Electrode, electrochemical device, layered material, electrode material for electrochemical device, and method for producing layered material

Abstract

An electrode 1a comprises a layered material 15. The layered material 15 includes a layer 15a and phosphonium 15p. The layer 15a includes a body 15b and an end 15c. The body 15b has a composition of MmXn. The end 15c is present on the surface of the body 15b. As regards the body 15b, M is at least one selected from the group consisting of Group 3 elements, Group 4 elements, Group 5 elements, Group 6 elements, and Group 7 elements. X includes at least one selected from the group consisting of carbon atoms and nitrogen atoms.

Description

Electrode, electrochemical device, layered material, electrode material for electrochemical device, and method for producing layered material

[0001] The present disclosure relates to electrodes, electrochemical devices, layered materials, electrode materials for electrochemical devices, and methods for producing layered materials.

[0002] In recent years, a material called MXene has been attracting attention. MXene is a two-dimensional (2D) material, and as described below, it is a layered material having one or more layers. MXene generally has the form of particles of such layered materials, and these particles can be in the form of powder, flakes, or sheets.

[0003] Currently, research is being conducted into the application of MXene to electrochemical capacitors. For example, Non-Patent Document 1 describes that when etching Al from Ti3AlC2 to produce two-dimensional titanium carbide, a type of MXene, the capacitance per volume increases when a solution of lithium fluoride and hydrochloric acid is used.

[0004] Michael Ghidiu et al., “Conductive two-dimensional titanium carbide 'clay' with high volumetric capacitance”, Nature volume 516, pages 78-81 (2014)

[0005] The present disclosure provides a novel electrode that is advantageous from the standpoint of improving the performance of electrochemical devices while comprising a predetermined layered material.

[0006] The electrode of the present disclosure comprises a layered material, the layered material comprising M m X n and a layer including a termination present on a surface of the body, the layer having a composition represented by the formula: and phosphonium, wherein in the body, M is at least one selected from the group consisting of Group 3 elements, Group 4 elements, Group 5 elements, Group 6 elements, and Group 7 elements, X includes at least one selected from the group consisting of carbon atoms and nitrogen atoms, n is 1 or more and 4 or less, and m is greater than n and 5 or less.

[0007] According to the present disclosure, a novel electrode can be provided that is advantageous from the viewpoint of improving the performance of electrochemical devices.

[0008] FIG. 1 is a side view schematically showing an example of an electrode. FIG. 2 is a view schematically showing an example of a layered material. FIG. 3 is a side view schematically showing another example of an electrode. FIG. 4 is a view schematically showing an example of an electrode material for electrochemical devices. FIG. 5 is a view schematically showing an example of an electrochemical device. FIG. 6 is a view schematically showing an example of an electricity storage device. FIG. 7 is a graph showing the results of X-ray diffraction (XRD) measurement of the layered materials and precursors according to Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3. FIG. 8 is a graph showing the results of XRD measurement of the layered material and precursor according to Example 2.

[0009] (Findings that form the basis of the present disclosure) As described in Non-Patent Document 1, it is conceivable to use MXene in electrodes of electrochemical devices such as electrochemical capacitors. In such electrochemical devices, for example, the capacitance per unit volume or unit mass of the electrode [F / cm 3 It is important that the specific capacitance (or F / g) is high. Therefore, the present inventors conducted extensive research into MXene-containing electrodes that can be used as electrodes for electrochemical devices. As a result, they discovered that electrodes with specific layered materials tend to improve the performance of electrochemical devices. Based on this new finding, the present inventors have completed the electrode of the present disclosure.

[0010] (Embodiments) Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments.

[0011] FIG. 1 is a side view schematically illustrating an example of an electrode according to the present disclosure. As shown in FIG. 1, an electrode 1a includes a layered material 15. FIG. 2 is a diagram schematically illustrating an example of the layered material. As shown in FIG. 2, the layered material 15 includes a layer 15a and a phosphonium 15p. The layer 15a includes a body 15b and a termination 15c. The body 15b includes M m X nThe termination 15c is present on the surface of the main body 15b. In the main body 15b, M is at least one selected from the group consisting of Group 3 elements, Group 4 elements, Group 5 elements, Group 6 elements, and Group 7 elements. X includes at least one selected from the group consisting of carbon atoms and nitrogen atoms. n is 1 or more and 4 or less. m is greater than n and 5 or less.

[0012] As described above, layered material 15 contains phosphonium 15p. Therefore, for example, when electrode 1a is used in an electrochemical device, a higher specific capacity is likely to be exhibited compared to when an electrode containing MXene that does not contain phosphonium or MXene that contains ammonium is used in the electrochemical device. The reason for this is unclear. The polarizability of phosphonium is relatively high. This is thought to affect the electronic state of terminal 15c and the surface of terminal 15c, making it easier for cations or anions contained in the electrolyte to be inserted into or removed from layered material 15. Therefore, when electrode 1a is used in an electrochemical device, the performance of the electrochemical device is likely to be improved.

[0013] The terminus 15c is not limited to a specific atom or atomic group as long as it can form the layer 15a together with the main body 15b. The terminus 15c includes, for example, an atom having an electronegativity greater than that of M. In this case, the terminus 15c is likely to exist in a desired state on the surface of the main body 11. Examples of atoms having an electronegativity greater than that of M include hydrogen atoms, oxygen atoms, halogen atoms, chalcogen atoms, nitrogen atoms, phosphorus atoms, carbon atoms, and antimony atoms. The electronegativity is based on Pauling's definition.

[0014] The termination 15c contains at least one selected from the group consisting of, for example, a hydroxyl group, a hydrogen atom, a halogen atom, a chalcogen atom, an amino group, a phosphorus atom, and an antimony atom, which makes it easier to adjust the surface state of the layer material 15 to a desired state.

[0015] When the atom or atomic group forming the terminal 15c is represented by T, the layer 15a is m X n T sThe composition is as follows: s is an arbitrary number.

[0016] In the main body 15b, the arrangement of M and X is not limited to a specific arrangement. For example, in the main body 15b, M is arranged at the vertices of an octahedron to form an octahedron array, which is an arrangement of multiple edge-sharing octahedrons. In addition, X is arranged inside each octahedron.

[0017] The phosphonium 15p may be a quaternary phosphonium, a tertiary phosphonium, a secondary phosphonium, or a primary phosphonium. The phosphonium 15p may be, for example, PR + In this cation, P is a phosphorus atom. In this cation, four Rs are bonded to the phosphorus atom. The four Rs are not limited to specific atoms or atomic groups as long as they can be bonded to the phosphorus atom. The four Rs may be the same or different. All four Rs may be the same, or only two or three of the four Rs may be the same, or all four Rs may be different. The four Rs may contain cationic functional groups. Preferably, the four Rs do not contain anionic functional groups.

[0018] For example, at least two of the four Rs have a meta-position substituent constant σ of 0.00 or less. m In this case, the performance of the electrochemical device is likely to be improved. R has a substituent constant σ of 0.00 or less. m Therefore, at least two of the four R in the above cation have a substituent constant σ of 0.00 or less. m It is considered that when the phosphonium 15p has a substituent constant σ, the repulsive force acting between the phosphonium 15p and the cations contained in the electrolyte tends to be small, and the cations contained in the electrolyte tend to be inserted into the layered material 15. m is the meta-position substituent constant defined according to Hammett's rule.

