Conductive two-dimensional particles and method for producing the same

Abstract

The present invention provides electroconductive two-dimensional particles that contain MXene and are capable of forming an electroconductive film that exhibits high electroconductivity for a long period of time. The electroconductive two-dimensional particles are a layered material including one or more layers. The layer includes: a layer body represented by formula MmXn (in the formula, M represents at least one metal in group 3, 4, 5, 6, or 7, X represents a carbon atom, a nitrogen atom, or a combination thereof, n is 1-4, m is more than n but not more than 5); and a modification or a terminal T (T represents at least one selected from the group consisting of a hydroxyl group, a fluorine atom, an oxygen atom, and a hydrogen atom) existing on the surface of the layer body. The layer does not include chlorine atoms, iodine atoms, or bromine atoms, and has, at least one selected from the group consisting of a fluorine atom, an oxygen atom, and a hydroxyl group. Titanium atoms of the layer body of one layer are bonded with titanium atoms of a layer body of another layer via the oxygen atoms.

Description

Technical Field

[0001] The present disclosure relates to conductive two-dimensional particles and a method for manufacturing the same.

Background Art

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

[0003] Currently, various studies are being conducted on the application of MXene to various fields. In order to enhance the properties of materials containing MXene for such applications, changing the structure of MXene has been considered. For example, Non-Patent Document 1 shows a separation technique for desalination using an MXene two-dimensional film. In order to suppress the swelling of the above-mentioned MXene two-dimensional film and efficiently capture monovalent metal ions, it has been shown that Ti-O-Ti bonds are formed between adjacent nanosheets by a self-crosslinking reaction using the hydroxyl groups of MXene nanosheets.

[0004] Also, Non-Patent Document 2 shows that an MXene film can be applied to ion sieving and water purification. In Non-Patent Document 2, in order to suppress the swelling of the MXene film and enhance the efficient ion sieving of a mixture of K + / Pb 2+ and the removal efficiency of heavy metal ions (Pb), it has been shown to use a thermally crosslinked two-dimensional MXene film.

Prior Art Documents

Non-Patent Documents

[0005]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] The cross-linked MXene membranes shown in Non-Patent Document 1 and Non-Patent Document 2 do not show excellent conductivity or are difficult to show a high conductivity over a long period of time when applied to various electric devices, for example. The present disclosure has been made in view of the above circumstances, and an object thereof is to provide conductive two-dimensional particles useful for forming a conductive film or the like that shows a high conductivity over a long period of time, a conductive film that shows a high conductivity over a long period of time, a method for producing the conductive two-dimensional particles, and a conductive paste and a conductive composite material containing the conductive two-dimensional particles.

Means for Solving the Problems

[0007] According to one gist of the present disclosure, Conductive two-dimensional particles of a layered material including one or more layers, wherein the layer has the following formula: M m X n (wherein M is at least one metal of Groups 3, 4, 5, 6, and 7, 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 5 or less) comprising a layer body represented by the formula, and a modification or termination T (T is at least one selected from the group consisting of a hydroxyl group, a fluorine atom, an oxygen atom, and a hydrogen atom) present on the surface of the layer body, not containing a chlorine atom, an iodine atom, and a bromine atom, having at least one selected from the group consisting of a fluorine atom, an oxygen atom, and a hydroxyl group, There is provided a conductive two-dimensional particle in which titanium atoms of the layer body of one layer are bonded to titanium atoms of the layer body of another layer via an oxygen atom.

[0008] According to another aspect of the present disclosure, (a) The following formula: M m AX n (wherein M is at least one metal of Groups 3, 4, 5, 6, 7, X is a carbon atom, a nitrogen atom, or a combination thereof, A is at least one element of Groups 12, 13, 14, 15, 16, n is 1 or more and 4 or less, m is greater than n and is 5 or less) preparing a precursor represented by the formula, (b) etching to remove at least a part of the A atoms from the precursor using an etching solution not containing a chlorine atom, an iodine atom, and a bromine atom, (c) washing the etched product obtained by etching with water to obtain a water-washed product, (d) performing an intercalation treatment of an intercalation compound for the layer by stirring a mixture containing the water-washed product and the intercalation compound for the layer, (e) delaminating using the intercalation-treated product obtained by the intercalation treatment, and (f) performing a heat treatment of heating the delamination-treated product obtained by the delamination at 200°C or higher in an inert gas atmosphere to obtain a conductive two-dimensional particle A method for manufacturing conductive two-dimensional particles, which includes , is provided.

Advantages of the Invention

[0009] According to the present disclosure, the conductive two-dimensional particles include a predetermined one or more layers, do not include chlorine atoms, iodine atoms, and bromine atoms, have at least one selected from the group consisting of fluorine atoms, oxygen atoms, and hydroxyl groups, and the titanium atoms of the layer main body of one layer and the titanium atoms of the layer main body of another layer are bonded through oxygen atoms, whereby conductive two-dimensional particles including MXene and exhibiting a high conductivity over a long period are provided.

Brief Description of the Drawings

[0010]

Figure 1

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Modes for Carrying Out the Invention

[0011] (Embodiment 1: Conductive Two-Dimensional Particles) Hereinafter, the conductive two-dimensional particles in one embodiment of the present disclosure will be described in detail, but the present disclosure is not limited to such an embodiment.

[0012] The conductive two-dimensional particles in this embodiment are Conductive two-dimensional particles of a layered material comprising one or more layers, wherein said layer has the following formula: M m X n (wherein M is at least one metal of Groups 3, 4, 5, 6, 7, X is a carbon atom, a nitrogen atom or a combination thereof, n is 1 or more and 4 or less, and m is greater than n and 5 or less) and comprises a layer body represented by the formula and a modification or termination T (T is at least one selected from the group consisting of a hydroxyl group, a fluorine atom, an oxygen atom and a hydrogen atom) present on the surface of the layer body, does not contain a chlorine atom, an iodine atom and a bromine atom, has at least one selected from the group consisting of a fluorine atom, an oxygen atom, and a hydroxyl group, and the titanium atoms of the layer body of one layer and the titanium atoms of the layer body of another layer are bonded via an oxygen atom. When a conductive film is formed using the conductive two-dimensional particles, for example, a conductive film having a high initial conductivity and suppressed deterioration of conductivity over time can be formed.

[0013] In the conductive two-dimensional particles, titanium atoms of the layer main body of one layer and titanium atoms of the layer main body of another layer are bonded via oxygen atoms. Hereinafter, this bond may be referred to as an "interlayer cross-linking bond". FIG. 1 is a schematic cross-sectional view for explaining the interlayer cross-linking bond in the conductive two-dimensional particles of the present embodiment. As schematically shown in FIG. 1, in the conductive two-dimensional particles 100, a titanium atom (not shown) of the layer main body of MXene 10a of one layer and a titanium atom (not shown) of the layer main body of MXene 10b of another layer are bonded via an oxygen atom 21, and a cross-linked structure 23 is formed between the two layers of MXene. In FIG. 1, for ease of explanation, the cross-linked structure between the two layers of MXene is shown. However, although not shown, the conductive two-dimensional particles of the present embodiment may also include a cross-linked structure between MXene 10a in FIG. 1 and another MXene existing above it, and a cross-linked structure between MXene 10b in FIG. 1 and another MXene existing below it, and may also include a case where three or more layers of MXene are bonded by a cross-linked structure. Further, although FIG. 1 shows a cross-linked structure between single-layer MXenes, at least one of the MXenes constituting the conductive two-dimensional particles of the present embodiment may be an MXene having a plurality of layers (preferably few-layer MXene described later).

