Particle manufacturing method

Abstract

Provided is a method for producing particles, the method making it possible to easily produce particles having exceptional electroconductivity.　A method for producing particles 1 provided with particle bodies 2 and a coating layer 3 that covers at least some of a surface 2a of the particle bodies 2, wherein the method for producing particles 1 comprises: a step in which a mixture containing particle bodies 2, a layered compound 11, and a dispersion medium 12 is prepared; and a step in which shear is applied to the mixture to delaminate the layered compound 11 and the particle bodies 2 are covered with the layered compound 11 to form a coating layer 3, the viscosity of the dispersion medium 12 at 25°C being 1 mPa·s or higher.

Description

[Technical Field]

[0001] The present invention relates to a method for producing particles comprising a particle body and a coating layer covering at least a portion of the particle body. [Background technology]

[0002] In recent years, research and development of energy storage devices has been actively conducted for applications such as mobile devices, hybrid vehicles, electric vehicles, and home energy storage. As electrode materials for energy storage devices, compounds such as graphene obtained by exfoliating layered compounds have attracted attention due to their electrical conductivity and environmental friendliness.

[0003] Patent Document 1 below discloses a battery electrode including a graphene-containing or graphene-encapsulated electrode active material. In Patent Document 1, when producing a graphene-containing or graphene-encapsulated electrode active material, in the first step, a mixture is formed by mixing a plurality of particles of a graphite material with a plurality of particles of a solid electrode active material in a collision chamber of an energy collision device. The graphite material is not previously intercalated, oxidized, or exfoliated. Furthermore, the mixture does not contain any ball milling media other than the plurality of particles of the solid electrode active material. In the next step, the energy collision device is operated to exfoliate graphene sheets from the particles of the graphite material, and the exfoliated graphene sheets are transported to the surface of the particles of the solid electrode active material, where they are completely encapsulated or encapsulated in the particles, thereby producing particles of the graphene-containing or graphene-encapsulated electrode active material. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2019-522868 Summary of the Invention [Problem to be solved by the invention]

[0005] However, even with the manufacturing method of Patent Document 1, the peeling force of the graphite material is weak and the surface of the solid electrode active material particles may not be uniformly coated in some cases. As a result, the graphene compound obtained by the manufacturing method of Patent Document 1 still does not have sufficient conductivity, and when used as an electrode material for a secondary battery, for example, there is a problem that the battery characteristics such as the rate characteristics and cycle characteristics of the secondary battery cannot be sufficiently improved.

[0006] Therefore, there has been no conventional method for efficiently exfoliating layered compounds such as graphite and coating the exfoliated material on particle surfaces without oxidation. Furthermore, there has been no technology for uniformly coating particles with exfoliated materials such as graphene without agglomeration. As a result, it has been impossible to sufficiently increase the conductivity of the particles.

[0007] An object of the present invention is to provide a method for producing particles that can easily produce particles with excellent conductivity. [Means for solving the problem]

[0008] The method for producing particles according to the present invention is a method for producing particles comprising a particle body and a coating layer covering at least a portion of the particle body, the method comprising the steps of: preparing a mixture containing the particle body, a layered compound, and a dispersion medium; and applying a shear force to the mixture to peel off the layered compound and coat the particle body with the layered compound to form the coating layer, wherein the viscosity of the dispersion medium at 25°C is 1 mPa·s or more.

[0009] In a specific aspect of the method for producing particles according to the present invention, the dispersion medium is in a sol state, a gel state, or a liquid state.

[0010] In another specific aspect of the particle production method according to the present invention, the dispersion medium includes a dispersion medium having an SP value of 5 or more and 20 or less.

[0011] In yet another specific aspect of the method for producing particles according to the present invention, the dispersion medium contains a solvent having a molecular weight of 40 or more.

[0012] In yet another specific aspect of the method for producing particles according to the present invention, the layered compound includes graphite or graphite oxide.

[0013] In yet another specific aspect of the method for producing particles according to the present invention, the layered compound includes boron nitride or a graphite-like layered compound.

[0014] In yet another specific aspect of the method for producing particles according to the present invention, the particle bodies have an average particle size of 20 μm or less.

[0015] In yet another specific aspect of the method for producing particles according to the present invention, the true density of the particle body is 0.8 g / cm 3 That's all.

[0016] In yet another specific aspect of the method for producing particles according to the present invention, the particle body is a metal or a metal compound.

[0017] In yet another specific aspect of the particle production method according to the present invention, the shear force is applied by at least one method selected from the group consisting of ball milling, stirring, ultrasonic waves, high pressure release, and planetary stirring.

[0018] In yet another specific aspect of the particle production method according to the present invention, the mixture is cooled to increase its viscosity, and then the shear force is applied to the mixture, thereby peeling off the layered compound and coating the particle body with the layered compound.

[0019] In still another particular aspect of the method for producing particles according to the present invention, the method further includes a step of removing the dispersion medium after the step of forming the coating layer.

[0020] In still another particular aspect of the method for producing particles according to the present invention, in the step of removing the dispersion medium, the dispersion medium is removed by solid-liquid separation or by evaporation due to heating or reduced pressure.

[0021] In still another particular aspect of the method for producing particles according to the present invention, the method further includes, after the step of forming the coating layer, a step of carbonizing the dispersion medium by heating.

