JP2012082125A - Porous silicon particle and method for manufacturing the same - Google Patents

Porous silicon particle and method for manufacturing the same Download PDF

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JP2012082125A
JP2012082125A JP2011195723A JP2011195723A JP2012082125A JP 2012082125 A JP2012082125 A JP 2012082125A JP 2011195723 A JP2011195723 A JP 2011195723A JP 2011195723 A JP2011195723 A JP 2011195723A JP 2012082125 A JP2012082125 A JP 2012082125A
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silicon
particles
alloy
step
intermediate alloy
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JP5598861B2 (en
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Koji Hataya
Hidemi Kato
Kazuhiko Kurusu
Kazutomi Miyoshi
Takeshi Nishimura
Toshio Tani
Takeshi Wada
Koichi Yoshida
一富 三好
一彦 久留須
秀実 加藤
浩一 吉田
武 和田
耕二 幡谷
健 西村
俊夫 谷
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Furukawa Electric Co Ltd:The
古河電気工業株式会社
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Priority claimed from PCT/JP2011/071214 external-priority patent/WO2012036265A1/en
Priority claimed from CN201180044169.1A external-priority patent/CN103118976B/en
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    • YGENERAL 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
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00Enabling technologies or technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10Energy storage
    • Y02E60/12Battery technologies with an indirect contribution to GHG emissions mitigation

Abstract

PROBLEM TO BE SOLVED: To provide a porous silicon particle suitable for a negative electrode material for a lithium-ion battery, which achieves high capacity and good cycling characteristics.SOLUTION: The porous silicon particle 1 is formed by joining a plurality of silicon microparticles 3, has an average particle diameter of 0.1 to 1,000 μm, has a three-dimensional network structure having continuous gaps and has an average porosity of 15 to 93%. The ratio Xs/Xi of the porosity Xs in a near-surface region accounting for ≥50% in the radial direction to the porosity Xi in a particle interior region accounting for ≤50% in the radial direction is 0.5 to 1.5, and silicon accounts for ≥80 atom% of elements excluding oxygen in the porous silicon particle 1.

Description

  The present invention relates to porous silicon particles used for a negative electrode for a lithium ion battery, and more particularly to a negative electrode for a lithium ion battery having a high capacity and a long life.

  Conventionally, lithium-ion batteries using various carbon-based materials such as natural graphite, artificial graphite, amorphous carbon, and mesophase carbon, lithium titanate, tin alloys, and the like as a negative electrode active material have been put into practical use. Also, 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.

  On the other hand, negative electrodes for lithium ion batteries using metals and alloys having a large theoretical capacity as lithium compounds, particularly silicon and alloys thereof as negative electrode active materials, have been developed with the aim of increasing the capacity. However, since the volume of silicon that occludes lithium ions expands to about 4 times that of silicon before occlusion, a negative electrode using silicon as a negative electrode active material repeats expansion and contraction during a charge / discharge cycle. For this reason, the negative electrode active material is peeled off, and there is a problem that the lifetime is extremely short compared to a negative electrode made of a conventional carbon-based active material.

As a conventional manufacturing method of a negative electrode using silicon, 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.
In addition, as a conventional manufacturing method of a negative electrode using silicon, a method of anodizing a silicon substrate to form grooves such as slits, a method of crystallizing fine silicon in a ribbon-shaped bulk metal (for example, , See Patent Document 2).
In addition, 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 (see, for example, Patent Document 3) for producing a material is also known.
Furthermore, 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.
In addition, 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.
Further, in connection with this technique, 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. Are known.
Further, a technique for etching metallic silicon with hydrofluoric acid or nitric acid (for example, Patent Documents 8 and 9) is also known.

Japanese Patent No. 4172443 JP 2008-135364 A JP 2006-260886 A JP 2000-149937 A JP 2004-362895 A JP 2009-032644 A Japanese Patent No. 3827642 US Application Publication No. 2006/0251561 US Application Publication No. 2009/0186267

  However, the technique of 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. Furthermore, in order to impart conductivity, silicon compounds (silicon carbide, silicon cyanide, silicon nitride, silicon oxide, silicon boride, silicon borate, silicon boronitride, silicon oxynitride, silicon alkali metal) One or more of a silicon compound group consisting of an alloy, a silicon alkaline earth metal alloy, and a silicon transition metal alloy). However, since silicon has a large volume change at the time of charging / discharging, 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.

  Moreover, the technique of patent document 2 applies and dries the slurry of a negative electrode active material, a conductive support agent, and a binder, and forms a negative electrode. In such a conventional negative electrode, 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. There is a weak binding force. Since silicon has a large volume change at the time of charging / discharging, in the technique of Patent Document 2, the negative electrode active material is pulverized from the negative electrode active material and peeled off from the negative electrode active material, generation of cracks in the negative electrode, A decrease in conductivity between substances occurs, resulting in a decrease in capacity. Therefore, there are problems that the cycle characteristics are poor and the life of the secondary battery is short.

