WO2021141014A1 - Carbon material-coated silicon particles, electrode for electricity storage devices, and electricity storage device - Google Patents

Carbon material-coated silicon particles, electrode for electricity storage devices, and electricity storage device Download PDF

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Publication number
WO2021141014A1
WO2021141014A1 PCT/JP2021/000055 JP2021000055W WO2021141014A1 WO 2021141014 A1 WO2021141014 A1 WO 2021141014A1 JP 2021000055 W JP2021000055 W JP 2021000055W WO 2021141014 A1 WO2021141014 A1 WO 2021141014A1
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silicon particles
carbon material
coated silicon
coated
particles
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PCT/JP2021/000055
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French (fr)
Japanese (ja)
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拓也 工藤
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積水化学工業株式会社
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES OR LIGHT-SENSITIVE DEVICES, OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/22—Electrodes
    • H01G11/24—Electrodes characterised by structural features of the materials making up or comprised in the electrodes, e.g. form, surface area or porosity; characterised by the structural features of powders or particles used therefor
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES OR LIGHT-SENSITIVE DEVICES, OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/22—Electrodes
    • H01G11/30—Electrodes characterised by their material
    • H01G11/32—Carbon-based
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES OR LIGHT-SENSITIVE DEVICES, OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/22—Electrodes
    • H01G11/30—Electrodes characterised by their material
    • H01G11/32—Carbon-based
    • H01G11/36—Nanostructures, e.g. nanofibres, nanotubes or fullerenes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present invention relates to carbon material-coated silicon particles coated with a carbon material, electrodes for a power storage device using the carbon material-coated silicon particles, and a power storage device.
  • the electrode material of the power storage device carbon materials such as graphite, activated carbon, carbon nanofibers, and carbon nanotubes are widely used from the environmental aspect.
  • Patent Document 1 discloses a battery electrode containing a graphene-encapsulating or graphene-encapsulating electrode active material.
  • Patent Document 1 when producing a graphene-containing or graphene-encapsulated electrode active material, in the first step, a plurality of particles of a graphite material and a plurality of particles of a solid electrode active material are mixed in a collision chamber of an energy collision device. The mixture is formed. At this time, the graphite material has not been intercalated, oxidized, and peeled in advance. In addition, it does not contain a ball mill pulverization medium other than a plurality of particles of the solid electrode active material.
  • the energy collision device is operated to peel the graphene sheet from the particles of the graphite material, move the peeled graphene sheet to the surface of the solid electrode active material particles, and completely enclose or enclose the particles.
  • the energy collision device is operated to peel the graphene sheet from the particles of the graphite material, move the peeled graphene sheet to the surface of the solid electrode active material particles, and completely enclose or enclose the particles.
  • Patent Document 1 has a problem that the graphite material cannot be sufficiently peeled off and the solid electrode active material cannot be uniformly coated.
  • battery characteristics such as rate characteristics and cycle characteristics of the secondary battery cannot be sufficiently improved.
  • An object of the present invention is to obtain a carbon material-coated silicon particle, an electrode for a power storage device using the carbon material-coated silicon particle, and a power storage device, which can improve characteristics such as cycle characteristics when used as an electrode material of the power storage device. To provide.
  • the carbon material-coated silicon particles according to the present invention are carbon material-coated silicon particles coated with a carbon material, and the silicon particles and at least a part of the surface of the silicon particles are coated and flaked.
  • a coating layer containing graphite is provided and the carbon material-coated silicon particles are subjected to thermal weight analysis under the conditions of an air atmosphere and a temperature rise rate of 10 ° C./min, the weight increase start temperature is 500 ° C. or higher. Is.
  • the silicon particles are made of Si or a compound of Si.
  • the average particle size of the silicon particles is 20 nm or more and 20 ⁇ m or less.
  • the peak height a derived from the graphene laminated structure and the silicon is 0.01 or more and 2 or less.
  • the thickness of the coating layer made of the carbon material in the carbon material-coated silicon particles is 30 nm or less.
  • the carbon material coating layer further comprises unsliced graphite.
  • the coating layer made of the carbon material further contains amorphous carbon.
  • the electrode for a power storage device according to the present invention contains carbon material-coated silicon particles configured according to the present invention.
  • the power storage device according to the present invention includes electrodes for the power storage device configured according to the present invention.
  • a carbon material-coated silicon particle an electrode for a power storage device using the carbon material-coated silicon particle, and a power storage device that can improve characteristics such as cycle characteristics when used as an electrode material of the power storage device are provided. Can be provided.
  • FIG. 1 is a schematic cross-sectional view showing carbon material-coated silicon particles according to an embodiment of the present invention.
  • 2A to 2C are diagrams for explaining an example of a method for producing carbon material-coated silicon particles according to the present invention.
  • FIG. 3 is a diagram showing the results of thermogravimetric analysis and measurement of carbon material-coated silicon particles before removing amorphous carbon in Example 1.
  • FIG. 4 is a diagram showing the results of thermogravimetric analysis and measurement of the carbon material-coated silicon particles after removing the amorphous carbon of Example 1.
  • FIG. 5 is a diagram showing the results of thermogravimetric analysis and measurement of carbon material-coated silicon particles before removing amorphous carbon in Example 2.
  • FIG. 3 is a diagram showing the results of thermogravimetric analysis and measurement of carbon material-coated silicon particles before removing amorphous carbon in Example 1.
  • FIG. 6 is a diagram showing the results of thermogravimetric analysis and measurement of carbon material-coated silicon particles after removing amorphous carbon in Example 2.
  • FIG. 7 is a diagram showing the results of thermogravimetric analysis measurement of the particles of Comparative Example 1.
  • FIG. 8 is an X-ray diffraction spectrum of the particles produced in Example 1 before removing amorphous carbon.
  • FIG. 9 is an X-ray diffraction spectrum of the particles produced in Example 1 after removing amorphous carbon.
  • FIG. 10 is an X-ray diffraction spectrum of the particles produced in Example 2 before removing amorphous carbon.
  • FIG. 11 is an X-ray diffraction spectrum of the particles produced in Example 2 after removing amorphous carbon.
  • FIG. 8 is an X-ray diffraction spectrum of the particles produced in Example 1 before removing amorphous carbon.
  • FIG. 9 is an X-ray diffraction spectrum of the particles produced in Example 1 after removing amorphous
  • FIG. 12 is a diagram showing a transmission electron micrograph of the carbon material-coated silicon particles obtained in Example 1.
  • FIG. 13 is a diagram showing the results of the cycle characteristics of the battery produced by using the carbon material-coated silicon particles obtained in Example 1.
  • FIG. 14 is a diagram showing the results of the cycle characteristics of the battery produced by using the carbon material-coated silicon particles obtained in Example 2.
  • FIG. 15 is a diagram showing the results of cycle characteristics of a battery manufactured using the particles of Comparative Example 1.
  • FIG. 16 is a diagram showing the results of cycle characteristics of an all-solid-state battery produced by using the carbon material-coated silicon particles obtained in Example 3 and the silicon particles of Comparative Example 2, respectively.
  • FIG. 1 is a schematic cross-sectional view showing carbon material-coated silicon particles according to an embodiment of the present invention. As shown in FIG. 1, the carbon material-coated silicon particles 1 include silicon particles 2 and a coating layer 3.
  • the shape of the silicon particles 2 is spherical.
  • the shape of the silicon particles 2 is not particularly limited, and may be a substantially spherical shape, an ellipsoidal shape, a substantially ellipsoidal shape, a flat plate shape, a scale shape, or the like.
  • a coating layer 3 is provided so as to cover the surface 2a of the silicon particles 2.
  • the coating layer 3 may cover the entire surface 2a of the silicon particles 2 or a part of the surface 2a as in the present embodiment.
  • the coating layer 3 contains flaky graphite. Therefore, the carbon material-coated silicon particles 1 are particles coated with a carbon material such as flaky graphite.
  • the flaky graphite is obtained by exfoliating the original graphite, and refers to a graphene sheet laminate thinner than the original graphite.
  • the number of graphene sheets laminated in the flaky graphite may be smaller than that of the original graphite.
  • the weight increase start temperature is 500 ° C. or higher.
  • thermogravimetric analysis can be measured using a thermogravimetric / calorific value simultaneous measuring device (manufactured by Hitachi High-Tech Science Corporation, product number: TGDTA6300).
  • the thermogravimetric analysis is measured under the following conditions.
  • Atmosphere Air Temperature rise rate: 10 ° C / min Temperature range: 40 ° C to 1000 ° C
  • the carbon material-coated silicon particles 1 of the present embodiment have the above-described configuration, characteristics such as cycle characteristics can be enhanced when used as an electrode material for a power storage device. This can be explained as follows.
  • the oxidation start temperature of silicon particles such as the silicon particles used in the present invention is 400 ° C. or higher and lower than 500 ° C. It should be noted that the silicon particles easily absorb moisture to become silicon oxide, and the smaller the particle size, the easier it is to oxidize, so there is a range in the oxidation start temperature. Further, the oxidation start temperature of the silicon particles can be confirmed by performing thermogravimetric differential thermal analysis (TG-DTA) measurement in an air atmosphere and monitoring the heating temperature and the sample weight. The weight increases when the silicon particles and oxygen in the air, which is the measurement atmosphere, start the reaction at the above temperature and the silicon becomes SiO or SiO 2. Therefore, the weight increase start temperature of silicon becomes the oxidation start temperature.
  • TG-DTA thermogravimetric differential thermal analysis
  • the weight increase start temperature is 500 ° C. or higher when thermogravimetric analysis is performed.
  • the decomposition temperature of graphite having a graphene laminated structure is usually 500 ° C. to 800 ° C. in an air atmosphere.
  • the decomposition temperature range of graphite depends on the number and area of graphite layers, the presence or absence of defects, and the degree of oxidation.
  • the carbon material-coated silicon particles of the present invention are uniformly coated with a carbon material having a graphene laminated structure, whereby the contact between air (oxygen) and the silicon particles is blocked, and thermogravimetric analysis is performed. Occasionally, oxidation is not initiated above 400 ° C and below 500 ° C. However, when the temperature is further raised and the temperature is 500 ° C to 800 ° C, the carbon material having a graphene laminated structure is decomposed by the air (oxygen) in the measurement atmosphere and converted into gas (CO, CO 2 ), and the weight of the carbon material is reduced. ..
  • the weight increase start temperature which is an index of the temperature at which the oxidation of the silicon particles is started, has shifted to 500 ° C. or higher.
  • the surface of the particles is uniformly coated with the carbon material having a graphene laminated structure. Therefore, for example, when the particles are used as the negative electrode active material of the secondary battery, they are charged. The volume change due to discharge can be reduced, and cracking of the negative electrode active material and peeling of the carbon material from the electrode can be suppressed.
  • the coating layer in the carbon material-coated silicon particles of the present invention contains flaky graphite. Therefore, the thickness of the coating layer does not become too thick, and ions such as lithium ions can be smoothly occluded and released. Therefore, the carbon material-coated silicon particles of the present invention can improve characteristics such as cycle characteristics when used as an electrode material for a power storage device.
  • the weight increase start temperature of the carbon material-coated silicon particles is 500 ° C. or higher, more preferably 600 ° C. or higher, further preferably 700 ° C. or higher, and preferably 900 ° C. or lower.
  • the weight increase start temperature of the carbon material-coated silicon particles is equal to or higher than the above lower limit, the surface of the silicon particles can be more uniformly coated by the carbon material having a graphene laminated structure, and when used as an electrode material for a power storage device.
  • characteristics such as cycle characteristics can be further improved.
  • the thickness of the coating layer does not become too thick, and ions such as lithium ions can be occluded and released more smoothly. Therefore, when used as an electrode material for a power storage device, characteristics such as cycle characteristics can be further improved.
  • the ratio a / b of the peak height a derived from the graphene laminated structure and the peak height b derived from the silicon particles b is preferably 0.01 or more, more preferably 0.03 or more, preferably 2 or less, more preferably 1.2 or less, still more preferably 0.6 or less.
  • the ratio a / b is not more than the above lower limit value, the number of graphene layers of the flaky graphite contained in the coating layer can be further increased, and the conductivity of the carbon material-coated silicon particles can be further enhanced.
  • characteristics such as rate characteristics and cycle characteristics can be further improved.
  • the ratio a / b is not more than the above upper limit value, the thickness of the coating layer can be further reduced, and ions such as lithium ions can be occluded and released more smoothly. Therefore, when used as an electrode material for a power storage device, characteristics such as cycle characteristics can be further improved.
  • the X-ray diffraction spectrum can be measured by a wide-angle X-ray diffraction method.
  • the X-ray diffractometer for example, SmartLab (manufactured by Rigaku Co., Ltd.) can be used, and measurement can be performed under the following conditions.
  • Radioactive source CuK ⁇ ray (wavelength 1.541 ⁇ ) Measuring range: 5 ° -80 ° Scanning speed: 5 ° / minute Tube current: 200mA Tube voltage: 40kV
  • the ratio of the number of carbon atoms (C / O ratio) to the number of oxygen atoms measured by elemental analysis of carbon material-coated silicon particles is preferably 9 or more, more preferably 99 or more.
  • the conductivity of the carbon material-coated silicon particles can be further increased. Therefore, when used as an electrode material for a power storage device, characteristics such as rate characteristics and cycle characteristics can be further improved.
  • the C / O ratio can be measured by, for example, X-ray photoelectron spectroscopy (XPS). Specifically, the photoelectron spectrum is measured under the conditions of an X-ray source: AlK ⁇ , a photoelectron extraction angle: 45 degrees, and an X-ray beam diameter of 200 ⁇ m (50W15kV). Then, the peak area of the C1s spectrum appearing in Binding Energy: 280 eV to 292 eV is divided by the peak area of the O1s spectrum appearing in Binding Energy: 525 eV to 540 eV. Thereby, the ratio of the number of carbon atoms to the number of oxygen atoms contained in the coating layer of the carbon material-coated silicon particles (C / O ratio) can be calculated.
  • XPS X-ray photoelectron spectroscopy
  • the D / G ratio is preferably 1 when the peak intensity ratio between the D band and the G band is defined as the D / G ratio. Below, it is more preferably 0.5 or less, still more preferably 0.1 or less.
  • the conductivity can be further enhanced, and when used as an electrode material for a power storage device, characteristics such as rate characteristics and cycle characteristics can be further improved.
  • the lower limit of the D / G ratio is not particularly limited, but can be set to 0, for example.
  • the shape of the silicon particles is not particularly limited, and for example, spherical, substantially spherical, scaly, planar, elliptical, and substantially elliptical shapes can be used. Further, in addition to the above shape, a structure having a hollow or porous structure inside can also be used. Of these, a spherical shape or a substantially spherical shape is preferable.
  • the average particle size of silicon particles is not particularly limited. However, the average particle size of the silicon particles is preferably 10 nm or more, more preferably 20 nm or more, still more preferably 50 nm or more, preferably 20 ⁇ m or less, more preferably 10 ⁇ m or less, still more preferably 5 ⁇ m or less. When the average particle size of the silicon particles is within the above range, the cycle characteristics due to charging and discharging of the power storage device can be further improved.
  • the average particle size refers to a value calculated by a volume reference distribution using a particle size distribution measuring device by a dynamic light scattering method or a particle size distribution measuring device by a laser diffraction method.
  • the coating layer covers at least a part of the surface of the silicon particles.
  • the coating layer preferably covers 50% or more of the surface of the silicon particles, more preferably 90% or more, further preferably 95% or more, and covers 99% or more. It is particularly preferable that the particles are completely covered, and it is most preferable that the particles are completely covered. In this case, characteristics such as cycle characteristics of the power storage device can be further improved.
  • the film thickness of the coating layer is preferably 0.5 nm or more, more preferably 2 nm or more, preferably 30 nm or less, and more preferably 10 nm or less.
  • the film thickness of the coating layer is at least the above lower limit value, the number of graphene layers of the flaky graphite contained in the coating layer can be further increased, and the conductivity of the carbon material-coated silicon particles can be further increased. Therefore, when used as an electrode material for a power storage device, characteristics such as rate characteristics and cycle characteristics can be further improved. Further, when the film thickness of the coating layer is not more than the above upper limit value, ions such as lithium ions can be occluded and released more smoothly. Therefore, when used as an electrode material for a power storage device, characteristics such as cycle characteristics can be further improved.
  • the thickness of the coating layer can be obtained from the average value of the thickness of the coating layer in any three carbon material-coated silicon particles observed by a transmission electron micrograph (TEM photograph).
  • the coating layer contains flaky graphite.
  • the number of laminated graphene sheets is not particularly limited, but is preferably 2 layers or more, more preferably 5 layers or more, preferably 1000 layers or less, and more preferably 100 layers or less.
  • the conductivity of flaky graphite can be further enhanced, and when used as an electrode material for a power storage device, characteristics such as cycle characteristics can be further improved.
  • the specific surface area of the flaky graphite can be further increased, and when used as an electrode material for a power storage device, characteristics such as capacity can be further improved. Can be done.
