Graphite and preparation method thereof

Abstract

The invention relates to the technical field of graphite, and provides graphite and a preparation method thereof.The preparation method comprises the steps that a solid carbon source is arranged on the surface of a carbon diffusion layer for solid purification, and the solid purification comprises the steps that the carbon diffusion layer with the solid carbon source arranged on the surface is heated, and carbon atoms in the solid carbon source are diffused into the carbon diffusion layer; a graphite carbon source is grown on the surface, opposite to the solid carbon source, of the carbon diffusion layer, and impurity atoms in the solid carbon source are prevented from diffusing and passing through the carbon diffusion layer; taking the graphite carbon source as a solid-state carbon source, and repeating the step of solid-state purification for at least one time to prepare the graphite. The preparation method is simple, and the purity of the graphite is high.

Description

Technical Field

[0001] The present application relates to the technical field of graphite, and in particular to graphite and a preparation method thereof. Background Art

[0002] High-purity graphite (impurity content less than 0.01% by mass) is the most common van der Waals crystal. It has extremely high in-plane thermal conductivity, good electrical conductivity, and extremely high heat resistance. It is widely used in semiconductor preparation and thermal insulation materials.

[0003] In traditional technology, the purification methods of high-purity materials are mostly divided into three methods: melting crystallization, chemical treatment, and high-temperature heat treatment. The melting crystallization method is aimed at traditional solid crystals with low melting points, such as semiconductors such as silicon. Melting crystallization can use the different characteristics of impurities and crystal melting points to precipitate high-purity crystals at a specific temperature. The chemical treatment method is aimed at crystals with more metal impurities. Strong acids and strong bases are used to dissolve metal impurities in the solution, and finally the chemical residues are washed away to obtain high-purity crystals. The high-temperature heat treatment method is aimed at crystals with higher sublimation points. High temperature and high pressure are used to make impurities with lower sublimation points sublimate at high temperatures, and finally cool down to obtain high-purity crystals. However, due to the high melting point characteristics of graphite, melting crystallization is not applicable. Although chemical treatment can effectively remove metal impurities, it is very easy to leave chemical residues. Although high-temperature treatment can obtain very high-purity crystals, it is easy to introduce more lattice defects in the crystal preparation process because the high temperature and high pressure process is too intense. Summary of the invention

[0004] Based on this, an embodiment of the present application provides a graphite with a simple method, high graphite purity and few lattice defects and a preparation method thereof.

[0005] In a first aspect, the present application provides a method for preparing graphite, the method for preparing graphite comprising:

[0006] The solid carbon source is arranged on the surface of the carbon diffusion layer for solid-state purification, wherein the solid-state purification comprises: heating the carbon diffusion layer on the surface of which the solid carbon source is arranged, so that carbon atoms in the solid carbon source diffuse into the carbon diffusion layer and grow on the surface of the carbon diffusion layer opposite to the solid carbon source to form a graphite carbon source, and the carbon diffusion layer prevents impurity atoms in the solid carbon source from diffusing through;

[0007] The graphite carbon source is used as a solid carbon source, and the solid-state purification step is repeated at least once to prepare the graphite.

[0008] In some embodiments, the absorption energy barrier of the carbon atoms in the carbon diffusion layer is 0-2 eV / atom.

[0009] In some embodiments, the transport energy barrier of the carbon atoms in the carbon diffusion layer is 0-2 eV / atom.

[0010] In some embodiments, the precipitation energy barrier of the carbon atoms in the carbon diffusion layer is 0-2 eV / atom.

[0011] In some embodiments, the carbon diffusion layer has a thickness of 50 μm to 200 μm.

[0012] In some embodiments, the material of the carbon diffusion layer includes at least one of nickel and iron.

[0013] In some embodiments, the material of the carbon diffusion layer is a single crystal material, and the graphite formed after the solid-state purification is single crystal graphite.

[0014] Optionally, at least one of the crystal plane indices hkl of the single crystal material is greater than 1.

[0015] In some embodiments, the material of the carbon diffusion layer is a polycrystalline material, and the graphite formed after the solid-state purification is polycrystalline graphite.

[0016] In some embodiments, the heating temperature is from 1200° C. to the melting temperature of the carbon diffusion layer, the heating time is from 5 h to 100 h, and the atmosphere is a protective atmosphere.

