A micrometer-thick graphite film and a method for growing the same

Abstract

The application provides a micron-thick graphite film and a growth method thereof. A substance with high carbon content is dispersed in an organic solvent and coated on a metal foil, and after drying, a carbon film / metal foil is obtained; or the substance with high carbon content is made into a sheet and placed on a metal foil, and a carbon film / metal foil is obtained; in a protective atmosphere, a current is applied to the sample, the carbon film / metal foil is heated by using the Joule effect of the current, and the power supply is stopped, so that a micron-thick graphite film is obtained on the surface of the metal foil. The graphite film is prepared by using the dissolution-precipitation of carbon in the metal substrate in the process of high-temperature-low-temperature temperature change. Since the metal substrate has an epitaxial relationship with the graphite lattice, the graphite film with AB stacking can be directly precipitated, so that the graphitization of carbon can be realized at a lower temperature. The reaction system is radiated and heated by using the Joule heating characteristic of the current, the heating efficiency is effectively improved, the temperature is raised from room temperature to the growth temperature in a few seconds, the influence of the side reaction is reduced, and the raw material utilization rate is improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of materials, and particularly relates to a micron-thick graphite film and a growth method thereof. BACKGROUND

[0002] Graphite is a traditional industrial raw material, and in the microcrystalline structure, it is the stacking of single-layer graphene, and in the macroscopic morphology, it often appears in the form of bulk, film and powder. The present application focuses on the field of graphite film. After the graphene is stacked into a layered structure, a flexible and low-thermal-expansion-coefficient film is formed, which provides a good solution for the development of heat-conducting films in thermal management materials. At present, the market scale of heat-conducting film industry is huge. Among them, the majority of market share has been occupied by PI (polyimide) based graphite film, artificial graphite film and graphene-based heat dissipation film. The mature preparation scheme of graphite film often adopts a top-down approach, such as expanded graphite calendering method, graphene oxide reduction method, PI film carbonization-graphitization method, etc., which can prepare graphite film with high thermal conductivity, high crystallinity and high orientation. In recent years, researchers have also focused on the bottom-up chemical vapor deposition (CVD) method, which uses the characteristics of gas-phase carbon source cracking at high temperature to deposit graphene and graphite film on metal substrates with catalytic activity such as copper and nickel.

[0003] However, for the prior art, the top-down preparation method often has the disadvantages of long time consumption, high energy consumption and environmental unfriendliness; for the bottom-up synthesis, the catalytic activity of the copper substrate used in the CVD method is low, and it is difficult to prepare thick-layer graphite; although the single-layer self-limiting growth can be broken on the nickel substrate, the efficiency of layer-by-layer deposition is still low. In view of the above shortcomings, it is urgent to develop a fast preparation method of graphite film with high preparation rate and low energy consumption. SUMMARY

[0004] In order to overcome the above-mentioned defects, the present application provides a growth method of micron-thick graphite film and a graphite film formed by the method.

[0005] The growth method of micron-thick graphite film provided by the present application comprises the following steps:

[0006] 1) Preparation of carbon film / metal foil

[0007] The substance with high carbon content is dispersed in an organic solvent and coated on the metal foil, and after drying, a carbon film / metal foil is obtained; or the substance with high carbon content is made into a sheet and placed on the metal foil to obtain a carbon film / metal foil;

[0008] 2) Preparation of graphite film

[0009] In a protective atmosphere, an electric current is applied to the sample, the carbon film / metal foil is heated by Joule heating effect for a certain time, the power supply is stopped, and a micron-level thick graphite film is obtained on the surface of the metal foil.

[0010] In the step 1) of the method, the metal foil is a commercially purchased metal foil, including one or more of nickel foil, cobalt foil, and iron foil;

[0011] In an embodiment of the present application, the metal foil is a nickel foil with a thickness of 50-200 μm.

[0012] The substance with high carbon content includes a high polymer, a solid carbon material, etc.

