Composite particle, production method for composite particle, negative electrode active material for secondary battery, negative electrode, and secondary battery

Abstract

The present invention pertains to a composite particle having a matrix phase, which contains at least one silicon particle and Si and O elements provided on the outer side of the silicon particle, the composite particle also containing a silicate compound, wherein the silicate compound contains at least one metal element selected from the group consisting of Li, K, Na, Ca, Mg, and Al.

Description

Composite particles, method for producing composite particles, negative electrode active material for secondary battery, negative electrode and secondary battery

[0001] The present invention relates to composite particles, a method for producing composite particles, a negative electrode active material for secondary batteries containing the composite particles, a negative electrode containing the negative electrode active material, and a secondary battery containing the negative electrode.

[0002] In response to environmental concerns about energy demand, the deployment of electric vehicles (EVs) is rapidly progressing, expanding the scope of use of lithium-ion batteries (LIBs). Graphite, the mainstream LIB anode material, has a low theoretical capacity density (372 mAh / g). To improve battery capacity, active materials using silicon, tin, and oxides have been actively developed. However, these materials undergo large volume expansion and contraction upon absorption and desorption of lithium ions, resulting in the active material becoming pulverized with repeated charge / discharge cycles, which leads to poor charge / discharge characteristics.

[0003] Patent Document 1 describes an anode active material comprising a carbonaceous matrix containing a plurality of nanoparticles, the nanoparticles comprising a silicon core, an oxide film layer containing SiOx (0<x≦2) disposed on the silicon core, and a coating layer containing LiF covering at least a portion of the surface of the oxide film layer.

[0004] Patent Document 2 discloses a negative electrode active material particle, which contains silicon compound (SiOx: 0.5≦x≦1.6) particles, and at least a part of the negative electrode active material particle is coated with a carbon material and Li ２ SiO ３ and Li ２ Si ２ O ５ When the negative electrode active material particles are measured by X-ray diffraction using Cu-Kα rays, the intensity of the peak at around 2θ = 28.4° attributed to a Si crystal structure obtained by the X-ray diffraction is Ia, and the intensity of the peak at around 2θ = 28.4° attributed to a Li crystal structure obtained by the X-ray diffraction is Ib. ２ SiO ３ The peak intensity Ib of the peak attributed to Li obtained by the X-ray diffraction ２ Si ２ O ５The document describes a negative electrode active material for a non-aqueous electrolyte secondary battery, in which the peak intensity Ic of the peak attributed to satisfies Ib / Ia≦4.8 and Ic / Ia≦6.0.

[0005] Patent Document 3 describes a Si—O—C—Li composite comprising nanosilicon, a silicon-oxygen-lithium compound, and a carbon coating, wherein the silicon-oxygen-lithium compound is partially crystallized, and the composite further comprises silicon oxide, wherein the nanosilicon is dispersed in the silicon-oxygen-lithium compound to form fused particles, and the fused particles are dispersed in a matrix of silicon oxide in an islands-in-a-sea fashion to form composite particles, and the carbon coating is applied to the surfaces of the composite particles.

[0006] Japanese Patent Publication No. 2022-125285 Japanese Patent Publication No. 2020-113495 Japanese Patent No. 7094957

[0007] However, the negative electrode active material described in Patent Document 1 has Si particles coated with LiF, which may not be able to withstand the silicon expansion that accompanies the absorption and desorption of lithium ions. To suppress such Si expansion, it is thought that it is necessary to provide a structure such as a matrix phase.

[0008] In the negative electrode active material of Patent Document 2, Li needs to be sufficiently diffused into the interior to improve performance, but this requires an increased amount of Li added. Increasing the amount of Li added leads to increased costs and may reduce the initial efficiency of secondary batteries when stored in air for long periods of time. Therefore, it is preferable to reduce the amount of Li added as much as possible. Furthermore, to improve performance, it is necessary to control the structure of the active material with a small amount of Li. Specifically, it is preferable for Li to be selectively present on the surface of the active material, which suppresses surface side reactions with the electrolyte and improves battery performance.

[0009] The composite described in Patent Document 3 simply covers silicon with a silicon-oxy-lithium compound, silicon oxide, and a carbon coating, which is not able to withstand the expansion suppression of Si. Patent Document 3 also describes that "the obtained composite has a stable structure, effectively preventing components such as air from penetrating the inside of the particles and causing the active ingredient to become ineffective, and the structure and properties do not deteriorate even after long-term storage," but this has not been substantiated by quantitative evaluation in the examples, etc., and it cannot necessarily be said that the quality is stable even after long-term storage as described above.

[0010] In the prior art described in the above Patent Documents 1 to 3, SiO ２ In order to improve charge-discharge characteristics, it is necessary to control the concentration of metal elements inside the active material, and furthermore, to suppress surface side reactions with the electrolyte, it is necessary to control the structure of the active material surface.

[0011] The present invention aims to provide composite particles that can suppress surface side reactions with an electrolyte and Si expansion during repeated charge and discharge, thereby further improving the initial charge and discharge efficiency and cycle characteristics of the active material, a method for producing the composite particles, a negative electrode active material for a secondary battery containing the composite particles, a negative electrode containing the negative electrode active material, and a secondary battery containing the negative electrode. The present invention also aims to provide composite particles and a negative electrode active material for a secondary battery containing the composite particles, which have stable quality and do not exhibit a decrease in initial efficiency or the like when used as a secondary battery after long-term storage in air by controlling the amount of Li added.

[0012] As a result of intensive research to solve the above problems, the inventors have discovered that a composite particle structure containing a specific metal silicate and a matrix phase containing Si and O elements that suppresses the expansion of Si during charge and discharge can be produced. Furthermore, they have discovered that by controlling the concentration of the metal portion of this metal silicate and selectively distributing the metal element, side reactions on the surface can be suppressed, leading to improved charge and discharge performance.

[0013] The present invention has the following aspects. [1] Composite particles having at least one silicon particle and a matrix phase containing Si and O elements outside the silicon particle, and further containing a silicate compound, the silicate compound containing at least one metal element selected from the group consisting of Li, K, Na, Ca, Mg, and Al. [2] The composite particles according to [1], in which the metal ion element concentration of the metal element is 0.1 to 40.0 atom % of the total elements of the composite particle. [3] The composite particles according to [1] or [2], in which, when A is the ratio of the metal ion element to all elements present in a region extending 30% inward from the surface of the composite particle and B is the ratio of the metal ion element to all elements present in the remaining region, the metal ion element abundance ratio satisfies 0.5<A / (A+B)<1.0. [4] The composite particles according to any one of [1] to [3], in which the silicate compound contains Li element. [5] The composite particle according to any one of [1] to [4], wherein the silicate compound has a crystal structure represented by LixSiyOz (where x, y, and z are integers greater than 0). [6] The composite particle according to any one of [1] to [5], wherein the silicate compound has a crystal structure represented by LixSiyOz (where x + 4y - 2z = 0 is satisfied). [7] The composite particle according to any one of [1] to [5], wherein the silicate compound is Li ２ SiO ３ , Li ４ SiO ４ , and Li ２ Si ２ O ５ [8] The composite particle according to any one of [1] to [7], which contains at least one crystal structure selected from the group consisting of:

[111] ,

[12] ,

[13] ,

[14] ,

[15] ,

[16] ,

[17] ,

[18] ,

[19] ,

[20] ,

[21] ,

[22] ,

[23] ,

[24] ,

[25] ,

[26] ,

[27] ,

[28] ,

[29] ,

[30] ,

[31] ,

[32] ,

[33] ,

[34] ,

[35] ,

[36] ,

[37] ,

[38] ,

[39] ,

[40] ,

[41] ,

[42] ,

[43] ,

[44] ,

[45] ,

[46] ,

[47] ,

[48] ,

[49] ,

[50] ,

[51] ,

[52] ,

[53] ,

[54] ,

[55] ,

[56] ,

[57] ,

[60] ,

[61] ,

[62] ,

[63] ,

[64] ,

[65] ,

[70] ,

[71] ,

[72] ,

[73] ,

[74] ,

[75] ,

[76] ,

[77] ,

[88] ,

[89] ,

[90] ,

[91] ,

[92] ,

[93] ,

[94] ,

[95] ,

[96] ,

[97] ,

[98] ,

[99] ,

[100] ,

[101] ,

[102] ,

[103] ,

[104] ,

[105] ,

[106] ,

[107] ,

[110] ,

[111] ,

[112] ,

[113] ,

[114] ,

[115] ,

[120] ,

[121] ,

[122] ,

[131] , [132 ２ SiO ３

[10] The composite particle according to any one of [1] to [8], wherein the peak intensity D corresponding to the (111) plane in the X-ray diffraction spectrum of the silicon particle satisfies 0<D / C≦0.6.