[0017] In some embodiments, the preparation method comprises:

[0018] Placing a solid carbon source on the surface of a first carbon diffusion layer and performing the solid-state purification at least once to obtain a graphite carbon source, wherein the material of the first carbon diffusion layer is a polycrystalline material;

[0019] The graphite carbon source is disposed as a solid carbon source on the surface of the second carbon diffusion layer to perform the solid purification at least once to obtain single crystal graphite, and the material of the second carbon diffusion layer is a single crystal material.

[0020] In some embodiments, the mass content of impurity atoms in the solid carbon source is ≤10000 ppm.

[0021] In some embodiments, the impurity atoms include at least one of copper, iron, aluminum, and zinc.

[0022] In some embodiments, the mass content of impurity atoms in the graphite is ≤10 ppm.

[0023] In a second aspect, the present application provides a graphite, which is prepared by the method for preparing graphite as described in the first aspect.

[0024] Compared with the traditional technology, this application has at least the following beneficial effects:

[0025] The present application uses a carbon diffusion layer to perform solid-state purification of carbon atoms in a solid carbon source. In the process of solid-state purification, the solid-state lattice transmission of atoms is used to enable carbon atoms in the solid carbon source to pass through the carbon diffusion layer and precipitate on the surface to form graphite, while impurity atoms are not easy to pass through the carbon diffusion layer or even cannot enter the carbon diffusion layer, thereby achieving filtration and purification of carbon atoms. In the preparation process of the present application, no impurities are introduced and the preparation process conditions are low. High-purity graphite with low lattice defects can be prepared by multiple solid-state purification methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A schematic diagram of a method for preparing graphite provided in one embodiment of the present application;

[0027] Figure 2 This is a scanning electron microscope image of the single crystal graphite prepared in Example 1 of the present application;

[0028] Figure 3 This is a scanning electron microscope image of the polycrystalline graphite prepared in Example 3 of the present application;

[0029] Figure 4 This is an atomic force microscope image of the single crystal graphite prepared in Example 1 of the present application;

[0030] Figure 5 This is an atomic force microscope image of HOPG in Comparative Example 4 of the present application. DETAILED DESCRIPTION

[0031] Below in conjunction with the embodiments and examples, the present application is further described in detail. These embodiments and examples are only used to illustrate the present application and are not used to limit the scope of the present application. The purpose of providing these embodiments and examples is to make the understanding of the disclosure of the present application more thorough and comprehensive. It should also be understood that the present application can be implemented in many different forms, and is not limited to the embodiments and examples described herein. Those skilled in the art can make various changes or modifications without violating the connotation of the present application, and the equivalent form obtained also falls within the protection scope of the present application. In addition, in the description below, a large number of specific details are given in order to provide a more comprehensive understanding of the present application. It should be understood that the present application can be implemented without one or more of these details.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0033] In this application, "optionally", "optional", and "optional" mean optional or dispensable, that is, any one of the two parallel schemes of "yes" or "no". If multiple "options" appear in a technical solution, unless otherwise specified and there is no contradiction or mutual restriction, each "optional" is independent.

[0034] In this application, the terms "first", "second", etc. in "the first aspect", "the second aspect", etc. are used only for descriptive purposes and cannot be understood as indicating or implying relative importance or quantity, nor can they be understood as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first", "second", etc. only serve the purpose of non-exhaustive enumeration and description, and it should be understood that they do not constitute a closed limitation on quantity.

[0035] In the present application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0036] In the present application, when it comes to a numerical interval (i.e., a numerical range), unless otherwise specified, the distribution of the optional numerical values ​​in the numerical interval is considered to be continuous, and includes the two numerical endpoints (i.e., the minimum and maximum values) of the numerical interval, and each numerical value between the two numerical endpoints. Unless otherwise specified, when the numerical interval only refers to an integer in the numerical interval, it includes the two endpoint integers of the numerical range, and each integer between the two endpoints, which is equivalent to directly listing each integer. When multiple numerical ranges are provided to describe features or characteristics, these numerical ranges can be combined. In other words, unless otherwise specified, the numerical range disclosed in the present application should be understood to include any and all sub-ranges included therein. The "numerical value" in the numerical interval can be any quantitative value, such as a number, a percentage, a ratio, etc. "Numerical interval" allows for a broad range of quantitative intervals such as percentage intervals, ratio intervals, and ratio intervals.

