TW202328000A - Silicon oxide particles and method for producing same, particles and method for producing same, and secondary battery and method for producing same - Google Patents

Abstract

Silicon oxide particles in which the total amount of zirconium, yttrium, hafnium, and manganese is 1000 ppm or less and d50 is 1 μm or less. Particles containing silicon oxide particles having a d50 of 1 μm or less and graphite, wherein the total amount of zirconium, yttrium, hafnium, and manganese is 600 ppm or less. A secondary battery including a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode includes a current collector and negative electrode active material layer formed on the current collector, and the negative electrode active material layer contains the aforementioned particles.

Description

Silicon oxide particle and its manufacturing method, particle and its manufacturing method, and secondary battery and its manufacturing method

The present invention relates to a silicon oxide particle that can be used as a negative electrode active material of a secondary battery, the particle and a manufacturing method thereof, and a secondary battery using the particle as a negative electrode active material and a manufacturing method thereof.

In recent years, with the miniaturization of electronic equipment, the demand for high-capacity secondary batteries has been increasing. In particular, non-aqueous secondary batteries, especially lithium-ion secondary batteries, which have higher energy density and excellent rapid charge and discharge characteristics than nickel-cadmium batteries or nickel-hydrogen batteries have attracted attention.

Lithium-ion secondary batteries have been developed and put into practical use, including positive and negative electrodes capable of storing and releasing lithium ions, and non-aqueous electrolytes in which lithium salts such as LiPF ₆ or LiBF ₄ are dissolved.

Various materials have been proposed as negative electrode materials for such batteries. As the negative electrode material, graphitic carbon such as natural graphite, artificial graphite obtained by graphitization of coke, graphitized mesophase pitch, and graphitized carbon fiber can be used in terms of high capacity and excellent flatness of discharge potential. Material.

Recently, the use of non-aqueous secondary batteries, especially lithium ion secondary batteries, is being developed. For example, it is not only for the previous notebook computers, or mobile communication devices, portable cameras, portable game consoles, etc., but also for electric tools, electric vehicles, etc. Therefore, more rapid charge and discharge performance than before is required. Furthermore, a lithium ion secondary battery having high capacity and high cycle characteristics is desired.

However, in the carbon-centered negative electrode, since the theoretical capacity of carbon is 372 mAh, it is impossible to expect a higher capacity. Therefore, the application of various negative electrode materials with high theoretical capacity, especially metal particles, to the negative electrode has been studied.

In Patent Document 1, it is proposed that "a kind of composite active material for lithium secondary battery, which is composed of Si or Si alloy, carbonaceous material or carbonaceous material and graphite components, is characterized in that: the average of the active material is The particle size (D50) is 1-40 μm, the specific surface area is 0.5-45 m ² /g, the average pore diameter is 10-40 nm, and the open pore volume is 0.06 cm ³ /g or less.”

Patent Document 1: Japanese Patent Laid-Open No. 2017-134937

The silicon oxide particles disclosed in Patent Document 1 are obtained by wet pulverization. Since impurities are easily mixed through the medium during the pulverization step, the total content of zirconium, yttrium, hafnium and manganese is relatively high. According to the research of the inventors of the present invention, it can be found that when the silicon oxide particles with more metal components are used as the negative electrode active material, the battery characteristics of the obtained secondary battery are relatively poor, especially those with electrode bulging. question.

The object of the present invention is to provide a particle in which the total content of zirconium, yttrium, hafnium, and manganese is low, and by using it as a negative electrode active material of a secondary battery, the battery characteristics, especially the effect of suppressing electrode swelling are excellent. .

The present inventors found that the total content of zirconium, yttrium, hafnium and manganese containing specific silicon oxide particles and graphite particles is low, and the battery characteristics of the secondary battery using it as the negative electrode active material, especially the electrode swelling The inhibitory effect was excellent, and the present invention was completed. That is, the present invention makes the gist of the following.

[1] A silicon oxide particle in which the total content of zirconium, yttrium, hafnium, and manganese is 1000 ppm or less, and the d ₅₀ of the silicon oxide particle is 1 μm or less.

[2] The silica particles described in [1], wherein the content of zirconium is 500 ppm or less.

[3] The silicon oxide particles according to [1] or [2], wherein the content of yttrium is 100 ppm or less.

[4] The silicon oxide particles according to any one of [1] to [3], wherein the hafnium content is 100 ppm or less.

[5] The silicon oxide particles according to any one of [1] to [4], wherein the manganese content is 300 ppm or less.

[6] The silicon oxide particle according to any one of [1] to [5], wherein d _max /d ₅₀ is 2-10.

[7] The silicon oxide particle according to any one of [1] to [6], which is used for a secondary battery.

[8] The method for producing silicon oxide particles according to any one of [1] to [7], which includes the step of dry pulverizing the silicon oxide particles.

[9] A particle comprising silicon oxide particles with a d ₅₀ of 1 μm or less and graphite, and the total content of zirconium, yttrium, hafnium, and manganese is 600 ppm or less.

[10] The particles according to [9], wherein the zirconium content is 300 ppm or less.

[11] The particles according to [9] or [10], wherein the content of yttrium is 60 ppm or less.

[12] The particle according to any one of [9] to [11], wherein the hafnium content is 60 ppm or less.

[13] The particles according to any one of [9] to [12], wherein the manganese content is 180 ppm or less.

[14] The method for producing particles according to any one of [9] to [13], which includes the step of: compounding silicon oxide particles and graphite.

[15] The method for producing particles as described in [14], wherein the composite method of silicon oxide particles and graphite is a method of mixing silicon oxide particles and graphite and then performing spheroidization treatment.

[16] A secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, and the negative electrode includes a current collector, and a negative electrode active material layer formed on the current collector, and the negative electrode active material layer includes such as [9] to [13] ] any one of the particles recorded.

[17] A method of manufacturing a secondary battery, which is a method of manufacturing a secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, comprising the following steps: forming a battery comprising any one of [9] to [13] on a current collector. The negative electrode active material layer of the particles is obtained to obtain the negative electrode. [Effect of Invention]

According to the silicon oxide particles of the present invention whose total content of zirconium, yttrium, hafnium and manganese is low and whose _d50 is below a specific value, a secondary battery can be provided by using it together with graphite as a secondary battery. Negative electrode active material, so that the battery characteristics, especially the effect of suppressing electrode swelling is excellent. Also, according to the particles of the present invention containing silicon oxide particles and graphite having a _d50 of not more than a specific value and having a relatively low total content of zirconium, yttrium, hafnium, and manganese, a secondary battery can be provided by using it as It is a negative electrode active material for secondary batteries, and it is excellent in battery characteristics, especially the suppression effect of electrode swelling.

Hereinafter, the present invention will be described in detail. The present invention is not limited to the following description, and can be implemented with any changes within the scope not departing from the gist of the present invention. In the present invention, when "~" is used and a numerical value or a physical property value is used before and after it to express, it is used as including the value before and after it.

In the present invention, "d ₅₀ " is the volume average particle diameter, which is defined as the volume-based median diameter measured by laser diffraction scattering particle size distribution measurement. In the present invention, "d ₉₀ " is equivalent to the particle diameter of 90% accumulated from the smaller particle side in the particle size distribution obtained at the time of the measurement of the d ₅₀ . In the present invention, "d _max " is the maximum particle diameter of the particles measured in the particle size distribution obtained during the measurement of d ₅₀ .

[Silicon oxide particles] The silicon oxide particles of the present invention are characterized in that the total content of zirconium, yttrium, hafnium and manganese is 1000 ppm or less, and the d ₅₀ of the silicon oxide particles is 1 μm or less.

Silicon oxide particles with a total content of zirconium, yttrium, hafnium, and manganese of 1000 ppm or less and d ₅₀ of 1 μm or less are excellent in improving battery characteristics, especially in suppressing electrode swelling, as particles compounded with graphite , the details of its mechanism are not clear, but it is presumed as follows. When the total content of zirconium, yttrium, hafnium, and manganese exceeds 1000 ppm, the above elements tend to be locally and unevenly present in the silicon oxide particles. The part where the above-mentioned elements exist unevenly in the silicon oxide particles can suppress the charge-discharge reaction in the battery, and induce uneven volume changes in the silicon oxide particles. As a result, irreversible changes occur in the silicon oxide particles in the electrode due to cracking of the particles or the unreduced volume of the enlarged silicon oxide particles, resulting in electrode swelling. When the total content rate of zirconium, yttrium, hafnium, and manganese is 1000 ppm or less, the above-mentioned change can be suppressed.

<Total content of zirconium, yttrium, hafnium and manganese> The total content of zirconium, yttrium, hafnium and manganese in the silicon oxide particles of the present invention is 1000 ppm or less, preferably 500 ppm or less, more preferably 300 ppm or less, further preferably 200 ppm or less, especially 100 ppm the following. If the total content of zirconium, yttrium, hafnium, and manganese in the silicon oxide particles is 1000 ppm or less, a secondary battery with excellent battery characteristics can be obtained, especially electrode swelling can be suppressed. The lower limit of the total content of zirconium, yttrium, hafnium and manganese is not particularly limited, and the smaller the better. The total content of zirconium, yttrium, hafnium and manganese in the silicon oxide particles of the present invention is usually 10 ppm or more.

As described above, as a method for producing the silicon oxide particles of the present invention having a low total content of zirconium, yttrium, hafnium, and manganese, as described in the following method for producing silicon oxide particles, the following method can be exemplified: The pulverization step, the method of performing dry pulverization instead of wet pulverization; the method of wet pulverization using equipment that does not contain zirconium, yttrium, hafnium and manganese as constituent elements; the method of using zirconium, yttrium, hafnium and manganese as constituent elements The equipment for wet grinding of elements, the method of washing silicon oxide particles obtained by wet grinding with a cleaning solution such as dilute alkaline aqueous solution in which zirconium, yttrium, hafnium and manganese are dissolved; etc.

<Zirconium content> As long as the total content of zirconium, yttrium, hafnium and manganese in the silicon oxide particles of the present invention is 1000 ppm or less, the content of each metal element is not particularly limited. Among these metal elements, the content of zirconium is preferably 500 ppm. It is at most ppm, more preferably at most 100 ppm, and still more preferably at most 50 ppm. When the zirconium content is not more than the above upper limit, generation of precipitates in the battery tends to be suppressed. The lower limit of the zirconium content of the silicon oxide particles of the present invention is not particularly limited, and the smaller the better. The zirconium content of the silica particles of the present invention is usually 0.1 ppm or more.

＜Yttrium content rate＞ As long as the total content of zirconium, yttrium, hafnium and manganese in the silicon oxide particles of the present invention is 1000 ppm or less, the content of each metal element is not particularly limited. Among these metal elements, the content of yttrium is preferably 100 ppm. ppm or less, more preferably 10 ppm or less, still more preferably 1 ppm or less. When the yttrium content is not more than the above-mentioned upper limit, generation of precipitates in the battery tends to be suppressed. The lower limit of the yttrium content of the silicon oxide particles of the present invention is not particularly limited, and the smaller the better. The yttrium content rate of the silicon oxide particle of this invention is 0.01 ppm or more normally.

