Conductive two-dimensional particles and methods for manufacturing the same, conductive films, conductive pastes, and conductive composite materials

Abstract

Electroconductive two-dimensional particles of a layered material including one or a plurality of layers, wherein: the layer includes a layer body represented by the formula TimXn (in the formula, X is a carbon atom, a nitrogen atom, or a combination thereof, n is 1-4, and m is greater than n and at most 5), and a modification or terminal T (where T is at least one selected from the group consisting of hydroxyl groups, fluorine atoms, chlorine atoms, oxygen atoms, and hydrogen atoms) that is present on the surface of the layer body; and furthermore, the atomic ratio (Al / Ti) of Al to Ti is 0-0.10 at% inclusive.

Description

[Technical Field]

[0001] This disclosure relates to conductive two-dimensional particles and methods for producing the same, conductive films, conductive pastes, and conductive composite materials. [Background technology]

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

[0003] Currently, various studies are being conducted to apply MXene to various electrical devices. For example, Non-Patent Literature 1 describes a study that, given the limited production of two-dimensional titanium carbide (MXene), varied the amount reacted at one time to synthesize 2D titanium carbide (MXene). The study then investigated whether mass production would affect the structure and composition of 2D titanium carbide (MXene) flakes, using scanning electron microscopy, X-ray diffraction, dynamic light scattering, Raman spectroscopy, X-ray photoelectron spectroscopy, ultraviolet-visible spectroscopy, and conductivity measurements. Non-Patent Literature 2 also describes how MXene antennas made from two-dimensional (2D) titanium carbide (MXene) are useful for fabricating thin, lightweight, and flexible antennas, demonstrating low reflectivity while also ensuring conductivity and water dispersibility. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Scalable Synthesis of Ti3C2Tx MXene, Christopher E. Shuck et al., ADVANCED ENGINEERING MATERIALS 2020 [Non-Patent Document 2] 2D Titanium carbide (MXene) for wireless communication, SCIENCE ADVANCES, 21 Sep 2018, Vol 4, Issue 9

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, it is difficult to say that the MXene antennas and the like shown in Non-Patent Document 1 and Non-Patent Document 2 have high conductivity, and it seems that improvement is necessary to realize a conductive film with higher conductivity. The present disclosure has been made in view of the above circumstances, and an object thereof is to provide conductive two-dimensional particles capable of forming a highly conductive conductive film and the like, a method for producing the conductive two-dimensional particles, and a conductive film, a conductive paste, and a conductive composite material using the conductive two-dimensional particles.

Means for Solving the Problems

[0006] According to one gist of the present disclosure, conductive two-dimensional particles of a layered material including one or more layers, where the layer has the following formula: Ti m X n (where 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, a chlorine atom, an oxygen atom and a hydrogen atom) present on the surface of the layer main body, Furthermore, conductive two-dimensional particles are provided in which the atomic ratio of Al to Ti (Al / Ti) is 0 atomic % or more and 0.10 atomic % or less.

[0007] According to another gist of the present disclosure, (a) The following formula: Ti m AlXn (where 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) Preparing a precursor represented by (b1) Contacting the precursor with an etching solution and performing etching to remove at least a part of Al from the precursor, (c) Washing the etched product obtained by etching to obtain a washed product, (d) Performing an intercalation treatment of an intercalation compound for the intercalation compound, including stirring a mixed solution containing the washed product and the intercalation compound for intercalation between layers of the washed product, and (e1) Using the intercalation-treated product obtained by the intercalation treatment to perform delamination to obtain conductive two-dimensional particles A method for producing conductive two-dimensional particles is provided, including the above steps, and the atomic ratio of Al to Ti (Al / Ti) in the conductive two-dimensional particles is 0 atomic % or more and 0.10 atomic % or less. [Advantages of the Invention]

[0008] According to the present disclosure, conductive two-dimensional particles are formed of a predetermined layered material (also referred to as "MXene" in this specification), and further, the atomic ratio of Al to Ti (Al / Ti) is 0 atomic % or more and 0.10 atomic % or less. Thereby, conductive two-dimensional particles including MXene and capable of forming a conductive film or the like showing high conductivity are provided. Furthermore, according to this disclosure, conductive two-dimensional particles can be produced in which the atomic ratio of Al to Ti (Al / Ti) is 0 atomic% or more and 0.10 atomic% or less by (a) preparing a predetermined precursor, (b1) bringing the precursor into contact with an etching solution and etching to remove at least a portion of Al from the precursor, (c) washing the etched product obtained by etching to obtain a washed product, (d) performing an intercalation treatment of an intercalation compound, which includes stirring a mixture containing the washed product and an intercalation compound of the washed product, and (e1) performing delamination using the intercalation product obtained by the intercalation treatment. [Brief explanation of the drawing]

[0009] [Figure 1] A schematic cross-sectional view showing MXene, a layered material usable for conductive films in one embodiment of the present disclosure, where (a) shows a single layer of MXene and (b) shows a multilayer (exemplarily two-layer) MXene. [Figure 2] A diagram illustrating a conductive film in one embodiment of the present disclosure, wherein (a) shows a schematic cross-sectional view of the conductive film, and (b) shows a schematic perspective view of MXene particles in the conductive film. [Figure 3] This figure shows the XRD measurement results of the precipitate (AlF3·3H2O) in the example. [Modes for carrying out the invention]

[0010] (Embodiment 1: Conductive two-dimensional particles) The following describes conductive two-dimensional particles in one embodiment of the present disclosure, but the present disclosure is not limited to such embodiment.

