Conductive film and method for manufacturing the same

Abstract

Provided is a conductive film containing MXene and capable of maintaining high electrical conductivity. A conductive film is a conductive film containing a layered material having one or more layers, wherein the layer includes: a layer main body represented by the following formula: M m X n (n is 1 or more and 4 or less, and m is greater than n and 5 or less) and a modification or a 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 main body, the conductive film further contains 0.001 mass% or more and less than 0.09 mass% of phosphorus atoms, and maintains an electrical conductivity of 2000 S / cm or more.

Description

Technical Field

[0001] This invention relates to conductive films and methods for manufacturing the same. Background Technology

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

[0003] Currently, various studies are underway regarding the application of MXene in various electrical devices. However, it is known that the conductivity of MXene decreases over time (e.g., from several days to about one month), primarily due to its susceptibility to oxidation. Oxidation of MXene is a significant issue for its industrial application.

[0004] Non-Patent Literature 1 reports that by adding polyphosphates (0.1M sodium polyphosphate) to an aqueous colloidal suspension of MXene, the edges of each MXene sheet can be covered, thus inhibiting the oxidation of MXene. Non-Patent Literature 2 reports that by adding L-ascorbic acid sodium to a dispersion of MXene nanosheets, the edges of the MXene nanosheets can be protected, thus inhibiting the oxidation of MXene.

[0005] Existing technical documents

[0006] Non-patent literature

[0007] Non-patent document 1: Varun Natu et ai., "Edge Capping of 2D-MXene Sheets with Polyanionic Salts to Mitigate Oxidation in Aqueous Colloidal Suspensions", Angewandte Chemie International Edition, 2019, Volume 58, Issue 36, pp.12655-12660

[0008] Non-patent literature 2: Xiaofei Zhao et al., "Antioxidants Unlock Shelf-Stable Ti3C2T" x (MXene)Nanosheet Dispersions",Matter,2019,Volume 1,Issue 2,pp.513-526 Summary of the Invention

[0009] The problem that the invention aims to solve

[0010] However, the antioxidant method reported in Non-Patent Document 1 is limited to MXene suspensions or dispersions, and no effect on initial conductivity or antioxidant effect (reducing conductivity decrease over time) has been confirmed in dried MXene films. Furthermore, the antioxidant method reported in Non-Patent Document 2 results in an initial conductivity of less than 1 / 2 in dried MXene films (referencing Figure S6 of Non-Patent Document 2). Existing antioxidant methods cannot achieve conductive films that maintain high conductivity in two ways: avoiding initial conductivity decrease in conductive films containing MXene, and effectively reducing conductivity decrease over time through antioxidant action.

[0011] The purpose of this invention is to provide a conductive film containing MXene that maintains high conductivity and a method for manufacturing the same.

[0012] Problem-solving methods

[0013] According to one aspect of the present invention, a conductive film is provided, which is a conductive film comprising particles of a layered material having one or more layers, wherein,

[0014] The layer comprises: M m X n The layer body represents (where M is at least one metal from Group 3, 4, 5, 6, or 7, X is a carbon atom, a nitrogen atom, or a combination thereof, n is 1 or more and 4 or less, and m is greater than n and 5 or less); the modification or terminal T present on the surface of the layer body (T is at least one selected from the group consisting of hydroxyl, fluorine, chlorine, oxygen, and hydrogen atoms).

[0015] The conductive film further contains phosphorus atoms at a mass percentage of 0.001% and less than 0.09%, and maintains a conductivity of 2000 S / cm or higher.

[0016] In one embodiment of the invention, the phosphorus atom may be derived from a polyanionic salt containing a phosphate group.

[0017] In one embodiment of the invention, the polyanionic salt containing phosphate groups may be at least one selected from the group consisting of polyphosphate metal salts, pyrophosphate metal salts, triphosphate metal salts and hexametaphosphate metal salts.

[0018] In one embodiment of the invention, the conductivity can be used as an electrode or an electromagnetic shield. The electrode, for example, can be any one of a capacitor electrode, a battery electrode, a bioelectrode, a sensor electrode, and an antenna electrode.

[0019] According to another aspect of the present invention, a method for manufacturing a conductive film is provided, comprising:

[0020] (a) Preparation of a mixture in an aqueous solvent containing particles of a layered material comprising one or more layers and a polyanionic salt containing phosphate groups.

[0021] The layer comprises: M m X n The layer body represents (where M is at least one metal from Group 3, 4, 5, 6, or 7, X is a carbon atom, a nitrogen atom, or a combination thereof, n is 1 or more and 4 or less, and m is greater than n and 5 or less); the modification or terminal T present on the surface of the layer body (T is at least one selected from the group consisting of hydroxyl, fluorine, chlorine, oxygen, and hydrogen atoms).

[0022] The concentration of the layered material particles in the mixture is above 10 mg / mL and below 250 mg / mL.

[0023] The molar concentration of the polyanionic salt containing phosphate groups in the mixture is 0.001 mol / L or more and 0.1 mol / L or less.

[0024] (b) The mixture is dried to obtain a conductive film.

[0025] In one aspect of the invention, the method for manufacturing the conductive film may further include, after (a) and before (b), applying shear force to the mixture and cleaning it using another aqueous solvent.

[0026] In one embodiment of the present invention,

[0027] The polyanionic salt containing phosphate groups in (a) is a salt of a polyanionic salt containing multiple phosphate groups and a metal ion.

[0028] The conductive film obtained from (b) may contain less than 0.5% by mass of the metal element corresponding to the metal ion.

[0029] The conductive film of the present invention can be manufactured by the manufacturing method of the conductive film of the present invention.

