Negative electrode active material for lithium ion secondary battery, negative electrode for lithium ion secondary battery using the material, and lithium ion secondary battery

Abstract

To provide a negative electrode active material for a lithium ion secondary battery that can have excellent charge / discharge capacity retention rate, initial coulombic efficiency, and other charge / discharge characteristics, a negative electrode for a lithium ion secondary battery that uses the material, and a lithium ion secondary battery.SOLUTION: A negative electrode active material for a lithium ion secondary battery according to the present invention is a negative electrode active material containing composite particles in which silicon nanoparticles are dispersed inside a matrix containing a carbonaceous phase, and in analysis of the X-ray diffraction pattern of the carbonaceous phase, the half-width of the diffraction line peak assigned to graphite (002) near 2θ=26.4° is 1° to 8°.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a negative electrode active material for a lithium ion secondary battery, a negative electrode for a lithium ion secondary battery using the material, and a lithium ion secondary battery, and in particular to a negative electrode active material for a lithium ion secondary battery that has excellent charge / discharge capacity retention rate, initial coulombic efficiency, and other charge / discharge characteristics, a negative electrode for a lithium ion secondary battery using the material, and a lithium ion secondary battery. [Background technology]

[0002] In recent years, the widespread use of smartphones and other portable electronic devices has led to an increasing demand for small, high-capacity secondary batteries. Among these, lithium-ion secondary batteries (sometimes abbreviated as LIBs) have been rapidly adopted for use in electric vehicles (EVs), and their range of industrial applications continues to expand. Graphite, a carbonaceous anode active material (natural or artificial), is widely used as the anode active material for lithium-ion secondary batteries. However, graphite has a low theoretical capacity density (372 mAh / g), and advances in lithium-ion secondary batteries are reaching their limits in improving battery capacity.

[0003] On the other hand, silicon (Si) can form an alloy (intermetallic compound) with metallic lithium, making it possible to electrochemically store and release lithium ions. 22 When Si5 is formed, the theoretical capacity is 4200 mAh / g, and the silicon-containing negative electrode active material can increase the capacity of the secondary battery compared to the graphite negative electrode active material.

[0004] However, silicon undergoes a large volume change of three to four times as it absorbs and releases lithium ions. As a result, when the battery is cycled, repeated expansion and contraction can cause the silicon to break down and become fine particles, which can lead to the electrode material peeling and breaking down, as well as a deterioration in electronic conductivity, resulting in poor charge-discharge cycle characteristics and an inability to achieve a good cycle life.

[0005] For example, Japanese Patent No. 7088438 (Patent Document 1) discloses an anode active material containing composite particles in which silicon nanoparticles are dispersed inside a matrix containing silicon oxycarbide and a carbonaceous phase, in which the ratio of the area intensity of the peak in the range of -70 ppm to -90 ppm attributable to Si (zero valence) to the area intensity of the peak in the range of -90 ppm to -130 ppm attributable to SiO4 bonds is within a specific range.

[0006] Japanese Patent No. 7074273 (Patent Document 2) discloses an anode active material containing composite particles in which silicon nanoparticles are dispersed within a matrix containing silicon oxycarbide and a carbonaceous phase, and in an analysis of an X-ray diffraction pattern, the crystal particle size determined by the Scherrer method from the full width at half maximum of the diffraction line assigned to Si(111) near 2θ=28.4° is 40 nm or less.

[0007] Furthermore, for example, Japanese Patent Laid-Open Publication No. 2017-084764 (Patent Document 3) discloses a method for producing a carbon material for a secondary battery anode, the method comprising: a mixing step of mixing a resin composition containing at least an aromatic condensation polymer that separates phenol molecules when heated to a first temperature higher than 25°C and an organic solvolysis material having a melting point or softening point that is 100 K or less different from the melting point or softening point of the aromatic condensation polymer, at a second temperature that is higher than the melting point or softening point of the aromatic condensation polymer and the melting point or softening point of the organic solvolysis material but lower than the first temperature to obtain a resin mixture; and a baking step of heating the resin mixture to a temperature higher than the first temperature to solvolyze the aromatic condensation polymer with the organic solvolysis material, followed by thermal curing and carbonization. The carbon material disclosed is a phosphorus compound and a phenol resin.

[0008] However, there is a demand for the development of a negative electrode active material that has charge / discharge characteristics, such as a charge / discharge capacity retention rate and an initial coulombic efficiency, that are even better than those exhibited by secondary batteries equipped with negative electrodes using the above-mentioned conventional negative electrode active materials. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Patent No. 7088438 [Patent Document 2] Patent No. 7074273 [Patent Document 3] Japanese Patent Application Publication No. 2017-084764 Summary of the Invention [Problem to be solved by the invention]

[0010] An object of the present invention is to solve the above problems and to provide a negative electrode active material for a lithium ion secondary battery that can have excellent charge / discharge capacity retention rate, initial coulombic efficiency, and other charge / discharge characteristics, as well as a negative electrode for a lithium ion secondary battery that uses the material, and a lithium ion secondary battery. In particular, the object of the present invention is to provide a negative electrode active material for a lithium ion secondary battery, which can improve charge / discharge characteristics such as the charge / discharge capacity retention rate and the initial coulombic efficiency by examining the carbon material of the carbonaceous phase in the negative electrode active material, and to provide a negative electrode for a lithium ion secondary battery and a lithium ion secondary battery using the material. [Means for solving the problem]

[0011] The present invention has been made by discovering that the above object can be achieved by controlling the half-width of the graphite diffraction line peak in an X-ray diffraction pattern of a carbon material in a negative electrode active material containing composite particles in which silicon particles are dispersed inside a matrix containing a carbonaceous phase to fall within a specific range, and has the following technical features.

[0012] 1) The negative electrode active material for a lithium ion secondary battery of the present invention is a negative electrode active material containing composite particles in which silicon nanoparticles are dispersed inside a matrix containing a carbonaceous phase, and is characterized in that, in an analysis of the X-ray diffraction pattern of the carbonaceous phase, the half-width of a diffraction line peak assigned to graphite (002) near 2θ=26.4° is 1° to 8°. 2) The negative electrode active material for a lithium ion secondary battery according to (1) above, characterized in that the matrix further contains silicon carbide. 3) In the negative electrode active material for a lithium ion secondary battery according to (1) or (2) above, the carbonaceous phase is a carbonized product of a naphthylene ether resin represented by the following formula (1):

[0013] [ka]

[0014] (In the above formula (1), q is an integer of 1 to 10, each p is independently an integer of 0 to 3, and X is a glycidyl group, a methylglycidyl group, or a hydrogen atom.) In addition, R1 in the above formula (1) is represented by the following formula (2), and R2 is a hydrogen atom or represented by the following general formula (3).

[0015] [ka]

[0016] (In the above formula (2), r is an integer of 1 to 10.)

[0017] [ka]

[0018] (In the above formula (3), R1, p, and X are the same as those in the above formula (1).)

[0019] 4) In the negative electrode active material for a lithium ion secondary battery according to the above (1) or (2), the carbonaceous phase is a carbonized product of a phenolic resin derived from a reaction between a phenol and an aldehyde, as represented by the following formula (4):

[0020] [ka]

[0021] (In the above formula (4), R3, R4, and R5 are each independently a hydrocarbon group having 1 to 5 carbon atoms or a hydrogen atom, and at least one of R3, R4, and R5 is a hydrocarbon group having 1 to 5 carbon atoms.)

[0022] 5) In the negative electrode active material for a lithium ion secondary battery according to the above (1) or (2), the carbonaceous phase is a carbonized product of a phenolic resin derived from a reaction between a phenol and an aldehyde, as represented by the following formula (5):

[0023] [ka]

[0024] (In the above formula (5), R6 each independently represents a hydrocarbon group having 1 to 5 carbon atoms, m represents an integer of 0 to 4, and n represents an integer of 1 or 2.)

