Electroconductive two-dimensional particles, method for producing same, electroconductive film, electroconductive paste, and electroconductive composite material

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

Conductive two-dimensional particles and their manufacturing method, conductive film, conductive paste, and conductive composite material

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

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

[0003] Currently, various studies are being conducted toward the application of MXene to various electrical devices. For example, Non-Patent Document 1, in light of the fact that two-dimensional titanium carbide (MXene) has rarely been mass-produced, describes the synthesis of two-dimensional titanium carbide (MXene) by varying the amount reacted at one time, and the effects of mass production on the structure and composition of the two-dimensional titanium carbide (MXene) flakes were confirmed using scanning electron microscopy, X-ray diffraction, dynamic light scattering, Raman spectroscopy, X-ray photoelectron spectroscopy, ultraviolet-visible spectroscopy, conductivity measurements, etc. Furthermore, Non-Patent Document 2 describes that MXene antennas formed from two-dimensional (2D) titanium carbide (MXene) are useful materials for fabricating thin, lightweight, and flexible antennas, and can also ensure low reflectivity, electrical conductivity, and water dispersibility.

[0004] Scalable Synthesis of Ti3C2Tx MXene, Christopher E. Shuck et al., ADVANCED ENGINEERING MATERIALS 20202D Titanium carbide (MXene) for wireless communication, SCIENCE ADVANCES, 21 Sep 2018, Vol 4, Issue 9

[0005] However, the MXene antennas and the like shown in Non-Patent Documents 1 and 2 cannot be said to have high conductivity, and improvements are thought to be necessary to realize conductive films with higher conductivity. The present disclosure has been made in consideration of the above circumstances, and its purpose is to provide conductive two-dimensional particles that can form highly conductive conductive films and the like, a method for manufacturing the conductive two-dimensional particles, and a conductive film, a conductive paste, and a conductive composite material that use the conductive two-dimensional particles.

[0006] According to one aspect of the present disclosure, there is provided an electrically conductive two-dimensional particle of layered material comprising one or more layers, wherein said layers are of the following formula: Ti ｍ X ｎ (wherein 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 modified or terminated 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, and further, the atomic ratio of Al to Ti (Al / Ti) is 0 atomic % or more and 0.10 atomic % or less.

[0007] According to another aspect of the present disclosure, there is provided a method for producing a compound of formula (a) Ti ｍ AlX ｎ(wherein 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); (b1) contacting the precursor with an etching solution to perform 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, the intercalation treatment comprising stirring a mixed solution containing the washed product and the intercalation compound of the washed product; and (e1) performing delamination using the intercalation product obtained by the intercalation treatment to obtain conductive two-dimensional particles, wherein an 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.

[0008] According to the present disclosure, there is provided a conductive two-dimensional particle formed of a predetermined layered material (also referred to herein as “MXene”), further comprising an Al / Ti atomic ratio of 0 atomic % or more and 0.10 atomic % or less, thereby enabling the formation of a conductive film or the like that contains MXene and exhibits high conductivity. The present disclosure also provides a conductive two-dimensional particle having an Al / Ti atomic ratio of 0 atomic % or more and 0.10 atomic % or less, which can be produced by (a) preparing a predetermined precursor, (b1) contacting the precursor with an etching solution to perform etching to remove at least a portion of the 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, including stirring a mixture containing the washed product and the intercalation compound, and (e1) performing delamination using the intercalation product obtained by the intercalation treatment.

[0009] 1A and 1B are schematic cross-sectional views showing MXene, a layered material that can be used in a conductive film according to one embodiment of the present disclosure, where (a) shows single-layer MXene and (b) shows multi-layer (exemplarily two-layer) MXene. 1B are diagrams illustrating a conductive film according to one embodiment of the present disclosure, where (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. 1C shows precipitates (AlF ３ ・3H ２ 1 is a diagram showing the results of XRD measurement of SiO.

[0010] (Embodiment 1: Conductive Two-Dimensional Particles) Hereinafter, conductive two-dimensional particles according to one embodiment of the present disclosure will be described in detail, but the present disclosure is not limited to such an embodiment.

[0011] The conductive two-dimensional particle in this embodiment is a conductive two-dimensional particle of a layered material comprising one or more layers, wherein said layers are of the following formula: Ti ｍ X ｎ (wherein 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 a modified or terminated T (T is at least one selected from the group consisting of a hydroxyl group, a fluorine atom, a chlorine atom, an oxygen atom, and a hydrogen atom) present on the surface of the layer body, and further, the atomic ratio of Al to Ti (Al / Ti) is 0 atomic % or more and 0.10 atomic % or less.

