Layered material, electrode active material for electrochemical device, electrochemical device, and electrochemical capacitor

Abstract

A layered material 1a includes layers 10. The layers 10 each include a body 11 and terminals 12. The body 11 has a composition of M1(1-a)mM2amXn. In this composition, M1 and M2 are mutually different kinds of atoms selected from the group consisting of Ti, Sc, Y, La, Zr, and Hf. X includes at least one kind of atoms selected from the group consisting of carbon atoms and nitrogen atoms. a is greater than 0 and is less than 1. n is 1-4. m is greater than n and is less than or equal to 5. The terminals 12 are present on the surface of the body 11.

Description

Layered material, electrode active material for electrochemical device, electrochemical device, and electrochemical capacitor

[0001] The present disclosure relates to layered materials, electrode active materials for electrochemical devices, electrochemical devices, and electrochemical capacitors.

[0002] Recently, 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, pages78-81 (2014)

[0005] The present disclosure provides novel layered materials that are advantageous in terms of enhancing the performance of electrochemical devices.

[0006] The layered materials of the present disclosure include: M1 (1-a)m M2 am X n and a layer including a body having a composition of the formula: and a termination present on a surface of the body, wherein in the composition, M1 and M2 are different atoms selected from the group consisting of Ti, Sc, Y, La, Zr, and Hf; X includes at least one selected from the group consisting of carbon atoms and nitrogen atoms; a is greater than 0 and less than 1; n is greater than 1 and less than 4; and m is greater than n and less than 5.

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

[0008] FIG. 1 is a schematic diagram of an example of a layered material. FIG. 2 is a schematic diagram of an example of an electrochemical capacitor. FIG. 3A is a graph showing the results of X-ray diffraction (XRD) measurement of precursors of the layered materials according to Examples 1, 2, 3, and Comparative Example 1. FIG. 3B is a graph showing the results of XRD measurement of the layered materials according to Examples 1, 2, 3, and Comparative Example 1. FIG. 4 is a graph showing the results of XRD measurement of the precursor, TiSnC, and ZrSnC according to Reference Example 1. FIG. 5 is a graph showing the particle size distribution of the layered materials according to Examples 1, 2, and Comparative Example 1. FIG. 6A is a scanning electron microscope (SEM) photograph of the layered material according to Example 1. FIG. 6B is a SEM photograph of the layered material according to Example 2. FIG. 6C is a SEM photograph of the layered material according to Comparative Example 1.

[0009] (Findings that form the basis of the present disclosure) As described in Non-Patent Document 1, it is conceivable to use MXene as an electrode active material in electrochemical devices such as electrochemical capacitors. In such electrochemical devices, the capacitance per unit volume or unit mass of the electrode active material [F / cm 3 It is important that the specific capacity, or F / g, is high. Therefore, the present inventors conducted extensive research into MXenes that can be used as electrode active materials in at least one of the negative and positive electrodes of electrochemical devices. As a result, they discovered that the use of a specific layered material as an electrode active material tends to increase the specific capacity in electrochemical devices. Based on this new finding, the present inventors have completed the layered material 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 schematic diagram of an example of a layered material according to the present disclosure. As shown in FIG. 1, the layered material 1a includes a layer 10. The layer 10 includes a body 11 and a terminal end 12. The body 11 includes a M1 (1-a)m M2 am X nIn this composition, M1 and M2 are different atoms selected from the group consisting of Ti, Sc, Y, La, Zr, and Hf. X is at least one selected from the group consisting of carbon atoms and nitrogen atoms. a is greater than 0 and less than 1. n is greater than 1 and less than 4. m is greater than n and less than 5. The termination 12 is an atom or atomic group present on the surface of the main body 11. When the atom or functional group forming the termination 12 is represented as T, the layer 10 has a structure in which M1 (1-a)m M2 am X n T s The composition is as follows: s is an arbitrary number.

[0012] As described above, in the layered material 1a, the main body 11 is M1 (1-a)m M2 am X n As a result, for example, when layered material 1a is used as an electrode active material in an electrochemical device, a higher specific capacity is likely to be exhibited compared to when MXene containing only Ti as a transition metal is used as an electrode active material in an electrochemical device. The reason for this is unclear. The atomic radius of M1 or M2 contained in the above composition is relatively large. This is thought to affect the arrangement of functional groups or atoms in terminal 12, making it likely that the thickness of the electric double layer generated in the electrochemical device is small. For this reason, it is thought that layered material 1a is likely to exhibit a high specific capacity when used as an electrode active material in an electrochemical device.

[0013] The arrangement of M1, M2, and X in the main body 11 is not limited to a specific arrangement. For example, in the main body 11, M1 and M2 are arranged at the vertices of an octahedron to form an octahedron array, which is an arrangement of a plurality of edge-sharing octahedrons. In addition, X is arranged inside each octahedron.