[0011] The conductive two-dimensional particles in this embodiment are Conductive two-dimensional particles of a layered material comprising one or more layers, The aforementioned layer is given by the following formula: Ti m Xn (In the formula, 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, a chlorine atom, an oxygen atom, and a hydrogen atom) present on the surface of the layer body, Furthermore, the atomic ratio of Al to Ti (Al / Ti) is 0 atomic % or more and 0.10 atomic % or less.

[0012] The above-described layered material can be understood as a layered compound and is also represented as "Ti 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.

[0013] MXene is known to be represented by the above formula: Ti m X n as follows. Ti2C, Ti2N, Ti3C2, Ti3N2, Ti3(CN), Ti4N3

[0014] Typically, for example, the MAX phase is Ti3AlC2, and MXene is Ti3C2T s (In other words, X is C, n is 2, and m is 3).

[0015] In this embodiment, MXene may contain a relatively small amount of residual Al, for example, 6 mass % or less with respect to the original Al. The residual amount of Al can preferably be 5 mass % or less. However, even if the residual amount of Al exceeds 6 mass %, there may be no problem depending on the use and usage conditions of the conductive two-dimensional particles.

[0016] The conductive two-dimensional particles of this embodiment are an aggregate containing one layer of MXene10a (single-layer MXene), schematically illustrated in Figure 1(a). More specifically, MXene10a is Ti m X n The layer body represented by (Ti m X n The MXene layer 7a has a layer 1a and modifications or terminations T3a, 5a present on the surface of the layer body 1a (more specifically, at least one of the two surfaces facing each other in each layer). Therefore, the MXene layer 7a is "Ti m X n T s It can also be expressed as , where s is any number.

[0017] The conductive two-dimensional particles of this embodiment may include multiple layers along with one layer. Examples of multiple-layer MXene (multilayer MXene) include, but are not limited to, two layers of MXene 10b as schematically shown in Figure 1(b). In Figure 1(b), 1b, 3b, 5b, and 7b are the same as 1a, 3a, 5a, and 7a in Figure 1(a) described above. Two adjacent MXene layers of multilayer MXene (e.g., 7a and 7b) do not necessarily have to be completely separated, but may be in partial contact. The MXene 10a may be a single layer in which the multilayer MXene 10b is individually separated, while the unseparated multilayer MXene 10b may remain, resulting in a mixture of single-layer MXene 10a and multilayer MXene 10b.

[0018] Although not limited to this embodiment, the thickness of each MXene layer (corresponding to the MXene layers 7a and 7b described above) can be, for example, 0.8 nm or more and 10 nm or less, and more specifically 0.8 nm or more and 5 nm or less, and more particularly 0.8 nm or more and 3 nm or less (mainly depending on the number of Ti layers contained in each layer). For each laminate of the multilayer MXene that may be included, the interlayer distance (or void dimension, shown as Δd in Figure 1(b)) is, for example, 0.8 nm or more and 10 nm or less, more specifically 0.8 nm or more and 5 nm or less, and more specifically about 1 nm, and the total number of layers can be 2 or more and 20,000 or less.

[0019] The conductive two-dimensional particles of this embodiment may contain multilayer MXene obtained through a delamination process, resulting in MXene with a small number of layers. "Small number of layers" means, for example, that the number of layers of MXene is 10 or less, and may be even 6 or less. Hereinafter, this "multilayer MXene with a small number of layers" may be referred to as "low-layer MXene." Furthermore, single-layer MXene and low-layer MXene may be collectively referred to as "single-layer low-layer MXene."

[0020] The conductive two-dimensional particles of this embodiment preferably include single-layer MXene and multi-layer MXene, i.e., single-layer / multi-layer MXene. The conductive two-dimensional particles may have a proportion of single-layer / multi-layer MXene of 50 volume% or more, or a proportion of multi-layer MXene of 50 volume% or more. Preferably, the proportion of single-layer / multi-layer MXene is 50 volume% or more. In the conductive two-dimensional particles of this embodiment, it is more preferable that the proportion of single-layer / multi-layer MXene with a thickness of 10 nm or less is 90 volume% or more, and even more preferable that it is 95 volume% or more, in relation to the total MXene.

[0021] Preferably, the conductive two-dimensional particles have a large volume proportion of single-layer / single-layer MXene, and the average thickness of the conductive two-dimensional particles is preferably 15 nm or less. More preferably, the average thickness is 10 nm or less. On the other hand, the lower limit of the average thickness of the conductive two-dimensional particles can be, for example, 0.5 nm.

[0022] The average thickness of the above conductive two-dimensional particles can be determined as a number-average dimension (e.g., the number average of at least 40 particles) based on atomic force microscope (AFM) images.

[0023] The conductive two-dimensional particles of this embodiment are low-Al concentration MXene two-dimensional particles, where the atomic ratio of Al to Ti (Al / Ti) is 0 atomic% or more and 0.10 atomic% or less. In other words, Al may not be present, or if it is present, it is kept within the above atomic ratio range. In this embodiment, the conductive two-dimensional particles are obtained by controlling the etching conditions, for example, as described later, during the etching of the precursor, for example, the MAX phase, thereby sufficiently removing Al. The MXene two-dimensional particles obtained through subsequent processes have a sufficiently low atomic ratio of Al to Ti (Al / Ti). The atomic ratio of Al to Ti (Al / Ti) is determined by analyzing the Al and Ti content using ICP emission spectroscopy, as shown in the examples described later.

[0024] (Embodiment 2: Method for producing conductive two-dimensional particles) The method for producing conductive two-dimensional particles in this embodiment will be described in detail below, but this disclosure is not limited to this embodiment.