[0037] All documents mentioned in this application are cited as references in this application, just as each document is cited as reference separately. Unless they conflict with the application purpose and / or technical solution of this application, the cited documents involved in this application are cited with all contents and all purposes. When the cited documents are involved in this application, the definitions of relevant technical features, terms, nouns, phrases, etc. in the cited documents are also cited. When the cited documents are involved in this application, the examples and preferred methods of the cited relevant technical features can also be incorporated into this application as references, but are limited to the implementation of this application. It should be understood that when the cited content conflicts with the description in this application, the present application shall prevail or be modified adaptively according to the description of this application.

[0038] In traditional technology, chemical treatment and high temperature treatment are mainly used to prepare high purity graphite. Among them, chemical treatment is a traditional technology that uses strong acid to replace the metal elements in the crystal with a solution. For example, natural graphite obtained from natural minerals and graphite phosphorus sheets precipitated in the process of cast iron contain a large amount of silicate and alkali metal impurities. Such impurities can be removed by strong acid. However, the reaction of this strong acid solution will greatly destroy the lattice structure in the crystal, and the chemical substances introduced during the chemical treatment will remain inside the crystal and are difficult to remove. Therefore, the chemical treatment method for graphite purification has certain limitations, and it is difficult for graphite to reach a high purity. The high temperature and high pressure method uses the high melting point of graphite to make the impurities sublimate or volatilize at a temperature slightly lower than the melting point of graphite to achieve the effect of removing impurities. The most typical graphite sample obtained in this way is HOPG (highly oriented pyrolytic graphite). However, due to the high temperature and high pressure method, the lattice structure of graphite itself is greatly damaged. Taking HOPG as an example, it has many grain boundaries and structural defects, and its electrical and thermal conductivity are poor, making it difficult to apply.

[0039] The first aspect of the present application provides a method for preparing graphite, such as Figure 1 The graphite preparation method comprises:

[0040] The solid carbon source is arranged on the surface of the carbon diffusion layer for solid-state purification, wherein the solid-state purification comprises: heating the carbon diffusion layer on the surface of which the solid carbon source is arranged, so that carbon atoms in the solid carbon source diffuse into the carbon diffusion layer and grow on the surface of the carbon diffusion layer opposite to the solid carbon source to form a graphite carbon source, and the carbon diffusion layer prevents impurity atoms in the solid carbon source from diffusing through;

[0041] The graphite carbon source is used as a solid carbon source, and the solid-state purification step is repeated at least once to prepare the graphite.

[0042] The present application uses a carbon diffusion layer to perform solid-state purification of carbon atoms in a solid carbon source. In the process of solid-state purification, the solid-state lattice transmission of atoms is used to enable carbon atoms in the solid carbon source to pass through the carbon diffusion layer and precipitate on the surface to form graphite, while impurity atoms are not easy to pass through the carbon diffusion layer or even cannot enter the carbon diffusion layer, thereby achieving filtration and purification of carbon atoms. In the preparation process of the present application, no impurities are introduced and the preparation process conditions are low. High-purity graphite with low lattice defects can be prepared by multiple solid-state purification methods.

[0043] It is understandable that the present application does not make any specific requirements or special limitations on the type of solid carbon source. For example, it can be at least one of carbon black, carbon nanotubes, graphite powder and graphite plates, as long as it can provide carbon atoms.

[0044] It is understandable that the carbon diffusion layer in the present application can ensure that carbon atoms pass through and prevent impurity atoms from passing through. For example, it can be achieved by adjusting the absorption energy barrier, transmission energy barrier and output energy barrier of the carbon diffusion layer for impurity atoms and carbon atoms. Optionally, in the solid-state purification process, when the absorption energy barrier, transmission energy barrier and precipitation energy barrier of carbon atoms in the carbon diffusion layer are low, that is, carbon atoms in the solid carbon source will be absorbed by the carbon diffusion layer, and after diffusion in the carbon diffusion layer, the surface of the carbon diffusion layer will grow to form graphite, that is, carbon atoms can completely pass through the carbon diffusion layer; and in the solid-state purification process, when at least one of the absorption energy barrier, transmission energy barrier and precipitation energy barrier of impurity atoms in the carbon diffusion layer is high, the impurity atoms cannot pass through the carbon diffusion layer, that is, it is difficult for impurity atoms to enter the carbon diffusion layer, difficult to be transmitted in the carbon diffusion layer or difficult to be precipitated in the carbon diffusion layer, so it is difficult for impurity atoms to pass through the carbon diffusion layer and remain on the surface or inside of the carbon diffusion layer.

