WO2013141230A1 - 多孔質シリコン粒子及び多孔質シリコン複合体粒子 - Google Patents

多孔質シリコン粒子及び多孔質シリコン複合体粒子 Download PDF

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WO2013141230A1
WO2013141230A1 PCT/JP2013/057780 JP2013057780W WO2013141230A1 WO 2013141230 A1 WO2013141230 A1 WO 2013141230A1 JP 2013057780 W JP2013057780 W JP 2013057780W WO 2013141230 A1 WO2013141230 A1 WO 2013141230A1
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silicon
particles
fine particles
particle
porous
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PCT/JP2013/057780
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English (en)
French (fr)
Japanese (ja)
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吉田　浩一
春彦 瀬川
俊夫 谷
西村　健
秀実 加藤
武 和田
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古河電気工業株式会社
株式会社東北テクノアーチ
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Priority to KR1020147019867A priority Critical patent/KR101625779B1/ko
Priority to CN201380010929.6A priority patent/CN104125927B/zh
Publication of WO2013141230A1 publication Critical patent/WO2013141230A1/ja

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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B33/00—Silicon; Compounds thereof
    • C01B33/02—Silicon
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
    • C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
    • C09C1/28—Compounds of silicon
    • C09C1/30—Silicic acid
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B21/00—Unidirectional solidification of eutectic materials
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/02—Elements
    • C30B29/06—Silicon
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-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
    • H01G11/50—Electrodes characterised by their material specially adapted for lithium-ion capacitors, e.g. for lithium-doping or for intercalation
    • 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
    • H01M4/362—Composites
    • 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
    • H01M4/386—Silicon or alloys based on silicon
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/40—Electric properties
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • 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
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • 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 porous silicon particles used for negative electrodes for lithium ion batteries.
  • the porous silicon particles according to the present invention can be used for capacitors, lithium ion capacitors, and silicon semiconductors for solar cells.
  • lithium ion batteries using various carbon-based materials such as natural graphite, artificial graphite, amorphous carbon, and mesophase carbon, lithium titanate, tin alloy, and the like as a negative electrode active material have been put into practical use.
  • a negative electrode is formed by kneading a negative electrode active material, a conductive aid such as carbon black, and a resin binder to prepare a slurry, and applying and drying on a copper foil. Yes.
  • a technique of using silicon as a negative electrode material for a lithium battery by mechanically pulverizing silicon to a size of several micrometers and applying a conductive material thereto (for example, patent document) 1) is known.
  • a method of forming a groove such as a slit by anodizing a silicon substrate a method of crystallizing fine silicon in a ribbon-shaped bulk metal (for example, , See Patent Document 2).
  • polymer particles such as polystyrene and PMMA are deposited on a conductive substrate, a metal alloying with lithium is plated on the conductive substrate, and then the polymer particles are removed to remove a porous metal (porous)
  • a technique for example, Patent Document 3 for producing a material is also known.
  • a technique for example, see Patent Documents 4 and 5 in which a material corresponding to a Si intermediate alloy which is an intermediate product of the present invention is used as a negative electrode material for a lithium battery is known.
  • a technique for example, see Patent Document 6) in which this is heat-treated and used as a negative electrode material for a lithium battery is known.
  • Patent Document 7 there is a technique (see, for example, Patent Document 7) in which element M is completely eluted and removed with an acid or alkali from a Si alloy of element M and Si produced by applying a rapid solidification technique.
  • a technique for etching metallic silicon or silicon alloy with hydrofluoric acid or nitric acid for example, Patent Documents 8, 9, and 10.
  • Patent Document 1 is a single crystal having a size of several micrometers obtained by pulverizing single crystal silicon, and a plate or powder in which silicon atoms have a layered or three-dimensional network structure is used for the negative electrode. It is used as a substance.
  • silicon compounds silicon carbide, silicon cyanide, silicon nitride, silicon oxide, silicon boride, silicon borate, silicon boronitride, silicon oxynitride, silicon alkali metal
  • silicon compounds silicon carbide, silicon cyanide, silicon nitride, silicon oxide, silicon boride, silicon borate, silicon boronitride, silicon oxynitride, silicon alkali metal
  • silicon compounds silicon carbide, silicon cyanide, silicon nitride, silicon oxide, silicon boride, silicon borate, silicon boronitride, silicon oxynitride, silicon alkali metal
  • silicon compound group consisting of an alloy, a silicon alkaline earth metal alloy, and a silicon transition metal alloy.
  • the negative electrode active material described in Patent Document 1 is finely pulverized negative electrode active material, peeling of the negative electrode active material, generation of cracks in the negative electrode, A decrease in electrical conductivity between the active materials occurs and the capacity decreases. Therefore, there are problems that the cycle characteristics are poor and the life of the secondary battery is short.
  • silicon which is expected to be put to practical use as a negative electrode material, has a problem that cracking easily occurs and charge / discharge cycle characteristics are poor because the volume change during charge / discharge is large.
  • a negative electrode is formed by applying and drying a slurry of a negative electrode active material, a conductive additive and a binder.
  • the negative electrode active material and the current collector are bound with a binder of a resin having low conductivity, and the amount of resin used must be minimized so that the internal resistance does not increase.
  • Patent Document 3 polymer particles such as polystyrene and PMMA are deposited on a conductive substrate, a metal alloying with lithium is applied thereto by plating, and then the polymer particles are removed.
  • a metal porous body porous body
  • Si porous body there is a problem that it is extremely difficult to plate Si on polymer particles such as polystyrene and PMMA, which is not industrially applicable.
  • Patent Document 4 cools and solidifies the raw material melt constituting the alloy particles so that the solidification rate is 100 ° C./second or more, and at least partially surrounds the Si phase grains.
  • Forming a negative electrode material for a non-aqueous electrolyte secondary battery comprising: forming an alloy containing a Si-containing solid solution or an intermetallic compound phase.
  • Li reacts
  • it is necessary to diffuse and move through the included Si-containing solid solution the reactivity is poor, and further, the practical application from the point that the content of Si that can contribute to charge and discharge is small. Has not reached.
  • Patent Document 5 discloses silicon containing silicon (the silicon content is 22% by mass or more and 60% by mass or less) and one or more metal elements of copper, nickel, and cobalt. It is composed of alloy powder. By synthesizing this by a single roll method or an atomizing method, pulverization based on volume change due to occlusion / release of lithium ions or the like is suppressed.
  • this method when Li reacts, it is necessary to diffuse and move through the included Si-containing solid solution, the reactivity is poor, and further, the practical application from the point that the content of Si that can contribute to charge and discharge is small. Has not reached.
  • Patent Document 6 is selected from Si, Co, Ni, Ag, Sn, Al, Fe, Zr, Cr, Cu, P, Bi, V, Mn, Nb, Mo, In, and rare earth elements. It includes a step of rapidly cooling a molten alloy containing one or more elements and obtaining a Si-based amorphous alloy and a step of heat-treating the obtained Si-based amorphous alloy. By heat-treating the Si-based amorphous alloy, fine crystalline Si nuclei of about several tens of nm to 300 nm are precipitated.
  • this method when Li reacts, it is necessary to diffuse and move through the included Si-containing solid solution, the reactivity is poor, and further, the practical application from the point that the content of Si that can contribute to charge and discharge is small. Has not reached.
  • Patent Document 7 is applied when producing an amorphous ribbon or fine powder, and solidifies at a cooling rate of 10 4 K / second or more.
  • a cooling rate 10 4 K / second or more.
  • a special alloy system Cu-Mg system, Ni-Ti system, etc.
  • Cu-Mg system, Ni-Ti system, etc. can form an amorphous metal at 10 4 K / second or more, but other systems (eg, Si-Ni system) have a cooling rate. Even when solidified at a rate of 10 4 K / sec or more, an amorphous metal cannot be obtained and a crystalline phase is formed.
  • the size of the crystal when this crystal phase is formed follows the relationship between the cooling rate (R: K / sec) and the dendrite arm spacing (DAS: ⁇ m).
  • DAS A ⁇ R B (generally A: 40 to 100, B: ⁇ 0.3 to ⁇ 0.4) Therefore, in the case of having a crystal phase, for example, in the case of A: 60, B: ⁇ 0.35, DAS becomes 1 ⁇ m at R: 10 4 K / sec.
  • the crystal phase is equivalent to this size, and a fine crystal phase of 10 nm or the like cannot be obtained. For these reasons, it is not possible to obtain a porous material composed of a fine crystal phase with this rapid solidification technique alone with materials such as Si—Ni.
  • metal silicon is etched using hydrofluoric acid or nitric acid to create fine holes on the surface.
  • the BET specific surface area is 140 to 400 m 2 / g, which is insufficient as an active material for Si negative electrode from the viewpoint of charge / discharge response.
  • the holes formed by etching are not uniformly dispersed, and the holes are not uniformly present from the particle surface to the center. Therefore, with the volume expansion and contraction during charging / discharging, there has been a problem that pulverization progresses inside the particles and the life is short.
  • a molten silicon alloy (silicon-containing aluminum alloy) is rapidly solidified and then etched using hydrofluoric acid or nitric acid to collect fine silicon particles.
  • silicon particles preferentially crystallize during solidification by using a hypereutectic composition, and fine granular / plate-like primary silicon can be obtained by increasing the cooling rate (100 K / s). Can be made in the alloy.
  • voids may be formed by the subsequent etching process.
  • a sponge-like silicon having a co-continuous structure cannot be produced from the mechanism of this rapid solidification.
  • the present invention has been made in view of the above-described problems, and the object of the present invention is to obtain porous silicon particles suitable for a negative electrode material for a lithium ion battery that achieves high capacity and good cycle characteristics. That is.
  • the present inventor has found that a fine porous material is formed by spinodal decomposition of silicon alloy (precipitation of silicon in the molten metal from the silicon alloy) and dealloying (dealloying). It has been found that silicon can be obtained. Since silicon is deposited in the molten metal from the silicon alloy in a high-temperature molten metal, a large distribution occurs in the primary particle size between the surface layer and the inside of the porous silicon particles obtained by dealloying. Hateful. This is diffusion using molten metal as a solvent.