[0013] The high polymer includes but is not limited to polyolefins or polyolefins containing functional groups (such as PE, PP, PB, PVC, PMMA), polyacetylene, and preferably PMMA.

[0014] The solid carbon material includes but is not limited to graphite, carbon black, activated carbon, carbon nanotubes, carbon fibers, pitch-based materials, and polycyclic aromatic hydrocarbons (PAHs).

[0015] In an embodiment of the present application, the substance with high carbon content is polymethyl methacrylate (PMMA).

[0016] The organic solvent can be DMF.

[0017] The baking temperature can be 150-200°C, and the time can be 30 min-1 h.

[0018] In the step 2) of the method, an electric current is directly applied to heat the metal foil at both ends, or the carbon film / metal foil is placed on a substrate with a passable path, and the whole is fixed on an electrode, an electric current is applied, and the substrate and the carbon film / metal foil are heated.

[0019] The material of the substrate with a passable path can be graphite.

[0020] In an embodiment of the present application, the carbon film / metal foil is clamped between two graphite plates, and the two ends of the graphite plates are fixed on graphite electrodes, the graphite electrodes are powered, and the graphite plates are heated.

[0021] The protective atmosphere includes one or more of hydrogen, argon, and hydrogen / argon mixed atmosphere.

[0022] After the protective gas is introduced, the chamber is maintained at a pressure range of less than 3 atm (specifically, 0.5-3 atm).

[0023] In one embodiment of the present application, 2000sccm of argon is introduced, and the reaction chamber is maintained at a pressure of 1 atm.

[0024] The introduced current is higher than 500A, and the voltage is not higher than 40V.

[0025] In one embodiment of the present application, a current of 300A and a voltage of 6V are introduced.

[0026] The temperature of the heating can be 700-2500℃, and the current-on time (i.e. growth time) is more than 1s, specifically 1s-1h, and more specifically 1s-30min.

[0027] In one embodiment of the present application, the temperature is maintained at 1300℃ for about 2min, and then the current is stopped.

[0028] In step 2), the current is stopped, and after cooling for 30s, the heating and cooling cycle can be repeated, and the current-on time of each cycle is more than 1s, specifically 1s-1h, and more specifically 1s-30min; the number of cycles can be 1-500.

[0029] The above method can further comprise the following step: transferring the thick graphite film formed on the metal foil substrate to a target substrate.

[0030] Specifically, the metal foil with the grown graphite film is placed in an etchant for etching, and after the metal foil and the graphite film are separated, the graphite film is fished out, washed with water, and then fished out using a target substrate, so that the graphite film on the target substrate is obtained.

[0031] The etchant can be one or more of an aqueous solution of ferric chloride, an aqueous solution of persulfate, hydrochloric acid and nitric acid, and the molar concentration of ferric chloride or persulfate in the aqueous solution of ferric chloride or persulfate is not less than 0.5mol / L; the persulfate can be sodium persulfate.

[0032] The etching time can be 30min-24h.

[0033] The micron-scale thick graphite film prepared by the above method also belongs to the protection scope of the present application.

[0034] The micron-scale thick graphite film has the structural feature of AB-stacked polycrystalline / single-crystalline graphite, and the thickness is 200nm-5μm, specifically 200nm, 500nm, 1μm, 2μm, 3μm, 4μm, 5μm, etc. (which are more typical results).

