JP7754458B2 - Composite particle material, manufacturing method thereof, and electrode - Google Patents

Description

The present invention relates to a novel composite particulate material of MXene nanosheets and microparticles, a method for producing the same, and an electrode using the composite particulate material.

Particle materials made of MXene layered compounds have been known for some time. These particles are obtained by removing Al from MAX-phase ceramic powder, such as _Ti3AlC2 , through acid treatment (Patent Documents 1 to ₆ ). These MXene layered compounds are capable of storing and desorbing Na and Li ions in the void spaces formed by removing the Al layer. Therefore, they are expected to be used as negative electrode active materials for secondary batteries (storage batteries), as well as positive and/or negative electrode active materials for pseudocapacitors (also known as redox capacitors) that utilize electrochemical reactions involving Faraday currents associated with oxidation-reduction reactions at electrode interfaces and electrochemical ion adsorption/desorption reactions at electrodes. Furthermore, due to their excellent electrical conductivity, they are expected to be used in electromagnetic wave shielding thin films, conductive thin films, and the like.

MAX phase ceramics are layered compounds with the general formula Mn _{+ 1AXn} , where M is a transition metal (Ti, Sc, Cr, Zr, Nb, etc.), A is an A group element, X is C or [C _{(1.0-x) Nx} (0<x≦1.0)], and n is 1 to 3.

When A is Al, the bond between M and A is weaker than the bond with M and X, so the Al layer is selectively removed by acid treatment. The inventors have proposed a method for preparing MXene nanosheets by exfoliating the layer using a bead mill with micro-sized beads (Patent Documents 5 and 6).

JP 2016-63171 A Japanese Patent Application Laid-Open No. 2017-76739 US Patent Application Publication No. 2017/0294546 US Patent Application Publication No. 2017/0088429 Patent No. 6564553 Patent No. 6564552

When MXene nanosheets are used in secondary batteries (storage batteries) or pseudocapacitors, acetylene black is added as a conductive additive in addition to the MXene nanosheets. To improve battery characteristics such as cycle characteristics (lifetime characteristics), rapid charge/discharge characteristics, and capacity, it is necessary to increase ion diffusion and ensure smooth electron transfer to the current collector. Specifically, it is necessary to exfoliate the nanosheets to a single layer level, increase the specific surface area of the composite particle material of MXene nanosheets and conductive microparticles, and ensure that the conductive microparticles are uniformly distributed between the nanosheets. After extensive investigation, we have succeeded in obtaining a composite particle material of MXene nanosheets and conductive microparticles that is effective as a negative electrode active material for secondary batteries (storage batteries) or as a positive and/or negative electrode active material for pseudocapacitors.

The composite particle material previously filed by the applicant forms clumps of aggregated primary particles. Therefore, for industrial use, milling and classification are essential. It was found that milling, which involves applying physical stress to the aggregates, as is commonly done, appears to result in a practically usable particle size, but that the aggregate structure is locally destroyed. Furthermore, because the strength of the aggregates is affected by the humidity environment, the resulting aggregate structure varies depending on the season, making it impossible to obtain an industrially usable composite particle material. Using portions with a destroyed aggregate structure in electrodes for secondary batteries or pseudocapacitors leads to significant degradation of performance. Furthermore, milling, which involves applying physical stress, results in irregular particle shapes, making it difficult to form uniform films when creating electrodes.

The present invention was completed in consideration of the above-mentioned situation, and its objective is to provide a composite particle material with high sphericity, a powder having a 3D porous aggregate structure with a high specific surface area, in which novel MXene nanosheets and microparticles are highly dispersed, a method for producing the same, and an electrode using the composite particle material.

The composite particle material of the present invention, which solves the above-mentioned problems, contains 3 to 10 parts by mass of conductive microparticles and 90 to 97 parts by mass of _Ti3Ala ( _C ( _{1.0 -x} ) _Nx ) ₂ (0≦x≦0.25, a is 0.01 or more) MXene nanosheets as primary particles, and the MXene nanosheets have an average thickness of 1.0 to 3.5 nm, a mutual dispersion index (described below) of 0.01 to 7.00, a volume average diameter of 1.0 μm to 15.0 μm, and a sphericity of 0.80 or more.

(mutual dispersion degree)
In Raman spectroscopy using a 532 nm laser, the ratio (B/A) of the peak height A at 400 cm ⁻¹ to the peak height B at 1332 cm ⁻¹ is calculated for 100 samples, and the standard deviation calculated from the 100 B/A values is taken as the mutual dispersion.

The method for producing a composite particulate material of the present invention that solves the above-mentioned problems includes a step of exfoliating _Ti3Ala (C( _{1.0 -x} ) _Nx ) ₂ , (0≦x≦0.25, a is 0.01 or more)MXene in a dispersion medium containing ₅₀ mass % or more of water to form an exfoliated product;
an acid treatment step in which the raw carbon particles are treated in a mixed acid solution of sulfuric acid and nitric acid at 70°C or higher for 10 minutes or more to obtain carbon particles;
a mixing step of adding 0.8 to 1.0 mol/L of a water-soluble lithium salt and/or a water-soluble sodium salt to a mixture slurry of the exfoliated material and the carbon fine particles in a mass ratio of 90:10 to 97:3 and having a particle concentration of 11.5 to 17.0 mg/L, and stirring the mixture;
an aggregating step of adding 0.4 to 0.7 mol/L of an alkaline aqueous solution to the mixture slurry to make the solution alkaline and cause agglomeration, thereby obtaining a slurry of agglomerates of the _Ti3Ala (C( _{1.0 -x} ) _Nx ) ₂ , (0≦x≦0.25 _, a is 0.01 or more)MXene and the carbon microparticles;
a granulation step in which the dispersion medium of the slurry is replaced with alcohol to prepare an alcohol slurry of the aggregate, and the alcohol slurry is granulated by a spray drying method under an inert atmosphere to obtain granules;
It has.

By having the above-mentioned configuration, the composite particle material of the present invention can be used as an active material to provide electrodes that can demonstrate high performance when used in secondary batteries (storage batteries) or pseudo-capacitors.

Furthermore, by using the manufacturing method for the composite particulate material of the present invention having the above-mentioned configuration, it is possible to produce a composite particulate material with a high degree of sphericity and an ideal 3D porous aggregation structure.

1 is an AFM image of a peeled product obtained in the peeling step of Example 1. 1 is a SEM photograph of a peeled product obtained in the peeling step of Example 1. 1 shows XRD profiles of Ti ₃ AlC ₂ and composite powder materials in Example 1. 1 is a SEM photograph of the composite powder material of Example 1. 1 shows adsorption isotherms of composite powder materials of Examples 1 and 2 and Comparative Example 4. 1 is an AFM image of a peeled product obtained in the peeling step of Example 2. 1 is a SEM photograph of a peeled product obtained in the peeling step of Example 2. 1 shows XRD profiles of Ti ₃ AlC ₂ and composite powder materials in Example 2. 1 is a SEM photograph of the composite powder material of Example 2. 1 is a SEM photograph of the composite powder material of Comparative Example 2. FIG. 1 is a schematic diagram showing a unit cell of the MAX phase (Ti ₃ AlC ₂ ).

The composite particle material, its manufacturing method, and electrode material of the present invention are described in detail below based on embodiments. The composite particle material of this embodiment has excellent electrical properties, such as electrical conductivity, and has a large void layer formed within the crystal due to the removal of the Al layer. Therefore, it can be applied to active materials such as secondary batteries (Li-ion secondary batteries, Na-ion secondary batteries, etc.), pseudocapacitors (negative electrode active materials in the case of secondary batteries, and positive and/or negative electrode active materials in the case of pseudocapacitors), electromagnetic wave shielding thin films, and conductive thin film materials. Note that the numerical values described in this specification can be used as the upper or lower limits of a numerical range, in which case the range can be either inclusive or exclusive of the numerical value.

(Composite particle material)
The composite particulate material of this embodiment is a composite of exfoliated MXene and particulate or tubular microparticles for application to electrode materials, etc. The exfoliated MXene particulate material is obtained by peeling off multilayer MXene, a powdered layered compound of several micrometers in size.

In this specification, when multiple upper and lower limit values are set for a parameter, these upper and lower limit values can be combined in any way unless otherwise specified. The composite particulate material of this embodiment is a composite particulate material of MXene and microparticles.

The MXene content is 90-97% based on the sum of the masses of MXene and microparticles, with the remaining 10-3% being microparticles. If the MXene content exceeds 97%, the effect of the microparticles as a barrier against drying shrinkage is reduced, and if it is below 90%, the function as an active material deteriorates. Furthermore, if the MXene content exceeds 97%, electrons become less likely to move to the current collector, and if it is below 90%, the function as an active material deteriorates. Lower limits for the MXene content include 93%, 92%, and 90%, and upper limits include 97%, 96%, and 95%.

The composite particle material has a mutual dispersity of 0.01 to 7.00. The mutual dispersity is a value that defines the degree of dispersion between MXene and the microparticles. When carbon microparticles are used as the microparticles, the mutual dispersity is the standard deviation calculated from the ratio (B/A) of the peak height A at 400 cm ^-1 to the peak height B at 1332 cm ^-1 by Raman spectroscopy using a 532 nm laser for 100 randomly selected composite particle materials. A small mutual dispersity is desirable; if it exceeds 7.00, electrons cannot be effectively transferred to the current collector. The mutual dispersity of the composite particle material can have a lower limit of 0.01, 0.05, or 0.10, and an upper limit of 7.00, 2.50, or 1.50. _Ti3Ala (C( _{1.0 -x} ) _Nx ) ₂ (0≦x≦0.25, a is 0.01 or greater) MXene nanosheets exfoliated to the monolayer level are easily oxidized to form anatase when irradiated with a laser, _so analysis is performed at a laser intensity that does not cause anatase precipitation. Analysis is performed in the range of 100 cm ^-1 to 2000 cm ^-1 . Vibrations due to functional groups adsorbed on titanium _atoms of _Ti3Ala (C( _{1.0 -x} ) _Nx ) ₂ (0≦x≦0.25, a is 0.01 or greater) MXene nanosheets appear at 230 to 470 cm ^-1 (A peak), and vibrations due to functional groups adsorbed on carbon atoms appear at 580 cm ^-1 . On the other hand, in acetylene black, the carbon of the SP3 hybrid orbital appears at 1332 cm ⁻¹ (peak B), and the carbon of the SP2 hybrid orbital appears at 1500 to 1600 cm ⁻¹ .

