio of pyridine:pyrrole:hydrazine hydrate:water of 5:5:1:80 to obtain an ammonia solution with a pH of 9-11, and the liquid level is at a certain distance (specifically 3 cm) from the GO / PAN composite film; the container is placed in a 98°C oven for 3 hours of fumigation treatment, and then dried at 55°C for 5 hours to obtain the N-rGO / PAN composite film;

[0100] Step (3), carbonization and graphitization treatment and pressing treatment of N-rGO / PAN composite film: the N-rGO / PAN composite film obtained in step (2) is placed in a muffle furnace and heated to 300°C for 1 hour to obtain a pre-oxidized N-rGO / PAN composite film; then the pre-oxidized N-rGO / PAN composite film is placed in a graphite furnace, inert gas is introduced, and the temperature is raised to 500°C at a rate of 3°C / min and kept constant for 30 min, then the temperature is raised to 700°C at a rate of 1°C / min and kept constant for 30 min, then the temperature is raised to 1500°C at a rate of 1°C / min and kept constant for 2 hours; finally, the temperature is raised to 3000°C at a rate of 5°C / min and kept constant for 2 hours, and then slowly cooled to room temperature, and the sample is taken out; the obtained composite film is pressed at 300Mpa for 10min to obtain a polyacrylonitrile-based graphite film product (in this example, the composite film at this time is marked as G-N-rGO / PAN-3).

[0101] Comparative Example 1

[0102] This example provides a graphene oxide-induced polyacrylonitrile-based graphite film and a preparation method thereof, which is different from Example 1 only in that the in-situ nitrogen doping process of step (2) GO / PAN composite film is not performed; the rest of the steps and parameters are the same.

[0103] The above preparation method of graphene oxide-induced polyacrylonitrile-based graphite film includes the following steps:

[0104] Step (1), preparation of GO / PAN composite film: the graphene oxide water dispersion with a sheet diameter of 22 microns was prepared into a DMF dispersion of GO by ultracentrifugation-solvent replacement, the centrifugal speed was 10000 rpm, the time was 1 h / time, and the supernatant was replaced with DMF after centrifugation; the GO DMF dispersion was obtained by stirring and ultrasonic centrifugation for 4 times; a DMF dispersion of GO with a weight percentage of 1% was obtained; then the GO DMF dispersion was mixed with a DMF solution of PAN with a weight percentage of 15% according to the weight ratio of graphene oxide to polyacrylonitrile of 50:50 to prepare a mixed slurry with a GO content of 50% of the GO / PAN composite material; the mixed slurry was uniformly dispersed by homogenizing stirring at a stirring speed of 150000 rpm for 1 h; then the GO / PAN mixed slurry was uniformly coated on a clean glass plate, and was slowly dried in a vacuum oven at 60°C for 5 hours by simple doctor blading, and a GO / PAN composite film was obtained;

[0105] Step (2), carbonization and graphitization treatment and pressing treatment of the GO / PAN composite film: the GO / PAN composite film obtained in step (1) was placed in a muffle furnace and heated to 300°C for 1 h to obtain a pre-oxidized GO / PAN composite film; then the pre-oxidized GO / PAN composite film was placed in a graphite furnace, inert gas was introduced, and the temperature was raised to 500°C at a rate of 3°C / min and kept constant for 30 min, then the temperature was raised to 700°C at a rate of 1°C / min and kept constant for 30 min, then the temperature was raised to 1500°C at a rate of 1°C / min and kept constant for 2 h (the composite film at this time is marked as C-rGO / PAN); finally, the temperature was raised to 3000°C at a rate of 5°C / min and kept constant for 2 h, and the sample was slowly cooled to room temperature; the obtained composite film was pressed at 300 MPa for 60-600 seconds to obtain a polyacrylonitrile-based graphite film product (the composite film at this time is marked as G-rGO / PAN).

