Two-dimensional particles, conductive film, conductive paste, and method for producing two-dimensional particles

Abstract

A purpose of the present disclosure is to provide a two-dimensional particle able to provide an electrically conductive film that can maintain high electrical conductivity even under conditions of high humidity. Another purpose of the present invention is to provide a method for producing said two-dimensional particle.　This two-dimensional particle has one or more layers and contains a metal cation. Said layer contains: a layer main body represented by formula: MmXn (in the formula, M is at least one type of group 3, 4, 5, 6 or 7 metal, X is a carbon atom, a nitrogen atom or a combination of these, the value of n is 1-4, and the value of m is greater than the value of n and is 5 or less); and a modification or a terminal T that is present at the surface of the layer main body (T is at least one type selected from the group consisting of a hydroxyl group, a fluorine atom, a chlorine atom, an oxygen atom and a hydrogen atom). Either the modification or terminal T contains a chlorine atom or M in the layer binds to at least one type selected from the group consisting of PO4 3-, I and SO4 2-. The metal cation includes at least one type of cation of a metal in the 3rd to 5th periods of the periodic table. The content of Li is less than 0.002 mass%.

Description

[Technical Field]

[0001] The present invention relates to two-dimensional particles, a conductive film, a conductive paste, and a method for producing the two-dimensional particles. [Background technology]

[0002] In recent years, MXene has attracted attention as a novel electrically conductive material. MXene is a type of so-called two-dimensional material, and as described below, it is a layered material having the form of one or more layers. Generally, MXene has the form of particles of such layered materials (which may include powders, flakes, nanosheets, etc.).

[0003] Currently, various research efforts are being conducted to apply MXene to various electrical devices. To achieve these applications, it is necessary to further improve the electrical conductivity of materials containing MXene. As part of this research, a delamination process for MXene obtained as a multilayered material is being investigated.

[0004] Non-Patent Document 1 discloses that a delamination treatment of multilayer MXene was carried out by handshaking using TMAOH (tetramethylammonium hydroxide).

[0005] Furthermore, Non-Patent Document 2 describes that Li cations exist in the interlayer space of MXene due to the LiCl used in chemical etching, and that the structure of the MXene powder changes when the Li cations are exchanged with other metal ions. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] Mohamed Alhabeb et al., "Guidelines for Synthesis and Processing of Two-Dimensional Titanium Carbide (Ti3C2Tx MXene)" Chem. Mater. 2017, 29, 7633-7644 [Non-patent document 2] Michael Ghidiu et al., "Ion-Exchange and Cation Solvation Reactions in Ti3C2 MXene" Chem. Mater. 2016, 28, 10, 3507-3514 Summary of the Invention [Problem to be solved by the invention]

[0007] In the MXene described in Non-Patent Document 1, the TMAOH used in the delamination treatment of the multilayer MXene remains, resulting in low conductivity, and moisture absorption further reduces the conductivity, resulting in insufficient reliability. In addition, in the MXene described in Non-Patent Document 2, although the Li cations are exchanged with other metal ions, the MXene remains in the form of multilayer MXene, resulting in low conductivity and making it difficult to form a conductive film.

[0008] The present invention aims to realize two-dimensional particles that can provide a conductive film that can maintain high conductivity even under high-humidity conditions, and to provide a method for producing such two-dimensional particles. [Means for solving the problem]

[0009] The present invention includes the following inventions. [1] A two-dimensional particle having one or more layers, containing a metal cation, The layer has the following formula: M m X n (wherein M is at least one Group 3, 4, 5, 6, or 7 metal; X is a carbon atom, a nitrogen atom, or a combination thereof; n is between 1 and 4, m is greater than n and less than or equal to 5) and a modified or terminated T (T is at least one selected from the group consisting of a hydroxyl group, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, an oxygen atom, a sulfur atom, Se, Te, and a hydrogen atom) present on the surface of the layer body, The modified or terminal T contains a chlorine atom, or the M of the layer and PO4 3- , I and SO4 2- and bonded to at least one selected from the group consisting of The metal cation includes at least one cation of a metal from periods 3 to 5 of the periodic table; Two-dimensional particles having a Li content of less than 0.002% by mass. [2] The two-dimensional particle according to [1], wherein the metal cations include cations of at least one metal selected from the group consisting of K, Na, Mg, Al, Mn, Ca, Fe, V, Cr, Co, Ni, Zn, Cu, and Sr. [3] The two-dimensional particle according to [1] or [2], wherein the metal cations include cations of at least one metal selected from the group consisting of K, Na, Mg, Al, Ca, and Sr. [4] The two-dimensional particles according to any one of [1] to [3], wherein the Li content is 0.0001 mass % or less. [5] The two-dimensional particles according to any one of [1] to [4], wherein the content of Al is 0.4 mass % or more. [6] The two-dimensional particle according to any one of [1] to [5], wherein Al cations are present between the layers. [7] The two-dimensional particle according to any one of [1] to [6], which has an average thickness of 1 nm or more and 10 nm or less. [8] The two-dimensional particle according to any one of [1] to [7], wherein the average value of the major axis of the two-dimensional surface is 1 μm or more and 20 μm or less. [9] A conductive film comprising the two-dimensional particles according to any one of [1] to [8].

[10] The conductive film according to [9], having a conductivity of 2,000 S / cm or more.

[11] A conductive paste comprising the two-dimensional particles according to any one of [1] to [8] and a dispersion medium.

[12] (a) The following formula: M m AX n (wherein M is at least one Group 3, 4, 5, 6, or 7 metal; X is a carbon atom, a nitrogen atom, or a combination thereof; A is at least one element of Groups 12, 13, 14, 15, or 16; n is between 1 and 4, m is greater than n and less than or equal to 5) providing a precursor represented by (b) performing an etching treatment using an etching solution to remove at least some of the A atoms from the precursor; (c) performing a first water washing treatment, which includes a step of washing the etched product obtained by the etching treatment with water; (d) performing a first intercalation treatment, which includes a step of mixing the first water-washed product obtained by the first water washing with a metal-containing compound; (e) performing a second water washing treatment, which includes a step of washing the first intercalation treatment product obtained by the first intercalation treatment with water; (f) performing a second intercalation treatment, which includes a step of mixing the second water-washed product obtained by the second water-washing treatment with an organic compound; (g) performing a delamination treatment, which includes a step of stirring the second intercalation treatment product obtained by the second intercalation treatment, to obtain two-dimensional particles. Including, the etching solution contains an anion containing at least one selected from the group consisting of a phosphorus atom, a sulfur atom, a chlorine atom, and an iodine atom; The metal-containing compound contains at least one cation of a metal from periods 3 to 5 of the periodic table, The solubility of the organic compound in water is 5 g / 100 g H2O or more at 25°C. Method for producing two-dimensional particles.

[13] The above delamination process is performed using PO4 3- The method for producing two-dimensional particles according to

[12] , comprising a step of stirring the second intercalation treatment product in the presence of

[14] The Hildebrand solubility parameter of the above organic compound is 19.0 MPa. 1 / 2 Over 47.8MPa 1 / 2 The method for producing two-dimensional particles according to

[12] or

[13] , wherein the method is as follows: [Effects of the Invention]

[0010] According to the present invention, it is possible to realize two-dimensional particles that can maintain high conductivity even under high humidity conditions, and it is also possible to provide a method for producing such two-dimensional particles. [Brief explanation of the drawings]

[0011] [Figure 1] 1A and 1B are schematic cross-sectional views showing MXene particles of layered material in one embodiment of the present invention, where (a) shows a single-layer MXene particle and (b) shows a multi-layer (exemplarily two-layer) MXene particle. [Figure 2] 1 is a schematic cross-sectional view showing a conductive film in one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] (Embodiment 1: Two-dimensional particles) Hereinafter, two-dimensional particles according to one embodiment of the present invention will be described in detail, but the present invention is not limited to this embodiment.

[0013] The two-dimensional particles in this embodiment are two-dimensional particles of layered material having one or more layers and comprising metal cations.

[0014] The layer has the following formula: M m X n (wherein M is at least one Group 3, 4, 5, 6, or 7 metal; X is a carbon atom, a nitrogen atom, or a combination thereof; n is between 1 and 4, m is greater than n and less than or equal to 5) and a modification or termination T (T is at least one selected from the group consisting of a hydroxyl group, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, an oxygen atom, a sulfur atom, Se, Te, and a hydrogen atom) present on a surface of the layer body (more specifically, on at least one of two opposing surfaces of the layer body), The modified or terminal T contains a chlorine atom, or the M of the layer and PO4 3- , I and SO4 2- is bonded to at least one selected from the group consisting of:

[0015] In this specification, when an "atom" refers to a certain element, the oxidation number of the element is not limited to 0, but may be any number within the range of oxidation numbers that the element can have.