[0045] It should be noted that the absorption energy barrier refers to the energy that atoms can enter the carbon diffusion layer, the transport energy barrier refers to the energy that atoms can be transported in the carbon diffusion layer, and the precipitation energy barrier refers to the energy that atoms can precipitate out of the carbon diffusion layer.

[0046] In some embodiments, the absorption energy barrier of the carbon atoms in the carbon diffusion layer is 0-2 eV / atom, for example, 0 eV / atom, 0.2 eV / atom, 0.4 eV / atom, 0.6 eV / atom, 0.8 eV / atom, 1.0 eV / atom, 1.2 eV / atom, 1.4 eV / atom, 1.6 eV / atom, 1.8 eV / atom or 2.0 eV / atom.

[0047] In some embodiments, the transmission energy barrier of the carbon atoms in the carbon diffusion layer is 0~2 eV / atom, for example, it can be 0 eV / atom, 0.2 eV / atom, 0.4 eV / atom, 0.6 eV / atom, 0.8 eV / atom, 1.0 eV / atom, 1.2 eV / atom, 1.4 eV / atom, 1.6 eV / atom, 1.8 eV / atom or 2.0 eV / atom.

[0048] In some embodiments, the precipitation energy barrier of the carbon atoms in the carbon diffusion layer is 0 to 2 eV / atom, and for example, it can be 0 eV / atom, 0.2 eV / atom, 0.4 eV / atom, 0.6 eV / atom, 0.8 eV / atom, 1.0 eV / atom, 1.2 eV / atom, 1.4 eV / atom, 1.6 eV / atom, 1.8 eV / atom, or 2.0 eV / atom.

[0049] By selecting the inhalation energy barrier, transmission energy barrier, and precipitation energy barrier of carbon atoms in the carbon diffusion layer as above in the present application, it is ensured that carbon atoms can continuously penetrate the diffusion layer during the solid-state purification process, while other various impurity atoms are difficult to overcome the relatively high inhalation, transmission, or diffusion barriers in the diffusion layer, resulting in their inability to penetrate the diffusion layer, achieving the effect of impurity purification and improving the purity of graphite.

[0050] In some embodiments, the thickness of the carbon diffusion layer is 50 μm to 200 μm, and for example, it can be 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm, 180 μm, 190 μm, or 200 μm. By selecting the thickness of the carbon diffusion layer as above in the present application, the solid-state purification efficiency is ensured. If the thickness of the carbon diffusion layer is relatively small, volatilization may occur during the heating process of the carbon diffusion layer, affecting the solid-state purification effect; if the thickness of the carbon diffusion layer is relatively large, the transmission distance of carbon atoms in the carbon diffusion layer is increased, which may lead to a relatively low purification efficiency and a long preparation time.

[0051] In some embodiments, the material of the carbon diffusion layer includes at least one of nickel and iron.

[0052] In some embodiments, the material of the carbon diffusion layer is a single-crystal material, and the graphite formed after the solid-state purification is single-crystal graphite. In the present application, a single-crystal material is used as the carbon diffusion layer, and the carbon diffusion layer can serve as a growth substrate for graphite, and carbon atoms epitaxially grow on the surface of the carbon diffusion layer of the single-crystal material to form single-crystal graphite. The present application can not only achieve the purification of graphite but also ensure the single-crystal growth of graphite.

[0053] Optionally, at least one of the crystal plane indices hkl of the single crystal material is greater than 1. Among them, at least one of the crystal plane indices hkl of the single crystal material is greater than 1, which refers to a high-index single crystal material. It should be noted that the crystal plane index hkl is an index system for describing the orientation of crystal planes in crystals, where h, k, and l are integers representing the intercept coefficients of the crystal planes with the three crystal axes of the crystal. When an index is greater than 1, it means that the crystal plane does not have a single intercept in the direction of the corresponding crystal axis, but there are multiple intercepts, which indicates that the crystal plane has high symmetry and complexity.

