JP7159838B2 - Negative electrode active material for lithium ion secondary battery, negative electrode for lithium ion secondary battery and lithium ion secondary battery - Google Patents

Description

The present invention relates to a negative electrode active material for lithium ion secondary batteries, a negative electrode for lithium ion secondary batteries, and a lithium ion secondary battery.

Currently, graphite is mainly used as a negative electrode active material for lithium ion secondary batteries, and it is known that graphite has a theoretical capacity limit of 372 mAh/g in discharge capacity. In recent years, as the performance of mobile devices such as mobile phones, notebook computers, and tablet terminals has improved, there has been a demand for the development of negative electrode active materials that can achieve even higher capacities for lithium ion secondary batteries.

Against the background of the above circumstances, studies have been made to use a material having a theoretical capacity higher than that of graphite as a negative electrode active material. Among them, silicon oxide has a large capacity, is inexpensive, and has good workability, and therefore, research on its use as a negative electrode active material is particularly active.

For example, in Patent Document 1, a peak derived from Si (111) is observed in X-ray diffraction, and the crystal size of silicon obtained by the Scherrer method based on the half-value width of the diffraction line is 1 to 500 nm. is a negative electrode active material in which the surface of particles having a structure in which silicon microcrystals are dispersed in a silicon-based compound is coated with carbon.
According to the technique of Patent Document 1, silicon microcrystals or fine particles are dispersed in an inert and strong substance such as silicon dioxide, and carbon is fused to at least part of the surface to impart conductivity. As a result, the conductivity of the surface is ensured, and the structure is stable against the volume change of silicon accompanying the absorption and release of lithium. This is said to result in long-term stability and improved initial efficiency.

Further, in Patent Document 2, the surface of silicon oxide particles is coated with a graphite film, the graphite coating amount is 3 to 40% by mass, the BET specific surface area is 2 to 30 m ² /g, and the graphite film is Raman A negative electrode active material is disclosed that has a spectrum characteristic of a graphite structure with Raman shifts in the vicinity of 1330 cm ⁻¹ and 1580 cm ⁻¹ in the spectral spectrum.
According to the technique of Patent Document 2, by controlling the physical properties of the graphite film covering the surface of the material capable of absorbing and desorbing lithium ions within a specific range, the lithium ion secondary can reach the level of characteristics required by the market. It is said that the negative electrode of the battery can be obtained.

Further, Patent Document 3 discloses a negative electrode active material in which the surfaces of silicon oxide particles represented by the general formula SiO 2 _x are coated with a carbon film that has been subjected to thermal plasma treatment.
According to the technique of Patent Document 3, it is said that a negative electrode active material with excellent cycle characteristics can be obtained by solving the drawbacks of silicon oxide such as electrode expansion and battery expansion due to gas generation.

Japanese Patent No. 3952180 Japanese Patent No. 4171897 JP 2011-90869 A

In the future, as a negative electrode active material for application to lithium-ion secondary batteries suitable for high performance mobile devices, it is necessary not only to store a large amount of lithium ions (high charging capacity), but also to store lithium ions. It is necessary to be able to release more Therefore, improvement of initial discharge capacity is important as a negative electrode active material that contributes to further improvement of the performance of lithium ion secondary batteries. In addition to this, as a negative electrode active material that contributes to further improvement in the performance of lithium ion secondary batteries, it is also important to suppress electrode swelling caused by charge/discharge reactions. Furthermore, further improvement in the high-temperature storage characteristics of lithium-ion secondary batteries, which are indexed by the recovery rate after charging and discharging, is also required.
One aspect of the present invention has been made in view of the above requirements, and is a negative electrode active material for a lithium ion secondary battery that can improve the initial discharge capacity and high-temperature storage characteristics of the lithium ion secondary battery and suppress the expansion of the electrode. An object of the present invention is to provide a substance, a negative electrode for a lithium ion secondary battery and a lithium ion secondary battery using the same.

Specific means for solving the above problems are as follows.
<1> containing silicon oxide particles in which carbon is present on part or all of the surface,
X-ray diffraction at 2θ = 27° to 29° derived from Si relative to X-ray diffraction peak intensity at 2θ = 20° to 25° derived from SiO ₂ when using CuKα rays with a wavelength of 0.15406 nm as the radiation source The peak intensity ratio (P _Si /P _SiO2 ) is in the range of 1.0 to 2.6,
A negative electrode active material for a lithium ion secondary battery, wherein the ratio of the specific surface area calculated from water vapor adsorption at 298K to the specific surface area calculated from nitrogen adsorption at 77K (S _H2O /S _N2 ) is 0.60 or less.
<2> The lithium ion secondary according to <1>, wherein the average value of the aspect ratio represented by the ratio of the major axis L to the minor axis S (S/L) is in the range of 0.45 ≤ S / L ≤ 1 Negative electrode active material for batteries.
<3> In the volume cumulative distribution curve obtained by the laser diffraction/scattering method, the accumulation from the small particle side is 10% with respect to the particle diameter (D90%) when the accumulation from the small particle side is 90%. The negative electrode active material for a lithium ion secondary battery according to <1> or <2>, wherein the ratio (D10%/D90%) of the particle diameters (D10%) at time is 0.1 or more.
<4> The lithium according to any one of <1> to <3>, wherein the carbon content is 0.1% by mass to 10.0% by mass of the total of the silicon oxide particles and the carbon. Negative electrode active material for ion secondary batteries.
<5> It has a diffraction peak attributed to Si (111) in the X-ray diffraction spectrum, and the crystallite size of silicon calculated from the diffraction peak is 1.0 nm to 15.0 nm, <1> The negative electrode active material for a lithium ion secondary battery according to any one of <4>.
<6> The negative electrode active material for a lithium ion secondary battery according to any one of <1> to <5>, which has a volume average particle size of 0.1 μm to 20 μm.
<7> The lithium ion secondary battery according to any one of <1> to <6>, having a specific surface area calculated from nitrogen adsorption at 77K of 0.1 m ² /g to 10 m ² /g. negative electrode active material.
<8> The negative electrode active material for a lithium ion secondary battery according to any one of <1> to <7>, further comprising a carbonaceous negative electrode active material.
<9> A current collector, and a negative electrode material layer containing the negative electrode active material for a lithium ion secondary battery according to any one of <1> to <8> provided on the current collector, A negative electrode for a lithium ion secondary battery having.
<10> A lithium ion secondary battery comprising a positive electrode, the negative electrode for a lithium ion secondary battery according to <9>, and an electrolyte.

According to one aspect of the present invention, a negative electrode active material for a lithium ion secondary battery that can improve the initial discharge capacity and high-temperature storage characteristics of the lithium ion secondary battery and suppress the expansion of the electrode, and lithium using the same A negative electrode for an ion secondary battery and a lithium ion secondary battery are provided.

1 is a schematic cross-sectional view showing an example of the configuration of a negative electrode active material of the present disclosure; FIG. FIG. 4 is a schematic cross-sectional view showing another example of the configuration of the negative electrode active material of the present disclosure; FIG. 4 is a schematic cross-sectional view showing another example of the configuration of the negative electrode active material of the present disclosure; FIG. 4 is a schematic cross-sectional view showing another example of the configuration of the negative electrode active material of the present disclosure; FIG. 4 is a schematic cross-sectional view showing another example of the configuration of the negative electrode active material of the present disclosure; FIG. 4 is an enlarged cross-sectional view of a part of the negative electrode active material of FIGS. 1 to 3, and is a view for explaining one aspect of the state of carbon 10 in the negative electrode active material. FIG. 4 is a partially enlarged cross-sectional view of the negative electrode active material of FIGS. 1 to 3, and is a view for explaining another aspect of the state of carbon 10 in the negative electrode active material.

DETAILED DESCRIPTION OF THE INVENTION Embodiments for carrying out the present invention will be described in detail below. However, the present invention is not limited to the following embodiments. In the following embodiments, the constituent elements (including element steps and the like) are not essential unless otherwise specified. The same applies to numerical values and their ranges, which do not limit the present invention.

In the present disclosure, the term "process" includes a process that is independent of other processes, and even if the purpose of the process is achieved even if it cannot be clearly distinguished from other processes. .
In the present disclosure, the numerical range indicated using "-" includes the numerical values before and after "-" as the minimum and maximum values, respectively.
In the numerical ranges described step by step in the present disclosure, the upper limit or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described step by step. . Moreover, in the numerical ranges described in the present disclosure, the upper or lower limits of the numerical ranges may be replaced with the values shown in the examples.
In the present disclosure, each component may contain multiple types of applicable substances. When there are multiple types of substances corresponding to each component in the composition, the content rate or content of each component is the total content rate or content of the multiple types of substances present in the composition unless otherwise specified. means quantity.
Particles corresponding to each component in the present disclosure may include a plurality of types. When multiple types of particles corresponding to each component are present in the composition, the particle size of each component means a value for a mixture of the multiple types of particles present in the composition, unless otherwise specified.
In the present disclosure, the term “layer” or “film” refers to the case where the layer or film is formed in the entire region when observing the region where the layer or film is present, and only a part of the region. It also includes the case where it is formed.
In the present disclosure, the term "laminate" indicates stacking layers, and two or more layers may be bonded, or two or more layers may be detachable.
When embodiments are described in the present disclosure with reference to drawings, the configurations of the embodiments are not limited to the configurations shown in the drawings. Also, the size of each member in each drawing is conceptual, and the relative size relationship between members is not limited to this. Further, in each drawing, members having substantially the same function are given the same reference numerals in all the drawings, and redundant description may be omitted.

<Negative electrode active material for lithium ion secondary battery>
The negative electrode active material for lithium ion secondary batteries of the present disclosure (hereinafter sometimes referred to as “negative electrode active material”) contains silicon oxide particles in which carbon is present on part or all of the surface, and the radiation source has a wavelength of Ratio of X-ray diffraction peak intensity at 2θ = 27° to 29° derived from Si to X-ray diffraction peak intensity at 2θ = 20° to 25° derived from _SiO2 when using 0.15406 nm CuKα radiation (P _Si /P _SiO2 ) is in the range of 1.0 to 2.6, and the ratio of the specific surface area calculated from water vapor adsorption at 298 K to the specific surface area calculated from nitrogen adsorption at 77 K (S _H2O /S _N2 ) is 0.60 or less.

