WO2023157642A1

WO2023157642A1 - Active material for secondary batteries, and secondary battery

Info

Publication number: WO2023157642A1
Application number: PCT/JP2023/003304
Authority: WO
Inventors: 培新諸; 賢一川瀬
Original assignee: Dic株式会社
Priority date: 2022-02-21
Filing date: 2023-02-02
Publication date: 2023-08-24
Also published as: JPWO2023157642A1; TW202345438A; JP7491478B2

Abstract

The present invention relates to an active material for secondary batteries, the active material being used for lithium ion secondary batteries, and a secondary battery which contains this active material for secondary batteries as a negative electrode active material; and the present invention provides a negative electrode active material for secondary batteries, the negative electrode active material enabling the achievement of a secondary battery which has low expansibility, high cycle performance and excellent initial coulombic efficiency.　The present invention provides: an active material for secondary batteries, the active material having silicon oxide particles in a silicon oxycarbide phase; and a secondary battery which contains this active material for secondary batteries in a negative electrode. It is preferable that the content of the silicon oxide particles is 1% by mass to 60% by mass. It is preferable that there is a peak ascribed to Si(111) around 2θ = 28.4° as determined by X-ray diffractometry. It is preferable that the average particle diameter of the silicon oxide particles is 5 μm or less. It is preferable that the average particle diameter of the composite particles is 2 μm to 15 μm. It is preferable that the specific surface area is 0.3 m2/g to 10 m2/g. It is preferable that the silicon oxycarbide phase additionally contains nitrogen atoms.

Description

Active material for secondary battery and secondary battery

The present invention relates to a secondary battery active material and a secondary battery. More specifically, the present invention relates to a secondary battery active material and a secondary battery containing the secondary battery active material in a negative electrode.

Non-aqueous electrolyte secondary batteries are used in mobile devices, hybrid vehicles, electric vehicles, household storage batteries, etc., and are required to have well-balanced characteristics such as electrical capacity, safety, and operational stability. ing.
Furthermore, in recent years, with the downsizing of various electronic devices and communication devices and the rapid spread of hybrid vehicles, etc., batteries with higher capacity and various battery characteristics such as cycle characteristics and discharge rate characteristics are required as power sources for driving these devices. There is a strong demand for the development of lithium-ion secondary batteries with further improved performance.

As negative electrode active materials for lithium-ion secondary batteries, silicon and amorphous silicon oxide are of great interest due to their large capacity. inferior in nature. In addition, since lithium secondary batteries using silicon oxide have low initial efficiency, various improvements have been attempted to use silicon oxide as a negative electrode active material.
For example, Patent Document 1 proposes a silicon composite in which silicon microcrystals are dispersed in silicon oxide as a negative electrode active material for secondary batteries.

However, silicon oxide contains many oxygen atoms that generate irreversible lithium silicate during charging, and has the problem of low initial efficiency. Therefore, when a battery was actually produced, an excessive battery capacity of the positive electrode was required, and an increase in battery capacity corresponding to the increase in capacity of the active material was not observed.

In order to solve the above problems, Patent Document 2 describes a silicon crystal for non-aqueous electrolyte secondary battery negative electrode material having a structure in which silicon crystallites are dispersed through siloxane bonds and have fine spaces between silicon crystallites. Oxides have been proposed.
However, when silicon oxide is used as the negative electrode active material for lithium-ion secondary batteries, the rapid decrease in charge-discharge capacity after many charge-discharge cycles is due to the large volume change caused by the absorption and release of large amounts of lithium. It is believed that this is due to the occurrence of particle destruction.

In order to suppress the destruction of particles accompanying this volume change, Patent Document 3 attempts to suppress the large volume change by using silicon flakes having a hyperporous structure as an active material.
However, it is considered that the provision of such pores increases the specific surface area of the active material and deteriorates the cycle characteristics.

JP 2004-323284 A JP 2015-18626 A Japanese Patent Publication No. 2019-519067

Therefore, the cyclability and initial efficiency of lithium secondary batteries using silicon oxide, which has a large electrical capacity, have not yet been sufficiently improved.

The present inventors have investigated a secondary battery active material using silicon oxide, which suppresses the destruction of particles due to volume change of silicon oxide, improves the cycle performance of lithium secondary batteries, and has a high electric capacity. As a result, the present inventors have found a composite active material for secondary batteries that improves the cyclability, initial coulombic efficiency and capacity retention rate of lithium secondary batteries.
That is, the present invention relates to a secondary battery active material used in a lithium-ion secondary battery and a secondary battery containing the above-mentioned secondary battery active material as a negative electrode active material. An object of the present invention is to provide an active material for a secondary battery that provides an excellent secondary battery.

The present invention has the following aspects.
[1] An active material for a secondary battery, which is a composite particle having a silicon oxycarbide phase and at least two silicon oxide particles in the silicon oxycarbide phase.
[2] The active material for a secondary battery according to [1], wherein the content of the silicon oxide particles is 1% by mass or more and 60% by mass or less.
[3] The active material for a secondary battery according to the above [1] to [2], which has a peak attributed to Si(111) near 28.4° in X-ray diffraction.
[4] The active material for a secondary battery according to [1] to [3], wherein the silicon oxide particles have an average particle size of 5 μm or less.
[5] The active material for a secondary battery according to [1] to [4], wherein the composite particles have an average particle diameter of 2 μm or more and 15 μm or less.
[6] The active material for a secondary battery according to any one of the above [1] to [5], which has a specific surface area of 0.3 m ² /g or more and 10 m ² /g or less.
[7] The active material for a secondary battery according to [1] to [6], wherein the silicon oxycarbide phase further contains nitrogen atoms.
[8] In the Raman spectrum, having a scattering peak near 1590 cm ⁻¹ attributed to the G band of the carbon structure and 1330 cm ⁻¹ attributed to the D band, the intensity ratio of the scattering peaks, I(G band)/ The active material for a secondary battery according to the above [1] to [7], wherein I (D band) is 0.7 or more and 2 or less.
[9] The active material for a secondary battery according to any one of [1] to [8], wherein the composite particles have a carbon coating on the surface thereof, and the amount of the carbon coating is 1% by mass or more and 10% by mass or less.
[10] The active material for a secondary battery according to [1] to [9] above, which contains at least one metal silicate compound selected from the group consisting of Li, K, Na, Ca, Mg and Al.

Moreover, this invention has the following aspects.
[11] A secondary battery comprising the secondary battery active material according to any one of [1] to [10] in a negative electrode.

According to the present invention, it relates to a secondary battery active material used in a lithium ion secondary battery and a secondary battery containing the secondary battery active material as a negative electrode active material. A secondary battery active material that provides an excellent secondary battery is provided.

The secondary battery active material of the present invention (hereinafter also referred to as "the present active material") comprises a silicon oxycarbide phase and at least two or more silicon oxide particles in the silicon oxycarbide phase (hereinafter referred to as "the present silicon oxide Also referred to as "particles").
As described above, silicon oxide has a high capacity, but when it absorbs and releases a large amount of lithium, it undergoes a large change in volume, and as a result, it is considered to be inferior in cycleability. On the other hand, although the silicon oxycarbide phase has a relatively low capacity, it has a small volume change with respect to lithium absorption and desorption, and is excellent in cycle characteristics. By combining the two, it is considered that the active material for a secondary battery that maintains a high capacity and provides a secondary battery that is excellent in volume expansion and cycle characteristics was obtained.

Silicon oxide is generally a general term for amorphous silicon oxides obtained by heating a mixture of silicon dioxide and metal silicon to generate silicon monoxide gas, which is then cooled and precipitated, and is represented by the following general formula ( 1).
SiOn (1)
However, in the formula (1), n is 0.4 or more and 1.8 or less, preferably 0.5 or more and 1.6 or less.

