Powder, electrode material for electrochemical device, and electrochemical device

Abstract

A powder 1a contains layered materials 1k. The layered materials 1k each comprise a layer 10. The layer 10 includes a body 11 and a terminus 12. The body 11 has the composition MmXn. The terminus 12 is present on the surface of the body 11. In the body 11, 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 1-4. m is higher than n but not higher than 5. The median diameter D50 in the volume-based particle diameter distribution of the powder 1a is 10 μm or smaller.

Description

Powder, electrode materials for electrochemical devices, and electrochemical devices

[0001] This disclosure relates to powders, electrode materials for electrochemical devices, and electrochemical devices.

[0002] In recent years, a material called MXene has attracted attention. MXene is a two-dimensional (2D) material, and as described below, it is a layered material having one or more layers. MXene generally exists in 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 on the application of MXene to electrochemical capacitors. For example, Non-Patent Literature 1 describes that when two-dimensional titanium carbide, a type of MXene, is produced by etching Al from Ti3AlC2, using a solution of lithium fluoride and hydrochloric acid increases the capacitance per unit volume.

[0004] Michael Ghidiu et al., “Conductive two-dimensional titanium carbide 'clay' with high volumetric capacitance”, Nature volume 516, pages78-81 (2014)

[0005] This disclosure provides a novel powder that contains a predetermined layered material and is advantageous from the viewpoint of improving the performance of electrochemical devices.

[0006] The powder of this disclosure comprises a layered material, the layered material being M m X n The device comprises a body having the composition and a layer including an end plate present on the surface of the body, 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, m is greater than n and 5 or less, and the median diameter in the volume-based particle size distribution is 10 μm or less.

[0007] According to the present disclosure, it is possible to provide a novel powder that is advantageous from the viewpoint of enhancing the performance of an electrochemical device while containing a predetermined layered material.

[0008] FIG. 1 is a side view schematically showing an example of the powder. FIG. 2 is a view schematically showing an example of the layered material. FIG. 3 is a view schematically showing an example of the electrochemical device. FIG. 4 is a view schematically showing another example of the electrochemical device. FIG. 5 is a graph showing the volume-based particle size distribution of the powders according to the examples and comparative examples. FIG. 6A is a scanning electron microscope (SEM) photograph of a cross-section of an electrode containing the powder according to Example 2. FIG. 6B is an SEM photograph of a cross-section of an electrode containing the powder according to Example 2. FIG. 7A is an SEM photograph of a cross-section of an electrode containing the powder according to Example 3. FIG. 7B is an SEM photograph of a cross-section of an electrode containing the powder according to Example 3. FIG. 8A is an SEM photograph of a cross-section of an electrode containing the powder according to Example 4. FIG. 8B is an SEM photograph of a cross-section of an electrode containing the powder according to Example 4.

[0009] (Finding underlying the present disclosure) As described in Non-Patent Document 1, it is conceivable to use MXene in an electrode of an electrochemical device such as an electrochemical capacitor. In such an electrochemical device, for example, it is important to enhance performance such as specific capacitance, which is the capacitance [F / cm 3 or F / g] per unit volume or unit mass of the electrode. Therefore, the present inventors have intensively studied MXene that can be used in an electrode of an electrochemical device. As a result, it has been newly found that using a powder having a predetermined particle size distribution while containing a predetermined layered material is advantageous from the viewpoint of enhancing the performance of the electrochemical device. Based on this new finding, the present inventors have completed the electrode of the present disclosure.

[0010] (Embodiment) 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 showing an example of the powder of the present disclosure. As shown in FIG. 1, the powder 1a contains a layered material 1k. FIG. 2 is a view schematically showing an example of the layered material. As shown in FIG. 2, the layered material 1k includes a layer 10. The layer 10 includes a main body 11 and a terminal 12. The main body 11 has a composition of M m X n n. In the main body 11, M is at least one selected from the group consisting of a Group 3 element, a Group 4 element, a Group 5 element, a Group 6 element, and a Group 7 element. X contains at least one selected from the group consisting of a carbon atom and a nitrogen atom. n is 1 or more and 4 or less. m is larger than n and 5 or less. The median diameter D50 in the volume-based particle size distribution of the powder 1a is 10 μm or less.

[0012] The terminal 12 is not limited to a specific atom or atomic group as long as it can form the layer 10 together with the main body 11. The terminal 12 includes, for example, an atom having an electronegativity larger than that of M. In this case, the terminal 12 is likely to exist on the surface of the main body 11 in a desired state. Examples of the atom having an electronegativity larger than that of M are a hydrogen atom, an oxygen atom, a halogen atom, a chalcogen atom, a nitrogen atom, a phosphorus atom, a carbon atom, and an antimony atom. The electronegativity is the electronegativity based on the definition of Pauling.

[0013] The terminal 12 includes, for example, 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. In this case, the terminal 12 is more likely to exist on the surface of the main body 11 in a desired state.

[0014] The median diameter D50 being 10 μm or less makes it easier for electrochemical devices equipped with electrodes containing powder 1a to exhibit high performance. The reason for this is unclear. For example, when the median diameter D50 is 10 μm or less, it is thought that the electrolyte can easily reach deep into the layered material 1k. Furthermore, in electrodes containing powder 1a, the layered material 1k is oriented in various directions, making it easier for the electrolyte to enter the layered material 1k. As a result, it is thought that the capacitance and electrical energy input / output performance of electrochemical devices equipped with electrodes containing powder 1a tend to be high.