  • the content of flaky graphite in the coating layer is preferably 10% by weight or more, more preferably 90% by weight or more, still more preferably 95% by weight or more, more preferably 95% by weight or more, based on 100% by weight of the material constituting the coating layer. It is 100% by weight.
  • characteristics such as cycle characteristics can be further improved when used as an electrode material for a power storage device.
  • the coating layer may further contain graphite.
  • characteristics such as rate characteristics and cycle characteristics can be further improved.
  • Graphite is a laminate of a plurality of graphene sheets.
  • the number of laminated graphene sheets of graphite is usually about 100,000 to 1,000,000.
  • As the graphite for example, natural graphite, artificial graphite, expanded graphite or the like can be used.
  • the coating layer may further contain amorphous carbon.
  • the surface of the silicon particles can be coated more uniformly, and when used as an electrode material for a power storage device, characteristics such as cycle characteristics can be further improved.
  • the content of amorphous carbon in the coating layer can be determined by the weight reduction rate at 600 ° C. or lower by TG-DTA measurement, and is preferably 0% by weight or more with respect to 100% by weight of the material constituting the coating layer. It is preferably 30% by weight or less, more preferably 5% by weight or less.
  • characteristics such as cycle characteristics can be further improved when used as an electrode material for a power storage device.
  • the coating layer may contain other materials as long as the effects of the present invention are not impaired.
  • 2 (a) to 2 (c) are diagrams for explaining an example of a method for producing carbon material-coated silicon particles according to the present invention.
  • a dispersion liquid in which the silicon particles 2 and the graphite 11 are dispersed in the liquid resin 12 is prepared.
  • the silicon particles 2 the above-mentioned silicon particles can be used.
  • the graphite 11 may be used as it is, or may be pulverized by an ultrasonic wave, a homogenizer or the like and used.
  • liquid resin 12 polyethylene glycol, polyvinyl alcohol, propylene glycol, polyvinyl acetate and the like can be used. These may be used alone or in combination of two or more.
  • the viscosity of the liquid resin 12 at 25 ° C. is preferably 1 mPa ⁇ s or more, more preferably 1.5 mPa ⁇ s or more, further preferably 10 mPa ⁇ s or more, and preferably 10,000,000 mPa ⁇ s or less. , More preferably 1,000,000 mPa ⁇ s or less.
  • the coating layer can be formed more reliably while the graphite 11 is more reliably peeled off by the ball mill described later.
  • the viscosity of the liquid resin can be measured under the condition of 25 ° C. using, for example, an E-type viscometer (TV-25 Type-H viscometer manufactured by Toki Sangyo Co., Ltd.).
  • the content of graphite 11 in the dispersion liquid can be, for example, 0.01% by weight or more and 30% by weight or less.
  • the content of the silicon particles 2 in the dispersion is preferably 1% by weight or more and 50% by weight or less.
  • the content of the liquid resin 12 in the dispersion liquid can be, for example, 20% by weight or more and 99% by weight or less.
  • the dispersion liquid is placed in the container 10 of the ball mill, and is rotated and revolved together with the ball 13 shown in FIG. 2 (b) to be rotated and mixed.
  • the graphite 11 is pressed against the silicon particles 2 by the balls 13 and peeled off.
  • the graphite 11 is peeled off to form the flaky graphite, and the flaky graphite 11a and the liquid resin 12 are adhered to the surface of the silicon particles 2.
  • a planetary ball mill (manufactured by Shinky Co., Ltd., product number "NP-100") can be used.
  • the rotation speed can be, for example, 400 rpm or more and 2000 rpm or less.
  • the rotation time can be, for example, 10 minutes or more and 600 minutes or less.
  • a seramic ball can be used as the ball 13.
  • a zirconia ball is used as the ball 13.
  • the silicon particles 2 to which the flaky graphite 11a and the liquid resin 12 are attached are taken out from the container 10. Subsequently, the silicon particles 2 to which the flaky graphite 11a and the liquid resin 12 adhere to the surface are heated at a temperature of 200 ° C. or higher and 600 ° C. or lower to carbonize the liquid resin 12 and form amorphous carbon. Thereby, carbon material-coated silicon particles having a coating layer containing flaky graphite 11a and amorphous carbon can be obtained.
  • the heating time of the silicon particles 2 on which the flaky graphite 11a and the liquid resin 12 adhere to the surface is not particularly limited, but can be, for example, 20 minutes or more and 480 minutes or less.
  • the heating may be performed in the atmosphere or in an atmosphere of an inert gas such as nitrogen gas.
  • the coating layer of the obtained carbon material-coated silicon particles may contain graphite that has not been peeled off.
  • the crystallinity of the coating layer can be adjusted, for example, by the amount of graphite 11 and liquid resin 12 charged. By increasing the amount of graphite 11 charged, the crystallinity of the coating layer can be increased. Alternatively, the crystallinity of the coating layer can be increased by reducing the amount of the liquid resin 12 charged.
  • the amorphous carbon in the coating layer may be removed by further heating the obtained carbon material-coated silicon particles at a temperature of 300 ° C. or higher and 800 ° C. or lower.
  • the conductivity of the carbon material-coated silicon particles can be further enhanced, and when used as an electrode material for a power storage device, characteristics such as cycle characteristics can be further improved.
  • the heating time at this time is not particularly limited, but can be, for example, 10 minutes or more and 300 minutes or less.
  • the heating may be performed in the atmosphere or in an atmosphere of an inert gas such as nitrogen gas, but an oxygen-containing atmosphere is preferable in order to efficiently remove amorphous carbon. Further, before heating, it may be crushed by a crusher or the like before use.
  • graphite is peeled off by mechanical treatment to form flaky graphite. Therefore, it does not include an oxidation step of graphite as in the case where graphite is peeled off by chemical treatment. Therefore, carbon material-coated silicon particles having excellent conductivity can be obtained.
  • the power storage device of the present invention is not particularly limited, but is a non-aqueous electrolyte primary battery, an aqueous electrolyte primary battery, a non-aqueous electrolyte secondary battery, an aqueous electrolyte secondary battery, an all-solid electrolyte primary battery, an all-solid electrolyte secondary battery, and the like.
  • Examples include capacitors, electric double layer capacitors, lithium ion capacitors and the like.
  • the power storage device of the present invention includes an electrode for a power storage device containing the carbon material-coated silicon particles of the present invention, characteristics such as rate characteristics and cycle characteristics of the power storage device can be improved.
  • the power storage device of the present invention can be suitably used for a secondary battery such as a lithium ion secondary battery or a capacitor.
  • the silicon particles act as an electrode active material, and the coating layer acts as a conductive auxiliary agent.
  • the electrode for the power storage device used in the power storage device of the present invention may be a positive electrode or a negative electrode. Therefore, the electrode active material may be a positive electrode active material or a negative electrode active material.
  • the electrode for a power storage device of the present invention can be obtained by shaping the carbon material-coated silicon particles of the present invention with an electrode material containing another conductive auxiliary agent, a binder, or a solvent, if necessary.
  • the shaping of the electrode material can be performed, for example, by forming a sheet with a rolling roller and then drying it. Further, a coating liquid composed of the carbon material-coated silicon particles of the present invention, a solvent, and if necessary, a conductive auxiliary agent or a binder may be applied to the current collector and then dried.
  • the other conductive auxiliary agent for example, graphene, artificial graphite, granular graphite compound, fibrous graphite compound, carbon black, activated carbon or the like can be used.
  • a fluorine-based polymer such as polyvinyl butyral, polytetrafluoroethylene, styrene-butadiene rubber, polyimide resin, acrylic resin, polyvinylidene fluoride, or a resin such as water-soluble carboxymethyl cellulose
  • a fluorine-based polymer such as polyvinyl butyral, polytetrafluoroethylene, styrene-butadiene rubber, polyimide resin, acrylic resin, polyvinylidene fluoride, or a resin such as water-soluble carboxymethyl cellulose
  • polytetrafluoroethylene can be used.
  • the dispersibility and heat resistance can be further improved.
  • solvent ethanol, N-methylpyrrolidone (NMP), water or the like can be used.
  • the content of the carbon material-coated silicon particles in the electrode material is not particularly limited, but when the entire electrode material is 100% by mass, it is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably. It is 50% by mass or more, preferably 90% by mass or less, and more preferably 80% by mass or less. When the content of the carbon material-coated silicon particles is within the above range, the rate characteristics and cycle characteristics of the power storage device can be further improved. As the carbon material-coated silicon particles, one type may be used, or two types or two or more types may be used.
  • the content of the other conductive auxiliary agent in the electrode material is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, preferably 50% by mass, when the entire electrode material is 100% by mass. Hereinafter, it is more preferably 30% by mass or less. When the content of the conductive auxiliary agent is within the above range, the rate characteristics and cycle characteristics of the power storage device can be further improved.
  • the content of the binder in the electrode material can be, for example, 0.1% by mass or more and 30% by mass or less when the entire electrode material is 100% by mass.
  • the positive electrode and the negative electrode of the non-aqueous electrolyte secondary battery may have the same electrodes formed on one side or both sides of the current collector.
  • a positive electrode may be formed on one surface of the above, and a negative electrode may be formed on the other surface, that is, a bipolar electrode.
  • the non-aqueous electrolyte secondary battery may be a battery in which a separator is arranged between the positive electrode side and the negative electrode side, or may be a laminated battery.
  • the positive electrode, negative electrode and separator contain a non-aqueous electrolyte responsible for lithium ion conduction.
  • the non-aqueous electrolyte secondary battery may be covered with a laminate film after laminating or a plurality of the above-mentioned laminates, or may be a square, oval, cylindrical, coin-shaped, button-shaped, or sheet-shaped metal can. It may be exteriorized. The exterior may be provided with a mechanism for releasing the generated gas.
  • the number of laminated bodies is not particularly limited, and the laminated bodies can be laminated until a desired voltage value and battery capacity are exhibited.
  • the non-aqueous electrolyte secondary battery can be an assembled battery connected in series or in parallel as appropriate depending on the desired size, capacity, and voltage.
  • the assembled battery is provided with a control circuit in order to confirm the charging state of each battery and improve safety.
  • Non-aqueous electrolyte used in the secondary battery is not particularly limited, but is a gel electrolyte obtained by impregnating a polymer with an electrolytic solution in which a solute is dissolved in a non-aqueous solvent, or a polymer solid electrolyte such as polyethylene oxide or polypropylene oxide. , Or an inorganic solid electrolyte such as sulfated glass or oxynitride can be used.
  • the non-aqueous solvent preferably contains a cyclic aprotic solvent and / or a chain aprotic solvent because the solute described later can be more easily dissolved.
  • the cyclic aprotic solvent include cyclic carbonates, cyclic esters, cyclic sulfones, and cyclic ethers.
  • the chain aprotic solvent include chain carbonate, chain carboxylic acid ester, and chain ether.
  • a solvent generally used as a solvent for a non-aqueous electrolyte such as acetonitrile may be used.
  • dimethyl carbonate, methyl ethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, ⁇ -butyl lactone, 1,2-dimethoxyethane, sulfolane, dioxolane, or Methyl propionate and the like can be used.
  • One type of these solvents may be used alone, or two or more types may be mixed or used. However, from the viewpoint of more easily dissolving the solute described later and further enhancing the conductivity of lithium ions, it is preferable to use a solvent in which two or more kinds are mixed.
  • the solute is not particularly limited, but for example, LiClO 4 , LiBF 4 , LiPF 6 , LiAsF 6 , LiCF 3 SO 3 , LiBOB (Lithium Bis (Oxalato) Borate), LiN (SO 2 CF 3 ) 2, and the like are preferable. .. In this case, it can be more easily dissolved with a solvent.
  • the power storage device may be an aqueous electrolyte secondary battery as described above.
  • aqueous electrolytic solution an aqueous solution in which a lithium salt such as lithium nitrate, lithium sulfate or lithium acetate is dissolved can be used.
  • aqueous electrolytic solution examples include an electrolytic solution in which water is used as a solvent and sulfuric acid, potassium hydroxide, or the like is used as an electrolyte.
  • non-aqueous electrolytic solution for example, an electrolytic solution using the following solvent, electrolyte, or ionic liquid can be used.
  • solvent examples include acetonitrile, propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), acrylonitrile (AN) and the like.
  • lithium hexafluorophosphate LiPF 6
  • lithium tetrafluoroborate LiBF 4
  • TEABF 4 tetraethylammonium tetrafluoroborate
  • TEMABF 4 triethylmethylammonium tetrafluoroborate
  • the obtained particles were heated at 500 ° C. for 10 minutes in an air atmosphere.
  • amorphous carbon was removed to obtain carbon material-coated silicon particles in which the surface of the silicon particles was coated with flaky graphite.
  • the obtained particles were heated at 500 ° C. for 10 minutes in an air atmosphere.
  • amorphous carbon was removed to obtain carbon material-coated silicon particles in which the surface of the Si particles was coated with flaky graphite.
  • Atmosphere Air Temperature rise rate: 10 ° C / min Temperature range: 40 ° C to 1000 ° C
  • FIG. 3 is a diagram showing the results of thermogravimetric analysis and measurement of particles before removing amorphous carbon in Example 1.
  • FIG. 4 is a diagram showing the results of thermogravimetric analysis and measurement of the carbon material-coated silicon particles after removing the amorphous carbon of Example 1.
  • FIG. 5 is a diagram showing the results of thermogravimetric analysis and measurement of particles before removing amorphous carbon in Example 2.
  • FIG. 6 is a diagram showing the results of thermogravimetric analysis and measurement of carbon material-coated silicon particles after removing amorphous carbon in Example 2.
  • FIG. 7 is a diagram showing the results of thermogravimetric analysis measurement of the particles of Comparative Example 1.
  • the weight increase start temperature of the particles obtained in Example 1 is around 700 ° C.
  • the weight increase start temperature of the particles obtained in Example 2 is around 800 ° C.
  • the weight increase start temperature is 400 ° C. or higher and lower than 500 ° C. From this, it can be seen that in Examples 1 and 2, the oxidation temperature of Si is shifted to the high temperature side, the Si particles are covered with a carbon material having a graphene laminated structure, and oxygen is shielded. .. Further, in FIGS. 4 and 6, it can be seen that the weight loss on the low temperature side existing in FIGS. 3 and 5 has disappeared. This makes it possible to confirm that the amorphous carbon has disappeared by heating at 500 ° C. for 10 minutes.
  • the X-ray diffraction spectra of the particles prepared in Examples 1 and 2 before and after removing the amorphous carbon were measured by a wide-angle X-ray diffraction method.
  • a SmartLab manufactured by Rigaku Co., Ltd. was used, and the measurement was performed under the following conditions.
  • Radioactive source CuK ⁇ ray (wavelength 1.541 ⁇ ) Measuring range: 5 ° -80 ° Scanning speed: 5 ° / minute Tube current: 200mA Tube voltage: 40kV
  • FIG. 8 is an X-ray diffraction spectrum of the particles prepared in Example 1 before removing amorphous carbon.
  • FIG. 9 is an X-ray diffraction spectrum of the particles produced in Example 1 after removing amorphous carbon.
  • FIG. 10 is an X-ray diffraction spectrum of the particles produced in Example 2 before removing amorphous carbon.
  • FIG. 11 is an X-ray diffraction spectrum of the particles produced in Example 2 after removing the amorphous carbon.
  • the ratio a / b before removing the amorphous carbon was 0.032, and the a / b after removing the amorphous carbon was 0.088.
  • the ratio a / b before removing the amorphous carbon was 0.501, and the a / b after removing the amorphous carbon was 1.053.
  • FIG. 12 is a diagram showing a transmission electron micrograph of the carbon material-coated silicon particles obtained in Example 1. As shown in FIG. 12, in Example 1, it was confirmed that a uniform coating layer was formed on the surface of the particles. Similarly, in Example 2, it was confirmed that a uniform coating layer could be produced on the surface of the particles. The thickness of the coating layer of the carbon material-coated silicon particles after removing the amorphous carbon was 1 nm in Example 1 and 40 nm in Example 2.
  • NMP N-methyl-2-pyrrolidone
  • the prepared paste was applied to the surface of a copper foil having a thickness of 20 ⁇ m with an applicator (manufactured by Tester Sangyo Co., Ltd., trade name “PI-1210”) so that the film thickness was 30 ⁇ m. After coating, it was vacuum dried at 120 ° C. for 15 hours and further heat-treated at 250 ° C. for 12 hours. As a result, a negative electrode film was obtained.
  • an applicator manufactured by Tester Sangyo Co., Ltd., trade name “PI-1210”
  • An evaluation cell was prepared using the obtained negative electrode film. The process of assembling the evaluation cell was all carried out in a vacuum glove box replaced with argon gas. As the evaluation cell, a coin-type cell (HS cell) was used.
  • HS cell coin-type cell
  • a metal lithium piece ( ⁇ 10 mm, 0.2 mm thick Li foil), a separator (manufactured by Sekisui Chemical Co., Ltd., trade name “Esfino” (25 ⁇ m)), and a negative electrode film. ( ⁇ 10 mm, heat-treated at the above 250 ° C.), a fixing jig made of resin, a collector electrode, and a spring were laminated.
  • the positive electrode is the above-mentioned metallic lithium piece.