[0106] Comparative Example 2

[0107] This example provides a polyacrylonitrile-based graphite film induced by nitrogen-doped graphene and a preparation method thereof, and the main difference from Example 1 is that the nitrogen-doped graphene is obtained by immersing the graphene oxide water dispersion in ammonia solution and then performing heat treatment.

[0108] The above preparation method of the polyacrylonitrile-based graphite film induced by nitrogen-doped graphene includes the following steps:

[0109] Step (1), preparation of N-rGO / PAN composite film: graphene oxide water dispersion with a sheet diameter of 22 microns was sealed in an ammonia solution with the same composition as in Example 1 and soaked for heat treatment at a temperature of 98°C for 3 hours; then, through the method of ultracentrifugation-solvent replacement, the centrifugal speed was 10000 revolutions / min, and the time was 1h / time. After centrifugation, the upper clear liquid was replaced with DMF to prepare a DMF dispersion of N-rGO; the N-rGO DMF dispersion was stirred and ultrasonicated and then centrifuged again, and this cycle of centrifugation was repeated 4 times to obtain a DMF dispersion of N-rGO with a weight percentage of 1%; then, the N-rGO DMF dispersion was mixed with a DMF solution of 1% PAN according to the weight ratio of graphene oxide to polyacrylonitrile of 50:50 to configure a mixed slurry with N-rGO content accounting for 50% of the N-rGO / PAN composite material; the mixed slurry was uniformly dispersed through homogenizing stirring at a stirring speed of 150000 revolutions / min for 1h; then, the N-rGO / PAN mixed slurry was uniformly coated on a clean glass plate through simple doctor blading, the doctor blading thickness was controlled at 1.5mm, and the N-rGO / PAN mixed slurry was slowly dried in a vacuum oven at 60°C for 5h to obtain an N-rGO / PAN composite film;

[0110] Step (2), carbonization and graphitization treatment and pressing treatment of the N-rGO / PAN composite film: the N-rGO / PAN composite film obtained in step (1) was placed in a muffle furnace and heated to 300°C for 1h to obtain a pre-oxidized N-rGO / PAN composite film; then, the pre-oxidized N-rGO / PAN composite film was placed in a graphite furnace, inert gas was introduced, the temperature was increased to 500°C at a rate of 3°C / min and kept constant for 30min, then the temperature was increased to 700°C at a rate of 1°C / min and kept constant for 30min, then the temperature was increased to 1500°C at a rate of 1°C / min and kept constant for 2h, and finally the temperature was increased to 3000°C at a rate of 5°C / min and kept constant for 2h, and the sample was slowly cooled to room temperature; the obtained composite film was then pressed at 300Mpa for 10min to obtain a polyacrylonitrile-based graphite film product (in this example, the composite film at this time is marked as N-rGO / PAN-a).

[0111] Comparative Example 3

[0112] This example provides a polyacrylonitrile-based graphite film induced by nitrogen-doped graphene and a preparation method thereof, and the main difference from Example 1 is that in the in-situ nitrogen-doping process of the GO / PAN composite film in step (2), the GO / PAN composite film is directly soaked.

[0113] The above preparation method of the polyacrylonitrile-based graphite film induced by nitrogen-doped graphene includes the following steps:

[0114] Step (1), preparation of GO / PAN composite film: the graphene oxide water dispersion with a sheet diameter of 22 microns was prepared by ultracentrifugation-solvent displacement, the centrifugal speed was 10000 rpm, the time was 1 h / time, after centrifugation, the upper clear liquid was replaced with DMF to prepare the GO DMF dispersion; stirring and ultrasonic centrifugation again, and such cycle centrifugation for 4 times, to obtain a 1% GO DMF dispersion; then the GO DMF dispersion was mixed with a 15% PAN DMF solution according to the weight ratio of graphene oxide to polyacrylonitrile of 50:50, to configure a mixed slurry with GO content of 50% of GO / PAN composite material, the mixed slurry was uniformly dispersed by homogenizing stirring, the stirring speed was 150000 rpm, the time was 1 h, to obtain a uniformly dispersed GO / PAN mixed slurry; then the GO / PAN mixed slurry was uniformly coated on a clean glass plate, and was simply blade-coated with a thickness of 1.5 mm, and was slowly dried in a 60°C vacuum oven for 5 hours to obtain a GO / PAN composite film;