[0030] Invention Effects

[0031] According to the present invention, the conductive film comprises particles of a defined layered material (also referred to as "MXene" in this specification), and contains 0.001% by mass and less than 0.09% by mass of phosphorus atoms, and maintains a conductivity of 2000 S / cm or more, thereby providing a conductive film containing MXene and capable of maintaining high conductivity. Furthermore, according to the present invention, a conductive film can be manufactured by preparing a mixture of particles of a defined layered material containing 10 mg / mL or more and 250 mg / mL or less, and a polyanionic salt containing phosphate groups containing 0.001 mol / L or more and 0.1 mol / L or less in an aqueous solvent, and then drying the mixture. Attached Figure Description

[0032] Figure 1 The figures illustrate a conductive film according to one embodiment of the present invention, (a) showing a schematic cross-sectional view of the conductive film, and (b) showing a schematic perspective view of the MXene of the conductive film.

[0033] Figure 2 This is a schematic cross-sectional view of MXene particles, a layered material that can be used in conductive films according to one embodiment of the present invention. (a) shows a single layer of MXene particles, and (b) shows a multilayer (e.g., two layers) of MXene particles.

[0034] Figure 3 This is a graph showing the change in conductivity over time of the conductive films manufactured in Examples 1-2 and Comparative Examples 1-3. Detailed Implementation

[0035] The conductive film and its manufacturing method according to one embodiment of the present invention are described in detail below, but the present invention is not limited to such an embodiment.

[0036] Reference Figure 1 The conductive film 30 of this embodiment includes particles 10 of a defined layered material, and also contains 0.001% by mass and less than 0.09% by mass of phosphorus atoms (not shown), and maintains a conductivity of 2000 S / cm or more. Hereinafter, the conductive film 30 of this embodiment will be described using this manufacturing method.

[0037] The method for manufacturing the conductive film 30 in this embodiment includes:

[0038] (a) Preparing a mixture of particles containing a specified layered material and a polyanionic salt containing phosphate groups in an aqueous solvent, wherein,

[0039] The concentration of the layered material particles in the mixture is above 10 mg / mL and below 250 mg / mL.

[0040] The molar concentration of the polyanionic salt containing phosphate groups in the mixture is 0.001 mol / L or more and 0.1 mol / L or less; and

[0041] (b) The mixture is dried to obtain a conductive film.

[0042] Process (a)

[0043] First, prepare the specified layered material particles. In this embodiment, the specified layered material that can be used is MXene, as specified below:

[0044] A layered material containing one or more layers (which can be understood as a layered compound, also referred to as "M") m X n T s "s is any number (in the past, x was sometimes used to replace s), where this layer includes:

[0045] From the following formula: M m X n (where M is at least one Group 3, 4, 5, 6, or 7 metal, a so-called early transition metal, which may include, for example, at least one selected from the group consisting of Sc, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and Mn; 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) a layer body (which may have a lattice in which each X is located within an octahedral array of M); and a modification or terminator T (T is at least one selected from the group consisting of hydroxyl, fluorine, chlorine, oxygen, and hydrogen atoms) present on the surface of the layer body (more specifically, at least one of the two opposing surfaces of the layer body). Typically, n can be 1, 2, 3, or 4, but is not limited thereto.

[0046] In the above formula for MXene, M is preferably selected from at least one of the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and Mn, and more preferably from at least one of the group consisting of Ti, V, Cr and Mo.

[0047] Such MXenes can be synthesized by selectively etching (removing and, depending on the case, separating the layers) A atoms (and, depending on the case, a portion of the M atoms) from MAX.

[0048] The MAX phase is given by the following formula: M m AX nThe expression (where M, X, n, and m are as described above, and A is at least one element from Group 12, 13, 14, 15, or 16, typically a Group A element, representatively Group IIIA and Group IVA, and more specifically, 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, preferably Al), and the layer having A atoms is located in the group consisting of M... m X n This represents the crystal structure between two layers (each X can have a lattice located within an octahedral array of M). Typically, in the case of m = n+1, the MAX phase has repeating units such that layers of M atoms (n+1 layers) are interspersed with layers of X atoms (these layers are collectively referred to as "M"). m X n A layer of A atoms (“layer of A atoms”) is configured as the layer below the (n+1)th M atom layer, but is not limited thereto. By selectively etching (removing and, depending on the case, separating the layers) the A atoms (and, depending on the case, a portion of the M atoms) from the MAX phase, the layer of A atoms (and, depending on the case, a portion of the M atoms) is removed, and hydroxyl, fluorine, chlorine, oxygen, and hydrogen atoms, etc., present in the etching solution (typically, an aqueous solution containing hydrofluoric acid can be used, but not limited thereto), are exposed for the M atoms. m X n The surface modification of the layer makes such a surface serve as the end. Etching can be performed using F-containing... － The etching solution can be implemented, for example, by a suitable mixture of lithium fluoride and hydrochloric acid, or by using hydrofluoric acid, etc.

[0049] As described later, in order to obtain a conductive film with high orientation of MXene particles, etching (including cleaning and centrifugation) is preferably performed to reduce the number of atom residues in the MXene particles. Fewer atom residues, in the particulate matter and the slurry containing it described later, contribute to further improving the purity of the monolayer MXene and further increasing the in-plane size of the monolayer MXene particles.

[0050] Furthermore, to obtain a conductive film with high orientation of MXene particles, it is preferable to perform a layer separation process (separating multiple layers of MXene into fewer layers of MXene, preferably into a single layer of MXene) after etching. For obtaining MXene particles with a larger aspect ratio and a two-dimensional shape (particles of single-layer or few-layer MXene, preferably single-layer MXene particles), such a layer separation process is more preferably performed in a way that minimizes damage to the MXene particles. The layer separation process can be performed by any suitable method, such as ultrasonic treatment, hand-cranking, or an automatic shaker. However, ultrasonic treatment can damage the MXene particles (causing them to fragment) due to excessive shear force, so it is preferable to apply appropriate shear force through hand-cranking or an automatic shaker. After applying shear force to the MXene particles, the layer separation process may include centrifugation and purification. If fewer A atoms remain in the MXene particles, the binding force of the A atoms has a smaller impact, thus enabling efficient layer separation of the MXene particles with less shear force.