[11] The composite particle according to any one of [1] to [8], wherein the peak intensity D corresponding to the (111) plane in the X-ray diffraction spectrum of the silicon particle satisfies 0<D / C≦0.6.

[12] The composite particle according to any one of [1] to [8], wherein the peak intensity D corresponding to the (111) plane in the X-ray diffraction spectrum of the silicon particle satisfies 0<D / C≦0.6. ２ SiO ３

[11] The composite particles according to any one of [1] to [9], wherein the crystallite size y satisfies 1 nm < y < 40 nm in the X-ray diffraction peak corresponding to the (111) plane of the composite particles.

[11] The composite particles according to any one of [1] to [9], wherein the average particle size x is 1 μm < x < 15 μm and the specific surface area n is 0.1 m ２ / g<n<20m ２ / g.

[12] Composite particles according to any one of [1] to

[11] , wherein the matrix phase contains not only Si and O elements but also C elements.

[13] A method for producing composite particles according to any one of [1] to

[12] , comprising the following steps 1 and 2: Step 1: mixing at least one metal element compound selected from the group consisting of Li, K, Na, Ca, Mg, and Al with an intermediate derived from a polysiloxane resin containing silicon particles; and Step 2: firing at 900°C or less in an oxygen-free atmosphere.

[14] A negative electrode active material for a secondary battery, comprising the composite particles according to any one of [1] to

[12] .

[15] A negative electrode comprising the negative electrode active material for a secondary battery according to

[14] .

[16] A secondary battery comprising the negative electrode according to

[15] .

[0014] The composite particles of the present invention can suppress surface side reactions and maintain high charge-discharge performance, such as capacity retention rate and initial coulombic efficiency, in secondary batteries. Furthermore, the composite particles of the present invention do not decrease in initial efficiency when used in secondary batteries after long-term storage in the atmosphere, and have stable quality.

[0015] Hereinafter, embodiments of the present invention will be described in detail. In this specification, "mass" is synonymous with "weight." Furthermore, in this specification, unless otherwise specified, the term "to" indicating a range of values ​​is used to mean that the values ​​before and after it are included as the lower and upper limits.

[0016] [Composite Particles] The composite particles of this embodiment have at least one silicon particle and a matrix phase containing Si and O elements outside the silicon particle, and further contain a silicate compound, where the silicate compound contains at least one metal element selected from the group consisting of Li, K, Na, Ca, Mg, and Al. The composite particles of this embodiment are characterized in that a plurality of silicon particles are dispersed and embedded in the matrix phase, and the silicate compound is further present as a distributed component. The silicate compound may be present outside the matrix phase as a silicate layer, or may be present inside the silicon particle or the matrix phase, or both.

[0017] (Silicon Particles) The silicon particles in the composite particles of this embodiment are composed of zero-valent silicon and have an average particle size of 300 nm or less. The average particle size of the silicon particles is preferably 5 nm to 300 nm, more preferably 20 nm to 250 nm, and even more preferably 50 nm to 200 nm. When the average particle size of the silicon particles is within this range, high charge / discharge performance such as the capacity retention rate and initial coulombic efficiency of the secondary battery can be maintained. The average particle size of the silicon particles can be obtained by observing the composite particles of this embodiment with a TEM and calculating the average particle size of 50 silicon particles randomly selected from the TEM image at 50,000 magnifications.

[0018] The silicon particles constituting the composite particles of this embodiment have a peak intensity C corresponding to the (111) plane of the silicon particles in the X-ray diffraction spectrum and Li ２ SiO ３ It is preferable that the peak intensity D corresponding to the (111) plane in the X-ray diffraction spectrum of the secondary battery satisfies the relationship 0<D / C≦0.6. The peak intensity range is more preferably 0.05<D / C≦0.5. When this peak intensity range is satisfied, the secondary battery can maintain high charge-discharge performance, such as the capacity retention rate and initial coulombic efficiency.

[0019] In the peak in the X-ray diffraction spectrum where 2θ corresponds to the (111) plane of the silicon crystal structure, the crystallite size x obtained by Scherrer's calculation using the peak half-width is 10 nm < x < 30 nm, and Li２ SiO ３ In the X-ray diffraction peak corresponding to the (111) plane, the crystallite size y is preferably 1 nm<y<40 nm. When the crystallite size satisfies this range, the charge-discharge performance such as the capacity retention rate and the initial coulombic efficiency of the secondary battery can be maintained at a high level.

[0020] The specific surface area of ​​the silicon particles is set to 50 m from the viewpoint of charge / discharge capacity, initial coulomb efficiency, and cycle characteristics. ２ / g~400m ２ / g is preferred, and 100m ２ / g to 300m ２ / g is more preferred, and 150m ２ / g~230m ２ / g is more preferable. The specific surface area is a value determined by the BET method, and can be determined by nitrogen gas adsorption measurement, for example, using a specific surface area measuring device. In addition, in order to remove organic deposits on the silicon particles, it is preferable to perform a heat treatment at 500°C for 2 hours in a nitrogen atmosphere before measuring the specific surface area.

[0021] The silicon particles are not particularly limited in shape and may be, for example, granular, needle-like, or flake-like. However, from the viewpoint of charge / discharge performance when used as a secondary battery, the length in the major axis direction is preferably 30 nm to 300 nm, and the thickness is preferably 1 nm to 60 nm. From the viewpoint of charge / discharge performance when used as a secondary battery, a needle-like or flake-like shape with an aspect ratio (length-to-thickness ratio) of 0.5 or less is preferred. The silicon particle morphology can be measured by dynamic light scattering to measure the average particle size, but the aspect ratio of a sample can be more easily and precisely identified using analytical tools such as a transmission electron microscope (TEM) or a field emission scanning electron microscope (FE-SEM). In the case of silicon particles, the sample can be cut with a focused ion beam (FIB) and the cross section can be observed with an FE-SEM, or the sample can be sliced ​​and the state can be identified by TEM observation. The aspect ratio of silicon particles is a calculation result based on the major portion of the sample (50 particles) within the field of view of the TEM image.

[0022] (Matrix Phase) The matrix phase present outside the silicon particles contains at least Si and O. The matrix phase preferably has a composition expressed by SiOx (1<x<2) and further preferably contains carbonaceous (C) as a component. The matrix phase is a three-dimensional network structure of a silicon-oxygen skeleton containing at least silicon and oxygen. Preferably, the matrix phase is a three-dimensional network structure of a silicon-oxygen-carbon skeleton containing silicon, carbon, and oxygen. This three-dimensional network structure of a silicon-oxygen-carbon skeleton has relatively high chemical stability, forms a composite structure with carbon (carbonaceous phase), and exhibits small volumetric changes with respect to the absorption and desorption of lithium. In particular, it is preferable that the three-dimensional network structure of the matrix phase contains a silicon oxycarbide (SiOC) structure. This three-dimensional network structure may contain nitrogen in addition to silicon, carbon, and oxygen.

[0023] (Silicate Compound) The silicate compound is generally a compound containing an anion having a structure in which one or more silicon atoms are at the center and electronegative ligands surround the silicon atom, and a silicate compound containing at least one metal (element) selected from the group consisting of Li, K, Na, Ca, Mg, and Al is a salt of the metal and a compound containing an anion.