[0019] In the above cation, the four Rs may be the same or different atoms or atomic groups selected from the group consisting of, for example, hydrogen atoms, halogen atoms, hydrocarbon groups, amino groups, and alkoxy groups. In this case, the interaction between phosphonium 15p and the cations or anions contained in the electrolyte is easily adjusted to a desired state, and when electrode 1a is used in an electrochemical device, the performance of the electrochemical device is likely to be improved. The above hydrocarbon groups, amino groups, and alkoxy groups may optionally have at least one selected from the group consisting of substituents and heteroatoms.

[0020] The hydrocarbon group and alkoxy group may be linear, branched, or cyclic. The hydrocarbon group may be an aryl group or an aliphatic functional group. Examples of the aliphatic functional group are an alkyl group, an alkenyl group, and an alkynyl group. The number of carbon atoms in the hydrocarbon group and alkoxy group is not limited to a specific value and may be 1 to 30, 1 to 16, or 4 to 16.

[0021] The substituents that the hydrocarbon group, amino group, and alkoxy group may optionally have may be, for example, a functional group, an aryl group, an aliphatic functional group, or a heterocycle. The heteroatoms that the hydrocarbon group, amino group, and alkoxy group may optionally have may be B, N, O, F, Si, P, S, Cl, Br, or I, or may form a heterocycle. The number of substituents and heteroatoms in the hydrocarbon group, amino group, and alkoxy group is not limited to a specific value and may be 1 to 10, 1 to 3, or 1.

[0022] The four Rs in the above cations are preferably aliphatic functional groups which may optionally have a substituent and a heteroatom, which tends to improve the performance of electrochemical devices.

[0023] The four Rs in the above cation are preferably alkyl groups which may optionally have a substituent and a heteroatom, which tends to improve the performance of the electrochemical device.

[0024] The four Rs in the above cation are preferably unsubstituted alkyl groups, which tends to further improve the performance of the electrochemical device.

[0025] The four R groups in the above cation are preferably butyl groups, which tends to improve the performance of electrochemical devices.

[0026] Desirable examples of phosphonium 15p include tetrabutylphosphonium, tetraethylphosphonium, tetramethylphosphonium, tributylmethylphosphonium, tributylethylphosphonium, triethylbutylphosphonium, triethylmethylphosphonium, trimethylbutylphosphonium, trimethylethylphosphonium, dibutyldimethylphosphonium, dibutyldiethylphosphonium, and diethyldimethylphosphonium. In this case, the performance of the electrochemical device is likely to be improved.

[0027] The arrangement of the phosphonium 15p in the layered material 15 is not limited to a specific arrangement. The phosphonium 15p is arranged, for example, on the surface of the layer 15a. Preferably, the layered material 15 includes a plurality of layers 15a, and the phosphonium 15p is arranged between the plurality of layers 15a. This tends to further improve the performance of the electrochemical device.

[0028] In the main body 15b of the layered material 15, n and m are not limited to specific values ​​as long as n is 1 or more and 4 or less, and m is greater than n and 5 or less. n may be, for example, 1, 2, 3, or 4, or may be a value that satisfies the condition 1<n<2, 2<n<3, or 3<n<4. For example, if defects such as vacancies exist in the crystal that constitutes the main body 15b, n may not be an integer. m may, for example, satisfy the condition m=n+1.

[0029] In the main body 15b, preferably, n is 1 and m is 2, or n is 2 and m is 3. When the electrode 1a is used in an electrochemical device, the performance of the electrochemical device is likely to be improved.

[0030] In the main body 15b, M is not limited to a specific atom as long as it is at least one selected from the group consisting of Group 3 elements, Group 4 elements, Group 5 elements, Group 6 elements, and Group 7 elements. Preferably, M includes at least one selected from the group consisting of Ti and Mo. In this case, the performance of the electrochemical device is likely to be further improved. M may include only at least one selected from the group consisting of Ti and Mo, or may include elements other than Ti and Mo.

[0031] In the main body 15b, X may include a carbon atom. In this case, the performance of the electrochemical device is likely to be improved. X may include only carbon atoms, only nitrogen atoms, or both carbon atoms and nitrogen atoms.

[0032] In the main body 15b, X may further contain oxygen atoms. The content of oxygen atoms in X may be 20% to 80%, or 30% to 75%. Even if it is not intended that X contain oxygen atoms, oxygen atoms derived from the raw material may be included in X by substituting carbon atoms. The content of oxygen atoms in X may be less than 20%, 10% or less, 5% or less, 1% or less, or 0.1% or less, based on the number of atoms. X may not contain oxygen atoms.

[0033] As shown in Figure 2, the layered material 15 includes, for example, a plurality of layers 15a. In this case, the layered material 15 has, for example, a multilayer structure in which a plurality of layers 15a are stacked apart from one another. In this case, two adjacent layers 15a do not need to be completely separated from one another and may include a contacting portion. The layered material 15 may also have a single-layer structure consisting of only one layer 15a. The aggregate of the single-layer structure or multilayer structure formed by the layered material 15 may be particles such as powder and flakes.

[0034] The thickness of the layer 15a is not limited to a specific value. For example, the thickness of the layer 15a may be 0.5 nm or more and 5 nm or less, and may be 0.5 nm or more and 3 nm or less. This thickness may vary depending on the number of atomic layers formed by M.

[0035] The maximum dimension of the layer 15a in an in-plane direction perpendicular to the thickness direction of the layer 15a is not limited to a specific value, and may be, for example, 0.1 μm or more and 200 μm or less, or 1 μm or more and 40 μm or less.

[0036] When the layered material 15 has a multilayer structure, the distance d between the layers 15 a in the multilayer structure is not limited to a specific value, and may be, for example, 0.1 nm to 10 nm, or 0.1 nm to 5 nm, or about 1 nm.

[0037] When the layer material 15 has a multilayer structure, the maximum dimension of the layer material 15 in the in-plane direction perpendicular to the thickness direction of the layer 15 a is not limited to a specific value. The maximum dimension may be, for example, 0.1 μm or more and 100 μm or less, or 1 μm or more and 20 μm or less.

[0038] When the layered material 15 has a multilayer structure, cations other than phosphonium may be present between adjacent layers 15a in the thickness direction of the layers 15a. Examples of cations include protons (H + cations, such as alkali metal ions, alkaline earth metal ions, and quaternary ammonium ions. Anions or solvents coordinated with cations present between the layers 15a may also be present. Examples of anions and solvents coordinated with cations include halide ions, HO, and propylene carbonate.

[0039] When the layered material 15 has a multilayer structure, the number of layers 15a included in the layered material 15 is two or more, and may be 20 to 100,000, or 1,000 to 20,000. The thickness of the layered material 15 in the thickness direction of the layers 15a is not limited to a specific value. The thickness may be, for example, 0.1 μm to 200 μm, or 1 μm to 40 μm.

[0040] When the layered material 15 has a multi-layer structure, the number of layers 15a included in the layered material 15 may be six or less. In this case, the layered material 15 is referred to as a low-layer structure.

[0041] In the assembly of layered materials 15, for example, the majority of the assembly may be layered materials 15 and / or low-layer structures having a single layer structure. For example, 50% by volume or more of the assembly may be layered materials 15 and / or low-layer structures having a single layer structure.