＜Content rate of hafnium＞ As long as the total content of zirconium, yttrium, hafnium and manganese in the silicon oxide particles of the present invention is 1000 ppm or less, the content of each metal element is not particularly limited. Among these metal elements, the content of hafnium is preferably 100 ppm. ppm or less, more preferably 10 ppm or less, still more preferably 1 ppm or less. When the hafnium content is below the above-mentioned upper limit, generation of precipitates in the battery tends to be suppressed. The lower limit of the hafnium content of the silicon oxide particles of the present invention is not particularly limited, and the smaller the better. The hafnium content rate of the silicon oxide particle of this invention is 0.01 ppm or more normally.

＜Manganese content＞ As long as the total content of zirconium, yttrium, hafnium and manganese in the silicon oxide particles of the present invention is 1000 ppm or less, the content of metal elements is not particularly limited. Among these metal elements, the content of manganese is preferably 300 ppm It is less than or equal to 200 ppm, more preferably less than 100 ppm. When the manganese content is below the above-mentioned upper limit, generation of precipitates in the battery tends to be suppressed. The lower limit of the manganese content of the silicon oxide particles of the present invention is not particularly limited, and the smaller the better. The manganese content of the silicon oxide particles of the present invention is usually 0.1 ppm or more.

In this specification, the contents of zirconium, yttrium, hafnium, and manganese in silicon oxide particles are values obtained by quantifying the elements in the solution of the prepared sample by the ICP-AES method.

<d ₅₀ > The volume average particle diameter (d ₅₀ ) of the silicon oxide particles of the present invention is 1 μm or less, preferably 0.1 μm to 0.9 μm, more preferably 0.2 μm to 0.8 μm. If the d ₅₀ of silicon oxide particles is within the above range, the volume expansion accompanying charge and discharge can be reduced, the charge and discharge capacity can be maintained, and good cycle characteristics can be obtained.

<d _max > The maximum particle size (d _max ) of the silicon oxide particles of the present invention is generally not less than 0.02 μm and not more than 20 μm, preferably not less than 0.03 μm and not more than 5 μm, more preferably not less than 0.04 μm and not more than 2 μm. When d _max is more than the above-mentioned lower limit, the capacity tends to be high. If d _max is not more than the above-mentioned upper limit, there exists a tendency for the silicon oxide particles which are insufficiently composited with the graphite mentioned later to be reduced.

<d _max /d ₅₀ > _{The ratio} d max /d 50 of the maximum particle diameter (d _max ) to the volume average particle diameter (d ₅₀ ) of the silicon oxide particles of the present invention is preferably 2-10, more preferably 2.5-8 , and more preferably 3-6. When d _max /d ₅₀ is more than the above-mentioned lower limit value, it is easy to increase the filling factor of the electrode. If d _max /d ₅₀ is not more than the above-mentioned upper limit, the difference in volume expansion per silicon oxide particle is unlikely to become large.

＜Types of silicon oxide particles＞ The crystal state of the silicon oxide particles of the present invention may be single crystal or polycrystalline. Silicon oxide particles are preferably polycrystalline or amorphous in that the particle size can be easily reduced and rate characteristics can be improved.

Silicon oxide is represented by the general formula SiOx, and is obtained by using silicon dioxide (SiO ₂ ) and metal Si (Si) as raw materials. The value of x is usually greater than 0 and less than 2, preferably not less than 0.1 and not more than 1.8, more preferably not less than 0.5 and not more than 1.5, and still more preferably not less than 0.8 and not more than 1.2. When x is within the above range, the irreversible capacity due to the bonding of Li and oxygen can be reduced while having a high capacity.

In this specification, the value of x in SiOx is measured by the pulse furnace heating extraction-IR detection method to measure the oxygen content of silicon oxide particles under an inert gas atmosphere, and by ICP (Inductively Coupled Plasma, inductively coupled plasma ) The silicon content of SiOx is measured by the emission spectrometry method, and the value obtained by calculating the ratio of the oxygen relative to the silicon content is obtained.

The theoretical capacity of SiOx is greater than that of graphite. Amorphous Si or nano-sized Si crystals can easily move in and out of alkaline ions such as lithium ions, and can obtain high capacity.

＜Other properties＞ The silicon oxide particle of the present invention preferably exhibits the following physical properties. The measurement method in the present invention is not particularly limited, unless otherwise specified, the measurement method described in the examples is followed.

・Specific surface area obtained by BET method The specific surface area of silicon oxide particles obtained by the BET method is usually not less than 0.5 m ² /g and not more than 120 m ² /g, preferably not less than 1 m ² /g and not more than 100 m ² /g. If the specific surface area of silicon oxide particles obtained by the BET method is within the above range, the charge and discharge efficiency and discharge capacity of the battery will be high, lithium will move in and out rapidly during high-speed charge and discharge, and the rate characteristics will be excellent, so it is preferable.

In this specification, the specific surface area is a value measured by the BET method using nitrogen adsorption.

・Oxygen content The oxygen content of the silicon oxide particles is usually not less than 0.01% by mass and not more than 50% by mass, preferably not less than 0.05% by mass and not more than 45% by mass, based on 100% by mass of the silicon oxide particles. The distribution state of oxygen in silicon oxide particles can exist near the surface, or inside the particles, or uniformly in the particles, preferably near the surface. If the oxygen content of the silicon oxide particles is within the above range, the strong bond between Si and O can suppress the volume expansion accompanying charging and discharging, and the cycle characteristics are excellent, which is preferable.

In this specification, the oxygen content of silicon oxide particles is the value obtained by measuring the oxygen content of silicon oxide particles by pulse furnace heating extraction-IR detection method in an inert gas atmosphere.

・Crystalline size Silicon oxide particles may contain a crystalline structure or may be amorphous. When the silicon oxide particles contain a crystalline structure, the crystallite size of the (111) plane calculated by the X-ray diffraction method of the silicon oxide particles is usually 0.05 nm to 100 nm, preferably 1 nm to 50 nm. When the crystallite size of the silicon oxide particles is within the above range, the reaction between Si and Li ions is rapid and the input and output are excellent, which is preferable.

In this specification, the crystallite size is determined by the Debye Scherrer method based on the diffraction peak attributable to the Si(111) plane centered around 2θ=28.4° observed by the X-ray wide-angle diffraction method value out.

[Manufacturing method of silicon oxide particles] As for the silicon oxide particles, commercially available silicon oxide particles can be purified and pulverized to be used. The silicon oxide particles can be obtained by applying mechanical energy treatment to silicon oxide particles with a large particle size by the following ball mill, etc., and performing a short-time cleaning treatment with an alkaline cleaning solution.

Also, the production method is not particularly limited. For example, silicon oxide particles produced by the method described in Japanese Patent No. 3952118 may also be used. For example, _SiO2 powder and metal Si powder are mixed at a specific ratio, the mixture is filled in a reactor, and the temperature is raised to 1000°C or higher at normal pressure or reduced to a specific pressure and maintained. SiOx gas is generated, cooled and precipitated to obtain silicon oxide particles (sputtering treatment). The precipitates are turned into particles by imparting pulverization treatment (mechanical energy treatment), and the particles can also be used.

When producing the silicon oxide particles of the present invention, in the case of passing through the pulverization step, if the pulverization is carried out by a wet method, impurities are easily mixed through the medium, so it is impossible to obtain a product with a low total content of zirconium, yttrium, hafnium and manganese. Silicon oxide particles. Therefore, pulverization is preferably performed by dry pulverization.

Dry pulverization treatment can be performed, for example, by using a ball mill, a vibrating ball mill, a planetary ball mill, a rolling ball mill, a bead mill, etc., and putting the raw material filled in the reactor and a moving body that does not react with the raw material , to impart vibration, rotation, or a combination of vibration and rotation to it.

The dry pulverization treatment time is usually at least 3 minutes, preferably at least 5 minutes, more preferably at least 10 minutes, further preferably at least 15 minutes, usually less than 5 hours, preferably less than 4 hours, more preferably 3 hours or less, and more preferably less than 1 hour. If the pulverization treatment time of several types is within the above range, both the improvement of productivity and the stability of the physical properties of the product can be achieved. Regarding the dry pulverization treatment temperature, in terms of technology, it is preferably a temperature above the freezing point of the solvent and below the boiling point.

＜Nitriding treatment of silicon oxide particles＞ Since the silicon oxide particles have bonds with nitrogen atoms on the surface, the presence of oxides of the silicon oxide particles that do not contribute to charge and discharge can be suppressed, and the capacity per unit weight of the silicon oxide particles can be improved, and can be In terms of reducing the reactivity of the surface of silicon oxide particles and improving charge and discharge efficiency, it is preferable to form bonds between silicon oxide particles and nitrogen atoms. The bonding between silicon oxide particles and nitrogen atoms can be detected by XPS (X-ray photoelectron spectroscopy, X-ray photoelectron spectroscopy), IR (Infrared Spectroscopy, infrared spectroscopy), XAFS (X-ray absorption fine structure, X-ray absorption fine structure) analysis by various methods. In order to form bonds between silicon oxide particles and nitrogen atoms, there is a method of mixing a gas containing nitrogen atoms in the above-mentioned sputtering treatment or dry pulverization treatment.

[Particles] The particles of the present invention are characterized in that they contain silicon oxide particles with ad ₅₀ of 1 μm or less and graphite, and the total content of zirconium, yttrium, hafnium and manganese is 600 ppm or less.

Particles containing silicon oxide particles and graphite with a d ₅₀ of 1 μm or less and a total content of zirconium, yttrium, hafnium, and manganese of 600 ppm or less exert an excellent effect of improving battery characteristics, especially suppressing electrode swelling, and the mechanism The details are not clear, but it is presumed as follows. When the total content of zirconium, yttrium, hafnium, and manganese exceeds 600 ppm, the above-mentioned elements tend to be locally and non-uniformly present in the particles. The part where the above-mentioned elements exist unevenly in the particle can suppress the charge-discharge reaction in the battery and induce a non-uniform volume change in the particle. As a result, irreversible changes occur in the particles in the electrode due to cracking of the particles or the unreduced volume of the enlarged particles, resulting in electrode swelling. When the total content rate of zirconium, yttrium, hafnium, and manganese is 600 ppm or less, the above-mentioned change can be suppressed.

<Total content of zirconium, yttrium, hafnium and manganese> The total content of zirconium, yttrium, hafnium and manganese in the particles of the present invention is 600 ppm or less, preferably 300 ppm or less, more preferably 120 ppm or less, and still more preferably 60 ppm or less. If the total content of zirconium, yttrium, hafnium, and manganese in the particles is 600 ppm or less, a secondary battery with excellent battery characteristics can be obtained, especially electrode swelling can be suppressed. The lower limit of the total content of zirconium, yttrium, hafnium and manganese is not particularly limited, and the smaller the better. The total content of zirconium, yttrium, hafnium and manganese in the particles of the present invention is usually 6 ppm or more.

