Conductive particles, film, paste, composite material, and method for producing conductive particles

Abstract

Disclosed are conductive particles which are each formed of a layered material that comprises one or more layers. The layers each comprises: a layer main body which is represented by formula MmXn (in the formula, M is at least one group 3, 4, 5, 6, 7 metal, X is a carbon atom and a nitrogen atom, n is 1 or more and 4 or less, and m is more than n but not more than 5); and a modification or termination T (T is a fluorine atom and at least one selected from the group consisting of a hydroxyl group, a chlorine atom, an oxygen atom, and a hydrogen atom) which is present on the surface of the layer main body. The nitrogen content is 0.05 mass% or more and 2.50 mass% or less.

Description

Conductive particles, films, pastes, composite materials, and methods for producing conductive particles

[0001] The present disclosure relates to conductive particles, films, pastes, composite materials, and methods for making conductive particles.

[0002] In recent years, MXene has been attracting attention as a new material. MXene is a type of so-called conductive material, and is a layered material having the form of one or more layers. ｍ X ｎ T s It is a layered compound represented by the following composition, which can be obtained by etching the precursor MAX. Due to the etching of the MAX, the surface of MXene is modified with -OH, ═O, -F, etc. or terminated with T s These modifications or terminations give MXene hydrophilic properties. Therefore, MXene has excellent water dispersion properties. MXene also exhibits excellent electrical conductivity. ｍ X ｎ For example, Ti ３ C ２ MXene, represented by the following formula, has been proposed.

[0003] Non-Patent Document 1 describes high-purity Ti ３ AlC ２ In Non-Patent Document 1, high-purity Ti powder is synthesized with a much lower external heat amount than when using conventional raw material powders of Ti, Al, and C by using powders of TiC, Ti, and Al as raw materials and heating them in a flowing argon atmosphere at 1300 to 1400°C for 15 to 30 minutes. ３ AlC ２ It is shown that a powder can be obtained.

[0004] In Non-Patent Document 2, Ti ３ AlC ２ By including excess aluminum during the synthesis of the MAX phase precursor, Ti with improved crystallinity and carbon stoichiometry can be obtained. ３ AlC ２ Particles (Al-Ti ３ AlC ２It has been shown that MXene nanosheets (Al-Ti) prepared from this precursor can be obtained. ３ C ２ ) has been shown to improve oxidation resistance. ３ C ２ Freestanding films prepared from the suspension have been shown to exhibit minimal loss in electrical conductivity and reduced oxidation.

[0005] Non-Patent Document 3 shows the results of depth profiling of single particles of MXene and its precursor phase, the MAX phase, at atomic resolution. Also, Non-Patent Documents 4 and 5 show methods for synthesizing two-dimensional titanium carbonitride.

[0006] Chunqing Peng et al., A novel simple method to stably synthesize Ti3AlC2 powder with high purity, Material Science and Engineering, Vol.428, 2006, Pages 54-58Tyler S. Mathis et al., Modified MAX Phase Synthesis for Environmentally Stable and Highly Conductive Ti3C2 MXene, ACS Nano 2021,15,6420-6429P. Michalowski et. al., Oxycarbide MXenes and MAX phases identification using monoatomic layer-by-layer analysis with ultralow-energy secondary-ion mass spectrometry, Nature nanotechnology 17,1192-1197 (2022)K. Hantanasirisakul et. al., Effects of Synthesis and Processing on Optoelectronic Properties of Titanium Carbonitride MXene, Chem. Mater. 31,2941-2951 (2019)T. Zhang et. al., Synthesis of Three Families of Titanium Carbonitride MXenes, J. Am. Chem. Soc. 145,41,22374-22383 (2023)

[0007] When MXene is used for a long period of time, for example, in electrodes, it is required to have oxidation resistance. The property of stably exhibiting oxidation resistance for a long period of time is hereinafter referred to as "oxidation resistance stability." ３ AlC ２Although powder has been obtained, further investigation is needed to obtain MXene with oxidation resistance and stability. ３ C ２ ) has been shown to have improved oxidation resistance. However, in order to obtain high-purity MAX, it is thought that a process for removing impurities such as excess Ti-Al alloys is necessary. Furthermore, Non-Patent Documents 3 to 5 do not examine MXene with oxidation stability.

[0008] The present disclosure has been made in consideration of the above circumstances, and its purpose is to provide conductive particles having excellent oxidation resistance stability, films, pastes, and composite materials containing the conductive particles, and a method for simply producing the conductive particles without requiring excessive processes.

[0009] According to one aspect of the present disclosure, there is provided a particle of layered material comprising one or more layers, wherein said layers are of the following formula: M ｍ X ｎ (wherein M is at least one metal of Group 3, 4, 5, 6, or 7; X is a carbon atom and a nitrogen atom; n is 1 or more and 4 or less; and m is greater than n and 5 or less), and modified or terminated T (said T is at least one selected from the group consisting of a hydroxyl group, a chlorine atom, an oxygen atom, and a hydrogen atom, and a fluorine atom) present on the surface of the layer body, wherein the conductive particle has a nitrogen content of 0.05% by mass or more and 2.50% by mass or less.

[0010] According to the present disclosure, it is possible to provide conductive particles having excellent oxidation resistance stability, films, pastes, and composite materials containing the conductive particles, and a method for simply producing the conductive particles.

[0011] 1 is a schematic cross-sectional view showing MXene, a layered material according to the present embodiment. 2 is a graph showing the relationship between the number of days elapsed in an accelerated test and the absorbance ratio for each nitrogen content.

[0012] Embodiment 1: Conductive Particles Hereinafter, conductive particles according to one embodiment of the present invention will be described in detail, but the present disclosure is not limited to such an embodiment.

