Conductive film, electrode, and method for manufacturing the conductive film

Abstract

Provided is a conductive film containing MXene and having sufficiently reduced impedance. The conductive film contains titanium oxide and a film that contains particles of a layered material including one or more layers, wherein: the layers each include a layer body represented by the formula MmXn (in the formula, M is at least one metal belonging to group 3, 4, 5, 6, or 7 and includes Ti, X is a carbon atom, a nitrogen atom, or a combination thereof, n is 1-4, and m is greater than n and at most 5) and a modification or terminal T (T is at least one selected from the group consisting of a hydroxyl group, a fluorine atom, a chlorine atom, an oxygen atom, and a hydrogen atom) present on the surface of the layer body; and the proportion of tetravalent titanium in divalent, trivalent, and tetravalent titanium, as determined from the spectra obtained by X-ray photoelectron spectroscopy, is 2-57 mol% (exclusive of 2).

Description

[Technical Field]

[0001] The present disclosure relates to conductive films, electrodes, and methods for manufacturing conductive films. [Background technology]

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

[0003] Currently, various research efforts are being conducted to apply MXene to various fields. For example, applications requiring high electrical conductivity, such as electrodes in electrical devices and electromagnetic shielding (EMI shielding), are being considered. For example, Non-Patent Document 1 describes that the two-dimensional material Ti3C2MXene is clearly different from carbon-based nanomaterials and that Ti3C2MXene microelectrodes are suitable for recording neural signals from living organisms, such as the brain. Non-Patent Document 2 also indicates that MXene may be effective in many applications in living organisms, from mapping extensive neuromuscular networks in humans to cortical microstimulation in small animal models. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Driscoll, Nicolette, et al. “Two-dimensional Ti3C2 MXene for high-resolution neural interfaces” ACS nano 12.10 (2018): 10419-10429 [Non-patent document 2] Driscoll, Nicolette, et al. “MXtrodes: MXene-infused bioelectronic interfaces for multiscale electrophysiology and stimulation” bioRxiv (2021) Summary of the Invention [Problem to be solved by the invention]

[0005] For example, to perform high-resolution sensing in the biological field, it is important to reduce the interfacial impedance as much as possible, and it is believed that improvements to this end are necessary for the electrodes containing MXene shown in Non-Patent Documents 1 and 2. The present disclosure has been made in consideration of the above circumstances, and its purpose is to provide a conductive film with sufficiently reduced impedance, an electrode including the conductive film, and a method for manufacturing the conductive film. [Means for solving the problem]

[0006] According to one aspect of the present invention, a film comprising particles of a layered material comprising one or more layers, and titanium oxide; The layer may comprise a compound having the following formula: M m X n (wherein M is at least one Group 3, 4, 5, 6, 7 metal, including Ti; X is a carbon atom, a nitrogen atom, or a combination thereof; n is between 1 and 4, m is greater than n and less than or equal to 5) and a modification or termination T (T is at least one selected from the group consisting of a hydroxyl group, a fluorine atom, a chlorine atom, an oxygen atom, and a hydrogen atom) present on the surface of the layer body, The conductive film has a ratio of tetravalent titanium to divalent, trivalent, and tetravalent titanium, determined from a spectrum obtained by X-ray photoelectron spectroscopy, of more than 2 mol % to 57 mol % or less. [Effects of the Invention]

[0007] According to the present disclosure, a conductive film is provided that includes a film containing particles of a specific layered material (also referred to herein as "MXene") and titanium oxide, and the proportion of tetravalent titanium in the divalent, trivalent, and tetravalent titanium, as determined from a spectrum obtained by X-ray photoelectron spectroscopy, is greater than 2 mol% and not more than 57 mol%. This provides a conductive film that contains MXene and has sufficiently reduced impedance. Also provided are an electrode that includes the conductive film and a manufacturing method that can easily produce the conductive film. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 2 is a schematic cross-sectional view illustrating MXene constituting the conductive film of the present embodiment. [Figure 2] FIG. 1 is a schematic cross-sectional view illustrating a conventional conductive film. [Figure 3] FIG. 2 is a schematic cross-sectional view illustrating a conductive film according to the present embodiment. [Figure 4] 1 is a scanning electron microscope photograph in an example. [Figure 5] FIG. 1 is a graph showing the relationship between the proportion of tetravalent titanium and the impedance at 10 Hz of an electrode with a diameter of 10 mm in an example. DETAILED DESCRIPTION OF THE INVENTION

[0009] (Embodiment 1: Conductive film) Hereinafter, a conductive film according to one embodiment of the present invention will be described in detail, but the present invention is not limited to this embodiment.

[0010] The conductive film in this embodiment is a film comprising particles of a layered material comprising one or more layers, and titanium oxide; The layer may comprise a compound having the following formula: M m X n (wherein M is at least one Group 3, 4, 5, 6, 7 metal, including Ti; X is a carbon atom, a nitrogen atom, or a combination thereof; n is between 1 and 4, m is greater than n and less than or equal to 5) and a modification or termination T (T is at least one selected from the group consisting of a hydroxyl group, a fluorine atom, a chlorine atom, an oxygen atom, and a hydrogen atom) present on the surface of the layer body, The ratio of tetravalent titanium to divalent, trivalent, and tetravalent titanium, as determined from a spectrum obtained by X-ray photoelectron spectroscopy, is more than 2 mol % and not more than 57 mol %. This allows for the realization of a conductive film containing MXene and having a sufficiently reduced impedance.