  • the atoms to be removed in the silicon alloy When the atoms to be removed in the silicon alloy are replaced with solvent atoms, they are immediately discharged from the diffusion interface by convection in the solvent, and the diffusion interface always has a predetermined composition. There is a certain concentration gradient due to the presence of molten metal. Therefore, since the diffusion in the silicon alloy proceeds at a constant rate, silicon atoms contributing to spinodal decomposition can be supplied at a constant rate, so that the size of the silicon fine particles is constant. Furthermore, in the porous silicon fine particles obtained by the above production method, a large distribution is hardly generated in the porosity.
  • the concentration inside the particle is restricted in the diffusion of decomponent elements, so the porosity of the particle surface layer portion increases and the porosity inside the particle decreases.
  • a Si core having no pores remains in the center of the particle, and pulverization occurs during reaction with Li, resulting in poor cycle characteristics.
  • the present invention has been made based on this finding.
  • the average x of the side is 2 nm to 2 ⁇ m
  • the particle size of the silicon fine particles, the column diameter or the standard deviation ⁇ of the column side is 1 to 500 nm
  • the shape of the silicon fine particles has a flat spherical shape, a cylindrical shape, or a polygonal column shape, and a ratio (a / b) of an average longest diameter or longest side a to an average shortest diameter or shortest side b is 1.1.
  • the average particle diameter of the porous silicon particles is 0.1 ⁇ m to 1000 ⁇ m, the average porosity of the porous silicon particles is 15 to 93%, and is 50% or more in the radial direction of the porous silicon particles.
  • Ds / Di which is a ratio of the average particle diameter Ds of the silicon fine particles in the region near the surface of the silicon particle and the average particle diameter Di of the silicon fine particles in the particle inner region within 50% in the radial direction of the porous silicon particles.
  • 0.5 to 1.5 and the porosity Xs in the region near the surface of 50% or more in the radial direction of the porous silicon particles, and the particle internal region within 50% in the radial direction of the porous silicon particles Xs / Xi, which is the ratio of the porosity Xi, is 0.5 to 1.5, and contains 80 atomic% or more of silicon in the ratio of elements excluding oxygen. Quality silicon particles.
  • the porous silicon particles are divided into a surface vicinity region S of 90% or more in the radial direction and a particle inner region I of 90% or less in the radial direction, and the silicon fine particles constituting the surface vicinity region S (1) characterized in that Es / Ei is 0.01 to 1.0 when the average particle diameter is Es and the average particle diameter of the silicon fine particles constituting the particle internal region I is Ei.
  • the porous silicon particles according to (1), wherein the silicon fine particles are solid silicon fine particles containing 80 atomic% or more of silicon in a ratio of an element excluding oxygen.
  • the porous silicon particle according to (1), wherein the area of the junction between the silicon particles is 30% or less of the surface area of the silicon particles.
  • the thickness or diameter of the joint is 80% or less of the diameter of the larger silicon fine particles of the adjacent silicon fine particles,
  • Porous silicon composite particles in which a plurality of silicon fine particles and a plurality of silicon compound particles are joined to form a continuous void, and the silicon compound particles include silicon, As, Ba, Ca, Ce, Co, Cr, Cu, Er, Fe, Gd, Hf, Lu, Mg, Mn, Mo, Nb, Nd, Ni, Os, Pr, Pt, Pu, Re, Rh, Ru, Sc, Sm, Sr, Containing a compound with one or more complex elements selected from the group consisting of Ta, Te, Th, Ti, Tm, U, V, W, Y, Yb, Zr, Alternatively, the average x of the column side is 2 nm to 2 ⁇ m, the particle size of the silicon fine particles, the column diameter or the standard deviation ⁇ of the column side is 1 to 500 nm, and the ratio of the average x to the standard deviation ⁇ ( ⁇ / x) is 0.01 to 0.5 Porous silicon composite particles characterized.
  • the shape of the silicon fine particles has a flat spherical shape, a cylindrical shape, or a polygonal column shape, and a ratio (a / b) of an average longest diameter or longest side a to an average shortest diameter or shortest side b is 1.1.
  • the porous silicon composite particles according to (9), wherein the number is from 50 to 50.
  • the porous silicon composite particles according to (9), wherein the porous silicon composite particles have an average particle size of 0.1 ⁇ m to 1000 ⁇ m.
  • the porous silicon composite particle according to (9), wherein the silicon fine particle is a solid silicon fine particle containing 80 atomic% or more of silicon in a ratio of an element excluding oxygen.
  • Solid silicon wherein the silicon compound particles have an average particle diameter of 50 nm to 50 ⁇ m, and the silicon compound particles contain 50 to 90 atomic% of silicon in a ratio of elements excluding oxygen.
  • the average particle diameter Ds of the silicon fine particles in the surface vicinity region of 50% or more in the radial direction of the porous silicon composite particles, and the particle internal region of 50% or less in the radial direction of the porous silicon composite particles The porous silicon composite particles according to (9), wherein Ds / Di, which is the ratio of the average particle diameter Di of the silicon fine particles, is 0.5 to 1.5.
  • the silicon constituting the surface vicinity region S by dividing the porous silicon composite particles into a surface vicinity region S of 90% or more in the radial direction and a particle inner region I of 90% or less in the radial direction.
  • Es / Ei is 0.01 to 1.0, where Es is the average particle size of the fine particles and Es is the average particle size of the silicon fine particles constituting the particle internal region I (9).
  • the porous silicon composite particles according to (1) In the junction between the silicon fine particles and the adjacent silicon fine particles, the thickness or radius of the joint is 80% or less of the radius of the larger silicon fine particles of the adjacent silicon fine particles.
  • porous silicon particles suitable for a negative electrode material for a lithium ion battery that achieves a high capacity and good cycle characteristics can be obtained.
  • FIG. 1 The figure which shows the porous silicon particle 1 concerning this invention
  • FIG. (b) The figure which shows the surface vicinity area
  • FIG. (A)-(c) The figure which shows the outline of the manufacturing method of the porous silicon particle 1.
  • FIG. The figure explaining the manufacturing process of the ribbon-shaped silicon intermediate alloy which concerns on this invention. The figure explaining the immersion process to the molten metal element of the ribbon-shaped silicon intermediate alloy which concerns on this invention.
  • A) The figure which shows the gas atomizer 31 which concerns on this invention,
  • (b) The figure which shows the rotary disk atomizer 41 concerning this invention.
  • (A)-(c) The figure explaining the manufacturing process of a lump silicon intermediate alloy.
  • FIGS. 5A to 5C are diagrams showing an outline of a first method for producing porous silicon composite particles 101.
  • FIGS. (A)-(c) The figure which shows the outline of the 2nd manufacturing method of the porous silicon composite particle 101.
  • FIG. The SEM photograph inside the porous silicon particle which concerns on Example 1-12. 4 is an SEM photograph of porous silicon particles according to Comparative Example 1-1.
  • FIG. 2 is an X-ray diffraction grating image of porous silicon particles according to Example 1-12.
  • 4 is a SEM photograph of the surface of porous silicon composite particles according to Example 2-1. 4 is an SEM photograph of a cross section inside the porous silicon composite particles according to Example 2-1. 4 is a SEM photograph of the surface of porous silicon composite particles according to Example 2-1. X-ray diffraction grating image of silicon fine particles of porous silicon composite particles according to Example 2-1. SEM photograph of porous silicon particles according to Example 3-7. 7 is a TEM photograph of silicon microparticles constituting the porous silicon particles according to Example 3-7.
  • FIG. 18 is a cross-sectional SEM photograph showing silicon fine particles and the second phase after immersion in molten metal in the step (b) of Example 1-15.
  • 4 is an SEM photograph of the surface of porous silicon particles in Comparative Example 2-4.
  • 3 is an SEM photograph of porous silicon particles of Example 3-1.
  • 4 is an SEM photograph of porous silicon particles of Example 3-2.
  • 4 is an SEM photograph of porous silicon particles of Comparative Example 3-3.
  • porous silicon particles (Configuration of porous silicon particles) A porous silicon particle 1 according to the present invention will be described with reference to FIG.
  • the porous silicon particles 1 are porous silicon particles having a continuous void formed by joining a plurality of silicon fine particles 3, and the shape of the silicon fine particles 3 is preferably spherical, cylindrical, or polygonal,
  • the silicon particle 3 particle diameter, column diameter or column side average x is 2 nm to 2 ⁇ m
  • the silicon particle 3 particle size, column diameter or column side standard deviation ⁇ is 1 to 500 nm, and the average x and standard deviation.
  • the ratio to ⁇ ( ⁇ / x) is 0.01 to 0.5. Since the ratio between the average x and the standard deviation ⁇ (so-called variation coefficient) is within a predetermined range, the size of the silicon fine particles 3 is uniform.
  • the shape of the silicon fine particles 3 has a flat spherical shape, cylindrical shape, or polygonal column shape, and the ratio (a / b) of the average longest diameter or longest side a of the silicon fine particles 3 to the average shortest diameter or shortest side b is 1. 1-50. Since the silicon fine particles 3 have a moderately flat shape, when the porous silicon particles 1 are used as a negative electrode active material of a lithium ion secondary battery, voids are generated when the silicon fine particles 3 expand and contract during charge / discharge. Therefore, the negative electrode is less likely to be cracked. In addition, when it is less than 1.1, cracks are likely to occur in the negative electrode due to isotropic expansion and contraction. Further, when it exceeds 50, for example, when it grows in a fiber shape, cracks are likely to occur in the negative electrode due to concentration of expansion and contraction in one direction.
  • the porous silicon particles 1 have a three-dimensional network structure having continuous voids, and are formed by bonding silicon fine particles 3, with an average particle size of 0.1 ⁇ m to 1000 ⁇ m and an average porosity of 15 to 93%. It is.
  • the porous silicon particles 1 contain 80 atomic% or more of silicon in a ratio of elements excluding oxygen, and the rest are solid particles containing intermediate alloy elements, molten metal elements, and other inevitable impurities described later. It is characterized by being.
  • the oxide layer (oxide film) on the surface of the silicon fine particles can be formed by immersing in 0.0001 to 0.1 N nitric acid after removing the second phase with hydrochloric acid or the like. Alternatively, it can also be formed by removing the second phase by distillation under reduced pressure and holding it under an oxygen partial pressure of 0.00000001 to 0.02 MPa.