[0013] The conductive particles according to this embodiment are particles of layered material comprising one or more layers, wherein said layers are represented by the following formula: M ｍ X ｎ (wherein M is at least one metal of Group 3, 4, 5, 6, or 7; X is a carbon atom and a nitrogen atom; n is 1 or more and 4 or less; and m is greater than n and 5 or less), and modified or terminated T (said T is at least one selected from the group consisting of a hydroxyl group, a chlorine atom, an oxygen atom, and a hydrogen atom, and a fluorine atom) present on the surface of the layer body, and conductive particles (hereinafter sometimes referred to as "first conductive particles") having a nitrogen content of 0.05% by mass or more and 2.50% by mass or less.

[0014] Another conductive particle according to this embodiment has the following formula: M ｍ AX ｎ (wherein M is at least one metal of Group 3, 4, 5, 6, or 7; X is a carbon atom and a nitrogen atom; A is at least one element of Group 12, 13, 14, 15, or 16; n is 1 or more and 4 or less; and m is greater than n and 5 or less), and the nitrogen content is 0.05% by mass or more and 2.50% by mass or less (hereinafter, may be referred to as "second conductive particles"). The second conductive particles may also be a substance used in producing the first conductive particles, i.e., a precursor (intermediate).

[0015] The first conductive particles will be described below, and the second conductive particles will be described in the method for producing the first conductive particles.

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

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

[0018] MXene is a compound represented by the formula: M ｍ X ｎ However, it is known that it can be expressed as follows: Sc ２ (CN), Ti ２ (CN), Zr ２ (CN), Hf ２ (CN), V ２ (CN), Nb ２ (CN), Ta ２ (CN), Cr ２ (CN), Mo ２ (CN), Mo １．３ (CN), Cr １．３ (CN), (Ti,V) ２ (CN), (Ti, Nb) ２ (CN), W ２ (CN), W １．３ (CN), Nb １．３ (CN), Mo １．３ Y ０．６ (CN) (in the above formula, "1.3" and "0.6" mean approximately 1.3 (= 4 / 3) and approximately 0.6 (= 2 / 3), respectively), Ti ３ (CN) ２ , Zr ３ (CN) ２ , (Ti, V) ３ (CN) ２ , (Ti ２ Nb) (CN) ２ , (Ti ２ Ta) (CN) ２ , (Ti ２ Mn)(CN) ２ , Hf ３ (CN) ２ , (Hf ２ V) (CN)２ , (Hf) ２ Mn)(CN) ２ , (V) ２ Ti)(CN) ２ , (Cr ２ Ti)(CN) ２ , (Cr ２ V) (C) ２ , (Cr ２ Nb)(CN) ２ , (Cr ２ (Ta) (CN) ２ , (Mo) ２ Sc)(CNｮ) ２ , (Mo) ２ Ti)(CN) ２ , (Mo) ２ Zr)(CN) ２ , (Mo) ２ Hf)(CN) ２ , (Mo) ２ V) (C) ２ , (Mo) ２ Nb)(CN) ２ , (Mo) ２ (Ta) (CN) ２ ,(W ２ Ti)(CN) ２ ,(W ２ Zr)(CN) ２ ,(W ２ Hf)(CN) ２ 、Ti ４ (CN) ３ ,V ４ (CN) ３ 、Nb ４ (CN) ３ 、That ４ (CN) ３ 、(Ti, Nb) ４ (CN) ３ , (Nb, Zr) ４ (CN) ３ , (Ti) ２ Nb ２ )(CN) ３ , (Ti) ２ That ２ )(CN) ３ , (V) ２ You ２ )(CN) ３ , (V) ２ Nb ２ )(CN) ３, (V ２ Ta ２ ) (CN) ３ , (Nb ２ Ta ２ ) (CN) ３ , (Cr ２ Ti ２ ) (CN) ３ , (Cr ２ V ２ ) (CN) ３ , (Cr ２ Nb ２ ) (CN) ３ , (Cr ２ Ta ２ ) (CN) ３ , (Mo ２ Ti ２ ) (CN) ３ , (Mo ２ Zr ２ ) (CN) ３ , (Mo ２ Hf ２ ) (CN) ３ , (Mo ２ V ２ ) (CN) ３ , (Mo ２ Nb ２ ) (CN) ３ , (Mo ２ Ta ２ ) (CN) ３ , (W ２ Ti ２ ) (CN) ３ , (W ２ Zr ２ ) (CN) ３ , (W ２ Hf ２ ) (CN) ３ , (Mo ２．７ V １．３ ) (CN) ３ (In the above formula, "2.7" and "1.3" mean approximately 2.7 (= 8 / 3) and approximately 1.3 (= 4 / 3), respectively.)

[0019] Typically, in the above formula, M can be titanium or vanadium, and X can be carbon or nitrogen atoms. For example, MAX (phase) can be Ti ３ Al(CN) ２ and MXene is Ti ３(CN) ２ T ｓ (in other words, M is Ti, X is C and N, n is 2, and m is 3).

[0020] The conductive particles of this embodiment contain (are doped with) a trace amount of nitrogen, for example, by partially substituting carbon atom sites of MXene or MAX with nitrogen atoms. This stabilizes the structure of MXene or MAX compared to when carbon atom sites are partially substituted with oxygen atoms, as described in detail below. As a result, even when these are present in an aqueous solution, hydrolysis and other reactions are suppressed, and excellent oxidation resistance stability is achieved. From these perspectives, a trace amount of nitrogen must be present to some extent. In this embodiment, the nitrogen content of the conductive particles is set to 0.05% by mass or more, particularly 0.050% by mass or more. The nitrogen content of the conductive particles is preferably 0.10% by mass or more, more preferably 0.15% by mass or more, and even more preferably 0.20% by mass or more.

