A method for controllably preparing different layer number high-quality graphene

Abstract

The application discloses a method for controllably preparing different layer numbers of high-quality graphene. The method comprises the following steps: 1) mixing original graphite powder with aromatic lithium reagent at normal temperature, stirring and reacting for a period of time, and centrifuging and washing to obtain different layer numbers of lithium-embedded graphite compounds; and 2) dispersing the different layer numbers of lithium-embedded graphite prepared freshly in a solvent, and ultrasonically peeling to obtain graphene with corresponding specific layer numbers. The method realizes accurate control of the layer number of the lithium-embedded compound by selecting a lithiumation reagent with a matching electric potential, thereby obtaining graphene with corresponding specific layer numbers. The method is simple in process, green and energy-saving, can accurately regulate the layer number of the graphene, and is mild in the peeling process, does not introduce oxygen-containing functional groups and does not damage the structure of the graphene, so that the prepared graphene is few in defects, high in quality and wide in application prospect.

Description

Technical Field

[0001] This invention belongs to the field of graphene exfoliation preparation technology, specifically relating to an efficient method for preparing graphene with controllable layer number. Background Technology

[0002] In 2004, two scientists at the University of Manchester in the UK successfully separated monolayer graphene using a mechanical exfoliation method. This type of graphene is only one atom thick and consists of sp... 2 Novel nanomaterials, consisting of hybridized carbon atoms tightly packed into a two-dimensional honeycomb lattice structure, have been a research hotspot in the field of nanomaterials science since their discovery. Graphene's perfect two-dimensional crystal structure endows it with ultra-high carrier mobility (15000 cm⁻¹). 2 / (V·s)), high specific surface area (2630m²) 2 With its unique properties such as high thermal conductivity (5000 W / (m·K)) and high chemical stability, it has wide applications in fields such as high-efficiency sensors, renewable energy, transparent electrodes, and nanocatalysts.

[0003] The properties of graphene are closely related to its number of layers; graphene with different numbers of layers exhibits different properties. Single-layer and bilayer graphene are zero-bandgap semiconductors, carrying only electrons and holes as charge carriers. In contrast, few-layer graphene (3-10 layers) possesses multiple charge carrier types, and its valence and conduction bands show significant overlap. This difference determines its varying properties and influences its applications in optoelectronic devices and other fields. Therefore, to broaden the application prospects of graphene and realize its industrialization, exploring methods for the controllable preparation of high-quality graphene with different numbers of layers is crucial.

[0004] Currently, the main methods for preparing graphene are as follows: (1) Micromechanical exfoliation, which can produce high-quality graphene, but it is inefficient and highly random, and is limited to laboratory research, making it difficult to achieve large-scale application; (2) Chemical vapor deposition (CVD), which can control the number of layers by manipulating experimental conditions, but it has high requirements for experimental processes, low yield, and poor controllability; (3) SiC epitaxial growth, which can prepare large-area graphene films, but the graphene sheets are difficult to separate from the SiC substrate, are expensive, and are not suitable for mass production; (4) Liquid phase exfoliation, which can obtain high-quality graphene sheets that are easy to transfer and disperse, but prolonged ultrasound results in small product size, uneven thickness distribution, and low yield; (5) Oxidation-reduction method, which is currently the most widely used method in industry and can achieve large-scale preparation of graphene powder, but the prepared product has great defects in structure and composition, which seriously affects its performance, and the number of layers is dispersed, making it difficult to achieve controllable preparation.

[0005] Patent application CN104058396A discloses an intercalation-expansion-exfoliation method. This method involves intercalating graphite raw materials with an intercalating agent to obtain graphite intercalation compounds (GICs). Highly expanded, worm-like graphene is then obtained under the action of an expanding agent and auxiliary agents. Finally, graphene dispersions with different numbers of layers are exfoliated in an auxiliary agent. However, this method requires the continuous use of large amounts of chemical reagents such as intercalating agents, expanding agents, and auxiliary agents. The preparation process is complex and cumbersome, and it is prone to environmental pollution. In particular, the intercalating agents used are strong acids and strong oxidants such as concentrated nitric acid, concentrated sulfuric acid, and potassium permanganate, which inevitably cause some oxidation to the graphite structure, leading to increased defects and decreased quality.