[0054] For example, a single crystal nickel material is used as a carbon diffusion layer, and the carbon diffusion layer of the single crystal nickel material is annealed at 1200°C to 1400°C by oxidation-reduction to obtain a carbon diffusion layer of a single crystal nickel material with a high index surface. The temperature can be 1300°C. It is understandable that other methods can also be used to prepare a carbon diffusion layer of a single crystal material with a high index surface.

[0055] The present application selects single crystal materials as above, that is, high-index surface single crystal materials. The high-index surface has asymmetric atomic-level steps. Such atomic-level steps will promote the growth of graphite, and it will preferentially nucleate, grow and splice at the steps, so that complete and extremely pure single crystal graphite can be prepared.

[0056] In some embodiments, the material of the carbon diffusion layer is a polycrystalline material, and the graphite formed after the solid-state purification is polycrystalline graphite. It is understandable that the material of the carbon diffusion layer is a polycrystalline material, and carbon atoms will form polycrystalline graphite when epitaxially growing on the surface of the carbon diffusion layer.

[0057] In some embodiments, the heating temperature is from 1200°C to the melting temperature of the carbon diffusion layer. The present application selects the heating temperature as above, and the purification efficiency of carbon atoms is high and the purity is high. It is understandable that the higher the heating temperature, the higher the diffusion efficiency of carbon atoms, but impurity atoms may also penetrate the carbon diffusion layer, affecting the purity of graphite; and because the thickness of the carbon diffusion layer is small, when the heating temperature is close to the melting temperature of the carbon diffusion layer material, the carbon diffusion layer may volatilize, causing the thickness of the carbon diffusion layer to change, affecting the solid-state purification effect. If the heating temperature is relatively low, the solid-state purification efficiency may be relatively low, resulting in a small amount of graphite formed and a relatively thin graphite thickness.

[0058] In some embodiments, the heating time is 5 h to 100 h, for example, it can be 5 h, 10 h, 20 h, 30 h, 40 h, 50 h, 60 h, 70 h, 80 h, 90 h or 100 h.

[0059] In some embodiments, the heated atmosphere is a protective atmosphere. It is understood that the protective atmosphere refers to a gas that does not react with the solid carbon source, graphite, and carbon diffusion layer. For example, it can be an inert gas.

[0060] In some embodiments, the heating pressure is normal pressure, for example, 0.09 MPa to 0.11 MPa.

[0061] In some embodiments, the preparation method comprises:

[0062] Placing a solid carbon source on the surface of a first carbon diffusion layer and performing the solid-state purification at least once to obtain a graphite carbon source, wherein the material of the first carbon diffusion layer is a polycrystalline material;

[0063] The graphite carbon source is disposed as a solid carbon source on the surface of the second carbon diffusion layer to perform the solid purification at least once to obtain single crystal graphite, and the material of the second carbon diffusion layer is a single crystal material.

[0064] In the process of preparing graphite, the present application first uses a carbon diffusion layer of a polycrystalline material for solid-state purification to achieve the purity requirement of the graphite; further, when the purity requirement of the graphite meets the use requirement, a carbon diffusion layer of a single crystal material is used for solid-state purification, and finally high-purity single-crystal graphite is obtained. The present application not only has high preparation efficiency, but also has few defects in the prepared graphite.

[0065] In some embodiments, the mass content of impurity atoms in the solid carbon source is ≤10000 ppm, for example, 1000 ppm, 2000 ppm, 3000 ppm, 4000 ppm, 5000 ppm, 6000 ppm, 7000 ppm, 8000 ppm, 9000 ppm or 10000 ppm. It is understood that when the mass content of impurity atoms in the solid carbon source is high, more solid-state purifications can be used to improve the purity of graphite.

[0066] In some embodiments, the impurity atoms include at least one of copper, iron, aluminum, and zinc.