[0021] On the other hand, if nitrogen atoms are contained in excess, oxidation resistance stability and conductivity tend to decrease. Therefore, the nitrogen content of the conductive particles according to this embodiment is set to 2.50 mass% or less. The nitrogen content of the conductive particles is preferably 2.00 mass% or less, more preferably 1.50 mass% or less, and even more preferably 1.00 mass% or less. In the present disclosure, nitrogen (N) is essential for ensuring excellent oxidation resistance stability, but it has been found that it is important to control the content to a small amount and within a narrow range.

[0022] The modification or terminal T present on the surface of the MXene layer body is at least one selected from the group consisting of a hydroxyl group, a chlorine atom, an oxygen atom, and a hydrogen atom, and a fluorine atom. The modification or terminal T of MXene according to this embodiment requires a fluorine atom. This fluorine atom is obtained by etching with F contained in the etching solution described in the manufacturing method described later. －The modification or terminal T of MXene according to this embodiment may contain chlorine atoms, but the proportion of chlorine atoms in all of the modification or terminal T is preferably less than 50 atomic %, more preferably 30 atomic % or less, and even more preferably 10 atomic %.

[0023] In the present disclosure, MXene may contain a relatively small amount of residual A atoms, for example, 10% by mass or less of the original A atoms. The amount of residual A atoms is preferably 8% by mass or less, and more preferably 6% by mass or less. However, even if the amount of residual A atoms exceeds 10% by mass, there may be cases where this does not pose a problem depending on the application and conditions of use.

[0024] MXene (sometimes referred to as "MXene particles") is an aggregate containing one layer of MXene 10a (single layer MXene) as shown in FIG. 1(a). MXene 10a is, more specifically, ｍ X ｎ The layer body (M ｍ X ｎ The MXene layer 7a has a main layer 1a and modifications or terminations T3a, 5a present on the surface of the main layer 1a (more specifically, on at least one of the two opposing surfaces of each layer). ｍ X ｎ T ｓ ", where s is an arbitrary number.

[0025] The MXene particles may contain both one layer of MXene and multiple layers of MXene. Examples of multiple-layer MXene (multilayer MXene) include, but are not limited to, two layers of MXene 10b, as shown schematically in Figure 1(b). 1b, 3b, 5b, and 7b in Figure 1(b) are the same as 1a, 3a, 5a, and 7a in Figure 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 mixture of the single layer MXene 10a and the multilayer MXene 10b, with the multilayer MXene 10b remaining unseparated.

[0026] Although this embodiment is not limited thereto, the thickness of each MXene layer (corresponding to the above-described MXene layers 7a and 7b) is, for example, 0.8 nm to 5 nm, particularly 0.8 nm to 3 nm (this may vary mainly depending on the number of M atomic layers contained in each layer). For each of the multiple MXene stacks that may be included, the interlayer distance (or gap dimension, shown as Δd in FIG. 1(b)) may 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 may be 2 to 20,000.

[0027] The MXene particles may be MXene with a reduced number of layers, obtained by subjecting the multilayer MXene to a delamination process (also called a delamination process). The term "reduced number of layers" refers to, for example, MXene having six or fewer stacked layers. Furthermore, the thickness of multilayer MXene with a reduced number of layers in the stacking direction may be 10 nm or less. Hereinafter, this "multilayer MXene with a reduced number of layers" may be referred to as "few-layer MXene." Furthermore, single-layer MXene and few-layer MXene may be collectively referred to as "single-layer / few-layer MXene."

[0028] The MXene particles may contain both single-layer and few-layer MXene. The proportion of single-layer and few-layer MXene with a thickness of 10 nm or less in the total MXene particles may be 1% by volume or more, and even 10% by volume or more.

[0029] Embodiment 2: Film This embodiment relates to a film containing the conductive particles according to embodiment 1. The film containing the conductive particles exhibits excellent oxidation resistance stability, and as a result, can maintain excellent conductivity for a long period of time. A film formed from the conductive particles is preferred.

[0030] The method for forming the film according to this embodiment is not limited, and examples thereof include filtration, coating, immersion, and the like. An example of a filtration method is suction filtration of the conductive particle-containing composition. A membrane filter (Durapore, manufactured by Merck Ltd., pore size 0.45 μm) can be used as the filter for suction filtration. Examples of application methods include spray coating, which involves spray coating using a nozzle such as a one-fluid nozzle, a two-fluid nozzle, or an airbrush; slit coating using a table coater, a comma coater, or a bar coater; screen printing, metal mask printing, spin coating, immersion, brushing, and dripping.

[0031] 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, using an atmospheric pressure oven or a vacuum oven at a temperature of 80° C. or higher and 400° C. or lower.

[0032] The film of this embodiment exhibits a conductivity of 5600 S / cm or more, preferably 5800 S / cm or more. There is no particular upper limit to the conductivity of the film, but it can be, for example, 20,000 S / cm or less. The conductivity is determined by the method described in the Examples below.

[0033] Specifically, the film of the present embodiment may have two opposing main surfaces. The thickness of the film, as well as the shape and dimensions in plan view, may be appropriately selected depending on the intended use of the film.

[0034] The film of the present embodiment may be used in any suitable application, such as an electrode or electromagnetic shield (EMI shield) in any suitable electrical device, where maintaining high electrical conductivity (reducing the decrease in initial electrical conductivity and preventing oxidation) is required.

[0035] The electrodes are not particularly limited, and may be, for example, capacitor electrodes, battery electrodes, bioelectrodes, sensor electrodes, antenna electrodes, etc. By using the film of this embodiment, it is possible to obtain large-capacity capacitors and batteries, low-impedance bioelectrodes, and highly sensitive sensors and antennas even in a smaller volume (volume occupied by the device).