[0042] The above dimensions and distances may be calculated by numerical averaging based on micrographs taken with a scanning electron microscope (SEM), a transmission electron microscope (TEM), an atomic force microscope (AFM), or the like. In this case, for example, the above dimensions and distances may be calculated by numerical averaging 40 or more pieces of data. Alternatively, the above dimensions and distances may be calculated as distances in real space calculated based on the position of the (002) plane in reciprocal lattice space in X-ray diffraction (XRD) measurements.

[0043] As shown in FIG. 1 , in electrode 1a, layer material 15 is disposed, for example, in contact with conductive substrate 12. Electrode 1a includes, for example, MXene-containing layer 11 containing layer material 15, with MXene-containing layer 11 having the surface shape of electrode 1a. MXene-containing layer 11 is disposed on conductive substrate 12. MXene-containing layer 11 may be composed essentially of layer material 15 alone. In MXene-containing layer 11, a conductive additive may be present between adjacent layers of layer material 15. The conductive additive may include, for example, at least one selected from the group consisting of carbon black, acetylene black, ketjen black, and carbon nanotubes. A binder may be present between adjacent layers of layer material 15. The binder may include, for example, a resin, including at least one selected from the group consisting of polytetrafluoroethylene, polyvinylidene fluoride, and styrene butadiene rubber.

[0044] The conductive substrate 12 is not limited to a specific substrate as long as its surface is conductive. The conductive substrate 12 may be a current collector, and examples of current collectors include aluminum foil and copper foil. The surface of the conductive substrate 12 may be smooth or may have an uneven surface.

[0045] Figure 3 is a schematic diagram showing another example of an electrode. Electrode 1a may be modified to electrode 1b shown in Figure 3. Electrode 1b is composed of only an MXene-containing layer 11. In this way, electrode 1b may have a single-layer structure containing layered material 15.

[0046] The shape of the electrode 1a or 1b is not limited to a particular shape, and the electrode 1a or 1b may be a plate, a rod, or a cylinder.

[0047] The density of the electrode 1a or 1b is not limited to a specific value. The density is, for example, 1.5 g / cm 3 Above, 2.0g / cm 3 or more, or 2.5 g / cm 3 or more, and preferably 3.0 g / cm 3 The density is more preferably 3.5 g / cm or more. 3 More preferably, it is 4.0 g / cm 3 More preferably, it is 4.5 g / cm 3 The density is, for example, 10 g / cm 3 The following is the result.

[0048] The thickness of the electrode is not limited to a specific value. The thickness is, for example, 3 μm or more, and may be 5 μm or more. The thickness is, for example, 500 μm or less.

[0049] The electrodes 1a and 1b are, for example, electrodes for electrochemical devices, and can be produced using, for example, an electrode material for electrochemical devices. The use of such an electrode material in an electrochemical device tends to improve the performance of the electrochemical device. FIG. 4 is a diagram schematically illustrating an example of an electrode material for electrochemical devices. As shown in FIG. 4, the electrode material for electrochemical devices 1k is, for example, an aggregate of layered materials 15. This aggregate is, for example, a powder of the layered materials 15. The electrode material for electrochemical devices 1k may be a mixture containing the layered materials 15. In addition to the layered materials 15, this mixture contains, for example, at least one selected from the group consisting of a conductive additive and a binder. The mixture may be a powder, a dispersion, or a slurry.

[0050] The method for producing the layered material 15 is not limited to a specific method. The method for producing the layered material 15 includes, for example, obtaining a layered material containing phosphonium using phosphonium hydroxide. In this case, the phosphonium 15p is likely to be arranged in a desired state in the layered material 15, and the performance of the electrochemical device is likely to be improved. The phosphonium hydroxide used for producing the layered material 15 may be used in the form of an aqueous solution. The layered material 15 can be produced, for example, by reacting the phosphonium hydroxide with the layer 15a.

[0051] The layer 15a is, for example, M m AX n The precursor can be synthesized by selectively etching A atoms from a precursor having the following composition: In the precursor composition, M collectively represents the metal atoms corresponding to M in the main body 15b of the layer 15a, and m and n correspond to m and n in the main body 15b, respectively. A is an element of Group 12, 13, 14, 15, or 16, and A may be at least one element selected from the group consisting of Al, Zn, Ga, In, Tl, Si, Ge, Sn, Pb, P, As, S, and Cd. A is preferably Al. This precursor is called MAX, and M m X n It has a crystal structure in which one layer composed of A atoms is arranged between two layers represented by M m X n In each layer, M is arranged at the vertices of the octahedron to form an octahedron array, which is an arrangement of multiple edge-sharing octahedrons. In addition, X is arranged inside each octahedron. In other words, M m X n Each layer of MAX has a crystal lattice in which M atoms are arranged to form an octahedron and X atoms are arranged inside the octahedron. The structure of MAX is not limited to a specific structure, but for example, when m = n + 1, it has a structure in which one layer of X atoms is arranged between (n + 1) M atomic layers. In addition, it has a repeating unit in which an A atomic layer is arranged adjacent to the n + 1 M atomic layer.

[0052] At MAX, the A atoms are selectively etched, removing the A atomic layer. This exposes M m X n The surface of the layer is modified with at least one atom selected from the group consisting of hydroxyl groups, hydrogen atoms, halogen atoms, chalcogen atoms, amino groups, phosphorus atoms, and antimony atoms, which are derived from the etching solution, thus forming termination 15c.

[0053] The etching solution used for selective etching of A atoms is, for example, fluoride ions F - The etching solution may be a mixture of lithium fluoride and hydrochloric acid or hydrofluoric acid. The selective etching of the A atoms may be performed using a molten salt of a Lewis acid such as CuCl, or may be performed using high-temperature, high-pressure HCl. The selective etching of the A atoms may be performed using a halogen gas such as Br and I, or may be performed using an organic solution in which halogens such as Br and I are dissolved.

[0054] Layered material 15 may be made from precursors other than MAX. For example, two M m X n The layered material 15 may be produced by selective etching of A atoms from a precursor having two or more layers of A atoms arranged between layers of A atoms.

[0055] After selectively etching the A atoms from a precursor such as MAX, treatments such as ultrasonication, handshaking, or shaking using an automatic shaker may be performed. These treatments can promote delamination of layers 15a in the layered material 15. This can result in, for example, a layered material 15 having a single-layer structure or a low-layer structure. For example, handshaking or shaking using an automatic shaker can impart a desired shear stress between the layers 15a in terms of separation of the layers 15a. Consider, for example, a case where the layered material 15 has a single-layer structure or a low-layer structure. In this case, the ratio of the dimension of the layered material 15 in the thickness direction of the layer 15a to the dimension of the layered material 15 in the in-plane direction of the layer 15a is small. Even in such cases, handshaking or shaking using an automatic shaker can impart a desired shear stress between the layers 15a in terms of separation of the layers 15a, making the layered material 15 less likely to break and more likely to maintain the desired size.

[0056] A portion of the A atoms derived from the precursor, such as MAX, may remain in the layered material 15. The amount of A atoms remaining in the layered material 15 is, for example, 10 mass % or less of the A atom content in the precursor, preferably 8 mass % or less, and more preferably 6 mass % or less. Depending on the application of the layered material 15, the amount of A atoms remaining in the layered material 15 may be more than 10 mass % of the A atom content in the precursor.

