Method for manufacturing flaked graphite dispersion, and flaked graphite dispersion

Abstract

To provide a method for manufacturing a flaked graphite dispersion which is intended to enhance dispersibility of flaked graphite.SOLUTION: A method for manufacturing a flaked graphite dispersion includes: a step 1 of obtaining flaked graphite by subjecting a material to be processed, which includes one kind selected from the group consisting of graphite and a graphite compound, and a first organic solvent except for an amide-based solvent, a ketone-based solvent, and a sulfoxide-based solvent, to wet jet mill processing; and a step 2 of obtaining a flaked graphite dispersion by mixing a product obtained in the step 1 and at least one kind of specific solvent selected from the group consisting of the amide-based solvent, the ketone-based solvent, and the sulfoxide-based solvent.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

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

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

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] When the present inventors produced a flaked graphite dispersion using the production method described in Patent Document 1, they found that it was difficult to increase the dispersibility of the flaked graphite in the obtained flaked graphite dispersion.

[0006] Therefore, an object of the present invention is to provide a method for producing a dispersed graphite nanoplatelet dispersion with high dispersibility of graphite nanoplatelets. Another object of the present invention is to provide a dispersed graphite nanoplatelet dispersion.

Means for Solving the Problems

[0007] As a result of intensive studies to solve 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 an object to be treated containing one selected from the group consisting of graphite and graphite compounds and a first organic solvent other than amide solvents, ketone solvents, and sulfoxide solvents to wet jet mill treatment to obtain exfoliated graphite; A method for producing a dispersed graphite nanoplatelet dispersion, comprising: a step 2 of mixing the product obtained in the above step 1 with at least one specific solvent selected from the group consisting of amide solvents, ketone solvents, and sulfoxide solvents to obtain a dispersed graphite nanoplatelet dispersion. 〔2〕 The method for producing a dispersed graphite nanoplatelet dispersion according to 〔1〕, wherein the graphite compound is used in the above step 1. 〔3〕 The method for producing a dispersed graphite nanoplatelet dispersion according to 〔2〕, wherein the graphite compound is a graphite compound in which an alkali metal source and graphite are mixed in a second organic solvent other than amide solvents, ketone solvents, and sulfoxide solvents, and the alkali metal is intercalated between graphene layers in the graphite. 〔4〕 The method for producing a dispersed graphite nanoplatelet dispersion according to any one of 〔1〕 to 〔3〕, wherein in the above step 2, the mass ratio of the specific solvent to the product is 0.5 to 100. 〔5〕 The method for producing a dispersed graphite nanoplatelet dispersion 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 dimethyl sulfoxide. 〔6〕 The method for producing a dispersed graphite nanoplatelet dispersion according to any one of 〔1〕 to 〔5〕, wherein the first organic solvent contains an ether-based solvent. 〔7〕A graphene nanoplatelet dispersion comprising exfoliated graphene, 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, wherein the content of the first organic solvent is 0.1% by mass or more and less than 50% by mass based on the total mass of the graphene nanoplatelet dispersion, and the content of the specific solvent is 50% by mass or more based on the total mass of the graphene nanoplatelet dispersion. 〔8〕The graphene nanoplatelet dispersion 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 dimethyl sulfoxide. 〔9〕The graphene nanoplatelet dispersion according to 〔7〕 or 〔8〕, wherein the first organic solvent is an ether-based solvent.

Advantages of the Invention

[0009] According to the present invention, a method for producing a graphene nanoplatelet dispersion with high dispersibility of exfoliated graphene can be provided. Also, according to the present invention, a graphene nanoplatelet dispersion can be provided.

Brief Description of the Drawings

[0010]

Figure 1

Embodiments for Carrying Out the Invention

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

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

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

[0014] <Method for producing exfoliated graphite dispersion> The method for producing an exfoliated graphite dispersion of the present invention includes a step 1 of subjecting an object to be treated containing one selected from the group consisting of graphite and graphite compounds and a first organic solvent other than an amide-based solvent, a ketone-based solvent, and a sulfoxide-based solvent to wet jet mill treatment to obtain exfoliated graphite. Further, the method for producing an exfoliated graphite dispersion of the present invention includes a step 2 of mixing the product obtained in the above step 1 with a specific solvent containing one selected from the group consisting of an amide-based solvent, a ketone-based solvent, and a sulfoxide-based solvent to obtain an exfoliated graphite dispersion.