[0014] The conductive two-dimensional particles of the present embodiment do not contain halogen atoms with a large atomic radius in the conductive two-dimensional particles, the distance between the layer main bodies of MXene becomes shorter, and it is considered that many cross-links are formed between the layer main bodies of MXene during the heat treatment in the manufacturing process of the conductive two-dimensional particles. As a result, the interlayer of MXene becomes sufficiently narrow, the intrusion of water molecules is sufficiently suppressed, and the moisture absorption resistance is considered to be enhanced. Also, the cross-linked structure is considered to be formed by the dehydration reaction of the hydroxyl groups on the MXene surface. The formation of the cross-linked structure also contributes to the improvement of the moisture absorption resistance by reducing the hydroxyl groups on the MXene surface, which are the water adsorption sites. The conductive film containing the conductive two-dimensional particles of the present embodiment, particularly the conductive film formed of the conductive two-dimensional particles of the present embodiment, has a high conductivity and can maintain the high conductivity over a long period. As shown in the examples described later, the interlayer cross-linking bond can be determined by the presence or absence of a peak at 800 to 900 cm -1 indicating the bond of titanium atom-oxygen atom-titanium atom (Ti-O-Ti) by FT-IR (Fourier transform infrared spectroscopy).

[0015] Hereinafter, MXene including one or more layers constituting the conductive two-dimensional particles of the present embodiment will be described. The above-mentioned layered material can be understood as a layered compound and is also represented as "M m X n T s ", where s is an arbitrary 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.

[0016] In the above formula of MXene, M is preferably at least one selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and Mn, and more preferably at least one selected from the group consisting of Ti, V, Cr, and Mo.

[0017] MXene has the above formula: M m X n which is known to 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" respectively mean approximately 1.3 (= 4 / 3) and approximately 0.6 (= 2 / 3).), Ti3C2, Ti3N2, Ti3(CN), Zr3C2, (Ti, V)3C2, (Ti2Nb)C2, (Ti2Ta)C2, (Ti2Mn)C2, Hf3C2, (Hf2V)C2, (Hf2Mn)C2, (V2Ti)C2, (Cr2Ti)C2, (Cr2V)C2, (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, (Cr2V2)C3, (Cr2Nb2)C3, (Cr2Ta2)C3, (Mo2Ti2)C3, (Mo2Zr2)C3, (Mo2Hf2)C3, (Mo2V2)C3, (Mo2Nb2)C3, (Mo2Ta2)C3, (W2Ti2)C3, (W2Zr2)C3, (W2Hf2)C3, (Mo 2.7 V 1.3 )C3 (in the above formula, "2.7" and "1.3" respectively mean approximately 2.7 (= 8 / 3) and approximately 1.3 (= 4 / 3).)

[0018] 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, which is a precursor of MXene, is Ti3AlC2, and MXene is Ti3C2T sThat is (in other words, M is Ti, X is C, n is 2, and m is 3).

[0019] In addition, in the present embodiment, the MXene may contain a relatively small amount of residual A atoms, for example, 10% by mass or less with respect to the original A atoms. The residual amount of A atoms can preferably be 8% by mass or less, more preferably 6% by mass or less. However, even if the residual amount of A atoms exceeds 10%, there may be no problem depending on the use of the electrode and the usage conditions.

[0020] Hereinafter, the MXene constituting the conductive two-dimensional particles according to the present embodiment will be described with reference to FIG. 2.

[0021] The conductive two-dimensional particles according to the present embodiment are an aggregate containing a cross-linked product of one layer of MXene 10c (single-layer MXene) schematically illustrated in FIG. 2(a), more specifically, an aggregate containing a plurality of cross-linked products in which two or more MXene 10c are cross-linked. MXene 10c, more specifically, is an MXene layer 7a having a layer main body (M m X n layer) 1a represented by and a modification or termination T3a, 5a present on the surface of the layer main body 1a (more specifically, at least one of two surfaces facing each other in each layer). Therefore, the MXene layer 7a is also represented as "M m X n layer) 1a represented by and a modification or termination T3a, 5a present on the surface of the layer main body 1a (more specifically, at least one of two surfaces facing each other in each layer). Therefore, the MXene layer 7a is also represented as "M m X n T s ", and s is an arbitrary number.

[0022] In the conductive two-dimensional particles according to this embodiment, the MXene forming the crosslinked structure can be one layer or a plurality of layers. Examples of the multi-layer MXene include, but are not limited to, two layers of MXene 10d schematically shown in Fig. 2(b). 1b, 3b, 5b, and 7b in Fig. 2(b) are the same as 1a, 3a, 5a, and 7a in Fig. 2(a) described above. Two adjacent MXene layers (for example, 7a and 7b) of the multi-layer MXene do not necessarily have to be completely separated and may be in partial contact. The MXene 10c is such that the multi-layer MXene 10d is individually separated and exists as one layer, and there may be a case where the non-separated multi-layer MXene 10d remains and is a mixture of the single-layer MXene 10c and the multi-layer MXene 10d. Even when the multi-layer MXene is included, the multi-layer MXene is preferably MXene with a small number of layers obtained through an interlayer delamination process. The term "a small number of layers" means, for example, that the number of stacked layers of MXene is 10 or less. Hereinafter, this "multi-layer MXene with a small number of layers" may be referred to as "few-layer MXene". The thickness of the few-layer MXene in the stacking direction is preferably 15 nm or less, and more preferably 10 nm or less. Also, the single-layer MXene and the few-layer MXene may be collectively referred to as "single-layer and few-layer MXene".

[0023] MXene forming the crosslinked structure is preferably mostly monolayer or few-layer MXene. By having most of the MXene forming the crosslinked structure be monolayer or few-layer MXene, the specific surface area of the MXene can be made larger than that of multilayer MXene, and as a result, the deterioration of conductivity over time can be further suppressed. For example, the proportion of monolayer or few-layer MXene, where the number of stacked layers of MXene is 10 or less and the thickness is 15 nm or less, preferably 10 nm or less, in all the MXene forming the crosslinked structure is preferably 80% by volume or more, more preferably 90% by volume or more, and still more preferably 95% by volume or more. Further, it is more preferable that the volume of monolayer MXene is larger than the volume of few-layer MXene. Since the true density of these MXene does not vary greatly depending on the form of existence, it can also be said that it is more preferable that the mass of monolayer MXene is larger than the mass of few-layer MXene. When in these relationships, the specific surface area of the MXene can be increased, and the deterioration of conductivity over time can be more further suppressed. Most preferably, the crosslinked structure is formed only of monolayer MXene.

[0024] Although not limiting the present embodiment, the thickness of each layer of MXene (corresponding to the above MXene layers 7a, 7b) can be, for example, 1 nm or more and 30 μm or less, and can be, for example, 1 nm or more and 5 nm or less, or further 1 nm or more and 3 nm or less (mainly depending on the number of M atomic layers contained in each layer). For each individual laminate of the multilayer MXene that can be contained, the interlayer distance (or void size, indicated by Δd in Fig. 2(b)) is, for example, 0.8 nm or more and 10 nm or less, particularly 0.8 nm or more and 5 nm or less, and more particularly about 1 nm, and the total number of layers can be 2 or more and 20,000 or less.

[0025] The aforementioned conductive two-dimensional particles do not contain chlorine atoms, iodine atoms, and bromine atoms (hereinafter, these may be collectively referred to as "halogen atoms"). Since the conductive two-dimensional particles do not contain halogen atoms, cross-linking between the layer bodies of MXene is likely to be formed during the manufacturing process of the conductive two-dimensional particles. A conductive film containing conductive two-dimensional particles with a large number of cross-links between the layer bodies of MXene is superior in moisture absorption resistance and exhibits a high conductivity over a long period compared to conventional cross-linked MXene films.

[0026] The above "not containing chlorine atoms, iodine atoms, and bromine atoms" means that when measured using an ion chromatography device as shown in the examples described later, the content rate of each atom is less than the quantitative lower limit value, that is, the chlorine atom is less than 0.004% by mass, the iodine atom is less than 0.04% by mass, and the bromine atom is less than 0.02% by mass. The content rates are most preferably all 0% by mass.