[0022] In yet another specific aspect of the method for producing particles according to the present invention, the method further includes a step of removing the carbonized dispersion medium. [Effects of the Invention]

[0023] According to the present invention, it is possible to provide a method for producing particles that can easily produce particles with excellent electrical conductivity. [Brief explanation of the drawings]

[0024] [Figure 1] 1(a) to 1(c) are schematic diagrams illustrating an example of the method for producing particles according to the present invention. [Figure 2] FIG. 2 is a schematic cross-sectional view showing an example of a particle produced by the particle production method according to the present invention. [Figure 3] FIG. 3 is a diagram showing the results of thermogravimetric analysis of particles before amorphous carbon removal in Example 1. [Figure 4] FIG. 4 is a diagram showing the results of thermogravimetric analysis of particles before removal of amorphous carbon in Example 2. [Figure 5] FIG. 5 is a diagram showing the results of thermogravimetric analysis of particles before removal of amorphous carbon in Example 3. [Figure 6] FIG. 6 is a diagram showing the results of thermogravimetric analysis of particles before removal of amorphous carbon in Example 4. [Figure 7] FIG. 7 is a diagram showing the results of thermogravimetric analysis of the particles after removing amorphous carbon in Example 1. [Figure 8] FIG. 8 is a diagram showing the results of thermogravimetric analysis of particles after removal of amorphous carbon in Example 2. [Figure 9] FIG. 9 is a diagram showing the results of thermogravimetric analysis of the particles after removing amorphous carbon in Example 3. [Figure 10] FIG. 10 is a diagram showing the results of thermogravimetric analysis of the particles after removing amorphous carbon in Example 4. [Figure 11] FIG. 11 is a diagram showing the results of thermogravimetric analysis of the particles of Comparative Example 1. [Figure 12] FIG. 12 is a diagram showing the results of thermogravimetric analysis of the particles of Comparative Example 2. [Figure 13] FIG. 13 is a diagram showing the results of thermogravimetric analysis of the particles of Comparative Example 3. [Figure 14] FIG. 14 is a diagram showing the results of thermogravimetric analysis of the particles of Comparative Example 4. [Figure 15] FIG. 15 is a transmission electron microscope photograph of the particles obtained in Example 4 before amorphous carbon removal. [Figure 16] FIG. 16 is a transmission electron microscope photograph of the particles obtained in Example 4 after amorphous carbon has been removed. DETAILED DESCRIPTION OF THE INVENTION

[0025] The present invention will be described in detail below.

[0026] [Particle manufacturing method] In the particle manufacturing method according to the present invention, particles are manufactured that include a particle body and a coating layer that covers at least a part of the particle body.

[0027] Specifically, a mixture containing the particle body, a layered compound, and a dispersion medium is first prepared. Next, a shear force is applied to the prepared mixture. This peels off the layered compound, and the layered compound coats the particle body to form a coating layer, thereby obtaining the particles of the present invention. In the present invention, the viscosity of the dispersion medium at 25°C is 1 mPa·s or more. In contrast, for example, water has a viscosity of 0.88 mPa·s at 25°C.

[0028] In the particle production method of the present invention, the viscosity of the dispersion medium is 1 mPa·s or more, so that the layered compound can be easily peeled off and the layered compound can coat the particle body simply by applying shear force to the mixture. Therefore, the particles of the present invention can be produced easily without requiring any complicated processes. Furthermore, the production process can be carried out in a non-oxidizing environment, which can also enhance the conductivity of the resulting particles.

[0029] The particles obtained by the production method of the present invention have excellent conductivity as described above, and therefore can be suitably used as electrode materials for electricity storage devices. In particular, they can be suitably used as positive electrode active materials or negative electrode active materials that constitute the electrodes of electricity storage devices. By using the particles obtained by the production method of the present invention as electrode materials for electricity storage devices, properties such as charge / discharge cycle characteristics can be improved.

[0030] Each step of the method for producing particles according to the present invention will be described in more detail below.

[0031] (Mixture preparation process) In the mixture preparation step, a mixture containing particle bodies, a layered compound, and a dispersion medium is prepared.

[0032] particle body; The shape of the particle body is not particularly limited, but may be, for example, spherical, approximately spherical, scale-like, flat, elliptical, or approximately elliptical. In addition to the above shapes, a hollow or porous structure may also be used. Of these, spherical or approximately spherical shapes are preferred.

[0033] The average particle size of the particle body is not particularly limited. However, the average particle size of the particle body is preferably 10 nm or more, more preferably 50 nm or more, and preferably 20 μm or less, more preferably 10 μm or less, and even more preferably 5 μm or less. When the average particle size of the particle body is within the above range, the layered compound can be more easily peeled off and the layered compound can be more reliably coated on the particle body. The average particle size refers to a value calculated from a volume-based distribution using a particle size distribution analyzer based on dynamic light scattering or laser diffraction.

[0034] The true density of the particle body is not particularly limited, but is preferably 0.8 g / cm 3 More preferably, 2 g / cm 3 In this case, the layered compound can be peeled off more easily and the particle body can be coated with the layered compound more reliably. The upper limit of the true density of the particle body is not particularly limited, but it can be, for example, 20 g / cm 3 It can be said that:

[0035] The particle body is not particularly limited, but examples thereof include metals or metal compounds, semiconductors or semiconductor compounds, and sulfur or sulfur compounds. In particular, when the particles constitute a negative electrode active material, the particle body is preferably a particle capable of absorbing and releasing alkali metal ions or alkaline earth metal ions. Examples of alkali metal ions include lithium ions, sodium ions, or potassium ions. Examples of alkaline earth metals include calcium ions or magnesium ions. In particular, a metal or metal compound capable of absorbing and releasing lithium ions is preferable.