[0015] The above median diameter D50 is calculated, for example, based on the results of particle size distribution measurement by laser diffraction. In this case, for example, the above median diameter D50 may be calculated in absorption mode. Alternatively, the above median diameter D50 may be calculated based on micrographs of powder 1a obtained using microscopes such as scanning electron microscopes (SEM), transmission electron microscopes (TEM), and atomic microscopes (AFM). In this case, for example, the above median diameter D50 may be calculated based on particle size data of 40 or more layered materials 1k.

[0016] The median diameter D50 mentioned above is, for example, 0.2 μm or more. In this case, aggregation of numerous layered materials 1k in the electrode containing powder 1a is easily suppressed, and electrochemical devices equipped with electrodes containing powder 1a tend to have higher performance.

[0017] The above median diameter D50 is preferably 8 μm or less, more preferably 7 μm or less, even more preferably 5 μm or less, particularly preferably 4 μm or less, and especially preferably 2.5 μm or less. The above median diameter D50 is preferably 0.3 μm or more, more preferably 0.4 μm or more. The above median diameter D50 may be, for example, 0.4 μm or more and 2.5 μm or less.

[0018] The volume-based particle size distribution of powder 1a is not limited to a specific distribution as long as the median diameter D50 is 10 μm or less. For example, in the volume-based particle size distribution of powder 1a, the ratio of the second particle size D90 to the first particle size D10, D90 / D10, is 4 or more. The first particle size D10 is the particle size at which the proportion of particles with a first particle size D10 or less accounts for 10% in the volume-based particle size distribution of powder 1a. The second particle size D90 is the particle size at which the proportion of particles with a second particle size D90 or less accounts for 90% in the volume-based particle size distribution of powder 1a. With such a configuration, layered material 1k with relatively small particle sizes is easily arranged between layered material 1k with relatively large particle sizes, and powder 1a is easily contained at a high density in the electrode. In addition, the layered material 1k is easily oriented in various directions. For this reason, the electrochemical device is more likely to have high performance.

[0019] The ratio D90 / D10 is preferably 5 or greater, and more preferably 10 or greater. For example, the ratio D90 / D10 is 20 or less.

[0020] If we represent the atoms or groups of atoms forming the terminal 12 as T, then layer 10 is M m X n T s It has the following composition. s is any number.

[0021] In the main body 11, the arrangement of M and X is not limited to a specific arrangement. For example, in the main body 11, M is arranged at the vertices of octahedrons so as to form an octahedron array, which is an arrangement of multiple octahedrons sharing edges. In addition, X is arranged inside each octahedron.

[0022] In the main body 11 of the layered material 1k, n and m are not limited to any specific values, as long as n is between 1 and 4 and m is greater than n and 5 or less. n may be, for example, 1, 2, 3, or 4, or it may be a value that satisfies the conditions 1 < n < 2, 2 < n < 3, or 3 < n < 4. For example, if defects such as vacancies exist in the crystals that make up the main body 11, n may not be an integer. m may, for example, satisfy the condition m = n + 1.

[0023] In the main body 11, preferably, n is 2 and m is 3. In this case, the electrochemical device equipped with an electrode containing powder 1a is more likely to have high performance.

[0024] In the main body 11, M is not limited to a specific atom, as long as it is at least one selected from the group consisting of Group 3, Group 4, Group 5, Group 6, and Group 7 elements. Preferably, M contains Ti. In this case, the electrochemical device is more likely to have higher performance. M may contain only Ti, or it may contain elements other than Ti.

[0025] In the main body 11, X may contain carbon atoms. In this case, the performance of the electrochemical device tends to be higher. X may contain only carbon atoms, only nitrogen atoms, or both carbon atoms and nitrogen atoms.

[0026] In the main body 11, X may further contain oxygen atoms. The oxygen atom content in X may be 20% to 80%, or 30% to 75%. Furthermore, even if it is not intended that X contain oxygen atoms, oxygen atoms may be included in X by substituting carbon atoms from the raw materials. The oxygen atom content 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 at all.

[0027] As shown in Figure 2, the layered material 1k has, for example, a multilayer structure. This makes it easier for electrochemical devices to have high performance. The layered material 1k has, for example, a multilayer structure in which a plurality of layers 10 are stacked apart from each other. In this case, two adjacent layers 10 do not have to be completely separated and may include contact areas. The layered material 1k may also have a single-layer structure composed of only one layer 10. The powder 1a is, for example, an aggregate of single-layer or multilayer structures composed of the layered material 1k. The layered material 1k may also be in the form of flake particles.

[0028] When the layered material 1k has a multilayer structure, cations may be present between adjacent layers 10 in the thickness direction of the layer 10. Examples of the cations include protons (H + ), alkali metal ions, alkaline earth metal ions, and quaternary ammonium ions. Anions or solvents coordinating to the cations present between the layers 10 may also be present. Examples of the anions and solvents coordinating to the cations include halide ions, H2O, and propylene carbonate.

[0029] When the layered material 1k has a multilayer structure, as long as the median diameter D50 is 10 μm or less, the number of layers 10 included in the layered material 1k is not limited to a specific value. The number of layers 10 included in the layered material 1k may be, for example, 2 or more, and may be 20 or more and 100,000 or less, or 1,000 or more and 20,000 or less.

[0030] When the layered material 1k has a multilayer structure, the number of layers 10 included in the layered material 1k may be 6 or less. In this case, the layered material 1k is referred to as a low-layer structure.

