Method for producing exfoliated graphite and method for producing exfoliated graphite dispersion

Abstract

To provide a method for producing exfoliated graphite, which has a higher yield of exfoliated graphite. [Solution] A method for producing exfoliated graphite includes step 1 of subjecting a workpiece 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 processing to obtain a product containing exfoliated graphite, and 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 liquid, and separating the exfoliated graphite from the mixed liquid.

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 technology]

[0002] In recent years, exfoliated graphite, which has a small number of graphene layers in the graphite, has been attracting attention. A method for producing exfoliated graphite is known in which a graphite intercalation compound (GIC) is produced from graphite and then subjected to an exfoliation treatment. As a method for producing the above-mentioned GIC, various methods have been proposed, such as a gas phase method and a solution method. Among them, the method for producing GIC by the solution method has attracted attention because it is easier to produce GIC than the gas phase method.

[0003] A method for producing exfoliated graphite by subjecting the GIC to an exfoliation treatment is disclosed, for example, in Patent Document 1. Specifically, the method disclosed includes adding a polar aprotic solvent to GIC and subjecting the resulting mixture to ultrasonic treatment to produce exfoliated graphite. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2015-105200 A Summary of the Invention [Problem to be solved by the invention]

[0005] The method for producing exfoliated graphite described in Patent Document 1 above is known, but there has been a demand for a method for producing exfoliated graphite with a higher yield.

[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 research into solving the above problems, the present inventors have found that the above problems can be solved by the following configuration.

[0008] [1] A step 1 of subjecting a workpiece containing one selected from the group consisting of graphite and graphite compounds and a first organic solvent which is an aprotic organic solvent to a wet jet mill treatment to obtain a product containing exfoliated graphite; A method for producing exfoliated graphite, comprising step 2 of mixing the above product with at least one specific solvent selected from the group consisting of water and protic organic solvents to obtain a mixed liquid, and separating exfoliated graphite from the mixed liquid. [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 is intercalated between graphene layers in graphite by mixing an alkali metal source and graphite in a second organic solvent which is an aprotic organic solvent. [4] The method for producing exfoliated graphite according to any one of [1] to [3], wherein in the step 2, a 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 alcohol-based solvents. [6] The SP value of the above specific solvent is 12.5 (cal / cm 3 ) 1 / 2 The method for producing exfoliated graphite according to any one of [1] to [5] above. [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. [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 [1] to [8] in a solvent. Effect of the Invention

[0009] According to the present invention, a method for producing exfoliated graphite with a higher yield of exfoliated graphite can be provided. Moreover, according to the present invention, a method for producing an exfoliated graphite dispersion can be provided. [Brief description of the drawings]

[0010] [Figure 1] FIG. 2 is a schematic diagram for explaining a distribution unit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The present invention will be described in detail below. The following description of the configuration may be based on a representative embodiment of the present invention, but the present invention is not limited to such an embodiment.

[0012] The following describes the meaning of each description in this specification. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits.

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

[0014] <Method of producing exfoliated graphite> The method for producing exfoliated graphite of the present invention includes step 1 of subjecting a workpiece containing one selected from the group consisting of graphite and graphite compounds and a first organic solvent which is an aprotic organic solvent to a wet jet mill treatment to obtain a product containing exfoliated graphite. In addition, the method for producing exfoliated graphite dispersion of the present invention includes a step 2 of mixing the above product with at least one specific solvent selected from the group consisting of water and protic organic solvents to obtain a mixed liquid, and separating exfoliated graphite from the mixed liquid.

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

[0016] The present manufacturing method will now be described. The present production method may include steps other than step 1 and step 2 described below.

[0017] [Process 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 a wet jet mill treatment to obtain a product containing exfoliated graphite. Step 1 will now be described in detail.

[0018] (Graphite and graphite compounds) In step 1, the object 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 fiber. Among them, natural graphite is preferable.