  • As the electrolytic solution a 1 mol / L LiPF 6 / EC: DMC (1: 2 v / v%) solution (manufactured by Kishida Chemical Co., Ltd.) was used.
  • Charge / discharge test In the coin-type cell assembled as described above , a charge / discharge test was performed under the condition that the voltage was in the range of 0.02-1.5 V (vs. Li + / Li) and the rate was 0.2 C (charge / discharge).
  • Test equipment Hokuto Denko Co., Ltd., trade name "HJ1005SD8"). Specifically, first, the battery was charged from 1.5V to 0.02V in the CCCV mode. After charging, it was rested for 15 minutes. Next, it was discharged from 0.02V to 1.5V in CC mode. Then I rested for 15 minutes. The cycle characteristics were evaluated up to 30 cycles.
  • FIG. 13 is a diagram showing the results of the cycle characteristics of the battery produced by using the carbon material-coated silicon particles obtained in Example 1.
  • FIG. 14 is a diagram showing the results of the cycle characteristics of the battery produced by using the carbon material-coated silicon particles obtained in Example 2.
  • FIG. 15 is a diagram showing the results of cycle characteristics of a battery manufactured using the particles of Comparative Example 1. In each figure, the vertical axis indicates the capacity (mAh / g).
  • Example 3 A carbon material coating in which the surface of the silicon particles is coated with flaky graphite in the same manner as in Example 1 except that silicon particles having an average particle diameter of 3 ⁇ m (manufactured by Sigma-Aldrich) are used as the silicon particles. Silicon particles were obtained. When the thermogravimetric analysis measurement was performed in the same manner as in Example 1, the weight increase start temperature of the particles obtained in Example 3 was around 800 ° C.
  • Comparative Example 2 Silicon particles (manufactured by Sigma-Aldrich, average particle size: 3 ⁇ m) were used as they were. When the thermogravimetric analysis measurement was performed in the same manner as in Comparative Example 1, the weight increase start temperature of the particles of Comparative Example 2 was about 350 ° C.
  • Solid electrolyte layer 80 mg of solid electrolyte (75Li 2 S-25P 2 S 5 ) was filled into the cell inner cylinder (diameter 10 mm) of the powder type all-solid-state battery, flattened, and then lightly pressed with a press pressure of 50 MPa. Pre-molding was performed.
  • Li-In was used as the counter electrode, and Li-In was arranged so as to come on the solid electrolyte from the opposite side of the working electrode via the solid electrolyte.
  • a powder-type cell was prepared using the working electrode, the solid electrolyte layer, and the counter electrode obtained as described above.
  • the working electrode, the solid electrolyte layer, and the counter electrode were laminated in this order.
  • the press pressure at the time of cell construction was 330 MPa.
  • the electrode area was 0.785 cm 2 ( ⁇ 10 mm), which is the same as the inner cylinder diameter of the cell.
  • Charge / discharge test In the powder type cell assembled as described above, a charge / discharge test was performed in a potential range of -0.6 V to 0.9 V (vs. Li-In) (charge / discharge test device: manufactured by Hokuto Denko Co., Ltd.). , Product name "HJ1001SD8"). Specifically, the current density is 0.898 mA / cm 2 (0.1 C) 5 times, the current density 0.0898 mA / cm 2 (0.01 C) is 5 times, and the current density 0.898 mA / cm 2 (0. The cycle characteristics were evaluated 30 times in 1C).
  • FIG. 16 is a diagram showing the results of cycle characteristics of an all-solid-state battery produced by using the carbon material-coated silicon particles obtained in Example 3 and the silicon particles of Comparative Example 2, respectively.
  • the vertical axis indicates the capacity (mAh / g).
  • the solid line shows the result of charge (Li release) evaluation, and the broken line shows the result of discharge (Li insertion) evaluation.

Abstract

The present invention provides carbon material-coated silicon particles which are capable of improving characteristics such as the cycle characteristics if used in an electrode material for electricity storage devices.　Carbon material-coated silicon particles 1 which are coated with a carbon material, and each of which is provided with a silicon particle 2 and a coating layer 3 that covers at least a part of a surface 2a of the silicon particle 2, while containing flake graphite. If the carbon material-coated silicon particles 1 are subjected to thermogravimetric analysis in the air atmosphere at a heating rate of 10°C/minute, the weight increase initiation temperature is 500°C or higher.

Description

炭素材料被覆シリコン粒子、蓄電デバイス用電極、並びに蓄電デバイスCarbon material coated silicon particles, electrodes for power storage devices, and power storage devices
　本発明は、炭素材料により被覆されている、炭素材料被覆シリコン粒子、上記炭素材料被覆シリコン粒子を用いた蓄電デバイス用電極及び蓄電デバイスに関する。 The present invention relates to carbon material-coated silicon particles coated with a carbon material, electrodes for a power storage device using the carbon material-coated silicon particles, and a power storage device.
　近年、携帯機器、ハイブリッド自動車、電気自動車、家庭用蓄電用途等に向けて、蓄電デバイスの研究開発が盛んに行われている。蓄電デバイスの電極材料としては、黒鉛、活性炭、カーボンナノファイバー、あるいはカーボンナノチューブなどの炭素材料が環境的側面から広く用いられている。 In recent years, research and development of power storage devices have been actively carried out for mobile devices, hybrid vehicles, electric vehicles, household power storage applications, and the like. As the electrode material of the power storage device, carbon materials such as graphite, activated carbon, carbon nanofibers, and carbon nanotubes are widely used from the environmental aspect.
　下記の特許文献１には、グラフェン包有又はグラフェン封入電極活物質を含む電池電極が開示されている。特許文献１では、グラフェン含有又はグラフェン封入電極活物質を製造するに際して、初めのステップでは、エネルギー衝突装置の衝突チャンバー中で黒鉛材料の複数の粒子と、固体電極活物質の複数の粒子とを混合して混合物が形成されている。この際、黒鉛材料は、インターカレート、酸化、及び剥離が予め行われていない。また、固体電極活物質の複数の粒子以外のボールミル粉砕媒体を含まない。そして、次のステップでは、エネルギー衝突装置を運転させ、黒鉛材料の粒子からグラフェンシートを剥離し、剥離したグラフェンシートを固体電極活物質粒子の表面まで移動させ、粒子を完全に包有又は封入することにより、グラフェン包有又はグラフェン封入電極活物質の粒子が製造されている。 Patent Document 1 below discloses a battery electrode containing a graphene-encapsulating or graphene-encapsulating electrode active material. In Patent Document 1, when producing a graphene-containing or graphene-encapsulated electrode active material, in the first step, a plurality of particles of a graphite material and a plurality of particles of a solid electrode active material are mixed in a collision chamber of an energy collision device. The mixture is formed. At this time, the graphite material has not been intercalated, oxidized, and peeled in advance. In addition, it does not contain a ball mill pulverization medium other than a plurality of particles of the solid electrode active material. Then, in the next step, the energy collision device is operated to peel the graphene sheet from the particles of the graphite material, move the peeled graphene sheet to the surface of the solid electrode active material particles, and completely enclose or enclose the particles. As a result, particles of graphene-encapsulated or graphene-encapsulated electrode active material are produced.
特表２０１９－５２２８６８号公報Special Table 2019-522868
　近年、ハイブリッド自動車、電気自動車等の用途に向けて、電池性能やキャパシタ性能のさらに一層優れた蓄電デバイスの開発が益々盛んに行われている。しかしながら、特許文献１の製造方法では、黒鉛材料を十分に剥離することができず、固体電極活物質を均一に被覆することができないという問題がある。例えば、二次電池の電極材料に用いたときに、二次電池のレート特性やサイクル特性などの電池特性を十分に向上させることができないという問題がある。 In recent years, the development of power storage devices with even better battery performance and capacitor performance has been actively carried out for applications such as hybrid vehicles and electric vehicles. However, the production method of Patent Document 1 has a problem that the graphite material cannot be sufficiently peeled off and the solid electrode active material cannot be uniformly coated. For example, when used as an electrode material for a secondary battery, there is a problem that battery characteristics such as rate characteristics and cycle characteristics of the secondary battery cannot be sufficiently improved.
　また、固体電極活物質に被覆されない黒鉛材料が大量に残存するので、二次電池を精緻に設計するためには、黒鉛材料と固体電極活物質を分離する工程が別途必要にもなる。 In addition, since a large amount of graphite material that is not coated with the solid electrode active material remains, a separate step of separating the graphite material and the solid electrode active material is required in order to precisely design the secondary battery.
　本発明の目的は、蓄電デバイスの電極材料に用いたときに、サイクル特性などの特性を向上させ得る、炭素材料被覆シリコン粒子、上記炭素材料被覆シリコン粒子を用いた蓄電デバイス用電極及び蓄電デバイスを提供することにある。 An object of the present invention is to obtain a carbon material-coated silicon particle, an electrode for a power storage device using the carbon material-coated silicon particle, and a power storage device, which can improve characteristics such as cycle characteristics when used as an electrode material of the power storage device. To provide.
　本発明に係る炭素材料被覆シリコン粒子は、炭素材料により被覆されている、炭素材料被覆シリコン粒子であって、シリコン粒子と、前記シリコン粒子の表面における少なくとも一部を被覆しており、かつ薄片化黒鉛を含む、被覆層と、を備え、空気雰囲気下及び昇温速度１０℃／分の条件で、前記炭素材料被覆シリコン粒子の熱重量分析をしたときに、重量増加開始温度が、５００℃以上である。　 The carbon material-coated silicon particles according to the present invention are carbon material-coated silicon particles coated with a carbon material, and the silicon particles and at least a part of the surface of the silicon particles are coated and flaked. When a coating layer containing graphite is provided and the carbon material-coated silicon particles are subjected to thermal weight analysis under the conditions of an air atmosphere and a temperature rise rate of 10 ° C./min, the weight increase start temperature is 500 ° C. or higher. Is.
　本発明に係る炭素材料被覆シリコン粒子のある特定の局面では、前記シリコン粒子が、Ｓｉ又はＳｉの化合物からなる。 In a specific aspect of the carbon material-coated silicon particles according to the present invention, the silicon particles are made of Si or a compound of Si.
　本発明に係る炭素材料被覆シリコン粒子の他の特定の局面では、前記シリコン粒子の平均粒子径が、２０ｎｍ以上、２０μｍ以下である。 In another specific aspect of the carbon material-coated silicon particles according to the present invention, the average particle size of the silicon particles is 20 nm or more and 20 μm or less.
　本発明に係る炭素材料被覆シリコン粒子のさらに他の特定の局面では、前記炭素材料被覆シリコン粒子のＸ線回折スペクトルを測定したときに、グラフェン積層構造に由来するピークの高さａと、前記シリコン粒子に由来するピークの高さｂとの比ａ／ｂが、０．０１以上、２以下である。 In still another specific aspect of the carbon material coated silicon particles according to the present invention, when the X-ray diffraction spectrum of the carbon material coated silicon particles is measured, the peak height a derived from the graphene laminated structure and the silicon The ratio a / b to the height b of the peak derived from the particles is 0.01 or more and 2 or less.
　本発明に係る炭素材料被覆シリコン粒子のさらに他の特定の局面では、前記シリコン粒子の表面における５０％以上が、前記被覆層により被覆されている。 In yet another specific aspect of the carbon material coated silicon particles according to the present invention, 50% or more of the surface of the silicon particles is coated with the coating layer.
　本発明に係る炭素材料被覆シリコン粒子のさらに他の特定の局面では、前記炭素材料被覆シリコン粒子における、前記炭素材料による被覆層の厚みが、３０ｎｍ以下である。 In still another specific aspect of the carbon material-coated silicon particles according to the present invention, the thickness of the coating layer made of the carbon material in the carbon material-coated silicon particles is 30 nm or less.
　本発明に係る炭素材料被覆シリコン粒子のさらに他の特定の局面では、前記炭素材料による被覆層が、薄片化されていない黒鉛をさらに含む。 In yet another particular aspect of the carbon material coated silicon particles according to the present invention, the carbon material coating layer further comprises unsliced graphite.
　本発明に係る炭素材料被覆シリコン粒子のさらに他の特定の局面では、前記炭素材料による被覆層が、アモルファスカーボンをさらに含む。 In yet another specific aspect of the carbon material coated silicon particles according to the present invention, the coating layer made of the carbon material further contains amorphous carbon.
　本発明に係る蓄電デバイス用電極は、本発明に従って構成される炭素材料被覆シリコン粒子を含む。 The electrode for a power storage device according to the present invention contains carbon material-coated silicon particles configured according to the present invention.
　本発明に係る蓄電デバイスは、本発明に従って構成される蓄電デバイス用電極を備える。 The power storage device according to the present invention includes electrodes for the power storage device configured according to the present invention.
　本発明によれば、蓄電デバイスの電極材料に用いたときに、サイクル特性などの特性を向上させ得る、炭素材料被覆シリコン粒子、上記炭素材料被覆シリコン粒子を用いた蓄電デバイス用電極及び蓄電デバイスを提供することができる。 According to the present invention, a carbon material-coated silicon particle, an electrode for a power storage device using the carbon material-coated silicon particle, and a power storage device that can improve characteristics such as cycle characteristics when used as an electrode material of the power storage device are provided. Can be provided.
図１は、本発明の一実施形態に係る炭素材料被覆シリコン粒子を示す模式的断面図である。FIG. 1 is a schematic cross-sectional view showing carbon material-coated silicon particles according to an embodiment of the present invention. 図２（ａ）～（ｃ）は、本発明に係る炭素材料被覆シリコン粒子の製造方法の一例を説明するための図である。2A to 2C are diagrams for explaining an example of a method for producing carbon material-coated silicon particles according to the present invention. 図３は、実施例１のアモルファスカーボン除去前における炭素材料被覆シリコン粒子の熱重量分析測定の結果を示す図である。FIG. 3 is a diagram showing the results of thermogravimetric analysis and measurement of carbon material-coated silicon particles before removing amorphous carbon in Example 1. 図４は、実施例１のアモルファスカーボン除去後における炭素材料被覆シリコン粒子の熱重量分析測定の結果を示す図である。FIG. 4 is a diagram showing the results of thermogravimetric analysis and measurement of the carbon material-coated silicon particles after removing the amorphous carbon of Example 1. 図５は、実施例２のアモルファスカーボン除去前における炭素材料被覆シリコン粒子の熱重量分析測定の結果を示す図である。FIG. 5 is a diagram showing the results of thermogravimetric analysis and measurement of carbon material-coated silicon particles before removing amorphous carbon in Example 2. 図６は、実施例２のアモルファスカーボン除去後における炭素材料被覆シリコン粒子の熱重量分析測定の結果を示す図である。FIG. 6 is a diagram showing the results of thermogravimetric analysis and measurement of carbon material-coated silicon particles after removing amorphous carbon in Example 2. 図７は、比較例１の粒子の熱重量分析測定の結果を示す図である。FIG. 7 is a diagram showing the results of thermogravimetric analysis measurement of the particles of Comparative Example 1. 図８は、実施例１で作製した粒子のアモルファスカーボン除去前におけるＸ線回折スペクトルである。FIG. 8 is an X-ray diffraction spectrum of the particles produced in Example 1 before removing amorphous carbon. 図９は、実施例１で作製した粒子のアモルファスカーボン除去後におけるＸ線回折スペクトルである。FIG. 9 is an X-ray diffraction spectrum of the particles produced in Example 1 after removing amorphous carbon. 図１０は、実施例２で作製した粒子のアモルファスカーボン除去前におけるＸ線回折スペクトルである。FIG. 10 is an X-ray diffraction spectrum of the particles produced in Example 2 before removing amorphous carbon. 図１１は、実施例２で作製した粒子のアモルファスカーボン除去後におけるＸ線回折スペクトルである。FIG. 11 is an X-ray diffraction spectrum of the particles produced in Example 2 after removing amorphous carbon. 図１２は、実施例１で得られた炭素材料被覆シリコン粒子の透過型電子顕微鏡写真を示す図である。FIG. 12 is a diagram showing a transmission electron micrograph of the carbon material-coated silicon particles obtained in Example 1. 図１３は、実施例１で得られた炭素材料被覆シリコン粒子を用いて作製した電池のサイクル特性の結果を示す図である。FIG. 13 is a diagram showing the results of the cycle characteristics of the battery produced by using the carbon material-coated silicon particles obtained in Example 1. 図１４は、実施例２で得られた炭素材料被覆シリコン粒子を用いて作製した電池のサイクル特性の結果を示す図である。FIG. 14 is a diagram showing the results of the cycle characteristics of the battery produced by using the carbon material-coated silicon particles obtained in Example 2. 図１５は、比較例１の粒子を用いて作製した電池のサイクル特性の結果を示す図である。FIG. 15 is a diagram showing the results of cycle characteristics of a battery manufactured using the particles of Comparative Example 1. 図１６は、実施例３で得られた炭素材料被覆シリコン粒子及び比較例２のシリコン粒子をそれぞれ用いて作製した全固体電池のサイクル特性の結果を示す図である。FIG. 16 is a diagram showing the results of cycle characteristics of an all-solid-state battery produced by using the carbon material-coated silicon particles obtained in Example 3 and the silicon particles of Comparative Example 2, respectively.