[0025] One method for manufacturing conductive two-dimensional particles in this embodiment (first manufacturing method) is: (a) The following equation: Ti m AlX n (In the formula, 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. Prepare a precursor represented by (b1) Bring the precursor into contact with an etching solution and perform etching to remove at least a portion of Al from the precursor. (c) Clean the etched material obtained by etching to obtain a cleaned material. (d) Performing an intercalation treatment of the intercalation compound, which includes stirring a mixture containing the washing material and the intercalation compound of the washing material, and (e1) Using the intercalation-treated material obtained by the intercalation process, delamination is performed to obtain conductive two-dimensional particles. A method for producing conductive two-dimensional particles, wherein the atomic ratio of Al to Ti in the conductive two-dimensional particles (Al / Ti) is 0 atomic% or more and 0.10 atomic% or less.

[0026] Another method for manufacturing conductive two-dimensional particles in this embodiment (second manufacturing method) is: (a) The following equation: Ti m AlX n (In the formula, 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. Prepare a precursor represented by (b2) The precursor is brought into contact with an etching solution containing an intercalation compound to perform etching to remove at least a portion of Al from the precursor, and an intercalation treatment of the intercalation compound is performed. (e2) Using the (etched + intercalated) material obtained by the etching and intercalation process, delamination is performed to obtain conductive two-dimensional particles. A method for producing conductive two-dimensional particles, wherein the atomic ratio of Al to Ti in the conductive two-dimensional particles (Al / Ti) is 0 atomic% or more and 0.10 atomic% or less. The following details each step of the first and second manufacturing methods.

[0027] ·Process (a) In both the first and second manufacturing methods, a predetermined precursor is first prepared. The predetermined precursor usable in this embodiment is the MAX phase, which is a precursor of MXene, and is given by the following formula: Ti m AlX n (In the formula, 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. It is represented as follows. The above X, n, and m are as explained in MXene.

[0028] The MAX phase is Ti m X n The crystal structure has two layers represented by (each X may have a crystal lattice located within an octahedral array of Ti) between which a layer composed of Al is located. In the MAX phase, typically when m=n+1, one layer of X atoms is placed between each of the n+1 Ti layers (these together are called "Ti"). m X n It has, but is not limited to, a repeating unit in which an Al layer ("Al layer") is placed as the layer following the (n+1)th Ti layer (also called a "layer").

[0029] The MAX phase described above can be manufactured by known methods. For example, TiC powder, Ti powder, and Al powder can be mixed in a ball mill, and the resulting mixed powder can be calcined in an Ar atmosphere to obtain a calcined body (block-shaped MAX phase). The calcined body can then be crushed with an end mill to obtain powdered MAX phase for the next process.

[0030] ·Process (b1) In the first manufacturing method, the precursor is brought into contact with an etching solution to perform etching, removing at least some of the Al from the precursor. The etching conditions are not limited to those such that the atomic ratio of Al to Ti (Al / Ti) in the finally obtained conductive two-dimensional particles is 0 atomic% or more and 0.10 atomic% or less. Preferably, an etching solution containing HF is used. HF may be mixed with other acids as auxiliary acids. Examples of other acids include hydrochloric acid, phosphoric acid, and hydroiodic acid. For example, pure water may be mixed as a solvent. Preferably, the etching solution contains HF and has an HF concentration of 7.0 M or more. More preferably, the HF concentration is 8.0 M or more. The upper limit of the HF concentration may be, for example, 30 M. From the viewpoint of performing etching in a short time and increasing the yield of conductive two-dimensional particles, it is preferable to increase the HF concentration of the etching solution.

[0031] The contact time with the etching solution (hereinafter referred to as "etching time") is preferably 8 hours or less. By shortening the etching time to preferably 8 hours or less, the formation of Al impurities in MXene, mainly insulating AlF3·3H2O, is suppressed, and MXene 2D particles suitable for forming highly conductive films can be obtained. The etching time is more preferably 6 hours or less. On the other hand, from the viewpoint of sufficiently removing Al from the MAX phase, the etching time is preferably, for example, 0.5 hours or more.

[0032] Methods for bringing the precursor into contact with the etching solution include immersing the precursor in the etching solution. Other preferred conditions for the etching process are not particularly limited and known conditions can be used. An example of an etched product obtained by the above etching process is a slurry.

[0033] ·Process (c) In the first manufacturing method, the etched product obtained by the etching is washed. Washing thoroughly removes the acid used in the etching process. It has been separately confirmed that even if the etching conditions are inappropriate and Al impurities form as precipitates during etching, these precipitates are not sufficiently removed by this washing. The washing medium mixed with the etched product is not limited as long as it can sufficiently remove the acid. For example, in addition to water (pure water), washing may be performed with a solution containing substances other than water, such as dilute hydrochloric acid. The amount of washing medium and the washing method are not particularly limited. For example, water may be added and stirred, or centrifuged. Stirring methods include handshake, automatic shaker, shear mixer, pot mill, etc. The degree of stirring, such as stirring speed and stirring time, should be adjusted according to the amount and concentration of the product to be treated. The washing may be performed once or more times. Preferably, the washing is performed multiple times. For example, the process of (i) adding a washing medium (to the etched material or the remaining precipitate obtained in (iv) below), (ii) stirring, (iii) centrifuging the stirred material, and (iv) discarding the supernatant after centrifugation and recovering the remaining precipitate is repeated two or more times, for example, up to 15 times.

[0034] ·Process (d) The first manufacturing method involves performing an intercalation treatment of the intercalation compound, which includes stirring a mixture containing the cleaned material and a compound for intercalation into the layers of the cleaned material (simply referred to as the "intercalation compound").

[0035] The interlayer insertion compound can be any compound that can be inserted between the layers of the washing material and separated into each layer in the subsequent delamination step (e1), but the specific type is not limited. Alkali metal compounds and alkaline earth metal compounds are preferred as the interlayer insertion compound. More preferably, a Li-containing compound is used. As the Li-containing compound, an ionic compound in which a Li ion and a cation are bonded can be used. Examples include Li chloride, Li phosphate, Li sulfate, Li nitrate, and Li carboxylate. Preferably, LiCl, which is Li chloride, is used.