As described above, as a method of producing the particles of the present invention having a small total content of zirconium, yttrium, hafnium, and manganese, the method of using the above-mentioned particles of the present invention having a small total content of zirconium, yttrium, hafnium, and manganese may be exemplified. The silicon oxide particle of the present invention is used as the silicon oxide particle, and the silicon oxide particle of the present invention is composited with graphite. In particular, a method of performing spheroidization after mixing silicon oxide particles and graphite in the compounding step of silicon oxide particles and graphite is preferable.

<Zirconium content> As long as the total content of zirconium, yttrium, hafnium and manganese in the particles of the present invention is 600 ppm or less, the content of each metal element is not particularly limited. Among these metal elements, the content of zirconium is preferably 300 ppm or less , more preferably 60 ppm or less, further preferably 30 ppm or less. When the zirconium content is not more than the above upper limit, generation of precipitates in the battery tends to be suppressed. The lower limit of the zirconium content of the particles of the present invention is not particularly limited, and the smaller the better. The zirconium content of the particles of the present invention is usually 0.06 ppm or more.

＜Yttrium content rate＞ As long as the total content of zirconium, yttrium, hafnium and manganese in the particles of the present invention is 600 ppm or less, the content of each metal element is not particularly limited. Among these metal elements, the content of yttrium is preferably 60 ppm or less , more preferably 6 ppm or less, further preferably 0.06 ppm or less. If the content of yttrium is not more than the above-mentioned upper limit, the generation of precipitates in the battery tends to be suppressed. The lower limit of the yttrium content of the particles of the present invention is not particularly limited, and the smaller the better. The yttrium content rate of the particle|grains of this invention is 0.006 ppm or more normally.

＜Content rate of hafnium＞ As long as the total content of zirconium, yttrium, hafnium and manganese in the particles of the present invention is 600 ppm or less, the content of each metal element is not particularly limited. Among these metal elements, the content of hafnium is preferably 60 ppm or less , more preferably 6 ppm or less, further preferably 0.6 ppm or less. When the hafnium content is below the above-mentioned upper limit, generation of precipitates in the battery tends to be suppressed. The lower limit of the hafnium content of the particles of the present invention is not particularly limited, and the smaller the better. The hafnium content rate of the particle|grains of this invention is 0.006 ppm or more normally.

＜Manganese content＞ As long as the total content of zirconium, yttrium, hafnium and manganese in the particles of the present invention is 600 ppm or less, the content of metal elements is not particularly limited. Among these metal elements, the content of manganese is preferably 180 ppm or less. More preferably, it is 120 ppm or less, and still more preferably, it is 60 ppm or less. When the manganese content is below the above-mentioned upper limit, generation of precipitates in the battery tends to be suppressed. The lower limit of the manganese content of the particles of the present invention is not particularly limited, and the smaller the better. The manganese content of the particles of the present invention is usually 0.06 ppm or more.

In this specification, the contents of zirconium, yttrium, hafnium, and manganese in the particles are values obtained by quantifying the elements in the solution of the prepared sample by the ICP-AES method.

＜Graphite＞ An example of graphite which is one of the constituent components of the particles of the present invention is shown below. As graphite, a known one or a commercially available one can be used.

(type of graphite) Graphite can be obtained, for example, by heating flake, block or plate natural graphite, petroleum coke, coal tar pitch coke, coal needle coke, mesophase pitch, etc. to above 2500° C. The prepared artificial graphite in the form of flakes, blocks or plates is subjected to impurity removal, crushing, sieving or grading treatment to obtain graphite. Among these graphites, flake-like, block-like or plate-like natural graphite is preferable, and flake-like natural graphite is more preferable in terms of low cost and high capacity.

Natural graphite is divided into flake graphite (Flake Graphite), scaly graphite (CrystalLine (Vein) Graphite) and soil-like graphite (Amorphous Graphite) according to its properties (refer to "Powder Granular Process Technology Integration" (Industrial Technology Center (Stock) , issued in 1974) and "HANDBOOK OF CARBON, GRAPHITE, DIAMOND AND FULLERENES" (issued by Noyes PubLications)). Regarding the degree of graphitization, flake graphite is the highest at 100%, followed by flake graphite at 99.9%. Therefore, it is preferable to use such graphites.

Flake graphite, which is natural graphite, is produced in Madagascar, China, Brazil, Ukraine, Canada, and the like. The origin of scaly graphite is mainly Sri Lanka. The main producing areas of earthy graphite are Korean Peninsula, China, Mexico, etc.

Among these natural graphites, flaky graphite or flaky graphite can be preferably used in the present invention because of its advantages of high degree of graphitization and low amount of impurities. As a visual method for confirming that the graphite is in the form of scales, for example: the method of observing the surface of the particles with a scanning electron microscope; embedding the particles in a resin to make a resin sheet, cutting out the cross section of the particles, and observing the surface of the particles with a scanning electron microscope The method of observing the particle cross section; or for the coating film containing particles, using a cross section polisher to make a coating film cross section, cutting out the particle cross section, and using a scanning electron microscope to observe the particle cross section; etc. The flaky graphite or flaky graphite includes highly purified natural graphite in which the crystallinity of graphite shows completely similar crystals, and artificially formed graphite. Among them, natural graphite is preferable in terms of softness and ease of making a folded structure.

(Physical properties of graphite) The preferred physical properties of graphite in the present invention are as follows.

・Volume average particle size (d ₅₀ ) The d ₅₀ of graphite is usually not less than 1 μm and not more than 120 μm, preferably not less than 3 μm and not more than 100 μm, more preferably not less than 5 μm and not more than 90 μm. If _d50 is within the above-mentioned range, high-performance particles can be produced by compounding with silicon oxide particles. If the d ₅₀ of graphite is equal to or greater than the above-mentioned lower limit, particles having a particle size within a range in which an electrode can be formed with an appropriate amount of binder can be produced. If the _d50 of graphite is below the above-mentioned upper limit, when manufacturing a secondary battery, in the step of adding a binder or water or an organic solvent to make the particles into a slurry and coating the particles, it is possible to suppress the formation of large particles. Caused by the generation of stripes or bumps.

・Particle size (d ₉₀ ) The d ₉₀ of graphite is usually not less than 1.5 μm and not more than 150 μm, preferably not less than 4 μm and not more than 120 μm, more preferably not less than 6 μm and not more than 100 μm. If the d ₉₀ of graphite is more than the above-mentioned lower limit value, when silicon oxide particles and graphite are composited, the composites can be efficiently performed. If the d ₉₀ of graphite is not more than the above-mentioned upper limit, the generation of coarse particles can be suppressed when silicon oxide particles and graphite are composited.

・Average aspect ratio The average aspect ratio, which is the ratio of the major axis to the minor axis of graphite, is usually not less than 2.1 and not more than 10, preferably not less than 2.3 and not more than 9, more preferably not less than 2.5 and not more than 8. If the aspect ratio is within the above range, spherical particles can be produced efficiently, and tiny voids can be formed in the obtained particles, which can reduce the volume expansion accompanying charge and discharge and contribute to the improvement of cycle characteristics.

In this specification, the aspect ratio is calculated in the form of A/B from the longest diameter A of the particle and the shortest diameter B among the diameters orthogonal to it when observed three-dimensionally with a scanning electron microscope By. The average aspect ratio is the average value of the aspect ratios of any 50 particles.

・Tap density The tap density of graphite is usually 0.1 g/cm ³ to 1.0 g/cm ³ , preferably 0.13 g/cm ³ to 0.8 g/cm ³ , more preferably 0.15 g/cm ³ to 0.6 g/ ^cm3 or less. When the tap density is within the above range, minute voids are easily formed in the obtained particles.

In this specification, the tap density refers to the use of a powder density tester. After filling a cylindrical tap cell with a diameter of 1.5 cm and a volume capacity of 20 cm ³ to the full cup, a stroke length of 10 mm is used. Vibrate 1000 times, calculate the density according to the volume at this time and the mass of the sample.

・Specific surface area obtained by the BET method The specific surface area of graphite obtained by the BET method is usually not less than 1 m ² /g and not more than 40 m 2 /g, preferably not less than 2 ^{m 2 /} g and not more than 35 m ² /g, more preferably It is not less than 3 m ² /g and not more than 30 m ² /g. The specific surface area of graphite obtained by the BET method is reflected in the specific surface area of the obtained particles. When the specific surface area of graphite is more than the above-mentioned lower limit, the lithium ion storage capacity of the particles increases, thereby improving the battery output. When the specific surface area of graphite is not more than the above-mentioned upper limit, the irreversible capacity of the particles increases, thereby preventing a decrease in battery capacity.

In this specification, the specific surface area is a value measured by the BET method using nitrogen adsorption.

・The interplanar distance (d 002 ) of the ( ₀₀₂ ) plane and the interplanar distance (d ₀₀₂ ) of the (002) plane obtained by the X-ray wide-angle diffraction method of Lc graphite are usually not less than 0.335 nm and not more than 0.337 nm. The Lc of graphite obtained by X-ray wide-angle diffraction method is usually above 90 nm, preferably above 95 nm. If the interplanar distance (d ₀₀₂ ) of (002) planes is 0.337 nm or less, it means that the crystallinity of graphite is high, and high-capacity particles for secondary battery negative electrode active materials can be obtained. When Lc is more than 90 nm, it also means that the crystallinity of graphite is high, and a high-capacity negative electrode active material can be obtained.

In this specification, the distance between (002) planes and Lc are values measured by X-ray wide-angle diffraction method.

・Length of major diameter and minor diameter The length of the major axis of graphite is usually not more than 100 μm, preferably not more than 90 μm, more preferably not more than 80 μm. The length of the minor axis of graphite is usually at least 0.9 μm, preferably at least 1.0 μm, more preferably at least 1.2 μm. If the lengths of the major axis and the minor axis of the graphite are within the above range, it is easy to form tiny voids in the obtained particles, which can reduce the volume expansion accompanying charging and discharging and improve the cycle characteristics.

<Content ratio of graphite and silicon oxide particles> Regarding the content ratio of graphite and silicon oxide particles in the particles of the present invention, it is preferable that the content ratio of graphite is 10 to 95% in the total of 100% by mass of graphite, silicon oxide particles, and the following carbonaceous substances used as needed. mass % and the content ratio of silicon oxide particles is 3 to 60 mass %, more preferably the content ratio of graphite is 30 to 90 mass % and the content ratio of silicon oxide particles is 5 to 50 mass %, and more preferably the content ratio of graphite is The ratio is 50 to 85% by mass, and the content ratio of silicon oxide particles is 8 to 40% by mass. When the content ratio of graphite is more than the above-mentioned lower limit and the content ratio of silicon oxide particles is below the above-mentioned upper limit, composite formation of graphite and silicon oxide particles will easily proceed. When the content ratio of graphite is below the above upper limit and the content ratio of silicon oxide particles is above the above lower limit, the particles of the present invention can have a high capacity.