[0016] The layered material may be understood as a layered compound and is referred to as "M m X n T s ", where s is any number, and conventionally, x or z may be used instead of s. Typically, n can be 1, 2, 3, or 4, but is not limited thereto.

[0017] In the above formula for MXene, M is preferably at least one selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, Sc, Y, W, and Mn, more preferably Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and Mn, and even more preferably at least one selected from the group consisting of Ti, V, Cr, and Mo.

[0018] MXene is a compound represented by the formula: M m X n However, it is known that it can be expressed as follows: Sc2C, Ti2C, Ti2N, Zr2C, Zr2N, Hf2C, Hf2N, V2C, V2N, Nb2C, Ta2C, Cr2C, Cr2N, Mo2C, Mo 1.3 C, Cr 1.3 C, (Ti,V)2C, (Ti,Nb)2C, W2C, W 1.3 C, Mo2N, Nb 1.3 C, Mo 1.3 Y 0.6 C (in the above formula, "1.3" and "0.6" mean approximately 1.3 (= 4 / 3) and approximately 0.6 (= 2 / 3), respectively), Ti3C2, Ti3N2, Ti3(CN), Zr3C2, (Ti,V)3C2, (Ti2Nb)C2, (Ti2Ta)C2, (Ti2Mn)C2, Hf3C2, (Hf2V)C2, (Hf2Mn)C2, (V2Ti)C2, (Cr2Ti)C2, (Cr2V)C 2, (Cr2Nb)C2, (Cr2Ta)C2, (Mo2Sc)C2, (Mo2Ti)C2, (Mo2Zr)C2, (Mo2Hf)C2, (Mo2V)C2, (Mo2Nb)C2, (Mo2Ta)C2, (W2Ti)C2, (W2Zr)C2, (W2Hf)C2, Ti4N3, V4C3, Nb4C3, Ta4C3, (Ti,Nb)4C3, (Nb,Zr)4C3, (Ti2Nb2)C3, (Ti2Ta2)C3, (V2Ti2)C3, (V2Nb2)C3, (V2Ta2)C3, (Nb2Ta2)C3, (Cr2Ti2)C3, (Cr2V 2)C3, (Cr2Nb2)C3, (Cr2Ta2)C3, (Mo2Ti2)C3, (Mo2Zr2)C3, (Mo2Hf2)C3, (Mo,V)C3, (Mo2Nb2)C3, (Mo2Ta2)C3, (W2Ti2)C3, (W2Zr2)C3, (W2Hf2)C3, (Mo 2.7 V 1.3 ) C3 (wherein "2.7" and "1.3" mean approximately 2.7 (= 8 / 3) and approximately 1.3 (= 4 / 3), respectively.) (Mo,V)5C4

[0019] Typically, in the above formula, M can be titanium or vanadium, and X can be a carbon atom or a nitrogen atom. For example, the MAX phase is Ti3AlC2, and MXene is Ti3C2T s (In other words, M is Ti, X is C, n is 2, and m is 3). Furthermore, T may preferably be at least one selected from the group consisting of a hydroxyl group, a fluorine atom, a chlorine atom, an oxygen atom, and a hydrogen atom.

[0020] In the present invention, MXene may contain a relatively small amount of A atoms derived from the MAX phase of the precursor, for example, 10% by mass or less of the original A atoms. The amount of residual A atoms is preferably 8% by mass or less, more preferably 6% by mass or less. However, even if the amount of residual A atoms exceeds 10% by mass, this may not be a problem depending on the application and use conditions of the two-dimensional particles.

[0021] In this specification, the layer may be referred to as an MXene layer, and the two-dimensional particles may be referred to as MXene two-dimensional particles or MXene particles.

[0022] The two-dimensional particle of this embodiment is an aggregate including one layer of MXene particles (hereinafter simply referred to as "MXene particles") 10a (single-layer MXene particles) as shown in FIG. 1(a). More specifically, the MXene particles 10a are m X n The layer body (M m X n The MXene layer 7a has a main layer 1a and modifications or terminations T3a, 5a present on the surface of the main layer 1a (more specifically, on at least one of the two surfaces facing each other in each layer). m X n T s ", where s is an arbitrary number. In FIG. 1(a), metal cations are not shown.

[0023] The two-dimensional particles of this embodiment may contain one or more layers. Examples of MXene particles with multiple layers (multilayer MXene particles) include, but are not limited to, the two-layer MXene particle 10b, as shown schematically in FIG. 1(b). 1b, 3b, 5b, and 7b in FIG. 1(b) are the same as 1a, 3a, 5a, and 7a in FIG. 1(a). Two adjacent MXene layers (e.g., 7a and 7b) in a multilayer MXene particle do not necessarily need to be completely separated and may be partially in contact. The MXene particle 10a may consist of the multilayer MXene particles 10b separated into a single layer. Alternatively, the multilayer MXene particles 10b may remain unseparated, resulting in a mixture of the single-layer MXene particles 10a and the multilayer MXene particles 10b. Metal cations are not shown in FIG. 1(b).

[0024] Although this embodiment is not limited thereto, the thickness of each layer (corresponding to the above-mentioned MXene layers 7a and 7b) contained in the MXene particle is, for example, 0.8 to 5 nm, particularly 0.8 to 3 nm (this can vary mainly depending on the number of M atomic layers contained in each layer). The interlayer distance (or gap dimension, shown as Δd in FIG. 1(b)) for each individual stack of the multilayer MXene particle that may be contained may be, for example, 0.8 to 10 nm, particularly 0.8 to 5 nm, more particularly about 1 nm, and the total number of layers may be 2 to 20,000.

[0025] The two-dimensional particles of this embodiment preferably contain multilayer MXene particles with a small number of layers obtained through a delamination process. The term "small number of layers" refers to, for example, six or fewer MXene layers. Furthermore, the thickness of the multilayer MXene particles with a small number of layers in the stacking direction is preferably 15 nm or less, and more preferably 10 nm or less. Hereinafter, these "multilayer MXene particles with a small number of layers" may be referred to as "small-layer MXene particles." Furthermore, single-layer MXene particles and small-layer MXene particles may be collectively referred to as "single-layer / small-layer MXene particles."

[0026] The two-dimensional particles of this embodiment preferably contain single-walled MXene particles and few-walled MXene particles, i.e., single-walled and few-walled MXene particles. In the two-dimensional particles of this embodiment, the proportion of single-walled and few-walled MXene particles with a thickness of 15 nm or less is preferably 90% by volume or more, more preferably 95% by volume or more.

[0027] The metal cation includes at least one cation of a metal from periods 3 to 5 of the periodic table. Metals from period 3 of the periodic table include Na, Mg, Al, and Si. Metals from period 4 of the periodic table include K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, and As. Metals from period 5 of the periodic table include Rb, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, and Te. The metal may be an alkali metal, alkaline earth metal, transition metal (metals from groups 3 to 11 of the periodic table), or main group metal (metals from groups 12 to 16 of the periodic table). Cations of metals from periods 3 to 5 of the periodic table have a moderate ion size, so they are believed to exist between layers and interact with the layers.

[0028] In one embodiment, the metal cation preferably comprises one cation selected from the group consisting of K, Na, Mg, Al, Mn, Ca, Fe, V, Cr, Co, Ni, Zn, Cu, and Sr, and more preferably comprises one cation selected from the group consisting of K, Na, Mg, Al, Ca, and Sr. In another embodiment, the metal cation preferably comprises one cation selected from the group consisting of K, Na, Mg, Mn, Ca, Fe, V, Cr, Co, Ni, Zn, Cu, and Sr, and more preferably comprises one cation selected from the group consisting of K, Na, and Ca. The valence of the metal cation may be monovalent or divalent or higher, preferably monovalent, divalent, or trivalent. When the valence of the metal cation is divalent or higher, the metal cation and the layer are more likely to interact with each other, and two adjacent layers are attracted to each other via the polyvalent metal cation, which is thought to make it difficult for water to penetrate between the layers. This is thought to make it easier to maintain high conductivity even under high temperature and high humidity conditions.

[0029] The metal cations preferably do not contain Li cations. The term "metal cations do not contain Li cations" means that the concentration of Li cations is less than 20 ppm by mass relative to the total amount of metal cations when measured, for example, by inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0030] The metal of the metal cation may be the same as or different from the metal contained in the precursor MAX phase, which makes it easy to confirm the presence of the metal in the two-dimensional particles.