Since this active material is a composite particle in which silicon oxide particles are present in the matrix of the silicon oxycarbide phase, it is conceivable that the particle size of the silicon oxide has a large effect on the performance of this active material. When the average particle diameter of the silicon oxide particles exceeds 5 μm, the silicon oxide particles become large lumps, and when the present active material is used as a negative electrode active material, the silicon oxide particles cause large expansion and contraction of the negative electrode active material during charging and discharging. As a result, the stress concentrates on a part of the matrix, so that the structure of the active material tends to collapse, and the capacity retention rate of the negative electrode active material tends to decrease. On the other hand, since silicon oxide particles with a small size of less than 300 nm are too fine, the silicon oxide particles tend to aggregate with each other. Therefore, the dispersibility of the silicon oxide particles in the negative electrode active material may deteriorate. In addition, if the silicon oxide particles are too fine, the specific surface area tends to increase, and by-products tend to increase on the surfaces of the silicon oxide particles when the negative electrode active material is baked at high temperature. These may lead to deterioration in charge/discharge performance.

Therefore, the average particle size of the present silicon oxide particles is preferably 3 μm or less, more preferably 2 μm or less, from the above viewpoint. The average particle size of the present silicon oxide particles is preferably 300 nm or more, more preferably 200 nm or more, from the viewpoint of particle dispersibility and specific surface area.
Here, the average particle size is a D50 value that can be measured using a laser diffraction particle size analyzer or the like. D50 can be measured by a dynamic light scattering method using a laser particle size analyzer or the like. The average particle diameter of the present silicon oxide particles is the particle diameter at which the volume cumulative distribution curve is drawn from the small diameter side to 50% in the particle diameter distribution.

The present silicon oxide particles can be granulated, for example, by pulverizing silicon oxide so that the average particle size falls within the above range.
Examples of pulverizers used for pulverization include pulverizers such as ball mills, bead mills, and jet mills. In addition, the pulverization may be wet pulverization using an organic solvent, and as the organic solvent, for example, alcohols, ketones, etc. can be preferably used. Group hydrocarbon solvents can also be used.
The average particle size of the silicon oxide particles can be controlled within the above range by classifying the obtained silicon oxide particles by controlling the bead mill conditions such as the bead particle size, blending ratio, number of revolutions, and pulverization time. .

The shape of the present silicon oxide particles may be granular, needle-like, or flake-like.
Regarding the morphology of the present silicon oxide particles, the average particle size can be measured by a dynamic light scattering method, but it is possible to use an analysis means such as a transmission electron microscope (TEM) or a field emission scanning electron microscope (FE-SEM). can more easily and precisely identify samples of said aspect ratio. In the case of the negative electrode active material containing the secondary battery material of the present invention, the sample can be cut with a focused ion beam (FIB) and the cross section can be observed with FE-SEM, or the sample can be sliced and observed with TEM. can identify the state of the present silicon oxide particles.
The aspect ratio of the present silicon oxide particles is the result of calculation based on 50 particles in the main portion of the sample within the field of view shown in the TEM image.

The silicon oxycarbide phase is composed of compounds containing silicon, oxygen, and carbon, and preferably has a three-dimensional network structure of silicon-oxygen-carbon skeleton and a structure containing free carbon. Here, free carbon is carbon that is not contained in the three-dimensional skeleton of silicon-oxygen-carbon. Free carbon includes carbon present as a carbon phase, carbon bonded between carbon phase carbons, and carbon bonded between a silicon-oxygen-carbon skeleton and a carbon phase.

Silicon oxycarbide is preferably represented by the following formula (2).
SiOx Cy (2)
In formula (2), x represents the molar ratio of oxygen to silicon, and y represents the molar ratio of carbon to silicon.
When the present active material is used in a secondary battery, 1 ≤ x < 2 is preferable, 1 ≤ x ≤ 1.9 is more preferable, and 1 ≤ x ≤ 1.8 is more preferred.
When the present active material is used in a secondary battery, 1≦y≦20 is preferable, and 1.2≦y≦15 is more preferable, from the viewpoint of the balance between charge/discharge performance and initial coulombic efficiency.

The above x and y can be obtained by measuring the content mass of each element and then converting it into a molar ratio (atomic number ratio). At this time, the content of oxygen and carbon can be quantified by using an inorganic elemental analyzer, and the content of silicon can be quantified by using an ICP optical emission spectrometer (ICP-OES).
Although it is preferable to measure x and y by the method described above, the present active material is locally analyzed, and a large number of measurement points for the content ratio data obtained thereby is obtained. It is also possible to analogize the content ratio of the entire substance. Local analysis includes, for example, Energy Dispersive X-ray Spectroscopy (SEM-EDX) and Electron Probe Microanalyzer (EPMA).

When the compound that constitutes the silicon oxycarbide phase is a compound containing silicon, oxygen, and carbon, and has a three-dimensional network structure of a silicon-oxygen-carbon skeleton and a structure containing free carbon, the silicon-oxygen- The carbon skeleton has high chemical stability, has a composite structure with free carbon, and has a small volume change with respect to lithium absorption and release. Since the silicon oxide particles are tightly wrapped in the composite structure of the silicon-oxygen-carbon skeleton and the free carbon, the volume change of the silicon oxide particles due to the intercalation and deintercalation of lithium is suppressed. As a result, when this active material is used as a negative electrode, the silicon oxide particles in the negative electrode play the role of being the main component for the expression of charge-discharge performance, while the silicon oxycarbide phase reacts to the volume change of the silicon oxide particles during charge-discharge. The accompanying particle destruction is suppressed, and the cyclability of the lithium secondary battery is improved.

In addition, when the compound that constitutes the silicon oxycarbide phase has a three-dimensional network structure of silicon-oxygen-carbon skeleton and a structure containing free carbon, the silicon-oxygen-carbon skeleton is converted into silicon-oxygen by the approach of lithium ions. - Electron distribution inside the carbon skeleton is changed, and electrostatic bonds and coordinate bonds are formed between the silicon-oxygen-carbon skeleton and lithium ions. Lithium ions are stored in the silicon-oxygen-carbon skeleton by this electrostatic bond and coordinate bond. On the other hand, since the coordination bond energy is relatively low, the desorption reaction of lithium ions easily occurs. In other words, it is considered that the silicon-oxygen-carbon skeleton can reversibly cause intercalation and deintercalation reactions of lithium ions during charging and discharging.

The silicon oxycarbide may contain nitrogen in addition to silicon, oxygen and carbon. Nitrogen contains nitrogen as a functional group in the molecule of raw materials used in the manufacturing method of the active material described later, such as phenolic resins, dispersants, polysiloxane compounds, other nitrogen compounds, and nitrogen gas used in the firing process. By forming an atomic group, it can be introduced into the silicon oxycarbide phase. Since the silicon oxycarbide phase contains nitrogen, the charge/discharge performance and the capacity retention rate tend to be excellent when this active material is used as a negative electrode active material.
When the compound constituting the silicon oxycarbide phase is a compound containing silicon, oxygen, carbon and nitrogen, the silicon oxycarbide phase preferably contains a compound represented by the following formula (3).
SiOxCyNz (3)
In formula (3), x and y have the same meanings as above, and z represents the molar ratio of nitrogen to silicon.
When the silicon oxycarbide phase contains the compound represented by the formula (3), 1 ≤ x ≤ 2, 1 ≤ y≦20 and 0<z≦0.5 are preferable, and 1≦x≦1.9, 1.2≦y≦15 and 0<z≦0.4 are more preferable.

As with x and y, z can be obtained by measuring the mass of the element contained and then converting it into a molar ratio (atomic number ratio).
As with x and y, it is preferable to measure z by the method described above. It is also possible to analogize the content ratio of the entire active material. Local analysis includes, for example, Energy Dispersive X-ray Spectroscopy (SEM-EDX) and Electron Probe Microanalyzer (EPMA).