[0012] The layered material can be understood as a layered compound, and is referred to as "Ti ｍ X ｎ T ｓ ", where s is any number, and conventionally, x or z may be used instead of s. Typically, n can be 1, 2, 3, or 4, but is not limited thereto.

[0013] MXene is a compound represented by the formula: Ti ｍ X ｎ However, it is known that it can be expressed as follows: Ti ２ C, Ti ２ N, Ti ３ C ２ , Ti３ N ２ , Ti ３ (CN), Ti ４ N ３

[0014] Typically, for example, the MAX phase is Ti ３ AlC ２ and MXene is Ti ３ C ２ T 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% by mass or less of the original Al. The residual Al amount may be preferably 5% by mass or less. However, even if the residual Al amount exceeds 6% by mass, there may be no problem depending on the application and use conditions of the conductive two-dimensional particles.

[0016] The conductive two-dimensional particles of this embodiment are aggregates containing one layer of MXene 10a (single layer MXene) as illustrated in FIG. 1(a). More specifically, MXene 10a is a Ti ｍ X ｎ The layer body (Ti ｍ X ｎ The MXene layer 7a has a main layer 1a and a modification or termination T3a, 5a present on the surface of the main layer 1a (more specifically, on at least one of the two surfaces facing each other in each layer). ｍ X ｎ T ｓ ", where s is an arbitrary number.

[0017] The conductive two-dimensional particles of this embodiment may include multiple layers as well as a single layer. Examples of multiple-layer MXene (multilayer MXene) include, but are not limited to, two layers of MXene 10b, as shown schematically in FIG. 1(b). 1b, 3b, 5b, and 7b in FIG. 1(b) are the same as 1a, 3a, 5a, and 7a in FIG. 1(a). Two adjacent MXene layers (e.g., 7a and 7b) in multilayer MXene do not necessarily need to be completely separated and may be partially in 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 the single layer MXene 10a and the multilayer MXene 10b.

[0018] Although this embodiment is not limited thereto, the thickness of each MXene layer (corresponding to the above-described MXene layers 7a and 7b) can be, for example, 0.8 nm to 10 nm, further 0.8 nm to 5 nm, particularly 0.8 nm to 3 nm (this can vary mainly depending on the number of Ti layers included in each layer). The interlayer distance (or gap dimension, shown as Δd in FIG. 1(b)) for each of the multiple MXene stacks that can be included can be, for example, 0.8 nm to 10 nm, particularly 0.8 nm to 5 nm, more particularly about 1 nm, and the total number of layers can be 2 to 20,000.

[0019] The conductive two-dimensional particles of this embodiment may contain multilayer MXene, which may be MXene with a small number of layers obtained through a delamination process. The term "small number of layers" refers to, for example, 10 or fewer MXene stacked layers, and may even be 6 or fewer layers. Hereinafter, this "multilayer MXene with a small number of layers" may be referred to as "small-layer MXene." Furthermore, single-layer MXene and small-layer MXene may be collectively referred to as "single-layer / small-layer MXene."

[0020] The conductive two-dimensional particles of this embodiment preferably contain single-layered MXene and few-layered MXene, i.e., single-layered and few-layered MXene. The conductive two-dimensional particles may contain single-layered and few-layered MXene at a ratio of 50% by volume or more, or may contain multi-layered MXene at a ratio of 50% by volume or more. The ratio of single-layered and few-layered MXene at a ratio of 50% by volume or more is preferred. In the conductive two-dimensional particles of this embodiment, the ratio of single-layered and few-layered MXene with a thickness of 10 nm or less to the total MXene is more preferably 90% by volume or more, and even more preferably 95% by volume or more.

[0021] The conductive two-dimensional particles preferably have a high volume ratio of single-layer / few-layer MXene, and the conductive two-dimensional particles preferably have an average thickness of 15 nm or less. The average thickness is more preferably 10 nm or less. Meanwhile, the lower limit of the average thickness of the conductive two-dimensional particles may be, for example, 0.5 nm.

[0022] The average thickness of the conductive two-dimensional particles is determined as a number-average size (for example, a number-average of at least 40 particles) based on an atomic force microscope (AFM) photograph.

[0023] The conductive two-dimensional particles of this embodiment are MXene two-dimensional particles with a low Al concentration, in which the atomic ratio of Al to Ti (Al / Ti) is 0 atomic % or more and 0.10 atomic % or less. In other words, Al does not need to be contained, and even if it is contained, it is kept within the above atomic ratio range. In the conductive two-dimensional particles of this embodiment, Al is sufficiently removed by controlling the etching conditions, for example, as described below, during etching of the precursor, such as the MAX phase, and the MXene two-dimensional particles obtained through the subsequent process have a sufficiently low atomic ratio of Al to Ti (Al / Ti). The atomic ratio of Al to Ti (Al / Ti) can be determined by analyzing the Al and Ti contents using ICP atomic emission spectroscopy, as shown in the examples described below.