[0115] Step (2), in-situ nitrogen-doping of GO / PAN composite film: the GO / PAN composite film obtained in step (1) was fixed in a hollow carbon fiber mold frame, and the GO / PAN composite film was in a natural stretched state without tension; a metal hollow support was used to suspend the GO / PAN composite film, and the middle part of the GO / PAN composite film was suspended; the entire support device was placed in a sealed container, water was first added to the bottom, and then ammonia water and hydrazine hydrate were added according to the weight ratio of liquid ammonia: hydrazine: water of 5:1:80 to obtain ammonia solution with pH of 9-11, and the GO / PAN composite film was completely soaked in the ammonia solution; the container was placed in a 98°C oven and heat-treated for 3 hours, and then dried at 55°C for 5 hours to obtain the N-rGO / PAN composite film;

[0116] Step (3), carbonization and graphitization treatment and pressing treatment of N-rGO / PAN composite film: the N-rGO / PAN composite film obtained in step (2) was placed in a muffle furnace and heated to 300°C for 1 h to obtain a pre-oxidized N-rGO / PAN composite film; then the pre-oxidized N-rGO / PAN composite film was placed in a graphite furnace, inert gas was introduced, the temperature was increased to 500°C at a rate of 3°C / min and kept constant for 30 min, then the temperature was increased to 700°C at a rate of 1°C / min and kept constant for 30 min, then the temperature was increased to 1500°C at a rate of 1°C / min and kept constant for 2 h, finally the temperature was increased to 3000°C at a rate of 5°C / min and kept constant for 2 h, and then the sample was taken out after slow cooling to room temperature; the obtained composite film was pressed at 300 MPa for 10 min to obtain a polyacrylonitrile-based graphite film product (in this example, the composite film at this time is marked as N-rGO / PAN-b).

[0117] Comparative Example 4

[0118] This example provides a polyacrylonitrile-based graphite film induced by nitrogen-doped graphene and a preparation method thereof. The main difference from Example 1 is that nitrogen doping is first achieved by fumigating graphene oxide powder with ammonia solution, and then compounding with PAN to obtain an N-rGO / PAN composite film.

[0119] The above-mentioned method for preparing polyacrylonitrile-based graphite film induced by nitrogen-doped graphene comprises the following steps:

[0120] Step (1), preparation of N-rGO / PAN composite film: Graphene oxide powder with a sheet diameter of 22 microns is evenly spread into a glass watch glass, and the watch glass is placed in a sealed container filled with ammonia solution with the same composition as in Example 1, the watch glass is not in direct contact with the ammonia solution, and the distance from the liquid surface is the same as in Example 1; the container is placed in a 98°C oven and fumigated for 3 hours, and then the fumigated powder is washed with water and dried in the same manner as in Example 1 to obtain N-rGO powder; the N-rGO powder is mixed with a DMF solution with a weight percentage of 15% PAN according to the N-rGO and The N-rGO / PAN composite material was prepared by mixing the N-rGO and polyacrylonitrile in a weight ratio of 50:50 to form a mixed slurry in which the N-rGO content accounted for 50%. The mixed slurry was homogenized and stirred at a speed of 150,000 rpm for 1 hour to obtain a uniformly dispersed N-rGO / PAN mixed slurry. The N-rGO / PAN mixed slurry was then evenly coated on a clean glass plate by simple doctor blade coating with a thickness of 1.5 mm. The N-rGO / PAN composite film was obtained by slow drying in a vacuum oven at 60°C for 5 hours.