[0067] In some embodiments, the mass content of impurity atoms in the graphite is ≤10 ppm, for example, 1 ppm, 2 ppm, 3 ppm, 4 ppm, 5 ppm, 6 ppm, 7 ppm, 8 ppm, 9 ppm or 10 ppm.

[0068] Exemplarily, a method for preparing the above graphite is provided, comprising the following steps:

[0069] S1. Arranging a solid carbon source on the surface of a carbon diffusion layer with a thickness of 50 μm to 200 μm for solid-state purification, wherein the solid-state purification comprises: heating the carbon diffusion layer with the solid carbon source arranged on the surface, the heating temperature is from 1200° C. to the melting temperature of the carbon diffusion layer, the time is 5 h to 100 h, the atmosphere is a protective atmosphere, the carbon atoms in the solid carbon source diffuse into the carbon diffusion layer, and grow on the surface of the carbon diffusion layer opposite to the solid carbon source to form a graphite carbon source, and the carbon diffusion layer prevents impurity atoms in the solid carbon source from diffusing through;

[0070] S2. Using the graphite carbon source as a solid carbon source, repeat the solid-state purification step in step S1 at least once to prepare the graphite.

[0071] A second aspect of the present application provides graphite, which is prepared using the method for preparing graphite as described in the first aspect.

[0072] In some embodiments, the in-plane conductivity of the graphite is ≥10 6 S.m.

[0073] In some embodiments, the in-plane thermal conductivity of the graphite is ≥ 1500 W / (m·K).

[0074] The embodiments of the present application will be described in detail below in conjunction with examples. It should be understood that these examples are only used to illustrate the present application and are not intended to limit the scope of the present application. The experimental methods for which specific conditions are not specified in the following examples are preferably referred to the guidance provided in the present application, and can also be based on the experimental manual or normal conditions in this area, can also be based on the conditions recommended by the manufacturer, or refer to experimental methods known in the art.

[0075] It is understandable that the present application can use a variety of solid carbon sources, the thickness of the graphite paper can be 100 μm~400 μm, and the solid carbon source in the following embodiments and comparative examples uses graphite paper with a thickness of 200 μm, the mass content of impurity atoms is 6000 ppm, and the main impurity atoms include B, Si, Al and Zn, etc. The material of the carbon diffusion layer is nickel, and the absorption barrier of carbon atoms in the carbon diffusion layer is 0.42 eV / atom, the transmission barrier is 1.68 eV / atom, and the precipitation barrier is 1.04 eV / atom.

[0076] Example 1

[0077] S1, placing a solid carbon source on a first carbon diffusion layer with a thickness of 100 μm, the material of the first carbon diffusion layer is polycrystalline nickel, introducing a protective carrier gas (800 sccm argon and 100 sccm hydrogen) under normal pressure, heating at 1200°C for 20 h, and growing a polycrystalline graphite carbon source on the surface of the carbon diffusion layer;

[0078] S2. The polycrystalline graphite carbon source is used as a solid carbon source and is disposed on a second carbon diffusion layer with a thickness of 100 μm. The material of the second carbon diffusion layer is single crystal nickel (high index surface single crystal nickel, index surface is (520)). A protective carrier gas (800 sccm argon and 100 sccm hydrogen) is introduced under normal pressure. The carbon diffusion layer is heated at 1200 °C for 20 h to grow on the surface of the carbon diffusion layer. Figure 2 The single crystal graphite shown has no obvious grain boundaries and the entire plane is relatively flat.

[0079] Example 2

[0080] S1. A solid carbon source is placed on a first carbon diffusion layer with a thickness of 100 μm. The material of the first carbon diffusion layer is single crystal nickel (high index surface single crystal nickel, index surface is (520)). A protective carrier gas (800 sccm argon and 100 sccm hydrogen) is introduced under normal pressure. The mixture is heated at 1300°C for 30 h to grow a single crystal graphite carbon source on the surface of the carbon diffusion layer.

[0081] S2. The above-mentioned single crystal graphite carbon source is used as a solid carbon source and is arranged on a second carbon diffusion layer with a thickness of 50 μm. The material of the second carbon diffusion layer is single crystal nickel (high index surface single crystal nickel, the index surface is (520)). A protective carrier gas (800 sccm argon and 100 sccm hydrogen) is introduced under normal pressure, and heated at 1200°C for 20 hours to grow single crystal graphite on the surface of the carbon diffusion layer.