[0036] Other conditions for the intercalation process are not particularly limited. The pH of the mixture containing the cleaning material and the intercalation compound for the cleaning material is also not a concern. Preferably, the mixture containing the cleaning material and the intercalation compound for the cleaning material is acidic, for example, with a pH of 6 or less.

[0037] The content of the intercalation compound in the intercalation formulation is preferably 0.001% by mass or more. More preferably, the content is 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 solution, the content of the intercalation compound is preferably 10% by mass or less, and more preferably 1% by mass or less.

[0038] The specific method of intercalation is not particularly limited. For example, the intercalation compound may be mixed with the water medium clay of the MXene, which is a water-treated product, and then stirred or left to stand. For example, stirring at room temperature is one method. Examples of stirring methods include using a stirrer or other stirring bar, using a stirring blade, using a mixer, and using a centrifugal apparatus. The stirring time can be set according to the scale of production of conductive two-dimensional particles, for example, between 12 and 24 hours.

[0039] ·Process (b2) In the second manufacturing method, the precursor is brought into contact with an etching solution containing an interlayer insertion compound to perform etching (removal and optionally layer separation) to remove at least some of the Al from the precursor, and intercalation treatment of the interlayer insertion compound is performed.

[0040] In this embodiment, when etching (removing and optionally separating layers) at least some of the Al from the MAX phase, Ti m X nAn intercalation process is performed to insert an intercalation compound, such as one containing Li, between the layers (which may include cases where some Al remains). The same intercalation compound as the one shown in step (b1) can be used. Lithium fluoride may also be used as the intercalation compound.

[0041] The content of the interlayer insertion compound in the etching solution is preferably 0.001% by mass or more. More preferably, the content is 0.01% by mass or more, and even more preferably, 0.1% by mass or more. On the other hand, from the viewpoint of ensuring dispersibility in the solution, the content of the interlayer insertion compound in the etching solution is preferably 10% by mass or less, and more preferably 1% by mass or less.

[0042] The etching solution in step (b2) contains the interlayer insertion compound, and the atomic ratio of Al to Ti in the finally obtained conductive two-dimensional particles (Al / Ti) is not limited to 0 atomic% or more and 0.10 atomic% or less. Preferably, an etching solution containing HF is used. More preferably, as shown in step (b1) above, the material is in contact with an etching solution with an HF concentration of 7.0 M or more for 8 hours or less. Other preferred conditions are not limited, and examples include a method using a mixture of lithium fluoride and hydrochloric acid. In these methods, a mixture with pure water as a solvent is used. An example of an etched product obtained by the above etching treatment is a slurry.

[0043] Of the first and second manufacturing methods, the manufacturing method described in the first manufacturing method, which separates the etching process (b1) and the intercalation process (c), is preferable because it makes it easier to form MXene into a single layer.

[0044] ·Process (e1), process (e2) In the first manufacturing method, the intercalated product obtained by the intercalation treatment is used, and in the second manufacturing method, the (etched + intercalated) product obtained by the etching and intercalation treatment is used, and delamination is performed in each case to obtain conductive two-dimensional particles in which the atomic ratio of Al to Ti in the particles (Al / Ti) is 0 atomic% or more and 0.10 atomic% or less. The conditions for the delamination treatment are not particularly limited and can be carried out by known methods. For example, it can be carried out by the method shown below.

[0045] For example, delamination can be performed by centrifuging the intercalation material, discarding the supernatant, and then washing the remaining precipitate. For example, a slurry-like intercalation material or an (etching + intercalation) material can be centrifuged, the supernatant can be discarded, and then the remaining precipitate can be washed with a washing medium, such as a solution containing water or a substance other than water, by (i) adding the washing medium to the precipitate remaining after discarding the supernatant and stirring, (ii) centrifuging, and (iii) recovering the supernatant. These operations (i) to (iii) can be repeated one or more times, preferably two or more times and no more than ten times, to obtain conductive two-dimensional particles as a delamination material. Alternatively, the supernatant can be centrifuged, the supernatant after centrifugation can be discarded, and conductive two-dimensional particles can be obtained as a delamination material.

[0046] In the manufacturing method of this embodiment, ultrasonic treatment is not performed as delamination after etching. As mentioned above, since ultrasonic treatment is not performed, particle breakage is less likely to occur, and conductive two-dimensional particles containing single-layer or thin-layer MXene with a large two-dimensional plane can be obtained. Conductive two-dimensional particles containing single-layer or thin-layer MXene with a large two-dimensional plane can form a film without using a binder, and the resulting film exhibits high conductivity.

[0047] (Embodiment 3: Conductive film) An example of a conductive film in this embodiment is a conductive film containing the conductive two-dimensional particles of this embodiment. Referring to Figure 2, the conductive film 30 of this embodiment contains conductive two-dimensional particles 10 of a predetermined layered material, as shown in Figure 2(a). Figure 2(b) is a schematic perspective view of the MXene particles contained in the conductive film 30. The conductive film of this embodiment may also be a film obtained by laminating only the conductive two-dimensional particles 10.

[0048] The conductive film may be a conductive composite material film (conductive composite film) further containing a polymer (resin). The polymer may be included, for example, as an additive such as a binder added during film formation, or it may be added to provide strength or flexibility. In the case of the conductive composite material film, the polymer may be greater than 0 volume% and preferably 30 volume% or less in proportion to the conductive composite material film (when dry). The proportion of the polymer may be further 10 volume% or less, and even further 5 volume% or less. In other words, the proportion of conductive two-dimensional particles (particles of the layered material) in the conductive composite material film (when dry) is preferably 70 volume% or more, and even further 90 volume% or more, and even further 95 volume% or more. The conductive film may be a laminated film of two or more conductive composite material films with different proportions of conductive two-dimensional particles.