[0027] The aforementioned conductive two-dimensional particles have at least one selected from the group consisting of fluorine atoms, oxygen atoms, and hydroxyl groups. Preferably, the surface of the layer body constituting MXene has at least one selected from the group consisting of fluorine atoms, oxygen atoms, and hydroxyl groups. In the conductive two-dimensional particles, at least one selected from the group consisting of fluorine atoms, oxygen atoms, and hydroxyl groups with a small atomic radius is present, for example, on the surface of the layer body constituting MXene, so that the interlayer distance becomes narrow, and cross-linking between the layer bodies of MXene is likely to be formed during the manufacturing process of the conductive two-dimensional particles. By forming a large number of cross-links between the layer bodies of MXene, high moisture absorption resistance can be achieved. The presence of at least one selected from the group consisting of fluorine atoms, oxygen atoms, and hydroxyl groups in the conductive two-dimensional particles can be confirmed by the XPS method as described later.

[0028] The aforementioned conductive two-dimensional particles further have phosphate ions (PO4 3-) may have. The above phosphate ions may be derived from H3PO4 (phosphoric acid), which is a raw material used in the manufacturing process of the conductive two-dimensional particles. By having the above phosphate ions, delamination of MXene is likely to occur during the manufacturing process of the conductive two-dimensional particles, and a product containing more monolayer and few-layer MXene as the conductive two-dimensional particles can be obtained. A conductive film formed using the conductive two-dimensional particles containing more monolayer and few-layer MXene is preferable because it has a higher conductivity. Furthermore, it may contain a phosphorus atom derived from the phosphate ion. It is preferable that the conductive two-dimensional particles contain a phosphorus atom because it is easy to achieve a high conductivity. The conductive two-dimensional particles of the present embodiment may have a phosphorus atom content of 0.2 mass% or more and 14 mass% or less. The presence of phosphate ions in the conductive two-dimensional particles can be confirmed, for example, by performing high-resolution analysis (narrow scan analysis) using an X-ray photoelectron spectrometer to bond with M in the layer of MXene. Also, the presence of phosphorus atoms in the conductive two-dimensional particles can be confirmed by the XPS method.

[0029] The conductive two-dimensional particles preferably have a peak of the (002) plane at 2θ = 8° or more in the profile obtained by X-ray diffraction measurement. As described above, the conductive two-dimensional particles of the present embodiment do not contain halogen atoms, dispersants, etc., and the distance between the layers constituting MXene is shorter than that of conventional MXene. Due to the narrow interlayer of MXene, it is difficult for water molecules to penetrate, and it has excellent moisture absorption resistance. The narrow interlayer of MXene can be determined from the XRD profile obtained by X-ray diffraction measurement. In the XRD profile obtained by X-ray diffraction measurement, it can be determined at the position of a low-angle peak of 10° (deg) or less corresponding to the (002) plane of MXene. The higher the angle of the peak in the XRD profile, the narrower the interlayer distance. The conductive two-dimensional particles in the present embodiment preferably have a peak of the (002) plane obtained by X-ray diffraction measurement at 2θ = 8.0° or more. The peak position is more preferably 8.5° or more. The upper limit of the peak position is about 9.0°. The peak position refers to the peak top. The X-ray diffraction measurement may be performed under the conditions shown in the examples described later. The measurement target may be conductive two-dimensional particles or a conductive film containing conductive two-dimensional particles.

[0030] (Embodiment 2: Method for manufacturing conductive two-dimensional particles) Hereinafter, the method for manufacturing conductive two-dimensional particles in the embodiments of the present invention will be described in detail, but the present disclosure is not limited to such embodiments.

[0031] The method for manufacturing conductive two-dimensional particles of the present embodiment is (a) The following formula: M m AX n (In the formula, M is at least one metal of Groups 3, 4, 5, 6, and 7, X is a carbon atom, a nitrogen atom, or a combination thereof, A is at least one element of Groups 12, 13, 14, 15, and 16, n is 1 or more and 4 or less, m is greater than n and 5 or less) Prepare a precursor represented by (b) Performing etching to remove at least a part of A atoms from the precursor using an etching solution that does not contain chlorine atoms, iodine atoms, and bromine atoms. (c) Washing the etched product obtained by etching with water to obtain a water-washed product. (d) Performing an intercalation treatment of an intercalation compound for the layer by stirring a mixed solution containing the water-washed product and the intercalation compound for the layer of the water-washed product. (e) Using the intercalation-treated product obtained by the intercalation treatment to perform delamination, and (f) Performing a heat treatment of heating the delamination-treated product obtained by the delamination at 200 °C or higher in an inert gas atmosphere to obtain conductive two-dimensional particles. is included. By this production method, conductive two-dimensional particles optimal for the production of a conductive film or the like that exhibits a high conductivity over a long period can be produced.

[0032] Hereinafter, each step of the above production method will be described in detail. · Step (a) First, prepare a predetermined precursor. The predetermined precursor that can be used in the present embodiment is a MAX phase, which is a precursor of MXene. The following formula: M m AX n (In the formula, M is at least one metal of Groups 3, 4, 5, 6, and 7. X is a carbon atom, a nitrogen atom, or a combination thereof. A is at least one element of Groups 12, 13, 14, 15, and 16. n is 1 or more and 4 or less. m is greater than n and 5 or less.) is represented by.

[0033] The above M, X, n, and m are as described for MXene. A is at least one Group 12, 13, 14, 15, or 16 element, usually a Group A element, typically Groups IIIA and IVA, and more particularly includes at least one selected from the group consisting of Al, Ga, In, Tl, Si, Ge, Sn, Pb, P, As, S, and Cd, preferably Al.

[0034] The MAX phase has a crystal structure in which a layer composed of A atoms is located between two layers represented by M m X n (each X may have a crystal lattice located within the octahedral array of M), and typically, when m = n + 1, one layer of X atoms is arranged between each of the n + 1 layers of M atoms (collectively referred to as the "M m X n layers"), and has a repeating unit in which a layer of A atoms (the "A atom layer") is arranged as the next layer after the n + 1th layer of M atoms, but is not limited thereto.

[0035] The above MAX phase can be produced by known methods. For example, TiC powder, Ti powder, and Al powder are mixed by ball milling, and the resulting mixed powder is fired in an Ar atmosphere to obtain a fired body (block-shaped MAX phase). Thereafter, the obtained fired body can be pulverized by an end mill to obtain a powdery MAX phase for the next step.

[0036] · Step (b) Etching is performed to remove at least a part of A atoms from the precursor using an etching solution that does not contain chlorine atoms, iodine atoms, and bromine atoms. The etching solution used in the manufacturing method of the present embodiment does not contain chlorine atoms, iodine atoms, and bromine atoms. That is, for example, it does not contain acids such as HCl, HI, and HBr, and other chlorides, iodides, and bromides. The etching solution contains at least hydrofluoric acid. The etching solution preferably further contains one or more of phosphoric acid and sulfuric acid, and more preferably further contains phosphoric acid. For example, it is possible to perform etching by the so-called MILD method in which HCl and LiF contained in the etching solution react in the system to generate HF, but preferably, etching is performed with an etching solution containing HF (hydrofluoric acid), that is, the so-called ACID method, or with an etching solution further containing phosphoric acid. According to these methods, it is preferable because it is easier to obtain flaky layered material particles (MXene particles) having a large planar region with a number average Feret diameter of preferably 3 μm or more than in the MILD method. Other conditions for etching are not particularly limited, and known conditions can be adopted. As the etching solution, a mixed solution of the above acid and, for example, pure water as a solvent can be used. The concentration of HF in the etching solution can be, for example, 1.5 M or more and 14 M or less, the concentration of H3PO4 can be, for example, 5.5 M or more, and the concentration of H2SO4 can be, for example, 5.0 M or more. In the etching of the A atoms, a part of the M atoms may also be selectively etched together with the A atoms. Examples of the etched product obtained by the above etching include a slurry.

[0037] · Step (c) The etched product obtained by the etching is washed with water. By performing the water washing, acids and the like used in the etching can be sufficiently removed. The amount of water to be mixed with the etched product and the washing method are not particularly limited. For example, adding water, stirring, centrifuging, etc. can be mentioned. As the stirring method, stirring using a hand shake, an automatic shaker, a share mixer, a pot mill, etc. can be mentioned. The degree of stirring such as the stirring speed and the stirring time may be adjusted according to the amount and concentration of the object to be treated. The washing with the water may be performed one or more times. Preferably, the washing with water is performed a plurality of times. For example, specifically, (i) water is added to (the etched product or the remaining precipitate obtained in (iv) below), (ii) stirred, (iii) the stirred product is centrifuged, (iv) after centrifugation, the supernatant is discarded, and the remaining precipitate is recovered, and the steps (i) to (iv) can be performed within a range of 2 or more times, for example, 15 times or less.

