WO2023074217A1

WO2023074217A1 - Silicon oxide particles and method for producing same, particles and method for producing same, and secondary battery and method for producing same

Info

Publication number: WO2023074217A1
Application number: PCT/JP2022/035677
Authority: WO
Inventors: 悠貴江夏; 亨布施; 宏允池田; 賢一郎林; 拓史福地
Original assignee: 三菱ケミカル株式会社
Priority date: 2021-10-27
Filing date: 2022-09-26
Publication date: 2023-05-04
Also published as: TW202328000A; JPWO2023074217A1

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 particles and manufacturing method thereof, particles and manufacturing method thereof, secondary battery and manufacturing method thereof

The present invention relates to silicon oxide particles and particles useful as a negative electrode active material for secondary batteries, a method for producing the same, a secondary battery using the particles as a negative electrode active material, and a method for producing the same.

In recent years, with the miniaturization of electronic devices, the demand for high-capacity secondary batteries has increased.
In particular, non-aqueous secondary batteries, especially lithium-ion secondary batteries, have been attracting attention because of their higher energy density and superior rapid charge/discharge characteristics than nickel-cadmium batteries and nickel-hydrogen batteries.

A lithium ion secondary battery comprising a positive electrode and a negative electrode capable of intercalating and deintercalating lithium ions and a non-aqueous electrolytic solution in which a lithium salt such as LiPF ₆ or LiBF ₄ is dissolved has been developed and put into practical use.

Various materials have been proposed as the negative electrode material for this battery. As a negative electrode material, natural graphite, artificial graphite obtained by graphitizing coke or the like, graphitized mesophase pitch, graphite such as graphitized carbon fiber are used because of their high capacity and excellent discharge potential flatness. quality carbon materials are used.

In recent years, efforts have been made to develop applications for non-aqueous secondary batteries, especially lithium-ion secondary batteries. For example, it is used not only for conventional notebook computers, mobile communication devices, portable cameras, portable game machines, etc., but also for power tools, electric vehicles, and the like. Therefore, there is a demand for rapid charge/discharge performance that is higher than before. Furthermore, a lithium ion secondary battery having both high capacity and high cycle characteristics is desired.

However, in the carbon-centered negative electrode, the theoretical capacity of carbon is 372 mAh, so it is impossible to expect a higher capacity. Therefore, application of various negative electrode materials having a high theoretical capacity, particularly metal particles, to the negative electrode has been investigated.

In Patent Document 1, "In a composite active material for a lithium secondary battery containing Si or a Si alloy, a carbonaceous material or a carbonaceous material and a graphite component, the average particle diameter (D50) of the active material is 1 to 1. 40 μm, a specific surface area of 0.5 to 45 m ² /g, an average pore diameter of 10 to 40 nm, and an open pore volume of 0.06 cm ³ /g or less”. Proposed.

JP 2017-134937 A

The silicon oxide particles disclosed in Patent Document 1 are obtained by wet pulverization, and are likely to be contaminated with impurities through a medium in the pulverization process. expensive.
According to the studies of the present inventors, when these silicon oxide particles containing a large amount of metal components are used as a negative electrode active material, the battery characteristics of the obtained secondary battery are poor, and in particular, the problem of electrode swelling occurs. There was found.

An object of the present invention is to provide particles having a low total content of zirconium, yttrium, hafnium and manganese and having excellent battery characteristics, particularly an effect of suppressing electrode swelling, by using them as a negative electrode active material for secondary batteries. do.

The inventors of the present invention have found that particles containing specific silicon oxide particles and graphite have a low total content of zirconium, yttrium, hafnium and manganese, and that a secondary battery using this as a negative electrode active material has battery characteristics, particularly The inventors have found that the effect of suppressing electrode swelling is excellent, and have completed the present invention.
That is, the gist of the present invention is as follows.

[1] Silicon oxide particles having a total content of zirconium, yttrium, hafnium and manganese of 1000 ppm or less and a _d50 of 1 μm or less.

[2] The silicon oxide particles according to [1], having a zirconium content of 500 ppm or less.

[3] The silicon oxide particles according to [1] or [2], which have an yttrium content of 100 ppm or less.

[4] The silicon oxide particles according to any one of [1] to [3], which have a hafnium content of 100 ppm or less.

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

[6] The silicon oxide particles according to any one of [1] to [5], wherein d _max / _d50 is 2-10.

[7] The silicon oxide particles according to any one of [1] to [6], which are used in secondary batteries.

[8] A method for producing silicon oxide particles according to any one of [1] to [7], including a step of dry pulverizing the silicon oxide particles.

[9] Particles containing silicon oxide particles having a _d50 of 1 μm or less and graphite, wherein the total content of zirconium, yttrium, hafnium and manganese is 600 ppm or less.

[10] The particles according to [9], having a zirconium content of 300 ppm or less.

[11] The particles according to [9] or [10], which have an yttrium content of 60 ppm or less.

