Method for producing exfoliated graphite dispersion and exfoliated graphite dispersion

Abstract

To provide a method for producing an exfoliated graphite dispersion liquid that enhances the dispersibility of exfoliated graphite. [Solution] A method for producing exfoliated graphite dispersion includes step 1 of subjecting a workpiece containing one selected from the group consisting of graphite and graphite compounds, and a first organic solvent other than amide-based solvents, ketone-based solvents, and sulfoxide-based solvents, to wet jet mill processing to obtain exfoliated graphite, and step 2 of mixing the product obtained in step 1 with at least one specific solvent selected from the group consisting of amide-based solvents, ketone-based solvents, and sulfoxide-based solvents to obtain exfoliated graphite dispersion.

Description

[Technical field]

[0001] The present invention relates to a method for producing an exfoliated graphite dispersion. The present invention also relates to 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 in, for example, Patent Document 1. Specifically, a method for producing exfoliated graphite by adding a polar aprotic solvent to GIC and subjecting it to ultrasonic treatment is disclosed. In the above procedure, an exfoliated graphite dispersion in which exfoliated graphite is dispersed in a solution is obtained. [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 present inventors produced an exfoliated graphite dispersion liquid using the production method described in Patent Document 1, and found that the dispersibility of exfoliated graphite in the obtained exfoliated graphite dispersion liquid was difficult to increase.

[0006] Therefore, an object of the present invention is to provide a method for producing an exfoliated graphite dispersion liquid that increases the dispersibility of exfoliated graphite. Another object of the present invention is to provide an exfoliated graphite dispersion liquid. [Means for solving the problem]

[0007] As a result of extensive 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 obtaining exfoliated graphite by subjecting a workpiece containing one selected from the group consisting of graphite and graphite compounds and a first organic solvent other than an amide-based solvent, a ketone-based solvent, and a sulfoxide-based solvent to a wet jet mill treatment; A method for producing an exfoliated graphite dispersion, comprising step 2 of mixing the product obtained in step 1 with at least one specific solvent selected from the group consisting of amide-based solvents, ketone-based solvents, and sulfoxide-based solvents to obtain an exfoliated graphite dispersion. [2] The method for producing an exfoliated graphite dispersion according to [1], wherein the graphite compound is used in the step 1. [3] The method for producing the exfoliated graphite dispersion according to [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 other than an amide-based solvent, a ketone-based solvent, and a sulfoxide-based solvent. [4] The method for producing an exfoliated graphite dispersion liquid 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 an exfoliated graphite dispersion liquid according to any one of [1] to [4], wherein the specific solvent is at least one solvent selected from the group consisting of N,N-dimethylformamide, N-methyl-2-pyrrolidone, N,N-dimethylacetamide, cyclohexanone, and dimethylsulfoxide. [6] The method for producing an exfoliated graphite dispersion liquid according to any one of [1] to [5], wherein the first organic solvent includes an ether-based solvent. [7] An exfoliated graphite dispersion liquid, comprising exfoliated graphite, a first organic solvent other than an amide solvent, a ketone solvent, and a sulfoxide solvent, and at least one specific solvent selected from the group consisting of an amide solvent, a ketone solvent, and a sulfoxide solvent, The content of the first organic solvent is 0.1 mass% or more and less than 50 mass% with respect to the total mass of the exfoliated graphite dispersion liquid, The content of the specific solvent is 50 mass% or more based on the total mass of the exfoliated graphite dispersion. [8] The exfoliated graphite dispersion liquid according to [7], wherein the specific solvent is at least one solvent selected from the group consisting of N,N-dimethylformamide, N-methyl-2-pyrrolidone, N,N-dimethylacetamide, cyclohexanone, and dimethylsulfoxide. [9] The exfoliated graphite dispersion liquid according to [7] or [8], wherein the first organic solvent is an ether-based solvent. Effect of the Invention

[0009] According to the present invention, a method for producing an exfoliated graphite dispersion liquid in which the dispersibility of exfoliated graphite is increased can be provided. Moreover, according to the present invention, an exfoliated graphite dispersion liquid 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 dispersion> The method for producing exfoliated graphite dispersion of the present invention includes a step 1 of subjecting a workpiece containing one selected from the group consisting of graphite and graphite compounds, and a first organic solvent other than an amide-based solvent, a ketone-based solvent, and a sulfoxide-based solvent, to a wet jet mill treatment to obtain exfoliated graphite. In addition, the method for producing exfoliated graphite dispersion of the present invention includes step 2 of mixing the product obtained in step 1 above with a specific solvent including one selected from the group consisting of amide-based solvents, ketone-based solvents, and sulfoxide-based solvents to obtain an exfoliated graphite dispersion.