[0014] M1 and M2 are not limited to specific atoms as long as they are different atoms selected from the group consisting of Ti, Sc, Y, La, Zr, and Hf. M1 and M2 are preferably different atoms selected from the group consisting of Ti, Zr, and Hf. In this case, when the layered material 1a is used as an electrode active material in an electrochemical device, a high specific capacity is more likely to be exhibited.

[0015] In the above composition, it is more preferable that M1 is Ti and M2 is Zr, in which case the layered material 1a is more likely to exhibit a high specific capacity when used as an electrode active material in an electrochemical device.

[0016] In the above composition, M1 may be Ti or Zr, and M2 may be Sc, Y, or La. In this case, when the layered material 1a is used as an electrode active material in an electrochemical device, it is more likely to exhibit a high specific capacity.

[0017] In the above composition, 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 forms the main body 11, n may not be an integer. m may, for example, satisfy the condition m=n+1.

[0018] In the above composition, n is preferably 2 and m is preferably 3. In this case, when the layered material 1a is used as an electrode active material in an electrochemical device, it is more likely to exhibit a high specific capacity.

[0019] In the above composition, a is not limited to a specific value as long as it is greater than 0 and less than 1. Preferably, a is greater than 0 and not greater than 0.33. In this case, when the layered material 1a is used as an electrode active material in an electrochemical device, it is more likely to exhibit a high specific capacity.

[0020] In the above composition, a may be greater than 0 and equal to or less than 0.2.

[0021] In the above composition, a may be greater than 0 and equal to or less than 0.1.

[0022] In the above composition, a may be greater than 0 and less than or equal to 0.67, or greater than 0 and less than or equal to 0.5.

[0023] In the above composition, M1 may be Ti or Zr, and M2 may be Hf, Sc, Y, or La. In this case, a may be greater than 0 and less than or equal to 0.67. In this case, when the layered material 1a is used as an electrode active material in an electrochemical device, a high specific capacity is more likely to be exhibited. In this case, a may further be greater than 0 and less than or equal to 0.5, or greater than 0 and less than or equal to 0.33.

[0024] In the above composition, X may contain a carbon atom. In this case, when the layered material 1a is used as an electrode active material of an electrochemical device, a high specific capacity is more likely to be exhibited. X may contain only carbon atoms, only nitrogen atoms, or both carbon atoms and nitrogen atoms.

[0025] In the above composition, 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 contains oxygen atoms, oxygen atoms derived from the raw materials 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.

[0026] Termination 12 is not limited to a specific atom or atomic group, as long as it is an atom or atomic group that can exist on the surface of main body 11. Termination 12 includes, for example, an atom having an electronegativity greater than that of M1 and M2 contained in main body 11. In this case, termination 12 is likely to exist in a desired state on the surface of main body 11. Examples of atoms having an electronegativity greater than that of M1 and M2 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.

[0027] The termination 12 may contain 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 for the termination 12 to exist on the surface of the main body 11 in a desired state.

[0028] As shown in FIG. 1 , the layered material 1a includes, for example, a plurality of layers 10. In this case, the layered material 1a has, for example, a multilayer structure in which a plurality of layers 10 are stacked apart from one another. In this case, two adjacent layers 10 do not need to be completely separated from one another and may include a contacting portion. The layered material 1a may also have a single-layer structure composed of only one layer 10. The aggregate of the single-layer structure or multilayer structure composed of the layered material 1a may be particles such as powder and flakes.

[0029] The thickness of the layer 10 is not limited to a specific value. For example, the thickness of the layer 10 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 M1 and M2.

[0030] The maximum dimension of the layer 10 in an in-plane direction perpendicular to the thickness direction of the layer 10 is not limited to a particular value. The maximum dimension may be, for example, 0.1 μm or more and 200 μm or less, or 1 μm or more and 40 μm or less.

[0031] When the layered material 1 a has a multilayer structure, the distance d between the layers 10 in the multilayer structure is not limited to a specific value. The distance d is, for example, 0.1 nm to 10 nm, or may be 0.1 nm to 5 nm, or may be approximately 1 nm.

[0032] When the layered material 1a has a multilayer structure, the maximum dimension of the layered material 1a in the in-plane direction perpendicular to the thickness direction of the layer 10 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 may be 1 μm or more and 20 μm or less.

[0033] When the layered material 1a has a multilayer structure, cations may be present between adjacent layers 10 in the thickness direction of the layers 10. Examples of cations include protons (H + ), alkali metal ions, alkaline earth metal ions, and quaternary ammonium ions. Anions or solvents may be present that coordinate with the cations present between the layers 10. Examples of anions and solvents that coordinate with the cations include halide ions, HO, and propylene carbonate.

[0034] When the layered material 1a has a multilayer structure, the number of layers 10 included in the layered material 1a is two or more, and may be 20 to 100,000, or 1,000 to 20,000. The thickness of the layered material 1a in the thickness direction of the layers 10 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.

[0035] When the layered material 1a has a multilayer structure, the number of layers 10 included in the layered material 1a may be six or less. In this case, the layered material 1a is referred to as a low-layer structure.