[0031] The metal cations are typically present on the layer, i.e., they may be in contact with the layer or may be present on the layer via another element.

[0032] The content of the metal cations in the two-dimensional particles (e.g., the sum of the layers and the metal cations) may be, for example, 20% by mass or less, even 10% by mass or less, particularly 5% by mass or less, and especially 3% by mass or less, and may be, for example, 0.1% by mass or more, even 0.2% by mass or more.

[0033] The content of the metal cations can be measured, for example, by inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0034] The modified or terminal T contains a chlorine atom, or the M of the layer and PO4 3- , I and SO4 2-The fact that at least one selected from the group consisting of the following can be confirmed by measuring the surface of the two-dimensional particle by X-ray photoelectron spectroscopy (XPS) or the like.

[0035] The two-dimensional particles of the present disclosure preferably contain Al cations as metal cations. While not limited to a particular theory, Al cations are trivalent metal cations and are thought to interact more strongly with the negatively charged layer than monovalent or divalent metal cations. This is thought to prevent moisture from penetrating between the layers, allowing high conductivity to be maintained even under high temperature and humidity conditions.

[0036] In one embodiment, it is preferable that Al cations are present between the layers, which may further strengthen the interaction with the layers, further suppress the penetration of moisture between the layers, and more reliably maintain high electrical conductivity even under high temperature and high humidity conditions.

[0037] The presence of Al cations between the layers is 27 This can be confirmed by Al NMR. For example, the solid state 27 In the spectrum obtained by Al NMR, it can be confirmed by a peak preferably in the range of 13 ppm or more and 18 ppm or less, for example.

[0038] The Al content of the two-dimensional particles of the present disclosure is preferably 0.4% by mass or more, more preferably 0.4% by mass to 12% by mass, more preferably 0.4% by mass to 5% by mass, and even more preferably 0.4% by mass to 1% by mass. The Al content of the two-dimensional particles is based on the content of Al cations contained as metal cations, but may also contain residues of the A phase of the precursor.

[0039] The Al content in the two-dimensional particles can be measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES) or the like.

[0040] The two-dimensional particles have a reduced Li content. Therefore, when using the two-dimensional particles, a conductive film can be provided that can maintain high conductivity even under high humidity conditions, such as a relative humidity of 99%. The Li content in the two-dimensional particles (e.g., the total of the layer and the metal cations) is less than 0.002% by mass, preferably 0.001% by mass or less, and more preferably 0.0001% by mass or less.

[0041] The Li content can be measured, for example, by inductively coupled plasma atomic emission spectroscopy (ICP-AES), etc. The detection limit of Li measured by ICP-AES is 0.0001 mass %.

[0042] The two-dimensional particles of this embodiment do not contain amines. As described in Non-Patent Document 1, when MXene is delaminated using TMAOH, a single layer of MXene is obtained. However, even after washing, TMAOH remains on the surface of the MXene layer, resulting in low electrical conductivity. TMAOH can be removed at high temperatures of 250°C to 500°C, but at such high temperatures, MXene may oxidize and decompose. In contrast, the two-dimensional particles of this embodiment do not use TMAOH for the delamination of MXene and do not contain amines. In this specification, "amine-free" refers to the presence of 10 ppm by mass or less of triethylamine (m / z = 42, 53, 54) derived from TMAOH when measured using a gas chromatography-mass spectrometry (GC-MS) device.

[0043] In this specification, two-dimensional particles refer to particles in which the ratio of (average major axis of the two-dimensional surface of the two-dimensional particle) / (average thickness of the two-dimensional particle) is 1.2 or more, preferably 1.5 or more, and more preferably 2 or more. The average major axis of the two-dimensional surface of the two-dimensional particle and the average thickness of the two-dimensional particle may be determined by the method described below.

[0044] (Average value of the longest diameter of the two-dimensional surface of a two-dimensional particle) The two-dimensional particles of this embodiment have an average major axis of the two-dimensional surface of 1 μm or more and 20 μm or less. Hereinafter, the average major axis of the two-dimensional surface may be referred to as the "average flake size."

[0045] The larger the average flake size, the higher the conductivity of the conductive film. The two-dimensional particles of this embodiment have a large average flake size of 1.0 μm or more. Therefore, a film formed using these two-dimensional particles, for example, a film obtained by stacking these two-dimensional particles, can achieve a conductivity of 2000 S / cm or more. The average long diameter of the two-dimensional surface is preferably 1.5 μm or more, more preferably 2.5 μm or more. In Non-Patent Document 2, MXene is delaminate-treated by ultrasonic treatment. However, because the ultrasonic treatment reduces the long diameter of most of the MXene to approximately several hundred nanometers, the film formed from the single-layer MXene obtained in Non-Patent Document 2 is thought to have low conductivity.

[0046] The average value of the major axis of the two-dimensional surface is 20 μm or less, preferably 15 μm or less, and more preferably 10 μm or less, from the viewpoint of dispersibility in the dispersion medium.

[0047] The longest diameter of the two-dimensional plane refers to the longest diameter when each MXene particle is approximated to an ellipse in an electron microscope photograph, as shown in the Examples below, and the average longest diameter of the two-dimensional plane refers to the number average of the longest diameters of 80 or more particles. As the electron microscope, a scanning electron microscope (SEM) or a transmission electron microscope (TEM) can be used.

[0048] The average major axis of the two-dimensional particles of this embodiment may be measured by dissolving the conductive film containing the two-dimensional particles in a solvent and dispersing the two-dimensional particles in the solvent, or by measuring the average major axis of the conductive film from an SEM image.

[0049] (average thickness of two-dimensional particles) The average thickness of the two-dimensional particles of this embodiment is preferably 1 nm or more and 15 nm or less. The thickness is preferably 10 nm, more preferably 7 nm or less, and even more preferably 5 nm or less. On the other hand, considering the thickness of a single-layer MXene particle, the lower limit of the thickness of the two-dimensional particles can be 1 nm.

[0050] The average thickness of the two-dimensional particles is determined as a number-average size (for example, a number-average of at least 40 particles) based on atomic force microscope (AFM) or transmission electron microscope (TEM) photographs.

[0051] (Embodiment 2: Method for producing two-dimensional particles) Hereinafter, a method for producing two-dimensional particles according to one embodiment of the present invention will be described in detail, but the present invention is not limited to this embodiment.

[0052] The method for producing two-dimensional particles of this embodiment includes: (a) providing a predetermined precursor; (b) performing an etching treatment using an etching solution to remove at least some of the A atoms from the precursor; (c) performing a first water washing treatment, which includes a step of washing the etched product obtained by the etching treatment with water; (d) performing a first intercalation treatment, which includes a step of mixing the first water-washed product obtained by the first water washing with a metal-containing compound; (e) performing a second water washing treatment, which includes a step of washing the first intercalation treatment product obtained by the first intercalation treatment with water; (f) performing a second intercalation treatment, which includes a step of mixing the second water-washed product obtained by the second water-washing treatment with an organic compound; (g) performing a delamination treatment, which includes a step of stirring the second intercalation treatment product obtained by the second intercalation treatment, to obtain two-dimensional particles. Including, the etching solution contains an anion containing at least one selected from the group consisting of a phosphorus atom, a sulfur atom, a chlorine atom, and an iodine atom; The metal-containing compound contains at least one cation of a metal from periods 3 to 5 of the periodic table, The solubility of the organic compound in water at 25°C is 5 g / 100 g H2O or more.

[0053] Typically, when an intercalation treatment is performed using a metal-containing compound containing a cation of a metal from Periods 3 to 5 of the periodic table, the absolute value of the hydration enthalpy of these metal cations is smaller than the absolute value of the hydration enthalpy of Li ions, so delamination hardly progresses. However, according to the studies of the present inventors, even when a metal compound containing a metal cation other than Li ions is used, further intercalation treatment using an organic compound that is soluble in water makes it easier for water to penetrate between the layers, and delamination can progress sufficiently.

[0054] Each step will be described in detail below.