[0015] The reason why the dispersibility of exfoliated graphite in the exfoliated graphite dispersion is increased by the method for producing an exfoliated graphite dispersion of the present invention (hereinafter, also referred to as "this production method") is not necessarily clear, but the present inventors presume as follows. In the above step 1, when wet jet mill treatment is performed in a first organic solvent that is not the above specific solvent, graphite or a graphite compound is easily exfoliated. Further, in the above step 2, when the obtained product and the above specific solvent are mixed, it is considered that the exfoliated graphite is easily dispersed in the specific solvent, and an exfoliated graphite dispersion with high dispersibility can be obtained.

[0016] Hereinafter, this production method will be described. In addition, this manufacturing method may have steps other than Step 1 and Step 2 described below.

[0017] [Step 1] In Step 1, a wet jet mill treatment is performed on an object to be treated 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 (hereinafter also referred to as "solvent X") to obtain exfoliated graphite. Hereinafter, Step 1 will 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 fibers. Among them, natural graphite is preferable.

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

[0020] (The first organic solvent (solvent X)) In step 1, the object to be treated contains a first organic solvent (solvent X) other than an amide-based solvent, a ketone-based solvent, and a sulfoxide-based solvent. The amide-based solvent, the ketone-based solvent, and the sulfoxide-based solvent will be described in detail later. Examples of the solvent X include a hydrocarbon-based solvent, an ether-based solvent, and an ester-based solvent. Among them, an ether-based solvent is preferable in that the graphite or graphite compound contained in the object to be treated is more easily exfoliated.

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

[0022] Only one kind of the solvent X may be used, or two or more kinds may be used.

[0023] (Wet jet mill treatment) In step 1, wet jet mill treatment is performed on the object to be treated containing one kind selected from the group consisting of the above-mentioned graphite and graphite compound and the above-mentioned solvent X. Hereinafter, the object to be treated and the wet jet mill treatment will be described.

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

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

[0026] From the viewpoint that the object to be treated can be processed by a wet jet mill, the viscosity is preferably 1 to 20,000 mPa·s. As a method for measuring the viscosity, a known method can be used, for example, the method of JIS Z 8803:2011.

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

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

[0029] Wet jet mill treatment is advantageous in that it can efficiently obtain flaky graphite by applying a shearing force to the object to be treated without pulverizing graphite or graphite compounds more than necessary. The wet jet mill treatment is not limited as long as it can cause a slurry containing a solvent and powder to flow at high speed, and as a result, the powder can be pulverized and / or crushed. For example, methods include causing a fluid flowing at high speed to collide with a fluid collision part substantially perpendicular to the flow direction of the fluid, causing a fluid flowing at high speed to flow through a constriction, causing a plurality of fluids flowing at high speed to collide head-on, generating a turbulent flow and causing the fluid to collide with the wall surface of a pipe or the like through which the fluid conducts, and applying a shearing force to the fluid by a cavitation jet generated by reduced pressure or the like. The wet jet mill treatment may combine these methods. Among them, the method of causing a plurality of fluids flowing at high speed to collide head-on is preferred.

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

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

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

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

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

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

[0036] The wet jet mill treatment is also preferably carried out in an inert gas atmosphere inside the apparatus. Examples of the inert gas include nitrogen gas and argon gas. In addition, since heat is generated during compression and the like in the wet jet mill treatment, it is also preferable to carry out the treatment while cooling. As the cooling method, a known method can be used. For example, a method of directly or indirectly bringing a refrigerant into contact with the heat generating part for heat exchange can be mentioned.

[0037] [Step 2] In Step 2, the product obtained in Step 1 above is mixed with at least one specific solvent selected from the group consisting of an amide-based solvent, a ketone-based solvent, and a sulfoxide-based solvent. By the above Step 2, a flake graphite dispersion is obtained. Hereinafter, Step 2 will 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 an amide-based solvent, a ketone-based solvent, and a sulfoxide-based solvent.

[0039] The amide-based solvent refers to a solvent composed of a compound having an amide structure in the molecule. Specifically, the amide-based solvent refers to a solvent composed of a compound represented by the following formula (a).