The present active material is composite particles having the present silicon oxide particles in the silicon oxycarbide phase, and composite particles in which the present silicon oxide is dispersed in the silicon oxycarbide phase are preferable. The number of the present silicon oxide particles dispersed in the silicon oxycarbide phase is 2 or more, and the upper limit is not particularly limited.

Silicon oxide may produce a silicon simple substance through a disproportionation reaction, but the present active material may have a structure containing a silicon simple substance produced by disproportionation from the viewpoint of increasing capacity and high initial efficiency. . When the present active material contains a simple substance of silicon, when the present active material is subjected to X-ray diffraction analysis, a peak attributed to the Si (111) plane near 28.4° of 2θ is detected in the X-ray diffraction pattern.
Silicon may be added to the present active material separately, but the silicon contained in the present active material is preferable because the silicon crystallites produced by the disproportionation reaction are relatively small.

If the average particle size of the active material is too small, the specific surface area of the active material increases significantly, and when the active material is used as a secondary battery, a solid phase interfacial electrolyte decomposition product (hereinafter also referred to as "SEI") is generated during charging and discharging. An increase in the production amount may reduce the reversible charge/discharge capacity per unit volume. If the average particle diameter is too large, there is a risk of separation from the current collector during electrode film production.
Therefore, the average particle size of the present active material is preferably 2 μm or more and 15 μm or less. The average particle size of the active material is more preferably 2.5 μm or more, particularly preferably 3.0 μm or more. Further, the average particle size of the present active material is more preferably 12 μm or less, particularly preferably 10 μm or less. The average particle size is the value of D50.

The specific surface area of the present active material is preferably 0.3 m ² /g or more and 10 m ² /g or less. The specific surface area of the active material is more preferably 0.5 m ² /g or more, particularly preferably 1 m ² /g or more. Further, the specific surface area of the present active material is more preferably 9 m ² /g or less, particularly preferably 8 m ² /g or less. When the specific surface area 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 is a value determined by the BET method, and can be determined by nitrogen gas adsorption measurement, for example, using a specific surface area measuring device.

The present active material preferably has a silicon-oxygen-carbon skeleton structure and free carbon composed only of carbon elements in the silicon oxycarbide phase. When the present active material has free carbon, in the Raman spectrum of the present active material, 1590 cm ⁻¹ attributed to the G band of the graphite long-period carbon lattice structure and the D band of the graphite short-period carbon lattice structure with disorder and defects A scattering peak is observed near 1330 cm ⁻¹ attributed to . The intensity ratio, I (G band)/I (D band), of the D band scattering peak intensity, I (G band), to the D band scattering intensity, I (D band), is preferably 0.7 or more and 2 or less. . The scattering peak intensity ratio, I (G band)/I (D band), is more preferably 0.7 or more and 1.8 or less. The fact that the scattering peak intensity ratio, I (G band)/I (D band), is within the above range means that the free carbon in the matrix has the following properties.

Some of the free carbon atoms are bonded to some silicon atoms in the silicon-oxygen-carbon framework. This free carbon is an important component that affects charge/discharge characteristics. Free carbon is mainly formed in the silicon-oxygen-carbon skeleton composed of SiO ₂ C ₂ , SiO ₃ C, and SiO ₄ , and some silicon atoms of the silicon-oxygen-carbon skeleton , electron transfer within the silicon-oxygen-carbon framework and between surface silicon atoms and free carbon is facilitated. For this reason, it is thought that the lithium ion intercalation and deintercalation reactions at the time of charging and discharging when the present active material is used in a secondary battery proceed rapidly, and the charging and discharging characteristics are improved. In addition, although the negative electrode active material may slightly expand and contract due to the insertion and extraction reactions of lithium ions, the presence of free carbon in the vicinity of the expansion and contraction of the active material as a whole mitigates the expansion and contraction. It is considered that there is an effect of greatly improving the capacity retention rate.

Free carbon is formed during the thermal decomposition of the silicon-containing compound and carbon source resin in an inert gas atmosphere during the production of the silicon oxycarbide phase. Specifically, the carbonizable sites in the molecular structures of the silicon-containing compound and the carbon source resin become carbon components by high-temperature pyrolysis in an inert atmosphere, and some of these carbons form a silicon-oxygen-carbon skeleton. combine with part of The carbonizable component is preferably a hydrocarbon, more preferably alkyls, alkylenes, alkenes, alkynes, aromatics, and more preferably aromatics.

In addition, the presence of free carbon is expected to reduce the resistance of this active material, and when this active material is used as the negative electrode of a secondary battery, the reaction inside this active material occurs uniformly and smoothly, resulting in charging and discharging. It is considered that a secondary battery active material having an excellent balance between performance and capacity retention can be obtained. Although free carbon can be introduced only from a silicon-containing compound, the combined use of a carbon source resin is expected to increase the abundance of free carbon and increase its effect. The type of carbon source resin is not particularly limited, but a carbon compound containing a six-membered ring of carbon is preferred.

The existence state of the free carbon can be identified by thermogravimetric differential thermal analysis (TG-DTA) as well as Raman spectrum. Unlike the carbon atoms in the silicon-oxygen-carbon skeleton, free carbon 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 using TG-DTA.
In addition, from the thermal weight loss behavior, changes in thermal decomposition temperature behavior such as decomposition reaction start temperature, decomposition reaction end temperature, number of thermal decomposition reaction species, temperature of maximum weight loss for each thermal decomposition reaction species can be easily grasped. . The temperature values of these behaviors can be used to determine the state of the carbon. On the other hand, the carbon atoms in the silicon-oxygen-carbon skeleton, that is, the carbon atoms bonded to the silicon atoms constituting the SiO ₂ C ₂ , SiO ₃ C, and SiO ₄ have very strong chemical bonds. It has high thermal stability, and it is thought that it will not be thermally decomposed in the air within the temperature range measured by thermal analysis equipment. In addition, since the carbon in the silicon oxycarbide phase of the present active material has properties similar to those of amorphous carbon, it is thermally decomposed within the temperature range of about 550° C. to 900° C. in the air. As a result, rapid weight loss occurs. The maximum temperature of the TG-DTA measurement conditions is not particularly limited, but TG-DTA measurement is performed in the air under conditions from about 25° C. to about 1000° C. or higher in order to completely complete the thermal decomposition reaction of carbon. is preferred.

Further, the present active material preferably has a film on the surface of the composite particles. As the film, it is preferable to use a film of a substance that can be expected to have electronic conductivity, lithium ion conductivity, and an effect of suppressing the decomposition of the electrolytic solution.
Examples of the coating include coatings of electron conductive substances such as carbon, titanium, and nickel. Among these, from the viewpoint of improving the chemical stability and thermal stability of the negative electrode active material, a carbon coating is preferable, and a low-crystalline carbon coating is more preferable.

In the case of a carbon coating, from the viewpoint of improving the chemical stability and thermal stability of the present active material, the average thickness of the coating is 10 nm or more and 300 nm or less, or the content of the carbon coating is based on the mass of the present active material as 100% by mass. , from 1 to 10% by weight.
In the case of a carbon coating, the carbon coating is preferably formed on the surface of the present active material by a vapor phase deposition method.
The mass of the present active material is the total amount of the present silicon oxide particles and the silicon oxycarbide phase that constitute the present active material. When the silicon oxycarbide phase contains nitrogen, it is the total amount including nitrogen, and when the present active material contains a third component such as silicon oxide described later, it is the total amount including the third component.

The present active material may contain other necessary third components in addition to the above.
Examples of the third component include a silicate compound of at least one metal selected from the group consisting of Li, K, Na, Ca, Mg and Al (hereinafter also referred to as "the present silicate compound").
A silicate compound is generally a compound containing an anion having a structure in which one or several silicon atoms are centered and surrounded by electronegative ligands. It is a salt of at least one metal selected from the group consisting of Mg and Al and a compound containing the anion.
Examples of compounds containing the anion include orthosilicate ion (SiO ₄ ^4- ), metasilicate ion (SiO ₃ ^2- ), pyrosilicate ion (Si ₂ O ₇ ^6- ), cyclic silicate ion (Si ₃ O ₉ ^6- or Si ₆ O ₁₈ ^12- ) are known. The present silicate compound is preferably a silicate compound which is a salt of metasilicate ion and at least one metal selected from the group consisting of Li, K, Na, Ca, Mg and Al. Li or Mg is preferred among the metals.