  • the porous silicon particles 1 are divided into a surface vicinity region S of 50% or more in the radial direction and a particle inner region I of 50% or less in the radial direction.
  • Ds average particle size of the silicon fine particles constituting the region near the surface of the particle
  • Di average particle size of the silicon fine particles constituting the particle internal region of the porous silicon particle
  • Ds / Di is 0.5 to 1 .5.
  • the crystal grains of the intermediate alloy (FIG. 28) change through immersion in the molten metal element in step (b) described later and decomponent corrosion in step (c), the crystal of this intermediate alloy changes.
  • Porous silicon particles having a size corresponding to the grains are obtained.
  • the porous silicon particles are divided into a surface vicinity region S of 90% or more in the radial direction and a particle inner region I of 90% or less in the radial direction, and the average particle size of the silicon fine particles constituting the surface vicinity region of the porous silicon particles Es / Ei is 0.01 to 1.0, where Es is the average particle size of the silicon fine particles constituting the internal region of the porous silicon particles. That is, it is preferable that the molten metal element is not excessively immersed in the particles so that the silicon fine particles in the inner region of the porous silicon particles do not become smaller than the silicon fine particles in the region near the surface.
  • the ratio Xs / Xi which is the ratio of the porosity Xs of the near-surface region S and the porosity Xi of the particle internal region I, is 0.5 to 1.5. That is, the porous silicon particle according to the present invention has a similar pore structure in the region near the surface and the region inside the particle, and the entire particle has a substantially uniform pore structure.
  • the silicon fine particles 3 constituting the porous silicon particles 1 are single crystals having an average particle diameter or average column diameter of 2 nm to 2 ⁇ m and having a crystallinity, and a solid containing 80 atomic% or more of silicon in a ratio of elements excluding oxygen. It is a characteristic particle. Further, the silicon fine particles 3 may include a silicon alloy / intermetallic compound containing silicon.
  • the particle diameter can be measured if substantially spherical fine particles exist independently, but in the case of a substantially polygonal column shape, the diameter or one side of the column in a cross section perpendicular to the major axis. The average column diameter or average column side corresponding to is used for evaluation.
  • the three-dimensional network structure in the present invention means a structure in which pores are connected to each other, such as a co-continuous structure or a sponge structure generated in the spinodal decomposition process.
  • the pores of the porous silicon particles have a pore diameter of about 0.1 to 300 nm.
  • the average particle diameter, average column diameter, and average column side of the silicon fine particles 3 are 2 nm to 2 ⁇ m, preferably 10 to 500 nm, and more preferably 15 to 100 nm.
  • the average porosity of the porous silicon particles 1 is 15 to 93%, preferably 30 to 80%, more preferably 40 to 70%.
  • the silicon fine particles 3 are locally bonded to each other, and the area of the bonded portion of the silicon fine particles 3 is 30% or less of the surface area of the silicon fine particles. That is, the surface area of the porous silicon particles 1 is 70% or more as compared with the surface area obtained on the assumption that the silicon fine particles 3 exist independently. Furthermore, the specific surface area of the porous silicon particles 1 is 1 to 100 m 2 / g.
  • the average particle size of the fine particles here refers to the average particle size of the primary particles.
  • the particle diameter is measured by using image information of an electron microscope (SEM) and a volume-based median diameter of a dynamic light scattering photometer (DLS).
  • SEM electron microscope
  • DLS dynamic light scattering photometer
  • the particle shape is confirmed in advance using an SEM image
  • the particle size is obtained using image analysis software (for example, “A Image-kun” (registered trademark) manufactured by Asahi Kasei Engineering), or DLS ( For example, it can be measured by DLS-8000 manufactured by Otsuka Electronics Co., Ltd.
  • the average particle diameter is obtained mainly using a surface scanning electron microscope or a transmission electron microscope.
  • the average column diameter is defined as the column diameter of rod-shaped (columnar) silicon particles having an aspect ratio of 5 or more. Let the average value of this support
  • the average longest diameter and average shortest diameter of the silicon fine particles are obtained from image processing using a transmission electron microscope.
  • silicon particles pulverized in an agate mortar were diluted with a methanol solution, and this was dropped and dried on a carbon mesh-coated grid mesh ( ⁇ 3 mm), and TEM observation was performed. However, those with overlapping particles were excluded from the evaluation target. It is confirmed that there is no change in the size of the silicon fine particles between the TEM observation result and the high resolution SEM observation result.
  • the average particle size of the flat spherical particles was obtained by approximating the area of the elliptical particles as a circle, and obtaining the diameter of the particle size obtained from the circle as an equivalent circle diameter, and further calculating the average value and standard deviation statistically.
  • the major axis and minor axis of the silicon fine particles were measured by TEM observation, and the average values of these were taken as the average longest diameter and the average shortest diameter.
  • the equivalent circle diameter was calculated from each major axis and minor axis, and the average value and standard deviation were calculated as the average particle diameter and standard deviation of the fine particles.
  • the average porosity means the ratio of voids in the particles.
  • Submicron pores can be measured by nitrogen gas adsorption, but when the pore size is wide, observation with an electron microscope or mercury intrusion method (JIS R 1655 “fine mercury intrusion method of fine ceramics” Method of measuring the pore size distribution of compacts by using “Derived from the relationship between pressure and mercury volume when mercury enters the voids", Gas adsorption method (JIS Z 8830: 2001) Specific surface area of powder (solid) by gas adsorption Measurement is possible by measuring method).
  • the porous silicon particles 1 according to the present invention have an average particle diameter of 0.1 ⁇ m to 1000 ⁇ m depending on the Si concentration of the Si intermediate alloy and the cooling rate at the time of manufacturing the intermediate alloy. Note that the particle size is reduced by decreasing the Si concentration or increasing the cooling rate.
  • the average particle diameter is preferably 0.1 to 50 ⁇ m, more preferably 1 to 30 ⁇ m, and further preferably 5 to 20 ⁇ m. Therefore, when the porous silicon particles are small, they are used as aggregates or granulated bodies. Further, when the porous silicon particles are large, there is no problem even if the porous silicon particles are roughly pulverized and used.
  • the thickness or diameter of the joint is 80% or less of the diameter of the larger silicon fine particles 3 of the adjacent silicon fine particles 3.
  • the junction is made of crystalline silicon or silicon oxide.
  • the thickness of the junction or connection was also determined by observing the silicon fine particles with a TEM. In this connection thickness ratio, first, the thickness or diameter of the connection part of two bonded silicon fine particles is measured, and compared with the diameter of the larger one of the two silicon fine particles. This comparison is performed at a connecting portion of a plurality of silicon fine particles, and the average is 80% or less.
  • the plurality of silicon fine particles 3 are oriented, and the major axis directions of the plurality of silicon fine particles 3 are all within ⁇ 30 ° of a certain direction.
  • the second phase 9 is an alloy of an intermediate alloy element and a molten metal element, or is composed of a molten metal element substituted for the intermediate alloy element. These silicon fine particles 3 are bonded to each other to form a three-dimensional network structure. Thereafter, in step (c), as shown in FIG. 2 (c), when the second phase is removed by a method such as decomponent corrosion using acid or alkali, porous silicon particles joined with silicon fine particles 3 are bonded. 1 is obtained.
  • step (a) when silicon and intermediate alloy element (X) are melted and solidified, silicon intermediate alloy 7 which is an alloy of silicon and intermediate alloy element is formed.
  • step (b) when this silicon intermediate alloy is immersed in the molten element (Y) bath specified in Table 1, the molten element (Y) penetrates into the silicon intermediate alloy while diffusing, and the silicon intermediate alloy
  • the intermediate alloy element (X) therein forms the alloy layer as a second phase with the molten metal element (Y).
  • the intermediate alloy element (X) in the alloy is eluted in the metal bath of the molten element (Y), and the molten element (Y) forms a new second phase. In this reaction, silicon atoms contained in the silicon intermediate alloy are left behind.
  • the silicon primary crystal which is not an alloy in the intermediate alloy greatly affects the precipitation of silicon fine particles in the dipping step (b) and acts as a production nucleus of silicon fine particles. For this reason, silicon fine particles having a large particle diameter with this primary crystal as a nucleus can be produced. In producing silicon fine particles of 100 nm or less, it is preferable to employ a composition in which this silicon primary crystal does not exist or non-equilibrium solidification.
  • Condition 1 The melting point of the molten element (Y) is lower than the melting point of silicon by 50K or more. If the melting point of the molten element (Y) and the melting point of silicon are close, when the silicon alloy is immersed in the molten molten element, silicon is dissolved in the molten metal, so condition 1 is necessary.
  • Condition 2 Si primary crystals do not occur when silicon and intermediate alloy elements are solidified. When an alloy of silicon and intermediate alloy element (X) is formed, a coarse silicon primary crystal is formed when the hypereutectic region is reached when the silicon concentration increases.
  • This silicon crystal does not cause diffusion or re-aggregation of silicon atoms during the dipping process, and does not form a three-dimensional network structure.
  • Condition 3 The solubility of silicon in the molten metal element is lower than 5 atomic%. This is because when the intermediate alloy element (X) and the molten metal element (Y) form the second phase, it is necessary not to include silicon in the second phase.
  • Condition 4 The intermediate alloy element and the molten metal element do not separate into two phases. When the intermediate alloy element (X) and the molten metal element (Y) are separated into two phases, the intermediate alloy element is not separated from the silicon alloy, and the silicon atoms do not diffuse and re-aggregate. Furthermore, even if the treatment with an acid is performed, the intermediate alloy element remains in the silicon particles.
  • the combinations of the intermediate alloy element and the molten metal element that can be used for producing the porous silicon particles are as follows. Moreover, the ratio of silicon is 10 atomic% or more of the whole, and is below the highest value among the maximum Si contents in Table 1 below corresponding to the intermediate alloy elements.
  • the Si content is 10 to 77 atomic% with respect to the sum of Si and the intermediate alloy element, and the average porosity of the obtained porous silicon particles is 15 to 84%. is there.
  • the Si content is 10 to 82 atomic% with respect to the sum of Si and the intermediate alloy element, and the average porosity of the obtained porous silicon particles is 12 to 85%. is there.
  • the Si content is 10 to 30 atomic% with respect to the sum of Si and the intermediate alloy element, and the average porosity of the obtained porous silicon particles is 47 to 85%. is there.