[0006] Patent application CN 105271205A reports a method for preparing high-quality graphene with controllable layer number using an electrochemical process. This method involves controllably inserting intercalation guests (such as metal salts, metal oxides, polymers, or elemental substances) capable of storing lithium ions between graphite layers to obtain intercalation compounds. These compounds serve as the negative electrode in the electrolyte of a lithium-ion battery. The irreversible electrochemical process during battery charging and discharging eliminates the intermolecular forces between graphene layers, dispersing them in a solvent to obtain graphene with different layer numbers. However, this method involves battery assembly and disassembly, making the process cumbersome and introducing electrolyte impurities. The relatively low loading capacity of the electrode material itself also limits its application in practical production. Furthermore, during the irreversible electrochemical reaction in the preparation process, the intercalation guests decompose to produce large amounts of elemental metals, lithium-containing chlorides, oxides, sulfides, etc., which are easily adsorbed on the graphene surface and difficult to remove, reducing the quality of the graphene and affecting its application in high-precision electronic devices.

[0007] Therefore, exploring a low-cost, simple, and easily scalable method to achieve the controllable preparation of high-quality graphene with different numbers of layers remains a major challenge in the field of graphene preparation.

[0008] Based on the above reasons, this application is hereby submitted. Summary of the Invention

[0009] Based on the above reasons, and in view of the problems or defects existing in the prior art, the purpose of this invention is to provide a method for controllably preparing high-quality graphene with different numbers of layers, thereby solving or at least partially solving the above-mentioned technical defects existing in the prior art: The graphene exfoliation method with controllable number of layers provided by this invention is used to achieve efficient preparation of graphene with a specific number of layers, so as to solve the problem that the number of graphene layers is uncontrollable and the large-scale application is limited in the existing preparation methods.

[0010] Graphite lithium intercalation compounds exhibit a tiered phenomenon, where the tier is equal to the number of graphite layers between two periodically intercalated lithium layers. With lithium-ion intercalation, graphite progresses from a fourth-tier lithium intercalation compound (LiC) to a higher tier. 24) converted to a third-order lithium-intercalated compound (LiC) 18 From ), to second-order lithium intercalation compounds (LiC) 12 Finally, we arrive at the first-order lithium-intercalation compound (LiC6). Different orders of lithium-intercalation compounds have specific lithium-intercalation potentials, ranging from fourth to first order, with potentials of 0.2V, 0.14V, 0.12V, and 0.085V respectively. Therefore, by selecting lithiation reagents with potentials falling precisely between the lithium-intercalation potentials of different orders, we can achieve precise control over the order of the lithium-intercalation compound. The different orders of lithium-intercalation compounds from graphite are shown in the attached figure. Figure 1 As shown.

[0011] When a graphite lithium-intercalation compound is placed in water, the active lithium interlayers react with the water to generate a large amount of hydrogen gas. This hydrogen gas creates expansion pressure, causing the graphite layers to expand and significantly weakening the original van der Waals forces between the graphite layers. This provides the driving force for exfoliation, and with the assistance of slight ultrasound, the graphite is exfoliated into graphene sheets. By precisely controlling the lithium intercalation order of graphite in the early stages, compounds of a specific order can be obtained. Then, by exfoliating and dispersing these compounds in a solvent, graphene of the corresponding order and specific number of layers can be obtained.

[0012] The reaction mechanism of graphite lithium intercalation compounds with water is shown in Equation 1 below:

[0013]

[0014] Based on the aforementioned scientific principles, this invention proposes a method for controllably preparing graphene with different numbers of layers. The technical solution includes two steps: precise chemical lithiation and liquid-phase exfoliation and dispersion.

[0015] (1) Precise lithiation by chemistry:

[0016] At room temperature, graphite was mixed with an aromatic lithium reagent, stirred and reacted for a period of time, and then centrifuged and washed to obtain graphite compounds of different orders of lithium intercalation.