  In the technique of 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) can be produced. However, in producing a Si porous body, there is a problem that it is extremely difficult to plate Si on polymer particles such as polystyrene and PMMA, which cannot be applied industrially.

  Further, the technique of 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. However, in 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.

  In addition, the technique of 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. However, in 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.

  The technique of 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. However, in 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.

The technique of 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. In the solidification of a general alloy, dendrites in which secondary dendrite grows while primary dendrite grows are taken. A special alloy system (Cu-Mg system, Ni-Ti system, etc.) can form an amorphous metal at 10 4 K / second or more, but other systems (for example, 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: μm).
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, when A: 60 and B: −0.35, DAS becomes 1 μm 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 crystalline phase with this rapid solidification technique alone with materials such as Si—Ni.

  In the techniques of Patent Documents 8 and 9, metal silicon is etched using hydrofluoric acid or nitric acid to form fine holes on the surface. However, the vacancies formed by etching tend to be harder to form as the inside of the particles. As a result, the vacancies do not exist uniformly from the particle surface to the center, and coarse silicon grains are formed near the particle center. The 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.

  The present invention has been made in view of the above-described problems, and its object is to obtain porous silicon particles suitable for a negative electrode material for a lithium ion battery that realizes high capacity and good cycle characteristics. It is.

  As a result of intensive studies to achieve the above object, 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. The present invention has been made based on this finding.

  Since silicon is precipitated in the molten metal from the silicon alloy in a high-temperature molten metal, the primary particle size and pore size are greatly distributed between the surface layer and the inside of the porous silicon obtained by dealloying (dealloying). Is unlikely to occur. On the other hand, for example, in etching with an acid, 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. Depending on the conditions, there is a possibility that a Si core having no pores remains in the center of the particle, and fine powder may be generated during the reaction with Li.