[0031] Most of the layered materials 1k included in the powder 1a may be layered materials 1k having a single-layer structure and / or low-layer structures. For example, 50% by volume or more of the powder 1a may be layered materials 1k having a single-layer structure and / or low-layer structures.

[0032] The method for producing the layered material 1k is not limited to a specific method. The layered material 1k can be synthesized, for example, by selectively etching A atoms from a precursor having a composition of M m AX n . In the composition of the precursor, M collectively represents the metal atoms corresponding to M in the main body 11 of the layer 10, and m and n respectively correspond to m and n in the main body 11. 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 nIt has a crystal structure in which one layer composed of A atoms is placed between two layers represented by M. m X n In each layer, M is positioned at the vertices of the octahedrons, forming an octahedron array which is an arrangement of multiple octahedrons sharing edges. In addition, X is positioned inside each octahedron. In other words, M m X n Each layer 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 is satisfied, it has a structure in which one layer of X atoms is arranged between (n+1) M atomic layers. In addition, it has repeating units in which an A atomic layer is arranged adjacent to the (n+1)th M atomic layer.

[0033] In MAX, the A atom layer is removed by selective etching of A atoms. This exposes M m X n The surface of the layer is modified by at least one element selected from the group consisting of, for example, hydroxyl groups, hydrogen atoms, halogen atoms, chalcogen atoms, amino groups, phosphorus atoms, and antimony atoms, which originate from the etching solution. In this way, the terminal 12 is formed.

[0034] An etching solution used for selective etching of A atoms is, for example, fluoride ions F - It contains [the following]. 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 CuCl2, or using HCl at high temperature and pressure. Selective etching of A atoms may be performed using halogen gases such as Br2 and I2, or using an organic solution in which halogens such as Br2 and I2 are dissolved.

[0035] The layered material 1k may be produced from a precursor other than MAX. For example, two M m X n A layered material 1k may be produced from a precursor in which two or more A atomic layers are arranged between the layers by selective etching of A atoms.

[0036] After selectively etching A atoms from a precursor such as MAX, the material may be subjected to processes such as ultrasonic treatment, handshake, or shaking using an automatic shaker. These processes can promote the separation (delamination) of layers 10 in the layered material 1k. This can result in a layered material 1k having, for example, a single-layer structure or a low-layer structure. For example, handshake or shaking using an automatic shaker can impart a desired shear stress between layers 10 from the viewpoint of separating the layers 10. For example, consider the case where the layered material 1k has a single-layer structure or a low-layer structure. In this case, the ratio of the layered material 1k in the thickness direction of the layer 10 to the dimension of the layered material 1k in the in-plane direction of the layer 10 is small. Even in such cases, handshake or shaking using an automatic shaker can impart a desired shear stress between layers 10 from the viewpoint of separating the layers 10, making the layered material 1k less prone to breakage and easier to maintain in the desired size.

[0037] In the layered material 1k, some A atoms derived from a precursor such as MAX may remain. The amount of A atoms remaining in the layered material 1k is, for example, 10% by mass or less of the A atom content in the precursor, preferably 8% by mass or less, and more preferably 6% by mass or less. Depending on the application of the layered material 1k, the amount of A atoms remaining in the layered material 1k may be greater than 10% by mass of the A atom content in the precursor.

[0038] The layered material 1k may be produced by a method other than selectively etching A atoms from a precursor such as MAX. The layered material 1k may be produced by a method that includes, for example, heat treatment of metal M, graphite, and a halide of M inside a sealed tube. The sealed tube is, for example, a quartz tube. The layered material 1k may also be produced by a method that includes chemical vapor deposition (CVD) using metal M, a halide of M, and CH4 or N2.

[0039] Powder 1a can be produced, for example, by performing a predetermined grinding treatment on an aggregate of layered material 1k obtained as described above. Examples of grinding treatments include grinding using a ball mill and grinding using a bead mill. The material of the container used in the grinding treatment and the material of the balls or beads may be the same or different. For example, the container, balls, and beads used in the grinding treatment may be made of zirconia. The grinding treatment using a ball mill and the grinding treatment using a bead mill may be dry or wet. In wet grinding treatment, for example, water may be used as a dispersion medium. After the grinding treatment, classification treatment may be performed as needed. By adjusting the conditions of such grinding treatments, the median diameter D50 of powder 1a can be adjusted to 10 μm or less.

[0040] Powder 1a may be produced, for example, by etching a precursor such as MAX that has been pulverized and, if necessary, classified. In this case, the etching time of the precursor can be easily shortened, and the concentration of the predetermined component in the etching solution can be easily reduced. Examples of pulverization processes include pulverization using a ball mill and pulverization using a bead mill.

[0041] For example, an electrode material for electrochemical devices containing powder 1a can be provided. As described above, when such an electrode material is used in an electrochemical device, the electrochemical device is more likely to exhibit high performance.

[0042] An electrode for an electrochemical device containing powder 1a can be provided. In this case, the surface of the electrode may consist substantially only of layered material 1k, or a conductive additive may be present between the layered materials 1k. The conductive additive includes, 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 the layered materials 1k. The binder includes, for example, a resin, and includes at least one selected from the group consisting of polytetrafluoroethylene, polyvinylidene fluoride, and styrene-butadiene rubber. The electrode can be manufactured by forming powder 1a, or a mixture containing powder 1a and a conductive additive or binder, into a film or sheet. For example, a method including suction filtration can be applied to manufacture the electrode. In addition, the electrode may be manufactured using a coating method such as spray coating, bar coating, or dip coating.