[0017] (2) Liquid phase exfoliation dispersion:

[0018] The freshly prepared lithium-intercalated graphene compounds of different orders in step (1) are dispersed in a solvent and ultrasonically exfoliated to obtain graphene with a specific number of layers.

[0019] Specifically, in the above technical solution, the normal temperature mentioned in step (1) refers to the natural room temperature conditions in all four seasons, without any additional cooling or heating treatment. The normal temperature is generally controlled at 10-30℃, preferably 15-25℃.

[0020] Furthermore, in the above technical solution, the graphite mentioned in step (1) refers to raw graphite powder, which can be any one or more of natural graphite powder, flake graphite powder, and various artificially modified graphite powders.

[0021] Furthermore, in the above technical solution, the aromatic lithium reagent in step (1) is composed of aromatic lithium and an organic solvent.

[0022] Furthermore, in the above technical solution, the concentration of aromatic lithium in the aromatic lithium reagent is 0.1–1 mol / L, preferably 0.5–1 mol / L.

[0023] Furthermore, in the above technical solution, the aromatic lithium is preferably a polycyclic aromatic lithium, including any one or more of polycyclic aromatic lithium reagents such as 2-methylbiphenyl lithium, 4-methylbiphenyl lithium, 4,4-dimethylbiphenyl lithium, 9,9-dimethylfluorene lithium, biphenyl lithium, 2-isopropylnaphthalene lithium, 2-ethylnaphthalene lithium, 1-ethylnaphthalene lithium, 2-methylnaphthalene lithium, 1-methylnaphthalene lithium, and naphtholite lithium.

[0024] Furthermore, in the above technical solution, the organic solvent is preferably dimethyltetrahydrofuran.

[0025] Furthermore, in the above technical solution, the molar ratio of aromatic lithium to graphite in the aromatic lithium reagent in step (1) is 1 to 20:6, preferably 2 to 6:6.

[0026] Furthermore, in the above technical solution, the reaction time in step (1) is 1 to 48 hours, preferably 1 to 8 hours.

[0027] Furthermore, in the above technical solution, the order of the lithium-intercalated graphite compounds of different orders mentioned in step (1) is generally controlled to be from order 1 to 4.

[0028] Furthermore, in the above technical solution, the dispersing solvent mentioned in step (2) can be any one or more of pure water, an aqueous solution containing surfactant, and commonly used dispersants such as ethanol, isopropanol, N-methylpyrrolidone (NMP), and N,N-dimethylformamide (DMF); wherein: the surfactant can be any one or more of sodium deoxycholate, sodium cholate, sodium dodecyl sulfate, etc.

[0029] The specific selection principles for the aromatic lithium reagents involved in the method described above in this invention are as follows:

[0030] Depending on the target product, a suitable lithiation reagent is selected to adjust the order of the lithium intercalation compound. Specifically, the selection principle of the aromatic lithium reagent in step (1) is as follows: For first-order lithium intercalation compounds, a lithiation reagent with a potential lower than 0.085V is used, namely 2-methylbiphenyllithium, 4-methylbiphenyllithium, 4,4-dimethylbiphenyllithium, and 9,9-dimethylfluorenelithium reagent; for second-order lithium intercalation compounds, a lithiation reagent with a potential between 0.085V and 0.12V is used, namely biphenyllithium reagent; for third-order lithium intercalation compounds, a lithiation reagent with a potential between 0.12V and 0.14V is used, namely 2-isopropylnaphthyllithium, 2-ethylnaphthyllithium, 1-ethylnaphthyllithium, and 2-methylnaphthyllithium reagent; for fourth-order lithium intercalation compounds, a lithiation reagent with a potential between 0.14V and 0.2V is used, namely 1-methylnaphthyllithium and naphthyllithium reagent.

[0031] Compared with the prior art, the beneficial technical effects of this invention are as follows:

[0032] 1. Graphite raw materials can be natural graphite and various artificial graphite. The raw materials are widely available and inexpensive.