[0049] Examples of the polymer include hydrophilic polymers (including hydrophobic polymers that exhibit hydrophilicity due to the addition of a hydrophilic additive, and hydrophilic polymers whose surfaces have been treated to make them hydrophilic), and more preferably the hydrophilic polymer includes 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.

[0050] The hydrophilic polymer is more preferably a hydrophilic polymer having polar groups, wherein the polar groups are groups that form hydrogen bonds with the modification or terminus T of the layer. For example, one or more polymers selected from the group consisting of water-soluble polyurethane, polyvinyl alcohol, sodium alginate, acrylic acid-based water-soluble polymers, polyacrylamide, polyaniline sulfonic acid, and nylon are preferably used as the polymer.

[0051] Among these, one or more polymers selected from the group consisting of water-soluble polyurethane, polyvinyl alcohol, and sodium alginate are more preferred. As the polymer, a polymer having a urethane bond that possesses both hydrogen bond donor and hydrogen bond acceptor properties is preferred, and from this viewpoint, the water-soluble polyurethane is particularly preferred.

[0052] The thickness of the conductive film is preferably 0.5 μm or more and 20 μm or less. A thickness of 0.5 μm or more is preferable because increasing the thickness of the conductive film reduces the contact resistance at the grain boundaries and tends to increase conductivity. More preferably, the thickness is 1.0 μm or more. While a thicker film is preferable from the viewpoint of conductivity, if flexibility or other properties are required, the thickness is preferably 20 μm or less, more preferably 15 μm or less. The thickness of the conductive film can be measured, for example, by cross-sectional observation using a micrometer, scanning electron microscope (SEM), microscope, or laser microscope.

[0053] The conductive film formed with conductive two-dimensional particles in this embodiment can preferably achieve an conductivity of 7000 S / cm or more, obtained by substituting the thickness of the conductive film measured by the method described above, for example, the thickness of the conductive film measured by the method described in the example, and the surface resistivity of the conductive film into the following formula. Conductivity [S / cm] = 1 / (Thickness of conductive film [cm] × Surface resistivity of conductive film [Ω / □])

[0054] (Methods for manufacturing conductive films) The method for manufacturing the conductive film of this embodiment using the MXene particles (conductive two-dimensional particles) generated as described above is not particularly limited. For example, a conductive film can be formed as illustrated below.

[0055] First, an MXene dispersion is prepared by placing the MXene particles prepared as described above in a medium liquid. Examples of the medium liquid include aqueous medium liquids and organic medium liquids. The medium liquid of the MXene dispersion is typically water, but in some cases, it may also contain a relatively small amount of other liquid substances in addition to water (for example, 30% by mass or less, preferably 20% by mass or less on a total basis).

[0056] Before drying, the MXene dispersion may be used to form a precursor of the conductive film (also called a "precursor film"). The method for forming the precursor film is not particularly limited, and methods such as suction filtration, coating, and spraying can be used.

[0057] More specifically, the supernatant liquid containing conductive two-dimensional particles as an MXene dispersion can be appropriately adjusted (for example, diluted with an aqueous medium) and filtered by suction through a filter installed in a Nutsch or the like (which may constitute a predetermined component together with the conductive film, or may be ultimately separated from the conductive film) to remove at least partially the aqueous medium, thereby forming a precursor film on the filter. The filter is not particularly limited, but a membrane filter or the like can be used. By performing the above suction filtration, a conductive film can be produced without using the binder or the like. Using the conductive two-dimensional particles of this embodiment, a conductive film can be produced in this way without using the binder or the like.

[0058] Alternatively, the MXene dispersion may be applied to the substrate as is, or after being appropriately adjusted (for example, by diluting it with an aqueous medium or by adding a binder). Application methods include, for example, spray coating using a nozzle such as a one-fluid nozzle, two-fluid nozzle, or airbrush; slit coating using a table coater, comma coater, or bar coater; screen printing; metal mask printing; spin coating; dip coating; and dropping. As the substrate, a substrate made of a metal material, resin, or the like suitable for biosignal sensing electrodes can be appropriately used. A precursor film can be formed on any suitable substrate (which may constitute a predetermined component together with the conductive film, or may ultimately be separated from the conductive film) by coating it.

[0059] Next, the precursor film formed above can be dried to obtain a conductive film 30, for example, as schematically shown in Figure 2. In this embodiment, "drying" means removing any aqueous media liquid that may be present in the precursor.

[0060] Drying may be carried out under mild conditions such as natural drying (typically by placing the material in an air atmosphere at room temperature and pressure) or air drying (by blowing air onto it), or under relatively active conditions such as hot air drying (by blowing heated air onto it), heat drying, and / or vacuum drying. The drying may be carried out, for example, at a temperature of 400 degrees Celsius or less using an atmospheric pressure oven or a vacuum oven.

[0061] The formation and drying of the precursor film may be repeated as needed until a conductive film of the desired thickness is obtained. For example, the spraying and drying combination may be repeated multiple times.

[0062] If the conductive composite material of this 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, the MXene dispersion or MXene powder, which consists of the above-mentioned conductive two-dimensional particles (MXene particles) in a medium liquid (aqueous medium liquid or organic medium liquid), is mixed with a polymer. The medium liquid of the above-mentioned MXene dispersion is typically water, but in some cases, it may also contain a relatively small amount of other liquid substances in addition to water (for example, 30% by mass or less, preferably 20% by mass or less on a total basis).