[0057] The layered material 15 may be produced by a method other than selective etching of A atoms from a precursor such as MAX. The layered material 15 may be produced, for example, by a method including heat treatment of a metal M, graphite, and a halide of M inside a sealed tube. The sealed tube may be, for example, a quartz tube. The layered material 15 may be produced by a method including chemical vapor deposition (CVD) using a metal M, a halide of M, and CH or N.

[0058] The electrode 1a or 1b can be produced, for example, by forming the electrode material for electrochemical devices 1k into a predetermined shape such as a film or a sheet. For example, a method including suction filtration can be applied to produce the electrode 1a or 1b. Alternatively, the electrode 1a or 1b may be produced using a coating method such as spray coating, bar coating, or dip coating.

[0059] Electrode 1a or 1b may be fabricated using a precursor of layered material 15 or a modified version of layered material 15. For example, coated particles are obtained by coating the surface of polymer particles such as polystyrene with layered material 15 in a solvent. The solvent is then removed to form an aggregate of coated particles into a film. Next, the polymer is removed by high-temperature treatment or the like, while forming hollow particles with the layered material 15 remaining in a shell shape. Electrode 1a or 1b may be fabricated in this manner. In this case, the performance of the electrochemical device is likely to be improved. For example, the Coulombic efficiency of the electrochemical device is likely to be increased.

[0060] The electrode 1a or 1b may be fabricated by forming a layer containing the layered material 15 on a conductive substrate 12, such as a current collector.

[0061] Fig. 5 is a diagram schematically illustrating an example of an electrochemical device. As shown in Fig. 5, the electrochemical device 2a includes the above-described electrode 1a. The electrochemical device 2a may also include the above-described electrode 1b. The electrochemical device 2a includes the electrode 1a or 1b, and therefore can exhibit high performance.

[0062] The electrochemical device 2a is not limited to a specific electrochemical device as long as it includes the electrode 1a or 1b. The electrochemical device 2a may be an electricity storage device, a fuel cell, or an electrolysis cell. Examples of electricity storage devices include a capacitor and a secondary battery.

[0063] When the electrochemical device 2a is an electricity storage device, the electrochemical device 2a includes, for example, a pair of electrodes, at least one of which is the electrode 1a or 1b.

[0064] Fig. 6 is a diagram schematically illustrating an example of an electricity storage device. The electricity storage device 2b shown in Fig. 6 is an electrochemical capacitor and includes a first electrode 3a and a second electrode 3b. The first electrode 3a is, for example, a positive electrode. The second electrode 3b is, for example, a negative electrode. In the electricity storage device 2b, the first electrode 3a and the second electrode 3b are arranged apart from each other in the electrolytic solution 4. At least one selected from the group consisting of the first electrode 3a and the second electrode 3b is the electrode 1a or 1b. With this configuration, the electricity storage device 2b is likely to exhibit a high specific capacitance.

[0065] The energy density stored in an electrochemical capacitor is generally (1 / 2) x CV 2 where C is the specific capacitance [F / cm 3 or F / g], and V is the operating potential range [V]. The unit of energy density is FV 2 / cm 3 or FV 2 On the other hand, the energy density stored in an electrochemical capacitor can generally be expressed by converting it into units of Wh / L or Wh / kg.

[0066] The specific capacitance C of either the positive or negative electrode of the electrochemical capacitor is measured using a half cell according to the three-electrode method. 3p [F / cm 3 In this case, the specific capacitance C of a full cell constructed using the electrode as both the positive and negative electrodes is f [F / cm 3 or F / g] is (1 / 4)C 3p It can be estimated to be equal to

[0067] The electrolyte solution 4 is not limited to a specific electrolyte solution. The electrolyte solution 4 is, for example, a nonaqueous electrolyte solution. In this case, the operating potential range of the electricity storage device 2b is likely to be large. A large operating potential range is advantageous from the viewpoint of increasing the energy density stored in the electricity storage device 2b. The electrolyte solution 4 may be an aqueous electrolyte solution. In this case, the operating potential range can be adjusted to 1.2 V or less to prevent electrolysis of water. In addition, the usable temperature range of the electricity storage device 2b can be adjusted to a temperature range (e.g., −40° C. to 80° C.) in which water, which is the solvent, exists stably in liquid form and can be prevented from freezing and vaporizing. On the other hand, when the electrolyte solution 4 is a nonaqueous electrolyte solution, there are fewer restrictions on the operating potential range and usable temperature range of the electricity storage device 2b compared to when the electrolyte solution 4 is an aqueous electrolyte solution.

[0068] 6 , in an electricity storage device 2b, an electrolyte solution 4 is contained inside a cell 5, and the inside of the cell 5 is divided by a separator 7 into a space in which a first electrode 3a is disposed and a space in which a second electrode 3b is disposed. The first electrode 3a and the second electrode 3b are electrically connected to terminals 6a and 6b disposed outside the cell 5, respectively.

[0069] The separator 7 is not limited to a specific separator as long as it does not hinder the movement of electrolyte ions contained in the electrolytic solution 4. The separator 7 is, for example, a dielectric film. Examples of the dielectric film include porous films of polyolefins such as polypropylene and polytetrafluoroethylene. The separator 7 may also contain glass fibers.

[0070] The material of the cell 5 is not limited to a specific material. The material of the cell 5 may be a metal material such as stainless steel, a resin material such as polytetrafluoroethylene, or other materials. The cell 5 may be sealed or open. A void may or may not exist inside the cell 5.

[0071] The first electrode 3 a and the second electrode 3 b may be arranged, for example, inside the cell 5, in a state in which a separator 7 is disposed between the first electrode 3 a and the second electrode 3 b, and a laminate including the first electrode 3 a, the separator 7, and the second electrode 3 b is wound.

[0072] As described above, at least one selected from the group consisting of the first electrode 3 a and the second electrode 3 b is the electrode 1 a or 1 b. At the electrode 1 a or 1 b, for example, electrons are exchanged with electrolyte ions contained in the electrolyte solution 4.

[0073] For example, only the first electrode 3a may be the electrode 1a or 1b. In this case, the second electrode 3b may be made of a carbon material such as activated carbon, carbon nanotubes, or graphene, or Li4Ti5O 12 etc. Only the second electrode 3b may be electrode 1a or 1b. In this case, the first electrode 3a may contain graphite, activated carbon, carbon nanotubes, etc. as electrode materials. When only the first electrode 3a or the second electrode 3b is electrode 1a or 1b, the electrodes other than electrode 1a or 1b may be composed essentially of electrode material alone, or may be configured in a state in which a binder is present between the electrode materials. The binder includes, for example, a resin. The binder includes, for example, at least one selected from the group consisting of polytetrafluoroethylene, polyvinylidene fluoride, and styrene butadiene rubber. Both the first electrode 3a and the second electrode 3b may be electrodes 1a or 1b.

[0074] Each of the first electrode 3 a and the second electrode 3 b may be configured as a free-standing film, or may have a configuration in which a film and / or membrane containing an electrode material is formed on a conductive substrate such as a current collector. The current collector is not limited to a specific current collector as long as it is conductive. The current collector includes, for example, a material such as stainless steel, aluminum, or an aluminum alloy.

[0075] The electrolytic solution 4 contains, for example, an electrolyte and a non-aqueous solvent. The electrolytic solution 4 may contain an electrolyte and an aqueous solvent, or may be an ionic liquid. The electrolyte is dissolved in a non-aqueous solvent or an aqueous solvent and exists as a cation or an anion.