[0055] ·Process (a) First, a predetermined precursor is prepared. The predetermined precursor that can be used in this embodiment is a MAX phase, which is a precursor of MXene. The following formula: M m AX n (wherein M is at least one Group 3, 4, 5, 6, or 7 metal; X is a carbon atom, a nitrogen atom, or a combination thereof; A is at least one element of Groups 12, 13, 14, 15, or 16; n is between 1 and 4, m is greater than n and less than or equal to 5) It is expressed as:

[0056] The above M, X, n, and m are as described in the first embodiment. A is at least one element of Groups 12, 13, 14, 15, and 16, and is usually an element of Group A, typically Group IIIA and Group IVA, and more specifically, can include at least one element selected from the group consisting of Al, Ga, In, Tl, Si, Ge, Sn, Pb, P, As, S, and Cd, and is preferably Al.

[0057] The MAX phase is M m X n (each X may have a crystal lattice in which it is located in an octahedral array of M) and a layer composed of A atoms is located between them. In the MAX phase, typically when m=n+1, one layer of X atoms is arranged between each of the n+1 layers of M atoms (these are collectively referred to as "M m X n The repeating unit may have a layer of A atoms (also referred to as an "A atom layer") arranged as the next layer after the n+1th layer of M atoms, but is not limited thereto.

[0058] The MAX phase can be produced by a known method. For example, TiC powder, Ti powder, and Al powder are mixed in a ball mill, and the resulting mixed powder is sintered in an Ar atmosphere to obtain a sintered body (a block of MAX phase). The sintered body is then pulverized with an end mill to obtain a powdered MAX phase for the next step.

[0059] In the present disclosure, materials having a layered structure similar to the MAX phase may be used as precursors. Examples of such materials include Zr2Al3C4, Zr3Al3C5, Zr4(AlC2)3, Zr2Al4C5, Zr2Al3C4, Zr3Al3C5, and Zr2Al3C5.

[0060] ·Process (b) In step (b), an etching treatment is carried out using an etching solution to remove at least some of the A atoms from the precursor.

[0061] The etching solution contains an anion containing at least one selected from the group consisting of phosphorus atoms, sulfur atoms, chlorine atoms, and iodine atoms. This allows for sufficient etching and facilitates intercalation of metal cations in the subsequent first intercalation treatment. The anion may exist in any form, including ions, such as H + It may be combined with a cation to exist as an acid, or may be combined with a cation to exist as a salt.

[0062] Anions containing phosphorus atoms include PO4 3- Examples of anions containing sulfur atoms include SO4 2- Examples of anions containing chlorine atoms include Cl - Examples of anions containing an iodine atom include I - Examples include:

[0063] The etching solution preferably contains at least one selected from the group consisting of H3PO4, H2SO4, HCl, and HI, and may further contain HF. Specific examples of the etching solution include an aqueous solution of at least one selected from the group consisting of H3PO4, H2SO4, HCl, and HI; a mixed solution of an aqueous solution of HF and at least one selected from the group consisting of H3PO4, H2SO4, HCl, and HI, and particularly a mixed solution of an aqueous solution of HF and at least one selected from the group consisting of H3PO4, H2SO4, HCl, and HI.

[0064] In the etching solution, the concentration of one selected from the group consisting of H3PO4, H2SO4, HCl, and HI is 0.1 mol / L or more, preferably 1 mol / L or more, more preferably 2 mol / L or more, even more preferably 3 mol / L or more, still more preferably 5 mol / L or more, and may be, for example, 15 mol / L or less, or even 10 mol / L or less. In the etching solution, the concentration of HF is preferably 1 mol / L or more, more preferably 2 mol / L or more, even more preferably 3 mol / L or more, still more preferably 5 mol / L or more, and may be, for example, 15 mol / L or less, or even 10 mol / L or less.

[0065] In one embodiment, it is preferred that the concentration of one selected from the group consisting of H3PO4, H2SO4, HCl, and HI is 1 mol / L to 15 mol / L, and the concentration of HF is 1 mol / L to 15 mol / L; it is preferred that the concentration of one selected from the group consisting of H3PO4, H2SO4, HCl, and HI is 3 mol / L to 10 mol / L, and the concentration of HF is 3 mol / L to 10 mol / L.

[0066] The etching solution preferably does not contain lithium atoms. Here, the term "does not contain Li atoms" means that the Li concentration in the etching solution is less than 20 ppm by mass when measured by, for example, combustion ion chromatography.

[0067] The etching procedure and other conditions using the etching solution may be those conventionally used.

[0068] ·Process (c) The etched product obtained by the etching treatment is washed with water. Washing with water can sufficiently remove the acid used in the etching treatment. The amount of water to be mixed with the etched product and the washing method are not particularly limited. For example, adding water and stirring, centrifuging, etc. can be performed. Stirring methods include stirring using a hand shake, an automatic shaker, a shear mixer, a pot mill, etc. The degree of stirring, such as the stirring speed and stirring time, can be adjusted depending on the amount and concentration of the acid-treated product to be treated. The water washing can be performed one or more times. Preferably, water washing is performed multiple times. For example, steps (i) to (iii) of (i) adding water (to the etched product or the remaining precipitate obtained in (iii) below) and stirring, (ii) centrifuging the stirred product, and (iii) discarding the supernatant after centrifugation can be performed two or more times, for example, 15 or less times.

[0069] ·Process (d) A first intercalation treatment is carried out, which includes a step of mixing the first water-washed product obtained by the water washing with a metal-containing compound containing metal cations, thereby intercalating the metal cations between the layers.

[0070] The metal cation includes at least one cation of a metal from Periods 3 to 5 of the periodic table. Examples of metals from Period 3 of the periodic table include Na, Mg, Al, and Si. Examples of metals from Period 4 of the periodic table include K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, and As. Examples of metals from Period 5 of the periodic table include Rb, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, and Te. The metal may be an alkali metal, an alkaline earth metal, a transition metal (a metal from Groups 3 to 11 of the periodic table), or a main group metal (a metal from Groups 12 to 16 of the periodic table).

[0071] In one embodiment, the metal cation preferably comprises one cation selected from the group consisting of K, Na, Mg, Al, Mn, Ca, Fe, V, Cr, Co, Ni, Zn, Cu, and Sr, and more preferably comprises one cation selected from the group consisting of K, Na, Mg, Al, Ca, and Sr. In another embodiment, the metal cation preferably comprises a cation of one metal selected from the group consisting of K, Na, Mg, Mn, Ca, Fe, Zn, and Cu, and more preferably comprises a cation of one metal selected from the group consisting of K, Na, and Ca.

[0072] The metal of the metal cation may be the same as or different from the metal contained in the precursor MAX phase, which makes it easy to confirm the presence of the metal in the two-dimensional particles.

[0073] Examples of metal-containing compounds containing the above metal cations include ionic compounds in which the above metal cations are bound to cations and anions. Examples include chlorides, iodides, phosphates, sulfides including sulfates, nitrates, acetates, and carboxylates of the above metal cations. The above metal-containing compounds may also be hydrates of the above ionic compounds.

[0074] The content of the metal-containing compound in the first intercalation treatment formulation containing the metal-containing compound is preferably 0.001% by mass or more, more preferably 0.01% by mass or more, and even more preferably 0.1% by mass or more. On the other hand, from the viewpoint of dispersibility in the solution, the content of the metal-containing compound in the first intercalation treatment formulation is preferably 10% by mass or less, more preferably 1% by mass or less.

[0075] The first intercalation treatment formulation preferably does not contain lithium atoms. Note that the "does not contain Li atoms" of the first intercalation treatment formulation means that the Li concentration in the first intercalation treatment formulation is less than 20 ppm by mass as measured, for example, by combustion ion chromatography.

[0076] The specific method of the first intercalation treatment is not particularly limited. For example, the first water-washed product may be mixed with a metal-containing compound and stirred or left to stand. For example, stirring at room temperature may be used. Examples of the stirring method include a method using a stirring bar such as a stirrer, a method using a stirring blade, a method using a mixer, and a method using a centrifugal device. The stirring time can be set depending on the production scale of the single-walled / few-walled MXene particles, and can be set, for example, between 12 and 24 hours.

[0077] ·Process (e) The first intercalation treatment product obtained by the first intercalation treatment is washed with water. By washing with water, the excess metal-containing compound and the like used in the first intercalation treatment can be sufficiently removed. Since the first intercalation treatment is performed using a metal-containing compound that does not contain Li ions, delamination hardly progresses in step (e), and the excess metal-containing compound and the like are washed away.

[0078] The amount of water to be mixed with the first intercalation treatment product and the washing method are not particularly limited. For example, adding water and stirring, centrifuging, etc. can be used. Stirring methods include stirring using a hand shake, an automatic shaker, a shear mixer, a pot mill, etc. The degree of stirring, such as the stirring speed and stirring time, can be adjusted depending on the amount and concentration of the acid-treated product to be treated. The above-mentioned washing with water can be carried out one or more times. Preferably, washing with water is carried out multiple times. For example, steps (i) to (iii) of (i) adding water (to the etched product or the remaining precipitate obtained in (iii) below) and stirring, (ii) centrifuging the stirred product, and (iii) discarding the supernatant after centrifugation can be carried out two or more times, for example, 15 or less times.