[0036] The capacitor may be an electrochemical capacitor. An electrochemical capacitor is a capacitor that utilizes capacitance generated by a physicochemical reaction between an electrode (electrode active material) and ions (electrolyte ions) in an electrolyte solution, and can be used as a device for storing electrical energy (electrical storage device). The battery may be a chemical battery that can be repeatedly charged and discharged. The battery may be, for example, a lithium-ion battery, a magnesium-ion battery, a lithium-sulfur battery, a sodium-ion battery, or the like, but is not limited to these.

[0037] The bioelectrode is an electrode for acquiring a biosignal, and may be, for example, an electrode for measuring EEG (electroencephalogram), ECG (electrocardiogram), EMG (electromyogram), or EIT (electrical impedance tomography), but is not limited to these.

[0038] A sensor electrode is an electrode for detecting a target substance, state, abnormality, etc. The sensor may be, for example, a gas sensor, a biosensor (a chemical sensor that utilizes a molecular recognition mechanism of biological origin), etc., but is not limited to these.

[0039] The antenna electrode is an electrode for emitting electromagnetic waves into space and / or receiving electromagnetic waves in space.

[0040] Embodiment 3: Paste Examples include pastes containing the conductive particles according to embodiment 1. By containing the conductive particles according to this embodiment, the paste also exhibits excellent oxidation resistance stability, and as a result, can exhibit excellent conductivity for a long period of time.

[0041] An example of the paste is a paste containing the conductive particles according to this embodiment and a dispersion medium. Examples of dispersion media that can be contained in the paste include water; organic media such as N-methylpyrrolidone, N-methylformamide, N,N-dimethylformamide, methanol, ethanol, dimethyl sulfoxide, ethylene glycol, and acetic acid; and the like. The mass ratio of the conductive particles in the paste is, for example, 50% or more. One example of the paste is a conductive paste of a composite material containing a polymer.

[0042] Embodiment 4: Composite Material A composite material may include the conductive particles according to embodiment 1. By including the conductive particles according to this embodiment, the composite material also exhibits excellent oxidation resistance stability, and as a result, can maintain excellent conductivity for a long period of time. The composite material may include the conductive particles according to this embodiment and a resin. Examples of the resin include acrylic resin, polyester resin, polyamide resin, polyolefin resin, polycarbonate resin, polyurethane resin, polystyrene resin, and polyether resin, and one or more of these may be used.

[0043] Embodiment 5: Method for manufacturing conductive particles A method for manufacturing conductive particles according to embodiment 1, particularly first conductive particles, will be described below. The method for manufacturing conductive particles according to this embodiment includes: (a) blending and mixing a raw material containing M, which is at least one metal of Groups 3, 4, 5, 6, and 7; a raw material containing A, which is at least one element of Groups 12, 13, 14, 15, and 16; a raw material containing carbon; and a raw material containing nitrogen so that the nitrogen content of the total raw materials is 0.05 mass % or more and 2.50 mass % or less; (b) firing the mixture to obtain a mixture of the following formula: M ｍ AX ｎ(wherein M is at least one metal of Groups 3, 4, 5, 6, and 7; X is a carbon atom and a nitrogen atom; A is at least one element of Groups 12, 13, 14, 15, and 16; n is 1 or more and 4 or less; and m is greater than n and 5 or less), and the nitrogen content is 0.05% by mass or more and 2.50% by mass or less; (c) F － (d) performing an etching treatment to remove at least some of the A atoms from the precursor using an etching solution containing the compound; (d) washing the etched product obtained by the etching treatment with water to obtain a water-washed product; (e) performing an intercalation treatment of the intercalation compound, which includes stirring a mixture of the water-washed product and the intercalation compound; and (f) performing delamination using the intercalation product obtained by the intercalation treatment to obtain the first conductive particles. This method makes it possible to obtain conductive particles containing a predetermined trace amount of nitrogen and having excellent oxidation resistance stability.

[0044] Each step of the above manufacturing method will be described in detail below.

[0045] Step (a): A raw material containing at least one Group 3, 4, 5, 6, or 7 metal (M), a raw material containing at least one Group 12, 13, 14, 15, or 16 element (A), a carbon-containing raw material, and a nitrogen-containing raw material are blended so that the nitrogen content of the total raw materials is at least 0.05% by mass or more and not more than 2.50% by mass, and then mixed to obtain a mixture. The nitrogen content of the total raw materials may further be 0.10% by mass or more, even 0.15% by mass or more, or even 0.20% by mass or more. Furthermore, the nitrogen content of the total raw materials may further be 2.00% by mass or less, even 1.50% by mass or less, or even 1.00% by mass or less. Conventionally, MXene, such as titanium aluminum carbide, has generally been produced using TiC, Ti, and Al as starting materials. However, in the above process, nitrogen-containing raw materials are essential, and by adjusting the amount of nitrogen added, it is possible to reliably synthesize MAX and MXene, which have high oxidation resistance and stability.

[0046] The raw material containing M and the raw material containing A may be a metal powder or a metal compound powder. The raw material containing carbon may be a carbon powder, and the raw material containing nitrogen may be a nitrogen compound powder such as a metal nitride powder. The raw material containing M, the raw material containing A, the raw material containing carbon, and the raw material containing nitrogen may be separate, or two or more raw materials may be the same raw material, for example, the raw material containing nitrogen may also be the raw material containing M. Examples of the raw material containing nitrogen and the raw material containing M include titanium nitride (TiN) and vanadium nitride (VN).

[0047] The nitrogen-containing source material is preferably a nitride of M, such as titanium nitride.

[0048] The raw materials can be mixed using, for example, a ball mill.

