Electrode

Abstract

Disclosed is an electrode in which at least a contact surface that comes into contact with an object to be measured is formed of a conductive composite material that includes an elastomer material and layered material particles that include one or more layers, wherein the layer includes a layer main body that is represented by formula MmXn (where M represents at least one metal in groups 3, 4, 5, 6, and 7, including Ti, X represents a carbon atom, a nitrogen atom, or a combination thereof, n represents a number of 1 or greater and not greater than 4, and m represents a number that is greater than n and not greater than 5), and a modification or terminal T (T is at least one selected from the group consisting of a hydroxyl group, a fluorine atom, a chlorine atom, an oxygen atom, and a hydrogen atom) that is present on the surface of the layer main body.

Description

electrode

[0001] The present disclosure relates to electrodes.

[0002] As an electrode for detecting bioelectric signals, such as electroencephalogram signals, from a subject, a soft electrode made of an elastomer material is known. For example, Patent Document 1 discloses a soft electrode (1) for measuring bioelectric signals of an individual, the soft electrode (1) comprising a support (2) having a contact side (21) facing the individual when the electrode (1) is applied to the individual, and a connector side (22) opposite the contact side (21).

[0003] International Publication No. 2022 / 047595

[0004] However, Patent Document 1 does not particularly consider electrodes with reduced impedance. An object of the present disclosure is to provide an electrode with reduced impedance.

[0005] According to one aspect of the present disclosure, there is provided an electrode, at least a contact surface with an object to be measured, formed of a conductive composite material including layered material particles having one or more layers and an elastomer material, wherein the layer is represented by the following formula: M m X n (wherein M is at least one metal of Group 3, 4, 5, 6, or 7, including Ti; X is a carbon atom, a nitrogen atom, or a combination thereof; n is 1 or more and 4 or less; and m is greater than n and 5 or less), and a modified or terminated T (T is at least one selected from the group consisting of a hydroxyl group, a fluorine atom, a chlorine atom, an oxygen atom, and a hydrogen atom) present on the surface of the layer body.

[0006] According to the present disclosure, an electrode with reduced impedance can be provided.

[0007] 1 is a schematic cross-sectional view of a layered material particle that can be used in one embodiment of the present disclosure, where (a) shows a single-layer MXene particle and (b) shows a multi-layer (exemplarily two-layer) MXene particle;

[0023] FIG. 1 is a schematic cross-sectional view of one embodiment of an electrode of the present disclosure;

[0024] FIG. 2 is a schematic cross-sectional view of another embodiment of an electrode of the present disclosure;

[0025] FIG. 3 is a schematic cross-sectional view of another embodiment of an electrode of the present disclosure;

[0026] FIG. 4 is a schematic cross-sectional view of another embodiment of an electrode of the present disclosure;

[0027] FIG. 5 is a schematic cross-sectional view of another embodiment of an electrode of the present disclosure;

[0028] FIG. 6 is a schematic cross-sectional view of another embodiment of an electrode of the present disclosure;

[0029] FIG. 7 is a schematic cross-sectional view of another embodiment of an electrode of the present disclosure;

[0030] FIG. 8 is a schematic cross-sectional view of another embodiment of an electrode of the present disclosure;

[0031] FIG. 9 is a schematic cross-sectional view of another embodiment of an electrode of the present disclosure;

[0032] FIG. 10 is a schematic cross-sectional view of another embodiment of an electrode of the present disclosure;

[0033]

[0008] An electrode according to one embodiment of the present disclosure will be described in detail below, but the present disclosure is not limited to such an embodiment.

[0009] [Electrode] The electrode in this embodiment is an electrode in which at least the contact surface with the object to be measured is formed of a conductive composite material containing layered material particles including one or more layers and an elastomer material, and the layer is represented by 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; and m is greater than n and 5 or less), and a modified or terminated T (T is at least one selected from the group consisting of hydroxyl groups, fluorine atoms, chlorine atoms, oxygen atoms, and hydrogen atoms) present on the surface of the layer body. This makes it possible to realize an electrode that exhibits low impedance and includes particles of a layered material (MXene) having one or more layers, and that also includes an elastomeric material. Because MXene exhibits higher electrical conductivity than carbon fillers, even when MXene powder is dispersed in an elastomeric material without adding a carbon filler, it is possible to achieve both the low contact impedance required for electrodes such as bioelectrodes and the electrical conductivity of the elastomeric material.

[0010] (Layered Material Particles) Hereinafter, layered material particles including one or more layers that constitute the electrode of this embodiment will be described.

[0011] The layered material constituting the layered material particles can be understood as a layered compound and is referred to as "M ｍ X ｎ T ｓ ", where s is any number, and conventionally, x or z may be used instead of s. Typically, n can be 1, 2, 3, or 4, but is not limited thereto.

[0012] In the above formula for MXene, M may be only Ti, or may include Ti and further include one or more Group 3, 4, 5, 6, and 7 metals other than Ti. For example, M may include Ti and further include at least one element selected from the group consisting of Zr, Hf, V, Nb, Ta, Cr, Mo, and Mn. When M includes 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: Ti ２ C, Ti ２ N, (Ti, V) ２ C, (Ti, Nb) ２ C, Ti ３ C ２ , Ti ３ N ２ , Ti ３ (CN), (Ti,V) ３ C ２ , (Ti ２ Nb)C ２ , (Ti ２ Ta) C ２ , (Ti ２ Mn)C ２ , (V ２ Ti)C ２ , (Cr ２ Ti)C ２ , (Mo ２ Ti)C ２ , (W ２ Ti)C ２, Ti ４ N ３ , (Ti, Nb) ４ C ３ , (Ti ２ Nb ２ ) C ３ , (Ti ２ Ta ２ ) C ３ , (V ２ Ti ２ ) C ３ , (Cr ２ Ti ２ ) C ３ , (Mo ２ Ti ２ ) C ３ , (W ２ Ti ２ ) C ３

[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, which is a precursor of MXene, can be Ti ３ AlC ２ and MXene is Ti ３ C ２ T 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 conditions of use of the electrode.