[0025] 6) The negative electrode active material for a lithium ion secondary battery according to (1) or (2) above, wherein the carbonaceous phase is a carbonized product of a phenolic resin or an epoxy resin having a structure represented by the following formula (6):

[0026] [ka]

[0027] 7) The negative electrode for a lithium ion secondary battery of the present invention is a negative electrode for a lithium ion secondary battery, characterized by comprising: a negative electrode active material layer for a secondary battery containing the negative electrode active material for a lithium ion secondary battery according to any one of items (1) to (6) above; and a negative electrode current collector having the negative electrode active material layer for a secondary battery disposed on at least a part of its surface. 8) The lithium ion secondary battery of the present invention is a lithium ion secondary battery characterized by comprising the negative electrode for secondary batteries described in 7) above, an electrolyte layer, a separator, and a positive electrode. [Effects of the Invention]

[0028] According to the present invention, it is possible to realize a negative electrode active material that can improve the retention rate of charge / discharge capacity of a lithium ion battery compared to conventional materials and that can provide excellent initial coulombic efficiency, as well as a negative electrode for a lithium ion secondary battery and a lithium ion secondary battery that use the material. DETAILED DESCRIPTION OF THE INVENTION

[0029] The present invention will be described based on the following preferred embodiments, but is not limited thereto. [Negative electrode active material] The negative electrode active material for a lithium ion secondary battery of the present invention is a negative electrode active material comprising composite particles in which silicon nanoparticles are dispersed within a matrix containing a carbonaceous phase, and in an analysis of the X-ray diffraction pattern of the carbonaceous phase, the half-width of the X-ray diffraction peak attributable to graphite (002) near 2θ=26.4° is 1° to 8°, preferably 2° to 7°, and more preferably 2.5° to 6.5°. By including a carbon material having the above-described half-width as a carbon phase, the negative electrode active material, and the negative electrode and secondary battery using the negative electrode active material can improve the retention rate of favorable charge / discharge capacity and have excellent initial coulombic efficiency. Particularly preferably, by further including silicon carbide in the matrix, the above-described effects can be more effectively exerted, and a higher capacitance can be achieved.

[0030] The half-width can be a value calculated by, for example, measuring using an X-ray analyzer and under conditions described in the test examples below, processing the data, and fitting a Lorentz function using the nonlinear least squares method.

[0031] In the charge / discharge process of a lithium-ion secondary battery, when carbon is used as the active material for the negative electrode, a chemical bond is formed between the carbon and lithium ions through an insertion reaction during charging, and the carbon captures lithium. During discharge, the lithium captured by the carbon releases electrons to become lithium ions, which then undergo a desorption reaction, leaving the carbon. Charging and discharging are performed by repeating this insertion and desorption reaction between the carbon and lithium ions, that is, by the reversible progress of the reaction. However, when the half-width of the X-ray diffraction peak attributable to graphite (002) near 2θ = 26.4° of the carbon phase is within the above range, the effects of the present invention can be effectively achieved.

[0032] The content of the carbonaceous phase in the matrix of the composite particles is not particularly limited, but is preferably 30 to 85 mass %, more preferably 40 to 70 mass %, and even more preferably 45 to 60 mass % of the total weight of the matrix. When the content of the carbonaceous phase is within this range, the active material resistance is sufficiently reduced, and penetration of the electrolyte into the active material is suppressed, thereby more effectively suppressing decomposition of the electrolyte and the generation of solid-phase interface electrolyte decomposition products (SEI) on the surface of the active material.

[0033] In the present invention, the carbon material of the carbonaceous phase can be, for example, one obtained by thermal decomposition of a carbon source resin, and it is thought that carbon leads to the effect of reducing the resistance of the active material and, when used in the negative electrode of a secondary battery, can flexibly follow the volume change of the silicon particles during charge and discharge. The type of carbon source resin is not particularly limited, but a carbon compound containing a six-membered carbon ring is preferred.

[0034] In particular, carbon compounds having a naphthylene ether skeleton, a naphthalene skeleton, an anthracene skeleton, a biphenyl skeleton, or a phenol resin skeleton having a substituent at any one of the 3-, 4-, or 5-positions can be preferably used as carbon source resins in the present invention, and by carbonizing such carbon compounds, a charcoal (graphitized product) having a half-width within the above-mentioned range of the present invention can be obtained. Common phenolic resins such as phenol are difficult to graphitize, and may result in low initial efficiency and low retention, and are therefore not preferably used in the present invention. In particular, a preferred carbon source resin having a half-value width specified in the present invention is a carbon compound that is a naphthylene ether resin represented by the following formula (1).

[0035] [ka]

[0036] (In the above formula (1), q is an integer of 1 to 10, each p is independently an integer of 0 to 3, and X is a glycidyl group, a methylglycidyl group, or a hydrogen atom.) In addition, R1 in the above formula (1) is represented by the following formula (2), and R2 is a hydrogen atom or represented by the following general formula (3).

[0037] [ka]

[0038] (In the above formula (2), r is an integer of 1 to 10.)

[0039] [ka]

[0040] (In the above formula (3), R1, p, and X are the same as those in the above formula (1).) Another preferred carbon source resin for use in the present invention is a carbon compound which is a phenolic resin derived from the reaction of a phenol with an aldehyde, represented by the following formula (4).

[0041] [ka]

[0042] (In the above formula (4), R3, R4, and R5 are each independently a hydrocarbon group having 1 to 5 carbon atoms or a hydrogen atom, and at least one of R3, R4, and R5 is a hydrocarbon group having 1 to 5 carbon atoms.)

[0043] Another preferred carbon source resin for use in the present invention is a carbon compound which is a phenolic resin derived from the reaction of a phenol with an aldehyde, represented by the following formula (5).

[0044] [ka]

[0045] (In the above formula (5), R6 each independently represents a hydrocarbon group having 1 to 5 carbon atoms, m represents an integer of 0 to 4, and n represents an integer of 1 or 2.)

[0046] Another preferred carbon source resin for use in the present invention is a carbon compound that is a phenol resin or an epoxy resin and has a structure represented by the following formula (6):

[0047] [ka]

[0048] By including a carbon material derived from each of the above preferred carbon compounds in the composite particles, the above-mentioned effects of the present invention can be effectively exhibited.

[0049] The silicon nanoparticles contained in the composite particles are particles composed of silicon (Si, 0 valent), and any commercially available silicon particles can be used. Silicon nanoparticles can be obtained, for example, by pulverizing silicon particles having a particle size of about several hundred μm to nano-size.

[0050] The pulverization of silicon particles is not particularly limited and can be performed by any means, for example, using a pulverizer such as a ball mill, a bead mill, or a jet mill, and the pulverization may be wet pulverization or dry pulverization. The organic solvent used for wet pulverization is not particularly limited as long as it is an organic solvent that can be suitably used for pulverization, and examples thereof include aromatic hydrocarbons such as alcohols, ketones, toluene, xylene, naphthalene, and methylnaphthalene.

[0051] The silicon nanoparticles preferably have an average particle diameter (D50) of 10 nm or more, more preferably 20 nm or more, and even more preferably 30 nm or more, and preferably 300 nm or less, more preferably 250 nm or less, and even more preferably 200 nm or less. An average particle diameter of 10 nm or more suppresses aggregation of the silicon nanoparticles, facilitating uniform dispersion of the silicon nanoparticles in the negative electrode active material, and also suppressing the buildup of by-products on the surface when the silicon nanoparticles are calcined, which is more desirable. Furthermore, an average particle diameter of 300 nm or less can further suppress the deterioration of the charge / discharge performance of the negative electrode active material due to pulverization during charge / discharge. The composite particles have a structure in which the silicon particles are uniformly dispersed in a matrix containing carbon.

[0052] The average particle diameter (D50) refers to the particle diameter at which the cumulative volume distribution curve of the silicon nanoparticles reaches 50% of the cumulative volume when plotted from the smallest diameter side. The average particle diameter (D50) can be measured using a laser diffraction particle size distribution analyzer.

[0053] The content of silicon nanoparticles in the composite particles is not particularly limited, but adjusting the content of silicon nanoparticles can control battery capacity. In the negative electrode active material of the present invention, the content of silicon particles in the composite particles is preferably 1 to 80 mass%, more preferably 10 to 70 mass%, and even more preferably 20 to 65 mass%. In particular, by setting the content of silicon particles to 20 mass% or more, the charge / discharge capacity when used as a negative electrode material for a battery can be significantly increased and the initial coulombic efficiency can be maintained at a significantly high level. Furthermore, by setting the content to 65 mass% or less, the silicon particles can be sufficiently coated with a matrix containing silicon oxycarbide and a carbonaceous phase, which can significantly and effectively suppress volume expansion / contraction changes of the active material during charge / discharge, thereby further improving cycle characteristics, which is desirable.

