Method for manufacturing flaked graphite and method for manufacturing flaked graphite dispersion

Abstract

To provide a method for manufacturing flaked graphite which achieves a higher yield of flaked graphite.SOLUTION: A method for manufacturing flaked graphite includes: a step 1 of obtaining a product including flaked graphite by subjecting a material to be processed, which includes one kind selected from the group consisting of graphite and a graphite compound, and a first organic solvent that is an aprotic organic solvent, to wet jet mill processing; and a step 2 of obtaining a mixed solution by mixing the product and at least one kind of specific solvent selected from the group consisting of water and a protic organic solvent, followed by separating the flaked graphite from the mixed solution.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing exfoliated graphite. The present invention also relates to a method for producing an exfoliated graphite dispersion.

Background Art

[0002] In recent years, exfoliated graphite with a small number of graphene layers in graphite has attracted attention. As a method for producing exfoliated graphite, a method of producing a graphite intercalation compound (GIC) from graphite and performing a peeling treatment is known. As the method for producing the above GIC, various methods such as a gas phase method and a solution method have been proposed. Among them, the method for producing GIC by the solution method has attracted attention because GIC can be produced more simply compared to the gas phase method.

[0003] As a method for producing exfoliated graphite by subjecting the above GIC to a peeling treatment, for example, it is disclosed in Patent Document 1. Specifically, a method of adding an aprotic polar solvent to GIC and subjecting it to ultrasonic treatment to produce exfoliated graphite is disclosed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Although the method for producing exfoliated graphite described in the above Patent Document 1 is known, a method for producing exfoliated graphite with a higher yield of exfoliated graphite has been demanded.

[0006] Therefore, an object of the present invention is to provide a method for producing exfoliated graphite with a higher yield of exfoliated graphite. Another object of the present invention is to provide a method for producing an exfoliated graphite dispersion.

Means for Solving the Problem

[0007] As a result of intensive studies to solve the above problems, the present inventor has found that the above problems can be solved by the following configuration.

[0008] [1] Step 1 of subjecting an object to be treated containing one selected from the group consisting of graphite and graphite compounds and a first organic solvent which is an aprotic organic solvent to wet jet mill treatment to obtain a product containing exfoliated graphite; A method for producing exfoliated graphite, comprising: Step 2 of mixing the product with at least one specific solvent selected from the group consisting of water and a protic organic solvent to obtain a mixed solution, and separating exfoliated graphite from the mixed solution. [2] The method for producing exfoliated graphite according to [1], wherein the graphite compound is used in the step 1. [3] The method for producing exfoliated graphite according to [2], wherein the graphite compound is a graphite compound in which an alkali metal source and graphite are mixed in a second organic solvent which is an aprotic organic solvent, and the alkali metal is intercalated between graphene layers in the graphite. [4] The method for producing exfoliated graphite according to any one of [1] to [3], wherein in the step 2, the mass ratio of the specific solvent to the product is 0.5 to 100. [5] The method for producing exfoliated graphite according to any one of [1] to [4], wherein the specific solvent is at least one solvent selected from the group consisting of water and an alcohol-based solvent. [6] The method for producing exfoliated graphite according to any one of [1] to [5], wherein the SP value of the specific solvent is 12.5 (cal / cm 3 ) 1 / 2 or more. [7] The method for producing exfoliated graphite according to any one of [1] to [6], wherein the first organic solvent is an ether-based solvent. [8] The method for producing exfoliated graphite according to any one of [1] to [7], wherein the second organic solvent is an ether-based solvent. A method for producing a dispersed graphite nanoplatelet liquid, comprising a step of dispersing the graphite nanoplatelets obtained by the method for producing graphite nanoplatelets according to any one of [1] to [8] in a solvent.

Advantages of the Invention

[0009] According to the present invention, a method for producing graphite nanoplatelets with a higher yield of graphite nanoplatelets can be provided. Also, according to the present invention, a method for producing a dispersed graphite nanoplatelet liquid can be provided.

Brief Description of the Drawings

[0010]

Figure 1

Embodiments for Carrying Out the Invention

[0011] Hereinafter, the present invention will be described in detail. The description of the constituent elements described below may be made based on typical embodiments of the present invention, but the present invention is not limited to such embodiments.

[0012] Hereinafter, the meaning of each description in this specification will be represented. In this specification, a numerical range represented using "~" means a range including the numerical values described before and after "~" as the lower limit value and the upper limit value.

[0013] In this specification, graphite nanoplatelets are those obtained by exfoliating original graphite, and the number of stacked graphene layers (graphene sheets) in the graphite nanoplatelets may be less than that of the original graphite. Examples of the graphite nanoplatelets include graphene or a laminate of graphene. When the graphite nanoplatelets are a laminate of graphene, the number of stacked graphene layers in the laminate is not particularly limited, but 2 or more layers are preferred. The upper limit is not particularly limited, but 100 layers or less are preferred, and 30 layers or less are more preferred.

[0014] <Method for Producing Graphite Nanoplatelets> The method for producing exfoliated graphite of the present invention comprises a step 1 of subjecting a material to be treated, which contains one selected from the group consisting of graphite and graphite compounds and a first organic solvent which is an aprotic organic solvent, to wet jet mill treatment to obtain a product containing exfoliated graphite. Further, the method for producing an exfoliated graphite dispersion of the present invention comprises a step 2 of mixing the above product with at least one specific solvent selected from the group consisting of water and a protic organic solvent to obtain a mixed solution, and separating exfoliated graphite from the above mixed solution.