[0024] (Embodiment 2: Method for Producing Conductive Two-Dimensional Particles) Hereinafter, a method for producing conductive two-dimensional particles in this embodiment will be described in detail, but the present disclosure is not limited to this embodiment.

[0025] One method for producing conductive two-dimensional particles (first production method) of this embodiment is to: (a) prepare a conductive two-dimensional particle having the following formula: Ti ｍ AlX ｎ (wherein 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); (b1) contacting the precursor with an etching solution to perform 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, the intercalation treatment including stirring a mixed solution containing the washed product and the intercalation compound of the washed product; and (e1) performing delamination using the intercalation product obtained by the intercalation treatment to obtain conductive two-dimensional particles, wherein an 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.

[0026] Another method for producing conductive two-dimensional particles (second production method) of this embodiment is to: (a) produce a conductive two-dimensional particle having the following formula: Ti ｍ AlX ｎ (b1) preparing a precursor represented by the formula: (b2) contacting the precursor with an etching solution containing an intercalation compound to perform etching to remove at least a portion of Al from the precursor and intercalate the intercalation compound; and (e2) performing delamination using the (etching + intercalation) treated product obtained by the etching and intercalation treatments to obtain conductive two-dimensional particles, wherein 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. Each step of the first and second production methods will be described in detail below.

[0027] Step (a) In both the first and second production methods, a predetermined precursor is first prepared. The predetermined precursor that can be used in this embodiment is the MAX phase, which is a precursor of MXene, and has the following formula: Ti ｍ AlX ｎ (wherein 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), where X, n and m are as described above for MXene.

[0028] The MAX phase is Ti ｍ X ｎ The MAX phase has a crystal structure in which a layer of Al is located between two layers represented by the formula (each X may have a crystal lattice in which X is located in the octahedral array of Ti). In the MAX phase, typically when m=n+1, one layer of X atoms is arranged between each of the n+1 Ti layers (collectively referred to as "Ti ｍ X ｎ The repeating unit may be, but is not limited to, a layer of Al (also referred to as an "Al layer") disposed as the next layer after the n+1th Ti layer.

[0029] The MAX phase can be produced by a known method. For example, TiC powder, Ti powder, and Al powder are mixed in a ball mill, and the resulting mixed powder is sintered in an Ar atmosphere to obtain a sintered body (a block of the MAX phase). The sintered body is then pulverized with an end mill to obtain the powdered MAX phase for the next step.

[0030] Step (b1) In the first manufacturing method, the precursor is brought into contact with an etching solution to perform etching to remove at least a portion of Al from the precursor. The etching conditions are not limited as long as the atomic ratio of Al to Ti (Al / Ti) in the final 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 another acid as an auxiliary acid. Examples of other acids include hydrochloric acid, phosphoric acid, and hydroiodic acid. Pure water may also be mixed as a solvent. The etching solution preferably contains HF and has an HF concentration of 7.0 M or more. The HF concentration is more preferably 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 time for contact 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 Al impurities in MXene are mainly insulating AlF ３ ・3H ２ This suppresses the formation of O, resulting in MXene two-dimensional particles suitable for forming a film with high conductivity. 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] The precursor may be brought into contact with the etching solution by, for example, immersing the precursor in the etching solution. Other preferred conditions for the etching treatment are not particularly limited, and known conditions may be employed. The etched product obtained by the etching treatment may be, for example, a slurry.

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

[0034] Step (d) In the first production method, an intercalation treatment of the intercalation compound is carried out, which includes stirring a mixture containing the washed material and a compound for intercalation between the layers of the washed material (simply referred to as an "intercalation compound").

[0035] The specific type of intercalation compound is not important as long as it can be inserted between the layers of the washed material and can be separated into each layer by delamination in the next step (e1). Alkali metal compounds and alkaline earth metal compounds are preferred as the intercalation compound. Lithium-containing compounds are more preferred. Ionic compounds in which Li ions and cations are bonded can be used as the Lithium-containing compound. Examples of the Lithium-containing compound include Li chloride, Li phosphate, Li sulfate, Li nitrate, and Li carboxylate. Lithium chloride, LiCl, is preferred.

[0036] Other conditions for the intercalation treatment are not particularly limited. The property of the mixture containing the washed material and the intercalation compound for the washed material is also not important. The mixture containing the washed material and the intercalation compound for the washed material is preferably acidic, for example, having a pH of 6 or less.

