WO2022172585A1

WO2022172585A1 - Negative electrode active material, method for manufacturing negative electrode active material, and non-aqueous electrolyte secondary battery

Info

Publication number: WO2022172585A1
Application number: PCT/JP2021/046423
Authority: WO
Inventors: 培新諸; 聡片野; 賢一川瀬
Original assignee: Dic株式会社
Priority date: 2021-02-09
Filing date: 2021-12-16
Publication date: 2022-08-18

Abstract

The purpose of the present invention is to provide: a negative electrode active material having excellent charge and discharge characteristics (charge and discharge capacity, initial Coulombic efficiency, and cycle characteristics); and a non-aqueous electrolyte secondary battery using the same.　A negative electrode active material according to the present invention comprises: silicon oxycarbide; and composite particles in which silicon nanoparticles are dispersed in a matrix including a carbonaceous phase, wherein the composite particles satisfy expression 1 in a chemical shift value obtained from a 29Si-NMR spectrum. Expression 1: 0.7≤A/B≤3.0 A: The area intensity of a peak within the range of -70 ppm to -90 ppm belonging to Si (zero-valent) B: The area intensity of a peak within the range of -90 ppm to -130 ppm derived from a SiO4 bond

Description

Negative electrode active material, method for producing negative electrode active material, and non-aqueous electrolyte secondary battery

The present invention relates to a negative electrode active material, a manufacturing method thereof, and a non-aqueous electrolyte secondary battery using the negative electrode active material.

In recent years, with the spread of mobile electronic devices such as smartphones, the demand for small, high-capacity secondary batteries has increased. Among them, lithium ion secondary batteries (sometimes abbreviated as LIB) are rapidly being developed for electric vehicles (EV), and their industrial application range continues to expand. Carbon-based graphite active materials (natural and artificial) are widely used as negative electrode materials for lithium ion secondary batteries. Due to evolution, the improvement of battery capacity is approaching the limit.

Since silicon (Si) can form an alloy (intermetallic compound) with metallic lithium, it can electrochemically store and release lithium ions. The lithium ion storage/discharge capacity has a theoretical capacity of 4200 mAh/g when Li ₂₂ Si ₅ is formed, which can be much higher than that of a graphite negative electrode.

However, silicon undergoes a large volume change of 3 to 4 times as it absorbs and releases lithium ions. For this reason, when a charge-discharge cycle is performed, repeated expansion and contraction causes the silicon to collapse and become finely divided, which causes peeling and collapse of the electrode material and deterioration of electronic conductivity, resulting in poor charge-discharge cycle characteristics. There was a problem that it deteriorated and a good cycle life could not be obtained.

Patent Documents 1 to 3 below describe silicon-based compounds used as negative electrode active materials in non-aqueous electrolyte secondary batteries such as LIB.

Japanese translation of PCT publication No. 2015-156355 International Publication No. 2014-002602 pamphlet Japanese Patent No. 5892264

For example, in the conventional Si-based compounds described in Patent Documents 1 to 3, in controlling the negative electrode active material matrix structure and the silicon particle state, the composition of the matrix containing Si (zero valence) or the matrix containing silicon oxycarbide and carbon The carbon phase structure has not been sufficiently studied, and there is room for improvement in charge/discharge performance, particularly cycle characteristics, when used as a secondary battery.

In view of the above circumstances, the problem to be solved by the present invention is a negative electrode active material having excellent charge-discharge characteristics (charge-discharge capacity, initial coulombic efficiency and cycle characteristics), a non-aqueous electrolyte secondary battery using the same, and An object of the present invention is to provide a method for producing a negative electrode active material.

As a result of intensive studies by the present inventors to solve the above problems, in composite particles in which silicon nanoparticles are dispersed inside a matrix containing silicon oxycarbide and a carbonaceous phase, zerovalent Si which is silicon nanoparticles and a matrix containing SiOC. As a result, by setting the ²⁹ Si-NMR peak area intensity ratio of Si attributed to Si (zero valence) and SiO ₄ bonds to a specific range, the charge / discharge performance, especially the cycle characteristics, in the secondary battery is further improved. The discovery led to the present invention.

That is, the present invention relates to the following.
[1] A negative electrode active material containing composite particles in which silicon nanoparticles are dispersed in a matrix containing silicon oxycarbide and a carbonaceous phase, wherein the composite particles have a chemical shift value obtained from a ²⁹ Si-NMR spectrum, A negative electrode active material that satisfies the following formula 1.
Formula 1: 0.7≤A/B≤3.0
A: Area intensity of the peak within the range of -70 ppm to -90 ppm attributed to Si (zero valence) B: Area intensity of the peak within the range of -90 ppm to -130 ppm derived from the bond of SiO ₄ [2] Includes carbonaceous phase The Raman spectrum of the composite particles has scattering peaks near 1590 cm ⁻¹ and 1330 cm ⁻¹ attributed to the G band and D band of the carbon structure, and their scattering peak intensity ratio I (G band/D band) is The negative electrode active material according to [1], which is in the range of 0.7 to 2.0.
[3] The negative electrode active material according to [1] or [2], wherein the composite particles have an average particle diameter (D50) of 1 μm to 20 μm.
[4] The negative electrode active material according to any one of [1] to [3], wherein the composite particles have a specific surface area (BET) in the range of 1 m ² /g to 20 m ² /g.
[5] A nonaqueous electrolyte secondary battery comprising the negative electrode active material according to any one of [1] to [4].
[6] The method for producing a negative electrode active material according to any one of [1] to [4], including the following steps 1 to 3 as the steps for producing the composite particles.
Step 1: A silicon (zero-valent) slurry pulverized by a wet method is mixed with an aggregate containing a polysiloxane compound and a carbon source resin, stirred and dried to obtain a precursor Step 2: Obtained in Step 1 above Step 3 of obtaining a fired product by firing the precursor in an inert atmosphere within a temperature range of a maximum temperature of 1000° C. to 1180° C.: Pulverizing the fired product obtained in Step 2 to obtain a negative electrode active material. [7] The negative electrode according to [6], wherein the polysiloxane compound has a carboxy group, an epoxy group, an amino group, or a polyether group at the side chain or end of the siloxane bond (Si—O—Si) main skeleton. A method for producing an active material.
[8] The method for producing a negative electrode active material according to [6] or [7], wherein the carbon source resin is a resin containing an aromatic hydrocarbon moiety.
[9] The method for producing a negative electrode active material according to [8], wherein the resin containing an aromatic hydrocarbon moiety is a phenol resin, an epoxy resin, or a thermosetting resin.