[0016] The layered material particles (also referred to as "MXene particles") contained in the electrode according to this embodiment will be described below with reference to FIG.

[0017] The layered material particles of this embodiment are aggregates containing one layer of MXene 10a (single layer MXene) as shown in FIG. 1(a). More specifically, MXene 10a is ｍ X ｎ The layer body (Mｍ X ｎ The MXene layer 7a has a main layer 1a and modifications or terminations T3a, 5a present on the surface of the main layer 1a (more specifically, on at least one of the two opposing surfaces of each layer). ｍ X ｎ T ｓ ", where s is an arbitrary number.

[0018] The layered material particles according to this embodiment may contain multiple layers, as well as a single layer. Examples of multiple-layer MXene (multilayer MXene) include, but are not limited to, two-layer 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 multilayer MXene do not necessarily need to be completely separated and may be partially in contact. The MXene 10a may be a single layer in which the multilayer MXene 10b is individually separated, while the unseparated multilayer MXene 10b may remain, forming a mixture of the single layer MXene 10a and the multilayer MXene 10b. From the viewpoint of achieving low impedance due to MXene while ensuring strength by including an elastomer material, it is preferable that the layered material particles according to this embodiment include multi-layered MXene.

[0019] Although not limiting this embodiment, 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 multiple MXene stacks that may 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.

[0020] (Elastomer Material) The electrode of this embodiment contains an elastomer material. MXene alone cannot be formed into the shape of an electrode, such as a bioelectrode. However, by including an elastomer material in addition to MXene, it is possible to easily form the electrode into a shape. MXene exhibits lower AC impedance than conventional materials. The electrode of this embodiment contains MXene, preferably multilayer MXene. Compared to monolayer MXene, multilayer MXene has MXene flakes that are more firmly bonded to each other, so the elastomer material does not intercalate between the layers. Since the surfaces between the stacked MXene flakes in multilayer MXene are at least not covered with the elastomer material, it is believed that using multilayer MXene as MXene can reduce impedance compared to when the entire surface of monolayer MXene is covered with the elastomer material.

[0021] The elastomeric material included in the electrodes of the present embodiments may be, for example, synthetic or natural rubber, such as butyl rubber, isoprene rubber, butadiene rubber, halogenated butyl rubber (e.g., bromobutyl rubber), ethylene propylene terpolymer, silicone rubber, fluoro- or perfluoroelastomeric materials, chlorosulfonic acid, copolymer rubbers such as polybutadiene, butyl rubber, neoprene, nitrile, polyisoprene, Buna N, ethylene propylene (EPR), ethylene propylene diene monomer (EPDM), acrylonitrile-butadiene (NBR or HNBR) and styrene-butadiene (SBR), blends of ethylene or propylene with EPDM, EPR, or NBR, or combinations thereof. The term "synthetic rubber" also encompasses materials that may alternatively be broadly classified as thermoplastic or thermoset elastomeric materials, such as polyurethanes, silicones, fluorosilicones, styrene-isoprene-styrene (SIS), and styrene-butadiene-styrene (SBS), as well as other polymers that exhibit rubber-like properties, such as plasticized nylon, polyolefins, polyesters, ethylene vinyl acetate, fluoropolymers, and polyvinyl chloride.

[0022] The volume ratio of the layered material particles to the total of the layered material particles and the elastomer material is preferably 20% by volume or more and 80% by volume or less. By setting the volume ratio of the layered material particles to 20% by volume or more, impedance can be easily reduced. The volume ratio is more preferably 25% by volume or more, and even more preferably 30% by volume or more. The higher the volume ratio of the layered material particles, the easier it is to reduce impedance. On the other hand, from the viewpoint of easily ensuring the strength of the electrode, the volume ratio of the layered material particles is preferably 80% by volume or less. The electrode of this embodiment is made of the conductive composite material, and the volume ratio of the layered material particles in the conductive composite material is preferably 20% by volume or more and 80% by volume or less.

[0023] (Metal Atoms) The layered material particles of this embodiment are preferably metal-atom-containing layered material particles containing metal atoms. By including metal atoms, the electric double layer capacity can be further increased and the impedance can be further reduced. Note that the metal atoms are preferably alkali metal atoms with monovalent cations rather than those with divalent cations. The metal atoms are preferably one or more of lithium, sodium, and potassium. The metal atoms are preferably present between the layers of MXene due to intercalation of the metal atoms. The metal atoms can be in the form of metal cations in MXene. That is, they can be present between the layers of MXene as monovalent metal cations.

[0024] The metal atoms are preferably present in an amount of 6.0×10 per 1 g of metal atom-containing layered material particles. －４ By containing at least 1 mol of the compound, the impedance can be further reduced while maintaining the adhesive strength with the substrate, etc., and this is preferable.

[0025] (Electrode Configuration) The electrode of this embodiment may be any electrode in which at least the contact surface with the object to be measured is formed of a conductive composite material containing predetermined layered material particles and an elastomer material. Several specific examples of the electrode of this embodiment are given below, but the electrode is not limited to these.

[0026] One preferred aspect of the electrode of this embodiment is a brush-shaped electrode having a support and a plurality of contact pins for contacting the object to be measured, wherein the contact surface with the object to be measured is at least a portion of the surface of at least one of the plurality of contact pins.