[12] The particles according to any one of [9] to [11], which have a hafnium content of 60 ppm or less.

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

[14] A method for producing particles according to any one of [9] to [13], including a step of combining silicon oxide particles and graphite.

[15] The method for producing particles according to [14], wherein the method of combining silicon oxide particles and graphite is a method of mixing the silicon oxide particles and graphite and then performing a spheroidization treatment.

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

[17] A method for manufacturing a secondary battery containing a positive electrode, a negative electrode and an electrolyte, comprising forming a negative electrode active material layer containing the particles according to any one of [9] to [13] on a current collector. A method for manufacturing a secondary battery, comprising the step of obtaining a negative electrode.

According to the silicon oxide particles of the present invention, which have a low total content of zirconium, yttrium, hafnium and manganese, and have a _d50 of a predetermined value or less, when used together with graphite as a negative electrode active material for a secondary battery, battery characteristics, In particular, it is possible to provide a secondary battery that is excellent in the effect of suppressing electrode swelling.
In addition, according to the particles of the present invention containing silicon oxide particles having a _d50 of a predetermined value or less and graphite, and having a low total content of zirconium, yttrium, hafnium and manganese, the particles can be used as a negative electrode active material for secondary batteries. Thus, it is possible to provide a secondary battery having excellent battery characteristics, particularly an effect of suppressing electrode swelling.

The present invention will be described in detail below. The present invention is not limited to the following description, and can be arbitrarily modified without departing from the gist of the present invention.
In the present invention, when a numerical value or a physical property value is sandwiched before and after the "~", it is used to include the values before and after it.

In the present invention, “d ₅₀ ” is the volume average particle diameter, which is the volume-based median diameter measured by laser diffraction/scattering particle size distribution measurement.
In the present invention, “d ₉₀ ” is defined as a particle diameter corresponding to cumulative 90% from the smaller particle side in the particle size distribution obtained during the measurement of d ₅₀ .
In the present invention, “d _max ” is the largest particle size measured for particles 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 _d50 is 1 μm or less.

The total content of zirconium, yttrium, hafnium and manganese is 1000 ppm or less, and silicon oxide particles having _d50 of 1 μm or less are combined with graphite to improve battery characteristics, particularly to suppress electrode swelling. Although the details of the mechanism of the excellent effect are not clear, it is presumed as follows.
When the total content of zirconium, yttrium, hafnium and manganese exceeds 1000 ppm, the above elements tend to exist locally non-uniformly within the silicon oxide particles. Locations in the silicon oxide particles where the above elements exist non-uniformly impede charge-discharge reactions in the battery and induce non-uniform volume changes in the silicon oxide particles. As a result, irreversible changes occur in the silicon oxide particles within the electrode, such as cracking of the particles and no decrease in the volume of the increased silicon oxide particles, resulting in swelling of the electrode. When the total content of zirconium, yttrium, hafnium and manganese is 1000 ppm or less, the above changes 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, still more preferably 200 ppm or less, and particularly preferably 100 ppm or less.
When 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, and in particular, the occurrence of electrode swelling can be suppressed.
There is no particular lower limit for the total content of zirconium, yttrium, hafnium and manganese, and the lower 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, the method for producing the silicon oxide particles of the present invention having a low total content of zirconium, yttrium, hafnium and manganese includes: , a method of performing dry grinding instead of wet grinding; a method of wet grinding using equipment that does not contain zirconium, yttrium, hafnium and manganese as constituent elements; using equipment that contains zirconium, yttrium, hafnium and manganese as constituent elements and a method of washing silicon oxide particles obtained by wet pulverization with a washing liquid such as a diluted alkaline aqueous solution that dissolves zirconium, yttrium, hafnium and manganese.

<Zirconium content>
In the silicon oxide particles of the present invention, the content of each metal element is not particularly limited as long as the total content of zirconium, yttrium, hafnium and manganese is 1000 ppm or less. is preferably 500 ppm or less, more preferably 100 ppm or less, and even more preferably 50 ppm or less. When the zirconium content is equal to or less than the above upper limit, there is a tendency to suppress the generation of deposits within the battery.
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 silicon oxide particles of the present invention is usually 0.1 ppm or more.

<Yttrium content>
In the silicon oxide particles of the present invention, the content of each metal element is not particularly limited as long as the total content of zirconium, yttrium, hafnium and manganese is 1000 ppm or less. is preferably 100 ppm or less, more preferably 10 ppm or less, and even more preferably 1 ppm or less. When the yttrium content is equal to or less than the above upper limit, there is a tendency to suppress the generation of deposits within the battery.
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 of the silicon oxide particles of the present invention is usually 0.01 ppm or more.