[0040] [Chemical Formula]

[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 carbon number of the alkyl group portion of the alkyl group which may have a substituent represented by R1, R2, and R3 is preferably 1 to 8, more preferably 1 to 3. The alkyl group which may have substituents represented by R1, R2 and R3 is preferably an alkyl group having no substituent. Further, R2 and R3 each preferably represent an alkyl group which may have a substituent (more preferably an alkyl group having no substituent). That is, the amide solvent is preferably a solvent composed of a tertiary amide compound. Also, an embodiment in which R1 represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms and no substituent, and R2 and R3 are alkyl groups having 1 to 3 carbon atoms and no substituent is also preferable.

[0042] Examples of the amide solvent include N,N-dimethylformamide (DMF), N,N-diethylformamide (DEF), N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide (DMAc), tetramethylurea, and 1,3-dimethyl-2-imidazolidinone. Among them, as the amide solvent, N,N-dimethylformamide, N-methyl-2-pyrrolidone, or N,N-dimethylacetamide is preferable.

[0043] The ketone solvent refers to a solvent composed of a compound having a carbonyl group (-CO-) in the molecule and a carbon atom bonded to the carbon atom of the carbonyl group. That is, a compound having a ketone structure as an ester structure (-COO-), an amide structure, etc. is not included in the ketone solvent. Specifically, the ketone solvent refers to a solvent composed of a compound represented by the following formula (b).

[0044]

Chemical formula

[0045] In formula (b), R4 and R5 represent an alkyl group which may have a substituent. The alkyl group which may have substituents represented by R4 and R5 may be bonded to each other to form a ring. The number of carbon atoms in the alkyl group portion of the alkyl group which may have substituents represented by R4 and R5 is preferably from 1 to 8, more preferably from 1 to 3. Also, the alkyl group which may have substituents represented by R4 and R5 is preferably each an alkyl group having no substituent.

[0046] Examples of the ketone solvents include acetone, methyl ethyl ketone (MEK), diethyl ketone, methyl isobutyl ketone (MIBK), diisobutyl ketone (DIBK), cyclopentanone, and cyclohexanone. Among them, cyclohexanone is preferred as the ketone solvent.

[0047] The sulfoxide solvent refers to a solvent composed of a compound having a sulfinyl group (-SO-) in the molecule and a carbon atom bonded to the sulfur atom of the sulfinyl group. Specifically, the sulfoxide solvent refers to a solvent composed of a compound represented by the following formula (c).

[0048]

Chemical formula

[0049] In formula (c), R6 and R7 represent an alkyl group which may have a substituent. The alkyl groups which may have substituents represented by R6 and R7 may be bonded to each other to form a ring. The number of carbon atoms in the alkyl group portion of the alkyl group which may have substituents represented by R6 and R7 is preferably from 1 to 8, more preferably from 1 to 3. Also, the alkyl group which may have substituents represented by R6 and R7 is preferably each an alkyl group having no substituent.

[0050] Examples of the sulfoxide solvents include dimethyl sulfoxide, di-n-butyl sulfoxide, tert-butyl methyl sulfoxide, and tetramethylene sulfoxide. Among these, as the sulfoxide-based solvent, dimethyl sulfoxide is preferable.

[0051] As for the specific solvent, only one kind may be used, or two or more kinds may be used.

[0052] The SP value (solubility parameter) of the specific solvent is preferably 9.0 (cal / cm 3 ) 1 / 2 or more, more preferably 9.2 (cal / cm 3 ) 1 / 2 or more, and even more preferably 9.5 (cal / cm 3 ) 1 / 2 or more. Also, the SP value of the specific solvent is preferably 18.0 (cal / cm 3 ) 1 / 2 or less, more preferably 15.0 (cal / cm 3 ) 1 / 2 or less, and even more preferably 13.0 (cal / cm 3 ) 1 / 2 or less. Incidentally, the SP value is a value also called the Hildebrand parameter, and literature values can be adopted.

[0053] In Step 2, the product obtained in Step 1 and the above specific solvent are mixed. The mixing ratio of the product and the specific solvent is not particularly limited, but the mass ratio of the specific solvent to the product is preferably 0.5 or more, more preferably 1 or more, even more preferably 2 or more, and particularly preferably 5 or more. Also, the above ratio is often 200 or less, preferably 100 or less, more preferably 50 or less, and even more preferably 15 or less.