[0011] Hereinafter, a film including particles of a layered material including one or more layers, which constitutes the conductive film of this embodiment, will be described. The layered material can be understood as a layered compound, and is also 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 to this.

[0012] In the above formula for MXene, M may be only Ti, or may contain Ti and at least one element selected from the group consisting of Zr, Hf, V, Nb, Ta, Cr, Mo, and Mn. When M contains an element other than Ti, it is more preferable that the element other than Ti is at least one element selected from the group consisting of V, Cr, and Mo.

[0013] MXene is a compound represented by the formula: M m X n However, it is known that it can be expressed as follows: Ti2C, Ti2N, (Ti,V)2C, (Ti,Nb)2C, Ti3C2, Ti3N2, Ti3(CN), (Ti,V)3C2, (Ti2Nb)C2, (Ti2Ta)C2, (Ti2Mn)C2, (V2Ti)C2, (Cr2Ti)C2, (Mo2Ti)C2, (W2Ti)C2, Ti4N3, (Ti,Nb)4C3, (Ti2Nb2)C3, (Ti2Ta2)C3, (V2Ti2)C3, (Cr2Ti2)C3, (Mo2Ti2)C3, (W2Ti2)C3

[0014] Typically, in the above formula, M can be titanium or titanium and 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).

[0015] In this embodiment, 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, this may not be a problem depending on the application and use conditions of the conductive film and electrode.

[0016] The MXene constituting the MXene particles according to this embodiment is described below with reference to Figure 1. The skeletal structure of the titanium oxide-containing MXene particles according to this embodiment is almost the same as that of the MXene particles constituting the precursor film. Figure 1 explains the skeletal structure of the titanium oxide-containing MXene particles, and does not show titanium oxide in Figure 1.

[0017] The MXene particle according to this embodiment is an aggregate containing a plurality of MXene 10a particles (single-layer MXene particles) each having one layer, as shown in FIG. 1(a). More specifically, MXene 10a particles are m X n The layer body (M m X nThe MXene layer 7a has a main layer 1a and a modification or termination T3a, 5a present on the surface of the main layer 1a (more specifically, on at least one of the two surfaces of the main layer 1a). m X n T s ", where s is an arbitrary number.

[0018] The MXene particles according to this embodiment may contain one or more layers of MXene. An example of a multilayer MXene (multilayer MXene) is, but is not limited to, two layers of MXene 10b, as shown in FIG. 1(b). 1b, 3b, 5b, and 7b in FIG. 1(b) are the same as 1a, 3a, 5a, and 7a in FIG. 1(a). Two adjacent MXene layers (e.g., 7a and 7b) in a multilayer MXene do not necessarily need to be completely separated and may be partially in contact. The MXene 10a may be a single layer in which the multilayer MXene 10b is individually separated. Alternatively, the multilayer MXene 10b may remain unseparated, resulting in a mixture of the single layer MXene 10a and the multilayer MXene 10b. Even when the multilayer MXene is included, the multilayer MXene is preferably a MXene with a small number of layers obtained through a delamination process. The term "small number of layers" refers to, for example, a MXene having 10 or fewer layers. Hereinafter, this "multilayer MXene with a small number of layers" may be referred to as "few-layer MXene." The thickness of the few-layer MXene in the stacking direction may be 15 nm or less, or even 10 nm or less. Furthermore, the single-layer MXene and few-layer MXene may be collectively referred to as "single-layer / few-layer MXene."

[0019] The majority of the MXenes may be single-layered or few-layered MXenes. By using single-layered or few-layered MXenes as the majority of the MXenes, the specific surface area of ​​the MXenes can be larger than that of multi-layered MXenes. As a result, when the laminate is used in applications requiring electrical conductivity, degradation of electrical conductivity over time can be suppressed. For example, single-layered or few-layered MXenes having 10 or fewer MXene layers and a thickness of 15 nm or less, preferably 10 nm or less, may account for, for example, 80% by volume or more, even 90% by volume or more, or even 95% by volume or more of the total MXenes. Furthermore, the volume of the single-layered MXenes may be larger than the volume of the few-layered MXenes. Because the true density of these MXenes does not vary significantly depending on their form, it can also be said that the mass of the single-layered MXenes is larger than the mass of the few-layered MXenes. When these relationships are satisfied, the specific surface area of ​​the MXenes can be increased, and when used in applications requiring electrical conductivity, degradation of electrical conductivity over time can be suppressed. For example, a film may be formed solely from single-layered MXenes.

[0020] Although this embodiment is not limited thereto, the thickness of each MXene layer (corresponding to the above-described MXene layers 7a and 7b) can be, for example, 1 nm to 30 μm, and may be, for example, 1 nm to 5 nm, or even 1 nm to 3 nm (this can vary mainly depending on the number of M atomic layers contained in each layer). For each of the multilayer MXene stacks that can be included, the interlayer distance (or gap dimension, shown as Δd in FIG. 1(b)) can be, for example, 0.8 nm to 10 nm, particularly 0.8 nm to 5 nm, and more particularly about 1 nm, and the total number of layers can be 2 to 20,000.