[0037] The content of the intercalation compound in the intercalation blend is preferably 0.001% by mass or more, more preferably 0.01% by mass or more, and even more preferably 0.1% by mass or more. On the other hand, from the viewpoint of dispersibility in the solution, the content of the intercalation compound is preferably 10% by mass or less, 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 MXene water medium clay, which is a water treatment product, and the mixture may be stirred or left to stand. For example, stirring at room temperature may be used. Examples of the stirring method include a method using a stirring bar such as a stirrer, a method using a stirring blade, a method using a mixer, and a method using a centrifugal device. The stirring time can be set depending on the production scale of the conductive two-dimensional particles, and may be set, for example, between 12 and 24 hours.

[0039] Step (b2) In the second production method, the precursor is brought into contact with an etching solution containing an intercalation compound to perform etching (removal and, optionally, layer separation) to remove at least a portion of the Al from the precursor, and also to perform an intercalation treatment of the intercalation compound.

[0040] In this embodiment, during etching (removal and possibly layer separation) of at least a portion of Al from the MAX phase, Ti ｍ X ｎ An intercalation treatment is performed to insert an intercalation compound containing, for example, Li between the layers (which may include a case where some Al remains). The intercalation compound may be the same compound as the intercalation compound shown in step (b1). Lithium fluoride may also be used as the intercalation compound.

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

[0042] The etching solution in step (b2) is not limited as long as it contains the intercalation compound and 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. More preferably, as shown in step (b1) above, contact with an etching solution having an HF concentration of 7.0 M or more for 8 hours or less is performed. Other preferred conditions are not limited, and include, for example, a method using a mixed solution of lithium fluoride and hydrochloric acid. These methods include a method using a mixed solution with pure water as a solvent. The etched product obtained by the above etching process may be, for example, a slurry.

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

[0044] Steps (e1) and (e2) In the first manufacturing method, the intercalation-treated product obtained by the intercalation treatment is used, and in the second manufacturing method, the (etching + intercalation)-treated product obtained by the etching and intercalation treatment is used, and delamination is performed on each to obtain conductive two-dimensional particles having an atomic ratio of Al to Ti (Al / Ti) in the particles of 0 atomic % or more and 0.10 atomic % or less. The conditions for the delamination treatment are not particularly limited, and can be performed by a known method. For example, the method shown below can be used.

[0045] For example, a delamination process can be performed that includes centrifuging the intercalation-treated product, discarding the supernatant, and then washing the remaining precipitate. For example, the slurry intercalation-treated product or the (etching + intercalation)-treated product can be centrifuged to discard the supernatant, and the remaining precipitate can be washed with a washing medium, such as water or a solution containing a substance other than water, by (i) adding the washing medium to the remaining precipitate after discarding the supernatant and stirring, (ii) centrifuging, and (iii) recovering the supernatant. These steps (i) to (iii) can be repeated one or more times, preferably two or more times, but not more than 10 times, to obtain conductive two-dimensional particles as a delamination-treated product. Alternatively, the supernatant can be centrifuged, the supernatant after centrifugation discarded, and conductive two-dimensional particles can be obtained as a delamination-treated product.

[0046] In the manufacturing method of this embodiment, ultrasonic treatment is not performed as delamination after etching. As described above, the absence of ultrasonic treatment makes it difficult for particles to be destroyed, and conductive two-dimensional particles containing single-layer and few-layer MXene with large two-dimensional surfaces can be obtained. The conductive two-dimensional particles containing single-layer and few-layer MXene with large two-dimensional surfaces can be formed into a film without using a binder, and the resulting film exhibits high conductivity.

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

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

[0049] Examples of the polymer include hydrophilic polymers (including hydrophobic polymers that exhibit hydrophilicity by being blended with a hydrophilic auxiliary, and hydrophobic polymers or the like that have been subjected to a hydrophilization treatment on their surfaces), 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 polymers, polyacrylamide, polyaniline sulfonic acid, and nylon.

[0050] The hydrophilic polymer is more preferably a hydrophilic polymer having a polar group, wherein the polar group is a group that forms a hydrogen bond with the modification of the layer or with the terminal T. 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.

[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 has 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. Since increasing the thickness of the conductive film reduces the contact resistance of grain boundaries and tends to increase conductivity, a thickness of 0.5 μm or more is preferable. The thickness is more preferably 1.0 μm or more. From the viewpoint of conductivity, a thicker film is preferable, but when flexibility or the like is 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 measuring with a micrometer or by observing the cross section using a scanning electron microscope (SEM), a microscope, a laser microscope, or the like.

[0053] The conductive film formed from the conductive two-dimensional particles of this embodiment preferably achieves a conductivity of 7000 S / cm or more, calculated 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 Examples, 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] (Method for Producing Conductive Film) The method for producing the conductive film of this embodiment using the MXene particles (conductive two-dimensional particles) produced as described above is not particularly limited. For example, a conductive film can be formed as shown below.