[0015] The reason why the dispersibility of exfoliated graphite in the exfoliated graphite dispersion liquid is increased by the exfoliated graphite dispersion liquid manufacturing method of the present invention (hereinafter also referred to as "the present manufacturing 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 a first organic solvent that is not the specific 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, it is believed that the exfoliated graphite is likely to be dispersed in the specific solvent, and a highly dispersible exfoliated graphite dispersion liquid is obtained.

[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 workpiece containing one selected from the group consisting of graphite and graphite compounds and a first organic solvent other than amide-based solvents, ketone-based solvents, and sulfoxide-based solvents (hereinafter also referred to as "solvent X") is subjected to a wet jet mill treatment to obtain 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 a second organic solvent (solvent Y) described later. A 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 (solvent X)) In step 1, the material to be treated contains a first organic solvent (solvent X) other than amide-based solvents, ketone-based solvents, and sulfoxide-based solvents. The amide-based solvents, ketone-based solvents, and sulfoxide-based solvents will be described in detail later. Examples of the solvent X include hydrocarbon solvents, ether solvents, and ester solvents. Among them, ether solvents are preferred because they tend to exfoliate the graphite or graphite compounds contained in the material to be treated.

[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 solvent X may be used alone or in combination of two or more.

[0023] (Wet jet mill processing) In step 1, a material to be treated containing one selected from the group consisting of the graphite and graphite compounds and the solvent X 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 solvent X 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 Tokoh 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 product obtained in step 1 is mixed with at least one specific solvent selected from the group consisting of amide-based solvents, ketone-based solvents, and sulfoxide-based solvents. By the above step 2, an exfoliated graphite dispersion liquid 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 solvent selected from the group consisting of amide-based solvents, ketone-based solvents, and sulfoxide-based solvents.

[0039] 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).

[0040] [ka]

[0041] 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.

[0042] 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.

[0043] 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).

[0044] [ka]

[0045] 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.

[0046] 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.

[0047] 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).

[0048] [ka]

[0049] 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.

[0050] 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.

[0051] The specific solvent may be used alone or in combination of two or more.

[0052] The SP value (solubility parameter) of a particular solvent 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 specific solvent 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.

[0053] 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.

[0054] 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.

[0055] [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, in step 3, an alkali metal source and graphite are mixed in a second organic solvent (hereinafter also referred to as "solvent Y") 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.

[0056] (Second organic solvent (solvent Y)) The second organic solvent (solvent Y) used in step 3 is not particularly limited, but the first organic solvent (solvent X) 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.

[0057] (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.

[0058] (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.

[0059] (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.

[0060] (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 solvent Y, the alkali metal source, the graphite, and any optional components.

[0061] The order of mixing the components used in step 3 is not particularly limited, and for example, various components (alkali metal, graphite, etc.) may be added sequentially to solvent Y, or various components may be added simultaneously to solvent Y. Among these, it is preferable to add an aromatic hydrocarbon to solvent Y, and then add an alkali metal and graphite to solvent Y 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 solvent Y 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 solvent Y, an alkali metal source, graphite, and optional components. When two or more types of solvent Y are used in combination, the total mass of the solvent Y 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 % relative to the total mass of the solvent Y, and more preferably 1 to 5 mass %. 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] (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 solvent Y, 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.

[0066] [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.

[0067] [Step 5] In the present production method, the exfoliated graphite dispersion obtained by carrying out step 2 may be subjected to a coarse powder removal treatment. As the coarse powder removal treatment, a known treatment method (specifically, a classification treatment method) can be applied, and examples thereof include filtering, wet cyclone treatment, and centrifugal separation treatment.