[0035] The growth method provided by this invention utilizes the dissolution and precipitation of carbon on a metal substrate during a temperature-varying process from high to low temperature to prepare a graphite film. Due to the epitaxial relationship between the metal substrate and the graphite lattice, an AB-stacked graphite film can be directly precipitated, thereby achieving carbon graphitization at a lower temperature. The Joule heating characteristic of electric current is used to radiate heat the reaction system, effectively improving the heating efficiency of the system and enabling the temperature to rise from room temperature to the growth temperature within seconds, reducing the impact of side reactions and improving the utilization rate of raw materials. By utilizing the difference in chemical potential of carbon on both sides of the metal substrate, a cyclic heating-cooling process is designed. By increasing the number of cycles, active carbon continuously dissolves from one side of the metal substrate and precipitates a graphite film from the other side, thereby breaking the solubility limitation of the metal and obtaining a graphite film with controllable thickness. Attached Figure Description

[0036] Figure 1 This is a flowchart illustrating the preparation process of the micron-scale thick graphite film of the present invention.

[0037] Figure 2 This is a schematic diagram illustrating the preparation principle of the micron-scale thick graphite film of the present invention.

[0038] Figure 3 This is a light microscope image of the graphite film obtained in Example 1 of the present invention.

[0039] Figure 4 The images show the Raman spectra of the graphite film obtained in Example 1 of this invention at six random positions.

[0040] Figure 5 The image shows the XRD pattern of the graphite film obtained in Example 1 of this invention.

[0041] Figure 6 The image shows a white light interference pattern and thickness analysis curve of the graphite film obtained in Example 1 of this invention.

[0042] Figure 7 The image shows a white light interference pattern and thickness analysis curve of the graphite film obtained in Example 2 of this invention.

[0043] Figure 8 White light interference images and thickness analysis of the graphite film obtained in Comparative Example 1. Detailed Implementation

[0044] The present invention will now be described in further detail with reference to specific embodiments. The given embodiments are merely illustrative of the invention and not intended to limit its scope. The embodiments provided below can serve as a guide for further improvements by those skilled in the art and do not constitute a limitation on the invention in any way.

[0045] The experimental methods in the following examples are all conventional methods, and are carried out according to the techniques or conditions described in the literature in the art or according to the product instructions, unless otherwise specified. The materials, reagents, etc. used in the following examples can be obtained commercially, unless otherwise specified.

[0046] The following examples were prepared according to the preparation flow chart shown in Figure 1 The micrometer-thick graphite film was prepared according to the preparation flow chart shown in Figure 2

[0047] Example 1

[0048] 1) Dissolve polymethyl methacrylate (PMMA) in DMF to obtain a coating glue (liquid) with a concentration of 0.5 g / mL, coat it on a commercial nickel foil (50 μm), and place it in an oven at 180°C for 30 min to solidify the polymer PMMA on the nickel foil;

[0049] 2) Place the nickel foil covered with the carbon source film between two graphite plates, and fix the two ends of the graphite plates on the graphite electrodes;

[0050] 3) Then, vacuumize the system chamber, and introduce 2000 sccm of argon to maintain the chamber pressure at 1 atm;

[0051] 4) Introduce a direct current (6 V) of 300 A to the two ends of the graphite electrodes to heat the graphite plates to 1300°C, and maintain the current constant for 2 min to perform annealing;

[0052] 5) After the annealing is completed, turn off the current, and keep the gas environment unchanged to cool to room temperature, and obtain a graphite film with a thickness of about 1 μm on the surface of the nickel foil.

[0053] Figure 3 The optical microscope photo of the obtained graphite film.

[0054] Figure 4 The Raman spectra of the obtained graphite film at 6 random positions.

[0055] Figure 5 The XRD spectrum of the obtained graphite film.

[0056] Figure 6 The white light interference image and thickness analysis curve of the obtained graphite film.

[0057] Example 2

[0058] 1) Place a 50 μm-thick commercial cobalt foil between two graphite plates together with a piece of graphite paper, and fix the two ends of the graphite plates on the graphite electrodes;

[0059] ​2) The chamber was then pumped down to vacuum and 2000 seem of argon was introduced to maintain the chamber pressure at 1 atm;

[0060] 3) A direct current of 350 A was applied to the graphite electrode to heat the graphite plate to 1300 °C. The current was held constant for 1 min to anneal the graphite plate.