[0019] The graphite compound includes a graphite intercalation compound in which other compounds are inserted between the graphene layers in graphite. Examples of other compounds contained in the graphite compound (graphite intercalation compound) include, for example, one or more compounds selected from the group consisting of alkali metals, organic compounds, inorganic compounds, and ions thereof. The other compounds may form a complex. More specifically, examples of the other compounds include alkali metals, ether solvents, aromatic compounds, and inorganic ions. The graphite compound is preferably a graphite compound in which an alkali metal is intercalated between graphene layers in graphite. The graphite compound of the above embodiment can be obtained, for example, by mixing an alkali metal source and graphite in an organic solvent (solvent Y described below). The method for producing the graphite compound of the above embodiment will be described in detail later. The graphite compound may be so-called expanded graphite. Expanded graphite refers to a graphite compound in which sulfate ions, nitrate ions, etc. are inserted between 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 material 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-based solvents, ketone-based solvents, sulfoxide-based solvents, hydrocarbon-based solvents, ether-based solvents, and ester-based solvents. Among them, ether-based solvents are preferred because they increase the yield of exfoliated graphite.

[0021] The ether solvent is not particularly limited as long as it has an ether bond (-O-), and there is no limit to the number of ether bonds in the molecule. The ether solvent may have a cyclic structure. Examples of ether-based solvents 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 these, 1,2-dimethoxyethane or tetrahydrofuran is preferred because it is more likely to exfoliate the graphite or graphite compound contained in the material to be treated.

[0022] The first organic solvent may be used alone or in combination of two or more.

[0023] (Wet jet mill processing) In step 1, a material to be treated, which contains one selected from the group consisting of the graphite and graphite compounds, and the first organic solvent, is subjected to a wet jet mill treatment. The material to be treated and the wet jet mill treatment will be described below.

[0024] The material to be treated is preferably subjected to wet jet mill treatment to efficiently obtain exfoliated graphite, so that the solids concentration and viscosity are within the ranges described in detail below.

[0025] In order to efficiently obtain exfoliated graphite, the solid content concentration of the material to be treated is preferably 0.1 to 10 mass %, and more preferably 0.5 to 5 mass %, based on the total mass of the material to be treated. The solid content in the material to be treated refers to the components in the material to be treated excluding the solvent.

[0026] The viscosity of the material to be treated is preferably 1 to 20,000 mPa·s so that the material can be treated by a wet jet mill. The viscosity can be measured by a known method, for example, the method of JIS Z 8803:2011.

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

[0028] The object to be treated may contain one selected from the group consisting of the graphite and graphite compounds, as well as components other than the organic solvent (other components). Examples of other components include surfactants. Other components also include components used to produce the graphite compound.

[0029] The wet jet mill treatment is advantageous in that it applies a shear force to the material to be treated and allows for efficient production of exfoliated graphite without pulverizing the graphite or graphite compound more than necessary. The wet jet milling process is not limited as long as it can flow a slurry containing a solvent and a powder at high speed and can pulverize and / or disintegrate the powder as a result. For example, a method of causing a high-speed flowing fluid to collide with a fluid collision part that is approximately perpendicular to the flow direction of the fluid, a method of causing a high-speed flowing fluid to flow through a narrowed part, a method of causing multiple high-speed flowing fluids to collide against each other, a method of generating turbulence and causing a fluid to collide against the wall of a pipe or the like through which the fluid flows, and a method of applying a shear force to a fluid by a cavitation jet generated by reducing pressure or the like. The wet jet milling process may be a combination of these methods. Among them, a method of causing multiple high-speed flowing fluids to collide against each other is preferable.

[0030] An example of the wet jet mill process in which a plurality of fluids are collided against each other in a counter-flow manner includes the following process A, process B, and process C in this order. Step A: A step of subjecting the object to be treated to a head-on collision Process B: A process of flowing the collided object in a direction different from the direction in process A. Process C: Separating and flushing the material to be treated

[0031] Although there is no particular limitation on the method for carrying out the above steps A to C, it is preferable to use a 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 disposed in an apparatus for performing wet jet mill processing, and as will be described later, steps A to C can be carried out by passing a material to be processed through a flow path in this dispersion unit 10. The distribution unit 10 includes an introduction side disk 12, an intermediate disk 14, and a discharge side disk 16. The introduction side disk 12, the intermediate disk 14, and the discharge side disk 16 are shaped like disks with substantially the same diameter. The intermediate disk 14 is disposed downstream of the introduction side disk 12 in close contact with the center axis C1. The discharge side disk 16 is disposed downstream of the intermediate disk 14 in close contact with the center axis C1. The lead-in side disk 12, intermediate disk 14, and discharge-side disk 16 are made of wear-resistant materials such as ceramics, cemented carbide, and diamond, and are formed to have approximately the same diameter. The lead-in side disk 12 and the discharge-side disk 16 are formed to have approximately the same plate thickness, and the intermediate disk 14 is formed to have a plate thickness thinner than the lead-in side disk 12 and the discharge-side disk 16.