　以下、図面を参照しつつ、本発明の具体的な実施形態を説明することにより、本発明を明らかにする。 Hereinafter, the present invention will be clarified by explaining a specific embodiment of the present invention with reference to the drawings.
　［炭素材料被覆シリコン粒子］
　図１は、本発明の一実施形態に係る炭素材料被覆シリコン粒子を示す模式的断面図である。図１に示すように、炭素材料被覆シリコン粒子１は、シリコン粒子２と、被覆層３とを備える。 [Carbon material coated silicon particles]
FIG. 1 is a schematic cross-sectional view showing carbon material-coated silicon particles according to an embodiment of the present invention. As shown in FIG. 1, the carbon material-coated silicon particles 1 include silicon particles 2 and a coating layer 3.
　本実施形態において、シリコン粒子２の形状は、球状である。もっとも、シリコン粒子２の形状は、特に限定されず、略球状、楕円体状、略楕円体状、平板状、鱗片状などの形状であってもよい。 In the present embodiment, the shape of the silicon particles 2 is spherical. However, the shape of the silicon particles 2 is not particularly limited, and may be a substantially spherical shape, an ellipsoidal shape, a substantially ellipsoidal shape, a flat plate shape, a scale shape, or the like.
　シリコン粒子２の表面２ａを覆うように、被覆層３が設けられている。被覆層３は、本実施形態のように、シリコン粒子２の表面２ａの全部を覆っていてもよく、一部を覆っていてもよい。 A coating layer 3 is provided so as to cover the surface 2a of the silicon particles 2. The coating layer 3 may cover the entire surface 2a of the silicon particles 2 or a part of the surface 2a as in the present embodiment.
　被覆層３は、薄片化黒鉛を含んでいる。従って、炭素材料被覆シリコン粒子１は、薄片化黒鉛のような炭素材料により被覆されている粒子である。 The coating layer 3 contains flaky graphite. Therefore, the carbon material-coated silicon particles 1 are particles coated with a carbon material such as flaky graphite.
　なお、本明細書において、薄片化黒鉛とは、元の黒鉛を剥離処理して得られるものであり、元の黒鉛よりも薄いグラフェンシート積層体をいう。薄片化黒鉛におけるグラフェンシートの積層数は、元の黒鉛より少なければよい。 In the present specification, the flaky graphite is obtained by exfoliating the original graphite, and refers to a graphene sheet laminate thinner than the original graphite. The number of graphene sheets laminated in the flaky graphite may be smaller than that of the original graphite.
　また、本実施形態においては、空気雰囲気下及び昇温速度１０℃／分の条件で、炭素材料被覆シリコン粒子１の熱重量分析をしたときに、重量増加開始温度が、５００℃以上である。 Further, in the present embodiment, when the thermogravimetric analysis of the carbon material-coated silicon particles 1 is performed under the conditions of an air atmosphere and a temperature rising rate of 10 ° C./min, the weight increase start temperature is 500 ° C. or higher.
　上記熱重量分析は、熱重量・熱量同時測定装置（日立ハイテクサイエンス社製、品番：ＴＧＤＴＡ６３００）を用いて測定することができる。なお、上記熱重量分析は、下記の条件で測定する。 The above thermogravimetric analysis can be measured using a thermogravimetric / calorific value simultaneous measuring device (manufactured by Hitachi High-Tech Science Corporation, product number: TGDTA6300). The thermogravimetric analysis is measured under the following conditions.
　雰囲気：空気
　昇温速度：１０℃／分
　温度範囲：４０℃～１０００℃ Atmosphere: Air Temperature rise rate: 10 ° C / min Temperature range: 40 ° C to 1000 ° C
　本実施形態の炭素材料被覆シリコン粒子１は、上記のような構成を備えるので、蓄電デバイスの電極材料に用いたときに、サイクル特性などの特性を高めることができる。これについては、以下のようにして説明することができる。 Since the carbon material-coated silicon particles 1 of the present embodiment have the above-described configuration, characteristics such as cycle characteristics can be enhanced when used as an electrode material for a power storage device. This can be explained as follows.
　本発明に用いるシリコン粒子など、一般にシリコン粒子の酸化開始温度は４００℃以上、５００℃未満である。なお、シリコン粒子は吸湿して酸化シリコンになりやすく、また小粒径のものほど酸化しやすいため酸化開始温度には幅がある。また、シリコン粒子の酸化開始温度は空気雰囲気で熱重量示唆熱分析（ＴＧ－ＤＴＡ）測定を行い、加熱温度と試料重量をモニタリングすることで確認することができる。シリコン粒子と測定雰囲気である空気中の酸素が上記温度で反応を開始し、シリコンがＳｉＯ、あるいはＳｉＯ２になることで重量が増加する。従って、シリコンの重量増加開始温度が、酸化開始温度となる。 Generally, the oxidation start temperature of silicon particles such as the silicon particles used in the present invention is 400 ° C. or higher and lower than 500 ° C. It should be noted that the silicon particles easily absorb moisture to become silicon oxide, and the smaller the particle size, the easier it is to oxidize, so there is a range in the oxidation start temperature. Further, the oxidation start temperature of the silicon particles can be confirmed by performing thermogravimetric differential thermal analysis (TG-DTA) measurement in an air atmosphere and monitoring the heating temperature and the sample weight. The weight increases when the silicon particles and oxygen in the air, which is the measurement atmosphere, start the reaction at the above temperature and the silicon becomes SiO or SiO 2. Therefore, the weight increase start temperature of silicon becomes the oxidation start temperature.
　一方で、本発明の炭素材料被覆シリコン粒子では、熱重量分析をしたときに、重量増加開始温度が、５００℃以上である。この際、グラフェン積層構造を有する黒鉛の分解温度は、通常、空気雰囲気では５００℃～８００℃である。なお、この黒鉛の分解温度幅は黒鉛の積層数や面積、欠陥の有無、酸化の度合いに依存する。 On the other hand, in the carbon material-coated silicon particles of the present invention, the weight increase start temperature is 500 ° C. or higher when thermogravimetric analysis is performed. At this time, the decomposition temperature of graphite having a graphene laminated structure is usually 500 ° C. to 800 ° C. in an air atmosphere. The decomposition temperature range of graphite depends on the number and area of graphite layers, the presence or absence of defects, and the degree of oxidation.
　そのため、本発明の炭素材料被覆シリコン粒子では、グラフェン積層構造を有する炭素材料により均一に被覆されており、それによって、空気（酸素）とシリコン粒子の接触が遮断されており、熱重量分析をしたときに、４００℃以上、５００℃未満で酸化は開始されない。しかしながら、さらに温度を上げ、５００℃～８００℃では、グラフェン積層構造を有する炭素材料が測定雰囲気の空気（酸素）で分解してガス（ＣＯ、ＣＯ２）化し、炭素材料分の重量減少が起こる。そして、さらにシリコン粒子表面を被覆していた炭素材料が焼失するため、シリコン粒子と空気が接触するようになり、シリコンが空気中の酸素と反応して、ＳｉＯやＳｉＯ２になることで重量増加が始まる。よって、シリコン粒子の酸化が開始される温度の指標となる重量増加開始温度が５００℃以上にシフトしているものと考えられる。 Therefore, the carbon material-coated silicon particles of the present invention are uniformly coated with a carbon material having a graphene laminated structure, whereby the contact between air (oxygen) and the silicon particles is blocked, and thermogravimetric analysis is performed. Occasionally, oxidation is not initiated above 400 ° C and below 500 ° C. However, when the temperature is further raised and the temperature is 500 ° C to 800 ° C, the carbon material having a graphene laminated structure is decomposed by the air (oxygen) in the measurement atmosphere and converted into gas (CO, CO 2 ), and the weight of the carbon material is reduced. .. Then, since the carbon material covering the surface of the silicon particles is burnt down, the silicon particles come into contact with air, and the silicon reacts with oxygen in the air to become SiO or SiO 2 , which increases the weight. Begins. Therefore, it is considered that the weight increase start temperature, which is an index of the temperature at which the oxidation of the silicon particles is started, has shifted to 500 ° C. or higher.
　このように、本発明の炭素材料被覆シリコン粒子では、グラフェン積層構造を有する炭素材料により、粒子表面が均一に被覆されているので、例えば、二次電池の負極活物質に用いたときに、充放電に伴う体積変化を小さくすることができ、負極活物質が割れたり、炭素材料が電極から剥がれたりすることを抑制することができる。 As described above, in the carbon material-coated silicon particles of the present invention, the surface of the particles is uniformly coated with the carbon material having a graphene laminated structure. Therefore, for example, when the particles are used as the negative electrode active material of the secondary battery, they are charged. The volume change due to discharge can be reduced, and cracking of the negative electrode active material and peeling of the carbon material from the electrode can be suppressed.
　もっとも、被覆層の厚みが厚いとリチウムイオン等のイオンを放出できない場合がある。これに対して、本発明の炭素材料被覆シリコン粒子における被覆層は、薄片化黒鉛を含んでいる。そのため、被覆層の厚みが厚くなりすぎず、リチウムイオン等のイオンをスムーズに吸蔵し、放出することができる。よって、本発明の炭素材料被覆シリコン粒子は、蓄電デバイスの電極材料に用いたときに、サイクル特性などの特性を向上させることができる。 However, if the coating layer is thick, it may not be possible to release ions such as lithium ions. On the other hand, the coating layer in the carbon material-coated silicon particles of the present invention contains flaky graphite. Therefore, the thickness of the coating layer does not become too thick, and ions such as lithium ions can be smoothly occluded and released. Therefore, the carbon material-coated silicon particles of the present invention can improve characteristics such as cycle characteristics when used as an electrode material for a power storage device.
　本発明においては、炭素材料被覆シリコン粒子の上記重量増加開始温度が、５００℃以上、より好ましくは６００℃以上、さらに好ましくは７００℃以上であり、好ましくは９００℃以下である。炭素材料被覆シリコン粒子の重量増加開始温度が上記下限値以上である場合、グラフェン積層構造を有する炭素材料によって、シリコン粒子表面をより均一に被覆することができ、蓄電デバイスの電極材料に用いたときに、サイクル特性などの特性をより一層向上させることができる。炭素材料被覆シリコン粒子の上記重量増加開始温度が上記上限値以下である場合、被覆層の厚みが厚くなり過ぎず、リチウムイオン等のイオンをより一層スムーズに吸蔵し、放出することができる。そのため、蓄電デバイスの電極材料に用いたときに、サイクル特性などの特性をより一層向上させることができる。 In the present invention, the weight increase start temperature of the carbon material-coated silicon particles is 500 ° C. or higher, more preferably 600 ° C. or higher, further preferably 700 ° C. or higher, and preferably 900 ° C. or lower. When the weight increase start temperature of the carbon material-coated silicon particles is equal to or higher than the above lower limit, the surface of the silicon particles can be more uniformly coated by the carbon material having a graphene laminated structure, and when used as an electrode material for a power storage device. In addition, characteristics such as cycle characteristics can be further improved. When the weight increase start temperature of the carbon material-coated silicon particles is not more than the above upper limit value, the thickness of the coating layer does not become too thick, and ions such as lithium ions can be occluded and released more smoothly. Therefore, when used as an electrode material for a power storage device, characteristics such as cycle characteristics can be further improved.
　本発明においては、炭素材料被覆シリコン粒子のＸ線回折スペクトルを測定したときに、グラフェン積層構造に由来するピークの高さａと、シリコン粒子に由来するピークの高さｂとの比ａ／ｂが、好ましくは０．０１以上、より好ましくは０．０３以上、好ましくは２以下、より好ましくは１．２以下、さらに好ましくは０．６以下である。比ａ／ｂが上記下限値以上である場合、被覆層に含まれる薄片化黒鉛のグラフェン積層数をより一層多くすることができ、炭素材料被覆シリコン粒子の導電性をより一層高めることができる。そのため、蓄電デバイスの電極材料に用いたときに、レート特性やサイクル特性などの特性をより一層向上させることができる。比ａ／ｂが上記上限値以下である場合、被覆層の厚みをより一層薄くすることができ、リチウムイオン等のイオンをより一層スムーズに吸蔵し、放出することができる。そのため、蓄電デバイスの電極材料に用いたときに、サイクル特性などの特性をより一層向上させることができる。 In the present invention, when the X-ray diffraction spectrum of the carbon material-coated silicon particles is measured, the ratio a / b of the peak height a derived from the graphene laminated structure and the peak height b derived from the silicon particles b. However, it is preferably 0.01 or more, more preferably 0.03 or more, preferably 2 or less, more preferably 1.2 or less, still more preferably 0.6 or less. When the ratio a / b is not more than the above lower limit value, the number of graphene layers of the flaky graphite contained in the coating layer can be further increased, and the conductivity of the carbon material-coated silicon particles can be further enhanced. Therefore, when used as an electrode material for a power storage device, characteristics such as rate characteristics and cycle characteristics can be further improved. When the ratio a / b is not more than the above upper limit value, the thickness of the coating layer can be further reduced, and ions such as lithium ions can be occluded and released more smoothly. Therefore, when used as an electrode material for a power storage device, characteristics such as cycle characteristics can be further improved.
　上記Ｘ線回折スペクトルは、広角Ｘ線回折法によって測定することができる。Ｘ線回折装置としては、例えば、ＳｍａｒｔＬａｂ（リガク社製）を用いることができ、以下の条件で測定することができる。 The X-ray diffraction spectrum can be measured by a wide-angle X-ray diffraction method. As the X-ray diffractometer, for example, SmartLab (manufactured by Rigaku Co., Ltd.) can be used, and measurement can be performed under the following conditions.
　線源：ＣｕＫα線（波長１．５４１Å）
　測定範囲：５°～８０°
　走査速度：５°／分
　管電流：２００ｍＡ
　管電圧：４０ｋＶ Radioactive source: CuKα ray (wavelength 1.541 Å)
Measuring range: 5 ° -80 °
Scanning speed: 5 ° / minute Tube current: 200mA
Tube voltage: 40kV
　Ｘ線回折スペクトルにおいて、グラファイト構造に代表されるグラフェン積層構造に由来するピークは、２θ＝２６．４°付近に現れる。一方、粒子としてシリコン粒子を用いた場合、シリコンに由来するピークは、２θ＝２８．５°、４７．３°、５６．１°、６９．２°、７６．３°付近に現れる。このうち、ピーク強度の大きい２８．５°付近のピーク強度を本発明ではシリコン粒子のピーク強度とする。従って、この場合、上記比ａ／ｂは、２θ＝２６．４°付近のピークと２θ＝２８．５°付近のピークとのピーク比（２θ＝２６．４°付近のピーク／２θ＝２８．５°付近のピーク）により求めることができる。 In the X-ray diffraction spectrum, the peak derived from the graphene laminated structure represented by the graphite structure appears in the vicinity of 2θ = 26.4 °. On the other hand, when silicon particles are used as the particles, peaks derived from silicon appear near 2θ = 28.5 °, 47.3 °, 56.1 °, 69.2 °, and 76.3 °. Of these, the peak intensity near 28.5 °, which has a large peak intensity, is defined as the peak intensity of the silicon particles in the present invention. Therefore, in this case, the ratio a / b is the peak ratio between the peak near 2θ = 26.4 ° and the peak near 2θ = 28.5 ° (peak around 2θ = 26.4 ° / 2θ = 28. It can be obtained from the peak near 5 °).
　本発明においては、炭素材料被覆シリコン粒子の元素分析により測定された酸素原子数に対する炭素原子数の比（Ｃ／Ｏ比）が、好ましくは９以上、より好ましくは９９以上である。Ｃ／Ｏ比が上記範囲内にある場合、炭素材料被覆シリコン粒子の導電性をより一層高めることができる。そのため、蓄電デバイスの電極材料に用いたときに、レート特性やサイクル特性などの特性をより一層向上させることができる。 In the present invention, the ratio of the number of carbon atoms (C / O ratio) to the number of oxygen atoms measured by elemental analysis of carbon material-coated silicon particles is preferably 9 or more, more preferably 99 or more. When the C / O ratio is within the above range, the conductivity of the carbon material-coated silicon particles can be further increased. Therefore, when used as an electrode material for a power storage device, characteristics such as rate characteristics and cycle characteristics can be further improved.
　上記Ｃ／Ｏ比は、例えば、Ｘ線光電子分光法（ＸＰＳ）により、測定することができる。具体的には、Ｘ線源：ＡｌＫα、光電子取出角：４５度、Ｘ線ビーム径２００μｍ　（５０Ｗ１５ｋＶ）の条件で、光電子スペクトルを測定する。そして、Ｂｉｎｄｉｎｇ　Ｅｎｅｒｇｙ：２８０ｅＶ～２９２ｅＶに現れるＣ１ｓスペクトルのピーク面積を、Ｂｉｎｄｉｎｇ　Ｅｎｅｒｇｙ：５２５ｅＶ～５４０ｅＶに現れるＯ１ｓスペクトルのピーク面積で除する。それによって、炭素材料被覆シリコン粒子の被覆層に含まれる酸素原子数に対する炭素原子数の比（Ｃ／Ｏ比）を算出することができる。 The C / O ratio can be measured by, for example, X-ray photoelectron spectroscopy (XPS). Specifically, the photoelectron spectrum is measured under the conditions of an X-ray source: AlKα, a photoelectron extraction angle: 45 degrees, and an X-ray beam diameter of 200 μm (50W15kV). Then, the peak area of the C1s spectrum appearing in Binding Energy: 280 eV to 292 eV is divided by the peak area of the O1s spectrum appearing in Binding Energy: 525 eV to 540 eV. Thereby, the ratio of the number of carbon atoms to the number of oxygen atoms contained in the coating layer of the carbon material-coated silicon particles (C / O ratio) can be calculated.