[0068] <Exfoliated graphite dispersion> The exfoliated graphite dispersion of the present invention contains exfoliated graphite, a first organic solvent other than amide-based solvents, ketone-based solvents, and sulfoxide-based solvents, and at least one specific solvent selected from the group consisting of amide-based solvents, ketone-based solvents, and sulfoxide-based solvents. In addition, the content of the first organic solvent is 0.1 mass % or more and less than 50 mass % with respect to the total mass of the exfoliated graphite dispersion, and the content of the specific solvent is 50 mass % or more with respect to the total mass of the exfoliated graphite dispersion. The exfoliated graphite dispersion of the present invention is obtained by the method for producing an exfoliated graphite dispersion of the present invention.

[0069] Examples of the first organic solvent in the exfoliated graphite dispersion of the present invention include the same as the solvent X described above, and preferred embodiments are also the same as the solvent X. In addition, examples of the specific solvent in the exfoliated graphite dispersion of the present invention include the same as the specific solvent described above, and preferred embodiments are also the same as the specific solvent described above. Furthermore, the exfoliated graphite dispersion of the present invention may contain the components used in each step of the above-mentioned production method. For example, the exfoliated graphite dispersion of the present invention may contain an aromatic hydrocarbon.

[0070] In addition, regarding the exfoliated graphite dispersion of the present invention, the absorbance at a wavelength of 660 nm of the diluted solution obtained by diluting the exfoliated graphite dispersion of the present invention 50 times is preferably 0.25 or more, more preferably 0.30 or more, even more preferably 0.40 or more, and particularly preferably 0.50 or more. The upper limit of the absorbance is not particularly limited, but may be, for example, 50.0 or less, often 30.0 or less, and preferably 20.0 or less. When the absorbance at a wavelength of 660 nm is within the above range, it is considered that the dispersibility of exfoliated graphite is high in the exfoliated graphite dispersion liquid of the present invention.

[0071] In the present invention, the absorbance is measured using a spectrophotometer V-770 (manufactured by JASCO Corporation). First, the exfoliated graphite dispersion of the present invention is diluted 50 times with the specific solvent contained therein to obtain a diluted solution. Next, the absorbance at 660 nm is measured using the above spectrophotometer. If the absorbance is 1 or more, the diluted solution is further diluted so that the absorbance is 1 or less, and the absorbance is measured, and the absorbance of 1 or less is converted to the absorbance before dilution, and this is regarded as the absorbance of the exfoliated graphite dispersion of the present invention.

[0072] In the exfoliated graphite dispersion of the present invention, the content of exfoliated graphite is often 0.05% by mass or more, preferably 0.1% by mass or more, based on the total mass of the exfoliated graphite dispersion. Also, the content of exfoliated graphite is often 25% by mass or less, preferably 15% by mass or less, more preferably 10% by mass or less, based on the total mass of the exfoliated graphite dispersion.

[0073] The content of the first organic solvent other than the amide-based solvent, ketone-based solvent, and sulfoxide-based solvent in the exfoliated graphite dispersion of the present invention is 0.1% by mass or more, often 1% by mass or more, preferably 3% by mass or more, and more preferably 5% by mass or more, based on the total mass of the exfoliated graphite dispersion. The content of the first organic solvent is less than 50% by mass, preferably 30% by mass or less, and more preferably 15% by mass or less, based on the total mass of the exfoliated graphite dispersion. The content of the first organic solvent may be 10% by mass or less, based on the total mass of the exfoliated graphite dispersion.

[0074] The content of the specific solvent in the exfoliated graphite dispersion of the present invention is 50% by mass or more relative to the total mass of the exfoliated graphite dispersion, and is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more in terms of increasing the dispersion stability of exfoliated graphite. The content of the specific solvent is often 99.8% by mass or less relative to the total mass of the exfoliated graphite dispersion, preferably 99% by mass or less, and more preferably 95% by mass or less. The dispersion stability means that there is little change in dispersibility over time, and is evaluated by the method described later.