[0032] A first through hole 12A and a second through hole 12B are arranged in the lead-in side disk 12. The first through hole 12A and the second through hole 12B are formed to have approximately the same diameter and are arranged at approximately symmetrical positions with respect to the center of the lead-in side disk 12. An introduction side groove-like passage 18 (first flow path) formed with a width smaller than the hole diameters of the first through hole 12A and the second through hole 12B is arranged in a straight line on the surface of the introduction side disk 12 facing the intermediate disk 14. The first through hole 12A and the second through hole 12B are communicated with each other via the introduction side groove-like passage 18. The intermediate disk 14 has a third through hole 14A (second flow passage) disposed in the center thereof. In the discharge side disc 16, a fourth through hole 16A and a fifth through hole 16B are arranged at symmetrical positions with substantially the same diameter and sandwiching the center of the discharge side disc 16 therebetween. A discharge-side groove-like passage 20 (third flow path) formed with a width smaller than the diameters of the fourth through hole 16A and the fifth through hole 16B is disposed on the surface of the discharge-side disk 16 facing the intermediate disk 14. The fourth through hole 16A and the fifth through hole 16B are communicated with each other via the discharge-side groove-like passage 20.

[0033] Next, the flow of steps A to C using the dispersion unit will be described. First, the material to be treated is pressurized and introduced as an ultra-high speed fluid into the dispersion unit 10. At this time, it is preferable to pressurize the material to a pressure of 100 MPa or more and 250 MPa or less. When the introduced workpiece L reaches the inlet side disk 12, it branches off and flows through the first through hole 12A and the second through hole 12B. After passing through the first through hole 12A and the second through hole 12B, the branched workpiece L is forcibly changed in direction toward the center of the inlet side disk 12 in the inlet side groove-like passage 18 while colliding with the intermediate disk 14. Then, the workpieces flow in opposing directions in a straight line while being accelerated, and collide with each other. In this manner, step A is carried out. Next, the flow direction of the workpieces L that collide and rejoin is changed to approximately vertical direction, and the workpieces L are 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 inlet side groove-like passage 18 of the inlet side disk 12 is reduced. The turbulent flow generated by the collision is maintained in that state. In this manner, step B is carried out. Next, the material L that has passed through the third through hole 14A collides with the discharge side disk 16 and branches again to flow in the discharge side groove-like passage 20 toward the outer periphery of the discharge side disk 16. In this way, the material L that has passed through the fourth through hole 16A and the fifth through hole 16B is discharged from the discharge side disk 16, reunites, and is discharged from the dispersion unit 10. In this manner, step C is performed.

[0034] Apparatuses for carrying out the wet jet mill treatment comprising the above steps A, B and C include, for example, "NAGS20", "NAGS100", "NAGS500" and "NAGS1000" manufactured by Joko Co., Ltd.

[0035] The wet jet mill treatment is preferably carried out multiple times. The number of passes is not particularly limited, but is preferably 2 to 100 passes. In most cases, it is 2 to 20 passes. In addition, the wet jet milling may be performed at two or more different liquid sending pressures. For example, the wet jet milling may be performed at a low liquid sending pressure, and then at a high liquid sending pressure. Each treatment at each pressure may be performed multiple times.

[0036] The wet jet mill treatment is preferably carried out in an inert gas atmosphere inside the apparatus, such as nitrogen gas and argon gas. In addition, since the wet jet mill treatment generates heat due to compression, etc., it is also preferable to carry out the treatment while cooling. The cooling method can be a known method, and examples thereof include a method of exchanging heat by directly or indirectly bringing a refrigerant into contact with a heat generating portion.

[0037] [Process 2] In step 2, the above product is mixed with at least one specific solvent selected from the group consisting of water and protic organic solvents to obtain a mixed liquid, and exfoliated graphite is separated from the mixed liquid. By the above step 2, exfoliated graphite is obtained. Step 2 will now 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 protic organic solvents. Examples of the protic organic solvent include carboxylic acid solvents and alcohol solvents, with alcohol solvents being preferred. The specific solvent is preferably at least one solvent selected from the group consisting of water and alcohol-based solvents.