The negative electrode active material of the present invention is obtained by skillfully controlling the combination of Si (zero valence), silicon oxycarbide (SiOC), and a matrix phase containing a carbonaceous phase, and by skillfully controlling the structure of the carbon phase. The inherent silicon nanoparticles are likely to exhibit performance, and the charge and discharge performance, especially the cycle characteristics, when used as a secondary battery are excellent. By using the negative electrode active material of the present invention in a non-aqueous electrolyte secondary battery, the charge/discharge capacity, the initial coulombic efficiency, and the cycle characteristics can be exhibited at a high level at the same time.

²⁹ Si-NMR spectrum of Example 1. FIG. ²⁹ Si-NMR spectrum of Comparative Example 1. FIG.

<Negative electrode active material>
The negative electrode active material of the present invention is a negative electrode active material containing composite particles in which silicon nanoparticles are dispersed in a matrix containing silicon oxycarbide and a carbonaceous phase, and the composite particles are obtained from a ²⁹ Si-NMR spectrum. The chemical shift value satisfies the following formula 1.
Formula 1: 0.7≤A/B≤3.0
A: Area intensity of the peak within the range of −70 ppm to −90 ppm attributed to Si (0 valence) B: Area intensity of the peak within the range of −90 ppm to −130 ppm derived from the bond of SiO ₄

The composite particles have a structure in which silicon nanoparticles are uniformly dispersed in a three-dimensional network structure of SiOC composed of elements Si, O, and C and a matrix composed of carbon. In the three-dimensional network structure of SiOC, the type of atom (O or C) that bonds to Si and the number of bonds with each atom can be mainly divided into three types, each of which is SiO ₂ C ₂ , SiO ₃ C, and SiO ₄ domains. Silicon oxycarbide (SiOC) described above is obtained by further randomly combining these domains. The chemical shift (solid-state NMR) of the SiO ₃ C domain is in the range of −60 ppm to −80 ppm (central position −70 ppm), and overlaps somewhat with the peak derived from Si (zero valence).
In the negative electrode active material of the present invention, the fact that the chemical shift value obtained from the ²⁹ Si-NMR spectrum satisfies the above formula 1 means that the silicon nanoparticles (Si: 0 valence) and silicon oxycarbide (SiOC) in the composite particles It means that the ratio with the existing SiO ₄ is optimal, which makes it easy for the silicon nanoparticles to exhibit performance, and when used as a secondary battery, the charge-discharge performance, especially the cycle characteristics, is excellent. The above A/B is more preferably in the range of 0.8≦A/B≦2.9, still more preferably in the range of 0.9≦A/B≦2.8.

In the charging and discharging process of a lithium-ion secondary battery, taking the example of a negative electrode that uses carbon as an active material, during charging, a chemical bond occurs due to an insertion reaction between carbon and lithium ions, and the carbon captures lithium. At the time of discharge, the lithium captured by the carbon becomes lithium ions by releasing electrons, and a desorption reaction occurs in which the lithium is separated from the carbon. Charging and discharging are performed by repeating the intercalation and deintercalation reactions between carbon and lithium ions, that is, the reaction progresses reversibly. The negative electrode active material of the present invention has an active material structure in which single silicon particles (zero valence) are present in a matrix of SiOC skeleton and carbon. The SiOC skeleton is characterized by high chemical stability, and the composite structure with the carbon phase facilitates the diffusion of lithium ions as the electronic transition resistance is reduced. When the single silicon particles (zero valence) are densely wrapped in the composite structure of SiOC and carbon, the function of preventing direct contact between the silicon particles and the electrolytic solution may be exhibited. Therefore, while the single silicon particles in the negative electrode active material of the present invention play a role as a main component for the expression of charge/discharge performance, the chemical reaction between the silicon and the electrolyte solution is avoided during charge/discharge, thereby maximizing the performance deterioration of the silicon particles. can be prevented.

More specifically, SiOC causes changes in the electron distribution inside SiOC due to the approach of lithium ions, and electrostatic bonds and coordinate bonds are formed between SiOC and lithium ions. Lithium ions are stored in the framework of SiOC. Since the energy of these coordination bonds is relatively low, the desorption reaction of lithium ions is easily carried out. That is, SiOC can reversibly cause lithium ion insertion/extraction reactions during charging and discharging. Therefore, by capturing this mechanism, we have found that the ratio of silicon nanoparticles ₍ Si:0 valence) to SiO4 strongly contributes to the improvement of the reversible capacity and can improve the first coulombic efficiency.

The ²⁹ Si-NMR spectrum can be easily obtained using a solid-state NMR apparatus, and the solid-state NMR measurements herein are performed using, for example, an apparatus manufactured by JEOL Co., Ltd. (JNM-ECA600). is. The area intensity ratio (A/B) of the above peaks was obtained by single-pulse measurement with an 8 mm probe after 10 minutes of tuning with a solid-state NMR spectrometer. Then, waveform separation is performed using the Gauss+Lorentz function. Next, based on the peak area obtained by waveform separation, the ratio of the area intensity (A) of the peak in the range of -70 ppm to -90 ppm to the area intensity (B) of the peak in the range of -90 ppm to -130 ppm Obtained by asking.

The negative electrode active material of the present invention has a carbon structure G band (graphite long period carbon lattice structure) and D band (graphite short period carbon lattice structure with disorder and defects) in the Raman spectrum of the composite particles containing the carbonaceous phase. , and the ^scattering ^peak intensity ratio I (G band/D band) is preferably in the range of 0.7 to 2.0. The scattering peak intensity ratio I is preferably 0.7 to 1.8. The fact that the scattering peak intensity ratio I is within the above range means the following for the carbonaceous phase in the matrix.

The negative electrode active material of the present invention has a carbonaceous phase composed only of carbon together with the SiOC skeleton structure and the like in the matrix. Some carbon atoms in this carbonaceous phase are bonded to some Si atoms in the SiOC skeleton. This carbonaceous phase is an important component that affects charge-discharge characteristics. The carbon phase is formed in SiOC composed of SiO ₂ C ₂ , SiO ₃ C, and SiO ₄ , and is bonded to some Si atoms of the SiOC, so the inside of SiOC and the surface electron transfer between Si atoms and free carbon becomes easier. Therefore, it can be considered that the intercalation/deintercalation reaction of lithium ions proceeds rapidly during charge/discharge, and the charge/discharge characteristics are improved. In addition, although the negative electrode active material may slightly expand or contract due to the insertion/extraction reaction of lithium ions, the presence of free carbon in the vicinity of the expansion/contraction of the active material as a whole mitigates the expansion/contraction. This is considered to have the effect of greatly improving the cycle characteristics.

Some carbonaceous phases are formed due to thermal decomposition of precursor silane compounds in an inert gas atmosphere. Specifically, carbonizable sites and substituents in the molecular structure of the silane compound become carbon components by high-temperature pyrolysis in an inert atmosphere, and some of these carbons become part of the SiOC skeleton. There are features that connect The carbonizable component is not particularly limited, but hydrocarbons are preferred, alkyls, alkylenes, alkenes, alkynes and aromatics are more preferred, and aromatics are more preferred.