[0015] In the method for producing exfoliated graphite of the present invention (hereinafter, also referred to as "the present production method"), the reason for the high yield of exfoliated graphite is not necessarily clear, but the present inventors presume as follows. In the above step 1, when wet jet mill treatment is performed in the above first organic solvent, graphite or a graphite compound is likely to be exfoliated. Further, in the above step 2, when the obtained product and the above specific solvent are mixed, exfoliated graphite tends not to be easily dispersed in the specific solvent, and exfoliated graphite is easily separated in step 2. As a result, in the present production method having steps 1 and 2, the yield of exfoliated graphite becomes higher.

[0016] Hereinafter, the present production method will be described. Note that the present production method may have steps other than steps 1 and 2 described later.

[0017] [Step 1] In step 1, a material to be treated, which contains one selected from the group consisting of graphite and graphite compounds and a first organic solvent which is an aprotic organic solvent, is subjected to wet jet mill treatment to obtain a product containing exfoliated graphite. Hereinafter, step 1 will be described in detail.

[0018] (Graphite and Graphite Compounds) In step 1, the material to be treated contains one selected from the group consisting of graphite and graphite compounds. The graphite is not particularly limited as long as it is a compound having a structure in which graphene is laminated. Examples of the graphite include natural graphite, synthetic graphite (artificial graphite), highly oriented pyrolytic graphite, and graphite fibers. Among them, natural graphite is preferable.

[0019] Examples of the graphite compound include graphite intercalation compounds in which other compounds or the like are inserted between the graphene layers in the graphite. Examples of the other compounds or the like contained in the graphite compound (graphite intercalation compound) include, for example, one or more selected from the group consisting of alkali metals, organic compounds, inorganic compounds, and their ions. The above other compounds or the like may form a complex. More specifically, alkali metals, ether solvents, aromatic compounds, inorganic ions, and the like can be mentioned. The graphite compound is preferably a graphite compound in which an alkali metal is intercalated between the graphene layers in the graphite. The graphite compound of the above aspect can be obtained, for example, by mixing an alkali metal source and graphite in an organic solvent (solvent Y described later). The production method of the graphite compound of the above aspect will be described in detail later. Further, the graphite compound may be so-called expanded graphite. Expanded graphite refers to a graphite compound in which sulfate ions, nitrate ions, and the like are inserted between the graphene layers. Expanded graphite can be obtained, for example, by immersing graphite in an aqueous sulfuric acid solution containing an oxidizing agent.

[0020] (First organic solvent) In Step 1, the object to be treated contains a first organic solvent which is an aprotic organic solvent. The first organic solvent is not particularly limited as long as it is an aprotic organic solvent. Examples of the aprotic organic solvent include amide solvents, ketone solvents, sulfoxide solvents, hydrocarbon solvents, ether solvents, and ester solvents. Among them, ether solvents are preferable in terms of higher yield of exfoliated graphite.

[0021] The ether solvent is not particularly limited as long as it has an ether bond (-O-), and the number of ether bonds in the molecule is not limited. In addition, the ether-based solvent may have a cyclic structure. Examples of the ether-based solvent include dimethyl ether, diethyl ether, 1,2-dimethoxyethane (DME, or glyme), diethylene glycol dimethyl ether (diglyme), furan, tetrahydrofuran (THF), 1,3-dioxolane (DOL), tetraethylene glycol dimethyl ether (TEGDME), poly(ethylene glycol) dimethyl ether (PEGDME), tetraethylene glycol dibutyl ether (DEGDBE), bis(2-ethoxyethyl) ether, and dihydrolevoglucosenone (Cyrene (registered trademark)). Among them, 1,2-dimethoxyethane or tetrahydrofuran is preferable in that the graphite or graphite compound contained in the object to be treated is more easily exfoliated.

[0022] Only one type of the first organic solvent may be used, or two or more types may be used.

[0023] (Wet jet mill treatment) In step 1, a wet jet mill treatment is performed on the object to be treated containing one type selected from the group consisting of the above graphite and graphite compounds and the above first organic solvent. Hereinafter, the object to be treated and the wet jet mill treatment will be described.

[0024] The object to be treated is subjected to a wet jet mill treatment, and in order to efficiently obtain exfoliated graphite, the solid content concentration and viscosity are preferably within the ranges detailed below.

[0025] The solid content concentration of the object to be treated is preferably 0.1 to 10% by mass, more preferably 0.5 to 5% by mass, based on the total mass of the object to be treated, from the viewpoint of efficiently obtaining exfoliated graphite. The solid content in the object to be treated refers to the components excluding the solvent in the object to be treated.

[0026] The viscosity of the object to be treated is preferably 1 to 20000 mPa·s from the viewpoint of being processable by a wet jet mill. As the method for measuring viscosity, a known method can be used, for example, the method of JIS Z 8803:2011.

[0027] The solid content concentration and viscosity of the object to be treated can be adjusted, for example, by the content of the first organic solvent in the object to be treated.

[0028] The object to be treated may contain one selected from the group consisting of the above graphite and graphite compounds, and components other than the above organic solvent (other components). Examples of other components include surfactants. In addition, as other components, components used for producing the graphite compound are also included.

[0029] Wet jet milling treatment is advantageous in that it can efficiently obtain exfoliated graphite without pulverizing graphite or graphite compounds more than necessary by applying a shearing force to the object to be treated. The wet jet milling treatment is not limited as long as it can fluidize a slurry containing a solvent and powder at a high speed and as a result pulverize and / or disintegrate the powder. For example, methods such as a method of colliding a fluid flowing at a high speed with a fluid collision part substantially perpendicular to the flow direction of the fluid, a method of flowing a fluid flowing at a high speed through a constriction, a method of oppositely colliding a plurality of fluids flowing at a high speed, a method of generating a turbulent flow and colliding the fluid with the wall surface of a pipe or the like through which the fluid conducts, and a method of applying a shearing force to the fluid by a cavitation jet generated by reduced pressure or the like can be mentioned. The wet jet milling treatment may combine these methods. Among them, a method of oppositely colliding a plurality of fluids flowing at a high speed is preferable.