[0043] The electrodes described above may be fabricated using a precursor of the layered material 1k or a modified version of the layered material 1k. For example, coated particles are obtained by coating the surface of polymer particles such as polystyrene with the layered material 1k in a solvent. Next, the solvent is removed and the aggregate of coated particles is formed into a film. Then, hollow particles are formed in which the layered material 1k remains in a shell-like structure while removing the polymer by high-temperature treatment or the like. Electrodes may be fabricated in this way. In this case, electrochemical devices using these electrodes are more likely to have higher performance and higher Coulomb efficiency.

[0044] The density of the electrodes described above is not limited to a specific value. For example, it could be 1.5 g / cm³. 3 Above, 2.0g / cm 3 The above, or 2.5 g / cm³ 3 The above is the preferred value, preferably 3.0 g / cm³. 3 That is all. The density is more preferably 3.5 g / cm³. 3 The above is preferable, and more preferably 4.0 g / cm³. 3 The above applies, with 4.5 g / cm³ being particularly preferable. 3 That's all. Its density is, for example, 10 g / cm³. 3 The following applies:

[0045] The thickness of the electrode described above is not limited to a specific value. It may be, for example, 3 μm or more, or 5 μm or more. It may also be 500 μm or less.

[0046] Figure 3 is a schematic diagram showing an example of an electrochemical device. As shown in Figure 3, the electrochemical device 2a comprises a pair of electrodes 3. At least one of the pair of electrodes 3 contains powder 1a. For this reason, the electrochemical device 2a tends to have high performance. The electrochemical device 2a may be an energy storage device, or it may be an electrochemical device other than an energy storage device, such as an electrolysis device.

[0047] The electrode 3 containing powder 1a also contains a layered material 1k. In this case, the average aspect ratio r of the layered material 1k in the cross-section of the electrode along the direction perpendicular to the surface of the electrode 3 is... 1ka This is not limited to a specific value. Average aspect ratio r 1ka This may be calculated, for example, based on a micrograph of a cross-section perpendicular to the surface of the electrode 3 obtained using a microscope such as a SEM, TEM, and AFM. For example, in the micrograph, the maximum diameter d1 of 40 or more layered materials 1k that are visible in their entirety is identified. Next, the diameter d2 of each layered material 1k in a direction perpendicular to the direction in which the maximum diameter d1 of each layered material 1k is determined is identified. The ratio d1 / d2 of the maximum diameter d1 to the diameter d2 of each layered material 1k is the aspect ratio r of each layered material 1k. 1k This is the decision. The aspect ratio r of 40 or more layered materials 1k 1k The arithmetic mean of the average aspect ratio r of the layered material 1k 1ka This is the decision.

[0048] Figure 4 is a schematic diagram showing another example of an electrochemical device. Electrochemical device 2b is configured similarly to electrochemical device 2a, except for parts that are specifically described. Components of electrochemical device 2b that are the same as or correspond to components of electrochemical device 2a are denoted by the same reference numerals, and detailed descriptions are omitted.

[0049] As shown in Figure 4, in the electrochemical device 2b, the pair of electrodes 3 includes a positive electrode 3a and a negative electrode 3b. The positive electrode 3a and the negative electrode 3b are arranged apart from each other in the electrolyte 4. In addition, the electrochemical device 2b is capable of storing energy. In the electrochemical device 2b, at least one of the positive electrode 3a and the negative electrode 3b contains powder 1a. Therefore, the electrochemical device 2b tends to have high energy storage performance. For example, the electrochemical device 2b tends to have a high specific capacity.

[0050] The electrochemical device 2b is, for example, an energy storage device such as an electrochemical capacitor and a secondary battery. For example, the energy density stored in an electrochemical capacitor is generally (1 / 2) × CV 2 This is calculated as follows: Here, C is the specific volume [F / cm²]. 3 The unit of energy density is F / g, where V is the operating potential range [V]. 2 / cm 3 or FV 2 It can be expressed as / g. On the other hand, the energy density stored in an electrochemical capacitor can generally be expressed in units of Wh / L or Wh / kg.

[0051] The specific capacitance C of an electrochemical capacitor is measured using a three-electrode method with a half-cell, on either the positive or negative electrode. 3p [F / cm] 3 Or consider the case where F / g is known. In this case, the specific capacitance C of the full cell constructed using that electrode as both the positive and negative electrode. f [F / cm] 3 Or F / g] is (1 / 4) C 3p It can be estimated to be equal to .

[0052] In the electrochemical device 2b, the electrolyte 4 is not limited to a specific electrolyte. For example, the electrolyte 4 is a non-aqueous electrolyte. In this case, the operating potential range of the electrochemical device 2b tends to be larger. A larger operating potential range is advantageous from the viewpoint of increasing the energy density that can be stored in the electrochemical device 2b. The electrolyte 4 may also be an aqueous electrolyte. In this case, the operating potential range can be adjusted to 1.2V or less to prevent the electrolysis of water. In addition, the usable temperature range of the electrochemical device 2b can be adjusted to a temperature range in which the solvent, water, exists stably in liquid form and freezing and vaporization can be prevented (for example, from -40°C to 80°C). On the other hand, when the electrolyte 4 is a non-aqueous electrolyte, there are fewer constraints on the operating potential range and usable temperature range of the electrochemical device 2b compared to when the electrolyte 4 is an aqueous electrolyte.