[0021] The conductive film of this embodiment contains titanium oxide. In this embodiment, the proportion of titanium oxide contained in the conductive film is evaluated by the proportion of tetravalent titanium that constitutes titanium oxide. That is, in addition to the tetravalent titanium that constitutes titanium oxide, divalent and trivalent titanium that form the structure of, for example, MXene are also present. In this embodiment, the proportion of tetravalent titanium in the divalent, trivalent, and tetravalent titanium, as determined from a spectrum obtained by X-ray photoelectron spectroscopy (XPS), is in the range of more than 2 mol% and not more than 57 mol%. By being within this range, it is believed that titanium oxide can partially modify the structure of the MXene film as described below, thereby increasing the conductivity, without reducing the inherent conductivity of the MXene film.

[0022] FIG. 2 is a cross-sectional view schematically illustrating a conventional conductive film. Meanwhile, FIG. 3 is a cross-sectional view schematically illustrating a conductive film according to the present embodiment. Note that FIG. 3 is merely an illustration used for convenience of explanation, and the morphology (shape, size, etc.) of the titanium oxide crystals, their arrangement in the MXene film, and the arrangement of the MXene particles are depicted for ease of explanation and are not limited to the configuration shown in FIG. 3. While this embodiment is not bound by any theory, the reason why the conductive film according to the present embodiment exhibits excellent conductivity is presumed to be as follows. Specifically, as shown in FIG. 3, by realizing a state in which titanium oxide 51 is present near the surface of MXene 10d, the titanium oxide 51 is thought to penetrate between the layers of MXene 10d and spread the gap between the layers. When this state is applied to, for example, an electrode, in the conventional conductive film shown in FIG. 2, ions in the electrolyte solution contact only the outermost surface of the conductive film. In contrast, in the conductive film shown in FIG. 3, the electrolyte solution penetrates into the shallow surface region 53 of the conductive film in the thickness direction, and ions in the electrolyte solution are thought to also contact the surface of the inner MXene layer. As a result, not only the outermost surface of the conductive film but also the MXene layer inside it acts as an electrode, which is thought to reduce impedance. Meanwhile, in the inner region 55 deeper from the outermost surface of the conductive film, MXene layers are stacked, which is thought to exert the effect of MXene as an extraction electrode, which is an inherent property of MXene. As a result, while suppressing the increase in impedance due to titanium oxide, the impedance reduction due to the above effect is fully exerted, and high conductivity is thought to be exhibited.

[0023] The titanium oxide is preferably one in which the titanium constituting MXene has been oxidized by aging, as described below.

[0024] (Embodiment 2: Electrode) The electrode according to this embodiment includes the conductive film. The electrode may be formed only from the conductive film, or may include the conductive film and, for example, a substrate.

[0025] The electrode of this embodiment is not limited to a specific form as long as it includes the conductive film. Examples of the electrode include those in a solid state and those in a flexible, soft state.

[0026] One of the characteristics of the electrode of this embodiment is impedance. According to the measurement conditions shown in the Examples below, the impedance is preferably 49.0 ohms or less at 10 Hz, more preferably 45.0 ohms or less, and even more preferably 30.0 ohms or less.

[0027] In the electrode of this embodiment, the conductive film may be exposed to the outside air so as to be in direct contact with the object to be measured, or may be formed with other laminates, such as an ion-permeable gel or a film including a porous membrane. The porous membrane may be a membrane having a large number of fine pores that selectively transmits ions or molecules smaller than the pore diameter. The material of these other laminates is not particularly limited and may be formed from organic materials, inorganic materials, or mixtures thereof. For example, the organic material may be a polymer such as a hydrophilic polymer, the inorganic material may be ceramics, or a combination thereof. The film thickness of these other laminates may be, for example, 0.1 μm to 300 μm. The porous membrane may have an average pore diameter of, for example, 1 nm to 1 μm. Examples of the porous membrane, depending on the pore shape, include agglomerated particulate porous membranes, mesh-like porous membranes, fibrous porous membranes, porous membranes having a plurality of isolated and / or interconnected pores, and honeycomb-structured porous membranes.

[0028] When the electrode of this embodiment has a substrate, the conductive film and the substrate may be in direct contact. The material of the substrate is not particularly limited. The substrate may be formed of a conductive material. Examples of conductive materials include at least one of metal materials such as gold, silver, copper, platinum, nickel, titanium, tin, iron, zinc, magnesium, aluminum, tungsten, and molybdenum, and conductive polymers. The substrate may have a conductive film, such as a metal film, separate from the conductive film of this embodiment on the surface that contacts the conductive film of this embodiment. Alternatively, the substrate may be formed of an organic material. Examples of the organic material include flexible organic materials, such as thermoplastic polyurethane elastomer (TPU), PET film, and polyimide film.

[0029] (Electrode applications) The electrode of this embodiment can be used for any appropriate application. Examples include a biological electrode, a battery electrode, a counter electrode or reference electrode for electrochemical measurements, and an electrode for an electrochemical capacitor. It can also be used for applications that require maintaining high conductivity (reducing the decrease in initial conductivity and preventing oxidation), such as electromagnetic shielding (EMI shielding). Details of these applications are described below.

[0030] The electrodes are not particularly limited, and may be, for example, capacitor electrodes, battery electrodes, biosignal sensing electrodes, sensor electrodes, antenna electrodes, etc. By using the conductive film of this embodiment, it is possible to obtain large-capacity capacitors and batteries, low-impedance biosignal sensing electrodes, and highly sensitive sensors and antennas even in a smaller volume (volume occupied by the device).

[0031] The capacitor may be an electrochemical capacitor. An electrochemical capacitor is a capacitor that utilizes a 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 (electricity 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.

[0032] The biosignal sensing electrode is an electrode for acquiring a biosignal, and may be, for example, but not limited to, an electrode for measuring EEG (electroencephalogram), ECG (electrocardiogram), EMG (electromyogram), or EIT (electrical impedance tomography).