[0076] The electrolytic solution 4 contains, as an electrolyte, for example, at least one cation selected from the following cation group and at least one anion selected from the following anion group. <Cation group> Sodium ion (Na + ), magnesium ions (Mg 2+ ), 1-ethyl-3-methylimidazolium ion (EMI + ), tributylmethylammonium ion (TrBMAm + ), tetrabutylammonium ion (TeBAm + ), tributylethylphosphonium ion (TrBEPh + ), tributylmethylphosphonium ion (TrBMPh + ), 1-butyl-1-methylpyrrolidinium ion (1B1MPy + ), 1-methyl-1-propylpyrrolidinium ion (1M1PPy + ), tetraethylammonium ion (Et4N+, TEA + ) Lithium ion (Li + ), and protons (H + ) <Anion group> Diethyl phosphate ion (DEPh ‐ ), bis(fluorosulfonyl)imide ion (FSI - ), perchlorate ion (ClO3O - ), bis(trifluoromethanesulfonyl)imide ion (TFSI - ), trifluoromethanesulfonate ion (Triflate - ), hexafluorophosphate ion (P-F6), tetrafluoroborate ion (B-F4), sulfate ion (SO4 2- ), chloride ions (Cl - ), and iodine ion (I - )

[0077] The non-aqueous solvent that can be contained in the electrolytic solution 4 is not limited to a specific non-aqueous solvent. The electrolytic solution 4 may contain, for example, at least one selected from the following solvent group. The non-aqueous solvent may contain only a single type of solvent, or may be a mixture of multiple types of solvents. <Solvent group> Propylene carbonate (PC), gamma butyrolactone (gBL), ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethoxyethane (DME), dimethyl carbonate (DMC), diethyl carbonate (DEC), and acetonitrile (AN).

[0078] The electrolytic solution 4 may contain, as needed, predetermined additives in addition to the solvent and electrolyte.

[0079] When the terminals 6a and 6b of the power storage device 2b are connected to a load, the power storage device 2b is discharged. On the other hand, when the terminals 6a and 6b of the power storage device 2b are connected to a power source, the power storage device 2b is charged.

[0080] Depending on the combination of the electrode material and the electrolyte solution 4, the electricity storage device 2b may be configured as a pseudocapacitor or a hybrid capacitor involving a Faraday reaction.

[0081] (Supplementary Note) From the above description, the following technology is disclosed. (Technology 1) A layered material is provided, and the layered material is M m X nAn electrode comprising: a body having a composition represented by the formula (I) and a layer including terminations present on the surface of the body; and phosphonium, wherein in the body, M is at least one selected from the group consisting of Group 3 elements, Group 4 elements, Group 5 elements, Group 6 elements, and Group 7 elements, X includes at least one selected from the group consisting of carbon atoms and nitrogen atoms, n is 1 or more and 4 or less, and m is greater than n and 5 or less. (Technology 2) The electrode according to Technology 1, wherein the terminations include atoms having an electronegativity greater than that of M. (Technology 3) The electrode according to Technology 1 or 2, wherein the terminations include at least one selected from the group consisting of hydroxyl groups, hydrogen atoms, halogen atoms, chalcogen atoms, amino groups, phosphorus atoms, and antimony atoms. (Technology 4) The electrode according to any one of Technology 1 to 3, wherein in the body, n is 1 and m is 2, or n is 2 and m is 3. (Technology 5) The electrode according to any one of Techniques 1 to 4, wherein in the main body, M includes at least one selected from the group consisting of Ti and Mo. (Technology 6) The electrode according to any one of Techniques 1 to 5, wherein in the main body, X includes a carbon atom. (Technology 7) The phosphonium is PR4 + The electrode according to any one of the techniques 1 to 6, wherein P in the cation is a phosphorus atom, and at least two of the four R in the cation have a meta-position substituent constant of 0.00 or less. (Technology 8) The phosphonium is a cation represented by PR4 +The electrode according to any one of Techniques 1 to 6, wherein P of the cation is a phosphorus atom, and four R of the cation are selected from the group consisting of a hydrogen atom, a halogen atom, a hydrocarbon group, an amino group, and an alkoxy group, and are the same or different from one another, and the hydrocarbon group, the amino group, and the alkoxy group may optionally have at least one selected from the group consisting of a substituent and a heteroatom. (Technology 9) The electrode according to Technique 8, wherein the four R of the cation are an aliphatic functional group optionally having at least one selected from the group consisting of a substituent and a heteroatom. (Technology 10) The electrode according to Technique 8, wherein the four R of the cation are an alkyl group optionally having at least one selected from the group consisting of a substituent and a heteroatom. (Technology 11) The electrode according to Technique 8, wherein the four R of the cation are unsubstituted alkyl groups. (Technology 12) The electrode according to Technique 8, wherein the four R of the cation are butyl groups. (Technology 13) The electrode according to any one of Technologies 1 to 12, wherein the layered material comprises a plurality of the layers, and the phosphonium is disposed between the plurality of layers. (Technology 14) The electrode according to any one of Technologies 1 to 13, wherein the layered material is disposed in contact with a conductive substrate. (Technology 15) An electrochemical device comprising the electrode according to any one of Technologies 1 to 14. (Technology 16) An electrochemical device according to Technology 15, comprising a first electrode and a second electrode, wherein the first electrode and the second electrode are disposed apart from each other in an electrolyte, and at least one selected from the group consisting of the first electrode and the second electrode is the electrode, and wherein the electrochemical device is capable of storing electricity. (Technology 17) M m X n a layer including a body having a composition of PR4 and a termination present on a surface of the body; +and a phosphonium cation represented by the formula: wherein in the main body, M is at least one selected from the group consisting of Group 3 elements, Group 4 elements, Group 5 elements, Group 6 elements, and Group 7 elements; X includes at least one selected from the group consisting of carbon atoms and nitrogen atoms; n is 1 or more and 4 or less; m is greater than n and 5 or less; in the cation, P is a phosphorus atom; and the four Rs of the cation satisfy at least one condition selected from the group consisting of (I) and (II) below. (I) The four Rs of the cation are aliphatic functional groups optionally having at least one selected from the group consisting of substituents and heteroatoms; (II) At least two of the four Rs of the cation have a meta-position substituent constant of 0.00 or less. (Technology 18) The layered material according to Technology 17, wherein the terminus includes an atom having an electronegativity greater than that of M. (Technology 19) The layered material according to Technology 17, wherein the terminus includes at least one selected from the group consisting of a hydroxyl group, a hydrogen atom, a halogen atom, a chalcogen atom, an amino group, a phosphorus atom, and an antimony atom. (Technology 20) The layered material according to any one of Technology 17 to 19, wherein, in the main body, n is 1 and m is 2, or n is 2 and m is 3. (Technology 21) The layered material according to any one of Technology 17 to 20, wherein, in the main body, M includes at least one selected from the group consisting of Ti and Mo. (Technology 22) The layered material according to any one of Technology 17 to 21, wherein, in the main body, X includes a carbon atom. (Technology 23) The layered material according to any one of Technology 17 to 22, wherein the four R of the cation are alkyl groups optionally having at least one selected from the group consisting of a substituent and a heteroatom. (Technology 24) The layered material according to any one of Techniques 17 to 22, wherein the four R of the cation are unsubstituted alkyl groups. (Technology 25) The layered material according to any one of Techniques 17 to 22, wherein the four R of the cation are butyl groups.(Technology 26) The layered material according to any one of Technologies 17 to 25, comprising a plurality of the layers, wherein the phosphonium is disposed between the plurality of layers. (Technology 27) An electrode material for an electrochemical device, comprising the layered material according to any one of Technologies 17 to 26. (Technology 28) A method for producing a layered material containing phosphonium using a phosphonium hydroxide, wherein the layered material is M. m X n A method for producing a layered material, comprising: a body having a composition represented by the formula (I) and a layer including a termination present on a surface of the body; and the phosphonium, wherein in the body, M is at least one selected from the group consisting of Group 3 elements, Group 4 elements, Group 5 elements, Group 6 elements, and Group 7 elements, X includes at least one selected from the group consisting of carbon atoms and nitrogen atoms, n is 1 or more and 4 or less, and m is greater than n and 5 or less. (Technology 29) A method for producing a layered material according to Technology 28, wherein the termination includes an atom having an electronegativity greater than that of M. (Technology 30) A method for producing a layered material according to Technology 28, wherein the termination includes at least one selected from the group consisting of a hydroxyl group, a hydrogen atom, a halogen atom, a chalcogen atom, an amino group, a phosphorus atom, and an antimony atom. (Technology 31) The phosphonium is PR4 + The method for producing a layered material according to any one of Techniques 28 to 30, wherein P in the cation is a phosphorus atom, and at least two of the four R in the cation have a meta-position substituent constant of 0.00 or less. (Technology 32) The phosphonium is a cation represented by PR4 +The method for producing a layered material according to any one of Techniques 28 to 31, wherein the cation is a cation represented by the formula: wherein P of the cation is a phosphorus atom, and four R of the cation are selected from the group consisting of a hydrogen atom, a halogen atom, a hydrocarbon group, an amino group, and an alkoxy group, and are the same or different from one another, and the hydrocarbon group, the amino group, and the alkoxy group may optionally have at least one selected from the group consisting of a substituent and a heteroatom. (Technology 33) The method for producing a layered material according to Technique 32, wherein the four R of the cation are aliphatic functional groups optionally having at least one selected from the group consisting of a substituent and a heteroatom. (Technology 34) The method for producing a layered material according to Technique 32, wherein the four R of the cation are alkyl groups optionally having at least one selected from the group consisting of a substituent and a heteroatom. (Technology 35) The method for producing a layered material according to Technique 32, wherein the four R of the cation are unsubstituted alkyl groups. (Technology 36) The method for producing a layered material according to Technique 32, wherein the four R of the cation are butyl groups.