(Silicon oxide particles)
The silicon oxide constituting the silicon oxide particles contained in the negative electrode active material may be an oxide containing silicon element, and examples thereof include silicon oxide, silicon dioxide, and silicon suboxide. The silicon oxides contained in the silicon oxide particles may be of one type or a combination of two or more types.

Among silicon oxides, silicon oxide and silicon dioxide are commonly referred to as silicon monoxide (SiO) and silicon dioxide (SiO ₂ ), respectively, although the surface conditions (e.g., the presence of an oxide film) or Depending on the production situation of the compound, the measured value (or converted value) of the contained element may be represented by the composition formula SiO _x (where x is 0 < x ≤ 2). do. The value of x in the composition formula can be calculated, for example, by quantifying oxygen contained in the silicon oxide by an inert gas fusion-nondispersive infrared absorption method. In addition, when a disproportionation reaction of silicon oxide (2SiO → Si + SiO ₂ ) is involved during the manufacturing process of the negative electrode active material, it exists in a state containing silicon and silicon dioxide (or silicon oxide in some cases) due to the chemical reaction. In this case, too, it is the silicon oxide according to the present disclosure.

The average particle size of the silicon oxide particles is not particularly limited. For example, the volume average particle size is preferably 0.1 μm to 20 μm, more preferably 0.5 μm to 10 μm, depending on the size of the final desired negative electrode active material. The volume average particle diameter of the silicon oxide particles is the particle diameter (D50%) when the volume accumulation from the small diameter side is 50% in the volume-based particle size distribution curve. The same applies to the average particle size described below. The volume average particle size is measured by a laser diffraction/scattering method according to the method described in Examples.

(carbon)
Carbon is present on part or all of the surface of the silicon oxide particles. The presence of carbon on part or all of the surface of the silicon oxide particles imparts electrical conductivity to the silicon oxide particles, which are insulators, and improves the efficiency of the charge-discharge reaction. Therefore, it is considered that the initial discharge capacity and the initial charge/discharge efficiency are improved. Hereinafter, silicon oxide particles having carbon present on part or all of the surface may be referred to as "SiO—C particles".

In the present disclosure, examples of carbon present on part or all of the surface of silicon oxide particles include graphite, amorphous carbon, and the like. It should be noted that the organic substance described below does not correspond to the “carbon” present on part or all of the surface of the silicon oxide particles as used in the present disclosure.
There is no particular limitation on the mode in which carbon is present on part or all of the surface of the silicon oxide particles. Examples include continuous or discontinuous coating.
The presence or absence of carbon in the negative electrode active material for lithium ion secondary batteries can be confirmed, for example, by laser Raman spectrometry at an excitation wavelength of 532 nm.

The content of carbon is preferably 0.1% by mass to 10.0% by mass in the total of silicon oxide particles and carbon. Such a configuration tends to further improve the initial discharge capacity and the initial charge/discharge efficiency. The carbon content is more preferably 1.0% by mass to 9.0% by mass, still more preferably 2.0% by mass to 8.0% by mass, and particularly preferably 3.0% by mass to 7.0% by mass. .

The carbon content (mass basis) can be determined, for example, by high-frequency firing-infrared analysis. In the high-frequency sintering-infrared analysis method, for example, a simultaneous carbon and sulfur analyzer (LECO Japan LLC, CSLS600) can be applied. When the negative electrode active material contains an organic substance, which will be described later, the carbon content is reduced by heating to a temperature at which the organic substance decomposes (for example, 300 ° C.) or higher to remove the mass reduction due to the organic substance in advance. can be measured.

Carbon is preferably of low crystallinity. In the present disclosure, the carbon "having low crystallinity" means that the negative electrode active material obtained by the method described below has an R value of 0.5 or more.
The R value of the negative electrode active material is the intensity of the peak appearing near 1360 cm ⁻¹ in the profile obtained by laser Raman spectrometry at an excitation wavelength of 532 nm, and the intensity of the peak appearing near 1580 cm ⁻¹ as Ig. , the intensity ratio Id/Ig (also denoted as D/G) of both peaks.

Here, the peak appearing around 1360 cm ⁻¹ is usually identified as corresponding to an amorphous structure, and means, for example, the peak observed at 1300 cm ⁻¹ to 1400 cm ⁻¹ . The peak appearing around 1580 cm ⁻¹ is usually identified as corresponding to the graphite crystal structure, and means, for example, the peak observed at 1530 cm ⁻¹ to 1630 cm ⁻¹ .
In addition, the R value is measured using a Raman spectrum measuring device (for example, NSR-1000 type, JASCO Corporation), with a baseline of 1050 cm ^-1 to 1750 cm ^-1 for the measurement range (830 cm ^-1 to 1940 cm ^-1 ). can ask.

The R value of the negative electrode active material is preferably 0.5 to 1.5, more preferably 0.7 to 1.3, even more preferably 0.8 to 1.2. When the R value is 0.5 to 1.5, the surface of the silicon oxide particles is sufficiently coated with low-crystalline carbon in which the carbon crystallites are randomly oriented, so that the reactivity with the electrolyte can be reduced. Cycle characteristics tend to improve.

The method of adding carbon to the surface of silicon oxide particles is not particularly limited. Specifically, a wet mixing method, a dry mixing method, a chemical vapor deposition method, and the like can be mentioned.

When carbon is applied by a wet mixing method, for example, silicon oxide particles and a carbon raw material (carbon source) dissolved or dispersed in a solvent are mixed, and the carbon source is added to the surface of the silicon oxide particles. , removing the solvent if necessary, and then heat-treating in an inert atmosphere to carbonize the carbon source.

When the carbon is imparted by a dry mixing method, for example, the silicon oxide particles and the carbon source are mixed in a solid state to form a mixture, and the mixture is heat-treated in an inert atmosphere to convert the carbon source to carbon. A method of making When mixing the silicon oxide particles and the carbon source, a treatment of applying mechanical energy (for example, a mechanochemical treatment) may be performed.

When applying carbon by chemical vapor deposition, a known method can be applied. For example, by heat-treating the silicon oxide particles in an atmosphere containing a gas obtained by vaporizing a carbon source, carbon can be imparted to the surfaces of the silicon oxide particles.

When applying carbon to the surface of silicon oxide particles by a wet mixing method or a dry mixing method, the carbon source to be used is not particularly limited as long as it can be converted to carbon by heat treatment. Specifically, polymer compounds such as phenolic resin, styrene resin, polyvinyl alcohol, polyvinyl chloride, polyvinyl acetate, polybutyral; ethylene heavy end pitch, coal-based pitch, petroleum-based pitch, coal tar pitch, asphalt cracked pitch , PVC pitch produced by pyrolyzing polyvinyl chloride or the like, pitches such as naphthalene pitch produced by polymerizing naphthalene or the like in the presence of a super strong acid; polysaccharides such as starch and cellulose. You may use a carbon source individually by 1 type or in combination of 2 or more types.

When carbon is applied to the surface of silicon oxide particles by chemical vapor deposition, the carbon source to be used includes aliphatic hydrocarbons, aromatic hydrocarbons, alicyclic hydrocarbons, etc., which are gaseous or easily gasified. It is preferable to use materials that are available. Specific examples include methane, ethane, ethylene, acetylene, propane, toluene, benzene, xylene, styrene, naphthalene, cresol, anthracene, and derivatives thereof. Natural gas can also be used as a carbon source. You may use a carbon source individually by 1 type or in combination of 2 or more types.

The heat treatment temperature for carbonizing the carbon source is not particularly limited as long as it is a temperature at which the carbon source is carbonized. It is even more preferable to have In addition, from the viewpoint of obtaining low-crystalline carbon and from the viewpoint of generating silicon crystallites of a desired size by the disproportionation reaction described later, the heat treatment temperature is preferably 1300° C. or less, and 1200° C. or less. It is more preferably 1100° C. or less.

The heat treatment time for carbonizing the carbon source can be selected according to the type, amount, etc. of the carbon source used. For example, 1 hour to 10 hours is preferred, and 2 hours to 7 hours is more preferred.

The heat treatment for carbonizing the carbon source is preferably performed in an inert atmosphere such as nitrogen or argon. The heat treatment apparatus is not particularly limited, and examples thereof include a heating apparatus capable of performing treatment by a continuous method, a batch method, or the like. Specifically, 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 according to the purpose.

Further, when carbon is applied to the surface of silicon oxide particles by a chemical vapor deposition method using a rotary furnace or rotary kiln, the furnace core tube of the rotary furnace or rotary kiln is arranged in a horizontal direction, and the furnace core tube rotates. Structural devices are preferred. By performing the chemical vapor deposition treatment while rolling the silicon oxide particles, stable production becomes possible without agglomeration of the silicon oxide particles. The apparatus is not particularly limited as long as it has a furnace core tube capable of retaining an atmosphere, a rotating mechanism for rotating the furnace core tube, and a heating mechanism capable of increasing and maintaining the temperature. Depending on the purpose, the apparatus may be provided with a raw material supply mechanism (e.g., feeder) and a product recovery mechanism (e.g., hopper). A baffle plate can also be provided at . The material of the furnace core tube is also not particularly limited, and ceramics such as alumina and silicon carbide, refractory metals such as molybdenum and tungsten, SUS, and quartz can be appropriately selected depending on the processing conditions and processing purpose.

When the heat-treated product obtained by heat treatment is in a state in which a plurality of particles are aggregated, crushing treatment may be further performed. In addition, if it is necessary to adjust the average particle size to a desired value, pulverization may be performed.

(X-ray diffraction peak intensity ratio)
The negative electrode active material has an X-ray diffraction peak intensity ratio (P _Si /P _SiO2 ) in the range of 1.0 to 2.6. The X-ray diffraction peak intensity ratio (P _Si /P _SiO2 ) is the X-ray diffraction peak intensity at 2θ = 20 ° to 25 ° derived from SiO ₂ when CuKα rays with a wavelength of 0.15406 nm are used as the radiation source. It is the ratio of the X-ray diffraction peak intensity at 2θ = 27° to 29° derived from Si.