　本発明においては、炭素材料被覆シリコン粒子のラマン分光法によって得られるラマンスペクトルにおいて、Ｄバンドと、Ｇバンドとのピーク強度比をＤ／Ｇ比としたときに、Ｄ／Ｇ比が好ましくは１以下、より好ましくは０．５以下、さらに好ましくは０．１以下である。Ｄ／Ｇ比が上記範囲内にある場合、導電性をより一層高めることができ、蓄電デバイスの電極材料に用いたときに、レート特性やサイクル特性などの特性をより一層向上させることができる。なお、Ｄ／Ｇ比の下限値は、特に限定されないが、例えば、０とすることができる。 In the present invention, in the Raman spectrum obtained by Raman spectroscopy of carbon material-coated silicon particles, the D / G ratio is preferably 1 when the peak intensity ratio between the D band and the G band is defined as the D / G ratio. Below, it is more preferably 0.5 or less, still more preferably 0.1 or less. When the D / G ratio is within the above range, the conductivity can be further enhanced, and when used as an electrode material for a power storage device, characteristics such as rate characteristics and cycle characteristics can be further improved. The lower limit of the D / G ratio is not particularly limited, but can be set to 0, for example.
　以下、炭素材料被覆シリコン粒子を構成する各材料の詳細について説明する。 The details of each material constituting the carbon material-coated silicon particles will be described below.
　（シリコン粒子）
　シリコン粒子の形状としては、特に限定されないが、例えば、球状、略球状、鱗片状、平面状、楕円状、略楕円状などのものを用いることができる。また、上記形状に加え、内部に中空、または多孔質を有する構造を用いることもできる。なかでも、球状又は略球状が好ましい。 (Silicon particles)
The shape of the silicon particles is not particularly limited, and for example, spherical, substantially spherical, scaly, planar, elliptical, and substantially elliptical shapes can be used. Further, in addition to the above shape, a structure having a hollow or porous structure inside can also be used. Of these, a spherical shape or a substantially spherical shape is preferable.
　シリコン粒子の平均粒子径は、特に限定されない。もっとも、シリコン粒子の平均粒子径は、好ましくは１０ｎｍ以上、より好ましくは２０ｎｍ以上、さらに好ましくは５０ｎｍ以上、好ましくは２０μｍ以下、より好ましくは１０μｍ以下、さらに好ましくは５μｍ以下である。シリコン粒子の平均粒子径が上記範囲内にある場合、蓄電デバイスの充放電によるサイクル特性をより一層向上させることができる。なお、平均粒子径は、動的光散乱法による粒度分布測定装置又はレーザー回折法による粒度分布測定装置を用いて、体積基準分布で算出した値をいう。 The average particle size of silicon particles is not particularly limited. However, the average particle size of the silicon particles is preferably 10 nm or more, more preferably 20 nm or more, still more preferably 50 nm or more, preferably 20 μm or less, more preferably 10 μm or less, still more preferably 5 μm or less. When the average particle size of the silicon particles is within the above range, the cycle characteristics due to charging and discharging of the power storage device can be further improved. The average particle size refers to a value calculated by a volume reference distribution using a particle size distribution measuring device by a dynamic light scattering method or a particle size distribution measuring device by a laser diffraction method.
　（被覆層）
　被覆層は、シリコン粒子の表面の少なくとも一部を覆っている。被覆層は、シリコン粒子の表面の５０％以上を覆っていることが好ましく、９０％以上を覆っていることがより好ましく、９５％以上を覆っていることがさらに好ましく、９９％以上を覆っていることが特に好ましく、完全に覆っていることが最も好ましい。この場合、蓄電デバイスのサイクル特性などの特性をより一層向上させることができる。 (Coating layer)
The coating layer covers at least a part of the surface of the silicon particles. The coating layer preferably covers 50% or more of the surface of the silicon particles, more preferably 90% or more, further preferably 95% or more, and covers 99% or more. It is particularly preferable that the particles are completely covered, and it is most preferable that the particles are completely covered. In this case, characteristics such as cycle characteristics of the power storage device can be further improved.
　被覆層の膜厚は、好ましくは０．５ｎｍ以上、より好ましくは２ｎｍ以上、好ましくは３０ｎｍ以下、より好ましくは１０ｎｍ以下である。被覆層の膜厚が上記下限値以上である場合、被覆層に含まれる薄片化黒鉛のグラフェン積層数をより一層高めることができ、炭素材料被覆シリコン粒子の導電性をより一層高めることができる。そのため、蓄電デバイスの電極材料に用いたときに、レート特性やサイクル特性などの特性をより一層向上させることができる。また、被覆層の膜厚が上記上限値以下である場合、リチウムイオン等のイオンをより一層スムーズに吸蔵し、放出することができる。そのため、蓄電デバイスの電極材料に用いたときに、サイクル特性などの特性をより一層向上させることができる。 The film thickness of the coating layer is preferably 0.5 nm or more, more preferably 2 nm or more, preferably 30 nm or less, and more preferably 10 nm or less. When the film thickness of the coating layer is at least the above lower limit value, the number of graphene layers of the flaky graphite contained in the coating layer can be further increased, and the conductivity of the carbon material-coated silicon particles can be further increased. Therefore, when used as an electrode material for a power storage device, characteristics such as rate characteristics and cycle characteristics can be further improved. Further, when the film thickness of the coating layer is not more than the above upper limit value, ions such as lithium ions can be occluded and released more smoothly. Therefore, when used as an electrode material for a power storage device, characteristics such as cycle characteristics can be further improved.
　なお、被覆層の厚みは、透過型電子顕微鏡写真（ＴＥＭ写真）により観察した任意の３個の炭素材料被覆シリコン粒子における被覆層の厚みの平均値から求めることができる。 The thickness of the coating layer can be obtained from the average value of the thickness of the coating layer in any three carbon material-coated silicon particles observed by a transmission electron micrograph (TEM photograph).
　被覆層は、薄片化黒鉛を含んでいる。薄片化黒鉛において、グラフェンシートの積層数は、特に限定されないが、好ましくは２層以上、より好ましくは５層以上、好ましくは１０００層以下、より好ましくは１００層以下である。グラフェンシートの積層数が上記下限値以上である場合、薄片化黒鉛の導電性をより一層高めることができ、蓄電デバイスの電極材料に用いたときに、サイクル特性などの特性をより一層向上させることができる。グラフェンシートの積層数が上記上限値以下である場合、薄片化黒鉛の比表面積をより一層大きくすることができ、蓄電デバイスの電極材料に用いたときに、容量などの特性をより一層向上させることができる。 The coating layer contains flaky graphite. In the flaky graphite, the number of laminated graphene sheets is not particularly limited, but is preferably 2 layers or more, more preferably 5 layers or more, preferably 1000 layers or less, and more preferably 100 layers or less. When the number of graphene sheets laminated is equal to or greater than the above lower limit, the conductivity of flaky graphite can be further enhanced, and when used as an electrode material for a power storage device, characteristics such as cycle characteristics can be further improved. Can be done. When the number of laminated graphene sheets is not more than the above upper limit value, the specific surface area of the flaky graphite can be further increased, and when used as an electrode material for a power storage device, characteristics such as capacity can be further improved. Can be done.
　被覆層中における薄片化黒鉛の含有量は、被覆層を構成する材料１００重量％に対し、好ましくは１０重量％以上、より好ましくは９０重量％以上、更に好ましくは９５重量％以上、より好ましくは１００重量％である。薄片化黒鉛の含有量が上記範囲にある場合、蓄電デバイスの電極材料に用いたときに、サイクル特性などの特性をより一層向上させることができる。 The content of flaky graphite in the coating layer is preferably 10% by weight or more, more preferably 90% by weight or more, still more preferably 95% by weight or more, more preferably 95% by weight or more, based on 100% by weight of the material constituting the coating layer. It is 100% by weight. When the content of flaky graphite is in the above range, characteristics such as cycle characteristics can be further improved when used as an electrode material for a power storage device.
　被覆層には、さらに黒鉛が含まれていてもよい。この場合、蓄電デバイスの電極材料に用いたときに、レート特性やサイクル特性などの特性をより一層向上させることができる。 The coating layer may further contain graphite. In this case, when used as an electrode material for a power storage device, characteristics such as rate characteristics and cycle characteristics can be further improved.
　なお、黒鉛とは、複数のグラフェンシートの積層体である。黒鉛のグラフェンシートの積層数は、通常、１０万層～１００万層程度である。黒鉛としては、例えば、天然黒鉛、人造黒鉛又は膨張黒鉛などを用いることができる。 Graphite is a laminate of a plurality of graphene sheets. The number of laminated graphene sheets of graphite is usually about 100,000 to 1,000,000. As the graphite, for example, natural graphite, artificial graphite, expanded graphite or the like can be used.
　被覆層は、さらにアモルファスカーボンを含んでいてもよい。この場合、シリコン粒子の表面をより一層均一に被覆することができ、蓄電デバイスの電極材料に用いたときに、サイクル特性などの特性をより一層向上させることができる。 The coating layer may further contain amorphous carbon. In this case, the surface of the silicon particles can be coated more uniformly, and when used as an electrode material for a power storage device, characteristics such as cycle characteristics can be further improved.
　なお、アモルファスカーボンが含まれているか否かは、Ｘ線回折スペクトルにおいて、２θ＝１５°～３０°付近にブロードなピークが観察されるか否かにより確認することができる。 Whether or not amorphous carbon is contained can be confirmed by whether or not a broad peak is observed in the vicinity of 2θ = 15 ° to 30 ° in the X-ray diffraction spectrum.
　また、被覆層中におけるアモルファスカーボンの含有量は、ＴＧ－ＤＴＡ測定により、６００℃以下における重量減少率により求めることができ、被覆層を構成する材料１００重量％に対し、好ましくは０重量％以上、好ましくは３０重量％以下、より好ましくは５重量％以下である。アモルファスカーボンの含有量が上記範囲にある場合、蓄電デバイスの電極材料に用いたときに、サイクル特性などの特性をより一層向上させることができる。 The content of amorphous carbon in the coating layer can be determined by the weight reduction rate at 600 ° C. or lower by TG-DTA measurement, and is preferably 0% by weight or more with respect to 100% by weight of the material constituting the coating layer. It is preferably 30% by weight or less, more preferably 5% by weight or less. When the content of amorphous carbon is in the above range, characteristics such as cycle characteristics can be further improved when used as an electrode material for a power storage device.
　なお、被覆層には、本発明の効果を阻害しない範囲において、他の材料が含まれていてもよい。 The coating layer may contain other materials as long as the effects of the present invention are not impaired.
　［炭素材料被覆シリコン粒子の製造方法］
　以下、図２を参照して、本発明に係る炭素材料被覆シリコン粒子の製造方法の一例について説明する。 [Manufacturing method of carbon material-coated silicon particles]
Hereinafter, an example of a method for producing carbon material-coated silicon particles according to the present invention will be described with reference to FIG.
　図２（ａ）～（ｃ）は、本発明に係る炭素材料被覆シリコン粒子の製造方法の一例を説明するための図である。 2 (a) to 2 (c) are diagrams for explaining an example of a method for producing carbon material-coated silicon particles according to the present invention.
　まず、図２に示すように、シリコン粒子２及び黒鉛１１が液状樹脂１２中に分散されている分散液を用意する。シリコン粒子２としては、上述したシリコン粒子を用いることができる。また、黒鉛１１は、そのまま用いてもよいが、超音波、ホモジナイザー等により粉砕して用いてもよい。 First, as shown in FIG. 2, a dispersion liquid in which the silicon particles 2 and the graphite 11 are dispersed in the liquid resin 12 is prepared. As the silicon particles 2, the above-mentioned silicon particles can be used. Further, the graphite 11 may be used as it is, or may be pulverized by an ultrasonic wave, a homogenizer or the like and used.
　また、液状樹脂１２としては、ポリエチレングリコール、ポリビニルアルコール、プロピレングリコール、ポリ酢酸ビニル等を用いることができる。これらは、１種を単独で用いてもよく、複数種を併用してもよい。 Further, as the liquid resin 12, polyethylene glycol, polyvinyl alcohol, propylene glycol, polyvinyl acetate and the like can be used. These may be used alone or in combination of two or more.
　液状樹脂１２の２５℃での粘度は、好ましくは１ｍＰａ・ｓ以上、より好ましくは１．５ｍＰａ・ｓ以上、更に好ましくは１０ｍＰａ・ｓ以上であり、好ましくは１０，０００，０００ｍＰａ・ｓ以下であり、より好ましくは１，０００，０００ｍＰａ・ｓ以下である。液状樹脂１２の粘度が上記範囲内にある場合、後述のボールミルにより、黒鉛１１をより一層確実に剥離しつつ、被覆層をより一層確実に形成することができる。 The viscosity of the liquid resin 12 at 25 ° C. is preferably 1 mPa · s or more, more preferably 1.5 mPa · s or more, further preferably 10 mPa · s or more, and preferably 10,000,000 mPa · s or less. , More preferably 1,000,000 mPa · s or less. When the viscosity of the liquid resin 12 is within the above range, the coating layer can be formed more reliably while the graphite 11 is more reliably peeled off by the ball mill described later.
　液状樹脂の粘度は、例えば、Ｅ型粘度計（東機産業社製、ＴＶ-２５　Ｔｙｐｅ－Ｈ粘度計）を用いて、２５℃の条件で測定することができる。 The viscosity of the liquid resin can be measured under the condition of 25 ° C. using, for example, an E-type viscometer (TV-25 Type-H viscometer manufactured by Toki Sangyo Co., Ltd.).
　分散液中における黒鉛１１の含有量は、例えば、０．０１重量％以上、３０重量％以下とすることができる。分散液中におけるシリコン粒子２の含有量は、好ましくは１重量％以上、５０重量％以下である。分散液中における液状樹脂１２の含有量は、例えば、２０重量％以上、９９重量％以下とすることができる。 The content of graphite 11 in the dispersion liquid can be, for example, 0.01% by weight or more and 30% by weight or less. The content of the silicon particles 2 in the dispersion is preferably 1% by weight or more and 50% by weight or less. The content of the liquid resin 12 in the dispersion liquid can be, for example, 20% by weight or more and 99% by weight or less.
　次に、図２（ａ）に示すように、分散液をボールミルの容器１０に入れ、図２（ｂ）に示すボール１３とともに自転・公転運動させることにより回転させ、混合させる。それによって、図２（ｂ）及び図２（ｃ）に示すように、ボール１３により黒鉛１１がシリコン粒子２に押しつけられ、剥離される。この操作を繰り返すことにより、黒鉛１１を剥離して薄片化黒鉛を形成しつつ、シリコン粒子２の表面に薄片化黒鉛１１ａ及び液状樹脂１２を付着させる。 Next, as shown in FIG. 2 (a), the dispersion liquid is placed in the container 10 of the ball mill, and is rotated and revolved together with the ball 13 shown in FIG. 2 (b) to be rotated and mixed. As a result, as shown in FIGS. 2 (b) and 2 (c), the graphite 11 is pressed against the silicon particles 2 by the balls 13 and peeled off. By repeating this operation, the graphite 11 is peeled off to form the flaky graphite, and the flaky graphite 11a and the liquid resin 12 are adhered to the surface of the silicon particles 2.
　なお、ボールミルとしては、例えば、遊星ボールミル（シンキー社製、品番「ＮＰ－１００」）を用いることができる。回転数は、例えば、４００ｒｐｍ以上、２０００ｒｐｍ以下とすることができる。回転時間は、例えば、１０分以上、６００分以下とすることができる。また、ボール１３としては、例えば、セラッミックボールを用いることができる。本実施形態では、ボール１３としてジルコニアボールが用いられている。 As the ball mill, for example, a planetary ball mill (manufactured by Shinky Co., Ltd., product number "NP-100") can be used. The rotation speed can be, for example, 400 rpm or more and 2000 rpm or less. The rotation time can be, for example, 10 minutes or more and 600 minutes or less. Further, as the ball 13, for example, a seramic ball can be used. In this embodiment, a zirconia ball is used as the ball 13.