[0082] The present disclosure will be described in more detail below with reference to examples. Note that the following examples are illustrative and the present disclosure is not limited to the following examples.

[0083] Example 1: TiC powder, Ti powder, and Al powder were mixed in a zirconia mortar to obtain a mixed powder according to Example 1. These powders were provided by Kojundo Chemical Laboratory Co., Ltd. The molar ratio of TiC:Ti:Al in the mixed powder according to Example 1 was 2:1:1. The mixed powder according to Example 1 was fired at 1400°C for 3 hours in an argon gas atmosphere to obtain a fired body (block) according to Example 1. The fired body according to Example 1 was pulverized in a zirconia mortar. Next, using zirconia balls with a diameter of 5 mm and a zirconia pot, the mixture was pulverized in a wet ball mill in H2O until the maximum particle size was 20 μm or less. In this way, a precursor powder according to Example 1 having a composition of Ti3AlC2 was obtained.

[0084] A LiF solution was obtained by dissolving 160 g of LiF in 2000 mL of HCl solution with a concentration of 9 mol / L. 100 g of the precursor powder according to Example 1 was added to this LiF solution and stirred at 40°C for 24 hours. Next, centrifugation and water washing were repeated multiple times until the pH reached 5 or higher. Subsequently, suction filtration was performed and the solution was vacuum dried at 80°C. This resulted in the formation of Ti3C2T s Thus, a powder of MXene according to Example 1 was obtained having the following composition: T represents an atom or functional group that terminates the layered material, and s is an arbitrary number.

[0085] 10 g of the MXene powder according to Example 1 was added to 300 mL of a 1 mol / L HCl solution and stirred for 1 hour at room temperature between 15°C and 28°C. Next, suction filtration was performed and the mixture was vacuum dried at 80°C. 1 g of the dried powder thus obtained was added to 100 mL of a 14% by mass aqueous solution of tetrabutylphosphonium hydroxide and stirred for 1 hour at room temperature between 15°C and 28°C. Next, water washing and suction filtration were repeated multiple times, and the mixture was vacuum dried at 80°C. This resulted in a powder of the layered material according to Example 1 containing tetrabutylphosphonium.

[0086] While adding N-methyl-2-pyrrolidone, the powder of the layered material according to Example 1 and polyvinylidene fluoride were mixed in a mass ratio of 9:1 to obtain a slurry. This slurry was applied to an aluminum foil having an etched surface as a current collector using an applicator, and the resulting coating was dried in vacuum at 80°C to obtain an MXene-containing film. The laminate of the aluminum foil and the MXene-containing film was cut into a circle with a diameter of 16 mm in plan view and dried in vacuum at 110°C to obtain the electrode according to Example 1.

[0087] Next, an electrochemical capacitor was assembled as a three-electrode cell, which was a half-cell for evaluation. This half-cell was configured so that the entire voltage to be applied was applied to the electrodes according to Example 1. The assembly of the electrochemical capacitor was carried out in a glove box with an argon gas atmosphere, simulating the actual manufacturing and usage conditions.

[0088] The electrode according to Example 1 was used as the working electrode of the three-electrode cell. An activated carbon electrode (AC) with a diameter of 26 mm coated on aluminum foil was used as the counter electrode of the three-electrode cell. This activated carbon electrode has a capacitance approximately 10 times or more that of the electrode according to Example 1. An Ag / Ag electrode manufactured by EC Frontier was used as the reference electrode of the three-electrode cell. + A reference electrode was used. Commercially available 1 mol / L Li-PF6 / PC electrolyte and 1 mol / L TEA-BF4 / PC electrolyte were used as the electrolytes for the three-electrode cell.

[0089] An EC Frontier battery evaluation cell (product code SB3A) was used as the cell body for the three-electrode cell. An activated carbon electrode was placed on top of a lower body equipped with a counter electrode terminal and an O-ring, with the activated carbon membrane facing upward. Next, a Whatman glass fiber filter cut to a diameter of 28 mm was placed on top of the activated carbon electrode as a separator. An electrode guide was then placed on top of the separator, and the electrode according to Example 1 was placed in the circular hole in the center of the electrode guide, with the MXene-containing membrane facing downward. Next, an electrode holder and spring were placed on top of the electrode according to Example 1, and approximately 1 mL of electrolyte was added to the space in the lower body. An upper body equipped with a working terminal and an insulating spacer was then placed over the electrode. The lower and upper bodies were joined using bolts, wing nuts, and an insulating sleeve. A reference electrode was inserted and secured in the reference electrode holder provided on the upper body. In this way, an electrochemical capacitor, a half-cell for evaluation, was assembled as an electrode evaluation cell.