＜Carbonaceous matter＞ The particles of the present invention may contain carbonaceous substances other than graphite. It is preferable to compound graphite and silicon oxide particles by making the particles of the present invention contain carbonaceous substances other than graphite, because the influence of the size or shape of graphite and silicon oxide particles can be reduced. In this case, as the carbonaceous substance, amorphous carbon is preferable in terms of being excellent in acceptability of lithium ions.

Specifically, the above-mentioned carbonaceous substance can be obtained by heat-treating its carbon precursor as described below. As the above-mentioned carbon precursor, carbon materials described in (i) and/or (ii) below are preferable. (i) selected from coal-based heavy oil, straight-line heavy oil, decomposition-based petroleum heavy oil, aromatic hydrocarbons, N-ring compounds, S-ring compounds, polyphenylene, organic synthetic polymers, natural polymers, thermoplastic resins, and thermosetting resins carbonizable organic matter (ii) Obtained by dissolving carbonizable organic substances in low-molecular organic solvents

When the particles of the present invention contain carbonaceous substances, the content ratio of the carbonaceous substances is preferably 2 to 30 mass%, more preferably 5 to 100% by mass of the total of graphite, silicon oxide particles, and carbonaceous substances. 25% by mass, more preferably 7 to 20% by mass. When the content ratio of carbonaceous substance is more than the above-mentioned lower limit value, the specific surface area of the particle|grains of this invention can be reduced, and initial charge-discharge efficiency can be improved. The particle|grains of this invention can have a high capacity as the content rate of a carbonaceous substance is below the said upper limit.

<Physical properties of the particles of the present invention> The preferred physical properties of the particles of the present invention are as follows.

・The interplanar distance (d 002 ) of the (002) plane of the particles The interplanar distance (d ₀₀₂ ) of the (002) plane obtained by the X-ray wide-angle diffraction method of the graphite (A) contained in the particles of the present invention is usually _0.335 Above nm and below 0.337 nm. The Lc obtained by the X-ray wide-angle diffraction method of the particles of the present invention is usually above 90 nm, preferably above 95 nm. If the interplanar distance (d ₀₀₂ ) and Lc of the (002) plane obtained by the X-ray wide-angle diffraction method are within the above-mentioned ranges, it is a particle for a negative electrode active material of a secondary battery constituting a high-capacity electrode.

・Tap density of particles The tap density of the particles of the present invention is usually at least 0.5 g/cm ³ , preferably at least 0.6 g/cm ³ , more preferably at least 0.8 g/cm ³ . If the tap density of the particles of the present invention is above the above-mentioned lower limit, the particles are spherical, and sufficient continuous gaps can be ensured in the electrode, and the mobility of Li ions in the electrolyte solution held in the gaps increases. Thereby, there exists a tendency for a rapid charge-discharge characteristic to improve.

・Raman R value of particles The Raman R value of the particles of the present invention is usually not less than 0.05 and not more than 0.4, preferably not less than 0.1 and not more than 0.35. If the Raman R value of the particle of the present invention is within the above-mentioned range, the crystallinity of the surface of the particle is uniform, and a higher capacity can be expected.

In this specification, the Raman R value refers to the intensity IA of the peak PA near 1580 cm ^-1 and the intensity IB of the peak PB near 1360 cm ^-1 in the Raman spectrum obtained by Raman spectroscopy The value is calculated in the form of its intensity ratio (IB/IA) after the measurement. "Near 1580 cm ^-1 " refers to the range from 1580 to 1620 cm ^-1 , and "near 1360 cm ^-1 " refers to the range from 1350 to 1370 cm ^-1 .

The Raman spectrum can be measured using a Raman spectrometer. Specifically, the sample is filled by naturally dropping the particles to be measured into the measurement cell, and the measurement cell is irradiated with argon ion laser light while the measurement cell is placed in contact with the laser. Measurement is performed by in-plane rotation of the incident light perpendicular to it.

・Specific surface area of particles obtained by the BET method The specific surface area of the particles of the present invention obtained by the BET method is usually not less than 0.1 m ² /g and not more than 40 m ² /g, preferably not less than 0.7 m ² /g and not more than 35 m ^{2 /g} g or less, more preferably 1 m ² /g or more and 30 m ² /g or less. When the specific surface area obtained by the BET method of the particle|grains of this invention is more than the said lower limit, when using it as the active material for negative electrodes, there exists a tendency for lithium ion acceptance at the time of charge to be favorable. If the specific surface area obtained by the BET method of the particles of the present invention is below the above-mentioned upper limit, when used as an active material for negative electrodes, the contact portion between the particles and the non-aqueous electrolyte can be suppressed, resulting in reduced reactivity. This tends to make it easier to suppress gas generation and obtain a better battery.

・Volume-average particle diameter (d ₅₀ ) of the particles of the present invention. The d ₅₀ of the particles of the present invention is usually not less than 1 μm and not more than 50 μm, preferably not less than 4 μm and not more than 40 μm, more preferably not less than 6 μm and not more than 30 μm. If the d ₅₀ of the particles of the present invention is equal to or greater than the above-mentioned lower limit, particles having a particle size within a range in which an electrode can be formed with an appropriate amount of binder can be produced. If the d ₅₀ of the particles of the present invention is below the above-mentioned upper limit, when manufacturing a secondary battery, in the step of adding a binder or water or an organic solvent to make the particles into a slurry and coating the particles, the Streaks or unevenness caused by large particles.

[Method for producing particles of the present invention] The particles of the present invention can be produced in the following manner, that is, according to the production method of the particles of the present invention, it is preferable to compound graphite and silicon oxide particles and then perform spheroidization treatment. Here, when graphite and silicon oxide particles are mixed, the above-mentioned carbonaceous substance may be further mixed.

The mixing ratio of graphite, silicon oxide particles, and optionally used carbonaceous material can be set according to the above-mentioned content ratio.

A preferred production method of the particles of the present invention includes at least the following steps 1 and 2. Step 1: Step of obtaining a mixture comprising at least graphite and silicon oxide particles Step 2: The step of imparting mechanical energy to the mixture in step 1 to perform spheroidization

Hereinafter, the production method of the present invention will be described in detail.

(Step 1: The step of obtaining a mixture containing at least graphite and silicon oxide particles) The mixture obtained in this step may, for example, be in the form of powder, solidified, block, or slurry, and is preferably block in terms of ease of handling.

In this step, as long as a mixture containing at least graphite and silicon oxide particles can be obtained, the mixing method of graphite and silicon oxide particles is not particularly limited. As a mixing method, graphite and silicon oxide particles may be added and mixed at one time, or may be mixed while being added one by one.

As a preferred method for obtaining the mixture, for example, the method of using wet silicon oxide particles and mixing them with graphite to prevent the silicon oxide particles from drying out.

As wet silicon oxide particles, silicon oxide particles obtained in the case of producing the above-mentioned silicon oxide particles by a wet method can be used, and it is also possible to disperse the silicon oxide particles obtained by a dry method with graphite before mixing Humidify it in a dispersion solvent. Since the silicon oxide particles wetted in this way inhibit the aggregation of the silicon oxide particles, they can be uniformly dispersed when mixed, and the silicon oxide particles are easily immobilized on the surface of the graphite, so it is preferable.

In order to facilitate uniform dispersion of silicon oxide particles on the surface of graphite, an excess amount of a dispersion solvent used for wet grinding of silicon oxide particles may be added during mixing. In this specification, when mixing silicon oxide particles with graphite as a slurry, the solid content of the silicon oxide particles is usually 10% by mass or more and 90% by mass or less in 100% by mass of the slurry , preferably not less than 15% by mass and not more than 85% by mass, more preferably not less than 20% by mass and not more than 80% by mass. If the solid content of the silicon oxide particles is more than the above lower limit, it tends to be easy to handle in terms of steps. If the solid content of the silicon oxide particles is not more than the above-mentioned upper limit, the fluidity of the slurry is excellent, and the silicon oxide particles tend to be easily dispersed in the graphite.

It is preferable to immobilize the silica particles on the graphite by evaporating and drying the dispersion solvent using an evaporator, a drier, or the like after mixing. Or, preferably without adding an excessive amount of dispersing solvent, while directly heating in a high-speed mixer, evaporating the dispersing solvent, and mixing, the silicon oxide particles are immobilized on the graphite.

At this time, the following carbon precursor etc. can be mixed from the point which can suppress the reactivity of silicon oxide particle and electrolytic solution. Furthermore, at this time, in order to reduce the cracking of the particles caused by the expansion and contraction of the silicon oxide particles, a resin or the like may be mixed as a void forming material.

Examples of resins that can be used as the void forming material in this step 1 include polyvinyl alcohol, polyethylene glycol, polycarbosilane, polyacrylic acid, and cellulose-based polymers. Polyvinyl alcohol and polyethylene glycol are preferred in terms of less carbon residue during calcination and relatively lower decomposition temperature.

Mixing is usually performed under normal pressure, but it can also be performed under reduced pressure or increased pressure. Mixing can also be performed by any of a batch system and a continuous system. In either case, the mixing efficiency can be improved by combining a device suitable for rough mixing and a device suitable for fine mixing. Also, an apparatus that simultaneously performs mixing and immobilization (drying) can also be used. Drying is usually performed under reduced pressure or increased pressure. Drying under reduced pressure is preferred.

The drying time is usually not less than 5 minutes and not more than two hours, preferably not less than 10 minutes and not more than one and a half hours, more preferably not less than 20 minutes and not more than one hour. Although the drying temperature varies depending on the solvent, it is preferably a time that can achieve the above-mentioned time. Also, it is preferably below the temperature at which the resin is not modified.

As a batch mixing device, you can use: a mixer with two frames that rotate on one side and revolve on the other; a high-speed high-shear mixer such as a dispersing mixer or a high-viscosity butterfly mixer that can be used in a tank. A device with a stirring and dispersing structure; a so-called kneader-type device with a structure such as a Sigma-type stirring blade that rotates along the side of a semi-cylindrical mixing tank; a Trimix type that uses three shafts for the stirring blade Device; a so-called bead mill type device with a rotating disk and a dispersing solvent in the container; etc.

It is also possible to use a device with the following structure: there is a container with a paddle that is rotated by a shaft inside, and the inner wall of the container is preferably formed into a longer double-body shape substantially along the outermost line of rotation of the paddle, so that the paddle can There are many pairs arranged in the axial direction of the shaft to slidably engage the opposite sides (for example, KRC reactor and SC processor manufactured by Kurimoto Iron Works, TEM manufactured by Toshiba Machinery Cermak (セルマッック), Japan Steel Works manufactured TEX-K, etc.); and a (external heating) device constructed as follows: a container with a shaft inside and a plurality of plow-shaped or serrated paddles fixed to the shaft are arranged in varying phases, and inside The wall surface is preferably formed in a cylindrical shape substantially along the outermost line of rotation of the paddle (for example, Loedige Mixer manufactured by Loedige Company, Plowshare Mixer manufactured by Pacific Machinery & Engineering Company, DT Dryer manufactured by Tsukishima Machinery Co., Ltd., etc.). When mixing continuously, a pipeline mixer, a continuous bead mill, etc. can be used. Moreover, homogenization can also be performed by methods, such as ultrasonic dispersion. The mixture obtained in this step can also be suitably subjected to powder processing such as pulverization, crushing, and classification treatment.