[0075] In the exfoliated graphite dispersion of the present invention, the mass ratio of the content of the specific solvent to the content of the first organic solvent is preferably 0.5 or more, more preferably 1 or more, even more preferably 2 or more, and particularly preferably 5 or more. The mass ratio may be 8 or more. In addition, the mass ratio is often 200 or less, preferably 100 or less, more preferably 50 or less, and even more preferably 15 or less.

[0076] <Applications of exfoliated graphite> The use of the exfoliated graphite contained in the exfoliated graphite dispersion 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.

[0077] 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 contained in the slurry (for example, the first organic solvent and the specific solvent) may be removed.The exfoliated graphite dispersion of the present invention has excellent dispersibility, so that exfoliated graphite is easily dispersed uniformly in each application, and desired properties are easily obtained. EXAMPLES

[0078] 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.

[0079] <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.

[0080] [Process 1] 200 mL of THF (tetrahydrofuran, which corresponds to the above-mentioned solvent X) was added to the mixture containing the graphite intercalation compound obtained by the above-mentioned procedure to obtain a material to be treated, which was then subjected to a wet jet mill treatment. The wet jet mill treatment was performed using a Joko Co., Ltd. "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.

[0081] [Process 2] 10 mL of the product (dispersion A) obtained in step 1 was mixed with 90 mL of NMP (N-methyl-2-pyrrolidone, a specific solvent) to obtain an exfoliated graphite dispersion.

[0082] [Step 5] After obtaining the exfoliated graphite dispersion liquid obtained in step 2, the exfoliated graphite dispersion liquid was centrifuged at 2000 rpm for 2 minutes using a centrifuge (Optima XE-90 manufactured by Beckman) to recover the supernatant. By the above treatment, coarse particles were removed to obtain exfoliated graphite dispersion liquid 1. In addition, if coarse particles were floating on the surface of the exfoliated graphite dispersion liquid after the above treatment, the intermediate liquid was collected.

[0083] [Measurement of absorbance] The obtained exfoliated graphite dispersion 1 was diluted 50 times with NMP to obtain a diluted solution, and the absorbance at 660 nm was measured using a spectrophotometer V-770 (JASCO Corporation). The measurement method was as described above.

[0084] [Dispersion stability evaluation] The exfoliated graphite dispersion 1 was allowed to stand for 7 days, and then the absorbance was measured in the same manner as above. The standing was performed in an environment of 20°C.

[0085] <Examples 2 to 10> In the procedure for obtaining exfoliated graphite dispersion 1 of Example 1 above, the dilution ratio and the type of specific solvent used in step 2 were changed as shown in the table below, but exfoliated graphite dispersions 2 to 10 were obtained in the same manner as Example 1. In addition, the absorbance was measured in the same manner as in Example 1. In addition, for Examples 2 to 4, the dispersion stability was evaluated in the same manner as in Example 1.

[0086] <Comparative Examples 1 to 7> Exfoliated graphite dispersions C1 to C7 were obtained in the same manner as in Example 1, except that in the procedure for obtaining exfoliated graphite dispersion 1 in Example 1 above, the specific solvent used in step 2 was replaced with the solvent shown in the table below.

[0087] <Example 21> [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.

[0088] [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.

[0089] [Process 2] 10 mL of the product (dispersion B) obtained in step 1 and 90 mL of NMP (corresponding to a specific solvent) were mixed to obtain exfoliated graphite dispersion 21.

[0090] [Measurement of absorbance] The absorbance of exfoliated graphite dispersion 21 of Example 21 was measured in the same manner as in exfoliated graphite dispersion 1 of Example 1.

[0091] <Examples 22 to 25> In the procedure for obtaining exfoliated graphite dispersion 21 of Example 21 above, except that the dilution ratio and the type of specific solvent used in step 2 were changed as shown in the table below, exfoliated graphite dispersions 22 to 25 were obtained in the same manner as Example 21. In addition, the absorbance was measured in the same manner as in Example 21.

[0092] <Comparative Examples 21 and 22> In the procedure for obtaining exfoliated graphite dispersion 21 of Example 21 above, exfoliated graphite dispersions C21 and C22 were obtained in the same manner as in Example 1, except that the specific solvent used in step 2 was replaced with the solvent shown in the table below.