That is, the present invention provides the following inventions.
(1) Porous silicon particles formed by joining a plurality of silicon fine particles, wherein the porous silicon particles have an average particle size of 0.1 μm to 1000 μm, and the porous silicon particles have a continuous void. The porous silicon particles have an original network structure, the average porosity of the porous silicon particles is 15 to 93%, the porosity Xs of the surface vicinity region of 50% or more in the radial direction, and the particle internal region of 50% or less in the radial direction A porous silicon particle characterized in that Xs / Xi, which is a ratio of the porosity Xi, is 0.5 to 1.5 and contains 80 atomic% or more of silicon in a ratio of elements excluding oxygen.
(2) The silicon fine particles have an average particle diameter or average column diameter of 2 nm to 2 μm, and an average particle diameter Ds of the silicon fine particles in the vicinity of the surface of 50% or more in the radial direction and within 50% in the radial direction. Ds / Di, which is the ratio of the average particle diameter Di of the silicon fine particles in the particle internal region, is 0.5 to 1.5, and the silicon fine particles contain 80 atomic% or more of silicon in the ratio of elements excluding oxygen. The porous silicon particle according to (1), which is a solid silicon fine particle characterized by the above.
(1) Silicon fine particles are bonded, the average particle size is 0.1 μm to 1000 μm, the average porosity is 15 to 93%, and it has a three-dimensional network structure with continuous voids and 50 in the radial direction. % Ds / Di, which is the ratio of the average particle diameter Ds of the silicon particles in the region near the surface of not less than 50% and the average particle diameter Di of the silicon particles in the particle inner region within 50% in the radial direction, Xs / Xi, which is the ratio of the porosity Xs of the surface vicinity region of 50% or more in the radial direction and the porosity Xi of the particle internal region within 50% in the radial direction, is 0.5 to 1. A porous silicon particle comprising 5 and containing 80 atomic% or more of silicon at a ratio of elements excluding oxygen.
(2) The silicon fine particles are solid silicon fine particles having an average particle diameter or average column diameter of 2 nm to 2 μm and containing 80 atomic% or more of silicon in a ratio of elements excluding oxygen. The porous silicon particle according to (1), which is characterized.
(3) The porous silicon particles according to (1) or (2), wherein the area of the junction between the silicon fine particles is 30% or less of the surface area of the silicon fine particles.
(4) It is an alloy of silicon and one or more intermediate alloy elements shown in the following Table 1, and the ratio of silicon is 10 atomic% or more of the whole, and the following Table 1 corresponding to the intermediate alloy element to be contained A step (a) of producing a silicon intermediate alloy having a maximum Si content of not more than the highest value, and dipping in a molten metal of one or more molten elements shown in Table 1 corresponding to the intermediate alloy element A step (b) for separating silicon fine particles into a second phase, and a step (c) for removing the second phase, wherein the second phase comprises the intermediate alloy element and the molten element. A method for producing porous silicon particles, characterized in that the molten silicon element is replaced with an alloy of the above and / or the molten alloy element substituted with the intermediate alloy element.
(5) In the step (a), the silicon intermediate alloy has a ribbon shape, a foil piece shape or a linear shape with a thickness of 0.1 μm to 2 mm, or a granular shape or a lump shape with a particle size of 10 μm to 50 mm. The method for producing porous silicon particles according to (4), which is characterized.
(6) In the step (c), the second phase is dissolved and removed with at least one of an acid, an alkali, and an organic solvent, or only the second phase is evaporated by heating and depressurizing. The method for producing porous silicon particles according to (4) or (5), further comprising a step of removing them.
(7) The step (a) is a step of producing a ribbon-shaped silicon intermediate alloy from a molten metal of the silicon and the intermediate alloy element by a single roll casting machine (4) to (6) The method for producing porous silicon particles according to any one of the above.
(8) The step (a) is a step of producing a powdery silicon intermediate alloy by using a gas atomization method or a rotating disk atomization method with a molten metal of the silicon and the intermediate alloy element (4) ) To (6) manufacturing method of porous silicon particles (9) In the step (a), the molten silicon and the intermediate alloy element are cooled in a mold to form a lump silicon intermediate The method for producing porous silicon particles according to any one of (4) to (6), comprising a step of producing an alloy.
(10) Silicon is mixed with Cu so that the silicon ratio is 10 to 30 atomic% of the total, and the ribbon shape, foil piece shape, linear shape with a thickness of 0.1 μm to 2 mm, or a particle size of 10 μm to 50 mm The step (a) of producing a granular / lumped silicon intermediate alloy, and the silicon alloy as a main component comprising at least one molten element selected from the group consisting of Al, Be, Cd, Ga, In, Sb, Sn, Zn A step (b) of immersing in the molten metal to separate the silicon fine particles and the second phase, and a step (c) of removing the second phase, wherein the second step in the step (b). A method for producing porous silicon particles, wherein the phase is composed of an alloy of the Cu and the molten element and / or the molten element substituted for the Cu.
(11) Silicon is mixed with Mg so that the ratio of silicon is 10 to 50 atomic%, and the thickness is 0.1 μm to 2 mm in ribbon shape, foil piece shape, linear shape, or particle size of 10 μm to 50 mm. The step (a) for producing a granular / lumped silicon intermediate alloy, and the silicon alloy is selected from the group consisting of Ag, Al, Au, Be, Bi, Ga, In, Pb, Sb, Sn, Tl, and Zn. A step (b) of immersing in a molten metal containing at least one molten element as a main component to separate into silicon fine particles and a second phase, and a step (c) of removing the second phase, The method for producing porous silicon particles, wherein in the step (b), the second phase is composed of an alloy of the Mg and the molten metal element and / or the molten metal element substituted for the Mg.
(12) Silicon is blended with Ni so that the silicon content is 10 to 55 atomic% of the whole, and the thickness is 0.1 μm to 2 mm in a ribbon shape, foil piece shape, linear shape, or a particle size of 10 μm to 50 mm. The step (a) of producing a granular / lumped silicon intermediate alloy, and the silicon alloy as a main component comprising at least one molten element selected from the group consisting of Al, Be, Cd, Ga, In, Sb, Sn, Zn A step (b) of immersing in the molten metal to separate the silicon fine particles and the second phase, and a step (c) of removing the second phase, wherein the second step in the step (b). A method for producing porous silicon particles, characterized in that a phase is composed of an alloy of Ni and the molten element and / or the molten element substituted for Ni.
(13) Silicon is mixed with Ti so that the silicon ratio is 10 to 82 atomic% of the whole, and the thickness is 0.1 μm to 2 mm in a ribbon shape, foil piece shape, linear shape, or a particle size of 10 μm to 50 mm. The step (a) for producing a granular / lumped silicon intermediate alloy, and the silicon alloy is selected from the group consisting of Ag, Al, Au, Be, Bi, Cd, Ga, In, Pb, Sb, Sn, Zn A step (b) of immersing in a molten metal containing at least one molten element as a main component to separate into silicon fine particles and a second phase, and a step (c) of removing the second phase, The method for producing porous silicon particles, wherein in the step (b), the second phase is composed of an alloy of the Ti and the molten element and / or the molten element replaced with the Ti.

  According to the present invention, 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. Further, the porous silicon 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 battery, a light emitting material, and a filter material.

(A) The figure which shows the porous silicon particle 1 concerning this invention, (b) The figure which shows the surface vicinity area | region S and the particle | grain internal area | region I of the porous silicon particle 1. 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. The figure explaining the manufacturing process of (a)-(c) lump silicon intermediate alloy. (A), (b) The figure which shows the molten metal immersion apparatus concerning this invention. 14 is an SEM photograph of the surface of porous silicon particles according to Example 12. 3 is an SEM photograph of porous silicon particles according to Comparative Example 1. 12 is an X-ray diffraction grating image of porous silicon particles according to Example 12. FIG.