Even if the X-ray diffraction peak intensity ratio (P _Si /P _SiO2 ) of the negative electrode active material is a value measured in a state where carbon, organic matter, conductive particles, etc. are attached to the silicon oxide particles, it is It may be a value measured without

As a negative electrode active material having an X-ray diffraction peak intensity ratio (P _Si /P _SiO2 ) in the range of 1.0 to 2.6, a silicon oxide having a structure in which silicon crystallites are present in the silicon oxide Examples include a negative electrode active material containing particles.

Silicon oxide particles having a structure in which silicon crystallites are dispersed in silicon oxide cause, for example, a disproportionation reaction (2SiO→Si+SiO ₂ ) of silicon oxide to generate silicon in the silicon oxide particles. It can be produced by generating crystallites. By controlling the degree of formation of silicon crystallites in silicon oxide particles, the ratio of X-ray diffraction peak intensities can be controlled to a desired value.

The advantage of making silicon crystallites exist in silicon oxide particles by the disproportionation reaction of silicon oxide can be considered as follows. The above-described SiO _x (where x is 0<x≦2) tends to trap lithium ions during initial charge, resulting in poor initial charge/discharge characteristics. This is because lithium ions are trapped by oxygen dangling bonds (unshared electron pairs) present in the amorphous SiO ₂ phase. Therefore, it is considered preferable from the viewpoint of improving the charge-discharge characteristics to suppress the generation of dangling bonds of active oxygen atoms by reconstructing the amorphous SiO ₂ phase by heat treatment.

When the X-ray diffraction peak intensity ratio (P _Si /P _SiO2 ) of the negative electrode active material is 1.0 or more, the silicon crystallites in the silicon oxide particles are sufficiently grown, and the ratio of SiO ₂ is Since the capacity does not increase, the initial discharge capacity tends to be large, and deterioration in high-temperature storage characteristics due to irreversible reactions tends to be suppressed. On the other hand, when P _Si /P 2 _SiO2 is 2.6 or less, the silicon crystallites formed are not too large, and expansion and contraction are easily alleviated, and a decrease in initial discharge capacity tends to be suppressed. From the viewpoint of obtaining a negative electrode active material with better charge/discharge characteristics, P _Si /P _SiO2 is preferably in the range of 1.5 to 2.0.

The X-ray diffraction peak intensity ratio (P _Si /P _SiO2 ) of the negative electrode active material can be controlled, for example, by the conditions of the heat treatment that causes the disproportionation reaction of silicon oxide. For example, increasing the heat treatment temperature or extending the heat treatment time promotes the formation and enlargement of silicon crystallites, and tends to increase the X-ray diffraction peak intensity ratio. On the other hand, lowering the heat treatment temperature or shortening the heat treatment time tends to suppress the formation of silicon crystallites and reduce the X-ray diffraction peak intensity ratio.

When silicon oxide particles are produced by a disproportionation reaction of silicon oxide, the raw material silicon oxide is, for example, a mixture of silicon dioxide and metal silicon that is heated to generate a silicon monoxide gas that is cooled and cooled. It can be obtained by a known sublimation method for precipitation. Moreover, the silicon oxide used as a raw material can be obtained from the market as silicon oxide, silicon monoxide, or the like.

(Silicon crystallite size)
The negative electrode active material has a diffraction peak attributed to Si (111) in the X-ray diffraction spectrum, and the crystallite size of silicon calculated from the diffraction peak is in the range of 1.0 nm to 15.0 nm. is preferred. Whether silicon crystallites are present or not can be confirmed by powder X-ray diffraction (XRD) measurement. When silicon crystallites are present in the silicon oxide particles, powder X-ray diffraction (XRD) measurement using a CuKα ray with a wavelength of 0.15406 nm as a radiation source shows that 2θ is around 28.4°. A diffraction peak derived from Si(111) is observed in .

The crystallite size of silicon is more preferably 2.0 nm to 10.0 nm, more preferably 3.0 nm to 8.0 nm. When the silicon crystallite size is 15.0 nm or less, the silicon crystallites are less likely to be localized in the silicon oxide particles, and tend to be dispersed throughout the particles. Lithium ions tend to diffuse easily, and good charge capacity tends to be obtained. Moreover, when the crystallite size of silicon is 1.0 nm or more, the reaction between lithium ions and silicon oxide is well controlled, and there is a tendency to easily obtain good charge-discharge efficiency.

The size of silicon crystallites is the size of silicon single crystals contained in silicon oxide particles, and Si (111) obtained by powder X-ray diffraction analysis using a CuKα ray with a wavelength of 0.15406 nm as a radiation source. It can be obtained using Scherrer's formula from the half-value width of the derived diffraction peak near 2θ=28.4°.

The method for forming silicon crystallites in silicon oxide particles is not particularly limited. For example, it can be produced by heat-treating silicon oxide particles in a temperature range of 700° C. to 1300° C. in an inert atmosphere to cause a disproportionation reaction (2SiO→Si+SiO ₂ ). The heat treatment for causing the disproportionation reaction may be performed in the same step as the heat treatment for imparting carbon to the surface of the silicon oxide particles.

The heat treatment conditions for causing the disproportionation reaction of the silicon oxide are, for example, the temperature range of 700° C. to 1300° C., preferably the temperature range of 800° C. to 1200° C. in an inert atmosphere. can be done. From the viewpoint of generating silicon crystallites of a desired size, the heat treatment temperature preferably exceeds 900° C., more preferably 950° C. or higher. Also, the heat treatment temperature is preferably less than 1150° C., more preferably 1100° C. or less.

(average aspect ratio)
The negative electrode active material preferably has an average value of aspect ratios (average aspect ratio) represented by the ratio of major axis L to minor axis S (S/L) in the range of 0.45≦S/L≦1.

In general, when silicon oxide is used as a negative electrode active material, a large volume change occurs due to insertion and extraction of lithium ions during charging and discharging. Therefore, when charging and discharging are repeated, the silicon oxide particles may crack and become finer, and furthermore, the electrode structure of the negative electrode using these may be destroyed and the conductive path may be cut off. In the present disclosure, by setting the average aspect ratio of the negative electrode active material in the range of 0.45 ≤ S / L ≤ 1, the difference in volume change during expansion and contraction as an electrode is averaged, and the electrode structure is improved. Collapse is suppressed. As a result, even if the silicon oxide particles expand and contract, it is believed that the adjacent particles are more likely to be electrically connected to each other.

The average aspect ratio of the negative electrode active material is preferably in the range of 0.45≦S/L≦1, more preferably in the range of 0.55≦S/L≦1, and 0.65≦S/L. More preferably, L≤1. When the average aspect ratio of the negative electrode active material is 0.45 or more, there is a small difference in the amount of volumetric change due to expansion and contraction as an electrode, and deterioration in cycle characteristics tends to be suppressed.

The aspect ratio of the negative electrode active material is measured by observation using a scanning electron microscope (SEM). In addition, the average aspect ratio is calculated as the arithmetic mean value of the aspect ratios measured for each of 100 particles selected arbitrarily from the SEM image.

The ratio of the major axis L to the minor axis S (S/L) of the particle to be measured means the ratio of minor axis (minimum diameter) / major axis (maximum diameter) for spherical particles, and is a hexagonal plate-like or disk-like particle. For each, in the projection image of the particle observed from the thickness direction (observed with the surface corresponding to the thickness facing the front), the minor axis (minimum diameter or minimum diagonal length) / major axis (maximum diameter or maximum diagonal length) means the ratio of

When the negative electrode active material contains conductive particles, which will be described later, the conductive particles are excluded from the measurement of the average aspect ratio.

When the negative electrode active material is obtained through heat treatment for disproportionation reaction of silicon oxide, individual particles may aggregate. The particles used for calculating the average aspect ratio in this case mean the smallest unit particles (primary particles) that can exist as particles alone.

The value of the average aspect ratio of the negative electrode active material can be adjusted, for example, by the pulverization conditions when producing the negative electrode active material. Generally known pulverizers can be used for pulverizing the negative electrode active material, and those to which mechanical energy such as shear force, impact force, compression force, and frictional force can be applied can be used without particular limitation. can. For example, pulverizers (ball mills, bead mills, vibration mills, etc.) that pulverize using the impact force and frictional force due to the kinetic energy of the pulverizing media, high-pressure gas of several atmospheres or more is ejected from the injection nozzle, and the raw material is Pulverizers (jet mills, etc.) that pulverize particles by accelerating the particles by impact and grinding, pulverizers (hammer mills) that pulverize raw material particles by impacting them with high-speed rotating hammers, pins, or discs , pin mills, disk mills, etc.).

When the negative electrode active material is obtained through a pulverization step, the particle size distribution may be adjusted by performing a classification treatment after pulverization. The classification method is not particularly limited, and can be selected from dry classification, wet classification, sieving, and the like. From the viewpoint of productivity, it is preferable to perform pulverization and classification collectively. For example, a coupling system of a jet mill and a cyclone makes it possible to classify the particles before re-agglomeration, and to easily obtain a desired particle size distribution shape.

When necessary (for example, when the aspect ratio of the negative electrode active material cannot be adjusted to the desired range by pulverization alone), the pulverized negative electrode active material is further subjected to surface modification treatment to adjust the aspect ratio. You may An apparatus for performing surface modification treatment is not particularly limited. For example, Mechanofusion system, Nobilta, Hybridization system and the like can be mentioned.

(Specific surface area calculated from nitrogen adsorption)
The negative electrode active material preferably has a specific surface area of 0.1 m ² /g to 10 m ² /g, more preferably 0.5 m ² /g to 5.0 m ² /g, calculated from nitrogen adsorption at 77 K. more preferably 1.0 m ² /g to 4.0 m ² /g, particularly preferably 1.0 m ² /g to 3.0 m ² /g. When the specific surface area of the negative electrode active material is 10 m ² /g or less, the increase in the initial irreversible capacity of the obtained lithium ion secondary battery tends to be suppressed. In addition, there is a tendency that the amount of the binder used when producing the negative electrode can be reduced. When the specific surface area of the negative electrode active material is 0.1 m ² /g or more, the contact area between the negative electrode active material and the electrolytic solution is sufficiently ensured, and good charge-discharge efficiency tends to be obtained.
The specific surface area calculated from the nitrogen adsorption at 77K can be calculated from the adsorption isotherm obtained from the nitrogen adsorption measurement at 77K using the BET method.