[0054] Preferably, the matrix further contains silicon carbide. In this case, the composite particles have a matrix consisting of a three-dimensional network structure of SiOC with the elements Si, O, and C, and carbon from the carbon material, with silicon nanoparticles uniformly dispersed therein. In such a three-dimensional network structure of SiOC, the bonds can be divided into three main types based on the type of atom (O or C) bonding with Si and the number of bonds with each atom, and these include domains of SiO2C2, SiO3C, and SiO4. These domains are further bonded randomly to form the above-mentioned silicon oxycarbide (SiOC).

[0055] The SiOC framework is characterized by high chemical stability, and its composite structure with the carbon phase reduces electronic transition resistance, facilitating the diffusion of lithium ions. The tight encapsulation of silicon nanoparticles within the SiOC / carbon composite structure can prevent direct contact between the silicon particles and the electrolyte. Therefore, while the silicon nanoparticles in the anode active material function as a key component in the expression of charge / discharge performance, it is also possible to minimize performance degradation of the silicon particles by avoiding chemical reactions between the silicon and the electrolyte during charge / discharge.

[0056] An example of a suitable method for producing the negative electrode active material of the present invention will be described below. The negative electrode active material of the present invention preferably includes the following steps 1 to 3 as a process for producing the composite particles. Step 1: A precursor is obtained by mixing a wet-milled silicon (zero valent) slurry with a carbon source resin, preferably the above-mentioned carbon source resin, followed by stirring and drying. Preferably, a precursor is obtained by mixing a wet-milled silicon (zero valent) slurry with a carbon source resin and a polysiloxane compound, followed by stirring and drying. Step 2: The precursor obtained in step 1 is fired in an inert atmosphere at a maximum temperature within the range of 1000°C to 1180°C to obtain a carbide (fired product). Step 3: The fired product obtained in step 2 is pulverized to obtain a negative electrode active material.

[0057] <Process 1> (Silicon (0 valent) slurry) The wet-milled silicon (zero-valent) slurry (slurry of the above silicon nanoparticles) used in step 1 can be prepared, for example, using an organic solvent in a wet powder mill. A dispersant may be used to promote the milling of silicon particles in the organic solvent. The wet mill is not particularly limited, and examples include a roller mill, a jet mill, a high-speed rotary mill, a container-driven mill, and a bead mill.

[0058] Any solvent can be used in the wet method. There are no particular limitations on the organic solvent, but it is sufficient if it does not chemically react with silicon. Examples 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.

[0059] The type of dispersant is not particularly limited, and known, commonly used, aqueous or non-aqueous commercially available products can be used. However, to avoid excessive surface oxidation of silicon particles, non-aqueous dispersants are preferred. Examples of non-aqueous dispersants include polymeric types (polyethers, polyalkylene polyamines, polycarboxylic acid partial alkyl esters, etc.), low molecular weight types (polyhydric alcohol esters, alkyl polyamines, etc.), and inorganic polyphosphates. The silicon concentration in the silicon (zero-valent) slurry is not particularly limited, but is preferably in the range of 5 to 40% by mass, more preferably 10 to 30% by mass.

[0060] (Polysiloxane compound) The polysiloxane compound suitable for use in step 1 is not particularly limited as long as it is a resin containing at least one of polycarbosilane, polysilazane, polysilane, and polysiloxane structures. It may be a single resin, or a composite resin having this as a segment and chemically bonded to other polymer segments. The composite may be a copolymer such as a graft, block, random, or alternating copolymer. For example, there is a composite resin having a graft structure in which a polysiloxane segment is chemically bonded to the side chain of a polymer segment, and a composite resin having a block structure in which a polysiloxane segment is chemically bonded to the end of a polymer segment.

[0061] The polysiloxane segment preferably has a structural unit represented by the following general formula (S-1) and / or the following general formula (S-2): It is particularly preferred that the polysiloxane compound has a carboxy group, an epoxy group, an amino group, or a polyether group on a side chain or terminal of the siloxane bond (Si-O-Si) main skeleton.

[0062] [ka]

[0063] [ka]

[0064] (In the general formulas (S-1) and (S-2), R1 represents an aromatic hydrocarbon substituent, an alkyl group, an epoxy group, a carboxy group, or the like. R2 and R3 each represent an alkyl group, a cycloalkyl group, an aryl group or an aralkyl group, an epoxy group, a carboxy group, or the like.)

[0065] 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, a cyclohexyl group, etc.

[0066] 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.

[0067] Examples of the aralkyl group include a benzyl group, a diphenylmethyl group, and a naphthylmethyl group.

[0068] 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 polyolefin polymers, as well as polymer segments such as polyurethane polymer segments, polyester polymer segments, and polyether polymer segments. Vinyl polymer segments are particularly preferred.

[0069] 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.

[0070] [ka]

[0071] (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.)

[0072] The polysiloxane segment of the polysiloxane compound may have a functional group capable of reacting by heating, such as a polymerizable double bond, within the polysiloxane segment. By subjecting the polysiloxane compound to heat treatment before thermal decomposition, a crosslinking reaction progresses and the compound is solidified, facilitating thermal decomposition treatment.

[0073] 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 about 3 to 200, and even more preferably about 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.

[0074] 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 producing a solid polysiloxane compound.

[0075] The silanol group is a silicon-containing group having a hydroxyl group directly bonded to a silicon atom. The hydrolyzable silyl group 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):

[0076] [ka]

[0077] (In the formula, R4 is a monovalent organic group such as an alkyl group, an aryl group, or an aralkyl group, R5 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.)

[0078] 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.

[0079] 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.

[0080] Examples of the aralkyl group include a benzyl group, a diphenylmethyl group, and a naphthylmethyl group.

[0081] Examples of halogen atoms include fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms.

[0082] 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.

[0083] Examples of the acyloxy group include formyloxy, acetoxy, propanoyloxy, butanoyloxy, pivaloyloxy, pentanoyloxy, phenylacetoxy, acetoacetoxy, benzoyloxy, and naphthoyloxy.

[0084] The allyloxy group includes, for example, phenyloxy, naphthyloxy, and the like.

[0085] 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.

[0086] Examples of polysiloxane segments having structural units represented by the above general formula (S-1) and / or the above general formula (S-2) include those having the following structures.

[0087] [ka]

[0088] [ka]

[0089] [ka]

[0090] The polymer segment may have various functional groups as needed, provided that 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).

[0091] [ka]

[0092] The polymer segment may also have a polymerizable double bond such as a vinyl group or a (meth)acryloyl group.

[0093] The polysiloxane compound can be produced by known methods, including, but not limited to, the following methods (1) to (3).

[0094] (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 containing a silanol group and / or a hydrolyzable silyl group and a silane compound having both a polymerizable double bond, followed by a hydrolysis and condensation reaction.

[0095] (2) As a raw material for the polymer segment, a polymer segment containing a silanol group and / or a hydrolyzable silyl group is prepared in advance. A polysiloxane is also prepared in advance by subjecting a silane compound containing 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.

[0096] (3) A method in which the polymer segment, a silane compound containing a silane compound having both a silanol group and / or a hydrolyzable silyl group and a polymerizable double bond, and a polysiloxane are mixed together to carry out a hydrolysis and condensation reaction.

[0097] (precursor) The silicon (0-valent) slurry and an aggregate containing a carbon source resin are uniformly mixed, preferably the silicon (0-valent) slurry, polysiloxane compound, and carbon source resin, and the mixture is stirred, followed by desolvation and drying to obtain a precursor. The raw materials can be mixed using any suitable device with general-purpose dispersion and mixing functions, including, but not limited to, a stirrer, ultrasonic mixer, and premix disperser. The desolvation and drying steps, which are aimed at distilling off the organic solvent, can be performed using a dryer, reduced pressure dryer, spray dryer, or the like.

[0098] Preferably, this negative electrode active material precursor is set so that it contains 3 to 50 mass% silicon nanoparticles (zero-valent silicon), 15 to 85 mass% solids of polysiloxane compound, and 3 to 70 mass% solids of carbon source resin, and more preferably the solids content of silicon nanoparticles is set to 8 to 40 mass%, the solids content of carbon source resin is set to 3 to 60 mass%, and the solids content of the suitably contained polysiloxane compound is set to 20 to 70 mass%.