(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 particle 1 is a porous body having a three-dimensional network structure having continuous voids, which is formed by bonding silicon fine particles 3, having an average particle diameter of 0.1 μm to 1000 μm, and an average porosity of 15 to 93. %. 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.

Note that there is no problem in characteristics even if an oxide layer of 20 nm or less is formed on the surface of the silicon fine particles.
Furthermore, 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. Or it can also form by hold | maintaining under the oxygen partial pressure of 0.00000001-0.02 MPa, after removing a 2nd phase by vacuum distillation.

  Further, as shown in FIG. 1 (b), 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. When the average particle size of the silicon fine particles constituting the region near the surface of the particle is Ds and the average particle size of the silicon fine particles constituting the particle internal region of the porous silicon particle is Di, Ds / Di is 0.5 to 1. .5.

Further, in the porous silicon particles, 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 μm and crystallinity, and a solid containing 80 atomic% or more of silicon in a ratio of elements excluding oxygen. It is a characteristic particle. The particle diameter can be measured if substantially spherical fine particles exist independently, but when a plurality of fine particles are joined to form a substantially columnar shape, a cross section perpendicular to the long axis. The average strut diameter corresponding to the column diameter 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 or the average column diameter of the silicon fine particles 3 is 2 nm to 2 μm, preferably 10 to 500 nm, more preferably 15 to 100 nm. Moreover, the average porosity of the porous silicon particle 1 is 15 to 93%, preferably 30 to 80%, and 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.

The porous silicon particles according to the present invention are usually present in an aggregated state. 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). For the average particle size, 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 Otsuka Electronics DLS-8000). If the particles are sufficiently dispersed and not agglomerated at the time of DLS measurement, almost the same measurement results can be obtained with SEM and DLS.
Further, since the silicon fine particles constituting the porous silicon particles are bonded to each other, 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 | pillar diameter be an average support | pillar diameter. This strut diameter is obtained mainly by SEM observation of particles.

  The average porosity refers to the proportion of voids in the particles. Submicron or smaller pores can be measured by nitrogen gas adsorption, but when the pore size is in a wide range, electron microscope observation or mercury intrusion method (JIS R 1655 “fine ceramics mercury intrusion method” Method for measuring pore size distribution of compact by using "Derived from the relationship between pressure and mercury volume when mercury enters the void", 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 size of 0.1 μm to 1000 μm 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. When used as the negative electrode active material, the average particle diameter is preferably 0.1 to 50 μm, more preferably 1 to 30 μm, and further preferably 5 to 20 μm. 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.

(Outline of production method of porous silicon particles)
The outline of the manufacturing method of the porous silicon particle 1 is demonstrated using FIG.
First, as shown in FIG. 2A, silicon and an intermediate alloy element are heated and melted to produce a silicon intermediate alloy 7.
Thereafter, the silicon intermediate alloy 7 is immersed in a molten metal element shown in Table 1. At this time, as shown in FIG. 2B, the intermediate alloy element of the silicon intermediate alloy 7 is eluted into the molten metal to form the second phase 9 mainly composed of the molten element, and only silicon is silicon. Precipitate or crystallize as fine particles 3. 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, 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 1 joined with silicon fine particles 3 are obtained.

  The phenomenon in each process will be described. When silicon and the intermediate alloy element (X) are melted and solidified, a silicon intermediate alloy 7 which is an alloy of silicon and the intermediate alloy element is formed.

  Thereafter, when this silicon intermediate alloy is immersed in a molten element (Y) bath specified in Table 1, the molten element (Y) penetrates while diffusing into the silicon intermediate alloy, and the intermediate alloy element ( X) forms a molten element (Y) and an alloy layer as a second phase. Alternatively, 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. As a result, when the silicon atoms are aggregated in a nano size from the diffused state, a network of silicon atoms is formed, and a three-dimensional network structure is formed.

  In addition, the silicon primary crystal which is not an alloy in the intermediate alloy remains in the silicon primary crystal regardless of the precipitation of silicon fine particles in the dipping process and not related to the removal of the second phase such as decomponent corrosion. Therefore, silicon once crystallized is coarse and does not form a three-dimensional network structure. Therefore, in the step of forming the silicon intermediate alloy, it is preferable that no silicon crystal is generated in the silicon alloy.

From the above process, the following conditions are required for the intermediate alloy element (X) and the molten metal element (Y).
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.

  Considering the above conditions 1 to 4, 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.

  When Cu is used as the intermediate alloy element, 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.

  When Mg is used as the intermediate alloy element, 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.

  When Ni is used as the intermediate alloy element, 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.