The composite particle material has a specific surface area of 75 m ² /g or more. The specific surface area is measured by the BET method using nitrogen after pre-treatment of heating in a vacuum at 110°C for 6 hours. The lower limit of the specific surface area of the composite particle material can be 75 m ² /g, 80 m ² /g, or 105 ^{m 2} /g, and the upper limit can be 200 ^{m 2} /g, 185 ^{m 2} /g, or 170 ^{m 2} /g. The composite particle material preferably has an average pore diameter of 10.0 to 20.0 nm and an average pore volume of 0.30 to 0.70 mL/g. The average pore diameter is more preferably 10.0 to 15.0 nm and an average pore volume of 0.40 to 0.60 mL/g. The average pore diameter and pore volume are measured by the BET method using nitrogen after pre-treatment of heating in a vacuum at 110°C for 6 hours.

In our previously filed PCT/JP2021/018296 application, we disclosed a composite material obtained by preparing a slurry of agglomerated particle material in a liquid, centrifuging the resulting sediment, air-drying it at room temperature, and then vacuum-drying it at 60°C to form agglomerates, which were then pulverized by applying physical stress to produce a composite particle material (secondary particles). Air-drying takes more than 24 hours. The material shrinks during air-drying and vacuum-drying at 60°C. The shrinkage mechanism is that MXene nanosheets overlap and integrate, while carbon microparticles added as a shrinkage barrier migrate. This mechanism reduces the interdispersity and the specific surface area. Furthermore, the average pore diameter and average pore volume also decrease. Vacuum drying at 110°C after air-drying significantly shrinks the material, significantly reducing the specific surface area. On the other hand, spray-drying a composite agglomerated particle slurry in an alcohol solvent allows the droplets to dry instantly without shrinkage, resulting in a spherical composite particle material with a 3D porous agglomerated structure that has excellent interdispersity and a high specific surface area. The method of obtaining a composite particulate material by spray drying, which dries instantly, results in a larger specific surface area and larger average pore diameter and average pore volume than the commonly used method of obtaining a composite particulate material as secondary particles by applying physical stress to agglomerates. Note that the 3D porous aggregate structure refers to a structure in which primary particles aggregate with gaps forming, resulting in pores formed in a three-dimensional network.

The composite particle material preferably exhibits a mass change of 1.0% or less when a 0.3 g sample is uniformly spread on a ²⁰ cm or larger dish and heated in a vacuum at 110°C for 5 hours. Under these heating conditions, the moisture contained between the MXene layers and the moisture attached to the outer surface volatilize. By specifying the amount of volatilization, a composite particle material with a low interlayer moisture content can be specified. Upper limits of mass change can be set to 0.8%, 0.6%, 0.4%, or 0.2%. The mass change within the specified range refers to the amount of moisture adsorbed from the air onto the outer surface of the composite particle material, not the water between the MXene layers. Residual moisture between the MXene layers can degrade the cycle characteristics of secondary batteries and pseudocapacitors. The residual water between the layers cannot be completely removed by vacuum heat treatment after cell fabrication of secondary batteries or pseudocapacitors. The spray-dried composite particle material is preferably dried in a vacuum or inert atmosphere at 100-120°C.

The composite particulate material preferably has a bulk density of 0.1 to 0.5 g/cm ^3. As the lower limit, 0.1 g/cm ³ or 0.15 g/cm ³ can be adopted, and as the upper limit, 0.45 g/cm ³ or 0.50 g/cm ³ can be adopted. When producing a cell for a secondary battery or pseudocapacitor, the method for producing an electrode film is not particularly limited, but it is preferable to produce the composite particulate material to be contained so that the volume packing density is as high as possible.

For example, using general-purpose technology, films can be formed by mixing composite particle materials with several different average secondary particle sizes and bulk densities, such as continuous particle blending (meaning that the particle sizes of the composite particle materials blended change continuously, resulting in a relatively broad particle size distribution) in which composite particle materials with several different secondary particle sizes are blended to achieve the particle size distribution shown by Andreasen, which results in a close-packed structure, or two-stage particle blending in which composite particle materials with large and small secondary particle sizes are blended.

MXene is obtained by using Al for A in the formula Mn _{+ 1AXn} (M is a transition metal, A is an A group element, X is C or [C _{(1.0-x) Nx} (0<x≦1.0)], n is 1 to 3), which represents the aforementioned MAX phase, and removing the Al _phase by acid treatment. Among them, _Ti3Ala (C( _{1.0 -x} ) _Nx ) ₂ (0≦x≦0.25, a is 0.01 or more) is preferred. The lower limit of a can be 0.002. The upper limit of a is more preferably 0.05. If x exceeds 0.25, bead milling using microbeads will result in more microparticulation than exfoliation, making it impossible to obtain thin, large nanosheets. In addition to these elements, O, OH, and halogen groups can also be present as surface functional groups.

MXene may be in the form of a plate, leaf, flake, or sheet, collectively defined as a sheet. The direction in which the layers of the layered compound are stacked is defined as the "thickness" of MXene, and the countless directions perpendicular to that thickness are defined as the "sheet spreading direction." The average thickness of MXene is 1.0 to 3.5 nm, preferably 1.5 to 3.0 nm. The average thickness is calculated as the average value of the values measured by AFM analysis using a hydrophilized Si wafer for 100 randomly selected particles. The sheet size can be measured by SEM after dropping a nanosheet onto a hydrophilized Si wafer. The average size in the sheet spreading direction is preferably 0.1 to 2.0 μm, and more preferably 0.1 to 1.7 μm. The maximum value in the direction perpendicular to the thickness is defined as the "long side" and the minimum value as the "short side," and the average value of [(long side + short side)/2] measured by SEM for 100 randomly selected particles is defined as the average size in the spreading direction. _{In Ti3Ala} (C( _{1.0 -x} ) _Nx ) ₂ (0≦x≦0.25, a is 0.01 or more)MXene, _{Ti3Al0.02C2MXene} has an average thickness of _{1.74 nm} and an average size of 0.78 μm. However, when 5% of the carbon sites are replaced with nitrogen, the average thickness becomes 1.66 nm and the average size becomes 1.17 μm, and when 25% of the carbon sites are replaced with nitrogen, the average thickness becomes 1.81 nm and the average size becomes 1.61 μm. Substituting nitrogen for carbon sites facilitates the formation of functional groups in water, weakening the interlayer bonding strength of MXene, resulting in larger nanosheets with monolayer thicknesses. Lowering the sintering (synthesis) temperature of MAX phase ceramics without impurity formation also reduces the interlayer bonding strength, enabling the average size to be reduced while maintaining monolayer thickness. For example, in the case of _{Ti3Al0.02C2MXene} , lowering the sintering (synthesis) temperature of MAX _phase ceramics from ₁₄₅₀ °C to 1430°C reduces the average thickness to 2.06 nm and the average size to 0.25 μm. Further lowering the temperature to 1410°C reduces the average thickness to 1.98 nm and the average size to 0.10 μm.

By producing composite particle materials from MXene nanosheets exfoliated to the monolayer level without shrinkage, it is possible to obtain electrode materials with excellent ion diffusion. Furthermore, by using MXene nanosheets of an appropriate size, it is possible to obtain composite particle materials with a high specific surface area. By reducing the average size while maintaining monolayer-level thickness, it is possible to obtain composite particle materials with an even higher specific surface area.

The interlayer distance of the (002) plane of MXene obtained by XRD analysis is preferably 1.400 nm to 1.700 nm. The interlayer distance of the void layer formed by removing the Al phase of the MAX phase by acid treatment is 0.770 nm to 0.470 nm, defined as the interlayer distance of the (002) plane in the XRD of the MXene nanosheet powder minus the interlayer distance of the (002) plane in the XRD of the corresponding MAX phase ceramic powder. The Li ion diameter is 0.18 nm, and the Na ion diameter is 0.28 nm, making it suitable for use as a negative electrode active material in both Li-ion secondary batteries and Na-ion secondary batteries. Because the interlayer distance of the (002) plane of graphite powder is 0.33 nm, repeated insertion and desorption of Na ions causes rapid deterioration in a short period of time, leading to the conclusion that it cannot be used in Na-ion secondary batteries. This is why MXene nanosheets are particularly promising as anode active materials for Na-ion secondary batteries. Larger gaps reduce expansion and contraction due to ion transfer, allowing for rapid charge/discharge without cycle degradation. The corresponding MAX-phase ceramic powder is a particulate material composed of _the MXene composition _Ti3Ala (C( _{1.0 -x} ) _Nx ) ₂ , where a is 1. If the interlayer distance of the (002) plane of an MXene nanosheet is less than 1.400 nm, rapid charge/discharge degradation occurs when used as anode active materials for Na-ion secondary batteries. If the interlayer distance exceeds 1.700 nm, the capacity per gram decreases.

It is sufficient for the size of the microparticles to be on the order of nanometers, where nanometers means that the longest part of the length of the microparticle is 100 nm or less. The shape of the microparticles may be any shape, including amorphous, spherical, thin film, or fibrous.

The primary particle diameter of the microparticles is preferably 100 nm or less, more preferably 30 to 50 nm, and even more preferably 30 to 40 nm, and they may be in the form of aggregates. The shape of the microparticles is not limited, and examples include spherical, sheet-like, tubular, hollow, and amorphous shapes.