[0099] <Process 2> In step 2, the precursor obtained in step 1 is calcined in an inert atmosphere at a maximum temperature within a range of approximately 1000°C to 1180°C to completely decompose the thermally decomposable organic components, and the calcination conditions are precisely controlled to convert the other main components into a carbonized product (calcined product) suitable for the negative electrode active material of the present invention. When a polysiloxane compound is suitably contained, the "Si-O" bonds present in the raw material polysiloxane compound undergo a dehydration condensation reaction due to the energy of the high-temperature treatment, forming an "Si-OC" skeletal structure (referred to as "SiOC"), and the carbon source resin that was uniformly dispersed is also carbonized and converted into free carbon in a three-dimensional structure having an "Si-OC" skeleton.

[0100] In step 2, the precursor obtained in step 1 is calcined in an inert atmosphere according to a calcination program that is determined by factors such as the rate of temperature rise and the time the material is held at a constant temperature. The maximum temperature is the highest temperature that can be set and affects the structure and performance of the calcined product, the negative electrode active material. By keeping the maximum temperature between 1000°C and 1180°C, the microstructure of the negative electrode active material, which retains the aforementioned chemical bonding state between silicon and carbon, can be precisely controlled, and oxidation of silicon particles due to excessively high temperature calcination can be avoided, resulting in better charge / discharge characteristics, which is desirable.

[0101] The calcination method is not particularly limited, but a reaction device having a heating function in an inert atmosphere may be used, and treatment by a continuous method or a batch method is possible. The calcination device may 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, etc.

[0102] <Process 3> Step 3 is a step in which the sintered product obtained in Step 2 is pulverized and, if necessary, classified to obtain the negative electrode active material of the present invention. The pulverization can be performed in one step or in several steps until the desired particle size is reached. For example, to produce an active material with a particle size of approximately 10 μm from lumps or agglomerates of 10 mm or larger, the sintered product can be coarsely pulverized using a jaw crusher, roll crusher, or the like to produce particles of approximately 1 mm, then pulverized to approximately 100 μm using a glow mill, ball mill, or the like, and then pulverized to approximately 10 μm using a bead mill, jet mill, or the like. The particles produced by pulverization may contain coarse particles, and classification is performed to remove these and to remove fine powder and adjust the particle size distribution. Classifiers such as air classifiers and wet classifiers can be used. To remove coarse particles, sieving is preferred because it ensures the desired results. It is possible to omit the pulverization step if the precursor mixture is controlled to a shape close to the desired particle size by spray drying or the like before the calcination and then calcined in that shape. The negative electrode active material of the present invention obtained in this manner is a negative electrode active material comprising particles in which silicon nanoparticles are dispersed within a matrix containing a carbonaceous phase, preferably composite particles in which silicon carbide is also dispersed within the matrix, and in analysis of the X-ray diffraction pattern of the carbonaceous phase, the half-width of the X-ray diffraction peak attributable to graphite (002) in the vicinity of 2θ=26.4° is 1° to 8°, preferably 2° to 7°, and more preferably 2.5° to 6.5°, and the negative electrode active material can exhibit the effects of the present invention, such as excellent charge-discharge characteristics.

[0103] <Production of negative electrodes> The negative electrode active material of the present invention exhibits excellent charge-discharge characteristics as described above, and therefore exhibits good charge-discharge characteristics when used as a battery negative electrode. Specifically, a slurry containing the negative electrode active material of the present invention, an organic binder, and, if necessary, other components such as a conductive additive can be applied to a copper foil current collector in the form of a thin film and used as a negative electrode.

[0104] The negative electrode thus obtained contains the negative electrode active material of the present invention as an active material, and therefore is a negative electrode for a secondary battery that has high capacity, excellent cycle characteristics, and also has excellent initial coulombic efficiency. The negative electrode can be obtained, for example, by kneading the aforementioned negative electrode active material for a secondary battery and an organic binder together with a solvent using a dispersing device such as a mixer, ball mill, super sand mill, or 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 can be obtained by forming the paste-like negative electrode material slurry into a shape such as a sheet or pellet and integrating it with a current collector.

[0105] The organic binder is not particularly limited, but examples thereof include styrene-butadiene rubber copolymers (SBR); (meth)acrylic copolymers composed of ethylenically unsaturated carboxylic acid esters (e.g., methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, (meth)acrylonitrile, and hydroxyethyl (meth)acrylate, etc.) and ethylenically unsaturated carboxylic acids (e.g., 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 carboxymethylcellulose (CMC).

[0106] 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 not particularly limited, but is preferably 1 to 30 mass %, more preferably 2 to 20 mass %, and even more preferably 3 to 15 mass %.

[0107] A content of the organic binder of 1% by mass or more provides better adhesion and further suppresses destruction of the negative electrode structure due to expansion and contraction during charge and discharge, while a content of 30% by mass or less further suppresses an increase in electrode resistance, which is desirable.

[0108] In this case, the negative electrode active material of the present invention has high chemical stability and can employ an aqueous binder, which makes it easy to handle in practical use.

[0109] 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 is not particularly limited, but is preferably about 1% by mass to 15% by mass relative to the negative electrode active material of the present invention.

[0110] The material and shape of the current collector are not particularly limited, and for example, a strip of copper, nickel, titanium, stainless steel, or the like in foil, perforated foil, mesh, or the like can be used. Porous materials such as porous metal (foamed metal) and carbon paper can also be used.

[0111] The method for applying the negative electrode material slurry to the current collector is not particularly limited, and examples thereof include known methods such as 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 perform a rolling treatment using a flat plate press, a calendar roll, or the like, as necessary.

[0112] Furthermore, the current collector formed into a sheet, pellet, or other shape can be integrated with the negative electrode material slurry by a known method, such as rolling, pressing, or a combination thereof.

[0113] The negative electrode layer formed on the current collector and the negative electrode layer integrated with the current collector are preferably heat-treated at an appropriate temperature depending on the organic binder used. For example, when a known and commonly used water-based styrene-butadiene rubber copolymer (SBR) 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.

[0114] Such heat treatment removes the solvent and hardens the organic 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 reduced pressure or vacuum atmosphere to prevent oxidation of the current collector during treatment.

[0115] After the heat treatment, the negative electrode is preferably pressed (pressurized). The negative electrode using the negative electrode active material of the present invention has an electrode density of 1.0 g / cm. 3 ~1.8g / cm 3 and preferably 1.1 g / cm 3 ~1.7g / cm 3 More preferably, it is 1.2 g / cm 3 ~1.6g / cm 3 With regard to the electrode density, the higher the density, the more the adhesion and the volumetric capacity density of the electrode tend to improve, but if the density is too high, the voids in the electrode decrease, weakening the effect of suppressing the volume expansion of silicon and the like, and deteriorating the cycle characteristics, so an optimal range should be selected as appropriate.

[0116] <Structure of secondary battery> As described above, a negative electrode using the negative electrode active material of the present invention has excellent charge-discharge characteristics, and therefore is not particularly limited as long as it is used in a secondary battery, but is preferably used in a nonaqueous electrolyte secondary battery and a solid electrolyte secondary battery. In particular, when used as a negative electrode of a nonaqueous electrolyte secondary battery, the excellent performance described in the above-mentioned effects of the present invention is exhibited.

[0117] When the nonaqueous electrolyte secondary battery of the present invention is used as a wet electrolyte secondary battery, for example, it can be constructed by disposing a positive electrode and a negative electrode of the present invention opposite each other with a separator interposed therebetween and injecting an electrolytic solution.

[0118] 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.

[0119] The positive electrode material used in 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, and is not particularly limited. For example, lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2), and composite oxides thereof (LiCoO2) may be used. x Ni y Mn z O2, x+y+z=1), lithium manganese spinel (LiMn2O4), lithium vanadium compounds, V2O5, V6O 13 , VO2, MnO2, TiO2, MoV2O8, TiS2, V2S5, VS2, MoS2, MoS3, Cr3O8, Cr2O5, olivine-type LiMPO4 (M: Co, Ni, Mn, Fe), conductive polymers such as polyacetylene, polyaniline, polypyrrole, polythiophene, polyacene, porous carbon, etc. can be used alone or in combination.