[0024] Examples of compounds containing the above anions include orthosilicate ions (SiO ４ ４－ ), metasilicate ions (SiO ３ ２－ ), pyrosilicate ions (Si ２ O ７ ６－ ), cyclic silicate ions (Si ３ O ９ ６－ or Si ６ O １８ １２－ ) and other silicate ions.

[0025] The silicate compound is preferably a lithium silicate compound, a magnesium silicate compound, or a sodium silicate compound, more preferably a lithium silicate compound or a magnesium silicate compound, and particularly preferably a lithium silicate compound.

[0026] The lithium silicate compound includes Li ｘ Si ｙ O ｚ (where x, y, and z are integers greater than 0), and Li ｘ Si ｙ O ｚ It is more preferable that the lithium silicate compound has a crystal structure represented by (x + 4y - 2z = 0). Examples of such lithium silicate compounds include lithium metasilicate (Li ２ SiO ３ , Li ２ Si ２ O ５ , Li ４ SiO ４ ) and the lithium silicate compound is Li ２ SiO ３ , Li ４ SiO ４ , and Li ２ Si ２ O ５ It is preferable that the material contains at least one crystal structure selected from the group consisting of:

[0027] Examples of magnesium silicate compounds include magnesium metasilicate (MgSiO ３、 Mg ２ SiO ４ ) are listed.

[0028] Examples of sodium silicate compounds include sodium metasilicate (Na ２ SiO ３ , Na ４ SiO ４ , Na ２ Si ２ O ５ , Na ２ Si ４ O ９ ) are listed.

[0029] The silicate compound may contain two or more of the above metals. When two or more metals are contained, one silicate ion may contain multiple metals, or a mixture of silicate compounds containing different metals may be used. The silicate compound may also contain metals other than the above metals. When the silicate compound is in a crystalline state, it can be detected by powder X-ray diffraction measurement (XRD), and when it is amorphous, it can be detected by powder X-ray diffraction measurement (XRD). ２９ This can be confirmed by Si-NMR measurement.

[0030] The content of the metal element is preferably 25% by mass or less, more preferably 0.1 to 20% by mass, even more preferably 0.2 to 18% by mass, and particularly preferably 0.3 to 15% by mass, relative to the total mass of the composite particles. When the content of the metal element is within this range, surface side reactions of the composite particles can be suppressed, and the charge / discharge performance of the resulting secondary battery can be further improved. It is preferable that the metal element is uniformly dispersed (distributed) within the composite particles, rather than being localized as metal ions in only a few areas. The content of the metal element can be measured, for example, by Auger electron spectroscopy (AES) or an ICP-OES analyzer.

[0031] The silicate compound preferably contains Li, and the Li content is preferably 20 mass % or less, more preferably 0.1 to 19 mass %, even more preferably 0.2 to 17 mass %, and particularly preferably 0.3 to 15 mass %, relative to the total mass of the composite particles. When the Li content is within this range, surface side reactions of the composite particles can be suppressed, and the charge / discharge performance of the secondary battery when formed can be further improved.

[0032] In the composite particle of this embodiment, the metal ion element concentration of the metal element in the total elements of the composite particle is preferably 0.1 to 40.0 atom%, more preferably 0.3 to 35.0 atom%, and particularly preferably 0.5 to 30.0 atom%. When the metal ion element concentration is within this range, side reactions on the surface of the composite particle can be suppressed, and the charge / discharge performance when used as a secondary battery can be further improved. The metal ion element concentration of the metal element can also be measured, for example, by Auger electron spectroscopy (AES).

[0033] In the composite particle of this embodiment, a concentration gradient of the metal ion element may exist, and it is preferable that the concentration is higher in the surface portion of the composite particle than in the interior. Specifically, when the ratio A of the metal ion element to all elements present in the region 30% inward from the surface portion of the composite particle is taken as the ratio B of the metal ion element to all elements present in the remaining region, it is preferable that the metal ion element abundance ratio satisfies 0.5 < A / (A + B) < 1.0. The metal ion element abundance ratio is more preferably 0.6 < A / (A + B) < 0.99, and even more preferably 0.7 < A / (A + B) < 0.98. When the metal ion element abundance ratio is within this range, side reactions on the surface can be suppressed, and the charge / discharge performance of the secondary battery can be further improved.

[0034] The composite particles of this embodiment preferably have an average particle diameter x of 1 μm<x<15 μm, more preferably 2 μm<x<13 μm, and even more preferably 3 μm<x<10 μm. The specific surface area n is preferably 0.1 m ２ / g<n<20m ２ / g, more preferably 0.5m ２ / g<n<18m ２ / g, and more preferably 0.7m ２ / g<n<15m ２ When the average particle diameter and specific surface area of ​​the composite particles are within these ranges, side reactions on the surface can be suppressed, and the charge / discharge performance of the secondary battery can be further improved. In particular, when the average particle diameter x is 1 μm<x<15 μm and the specific surface area n is 0.1 m ２ / g<n<20m ２ / g.

[0035] [Negative electrode active material for secondary battery] The negative electrode active material for secondary battery of this embodiment includes the composite particles of this embodiment. The composite particles of this embodiment themselves have the performance as a negative electrode active material, but the negative electrode active material for secondary battery may also contain components other than the composite particles.

[0036] The negative electrode active material for a secondary battery may have a carbon layer on the surface of the composite particle. That is, at least a portion of the surface of the composite particle may have a carbon coating. The carbon layer (carbon coating) is preferably a coating made of low-crystalline carbon. From the viewpoint of improving chemical stability and thermal stability, the amount of the carbon layer (carbon coating) is preferably 0.1% by mass or more and 30% by mass or less, more preferably 1% by mass or more and 25% by mass or less, and even more preferably 5% by mass or more and 20% by mass or less, based on 100% by mass of the composite active material for a secondary battery. The composite active material for a secondary battery may have a carbon layer (carbon coating) on ​​its surface continuously or intermittently. The carbon layer (carbon coating) is preferably formed on the surface of the active material by chemical vapor deposition.

[0037] The true density of the negative electrode active material for secondary batteries is preferably 1.6 g / cm ３ 2.6g / cm or more ３ From the viewpoint of improving the energy density of the resulting secondary battery, the true density is 1.75 g / cm ３ More preferably, 1.80 g / cm ３ The above is more preferable. The true density is a value measured using a true density measuring device.

[0038] The average particle size of the negative electrode active material for secondary batteries is preferably 2 μm or more and 15 μm or less. When the average particle size is 2 μm or more, a significant increase in the specific surface area can be suppressed, and when used in a secondary battery, the amount of SEI generated during charge and discharge can be suppressed, thereby improving the reversible charge and discharge capacity per unit volume. Furthermore, when the average particle size is 15 μm or less, the adhesion strength with the current collector can be improved, thereby suppressing peeling from the current collector.

[0039] The specific surface area of ​​the negative electrode active material for secondary batteries is 0.1 m ２ / g or more 10m ２ / g or less. The specific surface area is preferably 0.3 m ２ / g or more is more preferable, and 0.5m ２ / g or more is particularly preferred. When the specific surface area is in the above range, the amount of solvent absorbed during electrode preparation can be kept appropriate, and the amount of binder used to maintain binding properties can also be kept appropriate. The specific surface area is a value determined by the BET method, and can be determined by nitrogen gas adsorption measurement, for example, using a specific surface area measurement device.

[0040] [Method for producing composite particles] The method for producing composite particles of this embodiment includes the following steps 1 and 2. Step 1: Mixing at least one metal element compound selected from the group consisting of Li, K, Na, Ca, Mg, and Al with an intermediate derived from a polysiloxane resin containing silicon particles. Step 2: Firing at 900°C or less in an oxygen-free atmosphere. Note that the composite particles of this embodiment are not limited to those obtained by the above-mentioned production method. The description of the production method below is merely one aspect of the method for producing composite particles of this embodiment, and may include steps other than the above steps 1 and 2, and the order of steps 1 and 2 is not particularly limited.