[0121] Step (2), carbonization and graphitization treatment and pressing treatment of the N-rGO / PAN composite membrane: the N-rGO / PAN composite membrane obtained in step (1) is placed in a muffle furnace and heated to 300°C and kept at this temperature for 1 hour to obtain a pre-oxidized N-rGO / PAN composite membrane; the pre-oxidized N-rGO / PAN composite membrane is then placed in a graphite furnace, an inert gas is introduced, and the temperature is increased to 500°C at a heating rate of 3°C / min and kept at this temperature for 30 minutes, then the temperature is increased to 700°C at a heating rate of 1°C / min and kept at this temperature for 30 minutes, then the temperature is increased to 1500°C at a heating rate of 1°C / min and kept at this temperature for 2 hours; finally, the temperature is increased to 3000°C at a heating rate of 5°C / min and kept at this temperature for 2 hours, slowly cooled to room temperature, and the sample is taken out; the obtained composite membrane is then pressed at 300 MPa for 10 minutes to obtain a polyacrylonitrile-based graphite membrane product (the composite membrane at this time is marked as N-rGO / PAN-c in this example).

[0122] Comparative Example 5

[0123] The example provides a polyacrylonitrile-based graphite film induced by nitrogen-doped graphene and a preparation method thereof, and the main difference from Example 1 is that the nitrogen-doped graphene is obtained by immersing and heat-treating graphene oxide powder in ammonia solution, and then the N-rGO / PAN composite film is obtained by compounding the N-rGO with PAN.

[0124] The preparation method of the polyacrylonitrile-based graphite film induced by nitrogen-doped graphene includes the following steps:

[0125] Step (1), preparation of N-rGO / PAN composite film: graphene oxide powder with a sheet diameter of 22 microns is added to the ammonia solution with the same composition as in Example 1, and then immersed and heat-treated at 98°C for 3 hours. After the immersion and heat treatment, the powder is washed with water and dried in the same way as in Example 1 to obtain N-rGO powder. The N-rGO powder and the 15% PAN DMF solution are mixed according to the weight ratio of N-rGO to polyacrylonitrile of 50:50, and the mixed slurry with N-rGO content of 50% of the N-rGO / PAN composite material is prepared. The mixed slurry is uniformly dispersed by homogenizing stirring at a stirring speed of 150,000 rpm for 1 hour. Then the N-rGO / PAN mixed slurry is uniformly coated on a clean glass plate, and a simple doctor blade coating is performed with a coating thickness of 1.5 mm. The coated glass plate is placed in a vacuum oven at 60°C and slowly dried for 5 hours to obtain the N-rGO / PAN composite film.

[0126] Step (2), carbonization and graphitization treatment of N-rGO / PAN composite film and pressing treatment: the N-rGO / PAN composite film obtained in step (1) is placed in a muffle furnace and heated to 300°C for 1 hour to obtain a pre-oxidized N-rGO / PAN composite film. Then the pre-oxidized N-rGO / PAN composite film is placed in a graphite furnace and inert gas is introduced. The temperature is raised to 500°C at a rate of 3°C / min and held for 30 min. Then the temperature is raised to 700°C at a rate of 1°C / min and held for 30 min. Then the temperature is raised to 1500°C at a rate of 1°C / min and held for 2 hours. Finally, the temperature is raised to 3000°C at a rate of 5°C / min and held for 2 hours, and then slowly cooled to room temperature. The sample is taken out. The obtained composite film is pressed at 300 MPa for 10 min to obtain a polyacrylonitrile-based graphite film (the composite film at this time is marked as N-rGO / PAN-d in this example).

[0127] Comparative Example 6

[0128] The example provides a polyacrylonitrile-based graphite film induced by nitrogen-doped graphene and a preparation method thereof, and the main difference from Example 1 is that the nitrogen-doped graphene is obtained by immersing and heat-treating graphene oxide powder in ammonia solution, and then the N-rGO / PAN composite film is obtained by compounding the N-rGO with PAN.