　次に、薄片化黒鉛１１ａ及び液状樹脂１２が付着したシリコン粒子２を容器１０から取り出す。続いて、薄片化黒鉛１１ａ及び液状樹脂１２が表面に付着したシリコン粒子２を２００℃以上、６００℃以下の温度で加熱することにより、液状樹脂１２を炭化させ、アモルファスカーボンを形成させる。それによって、薄片化黒鉛１１ａ及びアモルファスカーボンを含む被覆層を備える炭素材料被覆シリコン粒子を得ることができる。 Next, the silicon particles 2 to which the flaky graphite 11a and the liquid resin 12 are attached are taken out from the container 10. Subsequently, the silicon particles 2 to which the flaky graphite 11a and the liquid resin 12 adhere to the surface are heated at a temperature of 200 ° C. or higher and 600 ° C. or lower to carbonize the liquid resin 12 and form amorphous carbon. Thereby, carbon material-coated silicon particles having a coating layer containing flaky graphite 11a and amorphous carbon can be obtained.
　なお、薄片化黒鉛１１ａ及び液状樹脂１２が表面に付着したシリコン粒子２の加熱時間は、特に限定されないが、例えば、２０分以上、４８０分以下とすることができる。上記加熱は、大気中で行ってもよく、窒素ガスなどの不活性ガス雰囲気下で行ってもよい。また、得られた炭素材料被覆シリコン粒子の被覆層には、剥離されていない黒鉛が含まれていてもよい。 The heating time of the silicon particles 2 on which the flaky graphite 11a and the liquid resin 12 adhere to the surface is not particularly limited, but can be, for example, 20 minutes or more and 480 minutes or less. The heating may be performed in the atmosphere or in an atmosphere of an inert gas such as nitrogen gas. Further, the coating layer of the obtained carbon material-coated silicon particles may contain graphite that has not been peeled off.
　被覆層の結晶化度は、例えば、黒鉛１１及び液状樹脂１２の仕込み量により調整することができる。黒鉛１１の仕込み量を多くすることにより、被覆層の結晶化度を高めることができる。あるいは、液状樹脂１２の仕込み量を少なくすることにより、被覆層の結晶化度を高めることができる。 The crystallinity of the coating layer can be adjusted, for example, by the amount of graphite 11 and liquid resin 12 charged. By increasing the amount of graphite 11 charged, the crystallinity of the coating layer can be increased. Alternatively, the crystallinity of the coating layer can be increased by reducing the amount of the liquid resin 12 charged.
　また、得られた炭素材料被覆シリコン粒子をさらに３００℃以上、８００℃以下の温度で加熱することにより、被覆層中におけるアモルファスカーボンを除去してもよい。それによって、炭素材料被覆シリコン粒子の導電性をより一層高めることができ、蓄電デバイスの電極材料に用いたときに、サイクル特性などの特性をより一層向上させることができる。なお、この際の加熱時間としては、特に限定されないが、例えば、１０分以上、３００分以下とすることができる。上記加熱は、大気中で行ってもよく、窒素ガスなどの不活性ガス雰囲気下で行ってもよいが、効率よくアモルファスカーボンを除去するには酸素含有雰囲気が好ましい。また、加熱前には、粉砕機等により粉砕して用いてもよい。 Further, the amorphous carbon in the coating layer may be removed by further heating the obtained carbon material-coated silicon particles at a temperature of 300 ° C. or higher and 800 ° C. or lower. As a result, the conductivity of the carbon material-coated silicon particles can be further enhanced, and when used as an electrode material for a power storage device, characteristics such as cycle characteristics can be further improved. The heating time at this time is not particularly limited, but can be, for example, 10 minutes or more and 300 minutes or less. The heating may be performed in the atmosphere or in an atmosphere of an inert gas such as nitrogen gas, but an oxygen-containing atmosphere is preferable in order to efficiently remove amorphous carbon. Further, before heating, it may be crushed by a crusher or the like before use.
　以上のように、本発明の炭素材料被覆シリコン粒子の製造方法では、機械的処理により黒鉛が剥離され、薄片化黒鉛が形成されている。そのため、化学的処理により黒鉛が剥離されている場合のように、黒鉛の酸化工程を含まない。よって、導電性に優れた炭素材料被覆シリコン粒子を得ることができる。 As described above, in the method for producing carbon material-coated silicon particles of the present invention, graphite is peeled off by mechanical treatment to form flaky graphite. Therefore, it does not include an oxidation step of graphite as in the case where graphite is peeled off by chemical treatment. Therefore, carbon material-coated silicon particles having excellent conductivity can be obtained.
　［蓄電デバイス用電極及び蓄電デバイス］
　本発明の蓄電デバイスとしては、特に限定されないが、非水電解質一次電池、水系電解質一次電池、非水電解質二次電池、水系電解質二次電池、全固体電解質一次電池、全固体電解質二次電池、コンデンサ、電気二重層キャパシタ、又はリチウムイオンキャパシタなどが挙げられる。 [Electrodes for power storage devices and power storage devices]
The power storage device of the present invention is not particularly limited, but is a non-aqueous electrolyte primary battery, an aqueous electrolyte primary battery, a non-aqueous electrolyte secondary battery, an aqueous electrolyte secondary battery, an all-solid electrolyte primary battery, an all-solid electrolyte secondary battery, and the like. Examples include capacitors, electric double layer capacitors, lithium ion capacitors and the like.
　本発明の蓄電デバイスは、本発明の炭素材料被覆シリコン粒子を含む蓄電デバイス用電極を備えているので、蓄電デバイスのレート特性やサイクル特性などの特性を向上させることができる。 Since the power storage device of the present invention includes an electrode for a power storage device containing the carbon material-coated silicon particles of the present invention, characteristics such as rate characteristics and cycle characteristics of the power storage device can be improved.
　特に、本発明の蓄電デバイスは、リチウムイオン二次電池などの二次電池やキャパシタに好適に用いることができる。 In particular, the power storage device of the present invention can be suitably used for a secondary battery such as a lithium ion secondary battery or a capacitor.
　本発明の炭素材料被覆シリコン粒子では、例えば、シリコン粒子が電極活物質として作用し、被覆層が導電助剤として作用する。 In the carbon material-coated silicon particles of the present invention, for example, the silicon particles act as an electrode active material, and the coating layer acts as a conductive auxiliary agent.
　本発明の蓄電デバイスに用いる蓄電デバイス用電極は、正極であってもよく、負極であってもよい。従って、電極活物質は、正極活物質であってもよく、負極活物質であってもよい。 The electrode for the power storage device used in the power storage device of the present invention may be a positive electrode or a negative electrode. Therefore, the electrode active material may be a positive electrode active material or a negative electrode active material.
　本発明の蓄電デバイス用電極は、本発明の炭素材料被覆シリコン粒子に、必要に応じて他の導電助剤や、バインダー、あるいは溶媒を含めた電極材料を賦形することにより得ることができる。 The electrode for a power storage device of the present invention can be obtained by shaping the carbon material-coated silicon particles of the present invention with an electrode material containing another conductive auxiliary agent, a binder, or a solvent, if necessary.
　電極材料の賦形は、例えば、圧延ローラーでシート化した後、乾燥することにより行うことができる。また、本発明の炭素材料被覆シリコン粒子と溶媒と必要に応じて導電助剤やバインダーとからなる塗液を集電体に塗工し、その後乾燥することにより行ってもよい。 The shaping of the electrode material can be performed, for example, by forming a sheet with a rolling roller and then drying it. Further, a coating liquid composed of the carbon material-coated silicon particles of the present invention, a solvent, and if necessary, a conductive auxiliary agent or a binder may be applied to the current collector and then dried.
　他の導電助剤としては、例えば、グラフェン、人造黒鉛、粒状黒鉛化合物、繊維状黒鉛化合物、カーボンブラック、又は活性炭等を用いることができる。 As the other conductive auxiliary agent, for example, graphene, artificial graphite, granular graphite compound, fibrous graphite compound, carbon black, activated carbon or the like can be used.
　バインダーとしては、例えば、ポリビニルブチラール、ポリテトラフルオロエチレン、スチレンブタジエンゴム、ポリイミド樹脂、アクリル系樹脂、ポリフッ化ビニリデンなどのフッ素系ポリマーや、水溶性のカルボキシメチルセルロースなどの樹脂を用いることができる。好ましくは、ポリテトラフルオロエチレンを用いることができる。ポリテトラフルオロエチレンを用いた場合、分散性や耐熱性をより一層向上させることができる。 As the binder, for example, a fluorine-based polymer such as polyvinyl butyral, polytetrafluoroethylene, styrene-butadiene rubber, polyimide resin, acrylic resin, polyvinylidene fluoride, or a resin such as water-soluble carboxymethyl cellulose can be used. Preferably, polytetrafluoroethylene can be used. When polytetrafluoroethylene is used, the dispersibility and heat resistance can be further improved.
　なお、上記溶媒としては、エタノール、Ｎ－メチルピロリドン（ＮＭＰ）又は水等を使用することができる。 As the solvent, ethanol, N-methylpyrrolidone (NMP), water or the like can be used.
　電極材料中における炭素材料被覆シリコン粒子の含有量は、特に限定されないが、電極材料全体を１００質量％としたときに、好ましくは１０質量％以上、より好ましくは２０質量％以上、更により好ましくは５０質量％以上、好ましくは９０質量％以下、より好ましくは８０質量％以下である。炭素材料被覆シリコン粒子の含有量が上記範囲内にある場合、蓄電デバイスのレート特性やサイクル特性をより一層向上させることができる。なお、炭素材料被覆シリコン粒子は、一種類を用いてもよく、二種類または二種類以上を用いてもよい。 The content of the carbon material-coated silicon particles in the electrode material is not particularly limited, but when the entire electrode material is 100% by mass, it is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably. It is 50% by mass or more, preferably 90% by mass or less, and more preferably 80% by mass or less. When the content of the carbon material-coated silicon particles is within the above range, the rate characteristics and cycle characteristics of the power storage device can be further improved. As the carbon material-coated silicon particles, one type may be used, or two types or two or more types may be used.
　電極材料中における他の導電助剤の含有量は、電極材料全体を１００質量％としたときに、好ましくは０．１質量％以上、より好ましくは０．５質量％以上、好ましくは５０質量％以下、より好ましくは３０質量％以下である。導電助剤の含有量が上記範囲内にある場合、蓄電デバイスのレート特性やサイクル特性をより一層向上させることができる。 The content of the other conductive auxiliary agent in the electrode material is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, preferably 50% by mass, when the entire electrode material is 100% by mass. Hereinafter, it is more preferably 30% by mass or less. When the content of the conductive auxiliary agent is within the above range, the rate characteristics and cycle characteristics of the power storage device can be further improved.
　電極材料中におけるバインダーの含有量は、電極材料全体を１００質量％としたときに、例えば、０．１質量％以上、３０質量％以下とすることができる。 The content of the binder in the electrode material can be, for example, 0.1% by mass or more and 30% by mass or less when the entire electrode material is 100% by mass.
　蓄電デバイスが、非水電解質二次電池である場合、非水電解質二次電池の正極及び負極は、集電体の片面又は両面に同じ電極を形成させた形態であってもよく、集電体の片面に正極、他方の面に負極を形成させた形態、すなわち、バイポーラ電極であってもよい。 When the power storage device is a non-aqueous electrolyte secondary battery, the positive electrode and the negative electrode of the non-aqueous electrolyte secondary battery may have the same electrodes formed on one side or both sides of the current collector. A positive electrode may be formed on one surface of the above, and a negative electrode may be formed on the other surface, that is, a bipolar electrode.
　非水電解質二次電池は、正極側と負極側との間にセパレータを配置したものを倦回したものであってもよいし、積層したものであってもよい。正極、負極及びセパレータには、リチウムイオン伝導を担う非水電解質が含まれている。 The non-aqueous electrolyte secondary battery may be a battery in which a separator is arranged between the positive electrode side and the negative electrode side, or may be a laminated battery. The positive electrode, negative electrode and separator contain a non-aqueous electrolyte responsible for lithium ion conduction.
　非水電解質二次電池は、上記積層体を倦回、あるいは複数積層した後にラミネートフィルムで外装してもよいし、角形、楕円形、円筒形、コイン形、ボタン形、シート形の金属缶で外装してもよい。外装には発生したガスを放出するための機構が備わっていてもよい。積層体の積層数は、特に限定されず、所望の電圧値、電池容量を発現するまで積層させることができる。 The non-aqueous electrolyte secondary battery may be covered with a laminate film after laminating or a plurality of the above-mentioned laminates, or may be a square, oval, cylindrical, coin-shaped, button-shaped, or sheet-shaped metal can. It may be exteriorized. The exterior may be provided with a mechanism for releasing the generated gas. The number of laminated bodies is not particularly limited, and the laminated bodies can be laminated until a desired voltage value and battery capacity are exhibited.
　非水電解質二次電池は、所望の大きさ、容量、電圧によって、適宜直列、並列に接続した組電池とすることができる。上記組電池においては、各電池の充電状態の確認、安全性向上のため、組電池に制御回路が付属されていることが好ましい。 The non-aqueous electrolyte secondary battery can be an assembled battery connected in series or in parallel as appropriate depending on the desired size, capacity, and voltage. In the above-mentioned assembled battery, it is preferable that the assembled battery is provided with a control circuit in order to confirm the charging state of each battery and improve safety.
　非水電解質二次電池に用いる非水電解質は、特に限定されないが、非水溶媒に溶質を溶解させた電解液を高分子に含浸させたゲル電解質、ポリエチレンオキシド、ポリプロピレンオキシドなどの高分子固体電解質、又はサルファイドガラス、オキシナイトライドなどの無機固体電解質を用いることができる。 Non-aqueous electrolyte The non-aqueous electrolyte used in the secondary battery is not particularly limited, but is a gel electrolyte obtained by impregnating a polymer with an electrolytic solution in which a solute is dissolved in a non-aqueous solvent, or a polymer solid electrolyte such as polyethylene oxide or polypropylene oxide. , Or an inorganic solid electrolyte such as sulfated glass or oxynitride can be used.
　非水溶媒としては、後述の溶質をより一層溶解させやすいことから、環状の非プロトン性溶媒及び／又は鎖状の非プロトン性溶媒を含むことが好ましい。環状の非プロトン性溶媒としては、環状カーボネート、環状エステル、環状スルホン又は環状エーテルなどが例示される。鎖状の非プロトン性溶媒としては、鎖状カーボネート、鎖状カルボン酸エステル又は鎖状エーテルなどが例示される。また、上記に加え、アセトニトリルなどの一般的に非水電解質の溶媒として用いられる溶媒を用いてもよい。より具体的には、ジメチルカーボネート、メチルエチルカーボネート、ジメチルカーボネート、ジプロピルカーボネート、メチルプロピルカーボネート、エチレンカーボネート、プロピレンカーボネート、ブチレンカーボネート、γ－ブチルラクトン、１，２－ジメトキシエタン、スルホラン、ジオキソラン、又はプロピオン酸メチルなどを用いることができる。これら溶媒は、１種類を単独で用いてもよいし、２種類以上を混合しても用いてもよい。もっとも、後述の溶質をより一層容易に溶解させ、リチウムイオンの伝導性をより一層高める観点から、２種類以上混合した溶媒を用いることが好ましい。 The non-aqueous solvent preferably contains a cyclic aprotic solvent and / or a chain aprotic solvent because the solute described later can be more easily dissolved. Examples of the cyclic aprotic solvent include cyclic carbonates, cyclic esters, cyclic sulfones, and cyclic ethers. Examples of the chain aprotic solvent include chain carbonate, chain carboxylic acid ester, and chain ether. In addition to the above, a solvent generally used as a solvent for a non-aqueous electrolyte such as acetonitrile may be used. More specifically, dimethyl carbonate, methyl ethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyl lactone, 1,2-dimethoxyethane, sulfolane, dioxolane, or Methyl propionate and the like can be used. One type of these solvents may be used alone, or two or more types may be mixed or used. However, from the viewpoint of more easily dissolving the solute described later and further enhancing the conductivity of lithium ions, it is preferable to use a solvent in which two or more kinds are mixed.
　溶質としては、特に限定されないが、例えば、ＬｉＣｌＯ４、ＬｉＢＦ４、ＬｉＰＦ６、ＬｉＡｓＦ６、ＬｉＣＦ３ＳＯ３、ＬｉＢＯＢ（Ｌｉｔｈｉｕｍ　Ｂｉｓ　（Ｏｘａｌａｔｏ）　Ｂｏｒａｔｅ）、又はＬｉＮ（ＳＯ２ＣＦ３）２などが好ましい。この場合、溶媒により一層容易に溶解させることができる。 The solute is not particularly limited, but for example, LiClO 4 , LiBF 4 , LiPF 6 , LiAsF 6 , LiCF 3 SO 3 , LiBOB (Lithium Bis (Oxalato) Borate), LiN (SO 2 CF 3 ) 2, and the like are preferable. .. In this case, it can be more easily dissolved with a solvent.
　蓄電デバイスは、上述したように水系電解質二次電池であってもよい。この場合、水系電解液としては、硝酸リチウム、硫酸リチウム、酢酸リチウムなどのリチウム塩等を溶解した水溶液を用いることができる。 The power storage device may be an aqueous electrolyte secondary battery as described above. In this case, as the aqueous electrolytic solution, an aqueous solution in which a lithium salt such as lithium nitrate, lithium sulfate or lithium acetate is dissolved can be used.