In particular, the microparticles are electrically conductive. Examples of the microparticles include carbon microparticles made of a carbon material and metal microparticles made of a metal material. As the carbon microparticles, it is preferable to use highly conductive materials such as acetylene black, Ketjen black, carbon nanotubes, graphene, carbon fiber, graphite powder, and hard carbon powder. In addition to carbon microparticles and metal microparticles, inorganic microparticles made of other inorganic substances can also be used. As the inorganic microparticles, _TiO2 , _Al2O3 , _SiO2 , and _{BaTiO3 with} a primary particle diameter of 100 nm or less can be used.

(Method for producing composite particle material)
The method for producing a composite particulate material of this embodiment includes an exfoliation step, a mixing step, an aggregation step, a granulation step, and other necessary steps, and is a production method that can be suitably employed for producing the composite particulate material of this embodiment described above.
Peeling process: The peeling process involves exfoliating layered multilayer MXene particles of several micrometers in size by colliding microbeads between the layers in a dispersion medium, thereby obtaining nanosheet-like exfoliated material slurry. Peeling occurs between each layer of the layered multilayer MXene. There are no particular limitations on the exfoliated material, but it is preferable for it to have about 1 to 3 layers.

The resulting exfoliated material becomes an exfoliated material suspension suspended in a dispersion medium. This exfoliated material suspension can be subjected to the mixing process as is, or the dispersion medium can be removed before the mixing process. There are no particular limitations on the method for obtaining the particulate, layered multilayer MXene material, but examples include the following methods.

MXene is obtained by acid-treating a raw material consisting of a Ti3-layer MAX phase ceramic powder to partially dissolve the Al layer. An example of a method for producing MXene is described below as a pretreatment process. The raw material used in the peeling process can have the same composition as the material that makes up the particle material described above. The composition does not change significantly during the peeling process.

This particulate material is treated with acid to dissolve some of the Al, turning it into layered multilayer MXene particles of several microns in size. This multilayer MXene is then mixed into a solvent whose main component is water to form a mixture, which is then subjected to an exfoliation process in which a bead mill is used to rotate at high speed using beads of 10 μm to 300 μm, resulting in an exfoliated suspension of nanosheet-like MXene exfoliated material.

The dispersion medium used in the peeling process is not particularly limited, but preferably contains at least 50% water by mass, and may also contain alcohols such as methanol, ethanol, and isopropanol, ketones such as methyl ethyl ketone, acetone, dimethylformamide, and dimethyl sulfoxide. It is more preferable to use 100% water by mass.

The concentration of MXene in the mixture used in the peeling process is not particularly limited, but can be approximately 10.0 mg/mL to 20.0 mg/mL. The liquid properties of the mixture are not particularly limited, but the pH can be approximately 6.0 to 8.0.

The specific bead mill processing used in the peeling process will be explained below. Peeling can be performed using a bead mill equipped with a mechanism for classifying the slurry mixture into tiny beads using centrifugation. The peeled material obtained by bead mill processing can be separated from the mixture before peeling at any time using centrifugation, and ultimately all of the MXene can be removed as peeled material.

For example, the lower limit of the bead size can be 10 μm, 15 μm, 20 μm, 30 μm, or 40 μm, with the upper limit being 300 μm, 200 μm, or 100 μm. Beads of 10 μm or larger facilitate easy classification of the beads and slurry. Using beads of 300 μm or smaller allows for prioritizing exfoliation over reducing the size of the particulate material. These lower and upper limits can be used in any combination. Because the appropriate bead size allows for greater applied energy and prioritizes exfoliation, it is most preferable to use beads between 50 μm and 100 μm.

The material of the beads is not particularly limited, but ceramics such as zirconia, alumina, and silicon nitride can be used. Partially stabilized zirconia, which has high fracture toughness, is particularly preferred. On the other hand, with commonly used bead mills that use beads larger than 300 μm and separate beads and slurry through tiny gaps, reducing the size of the particulate material takes precedence over exfoliation. Similarly, with ball mills such as planetary ball mills that use beads or balls larger than 300 μm, reducing the size of the particulate material takes precedence over exfoliation. As a result, only a portion of the material is exfoliated, and only a portion of the exfoliated material is classified by centrifugation, which is not at a level suitable for industrial use.

Furthermore, traditionally, MXene has been exfoliated using ultrasonic irradiation. When ultrasonic waves are applied to a solvent, cavitation occurs, and the resulting collapse causes powder particles to collide with each other, resulting in the exfoliation of the layers that make up the layered compound. However, even when water, which is prone to cavitation, is used, only partial exfoliation occurs, making it unsuitable for industrial use. Even with the planetary ball mill method, only partial exfoliation occurs; grinding takes precedence, and the temperature rises, causing significant surface oxidation, making it unsuitable for industrial use. For these reasons, the method used involves exfoliating only a portion of the powder using ultrasonic irradiation, followed by collection by centrifugation and classification.

A peripheral speed of 6 m/sec to 12 m/sec can be used in the peeling process. A peripheral speed of 8 m/sec to 10 m/sec is more preferable. A speed of 6 m/sec or higher improves peeling efficiency, while a speed of 12 m/sec or lower prevents excessive energy from being applied, suppressing the temperature rise of the resulting particulate material. This prevents the progression of oxidation on the surface of the resulting particulate material and reduces electrical resistance. A slurry feed rate of 100 mL/min to 300 mL/min can be used. A slurry particle concentration of 10.0 mg/mL to 20.0 mg/mL can be used.

If the concentration is below 10.0 mg/mL, the efficiency of producing MXene nanosheets will decrease, and if the concentration is above 20.0 mg/mL, peeling will not proceed sufficiently, so this range is preferable.

The slurry temperature is preferably in the range of 35°C or below. Keeping it below 35°C suppresses surface oxidation and keeps the electrical resistance of the particulate material low.

A bead filling rate of 40% to 80% can be used. A rate of 40% or higher improves peeling efficiency, while a rate of 80% or lower makes it easier to separate the beads and slurry. Whether a particulate material containing a large amount of the desired sheet-like particles has been produced can be determined by observation using an SEM, TEM, etc. The thickness of the particulate material in particular can be determined by AFM analysis. If necessary, the particulate material obtained in the peeling process can be classified using methods such as centrifugation and then used. The optimal conditions for the peeling process vary depending on the size of the equipment, so these values are not limited.

It is preferable to use bead mill processing so that 98% or more of the MXene is exfoliated by mass, more preferably 99% or more, and even more preferably 100%. If the exfoliation process is completed under conditions where all of the MXene is exfoliated, the MXene can be used directly in the mixing process without removing the unexfoliated MXene. To remove MXene other than the exfoliated MXene, it can be separated by centrifugation, filtration, etc.

The zeta potential of the resulting exfoliated MXene is measured in water with a pH of 6 to 8. If no particular problems arise, the zeta potential is measured at pH 7. The zeta potential is preferably between -25.0 mV and -35.0 mV. It is even more preferably between -28.0 mV and -34.0 mV. The zeta potential _{of Ti3C2MXene} nanosheets was -28.9 mV. Nanosheets with 3% of the carbon sites substituted with nitrogen had a zeta potential of -29.3 mV, nanosheets with 5% of the carbon sites substituted with nitrogen had a zeta potential of -31.5 mV, nanosheets with 10% of the carbon sites substituted with nitrogen had a zeta potential of -32.1 mV, nanosheets with 15% of the carbon sites substituted with nitrogen had a zeta potential of -32.4 mV, and nanosheets with 25% of the carbon sites substituted with nitrogen had a zeta potential of -33.1 mV. The absolute value of the zeta potential can be interpreted as the amount of functional groups attached in water. The greater the amount of water-soluble functional groups attached, the greater the absolute value of the zeta potential. The formation of an adequate amount of water-soluble functional groups results in excellent peelability. The zeta potential of the MXene nanosheets and carbon microparticles is a negative zeta potential, as explained in the mixing process. The MXene nanosheets and carbon microparticles are immobilized with positively charged Li ions and/or Na ions in water by adding a water-soluble Li salt and/or a water-soluble Na salt. A moderate zeta potential is necessary; if the absolute value of the zeta potential is small, the resulting composite particle material will have a low degree of mutual dispersion and a low specific surface area. A high absolute value of the zeta potential makes it difficult for electrons to move, so it is preferable to select MXene nanosheets and carbon microparticles with a moderate absolute value of the zeta potential.

The chemical composition of MXene nanosheets was calculated using the atom percentages of Ti, Al, C, and N, with the amount of Al, C, and N being taken as 3 for Ti. For chemical analysis, the sample was weighed onto a platinum dish, nitric acid + sulfuric acid + hydrofluoric acid was added, and the solution was heated (to approximately 120°C) to dissolve it. It was then further heated at a high temperature (300°C) to evaporate the nitric acid and hydrofluoric acid, creating a sample solution (sulfuric acid). The resulting sample solution was then diluted appropriately and quantitatively analyzed using ICP.

Acid Treatment Step In the acid treatment step, the raw carbon particles are treated with a mixed acid solution of sulfuric acid and nitric acid to obtain highly hydrophilic carbon particles. Examples of the raw carbon particles include acetylene black, Ketjen black, carbon nanotubes, graphene, carbon fiber, graphite powder, and hard carbon powder. Acetylene black, Ketjen black, and carbon nanotubes are preferred in terms of electrical conductivity, purity, and price, and acetylene black is more preferred.

The acid treatment process results in a suspension of carbon particles suspended in mixed acid, which can be used as is in the mixing process, or the mixed acid can be removed as needed by repeated washing with water or other means and the resulting carbon particles can be used. Washing can be carried out until the pH of the washing solution reaches around 6, and can even be continued until the pH reaches around 6.5, 7, or 8.

This treatment introduces functional groups such as COOH groups and CO groups onto the surface of the carbon particles, making them hydrophilic. After the treatment, the carbon particles become a carbon particle suspension dispersed in mixed acid. This treatment can be performed either before or after the acid treatment process and the peeling process.