[0027] An example of the electrode of this embodiment is an electrode made of a conductive composite material. For example, as shown in the schematic cross-sectional view of Figure 2, a brush-shaped electrode 40a having an elastomer material with MXene dispersed throughout is exemplified. The volume ratio of the layered material particles in the conductive composite material is preferably 20% by volume or more and 80% by volume or less.

[0028] The electrode of this embodiment may have a substrate containing carbon and an elastomer material. Examples of substrates containing carbon and an elastomer material include those made of carbon and an elastomer material, or those made essentially of carbon and an elastomer material, with other components contained in an amount of, for example, 5% by volume or less, or even 1% by volume or less. The volume ratio of carbon in the substrate is preferably 20% by volume or more and 60% by volume or less, more preferably 20% by volume or more and 40% by volume or less, and even more preferably 20% by volume or more and 35% by volume or less. The mass ratio of carbon in the substrate is preferably 35% by volume or more and 45% by volume or less.

[0029] The electrode of this embodiment further has a substrate portion containing carbon and an elastomer material, and it is preferable that the volume ratio of carbon in the substrate portion is 20 volume % or more and 60 volume % or less, and that the volume ratio of layered material particles in the conductive composite material is 20 volume % or more and 80 volume % or less.

[0030] As another example of an electrode according to this embodiment, an electrode having a substrate portion made of carbon and an elastomer material is shown in FIGS. 3 to 5 . These are schematic cross-sectional views of electrodes 40 b, 40 c, and 40 d, each of which has a portion 41 made of a conductive composite material and a substrate portion 43 made of carbon and an elastomer material. For example, as shown in FIGS. 3 to 5 , a brush-shaped electrode may be used, which has a support 45 and a plurality of contact pins 47 for contacting the object to be measured. The portion that includes the contact surface with the object to be measured is a brush-shaped electrode 41, where at least a portion of the surface of the contact pins 47 (the tips in FIGS. 3 and 5 , and the surface of the tips in FIG. 4 ) is made of a conductive composite material. In FIG. 5 , the tips of the contact pins 47 are made of a conductive composite material 41, which is a porous material made of carbon and an elastomer material impregnated with MXene.

[0031] Although not shown, the tip of the contact pin 47 may be porous in the electrode made of the conductive composite material of Figure 2. In this embodiment, the porous tip of the contact pin may or may not be impregnated with MXene.

[0032] 3 to 5, the tips of all the contact pins are formed from a conductive composite material, but this is not a limitation, and it is sufficient that at least one of the multiple contact pins has a portion formed from a conductive composite material. In addition, in FIGS. 3 to 5, the support 45 and the portion of the contact pin 47 other than the portion 41 formed from the conductive composite material constitute a base material portion made from carbon and an elastomer material, but this is not a limitation. For example, a conductive material other than carbon may be used instead of the carbon.

[0033] The conductive composite material preferably has a thickness of 1 μm or more in the depth direction from the contact surface with the object to be measured. For example, as shown in FIG. 4 , a preferred embodiment of the conductive composite material is a thickness of 1 μm or more in the depth direction from the surface of a portion of the contact pin 47, which is the contact surface with the object to be measured. The thickness may be, for example, 10 μm or more, or even 50 μm or more. However, if the thickness is too thick, the surface of the electrode is prone to peeling, so it is preferably 1 mm or less. The electrode of this embodiment further has a substrate containing carbon and an elastomer material, and the volume ratio of carbon in the substrate is 20% by volume or more and 60% by volume or less, and the conductive composite material preferably has a thickness of 1 μm or more in the depth direction from the contact surface with the object to be measured.

[0034] The volume ratio of the layered material particles in the conductive composite material is preferably 20% by volume or more and 80% by volume or less. In brush-shaped electrodes such as those shown in Figures 3 to 5, the volume ratio of carbon in the substrate is preferably 20% by volume or more and 60% by volume or less. Furthermore, in brush-shaped electrodes such as those shown in Figures 3 to 5, the volume ratio of the layered material particles in the conductive composite material is preferably 20% by volume or more and 80% by volume or less.

[0035] Another preferred embodiment of the electrode of this embodiment is a disk-shaped electrode, in which the contact surface with the object to be measured is at least a portion of the circular surface of the disk. Schematic cross-sectional views of disk-shaped electrodes are shown in FIGS. 6 and 7. FIG. 6 shows an electrode 50a having a portion 41 formed of a conductive composite material, in which MXene is dispersed throughout an elastomer material. FIG. 7 shows a disk-shaped electrode 50b having a portion 41 formed of a conductive composite material and a substrate portion 43 made of carbon and an elastomer material. In FIG. 7, the circular surface including the contact surface with the object to be measured is formed of the conductive composite material. In a disk-shaped electrode such as that shown in FIG. 7, the volume ratio of carbon in the substrate portion is preferably 20% by volume or more and 60% by volume or less. In a disk-shaped electrode such as that shown in FIGS. 6 and 7, the volume ratio of layered material particles in the conductive composite material is preferably 20% by volume or more and 80% by volume or less.

[0036] Another preferred embodiment of the electrode of this embodiment is an electrode further comprising a silver / silver chloride electrode portion. Schematic cross-sectional views of electrodes further comprising a silver / silver chloride electrode portion are shown in Figures 8 to 11.

[0037] In one preferred embodiment, the electrode according to this embodiment comprises a portion formed of a conductive composite material, a substrate, and a silver / silver chloride electrode portion. One embodiment of the electrode according to this embodiment comprises a silver / silver chloride electrode portion disposed on at least a portion of the surface of the substrate, and a portion formed of a conductive composite material, for example, as a conductive film, disposed on at least a portion of the surface of the silver / silver chloride electrode portion exposed to the external environment. For example, as shown in the schematic cross-sectional view of FIG. 8 , an electrode 20 a may be provided, in which a silver / silver chloride electrode portion 23 is disposed on the surface of an electrode substrate 21, and a portion (conductive film) 25 formed of a conductive composite material is disposed on the surface of the silver / silver chloride electrode portion 23. As shown in FIG. 8 , the substrate has a tip and a longitudinal direction, the silver / silver chloride electrode portion 23 is disposed on the surface of the tip and side portions of the substrate, and the portion (conductive film) 25 formed of a conductive composite material is disposed on at least about 50% of the surface of the silver / silver chloride electrode portion 23 exposed to the external environment.