[0120] The separator may be, for example, a nonwoven fabric, cloth, or microporous film primarily composed of a polyolefin such as polyethylene or polypropylene, or a combination thereof. Note that if the nonaqueous electrolyte secondary battery to be fabricated has a structure in which the positive electrode and the negative electrode are not in direct contact with each other, it is not necessary to use a separator.

[0121] As the electrolyte, for example, a so-called organic electrolyte can be used, which is obtained by dissolving a lithium salt such as LiClO4, LiPF6, LiAsF6, LiBF4, or LiSO3CF3 in a non-aqueous solvent 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, or ethyl acetate, either alone or as a mixture of two or more components.

[0122] The structure of the nonaqueous electrolyte secondary battery of the present invention 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 the electrode assembly is sealed in an outer casing. The half-cells (half-secondary batteries) in the following examples and the like have a negative electrode mainly composed of the active material of the present invention, and a simple evaluation was performed using metallic lithium as the counter electrode, in order to clearly compare the cycle characteristics of the active material itself.

[0123] By using a negative electrode that uses the negative electrode active material of the present invention in a secondary battery, the initial efficiency of the lithium secondary battery can be 84% or more, and the retention rate can be 80% or more, making it possible to have excellent charge / discharge characteristics. [Example]

[0124] The present invention will be described in detail below with reference to the following examples, comparative examples and test examples, but is not limited thereto. Unless otherwise specified, "parts" means parts by mass and "%" means % by mass.

[0125] (1) Preparation of carbide (Synthesis Example 1) Preparation of carbonized phenolic resin B1 A flask equipped with a thermometer, dropping funnel, condenser, distillation column, and stirrer was charged with 160 parts (1.0 mol) of 2,7-dihydroxynaphthalene, 25 parts (0.25 mol) of benzyl alcohol, 160 parts of xylene, and 2 parts of paratoluenesulfonic acid monohydrate. The mixture was stirred at room temperature while blowing in nitrogen. The temperature was then raised to 140°C and the mixture was stirred for 4 hours while the generated water was distilled out of the system (the xylene that was distilled out at the same time was returned to the system). The mixture in the flask was then heated to 150°C and stirred for an additional 3 hours while the generated water and xylene were distilled out of the system. After the reaction was completed, 2 parts of 20% aqueous sodium hydroxide solution was added to the mixture in the flask to neutralize it, and the water and xylene were then removed under reduced pressure. An organic solvent, methyl ethyl ketone, was added to adjust the nonvolatile content to 60.0%, to obtain phenolic resin B1 having a naphthylene ether skeleton and a weight-average molecular weight of 510 measured by the method in Test Example 2 below. The representative structure of phenolic resin B1, which is a carbon source resin, is represented by the following formula.

[0126] [ka]

[0127] 50 parts of the phenol resin B1 thus obtained was dried under reduced pressure at 110°C for 10 hours, and then calcined at 1100°C for 4 hours in a nitrogen atmosphere to obtain a black solid product which was a carbonized product. The black solid was pulverized in a planetary ball mill to form a powder, and the powder was subjected to XRD measurement, which revealed that the half-width of the peak near 2θ=26.4° measured in the following Test Example 1 was 2°. The results are shown in Tables 1 and 2 below.

[0128] (Synthesis Example 2) Preparation of carbonized epoxy resin B2 A flask equipped with a thermometer, dropping funnel, condenser, and stirrer was charged with 169 g of phenolic resin B1 obtained in Synthesis Example B1, 463 g (5.0 mol) of epichlorohydrin, 139 g of n-butanol, and 2 g of tetraethylbenzylammonium chloride while purging with nitrogen gas. The mixture was then heated to 65°C, after which the pressure was reduced to an azeotropic pressure, and 90 g (1.1 mol) of 49% aqueous sodium hydroxide solution was added dropwise over 5 hours. Stirring was then continued under the same conditions for 0.5 hours. During this time, the azeotropically distilled fraction was separated using a Dean-Stark trap, the aqueous layer was removed, and the oil layer was returned to the reaction system while the reaction was continued. Unreacted epichlorohydrin was then removed by vacuum distillation, and 432 g of methyl isobutyl ketone and 130 g of n-butanol were added to the resulting crude epoxy resin and dissolved. 10 g of a 10% aqueous solution of sodium hydroxide was then added to this solution and reacted at 80°C for 2 hours. The reaction product was then washed three times with 150 g of water until the pH of the washings became neutral. The system was then dehydrated by azeotropy, and after microfiltration, the solvent was distilled off under reduced pressure. The nonvolatile content was adjusted to 60.0% with methyl ethyl ketone, an organic solvent, to obtain epoxy resin B2 having a naphthylene ether skeleton (epoxy-modified) and a weight-average molecular weight of 560, as measured by the method in Test Example 2 below. The representative structure of epoxy resin B2, the carbon source resin, is shown in the following formula:

[0129] [ka]

[0130] 50 parts of the epoxy resin thus obtained was dried under reduced pressure at 110°C for 10 hours, and then baked at 1100°C for 4 hours in a nitrogen atmosphere to obtain a black solid product which was a charcoal. The black solid was pulverized in a planetary ball mill to obtain a powder, and the powder was subjected to XRD measurement, which revealed that the half-width of the peak near 2θ=26.4° measured in the following Test Example 1 was 1.5°. The results are shown in Tables 1 and 2 below.

[0131] (Synthesis Example 3) Preparation of carbonized phenolic resin B3 A flask equipped with a thermometer, dropping funnel, condenser, nitrogen gas inlet, and stirrer was charged with 496 parts of 3,5-xylenol, 292 parts of 50% formalin, and 9.9 parts of 25% aqueous ammonia. The mixture was heated to 80°C with stirring and allowed to react at 80°C for 2 hours. Water was then removed (dehydration) under reduced pressure. The mixture was adjusted with methyl ethyl ketone, an organic solvent, to a nonvolatile content of 60.0%, yielding phenolic resin B3 with a weight-average molecular weight of 1200, as measured by the method in Test Example 2 below. The representative structure of phenolic resin B3, the carbon source resin, is shown by the following formula:

[0132] [ka]

[0133] 50 parts of the phenol resin B3 thus obtained was dried under reduced pressure at 110°C for 10 hours, and then calcined at 1100°C for 4 hours in a nitrogen atmosphere to obtain a black solid product which was a carbonized product. The black solid was pulverized in a planetary ball mill to obtain a powder, and the powder was subjected to XRD measurement, which revealed that the half-value width of the peak near 2θ=26.4° measured in the following Test Example 1 was 2.5°. The results are shown in Tables 1 and 2 below.

[0134] (Synthesis Example 4) Preparation of carbonized phenolic resin B4 A flask equipped with a thermometer, dropping funnel, condenser, nitrogen gas inlet, and stirrer was charged with 439 parts of mixed cresol (m-cresol / p-cresol = 60 / 40 mol %), 292 parts of 50% formalin, and 9.9 parts of 25% aqueous ammonia. The mixture was heated to 80°C with stirring and reacted at 80°C for 2 hours. Water was then removed (dehydration) under reduced pressure. The mixture was adjusted with methyl ethyl ketone, an organic solvent, to a nonvolatile content of 60.0%, yielding phenolic resin B4 with a weight-average molecular weight of 1100 as measured by the method in Test Example 2 below. The representative structure of phenolic resin B4, the carbon source resin, is shown in the following formula:

[0135] [ka]

[0136] 50 parts of the phenol resin B4 thus obtained was dried under reduced pressure at 110°C for 10 hours, and then calcined in a nitrogen atmosphere at 1100°C for 4 hours to obtain a black solid carbonized product. The black solid was pulverized in a planetary ball mill to obtain a powder, and the powder was subjected to XRD measurement, which revealed that the half-width of the peak near 2θ=26.4° measured in the following Test Example 1 was 4°. The results are shown in Tables 1 and 2 below.