The treatment temperature is preferably 70°C or higher. It is particularly preferable to keep it below 95°C to prevent boiling. There are no particular restrictions on the treatment time, but treatment for 10 minutes or more will ensure hydrophilization. During treatment, stirring or ultrasonic irradiation can be performed. After treatment, the mixture can be directly subjected to the mixing process, or the acid can be neutralized or separated. If the pH is raised above a predetermined value by neutralizing or separating the acid, the carbon microparticles will aggregate, so neutralization can be performed to a degree that does not cause the pH to reach the predetermined value. An example of a method for separating the acid is to separate the solids by a classification operation such as centrifugation.

The mixing ratio of sulfuric acid to nitric acid can be approximately 4:1 to 1:1 by volume, with approximately 3:1 to 3:2 being particularly preferred. The concentration of the mixed acid can be approximately 42% to 96%, with approximately 90.0% to 95.0% being particularly preferred.

The zeta potential of the resulting hydrophilic carbon microparticles is preferably between -20.0 mV and -25.0 mV in water at pH 6-8. The zeta potential is negative due to the adsorption of COOH and CO as functional groups. If the absolute value is less than -20.0 mV, the MXene nanosheets, which have a negative zeta potential as described in the mixing process, cannot be immobilized with positively charged Li ions and/or Na ions in water by adding water-soluble Li salt and/or water-soluble Na salt, resulting in a composite particle material with low mutual dispersion and a low specific surface area. It is preferable to select MXene nanosheets and carbon microparticles with an appropriate absolute value of zeta potential.

Mixing Step: The mixing step is a step of obtaining a mixture in which the exfoliated material and carbon microparticles are dispersed in a second dispersion medium containing 50% by mass or more of water at a mass ratio of 90:10 to 97:3 and a concentration of the exfoliated material of 11.5-17.0 mg/mL. It is more preferable that the second dispersion medium contains 100% by mass of water. By adding other substances to the mixture, the substances can also be incorporated into the composite particle material.

In particular, the coexistence of Li ions or Na ions enables the immobilization of the MXene and carbon microparticles that constitute the exfoliated material. Specifically, it is preferable to immobilize the negatively charged functional groups adsorbed on MXene in water and the negatively charged functional groups adsorbed on the carbon microparticles with Li ions and/or Na ions that are positively charged in water. Examples of water-soluble lithium salts include lithium chloride and lithium carbonate, and examples of water-soluble sodium salts include sodium chloride and sodium carbonate. Adding a water-soluble salt of a strong alkali or strong acid and stirring for a long period of time can cause the MXene nanosheets to react with the water-soluble salt, resulting in the precipitation of lithium titanate or sodium titanate locally on the MXene surface. Therefore, water-soluble salts that maintain neutrality after dissolution in water are preferred. It is preferable to add a water-soluble salt to the MXene aqueous slurry so that the concentration is 0.8 mol/L to 1.0 mol/L. A concentration below 0.8 mol/L will not result in sufficient immobilization, while a concentration above 1.0 mol/L will leave a large amount of excess ions. The mixture contains exfoliated material at a concentration of 11.5-17.0 mg/mL. The second dispersion medium may be the same as or different from the dispersion medium used in the exfoliation step or the solvent that can be used in other steps. When the exfoliated material suspension obtained in the exfoliation step is directly subjected to the mixing step, the second dispersion medium contains the dispersion medium used in the exfoliation step. The reason for limiting the MXene particle concentration in the composite slurry to 11.5-17.0 mg/mL is that if the concentration is below 11.5 or above 17.0, the specific surface area of the composite particle material obtained in the aggregation step described below will be small.

For the acid-treated carbon microparticles, a predetermined amount of carbon microparticles is added to pure water and stirred for 12 hours or more using a shaker at a rotation speed of 100 to 300 rpm and an amplitude of 40 to 50 mm, more preferably at a rotation speed of 100 to 200 rpm and an amplitude of 45 to 50 mm. The resulting carbon microparticle water slurry is then added to and mixed with the MXene water slurry. The shaker conditions for this are preferably a rotation speed of 100 to 300 rpm and an amplitude of 40 to 50 mm, more preferably a rotation speed of 100 to 200 rpm and an amplitude of 45 to 50 mm. It is more preferable to simultaneously add an aqueous slurry of acid-treated carbon microparticles and a water-soluble salt to an aqueous MXene slurry and stir the mixture for 4-6 hours using a shaker at a rotation speed of 100 to 300 rpm and an amplitude of 40 to 50 mm, thereby immobilizing the uniform arrangement of MXene nanosheets, Na and/or Li ions, and carbon microparticles in the liquid and obtaining an aqueous slurry of uniformly dispersed composite agglomerated particles. In both cases, if the rotation speed exceeds 300 rpm, the nanosheets are likely to be destroyed, and if the rotation speed is below 100 rpm, uniform mixing is not possible. If the amplitude exceeds 50 mm, the nanosheets are likely to be destroyed, and if the amplitude is below 40 mm, uniform mixing is not possible.

The flocculation step is a step in which an alkaline aqueous solution of 0.4 to 0.7 mol/L is added to the mixture slurry obtained in the mixing step to increase the pH of the liquid, thereby flocculating the exfoliated material and carbon microparticles contained in the mixture to form flocs dispersed in the liquid. The pH is preferably increased to about 12 to 14.

The alkaline aqueous solution is preferably lithium hydroxide and/or sodium hydroxide. The pH can be increased by adding an alkaline substance or by removing or diluting an acidic substance. The pH can be increased by adding the alkaline aqueous solution over a few seconds and stirring within one hour using a shaker at a rotation speed of 100 to 300 rpm. The amplitude of the shaker is preferably 40 to 50 mm. In either case, a rotation speed of 300 rpm or less prevents destruction of the nanosheets, while a rotation speed of 100 rpm or more facilitates uniform mixing.

An amplitude of 50 mm or less prevents nanosheet destruction, while 40 mm or more facilitates uniform mixing. It is more preferable to use a shaker with a rotation speed of 100 to 200 rpm and an amplitude of 45 to 50 mm for less than one hour. The alkaline aqueous solution is preferably added so that the total amount of water contained in the aqueous slurry of the composite agglomerated particle material is 0.4 mol/L to 0.7 mol/L. A concentration of 0.4 mol/L or more ensures sufficient agglomeration, while a concentration of 0.7 mol/L or less is preferable because it prevents excess ions from remaining. Adding an amount within this range allows for a composite particle material with a high specific surface area, although the exact reason is unclear. A highly hydrophobic organic solvent with a low dielectric constant can also be added.

Granulation process: In the granulation process, the main component of the dispersion medium contained in the aggregates dispersed in the liquid obtained in the aggregation process is replaced with alcohol to form an alcohol slurry, and the alcohol slurry is granulated by a spray-drying method to form granules. These granules are used as they are or dried to form the composite particulate material of this embodiment. In this process, the droplets are instantly dried by the spray-drying method to form spherical granules with a porous structure.

There are no particular limitations on the method for replacing the main component of the dispersant contained in the aggregates dispersed in the liquid with alcohol. For example, the alcohol content can be increased by simply adding alcohol, or by repeatedly adding alcohol and then removing the dispersant. The dispersant can be removed by centrifuging the separated dispersant as the supernatant, or by evaporating the dispersant.

Here, alcohol being the main component means that the alcohol content is 50% or more based on the entire dispersion medium, but it is particularly preferable that the lower limit of the alcohol content be 90% by volume, 95% by volume, or 99% by volume.

The alcohol that can be contained in the alcohol slurry is not particularly limited, but it is preferable to select an alcohol solvent that evaporates at low temperatures to further suppress surface oxidation of the MXene nanosheets. For example, it is preferable to use at least one of methanol, ethanol, and isopropanol as the alcohol used as the dispersion medium. In addition to alcohol, water, ketones such as MEK, or DMSO may also be contained. The lower limit of the alcohol content, based on the volume of the dispersion medium, can be 99%, 95%, or 90%.

The spray-drying method is carried out in an inert atmosphere that has low reactivity with the materials that make up the composite particle material. The inert atmosphere can be an atmosphere filled with an inert gas such as nitrogen or argon, or a reduced-pressure or vacuum atmosphere. The temperature of the inert atmosphere is the temperature at which the alcohol contained in the alcohol slurry can evaporate. For example, the lower limit of the temperature of the inert atmosphere can be 80°C, 90°C, or 100°C, and the upper limit can be 100°C, 110°C, or 120°C. The upper and lower limits can be combined in any way.

The spray drying method involves spraying droplets of a slurry of composite agglomerated material into a high-temperature atmosphere. Conventional spraying methods can be used, such as those using a rotating disk or a nozzle such as a two-fluid nozzle. The method using a rotating disk is preferred because the agglomerated particles in the alcohol slurry are less likely to clog during spraying, and it is possible to produce spherical granules with any secondary particle size. Spherical granules with the required secondary particle size can be easily obtained by arbitrarily selecting the rotation speed of the rotating disk. Note that a granulation step using a fluidized bed granulation method can be included instead of, or in addition to, the spray drying method.