  • the Si content is 10 to 67 atomic% relative to the sum of Si and the intermediate alloy element, and the average porosity of the obtained porous silicon particles is 15 to 85%. is there.
  • the Si content is 10 to 50 atomic% with respect to the sum of Si and the intermediate alloy element, and the average porosity of the obtained porous silicon particles is 42 to 92%. is there.
  • the Si content is 10 to 67 atomic% with respect to the sum of Si and the intermediate alloy element, and the average porosity of the obtained porous silicon particles is 15 to 85%. is there.
  • the Si content is 10 to 98 atomic% with respect to the sum of Si and the intermediate alloy element, and the average porosity of the obtained porous silicon particles is 15 to 88%. is there.
  • the Si content is 10 to 55 atomic% with respect to the sum of Si and the intermediate alloy element, and the average porosity of the obtained porous silicon particles is 15 to 85%. is there.
  • the Si content is 10 to 50 atomic% with respect to the sum of Si and the intermediate alloy element, and the average porosity of the obtained porous silicon particles is 48 to 93%. is there.
  • the Si content is 10 to 82 atomic% with respect to the sum of Si and the intermediate alloy element, and the average porosity of the obtained porous silicon particles is 15 to 89%. is there.
  • the Si content is 10 to 90 atomic% with respect to the sum of Si and the intermediate alloy element, and the average porosity of the obtained porous silicon particles is 15 to 92%. is there.
  • the intermediate alloy element two or more of the listed elements can be used as the intermediate alloy element.
  • the molten element corresponding to any of these intermediate alloy elements is used as the molten element.
  • the molten silicon alloy 13 is dropped from the crucible 15 using, for example, thin plate continuous casting in a twin roll casting machine or a single roll casting machine 11 as shown in FIG.
  • the silicon intermediate alloy 19 in a linear or ribbon shape is produced by solidification while in contact with the substrate.
  • the linear mother alloy may be manufactured by a direct spinning method.
  • the silicon intermediate alloy may be in the form of a foil piece having a certain length, unlike a linear shape or a ribbon shape.
  • the thickness of the linear or ribbon-like silicon intermediate alloy 19 is preferably 0.1 ⁇ m to 2 mm, more preferably 0.1 to 500 ⁇ m, and further preferably 0.1 to 50 ⁇ m.
  • the cooling rate during solidification of the silicon intermediate alloy is 0.1 K / s or more, preferably 100 K / s or more, more preferably 400 K / s or more. This contributes to shortening the heat treatment time in the next step by reducing the grain size of the primary crystal formed in the initial stage of solidification. Further, the particle diameter of the porous silicon particles is reduced proportionally by reducing the particle diameter of the primary crystal. If the thickness of the silicon alloy (intermediate alloy) is 2 mm or more, it is not preferable because the Si content is high and the toughness is poor and cracks and disconnections occur.
  • the silicon intermediate alloy was selected from Ag, Al, Au, Be, Bi, Cd, Ga, In, Pb, Sb, Sn, Tl, Zn listed in Table 1 corresponding to the intermediate alloy element used.
  • the molten metal 23 is heated to a temperature higher than the liquidus temperature of the molten element by 10K or more.
  • immersion in the molten metal 23 depends on the molten metal temperature, it is preferably 5 seconds or more and 10,000 seconds or less. This is because coarse Si grains are produced when the immersion is performed for 10,000 seconds or more. Further, only the silicon fine particles on the surface of the porous particles grow abnormally by the long immersion. Then, it is cooled in a non-oxidizing atmosphere. As described later, it is preferable that oxygen is not contained in the molten metal 23.
  • the second phase which is an alloy of the intermediate alloy element and the molten metal element or the second phase composed of the molten metal element replaced with the intermediate alloy element is dissolved and removed with at least one of an acid, an alkali and an organic solvent.
  • the step or the second phase is heated and decompressed to remove only the second phase by evaporation. By removing the second phase, porous silicon particles are obtained.
  • the acid may be any acid that dissolves the intermediate alloy element and the molten metal element and does not dissolve silicon, and examples thereof include nitric acid, hydrochloric acid, and sulfuric acid.
  • the particle diameter becomes 0.1 ⁇ m to 1000 ⁇ m. Note that the particle size is reduced by lowering the silicon concentration or increasing the cooling rate.
  • the average particle diameter is preferably 0.1 to 50 ⁇ m, more preferably 1 to 30 ⁇ m, and further preferably 5 to 20 ⁇ m.
  • porous silicon particles when the porous silicon particles are small, an aggregate or a granulated body is prepared using a conductive binder, and is used after being formed into a slurry and applied to a current collector. Further, when the porous silicon particles are large, there is no problem even if the porous silicon particles are roughly pulverized with a mortar or the like. Since the fine particles are locally joined, they can be easily crushed.
  • a powdery, granular, or massive silicon intermediate alloy may be used instead of the linear or ribbon-like silicon intermediate alloy 19.
  • Table 1 As, Ba, Ca, Ce, Co, Cr, Cu, Er, Fe, Gd, Hf, Lu, Mg, Mn, Mo, Nb, Nd, Ni, P, Pd, One or more selected from the group consisting of Pr, Pt, Pu, Re, Rh, Ru, Sc, Sm, Sr, Ta, Te, Th, Ti, Tm, U, V, W, Y, Yb, Zr A mixture in which the intermediate alloy element is blended so that the ratio of silicon is 10 to 98 atomic%, preferably 15 to 50 atomic%, is heated and melted in a vacuum furnace or a non-oxidizing atmosphere furnace. Thereafter, a method of producing a grain / powder silicon intermediate alloy by the atomizing method as shown in FIG. 5 or
  • FIG. 5 (a) shows a gas atomizing apparatus 31 capable of producing a powdered silicon intermediate alloy 39 by a gas atomizing method.
  • the crucible 33 there is silicon melted by induction heating or the like and the silicon alloy 13 of the intermediate alloy element.
  • the silicon alloy is dropped from the nozzle 35 and at the same time, a jet stream of inert gas from the gas injector 37 is blown. Then, the molten silicon alloy 13 is pulverized and solidified as droplets to form a powdery silicon intermediate alloy 39.
  • FIG. 5B shows a rotating disk atomizing device 41 that can manufacture the powdered silicon intermediate alloy 51 by the rotating disk atomizing method.
  • the crucible 43 In the crucible 43, there is dissolved silicon and the silicon alloy 13 of the intermediate alloy element. This silicon alloy is dropped from the nozzle 45, and the molten metal of the silicon alloy 13 is dropped on the rotating disk 49 that rotates at high speed, thereby tangentially.
  • a powdery silicon intermediate alloy 51 is formed by applying a shearing force in the direction and crushing.
  • FIG. 6 is a diagram illustrating a process of forming the massive silicon intermediate alloy 57 by the ingot manufacturing method.
  • the molten silicon alloy 13 is put into the mold 55 from the crucible 53. Thereafter, the silicon alloy 13 is cooled in the mold 55 and solidified, and then the mold 55 is removed to obtain a bulk silicon intermediate alloy 57. If necessary, the bulk silicon intermediate alloy 57 is crushed to obtain a granular silicon intermediate alloy.
  • the thickness of the granular silicon intermediate alloy is preferably 10 ⁇ m to 50 mm, more preferably 0.1 to 10 mm, and further preferably 1 to 5 mm.
  • the cooling rate during solidification of the silicon alloy is 0.1 K / s or more. If the thickness of the silicon intermediate alloy is increased to 50 mm or more, the heat treatment time becomes longer, which is not preferable because the particle diameter of the porous silicon particles grows and becomes coarse. In that case, this silicon intermediate alloy can be dealt with by mechanically grinding it to 50 mm or less.
  • the silicon intermediate alloy was selected from Ag, Al, Au, Be, Bi, Cd, Ga, In, Pb, Sb, Sn, Tl, Zn listed in Table 1 corresponding to the intermediate alloy element used. It is immersed in the molten metal element to form a spinodal decomposition of silicon and a second phase which is an alloy of the intermediate alloy element and the molten element element.
  • the oxygen in the molten metal is desirably reduced in advance to 100 ppm or less, preferably 10 ppm or less, more preferably 2 ppm or less. This is because dissolved oxygen in the molten metal reacts with silicon to form silica, and with this as a nucleus, silicon grows in a facet shape and becomes coarse.
  • a countermeasure it can be reduced by a solid reducing material such as charcoal / graphite or a non-oxidizing gas, or an element having a strong affinity for oxygen may be added in advance. Silicon particles are formed for the first time in this dipping process.
  • a solid reducing material such as charcoal / graphite or a non-oxidizing gas, or an element having a strong affinity for oxygen may be added in advance. Silicon particles are formed for the first time in this dipping process.
  • a molten silicon immersion device 61 as shown in FIG. 7A is used, and the granular silicon intermediate alloy 63 is placed in a dipping bowl 65 and dipped in a molten metal 69 of a molten element.
  • the pressing cylinder 67 is moved up and down to give mechanical vibration to the silicon intermediate alloy or molten metal, or to give vibration by ultrasonic waves, as shown in FIG.
  • the reaction can be advanced in a short time by stirring the molten metal using mechanical stirring using the mechanical stirrer 81 and gas injection using the gas blowing plug 83 or electromagnetic force. Then, it is pulled up in a non-oxidizing atmosphere and cooled.
  • the molten metal 69 or 79 is heated to a temperature higher than the liquidus temperature of the molten element by 10K or more.
  • the immersion in the molten metal depends on the molten metal temperature, but is preferably 5 seconds or longer and 10,000 seconds or shorter. This is because coarse Si grains are produced when immersion is performed for 10,000 seconds or more. Further, only the silicon fine particles on the surface of the porous particles grow abnormally by the long immersion.
  • porous silicon particles having an unprecedented three-dimensional network structure can be obtained.
  • porous silicon particles having a substantially uniform pore structure can be obtained. This is because precipitation of silicon fine particles from the silicon intermediate alloy in the molten metal is performed in the molten metal at a high temperature, so that the molten metal penetrates into the particles.
  • porous silicon particles according to the present invention are used as a negative electrode active material of a lithium ion battery, a high capacity and long life negative electrode can be obtained.