[0038] · Step (d) An intercalation treatment of the intercalation compound for layer insertion is performed, which includes stirring a mixed solution containing the water-washed product and the intercalation compound for layer insertion of the water-washed product.

[0039] The intercalation compound for layer insertion of the water-treated product may be any specific type as long as it can be inserted between the layers of the water-treated product and can be separated into each layer by delamination in step (e), which is the next step. As the intercalation compound for layer insertion, an alkali metal compound and an alkaline earth metal compound are preferable. More preferably, it is a Li-containing compound. As the Li-containing compound, an ionic compound in which Li ions are bonded to cations can be used. For example, hydroxides, phosphates, sulfide salts containing sulfates, nitrates, acetates, and carboxylates of Li ions can be mentioned. Preferably, it is a hydroxide, and more preferably, it is lithium hydroxide.

[0040] Other conditions for the intercalation process are not particularly limited. The liquidity of the mixed solution containing the water-washed product and the intercalation compound for the water-washed product is also not restricted. The mixed solution containing the water-washed product and the intercalation compound for the water-washed product is preferably alkaline. The pH of the mixed solution is preferably in the range of 8 to 14. The method for making the mixed solution alkaline is not limited. As the intercalation compound, a mixed solution containing a hydroxide, preferably lithium hydroxide as a Li-containing compound, or a mixed solution containing the intercalation compound and a pH adjuster such as hydroxides like ammonia, potassium hydroxide, sodium hydroxide, calcium hydroxide, magnesium hydroxide, etc. can be mentioned.

[0041] The content of the intercalation compound in the intercalation formulation is preferably 0.001% by mass or more. The above content is more preferably 0.01% by mass or more, and even more preferably 0.1% by mass or more. On the other hand, from the perspective of dispersibility in the solution, the content of the intercalation compound is preferably 10% by mass or less, and more preferably 1% by mass or less.

[0042] The specific method of intercalation is not particularly limited. For example, the intercalation compound may be mixed with the above-mentioned MXene aqueous medium clay and stirred or allowed to stand. For example, stirring at room temperature can be mentioned. The above stirring methods include, for example, the method using a stirrer such as a magnetic stirrer, the method using a stirring blade, the method using a mixer, and the method using a centrifuge. The stirring time can be set according to the production scale of the electrode, and for example, it can be set within 12 to 24 hours.

[0043] · Step (e) Using the intercalation product obtained by intercalation, delamination is performed. For example, delamination includes a step of centrifuging the intercalation product, discarding the supernatant, and washing the remaining precipitate with water. The conditions for the delamination treatment are not particularly limited. The dispersion medium used for delamination is also not particularly limited, and for example, it can be performed using one or more of a polar organic dispersion medium and an aqueous dispersion medium. As the polar organic dispersion medium, for example, a polar organic dispersion medium having a boiling point of 285 ° C or lower and 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 can be mentioned. More specifically, as the polar organic dispersion medium, for example, methanol (MeOH), ethanol (EtOH), dimethyl sulfoxide (DMSO), propylene carbonate (PC), N-methylformamide (NMF), acetone, methyl ethyl ketone (MEK), and tetrahydrofuran (THF), acetonitrile, N-methylacetamide (NMAc), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), sulfolane, N-methylpyrrolidone (NMP), etc. can be mentioned. The aqueous dispersion medium is typically water, and in some cases, it may contain a relatively small amount (for example, 30% by mass or less, preferably 20% by mass or less based on the total) of other liquid substances in addition to water. For example, multiple stirrings in delamination can be performed with a polar organic dispersion medium and an aqueous dispersion medium. For example, adding a polar organic dispersion medium such as N-methylformamide (NMF) to the intercalation product, stirring, then adding an aqueous dispersion medium and stirring, centrifuging, and recovering the supernatant liquid, repeating this one or more times, preferably 2 or more times and 10 times or less, to obtain a supernatant liquid containing monolayer or few-layer MXene as the delamination product. Or, this supernatant liquid can be centrifuged, and the supernatant liquid after centrifugation can be discarded to obtain monolayer or few-layer MXene-containing clay as the delamination product.

[0044] · Step (f) The delaminated product obtained by performing the delamination is heat-treated at 200 °C or higher in an inert gas atmosphere to obtain conductive two-dimensional particles. The temperature of the heat treatment is preferably 300 °C or higher, more preferably 400 °C or higher. The temperature of the heat treatment can be, for example, 700 °C or lower. The atmosphere for the heat treatment is an inert gas atmosphere such as argon or nitrogen. The pressure during the heat treatment is not particularly limited and may be normal pressure or vacuum. In the present embodiment, MXene that does not contain elements with a large steric size such as chlorine is annealed at a high temperature without oxidation, thereby realizing crosslinked MXene having narrow interlayer spaces and significantly improved moisture absorption resistance (reliability), which could not be achieved with conventional crosslinked MXene.

[0045] (Embodiment 3: Conductive film) Examples of the conductive film of the present embodiment include a conductive film (crosslinked MXene film) containing the conductive two-dimensional particles of the present embodiment. With reference to FIG. 3, the conductive film of the present embodiment will be described. FIG. 3 illustrates a conductive film 30 obtained by laminating only the conductive two-dimensional particles 100. The conductive film of the present embodiment is not limited thereto.

[0046] The conductive film may be a conductive composite material film (conductive composite material membrane) further containing a polymer (resin). The polymer may be included, for example, as an additive such as a binder added during film formation, or may be added to provide strength or flexibility. In the case of the conductive composite material film, the polymer can be more than 0% by volume and preferably 30% by volume or less in terms of the proportion in the conductive composite material film (when dry). The proportion of the polymer may further be 10% by volume or less, and even more preferably 5% by volume or less. In other words, the proportion of the conductive two-dimensional particles (particles of the layered material) in the conductive composite material film (when dry) is preferably 70% by volume or more, and may further be 90% by volume or more, and even more preferably 95% by volume or more. The conductive film may be a laminated film of two or more conductive composite material films having different proportions of the conductive two-dimensional particles.

[0047] Examples of the polymer include hydrophilic polymers (including those obtained by blending a hydrophilic auxiliary agent with a hydrophobic polymer to exhibit hydrophilicity and those obtained by hydrophilizing the surface of a hydrophobic polymer or the like). Preferred examples of the hydrophilic polymer include one or more selected from the group consisting of polysulfone, cellulose acetate, regenerated cellulose, polyethersulfone, water-soluble polyurethane, polyvinyl alcohol, sodium alginate, acrylic acid-based water-soluble polymer, polyacrylamide, polyaniline sulfonic acid, and nylon.

[0048] As the hydrophilic polymer, a hydrophilic polymer having a polar group, and the polar group is more preferably a group that forms a hydrogen bond with the modification or termination T of the layer. Examples of the polymer include one or more polymers selected from the group consisting of water-soluble polyurethane, polyvinyl alcohol, sodium alginate, acrylic acid-based water-soluble polymer, polyacrylamide, polyaniline sulfonic acid, and nylon, which are preferably used.

[0049] Among these, one or more polymers selected from the group consisting of water-soluble polyurethane, polyvinyl alcohol, and sodium alginate are more preferable. As the polymer, a polymer having a urethane bond having both hydrogen bond donor properties and hydrogen bond acceptor properties is preferable, and from this viewpoint, the water-soluble polyurethane is particularly preferable.