(Specific surface area and water vapor adsorption amount calculated from water vapor adsorption)
The negative electrode active material preferably has a specific surface area calculated from water vapor adsorption at 298 K of 6.5 m ² /g or less, more preferably 3.0 m ² /g or less, and more preferably 2.0 m ² /g. More preferably: When the specific surface area calculated from water vapor adsorption at 298 K is 6.5 m ² /g or less, the decomposition reaction that occurs at the interface between the negative electrode active material and the electrolyte can be suppressed, and the deterioration of high-temperature storage characteristics can be suppressed. tend to be The specific surface area calculated from water vapor adsorption at 298K may be 0.1 m ² /g or more, or may be 0.5 m ² /g or more.
Further, the water vapor adsorption amount up to a relative pressure of 0.95 at 298 K is preferably 8.5 cm ³ /g or less, more preferably 6.5 cm ³ /g or less, and 3.0 cm ³ /g or less. It is even more preferable to have When the amount of water vapor adsorption up to a relative pressure of 0.95 at 298 K is 8.5 cm ³ /g or less, the decomposition reaction that occurs at the interface between the negative electrode active material and the electrolytic solution can be suppressed, and the deterioration of high-temperature storage characteristics can be suppressed. tend to be The water vapor adsorption amount up to a relative pressure of 0.95 at 298 K may be 1.0 cm ³ /g or more, or 1.5 cm ³ /g or more.
The specific surface area calculated from the water vapor adsorption at 298K can be calculated using the BET method from the adsorption isotherm obtained from the water vapor adsorption measurement at 298K. The amount of water vapor adsorption up to a relative pressure of 0.95 at 298K can be calculated by measuring the water vapor adsorption up to a relative pressure of 0.95 at 298K by a multipoint method.

(Specific surface area and carbon dioxide adsorption amount calculated from carbon dioxide adsorption)
The negative electrode active material preferably has a specific surface area calculated from carbon dioxide adsorption at 273 K of 8.5 m ² /g or less, more preferably 5 m ² /g or less, and 1 m ² /g or less. is more preferred. When the specific surface area calculated from carbon dioxide adsorption at 273 K is 8.5 m ² /g or less, the decomposition reaction that occurs at the interface between the negative electrode active material and the electrolytic solution can be suppressed, and the deterioration of high-temperature storage characteristics can be prevented. tend to be suppressed. The specific surface area calculated from carbon dioxide adsorption at 273 K may be 0.01 m ² /g or more, or 0.1 m ² /g or more.
In addition, the carbon dioxide adsorption amount up to a relative pressure of 0.03 at 273 K is preferably 2 cm ³ /g or less, more preferably 0.5 cm ³ /g or less, and 0.1 cm ³ /g or less. is more preferred. When the amount of carbon dioxide adsorption up to a relative pressure of 0.03 at 273 K is 2 cm ³ /g or less, the decomposition reaction that occurs at the interface between the negative electrode active material and the electrolytic solution can be suppressed, and the deterioration of high-temperature storage characteristics can be suppressed. tend to The carbon dioxide adsorption amount up to a relative pressure of 0.03 at 273 K may be 0.005 cm ³ /g or more, or may be 0.01 cm ³ /g or more.
The specific surface area calculated from the carbon dioxide adsorption at 273K can be calculated from the adsorption isotherm obtained from the carbon dioxide adsorption measurement at 273K using the BET method. The amount of carbon dioxide adsorption up to a relative pressure of 0.03 at 273K can be calculated by measuring the carbon dioxide adsorption up to a relative pressure of 0.03 at 273K by a multipoint method.

(Ratio of specific surface area calculated from water vapor adsorption to specific surface area calculated from nitrogen adsorption)
In the negative electrode active material, the ratio of the specific surface area calculated from water vapor adsorption at 298 K to the specific surface area calculated from nitrogen adsorption at 77 K (S _H2O /S _N2 ) is 0.60 or less, and 0.40 or less. It is preferably 0.30 or less, more preferably 0.30 or less. When the ratio (S _H2O /S _N2 ) is 0.60 or less, the decomposition reaction that occurs at the interface between the negative electrode active material and the electrolytic solution can be suppressed, and electrode expansion and deterioration of high-temperature storage characteristics can be suppressed. There is a tendency.
The specific surface area calculated from water vapor adsorption can be calculated using the BET method from the adsorption isotherm obtained from the water vapor adsorption measurement at 298K. Similarly, the specific surface area calculated from nitrogen adsorption can be calculated using the BET method from the adsorption isotherm obtained from the nitrogen adsorption measurement at 77K. The ratio (S _H2O /S _N2 ) may be 0.01 or more, or 0.05 or more.

From the ratio (S _H2O /S _N2 ) mentioned above, the hydrophilicity of the material surface can usually be evaluated. A large ratio (S _H2O /S _N2 ) in the negative electrode active material of the present disclosure means that the surface of the active material is hydrophilic.
Here, it is generally known that the surface of silicon oxide is hydrophilic and the surface of carbon is hydrophobic. That is, when the ratio (S _H2O /S _N2 ) in the negative electrode active material of the present disclosure is small, the hydrophobic carbon covers the entire surface of the hydrophilic silicon oxide as shown in FIG. 1 or 2 described later. It means that it is fully covered. On the other hand, when the ratio (S _H2O /S _N2 ) is large, carbon partially exists on the surface of the silicon oxide, and the surface of the silicon oxide is partially exposed as shown in FIGS. means that Therefore, from the evaluation of the ratio (S _H2O /S _N2 ), the carbon coating state (degree of silicon oxide exposure) in the negative electrode active material of the present disclosure can be easily evaluated.

(Volume average particle size)
The volume average particle size of the negative electrode active material is preferably in the range of 0.1 μm to 20 μm, more preferably 0.5 μm to 10 μm. The volume average particle diameter of the negative electrode active material is the particle diameter (D50%) when the volume accumulation from the small diameter side is 50% in the volume-based particle size distribution curve. If the volume average particle size is 0.1 μm or more, the specific surface area does not become too large, so the increase in the contact area with the electrolytic solution is suppressed, and the decrease in charge-discharge efficiency tends to be less likely to occur. If the volume average particle size is 20 μm or less, unevenness is less likely to occur on the electrode surface, and short circuits in the battery tend to be less likely to occur. Furthermore, since the diffusion distance of lithium from the particle surface to the inside does not become too long, there is a tendency that the acceptability of lithium is less likely to decrease and the charge/discharge efficiency is less likely to decrease.
A known method such as a laser diffraction particle size distribution analyzer can be used to measure the volume average particle size.

In the volume cumulative distribution curve obtained by the laser diffraction/scattering method of the negative electrode active material, the accumulation from the small particle side is 10% with respect to the particle diameter (D90%) when the accumulation from the small particle side is 90%. The ratio (D10%/D90%) of the particle diameters (D10%) is preferably 0.1 or more, more preferably 0.2 or more, and further preferably 0.3 or more . When the value of the ratio (D10%/D90%) of the negative electrode active material is 0.1 or more, the difference in the amount of change in expansion and contraction when used as an electrode becomes small, and deterioration in cycle characteristics tends to be suppressed. be. The ratio (D10%/D90%) is preferably 1.0 or less, more preferably 0.8 or less, even more preferably 0.6 or less.

The value of the negative electrode active material ratio (D10%/D90%) is an index of the width of the particle size distribution of the negative electrode active material, and a large value means that the particle size distribution of the negative electrode active material is narrow.

D90% and D10% of the negative electrode active material are measured by the laser diffraction/scattering method using a sample in which the negative electrode active material is dispersed in water. The particle diameter when the accumulation reaches 90% and the particle diameter when the volume accumulation from the small particle diameter side reaches 10% are obtained.

(organic matter)
The negative electrode active material (SiO-based negative electrode active material) of the present disclosure may be coated with an organic substance, if necessary. The coating treatment with an organic substance tends to further improve the initial discharge capacity, the initial charge/discharge efficiency, and the recovery rate after charge/discharge. This is probably because the coating treatment with the organic substance reduces the specific surface area of the negative electrode active material and suppresses the reaction with the electrolyte. The number of organic substances contained in the negative electrode active material may be one or two or more.

The content of the organic substance is preferably 0.1% by mass to 5.0% by mass of the entire negative electrode active material. When the content of the organic substance is within the above range, the effect of improving the recovery rate after charge/discharge tends to be sufficiently obtained while suppressing the decrease in conductivity. The content of the organic substance in the entire negative electrode active material is more preferably 0.2% by mass to 3.0% by mass, and even more preferably 0.3% by mass to 1.0% by mass.

Whether or not the negative electrode active material contains an organic matter can be determined, for example, by heating the sufficiently dried negative electrode active material to a temperature (for example, 300° C.) that is higher than the temperature at which the organic matter decomposes and lower than the temperature at which carbon decomposes. can be confirmed by measuring the mass of the negative electrode active material after the organic matter is decomposed. Specifically, when the mass of the negative electrode active material before heating is A (g) and the mass of the negative electrode active material after heating is B (g), it is represented by {(AB)/A}×100. If the rate of change in mass is 0.1% or more, it can be determined that the negative electrode active material contains an organic substance.

The rate of change in mass is preferably 0.1% to 5.0%, more preferably 0.3% to 1.0%. When the rate of change is 0.1% or more, a sufficient amount of organic matter is present on the surface of the SiO—C particles, so there is a tendency that the effect of including the organic matter is sufficiently obtained.

The kind of organic matter is not particularly limited. For example, starch derivatives having a basic structure of C ₆ H ₁₀ O ₅ , viscous polysaccharides having a basic structure of C ₆ H ₁₀ O ₅ , water-soluble cellulose derivatives having a basic structure of C ₆ H ₁₀ O ₅ , polyuronides and At least one selected from the group consisting of water-soluble synthetic resins can be used.