[0054] The mixing method in Step 2 is not particularly limited, and known mixing methods can be applied. For example, methods of stirring the solution with a rotary blade, generating convection with a pump, and vibrating the container in which the object to be treated is housed can be mentioned. Specifically, a mixer, a magnetic stirrer, a mechanical stirrer, and a shaker can be mentioned. It is also preferable that the mixing in Step 2 is carried out in an inert atmosphere.

[0055] [Process 3] When the object to be processed in Process 1 contains a graphite compound, this manufacturing method may have Process 3 for obtaining a graphite compound (graphite intercalation compound) before Process 1. Specifically, in Process 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 addition, in Process 3, components other than the above components may be added. Hereinafter, Process 3 will be described.

[0056] (Second organic solvent (solvent Y)) The second organic solvent (solvent Y) used in Process 3 is not particularly limited, but the first organic solvent (solvent X) used in the above Process 1 is preferably mentioned. Among them, as solvent Y, an ether-based solvent is preferable. Examples and preferred examples of the ether-based solvent are as described above in the part of Process 1.

[0057] (Alkali metal source) The alkali metal source used in Process 3 is not particularly limited as long as it contains an alkali metal, and examples include a simple alkali metal (zero-valent alkali metal) and a salt containing an alkali metal. Examples of the alkali metal contained in the alkali metal source include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr). As the alkali metal, Li, Na, or K is preferable, Li or K is more preferable, and Li is even more preferable. As the alkali metal source, lithium metal, potassium metal, or sodium metal is preferable, lithium metal or sodium metal is more preferable, and lithium metal is even more preferable. Only one type of alkali metal source may be used, or two or more types may be used.

[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 laminated. Examples and preferred examples of graphite are as described above in the part of Step 1.

[0059] (Aromatic hydrocarbon) In Step 3, it is preferable to mix an alkali metal source, graphite, and an aromatic hydrocarbon together. By mixing an aromatic hydrocarbon together with the above components, the dissolution of the alkali metal in the alkali metal source into the solvent is promoted, and due to the difference in the electron affinity with graphite, the alkali metal can be easily intercalated into the graphite. Examples of the aromatic hydrocarbon include benzene, naphthalene, phenanthrene, anthracene, and pyrene. Among them, naphthalene is preferable.

[0060] (Mixing method and conditions) The mixing method of various components in Step 3 is not particularly limited as long as the solvent Y, the alkali metal source, graphite, and optional components can be mixed.

[0061] The mixing order of the components used in Step 3 is not particularly limited. For example, various components (such as alkali metal, graphite, etc.) may be sequentially added to the solvent Y, or various components may be added to the solvent Y simultaneously. Among them, it is preferable to add the aromatic hydrocarbon to the solvent Y first, and then add the alkali metal and graphite to the solvent Y in this order. The usage amounts of various components in Step 3 are not particularly limited and can be adjusted as appropriate. The usage amount of the solvent Y is preferably 50 to 99.9% by mass, more preferably 60 to 99% by mass, and even more preferably 70 to 95% by mass with respect to the total amount of the components used in Step 3. Note that the components used in Step 3 include the solvent Y, the alkali metal source, graphite, and optional components. When two or more types of the solvent Y are mixed and used, it is preferable that the total mass of the solvent Y is within the above range. The usage amount of the alkali metal source is not particularly limited, and is preferably 2.5 to 300% by mass, more preferably 4 to 150% by mass, based on the usage amount of graphite. The usage amount of graphite is not particularly limited, and is preferably 0.1 to 10% by mass, more preferably 1 to 5% by mass, based on the total mass of the solvent Y. The usage amount of the aromatic hydrocarbon is not particularly limited, and is preferably 50 to 500% by mass, more preferably 100 to 500% by mass, based on the usage amount of graphite.

[0062] Examples of the method for mixing the above components include known methods. For example, a method of stirring the solution with a rotary blade, a method of generating convection with a pump, and a method of vibrating a container containing the object to be treated can be mentioned. Specifically, a magnetic stirrer, a mechanical stirrer, and a shaker can be mentioned.