[0051] Given MXene from the above formula: M m X n Express it like this:

[0052] Sc2C, Ti2C, Ti2N, Zr2C, Zr2N, Hf2C, Hf2N, V2C, V2N, Nb2C, Ta2C, Cr2C, Cr2N, Mo2C, Mo 1.3 C, Cr 1.3 C, (Ti, V)2C, (Ti, Nb)2C, W2C, W 1.3 C, Mo2N, Nb 1.3 C, Mo 1.3 Y 0.6 C (In the above formula, "1.3" and "0.6" mean approximately 1.3 (= 4 / 3) and approximately 0.6 (= 2 / 3), respectively).

[0053] Ti3 C2, Ti3N2, Ti3(CN), Zr3 C2, (Ti, V)3C2, (Ti2Nb)C2, (Ti2Ta)C2, (Ti2Mn)C2, Hf3 C2, (Hf2V)C2, (Hf2Mn)C2, (V2Ti)C2, (Cr2Ti)C2, (Cr2V)C2, (Cr2Nb)C2, (Cr2Ta)C2, (Mo2 Sc)C2, (Mo2Ti)C2, (Mo2Zr)C2, (Mo2Hf)C2, (Mo2V)C2, (Mo2Nb)C2, (Mo2Ta)C2, (W2Ti)C2, (W2Zr)C2, (W2Hf)C2,

[0054] Ti4N3, V4C3, Nb4C3, Ta4C3, (Ti, Nb)4C3, (Nb, Zr)4C3, (Ti2Nb2)C3, (Ti2Ta2)C3, (V2Ti2)C3, (V2Nb2)C3, (V2Ta2)C3, (Nb2Ta2)C3, (Cr2Ti2)C3, (Cr 2V2)C3, (Cr2Nb2)C3, (Cr2Ta2)C3, (Mo2Ti2)C3, (Mo2Zr2)C3, (Mo2Hf2)C3, (Mo2V2)C3, (Mo2Nb2)C3, (Mo2Ta2)C3, (W2Ti2)C3, (W2Zr2)C3, (W2Hf2)C3

[0055] Representatively, in the above formula, M can be titanium or vanadium, and X can be a carbon atom or a nitrogen atom. For example, the MAX phase is Ti3AlC2, and MXene is Ti3C2T. s (In other words, M is Ti, X is C, n is 2, and m is 3).

[0056] Furthermore, in this invention, MXene may contain a relatively small amount of residual A atoms, for example, less than 10% by mass relative to the original A atoms. The residual amount of A atoms is preferably less than 8% by mass, more preferably less than 6% by mass. However, even if the residual amount of A atoms exceeds 10% by mass, there may be cases where this is not a problem depending on the application and operating conditions of the conductive film.

[0057] The synthesized MXene particles 10, such as Figure 2 As schematically shown, it can be a layered material containing one or more MXene layers 7a, 7b (as an example of MXene particle 10, in...). Figure 2 (a) represents MXene particles 10a in one layer. Figure 2 (b) represents MXene particles 10b in two layers, but is not limited to these examples). More specifically, MXene layers 7a and 7b have: [The text abruptly ends here, so the translation stops as well.] m X n The layer body (M) is represented m X n Layers 1a and 1b; modifications or ends T 3a, 5a, 3b, and 5b existing on the surfaces of the layers 1a and 1b (more specifically, at least one of the two opposing surfaces of each layer). Therefore, MXene layers 7a and 7b are also represented as "M". m X n T s 's' is an arbitrary number. MXene particles 10 can be particles where each MXene layer exists independently, with each layer separate. Figure 2The monolayer structure shown in (a), the so-called monolayer MXene particle 10a), can also be a particle of a stack of multiple MXene layers separated from each other. Figure 2 (b) The multilayer structure shown, the so-called multilayer MXene particles 10b, can also be a mixture thereof. MXene particles 10 can also be particles (also referred to as powder or flakes) that are aggregates composed of monolayer MXene particles 10a and / or multilayer MXene particles 10b. In the case of multilayer MXene particles, two adjacent MXene layers (e.g., 7a and 7b) are not necessarily completely separated, but can be in partial contact. In this embodiment, as described later, it is preferable that the MXene particles 10 contain as many monolayer MXene particles as possible than multilayer MXene particles (a higher proportion of monolayer MXene particles).

[0058] While not limiting this embodiment, the thickness of each MXene layer (equivalent to MXene layers 7a and 7b described above) can, for example, be 0.8 nm or more and 5 nm or less, particularly 0.8 nm or more and 3 nm or less (mainly varying depending on the number of M atoms contained in each layer). When the MXene particles are particles of a stack (multi-layer MXene), the interlayer distance (or void size) for each stack is... Figure 2 (b) is represented by Δd), for example, 0.8 nm or more and 10 nm or less, especially 0.8 nm or more and 5 nm or less, and even more especially about 1 nm.

[0059] The thickness in the direction perpendicular to the MXene particle layer (which can correspond to the "thickness" of the MXene particle as a two-dimensional particle) is, for example, 0.8 nm or more, for example, 20 nm or less, particularly 15 nm or less, and even more particularly 10 nm or less. The total number of MXene particle layers can be 1 or 2 or more, for example, 1 or more and 10 or less, particularly 1 or more and 6 or less. When the MXene particles are particles of a stack (multi-layer MXene), it is preferable to have MXene particles with fewer layers. The term "few layers" means, for example, that the number of MXene layers is 6 or less. In addition, the thickness in the stacking direction of multi-layer MXene particles with fewer layers can be 15 nm or less, particularly 10 nm or less. In this specification, this "multi-layer MXene with fewer layers" is also referred to as "few-layer MXene". In this embodiment, the MXene particles can mostly be single-layer MXene and / or few-layer MXene particles, and moreover, most of them can be single-layer MXene particles. In other words, the average thickness of the MXene particles can be 10 nm or less. The average thickness can be, for example, less than 7 nm, and further less than 5 nm. On the other hand, if the thickness of a single layer of MXene is considered, the lower limit of the thickness of MXene particles can be 0.8 nm. Therefore, the average thickness of MXene particles can be approximately 1 nm or more.