In addition, in the carbonaceous phase of the present invention, some are obtained by thermal decomposition of the carbon source resin. These carbons also lead to the effect of reducing the resistance of the active material, and are considered to be able to flexibly follow the volume change of the silicon particles during charging and discharging when used in the negative electrode of the secondary battery. The type of carbon source resin is not particularly limited, but a carbon compound containing a six-membered carbon ring is preferred.

The amount of the carbonaceous phase can affect the charge/discharge characteristics of the negative electrode active material. If the amount of carbon is insufficient, the electrical conductivity may be poor and the charge/discharge characteristics may be deteriorated. On the other hand, if the amount of carbon is too large, the charge/discharge capacity of the entire negative electrode active material may decrease because the theoretical capacity of carbon itself is low.

The existing state of the carbonaceous phase can be identified by thermal analysis (TG-DTA) as well as Raman spectrum. Unlike the C atoms in the SiOC skeleton, the carbonaceous phase is easily thermally decomposed in the atmosphere, and the amount of carbon present can be determined from the amount of thermogravimetric loss measured in the presence of air. That is, the carbon content can be quantified by using a Thermogravimeter-Differential Thermal Analyzer (TG-DTA). In addition, thermal decomposition temperature behavior (decomposition reaction start temperature, decomposition reaction end temperature, number of thermal decomposition reaction species, temperature of maximum weight loss in each thermal decomposition reaction species, etc.) obtained from the thermal weight loss behavior from the measurement. Changes can also be easily comprehended and these temperature values can be used to determine the state of the carbon. On the other hand, the C atoms in the SiOC skeleton, that is, the carbon atoms bonded to the Si atoms constituting the SiO ₂ C ₂ , SiO ₃ C, and SiO ₄ have very strong chemical bonds and are therefore thermally stable. It is considered that it will not be thermally decomposed in the air in the temperature range measured by the thermal analyzer. In addition, since the carbon in the active material of the present invention has properties similar to those of hard carbon, it is thermally decomposed in the air in the temperature range of about 550° C. to 900° C., resulting in rapid weight loss. Occur. The maximum temperature of the TG-DTA measurement conditions is not particularly limited, but in order to completely complete the thermal decomposition reaction of carbon, the TG-DTA measurement is performed under conditions from room temperature (about 25°C) to 1000°C or higher in the air. It is preferable to

In the matrix in the composite particles, the ratio of the carbonaceous phase present is important, and the content is preferably 30% to 85% by weight of the total weight of the matrix. Also, the content of the carbonaceous phase is more preferably 40% to 70% by weight, more preferably 45% to 60% by weight. When the content of the carbonaceous phase is within the above range, a sufficient effect of reducing the resistance of the active material can be obtained, and the permeation of the electrolyte into the active material is suppressed. Generation of interfacial electrolyte decomposition products (SEI) may be suppressed.

The silicon nanoparticles are obtained by pulverizing silicon (zero-valent) particles into nano particles. The presence of the silicon (0-valent) particles can improve charge/discharge capacity and initial coulombic efficiency when used as a secondary battery. In the negative electrode active material of the present invention, as described above, the ratio of silicon nanoparticles (Si: 0 valence) to SiO ₄ is important, and it is important to satisfy formula 1 above.

The silicon nanoparticles can be pulverized using a pulverizer such as a ball mill, bead mill, or jet mill. In addition, the pulverization may be wet pulverization, and there is no particular limitation on the solvent composition as long as the pulverization process can be performed well as an organic solvent, but alcohols, ketones, etc. can be preferably used, but toluene, xylene, naphthalene. , methylnaphthalene, and other aromatic hydrocarbon solvents can also be used.

The content of silicon nanoparticles in the composite particles is not particularly limited, but the battery capacity can be controlled by adjusting the content of silicon nanoparticles. In the negative electrode active material of the present invention, the content ratio of silicon particles in the composite particles is preferably 1% by mass to 80% by mass, more preferably 10% by mass to 70% by mass, and more preferably 20% by mass to 60% by mass. % by mass is more preferred. When the content ratio of the silicon particles is 20% by mass or more, the charge-discharge capacity when used as a negative electrode material for a battery can be increased, and the capacity is superior to graphite as a negative electrode material, and the initial coulomb efficiency is also high. level can be maintained. On the other hand, by making it 60% by mass or less, the silicon particles are sufficiently coated with the matrix containing the silicon oxycarbide and the carbonaceous phase, and the volume expansion and contraction changes of the active material during charging and discharging may be effectively suppressed. Improves properties.

The average particle diameter (D50) of the silicon nanoparticles is preferably 10 nm to 300 nm, more preferably 20 nm to 250 nm, still more preferably 30 nm to 200 nm. The average particle size (D50) can be measured by a dynamic light scattering method using a laser particle size analyzer or the like. Silicon particles having a large size exceeding 300 nm become large lumps, and are likely to be pulverized during charge/discharge, so it is assumed that the charge/discharge performance of the active material tends to decrease. On the other hand, since silicon particles having a small size of less than 10 nm are too fine, the silicon particles tend to agglomerate. Therefore, it becomes difficult to uniformly disperse the small silicon particles in the active material, and the surface activation energy of the fine particles is high, and by-products on the surface of the small silicon particles increase when the active material is fired at a high temperature. There is also a tendency, which leads to a significant decrease in charge/discharge performance.

The average particle diameter (D50) is the particle diameter at which the volume cumulative distribution curve is drawn from the small diameter side in the particle diameter distribution of the silicon nanoparticles in the negative electrode active material, and the cumulative distribution is 50%. The average particle size (D50) can be measured with a laser diffraction particle size distribution analyzer or the like.

As described above, the negative electrode active material of the present invention contains composite particles in which silicon nanoparticles are dispersed inside a matrix containing silicon oxycarbide (SiOC) and a carbonaceous phase. Silicon oxycarbide (SiOC) is a structure having a Si--O--C skeleton structure composed of silicon (excluding zero valence), oxygen and carbon. SiOC can be formed by baking a polysiloxane compound as described in the production method below. The details of the Si--O--C skeleton structure will be described later in the manufacturing method of the polysiloxane structure.

The average particle size (D50) of the composite particles is preferably 1 μm to 20 μm, more preferably 2 μm to 18 μm. If the average particle diameter (D50) is too small, the amount of SEI generated during charging and discharging increases as the specific surface area increases significantly, which may reduce the reversible charge-discharge capacity per unit volume. Electrode film preparation becomes difficult, and there is a possibility that it may peel off from the current collector.