[0038] Another embodiment of the electrode according to the present invention is an electrode in which a portion (conductive film) formed of a conductive composite material is disposed on at least a portion of the surface of a substrate, and a silver / silver chloride electrode portion is disposed on at least a portion of the surface of the portion (conductive film) formed of the conductive composite material that is exposed to the external environment. One example is an electrode 20b, as shown in the schematic cross-sectional view of Figure 9, in which a portion (conductive film) 25 formed of a conductive composite material is disposed on the surface of an electrode substrate 21, and a silver / silver chloride electrode portion 23 is disposed on the surface of the portion (conductive film) 25 formed of the conductive composite material. As shown in Figure 9, an example is an electrode in which the substrate has a tip and a longitudinal direction, the portion (conductive film) 25 formed of the conductive composite material is disposed on a surface including the tip of the substrate, and the silver / silver chloride electrode portion 23 is disposed on at least about 50% of the surface of the portion (conductive film) 25 formed of the conductive composite material that is exposed to the external environment.

[0039] As a modification of Fig. 8, there is an electrode 20c, in which the proportion of the silver / silver chloride electrode portion 23 disposed on the surface of the electrode substrate 21 is smaller than that of Fig. 8, as shown in the schematic cross-sectional view of Fig. 10. As shown in Fig. 10, an example of an electrode is one in which the substrate has a tip and a longitudinal direction, the silver / silver chloride electrode portion 23 is disposed on the surface including the tip of the substrate, and a portion (conductive film) 25 formed of a conductive composite material is disposed on the entire surface of the silver / silver chloride electrode portion 23 exposed to the external environment. An example of an electrode of this embodiment is a contact pin, for example, in which the substrate has a tip and a longitudinal direction as shown in Fig. 10, the silver / silver chloride electrode portion 23 is configured only in the tip region 27 of the contact pin, and a portion (conductive film) 25 formed of a conductive composite material is disposed so as to cover the entire surface of the silver / silver chloride electrode portion 23 exposed to the external environment. In this embodiment, when used as a biosensing electrode, for example, the surface that comes into contact with the skin is a portion (conductive film) formed of a conductive composite material, resulting in excellent biocompatibility. Furthermore, as shown in FIG. 10 , by reducing the proportion of the silver / silver chloride electrode portion 23 in the electrode and covering the silver / silver chloride electrode portion 23 with a portion (conductive film) 25 formed from a conductive composite material, deterioration of the silver / silver chloride electrode portion 23 is suppressed, and it is thought that the life of the electrode can be extended.

[0040] In the electrode according to this embodiment, as shown in FIG. 8 and other figures, it is preferable that the silver / silver chloride electrode portion and the conductive film are in direct contact at least in part.

[0041] Another aspect of the electrode according to this embodiment is a brush-shaped electrode having a support and a plurality of contact pins for contacting the measured object, in which the silver / silver chloride electrode portion is disposed on at least a portion of the surface of the base material, including the tips of the contact pins, and a portion (conductive film) formed of the conductive composite material is disposed on at least a portion of the surface of the silver / silver chloride electrode portion that is exposed to the external environment. For example, as shown in Fig. 11, a brush-shaped electrode 30 having a plurality of contact pins 33 connected to a support 31 can be exemplified, and each of the plurality of contact pins 33 can have any of the aspects shown in Figs. 8 to 11 described above.

[0042] 2 to 11 are explanatory diagrams for ease of understanding, and the shapes, sizes, and relative size ratios of the conductive composite material portion, substrate portion, and silver / silver chloride electrode portion in these figures, as well as the number, spacing, and arrangement of contact pins, may differ from those of an actual electrode. Furthermore, while the electrodes according to this embodiment have been described using the above drawings, the electrodes according to this embodiment are not limited to the forms shown in the above drawings. For example, the cross section of the contact pins of a brush-shaped electrode may be not only rectangular as shown in the above drawings, but also tapered triangular or tapered trapezoidal. Furthermore, the tip of the contact pin may be flat or convexly curved.

[0043] For example, when contacting a dry EEG electrode with hair, a brush-shaped electrode, like a hair-melting brush, as shown in Figure 2 is preferable. On the other hand, flat electrodes, such as those shown in Figure 6, are also suitable for areas without hair, such as the forehead or around the ears. For example, the electrode of this embodiment, which can be used by contacting the above-mentioned areas, contains a soft elastomer material to prevent pain on the scalp. Since the elastomer material itself has neither conductivity nor biosignal sensing capabilities, dispersing MXene, as described above, can provide conductivity and biosignal sensing capabilities. To further enhance biosignal sensing sensitivity, it is preferable for the MXene to contain multilayer MXene, which has a multilayer structure. The inclusion of multilayer MXene is preferable because it allows sensing capabilities to be exerted in areas of the multilayer structure that are not in contact with the elastomer material.

[0044] [Method for Producing Electrode] The electrode according to this embodiment can be produced by, for example, the method described below. However, the method for producing the electrode according to this embodiment is not limited to this embodiment. (a) A compound represented by the following formula: M m AX n(b) preparing a precursor represented by the formula: (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; A is at least one Group 12, 13, 14, 15, or 16 element; n is 1 or more and 4 or less; and m is greater than n and 5 or less; － (c) performing an etching treatment to remove at least some of the A atoms from the precursor using an etching solution containing the compound (a), (b) washing the etched product obtained by the etching treatment with water to obtain layered material particles, and (d) molding a mixture of the layered material particles and an elastomer material to form at least a part of an electrode. This manufacturing method makes it possible to manufacture an electrode with low impedance.