[0060] The dimensions within a plane (two-dimensional unfolded plane) parallel to the layer of MXene particles (which can correspond to the "in-plane dimensions" of MXene particles as two-dimensional particles) are, for example, 0.1 μm or more, particularly 1 μm or more, for example 200 μm or less, particularly 40 μm or less.

[0061] Furthermore, these dimensions can be obtained as digital averages (e.g., at least 40 digital averages) based on scanning electron microscope (SEM), transmission electron microscope (TEM) images, or atomic force microscope (AFM) images, or as distances in real space calculated from the positions of the (002) planes in the reciprocal lattice space measured by X-ray diffraction (XRD).

[0062] The polyanionic salt containing phosphate groups can be a salt of a polyanion having multiple phosphate groups (also simply referred to as "phosphate-containing polyanion") and a metal ion (cation). It is particularly preferred when it is a salt of a polyanion having multiple phosphate groups and an alkali metal ion, as it is readily soluble in aqueous solvents. More specifically, the polyanionic salt containing phosphate groups can be at least one selected from the group consisting of polyphosphate metal salts, pyrophosphate metal salts, tripolyphosphate metal salts, and hexametaphosphate metal salts, preferably a polyphosphate metal salt and / or a hexametaphosphate metal salt, more preferably a hexametaphosphate metal salt. The average degree of polymerization of the polyphosphate metal salt can, for example, be 2 or more and 100,000 or less. When the metal salt is an alkali metal salt, the alkali metal element can be, for example, lithium, sodium, potassium, etc., preferably sodium.

[0063] Next, a mixture containing MXene particles and a polyanionic salt containing phosphate groups is prepared in an aqueous solvent. The mixture is prepared such that the concentration of MXene particles is 10 mg / mL or more and 250 mg / mL or less, and the molar concentration (M) of the polyanionic salt containing phosphate groups is 0.001 mol / L or more and 0.1 mol / L or less.

[0064] By ensuring the concentration of MXene particles in the mixture is 10 mg / mL or higher, conductive films can be manufactured at a cost acceptable for industrial-scale production. Conversely, a concentration of 250 mg / mL or lower allows for processing the mixture at a viscosity acceptable for industrial-scale production. Preferably, the concentration of MXene particles is 20 mg / mL or higher and / or 140 mg / mL or lower. The concentration of MXene particles can be understood as the concentration of the solid components in the mixture, which can be measured, for example, using methods such as heat drying gravimetric analysis, freeze drying gravimetric analysis, or filtration gravimetric analysis.

[0065] The concentration of the polyanionic salt containing phosphate groups in the mixture is 0.001 mol / L or more, which effectively prevents oxidation of the final conductive film (in other words, effectively reduces the time-dependent decrease in conductivity), and by being 0.1 mol / L or less, it effectively prevents the decrease in the initial conductivity of the final conductive film. Preferably, the concentration of the salt is 0.01 mol / L or more and / or 0.09 mol / L or less.

[0066] Aqueous solvents are typically water, but depending on the circumstances, a relatively small amount (based on the total amount of aqueous solvents, for example, less than 30% by mass, preferably less than 20% by mass) of its liquid substances may also be contained (the same applies below).

[0067] There are no particular limitations on the preparation method of the mixture. For example, a slurry containing MXene particles in an aqueous solvent (hereinafter also referred to as "MXene slurry") and a solution containing a phosphate-containing polyanionic salt in an aqueous solvent (hereinafter also referred to as "phosphate-containing polyanionic salt aqueous solution") can be prepared by mixing them. The mixing of the phosphate-containing polyanionic salt aqueous solution and the MXene slurry can be carried out in any suitable manner. For example, the MXene slurry can be added to the phosphate-containing polyanionic salt aqueous solution and then mixed, or vice versa.

[0068] This embodiment is not bound by any theory, but in this mixture, phosphate-containing polyanions are bonded (strongly adsorbed) at sites on MXene particles that are easily oxidized (oxygen-eroded sites, hereinafter referred to as "oxidation sites"). Oxidation sites for MXene particles are known to be the edges of the MXene particle layers (plates) and the defects of the X atoms (carbon / nitrogen atoms). The edges of MXene particles carry a strong positive charge, and dangling bonds exist at the defects. On the other hand, the phosphate groups of the phosphate-containing polyanions have a large number of π electrons. Therefore, it can be considered that, through the interaction of the phosphate groups of the phosphate-containing polyanions with the edges and defects of MXene particles (more specifically, due to the mixing of the π electrons of the phosphate groups with the electrons of the d orbitals of the M atoms located at the edges and defects of MXene particles), the phosphate-containing polyanions bond at the oxidation sites of MXene particles, ensuring a conductive path. Polyanionic salts containing phosphate groups, which are insulating when alone, can be considered to reduce the initial conductivity of the resulting conductive film (and consequently, the subsequent conductivity) when covering MXene particles. However, since π electrons contribute to improved conductivity, the phosphate-containing polyanions bind to the oxidation sites of MXene particles through the aforementioned interactions, thereby reducing the decrease in initial conductivity.

[0069] Process (p)

[0070] After step (a) and before step (b) described below, as an intermediate step (p), it is preferable to apply shear force and wash the mixture prepared by step (a) using a different (new or unused) aqueous solvent. This effectively removes excess phosphate-containing polyanions and other unwanted ions (cations forming polyanionic salts containing phosphate groups, more specifically, metal ions) that are not bonded to the oxidation sites of MXene particles. By effectively removing excess phosphate-containing polyanions that are not bonded to the oxidation sites of MXene particles, the decrease in the initial conductivity of the final conductive film can be reduced, and high conductivity can be maintained. Furthermore, if other unwanted metal ions (e.g., alkali metal ions such as sodium ions) are excessively present in the mixture, MXene particles are adsorbed and aggregated by the metal ions. Washing alone is insufficient to break up such aggregation, but by applying shear force while washing, the aggregation of MXene particles can be broken, effectively removing the excess metal ions that cause aggregation. This reduces or prevents the aggregation of MXene particles. By reducing or preventing the aggregation of MXene particles, such as… Figure 1 As illustrated, in the final conductive film 30, the MXene particles 10 exist in a relatively orderly arrangement. More specifically, relative to the main surface of the conductive film 30, there are more MXene particles with more consistent (preferably parallel) two-dimensional unfolded surfaces (planes parallel to the MXene layers) (which can also be characterized by high orientation / stackability). Therefore, the initial conductivity of the conductive film can be improved, and high conductivity can be maintained.