The specific surface area (BET) of the composite particles is preferably in the range of 1 m ² /g to 20 m ² /g, more preferably in the range of 3 m ² /g to 18 m ² /g. When the specific surface area (BET) is within the above range, the amount of solvent absorbed during electrode production can be appropriately maintained, and the amount of binder used for maintaining binding properties can also be properly maintained. The specific surface area (BET: Brunauer-Emmett-Teller) can be determined by nitrogen gas adsorption measurement, and can be easily measured using a general-purpose specific surface area measuring device.

The composite particles may have a coating layer mainly composed of low-crystalline carbon with an average thickness of 10 nm or more and 300 nm or less on the surface. The average thickness is preferably 20 nm or more and 200 nm or less. Since the composite particles have a coating layer with the above average thickness, it is possible to protect the silicon nanoparticles exposed on the particle surface, thereby improving the chemical stability and thermal stability of the composite particles. Performance degradation can be further suppressed.

<Description of manufacturing method>
An example of the 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 the manufacturing steps of the composite particles.
Step 1: A silicon (zero-valent) slurry pulverized by a wet method is mixed with an aggregate containing a polysiloxane compound and a carbon source resin, stirred and dried to obtain a precursor Step 2: Obtained in Step 1 above Step 3 of obtaining a fired product by firing the precursor in an inert atmosphere within a temperature range of a maximum temperature of 1000° C. to 1180° C.: Pulverizing the fired product obtained in Step 2 to obtain a negative electrode active material. obtain

<Step 1>
(Silicon (zero valent) slurry)
The wet-milled silicon (zero-valent) slurry (slurry of silicon nanoparticles described above) used in step 1 can be prepared using an organic solvent and a wet powder mill. A dispersant may be used to facilitate the grinding of the silicon particles in the organic solvent. The wet pulverizer is not particularly limited, and includes roller mills, jet mills, high-speed rotary pulverizers, container-driven mills, bead mills, and the like.

Any solvent can be used in the wet method. The organic solvent is not particularly limited as long as it does not chemically react with silicon. Examples thereof 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; aromatic benzene, toluene and xylene.

The type of the dispersant is not particularly limited, and aqueous or non-aqueous known and commonly used commercial products can be used. preferable. Types of non-aqueous dispersants include polymer type (polyether type, polyalkylene polyamine type, polycarboxylic acid partial alkyl ester type, etc.), low molecular type (polyhydric alcohol ester type, alkyl polyamine type, etc.), and inorganic type. A polyphosphate system etc. are illustrated. The concentration of silicon in the (0-valent) silicon slurry is not particularly limited, but is preferably in the range of 5% by mass to 40% by mass, more preferably 10% by mass to 30% by mass.

(Polysiloxane compound)
The polysiloxane compound used 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. These single resins may be used, or composite resins having these as segments and chemically bonding with other polymer segments may be used. There are copolymers of graft, block, random, alternating, etc. complexing forms. For example, there are composite resins that have a graft structure in which polysiloxane segments and side chains of polymer segments are chemically bonded, and there are composite resins that have a block structure in which polysiloxane segments are chemically bonded to the ends of polymer segments. mentioned.

The polysiloxane segment preferably has a structural unit represented by the following general formula (S-1) and/or the following general formula (S-2). Among them, the polysiloxane compound more preferably has a carboxy group, an epoxy group, an amino group, or a polyether group at the side chain or end of the siloxane bond (Si--O--Si) backbone.

(In general formulas (S-1) and (S-2) above, R ¹ represents an aromatic hydrocarbon substituent or an alkyl group, an epoxy group, a carboxy group, etc. R ² and R ³ each represent an alkyl group, Cycloalkyl group, aryl group, aralkyl group, epoxy group, carboxy group, etc.)

Alkyl groups include, for example, methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, sec-butyl group, tert-butyl group, pentyl group, isopentyl group, neopentyl group, tert-pentyl group, 1 -methylbutyl group, 2-methylbutyl group, 1,2-dimethylpropyl group, 1-ethylpropyl group, hexyl group, isohesyl group, 1-methylpentyl group, 2-methylpentyl group, 3-methylpentyl group, 1,1 -dimethylbutyl group, 1,2-dimethylbutyl group, 2,2-dimethylbutyl group, 1-ethylbutyl group, 1,1,2-trimethylpropyl group, 1,2,2-trimethylpropyl group, 1-ethyl- 2-methylpropyl group, 1-ethyl-1-methylpropyl group and the like. Examples of the cycloalkyl group include cyclopropyl group, cyclobutyl group, cyclopentyl group, cyclohexyl group and the like.

Examples of aryl groups include phenyl, naphthyl, 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, 4-vinylphenyl, and 3-isopropylphenyl groups.

The aralkyl group includes, for example, a benzyl group, a diphenylmethyl group, a naphthylmethyl group and the like.

Examples of polymer segments other than the polysiloxane segment possessed by the polysiloxane compound include vinyl polymer segments such as acrylic polymers, fluoroolefin polymers, vinyl ester polymers, aromatic vinyl polymers, and polyolefin polymers, Examples include polymer segments such as polyurethane polymer segments, polyester polymer segments, and polyether polymer segments. Among them, a vinyl polymer segment is preferred.

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-like polysiloxane structure.

(In the formula, the carbon atom is the carbon atom that constitutes the polymer segment, and the two silicon atoms are the silicon atoms that constitute the polysiloxane segment.)

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 heat-treating the polysiloxane compound before thermal decomposition, the cross-linking reaction proceeds and the polysiloxane compound is solidified, thereby facilitating the thermal decomposition treatment.

Examples of polymerizable double bonds include vinyl groups and (meth)acryloyl groups. Two or more polymerizable double bonds are preferably present in the polysiloxane segment, more preferably 3 to 200, and even more preferably 3 to 50. In addition, by using a composite resin having two or more polymerizable double bonds as the polysiloxane compound, the cross-linking reaction can be facilitated.

The polysiloxane segment may have silanol groups and/or hydrolyzable silyl groups. Hydrolyzable groups in hydrolyzable silyl groups include, for example, halogen atoms, alkoxy groups, substituted alkoxy groups, acyloxy groups, phenoxy groups, mercapto groups, amino groups, amido groups, aminooxy groups, iminooxy groups, alkenyloxy and the like, and the hydrolyzable silyl group becomes a silanol group by hydrolysis of these groups. In parallel with the thermosetting reaction, a hydrolytic condensation reaction proceeds between the hydroxyl group in the silanol group and the hydrolyzable group in the hydrolyzable silyl group, thereby obtaining a solid polysiloxane compound. can.

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. Specifically, for example, a group represented by the following general formula (S-4) is mentioned.

⁽ wherein ^R4 represents a monovalent organic group such as an alkyl group, an aryl group or an aralkyl group; R5 represents a halogen atom, an alkoxy group, an acyloxy group, an allyloxy group, a mercapto group, an amino group, an amido group, an aminooxy group, iminooxy group or alkenyloxy group, and b is an integer of 0 to 2.)