The equipment used for crushing or crushing is not particularly limited. For example, as a coarse grinder, a shear grinder, a jaw crusher, an impact crusher, a cone crusher, etc. are mentioned. As an intermediate pulverizer, a roll crusher, a hammer mill, etc. are mentioned, for example. The fine pulverizer may, for example, be a ball mill, a vibration mill, a pin mill, an agitation mill, or a jet mill.

As the device used for the classification treatment, in the case of dry sieving, rotary sieving, swing sieving, rotary sieving, vibrating sieving, etc. can be used. In the case of performing dry airflow classification, gravity classifiers, inertial force classifiers, and centrifugal force classifiers (classifiers, cyclone separators) can be used. Wet screening, mechanical wet classifiers, hydraulic classifiers, sedimentation classifiers, centrifugal wet classifiers, etc. can be used.

(Step 2: the step of imparting mechanical energy to the mixture of step 1 to perform spheroidization) By going through this step 2, the degree of composite of graphite and silicon oxide particles is greatly improved, and the particles of the present invention can be produced. The manufacturing method for obtaining the particles of the present invention is to carry out spheroidization treatment on the mixture (also referred to as the mixture in this specification) obtained in the above-mentioned step 1 and mixed with silicon oxide particles on the surface of graphite, especially in the present invention. In the invention, it is preferable to appropriately set the production conditions as described below so that silicon oxide particles within a specific range exist in the gaps within the graphite structure.

The spheroidization treatment basically uses mechanical energy (impact compression, friction and shear force and other mechanical effects) for treatment. Specifically, treatment using a hybrid system is preferred. The system has a rotor with multiple blades that exert mechanical effects such as impact compression, friction and shear force, and generates a large air flow through the rotation of the rotor. Thereby, a greater centrifugal force is applied to the graphite in the mixture obtained in the above step 1, thereby utilizing the collision of the graphite in the mixture obtained in the above step 1 and the graphite in the mixture obtained in the above step 1 Collision with walls or blades to efficiently compound graphite and silicon oxide particles in the mixture obtained in step 1 above.

As the device used for the spheroidization treatment, for example, the following device can be used: there is a rotor with a plurality of blades inside the casing, and the mixture obtained in the above-mentioned step 1 introduced into the interior by the high-speed rotation of the rotor The graphite in the middle imparts mechanical effects such as impact compression, friction, and shearing force, thereby performing surface treatment. Examples include: Hybrid System (manufactured by Nara Machinery Co., Ltd.), Kryptron, Kryptron orb (manufactured by Earth Technica), CF Mill (manufactured by Ube Industries, Ltd.), Mechanical Fusion System, Nobilta, Faculty (manufactured by Hosokawa Micron), Theta Composer (manufactured by Tokushou Works), COMPOSI (manufactured by Japan Coking Industry), etc. Among them, the hybrid system manufactured by Nara Machinery Manufacturing Co., Ltd. is preferable.

In the case of using the above-mentioned device for processing, the peripheral speed of the rotating rotor is usually 30-100 m/sec, preferably 40-100 m/sec, more preferably 50-100 m/sec. The treatment can be performed only by carbonaceous substances, and it is preferably processed by circulating or staying in the device for more than 30 seconds, more preferably by circulating or staying in the device for more than 1 minute.

・Granulating agent The spheroidization treatment can be performed in the presence of a granulating agent. By using a granulating agent, the adhesive force between carbon materials is increased, and spherical carbon materials to which carbon materials adhere more firmly can be manufactured.

The granulating agent used in this form does not contain an organic solvent, or when the granulating agent used in this form contains an organic solvent, it is preferable that at least one of the organic solvents does not have a flash point, or has a flash point When the ignition point is above 5 ℃. Thereby, when the carbon material in the subsequent step is granulated, the danger of ignition, fire and explosion of organic compounds induced by impact or heat can be prevented. Therefore, manufacturing can be carried out stably and efficiently.

Examples of granulating agents include: coal tar, petroleum-based heavy oil, paraffinic oils such as liquid paraffin, olefinic oils, naphthenic oils, aromatic oils and other synthetic oils; vegetable oils, animal-based aliphatic Natural oils such as ketones, esters, and higher alcohols; organic compounds such as resin binder solutions obtained by dissolving resin binders in organic solvents with a fire point above 5°C, preferably above 21°C; water-based solvents such as water; mixtures thereof, etc.

Examples of organic solvents having a flash point of 5°C or higher include alkylbenzenes such as xylene, cumene, ethylbenzene, and propylbenzene; alkylnaphthalenes such as methylnaphthalene, ethylnaphthalene, and propylnaphthalene; Aromatic hydrocarbons such as allylbenzene such as ethylene and allylnaphthalene; aliphatic hydrocarbons such as octane, nonane and decane; ketones such as methyl isobutyl ketone, diisobutyl ketone and cyclohexanone ; Propyl acetate, butyl acetate, isobutyl acetate, amyl acetate and other esters; Methanol, ethanol, propanol, butanol, isopropanol, isobutanol, ethylene glycol, propylene glycol, diethylene glycol, Triethylene glycol, tetraethylene glycol, glycerin and other alcohols; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether , tetraethylene glycol monobutyl ether, methoxypropanol, methoxypropyl-2-acetate, methoxymethylbutanol, methoxybutyl acetate, diethylene glycol dimethyl ether, Dipropylene glycol dimethyl ether, diethylene glycol methyl ethyl ether, triethylene glycol dimethyl ether, tripropylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol monophenyl ether and other glycol derivatives Classes; ethers such as 1,4-dioxane, or nitrogen-containing compounds such as dimethylformamide, pyridine, 2-pyrrolidone, and N-methyl-2-pyrrolidone; dimethylsulfoxide, etc. Sulfur-containing compounds; halogen-containing compounds such as dichloromethane, chloroform, carbon tetrachloride, dichloroethane, trichloroethane, and chlorobenzene; mixtures thereof, etc. For example, substances with low ignition points such as toluene are not included. These organic solvents can also be used as granulating agents in the form of simple substances. In this specification, the ignition point can be measured by a known method.

As the resin binder, for example, cellulose-based resin binders such as ethyl cellulose, methyl cellulose, and salts thereof; polymethyl acrylate, polyethyl acrylate, polybutyl acrylate, polyacrylic acid, Acrylic resin binders such as their salts; methacrylic resin binders such as polymethyl methacrylate, polyethyl methacrylate, and polybutyl methacrylate; phenolic resin binders, etc. As a granulating agent, among them, paraffinic oils such as coal tar, petroleum heavy oil, liquid paraffin, alcohols, and aromatic oils can produce spherical carbon materials with high circularity and less fine powder, so it is better .

As the granulating agent, those having properties that can be removed efficiently and do not adversely affect battery characteristics such as capacity, output characteristics, storage, and cycle characteristics are preferred. Specifically, it can be selected that the mass loss when heated to 700°C under an inert atmosphere is usually 50% by mass or more, preferably 80% by mass or more, more preferably 95% by mass or more, and more preferably 99% by mass or more, Especially preferably, it is 99.9 mass % or more.

The graphite (A) in the mixture obtained in the above-mentioned step 1 used for the spheroidization treatment may be obtained after a certain spheroidization treatment under the conditions of the previous method. In addition, the mechanical action can also be repeatedly imparted by circulating the complex obtained in the above-mentioned step 1 or by performing this step a plurality of times.

When performing the spheroidization treatment, the rotor speed is usually between 2000 rpm and 9000 rpm, preferably between 4000 rpm and 8000 rpm, more preferably between 5000 rpm and 7500 rpm, and more preferably between 6000 rpm and 7200 rpm The spheroidization process is usually carried out within a range of 30 seconds to 60 minutes, preferably 1 minute to 30 minutes, more preferably 1 minute to 30 seconds to 10 minutes, and more preferably 2 minutes to 5 minutes .

If the rotation speed of the rotor is too low, the process of forming a spherical shape will be weak, and the tap density may not be sufficiently improved. If the rotational speed of the rotor is too high, the effect of being crushed is stronger than that of forming a ball, which may cause the particles to disintegrate and reduce the tap density. If the spheroidization treatment time is too short, the particle size cannot be sufficiently reduced, and a high tap density cannot be achieved. If the spheroidization treatment time is too long, the graphite in the mixture obtained in the above step 1 will become pulverized, and the purpose of the present invention may not be achieved.

The obtained particles can also be classified. When the obtained particles are not within the range of physical properties specified in the present invention, they can be graded repeatedly (usually 2 to 10 times, preferably 2 to 5 times) to achieve the desired particle size. The required range of physical properties. The classification may, for example, be a dry type (air classification, sieving), a wet type classification, or the like. In terms of cost and productivity, dry classification, especially pneumatic classification is preferred.

The particles of the present invention can be produced by the production method as described above.

<Manufacturing method of carbonaceous material-coated particles> The particles of the present invention obtained in the above manner preferably contain carbonaceous substances. As a more specific aspect, it is more preferable that at least a part of the surface of the particle is coated with a carbonaceous substance (hereinafter also referred to as "carbonaceous substance-coated particle" or "carbonaceous substance-coated particle of the present invention").

The carbonaceous material-coated particles can be produced by performing the following step 3 after the above step 2. Step 3: A step of coating the particles spheroidized in step 2 with a carbonaceous substance Hereinafter, step 3 will be described in detail.

(Step 3: The step of coating the particles spheroidized in Step 2 with carbonaceous material) ・Carbonaceous matter As said carbonaceous substance, amorphous carbon and graphitized carbon are mentioned according to the difference in the heating temperature in the manufacturing method mentioned later. Among these, amorphous carbon is preferable in terms of the acceptability of lithium ions.

Specifically, the above-mentioned carbonaceous substance can be obtained by heat-treating its carbon precursor as described below. The carbon precursor described above is preferably the carbon material described in (i) and/or (ii) above.

・Coating treatment In the coating process, the particles obtained in the above step 2 are mixed and calcined using a carbon precursor for obtaining carbonaceous material as a coating material, thereby obtaining coated particles. If the calcination temperature is usually above 600°C, preferably above 700°C, more preferably above 900°C and usually below 2000°C, preferably below 1500°C, more preferably below 1200°C, amorphous Carbon is a carbonaceous substance. If the heat treatment is carried out under the condition that the calcination temperature is usually above 2000°C, preferably above 2500°C and usually below 3200°C, graphitized carbon can be obtained as the carbonaceous substance. The above-mentioned amorphous carbon is carbon with low crystallinity. The above-mentioned graphitized carbon is carbon with relatively high crystallinity. In the coating process, the above-mentioned particles are used as a core material, and a carbon precursor for obtaining carbonaceous substances is used as a coating raw material, and these are mixed and calcined to obtain carbonaceous substance-coated particles.