Specific examples of starch derivatives having a C ₆ H ₁₀ O ₅ basic structure include hydroxyalkyl starches such as acetate starch, phosphate starch, carboxymethyl starch, and hydroxyethyl starch. Specific examples of viscous polysaccharides having a basic structure of C ₆ H ₁₀ O ₅ include pullulan and dextrin. Examples of water-soluble cellulose derivatives having a C ₆ H ₁₀ O ₅ basic structure include carboxymethyl cellulose, methyl cellulose, hydroxyethyl cellulose and hydroxypropyl cellulose. Polyuronides include pectic acid, alginic acid and the like. Water-soluble synthetic resins include water-soluble acrylic resins, water-soluble epoxy resins, water-soluble polyester resins, water-soluble polyamide resins, etc. More specifically, polyvinyl alcohol, polyacrylic acid, polyacrylate, polyvinyl Sulfonic acid, polyvinylsulfonate, poly-4-vinylphenol, poly-4-vinylphenol salt, polystyrenesulfonic acid, polystyrenesulfonate, polyanilinesulfonic acid and the like. Organic substances may be used in the form of metal salts, alkylene glycol esters, or the like.

From the viewpoint of reducing the specific surface area of the negative electrode active material, the organic matter is part or all of the SiO—C particles (when the conductive particles described later are present on the surface of the SiO—C particles, the surface). is preferably covered.

There is no particular limitation on the method of causing the organic substance to exist on part or all of the surface of the SiO—C particles. For example, the SiO—C particles are added to a liquid in which the organic matter is dissolved or dispersed, and the liquid is stirred as necessary to allow the organic matter to adhere to the SiO—C particles. After that, the SiO--C particles with the organic matter adhered thereto are taken out from the liquid, and if necessary, dried to obtain the SiO--C particles with the organic matter adhered to the surface.
In the above method, the temperature of the liquid during stirring is not particularly limited, and can be selected, for example, from 5°C to 95°C. The temperature during drying is not particularly limited, and can be selected from, for example, 50°C to 200°C. The organic substance content in the solution is not particularly limited, and can be selected from, for example, 0.1% by mass to 20% by mass.

(Conductive particles)
In addition, the negative electrode active material (SiO-based negative electrode active material) of the present disclosure may contain conductive particles, if necessary. When the negative electrode active material contains the conductive particles, even if the silicon oxide particles expand and contract, the conductive particles tend to come into contact with each other, thereby making it easier to ensure conduction. In addition, the resistance value of the entire negative electrode active material tends to decrease. As a result, a decrease in capacity due to repeated charging and discharging is suppressed, and good cycle characteristics tend to be maintained.

From the viewpoint of ensuring conduction by contact between the negative electrode active materials, the conductive particles are preferably present on the surface of the SiO—C particles.

The type of conductive particles is not particularly limited. For example, at least one selected from the group consisting of granular graphite and carbon black is preferable, and granular graphite is preferable from the viewpoint of improving cycle characteristics. Granular graphite includes particles of artificial graphite, natural graphite, MC (mesophase carbon), and the like. Examples of carbon black include acetylene black, ketjen black, thermal black, furnace black and the like, and acetylene black is preferred from the viewpoint of conductivity.

Granular graphite preferably has higher crystallinity than carbon existing on the surface of the silicon oxide particles from the viewpoint of improving both battery capacity and charge/discharge efficiency. Specifically, the granular graphite preferably has an average interplanar spacing (d ₀₀₂ ) value of 0.335 nm to 0.347 nm, which is obtained by measurement based on the Gakushin method, and 0.335 nm to 0.345 nm. is more preferably 0.335 nm to 0.340 nm, and particularly preferably 0.335 nm to 0.337 nm. When the average interplanar spacing of granular graphite is 0.347 nm or less, the granular graphite has high crystallinity, and both battery capacity and charge/discharge efficiency tend to improve. On the other hand, since the theoretical value of the average interplanar spacing of graphite crystals is 0.335 nm, when the average interplanar spacing of granular graphite is close to this value, both battery capacity and charge/discharge efficiency tend to improve.

The shape of the granular graphite is not particularly limited, and may be flat graphite or spherical graphite. From the viewpoint of improving cycle characteristics, flat graphite is preferable.

In the present disclosure, flat graphite means graphite whose aspect ratio is not 1 (the lengths of the minor axis and the major axis are not equal). Examples of flat graphite include graphite having a shape such as scaly, scaly, or massive.

Although the aspect ratio of the conductive particles is not particularly limited, the average aspect ratio is preferably 0.3 or less, and 0.3 or less, from the viewpoint of easiness to ensure conduction between the conductive particles and improvement of cycle characteristics. It is more preferably 2 or less.

The aspect ratio of the conductive particles is a value measured by SEM observation. Specifically, for each of 100 arbitrarily selected conductive particles in the SEM image, the length in the major axis direction is A, and the length in the minor axis direction (the length in the thickness direction in the case of flat graphite) is It is a value calculated as B/A when B is assumed. The average aspect ratio is the arithmetic average of the aspect ratios of 100 conductive particles.

The conductive particles may be either primary particles (single particles) or secondary particles (granulated particles) formed from a plurality of primary particles. Further, the flat graphite may be porous graphite particles.

The content of the conductive particles is preferably 1.0% by mass to 10.0% by mass, more preferably 2.0% by mass to 9.0% by mass, in terms of improving cycle characteristics. more preferably 3.0% by mass to 8.0% by mass.

The content of the conductive particles can be determined, for example, by high-frequency firing-infrared analysis. In the high-frequency sintering-infrared analysis method, for example, a simultaneous carbon and sulfur analyzer (CSLS600, LECO Japan LLC) can be used. Since this measurement also includes the carbon content of the SiO—C particles, it may be subtracted from the separately measured carbon content.

A method for producing a negative electrode active material containing conductive particles is not particularly limited, and includes wet methods and dry methods.

As a method for producing a negative electrode active material containing conductive particles by a wet method, for example, SiO—C particles are added to a particle dispersion liquid in which conductive particles are dispersed in a dispersion medium, and after stirring, a dryer or the like is used. and removing the dispersion medium. The dispersion medium to be used is not particularly limited, and water, an organic solvent, or the like can be used. The organic solvent may be a water-soluble organic solvent such as alcohol or a water-insoluble organic solvent. The dispersion medium may contain a dispersant from the viewpoint of enhancing the dispersibility of the conductive particles and making the adhesion of the SiO—C particles to the surface more uniform. A dispersant can be selected according to the type of dispersion medium used. For example, when the dispersion medium is aqueous, carboxymethylcellulose is preferable from the viewpoint of dispersion stability.

Examples of a method for producing a negative electrode active material containing conductive particles by a dry method include a method of adding conductive particles together with a carbon source when applying a carbon source of carbon to the surface of silicon oxide particles. . Specifically, for example, a method of mixing silicon oxide particles with a carbon source and conductive particles and applying mechanical energy (for example, mechanochemical treatment) may be used.

If necessary, the obtained negative electrode active material may be further classified. The classification treatment can be performed using a sieve machine or the like.

An example of the configuration of the negative electrode active material will be described below with reference to the drawings.
The negative electrode active material has carbon on part or all of the surface of the silicon oxide particles. 1 to 5 are schematic cross-sectional views showing examples of the structure of the negative electrode active material. In FIG. 1, carbon 10 covers the entire surface of silicon oxide particles 20 . In FIG. 2, the carbon 10 covers the entire surface of the silicon oxide particles 20, but the thickness varies. In FIG. 3, carbon 10 is partially present on the surfaces of silicon oxide particles 20, and the surfaces of silicon oxide particles 20 are partially exposed. In FIG. 4 , carbon 10 particles having a smaller particle size than the silicon oxide particles 20 are present on the surfaces of the silicon oxide particles 20 . FIG. 5 shows a modification of FIG. 4, in which the carbon 10 particles are scaly. In FIGS. 1 to 5, the shape of the silicon oxide particles 20 is schematically represented as spherical (circular as a cross-sectional shape). Any shape (shape with corners) or the like may be used.

6A and 6B are cross-sectional views enlarging a part of the negative electrode active material of FIGS. 1 to 3. FIG. FIG. 6A illustrates one mode of the state of carbon 10 in the negative electrode active material, and FIG. 6B illustrates another mode of the state of carbon 10 in the negative electrode active material. 1 to 3, the carbon 10 may be in a continuous layer state as shown in FIG. 6A, or the carbon 10 may be composed of fine carbon particles 12 as shown in FIG. 6B. Although FIG. 6B shows a state in which the contour shape of the fine carbon particles 12 remains, the fine carbon particles 12 may be bonded to each other. When the fine particles 12 of carbon are bonded together, the carbon 10 may form a continuous layer as shown in FIG. 6A, but voids may be formed inside.
When the carbon 10 is particles, the carbon 10 particles partially exist on the surface of the silicon oxide particles 20 as shown in FIG. The carbon particles 12 may be present on the entire surface of the silicon oxide particles 20 as shown in FIG. 6B.

The negative electrode active material (SiO-based negative electrode active material) of the present disclosure may further contain a carbon-based negative electrode active material, if necessary. Depending on the type of carbon-based negative electrode active material used in combination, improvement in charge/discharge efficiency, improvement in cycle characteristics, effect of suppressing electrode expansion, and the like can be obtained. The carbon-based negative electrode active material used in combination with the negative electrode active material of the present disclosure may be one type or two or more types.

As the carbon-based negative electrode active material, known carbon-based materials conventionally known as active materials for negative electrodes of lithium ion secondary batteries can be used. Negative electrode active materials made of carbon materials such as natural graphites such as graphite, artificial graphite, and amorphous carbon can be used. In addition, these carbon-based negative electrode active materials may have carbon (such as the carbon described above) on part or all of the surface.

When the negative electrode active material of the present disclosure is used in combination with the carbon-based negative electrode active material, the ratio (A:B) of the negative electrode active material (A) and the carbon-based negative electrode active material (B) of the present disclosure is It is possible to adjust accordingly. For example, from the viewpoint of the effect of suppressing the expansion of the electrode, it is preferably 0.1:99.9 to 20:80, more preferably 0.5:99.5 to 15:85, on a mass basis. More preferably, it is 1:99 to 10:90.