[0053] As shown in Figure 4, in the electrochemical device 2b, the electrolyte 4 is contained inside the cell 5, and the inside of the cell 5 is divided by a separator 7 into a space where the positive electrode 3a is located and a space where the negative electrode 3b is located. The positive electrode 3a and the negative electrode 3b are electrically connected to terminals 6a and 6b located outside the cell 5, respectively.

[0054] The separator 7 is not limited to any particular separator, as long as it does not hinder the movement of electrolyte ions contained in the electrolyte 4. The separator 7 is, for example, a dielectric film. Examples of dielectric films are porous films of polyolefins such as polypropylene and polytetrafluoroethylene. The separator 7 may also contain glass fibers.

[0055] The material of cell 5 is not limited to a specific material. The material of cell 5 may be a metallic material such as stainless steel, a resin material such as polytetrafluoroethylene, or other materials. Cell 5 may be sealed or open. There may or may not be voids inside cell 5.

[0056] The positive electrode 3a and the negative electrode 3b may be arranged, for example, inside the cell 5, with a separator 7 placed between the positive electrode 3a and the negative electrode 3b, and a laminate including the positive electrode 3a, the separator 7, and the negative electrode 3b wound around it.

[0057] As described above, at least one selected from the group consisting of positive electrode 3a and negative electrode 3b contains powder 1a. The layered material 1k of powder 1a exchanges electrons with, for example, electrolyte ions contained in the electrolyte solution 4.

[0058] For example, only the positive electrode 3a may contain powder 1a. In this case, the negative electrode 3b may be made of carbon material such as activated carbon, carbon nanotubes, and graphene, or Li4Ti5O 12 These may include the following. Only the negative electrode 3b may contain powder 1a. In this case, the positive electrode 3a may contain graphite, activated carbon, and carbon nanotubes as electrode materials. When only the positive electrode 3a or the negative electrode 3b contains powder 1a, the electrode that does not contain powder 1a may be composed substantially only of electrode material, or it may be configured such that a binder exists between the electrode 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 powder 1a.

[0059] Each of the positive electrode 3a and the negative electrode 3b may be configured as a freestanding film, or it may have a configuration in which a film and / or membrane containing electrode material is formed on a current collector (not shown). The current collector is not limited to any particular current collector as long as it is conductive. The current collector may include, for example, stainless steel, aluminum, or an aluminum alloy.

[0060] The electrolyte 4 contains, for example, an electrolyte and a non-aqueous solvent. The electrolyte 4 may contain an electrolyte and an aqueous solvent, or it may be an ionic liquid. The electrolyte exists as a cation or anion dissolved in the non-aqueous or aqueous solvent.

[0061] The electrolyte 4, for example, contains at least one cation selected from the following cation group and at least one anion selected from the following anion group as an electrolyte. <Cation group> Sodium ion (Na + ), magnesium ions (Mg2+ ), 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 iodide ions (I - )

[0062] The non-aqueous solvent that may be included in the electrolyte 4 is not limited to a specific non-aqueous solvent. For example, the electrolyte 4 may contain at least one selected from the following group of solvents. The non-aqueous solvent may contain only one type of solvent or a mixture of multiple types of solvents. <Group of Solvents> Propylene carbonate (PC), gamma butyrolactone (gBL), ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethoxyethane (DME), dimethyl carbonate (DMC), diethyl carbonate (DEC), and acetonitrile (AN)

[0063] The electrolyte 4 may, if necessary, contain predetermined additives in addition to the solvent and electrolyte.

[0064] When terminals 6a and 6b of the electrochemical device 2a are connected to a load, the electrochemical device 2a discharges. Conversely, when terminals 6a and 6b of the electrochemical device 2a are connected to a power source, the electrochemical device 2a is charged.

[0065] The electrochemical device 2a may be configured as a pseudocapacitor or hybrid capacitor that includes a Faraday reaction, depending on the combination of electrode material and electrolyte 4.

[0066] (Note) Based on the above description, the following technologies are disclosed. (Technology 1) A layered material comprising, the layered material is M m X nA powder comprising a body having the composition and a layer having an end present on the surface of the body, 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, m is greater than n and 5 or less, and the median diameter in the volume-based particle size distribution is 10 μm or less. (Technical 2) The powder according to Technical 1, wherein the end contains an atom having an electronegativity greater than the electronegativity of M. (Technical 3) The powder according to Technical 1 or 2, wherein the end contains at least one selected from the group consisting of hydroxyl groups, hydrogen atoms, halogen atoms, chalcogen atoms, amino groups, phosphorus atoms, and antimony atoms. (Technical 4) The powder according to any one of Technical 1 to 3, wherein the layered material has a multilayer structure. (Technical 5) The powder according to any one of Technical 1 to 4, wherein in the main body, n is 2 and m is 3. (Technical 6) The powder according to any one of Technical 1 to 5, wherein in the main body, M contains Ti. (Technical 7) The powder according to any one of Technical 1 to 6, wherein in the main body, X contains carbon atoms. (Technical 8) The powder according to any one of Technical 1 to 7, wherein the median diameter is 0.2 μm or more. (Technical 9) The powder according to any one of Technical 1 to 7, wherein the median diameter is 0.4 μm or more and 2.5 μm or less. (Technology 10) The powder according to any one of Technology 1 to 9, wherein the ratio of the second particle diameter to the first particle diameter in the particle diameter distribution is 4 or more, the first particle diameter is a particle diameter D10 such that the proportion of particles smaller than or equal to the first particle diameter in the particle diameter distribution is 10%, and the second particle diameter is a particle diameter D90 such that the proportion of particles smaller than or equal to the second particle diameter in the particle diameter distribution is 90%. (Technology 11) The powder according to Technology 10, wherein the ratio is 5 or more. (Technology 12) An electrode material for an electrochemical device comprising the powder according to any one of Technology 1 to 11. (Technology 13) An electrochemical device comprising a pair of electrodes, wherein at least one of the pair of electrodes comprises the powder according to any one of Technology 1 to 11.(Technical 14) The electrochemical device according to Technical 13, wherein the pair of electrodes includes a positive electrode and a negative electrode, the positive electrode and the negative electrode are arranged apart from each other in an electrolyte and are capable of storing energy. (Technical 15) The electrochemical device according to Technical 14, wherein the electrolyte is a non-aqueous electrolyte. (Technical 16) The electrochemical device according to Technical 14 or 15, wherein the negative electrode includes the powder.