  • porous silicon composite particles (Configuration of porous silicon composite particles)
  • the porous silicon composite particles according to the present invention will be described with reference to FIG.
  • the porous silicon composite particles 101 according to the present invention are formed by bonding silicon fine particles 103 and silicon compound particles 105, and the average particle size of the porous silicon composite particles 101 is zero.
  • the average porosity of the porous silicon composite particles 101 is 15 to 93% and has a three-dimensional network structure composed of continuous voids.
  • the three-dimensional network structure in the present invention means a structure in which pores are connected to each other, such as a co-continuous structure or a sponge structure generated in the spinodal decomposition process.
  • the pores of the porous silicon composite particles have a pore diameter of about 0.1 to 300 nm.
  • Xs / Xi which is the ratio of the porosity Xs of the region near the surface of 50% or more in the radial direction and the porosity Xi of the particle internal region within 50% in the radial direction, is 0.00. 5 to 1.5.
  • the porous silicon composite particles according to the present invention have the same pore structure in the surface vicinity region and the particle internal region, and the whole particle has a substantially uniform pore structure.
  • the porosity Xs can be obtained by SEM observation of the surface of the porous silicon composite particle 101, and the porosity Xi is obtained by observing a portion corresponding to the particle internal region in the cross section of the porous silicon composite particle 101 by SEM. Can be obtained.
  • the crystal grains of the intermediate alloy correspond to the crystal grains of the intermediate alloy while changing through immersion in the molten metal element in the step (b) described later and decomponent corrosion in the step (c).
  • a porous silicon composite particle having a size (not pulverized by pulverization or the like) was obtained.
  • the porous silicon composite particles 101 are divided into a surface vicinity region S of 90% or more in the radial direction and a particle inner region I of 90% or less in the radial direction, and the average particle size of the silicon fine particles 103 constituting the surface vicinity region S
  • Es and the average particle diameter of the silicon fine particles 103 constituting the particle internal region I is Ei
  • Es / Ei is preferably 0.01 to 1.0.
  • the silicon fine particles 103 have an average particle diameter or one side of the average support column of 2 nm to 2 ⁇ m, preferably 10 to 500 nm, more preferably 20 to 300 nm.
  • the average porosity is 15 to 93%, preferably 50 to 80%, more preferably 60 to 70%.
  • the crystal structure of each silicon fine particle 103 is a single crystal having crystallinity.
  • the silicon fine particles 103 contain 80 atomic% or more of silicon in a ratio of elements excluding oxygen, and the remainder are solid fine particles containing an intermediate alloy element, a molten metal element, and other inevitable impurities described later.
  • the shape of the silicon fine particles 103 is spherical or polygonal, the particle size of the silicon fine particles 103, the average diameter of the support pillars or the support pillar side x is 2 nm to 2 ⁇ m, and the diameter of the silicon fine particles 103, the standard of the support pillar diameter or the support pillar side
  • the deviation ⁇ is 1 to 500 nm, and the ratio ( ⁇ / x) between the average x and the standard deviation ⁇ is 0.01 to 0.5.
  • the shape of the silicon fine particles 103 has a flat spherical shape, a cylindrical shape, or a polygonal column shape, and the ratio (a / b) of the average longest diameter or longest side a to the average shortest diameter or shortest side b is 1.1 to 1.1. 50.
  • the porous silicon composite particles 101 are divided into a surface vicinity region S of 50% or more in the radial direction and a particle inner region I of 50% or less in the radial direction.
  • Ds / Di where Ds is the average particle size of the silicon fine particles constituting the region near the surface of the porous silicon composite particles, and Di is the average particle size of the silicon fine particles constituting the particle internal region of the porous silicon composite particles Is 0.5 to 1.5.
  • the average particle diameter Ds can be obtained by observing the surface of the porous silicon composite particle 1 with an SEM, and the average particle diameter Di is obtained by SEM of a cross section of a portion corresponding to the particle internal region of the porous silicon composite particle 1. It can be obtained by observation.
  • the silicon compound particles 105 have an average particle size of 50 nm to 50 ⁇ m, preferably 100 nm to 20 ⁇ m, and more preferably 200 nm to 10 ⁇ m.
  • As Ba, Ca, Ce, Co, Cr, Cu, Er, Fe, Gd, Hf, Lu, Mg, Mn, Mo, Nb, Nd, Ni, Os, Pr, Pt, Pu
  • One or more complex elements selected from the group consisting of: Re, Rh, Ru, Sc, Sm, Sr, Ta, Te, Th, Ti, Tm, U, V, W, Y, Yb, Zr; It is a particle having solid crystallinity composed of 50 to 75 atomic% of silicon and an intermediate alloy element, a molten metal element, and other inevitable impurities described later.
  • the silicon compound particles 105 are larger than the silicon fine particles 103.
  • the surface of the porous silicon composite particle 101 that is, the silicon fine particle 103 or the silicon compound particle 105 has an oxide having a thickness of 20 nm or less or a particle size ratio of each silicon fine particle 103 or silicon compound particle 105 of 10% or less. Even if the layer is formed, there is no problem in characteristics.
  • the oxide layer on the surface of the porous silicon composite particles 101 can be formed by immersing in 0.0001 to 0.1 N nitric acid after removing the second phase. Alternatively, it can also be formed by holding under an oxygen partial pressure of 0.00000001 to 0.02 MPa after removing the second phase. When the oxide layer such as silicon is formed, the porous silicon composite particles 101 become extremely stable in the air and do not need to be handled in a glove box or the like.
  • the average particle size of the particles refers to the average particle size of the primary particles.
  • the particle diameter is measured by using image information of an electron microscope (SEM) and a volume-based median diameter of a dynamic light scattering photometer (DLS).
  • SEM electron microscope
  • DLS dynamic light scattering photometer
  • the particle shape is confirmed in advance using an SEM image
  • the particle size is obtained using image analysis software (for example, “A Image-kun” (registered trademark) manufactured by Asahi Kasei Engineering), or DLS ( For example, it can be measured by DLS-8000 manufactured by Otsuka Electronics Co., Ltd.
  • the average particle diameter is obtained mainly using a surface scanning electron microscope or a transmission electron microscope.
  • the average column diameter is defined as the column diameter of rod-shaped (columnar) silicon particles having an aspect ratio of 5 or more. Let the average value of this support
  • the average porosity means the ratio of voids in the particles.
  • Submicron pores can be measured by nitrogen gas adsorption method, but when the pore size is wide, electron microscope observation or mercury intrusion method (JIS R 1655 “fine ceramics mercury intrusion method” It is possible to measure by, for example, “a method for measuring the pore size distribution of a molded body”, derived from the relationship between pressure and mercury volume when mercury enters the void).
  • the BET specific surface area can be measured by a nitrogen gas adsorption method.
  • the porous silicon composite particles 101 according to the present invention have a particle size of 0.1 ⁇ m to 1000 ⁇ m depending on the Si concentration of the Si intermediate alloy and the cooling rate when manufacturing the intermediate alloy. Note that the particle size is reduced by decreasing the Si concentration or increasing the cooling rate.
  • the average particle diameter is preferably 0.1 to 50 ⁇ m, more preferably 1 to 30 ⁇ m, and further preferably 5 to 20 ⁇ m. For this reason, when the porous silicon composite particles are small, they are used as aggregates or granules. Further, when the porous silicon composite particles are large, there is no problem even if the porous silicon composite particles are roughly pulverized and used.
  • the thickness or diameter of the joint is 80% or less of the diameter of the larger silicon fine particles 103 of the adjacent silicon fine particles 103.
  • the plurality of silicon fine particles 103 are oriented, and the major axis directions of the plurality of silicon fine particles 103 are all within ⁇ 30 ° of a certain direction.
  • the measurement was performed based on, for example, SEM images as shown in FIGS. 22 and 23, and the orientation angle was defined by the magnitude of the deviation from the average value of the growth direction angles.
  • the silicon intermediate alloy 107 is immersed in the molten metal element.
  • the molten metal element penetrates into the silicon intermediate alloy 107.
  • the intermediate alloy element forms an alloy solid phase with the molten element, and further forms a liquid phase when the molten element permeates. Silicon atoms and complex elements are left in the liquid phase region.
  • the silicon fine particles 103 are precipitated, and an alloy network of silicon atoms and the composite element is formed, and a three-dimensional network structure is formed. That is, as shown in FIG.
  • the intermediate alloy element of the silicon intermediate alloy 107 is eluted into the molten metal to form the second phase 109 and silicon is precipitated as silicon fine particles 103.
  • the second phase 109 is an alloy of an intermediate alloy element and a molten element, or is composed of a molten element substituted for the intermediate alloy element.
  • the silicon compound particles 105 remain as they are without being influenced by the molten metal. These silicon fine particles 103 and silicon compound particles 105 are bonded to each other to form a three-dimensional network structure.
  • the silicon primary crystal of silicon alone or the compound of silicon and the complex element does not cause reaggregation of the silicon atom or complex element even if the molten metal penetrates,
  • the silicon primary crystal and the compound of the complex element remain as they are.
  • Condition 1 The melting point of the molten element is lower than the melting point of silicon by 50K or more. If the melting point of the molten element and the melting point of silicon are close, when the silicon intermediate alloy is immersed in the molten molten element, silicon is dissolved in the molten metal, so condition 1 is necessary.
  • Condition 2 Si primary crystals do not occur when silicon and intermediate alloy elements are solidified. When forming an alloy of silicon and an intermediate alloy element, when the silicon concentration increases, a coarse silicon primary crystal is formed in the hypereutectic region.
  • This silicon primary crystal does not cause diffusion or re-aggregation of silicon atoms during the dipping process, and does not form a three-dimensional network structure.
  • Condition 3 The solubility of silicon in the molten metal element is lower than 5 atomic%. This is because when the intermediate alloy element and the molten metal element form the second phase, it is necessary to prevent silicon from being included in the second phase.
  • Condition 4 The intermediate alloy element and the molten metal element do not separate into two phases. When the intermediate alloy element and the molten metal element are separated into two phases, the intermediate alloy element is not separated from the silicon intermediate alloy, and silicon atoms do not diffuse and reaggregate. Furthermore, even if the treatment with an acid is performed, the intermediate alloy element remains in the silicon particles.