[0033] 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.

[0034] The antenna electrode is an electrode for emitting electromagnetic waves into space and / or receiving electromagnetic waves in space.

[0035] The electrode of this embodiment is preferably used as a biosignal sensing electrode. As described above, a conductive film composed of MXene containing a moderate amount of titanium oxide hardly increases impedance due to titanium oxide, and it is thought that the impedance decreases due to the increased distance between MXene flakes in the surface layer region. As a result, it is thought that the sensitivity will be high when used as a biosignal sensing electrode.

[0036] (Embodiment 3: Method for producing conductive film) Hereinafter, the method for producing a conductive film according to the present disclosure will be described in detail, but the present disclosure is not limited to such an embodiment.

[0037] One method for producing a conductive film (first production method) of this embodiment is as follows: (a) Particles of layered material comprising one or more layers, The layer may comprise a compound having the following formula: M m X n (wherein M is at least one Group 3, 4, 5, 6, 7 metal, including Ti; X is a carbon atom, a nitrogen atom, or a combination thereof; n is between 1 and 4, m is greater than n and less than or equal to 5) and a modification or termination T present on the surface of the layer body (wherein 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); (b) using the particles of the layered material to form a precursor film comprising the particles of the layered material; (c) Aging the precursor film to obtain a conductive film. wherein the conductive film has a ratio of tetravalent titanium to divalent, trivalent, and tetravalent titanium, as determined from a spectrum obtained by X-ray photoelectron spectroscopy, of more than 2 mol % to 57 mol % or less.

[0038] Another method for producing a conductive film (second production method) according to this embodiment is as follows: (A) a particle of layered material comprising one or more layers, The layer may comprise a compound having the following formula: M m X n (wherein M is at least one Group 3, 4, 5, 6, 7 metal, including Ti; X is a carbon atom, a nitrogen atom, or a combination thereof; n is between 1 and 4, m is greater than n and less than or equal to 5) and a modification or termination T present on the surface of the layer body (wherein 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); (B) subjecting the dispersion containing particles of the layered material to aging; (C) forming a conductive film containing particles of the layered material using a dispersion containing the aged layered material particles, wherein the conductive film has a ratio of tetravalent titanium to divalent, trivalent, and tetravalent titanium of more than 2 mol% and not more than 57 mol%, as determined from a spectrum obtained by X-ray photoelectron spectroscopy. Each step of the first and second production methods will be described in detail below. Steps (a) and (A), which are common to these two production methods, will be described together.

[0039] Step (a) and Step (A) First, a predetermined precursor is prepared. The predetermined precursor that can be used in this embodiment is a MAX phase, which is a precursor of MXene. The following formula: M m AX n (wherein M is at least one Group 3, 4, 5, 6, 7 metal, including Ti; X is a carbon atom, a nitrogen atom, or a combination thereof; A is at least one element of Groups 12, 13, 14, 15, or 16; n is between 1 and 4, m is greater than n and less than or equal to 5) It is expressed as:

[0040] 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 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, and is preferably Al.

[0041] 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 may have 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.

[0042] The MAX phase can be produced by a known method. For example, TiC powder, Ti powder, and Al powder are mixed in a ball mill, and the resulting mixed powder is sintered in an Ar atmosphere to obtain a sintered body (a block of MAX phase). The sintered body is then pulverized with an end mill to obtain a powdered MAX phase for the next step.

[0043] Selective etching (removal and possibly layer separation) of A atoms (and possibly some M atoms) from the MAX phase removes the A atomic layer (and possibly some M atoms) to expose M m X n The surface of the layer is modified with hydroxyl groups, fluorine atoms, chlorine atoms, oxygen atoms, hydrogen atoms, etc. present in the etching solution (usually, an aqueous solution of fluorine-containing acid is used, but this is not limited to this) to terminate the surface.

[0044] The above etching is F -The etching can be carried out using an etching solution containing the above, for example, a method using a mixed solution of lithium fluoride and hydrochloric acid, or a method using hydrofluoric acid. The etching solution may contain a metal compound containing a monovalent metal ion, 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.

[0045] After the etching, any suitable post-treatment (e.g., ultrasonic treatment, handshaking, or automatic shaker) may be used to promote layer separation (delamination, separating multilayer MXene into monolayer MXene). Note that ultrasonic treatment can destroy MXene due to excessive shear force. Therefore, if a two-dimensional MXene with a larger aspect ratio (preferably monolayer MXene) is desired, it is preferable to apply an appropriate shear force using a handshaking or automatic shaker.

[0046] For the layer separation of the MXene, the following intercalation treatment and delamination may be carried out.

[0047] (Intercalation treatment) 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 ion, sodium ion, and potassium ion, copper ion, silver ion, and gold ion. Examples of the metal compound containing a monovalent metal ion include ionic compounds in which the above metal ions are combined with 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 sulfides of lithium ion. It is believed that using lithium ion as the metal ion facilitates monolayer formation because water hydrated with lithium ion has the most negative dielectric constant.

[0048] 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, and more preferably 1% by mass or less.

[0049] (Delamination) The intercalation product obtained by intercalation may be subjected to delamination. For example, delamination may involve centrifuging the intercalation 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 polar organic dispersion mediums and aqueous dispersion mediums. The process of adding one or more polar organic dispersion mediums and aqueous dispersion mediums, 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-walled or few-walled MXene as the delamination-treated product. Alternatively, the supernatant may be centrifuged, and the resulting supernatant may be discarded to obtain a single-walled or few-walled MXene-containing clay as the delamination-treated product.