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

[0040] The alcohol-based solvent refers to a solvent made of a compound having a hydroxyl group in the molecule. Specifically, the alcohol-based solvent refers to a solvent made 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 a substituent represented by R1 may have a branched structure or a cyclic structure. The number of carbon atoms in the alkyl group moiety 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. In other words, R1 also preferably represents an alkyl group having no substituent.

[0042] Examples of alcohol-based solvents include methanol, ethanol, 1-propanol, 2-propanol (isopropyl alcohol), 1-butanol, 2-butanol, tert-butyl alcohol, ethylene glycol, and propylene glycol. Of these, methanol, ethanol, 2-propanol, or ethylene glycol is preferred, and methanol, ethanol, or ethylene glycol is more preferred.

[0043] The 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 / 2More than 12.0 (cal / cm 3 ) 1 / 2 More preferably, 12.5 (cal / cm 3 ) 1 / 2 More preferably, the SP value of the specific solvent is 23.4 (cal / cm 3 ) 1 / 2 It is often the following: The SP value is also called the Hildebrand parameter, and the literature value can be used.

[0045] In step 2, the product obtained in step 1 is mixed with the specific solvent. 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. Moreover, 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 any known mixing method can be used. For example, there are a method of stirring the solution with a rotor, a method of generating convection with a pump, and a method of vibrating a container containing the material to be treated. Specific examples include a mixer, a magnetic stirrer, a mechanical stirrer, and a shaker. The mixing in step 2 is also preferably carried out in an inert atmosphere.

[0047] In step 2, the product is mixed with the specific solvent to obtain a mixed liquid, and exfoliated graphite is separated from the mixed liquid. The method for separating the exfoliated graphite from the above-mentioned mixed liquid is not particularly limited, and any known method can be applied, for example, a method of performing solid-liquid separation. Examples of methods for performing solid-liquid separation include filtration (including pressure filtration and vacuum filtration), decantation, and centrifugation. Among these, filtration is more preferable. Two or more methods for performing solid-liquid separation may be combined. As described above, in a mixed liquid containing the specific solvent, exfoliated graphite is difficult to disperse, and therefore, the exfoliated graphite is easy to separate from the mixed liquid.

[0048] After the mixture is obtained, it may be allowed to stand. The time for which the mixture is allowed to stand is not particularly limited, but may be, for example, 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, a known method can be applied, and examples thereof include natural drying, heat drying, vacuum drying, and freeze drying.

[0050] [Process 3] When the object to be treated in step 1 contains a graphite compound, the present production method may include, before step 1, step 3 for obtaining a graphite compound (graphite intercalation compound). 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-mentioned components may be added. Step 3 will now be described.

[0051] (Organic solvent (solvent Y)) The second organic solvent used in step 3 is not particularly limited, but the first organic solvent used in step 1 above is preferably used. Among them, ether solvents are preferable as the solvent Y. Examples and preferable examples of the ether solvent are as described above in the section on step 1.

[0052] (Alkaline metal source) The alkali metal source used in step 3 is not particularly limited as long as it contains an alkali metal, and examples of the alkali metal source include an alkali metal element (a zero-valent alkali metal) and a salt containing an alkali metal. Examples of the alkali metal contained in the alkali metal source include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr). The alkali metal is preferably Li, Na, or K, more preferably Li or K, and even more preferably Li. The alkali metal source is preferably lithium metal, potassium metal or sodium metal, more preferably lithium metal or sodium metal, and even more preferably lithium metal. The alkali metal source may be used alone or in combination of two or more kinds.

[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 stacked. Examples and preferred examples of graphite are as described above in the section on step 1.

[0054] (Aromatic Hydrocarbons) In step 3, it is preferable to mix an aromatic hydrocarbon with the alkali metal source and the graphite. Mixing an aromatic hydrocarbon with the above components promotes dissolution of the alkali metal in the alkali metal source into the solvent, and also makes it possible to easily intercalate the alkali metal into graphite due to the difference in electron affinity between the alkali metal and graphite. Examples of aromatic hydrocarbons include benzene, naphthalene, phenanthrene, anthracene, and pyrene. Of these, naphthalene is preferred.

[0055] (Mixing method and conditions) The method for mixing the various components in step 3 is not particularly limited as long as it is possible to mix the second organic solvent, the alkali metal source, the graphite, and any optional components.