[0049] Step (b) calcining the mixture to obtain a compound of the following formula: ｍ AX ｎ (wherein M is at least one metal of Group 3, 4, 5, 6, or 7; X is a carbon atom and a nitrogen atom; A is at least one element of Group 12, 13, 14, 15, or 16; n is 1 or more and 4 or less; and m is greater than n and 5 or less), and a precursor (second conductive particles) having a nitrogen content of 0.05 mass % or more and 2.50 mass % or less is obtained. The above-mentioned second conductive particles can be produced by including the steps (a) and (b).

[0050] The firing can be carried out, for example, in an Ar atmosphere, at a temperature rise rate of 3 to 20°C / min, at a heating temperature of 1350 to 1400°C, and for a heating holding time of 90 to 180 minutes. The resulting fired body can be pulverized with an end mill to obtain a powdered MAX phase for the next step.

[0051] The above M, X, n, and m are as described for MXene. A is at least one Group 12, 13, 14, 15, or 16 element, and is usually a Group A element, typically Group IIIA or Group IV A. More specifically, it may include at least one element selected from the group consisting of Al, Ga, In, Tl, Si, Ge, Sn, Pb, P, As, S, and Cd, and is preferably Al. The nitrogen content of the second conductive particles is as described for the first conductive particles.

[0052] The MAX phase is M ｍ X ｎ (each X may have a crystal lattice in which it is located in an octahedral array of M) and a layer composed of A atoms is located between them. In the MAX phase, typically when m=n+1, one layer of X atoms is arranged between each of the n+1 layers of M atoms (these are collectively referred to as "M ｍ X ｎ The repeating unit has a layer of A atoms (also referred to as an "A atom layer") arranged as the next layer after the n+1th layer of M atoms, but is not limited thereto.

[0053] ・Process (c) F － An etching treatment is performed to remove at least a part of the A atoms from the precursor using an etching solution containing the compound.

[0054] The A atoms (and possibly some of the M atoms) are selectively etched (removed and possibly separated from the MAX phase), thereby removing the A atom layer (and possibly some of the M atoms) and forming an exposed M ｍ X ｎ The surface of the layer is modified with fluorine atoms, hydroxyl groups, chlorine atoms, oxygen atoms, hydrogen atoms, and the like resulting from the etching solution, etc., and the surface is terminated.

[0055] The etching is carried out by F －The etching is carried out using an etching solution containing the compound. As a result, the conductive particles according to this embodiment contain a fluorine element as a modification or terminal T. For example, a method using a mixed solution of lithium fluoride and hydrochloric acid or a method using hydrofluoric acid may be used. A metal compound containing a monovalent metal ion may be included in the etching solution, and an intercalation treatment of the monovalent metal ion may be carried out simultaneously with the etching. Examples of metal compounds containing monovalent metal ions include those used in the intercalation treatment described below. The content of the metal compound containing a monovalent metal ion in the etching solution is preferably 0.001% by mass or more. The content is more preferably 0.01% by mass or more, and even more preferably 0.1% by mass or more. On the other hand, from the viewpoint of dispersibility in the solution, the content of the metal compound containing a monovalent metal ion in the etching solution is preferably 10% by mass or less, more preferably 1% by mass or less.

[0056] Step (d): The etched product obtained by the etching is washed with water. By washing with water, the acid used in the etching can be sufficiently removed. The amount of water to be mixed with the etched product and the washing method are not particularly limited. For example, adding water and stirring, centrifuging, or the like can be performed. Stirring methods include using a hand shake, an automatic shaker, a shear mixer, a pot mill, or the like. 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 water washing may be performed one or more times. Preferably, the water washing is performed multiple times. Specifically, for example, steps (i) to (iv) of (i) adding water (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 can be performed two or more times, for example, 15 or less times.

[0057] To separate the layers of MXene, the following intercalation and delamination processes are performed. If ultrasonic treatment is used as a post-treatment, the shear force may be too strong, destroying the MXene. Therefore, to obtain a two-dimensional MXene with a larger aspect ratio (preferably monolayer MXene), it is recommended to apply an appropriate shear force using a hand shake or automatic shaker instead of ultrasonic treatment.

[0058] Step (e) An intercalation treatment of the intercalation compound is carried out, which includes stirring a mixture of the water-washed product and the intercalation compound.

[0059] For example, a monovalent metal ion intercalation treatment may be performed, which includes a step of mixing the etched product obtained by the etching treatment with a metal compound containing a monovalent metal ion. Examples of the monovalent metal ion constituting the metal compound containing a monovalent metal ion include alkali metal ions such as lithium ions, sodium ions, and potassium ions, copper ions, silver ions, and gold ions. Examples of the metal compound containing a monovalent metal ion include ionic compounds in which the above metal ions are bonded to cations. Examples include iodides, phosphates, sulfide salts including sulfates, nitrates, acetates, and carboxylates of the above metal ions. The monovalent metal ion is preferably lithium ion, and the metal compound containing a monovalent metal ion is preferably a metal compound containing lithium ion, more preferably an ionic compound of lithium ion, and even more preferably one or more of iodides, phosphates, and sulfide salts of lithium ion. It is believed that using lithium ions as the metal ion facilitates monolayer formation because water hydrated with lithium ions has the most negative dielectric constant.

[0060] The content of the metal compound containing a monovalent metal ion in the formulation for intercalation treatment of a monovalent metal ion is preferably 0.001% by mass or more. The content is more preferably 0.01% by mass or more, and even more preferably 0.1% by mass or more. On the other hand, from the viewpoint of dispersibility in the solution, the content of the metal compound containing a monovalent metal ion is preferably 10% by mass or less, more preferably 1% by mass or less.

[0061] Step (f): The intercalation product obtained by the intercalation treatment is subjected to delamination to obtain conductive particles.