[0129] Step (1): A DMF solution of PAN with a weight percentage of 15% was simply coated by doctor blade, the coating thickness was controlled at 1.5 mm, and then was slowly dried in a vacuum oven at 60℃ for 5 hours to obtain a PAN film;

[0130] Step (2): The PAN film obtained in step (1) was placed in a muffle furnace and heated to 300℃ and kept for 1 hour to obtain a pre-oxidized PAN film; then the pre-oxidized PAN film was placed in a graphite furnace, inert gas was introduced, and the temperature was raised to 500℃ at a rate of 3℃ / min and kept for 30 min, then the temperature was raised to 700℃ at a rate of 1℃ / min and kept for 30 min; then the temperature was raised to 1500℃ at a rate of 1℃ / min and kept for 2 hours (in this example, the material at this time is marked as C-PAN); finally, the temperature was raised to 3000℃ at a rate of 5℃ / min and kept for 2 hours, and then slowly cooled to room temperature, and the sample was taken out (in this example, the material at this time is marked as G-PAN).

[0131] Test Example

[0132] In this example, the film samples obtained in the above examples and comparative examples were characterized and tested, and the test results are shown as follows:

[0133] Figure 5 The scanning electron microscope and element scanning results of graphene oxide nanosheets before and after in-situ nitrogen doping used in Example 1 of the application; wherein, Figure 5 In Figure (5), (a) is the scanning electron microscope and element scanning result of GO before in-situ nitrogen doping of graphene oxide nanosheets, and (b) is the scanning electron microscope and element scanning result of N-rGO (obtained by in-situ smoking of graphene oxide powder) after in-situ nitrogen doping of graphene oxide nanosheets.

[0134] Figure 6 The cross-sectional views of pre-oxidized films with and without in-situ nitrogen doping in the application; wherein, Figure 6 In Figure (3), (a) and (b) are cross-sectional views of GO / PAN pre-oxidized films of different sizes (Comparative Example 1), Figure 6 In Figure (3), (c) and (d) are cross-sectional views of in-situ nitrogen doped N-rGO / PAN pre-oxidized films of different sizes (Example 1).

[0135] Figure 7 The cross-sectional SEM images of polyacrylonitrile carbonized films before and after adding nitrogen doped graphene in the application; wherein, Figure 7 In Figure (4), (a) is a cross-sectional view of a PAN carbonized film (Comparative Example 6), Figure 7 In Figure (4), (b) is a cross-sectional view of a GO / PAN carbonized film (Comparative Example 1), Figure 7 In Figure (4), (c) is a cross-sectional view of an in-situ nitrogen doped N-rGO / PAN carbonized film (Example 1).

[0136] Figure 8 XRD and Raman spectra of polyacrylonitrile carbonized film before and after adding nitrogen-doped graphene in the application; wherein, Figure 8 (a) of the application is the XRD diffraction image of the carbonized film, Figure 8 (b) of the application is the Raman spectrum of the carbonized film.

[0137] Figure 9 SEM images of polyacrylonitrile graphitized film before and after adding nitrogen-doped graphene in the application; wherein, Figure 9 (a) of the application is the cross-section of the PAN carbonized film, Figure 9 (b) of the application is the cross-section of the GO / PAN carbonized film, Figure 9 (c) of the application is the cross-section of the in-situ nitrogen-doped N-rGO / PAN carbonized film.

[0138] Figure 10 XRD and Raman spectra of pure PAN graphitized film, rGO / PAN graphitized film before and after nitrogen doping in the application; wherein, Figure 10 (a) of the application is the XRD diffraction image of the graphitized film, Figure 10 (b) of the application is the Raman spectrum of the graphitized film.

[0139] Figure 11 With the addition of nitrogen-doped graphene, the thermal conductivity results of polyacrylonitrile graphitized film, the thermal conductivity comparison of the film graphitized film before and after in-situ nitrogen doping, and the comparison results of the graphene film prepared by other nitrogen doping and compounding methods in the application; wherein, Figure 11 (a) of the application is the thermal conductivity results of the graphitized film with the content of graphene in the composite film; Figure 11 (b) of the application is the thermal conductivity comparison results of the film graphitized film before and after in-situ nitrogen doping; Figure 11 (c) of the application is the comparison results of the graphene film prepared by other nitrogen doping and compounding methods.