[0036] Examples of metals or metal compounds that can be used include Mg, Al, Ca, Sc, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Ga, Sr, Y, Zr, Nb, Mo, Tc, Ru, Pd, Ag, Cd, In, Sn, Ba, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Tl, Pb, and compounds thereof.

[0037] Examples of the semiconductor or semiconductor compound that can be used include Si, P, Ge, As, Se, Sb, Te, Bi, Po, and compounds thereof.

[0038] In particular, when the particles are used as a negative electrode active material for a lithium ion secondary battery (LiB negative electrode active material), examples of the particle body include Si, Si compounds, Sn, and Sn compounds. Examples of the Si compounds include alloys of Si with other metals, and Si oxides such as SiO and SiO2. Examples of Sn compounds include alloys of Sn with other metals, and Sn oxides such as SnO and SnO2. In this case, the characteristics of the electricity storage device, such as the capacity, can be further improved. Note that these metals or metal compounds may be used alone or in combination.

[0039] When the particles are used as a positive electrode active material for a lithium ion secondary battery (LiB positive electrode active material), examples of the particle body include lithium metal oxide, lithium sulfide, nickel compound, and sulfur.

[0040] Examples of lithium metal oxides include compounds with a layered rock salt structure, compounds with a spinel structure, compounds with an olivine structure, and mixtures thereof.

[0041] Examples of compounds with a layered rock salt structure include lithium cobalt oxide and lithium nickel oxide.

[0042] An example of a compound having a spinel structure is lithium manganate.

[0043] An example of a compound having an olivine structure is lithium iron phosphate.

[0044] Among these, the particle body is preferably made of lithium cobalt oxide.

[0045] The particle body may also be a granule formed by bonding a plurality of particles together. For example, a ternary system of nickel, manganese, and cobalt, Li(NiMnCo)O2 (NMC), can be used as the granule.

[0046] The content of the particle body in the mixture is preferably 1% by weight or more and 50% by weight or less, in which case the layered compound can be peeled off more easily and the particle body can be coated with the layered compound more reliably.

[0047] Layered compounds; The layered compound is not particularly limited, and examples thereof include graphite, graphite oxide, boron nitride, and graphite-like layered compounds (BCN). These layered compounds may be used alone or in combination. Among them, when used in secondary batteries such as lithium-ion secondary batteries (LiB), the layered compound preferably contains graphite, and more preferably is graphite. In this case, the conductivity of the obtained particles can be further improved. On the other hand, for applications such as thermally conductive sheets that require insulation, it is preferable to use an insulating layered compound such as boron nitride.

[0048] Graphite is a laminate of multiple graphene sheets. The number of stacked graphene sheets in graphite is usually about 100,000 to 1,000,000. Examples of graphite that can be used include natural graphite, artificial graphite, and expanded graphite.

[0049] In this way, the layered compound can be a laminate of sheet-like materials.

[0050] The content of the layered compound in the mixture is preferably 0.01% by weight or more and 30% by weight or less, which allows the layered compound to be peeled off more easily and to coat the particle bodies with the layered compound more reliably.

[0051] dispersion medium; The viscosity of the dispersion medium at 25°C is 1 mPa·s or more, preferably 1.5 mPa·s or more, and more preferably 10 mPa·s or more. In this case, the layered compound can be more easily peeled off and the particle body can be more reliably coated with the layered compound. The upper limit of the viscosity of the dispersion medium at 25°C can be, for example, 10,000,000 mPa·s.

[0052] The viscosity of the dispersion medium can be measured at 25°C using, for example, an E-type viscometer (TV-25 Type-H viscometer, manufactured by Toki Sangyo Co., Ltd.).

[0053] The dispersion medium may be in the form of a sol, a gel, or a liquid.

[0054] The dispersion medium is not particularly limited, but examples thereof include polyethylene glycol, polypropylene glycol, sucrose, polyvinyl alcohol, vinyl acetate, polystyrene, polyamine, silicone oil, carboxymethyl cellulose, water, ethanol, methanol, propanol, and dimethylformamide. These dispersion media may be used alone or in combination. These dispersion media may also be in the form of a solution in which a solute is dissolved in a solvent such as water. In this case, the viscosity of the dispersion medium refers to the viscosity of the solution. Specifically, for example, an aqueous sucrose solution can be used as the dispersion medium. The viscosity of a 20% aqueous sucrose solution at 25°C is 1.68 mPa·s, and the viscosity of a 50% aqueous sucrose solution at 25°C is 12.98 mPa·s.

[0055] The SP value of the dispersion medium is not particularly limited, but is preferably at least 5, more preferably at least 8, and preferably at most 20, more preferably at most 18. In this case, the layered compound can be peeled off more easily and the particle body can be coated with the layered compound more reliably.

[0056] The SP value is a measure of the affinity between substances. The SP value can be calculated based on the theory of regular solutions by Hidebrand. The SP value can be obtained from literature information, or by the calculation methods of Hansen and Hoy, or the estimation method of Fedors. Among these, the Fedors formula δ 2 It is desirable to use the calculated value calculated by the formula: =ΣE / ΣV (δ is the SP value, E is the evaporation energy, and V is the molar volume). The unit of the SP value is (cal / cm 3 ) 0.5 The Fedors method is described in the Journal of the Japan Adhesion Association, Vol. 22, p. 566, 1986.

[0057] The molecular weight of the dispersion medium is not particularly limited, but is preferably 20 or more, more preferably 40 or more. This increases the viscosity of the dispersion medium, making it easier to peel off the layered compound and more reliably coating the particle body with the layered compound. The upper limit of the molecular weight of the dispersion medium is not particularly limited, but can be, for example, 10,000. When the dispersion medium is a mixed solvent of multiple solvents or a solution in which a solute is dissolved in a solvent, the molecular weight is weighted and averaged based on the blending ratio.