[0045] 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, and is represented by the following formula: M ｍ AX ｎ (wherein M is at least one metal of Groups 3, 4, 5, 6, and 7, 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, and 16; n is 1 or more and 4 or less; and m is greater than n and 5 or less).

[0046] The above M, X, n, and m are as explained 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, can 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.

[0047] The MAX phase is M ｍ X ｎ(each X may have a crystal lattice in which it is located in an octahedral array of M) and a layer composed of A atoms is located between them. In the MAX phase, typically when m=n+1, one layer of X atoms is arranged between each of the n+1 layers of M atoms (these are collectively referred to as "M ｍ X ｎ The repeating unit has a layer of A atoms (also referred to as an "A atom layer") arranged as the next layer after the n+1th layer of M atoms, but is not limited thereto.

[0048] The MAX phase can be produced by a known method. For example, TiC powder, Ti powder, and Al powder are mixed in a ball mill, and the resulting mixed powder is sintered in an Ar atmosphere to obtain a sintered body (a block of the MAX phase). The sintered body is then pulverized with an end mill to obtain the powdered MAX phase for the next step.

[0049] ・Process (b) F － An etching treatment is performed to remove at least a part of the A atoms from the precursor using an etching solution containing the compound.

[0050] The A atoms (and possibly some of the M atoms) are selectively etched (removed and possibly layer separated) from the MAX phase, thereby removing the A atom layer (and possibly some of the M atoms) to expose the 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.

[0051] The etching is carried out by F － For example, a method using a mixed solution of lithium fluoride and hydrochloric acid, or a method using hydrofluoric acid may be used.

[0052] When metal atom-containing layered material particles are obtained, the etching solution may contain a metal compound containing a monovalent metal ion, and an intercalation treatment of the monovalent metal ion may be performed 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 monovalent metal ions 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 monovalent metal ions in the etching solution is preferably 10% by mass or less, and more preferably 1% by mass or less.

[0053] Step (c): The etched product is washed with water to obtain layered material particles. After the etching, any suitable post-treatment (e.g., ultrasonic treatment, handshaking, or automatic shaking) may be used to promote layer separation of MXene (delamination, separating multilayer MXene into single-layer MXene). Note that delamination is not preferred when obtaining multilayer MXene as the multilayer material particles. Furthermore, ultrasonic treatment can cause MXene to be destroyed due to excessive shear force. Therefore, when obtaining two-dimensional MXene with a larger aspect ratio (preferably single-layer MXene) is desired, it is preferred to apply an appropriate shear force using a handshaking or automatic shaker.

[0054] For the purpose of separating the layers of MXene and obtaining metal atom-containing layered material particles, the following intercalation treatment and delamination may be further carried out.

[0055] (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 ions, sodium ions, and potassium ions, copper ions, silver ions, and gold ions. Examples of the metal compound containing a monovalent metal ion include ionic compounds in which the above metal ions are bonded to cations. Examples include iodides, phosphates, sulfide salts including sulfates, nitrates, acetates, and carboxylates of the above metal ions. As described above, lithium ions are preferred as the monovalent metal ion, and metal compounds containing lithium ions are preferred as metal compounds containing lithium ions, more preferably ionic compounds of lithium ions, and even more preferably one or more of iodides, phosphates, and sulfide salts of lithium ions. If lithium ions are used as the metal ion, it is thought that water hydrated with lithium ions has the most negative dielectric constant, making it easier to form a monolayer.

[0056] The content of the metal compound containing a monovalent metal ion in the formulation for intercalation treatment of a monovalent metal ion is preferably 0.001% by mass or more. The content is more preferably 0.01% by mass or more, and even more preferably 0.1% by mass or more. On the other hand, from the viewpoint of dispersibility in the solution, the content of the metal compound containing a monovalent metal ion is preferably 10% by mass or less, more preferably 1% by mass or less.

[0057] (Delamination) Delamination may be performed using the intercalation-treated product obtained by intercalation. For example, delamination may involve centrifuging the intercalation-treated product, discarding the supernatant, and then washing the remaining precipitate with water. The conditions for the delamination process 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. This process may be repeated once or more, preferably twice or more, but not more than 10 times, to obtain a supernatant containing single-layered and / or few-layered MXene as the delamination-treated product. Alternatively, the supernatant may be centrifuged, and the resulting supernatant may be discarded to obtain a single-layered and / or few-layered MXene-containing clay as the delamination-treated product. When obtaining multilayered MXene as multilayered material particles, it is preferable not to perform delamination.

[0058] (Powdering) The slurry that has been subjected to the steps of intercalation treatment and delamination treatment can be freeze-dried to obtain MXene powder.

[0059] MXene exhibits lower AC impedance than conventional materials. To maintain the conductivity of MXene, it is best to use it without drying it from the state in which it is dispersed in an aqueous slurry. The reason for this is that drying causes the MXene flakes to aggregate and become disorganized. However, the contact impedance decreases the larger the area of ​​the MXene surface that is in contact with an electrolyte such as human sweat. Therefore, from the perspective of reducing contact impedance, it is better to have a structure in which the arrangement of the MXene flakes is disorganized and the electrolyte can easily access them. Therefore, for example, in electrode applications such as bioelectrodes, MXene can be used in a dry powder state, and in some cases, it is even better to use it in a dry powder state.