[0061] 4) After the annealing was completed, the current was turned off for about 30 s to cool the graphite plate to 700 °C. Then the direct current of 350 A was applied to the graphite electrode to heat the graphite plate to 1300 °C. The current was held constant for 1 min to anneal the graphite plate.

[0062] 5) Step 4) was repeated. After 100 cycles, a graphite film of about 5 μm in thickness was obtained on the surface of the cobalt foil.

[0063] Figure 7 The white light interference image and the thickness profile of the obtained graphite film were analyzed.

[0064] Example 3

[0065] In this example, poly(methyl methacrylate) dissolved in DMF solution (0.5 g / mL) was coated on a 50 μm thick commercial cobalt foil and cured. The graphite plate was fixed on the graphite electrode and a direct current of 350 A was applied to heat the graphite plate to 1350 °C. The other conditions were the same as in Example 1. A graphite film of about 1.6 μm in thickness was obtained on the surface of the cobalt foil.

[0066] Example 4

[0067] In this example, poly(methyl methacrylate) dissolved in DMF solution (0.5 g / mL) was coated on a 50 μm thick commercial iron foil and cured. The graphite plate was fixed on the graphite electrode and a direct current of 400 A was applied to heat the graphite plate to 1400 °C. The other conditions were the same as in Example 1. A graphite film of about 500 nm in thickness was obtained on the surface of the iron foil.

[0068] Example 5

[0069] In this example, a 50 μm thick commercial nickel foil was sandwiched with a piece of graphite paper between two graphite plates. The graphite plates were fixed on the graphite electrode and a direct current was applied to the graphite electrode. The other conditions were the same as in Example 2. After 40 cycles, a graphite film of about 2 μm in thickness was obtained on the surface of the nickel foil.

[0070] Comparative Example 1

[0071] In this example, poly(methyl methacrylate) (PMMA) was dissolved in DMF to obtain a coating glue (liquid) with a concentration of 0.5 g / mL, which was coated on a commercial nickel foil (50 μm) and placed in an oven at 180°C for 30 min to allow the polymer PMMA to solidify on the nickel foil. The nickel foil covered with the carbon source film was clamped between two graphite plates, and the ends of the graphite plates were fixed on the graphite electrodes. The reaction device was placed in a tube furnace, and the temperature was raised to the growth temperature (1200°C) using argon for 2 h, hydrogen was used for annealing for 30 min, and argon was used for growth for 1 h. The other conditions were the same as in Example 1.

[0072] Figure 3 An optical microscope image of the graphite film obtained in Example 1. As can be seen from the figure, the graphite film as a whole shows uniform contrast, and the contrast at the folds is also consistent, indicating that the thickness is uniform.

[0073] Figure 4 Raman spectra of the graphite film obtained in Example 1 at 6 random positions. As can be seen from the figure, the Raman spectra of the graphite film at the 6 randomly selected positions are similar, and the ratio of the D peak intensity to the G peak intensity representing the defect concentration is not more than 0.1, indicating that the prepared graphite film is uniform in properties and has a low defect density.

[0074] Figure 5 An XRD spectrum of the graphite film obtained in Example 1. As can be seen from the figure, the prepared graphite film has a strong diffraction peak corresponding to the (0002) crystal plane, and the diffraction peak is located between 26.55-26.60°. The interlayer spacing of the graphite is calculated to be 0.335 nm using the Bragg formula calculator, which is consistent with the literature data. It is thus determined that the obtained graphite film is AB-stacked polycrystalline / single-crystalline graphite, and the thickness is characterized by a white light interferometer, Figure 6 A white light interference image and thickness analysis curve of the graphite film obtained in Example 1. As can be seen from the figure, the thickness of the graphite film is 1.045 μm.

[0075] Figure 7 A white light interference image and thickness analysis curve of the graphite film obtained in Example 2. As can be seen from the figure, the thickness of the graphite film is 5.3 μm.