[0030] Examples of the wet jet milling treatment for oppositely colliding a plurality of fluids include a treatment having the following steps A, B, and C in this order. Step A: A step of oppositely colliding the object to be treated Step B: A step of flowing the collided object to be treated in a direction different from the direction in Step A Step C: A step of separating and flowing the object to be treated

[0031] The method of carrying out the above steps A to C is not particularly limited, but it is preferable to use the dispersion unit shown in FIG. 1. First, the dispersion unit shown in FIG. 1 will be described below. The dispersion unit 10 shown in FIG. 1 is a unit arranged in an apparatus for performing wet jet mill treatment. As will be described later, by passing the object to be treated through the flow path in the dispersion unit 10, steps A to C can be carried out. The dispersion unit 10 includes an introduction side disk 12, an intermediate disk 14, and a discharge side disk 16. The shapes of the introduction side disk 12, the intermediate disk 14, and the discharge side disk 16 are disk-shaped with substantially the same diameter. The intermediate disk 14 is arranged in close contact with the downstream side of the introduction side disk 12 in the direction of the central axis C1. Also, the discharge side disk 16 is arranged in close contact with the downstream side of the intermediate disk 14 in the direction of the central axis C1. The introduction side disk 12, the intermediate disk 14, and the discharge side disk 16 are composed of wear-resistant members such as ceramics, cemented carbide, and diamond, and are formed with substantially the same diameter. The introduction side disk 12 and the discharge side disk 16 are formed with substantially the same plate thickness, and the intermediate disk 14 is formed with a plate thickness thinner than the plate thicknesses of the introduction side disk 12 and the discharge side disk 16.

[0032] The introduction side disk 12 is provided with a first through hole 12A and a second through hole 12B. The first through hole 12A and the second through hole 12B are formed with substantially the same diameter and are arranged at substantially symmetric positions with respect to the central portion of the introduction side disk 12. An introduction side groove-shaped passage 18 (first flow path) formed with a width smaller than the diameters of the first through hole 12A and the second through hole 12B is linearly arranged on the surface of the introduction side disk 12 facing the intermediate disk 14. And the first through hole 12A and the second through hole 12B are communicated through the introduction side groove-shaped passage 18. The intermediate disk 14 is provided with a third through hole 14A (second flow path) at the central portion. On the discharge side disk 16, a fourth through hole 16A and a fifth through hole 16B are arranged at symmetric positions sandwiching the center portion of the discharge side disk 16 with substantially the same diameter. A discharge side groove-shaped passage 20 (third flow path) formed with a width smaller than the aperture diameters of the fourth through hole 16A and the fifth through hole 16B is arranged on the surface of the discharge side disk 16 facing the intermediate disk 14. And the fourth through hole 16A and the fifth through hole 16B are communicated with each other through the discharge side groove-shaped passage 20.

[0033] Next, the flow of steps A to C using the above-described dispersion unit will be described. First, the object to be processed is pressurized and introduced into the dispersion unit 10 as an ultra-high-speed fluid. At this time, it is preferably pressurized at a pressure of 100 MPa or more and 250 MPa or less. When the introduced object to be processed L reaches the introduction side disk 12, it branches and flows through the first through hole 12A and the second through hole 12B. After the branched object to be processed L passes through each of the first through hole 12A and the second through hole 12B, while colliding with the intermediate disk 14, the direction is forcibly changed toward the center portion of the introduction side disk 12 within the introduction side groove-shaped passage 18. Then, they are accelerated and flow in directions facing each other in a straight line and collide with each other. By the above, step A is carried out. Next, the flowing direction of the object to be processed L that has collided and rejoined again is changed in a substantially perpendicular direction, and the object to be processed L is guided to the third through hole 14A of the intermediate disk 14. At this time, part of the collision energy is released, and wear occurring at the center portion of the introduction side groove-shaped passage 18 of the introduction side disk 12 is reduced. And the turbulent flow generated by the collision is maintained in that state. By the above, step B is carried out. Next, the object to be processed L that has passed through the third through hole 14A branches again and flows in the discharge side groove-shaped passage 20 while colliding with the discharge side disk 16 toward the outer peripheral side of the discharge side disk 16. Thus, the object to be processed L that has passed through the fourth through hole 16A and the fifth through hole 16B is discharged from the discharge side disk 16, rejoins again, and is discharged from the dispersion unit 10. By the above, step C is carried out.

[0034] Examples of the apparatus for performing the wet jet mill treatment having the above-described Step A, Step B, and Step C include "NAGS20", "NAGS100", "NAGS500", and "NAGS1000" manufactured by Tokko Co., Ltd.

[0035] The wet jet mill treatment is preferably performed multiple times. The number of times is not particularly limited, but 2 to 100 passes are preferred. Most are 2 to 20 passes. Also, the wet jet mill treatment may be performed at two or more different liquid feed pressures. For example, after performing the wet jet mill treatment at a low liquid feed pressure, the wet jet mill treatment can also be performed at a high liquid feed pressure. The treatment at each pressure may be performed multiple times.

[0036] The wet jet mill treatment is also preferably performed with an inert gas atmosphere inside the apparatus. Examples of the inert gas include nitrogen gas and argon gas. Also, since the wet jet mill treatment generates heat due to compression or the like, it is also preferably performed while cooling. As the cooling method, a known method can be used. For example, a method of directly or indirectly contacting a refrigerant with the heat generating part for heat exchange can be mentioned.