・Mixed with metal particles or carbon particles Alloyable metal particles or carbon fine particles may also be included in the coating layer. The shape of the carbon fine particles is not particularly limited, and may be any of granular, spherical, chain, needle, fibrous, plate, and scaly.

The carbon fine particles are not particularly limited, and specifically, coal fine powder, vapor phase toner, carbon black, ketjen black, carbon nanofiber, and the like may be mentioned. Among them, particularly preferred is carbon black. If it is carbon black, there is an advantage that input and output characteristics become high even at low temperature, and at the same time, it can be obtained cheaply and easily.

The volume average particle diameter (d ₅₀ ) of carbon fine particles is usually 0.01 μm to 10 μm, preferably 0.05 μm to 8 μm, more preferably 0.07 μm to 5 μm, and more preferably 0.1 μm to 1 μm .

When the carbon fine particles have a secondary structure in which primary particles aggregate or agglomerate, other physical properties or types are not particularly limited as long as the primary particle diameter is not less than 3 nm and not more than 500 nm. The primary particle size is preferably from 3 nm to 500 nm, more preferably from 15 nm to 200 nm, further preferably from 30 nm to 100 nm, especially preferably from 40 nm to 70 nm.

・Other steps The particles after the above steps can be subjected to powder processing such as pulverization, crushing, and classification treatment as described in step 1. The carbonaceous material-coated particle of the present invention can be produced by the production method as described above.

＜Use＞ The particles of the present invention can realize a secondary battery having excellent battery characteristics by being used as the negative electrode active material of the secondary battery. Therefore, the particles of the present invention can be used as negative electrode active materials of secondary batteries.

[Secondary battery] The secondary battery of the present invention includes a positive electrode, a negative electrode, and an electrolyte, and the negative electrode includes a current collector, and a negative electrode active material layer formed on the current collector, and the negative electrode active material layer includes the particles of the present invention. The secondary battery of the present invention is usually produced by the method for producing a secondary battery of the present invention including the step of forming a negative electrode active material layer containing the particles of the present invention on a collector to obtain a negative electrode.

＜Negative electrode＞ In order to use the particles of the present invention to produce a negative electrode (hereinafter, sometimes referred to as "the negative electrode of the present invention"), a binder (binding resin) is prepared in the particles of the present invention, and the resultant is dispersed in a dispersion medium to prepare a slurry , which is applied to a collector and dried to form a negative electrode active material layer on the collector.

As the binder, one having an olefinic unsaturated bond in the molecule is used. The type thereof is not particularly limited. Specific examples include: styrene-butadiene rubber, styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, ethylene-propylene-diene copolymer, etc. . By using such a binder having an olefinic unsaturated bond, the swelling property of the negative electrode active material layer in the electrolytic solution can be reduced. Among these, styrene-butadiene rubber is preferred in terms of ease of acquisition.

As a binder with olefinic unsaturated bonds in the molecule, it is ideal to have a larger molecular weight or a higher ratio of unsaturated bonds. As a binder with relatively large molecular weight, it is ideal that the weight average molecular weight is usually more than 10,000, preferably more than 50,000, and usually less than 1 million, preferably less than 300,000. As a binder with a relatively high ratio of unsaturated bonds, it is ideal that the number of moles of olefinic unsaturated bonds per 1 g of the total binder is usually 2.5×10 ^-7 or more, preferably 8×10 ^-7 or more, It is also usually in the range of 5×10 ^-6 or less, preferably 1×10 ^-6 or less.

As the binder, it is only necessary to satisfy at least one of the requirements related to the molecular weight of the binder and the requirements related to the ratio of unsaturated bonds, and it is more preferable to satisfy both requirements at the same time. If the molecular weight of the binder having olefinic unsaturated bonds is too small, the mechanical strength will be poor. If the molecular weight of the adhesive is too large, the flexibility will be poor. Also, if the ratio of olefinic unsaturated bonds in the adhesive is too low, the strength improvement effect will be poor, and if the ratio of olefinic unsaturated bonds in the adhesive is too high, the flexibility will be poor.

The binder having an olefinic unsaturated bond preferably has an unsaturation degree of usually 15% or more, preferably 20% or more, more preferably 40% or more, and usually 90% or less, preferably 80% or less the scope of those. The degree of unsaturation represents the ratio (%) of double bonds to the repeating units of the polymer.

In the present invention, a binder that does not have an olefinic unsaturated bond can also be used in combination with the above-mentioned binder that has an olefinic unsaturated bond within the range that does not impair the effects of the present invention. The mixing ratio of the binder not having an olefinic unsaturated bond to the amount of the binder having an olefinic unsaturated bond is usually 150% by mass or less, preferably 120% by mass or less. Coatability can be improved by using a binder that does not have an olefinic unsaturated bond in combination, but if the combined use is too large, the strength of the active material layer will decrease.

Examples of binders that do not have an olefinic unsaturated bond include polysaccharides such as methylcellulose, carboxymethylcellulose, and starch; carrageenan, pullulan, guar gum, and xanthan gum (Sanxian gum) and other thickening polysaccharides; polyethylene oxide, polypropylene oxide and other polyethers; polyvinyl alcohol, polyvinyl butyral and other vinyl alcohols; polyacrylic acid, polymethacrylic acid and other polyacids or the Metal salts of polymers such as polyvinylidene fluoride; fluorinated polymers such as polyvinylidene fluoride; alkane polymers such as polyethylene and polypropylene and their copolymers, etc.

The mass ratio (particle/binder of the present invention) of the particles of the present invention in the slurry to the binder (which may be a mixture of the binder with unsaturated bonds and the binder without unsaturated bonds as described above) is determined by the respective In terms of dry mass ratio, it is usually 90/10 or more, preferably 95/5 or more, and usually 99.9/0.1 or less, preferably 99.5/0.5 or less. If the ratio of the binder is too high, it will easily lead to a decrease in capacity or an increase in resistance. If the ratio of the binder is too small, the strength of the negative plate will be poor.

An organic solvent such as alcohol, or water can be used as a dispersion medium for preparing a slurry in which the particles of the present invention and a binder are dispersed. It is also possible to further add a conductive agent to the slurry as needed. The conductive agent may, for example, be carbon black such as acetylene black, ketjen black or furnace black, Cu or Ni having an average particle diameter of 1 μm or less, or fine powders containing these alloys. The added amount of the conductive agent is usually 10% by mass or less with respect to the particles of the present invention.

As the current collector on which the slurry is applied, a conventionally known one can be used. Specifically, metal thin films such as rolled copper foil, electrolytic copper foil, and stainless steel foil may be mentioned. The thickness of the current collector is usually at least 4 μm, preferably at least 6 μm, and usually at most 30 μm, preferably at most 20 μm.

The above-mentioned slurry is applied on the current collector using a doctor blade or the like, dried, and then pressed by a roll press or the like to form a negative electrode active material layer. At this time, the slurry is preferably applied so that the adhesion amount of the particles of the present invention on the current collector becomes 5 to 15 mg/cm ² .

With regard to the drying after coating the slurry on the current collector, at a temperature of usually 60° C. or higher, preferably 80° C. or higher, and usually 200° C. or lower, preferably 195° C. or lower, dry air or Dry under an inert atmosphere.

The thickness of the negative electrode active material layer obtained by applying the slurry and drying it is usually 5 μm or more, preferably 20 μm or more, further preferably 30 μm or more, and usually 200 μm in a pressurized state or less, preferably 100 μm or less, further preferably 75 μm or less. When the negative electrode active material layer is too thin, it lacks practicality as a negative electrode active material layer from the point of balance with the particle diameter of the particle of this invention which is a negative electrode active material. If the negative electrode active material layer is too thick, it is difficult to obtain sufficient Li ion storage and release functions for high-density current values.

The density of the particles of the present invention in the negative electrode active material layer varies according to the application. In applications where capacity is important, it is preferably 1.55 g/cm ³ or more, especially preferably 1.6 g/cm ³ or more, and even more preferably It is at least 1.65 g/cm ³ , more preferably at least 1.7 g/cm ³ . If the density is too low, the capacity of the battery per unit volume may not be sufficient. If the density is too high, the rate characteristic will decrease, so the density of graphite is preferably 1.9 g/cm ³ or less.

When the particles of the present invention described above are used to fabricate the negative electrode of the present invention, there is no particular limitation on the method or selection of other materials. When the negative electrode is used to manufacture a secondary battery, there is no particular limitation on the selection of components necessary for battery construction such as a positive electrode and an electrolyte that constitute the secondary battery.

＜Secondary battery＞ Hereinafter, the details of the secondary battery of the present invention including the negative electrode using the particles of the present invention will be described with an example of a lithium ion secondary battery. Materials and manufacturing methods that can be used in the secondary battery of the present invention are not limited to the following specific examples.

The basic structure of the secondary battery of the present invention, especially the lithium-ion secondary battery is the same as that of the previously known lithium-ion secondary battery, and usually includes a positive electrode and a negative electrode capable of absorbing and releasing lithium ions, and an electrolyte. As the negative electrode, the above-mentioned negative electrode of the present invention was used.

The positive electrode is one in which a positive electrode active material layer containing a positive electrode active material and a binder is formed on a current collector.

Examples of the positive electrode active material include metal chalcogen compounds capable of storing and releasing alkali metal cations such as lithium ions during charging and discharging. Examples of metal chalcogen compounds include transition metal oxides such as vanadium oxides, molybdenum oxides, manganese oxides, chromium oxides, titanium oxides, and tungsten oxides; vanadium sulfides , Molybdenum sulfide, titanium sulfide, CuS and other transition metal sulfides; NiPS ₃ , FePS ₃ and other transition metal phosphorus-sulfur compounds; VSe ₂ , NbSe ₃ and other transition metal selenium compounds; Fe _0.25 V _0.75 S ₂ , Na _0.1 CrS ₂ and other transition metal composite oxides; LiCoS ₂ , LiNiS ₂ and other transition metal composite sulfides, etc.

Among them, V ₂ O ₅ , V ₅ O ₁₃ , VO ₂ , Cr ₂ O ₅ , MnO ₂ , TiO, MoV ₂ O ₈ , LiCoO _{2 , LiNiO 2 ,} LiMn ₂ O ₄ , TiS ₂ , V ₂ S _5. Cr _0.25 V _0.75 S ₂ , Cr _0.5 V _0.5 S _{2 ,} etc., especially LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , or lithium transition metal composite oxidation in which part of these transition metals is replaced by other metals thing. These positive electrode active materials may be used alone or in combination of plural kinds.

As the binder for binding the positive electrode active material, known ones can be arbitrarily selected and used. Examples include inorganic compounds such as silicate and water glass, and resins that do not have unsaturated bonds such as Teflon (registered trademark) and polyvinylidene fluoride. Among them, a resin having no unsaturated bond is preferable. If a resin having an unsaturated bond is used as the resin to which the positive electrode active material is bound, there is a risk of decomposition during an oxidation reaction (during charging). The weight average molecular weight of these resins is usually above 10,000, preferably above 100,000, and usually below 3 million, preferably below 1 million.