[0041] First, the silicon particles used in step 1 are obtained by wet-pulverizing raw silicon. Specifically, the raw silicon is dispersed in a solvent such as an organic solvent during wet-pulverization to form a silicon slurry, which is a dispersion of silicon particles. The silicon slurry can be prepared while pulverizing the raw silicon in a wet powder pulverizer. It is preferable to add a dispersant to the organic solvent to promote pulverization of the raw silicon. Examples of wet-pulverizers include a roller mill, a high-speed rotary pulverizer, a container-driven mill, and a bead mill. The preferred range of the average particle size of the silicon particles in the obtained silicon slurry is as described above.

[0042] Examples of the organic solvent include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and diisobutyl ketone; alcohols such as ethanol, methanol, normal propyl alcohol, and isopropyl alcohol; and aromatics such as benzene, toluene, and xylene.

[0043] The type of dispersant may be aqueous or non-aqueous, with non-aqueous dispersants being preferred. Examples of non-aqueous dispersants include polymeric dispersants such as polyethers, alcohols, polyalkylene polyamines, and polycarboxylic acid partial alkyl esters, low molecular weight dispersants such as polyhydric alcohol esters and alkyl polyamines, and inorganic dispersants such as polyphosphates. The solids concentration of the silicon particles and dispersant in the silicon slurry is not particularly limited, but is preferably in the range of 5% to 40% by mass, more preferably 10% to 30% by mass, where the total amount of the solvent, dispersant, and silicon particles is 100% by mass. The amount of dispersant added is preferably in the range of 2% to 60% by mass, more preferably 5% to 50% by mass, relative to the total mass of the silicon particles.

[0044] Next, the polysiloxane compound and the silicon slurry obtained by the wet pulverization are uniformly mixed, followed by desolvation, drying, and high-temperature treatment to obtain an intermediate derived from a polysiloxane resin containing silicon particles. Specifically, the matrix phase, which is a three-dimensional network structure of a silicon-oxygen skeleton, and the silicon particles are mixed and homogenized, followed by desolvation, drying, and high-temperature treatment to obtain an intermediate.

[0045] Examples of the polysiloxane compound include resins containing at least one of a polycarbosilane structure, a polysilazane structure, a polysilane structure, and a polysiloxane structure. Resins containing only these structures may be used, or composite resins having at least one of these structures as a segment and chemically bonded to other polymer segments may be used. Forms of composites include graft copolymerization, block copolymerization, random copolymerization, and alternating copolymerization. Examples include composite resins having a graft structure in which a polysiloxane segment is chemically bonded to the side chain of a polymer segment, and composite resins having a block structure in which a polysiloxane segment is chemically bonded to the end of a polymer segment.

[0046] Polysiloxane compounds in which the polysiloxane segment has a structural unit represented by the following general formula (S-1) and / or the following general formula (S-2) are preferred. Among these, polysiloxane compounds in which a carboxy group, an epoxy group, an amino group, or a polyether group is present in a side chain or at the end of the siloxane bond (Si—O—Si) main skeleton are more preferred.

[0047]

[0048]

[0049] In the above general formulas (S-1) and (S-2), R １ represents an aromatic hydrocarbon group, an alkyl group, an epoxy group, a carboxy group, or the like, which may have a substituent. ２ and R ３ respectively represent an alkyl group, a cycloalkyl group, an aryl group or an aralkyl group, an epoxy group, a carboxy group, or the like.

[0050] Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, an isopentyl group, a neopentyl group, a tert-pentyl group, a 1-methylbutyl group, a 2-methylbutyl group, a 1,2-dimethylpropyl group, a 1-ethylpropyl group, a hexyl group, an isohexyl group, a 1-methylpentyl group, a 2-methylpentyl group, a 3-methylpentyl group, a 1,1-dimethylbutyl group, a 1,2-dimethylbutyl group, a 2,2-dimethylbutyl group, a 1-ethylbutyl group, a 1,1,2-trimethylpropyl group, a 1,2,2-trimethylpropyl group, a 1-ethyl-2-methylpropyl group, a 1-ethyl-1-methylpropyl group, etc. Examples of the cycloalkyl group include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group.

[0051] Examples of the aryl group include a phenyl group, a naphthyl group, a 2-methylphenyl group, a 3-methylphenyl group, a 4-methylphenyl group, a 4-vinylphenyl group, and a 3-isopropylphenyl group.

[0052] Examples of the aralkyl group include a benzyl group, a diphenylmethyl group, and a naphthylmethyl group.

[0053] Examples of polymer segments other than polysiloxane segments contained in the polysiloxane compound include vinyl polymer segments such as acrylic polymers, fluoroolefin polymers, vinyl ester polymers, aromatic vinyl polymers, and olefin polymers, as well as polymer segments such as urethane polymer segments, ester polymer segments, and ether polymer segments. Of these, vinyl polymer segments are preferred.

[0054] The polysiloxane compound may be a composite resin in which polysiloxane segments and polymer segments are bonded in a structure represented by the following structural formula (S-3), or may have a three-dimensional network polysiloxane structure.

[0055]

[0056] In the formula, the carbon atom is a carbon atom that constitutes a polymer segment, and the two silicon atoms are silicon atoms that constitute a polysiloxane segment.

[0057] The polysiloxane segment of the polysiloxane compound may have a functional group capable of reacting by heating, such as a polymerizable double bond, in the polysiloxane segment. By subjecting the polysiloxane compound to heat treatment before thermal decomposition, a crosslinking reaction progresses and the compound is solidified, which facilitates thermal decomposition treatment.

[0058] Examples of the polymerizable double bond include a vinyl group and a (meth)acryloyl group. Preferably, two or more polymerizable double bonds are present in the polysiloxane segment, more preferably 3 to 200, and even more preferably 3 to 50. Furthermore, by using a composite resin having two or more polymerizable double bonds as the polysiloxane compound, the crosslinking reaction can be easily promoted.

[0059] The polysiloxane segment may have a silanol group and / or a hydrolyzable silyl group. Examples of the hydrolyzable group in the hydrolyzable silyl group include a halogen atom, an alkoxy group, a substituted alkoxy group, an acyloxy group, a phenoxy group, a mercapto group, an amino group, an amide group, an aminooxy group, an iminoxy group, and an alkenyloxy group. When these groups are hydrolyzed, the hydrolyzable silyl group becomes a silanol group. In parallel with the thermosetting reaction, a hydrolysis condensation reaction occurs between the hydroxyl group in the silanol group and the hydrolyzable group in the hydrolyzable silyl group, thereby obtaining a solid polysiloxane compound.

[0060] The silanol group referred to in the present invention is a silicon-containing group having a hydroxyl group directly bonded to a silicon atom. The hydrolyzable silyl group referred to in the present invention is a silicon-containing group having a hydrolyzable group directly bonded to a silicon atom, and specific examples thereof include groups represented by the following general formula (S-4):

[0061]

[0062] In the formula, R ４ represents a monovalent organic group such as an alkyl group, an aryl group, or an aralkyl group, and R ５ is a halogen atom, an alkoxy group, an acyloxy group, an allyloxy group, a mercapto group, an amino group, an amido group, an aminooxy group, an iminoxy group, or an alkenyloxy group, and b is an integer of 0 to 2.

[0063] Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, an isopentyl group, a neopentyl group, a tert-pentyl group, a 1-methylbutyl group, a 2-methylbutyl group, a 1,2-dimethylpropyl group, a 1-ethylpropyl group, a hexyl group, an isohexyl group, a 1-methylpentyl group, a 2-methylpentyl group, a 3-methylpentyl group, a 1,1-dimethylbutyl group, a 1,2-dimethylbutyl group, a 2,2-dimethylbutyl group, a 1-ethylbutyl group, a 1,1,2-trimethylpropyl group, a 1,2,2-trimethylpropyl group, a 1-ethyl-2-methylpropyl group, and a 1-ethyl-1-methylpropyl group.