[0079] ·Process (f) A second intercalation treatment is carried out, which includes a step of mixing the second water-washed product obtained by the water washing with an organic compound that is soluble or miscible in water, whereby the organic compound is further intercalated between the layers, making it easier for water to penetrate between the layers, and as a result, delamination can proceed sufficiently in the subsequent delamination step.

[0080] The organic compound is soluble or miscible in water. The solubility of the organic compound in water at 25°C is 5 g / 100 g H2O or more, more preferably 10 g / 100 g H2O or more. In this specification, the solubility when miscible in water is treated as infinite.

[0081] The organic compound is preferably a compound with high polarity. In this specification, a compound with high polarity is a concept that includes not only compounds that exhibit clear charge separation but also compounds with high hydrophilicity. The polarity of a compound can be evaluated using the solubility parameter as an index. The Hildebrand solubility parameter (also referred to as the "SP value") of the organic compound is 19.0 MPa. 1 / 2 The SP value of the organic compound is preferably equal to or less than the SP value of water, and is 47.8 MPa or more.1 / 2 The SP value is an index of the polarity of a compound; the larger the SP value, the higher the polarity, and compounds with similar SP values ​​tend to be more compatible with each other.

[0082] The boiling point of the organic compound is, for example, 285°C or lower, preferably 240°C or lower, more preferably 200°C or lower, and is, for example, 50°C or higher.

[0083] The molecular weight of the organic compound is, for example, 500 or less, preferably 300 or less, more preferably 200 or less, and is, for example, 30 or more.

[0084] Examples of the organic compound include organic compounds having one or more of a carbonyl group, an ester group, an amide group, a formamide group, a carbamoyl group, a carbonate group, an aldehyde group, an ether group, a sulfonyl group, a sulfinyl group, a hydroxyl group, a cyano group, and a nitro group. Specific examples of the organic compound include alcohols such as methanol (MeOH), ethanol (EtOH), and 2-propanol; sulfone compounds such as sulfolane; sulfoxides such as dimethyl sulfoxide (DMSO); carbonates such as propylene carbonate (PC); amides such as N-methylformamide (NMF), N,N-dimethylformamide, N-methylpyrrolidone (NMP), and dimethylacetamide (DMAc); ketones such as acetone and methyl ethyl ketone (MEK); and tetrahydrofuran (THF).

[0085] The content of the organic compound in the second intercalation treatment formulation containing an organic compound can be 0.01 parts by mass or more and 1,000 parts by mass or less per part by mass of the layer portion (MXene layer) of the two-dimensional particle.

[0086] The second intercalation treatment formulation preferably does not contain lithium atoms. Note that the "does not contain Li atoms" of the second intercalation treatment formulation means that the Li concentration in the second intercalation treatment formulation is less than 20 ppm by mass as measured, for example, by combustion ion chromatography.

[0087] The specific method for the second intercalation treatment is not particularly limited. For example, the second water-washed product may be mixed with an organic compound and stirred or left to stand. For example, stirring at room temperature may be used. Examples of the stirring method include a method using a stirring bar such as a stirrer, a method using a stirring blade, a method using a mixer, and a method using a centrifugal device. The stirring time can be set depending on the production scale of the single-walled / few-walled MXene particles, and can be set, for example, between 12 and 24 hours.

[0088] The organic compound is preferably completely removed by washing after the second intercalation treatment, but a small amount may remain as long as it does not interfere with ensuring electrical conductivity. The content of the organic compound is preferably 0% by mass when the two-dimensional particles of this embodiment are measured by gas chromatography-mass spectrometry, and even if a small amount remains, it is, for example, more than 0% by mass and 0.01% by mass or less.

[0089] ·Process (g) In step (g), a delamination treatment is performed, which includes a step of stirring the second intercalation treatment product obtained by the second intercalation treatment. The delamination treatment can reduce the number of layers of MXene particles to a single layer.

[0090] The conditions for the delamination treatment are not particularly limited, and can be performed by any known method. Examples of agitation methods include ultrasonication, handshaking, and stirring using an automatic shaker. The degree of agitation, such as the agitation speed and agitation time, can be adjusted depending on the amount and concentration of the material to be treated. For example, the above-mentioned intercalated slurry can be centrifuged to discard the supernatant, and then pure water can be added to the remaining precipitate, for example, by handshaking or stirring using an automatic shaker, to separate the layers. Removal of unexfoliated material can be achieved by centrifuging, discarding the supernatant, and then washing the remaining precipitate with water. For example, (i) pure water can be added to the remaining precipitate after discarding the supernatant, followed by stirring, (ii) centrifugation, and (iii) recovery of the supernatant. These steps (i) to (iii) can be repeated at least once, preferably at least twice, but not more than 10 times, to obtain a supernatant containing single-layered or single-layered MXene particles as the delamination-treated product. Alternatively, the supernatant may be centrifuged, the supernatant after centrifugation discarded, and clay containing single-layer and few-layer MXene particles may be obtained as a delamination treatment product.

[0091] Phosphoric acid may be present during the delamination treatment. The presence of phosphoric acid facilitates delamination, particularly when a metal-containing compound containing polyvalent metal cations is used. While not limited to a specific theory, it is believed that polyvalent metal cations tend to interact with the layers, and that adjacent layers are attracted to each other with greater force through the polyvalent metal cations. Therefore, typically, delamination hardly occurs when a metal-containing compound containing polyvalent metal cations is used. However, the presence of phosphoric acid may allow phosphoric acid to interact with the polyvalent metal cations, suppressing the interaction between layers via the metal cations to some extent. Therefore, it is believed that delamination may occur even when a metal-containing compound containing polyvalent metal cations is used.

[0092] In the manufacturing method of this embodiment, ultrasonic treatment is not required during the delamination treatment. If ultrasonic treatment is not performed, particle destruction is unlikely to occur, and it becomes easier to obtain single-layered or few-layered MXene particles with large planes parallel to the particle layers, i.e., large two-dimensional surfaces.

[0093] The delamination product obtained by stirring can be used as is as two-dimensional particles containing single-layer and few-layer MXene particles, and may be washed with water if necessary.

[0094] (Embodiment 3: Conductive film) An example of an application of the two-dimensional particles of this embodiment is a conductive film containing the two-dimensional particles. The conductive film of this embodiment will be described with reference to FIG. 2. FIG. 2 illustrates a conductive film 30 obtained by laminating only two-dimensional particles 10, but the present invention is not limited to this. The conductive film may contain additives such as binders added during film formation, as needed. The additives preferably account for 30% by volume or less of the conductive film (when dried), more preferably 10% by volume or less, even more preferably 5% by volume or less, and most preferably 0% by volume.

[0095] A conductive film can be produced without using a binder or the like by suction filtering the supernatant containing the two-dimensional particles obtained by the delamination, or by spraying the two-dimensional particles mixed with a dispersion medium to form a slurry of an appropriate concentration, followed by removing the dispersion medium by drying or the like, once or multiple times. The spraying method can be, for example, an airless spray method or an air spray method. Specific examples include spraying using a nozzle such as a one-fluid nozzle, a two-fluid nozzle, or an airbrush. Examples of dispersion media that can be contained in the slurry include water; organic media such as N-methylpyrrolidone, N-methylformamide, N,N-dimethylformamide, methanol, ethanol, dimethyl sulfoxide, ethylene glycol, and acetic acid.

[0096] Examples of the binder include acrylic resin, polyester resin, polyamide resin, polyolefin resin, polycarbonate resin, polyurethane resin, polystyrene resin, polyether resin, and polylactic acid.

[0097] The conductivity of the conductive film is preferably 2,000 S / cm or more, more preferably 5,000 S / m or more, and may be, for example, 100,000 S / cm or less, or even 50,000 S / cm or less.

[0098] The conductivity of the conductive film of this embodiment can be determined by substituting the thickness of the conductive film and the surface resistivity of the conductive film measured by the four-probe method into the following formula. Conductivity [S / cm] = 1 / (thickness of conductive film [cm] x surface resistivity of conductive film [Ω / □])

[0099] Other applications of the two-dimensional particles of this embodiment include conductive pastes containing the two-dimensional particles and, if necessary, resins and additives (dispersion media, viscosity modifiers, etc.), and conductive composite materials containing the two-dimensional particles and resins. These are also suitable for applications that require high conductivity even under high humidity conditions.