[0082] Example 3

[0083] S1. A solid carbon source is placed on a first carbon diffusion layer with a thickness of 200 μm. The material of the first carbon diffusion layer is polycrystalline nickel. A protective carrier gas (800 sccm argon and 100 sccm hydrogen) is introduced under normal pressure. The mixture is heated at 1350 °C for 40 h to grow a polycrystalline graphite carbon source on the surface of the carbon diffusion layer.

[0084] S2, the above-mentioned polycrystalline graphite carbon source is used as a solid carbon source and is arranged on a second carbon diffusion layer with a thickness of 150 μm. The material of the second carbon diffusion layer is polycrystalline nickel. A protective carrier gas (800 sccm argon and 100 sccm hydrogen) is introduced under normal pressure, and heated at 1200 ° C for 30 h to grow on the surface of the carbon diffusion layer. Figure 3 Polycrystalline graphite shown.

[0085] Example 4

[0086] Graphite was prepared according to the method of Example 1, except that the thickness of the second carbon diffusion layer in step S2 was 30 μm.

[0087] Example 5

[0088] Graphite was prepared according to the method of Example 1, except that the thickness of the second carbon diffusion layer in step S2 was 300 μm.

[0089] Example 6

[0090] Graphite was prepared according to the method of Example 1, except that the heating temperature in step S1 was 1100°C.

[0091] Example 7

[0092] Graphite was prepared according to the method of Example 1, except that the heating temperature in step S2 was 1100°C.

[0093] Example 8

[0094] Graphite was prepared according to the method of Example 1, except that the heating time in step S2 was 3 h.

[0095] Comparative Example 1

[0096] Graphite was prepared according to the method of Example 1, except that only step S1 was performed.

[0097] Comparative Example 2

[0098] Graphite was prepared according to the method of Example 1, except that only step S1 was performed, and the first carbon diffusion layer in step S1 was replaced by the second carbon diffusion layer in step S2 of Example 1.

[0099] Comparative Example 3

[0100] Graphite is prepared according to the method of Example 1, except that only step S1 is performed, and the first carbon diffusion layer in step S1 is replaced by single crystal iron.

[0101] Comparative Example 4

[0102] HOPG was directly used as the graphite material, which was purchased from NT-MDT Spectrum Instruments with the brand name ZYA.

[0103] The graphite prepared in the above-mentioned embodiments and comparative examples was subjected to complete reaction and removal of the carbon diffusion layer of the nickel material using a 1 mol / L ferric chloride solution, and then cleaned with ultrapure water to obtain a clean high-purity graphite material.

[0104] The graphite prepared above was subjected to elemental analysis, and the analysis method included:

[0105] Dissociate and take 5 mg of graphite sample into a digestion tube, add 0.75 mL of 14.4 mol / L concentrated nitric acid and 0.25 mL of 12 mol / L concentrated hydrochloric acid, microwave heat to 260 °C and digest for 1 h, obtain the supernatant solution and dilute it to 25 mL constant volume tube, put it into ICP-MS instrument for analysis, and obtain the mass concentration of impurity atoms. The test results are shown in Table 1.

[0106] The graphite was placed in a quartz tube furnace and plasma etched at 500 °C in a low pressure (50 Pa) hydrogen environment. Finally, the in-plane lattice defects of the graphite were observed on the surface by atomic force microscopy. The test results are shown in Table 1. The test results of the single crystal graphite of Example 1 are shown in Table 1. Figure 4 As shown, the test results of HOPG graphite of Comparative Example 4 are as follows Figure 5 shown.

[0107] Table 1

[0108]

[0109] From the above table we can see that:

[0110] (1) Compared with Examples 4-5, it can be seen that the present application controls the thickness of the carbon diffusion layer to ensure that graphite can be smoothly precipitated into a thick layer, and avoids the occurrence of problems such as the diffusion layer being too thin to melt during the purification process or the diffusion layer being too thick to cause graphite to be unable to precipitate.

[0111] (2) Compared with Examples 6-7, it can be seen that the present application controls the temperature during the solid-state purification process to ensure the function of continuous growth of graphite, and avoids the occurrence of problems such as the temperature being too low, which causes carbon atoms to be unable to grow to form graphite, and the temperature being too high, which causes the carbon diffusion layer to melt.