Alkyl groups include, for example, methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, sec-butyl group, tert-butyl group, pentyl group, isopentyl group, neopentyl group, tert-pentyl group, 1 -methylbutyl group, 2-methylbutyl group, 1,2-dimethylpropyl group, 1-ethylpropyl group, hexyl group, isohesyl group, 1-methylpentyl group, 2-methylpentyl group, 3-methylpentyl group, 1,1 -dimethylbutyl group, 1,2-dimethylbutyl group, 2,2-dimethylbutyl group, 1-ethylbutyl group, 1,1,2-trimethylpropyl group, 1,2,2-trimethylpropyl group, 1-ethyl- 2-methylpropyl group, 1-ethyl-1-methylpropyl group and the like.

The halogen atom includes, for example, fluorine atom, chlorine atom, bromine atom, iodine atom and the like.

Examples of alkoxy groups include methoxy, ethoxy, propoxy, isopropoxy, butoxy, sec-butoxy, and tert-butoxy groups.

Examples of acyloxy groups include formyloxy, acetoxy, propanoyloxy, butanoyloxy, pivaloyloxy, pentanoyloxy, phenylacetoxy, acetoacetoxy, benzoyloxy, naphthoyloxy and the like.

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

Examples of alkenyloxy groups include vinyloxy, allyloxy, 1-propenyloxy, isopropenyloxy, 2-butenyloxy, 3-butenyloxy, 2-petenyloxy, 3-methyl-3-butenyloxy, 2 -hexenyloxy group and the like.

Examples of the polysiloxane segment having the structural unit represented by the above general formula (S-1) and/or the above general formula (S-2) include those having the following structures.

The polymer segment may have various functional groups as necessary to the extent that the effects of the present invention are not impaired. Such functional groups include, for example, carboxyl group, blocked carboxyl group, carboxylic anhydride group, tertiary amino group, hydroxyl group, blocked hydroxyl group, cyclocarbonate group, epoxy group, carbonyl group, primary amide group, secondary Amide, carbamate groups, functional groups represented by the following structural formula (S-5), and the like can be used.

In addition, the polymer segment may have polymerizable double bonds such as vinyl groups and (meth)acryloyl groups.

The above polysiloxane compound can be produced by known methods, but is preferably produced by the methods shown in (1) to (3) below. However, it is not limited to these.

(1) 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, and the polymer segment and the silanol group and/or the hydrolyzable silyl group are and a method of mixing with a silane compound containing a silane compound having a polymerizable double bond and performing a hydrolytic condensation reaction.

(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. Polysiloxane is also prepared in advance by subjecting a silane compound containing a silane compound having both a silanol group and/or a hydrolyzable silyl group and a polymerizable double bond to a hydrolytic condensation reaction. Then, a method of mixing the polymer segment and polysiloxane and performing a hydrolytic condensation reaction.

(3) mixing 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 to perform a hydrolytic condensation reaction; How to do it.

(Carbon source resin)
The carbon source resin used in step 1 is not particularly limited as long as it has good miscibility with the polysiloxane compound at the time of precursor preparation, and may be carbonized by baking at high temperature in an inert atmosphere. It is preferable to use synthetic resins or natural chemical raw materials possessed by the resin, and it is more preferable to use phenolic resin from the viewpoint of inexpensive availability and elimination of impurities.

Synthetic resins include thermoplastic resins such as polyvinyl alcohol and polyacrylic acid, and thermosetting resins such as phenol resin and furan resin. Natural chemical raw materials include heavy oils, especially tar pitches such as coal tar, light tar oil, medium tar oil, heavy tar oil, naphthalene oil, anthracene oil, coal tar pitch, pitch oil, mesophase pitch, and oxygen-crosslinked petroleum pitch. , heavy oil, etc.

In particular, in step 1 of the present invention, the carbon source resin is preferably a resin containing an aromatic hydrocarbon moiety, and the resin containing an aromatic hydrocarbon moiety is a phenol resin, an epoxy resin, or a thermosetting resin. It is preferably a flexible resin.

(precursor)
Then, the aggregate containing the silicon (zero-valent) slurry, the polysiloxane compound and the carbon source resin is uniformly mixed and stirred, and then the solvent is removed and dried to obtain a precursor. Mixing of raw materials is not particularly limited, but a general-purpose apparatus having a dispersing/mixing function can be used. Among them, stirrers, ultrasonic mixers, premix dispersers and the like are mentioned. A dryer, a reduced-pressure dryer, a spray dryer, or the like can be used for solvent removal and drying for the purpose of distilling off the organic solvent.

This negative electrode active material precursor contains 3% to 50% by mass of silicon nanoparticles, which are silicon (zero valent), and 15% to 85% by mass of the solid content of a polysiloxane compound, and the carbon source resin It is preferable to set the solid content of 3% to 70% by mass, the solid content of the silicon nanoparticles is 8% to 40% by mass, and the solid content of the polysiloxane compound is 20% to 70% by mass. Furthermore, it is more preferable to set the solid content of the carbon source resin to 3% by mass to 60% by mass.

<Step 2>
In step 2, the precursor obtained in step 1 is fired in an inert atmosphere at a maximum temperature of 1000° C. to 1180° C. to completely decompose the thermally decomposable organic components and other components. In this step, the main component is made into a sintered material suitable for the negative electrode active material of the present invention by precisely controlling the sintering conditions. Specifically, the “Si—O” bond present in the raw material polysiloxane compound is converted into a “Si—O—C” skeleton structure (hereinafter referred to as SiOC in the description) is formed, and the uniformly dispersed carbon source resin is also carbonized, so that it is converted as free carbon into a three-dimensional structure having a “Si—O—C” skeleton. .

In step 2, the precursor obtained in step 1 above is fired in an inert atmosphere according to a firing program determined by the rate of temperature increase, holding time at a constant temperature, and the like. The maximum attainable temperature is the maximum temperature to be set, and strongly affects the structure and performance of the negative electrode active material, which is the baked product. In the present invention, since the maximum temperature is 1000° C. to 1180° C., the fine structure of the negative electrode active material having the above-described chemical bonding state of silicon and carbon can be precisely controlled, and the oxidation of silicon particles by excessive high temperature firing. can also be avoided, resulting in better charge/discharge characteristics.

The calcination method is not particularly limited, but a reaction apparatus having a heating function may be used in an inert atmosphere, and continuous or batchwise processing is possible. A fluidized bed reactor, a rotary furnace, a vertical moving bed reactor, a tunnel furnace, a batch furnace, a rotary kiln, or the like can be appropriately selected as the firing apparatus according to the purpose.