[0058] The content of the dispersion medium in the mixture is not particularly limited, but is preferably 100 parts by weight or more per 100 parts by weight of the layered compound charged, since it is used when peeling off the layered compound. This makes it easier to peel off the layered compound and more reliably coats the particle body with the layered compound. On the other hand, the content of the dispersion medium in the mixture is preferably 500 parts by weight or less per 100 parts by weight of the particle body charged. In this case, the use of unnecessary dispersion medium can be reduced, and coated particles can be obtained more efficiently.

[0059] (Coating layer formation process) In the coating layer forming step, a shear force is applied to the mixture obtained in the mixture preparation step. This peels the layered compound and coats the particle body with the layered compound to form a coating layer. In the present invention, the particle body may be coated with the exfoliated product obtained by peeling the layered compound, or the layered compound coated on the particle body may be peeled. Alternatively, both may be performed. Either method can be used to form a coating layer containing the exfoliated product of the layered compound. Furthermore, the coating layer may contain the layered compound before peeling.

[0060] The method for applying shear force to the mixture is not particularly limited, but may be, for example, a ball mill, stirring, ultrasonic waves, high-pressure release, or planetary stirring. Among these, planetary stirring is preferred. In this case, the layered compound can be more easily peeled off and the particle bodies can be more reliably coated with the layered compound. The above-mentioned methods for applying shear force may be used alone or in combination.

[0061] When applying shear force to the mixture, the viscosity of the dispersion medium may be increased while cooling, and then shear force may be applied. In this case, even if a dispersion medium with a low viscosity at room temperature is used, the layered compound can be easily peeled off and the layered compound can be more reliably coated on the particle body, making it easier to remove the dispersion medium in a subsequent step. Furthermore, when applying shear force to the mixture, the viscosity of the dispersion medium may be reduced while heating, and then shear force may be applied. In this case, a dispersion medium with a high viscosity at room temperature can be used, making it easier to peel off the layered compound and more reliably coat the particle body. The temperature during cooling or heating depends on the type of dispersion medium, but can be, for example, from -30°C to 200°C.

[0062] When the mixture is cooled or heated while being subjected to shear force, the viscosity of the dispersion medium at the temperature during cooling or heating is preferably 1 mPa s or more, more preferably 1.5 mPa s or more, and particularly preferably 10 mPa s or more. In this case, the layered compound can be peeled off more easily and the particle bodies can be coated with the layered compound more reliably.

[0063] Furthermore, when the mixture is cooled or heated before shear force is applied, the viscosity of the dispersion medium at the cooling or heating temperature is preferably 10,000,000 mPa s or less, more preferably 1,000,000 mPa s or less, which makes it even easier to apply shear force to the mixture.

[0064] In the present invention, the dispersion medium may be removed after the particle body is coated with the layered compound. In this case, the dispersion medium can be removed, for example, by solid-liquid separation or by evaporation under heating or reduced pressure. Heating may be performed in the air or in an inert gas atmosphere such as nitrogen gas.

[0065] In the present invention, after the particle body is coated with the layered compound, the dispersion medium may be heated to carbonize it. This may result in a coating layer containing amorphous carbon and exfoliated material from the layered compound. In this case, the heating temperature may be, for example, 200°C or higher and 600°C or lower. The heating time may be 20 minutes or higher and 480 minutes or lower. The heating may be performed in air or in an inert gas atmosphere such as nitrogen gas.

[0066] The carbonized dispersion medium may be further removed by heating. This can further increase the conductivity of the resulting particles. In this case, the heating temperature can be, for example, 300°C or higher and 800°C or lower. The heating time can be 10 minutes or higher and 300 minutes or lower. Heating is preferably carried out under conditions that burn off the carbonized dispersion medium (amorphous carbon) but do not burn off the exfoliated layer compound. For example, heating may be carried out in air at 500°C for 30 minutes.

[0067] A specific example of the method for producing particles according to the present invention will be described below with reference to FIG.

[0068] 1(a) to 1(c) are schematic diagrams illustrating an example of the method for producing particles according to the present invention.

[0069] First, as shown in Fig. 1(a), a mixture is prepared by adding a particle body 2, a layered compound 11, and a dispersion medium 12 to a container 10. The layered compound 11 may be used as is, or may be crushed and classified using a ball mill, a feather mill, ultrasonic waves, a crusher / classifier, a sieve, or the like.

[0070] Next, the mixture is mixed by rotating and revolving the balls 13 shown in Fig. 1(b) in a ball mill. As a result, shear force is applied to the mixture by the balls 13, as shown in Fig. 1(b) and Fig. 1(c). By repeating this operation, the layered compound 11 is peeled off, and exfoliated layered compound 11a and dispersion medium 12 are adhered to the surface of the particle body 2.

[0071] The ball mill may be, for example, a planetary ball mill (manufactured by Thinky Corporation, product number "NP-100"). The rotation speed may be, for example, 400 rpm or more and 2000 rpm or less. The rotation time may be, for example, 5 minutes or more and 600 minutes or less. The balls 13 may be, for example, ceramic balls. In this embodiment, zirconia balls are used as the balls 13.

[0072] Next, the particle body 2 with the exfoliated material 11a of the layered compound and the dispersion medium 12 attached thereto is removed from the container 10. Subsequently, the particle body 2 with the exfoliated material 11a of the layered compound and the dispersion medium 12 attached to its surface is heated at a temperature of 200°C or higher and 600°C or lower in a nitrogen atmosphere to carbonize the dispersion medium 12 and form amorphous carbon. This allows the production of particles having the exfoliated material 11a of the layered compound and a coating layer containing amorphous carbon.