[0050] ·Process (b) In the first production method, particles of the layered material are used to form a precursor film containing the layered material particles. The precursor film can be formed using a dispersion of layered material particles (MXene particles), such as an MXene slurry prepared by diluting the single-layered or few-layered MXene-containing clay with a liquid medium. The dispersion may also be a suspension. The method for forming an MXene film using a dispersion of MXene particles is not particularly limited. The MXene particle dispersion may be applied to a substrate as is or after appropriate adjustment (e.g., dilution with a liquid medium or addition of a binder). Examples of application methods include spray application (using a spray coater) using a nozzle such as a one-fluid nozzle, a two-fluid nozzle, or an airbrush; slit coating using a table coater, comma coater, or bar coater; screen printing; metal mask printing; spin coating; dip coating; and dripping. Examples of the liquid medium include aqueous and organic liquid mediums. The liquid medium constituting the MXene particle dispersion is typically water, and may optionally contain a relatively small amount (e.g., 30% by mass or less, preferably 20% by mass or less, based on the total mass) of other liquid substances in addition to water. Examples of the organic liquid medium include N-methylpyrrolidone, N-methylformamide, N,N-dimethylformamide, ethanol, methanol, dimethyl sulfoxide, ethylene glycol, and acetic acid.

[0051] When forming the electrode using a spray coater, for example, MXene slurry is applied to a substrate such as PET or polyimide once or multiple times to form a film (electrode) before drying, with the atomization pressure set to between 0.1 MPa and 0.5 MPa, the distance between the nozzle tip and the substrate set to between 10 cm and 25 cm, the liquid delivery rate set to between 0.1 mL / s and 10 mL / s, the sweep speed set to between 1 mm / s and 30 mm / s, and the stage heater set to between 30°C and 60°C.

[0052] In addition to the spraying method, an MXene membrane can also be prepared by suction filtering the supernatant containing the MXene particles obtained by the slurry or delamination. More specifically, the supernatant containing the MXene particles is prepared as a dispersion of MXene particles (e.g., diluted with an aqueous medium) and then suction filtered through a filter (which may be part of a specific component together with the MXene membrane or may ultimately be separated from the MXene membrane) installed in a Nutsche or similar device. The aqueous medium is at least partially removed, forming an MXene membrane on the filter. The filter is not particularly limited, but a membrane filter or the like can be used. The suction filtering method allows the preparation of an MXene membrane without the use of binders or other additives. The MXene particles of this embodiment can be used to prepare an MXene membrane without the use of binders or other additives.

[0053] The substrate may or may not be present. If a substrate is present, the material constituting the substrate is not particularly limited and may be any appropriate material. The substrate may be, for example, a resin film, metal foil, printed wiring board, mounted electronic component, metal pin, metal wiring, metal wire, etc. For example, a substrate formed from a metal material, resin, etc. suitable for a biosignal sensing electrode can be appropriately used. An MXene film can be formed on any appropriate substrate (which may constitute a specified component together with the MXene film or may ultimately be separated from the MXene film) by coating the composition on the substrate.

[0054] Drying can be performed under mild conditions such as natural drying (typically placing the precursor in an air atmosphere at room temperature and pressure) or air drying (blowing air), or under relatively aggressive conditions such as hot air drying (blowing heated air), heat drying, and / or vacuum drying. In this embodiment, "drying" refers to removing any liquid medium that may be present in the precursor. The drying can be performed, for example, at a temperature of 400°C or less using a normal pressure oven or a vacuum oven. For example, drying can be performed at a temperature of 30°C to 200°C for 30 minutes to 24 hours.

[0055] The formation and drying of the MXene membrane may be repeated as needed until the desired MXene membrane thickness is achieved. For example, the combination of spraying and drying may be repeated multiple times. The above-described suction filtration allows the formation of a binder-free MXene membrane. The MXene membrane may or may not contain residual liquid components derived from the liquid medium of the slurry.

[0056] ·Process (c) The precursor film is aged to obtain a conductive film in which the proportion of tetravalent titanium in the divalent, trivalent, and tetravalent titanium, as determined from a spectrum obtained by X-ray photoelectron spectroscopy, is more than 2 mol % and not more than 57 mol %.

[0057] The aging conditions are not particularly limited as long as the aging process can produce a conductive film in which the proportion of tetravalent titanium in the divalent, trivalent, and tetravalent titanium is greater than 2 mol% and less than or equal to 57 mol%. The precursor film may be left at a temperature of 30°C to 200°C and a humidity of 45% to 99% RH for 24 hours to 30 days. The conditions may be appropriately set so that the proportion of tetravalent titanium is greater than 2 mol% and less than or equal to 57 mol%. Within the above range, lower temperatures require longer aging times because oxidation takes longer. On the other hand, higher temperatures accelerate oxidation, so shorter aging times are recommended. For example, when the temperature is at the lower limit of 30°C, the aging time may be longer, up to 30 days. On the other hand, when the temperature is 80°C or higher, as in the examples described below, the upper limit of the aging time may be 7 days or less. In this embodiment, the film is preferably maintained at a relatively low temperature for a long period of time in order to partially oxidize only the surface region in the film thickness direction. From this viewpoint, the temperature is more preferably 150°C or less, and even more preferably 100°C or less. The aging time can be, for example, less than 14 days. To accelerate aging, the temperature may be, for example, 40°C or more. To accelerate aging, the humidity may be, for example, 50 RH% or more, or even 60 RH% or more. The atmosphere for aging other than the above is not limited, and may be, for example, an oxygen-containing atmosphere such as air.