  When Ti is used as the intermediate alloy element, 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.

  Two or more of the listed elements can be used as the intermediate alloy element. In that case, as the molten element, a molten element corresponding to any of these intermediate alloy elements is used.

(First manufacturing method of porous silicon particles)
A method for producing porous silicon particles according to the present invention will be described.
First, as shown in 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, 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 intermediate alloy may be manufactured by a direct spinning method. Alternatively, 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 μm to 2 mm, more preferably 0.1 to 500 μm, and further preferably 0.1 to 50 μm. 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.

  Next, 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. A second phase composed of the molten metal element substituted by the spinodal decomposition of silicon (precipitation of silicon fine particles) and the second phase which is an alloy of the intermediate alloy element and the molten alloy element or the intermediate alloy element is immersed in the molten metal element. Let it form. Si fine particles are formed for the first time in this dipping process. In the dipping process, for example, a molten metal device 21 as shown in FIG. 4 is used, and the ribbon-shaped silicon intermediate alloy 19 is dipped in the molten metal 23 of the molten metal element. Thereafter, the film is wound up via the sink roll 25 and the support roll 27. 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 the immersion is performed for 10,000 seconds or more. 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.

  Thereafter, 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.

  After the second phase is removed by dissolution with an acid, alkali, organic solvent, or the like, or distillation at elevated temperature and reduced pressure, porous silicon particles composed of fine particles are obtained. If dissolved with acid, alkali, organic solvent, etc., wash and dry. Depending on the silicon concentration of the silicon intermediate alloy and the cooling rate during the production of the silicon intermediate alloy, the particle size becomes 0.1 μm to 1000 μm. Note that the particle size is reduced by lowering the silicon concentration or increasing the cooling rate. When used as the negative electrode active material, the average particle diameter is preferably 0.1 to 50 μm, more preferably 1 to 30 μm, and further preferably 5 to 20 μm. Therefore, 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.

(Second production method of porous silicon particles)
Silicon, As, Ba, Ca, Ce, Co, Cr, Cu, Er, Fe, Gd, Hf, Lu, Mg, Mn, Mo, Nb, Nd, Ni, P, Pd, Pr, listed in Table 1 One or more intermediate alloys selected from the group consisting of Pt, Pu, Re, Rh, Ru, Sc, Sm, Sr, Ta, Te, Th, Ti, Tm, U, V, W, Y, Yb, Zr A mixture in which the elements are mixed 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 a method of obtaining a massive ingot by the ingot producing method shown in FIG. A granular silicon intermediate alloy is produced.

  FIG. 5A shows a gas atomizing apparatus 31 that can produce a powdered silicon intermediate alloy 39 by a gas atomizing method. In 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. 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. First, 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 μm 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.

  Next, 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. As 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.

  In the 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 basin 65 and immersed in a molten metal 69 of a molten element. At that time, as shown in FIG. 7A, 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.

  Thereafter, as in the first production method, the second phase is removed to obtain porous silicon particles.

(Effect of porous silicon particles)
According to the present invention, porous silicon particles having an unprecedented three-dimensional network structure can be obtained.

  According to the present invention, 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.

  When the porous silicon 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 porous silicon particles according to the present invention can also be used as a solar cell, a light emitter, and further as a filter material.

Hereinafter, the present invention will be specifically described using examples and comparative examples.
[Example 1]
Silicon (lumpy, purity: 95.0% or more) and cobalt were blended at a ratio of Si: Co = 55: 45 (atomic%), and dissolved in a vacuum furnace at 1480 ° C. Thereafter, the ribbon was rapidly cooled using a single roll casting machine at a cooling rate of 800 K / s to produce a silicon alloy ribbon having a thickness of 200 μm. This was immersed in molten tin at 940 ° C. for 1 minute, and then immediately quenched with argon gas. By this treatment, a two-phase composite composed of Si and Co—Sn or Sn was obtained. This two-phase composite was immersed in a 20% nitric acid aqueous solution for 5 minutes to obtain porous silicon particles.

[Examples 2 to 11]
The production conditions for each example and comparative example are summarized in Table 2. In Examples 2 to 11, porous silicon composites were obtained in the same manner as in Example 1 except for the production conditions such as the intermediate alloy elements shown in Table 2 and the blending ratio of each element.

[Example 12]
Si (Mass, purity: 95.0% or more) and magnesium were blended at a ratio of Si: Mg = 12: 88 (atomic%), and this was melted at 1090 ° C. in a state where the inside of the vacuum furnace was replaced with argon gas. . Then, after casting into a mold and solidifying, it was mechanically pulverized to produce a 5 mm square silicon alloy ingot. This was immersed in molten lead at 470 ° C. for 30 minutes, and then immediately cooled with argon gas. By this treatment, a two-phase composite composed of Si and Mg—Pb or Pb was obtained. The two-phase composite was immersed in a 20% nitric acid aqueous solution for 180 minutes to obtain porous silicon particles.