The present silicate compound contains at least one metal selected from the group consisting of Li, K, Na, Ca, Mg and Al, and may contain two or more of these metals. When having two or more kinds of metals, one silicate ion may have a plurality of kinds of metals, or may be a mixture of silicate compounds having different metals. The present silicate compound may contain other metals as long as it contains at least one metal selected from the group consisting of Li, K, Na, Ca, Mg and Al.
The present silicate compound _is preferably a lithium silicate compound or a magnesium silicate compound, more preferably lithium _metasilicate ( _Li2SiO3 _, _Li2Si2O5 _, _Li4SiO4 ) or magnesium _metasilicate (MgSiO3 _, _Mg2SiO4 ). Magnesium metasilicate (MgSiO _{3 ,} Mg ₂ SiO ₄ ) is particularly preferred.

The silicate compound may be present in either the silicon oxycarbide phase or the silicon oxide particles, or may be present in both. When the present silicate compound exists in both the silicon oxycarbide phase and the present silicon oxide, the concentration of the present silicate compound in the present silicon oxide particles is preferably higher than the concentration in the silicon oxycarbide.
The present silicate compound can be detected by powder X-ray diffraction measurement (XRD) when it is in a crystalline state, and can be confirmed by solid ²⁹ Si-NMR measurement when it is amorphous.

This active material can be obtained, for example, by the following method.
As described above, the present silicon oxide particles can be produced by heating a mixture of silicon dioxide and metal silicon to produce silicon monoxide gas, which is then cooled and precipitated. Alternatively, commercially available silicon oxide may be used.
When producing the present active material, silicon oxide may be pulverized, classified, or the like to obtain a desired average particle size, and the present silicon oxide may be obtained. The pulverization and classification methods are as described above.

The slurry of the silicon oxide particles obtained above is mixed with the mixture of the polysiloxane compound and the carbon source resin to form a suspension, and the solvent is removed to obtain the precursor. The resulting precursor is calcined to obtain a calcined product, and if necessary, pulverized to obtain the present active material having a desired average particle size or specific surface area.
The slurry of silicon oxide particles can be prepared by using an organic solvent and pulverizing the silicon oxide particles with a wet powder pulverizer. A dispersant may be added to the organic solvent in order to accelerate the pulverization of the silicon oxide particles. Examples of wet pulverizers include roller mills, high-speed rotary pulverizers, container-driven mills, and bead mills.

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

Types of the dispersant include aqueous and non-aqueous dispersants, and non-aqueous dispersants are preferred. Types of non-aqueous dispersants include polymer types such as polyether, alcohol, polyalkylene polyamine, and polycarboxylic acid partial alkyl esters; low molecular types such as polyhydric alcohol esters and alkyl polyamines; Inorganic types such as salts are exemplified. The concentration of silicon oxide solids in the present silicon oxide slurry is not particularly limited. A range of 5% by mass to 40% by mass is preferred, and a range of 10% by mass to 30% by mass is more preferred.

Examples of the polysiloxane compound include resins containing at least one of a polycarbosilane structure, a polysilazane structure, a polysilane structure and a polysiloxane structure. A resin containing only these structures may be used, or a composite resin having at least one of these structures as a segment and chemically bonded to another polymer segment may be used. Forms of composite include graft copolymerization, block copolymerization, random copolymerization, alternating copolymerization, and the like. Examples include composite resins having a graft structure in which polysiloxane segments are chemically bonded to the side chains of polymer segments, composite resins having a block structure in which polysiloxane segments are chemically bonded to the ends of polymer segments, and the like. .

A polysiloxane compound in which the polysiloxane segment has a structural unit represented by the following general formula (S-1) and/or the following general formula (S-2) is preferred. 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) main skeleton.

In general formulas (S-1) and (S-2) above, R ¹ represents an optionally substituted aromatic hydrocarbon group, 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. )

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 becomes solid, 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.

A silanol group as used 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.

In the formula, ^R4 is a monovalent organic group such as an alkyl group, an aryl group or an ^aralkyl group; group, iminooxy group or alkenyloxy group. 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, and naphthoyloxy groups. mentioned.

Examples of allyloxy groups include phenyloxy groups and naphthyloxy groups.

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 polysiloxane segments having structural units represented by general formula (S-1) and/or 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 polysiloxane compound is preferably produced, for example, by the methods shown in (1) to (3) below.

(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 having a polymerizable double bond and carrying out 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 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) A method of mixing the polymer segment, a silane compound having both a silanol group and/or a hydrolyzable silyl group and a polymerizable double bond, and polysiloxane, and performing a hydrolytic condensation reaction.
A polysiloxane compound is obtained by the method described above.
Examples of the polysiloxane compound include the Ceranate (registered trademark) series (organic/inorganic hybrid type coating resin; manufactured by DIC Corporation) and the Compoceran SQ series (silsesquioxane type hybrid; manufactured by Arakawa Chemical Industries, Ltd.). .

The carbon source resin is preferably a synthetic resin or a natural chemical raw material that has good miscibility with the polysiloxane compound, is carbonized by high-temperature baking in an inert atmosphere, and has an aromatic functional group.

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., but the use of phenolic resin is more preferable from the viewpoint of inexpensive availability and removal of impurities.

In particular, the carbon source resin is preferably a resin containing an aromatic hydrocarbon moiety, the resin containing an aromatic hydrocarbon moiety is preferably a phenol resin, an epoxy resin, or a thermosetting resin, and the phenol resin is preferably a resol type. .
Examples of phenolic resins include the Sumilite Resin series (resol-type phenolic resin, manufactured by Sumitomo Bakelite Co., Ltd.).

A slurry of the present silicon oxide particles is mixed with a mixture of a polysiloxane compound and a carbon source resin, and the solvent is removed to obtain a precursor.
The mixture containing the polysiloxane compound and the carbon source resin is preferably in a state in which the polysiloxane compound and the carbon source resin are uniformly mixed. Said mixing is carried out using a device having the function of dispersing and mixing. Apparatuses having dispersing and mixing functions include, for example, stirrers, ultrasonic mixers, premix dispersers, and the like. 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.

The precursor preferably contains 3% to 50% by mass of the present silicon oxide particles, 15% to 85% by mass of the solid content of the polysiloxane compound, and 3% to 70% by mass of the solid content of the carbon source resin. , the solid content of the silicon oxide particles is 8% to 40% by mass, the solid content of the polysiloxane compound is 20% to 70% by mass, and the solid content of the carbon source resin is 3% to 60% by mass. more preferred.

The precursor obtained above is fired in an inert gas atmosphere to completely decompose the thermally decomposable organic component to obtain a fired product. As for the firing temperature, for example, by firing at a temperature in which the maximum reaching temperature is in the range of 900° C. to 1200° C., the thermally decomposable organic component can be completely decomposed. Also, the polysiloxane compound and the carbon source resin are converted into a silicon oxycarbide phase having a silicon-oxygen-carbon skeleton and free carbon by the energy of the high temperature treatment.

Firing is carried out according to a firing program that is defined by the rate of temperature increase, the holding time at a certain temperature, etc. The maximum attainable temperature is the maximum temperature to be set, and strongly affects the structure and performance of the fired product. Depending on the maximum temperature reached, the fine structure of the present active material, which possesses the chemical bonding state of silicon and carbon in the silicon oxycarbide phase, can be precisely controlled, and better charge-discharge characteristics can be obtained.