[0064] Examples of the aryl group include a phenyl group, a naphthyl group, a 2-methylphenyl group, a 3-methylphenyl group, a 4-methylphenyl group, a 4-vinylphenyl group, and a 3-isopropylphenyl group.

[0065] Examples of the aralkyl group include a benzyl group, a diphenylmethyl group, and a naphthylmethyl group.

[0066] Examples of halogen atoms include fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms.

[0067] Examples of the alkoxy group include a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, a butoxy group, a sec-butoxy group, and a tert-butoxy group.

[0068] Examples of the acyloxy group include a formyloxy group, an acetoxy group, a propanoyloxy group, a butanoyloxy group, a pivaloyloxy group, a pentanoyloxy group, a phenylacetoxy group, an acetoacetoxy group, a benzoyloxy group, and a naphthoyloxy group.

[0069] Examples of the allyloxy group include a phenyloxy group and a naphthyloxy group.

[0070] Examples of the alkenyloxy group include a vinyloxy group, an allyloxy group, a 1-propenyloxy group, an isopropenyloxy group, a 2-butenyloxy group, a 3-butenyloxy group, a 2-pentenyloxy group, a 3-methyl-3-butenyloxy group, and a 2-hexenyloxy group.

[0071] Examples of polysiloxane segments having structural units represented by the general formula (S-1) and / or the general formula (S-2) include those having the following structures:

[0072]

[0073]

[0074]

[0075] R in the above structural formulas (1) to (3) ６ is the above R １ In addition, R in the above structural formulas (4) to (8) has the same meaning as ７ and R ８ are the above R ２ and R ３ It has the same meaning as:

[0076] The polymer segment may have various functional groups as needed, as long as the effects of the present invention are not impaired. Examples of such functional groups include a carboxyl group, a blocked carboxyl group, a carboxylic anhydride group, a tertiary amino group, a hydroxyl group, a blocked hydroxyl group, a cyclocarbonate group, an epoxy group, a carbonyl group, a primary amide group, a secondary amide group, a carbamate group, and a functional group represented by the following structural formula (S-5).

[0077]

[0078] The polymer segment may also have a polymerizable double bond such as a vinyl group or a (meth)acryloyl group.

[0079] The polysiloxane compound is preferably produced by, for example, the following methods (1) to (3).

[0080] (1) A method in which a polymer segment containing a silanol group and / or a hydrolyzable silyl group is prepared in advance as a raw material for the polymer segment, and this polymer segment is mixed with a silane compound having both a silanol group and / or a hydrolyzable silyl group and a polymerizable double bond, followed by a hydrolysis and condensation reaction.

[0081] (2) A method in which a polymer segment containing a silanol group and / or a hydrolyzable silyl group is prepared in advance as a raw material for the polymer segment. A polysiloxane is also prepared in advance by subjecting a silane compound having both a silanol group and / or a hydrolyzable silyl group and a polymerizable double bond to a hydrolysis-condensation reaction. The polymer segment and the polysiloxane are then mixed together to carry out the hydrolysis-condensation reaction.

[0082] (3) A method in which a polymer segment, a silane compound having a silanol group and / or a hydrolyzable silyl group, and a polymerizable double bond, and a polysiloxane are mixed together, and a hydrolysis condensation reaction is carried out to obtain a polysiloxane compound.

[0083] Alternatively, commercially available polysiloxane compounds may be used, such as the Ceranate (registered trademark) series (organic-inorganic hybrid coating resins; manufactured by DIC Corporation) and the Compoceran SQ series (silsesquioxane hybrids; manufactured by Arakawa Chemical Industries, Ltd.).

[0084] To obtain a polysiloxane resin having a silicon-oxygen-carbon skeleton, a carbon source resin that is miscible with the polysiloxane compound may be used together with the polysiloxane compound. Examples of such a carbon source resin include thermosetting resins and thermoplastic resins that contain a molecular structure having a benzene ring or an aromatic functional group.

[0085] Examples of thermosetting resins include phenolic resins such as novolac phenolic resins and resol phenolic resins; epoxy resins such as bisphenol epoxy resins and novolac epoxy resins; melamine resins; urea resins; aniline resins; cyanate resins; furan resins; ketone resins; unsaturated polyester resins; and urethane resins.

[0086] Furthermore, the thermoplastic resin is not particularly limited, and examples thereof include polyethylene, polystyrene, polyacrylonitrile, acrylonitrile-styrene (AS) resin, acrylonitrile-butadiene-styrene (ABS) resin, polypropylene, vinyl chloride, methacrylic resin, polyethylene terephthalate, polyamide, polycarbonate, polyacetal, polyphenylene ether, polybutylene terephthalate, polyphenylene sulfide, polysulfone, polyethersulfone, polyetheretherketone, polyetherimide, polyamideimide, polyimide, and polyphthalamide.

[0087] Then, by removing the solvent, drying, and performing a high-temperature treatment, an intermediate derived from a polysiloxane resin containing silicon particles is obtained. Drying is performed using, for example, a dryer, a reduced-pressure dryer, a spray dryer, or the like. The drying temperature is preferably 80°C or higher and preferably 150°C or lower. Drying may be performed under reduced pressure. The high-temperature treatment is performed according to a firing program defined by the temperature rise rate, the holding time at a constant temperature, and the like. The treatment temperature is preferably, for example, a maximum temperature of 1000°C or higher. The treatment device can be appropriately selected depending on the purpose, from among a fluidized bed reactor, a rotary furnace, a vertical moving bed reactor, a tunnel furnace, a batch furnace, a rotary kiln, and the like.

[0088] (Step 1) Next, at least one metal element compound selected from the group consisting of Li, K, Na, Ca, Mg, and Al is mixed with the intermediate derived from the polysiloxane resin containing silicon particles obtained above (mixing step). Note that in the description of Step 1 below, some steps may be omitted, and there are no particular limitations on the mixing method.

[0089] The metal element compound is not particularly limited as long as it contains the elements described above, and examples of metal element compounds that can be used include oxides, hydroxides, oxyhydroxides, nitrates, oxalates, acetates, and carbonates. Specifically, representative examples include lithium oxide and lithium acetate anhydride when the metal element is Li, and magnesium acetate anhydride when the metal element is Mg. In this embodiment, the metal element compound is preferably lithium acetate anhydride when the metal element is Li, and magnesium acetate anhydride when the metal element is Mg. These metal element compounds may be added by dispersing them in an appropriate organic solvent (polar or non-polar), such as ethanol or MEK. The amount of the metal element compound added is preferably 0.1 to 30% by mass relative to the total mass of the composite particles.

[0090] After adding the metal element compound, mixing is performed to uniformly disperse the metal element in the polysiloxane resin-derived intermediate. Mixing can be performed, for example, using a stirrer equipped with a stirring blade, with the stirring time being, for example, 1 minute to 2 hours, preferably 2 minutes to 1 hour. Stirring can be performed at room temperature, or while heating to about 30 to 50°C. Alternatively, rather than dispersing the metal element compound in an organic solvent and then mixing, the powdered metal element compound may be directly added to the polysiloxane resin-derived intermediate and mixed. Mixing in powder form can be performed using a ball mill or bead mill, with the mixing time being, for example, 1 minute to 2 hours, preferably 2 minutes to 1 hour. Stirring can be performed at room temperature, or while heating to about 30 to 50°C.

[0091] After the mixing in step 1, the solvent is removed and the mixture is dried. The solvent can be removed by a conventional method such as filtration. Drying is carried out using, for example, a dryer, a vacuum dryer, or a spray dryer. The drying temperature is preferably 80°C or higher and 150°C or lower. Drying may be carried out under reduced pressure.