[0073] The resulting particles may be further heated in an air atmosphere at a temperature of 300° C. to 800° C. to remove the amorphous carbon in the coating layer, thereby further increasing the conductivity of the particles.

[0074] As described above, in the particle manufacturing method of the present invention, the layered compound is exfoliated by mechanical treatment. Therefore, unlike when the layered compound is exfoliated by chemical treatment, an oxidation step of the layered compound is not included. Therefore, particles with excellent conductivity can be obtained.

[0075] [particle] FIG. 2 is a schematic cross-sectional view showing an example of a particle produced by the particle production method according to the present invention.

[0076] 2, the particle 1 includes a particle body 2 and a coating layer 3. The coating layer 3 is provided so as to cover the surface 2a of the particle 2. The coating layer 3 may cover the entire surface 2a of the particle body 2, as in this embodiment, or may cover only a part of the surface 2a.

[0077] The coating layer 3 covers at least a portion of the surface 2a of the particle body 2. The coating layer 3 preferably covers 20% or more of the surface 2a of the particle body 2, more preferably 90% or more, even more preferably 95% or more, particularly preferably 98% or more, and most preferably completely. In this case, the conductivity of the particle can be further improved.

[0078] In the present invention, whether or not the surface of the particle body is covered with a coating layer can be confirmed by a scanning electron microscope (SEM), a transmission electron microscope (TEM), etc. In this case, energy dispersive X-ray spectroscopy (SEM-EDX, TEM-EDX) may be used to confirm whether or not the particle body is coated with carbon element (C element).

[0079] Furthermore, when the particle body is a particle that reacts with oxygen to form an oxide, such as a Si particle, the presence or absence of a coating can be confirmed by determining whether or not the weight increase starting temperature, which is an indicator of the temperature at which the particle body, such as Si, reacts with oxygen in the air gas being measured and begins to oxidize, shifts to 600°C or higher when the particle is subjected to thermogravimetric analysis under conditions of an air atmosphere and a temperature increase rate of 10°C / min.

[0080] The thermogravimetric analysis can be performed using a simultaneous thermogravimetric and calorimetric analyzer (manufactured by Hitachi High-Tech Science Corporation, product number "TGDTA6300") under the following conditions.

[0081] Atmosphere: Air atmosphere Heating rate: 10°C / min Temperature range: 40℃~1000℃

[0082] In the present invention, the weight gain initiation temperature of the obtained particles is preferably 600°C or higher, more preferably 700°C or higher, and preferably 900°C or lower. When the weight gain initiation temperature of the particles is equal to or higher than the lower limit, the particles can be more uniformly coated with a coating layer, and the conductivity of the particles can be further increased. When the weight gain initiation temperature of the particles is equal to or lower than the upper limit, the thickness of the coating layer is less likely to be large. Therefore, when used as an electrode material for an electricity storage device, ions such as lithium ions can be more smoothly absorbed and released, and characteristics such as charge / discharge cycle characteristics can be further improved.

[0083] The thickness of the coating layer is preferably 0.1 nm or more, more preferably 1 nm or more, and preferably 20 nm or less, more preferably 10 nm or less. When the thickness of the coating layer is equal to or greater than the above-mentioned lower limit, the conductivity of the particles can be further increased. When the thickness of the coating layer is equal to or less than the above-mentioned upper limit, when used as an electrode material for an electricity storage device, ions such as lithium ions can be absorbed and released more smoothly, and characteristics such as charge / discharge cycle characteristics can be further improved.

[0084] The thickness of the coating layer can be determined from the average value of the thicknesses of the coating layers of any three particles observed using a transmission electron microscope (TEM photograph).

[0085] The coating layer contains an exfoliated layer compound. Therefore, the particles are particles coated with the exfoliated layer compound. The exfoliated layer compound may be exfoliated graphite.

[0086] In this specification, exfoliated graphite refers to a graphene sheet laminate obtained by exfoliating original graphite and is thinner than the original graphite. The number of stacked graphene sheets in the exfoliated graphite may be smaller than that of the original graphite.

[0087] In the exfoliated product of the layered compound, the number of stacked sheets such as graphene sheets is not particularly limited, but is preferably 1 or more, more preferably 3 or more, and preferably 100 or less, more preferably 10 or less. When the number of stacked sheets is equal to or greater than the above-mentioned lower limit, the conductivity of the particles can be further increased. When the number of stacked sheets is equal to or less than the above-mentioned upper limit, when used as an electrode material for an electricity storage device, ions such as lithium ions can be more smoothly absorbed and released, and characteristics such as charge / discharge cycle characteristics can be further improved.

[0088] The content of exfoliated layer compound in the coating layer is preferably 0.01% by weight or more, more preferably 0.1% by weight or more, and preferably 30% by weight or less, more preferably 5% by weight or less, based on 100% by weight of the material constituting the coating layer. When the content of the layer compound is within the above range, the conductivity of the particles can be further improved.

[0089] The coating layer may further contain a layer compound as a raw material. Specifically, the content of the layer compound in the coating layer may be, for example, 0.01 wt % or more and 10 wt % or less relative to 100 wt % of the material constituting the coating layer.

[0090] The coating layer may further contain amorphous carbon, which allows the surface of the particle body to be coated more uniformly.