[0033] 2. The chemical lithiation-liquid phase stripping process used in this invention is simple, easy to operate, short in time, requires few types of equipment, and has the potential for large-scale application.

[0034] 3. The method used in this invention does not involve the oxidation-reduction process of graphite, does not require high temperature and high pressure reaction, and is simple, green and energy-saving.

[0035] 4. This invention uses reducing aromatic lithium as an intercalation reagent, which has mild reactivity and will not cause oxidation of graphite. It hardly destroys the structure of graphene, and can preserve the structure of graphene and its own thermal, electrical and mechanical properties to the greatest extent, so as to obtain high-quality graphene.

[0036] 5. This invention employs a two-step chemical lithiation-liquid phase exfoliation method, which is more operable than the cumbersome processing steps of patent CN104058396A. It can achieve efficient preparation of graphene with different numbers of layers, and the prepared graphene is of high quality. It does not involve a large amount of difficult-to-handle chemical reagents and has less environmental pollution.

[0037] 6. Compared with patent CN 105271205A, this invention does not involve the assembly and disassembly of batteries or the electrochemical charging and discharging process. The process is simple and easy to operate. Furthermore, it uses aromatic lithium as the lithiation reagent, which will not decompose and generate a large amount of impurities such as metal elements, lithium-containing chlorides, oxides, and sulfides. The resulting graphene has high purity and good prospects for industrial application.

[0038] 7. This invention innovatively selects an aromatic lithium reagent with matching potential, which can precisely control the lithiation order of graphite, thereby exfoliating graphene with different numbers of layers and realizing highly controllable preparation of graphene. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0040] Figure 1 This is a schematic diagram of different orders of lithium intercalation compounds of graphite involved in the present invention.

[0041] Figure 2 These are XRD patterns of graphite lithium intercalation compounds of different orders prepared in Examples 1-5 of this invention.

[0042] Figure 3 This is a TEM image of the monolayer graphene prepared in Example 1.

[0043] Figure 4 This is a SEM image of the monolayer graphene prepared in Example 1.

[0044] Figure 5 This is the AFM image of the monolayer graphene prepared in Example 1.

[0045] Figure 6 This is the Raman spectrum of the monolayer graphene prepared in Example 1.

[0046] Figure 7 This is an XPS image of the monolayer graphene prepared in Example 1.

[0047] Figure 8 This is a TEM image of the monolayer graphene prepared in Example 2.

[0048] Figure 9 This is a TEM image of the bilayer graphene prepared in Example 3.

[0049] Figure 10 This is the AFM image of the bilayer graphene prepared in Example 3.

[0050] Figure 11 This is a TEM image of the three-layer graphene prepared in Example 4.

[0051] Figure 12 This is a TEM image of the four-layer graphene prepared in Example 5. Detailed Implementation

[0052] This invention discloses a method for controllably preparing high-quality graphene with different numbers of layers. The method includes the following steps: 1) At room temperature, raw graphite powder is mixed with an aromatic lithium reagent, stirred and reacted for a period of time, and then centrifuged and washed to obtain lithium-intercalated graphene compounds of different orders; 2) The freshly prepared lithium-intercalated graphene of different orders is dispersed in a solvent and ultrasonically exfoliated to obtain graphene with the corresponding specific number of layers. This method achieves precise control of the order of the lithium-intercalated compound by selecting a lithium-intercalating reagent with a matching potential, thereby obtaining graphene with the corresponding specific number of layers. This invention has a simple process, is green and energy-saving, can precisely control the number of graphene layers, and the exfoliation process is gentle, does not introduce oxygen-containing functional groups or damage the structure of graphene, and the prepared graphene has few defects, high quality, and broad application prospects.

[0053] The present invention will be further described in detail below through implementation examples. These implementation examples are carried out based on the technology of the present invention. Detailed implementation methods and specific operating procedures are provided to illustrate the inventiveness of the present invention, but the scope of protection of the present invention is not limited to the following implementation examples.