[0055] First, an MXene dispersion is prepared by dissolving the MXene particles prepared as described above in a liquid medium. Examples of the liquid medium include aqueous and organic liquid mediums. The liquid medium for the MXene dispersion is typically water, and may optionally contain a relatively small amount of other liquid substance in addition to water (e.g., 30% by mass or less, preferably 20% by mass or less, based on the total).

[0056] Before drying, the MXene dispersion may be used to form a precursor of a conductive film (also referred to as a "precursor film"), which may be formed by any method, including suction filtration, coating, spraying, or the like.

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

[0058] Alternatively, the MXene dispersion may be applied to a substrate either directly or after appropriate adjustment (e.g., dilution with an aqueous medium or addition of a binder). Examples of application methods include spray application using a nozzle such as a one-fluid nozzle, a two-fluid nozzle, or an airbrush; slit coating using a table coater, comma coater, or bar coater; screen printing; metal mask printing; spin coating; dip coating; and dripping. The substrate may be, for example, a substrate formed of a metal material, resin, or the like suitable for a biosignal sensing electrode. 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 applying the MXene dispersion to the substrate.

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

[0060] Drying may be carried out under mild conditions such as natural drying (typically placing the substrate in an air atmosphere at room temperature and atmospheric 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 at a temperature of 400°C or less using an atmospheric pressure oven or a vacuum oven, for example.

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

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

[0063] First, a polymer is mixed with an MXene dispersion or MXene powder, in which the conductive two-dimensional particles (MXene particles) are present in a liquid medium (aqueous or organic). The liquid medium for the MXene dispersion is typically water, and may optionally contain a relatively small amount of other liquid substance in addition to water (for example, 30% by mass or less, preferably 20% by mass or less, based on the total).

[0064] The conductive two-dimensional particles (MXene particles) and polymer can be stirred using a dispersing device such as a homogenizer, a propeller stirrer, a thin film rotary stirrer, a planetary mixer, a mechanical shaker, or a vortex mixer.

[0065] The slurry, which is a mixture of the MXene particles and polymer, can be applied to a substrate (e.g., a substrate) by any method, including spray application using a nozzle such as a one-fluid nozzle, a two-fluid nozzle, or an 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 described above, the substrate can be appropriately made of, for example, a metal material, resin, or the like suitable for a biosignal sensing electrode.

[0066] The coating and drying steps may be repeated multiple times as necessary until a film of the desired thickness is obtained. Drying and curing may be carried out, for example, at a temperature of 400°C 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. Examples of the medium include aqueous medium liquids, organic medium liquids, polymers, metal particles, ceramic particles, and the like, and may include a mixture containing one or more of these. The mass ratio of the conductive two-dimensional particles (particles of a layered material) in the conductive paste may be, for example, 50% or more.

[0068] One example of the use of the conductive paste is to apply it to a substrate or the like and dry it to form a conductive film.

[0069] (Embodiment 5: Conductive Composite Material) Another application of the conductive two-dimensional particles of this embodiment is a conductive composite material 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. The shape of the conductive composite material may be a film shape, or may be a thick body, a rectangular parallelepiped, a sphere, a polygon, or the like.

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

[0071] Examples of the polymer include hydrophilic polymers (including hydrophobic polymers that exhibit hydrophilicity by being blended with a hydrophilic auxiliary, and hydrophobic polymers or the like that have been subjected to a hydrophilization treatment on their surfaces), 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 polymers, polyacrylamide, polyaniline sulfonic acid, and nylon.

[0072] The hydrophilic polymer is more preferably a hydrophilic polymer having a polar group, wherein the polar group is a group that modifies the layer or forms a hydrogen bond with the terminal T. 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 has both hydrogen bond donor and hydrogen bond acceptor properties is preferred, and from this viewpoint, the water-soluble polyurethane is particularly preferred.

[0074] Although 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 according to the present embodiment have been described in detail above, various modifications are possible. Note that the conductive two-dimensional particles according to the present embodiment may be manufactured by a method different from the manufacturing method according to the above embodiment, and that the manufacturing method of the conductive two-dimensional particles according to the present embodiment is not limited to only those that provide the conductive two-dimensional particles according to the above embodiment.

[0075] [Preparation of Single-Layered and Few-Layered MXene] [Examples 1 to 3, Comparative Examples 1 to 3] In Examples 1 to 4, single-layered and few-layered MXene-containing samples were prepared by sequentially carrying out the following steps, as detailed below: (1) preparation of precursor (MAX), (2) etching of the precursor, (3) cleaning after etching, (4) Li intercalation, and (5) delamination.