[0060] Step (d) is the molding of the mixture of layered material particles and elastomer material to form at least a portion of an electrode. To mix the MXene particles and elastomer material and mold them into the shape of an electrode or substrate, an elastomer extrusion machine is used, for example. The MXene and elastomer material are introduced into a hopper, and the raw materials are heated while being transported, melted, kneaded, and pressurized. A mold for a brush-shaped electrode, such as that shown in Figure 2, or a disk-shaped electrode, such as that shown in Figure 6, is then set, and extrusion molding is performed to obtain a brush-shaped electrode, such as that shown in Figure 2, or a disk-shaped electrode, such as that shown in Figure 6.

[0061] Alternatively, the following electrode manufacturing method can be used. Specifically, to mix carbon and an elastomer material and mold them into the shape of an electrode or substrate, for example, an elastomer extruder is used. The carbon and elastomer material are introduced into a hopper, and the raw materials are heated while being conveyed, melted, kneaded, and pressurized. A mold for a brush-shaped electrode such as that shown in FIG. 2 or a mold for a disk-shaped electrode such as that shown in FIG. 6 is set, and extrusion molding is performed to first obtain a brush-shaped electrode such as that shown in FIG. 2 or a disk-shaped electrode such as that shown in FIG. 6. The tips of the contact pins of the brush-shaped electrode such as that shown in FIG. 2 or the circular surface of the disk-shaped electrode such as that shown in FIG. 6 are then immersed (e.g., for 5 to 30 minutes) in a mixture of MXene particles and an elastomer material heated to, for example, 200°C, thereby melting the surfaces of the electrode contact pins and obtaining an electrode such as that shown in FIG. 4 or FIG. 7, which includes a portion formed of a conductive composite material composed of MXene particles, carbon, and an elastomer material. The thickness of the conductive composite material can be changed by changing the immersion time. By immersing for a long time, the conductive composite material is sufficiently immersed, and an electrode as shown in FIG. 3 can be obtained.

[0062] 5, a brush-shaped electrode made of carbon and an elastomer material can be fabricated, and the tip of the contact pin can be immersed in an inorganic acid, for example, to form voids and make it porous. The tip of the electrode (e.g., a soft electrode) can then be impregnated with an MXene slurry by capillary action and dried, resulting in an electrode in which MXene is dispersed within the pores, forming a conductive composite material exhibiting lower contact impedance on the surface that comes into contact with the object to be measured (e.g., a living organism).

[0063] The method for producing an electrode having a silver / silver chloride electrode part of FIGS. 8 to 11 includes the following steps: - using a conductive composite material, forming a film containing a conductive composite material on at least a part of the surface (surface exposed to the external environment) of a silver / silver chloride electrode part formed on the surface of a substrate part; or - using the conductive composite material, forming a film containing a conductive composite material on at least a part of the surface of a substrate part, and then forming a silver / silver chloride electrode part on at least a part of the surface (surface exposed to the external environment) of the film containing particles of a two-dimensional material.

[0064] The layered material particles and the elastomer material can be stirred to obtain a conductive composite material using a dispersing device such as a homogenizer, a propeller stirrer, a thin film rotary stirrer, a planetary mixer, a mechanical shaker, or a vortex mixer.

[0065] Drying after molding may be performed under mild conditions such as natural drying (typically, placing in an air atmosphere at room temperature and normal pressure) or air drying (blowing air), or under relatively active conditions such as hot air drying (blowing heated air), heat drying, and / or vacuum drying. In this embodiment, "drying" refers to removing any liquid medium that may be present in the precursor. The drying may be performed, for example, at a temperature of 400°C or less using a normal pressure oven or a vacuum oven. For example, drying may be performed at a temperature of 30°C to 200°C for 30 minutes to 24 hours.

[0066] Although the electrodes of the present disclosure have been described in detail above, various modifications are possible. It should be noted that the electrodes of the present disclosure may be manufactured by a method different from the manufacturing method in the above-described embodiment.

[0067] The present disclosure will be described in more detail below with reference to examples. The present disclosure is not limited to the following examples, and can be implemented by making appropriate modifications within the scope of the above-mentioned and below-mentioned aims, and all such modifications are included in the technical scope of the present disclosure.

[0068] Example 1 1. Preparation of MXene Layered material particles (MXene particles) were first obtained by sequentially carrying out the following steps, as detailed below: (1) preparation of a precursor (MAX), (2) etching of the precursor, (3) cleaning after etching, (4) intercalation of Li, (5) cleaning after the intercalation treatment, and (6) powderization.

[0069] (1) Preparation of Precursor (MAX) TiC powder, Ti powder, and Al powder (all manufactured by Kojundo Chemical Laboratory Co., Ltd.) were mixed in a molar ratio of 2:1:1 in a ball mill containing zirconia balls for 24 hours. The resulting mixed powder was sintered at 1350°C for 2 hours in an Ar atmosphere. The resulting sintered body (block-shaped MAX) was pulverized with an end mill to a maximum size of 40 μm or less. This resulted in the preparation of TiC powder as a precursor (powder-shaped MAX). ３ AlC ２ particles were obtained.

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

[0071] (3) Post-etching cleaning The above slurry was divided into two 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) stirring by hand shaking, (iii) centrifuging at 3500 G for 5 minutes, and (iv) removing the supernatant. These steps (i) to (iv) were repeated 10 times. Finally, centrifugation at 3500 G for 5 minutes was performed to remove Ti. ３ C ２ T ｓ - Water medium clay was obtained.