The dispersion medium is instantly removed from the sprayed droplets composed of the composite agglomerated particle material and alcohol, forming the composite particle material. This prevents shrinkage and maintains a high specific surface area and excellent mutual dispersion of the MXene nanosheets and carbon microparticles. The large particle size of the agglomerated particles in the alcohol slurry makes them prone to clogging during spraying or liquid delivery. Therefore, it is necessary to appropriately select the solids concentration, preferably 1.0 to 10.0 mass%. 1.0 to 5.0 mass% is even more preferable. Regarding secondary particle size, when using the rotating disk method, large secondary particle sizes can be obtained by lowering the rotation speed and increasing the spray temperature. On the other hand, small secondary particle sizes can be obtained by increasing the rotation speed. Furthermore, even smaller secondary particle sizes can be obtained by reducing the agglomerated particle size of the alcohol slurry of the composite agglomerated particle material and spray-drying it using a nozzle such as a two-fluid nozzle. By combining these methods, an average secondary particle size of 1.0 μm to 15.0 μm can be obtained. 1.0 μm to 10.0 μm is more preferable. For spray drying using a nozzle such as a two-fluid nozzle, it is preferable to use an alcohol slurry in which large aggregates have been removed with a sieve to prevent nozzle clogging. In practice, an average secondary particle diameter of 1.0 μm or more is preferable because it reduces the risk of the composite particle material scattering during operation. A value of 15.0 μm or less allows the composite particle material to be formed without using a high-particle-concentration alcohol slurry to enlarge droplets at low speeds or without instantaneously removing the alcohol at high temperatures. This is particularly preferable because it avoids high-temperature processing and reduces the risk of problems such as surface oxidation of MXene. For use as a battery material, an average secondary particle diameter of 1.0 μm to 15.0 μm is preferable, with 1.0 μm to 11.0 μm being more preferable. A value of 1.0 μm or more facilitates handling, while a value of 15.0 μm or less suppresses the formation of unevenness in the resulting film. A value of around 11.0 μm (10.5 μm to 11.5 μm) is particularly preferable.

Drying Step: The granules obtained in the granulation step can be used as the composite particulate material of this embodiment as is, but can also be dried afterwards to remove interlayer water from the MXene nanosheets. The drying step involves drying the granules at 100 to 120°C in a vacuum or inert atmosphere to produce the composite particulate material of this embodiment. Here, the vacuum and inert atmospheres are used to suppress oxidation of the MXene nanosheets, and any atmosphere that can suppress oxidation compared to air will suffice.

Preventing residual interlayer water in MXene nanosheets can suppress deterioration of characteristics when used as electrodes in secondary batteries or pseudocapacitors with increased cycle counts. The temperature in the drying process is determined by the temperature of the granules. The temperature of the granules can be controlled by controlling the ambient temperature, directly heating the granules using infrared rays, or controlling the temperature of the container that holds the granules to control the temperature of the granules through heat transfer.

The drying process is performed at a temperature at which the MXene nanosheets do not denature or denature is within an acceptable range, and at which the moisture contained between the layers of the MXene nanosheets can be removed. By performing the drying process, interlayer water can be effectively removed. For example, a moisture content of less than 10% by mass based on the total mass can be easily achieved. The drying time is not particularly limited, but it is preferable to perform the drying process until the moisture content is less than 10% based on the total mass, or until the mass change is 1.0% or less per hour. It is more preferable to perform the drying process until the moisture content is 8% or less, 6% or less, 4% or less, 2% or less, or 1% or less, and it is even more preferable to perform the drying process until the mass change is 0.5% or less per hour.

Other Necessary Steps: Examples of other necessary steps include, but are not limited to, a pretreatment step. The pretreatment step is an example of a method for producing MXene. For example, a mixed raw material of TiC, TiN, Al, and Ti is pressurized by CIP or uniaxial pressing at a pressure of 1 to ³ ton/ ^cm² , and the resulting compact fragments are heat-treated in an inert atmosphere at 1400 to 1600°C, or without pressure treatment, to obtain high-purity _Ti3Ala (C( _{1.0 -x} ) _Nx ) ₂ (0≦x≦0.25, a is 1.0), which is a MAX-phase ceramic with _three Ti layers. Alternatively, MXene can be produced by contacting the MAX-phase ceramic powder with an acidic substance at a controlled temperature of 20 to 30°C to remove a portion of the Al element contained in the MAX-phase ceramic powder.

The raw material used in the pretreatment step is a MAX-phase ceramic powder having a composition expressed as _Ti3Ala ( _C ( _{1.0 -x} ) _Nx ) ₂ (0≦x≦0.25, a is 1.0) for the Ti3 layer. Furthermore, the amount of Al removed is adjusted so that the amount of Al (corresponding to x) remaining in the MAX-phase ceramic powder produced by acid treatment with an acidic substance is 0.01 or more. A lower limit of 0.02 can be used. It is more preferable to adjust the upper limit to 0.05. It is also possible to remove all of the Al, and in that case, it is preferable not to proceed with the acid treatment beyond the removal of the Al.

The amount of Al removed can be adjusted by changing the contact time with the acidic substance (such as an acidic aqueous solution) (longer contact times increase the amount removed), the concentration of the acidic substance (higher concentrations increase the amount removed), the amount of acidic substance (higher absolute amounts of acidic substance increase the amount that can be removed), and the contact temperature (higher temperatures increase the amount removed).

A layered compound, MAX phase ceramic powder (A element is Al), is subjected to acid treatment to remove a portion of the Al, resulting in a multi-layered layered compound several microns in size with a void layer that constitutes the particle material. The acid used to remove the portion of the Al layer is an acidic substance that combines hydrofluoric acid and hydrochloric acid. To achieve this combination of hydrofluoric acid and hydrochloric acid, it is preferable to mix a salt of hydrofluoric acid (such as KF or LiF) with hydrochloric acid to obtain a mixture of hydrofluoric acid and hydrochloric acid.

In particular, aqueous solutions of these acids are used as acidic substances. There are no particular restrictions on the mixed concentration of hydrofluoric acid and hydrochloric acid formed when the fluoride salt is assumed to be completely dissociated. The lower limit of the hydrofluoric acid concentration can be approximately 1.7 mol/L, 2.0 mol/L, or 2.3 mol/L, and the upper limit can be approximately 2.5 mol/L, 2.6 mol/L, or 2.7 mol/L. The lower limit of the hydrochloric acid concentration can be approximately 2.0 mol/L, 3.0 mol/L, or 4.0 mol/L, and the upper limit can be approximately 13.0 mol/L, 14.0 mol/L, or 15.0 mol/L.

There are no particular restrictions on the mixing ratio (molar ratio) of hydrofluoric acid to hydrochloric acid formed when the fluoride salt is assumed to be completely dissociated, but lower limits for hydrofluoric acid can be 1:13, 1:12, or 1:11, and upper limits can be approximately 1:5, 1:6, or 1:7. The concentrations and mixing ratios of hydrofluoric acid and hydrochloric acid shown here can be used in any combination. The acid treatment temperature is preferably 20°C to 30°C, and more preferably 20°C to 25°C.

(electrode material)
The electrode material of this embodiment is a material that can be suitably used in secondary batteries. In particular, since it is possible to insert and desorb Li ions and Na ions between the layers, it can be suitably used as an electrode active material. In addition, due to its conductivity, it can also be used as a conductive auxiliary agent. It is effective in lithium secondary batteries and sodium secondary batteries. Lithium ions and sodium ions are stored and desorbed in the void layer formed by removing the Al layer by acid treatment.

Here, a lithium secondary battery will be used as an example. The electrode has an active material layer containing an active material made of the composite particle material of this embodiment, and a current collector made of a thin metal plate or the like, on whose surface an active material layer made of an active material is formed. A binder can be included to form the active material layer. Furthermore, the active material layer can contain active materials other than the composite particle material of this embodiment, conductive additives, and the like, as needed. Commonly used binders such as carboxymethyl cellulose, polyvinylidene fluoride, styrene-butadiene rubber, polyvinylpyrrolidone, and polyvinyl alcohol, as well as other binders, can be used as binders. Acetylene black, Ketjen black, carbon nanotubes, graphene, carbon fiber, graphite powder, hard carbon powder, and the like can be used as conductive additives.

The composite particle material of the present invention and its manufacturing method will be described in detail below based on the examples.

Example 1
Pretreatment step: 12.3 g of TiC powder (TI-30-10-0020, Rare Metallic Co., Ltd.), 4.9 g of Ti powder (TIE07PB 3N, Kojundo Chemical Co., Ltd.), and 2.8 g of Al powder (ALE15PB 3NG, Kojundo Chemical Co., Ltd.) were mixed in isopropanol (IPA) using a ball mill for 12 hours, and the IPA was removed using an evaporator to obtain a uniformly mixed dry powder.

The uniformly mixed dried powder was placed in an alumina crucible and fired in a graphite resistance furnace under Ar flow conditions at 1450°C for 2 hours to obtain _Ti3AlC2 as MAX phase ceramics. The obtained _Ti3AlC2 was coarsely ground using a mortar _and pestle, and then ball milled in IPA using 5 mm zirconia balls for 24 hours. _This was then ground in a planetary ball mill using 0.5 mm zirconia balls (200 rpm, 15 minutes, three times) to obtain a suspension. The IPA was removed from the suspension using an evaporator, and _{Ti3AlC2 powder} milled to approximately 3 μm was obtained.

An acidic aqueous solution of 18 g of LiF in 300 mL of concentrated HCl was prepared. 10 _g of _Ti3AlC2 powder was added while cooling with ice, and the mixture was stirred with a magnetic stirrer for 24 hours in an environment controlled at 10 to ₂₀ °C to etch and remove the Al, yielding a particulate material consisting _{of Ti3Al0.02C2MXene} . After etching, the material was washed with water until the pH reached about 6, and finally the water was replaced with ethanol. This operation yielded a raw material suspension of the particulate material suspended in ethanol.

The particle concentration of the raw material suspension was measured, and water was added to adjust the particle concentration of Ti ₃ Al _0.02 C ₂ MXene to 15.6 mg/mL.

This raw material suspension was treated in a bead mill with _ZrO2 beads of 50 μm diameter at a slurry feed rate of 150 mL/ _min and _{a ZrO2} bead loading of 80%, producing an exfoliated material made of _{Ti3Al0.02C2MXene} . By repeating this treatment _three times, almost all (99% or more by mass) of the particulate material made _{of Ti3Al0.02C2MXene} contained in _the raw material suspension was converted into exfoliated material, and an exfoliated material suspension containing this exfoliated material was obtained.