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

[0057] Methods for mixing the above components include known methods, such as stirring the solution with a rotor, generating convection with a pump, and vibrating a container containing the material to be treated. Specific examples include a magnetic stirrer, a mechanical stirrer, and a shaker.

[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 further preferably 1 to 100 hours. The temperature during mixing in step 3 is not particularly limited, but is preferably 10 to 50°C, more preferably 20 to 30°C. In step 3, the mixture may be left to stand after mixing. The time for leaving the mixture to stand may be, for example, 1 to 200 hours, and preferably 8 to 150 hours. When the mixture is left to stand, the graphite intercalation compound settles, and solid-liquid separation in step 4 described below can be easily performed.

[0059] Although there is no particular limitation on the atmosphere in which step 3 is carried out, step 3 is preferably carried out in an inert gas atmosphere. Examples of the inert gas include nitrogen gas and argon gas. The atmosphere in which step 3 is carried out preferably has a low water vapor content. The dew point of the atmosphere in which step 3 is carried out is preferably 0° C. or lower, more preferably −20° C. or lower, further preferably −40° C. or lower, and particularly preferably −50° C. or lower. The lower limit of the dew point of the atmosphere in which step 3 is carried out is not particularly limited, but is usually −100° C. or higher.

[0060] (Graphite intercalation compound) In step 3, a graphite intercalation compound is produced in which an alkali metal is intercalated between graphene layers in graphite. 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 or higher system containing additives in addition to the above ternary system. For example, the alkali metal may form a complex with THF, which is a solvent, and the complex may be intercalated. The formation of the graphite intercalation compound can be confirmed by X-ray diffraction, specifically, by the disappearance of the diffraction peaks due to the graphite structure and the appearance of diffraction peaks corresponding to the extension of the distance between the graphene layers due to intercalation.

[0061] [Step 4] When the material to be treated in step 1 contains a graphite compound, the present production method may include step 4 of recovering the graphite compound (graphite intercalation compound) after performing step 3 of obtaining the graphite compound. The method of recovery is not particularly limited, and includes known methods. For example, a method of performing solid-liquid separation and a method of evaporating liquid from a solid-liquid mixture are included. Specifically, filtration (including pressure filtration and reduced pressure filtration), decantation, centrifugation, natural drying, vacuum drying, freeze drying, and spray drying are included. Among them, decantation or filtration is preferred. Decantation refers to a method in which a solid-liquid mixture is allowed to stand and the supernatant liquid portion is removed to recover the solids. The above methods may be carried out alone or in combination. In addition, in the above recovery, for example, complete solid-liquid separation may not be performed, and the graphite compound and a solvent component (e.g., solvent Y) may be included.

[0062] <Method of producing exfoliated graphite dispersion> The method for producing an exfoliated graphite dispersion of the present invention includes a step of dispersing exfoliated graphite obtained by the method for producing exfoliated graphite of the present invention described above in a solvent. The solvent used in the method for producing an exfoliated graphite dispersion of the present invention is hereinafter also referred to as “solvent Z”.

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

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

[0065] [ka]

[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 alkyl group moiety of the alkyl group which may have a substituent represented by R1, R2 and R3 preferably has 1 to 8 carbon atoms, and more preferably has 1 to 3 carbon atoms. The alkyl group which may have a substituent represented by R1, R2 and R3 is also preferably an alkyl group which has no substituent. In addition, R2 and R3 each preferably represent an alkyl group which may have a substituent (more preferably an alkyl group which does not have a substituent). That is, the amide solvent is preferably a solvent made of a tertiary amide compound. Also preferred is an embodiment in which R1 represents a hydrogen atom or an unsubstituted alkyl group having 1 to 3 carbon atoms, and R2 and R3 each represent an unsubstituted alkyl group having 1 to 3 carbon atoms.

[0067] Examples of amide solvents 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 these, the amide solvent is preferably N,N-dimethylformamide, N-methyl-2-pyrrolidone, or N,N-dimethylacetamide.

[0068] A ketone solvent is a solvent consisting of a compound that has a carbonyl group (-CO-) in the molecule and a carbon atom is bonded to the carbonyl group's carbon atom. In other words, compounds that have a ketone structure, such as an ester structure (-COO-) or an amide structure, are not included in the ketone solvent. Specifically, the ketone solvent refers to a solvent made of a compound represented by the following formula (b).