<Negative electrode for lithium ion secondary battery>
A negative electrode for a lithium ion secondary battery of the present disclosure (hereinafter sometimes abbreviated as “negative electrode”) includes a current collector, a negative electrode material layer containing the above-described negative electrode active material provided on the current collector, have

The negative electrode can be produced, for example, by forming a negative electrode material layer on a current collector using the composition containing the negative electrode active material described above.
Examples of the composition containing the negative electrode active material include those obtained by mixing the negative electrode active material with an organic binder, a solvent, a thickener, a conductive aid, a carbonaceous negative electrode active material, and the like.

Specific examples of organic binders include styrene-butadiene copolymer; (Meth)acrylic copolymers obtained by copolymerizing unsaturated carboxylic acid esters and ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid, and maleic acid; polyvinylidene fluoride, polymer compounds such as polyethylene oxide, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polyimide, and polyamideimide; In addition, "(meth)acrylate" means "acrylate" and "methacrylate" corresponding thereto. The same applies to other similar expressions such as "(meth)acrylic copolymer". The organic binder may be one dispersed or dissolved in water, or one dissolved in an organic solvent such as N-methyl-2-pyrrolidone (NMP). An organic binder may be used individually by 1 type, or may be used in combination of 2 or more type.

From the viewpoint of adhesion, among organic binders, organic binders having a main skeleton of polyacrylonitrile, polyimide, or polyamideimide are preferable. Organic binders whose main skeleton is polyacrylonitrile are more preferred. Organic binders having polyacrylonitrile as a main skeleton include, for example, those obtained by adding acrylic acid that imparts adhesiveness and a linear ether group that imparts flexibility to a polyacrylonitrile skeleton.

The content of the organic binder in the negative electrode material layer is preferably 0.1% by mass to 20% by mass, more preferably 0.2% by mass to 20% by mass, and 0.3% by mass. More preferably, it is up to 15% by mass. When the content of the organic binder in the negative electrode material layer is 0.1% by mass or more, good adhesion is obtained, and destruction of the negative electrode due to expansion and contraction during charging and discharging is suppressed. There is a tendency. On the other hand, when it is 20% by mass or less, it tends to be possible to suppress an increase in electrode resistance.

Specific examples of thickeners include carboxymethylcellulose, methylcellulose, hydroxymethylcellulose, ethylcellulose, polyvinyl alcohol, polyacrylic acid (salt), oxidized starch, phosphorylated starch, casein and the like. A thickener may be used individually by 1 type, or may be used in combination of 2 or more type.

Specific examples of the solvent include N-methylpyrrolidone, dimethylacetamide, dimethylformamide, γ-butyrolactone and the like. A solvent may be used individually by 1 type, or may be used in combination of 2 or more type.

Specific examples of conductive aids include carbon black, acetylene black, conductive oxides, and conductive nitrides. A conductive support agent may be used individually by 1 type, or may be used in combination of 2 or more types. The content of the conductive aid in the negative electrode material layer is preferably 0.1% by mass to 20% by mass.

Materials for the current collector include aluminum, copper, nickel, titanium, stainless steel, porous metal (foamed metal), carbon paper, and the like. Examples of the shape of the current collector include a foil shape, a perforated foil shape, a mesh shape, and the like.

As a method for forming a negative electrode material layer on a current collector using a composition containing a negative electrode active material, a coating solution containing a negative electrode active material is applied onto a current collector, and volatile substances such as a solvent are removed. , a method of pressure molding, and a method of integrating a negative electrode material layer formed into a sheet-like, pellet-like shape, etc. with a current collector, and the like.
Examples of the method for applying the coating liquid to the current collector include metal mask printing, electrostatic coating, dip coating, spray coating, roll coating, doctor blade, gravure coating, and screen printing. . Pressurizing treatment after coating can be performed by a flat plate press, a calendar roll, or the like.
Integration of the negative electrode material layer and the current collector can be performed, for example, by roll integration, press integration, or a combination thereof.

The negative electrode material layer formed on the current collector or the negative electrode material layer integrated with the current collector may be subjected to heat treatment according to the type of organic binder used. For example, when using an organic binder having a main skeleton of polyacrylonitrile, it is preferable to heat-treat at 100 ° C. to 180 ° C. When using an organic binder having a main skeleton of polyimide or polyamideimide, 150 It is preferable to heat-treat at 0°C to 450°C.
This heat treatment promotes the removal of the solvent and the hardening of the organic binder to increase the strength, and tends to improve the adhesion between the negative electrode active material and the adhesion between the negative electrode active material and the current collector. Note that 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 material layer before the heat treatment. The electrode density can be adjusted by pressurizing. The electrode density is, for example, preferably 1.25 g/cm ³ to 1.9 g/cm ³ , more preferably 1.5 g/cm ³ to 1.85 g/cm ³ , and 1.6 g/cm 3 ³ to 1.8 g/cm ³ is more preferable. Regarding the electrode density, the higher the value, the more the volume capacity of the negative electrode tends to improve, and the adhesion between the negative electrode active material and the adhesion between the negative electrode active material and the current collector tend to improve. .

<Lithium ion secondary battery>
A lithium ion secondary battery of the present disclosure includes a positive electrode, the negative electrode described above, and an electrolyte.
Lithium ion secondary batteries are produced, for example, by placing the negative electrode and the positive electrode in a battery container so that the negative electrode and the positive electrode face each other with a separator interposed therebetween, and injecting an electrolytic solution obtained by dissolving the electrolyte in an organic solvent into the battery container. can do.
A solid electrolyte may be used as the electrolyte in the lithium ion secondary battery of the present disclosure. Since the solid electrolyte can also serve as a separator, the lithium ion secondary battery does not need to use a separator when the solid electrolyte is used as the electrolyte.

The positive electrode can be obtained by forming a positive electrode material layer on the surface of the current collector in the same manner as the negative electrode. As the current collector for the positive electrode, the same current collector as for the negative electrode can be used.

The material used for the positive electrode (also referred to as positive electrode material) may be any compound capable of doping or intercalating lithium ions, such as lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganate (LiMnO ₂ ) and the like.

For the positive electrode, for example, a positive electrode coating solution is prepared by mixing a positive electrode material, an organic binder such as polyvinylidene fluoride, and a solvent such as N-methyl-2-pyrrolidone or γ-butyrolactone, and this positive electrode coating solution is prepared. is applied to at least one surface of a current collector such as an aluminum foil, the solvent is removed by drying, and pressure treatment is performed as necessary.
A conductive aid may be added to the positive electrode coating liquid. Examples of conductive aids include carbon black, acetylene black, conductive oxides, and conductive nitrides. These conductive aids may be used singly or in combination of two or more.

_LiPF6 , LiClO4, _LiBF4 , _LiClF4 , _LiAsF6 , _LiSbF6 , _LiAlO4 , _LiAlCl4 , LiN _{( CF3SO2} ) ₂ , LiN _{( C2F5SO2} ) ₂ , _{LiC (} CF ₃ SO ₂ ) ₃ , LiCl, LiI and the like.

Examples of organic solvents that dissolve electrolytes include propylene carbonate, ethylene carbonate, diethyl carbonate, ethylmethyl carbonate, vinylene carbonate, γ-butyrolactone, 1,2-dimethoxyethane and 2-methyltetrahydrofuran.

Examples of separators include paper separators, polypropylene separators, polyethylene separators, glass fiber separators, and the like.

A method for manufacturing a lithium ion secondary battery is not particularly limited. For example, a cylindrical lithium ion secondary battery can be manufactured by the following steps. First, two electrodes, a positive electrode and a negative electrode, are wound with a separator interposed therebetween. The obtained spirally wound group is inserted into a battery can, and a tab terminal welded to the current collector of the negative electrode in advance is welded to the bottom of the battery can. An electrolytic solution is injected into the resulting battery can. Further, the tab terminal previously welded to the current collector of the positive electrode is welded to the lid of the battery, and the lid is placed on top of the battery can via an insulating gasket. A lithium ion secondary battery can be obtained by crimping and sealing the portion where the lid and the battery can are in contact with each other.

The form of the lithium ion secondary battery is not particularly limited, and lithium ion secondary batteries such as paper-type batteries, button-type batteries, coin-type batteries, stack-type batteries, cylindrical batteries, and rectangular batteries can be mentioned.

The negative electrode active material of the present disclosure is not limited to lithium ion secondary batteries, and can be applied to general electrochemical devices having a charge/discharge mechanism of intercalating and deintercalating lithium ions.

EXAMPLES Hereinafter, the above-described embodiments will be described in more detail based on examples, but the above-described embodiments are not limited to the following examples. Unless otherwise specified, "%" is based on mass.

[Example 1]
(Preparation of negative electrode active material)
Mass silicon oxide (Kojundo Chemical Laboratory Co., Ltd., standard 10 mm to 30 mm square) was coarsely pulverized in a mortar to obtain silicon oxide particles. After further pulverizing the silicon oxide particles with a jet mill (lab type, Nippon Pneumatic Industry Co., Ltd.), they were sized with a 300M (300 mesh) test sieve, and the volume average particle size (D50%) of silicon was 5 μm. Oxide particles were obtained. The average particle size was measured by the following method.

<Measurement of volume average particle size>
A measurement sample (5 mg) was placed in a 0.01% by mass aqueous solution of a surfactant (Esomin T/15, Lion Corporation) and dispersed with a vibration stirrer. The resulting dispersion was placed in a sample tank of a laser diffraction particle size distribution analyzer (SALD3000J, Shimadzu Corporation), circulated with a pump while applying ultrasonic waves, and measured by a laser diffraction method. The measurement conditions were as follows. The volume-accumulated 50% particle size (D50%) of the obtained particle size distribution was taken as the volume average particle size. In the following examples, the particle size was measured in the same manner.
・Light source: red semiconductor laser (690 nm)
・ Absorbance: 0.10 to 0.15
・Refractive index: 2.00 to 0.20

Silicon oxide particles having a volume average particle diameter (D50%) of 5 μm obtained after the silicon oxide pulverization step were subjected to chemical vapor deposition treatment under the following conditions to form a carbon film on the surface of the silicon oxide particles. .
1000 g of silicon oxide particles were placed in a batch heating furnace (rotary kiln furnace). Next, the temperature was raised to 950° C. under the temperature raising condition of 300° C./hour, and then a mixed gas of acetylene gas (carbon source)/nitrogen gas was introduced at 10 L/min (partial pressure of acetylene gas: 10% ), the chemical vapor deposition treatment was carried out under the conditions of 2 hours. After the treatment, the temperature was lowered to obtain a chemical vapor deposition product. The heat treatment was carried out under conditions that cause a disproportionation reaction of silicon oxide.