[0100] Resins that can be contained in the conductive paste and conductive composite material include the same resins that can be contained in the conductive film. Dispersion media that can be contained in the conductive paste include water, and organic media such as N-methylpyrrolidone, N-methylformamide, N,N-dimethylformamide, methanol, ethanol, dimethyl sulfoxide, ethylene glycol, and acetic acid.

[0101] Although two-dimensional particles according to one embodiment of the present invention have been described in detail above, various modifications are possible. Note that the two-dimensional particles of the present invention may be produced by a method different from the production method in the above-described embodiment, and that the production method for two-dimensional particles of the present invention is not limited to only those that provide the two-dimensional particles in the above-described embodiment. [Example]

[0102] [Examples 1 to 5, 13] [Creation of two-dimensional particles] In Examples 1 to 5, two-dimensional particles were produced by sequentially carrying out the following steps, as detailed below: (1) preparation of precursor (MAX), (2) etching of precursor, (3) first cleaning, (4) first intercalation, (5) second cleaning, (6) second intercalation, (7) delamination, and (8) water cleaning.

[0103] (1) Preparation of precursor (MAX) TiC powder, Ti powder, and Al powder (all manufactured by Kojundo Chemical Laboratory Co., Ltd.) were mixed in a 2:1:1 molar ratio in a ball mill containing zirconia balls for 24 hours. The resulting mixed powder was sintered at 1350°C for 2 hours in an Ar atmosphere. The resulting sintered body (block) was then pulverized using an end mill to a maximum size of 40 μm or less. This yielded Ti3AlC2 particles as the precursor (MAX).

[0104] (2) Etching of precursor Using the Ti3AlC2 particles (powder) prepared by the above method, etching was carried out under the following etching conditions to obtain a solid-liquid mixture (slurry) containing solid components derived from the Ti3AlC2 powder. (Etching conditions) Precursor: Ti3AlC2 (passed through a 45 μm sieve) See Table 1 for the etching solution composition. Precursor input: 3.0g Etching container: 100mL Eye Boy Etching temperature: 35℃ Etching time: 24 hours Stirrer rotation speed: 400 rpm

[0105] (3) First cleaning The slurry was divided into two parts and placed in two 50 mL centrifuge tubes. The tubes were centrifuged at 3500 G for 5 minutes, and the supernatant was discarded. 35 mL of pure water was added to each tube, and the tubes were centrifuged again at 3500 G for 5 minutes, and the supernatant was removed. This procedure was repeated 11 times. After the final centrifugation, the supernatant was discarded, and the Ti3C2T s -Water medium clay was obtained.

[0106] (4) First intercalation Ti3C2T prepared by the above method s 20 mL of pure water and the metal-containing compound shown in Table 1 were added to the water medium clay, and the mixture was stirred at 20°C to 25°C for 15 hours to carry out the first intercalation using metal cations as intercalators. The detailed conditions for the first intercalation are as follows: (Conditions for the first intercalation) Ti3C2T s -Water medium clay (MXene after washing): 0.5g solids -See Table 1 for metal-containing compounds and dosage amounts. Intercalation vessel: 100mL Eye Boy ·Temperature: 20℃ or higher and 25℃ or lower (room temperature) Duration: 15 hours Stirrer rotation speed: 700 rpm

[0107] (5) Second washing The above slurry was placed in a 50 mL centrifuge tube, 10 mL of pure water was added, and the mixture was centrifuged at 3500 G for 5 minutes, after which the supernatant was discarded. 35 mL of pure water was added to the centrifuge tube from which the supernatant had been discarded, and the mixture was centrifuged again at 3500 G for 5 minutes to separate and remove the supernatant. This procedure was repeated three times. After the final centrifugation, the supernatant was discarded, yielding MXene clay.

[0108] (6) Second intercalation The MXene clay prepared by the above method was subjected to a second intercalation using the organic compounds shown in Table 1 as intercalators by stirring for 11 hours at 20°C to 25°C. The detailed conditions for the second intercalation are as follows: (Conditions for the second intercalation) MXene Clay: 0.5g solid content See Table 1 for organic compounds and amounts added Intercalation vessel: 100mL Eye Boy ·Temperature: 20℃ or higher and 25℃ or lower (room temperature) Duration: 11 hours Stirrer rotation speed: 700 rpm

[0109] (7) Delamination The slurry obtained after the second intercalation was placed in a 50 mL centrifuge tube, 20 mL of pure water was added, and the mixture was centrifuged at 3500 G for 5 minutes. The supernatant was then collected. Another 35 mL of pure water was added, followed by 15 minutes of stirring on a shaker. The mixture was then centrifuged at 3500 G for 5 minutes, and the supernatant was collected as a solution containing single-layer MXene particles. This procedure was repeated four times to obtain a single-layer MXene particle-containing supernatant. The supernatant was then centrifuged at 4300 G for 2 hours. The supernatant was then discarded, yielding a clay containing two-dimensional particles (single-layer MXene particles).

[0110] [Examples 6, 7, 9, and 10] The precursor (MAX) was prepared in the same manner as in Examples 1 to 5, and then the following step (2) was carried out. The resulting solid-liquid mixture (slurry) containing solid components derived from the Ti3AlC2 powder was subjected to the first washing, first intercalation, second washing, second intercalation, and delamination in the same manner as in Examples 1 to 5 to produce clay containing two-dimensional particles (single-layer MXene particles). (1) Preparation of precursor (MAX): Same as in Examples 1 to 5 (2) Etching of precursor Using the Ti3AlC2 particles (powder) prepared in the above step (1), etching was carried out under the following etching conditions to obtain a solid-liquid mixture (slurry) containing solid components derived from the Ti3AlC2 powder. (Etching conditions) Precursor: Ti3AlC2 (passed through a 45 μm sieve) See Table 1 for the etching solution composition. Precursor input: 3.0g Etching container: 100mL Eye Boy Etching temperature: 35℃ Etching time: 24 hours Stirrer rotation speed: 400 rpm (3) First washing: same as in Examples 1 to 5 (4) First intercalation: same as in Examples 1 to 5 (5) Second washing: same as in Examples 1 to 5 (6) Second intercalation: same as in Examples 1 to 5 (7) Delamination: Same as in Examples 1 to 5

[0111] [Example 8] After the preparation of the precursor (MAX), etching, first cleaning, first intercalation, second cleaning, and second intercalation were carried out in the same manner as in Examples 1 to 5, the following step (7) was carried out to produce clay containing two-dimensional particles (single-layer MXene particles).

[0112] (1) Preparation of precursor (MAX): Same as in Examples 1 to 5 (2) Etching of precursor: same as in Examples 1 to 5 (3) First washing: same as in Examples 1 to 5 (4) First intercalation: same as in Examples 1 to 5 (5) Second washing: same as in Examples 1 to 5 (6) Second intercalation: same as in Examples 1 to 5 (7) Delamination The slurry obtained after the second intercalation was placed in a 50 mL centrifuge tube, and 5 g of aqueous phosphoric acid solution (0.85% by mass) was added. The mixture was then stirred by handshaking. Five mL of pure water was then added, and the mixture was centrifuged at 3500 G for 5 minutes. The supernatant was then collected. Another 35 mL of pure water was added, and the mixture was stirred for 15 minutes on a shaker. The mixture was then centrifuged at 3500 G for 5 minutes. The supernatant was then obtained as a solution containing single-layer MXene particles. This single-layer MXene particle-containing solution was then centrifuged at 4300 G for 2 hours. The supernatant was then discarded, and clay containing two-dimensional particles (single-layer MXene particles) was obtained.

[0113] [Examples 11 and 12] A precursor (MAX) was prepared in the same manner as in Examples 1 to 5, and then the following step (2) was carried out. The resulting solid-liquid mixture (slurry) containing solid components derived from the Ti3AlC2 powder was subjected to the first washing, first intercalation, second washing, and second intercalation in the same manner as in Examples 1 to 5, and then the following step (7) was carried out to produce clay containing two-dimensional particles (single-layer MXene particles). After the preparation of the precursor (MAX), etching, first cleaning, first intercalation, second cleaning, and second intercalation were carried out in the same manner as in Examples 1 to 5, the following step (7) was carried out to produce clay containing two-dimensional particles (single-layer MXene particles).