The calcination method is not particularly limited, but a reaction apparatus having a heating function may be used in an inert atmosphere, and continuous and batch processes are 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.

The obtained fired product is pulverized and, if necessary, classified to obtain the present active material, which is a composite particle having a silicon oxycarbide phase and at least two or more of the present silicon oxide particles in the silicon oxycarbide phase. be done. 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 producing an active material of about 10 μm from a sintered mass or agglomerated particles of 10 mm or more, it is roughly pulverized with a jaw crusher, a roll crusher, etc. to particles of about 1 mm, and then pulverized to about 100 μm with a glow mill, ball mill, etc. , a bead mill, a jet mill, or the like to a size of about 10 μm. 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. The pulverization step can be omitted when the precursor mixture is controlled to have a shape near the target particle size by spray drying or the like before firing, and firing is performed in that shape.

When the present active material has at least one metal silicate compound selected from the group consisting of Li, K, Na, Ca, Mg and Al, a slurry of the present silicon oxide particles is mixed with a mixture of a polysiloxane compound and a carbon source resin. To the suspension obtained by mixing with Li, K, Na, Ca, Mg and Al, at least one metal salt selected from the group consisting of is added, and then the same operation as described above is performed to obtain the silicate. A present active material having a compound is obtained.
Salts of at least one metal selected from the group consisting of Li, K, Na, Ca, Mg and Al include halides such as fluorides, chlorides and bromides of these metals, hydroxides and carbonates. mentioned.

The metal salt may be a salt of two or more metals, one salt may contain a plurality of metals, or a mixture of salts containing different metals.
When the metal salt is added to the suspension, the amount of the metal salt to be added is preferably 0.01 to 0.4 in molar ratio with respect to the number of moles of the silicon oxide particles.
When the metal salt is soluble in an organic solvent, the metal salt may be dissolved in the organic solvent, added to the suspension, and mixed. When the metal salt is insoluble in the organic solvent, the metal salt particles may be dispersed in the organic solvent and then added to the suspension and mixed. The metal salt is preferably nanoparticles having an average particle size of 100 nm or less from the viewpoint of improving the dispersion effect. Alcohols, ketones and the like can be suitably used as the organic solvent, but aromatic hydrocarbon solvents such as toluene, xylene, naphthalene and methylnaphthalene can also be used.

By uniformly dispersing the metal salt in the suspension, the metal salt molecules can be brought into sufficient contact with the silicon oxide particles. When silicon oxide exists on the surface or in the periphery of the silicon oxide particles, the metal salt molecules and the silicon oxide particles are sufficiently brought into contact with each other under conditions for a solid-phase reaction between the metal salt molecules and the silicon oxide particles. Thus, the present silicate compound can be present in the present silicon oxide particles. In order to make the concentration of the silicate compound in the silicon oxide particles higher than that in silicon oxycarbide, it is important to improve the contact state between the metal salt and the silicon oxide particles.
In addition, by surface-modifying the metal salt molecules with an organic additive, they can adhere to the surface of the present silicon oxide particles. The molecular structure of the organic additive is not particularly limited, but a molecular structure that allows physical or chemical bonding with the dispersant present on the surface of the silicon oxide particles is preferred. The physical or chemical bond includes electrostatic action, hydrogen bond, intermolecular Van der Waals force, ionic bond, covalent bond and the like. During high-temperature firing, the silicate compound can be formed in the silicon oxide particles by solid-phase reaction of the metal salt molecules with the silicon oxide particles.

When the present active material has the carbon coating on the surface of the composite particles, following the method, in a chemical vapor deposition apparatus, in a pyrolytic carbon source gas and a carrier inert gas flow , with a carbon coating in the temperature range from 700°C to 1000°C.
Thermally decomposable carbon source gases include acetylene, ethylene, acetone, alcohol, propane, methane, ethane, and the like.
Examples of the inert gas include nitrogen, helium, argon, etc. Nitrogen is usually used.

The present active material is excellent in cyclability, initial coulombic efficiency and capacity retention rate, and a secondary battery using the present active material as a negative electrode exhibits good characteristics.
Specifically, a slurry containing the present active material, an organic binder, and, if necessary, other components such as a conductive aid is applied in the form of a thin film onto a current collector copper foil to form a negative electrode. can be A negative electrode can also be produced by adding a carbon material such as graphite to the slurry.
Carbon materials include natural graphite, artificial graphite, amorphous carbon such as hard carbon or soft carbon, and the like.

For example, the present active material and a binder that is an organic binder are kneaded together with a solvent using a dispersing device such as a stirrer, ball mill, super sand mill, or pressure kneader to prepare a negative electrode material slurry, which is used as a current collector. It can be obtained by applying it to the body 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 styrene-butadiene rubber copolymer (hereinafter also referred to as "SBR"); methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, (meth) acrylonitrile , and ethylenically unsaturated carboxylic acid esters such as hydroxyethyl (meth)acrylate, and ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid, and maleic acid (meth)acrylic copolymerization Unsaturated carboxylic acid copolymers such as coalescence; A high molecular compound is mentioned.

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. to 15% by mass is more preferable.

When the content ratio 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.
Within this range, the present active material has high chemical stability and is easy to handle in terms of practical use in that an aqueous binder can also be used.

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.

Regarding the material and shape of the current collector, 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 a strip shape. Porous materials such as porous metal (foamed metal) and carbon paper can also be used.

Examples of the method for applying the negative electrode material slurry to the current collector 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, a gravure coating method, and a screen printing method. etc. After coating, it is preferable to carry out a rolling treatment using a flat plate press, calendar rolls, or the like, if necessary.

In addition, the negative electrode material slurry can be made into a sheet or pellet form, and integrated with the current collector by, for example, rolling, pressing, or a combination thereof.

The negative electrode layer formed on the current collector or the negative electrode layer integrated with the current collector is preferably heat-treated according to the organic binder used. For example, when a water-based styrene-butadiene rubber copolymer (SBR) or the like is used, heat treatment at 100 to 130° C. is sufficient, and when an organic binder having a main skeleton of polyimide or polyamideimide is 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 that the negative electrode is subjected to a pressure treatment after the heat treatment. The negative electrode using the present active material preferably has an electrode density of 1 g/cm ³ to 1.8 g/cm ³ , more preferably 1.1 g/cm ³ to 1.7 g/cm ³ . More preferably from 0.2 g/cm ³ to 1.6 g/cm ³ . Regarding the electrode density, there is a tendency that the higher the electrode density, the higher the adhesion and the volume capacity density of the electrode. On the other hand, if the electrode density is too high, the voids in the electrode are reduced, which weakens the effect of suppressing the volume expansion of silicon or the like, and the capacity retention rate may decrease. Therefore, an optimum range of electrode densities is selected.

The secondary battery of the present invention contains the present active material in the negative electrode. As a secondary battery having a negative electrode containing the present active material, a non-aqueous electrolyte secondary battery and a solid electrolyte secondary battery are preferable, and excellent performance is exhibited particularly when used as a negative electrode of a non-aqueous electrolyte secondary battery. It is.

When the secondary battery of the present invention is used for a wet electrolyte secondary battery, for example, a positive electrode and a negative electrode containing the negative electrode active material of the present invention are placed facing each other with a separator interposed therebetween, and an electrolytic solution is injected. It can be configured by

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 should be used. For example, lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (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 (where M is Co, Ni, Mn or Fe), conductive polymers such as polyacetylene, polyaniline, polypyrrole, polythiophene and polyacene, porous carbon, etc. can be used.

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, 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 secondary battery of the present invention is not particularly limited, but usually, a positive electrode, a negative electrode, and an optional separator are wound into a flat spiral to form a wound electrode plate group. It is common to have a structure in which flat plates are laminated to form a laminated electrode plate group, and these electrode plate groups are enclosed in an outer package. In the half-cell used in the examples of the present invention, the active material is mainly used for the negative electrode, and a simple evaluation is performed using metallic lithium for the counter electrode. for comparison.