[0062] The intercalation-treated product obtained by intercalation may be subjected to delamination. For example, delamination may involve centrifuging the intercalation-treated product, discarding the supernatant, and then washing the remaining precipitate with water. The conditions for the delamination treatment are not particularly limited. The dispersion medium used for delamination is also not particularly limited, and examples include using one or more of a polar organic dispersion medium and an aqueous dispersion medium. The process of adding one or more of the polar organic dispersion medium and the aqueous dispersion medium, stirring, centrifuging, and recovering the supernatant may be repeated at least once, preferably at least twice, but not more than 10 times, to obtain a supernatant containing single-layered and / or few-layered MXene as the delamination-treated product. Alternatively, the supernatant may be centrifuged, and the resulting supernatant may be discarded to obtain a single-layered and / or few-layered MXene-containing clay as the delamination-treated product.

[0063] In the above-described method, the nitrogen content of the conductive particles was controlled by adjusting the ratio of the raw materials used, but the method for producing conductive particles according to this embodiment is not limited to the above-described method. The nitrogen content of the conductive particles can be controlled by adjusting the introduced gas during the firing step in the production of MAX, for example, by controlling the ratio of nitrogen gas to argon gas and nitrogen gas. Alternatively, nitrogen-free MXene or MAX can be produced by a conventional method using TiC, Ti, and Al as starting materials, and then the MXene or MAX can be subjected to a nitriding treatment by exposing it to a nitrogen-containing gas such as ammonia.

[0064] The present invention will be described in more detail below with reference to examples. The present invention is not limited to the following examples, and can be practiced with appropriate modifications within the scope of the above-mentioned and below-mentioned aims, and all such modifications are included in the technical scope of the present invention.

[0065] [Preparation of Conductive Particles] In this example, conductive particles were obtained by sequentially carrying out the following steps: (1) preparation of a precursor (MAX), (2) etching of the precursor, (3) washing, (4) intercalation of metal cations, (5) delamination, and (6) washing with water, as detailed below. As a comparative example, MXene particles not satisfying the nitrogen content of this embodiment were also obtained.

[0066] (1) Preparation of Precursor (MAX) [Mixing of Materials] Ti powder (up to 45 μm; manufactured by Kojundo Chemical Laboratory Co., Ltd.), TiN powder (2-5 μm; manufactured by Kojundo Chemical Laboratory Co., Ltd.), Al powder (up to 45 μm; manufactured by Kojundo Chemical Laboratory Co., Ltd.), and C powder (up to 45 μm; manufactured by Kojundo Chemical Laboratory Co., Ltd.) were mixed in the molar ratios shown in Table 1 below to obtain a mixed powder. The ratios in the table below are those assuming that the materials do not contain impurities. The mixed size was 150 g of mixed powder per batch, and the mixing conditions were a ball mill at 60 rpm for 24 hours.

[0067]

[0068] The mixed powder was placed in an alumina container and fired in an argon atmosphere to obtain a MAX block. The firing conditions were a temperature rise rate of 10°C / min, a top temperature (maximum temperature inside the alumina container) of 1350 to 1400°C, and a top temperature holding time of 120 min.

[0069] [Crushing] The MAX block after firing is crushed in a crusher and sieved through a 100 to 300 mesh sieve to separate the Ti and ３ A1 (CN) ２ A powder was obtained.

[0070] [2] Etching of precursor (MAX) Ti prepared by the above method ３ Al(CN) ２ Using particles (powder), etching was performed under the following etching conditions to remove Ti ３ Al(CN) ２ A solid-liquid mixture (slurry) containing solid components derived from the powder was obtained. － Since the etching is performed using an etching solution containing Ti, the resulting MXene particles contain fluorine atoms as modified or terminated T. (Etching conditions) Precursor: Ti ３ Al(CN) ２ (Sieved through a 45 μm mesh) Etching solution composition: 49% HF 6 mL H ２ O 18 mL HCl (12 M) 36 mL Precursor input amount: 3.0 g Etching container: 100 mL Eye Boy Etching temperature: 35°C Etching time: 24 h Stirrer rotation speed: 400 rpm

[0071] [3] Post-etching cleaning The above slurry was divided into two parts and placed in two 50 mL centrifuge tubes. Then, after centrifuging at 3500 G for 5 minutes using a centrifuge, the supernatant was discarded. Thereafter, (i) 40 mL of pure water was added to the remaining precipitate in each centrifuge tube, (ii) centrifugation was again carried out at 3500 G for 5 minutes, and (iii) the supernatant was separated and removed. This procedure from (i) to (iii) was repeated 11 times. After the final centrifugation, the supernatant was discarded, and Ti ３ (CN) ２ T ｘ- Water medium clay was obtained.

[0072] [4] Li intercalation Ti prepared by the above method ３ (CN) ２ T ｘ The clay was subjected to Li intercalation using LiCl as a Li-containing compound under the following conditions: the clay was stirred at 20°C to 25°C for 10 hours. (Li intercalation conditions) ３ (CN) ２ T ｘ - 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: 10 hours Stirrer rotation speed: 800 rpm

[0073] [5] Delamination The slurry obtained by Li intercalation was placed in a 50 mL centrifuge tube and centrifuged at 3500 G using a centrifuge. The supernatant was then discarded. Next, (i) 40 mL of pure water was added to the remaining precipitate, followed by stirring for 15 minutes on a shaker. (ii) The mixture was centrifuged at 3500 G. (iii) The supernatant was recovered as a single-layer / sparse-layer MXene-containing solution. These steps (i) to (iii) were repeated four times to obtain a single-layer / sparse-layer MXene-containing supernatant. Furthermore, this supernatant was centrifuged at 4300 G for two hours using a centrifuge. The supernatant was then discarded, and the remaining precipitate, a single-layer / sparse-layer MXene-containing clay (hereinafter simply referred to as MXene clay), was obtained as a clay containing MXene particles (clays containing conductive particles according to this embodiment in Nos. 2 to 4).