[0058] According to the first manufacturing method, it is possible to simultaneously manufacture various electrodes, for example, by manufacturing multiple conductive films as electrodes and then aging some of the electrodes (conductive films) depending on the application, thereby reducing manufacturing costs, for example.

[0059] ·Process (B) In the second manufacturing method, the dispersion containing the layered material particles is subjected to aging. The aging conditions include leaving the dispersion containing the layered material particles at a temperature of 30°C or higher and 200°C or lower for 24 hours to 1 month (e.g., 30 days or shorter). In this embodiment, it is preferable to maintain the dispersion at a relatively low temperature for a long period of time in order to partially oxidize the film. From this perspective, the temperature is more preferably 150°C or lower, even more preferably 100°C or lower, even more preferably 80°C or lower, and particularly preferably 60°C or lower. The aging time can be, for example, less than 14 days.

[0060] ·Process (C) In the second manufacturing method, a dispersion containing particles of the aged layered material is used to form a conductive film containing the particles of the layered material, in which the proportion of tetravalent titanium in the divalent, trivalent, and tetravalent titanium, as determined from a spectrum obtained by X-ray photoelectron spectroscopy, is more than 2 mol % and not more than 57 mol %. The method for forming a film using the dispersion containing particles of the aged layered material may be the same as step (b) in the first manufacturing method.

[0061] According to the second manufacturing method, aging can be performed, for example, in a slurry state, making it possible to mass-produce aged electrodes (conductive films) at once, leading to reduced manufacturing costs. The conductive films obtained by the second manufacturing method also exhibit the same degree of oxidation and impedance values ​​as the conductive films obtained by the first manufacturing method. From this, it is believed that the conductive films obtained by the second manufacturing method also have the same titanium oxide morphology as the conductive films obtained by the first manufacturing method. Furthermore, while this embodiment is not bound by any theory, it is speculated as follows: It is believed that the particles of the layered material in the dispersion liquid are aged almost uniformly in step (B). However, when the dispersion liquid containing the aged layered material particles is spray-applied in step (C) to form a conductive film, it is speculated that the titanium oxide migrates to the outermost surface of the conductive film due to shear force, for example. This speculation is also likely to occur in formation methods other than the spray-applying method. [Example]

[0062] The present invention will be described in more detail below with reference to examples. The present disclosure is not limited to the following examples, and appropriate modifications can be made 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.

[0063] Example 1 1. Preparation of Layered Material Particles MXene particles were first obtained by carrying out the following steps in order: (1) preparation of the precursor (MAX), (2) etching of the precursor, (3) cleaning after etching, (4) intercalation of Li, and (5) delamination, as detailed below.

[0064] (1) Preparation of precursor (MAX) TiC powder, Ti powder, and Al powder (all manufactured by Kojundo Chemical Laboratory Co., Ltd.) were mixed in a 2:1:1 molar ratio in a ball mill containing zirconia balls for 24 hours. The resulting mixed powder was sintered at 1350°C for 2 hours in an Ar atmosphere. The resulting sintered body (block-shaped MAX) was then pulverized with an end mill to a maximum dimension of 40 μm or less. This yielded Ti3AlC2 particles as a precursor (powder-shaped MAX).

[0065] (2) Etching of precursor (MAX) Using the Ti3AlC2 particles (powder) prepared by the above method, etching was carried out under the following etching conditions to obtain a solid-liquid mixture (slurry) containing solid components derived from the Ti3AlC2 powder. (Etching conditions) Precursor: Ti3AlC2 (passed through a 45 μm sieve) Etching solution composition: 49% HF 6mL, 18mL of H2O HCl (12M) 36mL Precursor input: 3.0g Etching container: 100mL Eye Boy Etching temperature: 35℃ Etching time: 24 hours Stirrer rotation speed: 400 rpm

[0066] (3) Cleaning after etching The above slurry was divided into two equal 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. Then, (i) 35 mL of pure water was added to the remaining precipitate in each centrifuge tube, (ii) the mixture was stirred by hand shaking, (iii) the mixture was centrifuged at 3500 G for 5 minutes, and (iv) the supernatant was removed. These steps (i) to (iv) were repeated 10 times. Finally, the mixture was centrifuged at 3500 G for 5 minutes to obtain Ti3C2T. s -Water medium clay was obtained.

[0067] (4) Li intercalation Ti3C2T prepared by the above method s - Li intercalation was carried out on the water medium clay using LiCl as the Li-containing compound, stirring for 12 hours at 20°C to 25°C according to the Li intercalation conditions below. The detailed conditions for Li intercalation are as follows: (Li intercalation conditions) Ti3C2T s -Water medium clay (MXene after washing): solid content 0.75g LiCl: 0.75g Intercalation vessel: 100mL Eye Boy ·Temperature: 20℃ or higher and 25℃ or lower (room temperature) ·Time: 12h Stirrer rotation speed: 800 rpm

[0068] (5) Delamination and water washing The slurry obtained after 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, which was then stirred on a shaker for 15 minutes. (ii) The tube was then centrifuged at 3500 G. (iii) The supernatant was collected as a solution containing single- and few-layered MXene. These steps (i) to (iii) were repeated four times to obtain a supernatant containing single- and few-layered MXene. This supernatant was then centrifuged at 4300 G for two hours using a centrifuge. The supernatant was then discarded, and the remaining precipitate, MXene clay containing single- and few-layered MXene, was obtained.