[0036] In the assembly of layered materials 1a, for example, the majority of the assembly may be layered materials 1a and / or low-layer structures having a single layer structure, for example, 50% by volume or more of the assembly may be layered materials 1a and / or low-layer structures having a single layer structure.

[0037] 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.

[0038] The method for producing the layered material 1a is not limited to a specific method. m AX n The layered material 1a can be synthesized by selectively etching A atoms from a precursor having the following composition. In the precursor composition, M collectively represents metal atoms corresponding to M1 and M2 in the main body 11 of the layered material 1a, and m and n correspond to m and n in the main body 11, respectively. A is an element of Group 12, Group 13, Group 14, Group 15, or Group 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.

[0039] At MAX, the A atoms are selectively etched, removing the A atomic layer. This exposes M m X n Atoms or atomic groups derived from the etching solution modify the surface of the layer, forming terminations 12 .

[0040] 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. Selective etching of A atoms may be performed using a molten salt of a Lewis acid such as CuCl, high-temperature and high-pressure HCl, halogen gas such as Br and I, or an organic solution in which halogens such as Br and I are dissolved.

[0041] The layered material 1a may be made from precursors other than MAX. For example, two M m X n The layered material 1a 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.

[0042] 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 10 in the layered material 1a. This can result in, for example, a layered material 1a 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 10 from the perspective of separating the layers 10. Consider, for example, a case where the layered material 1a has a single-layer structure or a low-layer structure. In this case, the ratio of the dimension of the layered material 1a in the thickness direction of the layer 10 to the dimension of the layered material 1a in the in-plane direction of the layer 10 is small. Even in such cases, handshaking or shaking using an automatic shaker can impart a desired shear stress between the layers 10 from the perspective of separating the layers 10, making the layered material 1a less likely to break and more likely to maintain the desired size.

[0043] In the layered material 1a, some A atoms derived from the precursor such as MAX may remain. The amount of A atoms remaining in the layered material 1a is, for example, 10 mass % or less of the content of A atoms in the precursor, preferably 8 mass % or less, and more preferably 6 mass % or less. Depending on the application of the layered material 1a, the amount of A atoms remaining in the layered material 1a may be more than 10 mass % of the content of A atoms in the precursor.

[0044] The layered material 1a may be produced by a method other than selectively etching A atoms from a precursor such as MAX. For example, it may be produced by heat treating metal M1, metal M2, graphite, or a halide of M1 or M2 inside a sealed tube. The sealed tube may be, for example, a quartz tube. The layered material 1a may also be produced by chemical vapor deposition (CVD) using metal M1, metal M2, a halide of M1 or M2, and CH4 or N2.

[0045] For example, an electrode active material for an electrochemical device can be provided that contains the layered material 1a. As described above, when such an electrode active material is used in an electrochemical device, the electrochemical device is likely to exhibit a high specific capacity.

[0046] An electrode containing the layered material 1a as an electrode active material can be provided. In this case, the surface of the electrode may be substantially composed of the layered material 1a alone, or a binder may be present between the layered materials 1a. The binder may, for example, include a resin, including at least one selected from the group consisting of polytetrafluoroethylene, polyvinylidene fluoride, and styrene butadiene rubber. An electrode containing the layered material 1a as an electrode active material can be fabricated by forming an aggregate of the layered material 1a, or a mixture containing an aggregate of the layered material 1a and a binder, into a film or sheet. For example, a method including suction filtration can be used to fabricate the electrode. Alternatively, the electrode may be fabricated using a coating method such as spray coating, bar coating, or dip coating.

[0047] The above-described electrode may be fabricated using a precursor of layered material 1a or a modified version of layered material 1a. For example, coated particles are obtained by coating the surface of polymer particles such as polystyrene with layered material 1a 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 1a remaining in a shell shape. An electrode may be fabricated in this manner. In this case, the specific capacity of an electrochemical device using this electrode is likely to be large, and the coulombic efficiency is likely to be high.

[0048] The density of the electrode is not limited to a specific value. For example, the density is 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.

[0049] The thickness of the electrode is not limited to a specific value. The thickness is, for example, 3 μm or more, 5 μm or more, or may be 500 μm or less.

[0050] The electrochemical device includes, for example, a pair of electrodes and an electrode active material disposed in contact with at least one of the pair of electrodes. The electrode active material may include the layered material 1a.

[0051] Fig. 2 is a schematic diagram showing an example of an electrochemical capacitor. As shown in Fig. 2, the electrochemical capacitor 2a includes a positive electrode 3a and a negative electrode 3b. In the electrochemical capacitor 2a, the positive electrode 3a and the negative electrode 3b are arranged apart from each other in an electrolytic solution 4. At least one selected from the group consisting of the positive electrode 3a and the negative electrode 3b contains the layered material 1a as an electrode active material. With this configuration, the electrochemical capacitor 2a is likely to exhibit a high specific capacitance.

[0052] 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.