[0112] (3) Compared with Example 1 and Comparative Examples 1-4, it can be seen that Comparative Examples 1-3 only undergo one step of solid-state purification, and the obtained graphite has low purity and high impurity content. Comparative Example 4 is HOPG graphite, which has a high purity but a high defect concentration. Therefore, the present application uses a carbon diffusion layer to perform solid-state purification on carbon atoms in a solid carbon source. In the process of solid-state purification, the solid-state lattice transmission of atoms is utilized so that carbon atoms in the solid carbon source can pass through the carbon diffusion layer and precipitate on the surface to form graphite, while impurity atoms are not easy to pass through the carbon diffusion layer or even cannot enter the carbon diffusion layer, thereby achieving filtration and purification of carbon atoms. In the preparation process of the present application, no impurities are introduced and the preparation process conditions are low. High-purity graphite with low lattice defects can be prepared by multiple solid-state purification methods.

[0113] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0114] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be construed as limiting the scope of the application. It should be noted that, for a person of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A method for preparing graphite, characterized in that: The method for preparing graphite comprises: The solid carbon source is arranged on the surface of the carbon diffusion layer for solid-state purification, wherein the solid-state purification comprises: heating the carbon diffusion layer on the surface of which the solid carbon source is arranged, so that carbon atoms in the solid carbon source diffuse into the carbon diffusion layer and grow on the surface of the carbon diffusion layer opposite to the solid carbon source to form a graphite carbon source, and the carbon diffusion layer prevents impurity atoms in the solid carbon source from diffusing through; The graphite carbon source is used as a solid carbon source, and the solid-state purification step is repeated at least once to prepare the graphite.

2. The method for preparing graphite according to claim 1, characterized in that: The carbon diffusion layer also satisfies at least one of the following conditions: (1) The absorption energy barrier of the carbon atoms in the carbon diffusion layer is 0~2 eV / atom; (2) The transmission energy barrier of the carbon atoms in the carbon diffusion layer is 0~2 eV / atom; (3) The precipitation energy barrier of the carbon atoms in the carbon diffusion layer is 0~2 eV / atom.

3. The method for preparing graphite according to claim 1, characterized in that: The carbon diffusion layer satisfies at least one of the following conditions: (1) The thickness of the carbon diffusion layer is 50 μm to 200 μm; (2) The material of the carbon diffusion layer includes at least one of nickel and iron.

4. The method for preparing graphite according to claim 1, characterized in that: The material of the carbon diffusion layer is a single crystal material, and the graphite formed after the solid-state purification is a single crystal graphite; Optionally, at least one of the crystal plane indices hkl of the single crystal material is greater than 1.

5. The method for preparing graphite according to claim 1, characterized in that: The material of the carbon diffusion layer is a polycrystalline material, and the graphite formed after the solid-state purification is polycrystalline graphite.

6. The method for preparing graphite according to claim 1, characterized in that: The heating temperature is from 1200° C. to the melting temperature of the carbon diffusion layer, the heating time is from 5 h to 100 h, and the atmosphere is a protective atmosphere.

7. The method for preparing graphite according to claim 1, characterized in that: The preparation method comprises: Placing a solid carbon source on the surface of a first carbon diffusion layer and performing the solid-state purification at least once to obtain a graphite carbon source, wherein the material of the first carbon diffusion layer is a polycrystalline material; The graphite carbon source is disposed as a solid carbon source on the surface of the second carbon diffusion layer to perform the solid purification at least once to obtain single crystal graphite, and the material of the second carbon diffusion layer is a single crystal material.

8. The method for preparing graphite according to claim 1, characterized in that: The impurity atoms satisfy at least one of the following conditions: (1) The mass content of impurity atoms in the solid carbon source is ≤10000 ppm; (2) The impurity atoms include at least one of copper, iron, aluminum and zinc.

9. The method for preparing graphite according to any one of claims 1 to 8, characterized in that: The mass content of impurity atoms in the graphite is ≤10 ppm.

10. A graphite, characterized in that: The graphite is prepared by the method for preparing graphite according to any one of claims 1 to 9.

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