[0067] The present disclosure will be further described below with reference to examples. Note that the following examples are illustrative and the present disclosure is not limited to these examples.

[0068] (Example 1) TiC powder, Ti powder, and Al powder were mixed in a zirconia mortar to obtain the mixed powder according to Example 1. These powders were provided by Kojun Chemical Laboratory Co., Ltd. The molar ratio TiC:Ti:Al in the mixed powder according to Example 1 was 2:1:1. The mixed powder according to Example 1 was calcined at 1400°C for 3 hours in an argon gas atmosphere to obtain the calcined body (block) according to Example 1. Next, the calcined body according to Example 1 was crushed with a jaw crusher, and the resulting pulverized material was passed through a sieve with a mesh size of 1 mm to obtain the calcined powder according to Example 1. The calcined powder according to Example 1 was subjected to a first wet grinding treatment for 3 hours and a second wet grinding treatment for 6 hours using a planetary ball mill P-5 manufactured by Fritsch. The second wet grinding treatment was performed following the first wet grinding treatment. In the first grinding treatment, zirconia balls with a diameter of 15 mm were used, and water was used as the dispersion medium. In addition, the rotation speed of the planetary ball mill was adjusted to 100 rotations per minute (rpm). In the second wet grinding process, 5 mm diameter zirconia balls were used, and water was used as the dispersion medium. In addition, the rotation speed of the planetary ball mill was adjusted to 100 rpm. Next, a third wet grinding process was performed for 6 hours using a Fritsch P-7 planetary ball mill. In the third wet grinding process, 5 mm diameter zirconia balls were used, and water was used as the dispersion medium. In addition, the rotation speed of the planetary ball mill was adjusted to 500 rpm. After that, the dispersion medium was removed by drying at 100°C. In this way, MAX powder of the precursor according to Example 1, having the composition Ti3AlC2, was obtained.

[0069] One g of the MAX powder precursor according to Example 1 was added to 60 mL of a 10 M (mol / L) HCl solution containing 4.6 g of LiF, and the HCl solution was stirred at 40°C for 18 hours. Next, the solid obtained by suction filtration was vacuum-dried at 120°C to obtain a dry powder. Next, the dry powder was added to a 1 M HCl solution, and the HCl solution was stirred at room temperature in the range of 15°C to 28°C for 1 hour. Next, the solid obtained by suction filtration was vacuum-dried at 120°C. As a result, Ti3C2T sAn MXene powder according to Example 1 having the following composition was obtained. T represents an atom or functional group forming the end of the layered material, and s is any number.

[0070] A slurry was obtained by mixing the MXene powder, acetylene black powder, and polyvinylidene fluoride according to Example 1 in a mass ratio of 8:1:1 while adding N-methyl-2-pyrrolidone. This slurry was applied to titanium foil using an applicator, and the resulting coating was vacuum-dried at 60°C to obtain an MXene-containing film. The laminate of titanium foil and the MXene-containing film was cut into a circular shape with a diameter of 16 mm in a plan view, and vacuum-dried at 120°C to obtain the electrode according to Example 1.

[0071] Next, a three-electrode electrochemical capacitor, which served as a half-cell for evaluation, was assembled. This half-cell was configured so that all of the applied voltage was distributed across the electrodes according to Example 1. The assembly and evaluation of the electrochemical capacitor were performed inside a glove box under an argon gas atmosphere, simulating actual manufacturing and usage conditions.

[0072] The electrode according to Example 1 was used as the working electrode of the three-electrode cell. An activated carbon electrode (AC) coated on titanium foil was used as the counter electrode of the three-electrode cell. This activated carbon electrode has a capacitance of 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 1M TEA-BF4 / PC electrolyte was used as the electrolyte for the three-electrode cell.

[0073] A battery evaluation cell (product code SB3A) manufactured by EC Frontier was used for the cell body of the three-electrode cell. An activated carbon electrode was placed on the lower body, which is equipped with a counter electrode terminal and an O-ring, with the activated carbon film facing upwards. Next, a separator was placed on top of the activated carbon electrode. Subsequently, an electrode guide was placed on top of the separator, and the electrode was placed in the circular hole in the center of the electrode guide, with the MXene-containing film of the electrode according to Example 1 facing downwards. Next, an electrode retainer and a 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. Subsequently, an upper body equipped with working terminals and an insulating spacer was placed over it. The lower body and upper body were joined together using bolts, wing nuts, and insulating sleeves. A reference electrode was inserted and fixed into the reference electrode holder provided on the upper body. In this way, an electrochemical capacitor, which is an evaluation half-cell, was assembled as an electrode evaluation cell. After assembly, the electrochemical capacitor was left to stand for 3 hours.