[0071] More specifically, the mixture is subjected to solid-liquid separation (e.g., sedimentation, centrifugation, etc.), the aqueous solvent (liquid phase) is partially removed from the mixture, another (new or unused) aqueous solvent is added to the mixture, and shear force is applied to the mixture. These operations can be performed at any appropriate time. This process can be performed once or, depending on the circumstances, more than twice.

[0072] The application of shear force can be performed, for example, using a shaker, a shear mixer, or by hand-cranking, with the intensity and duration of the shear force appropriately selected. For example, shear force can be applied by using an automatic shaker (manufactured by FAST&FLUID, SK-550) for a specified time. Ideally, the application of shear force should not damage the MXene particles; rather, anisotropic energy should be applied to the MXene particles (e.g., thin sheets).

[0073] • Process (b)

[0074] Subsequently, the mixture obtained above is dried to obtain a conductive film 30.

[0075] Before drying, a precursor (also called a "precursor membrane") for forming a conductive film can be formed using the mixture. The method of forming the precursor is not particularly limited; for example, coating, suction filtration, spraying, etc., can be used. More specifically, the mixture, or a suitable one (e.g., diluted with an aqueous solvent), can be applied directly to any suitable substrate (which may form a defined component with the conductive film or ultimately separate from the conductive film) using a doctor blade coater, roller coater, spin coater, or doctor blade, thereby forming the precursor on that substrate. Alternatively, the mixture can be appropriately adjusted (e.g., diluted with an aqueous solvent) and filtered through a filter (which may form a defined component with the conductive film or ultimately separate from the conductive film) provided in a suction filtration flask, etc., to at least partially remove the aqueous solvent, thereby forming the precursor on that filter. The filter is not particularly limited; membrane filters, etc., can be used. Alternatively, the mixture can be appropriately adjusted (e.g., diluted with an aqueous solvent) and sprayed onto any suitable substrate using a spray gun, air brush, etc. (it can form a specified component together with the conductive film, or it can eventually be separated from the conductive film), thereby forming a precursor on the substrate.

[0076] Next, the precursor formed above is dried to obtain a conductive film 30. In this invention, "drying" means removing the aqueous solvent that may be present in the precursor.

[0077] Drying can be carried out under mild conditions such as natural drying (typically at normal temperature and pressure, in an air atmosphere) or air drying (air spraying), or under more intense conditions such as warm air drying (air spraying), heated drying, and / or vacuum drying.

[0078] The formation and drying of the precursor can be repeated until the desired conductive film thickness is achieved. For example, the combination of spraying and drying can be performed repeatedly.

[0079] The conductive film 30 obtained in this embodiment contains MXene particles 10 and also contains phosphorus atoms at a mass percentage of 0.001% and less than 0.09%.

[0080] The phosphorus atoms in the conductive film originate from polyanionic salts containing phosphate groups. As described above, these phosphorus atoms are preferably bonded to the oxidation sites of MXene particles in the form of polyanionic phosphate groups. Thus, the oxidation sites of MXene particles are protected by these polyanionic phosphate groups, preventing the oxidation sites of MXene particles from being eroded by oxygen even when the conductive film is exposed to an oxidizing atmosphere (typically air), thereby preventing the oxidation of the MXene particles.

[0081] The phosphorus atom content in the conductive film is 0.001% by mass or more, thereby achieving an antioxidant effect (reducing the time-dependent decrease in conductivity), and by being less than 0.09% by mass, the initial decrease in conductivity can be reduced. Preferably, the phosphorus atom content is 0.01% by mass or more and / or 0.08% by mass or less. The phosphorus atom content can be measured, for example, by elemental (atomic) analysis such as inductively coupled plasma atomic emission spectrometry (ICP-AES) and X-ray fluorescence analysis (XRF).

[0082] Furthermore, the conductive film may contain less than 0.5% by mass of a metal element (e.g., an alkali metal) corresponding to the metal ions from the polyanionic salt containing phosphate groups. By keeping the metal element content in the conductive film below 0.5% by mass, the aggregation of MXene particles can be reduced or prevented, thus reducing the decrease in initial conductivity. Preferably, the metal element content is 0.001% by mass or more and / or less than 0.09% by mass. The metal element content can be measured, for example, by ICP-AES and XRF.

[0083] The conductive film of this embodiment can be composed of a composite material of MXene particles, polyanions containing phosphate groups, and metal elements that may remain as appropriate.

[0084] The conductive film in this embodiment maintains a conductivity of 2000 S / cm or more, preferably 3000 S / cm or more. More specifically, the conductive film maintaining a conductivity of 2000 S / cm or more, preferably 3000 S / cm or more, means that when the conductive film is stored in air at room temperature (e.g., 0–40°C, particularly 10–30°C, typically 25°C) and at normal pressure (typically atmospheric pressure, particularly standard atmospheric pressure, specifically about 0.1 MPa) for, for example, 30 days, preferably 50 days or more, it exhibits a conductivity of 2000 S / cm or more, preferably 3000 S / cm or more. The conductivity of a conductive film, assuming no measurement bias, is considered to tend to decrease over time. Therefore, if the conductivity of the conductive film (preferably the initial conductivity) after a specified time (number of days) is 2000 S / cm or more, preferably 3000 S / cm or more, it can be understood that the conductive film maintains a conductivity of 2000 S / cm or more, preferably 3000 S / cm or more. The initial conductivity of the conductive film is representative of the conductivity after storage under the above conditions for one day following its fabrication; this can be 3000 S / cm or more, preferably 4000 S / cm or more. Subsequently, after storage under the above conditions for, for example, 30 days, preferably 50 days or longer, the conductivity can be 2000 S / cm or more, preferably 3000 S / cm or more, with a decrease rate of 30% or less, 15% or less, preferably 12% or less, based on the initial conductivity. If the exact date of manufacture of the conductive film is unclear, and the film is stored under the aforementioned conditions from any point in time, for example, 30 days, preferably 50 days, and if the conductivity is 2000 S / cm or higher, it can be understood that the conductive film maintains a conductivity of 2000 S / cm or higher. There is no specific upper limit to the conductivity of the conductive film, but it can be, for example, below 10000 S / cm. Conductivity can be calculated by measuring the resistivity and thickness of the conductive film and using these measurements.