[0050] The film thickness of the conductive film is preferably 0.5 μm or more and 20 μm or less. By increasing the film thickness of the conductive film, the contact resistance at the grain boundaries becomes small and the conductivity tends to be high, so it is preferably 0.5 μm or more. The film thickness is more preferably 1.0 μm or more. From the viewpoint of conductivity, the thicker the film thickness is, the more preferable it is. However, when flexibility or the like is required, the film thickness is preferably 20 μm or less, more preferably 15 μm or less. The film thickness of the conductive film can be measured, for example, by measurement in micrometers or by cross-sectional observation by methods such as a scanning electron microscope (SEM), a microscope, or a laser microscope.

[0051] When the conductive film of this embodiment is, for example, in the form of a sheet with a thickness of 10 μm formed of the conductive two-dimensional particles, it preferably maintains a conductivity of 5000 S / cm or more. The conductivity can more preferably achieve a conductivity of 5500 S / cm or more, and still more preferably 6000 S / cm or more. There is no particular upper limit to the conductivity of the conductive film, but it can be, for example, 10000 S / cm or less. The conductivity can be determined as follows. That is, the surface resistivity is measured by the four-probe method, and the value obtained by multiplying the thickness [cm] by the surface resistivity [Ω / sq] becomes the volume resistivity [Ω·cm], and the conductivity [S / cm] can be obtained as the reciprocal thereof.

[0052] (Method for manufacturing a conductive film)

[0053] The method for manufacturing the conductive film of this embodiment using the conductive two-dimensional particles generated as described above is not particularly limited. For example, as exemplified below, a conductive film can be formed.

[0054] First, a dispersion of conductive two-dimensional particles in which the conductive two-dimensional particles prepared as described above are present in a medium liquid is prepared. Examples of the medium liquid include an aqueous medium liquid and an organic medium liquid. The medium liquid constituting the dispersion of the conductive two-dimensional particles is typically water, and in some cases, in addition to water, other liquid substances may be contained in a relatively small amount (for example, 30% by mass or less, preferably 20% by mass or less based on the total).

[0055] Before drying, a precursor of the conductive film (also referred to as a "precursor film") may be formed using the dispersion of the conductive two-dimensional particles. The method for forming the precursor film is not particularly limited, and for example, suction filtration, coating, spraying, etc. can be used.

[0056] More specifically, as the dispersion of the conductive two-dimensional particles, for example, the supernatant containing the conductive two-dimensional particles is appropriately adjusted (for example, diluted with an aqueous medium solution) and suction filtered through a filter (which may constitute a predetermined member together with the conductive film or may be finally separated from the conductive film) installed in a Nutsche or the like to at least partially remove the aqueous medium solution, whereby a precursor film can be formed on the filter. The filter is not particularly limited, and a membrane filter or the like can be used. By performing the above suction filtration, a conductive film can be produced without using a binder or the like. By using the conductive two-dimensional particles of the present embodiment, a conductive film can be produced without using a binder or the like in this way.

[0057] Alternatively, the dispersion of the conductive two-dimensional particles may be used as it is or appropriately adjusted (for example, diluted with an aqueous medium solution or a binder is added) and applied to a substrate. As the application method, for example, a method of spray application using a nozzle such as a one-fluid nozzle, a two-fluid nozzle, or an airbrush, a slit coating using a table coater, a comma coater, or a bar coater, a method such as screen printing or metal mask printing, spin coating, dip coating, or dropping can be mentioned. As the substrate, for example, a substrate formed of a metal material, a resin, or the like suitable for a biosignal sensing electrode can be appropriately employed. By coating on any appropriate substrate (which may constitute a predetermined member together with the conductive film or may be finally separated from the conductive film), a precursor film can be formed on the substrate.

[0058] Next, the precursor film formed above is dried to obtain, for example, the conductive film 30 as schematically shown in FIG. 3 above. In the present disclosure, "drying" means removing the aqueous medium solution that may be present in the precursor.

[0059] Drying can be carried out under mild conditions such as natural drying (typically placing in an air atmosphere at normal temperature and pressure) or air drying (blowing air), or under relatively active conditions such as hot air drying (blowing heated air), heat drying, and / or vacuum drying. The drying may be carried out, for example, at a temperature of 400 degrees or less using an atmospheric oven or a vacuum oven.

[0060] The formation and drying of the precursor film may be appropriately repeated as necessary until a desired conductive film thickness is obtained. For example, a combination of spraying and drying may be repeated multiple times.

[0061] As another method for manufacturing the conductive film, as shown in the examples described later, a pre-crosslinking conductive film may be formed using pre-crosslinking conductive two-dimensional particles and then heat-treated to obtain a conductive film. The formation of the pre-crosslinking conductive film using the pre-crosslinking conductive two-dimensional particles and the heat treatment may be carried out under the conditions described above.

[0062] When the conductive composite material of the present embodiment has a sheet-like form, for example, as illustrated below, the conductive two-dimensional particles and the polymer can be mixed to form a coating film.

[0063] First, a dispersion of conductive two-dimensional particles in which the above-mentioned conductive two-dimensional particles are present in a medium liquid (one or more of an aqueous medium liquid and an organic medium liquid), or powdery conductive two-dimensional particles, and a polymer may be mixed. The medium liquid constituting the dispersion of the conductive two-dimensional particles is typically water, and in some cases, in addition to water, other liquid substances may be contained in a relatively small amount (for example, 30% by mass or less, preferably 20% by mass or less based on the total).

[0064] The stirring of the conductive two-dimensional particles and the polymer can be carried out using a dispersion device such as a homogenizer, a propeller stirrer, a thin film swirling stirrer, a planetary mixer, a mechanical shaker, or a vortex mixer.

[0065] A slurry that is a mixture of the above-described conductive two-dimensional particles and a polymer may be applied to a substrate (e.g., a substrate), and the coating method is not limited. For example, a method of spray coating using a nozzle such as a one-fluid nozzle, a two-fluid nozzle, an airbrush, etc., a slit coating using a table coater, a comma coater, a bar coater, a method such as screen printing, metal mask printing, etc., spin coating, dip coating, and a coating method by dropping. As the above-described substrate, a substrate formed of, for example, a metal material, a resin, etc. suitable for a biosignal sensing electrode can be appropriately employed.

[0066] The above coating and drying may be repeatedly performed a plurality of times as necessary until a film with a desired thickness is obtained. Drying and curing may be performed, for example, at a temperature of 400 degrees or less using an atmospheric oven or a vacuum oven.

[0067] (Embodiment 4: Conductive Paste) As another use of the conductive two-dimensional particles of the present embodiment, a conductive paste containing the conductive two-dimensional particles can be mentioned. Examples of the conductive paste include a mixture of conductive two-dimensional particles and a medium. Examples of the medium include an aqueous medium liquid, an organic medium liquid, a polymer, metal particles, ceramic particles, etc., and those containing one or more of these can be mentioned. The mass ratio of the conductive two-dimensional particles in the conductive paste is, for example, 50% or more.

[0068] Using the above conductive paste, for example, applying it to a substrate or the like and drying it to form a conductive film can be mentioned as an example of the use.

[0069] (Embodiment 5: Conductive Composite Material) As another use of the conductive two-dimensional particles of the present embodiment, a conductive composite material containing the conductive two-dimensional particles and a polymer can be mentioned. The conductive composite material is not limited to the shape of the above-described conductive composite material film (conductive composite material membrane). The shape of the conductive composite material may be, in addition to the film shape, one having a thickness, a rectangular parallelepiped, a sphere, a polyhedron, etc.

[0070] As the polymer, the same polymer as that used for the conductive composite material film (conductive composite material membrane) can be used. For example, it may be included as an additive such as a binder for molding, or it may be added to provide strength or flexibility. The polymer can be more than 0% by volume and preferably 30% by volume or less in terms of the proportion in the conductive composite material (when dry). The proportion of the polymer may further be 10% by volume or less, and even more preferably 5% by volume or less. In other words, the proportion of the particles of the layered material in the conductive composite material (when dry) is preferably 70% by volume or more, and may further be 90% by volume or more, and even more preferably 95% by volume or more.