[0074] (Electrochemical Measurement) Electrochemical measurements were performed using the evaluation half-cell, which is an electrochemical capacitor assembled as described above. The working electrode, counter electrode, and reference electrode of the electrochemical capacitor assembled above were connected to an external electrode. Using the VMP-300 electrochemical measurement device and EC-Lab software manufactured by Bio-Logic, the sweep speed was set to 1 mV / s or 10 mV / s, and the sweep range was set from 0 V (or open-circuit potential) to -2 V relative to the reference electrode. Since the open-circuit potential of the working electrode is approximately -0.5 V, the working electrode operates as both the positive and negative electrode under these measurement conditions. Cyclic voltammetry (CV) measurements were performed in this manner. From the results of the CV measurements using the evaluation half-cell, the capacitance [F / g] per unit mass of the MXene-containing film of the electrode according to Example 1 was calculated. The results are shown in Table 1.

[0075] (Example 2) MXene powder according to Example 2 was prepared in the same manner as in Example 1, except for the following points. Instead of the first wet grinding treatment, second wet grinding treatment, and third wet grinding treatment for the calcined powder according to Example 1, a fourth wet grinding treatment was performed for 6 hours. In the fourth wet grinding treatment, zirconia balls with a diameter of 5 mm were used, and water was used as the dispersion medium. In addition, the rotation speed of the planetary ball mill was adjusted to 300 rpm. After that, the dispersion medium was removed by drying at 100°C. This yielded the precursor MAX powder according to Example 2. MXene powder according to Example 1 was obtained in the same manner as in Example 1, except that the precursor MAX powder according to Example 2 was used instead of the precursor MAX powder according to Example 1. Electrodes according to Example 2 were obtained in the same manner as in Example 1, except that the MXene powder according to Example 2 was used instead of the MXene powder according to Example 1. An evaluation half-cell was assembled and electrochemical measurements were performed 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. The results are shown in Table 1.

[0076] (Example 3) MXene powder according to Example 3 was prepared in the same manner as in Example 1, except for the following points. Instead of the first, second, and third wet grinding treatments performed on the calcined powder according to Example 1, a 3-hour fifth wet grinding treatment, a 6-hour sixth wet grinding treatment, and a 3-hour seventh wet grinding treatment were performed. A Fritsch P-5 planetary ball mill was used for the fifth and sixth wet grinding treatments. In the fifth wet grinding treatment, 15 mm diameter zirconia balls were used, and water was used as the dispersion medium. In addition, the rotation speed of the planetary ball mill was adjusted to 100 rpm. In the sixth wet grinding treatment, 5 mm diameter zirconia balls were used, and water was used as the dispersion medium. In addition, the rotation speed of the planetary ball mill was adjusted to 100 rpm. A Fritsch P-7 planetary ball mill was used for the seventh wet grinding treatment. In the seventh wet grinding process, zirconia balls with a diameter of 1 mm were used, and water was used as the dispersion medium. In addition, the rotation speed of the planetary ball mill was adjusted to 500 rpm. Subsequently, the dispersion medium was removed by drying at 100°C. This yielded the MAX powder of the precursor according to Example 3. The MXene powder according to Example 3 was obtained in the same manner as in Example 1, except that the MAX powder of the precursor according to Example 3 was used instead of the MAX powder of the precursor according to Example 1. The electrode according to Example 3 was obtained in the same manner as in Example 1, except that the MXene powder according to Example 3 was used instead of the MXene powder according to Example 1. An evaluation half-cell was assembled and electrochemical measurements were performed in the same manner as in Example 1, except that the electrode according to Example 3 was used instead of the electrode according to Example 1. The results are shown in Table 1.

[0077] (Example 4) MXene powder according to Example 4 was prepared in the same manner as in Example 1, except for the points described below. Instead of the first wet grinding treatment, second wet grinding treatment, and third wet grinding treatment for the calcined powder according to Example 1, the calcined powder according to Example 1 was ground in a zirconia mortar to obtain the precursor MAX powder according to Example 4. 1 g of the precursor MAX powder according to Example 4 was added to 60 mL of a 10 M HCl solution in which 4.6 g of LiF was dissolved, and the HCl solution was stirred at 40°C for 48 hours. Next, the solid obtained by suction filtration was vacuum dried at 120°C to obtain the MXene powder according to Example 4. An electrode according to Example 4 was obtained in the same manner as in Example 1, except that the MXene powder according to Example 4 was used instead of the MXene powder according to Example 1. An evaluation half-cell was assembled and electrochemical measurements were performed in the same manner as in Example 1, except that the electrode according to Example 4 was used instead of the electrode according to Example 1. The results are shown in Table 1.