[0053] 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

[0054] The electrolytic solution 4 is not limited to a specific electrolyte solution. The electrolytic solution 4 is, for example, a nonaqueous electrolyte solution. In this case, the operating potential range of the electrochemical capacitor 2a is likely to be large. A large operating potential range is advantageous from the viewpoint of increasing the energy density stored in the electrochemical capacitor 2a. The electrolytic 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 electrochemical capacitor 2a 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 electrolytic solution 4 is a nonaqueous electrolyte solution, there are fewer restrictions on the operating potential range and usable temperature range of the electrochemical capacitor 2a compared to when the electrolytic solution 4 is an aqueous electrolyte solution.

[0055] 2 , in electrochemical capacitor 2 a, an electrolyte solution 4 is contained inside a cell 5, and the inside of cell 5 is divided by a separator 7 into a space in which a positive electrode 3 a is disposed and a space in which a negative electrode 3 b is disposed. The positive electrode 3 a and the negative electrode 3 b are electrically connected to terminals 6 a and 6 b disposed outside the cell 5, respectively.

[0056] 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.

[0057] 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.

[0058] The positive electrode 3 a and the negative electrode 3 b may be arranged, for example, inside the cell 5 in a state where a separator 7 is disposed between the positive electrode 3 a and the negative electrode 3 b, and a laminate including the positive electrode 3 a, the separator 7, and the negative electrode 3 b is wound.

[0059] As described above, at least one selected from the group consisting of the positive electrode 3 a and the negative electrode 3 b contains the layered material 1 a as an electrode active material. The electrode active material exchanges electrons with electrolyte ions contained in the electrolyte solution 4, for example.

[0060] For example, only the positive electrode 3a may contain the layered material 1a as the electrode active material. In this case, the negative electrode 3b may contain, as the electrode active material, a carbon material such as activated carbon, carbon nanotubes, or graphene, or Li4Ti5O 12The negative electrode 3b alone may contain the layered material 1a as the electrode active material. In this case, the positive electrode 3a may contain graphite, activated carbon, carbon nanotubes, or the like as the electrode active material. When only the positive electrode 3a or the negative electrode 3b contains the layered material 1a as the electrode active material, the electrode that does not contain the layered material 1a may be substantially composed of the electrode active material alone, or may be configured in such a way that a binder is present between the electrode active materials. The binder may include, for example, a resin. The binder may include, for example, at least one selected from the group consisting of polytetrafluoroethylene, polyvinylidene fluoride, and styrene butadiene rubber. Both the positive electrode 3a and the negative electrode 3b may contain the layered material 1a as the electrode active material.

[0061] Each of the positive electrode 3 a and the negative 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 active material is formed on a current collector (not shown). 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.

[0062] 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.

[0063] 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+), 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 - )

[0064] 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).

[0065] The electrolytic solution 4 may contain, as necessary, predetermined additives in addition to the solvent and electrolyte.

[0066] When the terminals 6a and 6b of the electrochemical capacitor 2a are connected to a load, the electrochemical capacitor 2a is discharged. On the other hand, when the terminals 6a and 6b of the electrochemical capacitor 2a are connected to a power source, the electrochemical capacitor 2a is charged.

[0067] Depending on the combination of the electrode active material and the electrolyte solution 4, the electrochemical capacitor 2a may be configured as a pseudocapacitor or a hybrid capacitor involving a Faraday reaction.

[0068] (Note) Based on the above description, the following techniques are disclosed. (Technology 1) M1 (1-a)m M2 am X nand a termination located on a surface of the body, wherein in the composition, M1 and M2 are different atoms selected from the group consisting of Ti, Sc, Y, La, Zr, and Hf, X includes at least one selected from the group consisting of carbon and nitrogen atoms, a is greater than 0 and less than 1, n is greater than 1 and less than 4, and m is greater than n and less than 5. (Technology 2) The layered material according to Technology 1, wherein the termination includes an atom having an electronegativity greater than that of M1 and M2. (Technology 3) The layered material according to Technology 1 or 2, 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 4) The layered material according to any one of Technology 1 to 3, wherein n is 2 and m is 3. (Technology 5) The layered material according to any one of Technologies 1 to 4, wherein X comprises a carbon atom. (Technology 6) The layered material according to any one of Technologies 1 to 5, wherein M1 and M2 are different atoms selected from the group consisting of Ti, Zr, and Hf. (Technology 7) The layered material according to any one of Technologies 1 to 6, wherein M1 is Ti and M2 is Zr. (Technology 8) The layered material according to Technology 7, wherein a is greater than 0 and equal to or less than 0.33. (Technology 9) The layered material according to Technology 7, wherein a is greater than 0 and equal to or less than 0.2. (Technology 10) The layered material according to Technology 5, wherein a is greater than 0 and equal to or less than 0.1. (Technology 11) The layered material according to any one of Technologies 1 to 5, wherein M1 is Ti or Zr, and M2 is Sc, Y, or La. (Technology 12) The layered material according to any one of Technologies 1 to 5, wherein M1 is Ti or Zr, M2 is Hf, Sc, Y, or La, and a is greater than 0 and not greater than 0.67. (Technology 13) The layered material according to Technology 12, wherein a is greater than 0 and not greater than 0.5. (Technology 14) The layered material according to Technology 12, wherein a is greater than 0 and not greater than 0.33. (Technology 15) An electrode active material for an electrochemical device, comprising the layered material according to any one of Technologies 1 to 14.(Technology 16) An electrochemical device comprising: a pair of electrodes; and an electrode active material disposed in contact with at least one of the pair of electrodes, wherein the electrode active material comprises the layered material according to any one of Technologies 1 to 14. (Technology 17) An electrochemical capacitor comprising: a positive electrode; and a negative electrode, wherein the positive electrode and the negative electrode are disposed apart from each other in an electrolyte, and at least one selected from the group consisting of the positive electrode and the negative electrode comprises, as an electrode active material, the layered material according to any one of Technologies 1 to 14. (Technology 18) The electrochemical capacitor according to Technology 17, wherein the negative electrode comprises the layered material as an electrode active material.