[0085] The conductive film of this embodiment can have a shape that is considered a thin film, specifically, it can have two main surfaces facing each other. The thickness of the conductive film, as well as its shape and size when viewed from above, can be appropriately selected according to the application of the conductive film.

[0086] The conductive film of this embodiment can be used for any suitable application. For example, it can be used in electrodes of any suitable electrical device, electromagnetic shielding (EMI shielding), and other applications requiring the maintenance of high conductivity (reducing the decrease in initial conductivity and preventing oxidation).

[0087] The electrode is not particularly limited and can be, for example, a capacitor electrode, a battery electrode, a bioelectrode, a sensor electrode, an antenna electrode, etc. By using the conductive film of this embodiment, large-capacity capacitors, batteries, low-impedance bioelectrodes, high-sensitivity sensors, and antennas can be obtained even with a smaller volume (device occupancy).

[0088] A capacitor can be an electrochemical capacitor. An electrochemical capacitor is a capacitor that utilizes the capacitance generated between electrodes (electrode active materials) and ions (electrolyte ions) in the electrolyte due to a physicochemical reaction, and can be used as a device for storing electrical energy (energy storage device). A battery is a chemical battery that can be repeatedly charged and discharged. Batteries can be, for example, lithium-ion batteries, magnesium-ion batteries, lithium-sulfur batteries, sodium-ion batteries, etc., but are not limited to these.

[0089] Bioelectrodes are electrodes used to acquire biological signals. Bioelectrodes are used to measure, for example, EEG (electroencephalography), ECG (electrocardiography), EMG (electromyography), and EIT (electrophysiological testing), but are not limited to these.

[0090] Sensor electrodes are used to detect target substances, states, anomalies, etc. Examples of sensors include gas sensors and biosensors (chemical sensors that utilize molecular recognition mechanisms of biological origin), but are not limited to these.

[0091] Antenna electrodes are electrodes used to radiate electromagnetic waves into space and / or receive electromagnetic waves in space.

[0092] In particular, by using the conductive film of this embodiment, electromagnetic shielding with high shielding efficiency (EMI shielding) can be obtained. Generally, EMI shielding can be calculated based on the following formula (1), with conductivity as shown in Table 1.

[0093]

Equation 1

[0094]

[0095] In equation (1), SE is the EMI shielding (dB), σ is the conductivity (S / cm), f is the frequency of the electromagnetic wave (MHz), and t is the thickness of the film (cm).

[0096] Table 1

[0097] Electrical conductivity (S / cm) EMI shielding (dB)* 100 41 1,000 52 2,000 55 3,000 58 4,000 59 5,000 61 6,000 62 7,000 63 8,000 64 9,000 65 10,000 65

[0098] *Where, f = 1000MHz, t = 1 × 10 －4 cm.

[0099] As can be seen from Table 1, high EMI shielding can be obtained if the conductivity is 2000 S / cm or higher. According to the conductive film of this embodiment, because the conductivity is 2000 S / cm or higher, higher EMI shielding can be obtained with a given thickness, and sufficient EMI shielding effect can be obtained even when the thickness is reduced.

[0100] The conductive film of one embodiment of the present invention has been described in detail above through its manufacturing method, but the present invention can be modified in various ways. Furthermore, the conductive film of the present invention can also be manufactured by methods different from those described in the above embodiment. It should also be noted that the manufacturing method of the conductive film of the present invention is not limited to providing the conductive film of the above embodiment.

[0101] Example

[0102] (Example 1)

[0103] Example 1 involves the manufacture of a conductive film using sodium hexametaphosphate at an appropriate concentration as a polyanionic salt containing phosphate groups.

[0104] Preparation of mixtures

[0105] Ti3AlC2 particles were prepared as MAX particles using known methods. These Ti3AlC2 particles (powder) were added together with LiF to 9 mol / L hydrochloric acid (1 g of LiF and 10 mL of 9 mol / L hydrochloric acid per 1 g of Ti3AlC2 particles). The mixture was stirred at 35°C for 24 hours to obtain a solid-liquid mixture (suspension) containing solid components from the Ti3AlC2 particles. The mixture was washed with pure water, and the supernatant was removed by centrifugation (the remaining sediment after supernatant removal was washed again). This process was repeated approximately 10 times. Then, the mixture containing pure water in the sediment was stirred with an automatic shaker for 15 minutes, followed by centrifugation for 5 minutes to separate the supernatant and sediment. The supernatant was removed by centrifugal dehydration. Finally, the remaining sediment after supernatant removal was diluted with pure water to obtain a crude purified slurry. The crude purified slurry can be understood as containing monolayer MXene particles and multilayer MXene particles that are not monolayered due to insufficient layer separation (layering). In addition, it also contains impurities other than MXene particles (unreacted MAX particles and crystals of byproducts from etched A atoms, such as AlF3 crystals).

[0106] The crude purified slurry obtained above was placed in a centrifuge tube and centrifuged for 5 minutes using a centrifuge at a relative centrifugal force (RCF) of 2600 × g. The supernatant obtained from the centrifugation was recovered to obtain the purified slurry. The purified slurry can be understood as containing a large number of monolayer MXene particles. The remaining sediment in the supernatant was removed and was not used thereafter.