　水系の電解液としては、例えば、溶媒に水を用い、電解質に硫酸や水酸化カリウムなどを用いた電解液が挙げられる。 Examples of the aqueous electrolytic solution include an electrolytic solution in which water is used as a solvent and sulfuric acid, potassium hydroxide, or the like is used as an electrolyte.
　他方、非水系の電解液としては、例えば、以下の溶媒や電解質、イオン性液体を用いた電解液を用いることができる。 On the other hand, as the non-aqueous electrolytic solution, for example, an electrolytic solution using the following solvent, electrolyte, or ionic liquid can be used.
　溶媒としては、アセトニトリル、プロピレンカーボネート（ＰＣ）、エチレンカーボネート（ＥＣ）、ジメチルカーボネート（ＤＭＣ）、ジエチルカーボネート（ＤＥＣ）、又はアクリロニトリル（ＡＮ）などが挙げられる。 Examples of the solvent include acetonitrile, propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), acrylonitrile (AN) and the like.
　電解質としては、６フッ化リン酸リチウム（ＬｉＰＦ６）、４フッ化ホウ酸リチウム（ＬｉＢＦ４）、４フッ化ホウ酸テトラエチルアンモニウム（ＴＥＡＢＦ４）又は４フッ化ホウ酸トリエチルメチルアンモニウム（ＴＥＭＡＢＦ４）などが挙げられる。 As the electrolyte, lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), tetraethylammonium tetrafluoroborate (TEABF 4 ) or triethylmethylammonium tetrafluoroborate (TEMABF 4 ) And so on.
　以下、実施例により本発明をさらに具体的に説明するが、本発明はこれらの実施例によって何ら限定されるものではなく、その要旨を変更しない範囲において適宜変更可能である。 Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples, and can be appropriately changed without changing the gist thereof.
　（実施例１）
　黒鉛（東洋炭素社製、品番「ＰＦ８」）１ｇを、液状樹脂としてのポリエチレングリコール（三洋化成社製、品番「ＰＥＧ６００」）２３４ｇ中に分散させ、分散液（黒鉛：ＰＥＧ＝１重量％：２３４重量％）を作製した。 (Example 1)
1 g of graphite (manufactured by Toyo Tanso Co., Ltd., product number "PF8") is dispersed in 234 g of polyethylene glycol (manufactured by Sanyo Kasei Co., Ltd., product number "PEG600") as a liquid resin, and a dispersion liquid (graphite: PEG = 1% by weight: 234) is dispersed. By weight%) was prepared.
　次に、作製した分散液６ｇとシリコン粒子（関東化学社製、平均粒子径：１００ｎｍ）０．６ｇとを、ジルコニアボール２．５ｇとともに、遊星ボールミル（シンキー社製、品番「ＮＰ－１００」）の容器に入れ、回転数２５００ｒｐｍで２５分間遊星撹拌させ、混合させた。混合後、取り出した粒子を窒素雰囲下において４２０℃で１時間加熱した。それによって、シリコン粒子の表面が薄片化黒鉛及びアモルファスカーボンにより被覆されている粒子を得た。 Next, 6 g of the prepared dispersion and 0.6 g of silicon particles (manufactured by Kanto Chemical Co., Inc., average particle diameter: 100 nm) were added together with 2.5 g of zirconia balls to a planetary ball mill (manufactured by Shinky Co., Ltd., product number "NP-100"). The particles were placed in the same container and stirred at a rotation speed of 2500 rpm for 25 minutes to mix them. After mixing, the removed particles were heated at 420 ° C. for 1 hour in a nitrogen atmosphere. As a result, particles in which the surface of the silicon particles was coated with flaky graphite and amorphous carbon were obtained.
　また、得られた粒子を空気雰囲気下において５００℃で１０分加熱した。それによって、アモルファスカーボンを除去し、シリコン粒子の表面が薄片化黒鉛により被覆されている炭素材料被覆シリコン粒子を得た。 Further, the obtained particles were heated at 500 ° C. for 10 minutes in an air atmosphere. As a result, amorphous carbon was removed to obtain carbon material-coated silicon particles in which the surface of the silicon particles was coated with flaky graphite.
　（実施例２）
　黒鉛（東洋炭素社製、品番「ＰＦ８」）１．２ｇを、液状樹脂としてのポリエチレングリコール（三洋化成社製、品番「ＰＥＧ６００」）２３．４ｇと水２３．０ｇの混合溶媒中に分散させ、混合液を気流循環型オーブンにて１５０℃で３時間処理することで水を除去し、黒鉛とＰＥＧの分散液（黒鉛：ＰＥＧ＝１重量％：１９．５重量％）を作製した。次に、作製した分散液６ｇとシリコン粒子（関東化学社製、平均粒子径：１００ｎｍ）０．６ｇとを、ジルコニアボール２．５ｇとともに、遊星ボールミル（シンキー社製、品番「ＮＰ－１００」）の容器に入れ、回転数２５００ｒｐｍで２５分間遊星撹拌させ、混合させた。混合後、取り出した粒子を窒素雰囲下において４２０℃で１時間加熱した。それによって、シリコン粒子の表面が薄片化黒鉛及びアモルファスカーボンにより被覆されている粒子を得た。 (Example 2)
1.2 g of graphite (manufactured by Toyo Carbon Co., Ltd., product number "PF8") was dispersed in a mixed solvent of 23.4 g of polyethylene glycol as a liquid resin (manufactured by Sanyo Kasei Co., Ltd., product number "PEG600") and 23.0 g of water. Water was removed by treating the mixed solution in an air flow circulation type oven at 150 ° C. for 3 hours to prepare a dispersion of graphite and PEG (graphite: PEG = 1% by weight: 19.5% by weight). Next, 6 g of the prepared dispersion and 0.6 g of silicon particles (manufactured by Kanto Chemical Co., Inc., average particle diameter: 100 nm) were added together with 2.5 g of zirconia balls to a planetary ball mill (manufactured by Shinky Co., Ltd., product number "NP-100"). The particles were placed in the same container and stirred at a rotation speed of 2500 rpm for 25 minutes to mix them. After mixing, the removed particles were heated at 420 ° C. for 1 hour in a nitrogen atmosphere. As a result, particles in which the surface of the silicon particles was coated with flaky graphite and amorphous carbon were obtained.
　また、得られた粒子を空気雰囲気下において５００℃で１０分加熱した。それによって、アモルファスカーボンを除去し、Ｓｉ粒子の表面が薄片化黒鉛により被覆されている炭素材料被覆シリコン粒子を得た。 Further, the obtained particles were heated at 500 ° C. for 10 minutes in an air atmosphere. As a result, amorphous carbon was removed to obtain carbon material-coated silicon particles in which the surface of the Si particles was coated with flaky graphite.
　（比較例１）
　シリコン粒子（関東化学社製、平均粒子径：１００ｎｍ）をそのまま用いた。 (Comparative Example 1)
Silicon particles (manufactured by Kanto Chemical Co., Inc., average particle size: 100 nm) were used as they were.
　＜評価＞
　（熱重量測定）
　実施例１～２で得られた炭素材料被覆シリコン粒子及び比較例１の粒子について、熱重量・熱量同時測定装置（株式会社日立ハイテクサイエンス社製、品番：ＴＧＤＴＡ６３００）を用いて、下記の条件で測定を行った。 <Evaluation>
(Thermogravimetric analysis)
The carbon material-coated silicon particles obtained in Examples 1 and 2 and the particles of Comparative Example 1 were subjected to the following conditions using a simultaneous measurement device for heat weight and calorific value (manufactured by Hitachi High-Tech Science Corporation, product number: TGDTA6300). Measurements were made.
　雰囲気：空気
　昇温速度：１０℃／分
　温度範囲：４０℃～１０００℃ Atmosphere: Air Temperature rise rate: 10 ° C / min Temperature range: 40 ° C to 1000 ° C
　図３は、実施例１のアモルファスカーボン除去前における粒子の熱重量分析測定の結果を示す図である。図４は、実施例１のアモルファスカーボン除去後における炭素材料被覆シリコン粒子の熱重量分析測定の結果を示す図である。図５は、実施例２のアモルファスカーボン除去前における粒子の熱重量分析測定の結果を示す図である。図６は、実施例２のアモルファスカーボン除去後における炭素材料被覆シリコン粒子の熱重量分析測定の結果を示す図である。また、図７は、比較例１の粒子の熱重量分析測定の結果を示す図である。 FIG. 3 is a diagram showing the results of thermogravimetric analysis and measurement of particles before removing amorphous carbon in Example 1. FIG. 4 is a diagram showing the results of thermogravimetric analysis and measurement of the carbon material-coated silicon particles after removing the amorphous carbon of Example 1. FIG. 5 is a diagram showing the results of thermogravimetric analysis and measurement of particles before removing amorphous carbon in Example 2. FIG. 6 is a diagram showing the results of thermogravimetric analysis and measurement of carbon material-coated silicon particles after removing amorphous carbon in Example 2. Further, FIG. 7 is a diagram showing the results of thermogravimetric analysis measurement of the particles of Comparative Example 1.
　図３及び図４より、実施例１で得られた粒子では、重量増加開始温度が７００℃付近であることがわかる。また、図５及び図６より、実施例２で得られた粒子では、重量増加開始温度が８００℃付近であることがわかる。一方、図７より、比較例１の粒子では、重量増加開始温度が４００℃以上、５００℃未満であることがわかる。これにより、実施例１及び実施例２では、Ｓｉの酸化温度が高温側にシフトしており、Ｓｉ粒子がグラフェン積層構造を有する炭素材料により被覆されており、酸素が遮蔽されていることがわかる。また、図４及び図６では、図３及び図５に存在している低温側の重量減少が消失していることがわかる。これにより、５００℃で１０分の加熱により、アモルファスカーボンが消失していることを確認することができる。 From FIGS. 3 and 4, it can be seen that the weight increase start temperature of the particles obtained in Example 1 is around 700 ° C. Further, from FIGS. 5 and 6, it can be seen that the weight increase start temperature of the particles obtained in Example 2 is around 800 ° C. On the other hand, from FIG. 7, it can be seen that in the particles of Comparative Example 1, the weight increase start temperature is 400 ° C. or higher and lower than 500 ° C. From this, it can be seen that in Examples 1 and 2, the oxidation temperature of Si is shifted to the high temperature side, the Si particles are covered with a carbon material having a graphene laminated structure, and oxygen is shielded. .. Further, in FIGS. 4 and 6, it can be seen that the weight loss on the low temperature side existing in FIGS. 3 and 5 has disappeared. This makes it possible to confirm that the amorphous carbon has disappeared by heating at 500 ° C. for 10 minutes.
　（Ｘ線回折測定）
　実施例１及び実施例２で作製した粒子のアモルファスカーボン除去前及び除去後におけるＸ線回折スペクトルを広角Ｘ線回折法により測定した。Ｘ線回折装置としては、リガク社製、ＳｍａｒｔＬａｂを用い、以下の条件で測定した。 (X-ray diffraction measurement)
The X-ray diffraction spectra of the particles prepared in Examples 1 and 2 before and after removing the amorphous carbon were measured by a wide-angle X-ray diffraction method. As the X-ray diffractometer, a SmartLab manufactured by Rigaku Co., Ltd. was used, and the measurement was performed under the following conditions.
　線源：ＣｕＫα線（波長１．５４１Å）
　測定範囲：５°～８０°
　走査速度：５°／分
　管電流：２００ｍＡ
　管電圧：４０ｋＶ Radioactive source: CuKα ray (wavelength 1.541 Å)
Measuring range: 5 ° -80 °
Scanning speed: 5 ° / minute Tube current: 200mA
Tube voltage: 40kV
　図８は、実施例１で作製した粒子のアモルファスカーボン除去前におけるＸ線回折スペクトルである。図９は、実施例１で作製した粒子のアモルファスカーボン除去後におけるＸ線回折スペクトルである。図１０は、実施例２で作製した粒子のアモルファスカーボン除去前におけるＸ線回折スペクトルである。また、図１１は、実施例２で作製した粒子のアモルファスカーボン除去後におけるＸ線回折スペクトルである。 FIG. 8 is an X-ray diffraction spectrum of the particles prepared in Example 1 before removing amorphous carbon. FIG. 9 is an X-ray diffraction spectrum of the particles produced in Example 1 after removing amorphous carbon. FIG. 10 is an X-ray diffraction spectrum of the particles produced in Example 2 before removing amorphous carbon. Further, FIG. 11 is an X-ray diffraction spectrum of the particles produced in Example 2 after removing the amorphous carbon.
　シリコンに由来するピークは、２θ＝２８．５°、４７．３°、５６．１°、６９．２°、７６．３°付近に現れる。このうち、ピーク強度の大きい２８．５°付近のピーク強度を本発明ではシリコン粒子のピーク強度とする。 Silicon-derived peaks appear near 2θ = 28.5 °, 47.3 °, 56.1 °, 69.2 °, and 76.3 °. Of these, the peak intensity near 28.5 °, which has a large peak intensity, is defined as the peak intensity of the silicon particles in the present invention.
　得られたＸ線回折スペクトルより、グラフェン積層構造に由来するピーク（２θ＝２６．４°付近）のピーク高さａと、Ｓｉに由来するピーク（２θ＝２８．５°付近）のピーク高さｂとの比を求めた。その結果、実施例１では、アモルファスカーボン除去前の比ａ／ｂが０．０３２であり、除去後のａ／ｂが０．０８８であった。また、実施例２では、アモルファスカーボン除去前の比ａ／ｂが０．５０１であり、除去後のａ／ｂが１．０５３であった。これにより、空気雰囲気にて５００℃で１０分の加熱により、グラフェン積層構造のピークが大きくなることが確認できた。 From the obtained X-ray diffraction spectrum, the peak height a of the peak derived from the graphene laminated structure (around 2θ = 26.4 °) and the peak height of the peak derived from Si (around 2θ = 28.5 °) The ratio with b was calculated. As a result, in Example 1, the ratio a / b before removing the amorphous carbon was 0.032, and the a / b after removing the amorphous carbon was 0.088. Further, in Example 2, the ratio a / b before removing the amorphous carbon was 0.501, and the a / b after removing the amorphous carbon was 1.053. As a result, it was confirmed that the peak of the graphene laminated structure was increased by heating at 500 ° C. for 10 minutes in an air atmosphere.
　なお、Ｘ線回折スペクトルによる観察によっても、５００℃で１０分の加熱により、加熱前に存在していた２θ＝１５°～３０°付近のブロードなピーク（アモルファスカーボンに起因するピーク）が消失していることが確認できた。 By observing with an X-ray diffraction spectrum, the broad peak (peak caused by amorphous carbon) around 2θ = 15 ° to 30 ° that existed before heating disappeared by heating at 500 ° C. for 10 minutes. I was able to confirm that.
　（被覆層の厚み測定）
　図１２は、実施例１で得られた炭素材料被覆シリコン粒子の透過型電子顕微鏡写真を示す図である。図１２に示すように、実施例１では、粒子の表面に均一な被覆層が作製できていることが確認できた。同様に、実施例２においても、粒子の表面に均一な被覆層が作製できていることが確認できた。また、炭素材料被覆シリコン粒子のアモルファスカーボン除去後の被覆層の厚みは、実施例１では１ｎｍであり、実施例２では４０ｎｍであった。 (Measurement of coating layer thickness)
FIG. 12 is a diagram showing a transmission electron micrograph of the carbon material-coated silicon particles obtained in Example 1. As shown in FIG. 12, in Example 1, it was confirmed that a uniform coating layer was formed on the surface of the particles. Similarly, in Example 2, it was confirmed that a uniform coating layer could be produced on the surface of the particles. The thickness of the coating layer of the carbon material-coated silicon particles after removing the amorphous carbon was 1 nm in Example 1 and 40 nm in Example 2.
　（サイクル特性）
　実施例１及び実施例２で得られた炭素材料被覆シリコン粒子及び比較例１の粒子を用いて、以下のようにして、サイクル特性の評価を行った。 (Cycle characteristics)
Using the carbon material-coated silicon particles obtained in Examples 1 and 2 and the particles of Comparative Example 1, the cycle characteristics were evaluated as follows.
　負極膜の作製；
　実施例１、実施例２で得られた炭素材料被覆シリコン粒子又は比較例１のシリコン粒子０．２２８ｇと、導電助剤としてのアセチレンブラックを０．０６２５ｇと、バインダー樹脂としてのポリイミドを０．１２５ｇと、黒鉛（ＭＣＭＢ、大阪ガス社製）０．８３５ｇとを混合し、混合物を作製した。 Fabrication of negative electrode film;
0.228 g of the carbon material-coated silicon particles obtained in Examples 1 and 2 or the silicon particles of Comparative Example 1, 0.0625 g of acetylene black as a conductive auxiliary agent, and 0.125 g of polyimide as a binder resin. And 0.835 g of graphite (MCMB, manufactured by Osaka Gas Co., Ltd.) were mixed to prepare a mixture.