[0071] Examples of the polymer include hydrophilic polymers (including those having hydrophilicity by blending a hydrophilic aid with a hydrophobic polymer and those obtained by hydrophilizing the surface of a hydrophobic polymer or the like). As the hydrophilic polymer, it is more preferably included one or more selected from the group consisting of polysulfone, cellulose acetate, regenerated cellulose, polyethersulfone, water-soluble polyurethane, polyvinyl alcohol, sodium alginate, acrylic acid-based water-soluble polymer, polyacrylamide, polyaniline sulfonic acid, and nylon.

[0072] As the hydrophilic polymer, a hydrophilic polymer having a polar group, and the polar group is more preferably a group that forms a hydrogen bond with the modification or termination T of the layer. As the polymer, for example, one or more polymers selected from the group consisting of water-soluble polyurethane, polyvinyl alcohol, sodium alginate, acrylic acid-based water-soluble polymer, polyacrylamide, polyaniline sulfonic acid, and nylon are preferably used.

[0073] Among these, one or more polymers selected from the group consisting of water-soluble polyurethane, polyvinyl alcohol, and sodium alginate are more preferable. As the polymer, a polymer having a urethane bond having both hydrogen bond donor properties and hydrogen bond acceptor properties is preferable, and from that viewpoint, the water-soluble polyurethane is particularly preferable.

[0074] As described above in detail regarding the conductive two-dimensional particles, the method for producing the conductive two-dimensional particles, the conductive film, the conductive paste, and the conductive composite material in the embodiments of the present invention, various modifications are possible. It should be noted that the conductive two-dimensional particles of the present disclosure may be produced by a method different from the production method in the above-described embodiments, and the method for producing the conductive two-dimensional particles of the present disclosure is not limited to providing only the conductive two-dimensional particles in the above-described embodiments.

Examples

[0075] [Preparation of Samples] [Examples 1 to 5, Comparative Examples 1 to 5] In the present embodiment, heat treatment is performed on the pre-crosslinked conductive two-dimensional particles to obtain the conductive two-dimensional particles of the present embodiment, that is, crosslinked conductive two-dimensional particles. In this example, a pre-crosslinked conductive film was formed using the pre-crosslinked conductive two-dimensional particles, and then heat treatment was performed to obtain a crosslinked conductive film, that is, a conductive film formed of the conductive two-dimensional particles of the present embodiment.

[0076] In Examples 1 to 5, (1) preparation of a precursor (MAX), (2) etching of the precursor, (3) washing after etching, (4) intercalation of Li, (5) delamination, and (6) formation and heat treatment of a film using pre-crosslinked conductive two-dimensional particles were sequentially performed to obtain samples, as described in detail below. Also, Comparative Examples 1 to 5 were carried out up to the formation of the film to obtain samples.

[0077] (1) Preparation of Precursor (MAX) TiC powder, Ti powder, and Al powder (all manufactured by High Purity Chemical Laboratory Co., Ltd.) were put into a ball mill containing zirconia balls at a molar ratio of 2:1:1 and mixed for 24 hours. The obtained mixed powder was sintered at 1350 °C for 2 hours under an Ar atmosphere. The sintered body (block-shaped MAX) thus obtained was ground with an end mill to a maximum size of 40 μm or less. Thereby, Ti3AlC2 particles were obtained as a precursor (powder-shaped MAX).

[0078] (2) Etching of the precursor Using the Ti3AlC2 particles (powder) prepared by the above method, etching was performed under the following etching conditions to obtain a solid-liquid mixture (slurry) containing a solid component derived from Ti3AlC2 powder. (Etching conditions) · Precursor: Ti3AlC2 (sieved through a 45 μm sieve opening) · Etching solution composition: The composition shown in Table 1 below. However, hydrofluoric acid was a reagent with a concentration of 48% and phosphoric acid was a reagent with a concentration of 85%. · Precursor input amount: 3.0 g · Reaction vessel: 100 mL Iwaki · Etching temperature: 35 °C · Etching time: 24 h · Stirrer rotation speed: 400 rpm

[0079]

Table 1

[0080] (3) Washing after etching The above slurry was evenly divided into two parts and inserted into two 50 mL centrifuge tubes respectively. Then, after centrifugation at 3500 G for 5 minutes using a centrifuge, the supernatant was discarded. Thereafter, (i) 35 mL of pure water was added to the remaining precipitate in each centrifuge tube, (ii) stirred by hand shaking, (iii) centrifuged at 3500 G for 5 minutes, and (iv) the supernatant was removed. The steps from (i) to (iv) were repeated 10 times. And finally, centrifugation was performed at 3500 G for 5 minutes to obtain Ti3C2T s - Moisture medium clay.

[0081] (4) Lithium intercalation Ti3C2T prepared by the above method s - Stirring was performed on the aqueous medium clay under the following conditions to perform lithium ion intercalation. (Conditions for lithium intercalation) · Ti3C2T s - Aqueous medium clay (washed MXene): Solids content 0.75 g · Pure water: 20 mL · Lithium ion source: 15 mL of pure water + 0.75 g of LiOH · Reaction vessel: 100 mL i-bottle · Temperature: 20 - 25 °C (room temperature) · Stirring time: 18 hours · Stirring speed: 700 rpm

[0082] After the above stirring was completed, it was transferred to a 50 mL centrifuge tube and centrifuged at 3500 G for 5 minutes using a centrifuge, and the supernatant was discarded. Then, (i) 35 mL of pure water was added to the remaining precipitate in the centrifuge tube, (ii) stirred by hand shaking, (iii) centrifuged at 3500 G for 5 minutes, and (iv) the supernatant was removed. The steps from (i) to (iv) were repeated 5 times. Finally, centrifugation was performed at 3500 G for 5 minutes to obtain the lithium intercalation-treated product.

[0083] (5) Delamination Delamination was performed on the lithium intercalation-treated product under the conditions described below. (Conditions for delamination) · MXene after intercalation (lithium intercalation-treated product): Solids content 0.75 g · Solvent: 15 mL of NMF · Reaction vessel: 100 mL i-bottle · Temperature: 20 - 25 °C (room temperature) · Stirring time: 18 hours · Stirring: 700 rpm

[0084] After the above stirring, 15 mL of pure water was added, and after stirring with a shaker for 15 minutes, centrifugation was performed using a centrifuge under the conditions of 3500 G for 5 minutes to recover the supernatant containing monolayered MXene. Further, 30 mL of pure water was added, and after stirring with a shaker in the same manner as above, centrifugation was performed. Thereafter, the obtained supernatant was recovered, and this was centrifuged using a centrifuge under the conditions of 4000 G for 2 hours to discard the supernatant, and monolayer and few-layer MXene (pre-crosslinking conductive two-dimensional particles) were obtained as the remaining precipitate.

[0085] (6) Formation and heat treatment of a film using pre-crosslinking conductive two-dimensional particles The clay of the pre-crosslinking conductive two-dimensional particles obtained by the above delamination was suction filtered. As the filter for suction filtration, a membrane filter (Durapore, pore size 0.45 μm, manufactured by Merck KGaA) was used. The above supernatant contained 0.05 g of the solid content of MXene two-dimensional particles and 40 mL of pure water. After filtration, in Examples 1 to 5, vacuum drying at 80 °C was carried out for 24 hours, and then annealing (heat treatment) was carried out at 500 °C in an inert (nitrogen) atmosphere to obtain a sample. On the other hand, in Comparative Examples 1 to 5, membranes were formed in the same manner as in Examples 1 to 5, respectively, vacuum drying was carried out at 80 °C for 24 hours, and samples were obtained without heat treatment. That is, Example 1 and Comparative Example 1, Example 2 and Comparative Example 2, Example 3 and Comparative Example 3, Example 4 and Comparative Example 4, and Example 5 and Comparative Example 5 are the same up to the production of the membrane (pre-crosslinking MXene film), and differ in the presence or absence of heat treatment.

[0086] [Comparative Examples 6, 7] In Comparative Example 7, (1) preparation of a precursor (MAX), (2) etching of the precursor and Li intercalation, (3) washing, (4) delamination, and (5) formation and heat treatment of a film using MXene particles were carried out in order as described in detail below to obtain a sample. Further, in Comparative Example 6, a sample was obtained up to the formation of the above membrane.