[0107] The purified slurry obtained above was placed in centrifuge tubes and centrifuged at 3500 × g RCF for 120 minutes. The supernatant obtained from the centrifugation was removed. The removed supernatant was not used thereafter. The remaining sediment after the supernatant was removed yielded a clay-like substance. Thus, Ti3C2T was obtained as MXene clay. s - Aqueous dispersion clay. Mix this MXene clay with an appropriate amount of pure water to prepare an MXene slurry with a solids concentration (MXene concentration) of approximately 74 mg / mL.

[0108] Measure 0.30g (approximately 5 x 10⁻⁶) of sodium hexametaphosphate (manufactured by Nacalai Tesque Co., Ltd.). －4 (mol), dissolved in 39.86 ml of pure water, to prepare an aqueous solution of sodium hexametaphosphate as a polyanionic salt containing phosphate groups.

[0109] To this phosphate-containing polyanionic salt aqueous solution, approximately 10.14 mL (10.89 g) of the prepared MXene slurry (solids concentration approximately 74 mg / mL) was added to prepare a mixture of 50 mL in total volume. In this mixture, the MXene concentration was 15 mg / mL and the sodium hexametaphosphate concentration was 0.01 mol / L.

[0110] • Washing of the mixture

[0111] The mixture prepared above was transferred to centrifuge tubes, shaken thoroughly, and allowed to stand for 3 hours. Then, the mixture in the centrifuge tubes was subjected to the following steps: (i) centrifugation at 5000 rpm for 2 minutes; (ii) removal of the supernatant from the centrifuged mixture; (iii) addition of pure water to the residue to a total volume of 50 mL; and (iv) application of shear force by hand shaking. Steps (i) through (iv) were repeated a total of 3 times.

[0112] • Removal and drying of aqueous media

[0113] After the third hand-shaking, 5 mL of the mixture in the centrifuge tube was extracted using a syringe and subjected to suction filtration. A membrane filter (Merck, Durapore, 0.45 μm pore size) was used for suction filtration. After suction filtration, the precursor membrane on the filter was dried overnight at 80°C in a vacuum drying oven to obtain a conductive membrane.

[0114] (Example 2)

[0115] Example 2 involves the manufacture of a conductive film using sodium polyphosphate at an appropriate concentration as a polyanionic salt containing phosphate groups.

[0116] As an aqueous solution of a polyanionic salt containing phosphate groups, 0.14 g (approximately 5 × 10⁻⁶) of sodium polyphosphate (manufactured by Kanto Chemical Co., Ltd.) was measured. －4 A sodium polyphosphate solution (mol) was dissolved in 39.86 ml of pure water. The mixture was prepared in the same manner as in Example 1, except that an aqueous solution of sodium polyphosphate was used. In this mixture, the concentration of MXene was 15 mg / mL and the concentration of sodium polyphosphate was 0.01 mol / L. Subsequently, a conductive film was obtained in the same manner as in Example 1.

[0117] (Comparative Example 1)

[0118] Comparative Example 1 involves the manufacture of a conductive film without using a polyanionic salt containing phosphate groups.

[0119] The mixture was prepared in the same manner as in Example 1, except that pure water was used instead of the aqueous solution of the phosphate-containing polyanionic salt. The concentration of MXene in this mixture was 15 mg / mL. Subsequently, a conductive film was obtained in the same manner as in Example 1.

[0120] (Comparative Example 2)

[0121] Comparative Example 2 involves the use of high-concentration sodium hexametaphosphate as a polyanionic salt containing phosphate groups to manufacture a conductive film.

[0122] As an aqueous solution of a polyanionic salt containing phosphate groups, 3.05 g (approximately 5 × 10⁻⁶) of sodium hexametaphosphate (manufactured by Nacalai Tesque Co., Ltd.) was measured. －3 A high concentration of sodium hexametaphosphate (mol) was dissolved in 39.86 ml of pure water. The mixture was prepared in the same manner as in Example 1, except that a high-concentration sodium hexametaphosphate aqueous solution was used. In this mixture, the concentration of MXene was 15 mg / mL and the concentration of sodium hexametaphosphate was 0.1 mol / L. Subsequently, a conductive film was obtained in the same manner as in Example 1.

[0123] (Comparative Example 3)

[0124] Comparative Example 3 involves the use of a high concentration of sodium polyphosphate, a polyanionic salt containing phosphate groups, to manufacture a conductive film. Comparative Example 3 can be understood as equivalent to the content disclosed in Non-Patent Document 1.

[0125] As an aqueous solution of a polyanionic salt containing phosphate groups, 1.33 g (approximately 5 × 10⁻⁶) of sodium polyphosphate (manufactured by Kanto Chemical Co., Ltd.) was measured. －3 A sodium polyphosphate solution (mol) was dissolved in 39.86 ml of pure water. The mixture was prepared in the same manner as in Example 1, except that an aqueous solution of sodium polyphosphate was used. In this mixture, the concentration of MXene was 15 mg / mL and the concentration of sodium polyphosphate was 0.1 mol / L. Subsequently, a conductive film was obtained in the same manner as in Example 1.

[0126] (evaluate)

[0127] For the conductive films (samples) on the filters of Examples 1-2 and Comparative Examples 1-3 prepared above, after preparation, they were stored in an atmospheric environment (0% humidity) at room temperature and pressure, and the conductivity (S / cm) of the conductive films was measured one day after preparation (initial) and for each subsequent specified period up to a maximum of 50 days. More specifically, for each sample, resistivity (surface resistivity) (Ω) and thickness (μm, excluding the filter) were measured at three locations, and the conductivity (S / cm) was calculated based on these measurements. The arithmetic mean of the conductivity obtained at the three locations was taken. For resistivity measurements, a low resistivity meter (Loresta AX MCP-T370, manufactured by Mitsubishi Chemical Analysis Co., Ltd.) was used. For thickness measurements, a micrometer (Toyota Corporation, MDH-25MB) was used. The results are shown in Table 2 and... Figure 3 middle.