The positive electrode active material layer may also contain a conductive agent to improve the conductivity of the electrode. The conductive agent is not particularly limited as long as it can be mixed in an appropriate amount in the active material to impart conductivity. As the conductive agent, generally, carbon powders such as acetylene black, carbon black, and graphite, fibers, powders, and foils of various metals may, for example, be mentioned.

The positive electrode plate is formed by slurring the positive electrode active material or binder with a dispersant, coating it on the current collector, and drying it by the same method as that of the above-mentioned negative electrode of the present invention. . As the current collector of the positive electrode, aluminum, nickel, stainless steel (SUS) or the like can be used without any limitation.

As the electrolyte, it is possible to use: a non-aqueous electrolyte solution in which lithium salt is dissolved in a non-aqueous solvent; or a non-aqueous electrolyte solution made into a gel, rubber, or solid sheet by an organic polymer compound, etc. .

The non-aqueous solvent used for the non-aqueous electrolytic solution is not particularly limited, and can be appropriately selected from known non-aqueous solvents proposed previously as solvents for the non-aqueous electrolytic solution. For example, it can be exemplified: chain carbonates such as diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate; cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate; 1,2 -Chain ethers such as dimethoxyethane; cyclic ethers such as tetrahydrofuran, 2-methyltetrahydrofuran, cyclobutane, 1,3-dioxolane; methyl formate, methyl acetate, propane chain esters such as methyl ester; cyclic esters such as γ-butyrolactone and γ-valerolactone, etc.

These non-aqueous solvents may be used alone or in combination of two or more. In the case of a mixed solvent, a combination of a mixed solvent containing a cyclic carbonate and a chain carbonate is preferable. It is particularly preferable that the cyclic carbonate is a mixed solvent of ethylene carbonate and propylene carbonate in terms of exhibiting high ionic conductivity even at low temperatures and improving low-temperature charge load characteristics.

Among them, the content of propylene carbonate is preferably in the range of 2% by mass to 80% by mass relative to the entire non-aqueous solvent, more preferably in the range of 5% by mass to 70% by mass, and still more preferably 10% by mass. % to 60% by mass. When the content rate of propylene carbonate is less than the said lower limit, the ion conductivity at low temperature will fall. If the content of propylene carbonate is higher than the above-mentioned upper limit, there is a problem that the graphite-based negative electrode active material will delaminate due to intercalation and degradation of the graphite-based negative electrode active material due to the co-intercalation of propylene carbonate solvated with Li ions into the graphite phase of the negative electrode. , so that sufficient capacity cannot be obtained.

The lithium salt used in the non-aqueous electrolytic solution is also not particularly limited, and can be appropriately selected from known lithium salts known to be used for this purpose. For example, halides such as LiCl and LiBr; perhalogenates such as LiClO ₄ , LiBrO ₄ , and LiClO ₄ ; inorganic lithium salts such as inorganic fluoride salts such as LiPF ₆ , LiBF ₄ , and LiAsF ₆ ; LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ and other perfluoroalkane sulfonates; perfluoroalkyl sulfonyl imide salts such as lithium bistrifluoromethanesulfonyl imide ((CF ₃ SO ₂ ) ₂ NLi) and other fluorine-containing organic lithium salts, etc. . Among them, LiClO ₄ , LiPF ₆ , and LiBF ₄ are preferred.

Lithium salts may be used alone or in combination of two or more. The concentration of lithium salt in the non-aqueous electrolyte is usually in the range of 0.5 mol/L to 2.0 mol/L.

In the case where the non-aqueous electrolytic solution contains an organic polymer compound and the electrolyte is used in the form of a gel, rubber or solid sheet, specific examples of the organic polymer compound include: polyethylene oxide, polyethylene Polyether-based polymer compounds such as propylene oxide; cross-linked polymers of polyether-based polymer compounds; vinyl alcohol-based polymer compounds such as polyvinyl alcohol and polyvinyl butyral; insolubles of vinyl alcohol-based polymer compounds ; polyepichlorohydrin; polyphosphazene; polysiloxane; Ethylene oxide), poly(ω-methoxy oligooxyethylene oxide methacrylate-co-methyl methacrylate), poly(hexafluoropropylene-vinylidene fluoride) and other polymer copolymers, etc.

The said non-aqueous electrolytic solution may further contain a film forming agent. Specific examples of coating forming agents include: carbonate compounds such as vinylene carbonate, vinyl ethyl carbonate, and methylphenyl carbonate; sulfurized olefins such as ethylene sulfide and propylene sulfide; 1,3-propanesulfonate Sultone compounds such as lactone and 1,4-butane sultone; acid anhydrides such as maleic anhydride and succinic anhydride, etc. Furthermore, an overcharge preventing agent such as diphenyl ether or cyclohexylbenzene may be added to the non-aqueous electrolytic solution.

When these additives are used, their content in the non-aqueous electrolyte is usually 10% by mass or less, preferably 8% by mass or less, further preferably 5% by mass or less, especially preferably 2% by mass %the following. If the content of the above-mentioned additives is too large, there is a possibility that other battery characteristics may be adversely affected by an increase in the initial irreversible capacity, a decrease in low-temperature characteristics, and a reduction in rate characteristics.

As the electrolyte, a polymer solid electrolyte that is a conductor of alkali metal cations such as lithium ions can also be used. Examples of the polymer solid electrolyte include those in which Li salt is dissolved in the above-mentioned polyether-based polymer compound, or polymers in which terminal hydroxyl groups of polyether are substituted with alkoxides, and the like.

Between the positive electrode and the negative electrode, a porous separator such as a porous film or non-woven fabric is usually interposed to prevent short circuits between the electrodes. In this case, the porous separator is impregnated with the non-aqueous electrolytic solution and used. As a material for the separator, polyolefins such as polyethylene and polypropylene, polyether sulfide, etc. can be used, and polyolefins are preferred.

The form of the lithium ion secondary battery to which the present invention is applied is not particularly limited. Examples include: a cylindrical shape in which a sheet electrode and a separator are spirally formed, a cylindrical shape in which an inside-out structure is formed by combining a particle electrode and a separator, and a cylindrical shape in which a particle electrode and a separator are combined Stacked coins, etc. By accommodating batteries of these forms in any external case, it can be used in any shape such as a coin shape, a cylindrical shape, or a square shape.

The order of assembling the lithium-ion secondary battery is not particularly limited, and can be assembled in an appropriate order according to the structure of the battery. For example, the negative electrode can be placed on the outer casing, and the electrolyte and separator can be placed on it, and then the positive electrode can be placed in a manner opposite to the negative electrode, and riveted together with the gasket and the sealing plate to form a battery.

＜Performance of secondary battery＞ In the secondary battery of the present invention, the particle of the present invention including the silicon oxide particle of the present invention and graphite is used as the negative electrode active material, so that the battery characteristics, especially the effect of suppressing electrode swelling are excellent. Specifically, it is preferable that the discharge capacity at the 50th cycle measured by the method described in the following examples is 400 mAh/g or more, and the charge-discharge efficiency is 99.8% or more. In the secondary battery of the present invention, it is preferable that the electrode swelling measured by the method described in the following examples is 1.4 or less. Example

Hereinafter, specific aspects of the present invention will be further described in detail by means of examples. The present invention is not limited to these examples.

[test methods] The measurement methods of the physical properties of the materials used in the following examples and comparative examples are as follows.

<Contents of zirconium, yttrium, hafnium and manganese in silicon oxide particles> The contents of zirconium (Zr), yttrium (Y), hafnium (Hf), and manganese (Mn) in the silicon oxide particles were measured by the following method. Heat and dissolve the sample in mixed acid (hydrofluoric acid, nitric acid), volatilize the silicon oxide particles, dissolve in sulfuric acid, and add water to dilute. The metal impurity in the decomposition solution was quantified by ICP-AES (iCAP7600DuO manufactured by Thermo Fisher Scientific) according to the acid matrix matching calibration curve method. The detection limit in this measurement method is: zirconium: 0.1 ppm, yttrium: 0.1 ppm, hafnium: 0.3 ppm, manganese: 0.1 ppm.

<Contents of zirconium, yttrium, hafnium and manganese in negative electrode active material particles> According to the content of zirconium, yttrium, hafnium and manganese in the silicon oxide particles used in the production of particles, and the content ratio of silicon oxide particles in the particles, the zirconium, yttrium, hafnium and manganese in the particles are calculated by calculation The content rate.

<Volume average particle diameter (d ₅₀ )> Add about 20 mg of particles to about 1 ml of a 2 volume % aqueous solution of polyoxyethylene (20) sorbitan monolaurate, and disperse it in about 200 ml of ion-exchanged water , using a laser diffraction particle size distribution meter (manufactured by Horiba, model name "LA-920"), the obtained product was measured for volume particle size distribution, and the median diameter (d ₅₀ ) was determined. The measurement conditions are: ultrasonic dispersion for 1 minute, ultrasonic intensity of 2, circulation speed of 2, and relative refractive index of 1.50.

<Particle diameter (d ₉₀ )> The particle diameter (d 90 ) is defined as the particle diameter corresponding to 90% accumulation from the smaller particle side in the particle size distribution obtained by the measurement _of the volume average particle diameter (d ₅₀ ).

<Maximum particle diameter (d _max )> The maximum diameter in the particle size distribution obtained in the measurement of the volume average particle diameter (d ₅₀ ) was defined as the maximum particle diameter (d _max ).

<The value of x in SiOx> The value of x in SiOx of the silicon oxide particles is calculated based on the values measured by pulse furnace heating extraction-IR detection method and ICP emission spectrometry in an inert gas atmosphere. Specifically, the sample was melted with alkali, and the amount of silicon in the diluted sample solution after constant volume was measured using ICP-AES (manufactured by Thermo Fisher Scientific, model name "iCAP7600Duo"). In addition, the oxygen content of the sample was measured using an oxygen, nitrogen and hydrogen analyzer (manufactured by LECO, model name "TCH600"). Calculate the amount of oxygen relative to silicon, and set it as the value of x in SiOx.

<Specific surface area obtained by BET method> Using a specific surface area measuring device (manufactured by Mountech, model name "Macsorb HM Model-1210"), the sample was filled into a dedicated cell, heated to 150°C for pretreatment, and then cooled to liquid nitrogen temperature, and the saturation adsorption was accurately determined. Adjust the gas with about 30% nitrogen and helium balance, then heat it to room temperature, measure the amount of desorbed gas, and calculate the specific surface area by BET 1-point analysis according to the obtained adsorption amount.

<Tap Density> Using a powder density tester (model name "Tap Denser KYT-5000", manufactured by Qingxin Enterprise Co., Ltd.), in a cylindrical tap cell with a diameter of 1.5 cm and a volume capacity of 20 cm ³ , Let the sample fall through a sieve with a pore size of 300 μm, and fill the container to the full. Afterwards, vibrate 1000 times with a stroke length of 10 mm, and use the density calculated based on the volume at this time and the mass of the sample as the tap density.