[0091] Whether or not amorphous carbon is contained can be confirmed by checking whether or not a broad peak is observed in the vicinity of 2θ=15° to 30° in the X-ray diffraction spectrum.

[0092] The content of amorphous carbon in the coating layer can be, for example, 1% by weight or more and 30% by weight or less relative to 100% by weight of the material that constitutes the coating layer.

[0093] As described above, the particles obtained by the particle manufacturing method according to the present invention are uniformly coated with exfoliated material of the layered compound having excellent electrical conductivity. Therefore, when the particles are used as a negative electrode active material for a secondary battery, for example, the volume change associated with charge and discharge can be reduced, and the negative electrode active material can be prevented from cracking or peeling off from the electrode.

[0094] However, if the coating layer is too thick, it may not be possible to release ions such as lithium ions. In contrast, the coating layer of the particles obtained by the production method of the present invention contains exfoliated material of the layered compound. Therefore, the coating layer does not become too thick, and ions such as lithium ions can be smoothly absorbed and released. Therefore, when the particles obtained by the present invention are used as an electrode material for an electricity storage device, properties such as cycle characteristics can be improved.

[0095] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples and can be modified as appropriate within the scope of the present invention.

[0096] Example 1 1.2 g of graphite (Toyo Tanso Co., Ltd., product number "PF8") was dispersed in a mixture of 23.4 g of polyethylene glycol (Sanyo Chemical Co., Ltd., product number "PEG600"; viscosity: 106 mPa·s (25°C), molecular weight: 600, SP value: 9.4) and 23.0 g of water (viscosity: 0.88 mPa·s (25°C), molecular weight: 18, SP value: 23.4). The mixture was stirred at 11,000 rpm for 30 minutes using a mixer (Primix Corporation, product number "PRIMIX2"), and then heated in an air-circulating oven at 150°C for 3 hours to remove water. The viscosity of the dispersion medium was measured at 25°C using an E-type viscometer (Toki Sangyo Co., Ltd., product number "TV-25 Type-H"; spindle number 1).

[0097] To 6 g of the resulting mixture of graphite and dispersion medium, 0.6 g of Si particles (manufactured by Kanto Chemical Co., Inc., average particle size: 100 nm, true density: 2.33) were added as the particle body to prepare a mixture (graphite:PEG:Si = 1.2 wt %: 23.4 wt %: 2.46 wt %).

[0098] Next, the prepared mixture was placed in a zirconia container of a planetary ball mill (Thinky Corporation, product number "NP-100") together with 2 mm zirconia balls (2.5 g) and mixed by planetary stirring at a rotation speed of 2000 rpm for 25 minutes. After mixing, the removed particles were heated at 420°C for 1 hour in a nitrogen atmosphere. This resulted in particles whose surfaces were coated with exfoliated graphite and amorphous carbon.

[0099] The obtained particles were then heated in an air atmosphere at 500° C. for 10 minutes, thereby removing the amorphous carbon and obtaining particles in which the surfaces of the Si particles were coated with exfoliated graphite.

[0100] Example 2 One gram of graphite (Toyo Tanso Co., Ltd., product number "PF8") serving as a layered compound was dispersed in 234 g of 20 wt% sucrose water (prepared by dissolving a specified amount of reagent-grade sucrose in water, Fujifilm Wako Pure Chemical Industries, Ltd.) serving as a dispersion medium. The mixture was stirred at 11,000 rpm for 30 minutes using a mixer (Primix Corporation, "PRIMIX2") to obtain a graphite / dispersion medium mixture. The viscosity of the dispersion medium was measured at 25°C using an E-type viscometer (Toki Sangyo Co., Ltd., product name "TV-25 Type-H", spindle No. 1) and found to be 1.68 mPa·s.

[0101] To 6 g of the resulting mixture of graphite and dispersion medium, 0.6 g of Si particles (manufactured by Kanto Chemical Co., Ltd., average particle size: 100 nm, true density: 2.33) was added as the particle body to prepare a mixture (graphite: 20% sucrose water: Si = 1 wt%: 234 wt%: 23.5 wt%).

[0102] Next, the prepared mixture was placed in the container of a planetary ball mill (Thinky Corporation, product number "NP-100") together with 2 mm zirconia balls (2.5 g) and mixed by planetary stirring at a rotation speed of 2000 rpm for 25 minutes. After mixing, the removed particles were heated at 250°C for 1 hour in a nitrogen atmosphere. This resulted in particles whose surfaces were coated with exfoliated graphite and amorphous carbon.

[0103] The obtained particles were then heated in an air atmosphere at 550° C. for 10 minutes, thereby removing the amorphous carbon and obtaining particles in which the surfaces of the Si particles were coated with exfoliated graphite.

[0104] Example 3 One gram of graphite (Toyo Tanso Co., Ltd., product number "PF8") serving as a layered compound was dispersed in 234 g of 50 wt% sucrose water (Fujifilm Wako Pure Chemical Industries, Ltd., prepared by dissolving a specified amount of reagent-grade sucrose in water) serving as a dispersion medium. The mixture was stirred at 11,000 rpm for 30 minutes using a mixer (Primix Corporation, "PRIMIX2") to obtain a mixture of graphite and dispersion medium. The viscosity of the dispersion medium was measured at 25°C using an E-type viscometer (Toki Sangyo Co., Ltd., product name "TV-25 Type-H", spindle No. 1) and was found to be 12.98 mPa·s.

[0105] To 6 g of the resulting mixture of graphite and dispersion medium, 0.6 g of Si particles (manufactured by Kanto Chemical Co., Ltd., average particle diameter: 100 nm, true density: 2.33) was added as the particle body to prepare a mixture (graphite: 50% sucrose water: Si = 1 wt%: 234 wt%: 23.5 wt%).