[0054] To better understand the invention and not to limit its scope, all figures indicating amounts, percentages, and other numerical values ​​used in this application should, in all cases, be understood to be modified by the word "approximately." Therefore, unless otherwise stated, the numerical parameters listed in the specification are approximate values ​​and may vary depending on the desired properties being sought. Each numerical parameter should at least be considered as obtained based on reported significant figures and through conventional rounding methods.

[0055] The equipment and raw materials used in this invention are all commercially available or commonly used in the field. Unless otherwise specified, the methods in the following embodiments are conventional methods in the field.

[0056] Example 1

[0057] This embodiment of a method for controllably preparing high-quality graphene with different numbers of layers includes the following steps:

[0058] (1) 1.8 g of natural flake graphite powder (particle size 2-20 μm) was added to 100 mL of 1 mol / L 4,4-dimethylbiphenyl lithium solution and stirred for 8 hours. The 4,4-dimethylbiphenyl lithium solution consisted of 4,4-dimethylbiphenyl lithium and dimethyltetrahydrofuran. After the reaction was completed, the mixture was centrifuged at 4000 rpm. The precipitate was repeatedly washed with dimethyltetrahydrofuran until the filtrate was basically colorless. The precipitate was then dried under vacuum to obtain a first-order graphitic lithium intercalation compound.

[0059] The XRD phase characterization of the first-order graphitic lithium intercalation compound powder prepared in this embodiment is as follows: Figure 1As shown, the main peak of (002) shifts to 24.2 degrees, verifying that it is a first-order lithium intercalation state;

[0060] (2) Place the freshly prepared first-order graphite lithium intercalation compound from step (1) into a 2 mg / ml sodium deoxycholate aqueous solution, sonicate for 30 minutes to obtain a uniform black suspension, centrifuge at 3000 rpm for 20 minutes to remove the graphite and thick graphene sheets that were not fully exfoliated, and high-quality monolayer graphene can be obtained.

[0061] The prepared graphene was tested by transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), Raman spectroscopy, and XPS energy dispersive spectroscopy. Figure 3 In the low-magnification TEM image, the graphene sheet structure is intact, while the high-resolution TEM image clearly shows the monolayer structure at the edges. From Figure 4 The SEM images show that the prepared graphene sheets are nearly transparent thin sheets. Figure 5 AFM analysis showed that the graphene sheet produced had a uniform thickness of 0.6 nm, confirming it as a single-layer graphene. Figure 6 In the Raman spectrum of graphene, the intensity ratio of the D peak to the G peak can determine its defect degree; the lower the value, the fewer the defects, and the higher the quality of the graphene. d / I g It is 0.12, far lower than the corresponding value for graphene oxide (I d / I g >1), indicating that the prepared graphene has few defects and is of high quality. Figure 7 The XPS image shows that the carbon-to-oxygen ratio of the obtained graphene is 25, indicating that no oxygen-containing functional groups were introduced during the exfoliation process, and the obtained graphene is of high quality.

[0062] Example 2

[0063] This embodiment of a method for controllably preparing high-quality graphene with different numbers of layers includes the following steps:

[0064] (1) 3.6 g of artificial graphite powder (particle size 5-10 μm) was added to 100 mL of 1 mol / L 9,9-dimethylfluorene lithium solution and stirred for 8 hours. The 9,9-dimethylfluorene lithium solution consisted of 9,9-dimethylfluorene lithium and dimethyltetrahydrofuran. After the reaction was completed, the mixture was centrifuged at 4000 rpm. The precipitate was repeatedly washed with dimethyltetrahydrofuran until the filtrate was basically colorless. The precipitate was then dried under vacuum to obtain a first-order graphite lithium intercalation compound.

[0065] In the XRD characterization of the first-order graphite lithium intercalation compound powder prepared in this embodiment, the (002) main peak shifted to 24.2 degrees, verifying that it is a first-order lithium intercalation state;

[0066] (2) Place the freshly prepared first-order graphite lithium intercalation compound in step (1) into a 50% ethanol aqueous solution, sonicate for 30 minutes to obtain a uniform black suspension, centrifuge at 3000 rpm for 20 minutes to remove the graphite and thick graphene sheets that are not fully exfoliated, and high-quality monolayer graphene can be obtained.