[0037] [Step 2] In Step 2, the above product is mixed with at least one specific solvent selected from the group consisting of water and a protic organic solvent to obtain a mixed solution, and the exfoliated graphite is separated from the above mixed solution. The exfoliated graphite is obtained by the above Step 2. Hereinafter, Step 2 will be described.

[0038] (Specific Solvent) In Step 2, a specific solvent is used. The specific solvent is at least one selected from the group consisting of water and a protic organic solvent. Examples of the protic organic solvent include carboxylic acid solvents and alcohol solvents, and alcohol solvents are preferred. The specific solvent is preferably at least one solvent selected from the group consisting of water and alcohol solvents.

[0039] Examples of water include distilled water, ion-exchanged water, pure water, and ultrapure water.

[0040] The alcohol solvent refers to a solvent composed of a compound having a hydroxyl group in the molecule. Specifically, the alcohol solvent refers to a solvent composed of a compound represented by the following formula (a).

[0041] R1-OH (a) In formula (a), R1 represents an alkyl group which may have a hydroxyl group as a substituent. The alkyl group portion of the alkyl group which may have the substituent represented by R1 may have a branched-chain structure or a cyclic structure. The number of carbon atoms of the alkyl group portion of the alkyl group which may have a hydroxyl group as a substituent represented by R1 is preferably 1 to 8, more preferably 1 to 3. The number of hydroxyl groups in the alkyl group is preferably 0 or 1, more preferably 0. That is, it is also preferable that R1 represents an alkyl group having no substituent.

[0042] Examples of the alcohol solvent include methanol, ethanol, 1-propanol, 2-propanol (isopropyl alcohol), 1-butanol, 2-butanol, tert-butyl alcohol, ethylene glycol, and propylene glycol. Among them, methanol, ethanol, 2-propanol, or ethylene glycol is preferable, and methanol, ethanol, or ethylene glycol is more preferable.

[0043] The above specific solvent may be used alone or in combination of two or more.

[0044] The SP value (solubility parameter) of the above specific solvent is 11.5 (cal / cm 3 ) 1 / 2The above is preferable, 12.0 (cal / cm 3 ) 1 / 2 The above is more preferable, 12.5 (cal / cm 3 ) 1 / 2 The above is even more preferable. Further, the SP value of the specific solvent is often 23.4 (cal / cm 3 ) 1 / 2 or less. Note that the SP value is also called the Hildebrand parameter, and literature values can be adopted.

[0045] In Step 2, the product obtained in Step 1 and the above specific solvent are mixed. The mixing ratio of the product and the specific solvent is not particularly limited, but the mass ratio of the specific solvent to the product is preferably 0.5 or more, more preferably 1 or more, even more preferably 2 or more, and particularly preferably 5 or more. Also, the above ratio is often 200 or less, preferably 100 or less, more preferably 50 or less, and even more preferably 15 or less.

[0046] The mixing method in Step 2 is not particularly limited, and known mixing methods can be applied. For example, methods of stirring the solution with a rotary blade, generating convection with a pump, and vibrating the container in which the object to be treated is accommodated can be mentioned. Specifically, a mixer, a magnetic stirrer, a mechanical stirrer, and a shaker can be mentioned. It is also preferable that the mixing in Step 2 is carried out in an inert atmosphere.

[0047] In Step 2, the above product and the above specific solvent are mixed to obtain a mixed solution, and exfoliated graphite is separated from the mixed solution. The method for separating exfoliated graphite from the above mixed solution is not particularly limited, and known methods can be applied. For example, a method of performing solid-liquid separation can be mentioned. Examples of the method for performing solid-liquid separation include filtration (including pressure filtration and vacuum filtration), decantation, and centrifugation. Among them, filtration is more preferable. The method for performing solid-liquid separation may be a combination of two or more kinds. As described above, in the mixed solution containing the specific solvent, since the exfoliated graphite is difficult to disperse, it is easy to separate the exfoliated graphite from the mixed solution.

[0048] Also, after obtaining the mixed solution, the mixed solution may be allowed to stand. The standing time is not particularly limited, and examples include 1 minute to 72 hours, and preferably 5 minutes to 48 hours.

[0049] The exfoliated graphite obtained by solid-liquid separation in Step 2 may be further dried. As the drying method, known methods can be applied, and examples include natural drying, heat drying, vacuum drying, and freeze drying.

[0050] [Step 3] In the case where the object to be processed in Step 1 contains a graphite compound, this production method may have Step 3 of obtaining a graphite compound (graphite intercalation compound) before Step 1. Specifically, Step 3 is a step of mixing an alkali metal source and graphite in a second organic solvent which is an aprotic organic solvent to produce a graphite intercalation compound in which the alkali metal is intercalated between the graphene layers in the graphite. In Step 3, components other than the above components may be added. Hereinafter, Step 3 will be described.

[0051] (Organic solvent (Solvent Y)) The second organic solvent used in Step 3 is not particularly limited, and the first organic solvent used in the above Step 1 is preferably mentioned. Among them, as Solvent Y, an ether-based solvent is preferable. Examples and preferred examples of the ether-based solvent are as described above in the part of Step 1.

[0052] (Alkali metal source) The alkali metal source used in Step 3 is not particularly limited as long as it contains an alkali metal, and examples include a simple alkali metal (zero-valent alkali metal) and a salt containing an alkali metal. Examples of the alkali metal contained in the alkali metal source include, for example, lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr). As the alkali metal, Li, Na, or K is preferable, Li or K is more preferable, and Li is even more preferable. As the alkali metal source, lithium metal, potassium metal, or sodium metal is preferable, lithium metal or sodium metal is more preferable, and lithium metal is even more preferable. Only one kind of alkali metal source may be used, or two or more kinds may be used.