[0069] 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.

[0070] Example 1 TiC powder, ZrC 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:ZrC:Ti:Al in the mixed powder according to Example 1 was 1.7:0.3:1:1. The mixed powder according to Example 1 was fired at 1500°C for 1 hour 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. In this way, Ti 2.7 Zr 0.3 A precursor powder according to Example 1 having a composition of AlC2 was obtained.

[0071] The precursor powder according to Example 1, CuCl powder, and NaCl powder were mixed in a zirconia mortar to obtain a mixed powder. 2.7 Zr 0.3The AlC2:CuCl2:NaCl ratio was 1:3:4. This mixed powder was fired in an argon gas atmosphere at 650°C for 10 hours to obtain a fired body (block). The fired body was then pulverized in a zirconia mortar. The powder was washed with pure water to remove chlorides. Next, the fired body was washed with 0.1M ammonium peroxodisulfate to remove Cu. Next, the washed fired body was subjected to suction filtration and vacuum dried at room temperature in the range of 15°C to 28°C. This resulted in the formation of Ti, 2.7 Zr 0.3 C2T s Thus, a powder of the layered material according to Example 1 was obtained, having the composition: T represents an atom or functional group that terminates the layered material, and s is an arbitrary number.

[0072] While adding N-methyl-2-pyrrolidone, the layered material powder of Example 1, acetylene black powder, and polyvinylidene fluoride were mixed to obtain a slurry. This slurry was applied to an aluminum foil having an etched surface using an applicator, and the resulting coating was dried in vacuum at 60°C to obtain an MXene-containing film. The laminate of the aluminum foil and the MXene-containing film was cut into a rectangular shape with a short side length of 10 mm and a long side length of 20 mm in plan view to obtain the electrode of Example 1.

[0073] Next, a three-electrode electrochemical capacitor half cell was assembled for evaluation. This half cell was configured so that the entire voltage applied was applied to the electrodes according to Example 1. The assembly and evaluation of the electrochemical capacitor were carried out in a glove box with an argon gas atmosphere, simulating actual manufacturing and usage conditions.

[0074] The electrode according to Example 1 was used as the working electrode of the three-electrode cell. An activated carbon electrode (AC) was used as the counter electrode of the three-electrode cell. Activated carbon and polytetrafluoroethylene, a binder, were mixed in a mass ratio of activated carbon:binder of 95:5 to obtain an activated carbon-containing mixture. This activated carbon-containing mixture was molded on a Ti mesh, and a Pt wire was attached to the molded product to obtain an activated carbon electrode. 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. A commercially available 1 M Li-PF6 / EC-DMC electrolyte was used as the electrolyte for the three-electrode cell.

[0075] A BAS plate electrode evaluation cell (product code 011951) was used as the cell body for the three-electrode cell. A rectangular aluminum substrate with a short side length of approximately 10 mm and a long side length of approximately 20 mm was placed on a fluororesin lower block, which served as a base. The electrode according to Example 1 was then placed on the aluminum substrate with the MXene-containing film of the electrode according to Example 1 facing upward. A main body block with a cylindrical through-hole and a fluororesin O-ring was placed on top of the electrode according to Example 1. A pair of screws located on both ends of the main body block were uniformly tightened to sandwich the electrode according to Example 1 between the lower block and the main body block. 1 mL of electrolyte was added to the space between the main body block. A counter electrode and a reference electrode were attached to the cell cap and fitted into the main body block. In this way, an electrochemical capacitor, a half cell for evaluation, was assembled as a plate electrode evaluation cell. After assembly, the electrochemical capacitor was allowed to stand for 1 hour.