[0092] (Step 2) After the drying, the mixture is fired at 900°C or less in an oxygen-free atmosphere (firing step). The firing apparatus can be selected appropriately depending on the purpose, such as a fluidized bed reactor, rotary furnace, vertical moving bed reactor, tunnel furnace, batch furnace, rotary kiln, etc. The firing is carried out according to a firing program specified by the temperature rise rate, holding time at a constant temperature, etc. The firing temperature is preferably, for example, a maximum temperature of 900°C or less. This allows composite particles containing the metal element of the metal element compound added in the mixing step as a compound to be obtained.

[0093] The non-oxidizing atmosphere during firing is not particularly limited to the type of gas used, and examples thereof include nitrogen, argon, hydrogen, and a mixed gas of nitrogen and hydrogen.

[0094] The fired product obtained above may be further pulverized and, if necessary, classified. The pulverization may be carried out in one stage until the target particle size is reached, or may be carried out in several stages. In addition, in the case of lumps or agglomerated particles with a particle size of 10 mm or more, the particles may be coarsely pulverized using a jaw crusher, a roll crusher, or the like, then pulverized using a glow mill, a ball mill, or the like, and further pulverized using a bead mill, a jet mill, or the like. Classification may be carried out using an air classifier, a wet classifier, or the like.

[0095] The composite particles thus obtained may be used as a secondary battery negative electrode active material as is. When the secondary battery negative electrode active material further has carbon (carbon coating) on ​​its surface, the obtained active material is coated with a carbon coating in a chemical vapor deposition apparatus at a temperature range of 700°C to 1000°C in a flow of a pyrolytic carbon source gas and a carrier inert gas. Examples of pyrolytic carbon source gases include acetylene, ethylene, acetone, alcohol, propane, methane, and ethane. Examples of inert gases include nitrogen, helium, and argon, with nitrogen being typically used.

[0096] In the method for producing composite particles of this embodiment, a metal element compound may be added to the intermediate product after the high-temperature treatment, and the mixture may be calcined. Alternatively, a metal element compound may be added to an intermediate product that has not been subjected to the high-temperature treatment, and the mixture may be calcined. Furthermore, the composite particles obtained by calcination may be washed with a liquid. The liquid washing is performed to remove impurities and unreacted substances, and the liquid preferably has an OH group, such as water or alcohol.

[0097] [Negative Electrode] The negative electrode of this embodiment is not particularly limited as long as it contains the above-described negative electrode active material for a secondary battery, but may also contain other components such as an organic binder and a conductive additive. The negative electrode of this embodiment can be produced by applying a thin film of a slurry containing the composite particles of this embodiment, an organic binder, and, if necessary, other components such as a conductive additive, onto a copper foil current collector. Alternatively, a carbon material such as graphite can be added to the slurry to produce the negative electrode. Examples of carbon materials include natural graphite, artificial graphite, and amorphous carbon such as hard carbon or soft carbon.

[0098] For example, the negative electrode active material for a secondary battery and a binder, which is an organic binding material, are mixed together with a solvent using a dispersing device such as a stirrer, a ball mill, a super sand mill, or a pressure kneader to prepare a negative electrode material slurry, which is then applied to a current collector to form a negative electrode layer. Alternatively, the negative electrode material slurry in paste form can be formed into a sheet, pellet, or other shape and integrated with a current collector.

[0099] Examples of the organic binder include styrene-butadiene rubber copolymers (hereinafter also referred to as "SBR"); unsaturated carboxylic acid copolymers such as ethylenically unsaturated carboxylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, (meth)acrylonitrile, and hydroxyethyl (meth)acrylate, and (meth)acrylic copolymers composed of ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid, and maleic acid; and polymer compounds such as polyvinylidene fluoride, polyethylene oxide, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polyimide, polyamideimide, and carboxymethyl cellulose (hereinafter also referred to as "CMC").

[0100] Depending on their physical properties, these organic binders may be dispersed or dissolved in water, or dissolved in an organic solvent such as N-methyl-2-pyrrolidone (NMP). The content of the organic binder in the negative electrode layer of the lithium ion secondary battery negative electrode is preferably 1% by mass to 30% by mass, more preferably 2% by mass to 20% by mass, and even more preferably 3% by mass to 15% by mass.

[0101] When the content of the organic binder is 1% by mass or more, adhesion is improved and destruction of the negative electrode structure due to expansion and contraction during charge and discharge is further suppressed, while when the content is 30% by mass or less, an increase in electrode resistance is further suppressed.

[0102] Furthermore, the negative electrode material slurry may contain a conductive additive, if necessary. Examples of the conductive additive include carbon black, graphite, acetylene black, and conductive oxides and nitrides. The amount of the conductive additive used may be, for example, 1% by mass to 15% by mass relative to the negative electrode active material of this embodiment.

[0103] The material and shape of the current collector may be, for example, copper, nickel, titanium, stainless steel, or the like, in the form of a foil, perforated foil, mesh, or strip. Porous materials such as porous metal (foamed metal) and carbon paper may also be used.

[0104] Examples of methods for applying the negative electrode material slurry to the current collector include metal mask printing, electrostatic coating, dip coating, spray coating, roll coating, doctor blade coating, gravure coating, screen printing, etc. After application, it is preferable to carry out a rolling treatment using a flat plate press, a calender roll, or the like, as necessary.

[0105] The negative electrode material slurry can be formed into a sheet or pellet form, and the sheet or pellet can be integrated with the current collector by, for example, rolling, pressing, or a combination thereof.

[0106] The negative electrode layer formed on the current collector or the negative electrode layer integrated with the current collector is preferably heat-treated depending on the organic binder used. For example, when an aqueous styrene-butadiene rubber copolymer (SBR) or the like is used, the heat treatment may be performed at 100 to 130°C, and when an organic binder having a polyimide or polyamideimide main skeleton is used, the heat treatment is preferably performed at 150 to 450°C.

[0107] This heat treatment removes the solvent and hardens the binder, increasing strength and improving adhesion between particles and between the particles and the current collector. These heat treatments are preferably carried out in an inert atmosphere such as helium, argon, or nitrogen, or in a vacuum atmosphere, to prevent oxidation of the current collector during treatment.

[0108] After the heat treatment, the negative electrode is preferably subjected to pressure treatment. ３ to 1.8 g / cm ３ and preferably 1.1 g / cm ３ to 1.7 g / cm ３ More preferably, it is 1.2 g / cm ３ to 1.6 g / cm ３ It is more preferable that the electrode density is higher. The higher the electrode density, the better the adhesion and volumetric capacity density of the electrode tend to be. On the other hand, if the electrode density is too high, the voids in the electrode are reduced, which weakens the effect of suppressing the volume expansion of silicon and the like, and the capacity retention rate may decrease. Therefore, an optimal range of electrode density is selected.

[0109] [Secondary Battery] The secondary battery of this embodiment includes the negative electrode of this embodiment. As the secondary battery, non-aqueous electrolyte secondary batteries and solid electrolyte secondary batteries are preferred, and the negative electrode of this embodiment exhibits excellent performance particularly when used as the negative electrode of a non-aqueous electrolyte secondary battery.

[0110] When the secondary battery of the present embodiment is used as, for example, a wet electrolyte secondary battery, it can be constructed by disposing a positive electrode and a negative electrode containing the negative electrode active material for a secondary battery of the present embodiment opposite each other with a separator interposed therebetween and injecting an electrolyte solution.

[0111] The positive electrode can be obtained by forming a positive electrode layer on the surface of a current collector in the same manner as the negative electrode. In this case, the current collector can be a strip-shaped current collector made of a metal or alloy such as aluminum, titanium, or stainless steel, in the form of a foil, perforated foil, mesh, or the like.