The resulting chemical vapor deposition product was pulverized with a mortar and sieved with a 300M (300 mesh) test sieve to obtain a negative electrode active material (SiO—C particles) were obtained. The volume average particle size (D50%) of the negative electrode active material was measured in the same manner as the method for measuring the volume average particle size of the silicon oxide particles. Also, the value of the ratio (D10%/D90%) was calculated from the values obtained by measuring D10% and D90%.

<Measurement of carbon content>
The carbon content of the negative electrode active material was measured by high-frequency firing-infrared analysis. The high-frequency firing-infrared analysis method is an analysis method in which a sample is heated and burned in an oxygen stream in a high-frequency furnace, carbon and sulfur in the sample are converted to CO ₂ and SO ₂ , respectively, and quantified by an infrared absorption method. The measuring apparatus, measuring conditions, etc. are as follows.
・Equipment: carbon and sulfur simultaneous analysis equipment (CSLS600, LECO Japan LLC)
・Frequency: 18MHz
・High frequency output: 1600W
・ Sample mass: about 0.05 g
・Analysis time: Use automatic mode in device setting mode ・Burning aid: Fe + W/Sn
・ Standard sample: Leco 501-024 (C: 3.03% ± 0.04 S: 0.055% ± 0.002) 97
・ Number of measurements: 2 times (The value of the content rate in the table is the average value of the measured values of 2 times)

<Measurement of crystallite size of silicon>
The X-ray diffraction peak intensity of the negative electrode active material was measured using a powder X-ray diffractometer (MultiFlex (2 kW), Rigaku Co., Ltd.), and the crystallite size of silicon was measured. Specifically, it was calculated using Scherrer's formula from the half-value width of the peak derived from the Si (111) crystal plane present near 2θ=28.4°. The measurement conditions were as follows.

・ Radiation source: CuKα ray (wavelength: 0.15406 nm)
・Measuring range: 2θ = 10° to 40°
・Sampling step width: 0.02°
・Scan speed: 1°/min ・Tube current: 40mA
・Tube voltage: 40 kV
・Divergence slit: 1°
・Scattering slit: 1°
・Light receiving slit: 0.3 mm

The obtained profile was subjected to background (BG) removal and peak separation using structural analysis software (JADE6, Rigaku Co., Ltd.) attached to the above apparatus under the following settings.

[Kα2 peak removal and background removal]
・Kα1/Kα2 intensity ratio: 2.0
・BG curve up and down (σ) from BG point: 0.0

[Peak specification]
· Peak derived from Si (111): 28.4 ° ± 0.3 °
・Peak derived from _SiO2 : 21° ± 0.3°

[Peak Separation]
・Profile shape function: Pseudo-Voigt
・Fixed background

The half width of the peak derived from Si(111) derived from the structure analysis software with the above settings was read, and the crystallite size of silicon was calculated from the following Scherrer equation.
D=Kλ/B cos θ
B=(B _obs ² -b ² ) ^1/2
D: crystallite size (nm)
K: Scherrer constant (0.94)
λ: source wavelength (0.15406 nm)
θ: measured half width peak angle B _obs : half width (measured value obtained from structural analysis software)
b: measured half width of standard silicon (Si)

<Measurement of X-ray diffraction peak intensity ratio (P _Si /P _SiO2 )>
The negative electrode active material was analyzed using a powder X-ray diffractometer (MultiFlex (2 kW), Rigaku Corporation) in the same manner as described above. In the negative electrode active material, the ratio of the X-ray diffraction peak intensity at 2θ = 27° to 29° derived from Si to the X-ray diffraction peak intensity at 2θ = 20° to 25° derived from SiO ₂ (P _Si /P _SiO2 ) was calculated.

<Measurement of average aspect ratio>
The average aspect ratio of the negative electrode active material was calculated by the method described above using an SEM device (TM-1000, Hitachi High-Technologies Corporation).
For the negative electrode active material containing conductive particles, which will be described later, only SiO—C particles were selected in advance by EDX elemental analysis, and the average aspect ratio was calculated.

<Measurement of R value>
The R value was calculated from the spectrum measured using a Raman spectrum measuring device (NSR-1000, JASCO Corporation). The measurement conditions were as follows.
・Laser wavelength: 532 nm
・Irradiation intensity: 1.5 mW (value measured with a laser power monitor)
・Irradiation time: 60 seconds ・Irradiation area: 4 μm ²
・Measurement range: 830 cm ^-1 to 1940 cm ^-1
・Baseline: 1050 cm ^-1 to 1750 cm ^-1

The wavenumber of the obtained spectrum is the wavenumber of each peak obtained by measuring the reference material indene (Wako First Class, Wako Pure Chemical Industries, Ltd.) under the same conditions as described above, and the theoretical value of the wavenumber of each peak of indene. Correction was performed using a calibration curve obtained from the difference in .
In the profile obtained after correction, the intensity of the peak appearing near 1360 cm ^-1 is Id, the intensity of the peak appearing near 1580 cm ^-1 is Ig, and the intensity ratio Id/Ig (D/G) of both peaks is It was obtained as an R value.

<Measurement of _N2 specific surface area: specific surface area calculated from nitrogen adsorption>
After vacuum drying the negative electrode active material at 200 ° C. for 2 hours, using a high-speed specific surface area / pore size distribution measuring device (ASAP2020, Micromeritics Japan G.K.), nitrogen adsorption at liquid nitrogen temperature (77 K) was performed at multiple points. The specific surface area of the negative electrode active material was calculated by the BET method (relative pressure range: 0.05 to 0.2).

<Measurement of CO ₂ specific surface area: specific surface area calculated from carbon dioxide adsorption>
After vacuum drying the negative electrode active material at 200 ° C. for 2 hours, carbon dioxide adsorption at 273 K was measured by a multipoint method using a fully automatic gas adsorption amount measuring device (AS1-MP, AS-iQ, Quantachrome), The specific surface area of the negative electrode active material was calculated by the BET method.

< _CO2 adsorption amount>
After vacuum drying the negative electrode active material at 200 ° C. for 2 hours, using a fully automatic gas adsorption amount measuring device (AS1-MP, AS-iQ, Quantachrome), carbon dioxide adsorption up to a relative pressure of 0.03 at 273 K was measured. Measurement was performed by the multipoint method, and the total amount of adsorption was calculated.

<Measurement of H ₂ O specific surface area: specific surface area calculated from water vapor adsorption>
After vacuum drying the negative electrode active material at 100 ° C. for 2 hours, water vapor adsorption at 298 K was measured by the multipoint method using a high-precision fully automatic gas adsorption measurement device (BELSORP18, Microtrac Bell), and the BET method. A specific surface area of the negative electrode active material was calculated.

<H ₂ O adsorption amount>
After vacuum-drying the negative electrode active material at 100 ° C. for 2 hours, using a high-precision fully automatic gas adsorption measurement device (BELSORP18, Microtrac Bell), water vapor adsorption up to a relative pressure of 0.95 at 298 K was performed by a multipoint method. , and the total amount of adsorption was calculated.

<Ratio of specific surface area calculated from water vapor adsorption to specific surface area calculated from nitrogen adsorption (ratio (S _H2O /S _N2 ))>
Using the H ₂ O specific surface area and N ₂ specific surface area calculated by the above method, the ratio of the specific surface area calculated by water vapor adsorption to the specific surface area calculated by nitrogen adsorption was calculated.

(Preparation of negative electrode)
Negative electrode active material powder (79.0% by mass), Ketjenblack powder (6.0% by mass) as a conductive agent, polyacrylonitrile as a main skeleton as a binder, acrylic acid and a linear ether group added A binder (15.0% by mass) was added and then kneaded to prepare a negative electrode composition. This negative electrode composition was applied to the glossy surface of the electrolytic copper foil so that the coating amount was 2.5 mg/cm ² , pre-dried at 90° C. for 2 hours, and roll-pressed to a density of 1.30 g/cm2. It was adjusted to be cm ³ . After that, a curing treatment was performed by drying at 120° C. for 4 hours in a vacuum atmosphere to obtain a negative electrode.

(Production of lithium ion secondary battery)
The negative electrode obtained above, metal lithium as the counter electrode, ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) containing 1M _LiPF6 as the electrolyte (volume ratio 1:1:1) and vinylene A 2016-type coin cell was fabricated using a mixed solution with carbonate (VC) (1.0% by mass), a 25 μm-thick polyethylene microporous membrane as a separator, and a 250 μm-thick copper plate as a spacer.

<Battery performance (initial discharge capacity and initial charge/discharge efficiency)>
The battery obtained above was placed in a constant temperature bath maintained at 25° C., and was charged at a constant current of 0.45 mA/cm ² to 0 V. After that, the current was 0.02 mA/cm ² at a constant voltage of 0 V. was further charged until it decayed to a value corresponding to , and the initial charge capacity was measured. After charging, the battery was rested for 30 minutes and then discharged. Discharge was performed at 0.45 mA/cm ² until the voltage reached 1.5 V, and the initial discharge capacity was measured. At this time, the capacity was converted to the mass of the negative electrode active material used. The value obtained by dividing the initial discharge capacity by the initial charge capacity and multiplying by 100 was calculated as the initial charge/discharge efficiency (%). Table 1 shows the results.