[0067] The graphene prepared in this embodiment was subjected to transmission electron microscopy (TEM). From... Figure 8 The TEM image shows that the prepared graphene sheet is a nearly transparent thin sheet, and its single-layer structure can be clearly seen at the edge, confirming that it is a single-layer graphene.

[0068] Example 3

[0069] This embodiment of a method for controllably preparing high-quality graphene with different numbers of layers includes the following steps:

[0070] (1) 1.44 g of natural flake graphite powder (particle size 10-50 μm) was added to 100 mL of 1 mol / L lithium biphenyl solution and stirred for 8 hours. The lithium biphenyl solution consisted of lithium biphenyl and dimethyltetrahydrofuran. After the reaction was completed, the mixture was centrifuged at 4000 rpm. The precipitate was repeatedly washed with dimethyltetrahydrofuran until the filtrate was basically colorless. The precipitate was then dried under vacuum to obtain a second-order graphitic lithium intercalation compound.

[0071] The XRD phase of the second-order graphitic lithium intercalation compound powder prepared in this embodiment is as follows: Figure 1 As shown, the main peak of 002 shifts to 25.2 degrees, verifying that it is a second-order lithium intercalation state;

[0072] (2) Place the freshly prepared second-order graphite lithium intercalation compound from step (1) into a 50% NMP aqueous solution, sonicate for 30 minutes to obtain a uniform black suspension, centrifuge at 3000 rpm for 20 minutes to remove the graphite and thick graphene sheets that were not fully exfoliated, and high-quality bilayer graphene can be obtained.

[0073] The graphene prepared in this embodiment was tested using transmission electron microscopy (TEM) and atomic force microscopy (AFM). Figure 9 The TEM image shows that the prepared graphene sheet is an ultrathin nanosheet with a smooth surface, and its two-layer structure can be clearly seen at the edges. Figure 10 AFM analysis showed that the graphene sheet produced had a uniform thickness of 1.2 nm, confirming it as bilayer graphene.

[0074] Example 4

[0075] This embodiment of a method for controllably preparing high-quality graphene with different numbers of layers includes the following steps:

[0076] (1) 2.4 g of natural flake graphite powder (particle size 2-20 μm) was added to 100 mL of 1 mol / L 2-ethylnaphthalene lithium solution and stirred for 8 hours. The 2-ethylnaphthalene lithium solution consisted of 2-ethylnaphthalene lithium and dimethyltetrahydrofuran. After the reaction was completed, the mixture was centrifuged at 4000 rpm. The precipitate was repeatedly washed with dimethyltetrahydrofuran until the filtrate was basically colorless. The precipitate was then dried under vacuum to obtain a third-order graphite lithium intercalation compound.

[0077] The XRD phase of the third-order graphitic lithium intercalation compound powder prepared in this embodiment is as follows: Figure 1 As shown, the main peak of (002) shifts to 25.7 degrees, verifying that it is a third-order lithium intercalation state;

[0078] (2) Place the freshly prepared tri-layer graphite lithium intercalation compound from step (1) into a 50% DMF aqueous solution, sonicate for 30 minutes to obtain a uniform black suspension, centrifuge at 3000 rpm for 20 minutes to remove the graphite and thick graphene sheets that were not fully exfoliated, and high-quality tri-layer graphene can be obtained.

[0079] The graphene prepared in this embodiment was tested using transmission electron microscopy (TEM). Figure 11 The TEM image shows that the prepared graphene sheet is a translucent thin sheet with a complete layer structure and good morphology. The three-layer structure can be clearly seen at the edge, confirming that it is a three-layer graphene.