[0140] From the above test results, it can be seen that:

[0141] 1) The same fumigation process is used to prepare nitrogen-doped graphene oxide. The morphology and elemental composition of graphene before and after in-situ nitrogen doping are observed by JSM-7500F scanning electron microscope. It can be seen that the in-situ nitrogen doping process can well dope nitrogen element into graphene. Further, after the pre-oxidation process, the film still shows good compactness and orientation degree as shown in the (c, d) of the figure, Figure 6 Figure 7 and Figure 9 respectively also show the carbonized cross-section of the composite film and the cross-section of the graphitized film, which all show good orientation and flatness. From the microscale, the composite film of the example shows good graphitization degree after carbonization and graphitization. For example,​Figure 8 and Figure 10 As shown, X-ray diffraction analysis using a Rigaku Ultima IV diffractometer characterized the lamellae structure of the composite film. The diffraction peaks during carbonization and graphitization reached 25.98° and 26.44°, respectively, demonstrating the continuous improvement of the graphite lattice and the promotion of nitrogen-doped graphite on the graphitization of PAN. The thermal conductivity of the graphene film was measured using a NETZSCH LFA467 laser thermal conductivity meter. With increasing nitrogen-doped graphene content, the thermal conductivity of the graphitized composite film at 50 wt% reached 1164.7 W / m K, significantly exceeding the carbonization result of pure PAN.

[0142] 2) GO also has the effect of inducing graphitization on PAN. However, in the traditional film-making process, a large number of oxygen-containing functional groups in GO will expand during the low-temperature heat treatment process and further affect the orientation structure of the film. Figure 6 Figures (a, b) show the partially expanded structure in the middle of the GO / PAN pre-oxidized film. This will also affect the carbonization and graphitization process of the film, such as Figure 7 and Figure 9 However, compared with PAN, the graphitization degree of GO / PAN composite film is still relatively high, as shown in Figure 2. Figure 8 and Figure 10 As shown in the XRD and Raman spectra, the degree of graphitization is slightly lower than that of in-situ nitrogen-doped graphite film. Of course, the thermal conductivity is also reduced.

[0143] 3) Due to the limited cyclization and two-dimensional in-plane orientation of linear PAN, it is difficult to prepare PAN thin films into two-dimensional continuous graphite film materials. It mostly generates graphite microcrystals. Therefore, PAN thin films are not easy to form during the pressure sintering process. This also further proves the importance of nitrogen-doped graphene inducing PAN graphitization. In the comparative example, we compared graphene films prepared by different nitrogen doping methods. Since the dispersion of graphene decreased after nitrogen doping, it affected the performance of subsequent carbon films, such as Figure 11 shown.

[0144] The foregoing description is intended only to provide specific embodiments of the present invention, which will enable those skilled in the art to understand and implement the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not intended to be limited to the embodiments shown herein, but is intended to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing polyacrylonitrile-based graphite film based on in-situ nitrogen-doped graphene, characterized in that: The preparation method comprises the following steps: Mixing the graphene oxide solution and the polyacrylonitrile solution to obtain a GO / PAN mixed slurry; The GO / PAN mixed slurry is coated and dried to obtain a GO / PAN composite membrane; The GO / PAN composite membrane is suspended above an aqueous solution of a nitrogen-containing compound, and then subjected to a fumigation treatment in an environment of 95-100° C. for 3-16 hours and a second drying to obtain an in-situ nitrogen-doped N-rGO / PAN composite membrane; The N-rGO / PAN composite film is subjected to carbonization and graphitization treatment and pressing treatment to obtain the polyacrylonitrile-based graphite film; The pH of the nitrogen-containing compound aqueous solution is 9-11, and the nitrogen-containing compound in the nitrogen-containing compound aqueous solution includes at least one of liquid ammonia, hydrazine, urea, triethylamine, ethylenediamine, hexamethylenediamine, pyridine, pyrrole and N-methylpyrrolidone.