[0114] (1) Preparation of precursor (MAX): Same as in Examples 1 to 5 (2) Etching of precursor Using the Ti3AlC2 particles (powder) prepared in the above step (1), etching was carried out under the following etching conditions to obtain a solid-liquid mixture (slurry) containing solid components derived from the Ti3AlC2 powder. (Etching conditions) Precursor: Ti3AlC2 (passed through a 45 μm sieve) See Table 1 for the etching solution composition. Precursor input: 3.0g Etching container: 100mL Eye Boy Etching temperature: 35℃ Etching time: 24 hours Stirrer rotation speed: 400 rpm (3) First washing: same as in Examples 1 to 5 (4) First intercalation: same as in Examples 1 to 5 (5) Second washing: same as in Examples 1 to 5 (6) Second intercalation: same as in Examples 1 to 5 (7) Delamination The slurry obtained after the second intercalation was placed in a 50 mL centrifuge tube, and 5 g of aqueous phosphoric acid solution (0.85% by mass) was added. The mixture was then stirred by handshaking. Next, 20 mL of the organic compound listed in Table 1 was added, and the mixture was centrifuged at 3,500 G for 5 minutes. The supernatant was then collected. Another 35 mL of organic compound was added, and the mixture was stirred for 15 minutes on a shaker. The mixture was then centrifuged at 3,500 G for 5 minutes. The supernatant was then obtained as a solution containing single-layer MXene particles. This single-layer MXene particle-containing solution was then centrifuged at 4,300 G for 2 hours. The supernatant was discarded, and clay containing two-dimensional particles (single-layer MXene particles) was obtained.

[0115] [Comparative Example 1] (1) The precursor (MAX) was prepared in the same manner as in Examples 1 to 5 above, and then (2) etching of the precursor and Li intercalation, (3) washing, and (4) delamination were carried out as follows. Samples containing single-layer and few-layer MXene particles were prepared without intercalation using an organic compound as an intercalator.

[0116] (1) Preparation of precursor (MAX): Same as in Examples 1 to 5 (2) Precursor etching and Li intercalation Using the Ti3AlC2 particles (powder) prepared by the above method, etching and Li intercalation were carried out under the following conditions to obtain a solid-liquid mixture (slurry) containing solid components derived from the Ti3AlC2 powder. (Etching and Li intercalation conditions) Precursor: Ti3AlC2 (passed through a 45 μm sieve) Etching solution composition: LiF 3g HCl (9M) 30mL Precursor dosage: 3g Etching container: 100mL Eye Boy Etching temperature: 35℃ Etching time: 24 hours Stirrer rotation speed: 400 rpm

[0117] (3) Cleaning The slurry was divided into two portions and placed in two 50 mL centrifuge tubes. After centrifugation at 3500 G using a centrifuge, the supernatant was discarded. (i) 40 mL of pure water was added to the remaining precipitate in each centrifuge tube, (ii) the tube was centrifuged again at 3500 G, and (iii) the supernatant was separated and removed. These steps (i) to (iii) were repeated 10 times, and after confirming that the pH of the 10th supernatant was above 5, the supernatant was discarded and Ti3C2T s -Water medium clay was obtained.

[0118] (4) Delamination The above Ti3C2T s (i) 40 mL of pure water was added to the aqueous clay medium, followed by stirring for 15 minutes on a shaker. (ii) The mixture was centrifuged at 3500 G, and (iii) the supernatant was collected as a solution containing single-layered MXene particles. These steps (i) to (iii) were repeated four times to obtain a single-layered MXene particle-containing supernatant. This supernatant was then centrifuged at 4300 G for two hours using a centrifuge, after which the supernatant was discarded. Clay containing single-layered and few-layered MXene particles was obtained as a sample containing single-layered and few-layered MXene particles.

[0119] Comparative Example 2 (1) The precursor (MAX) was prepared in the same manner as in Examples 1 to 5 above, and then (2) etching, (3) washing, (4) TMAOH intercalation, and (5) delamination were carried out as follows to obtain clay containing single- and few-layer MXene particles.

[0120] (1) Preparation of precursor (MAX): Same as in Examples 1 to 5 (2) Etching of precursor Using the Ti3AlC2 particles (powder) prepared by the above method, etching was carried out under the following etching conditions to obtain a solid-liquid mixture (slurry) containing solid components derived from the Ti3AlC2 powder. (Etching conditions) Precursor: Ti3AlC2 (passed through a 45 μm sieve) Etching solution composition: 49% HF 25mL, 25mL H2O Precursor input: 3.0g Etching container: 100mL Eye Boy Etching temperature: 20°C to 25°C (room temperature) Etching time: 24 hours Stirrer rotation speed: 400 rpm

[0121] (3) Cleaning The slurry was divided into two parts and placed in two 50 mL centrifuge tubes. The tubes were centrifuged at 3500 G using a centrifuge, and the supernatant was discarded. 40 mL of pure water was added to each tube, and the tubes were centrifuged again at 3500 G to separate and remove the supernatant. This procedure was repeated 11 times. After the final centrifugation, the supernatant was discarded, and the remaining precipitate was Ti3C2T. s -Water medium clay was obtained.

[0122] (4) Intercalation of TMAOH Ti3C2T prepared by the above method s -The water medium clay was subjected to intercalation of TMAOH using TMAOH as an intercalator, by stirring at 20°C or higher and 25°C or lower for 12 hours, according to the conditions for intercalation of TMAOH below. (TMAOH intercalation conditions) Ti3C2T s -Water medium clay (MXene after washing): solid content 1.0g TMAOH 5H2O: 1.98g ·Pure water: 100mL Intercalation vessel: 250mL Eye Boy ·Temperature: 20℃ or higher and 25℃ or lower (room temperature) ·Time: 12h Stirrer rotation speed: 800 rpm

[0123] (5) Delamination The slurry obtained by TMAOH intercalation was divided into two parts and placed in two 50 mL centrifuge tubes. The tubes were centrifuged at 3500 G and the supernatant was collected. 40 mL of pure water was added to each tube, and the tubes were centrifuged again at 3500 G and the supernatant was collected. This procedure was repeated twice to obtain a supernatant containing single- and few-layered MXene particles. The supernatant containing the single- and few-layered MXene particles was centrifuged at 3500 G for 1 hour to settle the single- and few-layered MXene particles, yielding a clay containing single- and few-layered MXene particles.

[0124] [Table 1]

[0125] [Table 2]

[0126] (Conductive film manufacturing method) The clay containing two-dimensional particles (single-layer MXene particles) obtained in Examples 1 to 10 and Comparative Examples 1 and 2 was subjected to suction filtration. After filtration, the clay was vacuum dried at 80°C for 24 hours to produce a conductive film containing two-dimensional particles. A membrane filter (Merck, Durapore, pore size 0.45 μm) was used for the suction filtration. The supernatant contained 0.05 g of two-dimensional particle solids and 40 mL of pure water.

[0127] (Method for detecting elements on the layer surface) The conductive film containing the obtained two-dimensional particles was measured by X-ray photoelectron spectroscopy (XPS) to detect the organic compounds contained in the two-dimensional particles and the elements on the layer surface. XPS measurements were performed using a Quantum 2000 manufactured by ULVAC-PHI, Inc.

[0128] (Method for detecting metal cations) The resulting 2D particles were dissolved by alkali fusion, and the resulting solution was analyzed by inductively coupled plasma atomic emission spectroscopy (ICP-AES) to detect the metal cations contained in the 2D particles. For ICP-AES analysis, a Thermo Fisher Scientific iCAP7400 was used.

[0129] (Detection of organic compounds) The obtained two-dimensional particles were analyzed by gas chromatography-mass spectrometry (GC-MS) to confirm the presence of organic compounds. For GC-MS analysis, an Agilent GCMS instrument (Aglient 5975C) was used.

[0130] (Measurement of the average long diameter of the two-dimensional surface of a two-dimensional particle) A slurry of two-dimensional particles dispersed in water was applied to a silicon substrate and dried. Scanning electron microscope (SEM) images were then taken and measured. At a magnification of 2,000x, one or more SEM images (approximately one to three fields of view) with a field size of 45 μm × 45 μm were used to visually identify 80 or more two-dimensional particles (MXene particles). The shape of each two-dimensional surface (viewed perpendicular to the layer of each two-dimensional particle) was approximated as an ellipse, and its long diameter was measured. The average long diameter measured for the two-dimensional particles (MXene particles) was used as the average long diameter of the two-dimensional surface of the two-dimensional particles. The elliptical shape was approximated using SEM image analysis software "Azokun" (registered trademark, manufactured by Asahi Kasei Engineering Co., Ltd.). When using a silicon substrate, minute black dots in the micrographs may originate from the substrate. Therefore, prior to image analysis, the porous background was removed as necessary.