[0076] (Electrochemical Measurement) Electrochemical measurements were performed using the evaluation half-cell, which was the electrochemical capacitor assembled above. In a glove box with an argon gas atmosphere, the working electrode and reference electrode of the assembled electrochemical capacitor were connected to external electrodes. Using a Solartron Analytical 1287A electrochemical measurement device and CorrWare software, 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. Cyclic voltammetry (CV) measurements were performed in this manner. From the results of the CV measurements using the evaluation half-cell, the capacitance per unit mass [F / g] of the MXene-containing film of the electrode according to Example 1 was calculated. The results are shown in Table 1A.

[0077] (Quantitative elemental analysis) Using a scanning X-ray fluorescence analyzer ZSX-Primus IV manufactured by Rigaku Corporation, quantitative elemental analysis of the sample obtained from the powder of the layered material according to Example 1 was performed by wavelength dispersive X-ray fluorescence analysis (WD-XRF). Elements that showed a content exceeding 0.01 mol% and their 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 into the mass-based content of each element. As described above, the composition based on the charge of the powder of the layered material according to Example 1 was Ti, 2.7 Zr 0.3 C2T s On the other hand, according to the elemental quantitative analysis, the results shown in Table 2 show that the composition of Ti and Zr in the layered material according to Example 1 was Ti 2.692 Zr 0.308 This was very close to the composition based on the initial charge. The mass ratio of O atoms to the total mass of O atoms, Cl atoms, and S atoms, which are thought to exist as the terminals of the layered material, was approximately 87%. This is similar to the condition for surface functional groups in the calculation model of electric double layer capacitance described below.

[0078] Example 2 A powder of the layered material according to Example 2 was prepared in the same manner as in Example 1, except for the following points. TiC powder, ZrC powder, Ti powder, Al powder, and Si powder were mixed in a zirconia mortar to obtain a mixed powder according to Example 2. These powders were provided by Kojundo Chemical Laboratory Co., Ltd. The molar ratio of TiC:ZrC:Ti:Al:Si in the mixed powder according to Example 2 was 1.7:0.3:1:0.9:0.1. A powder of the layered material according to Example 2 was prepared in the same manner as in Example 1, except that the mixed powder according to Example 2 was used instead of the mixed powder according to Example 1. An electrode according to Example 2 was prepared in the same manner as in Example 1, except that the layered material according to Example 2 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 Example 2 was used instead of the electrode according to Example 1. The results are shown in Table 1A.

[0079] Comparative Example 1 A powder of the layered material according to Comparative Example 1 was prepared in the same manner as in Example 1, except for the following points. TiC powder, Ti powder, and Al powder were mixed in a zirconia mortar to obtain a mixed powder according to Comparative 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 Comparative Example 1 was 2:1:1. A powder of the layered material according to Comparative Example 1 was prepared in the same manner as in Example 1, except that the mixed powder according to Comparative Example 1 was used instead of the mixed powder according to Example 1 and the firing temperature of the mixed powder was adjusted to 1400°C. An electrode according to Comparative Example 1 was prepared 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 and electrochemical measurements were performed in the same manner as in Example 1, 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 1A.

[0080] Example 3 A powder of the layered material according to Example 3 was prepared in the same manner as Example 1, except for the following points. TiC powder, ZrC powder, Ti powder, and Al powder were mixed in a zirconia mortar to obtain a mixed powder according to Example 3. These powders were provided by Kojundo Chemical Laboratory Co., Ltd. The molar ratio of TiC:ZrC:Ti:Al in the mixed powder according to Example 3 was 1.4:0.6:1:1.1. A powder of the layered material according to Example 3 was prepared in the same manner as Example 1, except that the mixed powder according to Example 3 was used instead of the mixed powder according to Example 1. The molar ratio Zr / (Ti+Zr) in the powder of the layered material according to Example 3 was 0.2.

[0081] Reference Example 1 A precursor powder according to Reference Example 1 was prepared in the same manner as in Example 1, except for the following points. ZrC powder, Ti powder, and Sn powder were mixed in a zirconia mortar to obtain a mixed powder according to Reference Example 1. The molar ratio of ZrC:Ti:Sn in the mixed powder according to Reference Example 1 was 1:1:1. A precursor powder according to Reference Example 1 was prepared in the same manner as in Example 1, except that the mixed powder according to Reference Example 1 was used instead of the mixed powder according to Example 1 and the firing temperature of the mixed powder was adjusted to 1200°C.

[0082] (X-ray Diffraction) Using an X-ray diffractometer X'Pert PRO MPD manufactured by PANalytical, X-ray diffraction (XRD) was performed on the powders of the precursors of the layered materials according to Examples 1, 2, and 3, and Comparative Example 1, and the powders of these layered materials. The results are shown in Figures 3A and 3B.

[0083] Fig. 3A is a graph showing the results of XRD measurement of precursors of the layered materials according to Examples 1, 2, 3, and Comparative Example 1. Fig. 3B is a graph showing the results of XRD measurement of the layered materials according to Examples 1, 2, 3, and Comparative Example 1. The vertical axis in Fig. 3A and Fig. 3B represents the diffraction intensity, and the horizontal axis represents the diffraction angle 2θ. The diffraction intensity on the vertical axis represents the relative relationship of the diffraction intensity in the results of one XRD measurement, and does not represent the relative results of the diffraction intensity in the results of multiple XRD measurements.