[0053] (Graphite) The graphite used in Step 3 is not particularly limited as long as it is a compound having a structure in which graphene is laminated. Examples and preferred examples of graphite are as described above in the part of Step 1.

[0054] (Aromatic hydrocarbon) In Step 3, it is preferable to mix an aromatic hydrocarbon together with the alkali metal source and graphite. By mixing an aromatic hydrocarbon together with the above components, the dissolution of the alkali metal in the alkali metal source into the solvent is promoted, and due to the difference in the electron affinity with graphite, the alkali metal can be easily intercalated into the graphite. Examples of the aromatic hydrocarbon include, for example, benzene, naphthalene, phenanthrene, anthracene, and pyrene. Among them, naphthalene is preferable.

[0055] (Mixing method and conditions) The mixing method of the various components in Step 3 is not particularly limited as long as the second organic solvent, the alkali metal source, graphite, and the optional components can be mixed.

[0056] The mixing order of the components used in Step 3 is not particularly limited. For example, various components (alkali metal, graphite, etc.) may be sequentially added to the second organic solvent, or various components may be simultaneously added to the second organic solvent. Among these, after adding an aromatic hydrocarbon to the second organic solvent, it is preferable to add the alkali metal and graphite to the second organic solvent in this order. The usage amounts of various components in Step 3 are not particularly limited and can be adjusted as appropriate. The usage amount of the second organic solvent is preferably 50 to 99.9% by mass, more preferably 60 to 99% by mass, and even more preferably 70 to 95% by mass, based on the total amount of the components used in Step 3. Note that the components used in Step 3 include the second organic solvent, an alkali metal source, graphite, and optional components. When two or more types of the second organic solvent are mixed and used, it is preferable that the total mass of the second organic solvent is within the above range. The usage amount of the alkali metal source is not particularly limited, and is preferably 2.5 to 300% by mass, more preferably 4 to 150% by mass, based on the usage amount of graphite. The usage amount of graphite is not particularly limited, and is preferably 0.1 to 10% by mass, more preferably 1 to 5% by mass, based on the total mass of the second organic solvent. The usage amount of the aromatic hydrocarbon is not particularly limited, and is preferably 50 to 500% by mass, more preferably 100 to 500% by mass, based on the usage amount of graphite.

[0057] Examples of the method for mixing the above components include known methods. For example, a method of stirring the solution with a rotary blade, a method of generating convection with a pump, and a method of vibrating a container containing the object to be treated can be mentioned. Specifically, a magnetic stirrer, a mechanical stirrer, and a shaker can be mentioned.

[0058] The mixing time in Step 3 is not particularly limited, and is preferably 1 minute to 300 hours, more preferably 30 minutes to 200 hours, and even more preferably 1 to 100 hours. The temperature during mixing in Step 3 is not particularly limited, and is preferably 10 to 50°C, more preferably 20 to 30°C. Also, in Step 3, after mixing, it may be left to stand. The standing time may be, for example, 1 to 200 hours, preferably 8 to 150 hours. When left to stand, the graphite intercalation compound precipitates, and solid-liquid separation in Step 4 described later can be easily carried out.

[0059] The atmosphere for carrying out Step 3 is not particularly limited, but Step 3 is preferably carried out in an inert gas atmosphere. Examples of the inert gas include nitrogen gas and argon gas. Also, the atmosphere for carrying out Step 3 preferably has a low water vapor content. The dew point of the atmosphere for carrying out Step 3 is preferably 0°C or lower, more preferably -20°C or lower, even more preferably -40°C or lower, and particularly preferably -50°C or lower. The lower limit of the dew point of the atmosphere for carrying out Step 3 is not particularly limited, but is usually -100°C or higher.

[0060] (Graphite intercalation compound) In Step 3, a graphite intercalation compound in which an alkali metal is intercalated between graphene layers in graphite is produced. The graphite intercalation compound may be a binary system of an alkali metal and graphene, a ternary system of an alkali metal, a second organic solvent, and graphene, or a quaternary system or higher including additives in addition to the above ternary system. For example, the alkali metal may form a complex with THF as a solvent, and the complex may be intercalated. The formation of the graphite intercalation compound can be confirmed by X-ray diffraction. Specifically, it can be confirmed by the disappearance of the diffraction peak derived from the structure of graphite and the appearance of the diffraction peak corresponding to the elongation of the distance between graphene layers due to intercalation.

[0061] [Step 4] When the object to be processed in Step 1 contains a graphite compound, this production method may have Step 4 of recovering the graphite compound (graphite intercalation compound) after carrying out Step 3 of obtaining the graphite compound. The method for the above-mentioned recovery is not particularly limited, and known methods may be mentioned. For example, methods for performing solid-liquid separation and methods for vaporizing a liquid from a solid-liquid mixture may be mentioned. Specifically, filtration (including pressure filtration and vacuum filtration), decantation, centrifugation, natural drying, vacuum drying, freeze drying, and spray drying may be mentioned. Among them, decantation or filtration is preferred. Note that decantation refers to a method of allowing a solid-liquid mixture to stand still, removing the supernatant liquid portion, and recovering the solid content. The above method may be carried out alone or in combination. Also, in the above recovery, for example, it may not be completely solid-liquid separated, and it may contain a graphite compound and a solvent component (for example, solvent Y).

[0062] <Method for Producing Flaked Graphite Dispersion> The method for producing a flaked graphite dispersion of the present invention includes a step of dispersing the flaked graphite obtained by the method for producing flaked graphite of the present invention in a solvent. The solvent used in the method for producing a flaked graphite dispersion of the present invention is also referred to as "solvent Z" hereinafter.