[0106] Next, the prepared mixture was placed in the container of a planetary ball mill (Thinky Corporation, product number "NP-100") together with 2 mm zirconia balls (2.5 g) and mixed by planetary stirring at a rotation speed of 2000 rpm for 25 minutes. After mixing, the removed particles were heated at 250°C for 1 hour in a nitrogen atmosphere. This resulted in particles whose surfaces were coated with exfoliated graphite and amorphous carbon.

[0107] The obtained particles were then heated in an air atmosphere at 600° C. for 10 minutes, thereby removing the amorphous carbon and obtaining particles in which the surfaces of the Si particles were coated with exfoliated graphite.

[0108] Example 4 One gram of graphite (Toyo Tanso Co., Ltd., product number "PF8") was dispersed in 234 g of polyethylene glycol (Sanyo Chemical Co., Ltd., product number "PEG600," viscosity: 106 mPa·s (25°C), molecular weight: 600, SP value: 9.4) as a dispersion medium. The mixture was stirred at 11,000 rpm for 30 minutes using a mixer (Primix Corporation, "PRIMIX2") to obtain a mixture of graphite and the PEG600 dispersion medium. The viscosity of the dispersion medium was measured at 25°C using an E-type viscometer (Toki Sangyo Co., Ltd., product name "TV-25 Type-H," spindle No. 1).

[0109] To 6 g of the resulting mixture of graphite and dispersion medium, 0.6 g of Si particles (manufactured by Kanto Chemical Co., Inc., average particle size: 100 nm, true density: 2.33) was added as the particle body to prepare a mixture (graphite:PEG:Si = 1 wt %:234 wt %:23.5 wt %).

[0110] Next, the prepared mixture was placed in a zirconia container of a planetary ball mill (Thinky Corporation, product number "NP-100") together with 2 mm zirconia balls (2.5 g) and mixed by planetary stirring at a rotation speed of 2000 rpm for 25 minutes. After mixing, the removed particles were heated at 420°C for 1 hour in a nitrogen atmosphere. This resulted in particles whose surfaces were coated with exfoliated graphite and amorphous carbon.

[0111] The obtained particles were then heated in an air atmosphere at 500° C. for 10 minutes, thereby removing the amorphous carbon and obtaining particles in which the surfaces of the Si particles were coated with exfoliated graphite.

[0112] (Comparative Example 1) Si particles (manufactured by Kanto Chemical Co., Ltd., average particle size: 100 nm) were used as they were.

[0113] (Comparative Example 2) 1 g of graphite (manufactured by Toyo Tanso Co., Ltd., product number "PF8") as a layered compound was dispersed in 234 g of water (viscosity: 0.88 mPa·s, SP value: 23.4), and the dispersion was stirred at a rotation speed of 11,000 rpm for 30 minutes using a mixer (manufactured by Primix Corporation, "PRIMIX2") to obtain a mixture of graphite and water.

[0114] To 6 g of the resulting mixture of graphite and water, 0.6 g of Si particles (manufactured by Kanto Chemical Co., Inc., average particle size: 100 nm, true density: 2.33) was added as the particle body to prepare a mixture (graphite:water:Si=1 wt %:234 wt %:23.5 wt %).

[0115] Next, the prepared mixture was placed in a zirconia container of a planetary ball mill (Thinky Corporation, product number "NP-100") together with 2 mm zirconia balls (2.5 g) and mixed by planetary stirring at a rotation speed of 2000 rpm for 25 minutes. The resulting mixture was transferred to a glass petri dish and vacuum dried at 120°C for 24 hours to remove water, yielding particles.

[0116] (Comparative Example 3) 0.0255 g of graphite (manufactured by Toyo Tanso Co., Ltd., product number "PF8") and 0.6 g of Si particles (manufactured by Kanto Chemical Co., Ltd., average particle size: 100 nm, true density: 2.33) were added to prepare a mixture (graphite:Si=1 wt%:23.5 wt%).

[0117] Next, the prepared mixture was placed in the container of a planetary ball mill (Thinky Corporation, product number "NP-100") together with 2 mm zirconia balls (2.5 g) and mixed by planetary stirring at a rotation speed of 2000 rpm for 25 minutes, thereby obtaining particles.

[0118] Comparative Example 4 0.0255 g of graphite (manufactured by Toyo Tanso Co., Ltd., product number "PF8") and 0.6 g of Si particles (manufactured by Kanto Chemical Co., Ltd., average particle diameter: 100 nm, true density: 2.33) were placed in the container of a planetary ball mill (manufactured by Thinky Corporation, product number "NP-100") and mixed by planetary stirring at a rotation speed of 2000 rpm for 25 minutes. Thus, particles were obtained. In Comparative Example 4, 2 mm zirconia balls were not used.

[0119] <Evaluation> (thermogravimetry) The particles obtained in Examples 1 to 4 and the particles in Comparative Examples 1 to 4 were measured under the following conditions using a simultaneous thermogravimetric and calorimetric analyzer (manufactured by Hitachi High-Tech Science Corporation, product number "TGDTA6300").

[0120] Atmosphere: Air atmosphere Heating rate: 10°C / min Temperature range: 40℃~1000℃

[0121] Figures 3 to 6 show the results of thermogravimetric analysis of particles before amorphous carbon removal in Examples 1 to 4, respectively. Figures 7 to 10 show the results of thermogravimetric analysis of particles after amorphous carbon removal in Examples 1 to 4, respectively. Figures 11 to 14 show the results of thermogravimetric analysis of particles in Comparative Examples 1 to 4, respectively.