[0074] [Evaluation] The clay containing MXene particles obtained above was used to measure the nitrogen content, evaluate the oxidation resistance stability, and evaluate the electrical conductivity, as described below.

[0075] [Measurement of Nitrogen Content] The nitrogen content of the resulting MXene was measured by an inert gas fusion-thermal conductivity method using an oxygen / nitrogen analyzer (TC-436AR manufactured by LECO Corporation). The results are shown in Table 2 below. In Table 2 below, the N amount of No. 1 is considered to be the amount of unavoidable impurities.

[0076]

[0077] [Evaluation of Oxidation Resistance Stability] Oxidation resistance stability was evaluated by preparing a dispersion solution of MXene, conducting an accelerated test, and then measuring the absorbance at a predetermined wavelength, as described in detail below.

[0078] (Solution Preparation) MXene was diluted with ultrapure water to prepare a dispersion solution with an MXene concentration of 0.001% by mass. The solution was then prepared so that the absorbance readings on the calibration curve at 780 nm, the wavelength at which MXene has a plasmon resonance peak, would be in the range of 0.4 to 0.5. To ensure dispersibility after preparation, the solution was treated in a 28 kHz ultrasonic bath for 10 seconds.

[0079] The accelerated test was carried out in a heated water bath with stirring. Specifically, 40 mL of the MXene dispersion solution was heated for 8 days at a set temperature of 60°C (actual temperature of 50°C) with stirring at 500 rpm.

[0080] (Absorbance Measurement) The absorbance of the dispersion solution before the accelerated test and the measurement solution were sampled at intervals of approximately 24 hours from the dispersion solution that had been heated and maintained thereafter were measured. An ASV-11D-H (manufactured by AS ONE) was used as the dispersion solution measuring instrument. As described above, the measurement wavelength was the wavelength at which each MXene has a plasmon resonance peak, i.e., 780 nm. The absorbance of the dispersion solution before the accelerated test was set to 1.00, and the ratio of the obtained absorbance to the absorbance of the dispersion solution before the accelerated test was calculated. A higher ratio indicates a smaller degree of oxidation and better oxidation resistance.

[0081] In this example, the ratio of the absorbance obtained to the absorbance of the dispersion solution before the accelerated test was calculated. As a result, the relationship between the number of days elapsed in the accelerated test and the absorbance ratio for each nitrogen content is shown in a graph in Figure 2.

[0082] [Evaluation of Conductivity] (Film Production) The clay containing MXene particles obtained by the delamination was subjected to suction filtration. After filtration, the clay was vacuum dried at 80°C for 24 hours to produce a film containing conductive particles. A membrane filter (Durapore, manufactured by Merck Ltd., pore size 0.45 μm) was used for the suction filtration. The supernatant contained 0.05 g of conductive particle solids and 40 mL of pure water.

[0083] (Measurement of Film Conductivity) The conductivity of the obtained film was determined. Resistivity (Ω) and thickness (μm) were measured at three locations per sample, and the conductivity (S / cm) was calculated from these measurements. The average of the three resulting conductivities was used. Resistivity was measured by measuring the surface resistance of the film using a simple low-resistivity meter (Loresta AX MCP-T370, manufactured by Mitsubishi Chemical Analytical Corporation) using the four-terminal method. Thickness was measured using a micrometer (MDH-25MB, manufactured by Mitutoyo Corporation). Volume resistivity was then calculated from the obtained surface resistance and film thickness, and the conductivity was calculated by taking the reciprocal of this value. The results are shown in Table 3.

[0084]

[0085] The following can be seen from Tables 1 to 3 and Figure 2. No. 1 is a conventional MXene that did not contain nitrogen. As shown in Figure 2, the conventional MXene (No. 1) that did not contain nitrogen had significantly poorer oxidation stability. As a result, as shown in Table 3, the film obtained using MXene No. 1 exhibited a certain degree of conductivity, but it is thought that it would be difficult to maintain this conductivity over an extended period of time. On the other hand, Nos. 2 to 4, which contained a certain amount of nitrogen, exhibited excellent oxidation stability, as shown in Figure 2. Note that No. 5, which contained an excessive amount of nitrogen, had poorer oxidation stability than the conventional MXene (No. 1) that did not contain nitrogen, as shown in Figure 2.

[0086] The above-mentioned evaluation of oxidation resistance and measurement of electrical conductivity suggested that there is an optimum amount of nitrogen added (also called "N doping amount"). The following is thought to occur depending on the N doping amount.

[0087] First, we will explain the case where the N doping amount is zero. In the MAX phase synthesized under stoichiometric conditions without N doping, it is clear that the C site is partially substituted with oxygen, as shown in the TOF-SIMS result report of the MAX phase (Fig. 4.1) in Non-Patent Document 3. Based on this document, the oxygen content of each sample in this example was quantitatively evaluated for reference. The oxygen content was quantified using an oxygen / nitrogen analyzer (LECO TC-436AR) using an inert gas container and infrared absorption method. The results are shown in Table 4 below.

[0088]

[0089] From the results in Table 4 above, it was confirmed that the amount of oxygen in No. 1, which was not doped with N, was the largest, which is in line with the results shown in Non-Patent Document 3.

[0090] The reason why O substitution at the C site adversely affects the electrical conductivity and oxidation resistance stability is thought to be local structural stress near the O substitution site. As shown in Non-Patent Document 4, past calculation results predict that the crystal structure will be distorted depending on the amount of O substitution. It is thought that such structural instability leads to a decrease in electrical conductivity and oxidation resistance stability. In this embodiment, N doping is performed, and N substitution is performed instead of O substitution, which is thought to have suppressed the distortion of the crystal structure.

[0091] On the other hand, when the amount of N doping is excessive, it is suggested that the random distribution of nitrogen atoms in the C site may cause them to act as electron scattering centers and reduce electron mobility, as shown in Non-Patent Document 5. When the amount of nitrogen doping is large, the above effect becomes significant, and it is thought that the conductivity is reduced.