[0090] (Electrochemical Measurement) Electrochemical measurements were carried out using the evaluation half-cell, which was the electrochemical capacitor assembled as described above. The working electrode, counter electrode, and reference electrode of the electrochemical capacitor assembled as described above were connected to external electrodes. Using an electrochemical measurement device VMP-300 manufactured by Bio-Logic and software EC-Lab, the sweep rate was set to 1 mV / s and the sweep range was set to 0 V (or open-circuit potential) to -2 V relative to the reference electrode. Since the open-circuit potential of the working electrode was approximately -0.7 V, the measurement conditions were such that the working electrodes operated as positive and negative electrodes. In this manner, cyclic voltammetry (CV) measurements were carried out. Using the volume of the MXene-containing film on the aluminum foil, the capacitance per unit volume (specific capacitance) [F / cm] of the MXene-containing film of the electrode according to Example 1 was determined from the results of the CV measurement using the evaluation half-cell. 3 The results are shown in Table 1.

[0091] (Elemental Quantitative Analysis) Elemental quantitative analysis of Ti and P in a sample obtained from the powder of the layered material according to Example 1 was performed by inductively coupled plasma atomic emission spectroscopy (ICP-AES) using an inductively coupled plasma atomic emission spectroscopy analyzer iCAP7400 Duo manufactured by Thermo Fisher Scientific. Nitric acid and hydrofluoric acid were added to approximately 10 mg of the powder of the layered material according to Example 1, and the mixture was heated in a sealed container to cause thermal decomposition, followed by cooling. The powder thus obtained was diluted with pure water to obtain a sample. This sample was subjected to elemental quantitative analysis. The Ti and P contents are shown in Table 2. The upper row of Table 2 shows the mass-based content of each element, and the lower row shows the results obtained by dividing the mass-based content of each element by the atomic weight [g / mol] of each atom and converting it to the mass-based content of each element. The elemental quantitative analysis confirmed that the layered material according to Example 1 contained P, which is believed to be derived from phosphonium. The phosphonium content was also determined to be Ti3C2T S The amount of the compound was about 0.12 moles per mole of the composition.

[0092] Example 2 MoC powder and Ga powder were mixed in an agate mortar to obtain a mixed powder according to Example 2. These powders were provided by High Purity Chemical Laboratory Co., Ltd. The molar ratio of MoC:Ga in the mixed powder according to Example 2 was 1:8. The mixed powder according to Example 2 was fired at 850°C for 80 hours in an argon gas atmosphere to obtain a fired body (block) according to Example 1. The fired body according to Example 2 was placed in a 9 mol / L HCl solution to dissolve the remaining Ga. Subsequently, water washing and suction filtration were repeated multiple times, and the mixture was vacuum dried at 60°C. In this way, a precursor powder according to Example 2 having a composition of MoGaC was obtained.

[0093] 90 mL of 12 mol / L HCl solution and 2 g of the precursor powder of Example 2 were placed in a 300 mL PTFE sample container for hydrothermal synthesis, and the sample container was placed inside a SUS pressure-resistant container for hydrothermal synthesis. Next, the heat-resistant container was left standing at 140°C for 6 days. Subsequently, water washing and suction filtration were repeated multiple times, and the mixture was vacuum-dried at 60°C. This resulted in Mo2CT. s Thus, a powder of MXene according to Example 2 was obtained having the following composition: T represents an atom or functional group that terminates the layered material, and s is an arbitrary number.

[0094] 10 g of the MXene powder according to Example 2 was added to 100 mL of a 14% by mass aqueous solution of tetrabutylphosphonium hydroxide and stirred for 1 hour at room temperature ranging from 15°C to 28°C. Next, water washing and suction filtration were repeated multiple times, followed by vacuum drying at 80°C. This yielded a powder of the layered material according to Example 2 containing tetrabutylphosphonium. A half-cell for evaluation was assembled in the same manner as in Example 1, except that the electrode according to Example 2 was used instead of the electrode according to Example 1, and electrochemical measurements were performed. The results are shown in Table 1.

[0095] Comparative Example 1 A dried powder after HCl treatment was prepared in the same manner as in Example 1, without performing the treatment with the tetrabutylphosphonium hydroxide aqueous solution, to obtain a powder of the layered material according to Comparative Example 1. An electrode according to Comparative Example 1 was obtained in the same manner as in Example 1, except that the layered material according to Comparative Example 1 was used instead of the layered material according to Example 1. A half cell for evaluation was assembled in the same manner as in Example 1, and electrochemical measurements were performed, except that the electrode according to Comparative Example 1 was used instead of the electrode according to Example 1. The results are shown in Table 1.

[0096] Comparative Example 2 A layered material powder according to Comparative Example 2 was prepared in the same manner as in Example 1, except for the following points. 1 g of the dried powder obtained in the same manner as in Example 1 was added to 100 mL of a 10% by mass aqueous solution of tetrabutylammonium hydroxide, and the mixture was stirred for 1 hour at room temperature ranging from 15°C to 28°C. Thus, a layered material powder according to Comparative Example 2 was obtained in the same manner as in Example 1, except that the tetrabutylammonium hydroxide aqueous solution according to Comparative Example 2 was used instead of the tetrabutylphosphonium hydroxide aqueous solution according to Example 1. A half-cell for evaluation was assembled and electrochemical measurements were performed in the same manner as in Example 1, except that the electrode according to Comparative Example 2 was used instead of the electrode according to Example 1. The results are shown in Table 1.

[0097] Comparative Example 3 A layered material powder according to Comparative Example 3 was prepared in the same manner as in Example 1, except for the following points. 1 g of the dry powder obtained in the same manner as in Example 1 was added to 100 mL of a 10% by mass aqueous solution of cetyltrimethylammonium hydroxide, and the mixture was stirred for 1 hour at room temperature between 15°C and 28°C. Thus, a layered material powder according to Comparative Example 3 was obtained in the same manner as in Example 1, except that the cetyltrimethylammonium hydroxide aqueous solution according to Comparative Example 3 was used instead of the tetrabutylphosphonium hydroxide aqueous solution according to Example 1. A half cell for evaluation was assembled in the same manner as in Example 1, and electrochemical measurements were performed, except that the electrode according to Comparative Example 3 was used instead of the electrode according to Example 1. The results are shown in Table 1.

[0098] (X-ray Diffraction) X-ray diffraction (XRD) was performed on the layered materials and precursor powders according to Examples 1, 2, Comparative Examples 1, 2, and 3 using a MiniFlex X-ray diffractometer manufactured by Rigaku. FIG. 7 is a graph showing the results of X-ray diffraction (XRD) measurements on the layered materials and precursors according to Examples 1, 1, 2, and 3. FIG. 8 is a graph showing the results of X-ray diffraction (XRD) measurements on the layered material and precursor according to Example 2. The vertical axis in FIGS. 7 and 8 represents the X-ray diffraction intensity expressed in arbitrary units, and the horizontal axis represents the diffraction angle 2θ [degrees]. The diffraction intensity on the vertical axis represents the relative relationship of the diffraction intensity in the results of a single XRD measurement, and does not represent the relative results of the diffraction intensity in the results of multiple XRD measurements.

[0099] 7 and 8, the layered materials according to Example 1, Example 2, Comparative Example 1, Comparative Example 2, and Comparative Example 3 do not contain any precursor, suggesting that the layered material MXene is produced from the precursor MAX.