Secondary batteries using this active material 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.

As described above, when this active material is used as a negative electrode active material for a secondary battery, it provides a secondary battery that is excellent in cyclability, initial coulombic efficiency, and capacity retention rate.
The present active material can be used as a negative electrode by the method described above to form a secondary battery having the negative electrode.

Although the present active material and the secondary battery including the present active material in the negative electrode have been described above, the present invention is not limited to the configurations of the above embodiments.
In the configuration of the present embodiment and the secondary battery containing the present active material in the negative electrode, any other configuration may be added, or any configuration that exhibits the same function may be substituted. good.

EXAMPLES The present invention will be described in detail below with reference to Examples, but the present invention is not limited to these.
In the half-cell used in the examples of the present invention, the negative electrode is composed mainly of the silicon-containing active material of the present invention, and the counter electrode is metallic lithium. This is to clearly compare the cycle characteristics.

Synthesis Example 1: Preparation of Polysiloxane Compound (Synthesis of Condensate (a1) of Methyltrimethoxysilane)
1,421 parts by mass of methyltrimethoxysilane (hereinafter abbreviated as "MTMS") was charged into a reaction vessel equipped with a stirrer, thermometer, dropping funnel, cooling tube and nitrogen gas inlet, and heated to 60°C. heated 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 dropped into the reaction vessel over 5 minutes. , and stirred at a temperature of 80° C. for 4 hours to cause a hydrolytic condensation reaction of MTMS.
The condensate obtained by the above hydrolytic condensation reaction was distilled at a temperature of 40 to 60° C. and under reduced pressure of 40 to 1.3 kPa. Note that "under a reduced pressure of 40 to 1.3 kPa" means that the reduced pressure condition is 40 kPa at the start of distillation of methanol, and the pressure is finally reduced to 1.3 kPa. The same applies to the following description. By removing the methanol and water produced in the reaction process, 1,000 mass of a liquid containing a condensate of MTMS having a number average molecular weight of 1,000 to 5,000 (hereinafter also referred to as "a1") I got it. The active ingredient content of the obtained liquid was 70% by mass.
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. Theoretical yield when all methoxy groups are condensed (parts by mass)/Actual yield after condensation reaction (parts by mass)].

Production of curable resin composition (1) 150 parts by mass of butanol (hereinafter also referred to as "BuOH") and 105 are added to a reaction vessel equipped with a stirrer, thermometer, dropping funnel, cooling tube and nitrogen gas inlet. Parts by mass of phenyltrimethoxysilane (hereinafter also referred to as "PTMS") and 277 parts by mass of dimethyldimethoxysilane (hereinafter also referred to as "DMDMS") were charged, and the temperature was raised to 80°C.
Then, at the same temperature, 21 parts by mass of methyl methacrylate (hereinafter also referred to as "MMA"), 4 parts by mass of butyl methacrylate (hereinafter also referred to as "BMA"), 3 parts by mass of butyric acid (hereinafter referred to as " BA”), 2 parts by mass of methacryloyloxypropyltrimethoxysilane (hereinafter also referred to as “MPTS”), 3 parts by mass of BuOH and 0.6 parts by mass of butylperoxy-2-ethylhexanoate ( hereinafter also referred to as “TBPEH”) was added dropwise into the reaction vessel over 6 hours. After completion of the dropwise addition, reaction was continued at the same temperature for 20 hours to obtain an organic solvent solution of a vinyl polymer (a2-1) having a hydrolyzable silyl group and a number average molecular weight of 10,000.

Next, a mixture of 0.04 parts by mass of iso-propyl acid phosphate (“Phoslex A-3” manufactured by SC Organic Chemical Co., Ltd.) and 112 parts by mass of deionized water was added dropwise over 5 minutes, and further at the same temperature. A hydrolytic condensation reaction is carried out with stirring for 10 hours, so that the hydrolyzable silyl group of the vinyl polymer (a2-1) and the hydrolyzable silyl group and silanol group of the PTMS- and DMDMS-derived polysiloxane are formed. A liquid containing bound composite resin was obtained.
Next, 472 parts by mass of the condensate (a1) of MTMS obtained in Synthesis Example 1 and 80 parts by mass of deionized water are added to this liquid, and the mixture is stirred at the same temperature for 10 hours for a hydrolytic condensation reaction to synthesize. The methanol and water produced were removed by distillation under the same conditions as in Example 1. Then, 250 parts by mass of BuOH was added to obtain 1,000 parts by mass of curable resin composition (1) having a non-volatile content of 60.1% by mass.

Production of curable resin composition (2) 150 parts by mass of BuOH, 249 parts by mass of PTMS and 263 parts by mass of DMDMS were added to a reaction vessel equipped with a stirrer, thermometer, dropping funnel, condenser and nitrogen gas inlet. was charged and the temperature was raised to 80°C.
Then, at the same temperature, 18 parts by mass of MMA, 14 parts by mass of BMA, 7 parts by mass of BA, 1 part by mass of acrylic acid (hereinafter also referred to as "AA"), 2 parts by mass of MPTS, and 6 parts by mass of A mixture containing BuOH and 0.9 parts by weight of TBPEH was added dropwise into the reaction vessel over 5 hours. After completion of the dropwise addition, reaction was continued at the same temperature for 10 hours to obtain an organic solvent solution of a vinyl polymer (a2-2) having a hydrolyzable silyl group and a number average molecular weight of 20 and 100.

Next, a mixture of 0.05 parts by mass of iso-propyl acid phosphate (“Phoslex A-3” manufactured by SC Organic Chemical Co., Ltd.) and 147 parts by mass of deionized water was added dropwise over 5 minutes, and further at the same temperature. A hydrolytic condensation reaction was carried out with stirring for 10 hours, so that the hydrolyzable silyl groups of the vinyl polymer (a2-2) and the hydrolyzable silyl groups and silanol groups of the PTMS- and DMDMS-derived polysiloxanes were formed. A liquid containing bound composite resin was obtained.
Next, 76 parts by mass of 3-glycidoxypropyltrimethoxysilane, 231 parts by mass of the condensate (a1) of MTMS obtained in Synthesis Example 1, and 56 parts by mass of deionized water were added to the liquid. The mixture was stirred at temperature for 15 hours to cause a hydrolytic condensation reaction, and distilled under the same conditions as in Synthesis Example 1 to remove the produced methanol and water. Then, 250 parts by mass of BuOH was added to obtain 1,000 parts by mass of curable resin composition (2) having a non-volatile content of 60.0% by mass.

Synthesis Example 2: Grinding Conditions for Silicon Oxide Particles Zirconia beads with a particle size of 0.2 mm as grinding media and 100 ml of methyl ethyl ketone solvent were placed in a container of a 150 ml small bead mill so that the filling rate was 60%. After that, 100 parts by mass of silicon oxide powder (commercial product) having an average particle diameter of 5 μm and 20 parts by mass of a cationic dispersant liquid (BYK145, BYK-Chemie Japan Co., Ltd.) were added, and the grinding conditions described in Table 1 were applied. Wet pulverization by a bead mill was performed to obtain a slurry of dark brown liquid silicon oxide, SiO-1 to SiO-3, with a solid concentration of 30% by mass. Table 1 shows the average particle size of each silicon oxide measured by laser light scattering measurement.

In addition, using a small ball mill apparatus having a container diameter of 150 mm and zirconia balls as grinding media, methanol as a grinding solvent, 100 parts by mass of silicon oxide powder (commercially available) having an average particle size of 5 μm and 20 parts of cation A polydispersant liquid (BYK-Chemie Japan Co., Ltd.: BYK145) is placed in a grinding container, and silicon oxide is ground under the grinding conditions shown in Table 1 to obtain a silicon oxide powder having a solid concentration of 30% by mass, SiO A slurry of SiO-4 to SiO-7 was obtained. Table 1 shows the average particle sizes of SiO-4 to SiO-7.