[0092] In Figure 2, when the nitrogen substitution amount (nitrogen content) was 0.21 mass% (No. 3), which had the maximum value, it is believed that almost all of the O substituted at the C site was substituted with N. On the other hand, when nitrogen was further added (No. 5), some of the C site was further substituted with N, which is thought to have resulted in distortion of the crystal structure and a decrease in oxidation resistance stability and electrical conductivity.

[0093] This application claims priority from Japanese Patent Application No. 2024-073006, which is incorporated herein by reference.

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

[0095] The disclosure of the present specification may include the following aspects: <1> A particle of a layered material including one or more layers, wherein the layer is represented by the following formula: M ｍ X ｎ (wherein M is at least one kind of Group 3, 4, 5, 6, or 7 metal; X is a carbon atom and a nitrogen atom; n is 1 or more and 4 or less; and m is greater than n and 5 or less), and modified or terminated T (the T is at least one kind selected from the group consisting of a hydroxyl group, a chlorine atom, an oxygen atom, and a hydrogen atom, and a fluorine atom) present on the surface of the layer body, and the nitrogen content is 0.05 mass % or more and 2.50 mass % or less. <2> Conductive particles comprising a layer body represented by the following formula: M ｍ AX ｎ(wherein M is at least one metal of Group 3, 4, 5, 6, or 7, X is a carbon atom and a nitrogen atom, A is at least one element of Group 12, 13, 14, 15, or 16, n is 1 or more and 4 or less, and m is greater than n and 5 or less), and the nitrogen content is 0.05 mass % or more and 2.50 mass % or less. <3> A film comprising the conductive particles according to <1> or <2> and having a conductivity of 5600 S / cm or more. <4> A paste comprising the conductive particles according to <1> or <2>. <5> A composite material comprising the conductive particles according to <1> or <2>. <6> (a) blending and mixing a raw material containing M, which is at least one Group 3, 4, 5, 6, and 7 metal; a raw material containing A, which is at least one Group 12, 13, 14, 15, and 16 element; a raw material containing carbon; and a raw material containing nitrogen so that the nitrogen content of the total raw materials is 0.05 mass% or more and 2.50 mass% or less; (b) firing the mixture to obtain a mixture of the following formula: M ｍ AX ｎ (wherein M is at least one metal of Groups 3, 4, 5, 6, and 7; X is a carbon atom and a nitrogen atom; A is at least one element of Groups 12, 13, 14, 15, and 16; n is 1 or more and 4 or less; and m is greater than n and 5 or less), and the nitrogen content is 0.05% by mass or more and 2.50% by mass or less; (c) F － (d) performing an etching treatment to remove at least a part of A atoms from the precursor using an etching solution containing the compound, (d) washing the etched product obtained by the etching treatment with water to obtain a water-washed product, (e) performing an intercalation treatment of an intercalation compound, which includes stirring a mixture of the water-washed product and the intercalation compound of the water-washed product, and (f) performing delamination using the intercalation product obtained by the intercalation treatment to obtain conductive particles. <7> The method according to <6>, wherein the nitrogen-containing raw material is a nitride of M.

[0096] 1a, 1b Layers (M) ｍ X ｎ Layers) 3a, 5a, 3b, 5b Modification (terminal T) 7a, 7b MXene layers 10a, 10b MXene particles

Claims

1. A particle of layered material comprising one or more layers, said layers having the following formula: M ｍ X ｎ (wherein M is at least one metal of Group 3, 4, 5, 6, or 7; X is a carbon atom and a nitrogen atom; n is 1 or more and 4 or less; and m is greater than n and 5 or less), and modified or terminated T (said T is at least one selected from the group consisting of a hydroxyl group, a chlorine atom, an oxygen atom, and a hydrogen atom, and a fluorine atom) present on the surface of the layer body, wherein the nitrogen content is 0.05% by mass or more and 2.50% by mass or less.

2. The formula: M ｍ AX ｎ (wherein M is at least one metal of Group 3, 4, 5, 6, or 7; X is a carbon atom and a nitrogen atom; A is at least one element of Group 12, 13, 14, 15, or 16; n is 1 or more and 4 or less; and m is greater than n and 5 or less), and the nitrogen content is 0.05 mass % or more and 2.50 mass % or less.

3. A film containing the conductive particles according to claim 1 or 2, and having a conductivity of 5600 S / cm or more.

4. A paste containing the conductive particles according to claim 1 or 2.

5. A composite material comprising the conductive particles according to claim 1 or 2.

6. (a) blending and mixing a raw material containing M, which is at least one metal of Groups 3, 4, 5, 6, and 7; a raw material containing A, which is at least one element of Groups 12, 13, 14, 15, and 16; a raw material containing carbon; and a raw material containing nitrogen so that the nitrogen content of the total raw materials is 0.05% by mass or more and 2.50% by mass or less; (b) calcining the mixture to obtain a mixture of the following formula: M ｍ AX ｎ (wherein M is at least one metal of Groups 3, 4, 5, 6, and 7; X is a carbon atom and a nitrogen atom; A is at least one element of Groups 12, 13, 14, 15, and 16; n is 1 or more and 4 or less; and m is greater than n and 5 or less), and the nitrogen content is 0.05% by mass or more and 2.50% by mass or less; (c) F － (d) washing the etched product obtained by the etching with water to obtain a water-washed product; (e) performing an intercalation treatment of an intercalation compound, which includes stirring a mixture of the water-washed product and the intercalation compound; and (f) performing delamination using the intercalation product obtained by the intercalation treatment to obtain conductive particles.

7. The manufacturing method according to claim 6, wherein the nitrogen-containing raw material is a nitride of M.

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