[0112] The positive electrode material used for the positive electrode layer is not particularly limited. When a lithium ion secondary battery is produced among non-aqueous electrolyte secondary batteries, for example, a metal compound, metal oxide, metal sulfide, or conductive polymer material capable of doping or intercalating lithium ions may be used. For example, lithium cobalt oxide (LiCoO ２ ), lithium nickel oxide (LiNiO ２ ), lithium manganese oxide (LiMnO ２ ), and their composite oxides (LiCoxNiyMnzO ２ , x + y + z = 1), lithium manganese spinel (LiMn ２ O ４ ), lithium vanadium compounds, V ２ O ５ , V ６ O １３ , V.O. ２ , MnO ２ , TiO ２ , MoV ２ O ８ , TiS ２ , V ２ S ５ , V.S. ２ , MoS ２ , MoS ３ , Cr ３ O ８, Cr ２ O ５ , olivine-type LiMPO ４ (wherein M is Co, Ni, Mn or Fe), conductive polymers such as polyacetylene, polyaniline, polypyrrole, polythiophene and polyacene, porous carbon, etc. can be used alone or in combination.

[0113] The separator may be a nonwoven fabric, cloth, microporous film, or a combination thereof, whose main component is a polyolefin such as polyethylene or polypropylene. If the positive electrode and negative electrode of the nonaqueous electrolyte secondary battery are not in direct contact with each other, a separator is not necessary.

[0114] The electrolyte may be, for example, LiClO ４ , LiPF ６ , LiAsF ６ , LiBF ４ , LiSO ３ CF ３ A so-called organic electrolyte solution can be used in which a lithium salt such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, fluoroethylene carbonate, cyclopentanone, sulfolane, 3-methylsulfolane, 2,4-dimethylsulfolane, 3-methyl-1,3-oxazolidin-2-one, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, butyl methyl carbonate, ethyl propyl carbonate, butyl ethyl carbonate, dipropyl carbonate, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, methyl acetate, ethyl acetate, or the like is dissolved in a non-aqueous solvent of a single component or a mixture of two or more components.

[0115] The structure of the secondary battery of this embodiment is not particularly limited, but typically, a positive electrode, a negative electrode, and an optional separator are wound into a flat spiral to form a wound electrode assembly, or these are stacked as flat plates to form a stacked electrode assembly, and these electrode assembly are sealed in an outer casing. Note that the half-cell used in the examples of the present invention has a negative electrode mainly made of this negative electrode active material, and a simple evaluation was performed using metallic lithium as the counter electrode, but this is to more clearly compare the cycle characteristics of the active material itself.

[0116] The secondary battery of this embodiment is not particularly limited, and is used as a paper battery, a button battery, a coin battery, a laminated battery, a cylindrical battery, a prismatic battery, etc. The negative electrode active material of this embodiment described above can also be applied to general electrochemical devices that use the insertion and desorption of lithium ions as a charge / discharge mechanism, such as hybrid capacitors and solid-state lithium secondary batteries.

[0117] The present invention will be described in detail below with reference to examples, but is not limited thereto. In these examples, [%] and [parts] represent "mass %" and "mass parts" unless otherwise specified. Silicon particles were obtained by the following method, composite particles were prepared, and secondary battery evaluation was performed.

[0118] (Production of silicon particles) Synthesis Example 1 Into a 150 ml container of a small bead mill device, zirconia beads with a particle size of 0.1 mm and 100 m methyl ethyl ketone (hereinafter also referred to as "MEK") solvent were placed at a filling rate of 60%. Then, silicon powder with an average particle size of 5 μm and a cationic dispersant liquid (BYK Japan Co., Ltd.: BYK145) were placed, and the bead mill wet pulverization was carried out under the conditions of a rotation speed of 1500 rpm and a pulverization time of 4 h, to obtain a dark brown liquid silicon slurry with a solid concentration of 30% by mass. When the morphology and size of the obtained silicon particles were confirmed by TEM observation, the average particle size of the silicon particles was 50 nm.

[0119] (Preparation of Composite Particles and Evaluation Thereof) Example 1 The silicon particles (average particle size = 50 nm) prepared in Synthesis Example 1 above were mixed with polysiloxane resin (CERANATE SSA-500: manufactured by DIC Corporation) so that the silicon element content after high-temperature firing with the silicon slurry would be 50%, and the mixture was desolvated in a nitrogen atmosphere in an oil bath at 120°C, and then dried under reduced pressure at 110°C for 10 hours to obtain a mixed dried product. Next, the mixed dried product was fired at a high temperature at 1100°C for 6 hours in a nitrogen atmosphere to obtain a black fired product. The black fired product was then pulverized in a planetary ball mill (ball mill P-6 Classic Line: manufactured by FRITSCH) to obtain a composite particle intermediate. The prepared composite particle intermediate was doped with lithium oxide (LiO ２ ) (manufactured by Wako Pure Chemical Industries, Ltd.) was added in an amount of 0.1 equivalent to the silicon particles, and mixed in a planetary ball mill. The mixture was sintered at a high temperature of 800°C for 2 hours in a nitrogen atmosphere, washed with distilled water, and dried under reduced pressure to obtain a powder with an average particle size of 6.4 μm and a specific surface area (SSA) of 5.1 m. ２ / g composite particles were obtained. The amount of metal ion elements relative to the total mass of the obtained composite particles was measured using an ICP-OES analyzer (ICAP-7400, manufactured by Thermo Fisher Scientific Co., Ltd.), and the amount of metal elements present was 4.2 mass%. In addition, the metal ion element concentration distribution ratio between the surface portion and the interior of the composite particles was measured by Auger electron spectroscopy (AES). As a result, when the ratio of metal ion elements to all elements in a region 30% inward from the particle surface and the ratio of metal ion elements to all elements present in the remaining region are defined as B, A / (A+B) was 0.9. The identification of the metal silicate species and the measurement of the crystallite size and intensity ratio were performed using an XRD device (Ultima 5, manufactured by Rigaku Corporation), and the results using Cu-Ka rays showed that the silicon (111) crystal plane, Li ２ SiO ３ The half-width of the diffraction peak (2θ = 28.4°, 26.9°) attributed to the (111) crystal plane was calculated using the Scherrer equation. The Si crystallite size was 22 nm, and the Li ２ SiO ３The crystallite size was 21 nm and the peak intensity ratio (D / C) was 0.28. A half-cell was evaluated to measure the initial efficiency and cycle characteristics of the electrode. The composite particles (8 parts) obtained above were mixed with the conductive additive acetylene black (1 part) and an organic binder (1 part, consisting of SBR (0.75 parts) + CMC (0.25 parts)) and stirred for 10 minutes using a rotating / revolving whisker to prepare a slurry. A 20 μm thick copper foil was coated using an applicator, and then dried at 110 ° C under reduced pressure to obtain a thin electrode film. A circular electrode with a diameter of 14 mm was punched out and pressed using a tablet press to a thickness of approximately 40 μm. The thickness was measured using a thickness gauge to calculate the average value of five locations on the electrode. In a dry room with extremely low moisture content (dew point -40°C or less), a Li foil was placed opposite the electrode of the present invention via a 25 μm polypropylene separator, and an electrolyte (Kishida Chemical Co., Ltd., 1 mol / L LiPF ６ A half-cell (CR2032 type) for evaluation was fabricated by adsorbing a mixture of diethyl carbonate and ethylene carbonate (diethyl carbonate: ethylene carbonate = 1:1 (capacity ratio)). The battery characteristics were measured using a secondary battery charge / discharge tester (manufactured by Hokuto Denko Corporation). The battery characteristics were evaluated under the following conditions: room temperature 25°C, cutoff voltage range 0.005-1.5 V, charge rate 0.1 C (1-3 times) and 0.2 C (after 4 cycles), constant current / low voltage charge / discharge / constant current charge / discharge. The initial efficiency was 86%. To evaluate the atmospheric stability of the sample, composite particles stored in a vial at room temperature in the atmosphere were evaluated in a half-cell. The initial efficiency of the sample stored in the atmosphere for 7 days was 85%, and the initial efficiency of the sample stored in the atmosphere for 14 days was also 85%. The full-cell evaluation was performed using LiCoO as the positive electrode material. ２A positive electrode film was prepared using a single-layer sheet of aluminum foil as the positive electrode active material and a current collector. A negative electrode film was prepared by mixing graphite powder, active material powder, and a binder with a design discharge capacity of 450 mAh / g. A non-aqueous electrolyte solution was used in which lithium hexafluorophosphate was dissolved at a concentration of 1 mol / L in a 1 / 1 volumetric mixture of ethylene carbonate and diethyl carbonate. A laminated lithium-ion secondary battery was prepared using a 30 μm-thick polyethylene microporous film as the separator. The laminated lithium-ion secondary battery was charged at a constant current of 1.2 mA (0.25 c based on the positive electrode) at room temperature until the test cell voltage reached 4.2 V. After reaching 4.2 V, the current was reduced to maintain the cell voltage at 4.2 V, and the battery was charged to determine the discharge capacity. The capacity retention rate at room temperature for 300 cycles was 89%.