[0076] (1) Preparation of Precursor (MAX) TiC powder, Ti powder, and Al powder (all manufactured by Kojundo Chemical Laboratory Co., Ltd.) were mixed in a molar ratio of 2:1:1 in a ball mill containing zirconia balls for 24 hours. The resulting mixed powder was sintered at 1350°C for 2 hours in an Ar atmosphere. The resulting sintered body (block-shaped MAX) was pulverized with an end mill to a maximum size of 40 μm or less. This resulted in the preparation of TiC powder as a precursor (powder-shaped MAX). ３ AlC ２ particles were obtained.

[0077] (2) Etching of the precursor Ti prepared by the above method ３ AlC ２ Using particles (powder), etching was performed under the following etching conditions to remove Ti ３ AlC ２ A solid-liquid mixture (slurry) containing solid components derived from the powder was obtained. (Etching conditions) Precursor: Ti ３ AlC ２ (Sieved through a 45 μm mesh) Etching solution composition: HF concentration as shown in Table 1 below HCl concentration: 7.4 M Etching solution volume: 60 mL Precursor (Ti ３ AlC ２) Amount added: 3.0 g Etching container: 100 mL Eye Boy Etching temperature: 35°C Etching time: as shown in Table 1 below Stirrer rotation speed: 400 rpm

[0078] (3) Post-etching cleaning The above slurry was divided into two parts and placed in two 50 mL centrifuge tubes, respectively. After centrifuging at 3500 G using a centrifuge, the supernatant was discarded. 40 mL of pure water was added to the remaining precipitate in each centrifuge tube, and the tubes were centrifuged again at 3500 G to separate and remove the supernatant. This procedure was repeated 11 times. After the final centrifugation, the supernatant was discarded, and Ti ３ C ２ T ｓ - Water medium clay was obtained. In this example, the clay was washed with pure water, but this is not limiting, and the clay may also be washed with, for example, diluted hydrochloric acid.

[0079] (4) Li intercalation Ti prepared by the above method ３ C ２ T ｓ Li intercalation was carried out on the clay in a water medium under the following conditions. (Li intercalation conditions) Ti ３ C ２ T ｓ - Water medium clay (MXene after washing): solid content 0.75 g LiCl: 0.75 g Intercalation container: 100 mL Eye Boy Temperature: 20 ° C or higher and 25 ° C or lower (room temperature) Time: 18 hours Stirrer rotation speed: 800 rpm

[0080] (5) Delamination The slurry obtained by Li intercalation 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, followed by stirring for 15 minutes on a shaker, (ii) centrifuging at 3500 G, and (iii) recovering the supernatant as a single-layer / sparse-layer MXene-containing solution. These steps (i) to (iii) were repeated a total of four times to obtain a single-layer / sparse-layer MXene-containing supernatant. Furthermore, this supernatant was centrifuged at 4500 G for 2 hours using a centrifuge, after which the supernatant was discarded, yielding a single-layer / sparse-layer MXene-containing clay.

[0081]

[0082] [Evaluation] [Atomic Ratio of Al to Ti (Al / Ti)] The single-layered and few-layered MXene-containing samples (single-layered and few-layered MXene-containing clays) obtained in Examples 1 to 3 and Comparative Examples 1 to 3 were freeze-dried to prepare powders, which were then dissolved by an alkali fusion method. The Al and Ti contents were analyzed by ICP atomic emission spectroscopy to determine the atomic ratio of Al to Ti. An iCAP6300 manufactured by Thermo Fisher Scientific was used for this analysis. The results are also shown in Table 1.

[0083] [Film Conductivity] (Film Preparation Method) The single-layer / few-layer MXene-containing clay (solid content 0.0375 g) obtained by delamination was mixed with 25 mL of pure water to form a slurry, which was then suction filtered to prepare an MXene film (MXene membrane). A membrane filter (Merck, Durapore, pore size 0.65 μm) was used for the suction filtration. After filtration, the mixture was vacuum dried at 80° C. for 8 hours or more to obtain an MXene film.

[0084] (Method for Measuring Film Density) The film was punched out into a disk shape with a diameter of 12 mm using a punch, and the weight was measured using an electronic balance and the thickness was measured using a height gauge. The film density was calculated from these measured values.

[0085] (Method for Measuring Film Conductivity) The conductivity of the obtained MXene film was determined. The resistivity (Ω) and thickness (μm) were measured at three locations per sample, and the conductivity (S / cm) was calculated from these measurements. The average value of the three resulting conductivities was used. The surface resistance of the film was measured by the four-terminal method using a simple low resistivity meter, Loresta AX MCP-T370 (manufactured by Mitsubishi Chemical Analytical). The volume resistivity was then calculated from the obtained surface resistance and the film thickness measured with a micrometer, and the conductivity was calculated by taking the reciprocal of this value. The conductivity was calculated based on the film density (2 g / cm) determined above. ３ The results are shown in Table 1 above.