[0069] 2. Preparation of MXene Slurry A predetermined amount of the MXene clay obtained in step 1 was placed in a 50 mL centrifuge tube, and pure water was added to make the MXene concentration 1.5 wt %. The mixture was then stirred for 15 minutes with a shaker to obtain an MXene slurry.

[0070] 3. Aging of MXene Slurry (No. 2 to 5 in Table 1) For Nos. 2 to 5 in Table 1, aging was carried out in the form of a slurry. Specifically, the slurry obtained in 2 above was placed in a resin container, placed in a normal pressure oven, and left at a temperature of 40°C for 1, 2, 3, or 6 days for aging. For Nos. 6 to 8 in Table 1, aging was not carried out in the form of a slurry.

[0071] 4. Electrode Sample Preparation Using the MXene slurries Nos. 6 to 8 in Table 1 obtained in 2 above or the aged MXene slurries Nos. 2 to 5 in Table 1 obtained in 3 above, electrode samples were produced in the following order. (a) The slurry was placed in a 25 mL syringe. (b) The syringe (a) was set in a spray coater. (c) A predetermined number of 3 cm square PET substrates were placed on the suction stage of a spray coater. (d) The atomization pressure was set to 0.5 MPa, the distance between the nozzle tip and the substrate was set to 15 cm, the liquid delivery rate was set to 5 mL / s, the sweep speed was set to 150 mm / s, and the stage heater was set to 45°C. (e) The electrode was formed by applying the solution 12 times to the substrate. (f) Using a normal pressure oven, drying was carried out at 80°C for 2 hours to obtain electrode samples. The obtained electrode samples Nos. 6 to 8 correspond to precursor films.

[0072] 5. Aging of electrode samples (No. 6 to 8 in Table 1) For Nos. 6 to 8 in Table 1, electrode samples corresponding to precursor films were aged. Specifically, the electrode samples Nos. 6 to 8 obtained in 4 above were placed in a normal pressure oven and left to stand for 1, 7, or 14 days at a temperature of 85°C and a humidity of 85 RH% for aging. As a comparative example, for No. 1 in Table 1, an electrode sample was prepared without any aging.

[0073] 6. Sample Evaluation (1) Impedance measurement Impedance measurements were carried out as follows. (a) A beaker cell was assembled using the obtained electrode sample as the working electrode, a platinum electrode or a carbon electrode as the counter electrode, and a silver-silver chloride electrode as the reference electrode. (b) The working electrode of (a) was prepared by opening a 10 mm diameter opening in the obtained electrode sample with Kapton (registered trademark) tape. (c) The counter electrode in (a) had an area larger than that of the working electrode. (d) Measurement conditions were as follows: frequency range 0.1 Hz to 106 Hz, voltage 1 mVrms to 20 mVrms relative to the open circuit voltage or reference electrode, number of plots 71, N per plot 1 to 10, and potentiostat mode. The equipment used was a Bio-Logic Science Instruments VMP-300 High-Performance Electrochemical Measurement System (16-channel, advanced model). The measurement results, impedance at 10 Hz for a 10 mm diameter electrode, are shown in Table 1.

[0074] (2) Measurement of oxidation degree by XPS The degree of oxidation was measured by XPS as follows. (a) The obtained electrode sample was cut into approximately 5 mm squares together with the substrate using scissors. (b) XPS analysis was performed on both the surface and the peeled surface. To expose the peeled surface, the MXene film formed on the film was transferred to the sticky side of cellophane tape, and then new cellophane tape was attached to the transferred MXene film and the two were peeled off. The inside of the MXene film exposed at this time was defined as the peeled surface. (c) Narrow spectra were obtained from both the surface and the peeled surface of the electrode sample using a multifunction scanning X-ray photoelectron spectrometer (XPS) PHI 5000 VersaProbe III (ULVAC-PHI, Inc.). Since tetravalent Ti is a component derived from titanium oxide, the obtained spectra were separated into divalent, trivalent, and tetravalent Ti. The sum of the areas of these spectral peaks was taken as 100, and the ratio of the tetravalent Ti spectral peak was calculated as the ratio of tetravalent Ti. This calculated value was defined as the "degree of oxidation." The XPS detection depth in the film thickness direction was approximately 5 nm, detecting information on the outermost surface. Furthermore, information was obtained not from a specific point, but from a 1000 μm × 200 μm area by scanning with an X-ray beam 100 μm in diameter. The measurement results are shown in Table 1.

[0075] (3) SEM observation The surface of electrode sample No. 7 in Table 1 was observed using a scanning electron microscope (Hitachi High-Technologies Corporation, field emission scanning electron microscope (FE-SEM) S-4800) and a micrograph was obtained. The micrograph is shown in Figure 4. In Figure 4, it was confirmed that titanium oxide crystals, which appear as white granules, had precipitated. The fact that the white granular crystals were titanium oxide was determined comprehensively from three pieces of information: the white charge-up, the XPS results, and the high level of oxygen detected within the range observed with EDX.