[0076] Figure 8 A white light interference image and thickness analysis of the graphite film obtained in Comparative Example 1. As can be seen from the thickness curve, the thickness of the graphite film obtained in Comparative Example 1 is 855 nm. It can be seen that, by using a tube furnace for static growth for a longer time, the thickness is still smaller than that of the graphite film obtained in Example 1, thus reflecting the advantages of fast and efficient preparation of the graphite film by the method.

[0077] The thickness of the graphite film prepared in Examples 3-5 and Comparative Example 1 was also confirmed by white light interferometry, similarly to Example 1. Unless otherwise specifically defined, the terms used in the present application are intended to have the meanings commonly used by those skilled in the art.

[0078] The application has been described in detail. Those skilled in the art who read the foregoing description will have the knowledge of how to carry out the application in a wider range of equivalent parameters, concentrations and conditions without departing from the spirit and scope of the application, and without unnecessary experiments. Although the application gives specific examples, it should be understood that further improvements can be made to the application. In general, according to the principle of the application, the present application is intended to include any changes, uses or improvements of the application, including changes made outside the scope disclosed in the present application, using conventional techniques known in the art.

Claims

1. A method for growing a micron-thick graphite film, comprising the following steps: 1) Preparation of carbon film / metal foil A carbon film / metal foil is obtained by dispersing a high-carbon substance in an organic solvent and coating it onto a metal foil, followed by drying; or by making a high-carbon substance into a thin sheet and placing it on a metal foil. 2) Preparation of graphite film In a protective atmosphere, an electric current is applied to the sample, and the carbon film / metal foil is heated for a certain period of time using the Joule heating effect. The current is then stopped, and a micron-thick graphite film is obtained on the surface of the metal foil. In step 2), the power supply is stopped, and after cooling, the cycle of power supply heating-power off cooling is repeated for growth. The power supply time ranges from 1 second to 1 hour each time.

2. The method according to claim 1, characterized in that, In step 1), the metal foil includes any one of nickel foil, cobalt foil, and iron foil; The substances with high carbon content include PE, PP, PB, PVC, PMMA, polyacetylene, graphite, carbon black, activated carbon, carbon nanotubes, carbon fibers, pitch-based materials, or polycyclic aromatic hydrocarbons.

3. The method according to claim 1, characterized in that, In step (2) of the method, current is applied directly to both ends of the metal foil for heating; or the carbon film / metal foil is placed on a substrate that can form a conductive path and fixed as a whole on the electrode, and current is applied to heat the substrate and the carbon film / metal foil.

4. The method according to claim 1, characterized in that, In step 2), the protective atmosphere includes one or more of hydrogen, argon, and a hydrogen / argon mixture. After the protective gas is introduced, the chamber is maintained at a pressure range below 3 atm.

5. The method according to claim 1, characterized in that, The current applied should not exceed 500 A, and the voltage should not exceed 40 V.

6. The method according to claim 1, characterized in that, The heating temperature is 700-2500 ℃, and the power-on time is 1 second or more.

7. The method according to claim 1, characterized in that, The method further includes the following step: transferring a thick graphite film formed on a metal foil substrate onto a target substrate; The specific operation is as follows: the metal foil on which the graphite film has been grown is placed in an etchant for etching. After the metal foil and the graphite film are separated, the graphite film is taken out, washed with water, and then the graphite film is taken out using the target substrate to obtain the graphite film on the target substrate. The etchant is one or more of the following: an aqueous solution of ferric chloride, an aqueous solution of persulfate, hydrochloric acid, and nitric acid.

8. A micron-thick graphite film prepared by the method of any one of claims 1-7.

9. The micron-thick graphite film according to claim 8, characterized in that, The structure of the micron-thick graphite film is characterized by AB stacked polycrystalline or single-crystal graphite with a thickness of 200 nm-5 μm.

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