[0086] The following can be said from Table 1 above. 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 resulting MXene films were conductive films in which the Al / Ti ratio was suppressed to 0.10 atomic % or less and exhibited 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 a conventional method, i.e., various HF concentrations in the etching solution and a long etching time of 24 hours. The resulting MXene films had an Al / Ti ratio exceeding 0.10 atomic % and conductivity below 7000 S / cm. While this embodiment is not bound by any theory, the reason why the MXene films of Examples 1 to 3 exhibited higher conductivity than the MXene films of Comparative Examples 1 to 3 is thought to be as follows: That is, as the etching time became longer, AlF ３ ・3H ２ O precipitates, and this AlF ３ ・3H ２ Since O is insoluble in water, it cannot be reduced by washing with pure water, for example, and it is thought that it remains on the surface of MXene, between layers, etc. As a result, AlF ３On the other hand, in Examples 1 to 3, the conductivity of the MXene film is thought to be reduced by using an etching solution containing HF at a certain concentration or more and shortening the etching time to a certain time or less. ３ It is considered that the conductivity of the film was improved by reducing the AlF ３ It has been separately confirmed that the compound is a trihydrate, but the presence or absence of hydrated water and the number of hydrated water are not limited.

[0087] The following Experiments 1 and 2 were also conducted to verify the above Examples. (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, and then left to stand for various periods shown in Table 2 below, and the amount of precipitate that had precipitated in the etching solution was then measured. The results are also shown in Table 2.

[0088]

[0089] The precipitates were subjected to XRD measurement under the following conditions. The XRD profile obtained as a result of the measurement is shown in FIG. 3. From FIG. 3, it can be seen that the precipitates are AlF ３ ・3H ２ It was confirmed that the crystal was O. (XRD measurement conditions) Apparatus used: MiniFlex 600 manufactured by Rigaku Corporation Measurement conditions Light source: Cu tube Characteristic X-rays: CuKα=1.54 Å Measurement range: 3°-20° Step: 50 steps / degree

[0090] From the results of Table 2 and the XRD measurement, it can be seen that the longer the etching time, which corresponds to the standing time, the more AlF precipitates are formed. ３ ・3H ２ It was confirmed that a large amount of O could be precipitated.

[0091] (Experiment 2) Etching was carried out for 1, 3 or 6 hours using etching solutions with different HF concentrations (other than HF, the same etching solutions as those used in the examples). The etching rate was then calculated for the resulting etched products. After the etching, the products were washed with water and analyzed by ICP atomic emission spectroscopy to determine the amount of Al (atomic %). The amount of Al detected was then calculated based on the ratio of Ti to Ti. ３ AlC２ Assuming that it is derived from [(Ti ３ AlC ２ (Al constituting Ti) / (Al detected) ３ AlC ２ The etching rate (%) was calculated from the atomic ratio of [Al constituting the alloy (Al)] × 100. The results are shown in Table 3.

[0092]

[0093] From the results in Table 3, when the HF concentration of the etching solution is as low as 2.8M, the etching rate is only 32.1% even when the etching time is 6 hours, and it is thought that the yield of MXene particles obtained through further intercalation after etching is low to begin with. Therefore, it is thought that it is 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 9.9M, the etching rate is 89.3% after 6 hours of etching, and it was found that etching can be performed in a short time and that it is possible to shorten the etching time. Furthermore, if the etching time is short, AlF ３ ・3H ２ The amount of O precipitated is small, and most of the detected Al is Ti. ３ AlC ２ This is thought to be the origin.