The resulting exfoliated material suspension was dropped onto a piranha-treated Si substrate (immersed in a mixed solution of 3 parts by volume _{of H2SO4} : _H2O2 :1 part by volume ₎ , and AFM analysis was performed. The AFM image is shown in Figure 1. One hundred exfoliated materials (nanosheets) were randomly sampled, and the average thickness measured by AFM was calculated and shown in Table 1. Furthermore, the results of SEM observation are shown in Figure 2. One hundred exfoliated materials were randomly sampled, and the vertical (maximum diameter in the direction perpendicular to the thickness) and horizontal (directions perpendicular to the vertical and thickness directions) dimensions were measured from the SEM photograph. The average value was defined as the size of the exfoliated material, and the average size of the 100 exfoliated materials is shown in Table 1. XRD measurement was performed on powder of _Ti3AlC2 , a MAX _phase ceramic, and the resulting profile is shown in Figure 3. The zeta potential of the exfoliated material in water at pH 7.0 was measured and found to be -28.9 mV.

Acid Treatment Step: The acid treatment of acetylene black as carbon microparticles was carried out by adding 1.0 part by mass of acetylene black to 100 parts by mass of a mixed acid (a 3:1 volumetric mixture of sulfuric acid (98% by mass) and nitric acid (68% by mass)) and immersing the mixture at 85°C for 10 minutes. The mixture was then washed with water until the pH reached approximately 6.0, after which the water was replaced with IPA. The mixture was air-dried at room temperature to obtain hydrophilic acid-treated acetylene black powder. FTIR analysis detected COOH and CO groups as surface functional groups. The zeta potential at pH 7.0 in water was measured to be -22.5 mV. The acid-treated acetylene black was disaggregated using a shaker at 140 rpm with an amplitude of 45 mm for 24 hours to prepare a hydrophilic acetylene black aqueous slurry. The hydrophilic acetylene black aqueous slurry was then dropped onto a hydrophilically treated Si wafer and observed using an SEM. One hundred primary particles were randomly observed, and the longitudinal and lateral dimensions were measured. The average primary particle diameter is shown in Table 1.

Mixing and Aggregation Steps: 5.3 g of lithium chloride powder and 0.172 g of acetylene black powder treated with acid in the acid treatment step (5% by mass based on the exfoliated material ( _{Ti3Al0.02C2MXene} )) were added to 220 mL of the exfoliated material suspension with a particle concentration of _15.6 mg _/ mL obtained in the exfoliation step, and the mixture was uniformly stirred for 5 hours at 140 rpm and an amplitude of 45 mm using a shaker. As described above, the acetylene black was added in the form of a slurry dispersed in 10 mL of water. After uniform stirring, an alkaline aqueous solution was added, which had been prepared by dissolving 3.5 g of lithium hydroxide in 30 mL of pure water and shaking it at 140 rpm and an amplitude of 45 mm for 1 hour, and the mixture was then stirred for 1 hour at 140 rpm and an amplitude of 45 mm using a shaker. The mixture was then washed with water once and substituted with ethanol three times. The mixture was then stirred in ethanol at 140 rpm for 6 hours using a shaker to loosen coarse aggregates, yielding an ethanol slurry of the aggregates with a particle concentration of 5.0 mg/mL. The water washing and ethanol substitution were carried out by adding water or ethanol, then centrifuging the aggregates at 1000-8000 G for 10 minutes, and removing the supernatant. The content of ethanol as alcohol in the resulting alcohol slurry was 99% based on the mass of the total dispersion medium.

Granulation step: Granules were prepared by spray-drying an alcohol slurry of the composite agglomerated particle material using a spray dryer under the following operating conditions: disk rotation speed: 20,000 rpm, nitrogen atmosphere, alcohol slurry charging temperature to the disk: 80°C, alcohol slurry charging rate: 1.4 kg/hour.

Drying Step The granules obtained in the granulation step were dried in a vacuum at 110°C for 6 hours to remove interlayer water, thereby obtaining the MXene/conductive carbon black composite particle material of this example.

Evaluation: An SEM photograph (Figure 4) of the obtained composite powder is shown. As is clear from the figure, the obtained composite particle material has high sphericity, and when magnified, it is clear that the 3D porous aggregate structure with extremely thin MXene nanosheets in which acetylene black is uniformly dispersed is maintained, resulting in a high specific surface area. Similarly, when 100 secondary particles were observed under SEM, they were all found to be composite particle materials with the same porous microstructure. In other words, it was clear that the microstructure was not disturbed by external stress.

Table 2 shows the average diameter and sphericity of secondary particles, and Table 3 shows the specific surface area, average pore diameter, average pore volume, and bulk density. Figure 5 shows the nitrogen adsorption isotherm. The average diameter of secondary particles was determined by randomly selecting 100 particles from an SEM image, calculating the average of (long side + short side)/2, which was the secondary particle diameter. The sphericity of secondary particles was determined by measuring the short side/long side of 100 particles, and calculating the average. The upper limit is 1.0, with values closer to 1.0 indicating higher sphericity. The bulk density of secondary particles was measured in accordance with JIS 1628-1997. The specific surface area, average pore diameter, and average pore volume were measured by the BET method immediately after heating in a vacuum at ₁₁₀ °C for ₆ hours. The degree of mutual dispersion, which represents the degree of dispersion of primary particles of _{Ti3Al0.02C2MXene} nanosheets and acetylene black as carbon microparticles, was measured. Specifically, the values were quantified using Raman spectroscopy. Analysis was performed at 100 points in the range of 100 cm ^-1 to 2000 cm ^-1 using a laser intensity at which anatase does not precipitate. The standard deviation of the B peak intensity/A peak intensity ratio was calculated and used as the interdispersity. The obtained interdispersity is shown in Table 4. The obtained composite particle material was heat-treated in a vacuum at 110°C for 5 hours, and the mass change was measured and shown in Table 5. The obtained composite particle material was also subjected to XRD measurement, and the profile is shown in Figure 3. From the results of the XRD measurement, the interlayer distance of the (002) plane of the MXene nanosheet is shown in Table 6. The obtained composite particle material was uniaxially pressed in a φ10 mm mold at a pressure of 0.5 kg/ ^cm2 , and then cold isostatically pressed (CIP) at a pressure of 1.0 ton/ ^cm2 . The surface electrical resistance was measured using a four-probe method using a φ0.1 mm copper wire and is shown in Table 7.

Example 2
The composite particle material was obtained in the same manner as in Example 1, except that the uniformly mixed dried powder was placed in an alumina crucible and fired in a graphite resistance furnace in an Ar stream at 1430°C for ₂ hours to obtain _Ti3AlC2 as a MAX phase ceramic. Measurements were performed in the same manner as in Example 1, and the results are shown in the figures and tables. An AFM image of the exfoliated MXene nanosheets is shown in Figure 6, and an SEM image is shown in Figure 7. XRD profiles of the MAX phase ceramics and the composite particle material are shown in Figure 8, and an SEM image is shown in Figure 9. The average thickness and size of the exfoliated MXene nanosheets are shown in Table 1, the average particle diameter and sphericity of the resulting composite particle material are shown in Table 2, the specific surface area, average pore diameter, average pore volume, and bulk density are shown in Table 3, the mutual dispersion is shown in Table 4, the mass change is shown in Table 5, the interlayer distance of the (002) plane of the MXene nanosheets is shown in Table 6, and the surface electrical resistivity is shown in Table 7.

Example 3
A composite particulate material of MXene and _acid -treated acetylene black was prepared in the same manner as in Example 2, except that the amount of acid-treated acetylene black added was 10 mass % based on the mass of the _{Ti3Al0.02C2MXene} nanosheets _. Measurements were performed in the same manner as in Example 1, and the average particle diameter and sphericity of the resulting composite particulate material are shown in Table 2, the specific surface area, average pore diameter, average pore volume, and bulk density in Table 3, the mutual dispersity in Table 4, the mass change in Table 5, the interlayer distance of the (002) plane of the MXene nanosheets in Table 6, and the surface electrical resistivity in Table 7.

Example 4
A composite particulate material of MXene and _acid -treated acetylene black was prepared in the same manner as in Example 2, except that the amount of acid-treated acetylene black added was 3 mass % based on the mass of the _{Ti3Al0.02C2MXene} nanosheets _. Measurements were performed in the same manner as in Example 1, and the average particle diameter and sphericity of the resulting composite particulate material are shown in Table 2, the specific surface area, average pore diameter, average pore volume, and bulk density in Table 3, the mutual dispersity in Table 4, the mass change in Table 5, the interlayer distance of the (002) plane of the MXene nanosheets in Table 6, and the surface electrical resistivity in Table 7.

Example 5
Starting materials were 9.2 g of TiC powder (TI-30-10-0020, Rare Metallic Co., Ltd.), 3.2 g of TiN powder (TN-30-10-0020, Rare Metallic Co., Ltd.), 4.9 g of Ti powder (TIE07PB 3N, Kojundo Chemical Co., Ltd.), and 2.8 g of Al powder (ALE15PB 3NG, Kojundo Chemical Co., Ltd.) _, and _Ti3Al ( _C0.75N0.25 ) ₂ powder was prepared in the same manner as in Example 1. XRD analysis confirmed that the powder was a MAX-phase ceramic powder without impurities. This powder was used to prepare a composite particle material in the same manner as in Example 1. The average particle diameter and sphericity of the obtained composite particle material were measured in the same manner as in Example 1, and are shown in Table 2, the specific surface area, average pore diameter, average pore volume, and bulk density in Table 3, the mutual dispersion in Table 4, the mass change in Table 5, and the interlayer distance of the (002) plane of the MXene nanosheet in Table 6.