  • Condition 5 Silicon and complex elements do not separate into two phases. In the case where silicon and the composite element are easily separated into two phases, finally, silicon compound particles composed of an alloy of silicon and the composite element cannot be obtained.
  • Condition 6 The intermediate alloy element corresponding to the molten metal element does not include a complex element in the selectable elements.
  • the composite element is an element that can be selected as an intermediate alloy element and has the characteristics of the intermediate alloy element as described above, when the molten metal element and the composite element form the second phase and the treatment with the acid is performed The complex element is removed.
  • the combination of the intermediate alloy element, the composite element, and the molten metal element that can be used for producing the porous silicon composite and the porosity of the obtained porous silicon composite are: It becomes as follows.
  • the ratio of the composite element is 1 to 33 atomic% of silicon.
  • the ratio of silicon is 10 atomic% or more with respect to the sum of silicon, the intermediate alloy element, and the complex element, and the value of the maximum Si content in Table 2 below corresponding to the intermediate alloy element (a plurality of intermediate elements)
  • the maximum Si content in Table 2 corresponding to each intermediate alloy element is a value that is prorated according to the ratio of the intermediate alloy element) or less.
  • a composite element and a molten element that can be used in common with each intermediate alloy element are used.
  • X atomic%), an intermediate alloy element (Y atomic%), and one or more complex elements Z 1 , Z 2 , Z 3 ,... Atomic%)
  • Y atom% is the sum of the ratios of the plurality of intermediate alloy elements.
  • silicon one or more intermediate alloy elements selected from the group consisting of Co, Cr, Cu, Fe, Mg, Mn, Mo, Ni, P, Ti, and Zr described in Table 2, and intermediate alloy elements
  • a mixture containing silicon, intermediate alloy elements, and composite elements is heated and melted in a vacuum furnace or the like.
  • an alloy of silicon and an intermediate alloy element and a compound of silicon and a complex element are formed.
  • the molten silicon alloy 13 is dropped from the crucible 15 and solidified while in contact with the rotating steel roll 17 to form a ribbon-like silicon intermediate alloy 19.
  • a linear silicon intermediate alloy is manufactured.
  • the cooling rate during solidification of the silicon intermediate alloy is 10 K / s or more, preferably 100 K / s or more, more preferably 200 K / s or more. This increase in the cooling rate contributes to reducing the size of silicon compound particles generated in the initial stage of solidification microscopically. Making the size of the silicon compound particles fine contributes to shortening the heat treatment time in the next step.
  • the thickness of the ribbon-like silicon intermediate alloy 19 or the linear silicon intermediate alloy is 0.1 ⁇ m to 2 mm, preferably 0.1 to 500 ⁇ m, and more preferably 0.1 to 50 ⁇ m.
  • the silicon intermediate alloy may be in the form of a foil piece having a certain length, unlike a linear shape or a ribbon shape.
  • the average size of the microstructure of the intermediate alloy is desirably 0.1 ⁇ m to 1 mm, preferably 0.1 to 500 ⁇ m, and more preferably 0.1 to 300 ⁇ m. This is because the bath element preferentially diffuses in the crystal grain boundary when it is immersed in the molten metal bath in the step (b), and then diffuses in the grain boundary.
  • the silicon intermediate alloy is made of at least one of Ag, Al, Au, Be, Bi, Cd, Ga, In, Pb, Sb, Sn, Tl, and Zn corresponding to the intermediate alloy elements described in Table 2.
  • Si is spinodal decomposed to form a second phase that is an alloy of the intermediate alloy element and the molten element or a second phase composed of the molten element replaced with the intermediate alloy element.
  • a ribbon-like silicon intermediate alloy 19 or a linear silicon intermediate alloy is dipped in a molten metal 23 of a molten element using a molten metal immersion device 21 as shown in FIG.
  • the molten metal 23 is heated to a temperature higher than the liquidus temperature of the molten element by 10K or more. Although immersion in the molten metal 23 depends on the molten metal temperature, it is preferably 5 seconds or more and 10,000 seconds or less. This is because coarse Si grains are produced when immersion is performed for 10,000 seconds or more. Further, only the silicon fine particles on the surface of the porous particles grow abnormally by the long immersion.
  • the ribbon-like silicon intermediate alloy 19 after the immersion is cooled in a non-oxidizing atmosphere to obtain a composite of the silicon fine particles 103, the silicon compound particles 105, and the second phase 109.
  • the second phase 109 which is an alloy of the intermediate alloy element and the molten element, or the second phase 109 composed of the molten element replaced with the intermediate alloy element is dissolved in at least one of an acid, an alkali, and an organic solvent. Then, only the second phase 109 is removed and washed and dried.
  • the acid may be any acid that dissolves the intermediate alloy element and the molten metal element and does not dissolve silicon, and examples thereof include nitric acid, hydrochloric acid, and sulfuric acid.
  • the second phase 109 is heated and decompressed to remove only the second phase by evaporation.
  • a coarse aggregate of the porous silicon composite particles 101 is obtained, so that the average particle diameter of the aggregate becomes 0.1 ⁇ m to 20 ⁇ m by pulverizing with a ball mill or the like.
  • a silicon intermediate alloy in the form of a powder, a particle, or a lump may be used in place of the linear or ribbon-like silicon intermediate alloy 19.
  • silicon one or more intermediate alloy elements selected from the group consisting of Co, Cr, Cu, Fe, Mg, Mn, Mo, Ni, P, Ti, and Zr described in Table 2, and intermediate alloy elements Using a corresponding one or more complex elements shown in Table 2, a mixture containing silicon, intermediate alloy elements, and complex elements is heated and melted in a vacuum furnace or the like.
  • a massive ingot is obtained by a method of producing a substantially spherical particle / powdered silicon intermediate alloy by an atomizing method as shown in FIGS. 5A and 5B or by an ingot producing method shown in FIG. If necessary, a powdery, granular or massive silicon intermediate alloy is produced by a mechanical pulverization method.
  • FIG. 5 (a) shows a gas atomizing apparatus 31 capable of producing a powdered silicon intermediate alloy 39 by a gas atomizing method.
  • the crucible 33 there is a silicon alloy 13 of silicon, an intermediate alloy element, and a composite element dissolved by induction heating or the like.
  • the silicon alloy 13 is dropped from the nozzle 35 and at the same time, a jet gas 36 such as an inert gas or air is ejected.
  • the gas jet flow 38 from the gas injector 37 supplied with is sprayed, the molten metal of the silicon alloy 13 is crushed and solidified as droplets to form a powdered silicon intermediate alloy 39.
  • FIG. 5B shows a rotating disk atomizing device 41 that can manufacture the powdered silicon intermediate alloy 51 by the rotating disk atomizing method.
  • the crucible 43 In the crucible 43, there is a silicon alloy 13 of dissolved silicon, intermediate alloy element, and complex element. This silicon alloy is dropped from the nozzle 45, and the molten silicon alloy 13 is dropped onto a rotating disk 49 that rotates at high speed. Then, a shearing force is applied in the tangential direction to crush and form a powdery silicon intermediate alloy 51.
  • FIG. 6 is a diagram illustrating a process of forming the massive silicon intermediate alloy 57 by the ingot manufacturing method.
  • the molten silicon alloy 13 is put into the mold 55 from the crucible 53. Thereafter, the silicon alloy 13 is cooled in the mold 55 and solidified, and then the mold 55 is removed to obtain a bulk silicon intermediate alloy 57.
  • the bulk silicon intermediate alloy 57 may be used as it is, or may be pulverized as necessary and used as a granular silicon intermediate alloy.
  • the particle size of the powdery, granular or massive silicon intermediate alloy is preferably 10 ⁇ m to 50 mm, more preferably 0.1 to 10 mm, and further preferably 1 to 5 mm.
  • the cooling rate during solidification of the silicon alloy is 0.1 K / s or more. If the thickness of the silicon intermediate alloy is increased to 50 mm or more, the heat treatment time becomes longer, which is not preferable because the particle diameter of the porous silicon composite particles grows and becomes coarse. In that case, the silicon intermediate alloy can be mechanically pulverized to reduce the thickness to 50 mm or less.
  • the crystal grain size of the intermediate alloy composed of silicon and the intermediate alloy element or the complex element is desirably 1000 ⁇ m or less, more preferably 500 ⁇ m or less, and further preferably 50 ⁇ m or less.
  • the crystal grain size is 1000 ⁇ m or more, the grain boundary diffusion of the molten metal in the step (b) proceeds preferentially, and the intragranular diffusion stagnate, so a homogeneous reaction cannot be performed.
  • the silicon intermediate alloy is immersed in the molten metal element shown in Table 2 corresponding to the used intermediate alloy element to form a spinodal decomposition of silicon and a second phase that is an alloy of the intermediate alloy element and the molten element.
  • the oxygen in the molten metal is desirably reduced in advance to 100 ppm or less, preferably 10 ppm or less, more preferably 2 ppm or less. This is because dissolved oxygen in the molten metal reacts with silicon to form silica, and with this as a nucleus, silicon grows in a facet shape and becomes coarse.
  • a countermeasure it can be reduced by a solid reducing material such as charcoal / graphite or a non-oxidizing gas, or an element having a strong affinity for oxygen may be added in advance. Silicon particles are formed for the first time in this dipping process.
  • a solid reducing material such as charcoal / graphite or a non-oxidizing gas, or an element having a strong affinity for oxygen may be added in advance. Silicon particles are formed for the first time in this dipping process.
  • a molten silicon immersion device 61 as shown in FIG. 7A is used, and the granular silicon intermediate alloy 63 is placed in a dipping bowl 65 and dipped in a molten metal 69 of a molten element.
  • the pressing cylinder 67 is moved up and down to give mechanical vibration to the silicon intermediate alloy or molten metal, or to give vibration by ultrasonic waves, as shown in FIG.
  • the reaction can be advanced in a short time by stirring the molten metal using mechanical stirring using the mechanical stirrer 81 and gas injection using the gas blowing plug 83 or electromagnetic force. Then, it is pulled up in a non-oxidizing atmosphere and cooled.
  • the molten metal 69 or 79 is heated to a temperature higher than the liquidus temperature of the molten element by 10K or more.