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

[0064] The atmosphere for carrying out Step 3 is not particularly limited, but Step 3 is preferably carried out in an inert gas atmosphere. Examples of the inert gas include nitrogen gas and argon gas. Also, the atmosphere for carrying out Step 3 preferably has a low water vapor content. The dew point of the atmosphere for carrying out Step 3 is preferably 0°C or lower, more preferably -20°C or lower, even more preferably -40°C or lower, and particularly preferably -50°C or lower. The lower limit of the dew point of the atmosphere for carrying out Step 3 is not particularly limited, but is usually -100°C or higher.

[0065] (Graphite intercalation compound) In Step 3, a graphite intercalation compound in which an alkali metal is intercalated between graphene layers in graphite is produced. The graphite intercalation compound may be a binary system of an alkali metal and graphene, may be a ternary system of an alkali metal, solvent Y, and graphene, or may be a quaternary system or higher including additives in addition to the above ternary system. For example, the alkali metal may form a complex with THF as a solvent, and the complex may be intercalated. The formation of the graphite intercalation compound can be confirmed by X-ray diffraction. Specifically, it can be confirmed by the disappearance of diffraction peaks derived from the structure of graphite and the appearance of diffraction peaks corresponding to the elongation of the distance between graphene layers due to intercalation.

[0066] [Step 4] When the object to be processed in Step 1 contains a graphite compound, this 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 for the above recovery is not particularly limited, and examples include known methods. For example, methods of performing solid-liquid separation and methods of vaporizing the liquid from the solid-liquid mixture can be mentioned. Specifically, filtration (including pressure filtration and vacuum filtration), decantation, centrifugation, natural drying, vacuum drying, freeze drying, and spray drying can be mentioned. Among them, decantation or filtration is preferable. Note that decantation refers to a method of allowing a solid-liquid mixture to stand still, removing the supernatant liquid portion, and recovering the solid content. One of the above methods may be carried out, or they may be carried out in combination. Further, in the above recovery, for example, it may not be completely solid-liquid separated, and it may contain a graphite compound and a solvent component (for example, solvent Y).

[0067] [Step 5] This production method may perform a coarse powder removal treatment on the exfoliated graphite dispersion obtained by performing Step 2. As the coarse powder removal treatment, known treatment methods (specifically, classification treatment methods) can be applied. For example, filtering, wet cyclone treatment, centrifugal separation treatment, and the like can be mentioned.

[0068] <Flaked graphite dispersion> The flaked graphite dispersion of the present invention contains flaked 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. In addition, the content of the first organic solvent is 0.1% by mass or more and less than 50% by mass with respect to the total mass of the flaked graphite dispersion, and the content of the specific solvent is 50% by mass or more with respect to the total mass of the flaked graphite dispersion. The flaked graphite dispersion of the present invention is obtained by the method for producing the flaked graphite dispersion of the present invention.

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

[0070] Also, for the flaked graphite dispersion of the present invention, the absorbance at a wavelength of 660 nm of a dilution obtained by diluting the flaked graphite dispersion of the present invention 50-fold is preferably 0.25 or more, more preferably 0.30 or more, still more preferably 0.40 or more, and particularly preferably 0.50 or more. The upper limit of the above absorbance is not particularly limited, and for example, 50.0 or less can be mentioned, 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 the flaked graphite in the flaked graphite dispersion of the present invention is high.

[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-fold using the specific solvent contained therein to obtain a diluted solution. Next, using the above spectrophotometer, the absorbance at 660 nm is measured. When the absorbance is 1 or more, the diluted solution is further diluted so that the absorbance becomes 1 or less, and the absorbance of 1 or less is converted to before dilution to obtain 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. Further, 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, more preferably 5% by mass or more, based on the total mass of the exfoliated graphite dispersion. Further, the content of the first organic solvent is less than 50% by mass, preferably 30% by mass or less, more preferably 15% by mass or less, based on the total mass of the exfoliated graphite dispersion. Further, 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, preferably 70% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, based on the total mass of the exfoliated graphite dispersion, in terms of higher dispersion stability of exfoliated graphite. Further, the content of the specific solvent is often 99.8% by mass or less, preferably 99% by mass or less, more preferably 95% by mass or less, based on the total mass of the exfoliated graphite dispersion. Note that the dispersion stability means that the change in dispersibility over time is small, and it is evaluated by the method described in the following section.