[0063] Solvent Z is not particularly limited, but an aprotic organic solvent is preferred. Examples of aprotic organic solvents are as described in the part of the first organic solvent above. Among them, as solvent Z, at least one selected from the group consisting of an amide-based solvent, a ketone-based solvent, and a sulfoxide-based solvent is preferred, and an amide-based solvent is more preferred.

[0064] An amide-based solvent refers to a solvent composed of a compound having an amide structure in the molecule. Specifically, an amide-based solvent refers to a solvent composed of a compound represented by the following formula (a).

[0065]

Chemical formula

[0066] In formula (a), R1, R2, and R3 each independently represent an alkyl group which may have a substituent or a hydrogen atom. In formula (a), R1 and R3 may be bonded to each other to form a ring, or R2 and R3 may be bonded to each other to form a ring. The number of carbon atoms in the alkyl group portion of the alkyl group which may have a substituent represented by R1, R2, and R3 is preferably 1 to 8, more preferably 1 to 3. The alkyl group which may have a substituent represented by R1, R2, and R3 is preferably an alkyl group having no substituent. Further, R2 and R3 each preferably represent an alkyl group which may have a substituent (more preferably an alkyl group having no substituent). That is, the amide-based solvent is preferably a solvent composed of a tertiary amide compound. In addition, an embodiment in which R1 represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms and no substituent, and R2 and R3 are alkyl groups having 1 to 3 carbon atoms and no substituent is also preferable.

[0067] Examples of the amide-based solvent include N,N-dimethylformamide (DMF), N,N-diethylformamide (DEF), N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide (DMAc), tetramethylurea, and 1,3-dimethyl-2-imidazolidinone. Among them, as the amide-based solvent, N,N-dimethylformamide, N-methyl-2-pyrrolidone, or N,N-dimethylacetamide is preferable.

[0068] The ketone-based solvent refers to a solvent composed of a compound having a carbonyl group (-CO-) in the molecule and a carbon atom bonded to the carbon atom of the carbonyl group. That is, a compound having a ketone structure as an ester structure (-COO-), an amide structure, etc. is not included in the ketone-based solvent. Specifically, the ketone-based solvent refers to a solvent composed of a compound represented by the following formula (b).

[0069] [Chemistry]

[0070] In formula (b), R4 and R5 each represent an alkyl group which may have a substituent. The alkyl groups which may have a substituent represented by R4 and R5 may be bonded to each other to form a ring. The number of carbon atoms in the alkyl group portion of the alkyl group which may have a substituent represented by R4 and R5 is preferably from 1 to 8, more preferably from 1 to 3. Also, the alkyl groups which may have a substituent represented by R4 and R5 are each preferably an alkyl group having no substituent.

[0071] Examples of the ketone solvents include acetone, methyl ethyl ketone (MEK), diethyl ketone, methyl isobutyl ketone (MIBK), diisobutyl ketone (DIBK), cyclopentanone, and cyclohexanone. Among them, cyclohexanone is preferred as the ketone solvent.

[0072] The sulfoxide solvent refers to a solvent composed of a compound having a sulfinyl group (-SO-) in the molecule and a carbon atom bonded to the sulfur atom of the sulfinyl group. Specifically, the sulfoxide solvent refers to a solvent composed of a compound represented by the following formula (c).

[0073] [Chemistry]

[0074] In formula (c), R6 and R7 each represent an alkyl group which may have a substituent. The alkyl groups which may have a substituent represented by R6 and R7 may be bonded to each other to form a ring. The number of carbon atoms in the alkyl group portion of the alkyl group which may have a substituent represented by R6 and R7 is preferably from 1 to 8, more preferably from 1 to 3. Moreover, the alkyl groups which may have the substituents represented by R6 and R7 are each preferably an alkyl group having no substituent.

[0075] Examples of the sulfoxide-based solvents include dimethyl sulfoxide, di-n-butyl sulfoxide, tert-butyl methyl sulfoxide, and tetramethylene sulfoxide. Among them, dimethyl sulfoxide is preferable as the sulfoxide-based solvent.

[0076] The solvent Z may be used alone or in combination of two or more.

[0077] The SP value (solubility parameter) of the solvent Z is preferably 9.0 (cal / cm 3 ) 1 / 2 or more, more preferably 9.2 (cal / cm 3 ) 1 / 2 or more, and even more preferably 9.5 (cal / cm 3 ) 1 / 2 or more. Also, the SP value of the solvent Z is preferably 18.0 (cal / cm 3 ) 1 / 2 or less, more preferably 15.0 (cal / cm 3 ) 1 / 2 or less, and even more preferably 13.0 (cal / cm 3 ) 1 / 2 or less. Incidentally, the SP value is a value also called the Hildebrand parameter, and literature values can be adopted.

[0078] The method for dispersing the exfoliated graphite in the solvent Z is not particularly limited. For example, a method of obtaining a mixed solution containing the exfoliated graphite and the solvent Z and performing a dispersion treatment on the mixed solution can be mentioned. The dispersion treatment is not particularly limited, and known methods can be applied. For example, as the dispersion treatment, methods of stirring the mixed solution with a rotary blade, generating convection in the mixed solution with a pump, and vibrating the container containing the mixed solution can be mentioned. Also, as the dispersion treatment, wet jet mill treatment, ultrasonic dispersion treatment, etc. are also preferable.