Example 1
The polysiloxane resin having an average molecular weight of 3500 (curable resin composition (1)) prepared in Synthesis Example 1 and the phenolic resin having an average molecular weight of 3000 were mixed at a weight ratio of 90/10 for the resin solids, and after high-temperature baking, The SiO-1 slurry obtained in Synthesis Example 2 was added so that the content of silicon oxide particles in the product was 50% by mass, and the mixture was thoroughly mixed in a stirrer. The resin mixture suspension containing the obtained silicon oxide particles was subjected to solvent removal in an oil bath at 120° C. under nitrogen flow conditions. Then, it was dried under reduced pressure at 110° C. for 10 hours using a vacuum dryer, and finally baked at a high temperature of 900° C. for 4 hours in a nitrogen atmosphere to obtain a black solid. The resulting black solid was pulverized with a planetary ball mill to prepare a black powder. 20 g of this black powder was put into a CVD device (desktop rotary kiln: manufactured by Takasago Kogyo Co., Ltd.), and while introducing a mixed gas of 0.2 L / min of ethylene gas and 0.8 L / min of nitrogen gas, it was heated at 850 ° C. The surface of the black powder was coated with carbon for 1 hour by chemical vapor deposition to prepare active material particles.

When the carbon coating amount of the active material powder after the carbon coating treatment was measured with a thermal analyzer, it was found that the weight increased by 2.1% from the weight before the treatment. The obtained active material powder had an average particle size of about 2.9 μm and a specific surface area of 6.5 m ² /g.
A diffraction peak at 2θ=28.4° attributed to the Si (111) crystal face was not detected by powder X-ray diffraction (XRD) measurement using Cu—Kα rays. Energy dispersive X-ray spectroscopy (EDS) results indicated that the nitrogen element content was 0.2% by mass. In addition, as a result of Raman scattering analysis, a peak near 1590 cm ⁻¹ attributed to the G band of carbon and a peak near 1330 cm ⁻¹ attributed to the D band are shown, and the intensity ratio I (G band) / I (D band ) was 1.4.

A slurry was prepared by mixing 80 parts by mass of the active material particles obtained above, 10 parts by mass of acetylene black as a conductive additive, and 10 parts by mass of a mixture of CMC and SBR as a binder. The obtained slurry was formed into a film on a copper foil. After drying under reduced pressure at 110° C., a coin-type lithium ion battery was produced as a half cell using a Li metal foil as a counter electrode. Using a secondary battery charge/discharge test device (manufactured by Hokuto Co., Ltd.), the charge/discharge characteristics of the half-cells produced were evaluated at 25°C. The cutoff voltage range was 0.005 to 1.5V. The charge/discharge measurement results were an initial discharge capacity of 1180 mAh/g and an initial coulombic efficiency of 67.5%.

In the evaluation of the full cell, a single-layer sheet using LiCoO ₂ as a positive electrode active material and aluminum foil as a current collector was used to prepare a positive electrode film, and graphite powder was used at a discharge capacity design value of 450 mAh / g. and the active material powder were mixed to prepare a negative electrode film. For the non-aqueous electrolyte, lithium hexafluorophosphate was added to a mixture of ethylene carbonate (hereinafter also referred to as “EC”) and diethyl carbonate (hereinafter also referred to as “DEC”) at a volume ratio of 1/1 at a concentration of 1 mol/mol. A laminated lithium ion secondary battery was fabricated using a non-aqueous electrolyte solution dissolved at a concentration of L and using a polyethylene microporous film having a thickness of 30 μm as a separator. A laminated lithium ion secondary battery was charged at 25°C at a constant current of 1.2mA (0.25c based on the positive electrode) until the voltage of the test cell reached 4.2V, and after reaching 4.2V, 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 was 90% after 300 cycles, where charging and discharging within a voltage range of 2.5 V to 4.2 V was defined as one cycle. After charging and discharging, the laminate cell was dismantled in an argon atmosphere in a glove box, the negative electrode was taken out, washed with an EC/DEC mixed solution, allowed to stand and dried, and then the thickness of the electrode film was measured. The rate of change in the thickness of the negative electrode film before and after charging/discharging was taken as the negative electrode expansion rate. The expansion rate of the negative electrode was 19%. Table 2 shows the results.

Examples 2 and 3
Silicon oxide slurries with SiO-2 in Example 2 and SiO-3 in Example 3 were used. The particle size and specific surface area of the obtained active material were measured, and the half-cell and full-cell charge/discharge performances were evaluated using the obtained active material. Various evaluation results are shown in Table 2.

Examples 4 to 8
SiO-4 was used as silicon oxide, and the content of silicon oxide was 5% by mass in Example 4, 10% by mass in Example 5, 30% by mass in Example 6, 50% by mass in Example 7, and 8% by mass. was 58% by mass, and the active material particles were obtained under the same conditions as in Example 1. Using the obtained active material particles, half-cell and full-cell charge/discharge performances were evaluated. Table 2 shows various evaluation results obtained.

Examples 9 and 10
Using SiO-4 as silicon oxide, under the same conditions as in Example 1, the resin mixture suspension containing silicon oxide particles was desolvated in an oil bath at 120° C. under nitrogen flow conditions, After that, high temperature firing was performed. A black powder is obtained by changing the pulverization conditions of the fired material, and it is put into a CVD device (desktop rotary kiln: manufactured by Takasago Kogyo Co., Ltd.), and a mixed gas of 0.3 L / min of ethylene gas and 0.7 L / min of nitrogen gas is introduced. did. In Example 9, the surface of the black powder was coated with carbon by chemical vapor deposition at 850 ° C. for 1 hour, and in Example 10, at 850 ° C. for 2 hours. Particles were produced. The particle size and specific surface area of the obtained active material were measured, and the obtained active material particles were used to evaluate charge/discharge performance in half-cell and full-cell. Various evaluation results are shown in Table 2.

Examples 11 to 13
The mass ratio of the polysiloxane resin (curable resin composition (2)) having an average molecular weight of 3500 prepared in Synthesis Example 1 and the phenolic resin having an average molecular weight of 3000 was 100/0 in Example 11 and 100/0 in Example 11. 12 was mixed at 50/50 and Example 13 was mixed at 30/70, and the SiO-4 slurry obtained in Synthesis Example 2 was mixed so that the silicon oxide particle content in the product after high temperature firing was 50% by mass. was added, and the resin mixture suspension containing silicon oxide particles was desolvated in an oil bath at 120° C. under nitrogen flow conditions. Subsequent conditions were the same as in Example 1, and active material particles were produced. The particle size and specific surface area of the obtained active material were measured, and the obtained active material particles were used to evaluate charge/discharge performance in half-cell and full-cell. Various evaluation results are shown in Table 2.

Example 14
Active material particles were obtained under the same conditions as in Example 1 except that SiO-5 was used as the silicon oxide. Using the obtained active material particles, half-cell and full-cell charge/discharge performances were evaluated. Table 2 shows various evaluation results obtained.

Examples 15 and 16
Silicon oxide slurries containing SiO-6 in Example 15 and SiO-7 in Example 16 were used, and mixed with a resin mixture suspension containing silicon oxide particles. A resin mixed suspension containing silicon oxide particles using LiCl as a raw material so that the molar ratio of Li ⁺ /silicon oxide to the amount of silicon oxide particles is 30/100 in Example 15 and 50/100 in Example 16. It was added to the liquid, and the solvent was removed in an oil bath at 120° C. under nitrogen follow conditions. Subsequent conditions were the same as in Example 1, and an active material powder was produced. The Li element content in the obtained active material particles was 2.5% by mass in Example and 5.1% by mass in Example 16. The particle size and specific surface area of the obtained active material particles were measured, and the obtained active material particles were used to evaluate charge/discharge performance in half-cell and full-cell. Various evaluation results are shown in Table 2.