[0072] (4) Li intercalation Ti prepared by the above method ３ C ２ T ｓ Li intercalation was carried out on the clay using a water medium, using LiCl as the Li-containing compound, and stirring at 20°C to 25°C for 12 hours according to the Li intercalation conditions below. The detailed conditions for Li intercalation are as follows: (Li intercalation conditions) Ti ３ C ２ T ｓ - Water medium clay (MXene after washing): solid content 0.75 g LiCl: 0.75 g Intercalation container: 100 mL Eye Boy Temperature: 20 ° C or higher and 25 ° C or lower (room temperature) Time: 12 hours Stirrer rotation speed: 800 rpm

[0073] (5) Washing after intercalation The slurries obtained after intercalation were transferred to centrifuge tubes, (i) 40 mL of pure water was added, (ii) centrifuged at 3500 G using a centrifuge, and (iii) the supernatant was separated and removed. These steps (i) to (iii) were repeated five times to remove excess Na, and Li-intercalated MXene clay was obtained as the intercalation-treated product.

[0074] (6) Powdering The intercalation-treated product was divided into appropriate portions in petri dishes and frozen at −18° C. or below, and then dried in a freeze dryer for 24 hours or more to obtain a powder (MXene powder).

[0075] 2-1. Fabrication of an electrode with MXene dispersed throughout The MXene powder obtained in (6) above and chips of the elastomer material EPDM were weighed and dry-mixed to obtain a mixture so that the MXene content (MXene volume ratio) in the mixture was the value shown in Tables 1 and 2. This mixture was placed in an injection molding machine, and the elastomer material with the MXene powder dispersed therein was injected into a metal mold engraved with the shape of the rubber substrate. After injection, the molded product was extruded from the metal mold to obtain an electrode.

[0076] The MXene content (MXene volume ratio) in the mixture was changed as shown in Tables 1 and 2, and the shape of the rubber substrate in the metal mold was changed to a brush type or a flat type to obtain electrodes of Examples 1 to 12 in Tables 1 and 2. In Comparative Example 1 in Table 1 and Comparative Example 2 in Table 2, electrodes were formed in the same manner as in the Examples, except that MXene was not used.

[0077] 2-2. Preparation of an electrode with partially dispersed MXene First, chips of the elastomer material EPDM and powder of carbon black were mixed together to form a structure in which the carbon content was 35 to 45 wt % (specific gravity of carbon black: 1.8 g / cm ３ and the specific gravity of the elastomer material is 1 g / cm ３The materials were weighed out so that the volume ratio was approximately 23 to 31% by volume, and dry mixed to obtain a mixture. The mixture was placed in an injection molding machine, and the elastomer material with the carbon black powder dispersed therein was injected into a metal mold engraved with the shape of the rubber substrate. After injection, the material was extruded from the metal mold to obtain a conductive rubber substrate for forming the MXene dispersion section.

[0078] Next, chips of the elastomer material and the mixture of the dry-dispersed MXene powder obtained in (6) above were packed into a heated metal mold separate from that used for producing the conductive rubber substrate. After they were melted, the conductive rubber substrate was dipped into the mixture for 5 minutes, then pulled out and dried to obtain an electrode. The volume ratio of MXene in the partially dispersed portion was 50% by volume.

[0079] The dipping time was changed between 5 and 30 minutes to change the MXene thickness as shown in Tables 3 and 4, and the shape of the rubber substrate in the metal mold was changed to either a brush type or a flat type to obtain electrodes of Examples 13 to 22 in Tables 3 and 4. The electrodes of Comparative Examples 1 and 2 in Tables 3 and 4 were prepared in the same manner as the electrodes of Comparative Examples 1 and 2 in Tables 1 and 2.

[0080] 3. Measurement of Impedance Using the electrodes of Examples 1 to 22 and Comparative Examples 1 and 2, impedance was measured as follows to evaluate conductivity.

[0081] A Natus gel electrode (product number: 019-415200) was placed on a WetLab biosheet (product number: OHMTS01212) as a counter electrode and a reference electrode. The electrode prepared in "2-1. Preparation of an electrode with MXene dispersed throughout" or "2-2. Preparation of an electrode with MXene partially dispersed throughout" above was placed on the biosheet as a working electrode.

[0082] Impedance measurements were performed using a Metrohm electrochemical measuring device (product number: PGSTAT302N). Detailed conditions are shown below. For electroencephalograms, signals of around 10 Hz are basically important, but 0.1 Hz signals are also sometimes used. For example, the signal known as a slow potential, which is a clue to diagnosing epilepsy, is 0.1 Hz. Therefore, in the measurements, values ​​of 0.1 Hz and 10 Hz were used as representative values ​​for analysis. (Impedance measurement conditions) Frequency range: 0.1 to 10 ４ Hz Number of plots: 51 points Voltage: 10mVrms

[0083] The results of these measurements are shown in Table 1 for the total dispersion of MXene with a brush-type electrode shape, Table 2 for the total dispersion of MXene with a flat-type electrode shape, Table 3 for the partial dispersion of MXene with a brush-type electrode shape, and Table 4 for the partial dispersion of MXene with a flat-type electrode shape.

[0084]

[0085]

[0086]

[0087]

[0088] Tables 1 and 2 reveal the following: Whether the electrode shape is brush-type or flat-type, when a small amount of layered material particles (MXene particles) is dispersed throughout the electrode, the impedance is actually higher than when no layered material particles (MXene particles) are present. However, when the layered material particles are dispersed throughout the electrode, the impedance is significantly lower than in Comparative Examples 1 and 2 when the layered material particles are contained in an amount of 20% by volume or more.

[0089] Although the impedance of Examples 6 and 12 was sufficiently smaller than that of Comparative Examples 1 and 2, the mechanical strength was apparently insufficient for use as an electrode. From this, in consideration of ensuring the mechanical strength of the electrode, it can be said that when layered material particles are dispersed throughout the electrode, the content thereof is preferably 80% by volume or less.

[0090] Tables 3 and 4 also reveal the following: In both brush-type and flat-type electrodes, when the MXene thickness was extremely thin, less than 1 μm, the impedance was actually higher than when no layered material particles (MXene particles) were present. However, in the case of partial dispersion, when the MXene thickness was 1 μm or more, the impedance was significantly lower than in Comparative Examples 1 and 2.