  • the immersion in the molten metal depends on the molten metal temperature, but is preferably 5 seconds or longer and 10,000 seconds or shorter. This is because coarse Si grains are produced when immersion is performed for 10,000 seconds or more. Further, only the silicon fine particles on the surface of the porous particles grow abnormally by the long immersion.
  • the above-mentioned powdery, granular, and lump shapes of silicon intermediate alloys are simply called silicon powders, particles, and lumps with a small aspect ratio (aspect ratio of 5 or less) depending on the size. It is not strictly defined.
  • the granular silicon intermediate alloys 63, 73, and 93 are represented as granular silicon intermediate alloys on behalf of the aforementioned powdery, granular, and massive silicon intermediate alloys.
  • FIG. 10A a silicon intermediate alloy 111 made of silicon and an intermediate alloy element is formed. Thereafter, the silicon fine particles 103, the silicon compound particles 105, and the second phase 109 are formed as shown in FIG. 10B by immersing in a molten metal obtained by adding a complex element to the molten metal element. Thereafter, as shown in FIG. 10C, the second phase 109 is removed to obtain porous silicon composite particles 101.
  • silicon powder and one or more intermediate alloy element powders selected from the group consisting of Co, Cr, Cu, Fe, Mg, Mn, Mo, Ni, P, Ti, and Zr listed in Table 2 are used.
  • Silicon (X atomic%) and intermediate alloy element (Y atomic%) are dissolved so as to satisfy the formula (3).
  • a ribbon-like silicon intermediate alloy 19 or a linear silicon intermediate alloy which is an alloy of silicon and an intermediate alloy element, is used by using a single roll casting machine 11 as shown in FIG. To manufacture.
  • a powdery silicon intermediate alloy is manufactured by an atomizing method as shown in FIGS.
  • a silicon intermediate alloy may be cast into an ingot, which may be mechanically pulverized into a granular shape.
  • the silicon intermediate alloy is made of at least one of Ag, Al, Au, Be, Bi, Cd, Ga, In, Pb, Sb, Sn, Tl, and Zn corresponding to the intermediate alloy elements described in Table 2.
  • One or more complex elements corresponding to the intermediate alloy elements listed in Table 2 are added to the molten metal element in an amount of 10 atomic% or less, and a total of 20 atomic% or less, respectively.
  • the dipping process uses a molten metal dipping device 21 as shown in FIG.
  • the molten silicon processing apparatus is used to immerse the granular silicon intermediate alloy in the molten metal element.
  • the molten metal 23 is heated to a temperature higher than the liquidus temperature of the molten element by 10K or more.
  • immersion in the molten metal 23 depends on the molten metal temperature, it is preferably 5 seconds or more and 10,000 seconds or less. This is because coarse Si grains are produced when immersion is performed for 10,000 seconds or more. Further, only the silicon fine particles on the surface of the porous particles grow abnormally by the long immersion. This is cooled in a non-oxidizing atmosphere to obtain a composite of silicon fine particles 103, silicon compound particles 105, and second phase 109.
  • the molten element shown in Table 2 corresponding to the intermediate alloy element corresponds to the intermediate alloy element.
  • One or more complex elements selected from the group consisting of the complex elements shown in Table 2 may be added to each of 10 atomic% or less and a total of 20 atomic% or less to be immersed in an alloy bath.
  • step (b) the preferential growth orientation inherent to the metal in the molten metal bath becomes the dominant factor, and the orientation of the silicon fine particles can be controlled. Further, the orientation of the silicon fine particles can be maintained even if the second phase is removed in the step (c). Therefore, the orientation of silicon fine particles can be controlled by selecting a molten metal bath. Although the reason is unknown, ⁇ 1010> is more preferable as the growth direction of the molten element.
  • FIG. 22 is a cross-sectional SEM photograph showing the silicon fine particles and the second phase after immersion in the molten metal in step (b) of Example 1-15 described later.
  • the region that appears black is the second phase containing bismuth, and the portion that appears white is the silicon fine particles. It can be seen that the silicon fine particles are aligned along the upper right direction in the figure. This is because when forming the second phase, silicon fine particles are formed along ⁇ 1010>, which is a crystal orientation in which bismuth is likely to grow.
  • FIG. 23 is a SEM photograph showing silicon fine particles on the surface of the porous silicon particles after the second phase is removed after the step (c) of Example 2-15 described later. It can be seen that the flat cylindrical silicon particles are arranged along the upper left direction in the figure.
  • porous silicon composite particles having an unprecedented three-dimensional network structure can be obtained.
  • porous silicon composite particles having a substantially uniform pore structure as a whole can be obtained. This is because precipitation of silicon fine particles from the silicon intermediate alloy in the molten metal is performed in the molten metal at a high temperature, so that the molten metal penetrates into the particles.
  • the porous silicon composite particles according to the present invention are used as a negative electrode active material of a lithium ion battery, a negative electrode having a high capacity and a long life can be obtained.
  • the complex element is an element that does not absorb lithium as much as silicon, the complex element is difficult to expand during storage of lithium ions, so that expansion of silicon is suppressed and a longer-life negative electrode is obtained. Can do.
  • silicon compound particles, which are compounds of silicon and a composite element have higher conductivity than silicon, the porous silicon composite particles according to the present invention are more rapidly charged / discharged than normal silicon particles. It can correspond to.
  • Examples 1-1 to 1-16 are examples relating to silicon porous particles
  • Examples 2-1 to 2-16 are examples relating to porous silicon composite particles containing a composite element.
  • Example 1-2 to 1-11 The production conditions for each example and comparative example are summarized in Table 4.
  • porous silicon composites were produced in the same manner as in Example 1-1, except for the production conditions such as the intermediate alloy elements shown in Table 4 and the blending ratio of each element. Got.
  • Example 1-13 to 1-16 porous silicon composites were produced in the same manner as in Example 1-12 except that the production conditions such as the intermediate alloy elements shown in Table 4 and the blending ratio of each element were used. Got.
  • Example 1-13 to 1-16 since the silicon particles were large, the characteristics were evaluated using particles that were pulverized and reduced in a mortar.
  • the porous silicon particles of Example 1-13 having a particle size of 130 ⁇ 33 were obtained by pulverizing porous silicon particles having an average particle size of 130 ⁇ m to obtain porous silicon particles having an average particle size of 33 ⁇ m. Means.
  • the average particle diameter x of the silicon fine particles is 2 nm to 2 ⁇ m
  • the standard deviation ⁇ of the particle diameter of the silicon fine particles is 1 to 500 nm
  • the ratio of the average x to the standard deviation ⁇ ( ⁇ / x) is 0.01 to 0.5.
  • the ratio (a / b) of the average longest diameter a to the average shortest diameter b is 1.1 to 50.
  • the ratio (connection thickness ratio) between the silicon fine particles, the thickness of the connecting portion of the adjacent silicon fine particles, and the diameter of the larger silicon fine particle of the adjacent silicon fine particles is 80% or less.
  • the porous silicon particles satisfying the requirements described in claim 1 were produced by a manufacturing method using dealloying (dealloying), so that the capacity retention rate after 50 cycles in each example.
  • dealloying dealloying
  • the capacity retention rate after 50 cycles in each example. was high and the cycle characteristics were good.
  • the silicon fine particles have a uniform particle size, it is presumed that the cycle characteristics are greatly improved by eliminating stress concentration on the non-uniform particle size portion during expansion / contraction of the active material during charge / discharge.
  • Each example has a higher capacity retention rate after 50 cycles than Comparative Examples 1-1 to 1-3, and the rate of decrease in discharge capacity due to repeated charge and discharge is small, so it is expected that the battery life is long. Is done.
  • the negative electrode active material is a porous silicon particle having a three-dimensional network structure or continuous voids, expansion / contraction due to alloying / dealloying of Li and Si during charge / discharge Even if the volume change occurs, the silicon particles are not broken or pulverized, and the discharge capacity retention rate is high.
  • Comparative Example 1-1 pure Si crystallized as an initial crystal when the intermediate alloy was produced, and a eutectic structure (Si and Mg 2 Si) was formed at the end of solidification.
  • Comparative Example 1-3 since it is a mere silicon particle having no pore structure, it cannot follow the volume change due to charge / discharge, and the cycle characteristics are considered to be poor.
  • FIG. 11 shows an SEM photograph of the particles according to Example 1-12
  • FIG. 12 shows an SEM photograph of the particles according to Comparative Example 1-1.
  • FIG. 11 it is observed that a large number of silicon fine particles having a particle diameter of 20 nm to 100 nm are joined together to form porous silicon particles.
  • FIG. 12 a wall-like structure having a thickness of about 5 ⁇ m is observed.
  • the average particle diameter of the silicon fine particles was measured by image information of an electron microscope (SEM). Further, the porous silicon particles were divided into a region near the surface of 50% or more in the radial direction and a particle internal region within 50% in the radial direction, and the ratio of the respective average particle diameters Ds and Di was calculated.
  • the values of Ds / Di were all in the range of 0.5 to 1.5 in the examples, but in Comparative Example 1-2 obtained by the etching method, near the surface compared to the particle internal region. The average particle size of the fine particles in the region was small, and the value of Ds / Di was small.
  • the Si concentration of silicon fine particles and porous silicon particles was measured with an ICP emission spectrometer. All contain 80 atomic% or more of silicon.
  • the average porosity of the porous silicon particles was measured by a mercury intrusion method (JIS R 1655) using a 15 mL cell.
  • the porous silicon particles are divided into a region near the surface of 50% or more in the radial direction and a particle internal region within 50% in the radial direction, and the average porosity Xs and Xi are measured by SEM image information. And the ratio of Xs to Xi was calculated.
  • the value of Xs / Xi is between 0.5 and 1.5, but in Comparative Example 1-2 obtained by the etching method, the pores in the region near the surface compared to the region inside the particle Xs / Xi increased due to the development of the structure.
  • FIG. 13 is an X-ray diffraction grating image obtained by measuring the silicon fine particles constituting the porous silicon particles according to Example 1-12. Diffraction derived from silicon crystals is observed, and point diffraction is obtained, which indicates that the silicon fine particles are composed of single crystal silicon.
  • SBR styrene butadiene rubber
  • BM400B carboxymethyl cellulose sodium
  • Example 2 Regard the porous silicon composite particles containing the composite element will be described.