<Step 3>
Step 3 is a step for obtaining the negative electrode active material of the present invention by pulverizing the baked product obtained in Step 2 and classifying if necessary. The pulverization may be carried out in one step until the target particle size is obtained, or may be carried out in several steps. For example, when the fired product is lumps or agglomerated particles of 10 mm or more and to produce an active material of 10 μm, it is coarsely pulverized with a jaw crusher, roll crusher, etc. to make particles of about 1 mm, and then 100 μm with a glow mill, ball mill, etc. and pulverized to 10 μm with a bead mill, jet mill, or the like. Particles produced by pulverization may contain coarse particles, and in order to remove them, or to adjust the particle size distribution by removing fine powder, classification is performed. The classifier to be used may be a wind classifier, a wet classifier, or the like depending on the purpose, but when removing coarse particles, the classification method through a sieve is preferable because the purpose can be reliably achieved. Incidentally, when the precursor mixture is controlled to have a shape close to the target particle size by spray drying or the like before the main firing and the main firing is performed in that shape, the pulverization step can of course be omitted.

<Production of negative electrode>
Since the negative electrode active material of the present invention exhibits excellent charge/discharge characteristics as described above, it exhibits good charge/discharge characteristics when used as a battery negative electrode.
Specifically, a slurry composed of the negative electrode active material of the present invention and an organic binder as essential components and, if necessary, other components such as a conductive aid is applied to a current collector copper foil as a thin film. It can be used as a negative electrode in the following manner. A negative electrode can also be produced by adding a known and commonly used carbon material such as graphite to the above slurry.

Carbon materials such as graphite include natural graphite, artificial graphite, hard carbon, and soft carbon. Since the negative electrode obtained in this way contains the negative electrode active material of the present invention as an active material, it has a high capacity and excellent cycle characteristics, and furthermore, it becomes a negative electrode for a secondary battery that also has excellent initial coulombic efficiency. . The negative electrode is prepared, for example, by kneading the negative electrode active material for a secondary battery and a binder, which is an organic binder, together with a solvent using a dispersing device such as a stirrer, a ball mill, a super sand mill, and a pressure kneader. It can be obtained by preparing a material slurry and coating it on a current collector to form a negative electrode layer. It can also be obtained by forming a paste-like negative electrode material slurry into a sheet-like or pellet-like shape and integrating this with a current collector.

Examples of the organic binder include, but are not limited to, styrene-butadiene rubber copolymer (SBR); ethylenically unsaturated carboxylic acid esters (e.g., methyl (meth) acrylate, ethyl (meth) acrylate, butyl ( (meth)acrylates, (meth)acrylonitrile, and hydroxyethyl (meth)acrylate, etc.), and ethylenically unsaturated carboxylic acids (e.g., acrylic acid, methacrylic acid, itaconic acid, fumaric acid, maleic acid, etc.). acrylic copolymers; polymeric compounds such as polyvinylidene fluoride, polyethylene oxide, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polyimide, polyamideimide, and carboxymethyl cellulose (CMC);

Depending on their physical properties, these organic binders can be dispersed or dissolved in water, or dissolved in an organic solvent such as N-methyl-2-pyrrolidone (NMP). The content ratio 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 3% by mass. More preferably, it is up to 15% by mass.

When the content of the organic binder is 1% by mass or more, the adhesion is better, and the destruction of the negative electrode structure due to expansion and contraction during charging and discharging is further suppressed. On the other hand, when the content is 30% by mass or less, an increase in electrode resistance can be further suppressed.

At this time, the negative electrode active material of the present invention has high chemical stability and can be used with an aqueous binder, and is easy to handle in terms of practical use.

In addition, the negative electrode material slurry may be mixed with a conductive aid, if necessary. Examples of conductive aids include carbon black, graphite, acetylene black, oxides and nitrides exhibiting conductivity, and the like. The amount of the conductive aid used may be about 1% by mass to 15% by mass with respect to the negative electrode active material of the present invention.

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

The method for applying the negative electrode material slurry to the current collector is not particularly limited, but examples include a metal mask printing method, an electrostatic coating method, a dip coating method, a spray coating method, a roll coating method, a doctor blade method, and a gravure coating. well-known methods such as a method, a screen printing method, and the like. After coating, it is preferable to carry out a rolling treatment using a flat plate press, calendar rolls, or the like, if necessary.

Also, the integration of the negative electrode material slurry molded into a sheet-like or pellet-like shape and the current collector can be performed by a known method such as roll, press, or a combination thereof.

The negative electrode layer formed on the current collector and the negative electrode layer integrated with the current collector are preferably heat-treated according to the organic binder used. For example, when a commonly used water-based styrene-butadiene rubber copolymer (SBR) or the like is used, it may be heat-treated at 100 to 130°C. When used, heat treatment at 150 to 450° C. is preferred.

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

Moreover, it is preferable to press (pressurize) the negative electrode after the heat treatment. The negative electrode using the negative electrode active material of the present invention preferably has an electrode density of 1.0 g/cm ³ to 1.8 g/cm ³ , more preferably 1.1 g/cm ³ to 1.7 g/cm ³ . is more preferable, and 1.2 g/cm ³ to 1.6 g/cm ³ is even more preferable. Regarding the electrode density, there is a tendency that the higher the density, the better the adhesion and the volume capacity density of the electrode. Select the optimum range because the characteristics will be degraded.

<Full battery configuration>
As described above, the negative electrode using the negative electrode active material of the present invention has excellent charge-discharge characteristics, and is not particularly limited as long as it is a secondary battery. In particular, when used as the negative electrode of a non-aqueous electrolyte secondary battery, it exhibits excellent performance.

The non-aqueous electrolyte secondary battery of the present invention, for example, when used in a wet electrolyte secondary battery, is configured by arranging a positive electrode and a negative electrode of the present invention facing each other with a separator interposed therebetween, and injecting an electrolytic solution. can do.

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

The positive electrode material used for the positive electrode layer is not particularly limited. Among non-aqueous electrolyte secondary batteries, when producing a lithium ion secondary battery, for example, a metal compound, a metal oxide, a metal sulfide, or a conductive polymer material capable of doping or intercalating lithium ions is not particularly limited. For example, lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganate (LiMnO ₂ ), composite oxides thereof (LiCoxNiyMnzO ₂ , x+y+z=1), lithium manganese spinel (LiMn ₂ O ₄ ) , _lithium _vanadium _compounds , _V2O5 , _V6O13 , _VO2 , _MnO2 , _TiO2 , _MoV2O8 _, _TiS2 , _V2S5 , _VS2 , _MoS2 , _MoS3 _, _Cr3O8 , Cr ₂ O ₅ , olivine-type LiMPO ₄ (M: Co, Ni, Mn, Fe), conductive polymers such as polyacetylene, polyaniline, polypyrrole, polythiophene, polyacene, etc., porous carbon, etc. are used singly or in combination. be able to.