[Examples 13 to 16]
In Examples 13 to 16, porous silicon composites were obtained in the same manner as in Example 12 except for the production conditions such as the intermediate alloy elements shown in Table 2 and the blending ratio of each element.

[Comparative Example 1]
Silicon powder and magnesium powder were blended at a ratio of Si: Mg = 55: 45 (atomic%) and dissolved at 1087 ° C. in an argon atmosphere. Thereafter, a silicon alloy tape having a thickness of 1 mm was produced at a cooling rate of 200 K / s using a twin roll casting machine. This was immersed in molten bismuth at 500 ° C. for 30 minutes, and then immediately cooled with argon gas. This composite was immersed in a 20% nitric acid aqueous solution for 180 minutes.

[Comparative Example 2]
Silicon particles having an average particle size of 5 μm (SIE23PB, manufactured by High Purity Chemical Laboratory) are etched using a mixed acid in which 20% by mass of hydrogen fluoride water and 25% by mass of nitric acid are mixed, filtered, and porous Quality silicon particles were obtained.

[Comparative Example 3]
Silicon particles having an average particle diameter of 5 μm (SIE23PB, manufactured by High Purity Chemical Laboratory) were used.

[Evaluation]
(Observation of particle shape)
The particle shape of the porous silicon particles was observed using a scanning transmission electron microscope (manufactured by JEOL, JEM 3100FEF). FIG. 8 shows an SEM photograph of the particles according to Example 12, and FIG. 9 shows an SEM photograph of the particles according to Comparative Example 1. In FIG. 8, 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. On the other hand, in FIG. 9, a wall-like structure having a thickness of about 5 μm 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 2 obtained by the etching method, the value in the region near the surface compared to the region inside the particle. The average particle size of the fine particles was small, and the value of Ds / Di was small.

  The Si concentration of the silicon fine particles and the porous silicon particles was measured by an electron beam microanalyzer (EPMA) or energy dispersive X-ray analysis (EDX). 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.

  In addition, 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. In the examples, the value of Xs / Xi is between 0.5 and 1.5. However, in Comparative Example 2 obtained by the etching method, the pore structure in the surface vicinity region is larger than that in the particle inner region. Because of its development, Xs / Xi increased.

  FIG. 10 is an X-ray diffraction grating image obtained by measuring silicon fine particles constituting the porous silicon particles according to Example 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.

(Evaluation of cycle characteristics when particles are used for negative electrode)
(I) Preparation of Negative Electrode Slurry 65 parts by mass of particles according to Examples and Comparative Examples and 20 parts by mass of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.) were charged into a mixer. Furthermore, 5 mass parts of a styrene butadiene rubber (SBR) 5 mass% emulsion (manufactured by Zeon Corporation, BM400B) as a binder, and carboxymethylcellulose sodium (Daicel) as a thickener to adjust the viscosity of the slurry. A slurry was prepared by mixing a 1% by mass solution of Chemical Industry Co., Ltd. at a ratio of 10 parts by mass in terms of solid content.
(Ii) Production of negative electrode Using the automatic coating apparatus, the prepared slurry was applied to a 10 μm thick electrolytic copper foil for current collector (manufactured by Furukawa Electric Co., Ltd., NC-WS) with a thickness of 10 μm. After drying at 70 ° C., a negative electrode for a lithium ion battery was manufactured through a thickness adjustment step using a press.
(Iii) Characteristic evaluation A negative electrode for a lithium ion battery is cut out to φ20 mm, a metal Li is used for a counter electrode and a reference electrode, and an electrolytic solution composed of a mixed solution of ethylene carbonate and diethyl carbonate containing 1 mol / L LiPF 6 is injected, An electrochemical test cell was constructed. The electrochemical test cell was assembled in a glove box having a dew point of −60 ° C. or lower. The charge / discharge characteristics were evaluated by measuring the initial discharge capacity and the discharge capacity after 50 cycles of charge / discharge, and calculating the discharge capacity retention rate. The discharge capacity was calculated based on the total weight of the active material Si effective for occlusion / release of lithium. First, in a 25 ° C. environment, charging is performed under a constant current condition of 0.1 C, and the voltage value is reduced to 0.02 V (the reference electrode Li / Li + oxidation-reduction potential is based on 0 V, the same applies hereinafter). At that point, charging was stopped. Next, discharging was performed under a condition of a current value of 0.1 C until the voltage with respect to the reference electrode became 1.5 V, and a 0.1 C initial discharge capacity was measured. In addition, 0.1 C is a current value that can be fully charged in 10 hours. Next, the above charge / discharge cycle was repeated 50 cycles at a charge / discharge rate of 0.1C. The ratio of the discharge capacity when charging / discharging was repeated 50 cycles with respect to the initial discharge capacity was obtained as a percentage, and the discharge capacity retention rate after 50 cycles was determined.