[0131] (Measurement of the average thickness of two-dimensional particles) Using an atomic force microscope (AFM), one or more photographs were taken with a field of view of 50 μm × 50 μm. In each photograph, 80 randomly selected two-dimensional particles were selected, and the thickness of each of the 2D particles was determined. The average thickness of the 80 particles was calculated.

[0132] (Method for measuring the conductivity of conductive films) The conductivity of the resulting conductive film containing two-dimensional particles was determined. Resistivity (Ω) and thickness (μm) were measured at three locations per sample. The conductivity (S / cm) was calculated from these measurements, and the average of the three resulting conductivities was used. Resistivity was measured using a simple low-resistivity meter (Loresta AX MCP-T370, manufactured by Mitsubishi Chemical Analytical Co., Ltd.) to measure the surface resistance of the conductive film using the four-terminal method. Thickness was measured using a micrometer (MDH-25MB, manufactured by Mitutoyo Corporation). The volume resistivity was then calculated from the measured surface resistance and the thickness of the conductive film, and the conductivity was calculated as E0 by taking the reciprocal of this value.

[0133] (Conductivity change rate measurement method) The conductive film was placed in a thermo-hygrostat chamber at a relative humidity of 99% and a temperature of 25°C. After leaving it for 7 days, the conductivity was measured and designated as E. E was divided by E0 to determine the rate of change in conductivity.

[0134] (Confirmation of the form of Al cation) The two-dimensional particles obtained in Example 13 were mixed with approximately 9 times the mass of KBr in a glove box under an Ar atmosphere, and then packed into a 4 mm zirconia sample tube. 27 Al NMR measurements were performed to obtain one-dimensional NMR spectra. Similar measurements were also performed for Ti3AlC2, AlCl3·6H2O, Al2O3, and AlF3. 27 The measurement conditions for Al NMR measurement were as follows: Observation kernel: 27 Al Measurement method: Magic angle rotation + Hahn echo method MAS rotation speed: 12kHz Accumulated delay time: 0.1 seconds Accumulation count: 160,000 times

[0135] Table 2 shows the measurement results of the type of element on the layer surface, metal cation, type of organic low molecular weight compound, average particle size, average thickness, conductivity, and rate of change in conductivity.

[0136] [Table 3]

[0137] From the results in Table 1 above, the MXene two-dimensional particles obtained in this embodiment did not contain Li and were able to maintain high conductivity even under high humidity conditions. In Examples 6 and 7, it was confirmed that P was contained as an element on the layer surface, and PO4 was added to the M of the layer of the MXene two-dimensional particles. 3- In Example 10, it was confirmed that S was contained as an element on the layer surface, and SO4 2- It was confirmed that the two-dimensional particles obtained in this embodiment had a two-dimensional surface with an average major axis of 1 μm or more and an average thickness of 10 nm or less. Therefore, the two-dimensional particles obtained in this embodiment could be used to prepare a film (conductive film) that could be handled without adding a binder. Furthermore, because the two-dimensional surface of the two-dimensional particles of MXene had a large average major axis of 1 μm, the obtained film (conductive film) exhibited high conductivity.

[0138] Regarding the Al content, the Al content in the two-dimensional particles of Example 13 was 0.43 mass%, which was confirmed to be a significant increase compared to 0.02 mass% in Comparative Example 1, which did not use a compound containing Al as the metal-containing compound. 27 In the spectrum obtained by Al NMR measurement, it was confirmed that Al contained in the two-dimensional particles of Example 13 had a peak near −15.6 ppm. The NMR spectrum of Ti3AlC2 showed a peak near 113.2 ppm, while the NMR spectrum of AlCl3·6H2O showed a peak near -1.3 ppm. This suggests that the Al contained in the 2D particles of Example 13 exists in a state different from that of the precursor or the metal-containing compound. Furthermore, the NMR spectrum of Al2O3 showed a peak near 12.8 ppm. Al2O3 is thought to form when Al is not intercalated between layers and forms an oxide by itself. Based on the above measurement results, it is believed that Al exists inside the 2D particles of Example 3, i.e., between the layers. On the other hand, it was confirmed that the peak in the NMR spectrum of AlF3 is around 16.2 ppm, which is close to the peak of Al in the two-dimensional particles of Example 13. Since AlF3 is an ionic compound, it is believed that the Al contained in the two-dimensional particles of Example 13 also exists as an ion (metal cation).

[0139] On the other hand, in Comparative Example 1, the conductivity significantly decreased under high humidity conditions because Li was used as an intercalator. In Comparative Example 2, the conductivity of the film was low because no metal cations were contained and the low-conductivity TMAOH remained in the MXene particles. [Industrial Applicability]

[0140] The two-dimensional particles, conductive film and conductive paste of the present invention can be used for any suitable application, and can be particularly preferably used as, for example, electrodes in electrical devices. [Explanation of symbols]

[0141] 1a, 1b layer body (M m X n layer) 3a, 5a, 3b, 5b Modified or terminal T 7a, 7b MXene layers 10, 10a, 10b MXene particles (two-dimensional particles of layered materials) 30 Conductive film

Claims

1. A two-dimensional particle having one or more layers, containing a metal cation, The layer comprises a compound having the following formula: M ｍ X ｎ wherein M is at least one Group 3, 4, 5, 6, or 7 metal; X is a carbon atom, a nitrogen atom, or a combination thereof; n is 1 or more and 4 or less, m is greater than n and is equal to or less than 5. and a modification or termination T (T is at least one selected from the group consisting of a hydroxyl group, a fluorine atom, a bromine atom, an oxygen atom, a sulfur atom, Se, Te, and a hydrogen atom) present on the surface of the layer body, M and PO ４ ３－ and S.O. ４ ２－ and at least one selected from the group consisting of the metal cations include cations of at least one metal selected from the group consisting of K, Na, Mg, Ca, and Sr; Two-dimensional particles having a Li content of less than 0.002% by mass.

2. The two-dimensional particle according to claim 1 , wherein the Li content is 0.0001 mass % or less.

3. The two-dimensional particle of claim 1 , wherein Al cations are present between the layers.

4. The two-dimensional particle according to claim 1 , wherein the average thickness is 1 nm or more and 10 nm or less.

5. The two-dimensional particle according to claim 1 , wherein the average value of the major axis of the two-dimensional surface is 1 μm or more and 20 μm or less.

6. A conductive film comprising the two-dimensional particles according to any one of claims 1 to 5.

7. The conductive film according to claim 6, having a conductivity of 2,000 S / cm or more.

8. A conductive paste comprising the two-dimensional particles according to any one of claims 1 to 5 and a dispersion medium.

9. (a) a compound of the formula: M ｍ AX ｎ wherein M is at least one Group 3, 4, 5, 6, or 7 metal; X is a carbon atom, a nitrogen atom, or a combination thereof; A is at least one Group 12, 13, 14, 15, or 16 element; n is 1 or more and 4 or less, m is greater than n and is equal to or less than 5. providing a precursor represented by (b) performing an etching treatment using an etching solution to remove at least some of the A atoms from the precursor; (c) performing a first water washing treatment, which includes a step of washing the etched product obtained by the etching treatment with water; (d) performing a first intercalation treatment, which includes a step of mixing the first water-washed product obtained by the first water washing with a metal-containing compound; (e) performing a second water washing treatment, which includes a step of washing the first intercalation treatment product obtained by the first intercalation treatment with water; (f) performing a second intercalation treatment, which includes a step of mixing the second water-washed product obtained by the second water-washing treatment with an organic compound; (g) performing a delamination treatment, which includes a step of stirring the second intercalation treatment product obtained by the second intercalation treatment, to obtain two-dimensional particles. Including, the etching solution contains an anion containing at least one selected from the group consisting of a phosphorus atom, a sulfur atom, a chlorine atom, and an iodine atom; the metal-containing compound contains a cation of at least one metal selected from the group consisting of K, Na, Mg, Ca, and Sr; The solubility of the organic compound in water is 5 g / 100 g H at 25°C. ２ O or higher, Method for producing two-dimensional particles.

10. The delamination process is carried out by ４ ３－ The method for producing two-dimensional particles according to claim 9, comprising the step of stirring the second intercalation product in the presence of

11. The Hildebrand solubility parameter of the organic compound is 19.0 MPa. １／２ Over 47.8 MPa １／２ The method for producing two-dimensional particles according to claim 9 or 10, wherein:

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