[0084] A comparison of Figures 3A and 3B suggests that the layered materials according to Examples 1, 2, 3, and Comparative Example 1 do not contain precursors, and that the layered material MXene is produced from the precursor MAX. A comparison of Examples 1 to 3 with Comparative Example 1 in Figure 3A reveals that the diffraction peaks corresponding to the (110) plane of the precursors according to Examples 1 to 3 are shifted to lower angles than the diffraction peaks corresponding to the (110) plane of the precursor according to Comparative Example 1. This suggests that the crystal lattice size of the precursors according to Examples 1 to 3 is larger than that of the precursor according to Comparative Example 1. Therefore, in the crystal lattice of the precursors and layered materials according to Examples 1 to 3, it is believed that a portion of the Ti in the crystal lattice of the precursor and layered material according to Comparative Example 1 is replaced with Zr, which has an atomic radius larger than that of Ti. The diffraction peak corresponding to the (110) plane of the precursor according to Example 3 is shifted to lower angles than the diffraction peaks corresponding to the (110) plane of the precursors according to Examples 1 and 2. Therefore, it is believed that the amount of Zr substituted in the crystal lattice of the precursor and layered material according to Example 3 is greater than the amount of Zr substituted in the crystal lattice of the precursor and layered material according to Examples 1 and 2.

[0085] XRD was performed on the precursor powder according to Reference Example 1, TiSnC powder, and ZrSnC powder using an X-ray diffractometer X'Pert PRO MPD manufactured by PANalytical. The results are shown in FIG. 4. FIG. 4 is a graph showing the results of XRD measurement of the precursor according to Reference Example 1, TiSnC, and ZrSnC. The vertical axis of FIG. 4 represents the diffraction intensity, and the horizontal axis represents the diffraction angle 2θ. The diffraction intensity on the vertical axis represents the relative relationship of the diffraction intensity in the results of one XRD measurement, and does not represent the relative results of the diffraction intensity in the results of multiple XRD measurements.

[0086] As shown in Figure 4, the position of the XRD diffraction peak of the precursor powder according to Reference Example 1 is confirmed to be intermediate between the position of the XRD diffraction peak of the TiSnC powder and the position of the XRD diffraction peak of the ZrSnC powder. Therefore, the precursor according to Reference Example 1 is considered to be TiZrSnC, which is a solid solution of TiSnC and ZrSnC. Therefore, by etching the precursor according to Reference Example 1 in the same manner as the precursor according to Example 1, a layered material TiZrCT corresponding to TiZrSnC can be obtained. s It is believed that can be generated.

[0087] (Particle Size Distribution Measurement) The particle size distribution of the powder of the layered material according to Example 1, Example 2, and Comparative Example 1 was measured using a laser diffraction particle size distribution analyzer MT3000EXII manufactured by Microtrac. The results are shown in Figure 5. Figure 5 is a graph showing the particle size distribution of the layered material according to Example 1, Example 2, and Comparative Example 1. In Figure 5, the vertical axis on the left represents frequency [%], the vertical axis on the right represents cumulative amount [%], and the horizontal axis represents particle size.

[0088] (SEM Observation) Using a scanning electron microscope VE-8800 manufactured by KEYENCE Corporation, SEM photographs were taken of the layered materials according to Examples 1 and 2, and Comparative Example 1. Fig. 6A is an SEM photograph of the layered material according to Example 1, Fig. 6B is an SEM photograph of the layered material according to Example 2, and Fig. 6C is an SEM photograph of the layered material according to Comparative Example 1.

[0089] As shown in Tables 1A and 1B, the capacitance per unit mass of the MXene-containing films of the electrodes in Examples 1 and 2 is greater than that of the MXene-containing film of the electrode in Comparative Example 1. Figure 5 shows that the particle size of the layered material powder in Examples 1 and 2 is greater than that of the layered material powder in Comparative Example 1. Generally, a smaller particle size of a material increases the specific surface area of ​​the material, and the larger the specific surface area of ​​a material, the greater the capacitance. However, referring to Tables 1A and 1B, the capacitance per unit mass of the MXene-containing films of the electrodes in Examples 1 and 2, which have larger particle sizes, is greater than that of the MXene-containing film of the electrode in Comparative Example 1, which has smaller particle sizes. This is thought to be due to the characteristics of the layered material itself. For example, consider the case where the specific surface area of ​​the layered materials in Examples 1 and 2 is the same as that of the layered material in Comparative Example 1. In this case, it is considered that the difference between the capacitance per unit mass of the MXene-containing film of the electrodes in Examples 1 and 2 and the capacitance per unit mass of the MXene-containing film of the electrode in Comparative Example 1 will be greater.