<Cycle characteristics>
The battery obtained above was placed in a constant temperature bath maintained at 25° C., and was charged at a constant current of 0.45 mA/cm ² to 0 V. After that, the current was 0.02 mA/cm ² at a constant voltage of 0 V. was further charged until it decayed to a value corresponding to . After charging, the battery was rested for 30 minutes and then discharged. Discharge was performed at 0.45 mA/cm ² to 1.5V. This charging and discharging was defined as one cycle, and a cycle test was conducted in which one cycle was performed 10 times, and the cycle characteristics calculated by the following formula were evaluated. Table 1 shows the results.
Formula: Cycle characteristics (10 cycle capacity retention rate) = (discharge capacity at 10th cycle/discharge capacity at 1st cycle) x 100 (%)

<High temperature storage characteristics (maintenance rate and recovery rate)>
The battery obtained above was placed in a constant temperature bath maintained at 25° C. and charged at a constant current of 0.45 mA/cm ² to 0 V. Then, the current was reduced to 0.02 mA/cm ² at a constant voltage of 0 V. It was further charged until it decayed to the corresponding value. After charging, the battery was rested for 30 minutes and then discharged. Discharge was performed at 0.45 mA/cm ² to 1.5V.
Next, after the second cycle charging was performed under the same conditions as above, the battery in the charged state was placed in a constant temperature bath maintained at 70° C. and stored for 72 hours. After that, it was placed in the constant temperature bath maintained at 25° C. again, and discharged at 0.45 mA/cm ² to 1.5 V. The ratio of the discharge capacity immediately after storage at 70° C. to the initial discharge capacity was defined as the retention rate of storage characteristics. Table 1 shows the results.
Then, in a constant temperature bath at 25° C., a third cycle charge/discharge test was performed under the same conditions as above. The ratio of the discharge capacity at the third cycle to the initial discharge capacity was defined as the recovery rate of storage characteristics. Table 1 shows the results.

<Expansion rate>
The battery obtained above was placed in a constant temperature bath maintained at 25° C. and charged at a constant current of 0.45 mA/cm ² to 0 V. Then, the current was reduced to 0.02 mA/cm ² at a constant voltage of 0 V. It was further charged until it decayed to the corresponding value. After charging, the battery was rested for 30 minutes and then discharged. Discharge was performed at 0.45 mA/cm ² to 1.5V.
Next, after the second cycle of charging was performed under the same conditions as above, the coin cell was disassembled and the thickness of the electrode was measured. A value obtained by dividing this thickness by the electrode thickness before the charge/discharge test and multiplying the result by 100 was taken as the electrode expansion coefficient.

[Examples 2 to 4]
Change the chemical vapor deposition temperature to 1000° C. (Example 2), 1050° C. (Example 3), and 1100° C. (Example 4) when causing the carbonization of the carbon source and the disproportionation reaction of the silicon oxide. A negative electrode active material was prepared in the same manner as in Example 1 except that the negative electrode active material was prepared, and the same evaluation was performed. Table 1 shows the results.

[Comparative Examples 1 and 2]
Example 1, except that the chemical vapor deposition temperature for causing the carbonization of the carbon source and the disproportionation reaction of the silicon oxide was changed to 900° C. (Comparative Example 1) and 1200° C. (Comparative Example 2). Negative electrode active materials were prepared in the same manner and evaluated in the same manner. Table 2 shows the results.

[Example 5]
Silicon oxide particles having a volume average particle diameter (D50%) of 5 μm obtained after the pulverization process of the silicon oxide particles were subjected to additional surface modification treatment using Nobilta (NOB-VC, Hosokawa Micron Corporation). prepared a negative electrode active material in the same manner as in Example 2, and performed the same evaluation. Table 1 shows the results.

[Example 6]
Silicon oxide particles having a volume average particle diameter (D50%) of 5 μm obtained after the pulverization process of the silicon oxide particles were subjected to additional surface modification treatment by a Mechanofusion system (Lab, Hosokawa Micron Corporation). prepared a negative electrode active material in the same manner as in Example 2, and performed the same evaluation. Table 1 shows the results.

[Example 7]
In the step of pulverizing silicon oxide particles, a fine impact mill: pin mill type (UPZ, Hosokawa Micron Corporation) was used as a pulverizing device, except that the silicon oxide particles were pulverized so that the volume average particle diameter (D50%) was 5 μm. prepared a negative electrode active material in the same manner as in Example 2, and performed the same evaluation. Table 1 shows the results.

[Example 8]
In the pulverization step of the silicon oxide particles, a fine mill (SF type, Nippon Coke Kogyo Co., Ltd.) was used as a pulverizer, and the silicon oxide particles were pulverized so that the volume average particle diameter (D50%) was 5 μm. , a negative electrode active material was prepared in the same manner as in Example 2, and the same evaluation was performed. Table 1 shows the results.

[Example 9]
A negative electrode active material was produced in the same manner as in Example 2, except that the partial pressure of the acetylene gas was changed to 20% and the treatment time was changed to 4 hours, and the same evaluation was performed. Table 1 shows the results.

[Example 10]
A negative electrode active material was prepared in the same manner as in Example 2, except that compressed natural gas was used as the carbon source, and the same evaluation was performed. Table 2 shows the results.

[Example 11]
A negative electrode active material was prepared in the same manner as in Example 10, except that the partial pressure of the compressed natural gas was changed to 20%, and the same evaluation was performed. Table 2 shows the results.

[Example 12]
A negative electrode active material was prepared in the same manner as in Example 2, except that methane gas was used as the carbon source, and the same evaluation was performed. Table 2 shows the results.

[Example 13]
A negative electrode active material was produced in the same manner as in Example 12, except that the partial pressure of methane gas was changed to 20%, and the same evaluation was performed. Table 2 shows the results.

[Example 14]
An apparatus for mixing 1000 g of silicon oxide particles having a volume average particle diameter (D50%) of 5 μm obtained after the silicon oxide pulverization step of Example 1 and 34 g of petroleum pitch (75% by mass of fixed carbon) as a carbon source. (Rocking Mixer RM-10G, Aichi Denki Co., Ltd.), mixed for 5 minutes, and then filled into a heat treatment container made of alumina. After filling the heat treatment container, this was heat treated at 1000° C. for 5 hours in an atmosphere firing furnace under a nitrogen atmosphere to carbonize the carbon source and obtain a heat treated product. The obtained heat-treated material was pulverized in a mortar and sieved through a 300M (300 mesh) test sieve to prepare a negative electrode active material. After that, the same evaluation as in Example 1 was performed. Table 2 shows the results.

[Example 15]
A negative electrode active material was prepared in the same manner as in Example 14, except that the amount of petroleum pitch used as the carbon source was changed to 67 g, and the same evaluation was performed. Table 2 shows the results.

[Comparative Example 3]
A negative electrode active material was produced in the same manner as in Example 9, except that the partial pressure of the acetylene gas was changed to 30%, and the same evaluation was performed. Table 2 shows the results.

As shown in Tables 1 and 2, the negative electrode active material that satisfies predetermined conditions for both the X-ray diffraction peak intensity ratio (P _Si /P _SiO2 ) and the ratio (S _H2O /S _N2 ) was used. The lithium ion secondary batteries of Examples 1 to 15 had a high initial discharge capacity, suppressed expansion of the electrode, and were excellent in high-temperature storage characteristics.
The negative electrode active materials of Comparative Examples 1 and 2, in which the X-ray diffraction peak intensity ratio (P _Si /P _SiO2 ) did not satisfy the predetermined condition, were inferior to those of Examples in initial discharge capacity.
The negative electrode active material of Comparative Example 3, in which the ratio (S _H2O /S _N2 ) does not satisfy the predetermined conditions, has better initial discharge capacity, initial charge-discharge efficiency, electrode expansion rate, cycle characteristics, and high-temperature storage characteristics than those of the examples. was inferior.

All publications, patent applications and technical standards mentioned herein are to the same extent as if each individual publication, patent application and technical standard were specifically and individually noted to be incorporated by reference. incorporated herein by reference.

10... Carbon, 12... Fine particles of carbon, 20... Silicon oxide particles

Claims (9)

comprising silicon oxide particles with carbon present on part or all of the surface;
X-ray diffraction at 2θ = 27° to 29° derived from Si relative to X-ray diffraction peak intensity at 2θ = 20° to 25° derived from SiO ₂ when using CuKα rays with a wavelength of 0.15406 nm as the radiation source The peak intensity ratio (P _Si /P _SiO2 ) is in the range of 1.0 to 2.6,
The ratio of the specific surface area calculated from water vapor adsorption at 298K to the specific surface area calculated from nitrogen adsorption at 77K (S _H2O /S _N2 ) is 0.60 or less ,
A negative electrode active material for a lithium ion secondary battery, having a specific surface area calculated from nitrogen adsorption at 77K of 0.1 m ² /g to 2.4 m ² /g. 2. The negative electrode for a lithium ion secondary battery according to claim 1, wherein the average value of the aspect ratio represented by the ratio (S/L) of the major axis L to the minor axis S is in the range of 0.45≦S/L≦1. active material. In the volume cumulative distribution curve obtained by the laser diffraction/scattering method, the particle diameter when the accumulation from the small particle side is 90% (D90%) Particles when the accumulation from the small particle side is 10% 3. The negative electrode active material for a lithium ion secondary battery according to claim 1, wherein the ratio (D10%/D90%) of diameters (D10%) is 0.1 or more. The lithium ion battery according to any one of claims 1 to 3, wherein the carbon content is 0.1% by mass to 10.0% by mass of the total of the silicon oxide particles and the carbon. Negative electrode active material for secondary batteries. Claims 1 to 1, wherein the X-ray diffraction spectrum has a diffraction peak attributed to Si(111), and the silicon crystallite size calculated from the diffraction peak is 1.0 nm to 15.0 nm. 5. The negative electrode active material for a lithium ion secondary battery according to any one of 4. The negative electrode active material for a lithium ion secondary battery according to any one of claims 1 to 5, having a volume average particle size of 0.1 µm to 20 µm. The negative electrode active material for a lithium ion secondary battery according to any one of claims 1 to 6 , further comprising a carbon-based negative electrode active material. A lithium ion having a current collector and a negative electrode material layer containing the negative electrode active material for a lithium ion secondary battery according to any one of claims 1 to 7 provided on the current collector. Negative electrode for secondary batteries. A lithium ion secondary battery comprising a positive electrode, the negative electrode for a lithium ion secondary battery according to claim 8 , and an electrolyte.

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