  • step (b) a second phase composite made of silicon fine particles, silicon compound particles made of Si—Fe alloy, and Mg—Bi alloy or Bi was obtained (step (b)).
  • This composite was immersed in a 20% nitric acid aqueous solution for 5 minutes to obtain porous silicon composite particles (step (c)).
  • Example 2-2 to 2-8, 2-10, 2-11) The production conditions for each example and comparative example are summarized in Table 6.
  • Examples 2-2 to 2-8, 2-10, and 2-11 are the same as in Example 2 except for manufacturing conditions such as intermediate alloy elements, composite elements, and blending ratio of each element shown in Table 6.
  • a porous silicon composite was obtained.
  • Example 2-4 a continuous ribbon-shaped silicon alloy could not be formed and was cut at 1 to 2 cm, so that a foil piece-shaped silicon alloy was obtained.
  • ⁇ 100 ⁇ m means that the diameter of the linear intermediate alloy is 100 ⁇ m. The same applies to Example 2-8.
  • step (c) This composite was immersed in a 20% nitric acid aqueous solution for 5 minutes to obtain porous silicon composite particles (step (c)).
  • ⁇ 40 ⁇ m in the granular intermediate alloy means that the average particle diameter of the granular intermediate alloy is 40 ⁇ m.
  • Example 2-13 to 2-16 porous silicon composites were produced in the same manner as in Example 2-12 except that the production conditions such as intermediate alloy elements shown in Table 6 and the blending ratio of each element were used. Particles were obtained. In Examples 2-13, 2-15, and 2-16, the water cooling block was used to increase the cooling rate.
  • Example 7 The evaluation results are summarized in Table 7.
  • the average particle size 130 ⁇ 33 of the porous silicon composite particles of Example 2-13 is obtained by pulverizing the porous silicon composite particles having an average particle size of 130 ⁇ m to obtain the porous silicon composite particles having an average particle size of 33 ⁇ m. It means that body particles were obtained.
  • the average particle size x of the silicon fine particles is 2 nm to 2 ⁇ m
  • the standard deviation ⁇ of the particle size of the silicon fine particles is 1 to 500 nm
  • the ratio of the average x to the standard deviation ⁇ ( ⁇ / x) is 0.01 to 0.5.
  • the ratio (a / b) of the average longest diameter a to the average shortest diameter b is 1.1 to 50.
  • the ratio of the diameter of the silicon fine particles and the connecting portion of the adjacent silicon fine particles to the diameter of the larger silicon fine particle of the adjacent silicon fine particles (connection thickness ratio) is 80% or less.
  • the porous silicon composite particles satisfying the respective requirements according to claim 9 were produced by a manufacturing method using dealloying (dealloying), and therefore the capacity after 50 cycles in each example.
  • the retention rate was high and the cycle characteristics were good. Since the silicon fine particles have a uniform particle size, it is presumed that the cycle characteristics are greatly improved by eliminating stress concentration on the non-uniform particle size portion during expansion / contraction of the active material during charge / discharge.
  • Each example has a capacity retention rate after 50 cycles higher than each comparative example, and the rate of decrease in discharge capacity due to repeated charge and discharge is small, so the battery life is expected to be long.
  • the negative electrode active material is a porous silicon composite particle having a three-dimensional network structure or continuous voids, expansion due to alloying / dealloying of Li and Si during charge / discharge -Even if the volume change of shrinkage occurs, the silicon composite particles are not cracked or pulverized, and the discharge capacity retention rate is high.
  • Comparative Example 2-1 pure Si crystallized as an initial crystal when the intermediate alloy was produced, and a eutectic structure (Si and Mg 2 Si) was formed at the end of solidification.
  • FIG. 24 is a SEM photograph of the surface of the porous silicon particles of Comparative Example 2-4. Many particles having a particle diameter of 1 to 2 ⁇ m are observed.
  • Comparative Example 2-4 since the pore structure was formed by etching with hydrofluoric acid or nitric acid, a portion where no pore was formed was formed at the center of the particle. This core portion cannot follow the volume change due to charging / discharging and is considered to have poor cycle characteristics.
  • Comparative Example 2-5 since it is a simple particle having no pore structure, it cannot follow the volume change due to charge / discharge, and the cycle characteristics are considered to be poor.
  • FIG. 14 shows an SEM photograph of the surface of the particle according to Example 2-1
  • FIG. 15 shows an SEM photograph of a cross section inside the particle according to Example 2-1
  • FIG. The SEM photograph of the surface of the particle which concerns on is shown.
  • FIG. 14 and FIG. 15 it is observed that a large number of silicon fine particles having a particle diameter of 20 nm to 50 nm are joined together to form porous silicon composite particles.
  • FIG. 14 and FIG. 15 it is observed in FIG. 14 and FIG. 15 that there is no big difference in the porosity and the particle size of the silicon fine particles.
  • FIG. 16 it is observed that small silicon particles are bonded to large silicide particles.
  • FIG. 17 is an X-ray diffraction grating image of silicon fine particles constituting the silicon composite particles. A spot derived from a crystal of silicon is observed, and it can be seen that the silicon fine particle is a single crystal.
  • the average particle size of silicon fine particles and silicon compound particles was measured by image information of an electron microscope (SEM).
  • SEM electron microscope
  • the porous silicon composite particles are divided into a surface vicinity region of 50% or more in the radial direction and a particle inner region of 50% or less in the radial direction, and the respective average particle diameters Ds and Di are obtained from the respective SEM photographs, These ratios were calculated.
  • the values of Ds / Di were all in the range of 0.5 to 1.5 in the examples, but in Comparative Example 2-4 obtained by the etching method, near the surface compared to the particle inner region.
  • the average particle size of the fine particles in the region was small, and the value of Ds / Di was small.
  • the above-described method using SEM observation and DLS was used for the average particle diameter of the porous silicon composite particles.
  • the Si concentration of silicon fine particles and the concentration of Si and complex elements in the porous silicon composite particles were measured with an ICP emission spectrometer.
  • the silicon fine particles contain 80 atomic% or more of silicon.
  • the average porosity of the porous silicon composite particles was measured by a mercury intrusion method (JIS R 1655) using a 15 mL cell.
  • the porous silicon composite particles are divided into a surface vicinity region of 50% or more in the radial direction and a particle internal region of 50% or less in the radial direction, and an arbitrary portion in each region is analyzed with a surface scanning electron microscope. Observed, Xs and Xi were obtained as the average porosity, and the ratio of Xs and Xi was calculated. In the examples, the value of Xs / Xi is between 0.5 and 1.5. However, in Comparative Example 2-4 obtained by the etching method, the pores in the region near the surface compared to the region inside the particle Xs / Xi increased due to the development of the structure.
  • Example 3-1 Using the same process as in Example 1, the conditions of steps (a) to (c) were changed to change the particle diameter, shape, and distribution of the silicon alloy fine particles. In particular, the immersion temperature and time in the step (b) were changed. As a comparative example, mechanical stirring (stirring energy) and vibration (amplitude: 1 mm ⁇ 60 Hz) were applied to the molten metal bath in step (b). These conditions are shown in Table 8. Table 9 shows the results of evaluating the porous silicon particles and silicon fine particles obtained by this production method in the same manner as in Example 1.
  • the capacity maintenance rate after 50 cycles is lower than 80%, whereas in each example, the capacity maintenance rate after 50 cycles is higher than 80%.
  • the average particle diameter x of the silicon fine particles is 2 nm to 2 ⁇ m
  • the standard deviation ⁇ of the particle diameter of the silicon fine particles is 1 to 500 nm
  • the ratio ( ⁇ / x) between the average x and the standard deviation ⁇ is 0.01 to 0.5.
  • the ratio (a / b) of the average longest diameter a to the average shortest diameter b is 1.1 to 50.
  • the ratio (connection thickness ratio) between the silicon fine particles, the thickness of the connecting portion of the adjacent silicon fine particles, and the diameter of the larger silicon fine particle of the adjacent silicon fine particles is 80% or less.
  • FIG. 18 is a SEM photograph of porous silicon particles according to Example 3-7. It can be seen that a large number of silicon fine particles having a diameter of about 30 nm are gathered.
  • FIG. 19 is a TEM photograph of silicon fine particles constituting the porous silicon particles according to Example 3-7.
  • FIG. 20 is a particle size distribution of silicon fine particles forming the porous silicon particles according to Example 3-7. Since each silicon fine particle is a flat spherical particle, and these particles are formed by bonding, it can be seen that the distribution is not a normal distribution.
  • FIG. 21 is a TEM photograph of silicon fine particles constituting the porous silicon particles according to Example 3-8, and the upper left is a limited-field electron diffraction image in the observation region with TEM.
  • the TEM photograph it can be seen that there is no grain boundary in one silicon fine particle and it is a single crystal.
  • the limited field electron diffraction pattern a spot derived from a silicon crystal is observed, and it can be seen that the silicon fine particle is a single crystal.
  • the silicon fine particles had a flat spherical shape, and the major axis diameter was 36 nm and the minor axis diameter was 27 nm.
  • the average shortest diameter a was 36 nm
  • the average shortest diameter b was 27 nm
  • a / b 1.33.
  • FIG. 25 is a SEM photograph of the porous silicon particles of Example 3-1. A large number of silicon fine particles grown in a polygonal column shape are observed. The average strut diameter x was 203.6 nm, the standard deviation ⁇ was 80.6 nm, and ⁇ / x was 0.40.
  • FIG. 26 is a SEM photograph of the porous silicon particles of Example 3-2. A large number of silicon fine particles grown in a columnar shape with a column diameter of about 20 nm are observed.
  • FIG. 27 is a SEM photograph of porous silicon particles of Comparative Example 3-3. Many large silicon particles are observed. The average particle size x was 694.0 nm, the standard deviation ⁇ was 231.7 nm, and ⁇ / x was 0.33. Further, because of the long-time immersion, the diameter of the fine particles on the surface of the silicon particles was large, and the ratio Es / Ei was 1.08.
  • FIG. 28 is a microstructure photograph of the intermediate alloy of Example 1-15.
  • the porous silicon composite particles according to the present invention can be used not only for a negative electrode of a lithium ion battery but also as a negative electrode of a lithium ion capacitor, a solar cell, a light emitting material, and a filter material.

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