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

[0077] When using exfoliated graphite for the above uses, for example, a slurry containing the exfoliated graphite dispersion of the present invention and other components according to the above respective uses is prepared, the slurry is applied in a desired form, and the solvent components (for example, the first 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, in each use, exfoliated graphite is easily uniformly dispersed, and desired properties are easily obtained.

Examples

[0078] Hereinafter, the present invention will be described in more detail based on examples. The materials, usage amounts, ratios, treatment details, apparatuses, treatment procedures, etc. shown in the following examples can be appropriately changed as long as they do not depart from the spirit of the present invention. Therefore, the scope of the present invention should not be construed restrictively by the examples shown below.

[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 therein. 0.5 g of metallic lithium (purity 99.5%) was added to this solution, and the solution was stirred to dissolve the metallic lithium. 2.5 g of graphite particles (manufactured by Sigma-Aldrich, 808091 - 2.5KG, average particle size: 150 μm) was added to the lithium dissolution solution, and the mixture was stirred at 25°C for 24 hours to obtain a mixture containing a graphite intercalation compound. When the mixture containing the obtained graphite intercalation compound was dried and subjected to XRD measurement, peaks were confirmed at 2θ = 6.5°, 13°, 21°, 28°, 36°, 43°, and 51°. These corresponded to the (001), (002), (003), (004), (005), (006), and (007) of stage-1 of A-phase Li-THF-GIC. This result corresponds to a structure in which a complex in which THF molecules are coordinated to lithium is intercalated into the graphite layer, indicating that the graphite interlayer is expanded to about 1.10 nm.

[0080] [Step 1] 200 mL of THF (tetrahydrofuran, corresponding to the above solvent X) was added to the mixture containing the graphite intercalation compound obtained by the above procedure to obtain an object to be treated, and wet jet mill treatment was performed. The wet jet mill treatment was carried out using "NAGS20 (AC200V specification)" manufactured by Tokuyama Corporation. The conditions of the apparatus were as follows. · Normal nozzle · Nozzle diameter: φ0.15 mm · Chiller set temperature: 0°C · Liquid delivery pressure: 200 MPa Under the conditions of the above device, wet jet mill treatment was performed 5 passes to obtain a dispersion liquid A of flaked graphite.

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

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

[0083] [Measurement of absorbance] The obtained flaked graphite dispersion liquid 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 (manufactured by JASCO Corporation). The measurement method was as described above.

[0084] [Evaluation of dispersion stability] After the above flaked graphite dispersion liquid 1 was allowed to stand for 7 days, the absorbance was measured in the same procedure as above. The above standing was performed in an environment at 20 °C.

[0085] <Examples 2 to 10> In the procedure for obtaining the flaked graphite dispersion liquid 1 of Example 1 above, except that the dilution ratio and the type of the specific solvent used in Step 2 were changed as shown in the table in the following stage, flaked graphite dispersion liquids 2 to 10 were obtained in the same manner as in Example 1. Also, the absorbance was measured in the same method as in Example 1. For Examples 2 to 4, the dispersion stability was evaluated in the same method as in Example 1.

[0086] <Comparative Examples 1 to 7> In the procedure for obtaining the exfoliated graphite dispersion 1 of Example 1 above, exfoliated graphite dispersions C1 to C7 were obtained in the same manner as in Example 1, except that the solvents shown in the table in the subsequent stage were used instead of the specific solvent used in Step 2.

[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 therein. 0.5 g of metallic lithium (purity 99.5%) was added to this solution, and the solution was stirred to dissolve the metallic lithium. 2.5 g of graphite particles (manufactured by Nippon Graphite, particle size: 500 μm to 1 mm) was added to the lithium dissolution solution, and the mixture was stirred at 25°C for 48 hours to obtain a mixture containing a graphite intercalation compound. This mixture was allowed to stand for 120 hours, and the supernatant was removed by solid-liquid separation to obtain a graphite intercalation compound (Step 4). When XRD measurement of the obtained graphite intercalation compound was performed, peaks were confirmed at 2θ = 6.5°, 13°, 21°, 28°, 36°, 43° and 51°, which corresponded to the (001), (002), (003), (004), (005), (006) and (007) of stage-1 of A-phase Li-THF-GIC. This result corresponds to a structure in which a complex in which THF molecules are coordinated to lithium is intercalated into the graphite layer, indicating that the graphite layer spacing is expanded to about 1.10 nm.