　続いて、得られた混合物に、溶媒としてのＮ－メチル－２－ピロリドン（ＮＭＰ）を適量添加し、自転・公転ミキサー（シンキー社製、「練太郎ＡＲ－１００」）を用いて混練し、均一なペーストを得た。 Subsequently, an appropriate amount of N-methyl-2-pyrrolidone (NMP) as a solvent was added to the obtained mixture, and the mixture was kneaded using a rotation / revolution mixer (Sinky Co., Ltd., "Kentaro AR-100"). A uniform paste was obtained.
　次に、調製したペーストをアプリケータ（テスター産業社製、商品名「ＰＩ－１２１０」）で膜厚が３０μｍとなるように、厚み２０μｍの銅箔の表面に塗布した。塗布後、１２０℃で１５時間真空乾燥し、さらに２５０℃で１２時間熱処理した。それによって、負極膜を得た。 Next, the prepared paste was applied to the surface of a copper foil having a thickness of 20 μm with an applicator (manufactured by Tester Sangyo Co., Ltd., trade name “PI-1210”) so that the film thickness was 30 μm. After coating, it was vacuum dried at 120 ° C. for 15 hours and further heat-treated at 250 ° C. for 12 hours. As a result, a negative electrode film was obtained.
　得られた負極膜を用いて、評価用セルを作製した。評価用セルの組み立てプロセスは、全てアルゴンガス置換の真空グローブボックス中で行った。評価用セルとしては、コイン型セル（ＨＳセル）を用いた。 An evaluation cell was prepared using the obtained negative electrode film. The process of assembling the evaluation cell was all carried out in a vacuum glove box replaced with argon gas. As the evaluation cell, a coin-type cell (HS cell) was used.
　対極と作用極との間に、作用極側から順に、金属リチウム片（φ１０ｍｍ、厚み０．２ｍｍのＬｉ箔）、セパレータ（積水化学工業社製、商品名「エスフィノ」（２５μｍ））、負極膜（φ１０ｍｍ、上記２５０℃で熱処理したもの）、樹脂からなる固定治具、集電極及びばねを積層した。正極は、上記金属リチウム片である。電解液は、１モル／ＬのＬｉＰＦ６／ＥＣ：ＤＭＣ（１：２ｖ／ｖ％）溶液（キシダ化学社製）を用いた。 Between the counter electrode and the working electrode, in order from the working electrode side, a metal lithium piece (φ10 mm, 0.2 mm thick Li foil), a separator (manufactured by Sekisui Chemical Co., Ltd., trade name “Esfino” (25 μm)), and a negative electrode film. (Φ10 mm, heat-treated at the above 250 ° C.), a fixing jig made of resin, a collector electrode, and a spring were laminated. The positive electrode is the above-mentioned metallic lithium piece. As the electrolytic solution, a 1 mol / L LiPF 6 / EC: DMC (1: 2 v / v%) solution (manufactured by Kishida Chemical Co., Ltd.) was used.
　充放電試験；
　上記のようにして組み立てたコイン型セルにおいて、電圧が０．０２－１．５Ｖ（ｖｓ．　Ｌｉ＋／Ｌｉ）の範囲で、レートが０．２Ｃの条件で充放電テストを行った（充放電試験装置：北斗電工社製、商品名「ＨＪ１００５ＳＤ８」）。具体的には、まずは１．５Ｖから０．０２ＶまでＣＣＣＶのモードで充電した。充電後は１５分間休止した。次に、ＣＣのモードで０．０２Ｖから１．５Ｖまで放電した。次に１５分間休止した。サイクル特性は、３０サイクルまでの評価を行った。 Charge / discharge test;
In the coin-type cell assembled as described above , a charge / discharge test was performed under the condition that the voltage was in the range of 0.02-1.5 V (vs. Li + / Li) and the rate was 0.2 C (charge / discharge). Test equipment: Hokuto Denko Co., Ltd., trade name "HJ1005SD8"). Specifically, first, the battery was charged from 1.5V to 0.02V in the CCCV mode. After charging, it was rested for 15 minutes. Next, it was discharged from 0.02V to 1.5V in CC mode. Then I rested for 15 minutes. The cycle characteristics were evaluated up to 30 cycles.
　図１３は、実施例１で得られた炭素材料被覆シリコン粒子を用いて作製した電池のサイクル特性の結果を示す図である。図１４は、実施例２で得られた炭素材料被覆シリコン粒子を用いて作製した電池のサイクル特性の結果を示す図である。また、図１５は、比較例１の粒子を用いて作製した電池のサイクル特性の結果を示す図である。なお、各図において、縦軸は、容量（ｍＡｈ／ｇ）を示している。 FIG. 13 is a diagram showing the results of the cycle characteristics of the battery produced by using the carbon material-coated silicon particles obtained in Example 1. FIG. 14 is a diagram showing the results of the cycle characteristics of the battery produced by using the carbon material-coated silicon particles obtained in Example 2. Further, FIG. 15 is a diagram showing the results of cycle characteristics of a battery manufactured using the particles of Comparative Example 1. In each figure, the vertical axis indicates the capacity (mAh / g).
　図１３～図１５より、実施例１（重量増加開始温度：７００℃）及び実施例２（重量増加開始温度：８００℃）の炭素材料被覆シリコン粒子を用いて作製した電池では、比較例１（重量増加開始温度：５００℃未満）の電池と比較して、サイクル特性が向上することが確認できた。 From FIGS. 13 to 15, in the batteries prepared using the carbon material-coated silicon particles of Example 1 (weight increase start temperature: 700 ° C.) and Example 2 (weight increase start temperature: 800 ° C.), Comparative Example 1 ( It was confirmed that the cycle characteristics were improved as compared with the battery (weight increase start temperature: less than 500 ° C.).
　（実施例３）
　シリコン粒子として、平均粒子径が３μｍのシリコン粒子（Ｓｉｇｍａ－Ａｌｄｒｉｃｈ社製）を用いたこと以外は、実施例１と同様にして、シリコン粒子の表面が薄片化黒鉛により被覆されている炭素材料被覆シリコン粒子を得た。なお、実施例１と同様にして熱重量分析測定を行ったところ、実施例３で得られた粒子では、重量増加開始温度が８００℃付近であった。 (Example 3)
A carbon material coating in which the surface of the silicon particles is coated with flaky graphite in the same manner as in Example 1 except that silicon particles having an average particle diameter of 3 μm (manufactured by Sigma-Aldrich) are used as the silicon particles. Silicon particles were obtained. When the thermogravimetric analysis measurement was performed in the same manner as in Example 1, the weight increase start temperature of the particles obtained in Example 3 was around 800 ° C.
　（比較例２）
　シリコン粒子（Ｓｉｇｍａ－Ａｌｄｒｉｃｈ社製、平均粒子径：３μｍ）をそのまま用いた。なお、比較例１と同様にして熱重量分析測定を行ったところ、比較例２の粒子では、重量増加開始温度が約３５０℃であった。 (Comparative Example 2)
Silicon particles (manufactured by Sigma-Aldrich, average particle size: 3 μm) were used as they were. When the thermogravimetric analysis measurement was performed in the same manner as in Comparative Example 1, the weight increase start temperature of the particles of Comparative Example 2 was about 350 ° C.
　（サイクル特性）
　実施例３で得られた炭素材料被覆シリコン粒子及び比較例２のシリコン粒子を用いて、以下のようにして、全固体電池におけるサイクル特性の評価を行った。 (Cycle characteristics)
Using the carbon material-coated silicon particles obtained in Example 3 and the silicon particles of Comparative Example 2, the cycle characteristics of the all-solid-state battery were evaluated as follows.
　固体電解質層：
　固体電解質（７５Ｌｉ２Ｓ－２５Ｐ２Ｓ５）８０ｍｇを圧粉型全固体電池のセル内筒部（直径１０ｍｍ）に充填し、平らにならした後、５０ＭＰａのプレス圧で軽くプレス処理を施し、予備成型を行った。 Solid electrolyte layer:
80 mg of solid electrolyte (75Li 2 S-25P 2 S 5 ) was filled into the cell inner cylinder (diameter 10 mm) of the powder type all-solid-state battery, flattened, and then lightly pressed with a press pressure of 50 MPa. Pre-molding was performed.
　作用極；
　得られた炭素材料被覆シリコン粒子又はシリコン粒子と、固体電解質（７５Ｌｉ２Ｓ－２５Ｐ２Ｓ５）と、導電助剤としてのアセチレンブラック（デンカ社製、品番「ＤｅｎｋａブラックＬｉ－１００」）との重量比が、５６：４２：２（重量％）となるように、乳鉢により十分に混合した。得られた混合粉末（３ｍｇ）を、上記で予備成型した固体電解質上に散布し、圧力３３０Ｍｐａでプレス成形することによって、作用極と固体電解質層の積層体をセル内筒内で作製した。 Working pole;
The obtained carbon material-coated silicon particles or silicon particles, a solid electrolyte (75Li 2 S-25P 2 S 5 ), and acetylene black as a conductive auxiliary agent (manufactured by Denka Co., Ltd., product number "Denka Black Li-100"). The mixture was sufficiently mixed in a dairy pot so that the weight ratio was 56:42: 2 (% by weight). The obtained mixed powder (3 mg) was sprayed on the solid electrolyte premolded above, and press-molded at a pressure of 330 MPa to prepare a laminate of the working electrode and the solid electrolyte layer in the inner cylinder of the cell.
　対極；
　対極として、Ｌｉ－Ｉｎを用い、固体電解質を介して作用極の反対側から、固体電解質上にＬｉ－Ｉｎがくるように配置した。 Opposite;
Li-In was used as the counter electrode, and Li-In was arranged so as to come on the solid electrolyte from the opposite side of the working electrode via the solid electrolyte.
　上記のようにして得られた作用極、固体電解質層、及び対極を用いて、圧粉型セルを作製した。圧粉型セルにおいては、作用極、固体電解質層、及び対極の順に積層した。セル構築時のプレス圧は、３３０ＭＰａとした。また、電極面積は、セルの内筒直径と同じ、０．７８５ｃｍ２（φ１０ｍｍ）とした。 A powder-type cell was prepared using the working electrode, the solid electrolyte layer, and the counter electrode obtained as described above. In the powder type cell, the working electrode, the solid electrolyte layer, and the counter electrode were laminated in this order. The press pressure at the time of cell construction was 330 MPa. The electrode area was 0.785 cm 2 (φ10 mm), which is the same as the inner cylinder diameter of the cell.
　充放電試験；
　上記のようにして組み立てた圧粉型セルにおいて、電位が－０．６Ｖ～０．９Ｖ（ｖｓ．Ｌｉ－Ｉｎ）の範囲で、充放電テストを行った（充放電試験装置：北斗電工社製、商品名「ＨＪ１００１ＳＤ８」）。具体的には、電流密度０．８９８ｍＡ／ｃｍ２（０．１Ｃ）で５回、電流密度０．０８９８ｍＡ／ｃｍ２（０．０１Ｃ）で５回、電流密度０．８９８ｍＡ／ｃｍ２（０．１Ｃ）で３０回、サイクル特性を評価した。 Charge / discharge test;
In the powder type cell assembled as described above, a charge / discharge test was performed in a potential range of -0.6 V to 0.9 V (vs. Li-In) (charge / discharge test device: manufactured by Hokuto Denko Co., Ltd.). , Product name "HJ1001SD8"). Specifically, the current density is 0.898 mA / cm 2 (0.1 C) 5 times, the current density 0.0898 mA / cm 2 (0.01 C) is 5 times, and the current density 0.898 mA / cm 2 (0. The cycle characteristics were evaluated 30 times in 1C).
　図１６は、実施例３で得られた炭素材料被覆シリコン粒子及び比較例２のシリコン粒子をそれぞれ用いて作製した全固体電池のサイクル特性の結果を示す図である。なお、図１６において、縦軸は、容量（ｍＡｈ／ｇ）を示している。また、実線で充電（Ｌｉ放出）評価の結果を示しており、破線で放電（Ｌｉ挿入）評価の結果を示している。 FIG. 16 is a diagram showing the results of cycle characteristics of an all-solid-state battery produced by using the carbon material-coated silicon particles obtained in Example 3 and the silicon particles of Comparative Example 2, respectively. In FIG. 16, the vertical axis indicates the capacity (mAh / g). The solid line shows the result of charge (Li release) evaluation, and the broken line shows the result of discharge (Li insertion) evaluation.
　図１６より、実施例３の炭素材料被覆シリコン粒子（重量増加開始温度：８００℃）を用いて作製した電池では、比較例２（重量増加開始温度：３５０℃）の電池と比較して、容量が高く、サイクル特性が向上することが確認できた。 From FIG. 16, the capacity of the battery produced by using the carbon material-coated silicon particles of Example 3 (weight increase start temperature: 800 ° C.) is higher than that of the battery of Comparative Example 2 (weight increase start temperature: 350 ° C.). It was confirmed that the temperature was high and the cycle characteristics were improved.
１…炭素材料被覆シリコン粒子
２…シリコン粒子
２ａ…表面
３…被覆層
１０…容器
１１…黒鉛
１１ａ…薄片化黒鉛
１２…液状樹脂
１３…ボール 1 ... Carbon material-coated silicon particles 2 ... Silicon particles 2a ... Surface 3 ... Coating layer 10 ... Container 11 ... Graphite 11a ... Flaked graphite 12 ... Liquid resin 13 ... Balls

Claims (10)

  1. 　炭素材料により被覆されている、炭素材料被覆シリコン粒子であって、
    　シリコン粒子と、
    　前記シリコン粒子の表面における少なくとも一部を被覆しており、かつ薄片化黒鉛を含む、被覆層と、
    を備え、
    　空気雰囲気下及び昇温速度１０℃／分の条件で、前記炭素材料被覆シリコン粒子の熱重量分析をしたときに、重量増加開始温度が、５００℃以上である、炭素材料被覆シリコン粒子。     Carbon material-coated silicon particles coated with a carbon material.
    With silicon particles
    A coating layer that covers at least a part of the surface of the silicon particles and contains flaky graphite.
    With
    Carbon material-coated silicon particles having a weight increase start temperature of 500 ° C. or higher when thermogravimetric analysis of the carbon material-coated silicon particles is performed under an air atmosphere and a heating rate of 10 ° C./min.
  2. 　前記シリコン粒子が、Ｓｉ又はＳｉの化合物からなる、請求項１に記載の炭素材料被覆シリコン粒子。 The carbon material-coated silicon particles according to claim 1, wherein the silicon particles are made of Si or a compound of Si.
  3. 　前記シリコン粒子の平均粒子径が、２０ｎｍ以上、２０μｍ以下である、請求項１又は２に記載の炭素材料被覆シリコン粒子。 The carbon material-coated silicon particles according to claim 1 or 2, wherein the average particle size of the silicon particles is 20 nm or more and 20 μm or less.
  4. 　前記炭素材料被覆シリコン粒子のＸ線回折スペクトルを測定したときに、グラフェン積層構造に由来するピークの高さａと、前記シリコン粒子に由来するピークの高さｂとの比ａ／ｂが、０．０１以上、２以下である、請求項１～３のいずれか１項に記載の炭素材料被覆シリコン粒子。 When the X-ray diffraction spectrum of the carbon material-coated silicon particles was measured, the ratio a / b of the peak height a derived from the graphene laminated structure to the peak height b derived from the silicon particles was 0. The carbon material-coated silicon particles according to any one of claims 1 to 3, which are 0.01 or more and 2 or less.
  5. 　前記シリコン粒子の表面における５０％以上が、前記被覆層により被覆されている、請求項１～４のいずれか１項に記載の炭素材料被覆シリコン粒子。 The carbon material-coated silicon particles according to any one of claims 1 to 4, wherein 50% or more of the surface of the silicon particles is coated with the coating layer.
  6. 　前記炭素材料被覆シリコン粒子における前記炭素材料による被覆層の厚みが、３０ｎｍ以下である、請求項１～５のいずれか１項に記載の炭素材料被覆シリコン粒子。 The carbon material-coated silicon particles according to any one of claims 1 to 5, wherein the thickness of the coating layer made of the carbon material in the carbon material-coated silicon particles is 30 nm or less.
  7. 　前記炭素材料による被覆層が、薄片化されていない黒鉛をさらに含む、請求項１～６のいずれか１項に記載の炭素材料被覆シリコン粒子。 The carbon material-coated silicon particles according to any one of claims 1 to 6, wherein the coating layer made of the carbon material further contains graphite that has not been sliced.
  8. 　前記炭素材料による被覆層が、アモルファスカーボンをさらに含む、請求項１～７のいずれか１項に記載の炭素材料被覆シリコン粒子。 The carbon material-coated silicon particles according to any one of claims 1 to 7, wherein the coating layer made of the carbon material further contains amorphous carbon.
  9. 　請求項１～８のいずれか１項に記載の炭素材料被覆シリコン粒子を含む、蓄電デバイス用電極。 An electrode for a power storage device containing the carbon material-coated silicon particles according to any one of claims 1 to 8.
  10. 　請求項９に記載の蓄電デバイス用電極を備える、蓄電デバイス。 A power storage device including the electrode for the power storage device according to claim 9.
PCT/JP2021/000055 2020-01-07 2021-01-05 Carbon material-coated silicon particles, electrode for electricity storage devices, and electricity storage device WO2021141014A1 (en)

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