[0137] (Synthesis Example 5) Preparation of carbonized phenolic resin B5 A flask equipped with a thermometer, dropping funnel, condenser, nitrogen gas inlet, and stirrer was charged with 585 parts of mixed naphthol (1-naphthol / 2-naphthol = 60 / 40 mol %), 292 parts of 50% formalin, and 9.9 parts of 25% aqueous ammonia. The mixture was heated to 80°C with stirring and allowed to react at 80°C for 2 hours. Water was then removed (dehydration) under reduced pressure. The mixture was adjusted with methyl ethyl ketone, an organic solvent, to a nonvolatile content of 60.0 mass%, yielding phenolic resin B5 having a naphthol skeleton and a weight-average molecular weight of 1,000, as measured by the method in Test Example 2 below. The representative structure of phenolic resin B5, the carbon source resin, is shown by the following formula:

[0138] [ka]

[0139] 50 parts of the phenol resin B5 resin thus obtained was dried under reduced pressure at 110°C for 10 hours, and then calcined in a nitrogen atmosphere at 1100°C for 4 hours to obtain a black solid carbonized product. The black solid was pulverized in a planetary ball mill to obtain a powder, and the powder was subjected to XRD measurement, which revealed that the half-width of the peak near 2θ=26.4° measured in the following Test Example 1 was 6.5°. The results are shown in Tables 1 and 2 below.

[0140] (Synthesis Example 6) Preparation of carbonized phenolic resin B6 A flask equipped with a thermometer, dropping funnel, condenser, nitrogen gas inlet, and stirrer was charged with 585 parts of 2-methyl-1-naphthol, 292 parts of 50% formalin, and 9.9 parts of 25% aqueous ammonia. The mixture was heated to 80°C with stirring and allowed to react at 80°C for 2 hours. Water was then removed (dehydration) under reduced pressure. Phenolic resin B6, having a naphthol skeleton and a weight-average molecular weight of 1,100 measured by the method in Test Example 2 below, was prepared using methyl ethyl ketone, an organic solvent, so that the nonvolatile content was 60.0% by mass. The representative structure of phenolic resin B6, the carbon source resin, is shown in the following formula:

[0141] [ka]

[0142] 50 parts by mass of the phenol resin B6 thus obtained was dried under reduced pressure at 110° C. for 10 hours, and then fired in a nitrogen atmosphere at 1100° C. for 4 hours to obtain a black solid carbonized product. The black solid was pulverized in a planetary ball mill to form a powder, and the powder was subjected to XRD measurement, which revealed that the half-width of the peak near 2θ=26.4° measured in the following Test Example 1 was 7°. The results are shown in Tables 1 and 2 below.

[0143] (Synthesis Example 7) Preparation of carbonized phenolic resin B7 A flask equipped with a thermometer, dropping funnel, condenser, nitrogen gas inlet, and stirrer was charged with 80 parts of 2-hydroxyanthracene, 340 parts of phenol, 292 parts of 50% formalin, and 9.9 parts of 25% aqueous ammonia. The mixture was heated to 80°C with stirring and allowed to react at 80°C for 2 hours. Water was then removed (dehydration) under reduced pressure. Phenolic resin B7 was prepared using methyl ethyl ketone, an organic solvent, so that the nonvolatile content was 60.0% by mass, and had a weight-average molecular weight of 1100, as measured by the method in Test Example 2 below. The representative structure of phenolic resin B7, the carbon source resin, is shown in the following formula:

[0144] [ka]

[0145] 50 parts by mass of the phenol resin B7 thus obtained was dried under reduced pressure at 110° C. for 10 hours, and then fired in a nitrogen atmosphere at 1100° C. for 4 hours to obtain a black solid carbonized product. The black solid was pulverized in a planetary ball mill to obtain a powder, and the powder was subjected to XRD measurement, which revealed that the half-width of the peak near 2θ=26.4° measured in the following Test Example 1 was 7.5°. The results are shown in Tables 1 and 2 below.

[0146] (Synthesis Example 8) Preparation of carbonized phenolic resin B8 A flask equipped with a thermometer, dropping funnel, condenser, nitrogen gas inlet, and stirrer was charged with 618 parts of phenol and 1 part of paratoluenesulfonic acid monohydrate. While stirring at 80°C, 500 parts of 4,4'-bis(chloromethyl)-1,1'-biphenyl was added over 2 hours, and the reaction was carried out at 80°C for 2 hours. After the reaction was completed, 1500 parts of methyl isobutyl ketone (MIBK) was added and the mixture was repeatedly washed with water. The unreacted phenol and MIBK were then distilled off under reduced pressure with heating. The organic solvent methyl ethyl ketone was added to adjust the nonvolatile content to 60.0%, yielding phenolic resin B8 with a biphenyl skeleton and a weight-average molecular weight of 770, as measured by the method in Test Example 2 below. The representative structure of phenolic resin B8, the carbon source resin, is shown below.

[0147] [ka]

[0148] 50 parts by mass of the phenol resin B8 thus obtained was dried under reduced pressure at 110°C for 10 hours, and then calcined in a nitrogen atmosphere at 1100°C for 4 hours to obtain a black solid carbonized product. The black solid was pulverized in a planetary ball mill to obtain a powder, and the powder was subjected to XRD measurement, which revealed that the half-value width of the peak near 2θ=26.4° measured in the following Test Example 1 was 2.0°. The results are shown in Tables 1 and 2 below.

[0149] (Synthesis Example 9) Preparation of carbonized epoxy resin B9 In a four-neck flask equipped with a stirrer, thermometer, and condenser, 104 parts of phenolic resin B8 obtained in Synthesis Example 8 were dissolved in 231 parts of epichlorohydrin and 58 parts of dimethyl sulfoxide. The mixture was then heated to 45°C, and 21 parts of sodium hydroxide was added over 90 minutes. The mixture was then reacted at 45°C for 2 hours and at 70°C for 1 hour. The oil layer was then repeatedly washed with water until the aqueous wash liquid became neutral. Excess epichlorohydrin was removed from the oil layer by distillation under heating and reduced pressure. 264 parts of MIBK was added to the residue and dissolved. The MIBK solution was then heated to 70°C, and 5 parts of a 30 wt% aqueous sodium hydroxide solution was added. The mixture was reacted for 1 hour. The mixture was then repeatedly washed with water until the aqueous wash liquid became neutral. The MIBK was then removed from the oil layer by distillation under heating and reduced pressure. The epoxy resin B9 was prepared using methyl ethyl ketone, an organic solvent, so that the nonvolatile content was 60.0%, and had a biphenyl skeleton (epoxy-modified) and a weight-average molecular weight of 800, as measured by the method in Test Example 2 below. The representative structure of the carbon source resin, epoxy resin B9, is shown in the following formula.

[0150] [ka]

[0151] 50 parts by mass of the epoxy resin B9 thus obtained was dried under reduced pressure at 110°C for 10 hours, and then baked in a nitrogen atmosphere at 1100°C for 4 hours to obtain a black solid product that was a charcoal. The black solid was pulverized in a planetary ball mill to obtain a powder, and the powder was subjected to XRD measurement, which revealed that the half-width of the peak near 2θ=26.4° measured in the following Test Example 1 was 2.2°. The results are shown in Tables 1 and 2 below.

[0152] (2) Preparation of polysiloxane (Synthesis Example 10) Preparation of Polysiloxane C A reaction vessel equipped with a stirrer, thermometer, dropping funnel, condenser, and nitrogen gas inlet was charged with 1,421 parts of MTMS and heated to 60° C. Next, a mixture of 0.17 parts of butyl acid phosphate and 207 parts of deionized water was added dropwise to the reaction vessel over 5 minutes, and the mixture was stirred at 80° C. for 4 hours to carry out the hydrolysis and condensation reaction of MTMS.

[0153] The condensate obtained by the hydrolysis and condensation reaction was distilled at a temperature of 40 to 60° C. under reduced pressure of 40 to 1.3 kPa. The methanol and water produced during the reaction were removed by distillation to obtain 1,000 parts of a liquid containing an MTMS condensate (c1) having a number average molecular weight of 1,000 to 5,000. The active ingredient content of the obtained liquid was 70%.

[0154] Here, the active ingredient is calculated by dividing the theoretical yield (parts) when all methoxy groups of a silane monomer such as MTMS undergo a condensation reaction by the actual yield (parts) after the condensation reaction, i.e., [theoretical yield (parts) when all methoxy groups of a silane monomer undergo a condensation reaction / actual yield (parts) after the condensation reaction].