[0087] (1) Preparation of a precursor (MAX): The same as in Examples 1 to 5

[0088] (2) Etching of the precursor and intercalation of Li ·Precursor: Ti3AlC2 (sieved through a 45 μm sieve) ·Etchant composition: 3 g of LiF 30 mL of HCl (9M) ·Precursor input amount: 3 g ·Etching container: 100 mL Erlenmeyer flask ·Etching temperature: 35 °C ·Etching time: 24 h ·Stirrer rotation speed: 400 rpm

[0089] (3) Washing The above slurry was divided into two parts and inserted into 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) centrifugation was performed again at 3500 G, and (iii) the supernatant was separated and removed. This operation of (i) - (iii) was repeated a total of 10 times. It was confirmed that the pH of the supernatant of the 10th time exceeded 5. The supernatant was discarded, and Ti3C2T s -aqueous media clay was obtained.

[0090] (4) Delamination To the above Ti3C2T s -aqueous media clay, (i) 40 mL of pure water was added, and after stirring with a shaker for 15 minutes, (ii) centrifugation was performed at 3500 G, and (iii) the supernatant was collected as a monolayer MXene-containing solution. This operation of (i) - (iii) was repeated a total of 4 times to obtain a monolayer MXene-containing supernatant. Furthermore, this supernatant was centrifuged at 4300 G for 2 hours using a centrifuge, and then the supernatant was discarded to obtain monolayer and few-layer MXene-containing clay as a monolayer and few-layer MXene-containing sample.

[0091] [Preparation and heat treatment of MXene film before crosslinking] The clay of the pre-crosslinked conductive two-dimensional particles obtained by the above delamination was suction filtered. As the filter for suction filtration, a membrane filter (Durapore, pore size 0.45 μm, manufactured by Merck KGaA) was used. The supernatant contained 0.05 g of the solid content of MXene two-dimensional particles and 40 mL of pure water. After filtration, Comparative Example 6 was vacuum dried at 80°C for 24 hours to obtain a sample without heat treatment. Further, in Comparative Example 7, after performing vacuum drying at 80°C for 24 hours, annealing (heat treatment) was performed at 500°C in an inert (nitrogen) atmosphere to obtain a sample.

[0092] 〔Evaluation〕 Using the samples of Examples 1 to 5 (crosslinked MXene films), the samples of Comparative Examples 1 to 6 (non-crosslinked MXene films), and the sample of Comparative Example 7 (crosslinked MXene film), measurement of the crosslinked structure, compositional analysis of the surface groups of MXene particles, measurement of the MXene interlayer distance, and measurement of the initial conductivity and σ / σ0 of each MXene film were performed. The details of each measurement method are shown below.

[0093] (Measurement of Crosslinked Structure (FT-IR Analysis)) The structures of the sample of Example 3 (crosslinked MXene film), the sample of Comparative Example 3 (non-crosslinked MXene film), the sample of Comparative Example 6 (non-crosslinked MXene film), and the sample of Comparative Example 7 (crosslinked MXene film) were confirmed using an FT-IR apparatus manufactured by Agilent. The results are shown in Fig. 4(a) for Comparative Example 3, Fig. 4(b) for Example 3, Fig. 5(a) for Comparative Example 6, and Fig. 5(b) for Comparative Example 7. From these drawings, in Example 3, an interlayer crosslinked bond of titanium atom-oxygen atom-titanium atom (Ti-O-Ti) could be confirmed. On the other hand, in Comparative Example 3, Comparative Example 6, and Comparative Example 7, the above interlayer crosslinked bond could not be confirmed. Further, in Comparative Example 3, Comparative Example 6, and Comparative Example 7, the peak of the hydroxyl group was clearly confirmed, but in Example 3, the peak of the hydroxyl group was not confirmed. From these facts, it is considered that in Example 3, an interlayer crosslinked bond of titanium atom-oxygen atom-titanium atom (Ti-O-Ti) was formed by the dehydration reaction of the hydroxyl groups on the MXene surface.

[0094] (Composition analysis of surface groups of MXene particles) The composition of the surface groups of the MXene particles in the samples of Examples 1 to 5 (crosslinked MXene films) and the sample of Comparative Example 7 (crosslinked MXene film) was determined by performing XPS measurement under the following conditions using an X-ray photoelectron spectrometer (product name: VersaProbe) manufactured by ULVAC-PHI, Inc. The results are shown in Table 2. Note that the amounts of chlorine atoms, iodine atoms, and bromine atoms in Examples 1 to 5 were all at the detection limit by ion chromatography (IC) (manufactured by Thermo Fisher Scientific, Dionex ICS-5000). That is, each atom was smaller than the quantitative lower limit of each atom in the above ion chromatography (quantitative lower limit of Cl: 0.004 mass%, quantitative lower limit of Br: 0.02 mass%, quantitative lower limit of I: 0.04 mass%). (XPS measurement conditions) Incident X-ray: Monochromatized AlKα X-ray output: 25.6 W Measurement area: 100 μm in diameter Photoelectron collection angle: 45.0 degrees Pass energy: 23.50 eV

[0095]

Table 2

[0096] Table 2 shows the composition analysis of the surface groups of Examples 1 to 5. For Comparative Examples 1 to 5, which have the same manufacturing method of MXene particles as Examples 1 to 5, it is considered that the composition analysis of the surface groups of the MXene particles is the same as that of Examples 1 to 5.

[0097] (Measurement of MXene interlayer distance) The interlayer distance of MXene can be measured using conductive two-dimensional particles, but in this example, it was measured using an MXene film. More specifically, under the following conditions, XRD measurements were performed on the samples (crosslinked MXene film or non-crosslinked MXene film) of Examples 1 to 5, Comparative Example 2, Comparative Example 6, and Comparative Example 7 to obtain two-dimensional X-ray diffraction images. Then, the peak position of the (002) plane was determined in the XRD profile. The results are shown in FIGS. 6 and 7. In FIG. 6, the profile of Example 1 is 1a, the profile of Example 2 is 2a, the profile of Example 3 is 3a, the profile of Example 4 is 4a, and the profile of Example 5 is 5a. Also in FIG. 7, the profile of Comparative Example 2 is 2b, the profile of Comparative Example 6 is 6b, and the profile of Comparative Example 7 is 7b.

[0098] (XRD Measurement Conditions) · Apparatus used: MiniFlex600 manufactured by Rigaku Corporation · Conditions Light source: Cu tube target Characteristic X-ray: CuKα = 1.54 Å Measurement range: 2 degrees to 20 degrees (only Comparative Example 6 is 5 degrees to 20 degrees) Step: 50 step / degree Sample: Filtered film

[0099] In FIGS. 6 and 7, it can be seen that in Examples 1 to 5, the peak of the (002) plane is at 2θ = 8° or more and on the high-angle side, indicating that the interlayer is narrowed. On the other hand, in Comparative Example 2, Comparative Example 6, and Comparative Example 7, the peak of the (002) plane is below 2θ = 8° and on the low-angle side, indicating that the interlayer is widened.

[0100] (Measurement of Initial Conductivity and σ / σ0 of MXene Film) The initial conductivity of the obtained MXene film was determined. For each sample, at three locations, first the surface resistivity was measured and designated as R0 (Ω). To measure the surface resistivity, a simple low-resistivity meter (manufactured by Mitsubishi Chemical Analytic Co., Ltd., Loresta AX MCP-T370) was used to measure the surface resistance of the film by the four-terminal method. Also, for each sample, at three locations, the thickness (μm) was measured. A micrometer (manufactured by Mitutoyo Corporation, MDH-25MB) was used for thickness measurement. The volume resistivity was determined from the above surface resistivity and film thickness, and the initial conductivity (S / cm) was calculated by taking the reciprocal of that value. The average value of the initial conductivity at the above three locations was adopted. The results are shown in Table 3.