  The evaluation results are summarized in Table 3. Since Examples 13 to 16 have large silicon particles, the characteristics were evaluated using particles that were pulverized and reduced in a mortar. For example, the particle size 130⇒33 of the porous silicon particles of Example 13 means that the porous silicon particles having an average particle size of 130 μm were pulverized to obtain porous silicon particles having an average particle size of 33 μm. To do.

As shown in the table, each example has a higher capacity retention after 50 cycles than Comparative Examples 1 to 3, 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. Is done.
In each example, since the negative electrode active material is a porous silicon particle having a three-dimensional network structure, even if a volume change of expansion / contraction occurs due to alloying / dealloying of Li and Si during charge / discharge. The silicon particles are not cracked or pulverized, and the discharge capacity retention rate is high.

Comparing in more detail, in Comparative Example 1, pure Si crystallized as an initial crystal when the intermediate alloy was produced, and a eutectic structure (Si and Mg 2 Si) was generated at the end of solidification. The primary crystal Si was as coarse as about 10 μm. Even if this was immersed in molten bismuth, it was not refined but was coarsened, and remained as it was even after the etching process. Therefore, when repeating intrusion / release of Li, Si alone including coarse Si cannot follow the volume change of expansion / contraction due to charge / discharge = Li / Si alloying / dealloying. It is considered that the percentage of the current collection path and electrode function lost due to collapse and the battery life was shortened.

  In Comparative Example 2, 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.

  In the comparative example 3, since it is a mere silicon particle which does not have a pore structure, it cannot follow the volume change by charging / discharging, and it is thought that cycling characteristics are bad.

  The preferred embodiments of the present invention have been described above with reference to the accompanying drawings, but the present invention is not limited to such examples. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the technical idea disclosed in the present application, and these are naturally within the technical scope of the present invention. Understood.

DESCRIPTION OF SYMBOLS 1 ......... Porous silicon particle 3 ......... Silicon fine particle S ......... Surface vicinity region I ......... Particle internal region 7 ......... Silicon intermediate alloy 9 ......... Second phase 11 ......... Single roll casting machine 13 ......... Silicon alloy 15 ......... Crucible 17 ......... Steel roll 19 ......... Ribbon-like silicon intermediate alloy 21 ......... Melting device 23 ......... Melting metal 25 ......... Sink roll 27 ......... Support roll 31 ……… Gas atomizing device 33 ……… Crucible 35 ……… Nozzle 37 ……… Gas injector 39 ……… Powdered silicon intermediate alloy 41 ……… Rotating disk atomizing device 43 ……… Crucible 45 ……… Nozzle 49 ......... Rotating disk 51 ......... Powdered silicon intermediate alloy 53 ......... Crucible 55 ......... Mold 57 ......... Lumped silicon intermediate alloy 61 ......... Melting device 63 ......... Granular silicon Intermediate alloy 65 ...... Immersion bowl 67 ......... Pressure cylinder 69 ......... Melute 71 ......... Melute immersion apparatus 73 ......... Particulate silicon intermediate alloy 75 ...... Immersion bowl 77 ......... Pressure cylinder 79 ……… Molten metal 81 ……… Mechanical stirrer 83 ……… Gas blowing plug

Claims (13)