[0088] [Step 1] 22 g of the obtained graphite intercalation compound and 88 mL of THF were mixed and subjected to wet jet mill treatment. The wet jet mill treatment was carried out using "NAGS20 (AC200V specification)" manufactured by Tokon Co., Ltd. The conditions of the apparatus were as follows. · Straight nozzle (model number: J01502S) · Nozzle diameter: φ0.15 mm · Chiller set temperature: 0°C · Spit-out speed: 38.5×10 4 ±1×10 4 · Liquid feeding pressure: 120 MPa Under the conditions of the above device, wet jet mill treatment was performed 22 passes to obtain a dispersion liquid B of exfoliated graphite.

[0089] [Step 2] 10 mL of the product (dispersion liquid B) obtained in Step 1 was mixed with 90 mL of NMP (corresponding to a specific solvent) to obtain a dispersion liquid 21 of exfoliated graphite.

[0090] [Measurement of absorbance] In the same procedure as the dispersion liquid 1 of exfoliated graphite in Example 1, the absorbance of the dispersion liquid 21 of exfoliated graphite in Example 21 was measured.

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

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

[0093] [Results] The types and dilution ratios of the solvents used in Step 2 of each example and each comparative example, and the measurement results of the absorbance are shown in Tables 1 and 2. In Tables 1 and 2, the abbreviations in the column of "solvent used in Step 2" represent the following solvents, respectively. · 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 Tables 1 and 2, in the "dilution ratio" column, for example, the notation "1:9" indicates that in Step 2, the product 1 obtained in Step 1 was mixed with a specific solvent or the like at a volume ratio such that the value became 9.

[0094]

Table 1

[0095]

Table 2

[0096] From the results shown in Tables 1 and 2, it was confirmed that in each example using the above-mentioned specific solvent as the solvent used in Step 2, the dispersibility of the exfoliated graphite in the obtained exfoliated graphite dispersion was high. On the other hand, in the comparative examples where the specific solvent was not used as the solvent used in Step 2, the dispersibility of the exfoliated graphite was not higher than that in each example. From the comparison between Examples 1 and 5 to 8 and Examples 9 and 10, it was confirmed that 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, the dispersibility of the exfoliated graphite becomes higher.

[0097] When the exfoliated graphite in the exfoliated graphite dispersion was recovered and analyzed by Raman spectroscopy, the exfoliated graphite was composed of graphene layers with an average of 2 to 3 layers.

Explanation of symbols

[0098] 10 Dispersion unit 12 Introduction-side disk 12A First through-hole 12B Second through-hole 14 Intermediate disk 14A Third through-hole 16 Discharge-side disk 16A Fourth through-hole 16B Fifth through-hole 18 Introduction-side grooved passage 20 Discharge-side grooved passage C1 Central axis

Claims

1. Step 1 of subjecting an object to be treated, which contains one selected from the group consisting of graphite and graphite compounds and a first organic solvent other than amide solvents, ketone solvents, and sulfoxide solvents, to wet jet milling treatment to obtain exfoliated graphite; 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 solvents, ketone solvents, and sulfoxide solvents to obtain an exfoliated graphite dispersion.

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

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 amide solvents, ketone solvents, and sulfoxide solvents, 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 Step 2, the 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 according to any one of Claims 1 to 3, wherein the first organic solvent is an ether solvent.

7. An exfoliated graphite dispersion containing exfoliated graphite, a first organic solvent other than amide solvents, ketone solvents, and sulfoxide solvents, and at least one specific solvent selected from the group consisting of amide solvents, ketone solvents, and sulfoxide solvents, wherein: The content of the first organic solvent is 0.1% by mass or more and less than 50% by mass based on the total mass of the exfoliated graphite dispersion; The content of the specific solvent is 50% by mass or more based on the total mass of the exfoliated graphite dispersion.

8. The thin-film graphite dispersion liquid according to claim 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 dimethyl sulfoxide.

9. The thin-film graphite dispersion liquid according to claim 7 or 8, wherein the first organic solvent contains an ether-based solvent.

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