[0079] <Use of exfoliated graphite> The use of the exfoliated graphite obtained by the method for producing exfoliated graphite of the present invention is not particularly limited, and for example, it can be used as a functional filler. Exfoliated graphite is known to be excellent in toughness, electrical conductivity, and thermal conductivity. By using exfoliated graphite as a functional filler and making a composite, a composite material with the above functions can be obtained. Examples of the base material for making the composite include resin, ceramic, and metal. In addition, since exfoliated graphite has a large specific surface area, functions such as toughness can be effectively imparted with a small amount of addition. In addition, since exfoliated graphite has electrical conductivity and a large specific surface area, it can also be used as an electrode material for secondary batteries, electrochemical capacitors, etc. For example, exfoliated graphite is preferably used as the negative electrode material of a secondary battery.

[0080] When using exfoliated graphite for the above applications, for example, a slurry containing the exfoliated graphite dispersion of the present invention and other components corresponding to each of the above applications is prepared, the slurry is applied in a desired form, and the solvent component contained in the slurry (for example, the above organic solvent and specific solvent) may be removed. Since the exfoliated graphite dispersion of the present invention has excellent dispersibility, in each application, exfoliated graphite is likely to be uniformly dispersed, and desired properties are likely to be obtained.

Example

[0081] Hereinafter, the present invention will be described in more detail based on examples. The materials, amounts used, ratios, treatment details, apparatuses, and treatment procedures shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed restrictively by the examples shown below.

[0082] <Example 1> [Synthesis of graphite intercalation compound (Step 3)] The synthesis of the graphite intercalation compound (Step 3) was carried out in a glove box filled with high-purity Ar (purity 99.999%). The dew point of the glove box was -55°C. First, 100 mL of tetrahydrofuran (THF, special grade) was placed in a 100 mL glass screw vial, and 7.5 g of naphthalene (special grade) was dissolved therein. 0.5 g of metallic lithium (purity 99.5%) was added to this solution, and the solution was stirred to dissolve the metallic lithium. 2.5 g of graphite particles (manufactured by Sigma-Aldrich, 808091 - 2.5 KG, average particle size: 150 μm) was added to the lithium-dissolved solution, and the mixture was stirred at 25 °C for 24 hours to obtain a mixture containing a graphite intercalation compound. The mixture containing the obtained graphite intercalation compound was dried and subjected to XRD measurement. As a result, peaks were confirmed at 2θ = 6.5°, 13°, 21°, 28°, 36°, 43° and 51°, which corresponded to (001), (002), (003), (004), (005), (006) and (007) of stage-1 of A-phase Li-THF-GIC. This result corresponds to a structure in which a complex in which THF molecules are coordinated to lithium is intercalated into the graphite layer, indicating that the graphite interlayer is expanded to about 1.10 nm.

[0083] [Step 1] 200 mL of THF (tetrahydrofuran, corresponding to the first organic solvent) was added to the mixture containing the graphite intercalation compound obtained by the above procedure to obtain a workpiece, and wet jet mill treatment was performed. The wet jet mill treatment was performed using "NAGS20 (AC200V specification)" manufactured by Tokoyo Co., Ltd. The conditions of the apparatus were as follows. · Normal nozzle · Nozzle diameter: φ0.15 mm · Chiller set temperature: 0 °C · Liquid feed pressure: 200 MPa Under the above apparatus conditions, the wet jet mill treatment was performed for 5 passes to obtain a dispersion A of exfoliated graphite.

[0084] [Step 2] 10 mL of the product (dispersion A) obtained in Step 1 was mixed with 90 mL of pure water (corresponding to the specific solvent) to obtain a mixed solution. After obtaining the mixed solution, it was allowed to stand for 24 hours. After standing, solid-liquid separation was performed using a metal mesh (#400) to obtain exfoliated graphite. Furthermore, the exfoliated graphite obtained by performing solid-liquid separation was dried in an oven at 105 °C for 90 minutes. 2 g of exfoliated graphite was obtained by the above procedure.

[0085] <Examples 2 to 5, Comparative Examples 1 to 3> In the procedure for obtaining the exfoliated graphite of Example 1 above, exfoliated graphite was obtained in the same manner as in Example 1, except that the type of specific solvent used in Step 2 was changed as shown in the table in the following stage. The amounts of exfoliated graphite obtained in each example and comparative example are shown in the table in the following stage.

[0086] <Example 6> [Synthesis of graphite intercalation compound (Steps 3 and 4)] The synthesis of the graphite intercalation compound (Step 3) was carried out in a glove box filled with high-purity Ar (purity 99.999%). The dew point of the glove box was -55 °C. First, 100 mL of tetrahydrofuran (THF, special grade) was placed in a 100 mL glass screw tube bottle, and 7.5 g of naphthalene (special grade) was dissolved therein. 0.5 g of metallic lithium (purity 99.5%) was added to this solution, and the solution was stirred to dissolve the metallic lithium. 2.5 g of graphite particles (manufactured by Nippon Graphite, particle size: 500 μm to 1 mm) was added to the lithium solution, and the mixture was stirred at 25 °C for 48 hours to obtain a mixture containing a graphite intercalation compound. This mixture was allowed to stand for 120 hours, and solid-liquid separation was performed by removing the supernatant to obtain a graphite intercalation compound (Step 4). When XRD measurement was performed on the obtained graphite intercalation compound, peaks were confirmed at 2θ = 6.5°, 13°, 21°, 28°, 36°, 43° and 51°, and these corresponded to the (001), (002), (003), (004), (005), (006) and (007) of stage-1 of A-phase Li-THF-GIC. This result corresponds to a structure in which a complex in which THF molecules are coordinated to lithium is intercalated into the graphite layer, indicating that the graphite layer spacing is extended to about 1.10 nm.