[0064] The above-mentioned conductive two-dimensional particles (MXene particles) and polymer can be stirred using dispersion devices such as homogenizers, propeller stirrers, thin-film swirling stirrers, planetary mixers, mechanical shakers, and vortex mixers.

[0065] The slurry, which is a mixture of the MXene particles and polymer, can be applied to a substrate (e.g., a circuit board), but the application method is not limited. For example, methods include spray coating using a nozzle such as a one-fluid nozzle, two-fluid nozzle, or airbrush; slit coating using a table coater, comma coater, or bar coater; screen printing; metal mask printing; spin coating; dip coating; and drop coating. As mentioned above, the substrate can be a circuit board made of a metal material, resin, or the like, suitable for biosignal sensing electrodes.

[0066] The above coating and drying process may be repeated multiple times as needed until a film of the desired thickness is obtained. Drying and curing may be carried out, for example, at a temperature of 400 degrees Celsius or less using an atmospheric pressure oven or a vacuum oven.

[0067] (Embodiment 4: Conductive paste) Another application of the conductive two-dimensional particles of this embodiment is a conductive paste containing the conductive two-dimensional particles. The conductive paste may be, for example, a mixture of conductive two-dimensional particles (particles of a predetermined layered material) and a medium. The medium may be an aqueous medium, an organic medium, a polymer, metal particles, ceramic particles, etc., and may contain one or more of these. The mass ratio of the conductive two-dimensional particles (particles of the layered material) to the conductive paste may be, for example, 50% or more.

[0068] One example of its application is to use the above-mentioned conductive paste by, for example, applying it to a substrate and drying it to form a conductive film.

[0069] (Embodiment 5: Conductive Composite Material) Other applications of the conductive two-dimensional particles of this embodiment include conductive composite materials containing the conductive two-dimensional particles and a polymer. The conductive composite material is not limited to the shape of the conductive composite material film (conductive composite material membrane) described above. In addition to the film shape, the conductive composite material may have thickness, be a rectangular parallelepiped, a sphere, a polygon, or the like.

[0070] As the polymer mentioned above, a polymer similar to the polymer used in 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 may be present in proportion to the conductive composite material (when dry) at more than 0 volume%, and preferably 30 volume% or less. The proportion of the polymer may be further 10 volume% or less, and even further 5 volume% or less. In other words, the proportion of layered material particles in the conductive composite material (when dry) is preferably 70 volume% or more, and even further 90 volume% or more, and even further 95 volume% or more.

[0071] Examples of the polymer include hydrophilic polymers (including hydrophobic polymers that exhibit hydrophilicity due to the addition of a hydrophilic additive, and hydrophilic polymers whose surfaces have been treated to make them hydrophilic), and more preferably the hydrophilic polymer includes 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, it is more preferable that the hydrophilic polymer has polar groups, wherein the polar groups are groups that form hydrogen bonds with the modification or terminus T of the layer. 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 as the polymer.

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

[0074] The conductive two-dimensional particles, the method for manufacturing the conductive two-dimensional particles, the conductive film, the conductive paste, and the conductive composite material in this embodiment have been described in detail above, but various modifications are possible. It should be noted that the conductive two-dimensional particles in this embodiment may be manufactured by a method different from the manufacturing method in the above-described embodiment, and the method for manufacturing the conductive two-dimensional particles in this embodiment is not limited to the one that provides the conductive two-dimensional particles in the above-described embodiment. [Examples]

[0075] [Fabrication of single-layer and low-layer MXene] [Examples 1-3, Comparative Examples 1-3] In Examples 1 to 4, single-layer and small-layer MXene-containing samples were prepared by sequentially performing the following steps, as detailed below: (1) preparation of the precursor (MAX), (2) etching of the precursor, (3) washing after etching, (4) Li intercalation, and (5) delamination.

[0076] (1) Preparation of the precursor (MAX) TiC powder, Ti powder, and Al powder (all manufactured by Kojun Chemical Laboratory Co., Ltd.) were placed in a ball mill containing zirconia balls in a molar ratio of 2:1:1 and mixed for 24 hours. The resulting mixed powder was calcined at 1350°C for 2 hours under an Ar atmosphere. The resulting calcined body (block-shaped MAX) was then pulverized with an end mill to a maximum size of 40 μm or less. This yielded Ti3AlC2 particles as a precursor (powdered MAX).

[0077] (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 solid components derived from the Ti3AlC2 powder. (Etching conditions) • Precursor: Ti3AlC2 (passed through a sieve with a mesh size of 45 μm) • Etching solution composition: HF concentration is as shown in Table 1 below. HCl concentration: 7.4M • Etching solution volume: 60 mL • Amount of precursor (Ti3AlC2) added: 3.0g • Etching container: 100mL iBoy Etching temperature: 35℃ • Etching time: As shown in Table 1 below. • Stirrer rotation speed: 400 rpm

[0078] (3) Cleaning after etching The slurry was divided into two portions and placed into two 50 mL centrifuge tubes. Centrifugation was performed at 3500 G using a centrifuge, and the supernatant was discarded. 40 mL of pure water was added to the remaining precipitate in each centrifuge tube, and the process of separating and removing the supernatant was repeated 11 times by centrifugation at 3500 G. After the final centrifugation, the supernatant was discarded, and Ti3C2T was extracted. s -A water-based clay was obtained. In this example, it was washed with pure water, but it is not limited to this, and may be washed with, for example, dilute hydrochloric acid.