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

[0095] The disclosure of the present specification may include the following aspects: <1> An electrically conductive two-dimensional particle of a layered material including one or more layers, wherein the layer is a compound represented by the following formula: Ti ｍ X ｎ(wherein 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 modified or terminated 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, and further, the atomic ratio of Al to Ti (Al / Ti) is 0 atomic % or more and 0.10 atomic % or less. <2> The conductive two-dimensional particle according to <1>, wherein the average thickness of the conductive two-dimensional particle is 15 nm or less. <3> The Ti ｍ X ｎ is Ti ３ C ２ <4> (a) The conductive two-dimensional particle according to <1> or <2>, wherein the conductive two-dimensional particle is represented by the following formula: Ti ｍ AlX ｎ (wherein 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); (b1) bringing the precursor into contact with an etching solution to perform 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, including stirring a mixed solution containing the washed product and the intercalation compound of the washed product; and (e1) performing delamination using the intercalation product obtained by the intercalation treatment to obtain conductive two-dimensional particles, wherein 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. <5> (a) preparing a precursor represented by the following formula: Ti ｍ AlX ｎ(b1) preparing a precursor represented by the formula: (b2) contacting the precursor with an etching solution containing an intercalation compound to perform etching to remove at least a portion of Al from the precursor and intercalate the intercalation compound; and (e2) performing delamination using a product obtained by the etching and intercalation treatments (etching + intercalation) to obtain conductive two-dimensional particles, wherein 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. <6> The method for producing conductive two-dimensional particles according to <4> or <5>, wherein the etching solution has an HF concentration of 7.0 M or more, and the precursor is kept in contact with the etching solution for 8 hours or less. <7> The method for producing conductive two-dimensional particles according to any one of <4> to <6>, wherein the time for contacting the precursor with the etching solution is 0.5 hours or more. <8> The Ti ｍ AlX ｎ is Ti ３ AlC ２ <9> A method for producing conductive two-dimensional particles according to any one of <4> to <7>, wherein the conductive two-dimensional particles are formed by the electroconductive two-dimensional particles. <10> The conductive film according to <9>, formed from the conductive two-dimensional particles, has a conductivity of 7000 S / cm or more as calculated by the following formula: Electrical conductivity [S / cm] = 1 / (Thickness of conductive film [cm] × Surface resistivity of conductive film [Ω / □]). <11> A conductive paste containing the conductive two-dimensional particles according to any one of <1> to <3>. <12> A conductive composite material comprising the conductive two-dimensional particles according to any one of <1> to <3> and a polymer.

[0096] This application claims priority from Japanese Patent Application No. 2022-080357, which is incorporated herein by reference.

[0097] 1a, 1b Layer body (M ｍ X ｎ Layer) 3a, 5a, 3b, 5b Modified or terminated T 7a, 7b MXene layer 10, 10a, 10b MXene particle (conductive two-dimensional particle, particle of layered material) 30 Conductive film (conductive film)

Claims

1. 1. An electrically conductive two-dimensional particle of a layered material comprising one or more layers, The layer has the following formula: Ti ｍ X ｎ wherein X is a carbon atom, a nitrogen atom, or a combination thereof; n is 1 or more and 4 or less, m is greater than n and is equal to or less than 5. and a modification or terminal 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 particles have an atomic ratio of Al to Ti (Al / Ti) of 0 atomic % or more and 0.10 atomic % or less.

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

3. The Ti ｍ X ｎ is Ti ３ C ２ The conductive two-dimensional particle according to claim 1 or 2,

4. (a) a compound of the formula: Till ｍ AllX ｎ wherein X is a carbon atom, a nitrogen atom, or a combination thereof; n is 1 or more and 4 or less, m is greater than n and is equal to or less than 5. providing a precursor represented by (b1) contacting the precursor with an etching solution to perform an etching process 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 the intercalation compound, which includes stirring a mixture containing the washed material and the intercalation compound of the washed material; and (e1) Using the intercalation product obtained by the intercalation treatment, delamination is performed to obtain conductive two-dimensional particles. wherein an 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.

5. (a) a compound of the formula: Till ｍ AllX ｎ wherein X is a carbon atom, a nitrogen atom, or a combination thereof; n is 1 or more and 4 or less, m is greater than n and is equal to or less than 5. providing a precursor represented by (b2) contacting the precursor with an etching solution containing an intercalation compound to perform an etching process to remove at least a portion of Al from the precursor and an intercalation process of the intercalation compound; (e2) Using the (etching + intercalation) treated product obtained by the etching and intercalation treatment, delamination is performed to obtain conductive two-dimensional particles. wherein an 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.

6. The method for producing conductive two-dimensional particles according to claim 4 or 5, wherein the etching solution has an HF concentration of 7.0 M or more, and the time for which the precursor is in contact with the etching solution is 8 hours or less.

7. The method for producing conductive two-dimensional particles according to claim 4 or 5, wherein the precursor is contacted with the etching solution for 0.5 hours or more.

8. The Ti ｍ AlX ｎ is Ti ３ AIC ２ The method for producing conductive two-dimensional particles according to claim 4 or 5,

9. A conductive film comprising the conductive two-dimensional particles according to claim 1 or 2.

10. The conductive film according to claim 9, which is formed from the conductive two-dimensional particles and has a conductivity calculated from the following formula of 7000 S / cm or more. Conductivity [S / cm] = 1 / (thickness of conductive film [cm] × surface resistivity of conductive film [Ω / □])

11. A conductive paste comprising the conductive two-dimensional particles according to claim 1 or 2.

12. A conductive composite material comprising the conductive two-dimensional particle according to claim 1 or 2 and a polymer.