[0091] This application claims priority from Japanese Patent Application No. 2023-208790, which is incorporated herein by reference.

[0092] The electrodes of the present disclosure may be used for any suitable purpose, and may be preferably used, for example, as biosignal sensing electrodes.

[0093] <1> An electrode, at least a contact surface with an object to be measured, formed of a conductive composite material containing layered material particles including one or more layers and an elastomer material, wherein the layer is represented by 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; and m is greater than n and 5 or less), and a modified or terminated T (T is at least one selected from the group consisting of a hydroxyl group, a fluorine atom, a chlorine atom, an oxygen atom, and a hydrogen atom) present on the surface of the layer body. <2> The electrode according to <1>, wherein the layered material particles are metal-atom-containing layered material particles containing metal atoms. <3> The electrode according to <2>, wherein the metal atoms are one or more of lithium, sodium, and potassium. <4> The electrode according to any one of <1> to <3>, wherein a volume ratio of the layered material particles to the conductive composite material is 20% by volume or more and 80% by volume or less. <5> The electrode according to any one of <1> to <4>, which is made of the conductive composite material, and the volume ratio of the layered material particles in the conductive composite material is 20 volume % or more and 80 volume % or less. <6> The electrode according to any one of <1> to <5>, which further includes a substrate containing carbon and an elastomer material, and the volume ratio of the carbon in the substrate is 20 volume % or more and 60 volume % or less, and the volume ratio of the layered material particles in the conductive composite material is 20 volume % or more and 80 volume % or less. <7> The electrode according to any one of <1> to <6>, which has a thickness of 1 μm or more in the depth direction from the contact surface with the object to be measured. <8> The electrode according to any one of <1> to <7>, which further includes a substrate containing carbon and an elastomer material, and the volume ratio of the carbon in the substrate is 20 volume % or more and 60 volume % or less, and the conductive composite material has a thickness of 1 μm or more in the depth direction from the contact surface with the object to be measured. <9> A brush-shaped electrode having a support and a plurality of contact pins for contacting an object to be measured, the electrode according to any one of <1> to <8>, wherein the contact surface with the object to be measured is at least a part of the surface of at least one of the plurality of contact pins. <10> The electrode according to any one of <1> to <9>, wherein the contact surface with the object to be measured is porous.<11> The electrode according to any one of <1> to <8>, which has a disk shape, and the surface that comes into contact with the object to be measured is at least a part of the circular surface of the disk. <12> The electrode according to any one of <1> to <11>, which further includes a silver / silver chloride electrode portion. <13> The electrode according to any one of <1> to <12>, which is a biosignal sensing electrode.

[0094] 1a, 1b Main layer (MmXn layer) 3a, 5a, 3b, 5b Modified or terminal T 7a, 7b MXene layer 10a, 10b MXene particle (layered material particle) 20a, 20b, 20c, 30, 40a, 40b, 40c, 40d, 50a, 50b Electrode 21, 31, 43 Base material portion (may include support) 23 Silver / silver chloride electrode portion 25 Conductive film 27 Tip region of contact pin 31, 45 Support 33, 47 Contact pin 41 Portion formed of conductive composite material

Claims

1. An electrode in which at least the contact surface with an object to be measured is formed of a conductive composite material including layered material particles having one or more layers and an elastomer material, wherein the layer is represented by the following formula: M m X n (wherein M is at least one metal of Group 3, 4, 5, 6, 7, and includes Ti; X is a carbon atom, a nitrogen atom, or a combination thereof; n is 1 or more and 4 or less; and m is greater than n and 5 or less), and a 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 a surface of the layer body.

2. The electrode according to claim 1, wherein the layered material particles are metal atom-containing layered material particles.

3. The electrode of claim 1 or 2, wherein the metal atom is one or more of lithium, sodium, and potassium.

4. The electrode according to any one of claims 1 to 3, wherein the volume ratio of layered material particles in the conductive composite material is 20 volume % or more and 80 volume % or less.

5. The electrode according to any one of claims 1 to 4, which is made of the conductive composite material, and the volume ratio of layered material particles in the conductive composite material is 20 volume % or more and 80 volume % or less.

6. The electrode according to any one of claims 1 to 5, further comprising a substrate containing carbon and an elastomer material, the volume ratio of carbon in said substrate being equal to or greater than 20 volume % and equal to or less than 60 volume %, and the volume ratio of layered material particles in said conductive composite material being equal to or greater than 20 volume % and equal to or less than 80 volume %.

7. An electrode according to any one of claims 1 to 6, wherein the conductive composite material has a thickness of 1 μm or more in the depth direction from the contact surface with the object to be measured.

8. The electrode according to any one of claims 1 to 7, further comprising a substrate containing carbon and an elastomer material, the volume ratio of carbon in said substrate being 20 volume % or more and 60 volume % or less, and said conductive composite material having a thickness of 1 μm or more in the depth direction from the contact surface with the object to be measured.

9. An electrode according to any one of claims 1 to 8, which is a brush-shaped electrode having a support and a plurality of contact pins for contacting an object to be measured, wherein the contact surface with the object to be measured is at least a portion of the surface of at least one of the plurality of contact pins.

10. The electrode according to any one of claims 1 to 9, wherein the surface that comes into contact with the object to be measured is porous.

11. The electrode according to any one of claims 1 to 10, wherein the electrode has a disk shape, and the contact surface with the object to be measured is at least a part of the circular surface of the disk shape.

12. The electrode of any one of claims 1 to 11, further comprising a silver / silver chloride electrode portion.

13. The electrode according to any one of claims 1 to 12, which is a biosignal sensing electrode.

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