As the separator, for example, a non-woven fabric, cloth, microporous film, or a combination of them can be used, the main component of which is polyolefin such as polyethylene or polypropylene. In addition, when the positive electrode and the negative electrode of the non-aqueous electrolyte secondary battery to be manufactured are structured such that they do not come into direct contact with each other, there is no need to use a separator.

Examples of electrolytes include lithium salts such as LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiBF ₄ and LiSO ₃ CF ₃ , ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, fluoroethylene carbonate, cyclopentanone, and 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 Non-aqueous solvents such as propyl carbonate, butyl ethyl carbonate, dipropyl carbonate, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, methyl acetate and ethyl acetate, or a mixture of two or more components. A dissolved, so-called organic electrolyte can be used.

The structure of the non-aqueous electrolyte secondary battery of the present invention is not particularly limited, but usually, a positive electrode, a negative electrode, and an optional separator are wound in a flat spiral shape to form a wound electrode plate group. Generally, these plates are laminated to form a laminated electrode plate group, and the electrode plate group is enclosed in an outer package. The half-cell used in the examples of the present invention has a negative electrode composed mainly of the silicon-containing active material of the present invention, and a simple evaluation using metallic lithium as the counter electrode. This is to clearly compare the cycle characteristics. As mentioned above, by adding a small amount to a mixture mainly composed of graphite-based active material (capacity of about 340 mAh/g), the negative electrode capacity is suppressed to about 400 to 700 mAh/g, which greatly exceeds the existing negative electrode capacity, and the cycle characteristics are improved. It is possible.

Non-aqueous electrolyte secondary batteries using the negative electrode active material of the present invention are not particularly limited, but are used as paper-type batteries, button-type batteries, coin-type batteries, laminate-type batteries, cylindrical batteries, prismatic batteries, and the like. . The negative electrode active material of the present invention described above can also be applied to general electrochemical devices having a charging/discharging mechanism of intercalating and deintercalating lithium ions, such as hybrid capacitors and solid lithium secondary batteries.

The present invention will be described in detail below with reference to examples. Parts and percentages are based on mass unless otherwise specified.

"Preparation of polysiloxane compound"
(Synthesis Example 1: Synthesis of condensate (m-1) of methyltrimethoxysilane)
A reactor equipped with a stirrer, a thermometer, a dropping funnel, a condenser and a nitrogen gas inlet was charged with 1,421 parts by mass of methyltrimethoxysilane (hereinafter abbreviated as "MTMS") and heated to 60°C. I warmed up. Then, a mixture of 0.17 parts by mass of iso-propyl acid phosphate ("Phoslex A-3" manufactured by SC Organic Chemical Co., Ltd.) and 207 parts by mass of deionized water was added dropwise to the reaction vessel over 5 minutes. C. for 4 hours to carry out a hydrolytic condensation reaction.

The condensate obtained by the above hydrolytic condensation reaction is subjected to a temperature of 40 to 60 ° C. and a reduced pressure of 40 to 1.3 kPa (the reduced pressure condition at the start of distillation of methanol is 40 kPa, and finally becomes 1.3 kPa. The same applies hereinafter) to remove the methanol and water produced in the above reaction process, thereby containing the condensate (m-1) of MTMS with a number average molecular weight of 1,000 1,000 parts by mass of a liquid (70% by mass of active ingredient) was obtained. The effective ingredient is the value obtained by dividing the theoretical yield (parts by mass) when all the methoxy groups of the silane monomer such as MTMS are condensed by the actual yield (parts by mass) after the condensation reaction [methoxy of the silane monomer] Theoretical yield (parts by mass) when all groups are subjected to condensation reaction/Actual yield after condensation reaction (parts by mass)].

[Evaluation method]
The evaluation method of the negative electrode active material in this example is as follows.
Average particle size (D50): Measured using a laser diffraction particle size distribution analyzer (SALD-3000J, manufactured by Shimadzu Corporation).
Specific surface area (BET): Measured by nitrogen adsorption measurement using a specific surface area measuring device (BELSORP-mini manufactured by BEL JAPAN).
²⁹ Si-NMR: JNM-ECA600 manufactured by JEOL RESONANCE was used.
Raman scattering analysis measurement: NRS-5500 manufactured by JASCO Corporation was used.

[Example 1]
A negative electrode active material of the present invention was produced as follows.
Zirconia beads (particle size range: 0.1 mm to 0.2 mm) and 100 ml of methyl ethyl ketone solvent (MEK) were added to a container (150 ml) of a small bead mill device, and silicon powder (manufactured by Wako Pharmaceutical Co., Ltd., average particle size of 3 to 5 μm) and a cationic dispersant liquid (BYK145, BYK-Chemie Japan Co., Ltd.) were added and wet pulverized by a bead mill to obtain a dark brown liquid silicon slurry. The average particle diameter (D50) of the silicon pulverized particles was 60 nm by light scattering measurement and TEM observation.
The polysiloxane resin (PSi resin: average molecular weight 3500) and the phenol resin (Ph-R resin; average molecular weight 3000) prepared in the above synthesis example were mixed at a resin solid weight composition ratio of 20:80, and the Si particle amount was adjusted. The above-mentioned brown liquid silicon slurry (average particle size: 60 nm) was added so as to be 50% by weight, and the mixture was sufficiently mixed in a stirrer. After that, the precursor was sintered at a high temperature of 1100° C./4 hours in a nitrogen atmosphere, and then pulverized with a planetary ball mill to obtain a black solid, which is a negative electrode active material powder.
The obtained negative electrode active material powder had an average particle size (D50) of about 6.3 μm and a specific surface area (BET) of 16.5 m ² /g. Further, according to the ²⁹ Si-NMR spectrum, peak A within the range of -70 ppm to -90 ppm and peak B within the range of -90 ppm to -130 ppm were detected, and the area ratio A/B was 1.83. Further, the results of Raman scattering analysis showed a peak near 1590 cm ⁻¹ belonging to the G band of carbon and a peak near 1330 cm ⁻¹ belonging to the D band, and the intensity ratio G/D was 0.79.