[0090] (Examples 4 to 16 and Comparative Examples 1 to 16) The electric double layer capacitance [μF / cm ] of the layered materials according to Examples 4 to 16 and Comparative Examples 1 to 16 was calculated using the ESM-RISM method, which is a type of first-principles calculation, for the MXene compositions shown in Tables 1A and 1B. 2 ] was calculated. The ESM-RISM method is a method for rapidly predicting the electronic state when an electric field is applied by describing the electronic states of the electrode and reactive species using density functional theory and describing the distribution of the electrolyte using RISM, a classical solution theory. The model used for the calculation was the structure of MAX, an MXene precursor, which was subjected to lattice relaxation using standard first-principles calculations. Next, a surface model was created by extracting one layer of the MAX structure, and functional O atoms were added to the surface, followed by atomic position relaxation. The ESM-RISM calculation was performed by adding electrons to the model in the same way as in the following literature. From the change in Fermi energy with respect to the applied charge, a Q-V curve showing the relationship between the surface charge Q and the applied voltage V was created, and the capacitance was evaluated from the slope of the curve. The charge was set to 0 to -10 μC / cm. 2The calculation was performed using the Quantum Espresso code. The results are shown in Table 1A and Table 1B. Reference: Chemistry of Materials (USA) 2022, 34, 5, 2069-2075 https: / / pubs.acs.org / doi / full / 10.1021 / acs.chemmater.1c03328

[0091] Although the electric double layer capacitance of the layered materials according to Examples 1 and 2 was not calculated, it is believed that there is a corresponding relationship between the electric double layer capacitance and the capacitance. The capacitance per unit mass of the MXene-containing film of the electrode according to Examples 1 and 2 is greater than the capacitance per unit mass of the MXene-containing film of the electrode according to Comparative Example 1. Therefore, it is believed that the electric double layer capacitance of the layered materials according to Examples 1 and 2 is higher than that of the layered material according to Comparative Example 1.

[0092] A comparison between Examples and Comparative Examples shows that when a layered material contains two or more elements selected from the group consisting of Ti, Sc, Y, La, Zr, and Hf, the specific capacitance and electric double layer capacity tend to be higher than when the layered material contains only one type of metal. According to Examples, when a layered material contains two or more elements selected from the group consisting of Ti, Sc, Y, La, Zr, and Hf, the electric double layer capacity of the layered material is 12 μF / cm 2 It could be more than that.

[0093]

[0094]

[0095]

[0096] The layered material of the present disclosure can be used as an electrode active material in an electrode of an electrochemical capacitor, and the electrochemical capacitor can be used for storing electricity in a variety of fields.

Claims

1. M1 (1-a)m M2 am X n A layer comprising a body having the composition of, and a termination present on the surface of the body, wherein in the composition, M1 and M2 are different atoms selected from the group consisting of Ti, Sc, Y, La, Zr, and Hf, X comprises at least one selected from the group consisting of carbon atoms and nitrogen atoms, a is greater than 0 and less than 1, n is 1 or more and 4 or less, and m is greater than n and 5 or less, a layered material.

2. The layered material according to claim 1, wherein the terminal includes an atom having an electronegativity greater than the electronegativities of M1 and M2.

3. The layered material according to claim 1, wherein the terminal 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 layered material according to claim 1, wherein n is 2 and m is 3.

5. The layered material according to claim 1, wherein X includes a carbon atom.

6. The layered material according to claim 1, wherein M1 and M2 are different atoms selected from the group consisting of Ti, Zr, and Hf.

7. The layered material according to claim 1, wherein M1 is Ti and M2 is Zr.

8. The layered material according to claim 7, wherein a is greater than 0 and not more than 0.

33.

9. The layered material according to claim 7, wherein a is greater than 0 and not more than 0.

2.

10. The layered material according to claim 7, wherein a is greater than 0 and not more than 0.

1.

11. The layered material according to claim 1, wherein M1 is Ti or Zr, and M2 is Sc, Y, or La.

12. The layered material according to claim 1, wherein M1 is Ti or Zr, M2 is Hf, Sc, Y, or La, and a is greater than 0 and not more than 0.

67.

13. The layered material according to claim 12, wherein a is greater than 0 and not more than 0.

5.

14. The layered material according to claim 12, wherein a is greater than 0 and not more than 0.

33.

15. An electrode active material for an electrochemical device, comprising the layered material according to any one of claims 1 to 14.

16. An electrochemical device, comprising a pair of electrodes and an electrode active material disposed in contact with at least one of the pair of electrodes, wherein the electrode active material includes the layered material according to any one of claims 1 to 14.

17. An electrochemical capacitor, comprising a positive electrode and a negative electrode, wherein the positive electrode and the negative electrode are disposed apart from each other in an electrolytic solution, and at least one selected from the group consisting of the positive electrode and the negative electrode includes the layered material according to any one of claims 1 to 14 as an electrode active material.

18. The electrochemical capacitor according to claim 17, wherein the negative electrode includes the layered material as an electrode active material.

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