[0069] [ka]

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

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

[0072] A sulfoxide solvent is a solvent made of a compound that has a sulfinyl group (-SO-) in the molecule and in which a carbon atom is bonded to the sulfur atom of the sulfinyl group. Specifically, the sulfoxide solvent refers to a solvent made of a compound represented by the following formula (c).

[0073] [ka]

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

[0075] Examples of sulfoxide solvents include dimethyl sulfoxide, di-n-butyl sulfoxide, tert-butyl methyl sulfoxide, and tetramethylene sulfoxide. Of these, the sulfoxide solvent is preferably dimethyl sulfoxide.

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

[0077] The SP value (solubility parameter) of solvent Z is 9.0 (cal / cm 3 ) 1 / 2 More than 9.2 (cal / cm 3 ) 1 / 2 More preferably, 9.5 (cal / cm 3 ) 1 / 2 More preferably, the SP value of the solvent Z is 18.0 (cal / cm 3 ) 1 / 2 Less than 15.0 (cal / cm 3 ) 1 / 2 Less than 13.0 (cal / cm 3 ) 1 / 2 The following is even more preferred: The SP value is also called the Hildebrand parameter, and the literature value can be used.

[0078] The method of dispersing exfoliated graphite in solvent Z is not particularly limited, and examples thereof include a method of obtaining a mixed liquid containing exfoliated graphite and solvent Z and subjecting the mixed liquid to a dispersion treatment. The dispersion treatment is not particularly limited, and known methods can be applied. Examples of the dispersion treatment include a method of stirring the mixed liquid with a rotor, a method of generating convection in the mixed liquid with a pump, and a method of vibrating a container containing the mixed liquid. In addition, examples of the dispersion treatment include wet jet mill treatment and ultrasonic dispersion treatment.

[0079] <Applications 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 it can be used, for example, as a functional filler. Exfoliated graphite is known to have excellent toughness, electrical conductivity, and thermal conductivity. By using exfoliated graphite as a functional filler and compounding it, a composite material having the above functions can be obtained. Examples of the base material to be compounded include resin, ceramic, and metal. In addition, since exfoliated graphite has a large specific surface area, it is possible to effectively impart functions such as toughness by adding a small amount of it. 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 a negative electrode material for secondary batteries.

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

[0081] The present invention will now be described in further detail with reference to examples. The materials, amounts used, ratios, processing contents, equipment, processing procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the following examples.

[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 tube bottle, and 7.5 g of naphthalene (special grade) was dissolved in it. 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 (Sigma-Aldrich, 808091-2.5KG, average particle size: 150 μm) were added to the lithium 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 graphite intercalation compound was dried and subjected to XRD measurement, revealing peaks 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 Li-THF-GIC in phase A. This result corresponds to a structure in which a complex in which THF molecules are coordinated to lithium is intercalated into the graphite layers, and indicates that the graphite interlayer spacing is approximately 1.10 nm.

[0083] [Process 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 material to be treated, which was then subjected to wet jet mill treatment. The wet jet mill treatment was performed using Joko Co., Ltd.'s "NAGS20 (AC200V specification)". The conditions of the apparatus were as follows. ·Normal nozzle Nozzle diameter: φ0.15mm Chiller temperature setting: 0℃ Liquid delivery pressure: 200MPa Under the above device conditions, the wet jet mill treatment was carried out five times to obtain a dispersion A of exfoliated graphite.

[0084] [Process 2] 10 mL of the product (dispersion A) obtained in step 1 was mixed with 90 mL of pure water (corresponding to a specific solvent) to obtain a mixed liquid. After obtaining the mixed liquid, the mixture was left to stand for 24 hours, and then subjected to solid-liquid separation using a metal mesh (#400) to obtain exfoliated graphite. The exfoliated graphite obtained by the solid-liquid separation was then dried in an oven at 105°C for 90 minutes. By the above procedure, 2 g of exfoliated graphite was obtained.

[0085] <Examples 2 to 5 and Comparative Examples 1 to 3> In the procedure for obtaining exfoliated graphite in Example 1 above, the type of the specific solvent used in step 2 was changed as shown in the table below, but exfoliated graphite was obtained in the same manner as in Example 1. The amount of exfoliated graphite obtained in each of the Examples and Comparative Examples is shown in the table below.