Next, using the negative electrode active material obtained above, a half cell and a full cell were produced by the following method, and a secondary battery charge/discharge test was performed.
A mixed slurry of an active material powder (80 parts), a conductive aid (acetylene black, 10 parts) and a binder (CMC+SBR, 10 parts) was prepared and formed into a film on a copper foil. After that, it was dried under reduced pressure at 110° C., and a Li metal foil was used as a counter electrode to prepare a half cell. This half cell was evaluated for charge/discharge characteristics (cutoff voltage range: 0.005 to 1.5 V) using a secondary battery charge/discharge test device (manufactured by Hokuto Co., Ltd.). The measurement results of charge and discharge were an initial discharge capacity of 1450 mAh/g and an initial coulombic efficiency of 85.1%.
A positive electrode film was prepared using a single-layer sheet using LiCoO ₂ as a positive electrode active material and aluminum foil as a current collector. Further, a negative electrode film was produced by mixing graphite powder, active material powder, and a binder at a discharge capacity design value of 450 mAh/g. A non-aqueous electrolyte solution prepared by dissolving lithium hexafluorophosphate in a 1/1 (volume ratio) mixed solution of ethylene carbonate and diethyl carbonate at a concentration of 1 mol/L was used as the non-aqueous electrolyte, and polyethylene having a thickness of 30 μm was used as the separator. A full-cell coin-type lithium-ion secondary battery was fabricated using the microporous film. This lithium ion secondary battery was charged at a constant current of 1.2 mA (0.25c based on the positive electrode) at room temperature until the voltage of the test cell reached 4.2 V. After reaching 4.2 V, Charging was performed by decreasing the current so as to keep the cell voltage at 4.2 V, and the discharge capacity was determined. The capacity retention rate after 200 cycles at room temperature was 84.5%.
Table 1 summarizes the above evaluation results.

[Examples 2 to 18]
As shown in Table 1, each negative electrode active material was prepared in the same manner as in Example 1 except that the resin composition ratio (PSi/Ph-R), Si content %, and firing temperature in the negative electrode active material precursor were changed. were produced, and the properties and charge/discharge characteristics of each material were evaluated. These results are shown in Table 1. In Examples 15 and 16, the powder was pulverized to 1.2 μm and 13.5 μm, respectively after firing (in Examples 15 and 16, the pulverization conditions in the planetary ball mill were changed). Table 1 summarizes the evaluation results of Examples 2 to 18 above.

[Comparative Example 1]
After drying the precursor under the same conditions as in Example 1 (resin composition 4/6, Si particle size and addition amount), the precursor was fired at 1200° C. in a nitrogen atmosphere for 4 hours to obtain a negative electrode active material. The negative electrode active material powder had an average particle size (D50) of about 5.8 μm and a specific surface area (BET) of 29 m ² /g. In the ²⁹ Si-NMR spectrum, peak A within the range of -70 ppm to -90 ppm and peak B within the range of -90 ppm to -130 ppm were detected, and the area ratio A/B was 0.61. Further, the results of Raman scattering analysis showed a peak near 1590 cm ⁻¹ belonging to the G band of carbon and a peak near 1330 cm −1 belonging to the D band, and the intensity ratio G/D was 2.1. The charge/discharge measurement results of the full cell showed a capacity retention rate of 91% after 200 cycles at room temperature, while the charge/discharge measurement results of the half cell showed an initial discharge capacity of 344 mAh/g and an initial coulombic efficiency of 54.6%. decreased significantly.

[Comparative Example 2]
By the same operation as in Example 1, the resin component ratio was changed to 1/9 to prepare a precursor, which was then fired at 1100° C. for 4 hours in a nitrogen atmosphere and pulverized to obtain a negative electrode active material. The negative electrode active material powder had an average particle size (D50) of about 5.7 μm and a specific surface area (BET) of 25.3 m ² /g. The area ratio A/B between the 29Si-NMR peak A and the peak was 3.9. Also, the intensity ratio G/D between the carbon G band and the carbon D band was 0.9. Half-cell charging/discharging measurement results showed an initial discharge capacity of 1320 mAh/g; an initial coulombic efficiency of 85.5%, but according to the full-cell charging/discharging measurement results, the capacity retention rate after 200 cycles at room temperature was 76%. decreased to

[Comparative Example 3]
By the same operation as in Example 1, after preparing a precursor with the resin composition ratio set to 1/9 and the amount of Si added to 70%, the precursor was fired at 1100 ° C. for 4 hours in a nitrogen atmosphere and pulverized. got the substance. The negative electrode active material powder had an average particle size (D50) of about 5.6 μm and a specific surface area (BET) of 19.7 m ² /g. The area ratio A/B between the 29Si-NMR peak A and the peak was 5.1. Also, the intensity ratio G/D between the carbon G band and the carbon D band was 0.96. Half-cell charging/discharging measurement results showed an initial discharge capacity of 1920 mAh/g; an initial coulombic efficiency of 87.9%, but according to the full-cell charging/discharging measurement results, the capacity retention rate after 200 cycles at room temperature was 43%. decreased to

From Table 1 above, it can be seen that when A/B satisfies Formula 1 (0.7≤A/B≤3.0), both the initial discharge capacity and the capacity retention rate are good.

Claims

A negative electrode active material containing composite particles in which silicon nanoparticles are dispersed in a matrix containing silicon oxycarbide and a carbonaceous phase, wherein the composite particles have a chemical shift value obtained from a 29 Si-NMR spectrum, represented by the following formula 1 A negative electrode active material that satisfies
Formula 1: 0.7≤A/B≤3.0
A: Area intensity of the peak within the range of −70 ppm to −90 ppm attributed to Si (0 valence) B: Area intensity of the peak within the range of −90 ppm to −130 ppm derived from the bond of SiO 4
The Raman spectrum of the composite particles containing a carbonaceous phase has scattering peaks near 1590 cm −1 and 1330 cm −1 attributed to the G band and D band of the carbon structure, and their scattering peak intensity ratio I (G band/ 2. The negative electrode active material according to claim 1, wherein the D band) is in the range of 0.7 to 2.0.
The negative electrode active material according to claim 1 or 2, wherein the composite particles have an average particle size (D50) of 1 µm to 20 µm.
4. The negative electrode active material according to claim 1, wherein the composite particles have a specific surface area (BET) in the range of 1 m 2 /g to 20 m 2 /g.
A nonaqueous electrolyte secondary battery containing the negative electrode active material according to any one of claims 1 to 4.
The method for producing a negative electrode active material according to any one of claims 1 to 4, wherein the steps 1 to 3 below are included as the steps for producing the composite particles.
Step 1: A silicon (zero-valent) slurry pulverized by a wet method is mixed with an aggregate containing a polysiloxane compound and a carbon source resin, stirred and dried to obtain a precursor Step 2: Obtained in Step 1 above Step 3 of obtaining a fired product by firing the precursor in an inert atmosphere within a temperature range of a maximum temperature of 1000° C. to 1180° C.: Pulverizing the fired product obtained in Step 2 to obtain a negative electrode active material. obtain
The production of the negative electrode active material according to claim 6, wherein the polysiloxane compound has a carboxy group, an epoxy group, an amino group, or a polyether group at the side chain or end of the siloxane bond (Si-O-Si) main skeleton. Method.
The method for producing a negative electrode active material according to claim 6 or 7, wherein the carbon source resin is a resin containing an aromatic hydrocarbon moiety.
The method for producing a negative electrode active material according to claim 8, wherein the resin containing an aromatic hydrocarbon moiety is a phenolic resin, an epoxy resin, or a thermosetting resin.