[0076] [Table 1]

[0077] Figure 5 shows the relationship between the surface tetravalent Ti percentage (oxidation degree) in Table 1 and the impedance value at 10 Hz for a 10 mm diameter electrode. Figure 5 reveals that impedance decreases when the tetravalent titanium percentage exceeds 2 mol %, and until it reaches 57 mol %, the impedance remains lower than the initial value, indicating high conductivity. While oxidation of MXene reduces conductivity, within a certain range of oxidation, titanium oxide barely increases impedance within a certain range. The presence of titanium oxide increases the distance between MXene flakes, significantly reducing impedance and resulting in high conductivity. On the other hand, when the surface tetravalent Ti percentage (oxidation degree) exceeds 57 mol % and reaches 72 mol %, the impedance significantly increases. Note that the electrode samples in this example were aged at a relatively high temperature of 85°C, so the maximum aging time required to obtain an MXene film with a tetravalent titanium percentage of 57 mol % or less was 7 days. Furthermore, in Table 1, the degree of oxidation on the peeled surface was lower than that on the surface for all samples. For example, the proportion of tetravalent titanium on the peeled surface of the film was 7 mol% in sample No. 8, and oxidation was suppressed.

[0078] This application claims priority from Japanese Patent Application No. 2021-199517, which is incorporated herein by reference. [Industrial Applicability]

[0079] The conductive film according to this embodiment can be used in any suitable application, but is preferably used in applications requiring high conductivity, and can be particularly preferably used as an electrode, for example. [Explanation of symbols]

[0080] 1a, 1b layer body (M m X n layer) 3a, 5a, 3b, 5b Modified or terminal T 7a, 7b MXene layers 10a, 10b, 10c, 10d MXene (particle) 30 Conventional MXene membrane 31 MXene membrane according to this embodiment 51 Titanium oxide crystals 53 MXene membrane surface region 55MXene membrane inner region

Claims

1. a film comprising particles of a layered material comprising one or more layers; and titanium oxide; The layer comprises a compound having the following formula: M ｍ X ｎ wherein M is at least one Group 3, 4, 5, 6, or 7 metal, including Ti; X is a carbon atom, a nitrogen atom, or a combination thereof; n is 1 or more and 4 or less, m is greater than n and is equal to or less than 5. and a modification or termination T (T is at least one selected from the group consisting of a hydroxyl group, a fluorine atom, a chlorine atom, an oxygen atom, and a hydrogen atom) present on the surface of the layer body, A conductive film in which the proportion of tetravalent titanium in divalent, trivalent and tetravalent titanium, as determined from a spectrum obtained by X-ray photoelectron spectroscopy, is more than 2 mol % and not more than 57 mol %.

2. A conductive film as described in claim 1, wherein M is Ti, or Ti and at least one selected from the group consisting of Zr, Hf, V, Nb, Ta, Cr, Mo and Mn.

3. An electrode comprising the conductive film according to claim 1 or 2.

4. The electrode of claim 3 , which is a biosignal sensing electrode.

5. (a) particles of layered material comprising one or more layers, The layer comprises a compound having the following formula: M ｍ X ｎ wherein M is at least one Group 3, 4, 5, 6, or 7 metal, including Ti; X is a carbon atom, a nitrogen atom, or a combination thereof; n is 1 or more and 4 or less, m is greater than n and is equal to or less than 5. and a modification or termination T present on the surface of the layer body (T is at least one selected from the group consisting of a hydroxyl group, a fluorine atom, a chlorine atom, an oxygen atom, and a hydrogen atom); (b) using the particles of the layered material to form a precursor film comprising the particles of the layered material; (c) Aging the precursor film to obtain a conductive film. wherein the conductive film has a ratio of tetravalent titanium to divalent, trivalent, and tetravalent titanium, as determined from a spectrum obtained by X-ray photoelectron spectroscopy, of more than 2 mol % to 57 mol % or less.

6. A method for producing a conductive film as described in claim 5, wherein M is Ti, or Ti and at least one selected from the group consisting of Zr, Hf, V, Nb, Ta, Cr, Mo and Mn.

7. 7. The method for producing a conductive film according to claim 5, wherein the aging step comprises leaving the precursor film at a temperature of 30° C. or higher and 200° C. or lower and a humidity of 45 RH % or higher and 99 RH % or lower for 24 hours or longer and 30 days or shorter.

8. (A) Particles of layered material comprising one or more layers, The layer comprises a compound having the following formula: M ｍ X ｎ wherein M is at least one Group 3, 4, 5, 6, or 7 metal, including Ti; X is a carbon atom, a nitrogen atom, or a combination thereof; n is 1 or more and 4 or less, m is greater than n and is equal to or less than 5. and a modification or termination T present on the surface of the layer body (T is at least one selected from the group consisting of a hydroxyl group, a fluorine atom, a chlorine atom, an oxygen atom, and a hydrogen atom); (B) subjecting the dispersion containing particles of the layered material to aging; (C) A method for producing a conductive film, comprising: using a dispersion containing particles of the layered material that has been subjected to the aging process to form a conductive film containing particles of the layered material, wherein the conductive film has a ratio of tetravalent titanium to divalent, trivalent, and tetravalent titanium of more than 2 mol % and not more than 57 mol % as determined from a spectrum obtained by X-ray photoelectron spectroscopy.

9. A method for producing a conductive film as described in claim 8, wherein M is Ti, or Ti and at least one selected from the group consisting of Zr, Hf, V, Nb, Ta, Cr, Mo and Mn.

10. The method for producing a conductive film according to claim 8 or 9, wherein the aging step comprises leaving the dispersion containing the particles of the layered material at a temperature of 30° C. or higher and 200° C. or lower for 24 hours or longer and 30 days or shorter.

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