Example 17
Using SiO-7 as the silicon oxide, under the same conditions as in Example 1, the resin mixture suspension containing silicon oxide particles was desolvated in an oil bath at 120° C. under nitrogen follow conditions, High-temperature firing was performed at 1000° C. for 4 hours in a nitrogen atmosphere to obtain active material particles. As a result of powder X-ray diffraction (XRD) measurement using Cu—Kα rays of the obtained active material particles, a diffraction peak at 2θ=28.4° attributed to the Si (111) crystal plane was detected. The particle size and specific surface area of the obtained active material particles were measured, and the obtained active material particles were used to evaluate charge/discharge performance in half-cell and full-cell. Various evaluation results are shown in Table 2.

Comparative example 1
20 g of silicon oxide powder with an average particle size of 5 μm is put into a CVD apparatus (desktop rotary kiln: manufactured by Takasago Kogyo Co., Ltd.), and a mixed gas of 0.2 L/min of ethylene gas and 0.8 L/min of nitrogen gas is introduced. Meanwhile, the surface of the black powder was coated with carbon by a chemical vapor deposition method at 850° C. for 1 hour to prepare active material particles. The amount of carbon coating after treatment was measured by a thermal analyzer and found to be 2.0% higher than the weight before treatment. As a result of powder X-ray diffraction (XRD) measurement using Cu—Kα rays of the obtained active material particles, no diffraction peak at 2θ=28.4° attributed to the Si (111) crystal plane was detected. . The particle size and specific surface area of the obtained active material particles were measured, and the obtained active material particles were used to evaluate charge/discharge performance in half-cell and full-cell. Various evaluation results are shown in Table 2.

Comparative example 2
The curable resin composition (1) prepared in Synthesis Example 1 was dried at 110° C. under reduced pressure and then baked at a high temperature of 1100° C. for 4 hours in a nitrogen atmosphere to obtain a black solid. The resulting black solid was pulverized in a planetary ball mill to produce a black powder, which was subjected to carbon coating treatment under the same CVD conditions as in Comparative Example 1.
The particle size and specific surface area of the black powder obtained after the carbon coating treatment were measured, and the half-cell and full-cell charging/discharging performances were evaluated using the black powder after the carbon coating treatment. Various evaluation results are shown in Table 2.

Comparative example 3
Using commercially available silicon particles (manufactured by Alfa Aesar) having an average particle size of 100 nm instead of silicon oxide particles, a resin mixture suspension containing silicon particles was placed in an oil bath at 120° C. under the same conditions as in Example 1. A black solid was obtained by removing the solvent under medium and nitrogen follow conditions, and sintering at a high temperature of 1000° C. for 4 hours in a nitrogen atmosphere. As a result of powder X-ray diffraction (XRD) measurement of the obtained active material particles using Cu-Kα rays, a strong diffraction peak at 2θ = 28.4° attributed to the Si (111) crystal plane was detected. . The particle size and specific surface area of the obtained active material particles were measured, and the obtained active material particles were used to evaluate charge/discharge performance in half-cell and full-cell. Various evaluation results are shown in Table 2.

Comparative example 4
After mixing the phenolic resin having an average molecular weight of 3000 and the SiO-4 slurry obtained in Synthesis Example 2 so that the content of silicon oxide particles in the product after high-temperature firing is 50% by mass, the oil is heated to 120°C. Desolvation was performed in a bath under nitrogen follow conditions. Active material particles were obtained under the same conditions as in Example 1, except that the CVD carbon coating was not performed. Using the obtained active material particles, half-cell and full-cell charge/discharge performances were evaluated. Table 2 shows various evaluation results obtained.

[Evaluation method]
In Table 2, each evaluation method is as follows.
Average particle size D50: Measured using a laser diffraction particle size distribution analyzer (Mastersizer 3000, manufactured by Malvern Panalytical).
Specific surface area: Measured by BET method from 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 spectrum measurement: NRS-5500 (manufactured by JASCO Corporation) was used as a measuring instrument. The measurement conditions were an excitation laser wavelength of 532 nm, an objective lens magnification of 100, and a measurement wavenumber range of 3500 to 100 cm ⁻¹ .
Powder X-ray diffraction (XRD): Measured in air using an X-ray diffractometer (manufactured by Rigaku, SmartLab).

Measurement of nitrogen content: An oxygen/nitrogen analyzer (EMGA-920) was used.
Measurement of carbon film amount: Weight loss was measured and calculated in the atmosphere using a thermal analysis device (manufactured by Rigaku, Thermo Plus EVO2).

Battery characteristics evaluation: Battery characteristics are measured using a secondary battery charge-discharge test device (manufactured by Hokuto Denko Co., Ltd.), room temperature 25 ° C., cutoff voltage range from 0.005 to 1.5 V, charge / discharge rate is 0 The charging/discharging characteristics were evaluated under conditions of constant current/constant voltage charging/constant current discharging at 0.2 C (after 4 cycles) and 1 C (1 to 3 cycles). At the time of switching between charging and discharging, the battery was left in an open circuit for 30 minutes. Discharge capacity, charge capacity, initial coulombic efficiency and cyclability (in the present application, refers to the capacity retention rate after 300 cycles of charging and discharging a full cell at 25° C.), and negative electrode expansion rate were obtained as follows. Charge capacity and discharge capacity of active material: Obtained by half-cell charge/discharge measurement. Initial coulomb efficiency (%) of active material = initial discharge capacity (mAh/g)/initial charge capacity (mAh/g) capacity retention rate (% @ 300th cycle) = 300th negative electrode discharge capacity (mAh/g)/negative electrode The initial discharge capacity (mAh/g) was obtained by measuring a full cell (laminate cell). Negative electrode expansion rate: After charging and discharging the full cell for 300 cycles, the negative electrode was taken out, washed with an EC/DEC mixed solution, left to stand and dried, and then the thickness of the electrode film was measured. The rate of change in the thickness of the negative electrode film before and after charging/discharging was taken as the negative electrode expansion rate.

As is clear from the above results, when the present active material is used as a negative electrode active material, the expansion rate of the negative electrode is low while maintaining a high capacity, and both the cycle property (or capacity retention rate) and the initial coulomb efficiency are high. In addition, the characteristics of these secondary batteries are well balanced. A secondary battery containing the present active material as a negative electrode active material has excellent battery characteristics.

Claims

A secondary battery active material that is a composite particle having a silicon oxycarbide phase and at least two or more silicon oxide particles in the silicon oxycarbide phase.
The active material for a secondary battery according to claim 1, wherein the content of the silicon oxide particles is 1% by mass or more and 60% by mass or less.
The active material for a secondary battery according to claim 1 or 2, which has a peak attributed to Si(111) near 28.4° in X-ray diffraction.
The active material for a secondary battery according to claim 1 or 2, wherein the silicon oxide particles have an average particle size of 5 µm or less.
The active material for a secondary battery according to claim 1 or 2, wherein the composite particles have an average particle size of 2 µm or more and 15 µm or less.
3. The active material for a secondary battery according to claim 1, which has a specific surface area of 0.3 m 2 /g or more and 10 m 2 /g or less.
The active material for a secondary battery according to claim 1 or 2, wherein the silicon oxycarbide phase further contains nitrogen atoms.
In the Raman spectrum, there are scattering peaks near 1590 cm −1 attributed to the G band of the carbon structure and 1330 cm −1 attributed to the D band, and the intensity ratio of the scattering peaks, I (G band) / I (D band) is 0.7 or more and 2 or less.
The active material for a secondary battery according to claim 1 or 2, wherein the surface of the composite particles has a carbon coating, and the amount of the carbon coating is 1% by mass or more and 10% by mass or less.
The secondary battery active material according to claim 1 or 2, comprising a silicate compound of at least one metal selected from the group consisting of Li, K, Na, Ca, Mg and Al.
A secondary battery comprising the secondary battery active material according to claim 1 or 2 in a negative electrode.