[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 in it. 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) were 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 left to stand for 120 hours, and the supernatant liquid was removed to perform solid-liquid separation to obtain a graphite intercalation compound (step 4). XRD measurement of the obtained graphite intercalation compound confirmed peaks 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 Li-THF-GIC in phase A. This result corresponds to a structure in which a complex in which THF molecules are coordinated to lithium is intercalated into the graphite layers, and indicates that the graphite interlayers extend to about 1.10 nm.

[0087] [Process 1] 22 g of the graphite intercalation compound obtained was mixed with 88 mL of THF and subjected to a wet jet mill treatment. The wet jet mill treatment was performed using a Joko Corporation "NAGS20 (AC200V specification)". The conditions of the apparatus were as follows. Straight nozzle (model number: J01502S) Nozzle diameter: φ0.15mm Chiller temperature setting: 0℃ ·Discharge speed: 38.5×10 4 ±1×10 4 Liquid delivery pressure: 120MPa Under the above device conditions, the wet jet mill treatment was carried out 22 times to obtain a dispersion B of exfoliated graphite.

[0088] [Process 2] 10 mL of the product (dispersion B) obtained in step 1 was mixed with 90 mL of pure water (corresponding to a specific solvent) to obtain a mixed liquid. After obtaining the mixed liquid, the mixture was left to stand for 24 hours, and then subjected to solid-liquid separation using a metal mesh (#400) to obtain exfoliated graphite. The exfoliated graphite obtained by the solid-liquid separation was then dried in an oven at 105°C for 90 minutes. Through the above procedure, 1.4 g of exfoliated graphite was obtained.

[0089] <Examples 7 and 8> In the procedure for obtaining exfoliated graphite in Example 6, the type of the specific solvent used in step 2 was changed as shown in the table below, but exfoliated graphite was obtained in the same manner as in Example 6. The amount of exfoliated graphite obtained in each of the Examples and Comparative Examples is shown in the table below.

[0090] <Result> Table 1 shows the type of solvent used in step 2 in each Example and Comparative Example and the amount of exfoliated graphite obtained. In Tables 1 and 2, the abbreviations in the column "Solvent used in step 2" represent the following solvents. 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 in which the above-mentioned specific solvent was used 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 Example in which the specific solvent was not used as the solvent used in step 2, the amount of exfoliated graphite obtained was smaller than that of each Example. In addition, a comparison between Example 5 and other Examples reveals that the SP value of the specific solvent used in step 2 is 12.0 (cal / cm 3 ) 1 / 2 More preferably, 12.5 (cal / cm 3 ) 1 / 2 It was confirmed that when the temperature is 50° C. or more, the amount of exfoliated graphite obtained is greater.

[0093] When the exfoliated graphite obtained in each example was analyzed by Raman spectroscopy, it was confirmed that the exfoliated graphite was composed of four or less layers of graphene.

[0094] <Exfoliated graphite dispersion> 0.1 g of the exfoliated graphite obtained in Example 1 was added to 100 mL of N-methyl-2-pyrrolidone (NMP), and the exfoliated graphite was dispersed by wet jet milling. The wet jet milling was performed using a "NAGS20 (AC200V specification)" manufactured by Joko Co., Ltd. The conditions of the apparatus were as follows. ·Normal nozzle Nozzle diameter: φ0.15mm Chiller temperature setting: 0℃ Liquid delivery pressure: 200MPa Under the above device conditions, the wet jet mill treatment was carried out five times to obtain a dispersion A of exfoliated graphite.

[0095] By the above jet mill treatment, an exfoliated graphite dispersion was obtained. The exfoliated graphite in the exfoliated graphite dispersion was collected and analyzed by Raman spectroscopy, and it was confirmed that the exfoliated graphite was composed of four or fewer layers of graphene. [Explanation of symbols]

[0096] 10 Distributed Units 12 Introduction Disk 12A First through hole 12B Second through hole 14 Middle disc 14A Third through hole 16 Discharge side disk 16A Fourth through hole 16B Fifth through hole 18 Inlet channel 20 Discharge gutter passage C1 center axis

Claims

1. A step 1 of subjecting a workpiece containing one selected from the group consisting of graphite and graphite compounds and a first organic solvent which is an aprotic organic solvent to a 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 protic organic solvents to obtain a mixed liquid, and separating exfoliated graphite from the mixed liquid.

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

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

4. The method for producing exfoliated graphite according to any one of claims 1 to 3, wherein in the step 2, a 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 exfoliated graphite according to any one of claims 1 to 3.

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 claim 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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