(Comparative Example 1)
A composite particulate material of MXene and _acid -treated acetylene black was prepared in the same manner as in Example 2, except that the amount of acid-treated acetylene black added was 2 mass % based on the mass of the _{Ti3Al0.02C2MXene} nanosheets _. Measurements were performed in the same manner as in Example 1, and the average particle diameter and sphericity of the resulting composite particulate material are shown in Table 2, the specific surface area, average pore diameter, average pore volume, and bulk density in Table 3, the mutual dispersity in Table 4, the mass change in Table 5, and the interlayer distance of the (002) plane of the MXene nanosheets in Table 6.

(Comparative Example 2)
An ethanol slurry of the composite agglomerated particle material was prepared in the same manner as in Example 2 up to the mixing and aggregating steps. To further reduce the amount of water remaining in the solvent, the solvent was replaced from ethanol to IPA, producing an IPA slurry of the composite agglomerated particle material. The IPA slurry was subjected to centrifugal sedimentation (7900 G), and the sediment was air-dried for 12 hours at room temperature. This was then heat-treated in a vacuum at 60°C for 6 hours to obtain a mass of the composite agglomerated particle material. This was then crushed by applying physical stress in a crusher consisting of a mortar and pestle, producing the composite particle material of this comparative example. The remaining steps were the same as in Example 1.

Measurements were performed in the same manner as in Example 1. The average particle diameter and sphericity of the resulting composite particle material are shown in Table 2, the specific surface area, average pore diameter, average pore volume, and bulk density in Table 3, the mutual dispersity in Table 4, the mass change in Table 5, the interlayer distance of the (002) plane of the MXene nanosheet in Table 6, and the surface electrical resistance in Table 7. Furthermore, 100 secondary particles were observed under SEM to examine the uniformity of their microstructure when crushed by applying physical stress. Most secondary particles maintained their aggregated structure, but the aggregated structure was destroyed for several secondary particles (Figure 10).

(Comparative Example 3)
A suspension of exfoliated material was obtained in the same manner as in Example 1 up to the peeling step. To 220 mL of the suspension of exfoliated material obtained in the peeling step, with a particle concentration of 15.6 mg/mL, was added an alkaline aqueous solution in which 3.5 g of lithium hydroxide had been dissolved in 40 mL of pure water and completely dissolved by shaking at 140 rpm and 45 mm amplitude for 1 hour. The mixture was then stirred for 1 hour at 140 rpm and 45 mm amplitude. The mixture was then washed with water once and substituted with ethanol three times. The mixture was then stirred in ethanol at 140 rpm for 6 hours using a shaker to loosen coarse aggregates, yielding an ethanol slurry of aggregates with a particle concentration of 5.0 mg/mL. The solvent was replaced with IPA in the same manner as in Comparative Example 2, producing an IPA slurry of the composite agglomerated particle material. The IPA slurry was subjected to centrifugal sedimentation (7900 G) to settle the composite agglomerated particle material, and the sediment was air-dried at room temperature for 12 hours. The mixture was then dried in a vacuum at 60°C for 6 hours to obtain a lump of composite agglomerated particle material. It was then crushed by applying physical stress in a grinder consisting of a mortar and pestle to produce a composite particle material. The produced secondary particles were then added with 5% acid-treated acetylene black and N-methylpyrrolidone (NMP) based on the mass of MXene to produce a paste. The paste was produced in a grinder consisting of a mortar and pestle. It was then dried in a vacuum at 110°C for 6 hours to remove the NMP, producing a composite particle material of MXene and acetylene black. The remaining steps were the same as in Comparative Example 2.

The average particle diameter and sphericity of the composite particle material obtained, measured in the same manner as in Example 1, are shown in Table 2, the specific surface area, average pore diameter, average pore volume, and bulk density in Table 3, the mutual dispersion in Table 4, the mass change in Table 5, and the interlayer distance of the (002) plane in Table 6.

(Comparative Example 4)
The procedure up to the peeling step was the same as in Example 1, yielding 220 mL of a suspension of exfoliated material. 220 mL of IPA was added to prepare an MXene agglomerated particle slurry in a mixed solution of IPA and water. This was centrifuged (7900 G), and the resulting sediment was air-dried at room temperature for 12 hours. It was then dried in a vacuum at 60°C for 6 hours to obtain agglomerated masses. Secondary particles were then prepared by applying physical stress and grinding in a grinder consisting of a mortar and pestle. The resulting secondary particles were then added to N-methylpyrrolidone (NMP) in which 5% acid-treated acetylene black was dispersed, based on the mass of MXene, to prepare a paste. The paste was prepared using a grinder consisting of a mortar and pestle. The NMP was then removed in a vacuum at 110°C for 6 hours to produce a composite particle material of MXene and acetylene black. The remaining steps were the same as in Comparative Example 3.

Measurements were carried out in the same manner as in Example 1. The average particle diameter and sphericity of the obtained composite particle material are shown in Table 2, the specific surface area, average pore diameter, average pore volume, and bulk density in Table 3, the nitrogen adsorption isotherm in Figure 5, the mutual dispersion in Table 4, the mass change in Table 5, the interlayer distance of the (002) plane of the MXene nanosheet in Table 6, and the surface electrical resistance in Table 7.

This will be explained in detail using tables and figures. Table 4 shows that composite powder materials prepared _{by spray} -drying alcohol slurries of agglomerated powders with _{a Ti3Al0.02C2MXene} (97.0-90.0% by mass)/carbon nanoparticle (3.0-10.0% by mass) composition and _{a Ti3Al0.02 ( C0.75N0.25} ) _2MXene (95% by mass)/carbon nanoparticle (5.0% by mass) composition are dried without shrinkage because the alcohol is removed instantly. As a result, the degree of mutual dispersion is remarkably excellent. The conductive carbon nanoparticles are uniformly distributed on the outer surface of the MXene nanosheets, allowing electrons to be smoothly transferred to the current collector.

As shown in Table 2, Figures 4, and 9, the composite powder materials prepared by spray-drying alcohol slurries _{of Ti3Al0.02C2MXene} ( _97.0-90.0 % by mass)/carbon nanoparticles ( _3.0-10.0 % by mass) and _{Ti3Al0.02 ( C0.75N0.25} ) _2MXene (95% by mass)/carbon nanoparticles (5.0% by mass) compositions had average secondary particle diameters of approximately single micrometers and excellent sphericity. High-magnification SEM observations of 100 secondary particles revealed the 3D porous structures shown in Figures 4 and 9 as representative examples. On the other hand, when the aggregated powder lumps were air-dried and vacuum-dried at 60°C and then crushed using a mortar and pestle under physical stress (crushing), finely crushed portions and large uncrushed portions coexisted, resulting in an amorphous structure, as seen in the SEM image in Figure 10. This makes it impossible to obtain a uniform film when fabricating the cell membrane. Furthermore, 100 pieces of composite powder material were observed under high magnification using an SEM to check whether the agglomerated structure had been destroyed by the application of physical stress. As shown in Figure 10 as a representative example, it was confirmed that the agglomerated structure had been destroyed in several pieces. Applying physical stress for a long period of time to reduce the secondary particle size further destroyed the agglomerated structure.

Table 3 shows the physical values of the 3D porous structure. Composite powder materials prepared by _spray - _drying agglomerated powder alcohol slurries of _{Ti3Al0.02C2MXene} ( _97.0-90.0 % by mass)/carbon nanoparticles (3.0-10.0% by mass) and _{Ti3Al0.02 ( C0.75N0.25} ) _2MXene (95% by mass)/carbon nanoparticles (5.0% by mass) have higher specific surface areas, average pore diameters, and average pore volumes than composite particle materials prepared by crushing agglomerates through physical stress application. This is because the droplets of the agglomerated powder alcohol slurry dry instantly, suppressing shrinkage during drying. As shown in Table 1, the MXene is exfoliated to a monolayer level, specifically, a thickness of 1.5 nm. Shrinkage during drying means that the MXene nanosheets adhere to each other, and obtaining a composite powder material without shrinkage indicates that the composite powder material is made while maintaining a monolayer of MXene nanosheets. Smooth ion diffusion leads to rapid charge/discharge, excellent cycle characteristics, and high capacity.

The effect of the average size of the MXene nanosheets on the physical values of the 3D porous structure of the composite particle material after granulation will be specifically explained. Comparing Example 1 and Example 2, Example 2 has a larger specific surface area. Lowering the firing (synthesis) temperature of the MAX phase ceramics within a range that does not generate impurities weakens the interlayer bonding force, reducing the average size while maintaining a monolayer-level thickness during the exfoliation process. A smaller average size of approximately 0.2 μm (Example 2) had a larger specific surface area, smaller average pore diameter, and larger pore volume than a size of approximately 0.8 μm (Example 1).

Figure 5 shows the adsorption isotherms of Examples 1 and 2 and Comparative Example 4 as representative examples. It can be seen that the composite particle material of the present invention is an excellent 3D porous material.

Table 5 shows the mass change when 0.3 g of composite powder material was uniformly spread on a 20 ^cm3 or larger dish and heated in a vacuum at ₁₁₀ °C for 5 hours. The composite powder material was prepared by spray-drying an alcohol slurry of agglomerated powder _{with a Ti3Al0.02C2MXene} (97.0-90.0 wt%)/carbon microparticle (3.0-10.0 wt%) composition and a _{Ti3Al0.02 ( C0.75N0.25} ) _2MXene (95 wt%)/carbon microparticle (5.0 wt%) composition. The droplets were instantly dried to produce granules, which were then vacuum-dried at 110°C to completely remove the water remaining between the MXene layers. On the other hand, the composite particle material prepared by pulverizing the agglomerates, which had been air-dried and then vacuum-dried at 60°C, by physical stress application, still had a large amount of water remaining between the MXene layers. When the aggregates are air-dried and then vacuum-dried at 110°C, they shrink significantly, resulting in a low specific surface area. While vacuum drying at 110°C is typically performed after membrane fabrication in cell fabrication, it is difficult to completely remove the water between the MXene layers, which can lead to problems such as deterioration of cycle characteristics.