2. The method for preparing a polyacrylonitrile-based graphite film based on in-situ nitrogen-doped graphene according to claim 1, characterized in that: The graphene oxide solution and the polyacrylonitrile solution have the same solvent, which includes at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone and dimethyl sulfoxide; the graphene oxide sheet has a diameter of 5 to 25 microns.

3. The method for preparing a polyacrylonitrile-based graphite film based on in-situ nitrogen-doped graphene induction according to claim 1, characterized in that: The weight ratio of graphene oxide to polyacrylonitrile in the GO / PAN mixed slurry is 10:90 to 50:

50.

4. The method for preparing a polyacrylonitrile-based graphite film based on in-situ nitrogen-doped graphene induction according to claim 1, characterized in that: The working condition parameters of the coating include: a coating thickness of 0.5 to 2 mm; the working condition parameters of the first drying include: a temperature of 45 to 75° C. and a time of 4 to 6 hours.

5. The method for preparing a polyacrylonitrile-based graphite film based on in-situ nitrogen-doped graphene induction according to claim 1, characterized in that: The GO / PAN composite membrane is suspended above an aqueous solution of a nitrogen-containing compound, and then subjected to a fumigation treatment in an environment of 95-100° C. for 3-16 hours and a second drying step to obtain an in-situ nitrogen-doped N-rGO / PAN composite membrane, comprising the following steps: The GO / PAN composite film is placed in a mold frame and fixed, and then the mold frame fixture is suspended above a container filled with the nitrogen-containing compound aqueous solution through a bracket to build a thin film in-situ nitrogen doping device; The thin film in-situ nitrogen doping device is placed in a 95-100° C. environment for fumigation treatment for 3-16 hours, and then a second drying is performed at 45-75° C. for 5-10 hours to obtain the N-rGO / PAN composite film.

6. The method for preparing a polyacrylonitrile-based graphite film based on in-situ nitrogen-doped graphene induction according to claim 1, characterized in that: The nitrogen-containing compound aqueous solution is composed of liquid ammonia, hydrazine and water in a weight ratio of (5-10): (0.05-5): (50-80).

7. The method for preparing polyacrylonitrile-based graphite film based on in-situ nitrogen-doped graphene induction according to claim 1, characterized in that: The steps of subjecting the N-rGO / PAN composite film to carbonization and graphitization treatment and pressing treatment to obtain the polyacrylonitrile-based graphite film include the following processes: pre-oxidizing the N-rGO / PAN composite membrane in an air atmosphere at 250° C. to 300° C. for 30 to 60 minutes to obtain a pre-oxidized N-rGO / PAN composite membrane; The pre-oxidized N-rGO / PAN composite film is carbonized and graphitized in an inert gas atmosphere by a gradient constant temperature method, and then pressed at a pressure of 250-350 MPa to obtain the polyacrylonitrile-based graphite film; The temperature rising program of the gradient constant temperature method includes: heating to 480-520°C at a heating rate of 2-5°C / min and holding the temperature for 25-35 min; then heating to 650-750°C at a heating rate of 1-2°C / min and holding the temperature for 25-35 min; then heating to 1450-1550°C at a heating rate of 1-2°C / min and holding the temperature for 1.5-2.5 h; finally, heating to 2800-3200°C at a heating rate of 4-7°C / min and holding the temperature for 1.5-2.5 h, and then cooling to room temperature.

8. A polyacrylonitrile-based graphite film induced by in-situ nitrogen-doped graphene, characterized in that: The polyacrylonitrile-based graphite film induced by in-situ nitrogen-doped graphene is prepared by the preparation method of the polyacrylonitrile-based graphite film induced by in-situ nitrogen-doped graphene according to any one of claims 1 to 7.

9. The polyacrylonitrile-based graphite film induced by in-situ nitrogen-doped graphene according to claim 8, characterized in that: The thermal conductivity of the polyacrylonitrile-based graphite film induced by in-situ nitrogen-doped graphene is 771.9~1164.7W / mK.

Images