[0128] For the conductive films (samples) of Examples 1-2 and Comparative Examples 1-3 prepared above, the phosphorus (more specifically, phosphorus atoms) content was measured by ICP-AES. The results are shown in Table 2. For the conductive film of Comparative Example 1, phosphorus was not detected because it was below the detection limit (0.0003% by mass).

[0129] Table 2

[0130]

[0131] In Table 2, the symbol "-" indicates that the measurement is omitted.

[0132] Referring to Table 2, the initial conductivity of the conductive film in Comparative Example 1 (control) was 6494 S / cm, the initial conductivity of the conductive film in Example 1 was 5899 S / cm, and the initial conductivity of the conductive film in Example 2 was 5713 S / cm. Therefore, based on the initial conductivity of the conductive film in Comparative Example 1, the reduction rate of the initial conductivity of the conductive film in Example 1 was approximately 9%, and the reduction rate of the initial conductivity of the conductive film in Example 2 was approximately 12%, both below 15%. In contrast, the initial conductivity of the conductive film in Comparative Example 2 was 2482 S / cm, and the initial conductivity of the conductive film in Comparative Example 3 was 519 S / cm. Therefore, based on the initial conductivity of the conductive film in Comparative Example 1, the reduction rate of the initial conductivity of the conductive film in Comparative Example 2 was approximately 62%, and the reduction rate of the initial conductivity of the conductive film in Comparative Example 3 was approximately 92%. These results confirm that an appropriate concentration of polyanionic salts containing phosphate groups can reduce the decrease in initial conductivity, while an excessively high concentration significantly reduces the initial conductivity. In Comparative Examples 2 and 3, MXene agglomeration occurred due to the excess presence of polyanionic salts containing phosphate groups (especially sodium ions), indicating a deterioration in the orientation of MXene particles. In particular, the conductive film of Comparative Example 3 (0.1 mol / L sodium polyphosphate) showed an initial conductivity reduction to approximately 1 / 10.

[0133] Refer to Table 2 and Figure 3 If we observe the change in conductivity of the conductive film over time, assuming the initial conductivity of the conductive film in Comparative Example 1 is 100%, after 50 days, the conductivity of Comparative Example 1 (controlled) decreases to approximately 63% or less. In contrast, assuming the initial conductivity of the conductive films in Examples 1 and 2 is 100% respectively, after 50 days, the conductivity of Examples 1 and 2 remains at approximately 95% or more (i.e., the reduction rate is 5% or less). Furthermore, for Comparative Examples 2 and 3, as mentioned above, because the initial conductivity decreased significantly, the conductivity of the conductive film after 36 days was not measured.

[0134] Industrial availability

[0135] The conductive film of the present invention can be used for any suitable purpose, for example, it is particularly preferred for use as an electrode and electromagnetic shield for electrical equipment.

[0136] Symbol Explanation

[0137] 1a and 1b main body (M) m X n layer)

[0138] 3a, 5a, 3b, 5b Modifications or terminal T

[0139] 7a, 7b MXene layers

[0140] 10, 10a, 10b MXene (layered material) particles

[0141] 30 Conductive film

Claims

1. A conductive film, which is a conductive film containing particles of a layered material having one or more layers, wherein, The layer includes: from the formula: M m X n layer body represented by the formula, In the formula, M is at least one selected from the group consisting of Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, and Mn, X is a carbon atom, a nitrogen atom, or a combination of a carbon atom and a nitrogen atom, n is 1 or more and 4 or less, m is greater than n and 5 or less; a modification or a terminal T present on a surface of a body of the layer, 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, The conductive film further contains phosphorus atoms of 0.001 mass% or more and less than 0.09 mass%, and maintains an electrical conductivity of 2000 S / cm or more.

2. The conductive film according to claim 1, wherein The phosphorus atoms are derived from a poly-anionic salt containing a phosphoric acid group.

3. The conductive film according to claim 2, wherein The poly-anionic salt containing a phosphoric acid group is at least one selected from the group consisting of a polyphosphate metal salt, a pyrophosphate metal salt, a tripolyphosphate metal salt, and a hexametaphosphate metal salt.

4. The conductive film according to any one of claims 1 to 3, wherein Used as an electrode or electromagnetic shield.

5. The conductive film according to claim 4, wherein The electrode is any one of a capacitor electrode, a battery electrode, a biological electrode, a sensor electrode, and an antenna electrode.

6. A method for producing an electroconductive film, wherein Comprising: (a) preparing a mixture of particles of a layered material having one or more layers and a poly-anionic salt containing a phosphoric acid group in an aqueous solvent, The layer includes: from the formula: M m X n layer body represented by the formula, In the formula, M is at least one selected from the group consisting of Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, and Mn, X is a carbon atom, a nitrogen atom, or a combination of a carbon atom and a nitrogen atom, n is 1 or more and 4 or less, m is greater than n and 5 or less; a modification or a terminal T present on a surface of a body of the layer, 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, The concentration of the particles of the layered material in the mixture is 10 mg / mL or more and 250 mg / mL or less, The molar concentration of the poly-anionic salt containing a phosphoric acid group in the mixture is 0.001 mol / L or more and 0.1 mol / L or less; and (b) drying the mixture to obtain a conductive film.

7. The method of producing a conductive film according to claim 6, wherein After the (a) and before the (b), further comprising, for the mixture, imparting a shear force using another aqueous solvent and performing a washing.

8. The method of producing a conductive film according to claim 6 or 7, wherein The poly-anionic salt containing a phosphoric acid group in the (a) is a salt of a poly-anion having a plurality of phosphoric acid groups and a metal ion, The conductive film obtained by the (b) contains a metal element corresponding to the metal ion at 0.5 mass% or less.

9. The method of producing a conductive film according to claim 6 or 7, wherein The conductive film according to any one of claims 1 to 5 can be obtained.

10. The method of producing a conductive film according to claim 8, wherein The conductive film according to any one of claims 1 to 5 can be obtained.

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