[0101] Also, the above MXene film was placed in the same way as the test apparatus shown in Figure 5c of the literature: Pristine Titanium Carbide MXene Films with Environmentally Stable Conductivity and Superior Mechanical Strength (Adv. Funct. Mater. 2020, 30, 1906996). A small amount of water was placed at the bottom of a sealed desiccator, and the MXene film was placed so as not to be in direct contact with the water. It was held for 7 days in a humid environment at room temperature with saturated humidity. Then, in the same manner as above, for each sample, at three locations, the surface resistivity was measured, and the conductivity (S / cm) was calculated from the film thickness. The average value (σ) of the conductivity after 7 days at the above three locations was adopted. And, as the ratio of the average value (σ) of the conductivity after 7 days to the average value (σ0) of the initial conductivity, (σ / σ0)×100 (%) was determined. The results are also shown in Table 3. In this example, when (σ / σ0)×100 (%) was 70% or more, it was evaluated that the moisture absorption resistance was high and it had high reliability. The above (σ / σ0)×100 (%) is preferably 80% or more.

[0102]

Table 3

[0103] From the above results, the conductive two-dimensional particles of the present embodiment do not have large three-dimensional halogen atoms (Cl, I, Br) on the surface, the MXene surface is mainly formed of small three-dimensional elements F and O, and a cross-linked structure (Ti-O-Ti) is formed. As a result, the conductive film obtained using the conductive two-dimensional particles has a narrow interlayer distance, is less likely to absorb moisture, exhibits a high initial conductivity, and shows high reliability with suppressed change in conductivity over time.

[0104] The disclosure of this specification may include the following aspects. <1> Conductive two-dimensional particles of a layered material including one or more layers, wherein the layer has the following formula: M m X n (wherein M is at least one metal of Groups 3, 4, 5, 6, and 7, 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 5 or less) and includes a layer main body represented by the formula and a modification or termination T (T is at least one selected from the group consisting of a hydroxyl group, a fluorine atom, an oxygen atom, and a hydrogen atom) present on the surface of the layer main body, does not include a chlorine atom, an iodine atom, and a bromine atom, has at least one selected from the group consisting of a fluorine atom, an oxygen atom, and a hydroxyl group, and conductive two-dimensional particles in which a titanium atom of the layer main body of one layer is bonded to a titanium atom of the layer main body of another layer via an oxygen atom. <2> The conductive two-dimensional particles according to <1>, wherein in the profile obtained by X-ray diffraction measurement, the peak of the (002) plane exists at 2θ = 8° or more. <3> The conductive two-dimensional particles according to <1> or <2>, including phosphate ions. <4> A conductive film including the conductive two-dimensional particles according to any one of <1> to <3>. <5> The conductive film according to <4>, having a conductivity of 5000 S / cm or more. <6> A conductive paste containing the conductive two-dimensional particles according to any one of <1> to <3>. <7> A conductive composite material containing the conductive two-dimensional particles according to any one of <1> to <3> and a polymer. <8> (a) The following formula: M m AX n (In the formula, M is at least one metal of Groups 3, 4, 5, 6, and 7, X is a carbon atom, a nitrogen atom, or a combination thereof, A is at least one element of Groups 12, 13, 14, 15, and 16, n is 1 or more and 4 or less, m is greater than n and 5 or less) Prepare a precursor represented by, (b) Etching is performed to remove at least some of the A atoms from the precursor using an etching solution that does not contain chlorine atoms, iodine atoms, and bromine atoms. (c) Wash the etched product obtained by etching with water to obtain a water-washed product. (d) Perform an intercalation treatment of the intercalation compound, including stirring a mixed solution containing the water-washed product and a compound for intercalating between the layers of the water-washed product. (e) Using the intercalation-treated product obtained by the intercalation treatment, delamination is performed, and (f) A heat treatment is performed on the delamination-treated product obtained by the delamination at 200 °C or higher in an inert gas atmosphere to obtain conductive two-dimensional particles A method for producing conductive two-dimensional particles, including. <9> The method for producing conductive two-dimensional particles according to <8>, wherein in the step (e), the delamination of the intercalation-treated product is performed using one or more of a polar organic dispersion medium and an aqueous dispersion medium. <10> The method for producing conductive two-dimensional particles according to <8> or <9>, wherein the etching solution contains at least hydrofluoric acid. <11> The manufacturing method of the conductive two-dimensional particles according to <10>, wherein the etching solution further contains phosphoric acid. <12> The manufacturing method of the conductive two-dimensional particles according to any one of <8> to <11>, wherein in <d>, lithium hydroxide is used as the intercalation compound for the water-washed product.

[0105] This application claims priority based on Japanese Patent Application No. 2021-161527, which is incorporated herein by reference.

Industrial Applicability

[0106] The conductive film and the conductive paste containing the conductive two-dimensional particles of the present embodiment can be used in any appropriate application, and are particularly preferably used as electrodes in electric devices, for example.

Explanation of Reference Numerals

[0107] 1a, 1b Layer body (M m X n Layer) 3a, 5a, 3b, 5b Modification or termination T 7a, 7b MXene layer 10a, 10b, 10c, 10d MXene 21 Oxygen atom 23 Crosslinked structure 30 Conductive film 100 Conductive two-dimensional particles

Claims

1. Conductive two-dimensional particles of a layered material comprising one or more layers, wherein the layer has the following formula: M ｍ X ｎ (wherein M is at least one metal of Groups 3, 4, 5, 6, 7, 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 5 or less) and includes a layer body represented by the formula and a modification or termination T (T is at least one selected from the group consisting of a hydroxyl group, a fluorine atom, an oxygen atom and a hydrogen atom) present on the surface of the layer body, does not contain chlorine atoms, iodine atoms and bromine atoms, has at least one selected from the group consisting of a fluorine atom, an oxygen atom, and a hydroxyl group, Conductive two-dimensional particles in which titanium atoms of the layer body of one layer are bonded to titanium atoms of the layer body of another layer via oxygen atoms.

2. The conductive two-dimensional particles according to Claim 1, wherein in the profile obtained by X-ray diffraction measurement, the peak of the (002) plane is present at 2θ = 8° or more.

3. The conductive two-dimensional particles according to Claim 1 or 2, which contain phosphate ions.

4. A conductive film comprising the conductive two-dimensional particles according to Claim 1 or 2.

5. The conductive film according to Claim 4, having a conductivity of 5000 S / cm or more.

6. A conductive paste comprising the conductive two-dimensional particles according to Claim 1 or 2.

7. A conductive composite material comprising the conductive two-dimensional particles according to Claim 1 or 2 and a polymer.

8. (a) Preparing a precursor represented by the following formula: M ｍ AX ｎ (wherein M is at least one metal of Groups 3, 4, 5, 6, 7, X is a carbon atom, a nitrogen atom or a combination thereof, A is at least one element of Groups 12, 13, 14, 15, 16, n is 1 or more and 4 or less, m is greater than n and 5 or less) (b) Performing etching to remove at least some of the A atoms from the precursor using an etching solution that does not contain chlorine atoms, iodine atoms and bromine atoms, (c) Washing the etched product obtained by etching with water to obtain a water-washed product, (d) Performing an intercalation treatment of an intercalation compound for the layer, including stirring a mixture containing the water-washed product and an intercalation compound for intercalating between the layers of the water-washed product, (e) Using the intercalation-treated product obtained by the intercalation treatment to perform delamination, and ​ (f) Performing a heat treatment by heating the delamination-treated product obtained by the delamination at 200°C or higher in an inert gas atmosphere to obtain conductive two-dimensional particles A method for producing conductive two-dimensional particles, comprising the above steps Claim 9 The method for producing conductive two-dimensional particles according to claim 8, wherein in the step (e), the delamination of the intercalation-treated product is performed using one or more of a polar organic dispersion medium and an aqueous dispersion medium Claim 10 The method for producing conductive two-dimensional particles according to claim 8 or 9, wherein the etching solution contains at least hydrofluoric acid Claim 11 The method for producing conductive two-dimensional particles according to claim 10, wherein the etching solution further contains phosphoric acid Claim 12 The method for producing conductive two-dimensional particles according to claim 8 or 9, wherein in the step (d), lithium hydroxide is used as the intercalation compound for the water-washed product

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