[0078] (Comparative Example 1) TiC powder, Ti powder, and Al powder were mixed in a zirconia mortar to obtain the mixed powder according to Comparative Example 1. The molar ratio TiC:Ti:Al in the mixed powder according to Comparative Example 1 was 2:1.25:2.2. The mixed powder according to Comparative Example 1 was calcined at 1400°C for 3 hours in an argon gas atmosphere to obtain a calcined body (block) according to Comparative Example 1. The calcined body according to Comparative Example 1 was crushed in a zirconia mortar, and the resulting pulverized material was passed through a sieve with a mesh size of 1 mm to obtain the calcined powder according to Comparative Example 1. The calcined powder according to Comparative Example 1 was placed in 9 M HCl and stirred at room temperature in the range of 15°C to 28°C for 96 hours to melt the titanium aluminum alloy. Next, the solid obtained by suction filtration was vacuum dried at 60°C. In this way, the MAX powder of the precursor according to Comparative Example 1, having the composition Ti3AlC2, was obtained. One g of the MAX powder precursor from Comparative Example 1 was added to 60 mL of a 10 M HCl solution containing 4.6 g of LiF, and the HCl solution was stirred at 40°C for 48 hours. Next, the solid obtained by suction filtration was vacuum-dried at 120°C to obtain a dry powder. Subsequently, the dry powder was added to a 1 M HCl solution and stirred at room temperature in the range of 15°C to 28°C for 1 hour. Next, the solid obtained by suction filtration was vacuum-dried at 120°C. This resulted in Ti3C2T sAn MXene powder according to Comparative Example 1, having the following composition, was obtained. T represents an atom or functional group forming the end of the layered material, and s is an arbitrary number. An electrode according to Comparative Example 1 was obtained in the same manner as in Example 1, except that the MXene powder according to Comparative Example 1 was used instead of the MXene powder according to Example 1. An evaluation half-cell was assembled 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, and electrochemical measurements were performed. The results are shown in Table 1.

[0079] (Particle Size Distribution Measurement) The volume-based particle size distribution of the precursor MAX powder and MXene powder for each example and Comparative Example 1 was measured using a Microtrac MT3000EXII laser diffraction particle size distribution analyzer. Each MAX powder and each MXene powder were placed in an aqueous sodium hexametaphosphate solution ranging from 0.2% to 10% by mass and thoroughly dispersed using an ultrasonic homogenizer to obtain the measurement sample. The absorption mode was selected for the calculation method. The results are shown in Table 1 and Figure 5. Figure 5 is a graph showing the volume-based particle size distribution of the powders for the examples and comparative examples. In Figure 5, the vertical axis represents frequency [%] and the horizontal axis represents particle size [μm].

[0080] (Cross-sectional SEM observation) Cross-sectional SEM images of the electrodes according to Example 2, Example 3, and Example 4 were obtained using a scanning electron microscope S-4800 manufactured by Hitachi High-Technologies Corporation. Figure 6A is a cross-sectional SEM image of the electrode according to Example 2, and Figure 6B is a magnified SEM image of a part of the cross-section of the electrode according to Example 2. Figure 7A is a cross-sectional SEM image of the electrode according to Example 3, and Figure 7B is a magnified SEM image of a part of the cross-section of the electrode according to Example 3. Figure 8A is a cross-sectional SEM image of the electrode according to Example 4, and Figure 8B is a magnified SEM image of a part of the cross-section of the electrode according to Example 4.

[0081] Table 1 shows that when the median diameter D50 in the volume-based particle size distribution of MXene is less than 10 μm, the capacitance per unit mass [F / g] of the MXene-containing film tends to be high. For example, when the median diameter D50 in the volume-based particle size distribution of MXene is between 0.4 μm and 2.5 μm, the capacitance per unit mass [F / g] of the MXene-containing film at a sweep rate of 1 mV / s can be 40 F / g or more.

[0082]

[0083] The powder of this disclosure can be used as an electrode for electrochemical devices, and these electrochemical devices can be used in energy storage devices and the like in various fields.

Claims

1. Includes a layered material, wherein the layered material is M m X n A powder comprising a body having the composition and a layer including an end present on the surface of the body, wherein in the body, M is at least one selected from the group consisting of Group 3, Group 4, Group 5, Group 6, 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, and the median diameter in the volume-based particle size distribution is 10 μm or less.

2. The powder according to claim 1, wherein the terminator contains an atom having an electronegativity greater than the electronegativity of M.

3. The powder according to claim 1, wherein the terminator comprises 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 powder according to claim 1, wherein the layered material has a multilayer structure.

5. The powder according to claim 1, wherein in the main body, n is 2 and m is 3.

6. The powder according to claim 1, wherein M is Ti in the main body.

7. The powder according to claim 1, wherein X in the main body comprises carbon atoms.

8. The powder according to claim 1, wherein the median diameter is 0.2 μm or more.

9. The powder according to claim 1, wherein the median diameter is 0.4 μm or more and 2.5 μm or less.

10. The powder according to claim 1, wherein the ratio of the second particle diameter to the first particle diameter in the particle diameter distribution is 4 or more, the first particle diameter is a particle diameter D10 such that the proportion of particles smaller than or equal to the first particle diameter in the particle diameter distribution is 10%, and the second particle diameter is a particle diameter D90 such that the proportion of particles smaller than or equal to the second particle diameter in the particle diameter distribution is 90%.

11. The powder according to claim 10, wherein the ratio is 5 or more.

12. An electrode material for an electrochemical device comprising the powder described in any one of claims 1 to 11.

13. An electrochemical device comprising a pair of electrodes, wherein at least one of the pair of electrodes contains the powder described in any one of claims 1 to 11.

14. The electrochemical device according to claim 13, wherein the pair of electrodes includes a positive electrode and a negative electrode, the positive electrode and the negative electrode are arranged apart from each other in an electrolyte and are capable of storing energy.

15. The electrochemical device according to claim 14, wherein the electrolyte is a non-aqueous electrolyte.

16. The electrochemical device according to claim 14, wherein the negative electrode contains the powder.

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