[0087] [Project 1] 22 g of the obtained graphite intercalation compound and 88 mL of THF were mixed and subjected to wet jet milling. The wet jet milling was carried out using "NAGS20 (AC200V specification)" manufactured by Tokoyo Co., Ltd. The conditions of the apparatus were as follows. · Straight nozzle (model number: J01502S) · Nozzle diameter: φ0.15 mm · Chiller set temperature: 0 °C · Discharge rate: 38.5×10 4 ±1×10 4 · Liquid feed pressure: 120 MPa Under the above conditions of the apparatus, wet jet milling was carried out for 22 passes to obtain a dispersion B of exfoliated graphite.

[0088] [Project 2] 10 mL of the product (dispersion B) obtained in Project 1 and 90 mL of pure water (corresponding to the specific solvent) were mixed to obtain a mixed solution. After obtaining the mixed solution, it was allowed to stand for 24 hours. After standing, solid-liquid separation was carried out using a metal mesh (#400) to obtain exfoliated graphite. Furthermore, the exfoliated graphite obtained by solid-liquid separation was dried in an oven at 105 °C for 90 minutes. By the above procedure, 1.4 g of exfoliated graphite was obtained.

[0089] [Examples 7 and 8] In the procedure for obtaining the exfoliated graphite of Example 6 above, exfoliated graphite was obtained in the same manner as in Example 6 except that the type of the specific solvent used in Project 2 was changed as shown in the table in the following stage. The amounts of exfoliated graphite obtained in each example and comparative example are shown in the table in the following stage.

[0090] [Results] Table 1 shows the types of solvents used in Project 2 of each example and each comparative example and the amounts of exfoliated graphite obtained. In Tables 1 and 2, the abbreviations in the column of "solvent used in Project 2" represent the following solvents, respectively. · MeOH: Methanol · EtOH: Ethanol ·EG: Ethylene glycol ·IPA: Isopropyl alcohol ·MNP: N-Methyl-2-pyrrolidone ·DMAc: N,N-Dimethylacetamide ·THF: Tetrahydrofuran

[0091]

Table 1

[0092] From the results shown in Table 1, in each example using the above specific solvent as the solvent used in Step 2, the amount of exfoliated graphite obtained was large and the yield was high. On the other hand, in the comparative examples where the specific solvent was not used as the solvent used in Step 2, the amount of exfoliated graphite obtained was less than that in each example. Also, from the comparison between Example 5 and other examples, when the SP value of the specific solvent used in Step 2 is 12.0 (cal / cm 3 ) 1 / 2 or more (more preferably 12.5 (cal / cm 3 ) 1 / 2 or more), it was confirmed that the amount of exfoliated graphite obtained becomes larger.

[0093] In addition, when the exfoliated graphite obtained in each example was analyzed by Raman spectroscopy, it was confirmed that the exfoliated graphite was composed of graphene with 4 layers or less.

[0094] <Exfoliated graphite dispersion liquid> 0.1 g of the exfoliated graphite obtained in Example 1 was added to 100 mL of N-methyl-2-pyrrolidone (NMP), and wet jet milling treatment was performed to disperse the exfoliated graphite. The wet jet milling treatment was performed using "NAGS20 (AC200V specification)" manufactured by Tokuyama Corporation. The conditions of the apparatus were as follows. · Normal nozzle · Nozzle diameter: φ0.15 mm · Chiller set temperature: 0°C · Liquid feed pressure: 200 MPa Under the conditions of the above apparatus, wet jet mill treatment was performed 5 passes to obtain a dispersion liquid A of exfoliated graphite.

[0095] An exfoliated graphite dispersion liquid was obtained by the above jet mill treatment. When the exfoliated graphite in the exfoliated graphite dispersion liquid was recovered and analyzed by Raman spectroscopy, it was confirmed that the exfoliated graphite was composed of graphene with 4 layers or less.

Explanation of symbols

[0096] 10 Dispersion unit 12 Introduction side disk 12A First through hole 12B Second through hole 14 Intermediate disk 14A Third through hole 16 Discharge side disk 16A Fourth through hole 16B Fifth through hole 18 Introduction side groove-shaped passage 20 Discharge side groove-shaped passage C1 Central axis

Claims

1. Step 1 of subjecting an object to be treated, which contains one type selected from the group consisting of graphite and graphite compounds and a first organic solvent which is an aprotic organic solvent, to wet jet milling treatment to obtain a product containing exfoliated graphite; A method for producing exfoliated graphite, comprising: Step 2 of mixing the product with at least one specific solvent selected from the group consisting of water and protic organic solvents to obtain a mixed solution, and separating exfoliated graphite from the mixed solution.

2. The method for producing exfoliated graphite according to Claim 1, wherein the graphite compound is used in Step 1.

3. The method for producing exfoliated graphite according to Claim 2, wherein the graphite compound is a graphite compound obtained by mixing an alkali metal source and graphite in a second organic solvent which is an aprotic organic solvent, such that the alkali metal is intercalated between graphene layers in the graphite.

4. The method for producing exfoliated graphite according to any one of Claims 1 to 3, wherein in Step 2, the mass ratio of the specific solvent to the product is 0.5 to 100.

5. The method for producing exfoliated graphite according to any one of Claims 1 to 3, wherein the specific solvent is at least one solvent selected from the group consisting of water and alcohol-based solvents.

6. The SP value of the specific solvent is 12.5 (cal / cm ３ ). １／２ The method for producing the thinned graphite according to any one of claims 1 to 3, wherein the above conditions are satisfied.

7. The method for producing exfoliated graphite according to any one of Claims 1 to 3, wherein the first organic solvent is an ether-based solvent.

8. The method for producing exfoliated graphite according to any one of Claims 1 to 3, wherein the second organic solvent is an ether-based solvent.

9. A method for producing an exfoliated graphite dispersion, comprising a step of dispersing exfoliated graphite obtained by the method for producing exfoliated graphite according to any one of Claims 1 to 3 in a solvent.

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