[0100] Comparing Example 1, Comparative Example 2, and Comparative Example 3 with Comparative Example 1 in FIG. 7, the diffraction peaks corresponding to the (002) plane in Example 1, Comparative Example 2, and Comparative Example 3 are shifted to a lower angle than the diffraction peak corresponding to the (002) plane in Comparative Example 1. This suggests that the c-axis lattice constants of Example 1, Comparative Example 2, and Comparative Example 3 are larger than the c-axis lattice constant of Comparative Example 1. Therefore, it is believed that ammonium or phosphonium is inserted between the layers of Example 1, Comparative Example 2, and Comparative Example 3, widening the interlayer distance and thereby increasing the c-axis lattice constant. The magnitudes of these c-axis lattice constants have the relationship Comparative Example 3 > Example 1 > Comparative Example 2. This corresponds to the order of the ion sizes of cetyltrimethylammonium, tetrabutylphosphonium, and tetrabutylammonium, which are believed to be inserted between the layers. Therefore, it is believed that ammonium or phosphonium is inserted between the layers in Example 1, Comparative Example 2, and Comparative Example 3.

[0101] FIG. 8 shows the layered material of Example 2 and the precursor of the layered material, MoCT, which is MXene before treatment with the aqueous tetrabutylphosphonium hydroxide solution. s The diffraction peak corresponding to the (002) plane of the layered material of Example 2 is the same as that of the precursor Mo2CT. s This means that the c-axis lattice constant of the layered material according to Example 2 is shifted to a lower angle than the diffraction peak corresponding to the (002) plane of the precursor Mo2CT. s This suggests that the c-axis lattice constant is larger than that of the layered material of Example 2. Therefore, it is considered that phosphonium is inserted between the layers of the layered material of Example 2, and the interlayer distance is widened, thereby increasing the c-axis lattice constant.

[0102] A comparison between the Examples and Comparative Examples shows that when the layered material contains phosphonium, the specific capacity of the electrode tends to be higher than when the layered material does not contain phosphonium or when the layered material contains ammonium. This is true regardless of the type of electrolyte. According to the Examples, when the layered material contains phosphonium in a LiPF6 electrolyte, the specific capacity of the electrode material is 100 F / cm. 3 This is thought to be related to the magnitude of the polarizability of ammonium. It is thought that a similar effect can be obtained even if the phosphonium substituent is a substituent other than butyl.

[0103]

[0104]

[0105] The electrode of the present disclosure can be used as an electrode for an electrochemical device, and the electrochemical device can be used as an electricity storage device or the like in various fields.

Claims

1. A layered material is provided, wherein the layered material is M m X n and a layer including a termination present on a surface of the body, the layer having a composition represented by the formula: and phosphonium, wherein in the body, M is at least one selected from the group consisting of Group 3 elements, Group 4 elements, Group 5 elements, Group 6 elements, and Group 7 elements, X includes at least one selected from the group consisting of carbon atoms and nitrogen atoms, n is 1 or more and 4 or less, and m is greater than n and 5 or less.

2. The electrode of claim 1, wherein the terminus includes an atom having an electronegativity greater than that of M.

3. The electrode according to claim 1, wherein the termination includes at least one selected from the group consisting of a hydroxyl group, a hydrogen atom, a halogen atom, a chalcogen atom, an amino group, a phosphorus atom, and an antimony atom.

4. The electrode of claim 1, wherein in said body, n is 1 and m is 2, or n is 2 and m is 3.

5. The electrode according to claim 1, wherein in said body, M includes at least one selected from the group consisting of Ti and Mo.

6. The electrode of claim 1, wherein in said body, X comprises a carbon atom.

7. The phosphonium is PR4 + 2. The electrode according to claim 1 , wherein P in the cation is a phosphorus atom, and at least two of the four R in the cation have a meta-position substituent constant of 0.00 or less.

8. The phosphonium is PR4 + 2. The electrode according to claim 1 , wherein P in the cation is a phosphorus atom, and four R in the cation are the same or different and are selected from the group consisting of a hydrogen atom, a halogen atom, a hydrocarbon group, an amino group, and an alkoxy group, and the hydrocarbon group, the amino group, and the alkoxy group may optionally have at least one selected from the group consisting of a substituent and a heteroatom.

9. The electrode according to claim 8, wherein the four Rs of the cation are aliphatic functional groups which may optionally have at least one selected from the group consisting of a substituent and a heteroatom.

10. The electrode according to claim 8, wherein the four Rs of the cation are alkyl groups which may optionally have at least one selected from the group consisting of a substituent and a heteroatom.

11. The electrode according to claim 8, wherein the four Rs of the cation are unsubstituted alkyl groups.

12. The electrode according to claim 8, wherein the four Rs of the cation are butyl groups.

13. The electrode of claim 1, wherein the layered material comprises a plurality of the layers, and the phosphonium is disposed between the plurality of layers.

14. The electrode of claim 1, wherein the layered material is disposed in contact with a conductive substrate.

15. An electrochemical device comprising an electrode according to any one of claims 1 to 14.

16. The electrochemical device according to claim 15, comprising a first electrode and a second electrode, the first electrode and the second electrode being disposed apart from each other in an electrolyte, and at least one selected from the group consisting of the first electrode and the second electrode being the electrode, and capable of storing electricity.

17. M m X n a layer including a body having a composition of PR4 and a termination present on a surface of the body; + and a phosphonium cation represented by the formula: wherein in the main body, M is at least one selected from the group consisting of Group 3 elements, Group 4 elements, Group 5 elements, Group 6 elements, and Group 7 elements, X includes at least one selected from the group consisting of carbon atoms and nitrogen atoms, n is 1 or more and 4 or less, m is greater than n and 5 or less, P in the cation is a phosphorus atom, and the four Rs of the cation satisfy at least one condition selected from the group consisting of (I) and (II) below. (I) The four Rs of the cation are aliphatic functional groups optionally having at least one selected from the group consisting of substituents and heteroatoms, and (II) at least two of the four Rs of the cation have a meta-position substituent constant of 0.00 or less.

18. The layered material of claim 17, wherein the terminus comprises an atom having an electronegativity greater than the electronegativity of the M.

19. The layered material according to claim 17, wherein the termination includes at least one selected from the group consisting of a hydroxyl group, a hydrogen atom, a halogen atom, a chalcogen atom, an amino group, a phosphorus atom, and an antimony atom.

20. The layered material of claim 17, wherein in the body, n is 1 and m is 2, or n is 2 and m is 3.

21. The layered material of claim 17, wherein in said body, M comprises at least one selected from the group consisting of Ti and Mo.

22. The layered material of claim 17, wherein in said body, X comprises a carbon atom.

23. The layered material of claim 17, wherein the four Rs of the cation are alkyl groups which may optionally have at least one selected from the group consisting of a substituent and a heteroatom.

24. The layered material according to claim 17, wherein the four Rs of the cation are unsubstituted alkyl groups.

25. The layered material of claim 17, wherein the four Rs of the cation are butyl groups.

26. The layered material of claim 17, comprising a plurality of said layers, and said phosphonium is disposed between said plurality of layers.

27. An electrode material for an electrochemical device, comprising the layered material according to any one of claims 17 to 26.

28. A method for producing a layered material containing phosphonium by using a phosphonium hydroxide, the layered material comprising: M m X n and a layer including a termination present on a surface of the body, the phosphonium, wherein in the body, M is at least one selected from the group consisting of Group 3 elements, Group 4 elements, Group 5 elements, Group 6 elements, and Group 7 elements, X includes at least one selected from the group consisting of carbon atoms and nitrogen atoms, n is 1 or more and 4 or less, and m is greater than n and 5 or less.

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