Table 3 shows the bulk densities of the resulting composite particulate materials. Composite powder materials prepared by _{spray -} drying alcohol slurries of agglomerated powders _{of Ti3Al0.02C2MXene} (97.0-90.0% by mass)/carbon microparticles (3.0-10.0% by mass) and _{Ti3Al0.02 ( C0.75N0.25} ) _2MXene (95% by mass)/carbon microparticles (5.0% by mass) were compared with composite particulate materials prepared by crushing the agglomerates by applying physical stress. The former are characterized by a 3D porous agglomerated structure, uniform secondary particle size, and spherical morphology, while the latter lack a 3D porous agglomerated structure and are denser and more amorphous than the former, resulting in a continuous particle blend. This results in a lower bulk density for the former.

However, when producing cells such as secondary batteries, the former method produces a uniform structure in the film, which can improve the performance of the manufactured secondary battery. To produce a high-density film, it is preferable to prepare composite particle materials with several different secondary particle sizes to achieve appropriately close packing, and to perform continuous particle blending, for which the Andreasen equation has proposed a distribution law for creating close packing, or to perform two-stage particle blending, in which two types of composite particle materials, one coarse and one fine, are blended.

Table 6 shows the interlayer distance of the (002) plane of MXene obtained by XRD of the resulting composite particle material. The composite particle material of the present invention, in which carbon nanoparticles are uniformly distributed, has a larger interlayer distance than the composite particle material of the present invention, in which agglomerated powder was prepared using only MXene, followed by the addition of NMP and the carbon nanoparticles. This is because Li and/or Na ions and chlorine ions intercalated between the MXene layers during the process of uniformly distributing the carbon nanoparticles, widening the gap between the layers. The value obtained by subtracting the interlayer distance of the (002) plane of the MAX-phase ceramic from the (002) plane of MXene can be considered the gap distance resulting from the removal of the Al phase from the MAX-phase ceramic (see Figure 11). For the composite particle material of the present invention, this is approximately 0.6 nm. Ions larger than Li ions, such as Na ions, can be inserted and removed. Furthermore, the larger gaps enable rapid charging and discharging, as well as a longer lifespan.

Table 7 shows the surface electrical resistance of the compact. This was done to determine the oxidation state of the MXene nanosheet surface and the amount of water remaining between the layers. When the surface of the MXene nanosheet is oxidized, the electrical resistance increases. Furthermore, if there is water remaining between the layers, the surface changes over time, causing oxidation of the interlayer surface to progress and increasing the surface electrical resistance. Therefore, if oxidation progresses or if there is a large amount of water between the layers, the surface electrical resistance increases.

The surface electrical resistance of a powder compact is also affected by the number of contacts between powder particles. The number of contacts is indicated by the relative density of the powder compact. Relative density is determined by (bulk specific gravity/true specific gravity) x 100. For composite particle materials used as negative electrode active materials in secondary batteries and electrodes in electrochemical capacitors, it is preferable that the surface electrical resistance of the powder compact be in the range of 1.0 to 100.0 Ω/□, as shown in Table 7.

As explained above, it has been found that a composite particle material can be obtained in which MXene and microparticles are highly dispersed, maintain an aggregated structure, and have high sphericity. As revealed in PCT/JP2021/018296, previously filed by the applicant, the original composite particle material has excellent ion diffusivity and is capable of smoothly transferring electrons to a current collector, making it ideal for use as a negative electrode active material in secondary batteries (storage batteries), or as an ideal positive and/or negative electrode active material in pseudocapacitors. Therefore, since the 3D porous aggregated structure can be maintained, it is expected that ion diffusivity will be further improved, and since the sphericity can be increased, it is expected that the uniformity of the formed film will be improved.

Furthermore, when a composite particulate material was produced using methanol or isopropanol instead of the ethanol used in Example 1, a composite particulate material similar to that used in Example 1 was obtained. Here, when isopropanol was used instead of the ethanol used in Example 1 to produce the composite particulate material, the spray temperature during the granulation process had to be increased to 85°C. As in Example 1, the surface electrical resistance was measured to be 60.5 Ω/□, compared to 41.1 Ω/□ when ethanol was used, resulting in a slight increase in resistance. This was due to slight oxidation on the surface caused by the slight increase in spray temperature. When a composite particulate material was produced using methanol instead of the ethanol used in Example 1, the spray temperature during the granulation process could be lowered to 75°C. As in Example 1, the surface electrical resistance was measured to be 40.7 Ω/□, which was approximately the same as when ethanol was used. Based on these findings, it is acceptable to use any of ethanol, methanol, and isopropyl alcohol as the solvent used in the granulation process.

Claims (15)

The conductive nanoparticles are contained as primary particles in an amount of 3 to 10 parts by mass, and _Ti3Ala (C( _{1.0 -x} ) _Nx ) ₂ (0≦x≦0.25 _, a is 0.01 or more) MXene nanosheets are contained in an amount of 90 to 97 parts by mass,
The MXene nanosheet has an average thickness of 1.0 to 3.5 nm;
The primary particle diameter of the microscopic objects is 100 nm or less,
A composite particle material having a mutual dispersion of 0.01 to 7.00, an average secondary particle diameter of 1.0 μm to 15.0 μm, and a sphericity of 0.8 or more.
(mutual dispersion degree)
In Raman spectroscopy using a 532 nm laser, the ratio (B/A) of the peak height A at 400 cm ⁻¹ to the peak height B at 1332 cm ⁻¹ is calculated for 100 samples, and the standard deviation calculated from the 100 B/A values is taken as the mutual dispersion. The composite particulate material according to claim 1, wherein the microparticles are carbon microparticles. 3. The composite particulate material according to claim 1, which has a specific surface area of 75 m ² /g or more, an average pore diameter of 10.0 to 20.0 nm, and an average pore volume of 0.30 to 0.70 mL/g. A composite particle material according to any one of claims 1 to 3, wherein when a 0.3 g sample is uniformly spread on a plate of ²⁰ cm2 or more and heated in a vacuum at 110°C for 5 hours, the mass changes by 1.0 mass% or less. 5. The composite particulate material according to claim 1, having a bulk density of 0.1 to 0.5 g/cm ³ . _{the Ti3Ala} (C( _{1.0 -x} ) _Nx ) ₂ (0≦x≦0.25, a is 0.01 or more) MXene nanosheet has an average size of 0.1 to 2.0 μm in the spreading direction;
6. The composite particulate material according to claim 1, wherein the primary particle diameter of the microparticles is 30 to 50 nm. The composite particulate material according to any one of claims 1 to 6, wherein in the crystal structure of _Ti3Ala ( _C ( _{1.0 -x} ) _Nx ) ₂ (0≦x≦0.25, a is 0.01 or more), MXene, the interlayer distance of the (002) plane is 1.400 nm to 1.700 nm. _8. The composite particle material according to claim 1, comprising _Ti3Ala (C( _{1.0 -x} ) _Nx ) ₂ , (0≦x≦0.25, a is 0.01 or more)MXene having a zeta potential of −25.0 mV to −35.0 mV, and carbon microparticles having a zeta potential of −20.0 mV to −25.0 mV.
(Zeta potential)
The zeta potential is measured in water in the pH range of 6.0 to 8.0. 9. The composite particle material according to claim 1, having a surface electrical resistance of 1.0 Ω/□ to 100.0 Ω/□.
(Surface Electrical Resistivity)
After heat treatment in a vacuum at 110°C for 5 hours, the powder was uniaxially pressed in a φ10 mm mold at a pressure of 0.5 kg/ ^cm² and then cold isostatically pressed at a pressure of 1.0 ton/ ^cm² . The surface electrical resistance of the green compact measured by the four-terminal method using φ0.1 mm copper wires was taken as the surface electrical resistance. A negative electrode for a secondary battery having the composite particle material described in any one of claims 1 to 9 as the negative electrode active material. An electrode for a pseudocapacitor having the composite particulate material described in any one of claims 1 to 9 as the active material for the positive electrode and/or negative electrode. a peeling _step of peeling _Ti3Ala (C( _{1.0 -x} ) _Nx ) ₂ , (0≦x≦0.25, a is 0.01 or more)MXene in a dispersion medium containing 50 mass % or more of water to form a peeled product;
an acid treatment step in which the raw carbon particles are treated in a mixed acid solution of sulfuric acid and nitric acid at 70°C or higher for 10 minutes or more to obtain carbon particles;
a mixing step of adding 0.8 to 1.0 mol/L of a water-soluble lithium salt and/or a water-soluble sodium salt to a mixture slurry of the exfoliated material and the carbon fine particles in a mass ratio of 90:10 to 97:3 and having a particle concentration of 11.5 to 17.0 mg/L, and stirring the mixture;
an aggregating step of adding 0.4 to 0.7 mol/L of an alkaline aqueous solution to the mixture slurry to make the solution alkaline and cause agglomeration, thereby obtaining a slurry of agglomerates of the _Ti3Ala (C( _{1.0 -x} ) _Nx ) ₂ , (0≦x≦0.25 _, a is 0.01 or more)MXene and the carbon microparticles;
a granulation step in which the dispersion medium of the slurry is replaced with alcohol to prepare an alcohol slurry of the aggregate, and the alcohol slurry is granulated by a spray drying method under an inert atmosphere to obtain granules;
and
The method for producing a composite particulate material , wherein the carbon microparticles have a primary particle diameter of 100 nm or less . The method for producing a composite particulate material described in claim 12, wherein the alcohol is methanol, ethanol, and/or isopropanol. The method for producing a composite particulate material according to claim 12 or 13, further comprising a drying step of drying the granules at 100 to 120°C in an inert atmosphere. The method for producing a composite particulate material according to any one of claims 12 to 14, wherein the exfoliation step is carried out until 99% or more by mass _of the _Ti3Ala (C( _{1.0 -x} ) _Nx ) ₂ , (0≦x≦0.25, a is 0.01 or more) becomes the exfoliated material.