[0122] 3 and 7 show that the weight gain starting temperature exceeds 800°C for the particles obtained in Example 1. FIG. 4 and 8 show that the weight gain starting temperature exceeds 800°C for the particles obtained in Example 2. FIG. 5 and 9 show that the weight gain starting temperature is around 800°C for the particles obtained in Example 3. FIG. 6 and 10 show that the weight gain starting temperature exceeds 700°C for the particles obtained in Example 4.

[0123] As shown in Figure 11, the Si particles (uncoated Si particles) used as the raw material in Comparative Example 1 had a weight gain start temperature of around 400 to 500°C. This indicates that in Examples 1 to 4, the oxidation temperature of Si shifted to the higher temperature side, and the Si particles were coated with exfoliated graphite. Furthermore, Figures 7 to 10 show that the weight loss on the low temperature side (around 500°C) present in Figures 3 to 6 has decreased or disappeared. This confirms that amorphous carbon has decreased or disappeared.

[0124] 12 to 14, the particles of Comparative Examples 2 to 4 showed a temperature range of 400°C to 500°C at which weight gain due to oxidation of Si began, similar to the particles of Comparative Example 1. This confirmed that the particles were not sufficiently coated with the carbon material.

[0125] (Observation of coating condition) FIG. 15 is a transmission electron microscope photograph of the particles obtained in Example 4 before amorphous carbon removal. FIG. 16 is a transmission electron microscope photograph of the particles obtained in Example 4 after amorphous carbon removal. As shown in FIGS. 15 and 16, it was confirmed that a coating layer was formed on the entire surface of the particle body in Example 4. Similarly, it was confirmed that a coating layer was formed on the entire surface of the particle body in Examples 1 to 3. Furthermore, the thickness of the coating layer in Example 4 was 5 nm to 40 nm before amorphous carbon removal and 0.5 nm to 10 nm after amorphous carbon removal. Furthermore, in Example 1, it was 20 nm to 100 nm before amorphous carbon removal.

[0126] (powder resistance measurement) The resistance of the particles obtained in Example 1 and Comparative Example 1 under a predetermined load was measured using a powder resistance measuring device (manufactured by Mitsubishi Chemical Analytech Co., Ltd., product number "PD-51").

[0127] Specifically, 0.2 g of each sample was weighed and placed in a sample holder, and the load was gradually increased from 0 kN to 16 kN, and the resistance at 16 kN was compared. The results are shown in Table 1 below.

[0128] [Table 1]

[0129] From Table 1, it was confirmed that the conductivity was improved by coating the silicon particles of Comparative Example 1, which had high resistance, with carbon, and that the conductivity was further improved by removing the amorphous carbon and increasing the coating ratio of crystalline carbon. [Explanation of symbols]

[0130] 1...Particle 2...Particle body 2a…Surface 3…Covering layer 10...Container 11...Layered compounds 11a...Exfoliated layered compound 12...Dispersion medium 13...Ball

Claims

1. A method for producing particles comprising a particle body and a coating layer covering at least a portion of the particle body, the method comprising: preparing a mixture containing the particle body, a layered compound, and a dispersion medium; applying a shear force to the mixture to peel off the layered compound and coat the particle bodies with the layered compound to form the coating layer; Equipped with the layered compound comprises graphite or graphite oxide, or boron nitride or a graphite-like layered compound; The viscosity of the dispersion medium at 25°C is 1 mPa s or more, a step of cooling the mixture to increase its viscosity and then applying the shear force to the mixture to exfoliate the layered compound and coat the particle bodies with the layered compound.

2. The method for producing particles according to claim 1 , wherein the dispersion medium is in a sol state, a gel state, or a liquid state.

3. The method for producing particles according to claim 1 or 2, wherein the dispersion medium contains a dispersion medium having an SP value of 5 or more and 20 or less.

4. The method for producing particles according to any one of claims 1 to 3, wherein the dispersion medium contains a solvent having a molecular weight of 40 or more.

5. The method for producing particles according to any one of claims 1 to 4, wherein the particle bodies have an average particle size of 20 µm or less.

6. The true density of the particle body is 0.8 g / cm ３ The method for producing particles according to any one of claims 1 to 5, wherein the above-mentioned

7. The method for producing particles according to any one of claims 1 to 6, wherein the particle body is a metal or a metal compound.

8. The method for producing particles according to any one of claims 1 to 7, wherein the shear force is applied by at least one method selected from the group consisting of ball milling, stirring, ultrasonic waves, high pressure release, and planetary stirring.

9. The method for producing particles according to any one of claims 1 to 8, further comprising the step of removing the dispersion medium after the step of forming the coating layer.

10. The method for producing particles according to claim 9 , wherein in the step of removing the dispersion medium, the dispersion medium is removed by solid-liquid separation or by volatilization by heating or reducing pressure.

11. A method for producing particles comprising a particle body and a coating layer covering at least a portion of the particle body, comprising: preparing a mixture containing the particle body, a layered compound, and a dispersion medium; applying a shear force to the mixture to peel off the layered compound and coat the particle bodies with the layered compound to form the coating layer; Equipped with the layered compound comprises graphite or graphite oxide, or boron nitride or a graphite-like layered compound; The viscosity of the dispersion medium at 25°C is 1 mPa s or more, The method for producing particles further comprises, after the step of forming the coating layer, a step of carbonizing the dispersion medium by heating.

12. The method for producing particles according to claim 11 , further comprising the step of removing the carbonized dispersion medium.

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