[0155] Next, 150 parts of MEK, 105 parts of MTMS, and 277 parts of DMDMS were placed in a reaction vessel equipped with a stirrer, a thermometer, a dropping funnel, a condenser, and a nitrogen gas inlet, and the mixture was heated to 80°C.

[0156] Then, at the same temperature (80°C), a mixture containing 21 parts of methyl methacrylate, 4 parts of butyl methacrylate, 3 parts of butyric acid, 2 parts of methacryloyloxypropyltrimethoxysilane, 3 parts of MEK, and 0.6 parts of butylperoxy-2-ethylhexanoate was added dropwise to the reaction vessel over 6 hours. After the addition was completed, the mixture was allowed to react for an additional 20 hours at the same temperature (80°C), yielding an organic solvent solution of a vinyl polymer (c2) having a number average molecular weight of 10,000 and having hydrolyzable silyl groups.

[0157] Next, a mixture of 0.04 parts of butyl acid phosphate and 112 parts of deionized water was added dropwise over 5 minutes, and the mixture was further stirred at the same temperature (80°C) for 10 hours to cause a hydrolysis and condensation reaction, thereby obtaining a liquid containing a resin in which the hydrolyzable silyl group of the vinyl polymer (c2) was bonded to the hydrolyzable silyl group and silanol group of the polysiloxane derived from MTMS and DMDMS.

[0158] To this resin-containing liquid, 472 parts of the MTMS condensate (c1) and 80 parts of deionized water were added, and the mixture was stirred at the same temperature (80°C) for 10 hours to cause a hydrolysis and condensation reaction, and the resulting methanol and water were removed by distillation under the same conditions as in Synthesis Example 2. Next, 250 parts of MEK was added to prepare 1,000 parts of a solution of polysiloxane C with a nonvolatile content of 60.1%.

[0159] (3) Synthesis of silicon slurry (Synthesis Example 11) Preparation of Silicon Nanoparticle Dispersion A (Silicon Nanoparticle Dispersion Step) A 150 ml container of a small bead mill was charged with zirconia beads with a particle size of 0.1 to 0.2 mm and a filling rate of 60% by volume, and 165 parts of methyl ethyl ketone (MEK) solvent. Next, 40 parts of silicon powder with an average particle size of 5 μm (manufactured by Kojundo Chemical Laboratory Co., Ltd., product name "SIE23PB") and 8 parts of a cationic dispersant liquid (manufactured by BYK Japan, product name "BYK102") were added, and the mixture was wet-pulverized in a bead mill to obtain a dark brown liquid silicon nanoparticle dispersion A with a solids concentration of 23%. The average particle size (D50) of the silicon nanoparticles was 85 nm. The silicon nanoparticle diameter (D50) was measured using a Mastersizer 3000 (manufactured by Myburn, product name "Caesar Micron Sizer LMS-3000").

[0160] [Examples 1 to 9] A. Preparation of negative electrode active material (Uniformization process) 666 parts of the silicon nanoparticle dispersion A obtained in Synthesis Example 11 above and 334 parts of each of the phenolic resins B1 to B9 to which methyl ethyl ketone was added as an organic solvent (solvent) obtained in Synthesis Examples 1 to 9 above were thoroughly mixed in a stirrer to obtain suspensions of negative electrode precursor mixtures with solid concentrations of 22%. Next, the solvent was removed (removal of methyl ethyl ketone) in a 120°C oil bath under nitrogen flow conditions, and then the mixture was dried under reduced pressure at 110°C for 10 hours using a vacuum dryer to obtain dried products of each precursor mixture as negative electrode active material precursors.

[0161] (Firing process) Each dried product obtained in the homogenization step was fired at 1100°C for 4 hours in a nitrogen atmosphere to obtain each black solid product, which was a carbide.

[0162] (Crushing process) Each black solid obtained in the firing step was pulverized in a planetary ball mill to prepare each negative electrode active material containing composite particles in which silicon nanoparticles were dispersed within a matrix containing a carbonaceous phase.

[0163] B. Manufacture of negative electrodes for secondary batteries and secondary batteries Each negative electrode active material (8 parts), the conductive additive acetylene black (1 part), and an organic binder (1 part, consisting of styrene-butadiene rubber copolymer (SBR) (0.75 parts) and carboxymethyl cellulose (CMC) (0.25 parts)) were mixed and stirred for 10 minutes in a planetary rotor type foam-removing blender to prepare each slurry. Each slurry was applied to a 20 μm-thick copper foil using an applicator, and then dried at 110°C under reduced pressure to obtain each thin electrode film. Each of the obtained electrode thin films was punched out into a circular electrode with a diameter of 14 mm, and pressed using a tablet press to a thickness of approximately 40 μm to produce each negative electrode for a secondary battery. The thickness was measured using a thickness meter, measuring the average value at five points on the circular electrode thin film.

[0164] Next, in a dry room with an extremely low moisture content (dew point of -40°C or less), a Li foil was placed opposite each of the circular electrode thin films (negative electrodes) with a 25 μm thick polypropylene separator in between, and then an electrolyte (Kishida Chemical Co., Ltd., 1 mol / L LiPF6, diethyl carbonate:ethylene carbonate = 1:1 (volume ratio)) was adsorbed to produce each half-secondary battery (CR2032 type) for evaluation.

[0165] [Examples 10 to 18] (Uniformization process) 666 parts of the silicon nanoparticle dispersion A obtained in Synthesis Example 11 above, 50 parts of the polysiloxane C obtained in Synthesis Example 10 above, and 284 parts each of the phenolic resins B1 to B9 to which methyl ethyl ketone was added as an organic solvent were thoroughly mixed in a stirrer to obtain suspensions of negative electrode precursor mixtures with solid concentrations of 22%. Next, the solvent was removed in a 120°C oil bath under nitrogen flow conditions, and then the mixture was dried under reduced pressure at 110°C for 10 hours using a vacuum dryer to obtain dried products of each precursor mixture as negative electrode active material precursors.

[0166] (Firing process) Each dried product obtained in the homogenization step was fired at 1100°C for 4 hours in a nitrogen atmosphere to obtain each black solid product, which was a carbide.

[0167] (Crushing process) Each black solid obtained in the firing step was pulverized in a planetary ball mill to prepare each negative electrode active material.

[0168] B. Manufacture of negative electrodes for secondary batteries and secondary batteries Each negative electrode and each half secondary battery (CR2032 type) for evaluation were manufactured in the same manner as in the manufacture of the negative electrodes for secondary batteries and secondary batteries of Examples 1 to 9 above, except that each of the negative electrode active materials was used.

[0169] [Comparative Example 1] (Uniformization process) 666 parts of the silicon nanoparticle dispersion A obtained in Synthesis Example 11 above and 334 parts of a phenolic resin synthesized from phenol and formaldehyde (manufactured by Sumitomo Bakelite Co., Ltd., product name "PR-51283") were thoroughly mixed in a stirrer to obtain a suspension of a negative electrode precursor mixture with a solid concentration of 22%. Next, the solvent was removed in a 120°C oil bath under nitrogen flow conditions, and then the mixture was dried under reduced pressure at 110°C for 10 hours using a vacuum dryer to obtain a dried precursor mixture as a negative electrode active material precursor.

[0170] (Firing process) The dried product obtained in the homogenization step was fired in a nitrogen atmosphere at 1100° C. for 4 hours to obtain a black solid product that was a carbide.

[0171] (Crushing process) The black solid obtained in the firing step was pulverized in a planetary ball mill to prepare a negative electrode active material. The black solid was pulverized in a planetary ball mill to obtain a powder, and the powder was subjected to XRD measurement. The half-width of the peak near 2θ=26.4° measured in Test Example 1 below was 9°. The results are shown in Table 1 below.

[0172] B. Manufacture of negative electrodes for secondary batteries and secondary batteries Each negative electrode and each half secondary battery (CR2032 type) for evaluation were produced in the same manner as in the production of the negative electrodes for secondary batteries and secondary batteries of Examples 1 to 9 above, except that the above negative electrode active material was used.