[0079] (4) Li intercalation Ti3C2T prepared by the above method s -Li intercalation was performed on a water-based clay medium under the following conditions. (Conditions for Li intercalation) ·Ti3C2T s - Moisture-based clay (MXene after washing): Solid content 0.75g LiCl: 0.75g Intercalation container: 100mL iBoy ·Temperature: 20℃ or higher and 25℃ or lower (room temperature) • Time: 18h • Stirrer rotation speed: 800 rpm

[0080] (5) Delamination The slurry obtained by intercalation with Li was placed in a 50 mL centrifuge tube and centrifuged at 3500 G using a centrifuge, after which the supernatant was discarded. Next, (i) 40 mL of pure water was added to the remaining precipitate and stirred in a shaker for 15 minutes, (ii) then centrifuged at 3500 G, and (iii) the supernatant was collected as a monolayer / minor-layer MXene-containing liquid. This procedure (i) to (iii) was repeated a total of four times to obtain a monolayer / minor-layer MXene-containing supernatant. Furthermore, this supernatant was centrifuged at 4500 G for 2 hours using a centrifuge, and the supernatant was discarded to obtain a monolayer / minor-layer MXene-containing clay.

[0081] [Table 1]

[0082] 〔evaluation〕 [Atomic ratio of Al to Ti (Al / Ti)] The single-layer and thin-layer MXene-containing samples (single-layer and thin-layer MXene-containing clay) obtained in Examples 1-3 and Comparative Examples 1-3 were freeze-dried to produce powder. This powder was then dissolved using an alkaline fusion method, and the Al and Ti content was analyzed by ICP emission spectrometry to determine the atomic ratio of Al to Ti. A Thermo Fisher Scientific iCAP6300 was used for the above analysis. The results are shown in Table 1 above.

[0083] [Film conductivity] (Film production method) A single-layer / sampling MXene-containing clay (solid content 0.0375 g) obtained by delamination was mixed with 25 mL of pure water to form a slurry, and an MXene film (MXene membrane) was prepared by suction filtration. A membrane filter (Merck KGaA, Durapore, pore size 0.65 μm) was used for suction filtration. After filtration, the MXene film was obtained by vacuum drying at 80°C for 8 hours or more.

[0084] (Method for measuring film density) The film was punched out into 12mm diameter discs, its weight was measured using an electronic balance, and its thickness was measured using a height gauge. The film density was then calculated from these measurements.

[0085] (Method for measuring film conductivity) The conductivity of the obtained MXene film was determined. For each sample, resistivity (Ω) and thickness (μm) were measured at three locations. The conductivity (S / cm) was calculated from these measurements, and the average of the three conductivity values ​​obtained was adopted. The surface resistance of the film was measured using a four-terminal method with a simple low-resistivity meter, Loresta AX MCP-T370 (manufactured by Mitsubishi Chemical Analytics). Then, the volume resistivity was calculated from the obtained surface resistance and the film thickness measured with a micrometer, and the conductivity was determined by taking the reciprocal of this value. The conductivity was calculated using the film density: 2 g / cm³. 3 These are the values ​​when normalized. The results are also shown in Table 1 above.

[0086] From Table 1 above, the following can be said. In Examples 1 to 3, MXene films were obtained by etching with a relatively high HF concentration in the etching solution and for a shorter time than conventional methods. The obtained MXene films were conductive films with an Al / Ti ratio of 0.10 atomic% or less and a high conductivity of 7000 S / cm or more. On the other hand, in Comparative Examples 1 to 3, MXene films were obtained by etching using conventional methods, i.e., with varying HF concentrations in the etching solution and a long etching time of 24 hours. The obtained MXene films had an Al / Ti ratio exceeding 0.10 atomic%, and their conductivity was below 7000 S / cm. Although this embodiment is not bound by any theory, the reason why the MXene films of Examples 1 to 3 showed higher conductivity than the MXene films of Comparative Examples 1 to 3 is thought to be as follows. That is, when the etching time is long, AlF3·3H2O precipitates during etching, and since this AlF3·3H2O is insoluble in water, it cannot be reduced even by washing with pure water, for example, and is thought to remain on the surface and between layers of MXene. As a result, it is thought that the presence of AlF3, an insulator contained in MXene, lowers the conductivity of the MXene film. On the other hand, in Examples 1 to 3, it is thought that by using an etching solution containing HF at a certain concentration or higher and shortening the etching time to a certain time or less, the amount of the insulator AlF3 was reduced and the conductivity of the film improved. It was separately confirmed that the above AlF3 is a trihydrate, but the presence or absence of hydration water and the number of hydration waters are not limited.

[0087] Experiments 1 and 2 below were also conducted to verify the above embodiment. (Experiment 1) 0.42 g of pure aluminum powder was added to 60 mL of etching solution (HF: 2.8 M, HCl: 7.4 M) and dissolved. The solution was then left to stand for various periods as shown in Table 2 below, and the amount of precipitate deposited in the etching solution was determined. The results are also shown in Table 2.

[0088] [Table 2]

[0089] Furthermore, XRD measurements of the above precipitate were performed under the following conditions. The XRD profile resulting from this measurement is shown in Figure 3. From Figure 3, it was confirmed that the above precipitate is AlF3·3H2O. (XRD measurement conditions) • Equipment used: Rigaku MiniFlex600 • Measurement conditions Light source: Cu tube Characteristic X-ray: CuKα=1.54Å Measurement range: 3°-20° Steps: 50 steps / degree

[0090] From Table 2 and the results of the XRD measurements, it was confirmed that the longer the etching time, which corresponds to the standing time, the more AlF3·3H2O precipitates.

[0091] (Experiment 2) Etching was performed using etching solutions with different concentrations of HF (other than HF, the same etching solutions were used in the examples) for etching times of 1, 3, or 6 hours. The etching rate was then determined for the resulting etched products. The etching rate was determined by analyzing the amount of Al (atomic %) by ICP emission spectrometry after rinsing with water following the etching process. Assuming that the detected Al originated from Ti3AlC2, the etching rate (%) was calculated from [(Al constituting Ti3AlC2 - detected Al) / (Al constituting Ti3AlC2)] × 100 (atomic ratio). The results are shown in Table 3.