[0080] Example 5

[0081] This embodiment of a method for controllably preparing high-quality graphene with different numbers of layers includes the following steps:

[0082] (1) 1.2 g of artificial graphite powder (particle size 5-10 μm) was added to 100 mL of 1 mol / L naphthalene lithium solution and stirred for 8 hours. The naphthalene lithium solution was composed of naphthalene lithium and dimethyltetrahydrofuran. After the reaction was completed, the mixture was centrifuged at 4000 rpm. The precipitate was repeatedly washed with dimethyltetrahydrofuran until the filtrate was basically colorless. The precipitate was then dried under vacuum to obtain a fourth-order graphite lithium intercalation compound.

[0083] The XRD phase of the fourth-order graphitic lithium intercalation compound powder prepared in this embodiment is as follows: Figure 1 As shown, the main peak of (002) shifts to 26.3 degrees, verifying that it is a fourth-order lithium intercalation state;

[0084] (2) Place the freshly prepared fourth-order graphite lithium intercalation compound from step (1) into a 50% isopropanol aqueous solution, sonicate for 30 minutes to obtain a uniform black suspension, centrifuge at 3000 rpm for 20 minutes to remove the graphite and thick graphene sheets that were not fully exfoliated, and high-quality four-layer graphene can be obtained.

[0085] The graphene prepared in this embodiment was characterized by transmission electron microscopy (TEM). Figure 12 The TEM image shows that the prepared graphene sheet is a nearly transparent thin sheet with a smooth surface. The edges clearly show that it has a four-layer structure, confirming that it is a four-layer graphene.

[0086] The above embodiments are typical examples of the present invention and are not intended to limit the invention in any way. For example, the type, purity, and amount of raw materials, stirring time, solvent type, and its volume ratio with water can all be further adjusted. Therefore, based on the overall concept of the present invention, any adjustments and modifications made to the described process parameters by those skilled in the art, as long as they do not deviate from the inventive concept or exceed the scope defined in these claims, should fall within the protection scope of the present invention.

Claims

1. A method for controllably preparing high-quality graphene with different numbers of layers, characterized in that: The method comprises two steps: precise chemical lithiation and liquid-phase exfoliation dispersion. (1) Precise lithiation by chemistry: At room temperature, graphite was mixed with an aromatic lithium reagent, stirred and reacted for a period of time, and then centrifuged and washed to obtain graphite compounds of different orders of lithium intercalation. (2) Liquid phase exfoliation dispersion: The freshly prepared lithium-intercalated graphene compounds of different orders in step (1) are dispersed in a solvent and ultrasonically exfoliated to obtain graphene with a specific number of layers. The graphite mentioned in step (1) is any one or more of natural graphite powder, flake graphite powder, and various artificially modified graphite powders. The aromatic lithium reagent mentioned in step (1) is composed of aromatic lithium and an organic solvent, wherein the concentration of aromatic lithium in the aromatic lithium reagent is 1 mol / L; The aromatic lithium is a polycyclic aromatic lithium; The order of the lithium-intercalated graphite compound described in step (1) is from 1 to 4; When the order of the lithium-intercalated graphite compound is 1, the polycyclic aromatic lithium is selected from either 4,4-dimethylbiphenyl lithium or 9,9-dimethylfluorene lithium; When the order of the lithium-intercalated graphite compound is 2, the polycyclic aromatic lithium is selected as lithium biphenyl. When the order of the lithium-intercalated graphite compound is 3, the polycyclic aromatic lithium is selected as 2-ethylnaphthalene lithium; When the order of the lithium-intercalated graphite compound is 4, the polycyclic aromatic lithium is naphthalene lithium; The molar ratio of aromatic lithium to graphite in the aromatic lithium reagent described in step (1) is 1~20:

6.

2. The method according to claim 1, characterized in that: The reaction time described in step (1) is 1 to 48 hours.

3. The method according to claim 1, characterized in that: The dispersing solvent mentioned in step (2) is pure water, an aqueous solution containing a surfactant, and any one or more of ethanol, isopropanol, N-methylpyrrolidone (NMP), and N,N-dimethylformamide (DMF); wherein the surfactant is any one or more of sodium deoxycholate, sodium cholate, and sodium dodecyl sulfate.

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