[0120] Example 2 Polysiloxane resin (CERANATE SSA-934: manufactured by DIC Corporation) and phenolic resin (SUMILITE RESIN: PR-53570, manufactured by Sumitomo Bakelite Co., Ltd.) were thoroughly mixed in a mixer at a resin solid matter ratio of 5:5, and mixed with silicon slurry so that the silicon element content after high-temperature baking was 50% to prepare a dried mixture. When the Li source was added, Li ２ The same procedure as in Example 1 was carried out except that the amount of O added was 0.05 equivalents relative to the silicon particles.

[0121] Example 3 Li ２ The same procedure as in Example 2 was carried out except that the amount of O added was 0.2 equivalents relative to the silicon particles.

[0122] Example 4 Li ２ The same procedure as in Example 1 was carried out except that the amount of O added was 0.1 equivalent relative to the silicon particles and the firing temperature was 800° C. / 1 h.

[0123] Example 5 Li ２ O to Li ２ CO ３ The same procedure as in Example 2 was carried out except that the amount added was changed to 1.0 equivalent relative to the silicon particles and the baking temperature was changed to 800° C. / 4 hours.

[0124] Example 6 Li ２The same procedure as in Example 2 was carried out except that the amount of O added was 0.07 equivalents relative to the silicon particles and the firing temperature was 800° C. / 1 h.

[0125] Example 7 Li ２ The same procedure as in Example 2 was carried out except that the amount of O added was 0.25 equivalents relative to the silicon particles and the firing temperature was 800° C. / 6 hours.

[0126] Example 8 Li ２ The same procedure as in Example 2 was carried out except that the amount of O added was 0.3 equivalents relative to the silicon particles and the firing temperature was 800° C. / 4 hours.

[0127] Example 9 The black fired product was pulverized in a planetary ball mill at 220 rpm for 10 minutes to obtain Li ２ The same procedure as in Example 2 was carried out except that the amount of O added was 0.5 equivalents relative to the silicon particles and the firing temperature was 800° C. / 6 hours.

[0128] Example 10 Li ２ The same procedure as in Example 2 was repeated except that the amount of O added was 0.4 equivalents relative to the silicon particles and the firing temperature was other than 700° C. / 6 hours.

[0129] Example 11 Li ２ The same procedure as in Example 2 was carried out except that the amount of O added was 0.5 equivalents relative to the silicon particles and the firing temperature was 900° C. / 2 hours.

[0130] Example 12 Li ２ The same procedure as in Example 2 was carried out except that the amount of O added was 0.1 equivalent relative to the silicon particles and the firing temperature was 800° C. / 24 hours.

[0131] Example 13 Li ２ O to Na ２ CO ３ The same procedure as in Example 2 was carried out except that the amount of the silicon particles was changed to 0.5 equivalents.

[0132] Example 14 Li ２ O to K ２ CO ３ The same procedure as in Example 2 was carried out except that the amount of the silicon particles was changed to 0.5 equivalents.

[0133] Comparative Example 1 Compared to Example 2, Li ２ The same procedure was carried out except that no O was added.

[0134] Comparative Example 2: No polysiloxane resin or phenolic resin was used. ２ The same procedure as in Example 2 was carried out except that the amount of O added was 0.1 equivalent relative to the silicon particles and the firing temperature was 800° C. / 2 hours.

[0135] Comparative Example 3: No silicon particles were used, and Li ２ The same procedure as in Example 2 was repeated except that the amount of O added was 0.3 equivalents relative to the material after firing at 1100° C. for 6 hours.

[0136] Comparative example 4 Li ２ O to Fe ２ O ３ The same procedure as in Example 2 was carried out except that the amount of the compound added was changed to 0.1 equivalent relative to the silicon particles and the baking temperature was changed to 800° C. / 2 hours.

[0137]

[0138] From Table 1 above, it can be seen that the composite particles of the present invention (Examples 1 to 14) have higher capacity retention rates and initial (Coulombic) efficiencies when used in secondary batteries, and there is almost no decrease in initial efficiency when stored in air for a long period of time, compared to Comparative Examples 1 to 4. This demonstrates that the composite particles of the present invention can maintain high charge / discharge performance, such as capacity retention rate and initial Coulombic efficiency, in secondary batteries.

Claims

1. A silicon oxide composition comprising at least one silicon particle and a matrix phase containing Si and O elements outside the silicon particle, and further containing a silicate compound, the silicate compound containing at least one metal element selected from the group consisting of Li, K, Na, Ca, Mg and Al; Composite particles, wherein the ratio of metal ion elements to all elements present in a region of 30% inward from the surface of the composite particle is A and the ratio of metal ion elements to all elements present in the other regions is B, the metal ion element abundance ratio satisfies 0.5<A / (A+B)<1.

0.

2. 2. The composite particle according to claim 1, wherein the metal ion element concentration of the metal element is 0.1 to 40.0 atom % based on the total elements of the composite particle.

3. The composite particle according to claim 1 , wherein the silicate compound contains Li element.

4. The silicate compound is Li ｘ S ｙ O ｚ 4. The composite particle according to claim 3, comprising a crystal structure represented by the formula: (where x, y, and z are integers greater than 0).

5. The silicate compound is Li ｘ S ｙ O ｚ 5. The composite particle according to claim 4, comprising a crystal structure represented by (x+4y-2z=0).

6. The silicate compound is Li ２ SiO ３ , Li ４ SiO ４ , and Li ２ S ２ O ５ 6. The composite particle according to claim 5, comprising at least one crystal structure selected from the group consisting of:

7. The composite particle according to claim 1 , wherein the Li element is contained in an amount of 20 mass % or less based on the total mass of the composite particle.

8. The peak intensity C and Li corresponding to the (111) plane of the silicon particle in the X-ray diffraction spectrum of the silicon particle ２ SiO ３ 2. The composite particle according to claim 1, wherein the peak intensity D corresponding to the (111) plane in the X-ray diffraction spectrum satisfies 0<D / C≦0.

6.

9. In the X-ray diffraction spectrum of the silicon particles, the crystallite size x is 10 nm<x<30 nm at a peak where 2θ corresponds to the (111) plane of the silicon particles, and Li ２ SiO ３ 2. The composite particle according to claim 1, wherein the crystallite size y satisfies 1 nm<y<40 nm in the X-ray diffraction peak corresponding to the (111) plane.

10. The average particle diameter x is 1 μm<x<15 μm, and the specific surface area n is 0.1 m ２ / g<n<20m ２ The composite particle according to claim 1, wherein the molecular weight is 1 / g.

11. The composite particle according to claim 1 , wherein the matrix phase contains C element in addition to Si and O elements.

12. A method for producing the composite particle according to claim 1, comprising the following steps 1 and 2: Step 1: A step of mixing at least one metal element compound selected from the group consisting of Li, K, Na, Ca, Mg, and Al with an intermediate derived from a polysiloxane resin containing silicon particles. Step 2: Firing at 900° C. or less in a non-oxygen atmosphere

13. A negative electrode active material for a secondary battery, comprising the composite particle according to any one of claims 1 to 11.

14. A negative electrode comprising the negative electrode active material for a secondary battery according to claim 13.

15. A secondary battery comprising the negative electrode according to claim 14.