[0173] Comparative Example 2 (Uniformization process) 666 parts of the silicon nanoparticle dispersion A obtained in Synthesis Example 11 above, 50 parts of the polysiloxane C obtained in Synthesis Example 10, and 284 parts of a phenolic resin synthesized from phenol and formaldehyde (manufactured by Sumitomo Bakelite Co., Ltd., product name "PR-51283") were thoroughly mixed in a stirrer to obtain a suspension of a negative electrode precursor mixture with a solid concentration of 22%. Next, the solvent was removed in a 120°C oil bath under nitrogen flow conditions, and then the mixture was dried under reduced pressure at 110°C for 10 hours using a vacuum dryer to obtain a dried precursor mixture as a negative electrode active material precursor.

[0174] (Firing process) The dried product obtained in the homogenization step was fired in a nitrogen atmosphere at 1100° C. for 4 hours to obtain a black solid product that was a carbide.

[0175] (Crushing process) The black solid obtained in the firing step was pulverized in a planetary ball mill to prepare a negative electrode active material. The black solid was pulverized in a planetary ball mill to obtain a powder, and the powder was subjected to XRD measurement. The half-width of the peak near 2θ=26.4° measured in Test Example 1 below was 9°. The results are shown in Table 2 below.

[0176] B. Manufacture of negative electrodes for secondary batteries and secondary batteries Each negative electrode and each half secondary battery (CR2032 type) for evaluation were produced in the same manner as in the production of the negative electrodes for secondary batteries and secondary batteries of Examples 1 to 9 above, except that the above negative electrode active material was used.

[0177] [Test example] (Test Example 1) Measurement of half-width The half-value widths of the carbides prepared in Synthesis Examples 1 to 9 were measured by the following method. The results are shown in Tables 1 and 2 below. Equipment: Rigaku Corporation "Ultima IV" (wide-angle X-ray diffraction (XRD)) Radiation source: Cu / Ka line, 40kV / 40mA Scan speed: 2 degrees / minute Scanning range: 10 degrees to 70 degrees Data processing: The full width at half maximum was calculated by fitting the following Lorentzian function to the peak in the range of 2θ=16.5 to 30.5 derived from the graphite layer structure (002) by the nonlinear least squares method. y=h / (1+(xu)2 / w2)+a×x+b (In the above formula, y is the intensity of the diffraction line, x is 2θ of the diffraction line, h is the peak height, u is 2θ of the peak, w is the half-width of the peak, and a and b are correction coefficients for the back content.)

[0178] (Test Example 2) Measurement of weight average molecular weight The weight average molecular weights described in the above Synthesis Examples 1 to 9 were measured using the following measuring device and under the following measuring conditions. Measurement equipment: Tosoh Corporation "HLC-8320 GPC" Column: Tosoh Corporation guard column "HXL-L" + Tosoh Corporation "TSK-GEL G2000HXL" + Tosoh Corporation "TSK-GEL G2000HXL" + Tosoh Corporation "TSK-GEL G3000HXL" + Tosoh Corporation "TSK-GEL G4000HXL" Detector: RI (differential refractometer) Data processing: Tosoh Corporation's "GPC Workstation EcoSEC-WorkStation" Measurement conditions: Column temperature 40℃ Developing solvent: tetrahydrofuran Flow rate 1.0ml / min Standard: In accordance with the measurement manual for the GPC Workstation EcoSEC-WorkStation, the following monodisperse polystyrene with known molecular weight was used. (Polystyrene used) Tosoh Corporation "A-500" Tosoh Corporation "A-1000" Tosoh Corporation "A-2500" Tosoh Corporation "A-50000" "F-1" manufactured by Tosoh Corporation "F-2" manufactured by Tosoh Corporation "F-4" manufactured by Tosoh Corporation "F-10" manufactured by Tosoh Corporation "F-20" manufactured by Tosoh Corporation "F-40" manufactured by Tosoh Corporation "F-80" manufactured by Tosoh Corporation Tosoh Corporation "F-128"

[0179] (Test Example 3) Evaluation of battery characteristics of secondary batteries The battery characteristics of each of the half batteries obtained in Examples 1 to 18 and Comparative Examples 1 and 2 were measured using a secondary battery charge / discharge tester (manufactured by Hokuto Denko Corporation). The measurement conditions were room temperature of 25°C, a cutoff voltage range of 0.005 to 1.5 V, and a charge / discharge rate of 0.1 C (1 to 3 times) and 0.2 C (after 4 cycles). The charge / discharge characteristics (charge / discharge capacity) were evaluated under the set conditions of constant current / constant voltage charge / constant current discharge. Between each charge / discharge cycle, the battery was left in an open circuit for 30 minutes. The initial efficiency and cycle characteristics (representing the retention rate of discharge capacity after 10 cycles) were determined as follows, and the evaluation results are shown in Tables 1 and 2 below. Initial efficiency (%) = Initial discharge capacity (mAh / g) / Initial charge capacity (mAh / g) Retention rate (%) = initial discharge capacity (mAh / g) / discharge capacity after 10 cycles (mAh / g) The results are shown in Tables 1 and 2 below.

[0180] [Table 1]

[0181] [Table 2]

[0182] From the above table, it is clear that the lithium secondary batteries of the examples of the present invention can achieve an initial efficiency of 84% or more and a retention rate of 80% or more, and have excellent charge / discharge characteristics. [Industrial Applicability]

[0183] A nonaqueous electrolyte secondary battery using the negative electrode active material of the present invention is used, for example, as a paper-type battery, a button-type battery, a coin-type battery, a laminated battery, a cylindrical battery, a prismatic battery, etc. The above-mentioned negative electrode active material of the present invention 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.

Claims

1. The negative electrode active material for a lithium ion secondary battery includes composite particles in which silicon nanoparticles are dispersed within a matrix containing a carbonaceous phase, and in an X-ray diffraction pattern analysis of the carbonaceous phase, the half-width of a diffraction line peak attributable to graphite (002) in the vicinity of 2θ = 26.4° is 1° to 8°.

2. 2. The negative electrode active material for a lithium ion secondary battery according to claim 1, wherein the matrix further contains silicon carbide.

3. 3. The negative electrode active material for a secondary battery according to claim 1, wherein the carbonaceous phase is a carbonized naphthylene ether resin represented by the following formula (1): 【Chemical 1】 (In the above formula (1), q is an integer of 1 to 10, each p is independently an integer of 0 to 3, and X is a glycidyl group, a methylglycidyl group, or a hydrogen atom.) In addition, R in the above formula (1) １ is expressed by the following formula (2), and R ２ is a hydrogen atom or is represented by the following general formula (3). 【Chemistry 2】 (In the above formula (2), r is an integer of 1 to 10.) 【Chemistry 3】 (In the above formula (3), R １ , p, and X are the same as those in the above formula (1).

4. 3. The negative electrode active material for a secondary battery according to claim 1, wherein the carbonaceous phase is a carbonized product of a phenolic resin derived from a reaction between a phenol and an aldehyde, as represented by the following formula (4): 【Chemistry 4】 (In the above formula (4), R ３ and R ４ and R ５ are each independently a hydrocarbon group having 1 to 5 carbon atoms or a hydrogen atom, and R ３ and R ４ and R ５ At least one of the groups is a hydrocarbon group having 1 to 5 carbon atoms.

5. 3. The negative electrode active material for a lithium ion secondary battery according to claim 1, wherein the carbonaceous phase is a carbonized product of a phenolic resin derived from a reaction between a phenol and an aldehyde, as represented by the following formula (5): 【Chemistry 5】 (In the above formula (5), R ６ each independently represents a hydrocarbon group having 1 to 5 carbon atoms, m represents an integer of 0 to 4, and n represents an integer of 1 or 2.

6. 3. The negative electrode active material for a secondary battery according to claim 1, wherein the carbonaceous phase is a carbonized product of a phenolic resin or an epoxy resin having a structure represented by the following formula (6): 【Chemistry 6】

7. 7. A negative electrode for a lithium ion secondary battery, comprising: a negative electrode active material layer for a secondary battery containing the negative electrode active material for a lithium ion secondary battery according to claim 1; and a negative electrode current collector having the negative electrode active material layer for a secondary battery disposed on at least a part of its surface.

8. A lithium ion secondary battery comprising the negative electrode for secondary batteries according to claim 7, an electrolyte layer, a separator, and a positive electrode.

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