[0093] <Result> Tables 1 and 2 show the type and dilution ratio of the solvent used in step 2 of each Example and Comparative Example, as well as the results of absorbance measurements. In Tables 1 and 2, the abbreviations in the column "Solvent used in step 2" represent the following solvents. ·MNP: N-methyl-2-pyrrolidone DMF: N,N-Dimethylformamide ·DMAc: N,N-Dimethylacetamide DMSO: Dimethyl sulfoxide MEK: Methyl ethyl ketone THF: Tetrahydrofuran MeOH: Methanol EtOH: Ethanol IPA: Isopropyl alcohol nBtOH: n-butanol In addition, in the "Dilution ratio" column in Tables 1 and 2, for example, the notation "1:9" indicates that 1 part of the product obtained in step 1 was mixed with 9 parts of the specific solvent in step 2 by volume.

[0094] [Table 1]

[0095] [Table 2]

[0096] From the results shown in Tables 1 and 2, it was confirmed that in each Example in which the above-mentioned specific solvent was used as the solvent used in step 2, the dispersibility of exfoliated graphite in the obtained exfoliated graphite dispersion liquid 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 dispersibility of exfoliated graphite was not higher than that of each Example. A comparison of Examples 1 and 5 to 8 with Examples 9 and 10 confirmed that the dispersibility of exfoliated graphite is higher when the specific solvent used in step 2 is at least one solvent selected from the group consisting of N,N-dimethylformamide, N-methyl-2-pyrrolidone, N,N-dimethylacetamide, cyclohexanone, and dimethyl sulfoxide.

[0097] When the exfoliated graphite in the exfoliated graphite dispersion was collected and analyzed by Raman spectroscopy, it was found that the exfoliated graphite was composed of an average of 2 to 3 graphene layers. [Explanation of symbols]

[0098] 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 obtaining exfoliated graphite by subjecting a workpiece containing one selected from the group consisting of graphite and graphite compounds and a first organic solvent other than an amide-based solvent, a ketone-based solvent, and a sulfoxide-based solvent to a wet jet mill treatment; and a step 2 of mixing the product obtained in the step 1 with at least one specific solvent selected from the group consisting of amide-based solvents, ketone-based solvents, and sulfoxide-based solvents to obtain an exfoliated graphite dispersion liquid, A method for producing an exfoliated graphite dispersion, wherein the first organic solvent is selected from the group consisting of hydrocarbon-based solvents, ether-based solvents, and ester-based solvents.

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

3. 3. The method for producing an exfoliated graphite dispersion according to claim 2, wherein the graphite compound is a graphite compound in which an alkali metal source and graphite are mixed in a second organic solvent other than an amide-based solvent, a ketone-based solvent, and a sulfoxide-based solvent, and the alkali metal is intercalated between graphene layers in the graphite.

4. The method for producing an exfoliated graphite dispersion 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 an exfoliated graphite dispersion according to any one of claims 1 to 3, wherein the specific solvent is at least one solvent selected from the group consisting of N,N-dimethylformamide, N-methyl-2-pyrrolidone, N,N-dimethylacetamide, cyclohexanone, and dimethyl sulfoxide.

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

7. An exfoliated graphite dispersion liquid comprising exfoliated graphite, a first organic solvent other than an amide-based solvent, a ketone-based solvent, and a sulfoxide-based solvent, and at least one specific solvent selected from the group consisting of an amide-based solvent, a ketone-based solvent, and a sulfoxide-based solvent, the first organic solvent comprises a solvent selected from the group consisting of a hydrocarbon solvent, an ether solvent, and an ester solvent; The content of the first organic solvent is 0.1 mass% or more and less than 50 mass% with respect to the total mass of the exfoliated graphite dispersion liquid, The content of the specific solvent is 50 mass% or more based on the total mass of the exfoliated graphite dispersion.

8. The specific solvent is at least one solvent selected from the group consisting of N,N-dimethylformamide, N-methyl-2-pyrrolidone, N,N-dimethylacetamide, cyclohexanone, and dimethylsulfoxide. The exfoliated graphite dispersion according to claim 7.

9. The exfoliated graphite dispersion according to claim 7 or 8, wherein the first organic solvent includes an ether-based solvent.

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