[0092] [Table 3]

[0093] From the results in Table 3, when the HF concentration of the etching solution is low at 2.8 M, the etching rate is only 32.1% even with an etching time of 6 hours, suggesting that the yield of MXene particles obtained after further intercalation, etc., is inherently low. Therefore, it is considered difficult to shorten the etching time when the HF concentration of the etching solution is low. On the other hand, when the HF concentration of the etching solution is 9.9 M, the etching rate is 89.3% with an etching time of 6 hours, indicating that etching can be done in a short time and that shortening the etching time is possible. Furthermore, if the etching time is short, the amount of AlF3·3H2O precipitated is small, and it is thought that the majority of the detected Al comes from Ti3AlC2. [Industrial applicability]

[0094] The conductive two-dimensional particles, conductive films, conductive pastes, and conductive composite materials of this disclosure can be used in any suitable application, and are preferably used, for example, as electrodes in electrical devices.

[0095] The disclosures in this specification may include the following aspects: <1> Conductive two-dimensional particles of a layered material comprising one or more layers, The aforementioned layer is given by the following formula: Ti m X n (In the formula, 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. The layer body is represented by and includes 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, an oxygen atom, and a hydrogen atom) present on the surface of the layer body, Furthermore, the conductive two-dimensional particle has an atomic ratio of Al to Ti (Al / Ti) of 0 atomic% or more and 0.10 atomic% or less. <2> The average thickness of the aforementioned conductive two-dimensional particles is 15 nm or less. <1> Conductive two-dimensional particles as described. <3> The aforementioned Com X n It is Ti3C2. <1> or <2> Conductive two-dimensional particles as described. <4> (a) The following equation: Ti m AlX n (In the formula, 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. Prepare a precursor represented by (b1) Bring the precursor into contact with an etching solution and perform etching to remove at least a portion of Al from the precursor. (c) Clean the etched material obtained by etching to obtain a cleaned material. (d) Performing an intercalation treatment of the intercalation compound, which includes stirring a mixture containing the washing material and the intercalation compound of the washing material, and (e1) Using the intercalation-treated material obtained by the intercalation process, delamination is performed to obtain conductive two-dimensional particles. A method for producing conductive two-dimensional particles, wherein the atomic ratio of Al to Ti in the conductive two-dimensional particles (Al / Ti) is 0 atomic% or more and 0.10 atomic% or less. <5> (a) The following equation: Ti m AlX n (In the formula, 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. Prepare a precursor represented by (b2) The precursor is brought into contact with an etching solution containing an intercalation compound to perform etching to remove at least a portion of Al from the precursor, and an intercalation treatment of the intercalation compound is performed. (e2) Using the (etched + intercalated) material obtained by the etching and intercalation process, delamination is performed to obtain conductive two-dimensional particles. A method for producing conductive two-dimensional particles, wherein the atomic ratio of Al to Ti in the conductive two-dimensional particles (Al / Ti) is 0 atomic% or more and 0.10 atomic% or less. <6> The etching solution has an HF concentration of 7.0 M or higher, and the contact time between the precursor and the etching solution is 8 hours or less. <4> or <5> A method for producing conductive two-dimensional particles as described above. <7> The contact time between the precursor and the etching solution is 0.5 hours or more. <4> ~ <6> A method for producing conductive two-dimensional particles as described in any one of the following. <8> The aforementioned Co m AlX n It is Ti3AlC2. <4> ~ <7> A method for producing conductive two-dimensional particles as described in any one of the following. <9> <1> ~ <3> A conductive film containing conductive two-dimensional particles as described in any one of the following. <10> A conductive film formed from the aforementioned conductive two-dimensional particles, wherein the conductivity calculated from the following formula is 7000 S / cm or more. <9> The conductive film described above. Conductivity [S / cm] = 1 / (Thickness of conductive film [cm] × Surface resistivity of conductive film [Ω / □]) <11> <1> ~ <3> A conductive paste containing conductive two-dimensional particles as described in any one of the following. <12> <1> ~ <3> A conductive composite material comprising conductive two-dimensional particles described in any one of the above and a polymer.

[0096] This application is based on a Japanese patent application, Japanese Patent Application No. 2022-080357, which is incorporated herein by reference. [Explanation of Symbols]

[0097] 1a, 1b layer body (M m X n layer) 3a, 5a, 3b, 5b Modifier or Terminus T 7a, 7b MXene layer 10, 10a, 10b MXene particles (conductive two-dimensional particles, layered material particles) 30. Conductive film

Claims

1. Conductive two-dimensional particles of a layered material comprising one or more layers, The aforementioned layer is given by the following formula: Ti 3 C 2 The layer body is represented by and includes a modification or termination T present on the surface of the layer body (T is 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), Furthermore, conductive two-dimensional particles containing Al, wherein the atomic ratio of Al to Ti (Al / Ti) is greater than 0 atomic percent and 0.10 atomic percent or less.

2. The conductive two-dimensional particle according to claim 1, wherein the average thickness of the conductive two-dimensional particle is 15 nm or less.

3. A conductive film containing conductive two-dimensional particles according to claim 1 or 2.

4. A conductive film formed of the aforementioned conductive two-dimensional particles, wherein the conductivity calculated from the following formula is 7000 S / cm or more, according to claim 3. Conductivity [S / cm] = 1 / (Thickness of conductive film [cm] × Surface resistivity of conductive film [Ω / □])

5. A conductive paste containing conductive two-dimensional particles as described in claim 1 or 2.

6. A conductive composite material comprising conductive two-dimensional particles according to claim 1 or 2 and a polymer.

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