  1. Porous silicon particles formed by bonding a plurality of silicon fine particles,
    The average particle diameter of the porous silicon particles is 0.1 μm to 1000 μm,
    The porous silicon particles have a three-dimensional network structure having continuous voids,
    The average porosity of the porous silicon particles is 15 to 93%,
    Xs / Xi, which is the ratio of the porosity Xs of the near-surface region of 50% or more in the radial direction and the porosity Xi of the particle internal region within 50% in the radial direction, is 0.5 to 1.5,
    A porous silicon particle comprising 80 atomic% or more of silicon in a ratio of elements excluding oxygen.
  2. The silicon fine particles have an average particle diameter or average column diameter of 2 nm to 2 μm,
    The ratio Ds / Di, which is the ratio of the average particle diameter Ds of the silicon fine particles in the region near the surface of 50% or more in the radial direction and the average particle diameter Di of the silicon fine particles in the particle inner region within 50% in the radial direction, is 0. .5 to 1.5,
    2. The porous silicon particle according to claim 1, wherein the silicon fine particle is a solid silicon fine particle containing 80 atomic% or more of silicon in an element ratio excluding oxygen.
  3.   3. The porous silicon particle according to claim 1, wherein an area of a joint portion between the silicon fine particles is 30% or less of a surface area of the silicon fine particles.
  4. It is an alloy of silicon and one or more intermediate alloy elements shown in the following Table 1, the ratio of silicon is 10 atomic% or more of the whole, and Si in Table 1 below corresponding to the intermediate alloy element contained A step (a) of producing a silicon intermediate alloy having a maximum content of not more than the highest value;
    A step (b) of separating the silicon fine particles and the second phase by immersing them in a melt of one or more melt elements listed in Table 1 corresponding to the intermediate alloy element;
    Removing the second phase (c);
    Comprising
    The method for producing porous silicon particles, wherein the second phase is composed of an alloy of the intermediate alloy element and the molten element and / or the molten element replaced with the intermediate alloy element.
  5. In the step (a),
    5. The porous structure according to claim 4, wherein the silicon intermediate alloy has a ribbon shape, a foil piece shape or a linear shape with a thickness of 0.1 μm to 2 mm, or a granular shape or a lump shape with a particle size of 10 μm to 50 mm. For producing fine silicon particles.
  6. The step (c)
    Removing the second phase by dissolving it in at least one of an acid, an alkali and an organic solvent;
    Alternatively, the method for producing porous silicon particles according to claim 4, further comprising a step of evaporating and removing only the second phase by heating and depressurizing.
  7. The step (a)
    The porous silicon particle according to any one of claims 4 to 6, which is a step of producing a ribbon-like silicon intermediate alloy from the molten metal of silicon and the intermediate alloy element by a single roll casting machine. Manufacturing method.
  8. The step (a)
    7. The process according to claim 4, wherein the molten silicon alloy is a step of producing a powdery silicon intermediate alloy using a gas atomizing method or a rotating disk atomizing method. Of producing porous silicon particles.
  9. The step (a)
    The porous silicon according to any one of claims 4 to 6, further comprising a step of producing a lump silicon intermediate alloy by cooling the molten metal of the silicon and the intermediate alloy element in a mold. Particle production method.
  10. Silicon is mixed with Cu so that the silicon ratio is 10 to 30 atomic% of the whole, and ribbons, foil pieces and lines having a thickness of 0.1 μm to 2 mm, or particles and blocks having a particle diameter of 10 μm to 50 mm are used. The step (a) of producing a silicon intermediate alloy of
    The silicon alloy is immersed in a melt mainly composed of one or more melt elements selected from the group consisting of Al, Be, Cd, Ga, In, Sb, Sn, and Zn, and silicon fine particles, a second phase, (B) separating into
    Removing the second phase (c);
    Comprising
    The method for producing porous silicon particles, wherein in the step (b), the second phase is composed of an alloy of the Cu and the molten metal element and / or the molten metal element substituted for the Cu.
  11. Silicon is blended in Mg so that the ratio of silicon is 10 to 50 atomic%, and ribbons, foil pieces and lines having a thickness of 0.1 μm to 2 mm, or particles and blocks having a particle diameter of 10 μm to 50 mm are used. The step (a) of producing a silicon intermediate alloy of
    The silicon alloy is immersed in a melt mainly composed of one or more melt elements selected from the group consisting of Ag, Al, Au, Be, Bi, Ga, In, Pb, Sb, Sn, Tl, and Zn, A step (b) of separating the silicon fine particles into a second phase;
    Removing the second phase (c);
    Comprising
    The method for producing porous silicon particles according to the step (b), wherein the second phase is composed of an alloy of the Mg and the molten metal element and / or the molten metal element substituted for the Mg.
  12. Silicon is blended in Ni so that the ratio of silicon is 10 to 55 atomic% of the whole, and ribbons, foil pieces and lines having a thickness of 0.1 μm to 2 mm, or particles and blocks having a particle diameter of 10 μm to 50 mm are used. The step (a) of producing a silicon intermediate alloy of
    The silicon alloy is immersed in a melt mainly composed of one or more melt elements selected from the group consisting of Al, Be, Cd, Ga, In, Sb, Sn, and Zn, and silicon fine particles, a second phase, (B) separating into
    Removing the second phase (c);
    Comprising
    The method for producing porous silicon particles, wherein in the step (b), the second phase is composed of an alloy of the Ni and the molten element and / or the molten element substituted for the Ni.
  13. Silicon is blended in Ti so that the proportion of silicon is 10 to 82 atomic% of the whole, and ribbons, foil pieces and lines having a thickness of 0.1 μm to 2 mm, or particles and blocks having a particle size of 10 μm to 50 mm are used. The step (a) of producing a silicon intermediate alloy of
    The silicon alloy is immersed in a melt mainly composed of one or more melt elements selected from the group consisting of Ag, Al, Au, Be, Bi, Cd, Ga, In, Pb, Sb, Sn, Zn, A step (b) of separating the silicon fine particles into a second phase;
    Removing the second phase (c);
    Comprising
    The method for producing porous silicon particles, wherein in the step (b), the second phase is composed of an alloy of the Ti and the molten element and / or the molten element substituted for the Ti.
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