[Example 1-1] Silicon and silicon dioxide were used as raw materials and synthesized by a vacuum evaporation method, followed by a coarse pulverization step by a fine pulverization corresponding jet mill (manufactured by Aishin Nano Technologies) equipped with a classifier The obtained silicon oxide powder was dry pulverized to manufacture silicon oxide particle No. 1 in which the value of x in SiOx was 0.9 and the content ratios of d ₅₀ , d _max , and metal elements were shown in Table 1.

[Comparative Example 1-1] In Example I-1, 2-propanol was used as a dispersion medium, and wet pulverization was performed using a bead mill (manufactured by Asada Iron Works) instead of dry pulverization. Silicon oxide particles No. 2 in which the value of x in SiOx is 0.9 and the content ratios of d ₅₀ , d _max , and metal elements are as shown in Table 1 were produced by this method.

[Table 1] crushing method Particle size [μm] Metal element content [ppm] d _{50 dmax} Zr Y f mn Example I-1 (Silicon Oxide Particle No.1) dry 0.5 1.7 14 <0.1 <0.3 44 Comparative Example I-1 (Silicon Oxide Particle No.2) wet 0.5 1.5 4630 271 106 493

[Examples II-1, 2, Comparative Example II-1] <Manufacture of Particles> As graphite, graphite having the following physical properties was used. (Physical properties of graphite No.1) d ₅₀ : 11.1 μm d ₉₀ : 21.1 μm Specific surface area by BET method: 9.9 m ² /g Tap density: 0.44 g/cm ³ (Physical properties of graphite No.2) d ₅₀ : 7.8 μm d ₉₀ : 14.1 μm Specific surface area obtained by BET method: 12.3 m ² /g Tap density: 0.45 g/cm ³

As the silicon oxide particles, in Examples II-1 and 2, the silicon oxide particle No.1 synthesized in Example I-1 was used, and in Comparative Example II-1, the silicon oxide synthesized in Comparative Example I-1 was used Particle No.2. As graphite, in Example II-1 and Comparative Example II-1, graphite No. 1 was used, and in Example II-2, graphite No. 2 was used.

Graphite and silicon oxide particles were mixed at a ratio of graphite: 70% by mass and silicon oxide particles: 16% by mass, and 9% by mass of liquid oil was added as a granulating agent, and stirred and mixed by a stirring granulator. The obtained mixture was put into the mixing system, and the granulation and spheroidization process was carried out by mechanical action for 5 minutes under the condition of the rotor peripheral speed of 85 m/s. Furthermore, liquid oil used as a granulating agent was removed by heat treatment to obtain spherical composite particles. The obtained spheroidized composite particles were mixed with pitch as a precursor of graphitic substances. The ash content of the above pitch was 0.02% by mass, the amount of metal impurities was 20% by mass, and the amount of Qi was 1% by mass. Heat treatment was performed at 1000° C. to obtain a calcined product. The calcined product was crushed and classified to obtain negative electrode active material particles in which graphite, silicon oxide particles, and amorphous carbon were composited at the ratio shown in Table 2A.

＜Production of lithium-ion secondary battery＞ Using each particle as a negative electrode active material, a lithium ion secondary battery was produced as follows.

95% by mass of the particles obtained in Examples and Comparative Examples, 2.5% by weight of acetylene black as a conductive material, 1.5% by mass of carboxymethylcellulose (CMC) as a binder, and styrene butadiene were mixed by a hybrid mixer. A 48% by mass aqueous dispersion of diene rubber (SBR) was kneaded at 3.1% by mass to prepare a slurry. The slurry was coated on a rolled copper foil with a thickness of 20 μm by the doctor blade coating method so that the weight per unit area was 7-8 mg/cm ² , and dried. Afterwards, by means of a 250 mϕ roller press with a load cell, the negative electrode active material layer is rolled to a density of 1.6-1.7 g/cm ³ , and punched into a circular shape with a diameter of 12.5 mm. It was dried under vacuum for 8 hours and used as a negative electrode for evaluation.

This negative electrode was laminated with a Li foil serving as a counter electrode via a separator impregnated with an electrolytic solution, and a battery for charge and discharge tests was fabricated. As the electrolytic solution, LiPF ₆ was dissolved in a mixture of ethylene carbonate/ethyl methyl carbonate/monofluoroethylene carbonate=3/6/1 (volume ratio) so that 1 mol/liter was used. By.

＜Evaluation of battery characteristics＞ About the obtained lithium secondary battery, the battery characteristic was evaluated by the following method, and the result is shown in Table 2B. Furthermore, in Table 2B, the total content of zirconium, yttrium, hafnium, and manganese in the silicon oxide particles used (in Table 2B, described as "total metal content") and each metal in the negative electrode active material particles are also described. The content rate of elements and their total content rate.

(Discharge capacity, charge-discharge efficiency) First, charge the positive and negative electrodes of the above-mentioned charge-discharge test battery to 5 mV at a current density of 0.08 mA/cm ² , and then charge at a constant voltage of 5 mV until the current value reaches 0.03 Up to mA, after doping lithium into the negative electrode, the above-mentioned positive and negative electrodes were discharged to 1.5 V at a current density of 0.2 mA/cm ² (initial first cycle). Thereafter, the current density during charging was set to 0.2 mA/cm ² , and the current density during discharging was set to 0.3 mA/cm ² . Charge and discharge were repeated 4 times under the same conditions as above (initial 2nd cycle to initial 5th cycle). The case where the current flows to the negative electrode for evaluation in the direction of lithium doping is described as "charging", and the case where the current flows from the negative electrode for evaluation in the direction of dedoping lithium is described as "discharge". The initial discharge capacity was obtained as follows. First, the mass of the negative electrode active material is obtained by subtracting the mass of the copper foil punched into the same area as the negative electrode from the mass of the negative electrode, and the mass of the negative electrode active material is divided by the discharge capacity of the initial 5th cycle to obtain the mass per unit mass the initial discharge capacity.

The charge-discharge efficiency was calculated|required by the following formula. The mass of the negative electrode active material was obtained by subtracting the mass of the copper foil punched into the same area as the negative electrode from the mass of the negative electrode. Charge-discharge efficiency (%)={discharge capacity of the initial 3rd cycle (mAh/g)/(charge capacity of the first initial cycle (mAh/g)+charge capacity of the initial 2nd cycle (mAh/g) - Discharge capacity of the second initial cycle (mAh/g) + charge capacity of the third initial cycle (mAh/g) - discharge capacity of the third initial cycle (mAh/g))}×100

(Electrode Swelling) The battery after the initial charge and discharge described above was further repeatedly charged and discharged 50 times (1st cycle to 50th cycle). Among them, except for the 25th cycle and the 50th cycle, the current density at the time of charging was set at 0.2 mA/cm ² , and the current density at the time of discharging was set at 0.3 mA/cm ² . 1 cycle with the same conditions. Also, the 25th cycle and the 50th cycle used the same conditions as the initial 2nd cycle. Disassemble the battery after repeated 50 cycles of charging and discharging, take out the negative electrode, measure the thickness of the negative electrode with a thickness gauge (manufactured by Mitutoyo), and subtract the thickness of the copper foil punched into the same area as the negative electrode from the thickness of the above negative electrode. Find the thickness of the negative electrode, divide it by the thickness of the negative electrode when the battery is manufactured, and set it as the index value of the electrode swelling.

[Table 2] <2A> graphite Silicon oxide particles amorphous carbon Type (No.) Mixing amount [mass%] Type (No.) Mixing amount [mass%] Mixing amount [mass%] Example II-1 1 71 1 16 13 Example II-2 2 71 1 16 13 Comparative Example II-1 1 71 2 16 13 <2B> Total metal content of silicon oxide particles [ppm] Metal element content of negative electrode active material particles [ppm] Discharge capacity[mAh/g] Charge and discharge efficiency[%] Electrode bulging Zr Y f mn total Example II-1 <55.4 2.2 <0.1 <0.3 7.0 <9.6 440.7 99.87 1.38 Example II-2 <55.4 2.2 <0.1 <0.3 7.0 <9.6 442.6 99.86 1.39 Comparative Example II-1 5500 740 43 17 79 880 440.5 99.89 1.51

As can be seen from Tables 2A and 2B, the total content of zirconium, yttrium, hafnium, and manganese is 600 ppm by using the silicon oxide particles and graphite of the present invention containing zirconium, yttrium, hafnium, and manganese with a total content of 1000 ppm or less. The following particles of the present invention can be used as negative electrode active materials to provide a secondary battery excellent in battery characteristics, especially excellent in the effect of suppressing electrode swelling.

Although this invention was demonstrated in detail using the specific aspect, it is clear for those skilled in the art that various changes can be added without deviating from the intent and range of this invention. This application is based on Japanese Patent Application No. 2021-175656 filed on October 27, 2021, the entirety of which is incorporated by reference.

Claims (17)

A silicon oxide particle, wherein the total content of zirconium, yttrium, hafnium, and manganese is 1000 ppm or less, and the d ₅₀ of the silicon oxide particle is 1 μm or less. The silica particles according to claim 1, wherein the content of zirconium is 500 ppm or less. The silicon oxide particles according to claim 1 or 2, wherein the content of yttrium is 100 ppm or less. The silicon oxide particles according to claim 1 or 2, wherein the content of hafnium is 100 ppm or less. The silicon oxide particles according to claim 1 or 2, wherein the manganese content is 300 ppm or less. The silicon oxide particle according to claim 1 or 2, wherein d _max /d ₅₀ is 2-10. The silicon oxide particle according to claim 1 or 2, which is used in a secondary battery. The method for producing silicon oxide particles according to claim 1 or 2, which includes the following steps: performing dry pulverization on the silicon oxide particles. A particle comprising silicon oxide particles with ad ₅₀ of 1 μm or less and graphite, and the total content of zirconium, yttrium, hafnium and manganese is 600 ppm or less. The particles according to claim 9, wherein the content of zirconium is 300 ppm or less. The particles according to claim 9 or 10, wherein the content of yttrium is 60 ppm or less. The particles according to claim 9 or 10, wherein the content of hafnium is 60 ppm or less. The particles according to claim 9 or 10, wherein the manganese content is 180 ppm or less. The method for producing particles according to claim 9 or 10, which includes the following steps: compounding silicon oxide particles and graphite. The method for producing particles according to Claim 14, wherein the composite method of silicon oxide particles and graphite is a method of mixing silicon oxide particles and graphite and then performing spheroidization treatment. A secondary battery comprising a positive electrode, a negative electrode and an electrolyte, and The negative electrode includes a current collector, and a negative active material layer formed on the current collector, The negative electrode active material layer contains the particles according to any one of Claims 9 to 13. A method for manufacturing a secondary battery, which is a method for manufacturing a secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, comprising the following steps: A negative electrode is obtained by forming a negative electrode active material layer containing particles according to any one of claims 9 to 13 on a current collector.