<Hafnium content>
In the silicon oxide particles of the present invention, the content of each metal element is not particularly limited as long as the total content of zirconium, yttrium, hafnium and manganese is 1000 ppm or less. is preferably 100 ppm or less, more preferably 10 ppm or less, and even more preferably 1 ppm or less. When the hafnium content is equal to or less than the above upper limit, there is a tendency to suppress the generation of deposits within the battery.
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 of the silicon oxide particles of the present invention is usually 0.01 ppm or more.

<Manganese content>
In the silicon oxide particles of the present invention, the content of metal elements is not particularly limited as long as the total content of zirconium, yttrium, hafnium and manganese is 1000 ppm or less. , preferably 300 ppm or less, more preferably 200 ppm or less, still more preferably 100 ppm or less. When the manganese content is equal to or less than the above upper limit, there is a tendency to suppress the generation of deposits within the battery.
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 prepared sample solution by the ICP-AES method.

_<d50>
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 or more and 0.9 μm or less, more preferably 0.2 μm or more and 0.8 μm or less. When the _d50 of the silicon oxide particles is within the above range, the volume expansion due to charge/discharge is reduced, and good cycle characteristics can be obtained while maintaining the charge/discharge capacity.

_<dmax>
The maximum particle diameter (d _max ) of the silicon oxide particles of the present invention is usually 0.02 μm or more and 20 μm or less, preferably 0.03 μm or more and 5 μm or less, more preferably 0.04 μm or more and 2 μm or less. When d _max is equal to or higher than the above lower limit, the capacity tends to be high. When d _max is equal to or less than the above upper limit, there is a tendency that silicon oxide particles insufficiently combined with graphite, which will be described later, can be reduced.

< _dmax / _d50 >
The ratio d _max /d ₅₀ between the maximum particle diameter (d _max ) and the volume average particle diameter (d ₅₀ ) of the silicon oxide particles of the present invention is preferably 2 to 10, more preferably 2.5 to 8. Yes, more preferably 3-6. When d _max /d ₅₀ is at least the above lower limit, it is easy to increase the weighting ratio of the electrode. When d _max /d ₅₀ is equal to or less than the above upper limit, the difference in volume expansion between silicon oxide particles is less likely to increase.

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

Silicon oxide is represented by the general formula SiOx and is obtained using silicon dioxide (SiO ₂ ) and metal Si (Si) as raw materials. The value of x is usually greater than 0 and 2 or less, preferably 0.1 or more and 1.8 or less, more preferably 0.5 or more and 1.5 or less, still more preferably 0.8 or more and 1 .2 or less. When x is within the above range, it is possible to reduce the irreversible capacity due to the combination of Li and oxygen while achieving a high capacity.

In this specification, the value of x in SiOx is measured by measuring the oxygen content of silicon oxide particles by impulse furnace heating extraction under an inert gas atmosphere-IR detection method, and measuring the silicon content of silicon oxide particles by ICP emission spectrometry. It is a value obtained by calculating the ratio of the amount of oxygen to silicon.

　SiOx has a larger theoretical capacity than graphite, and amorphous Si or nano-sized Si crystals facilitate the entry and exit of alkali ions such as lithium ions, making it possible to obtain a high capacity.

<Other physical properties>
The silicon oxide particles of the present invention preferably exhibit the following physical properties. The measuring method in the present invention is not particularly limited, but unless there are special circumstances, the measuring method described in the Examples applies.

- Specific Surface Area by BET Method The specific surface area of the silicon oxide particles by the BET method is usually 0.5 m ² /g or more and 120 m ² /g or less, preferably 1 m ² /g or more and 100 m ² /g or less. When the specific surface area of the silicon oxide particles as determined by the BET method is within the above range, the charge/discharge efficiency and discharge capacity of the battery are high, lithium is quickly taken in and out during high-speed charge/discharge, and the rate characteristics are excellent, which is preferable.

As used herein, 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 0.01% by mass or more and 50% by mass or less, preferably 0.05% by mass or more and 45% by mass or less, based on 100% by mass of the silicon oxide particles. The state of oxygen distribution in the silicon oxide particles may be in the vicinity of the surface, in the interior of the particles, or uniformly within the particles, but preferably in the vicinity of the surface. . When the oxygen content of the silicon oxide particles is within the above range, the strong bond between Si and O suppresses the volume expansion associated with charging and discharging, resulting in excellent cycle characteristics, which is preferable.

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

・Crystallite size Silicon oxide particles may contain a crystalline structure or may be amorphous. ) plane is usually 0.05 nm or more and 100 nm or less, preferably 1 nm or more and 50 nm or less. When the crystallite size of the silicon oxide particles is within the above range, the reaction between Si and Li ions proceeds rapidly, and the input/output is excellent, which is preferable.

In this specification, the crystallite size is a value obtained by the Debye-Scherrer method from the diffraction peak attributed to the Si (111) plane centered around 2θ = 28.4 ° observed by the X-ray wide-angle diffraction method. is.

[Method for producing silicon oxide particles]
As the silicon oxide particles, commercially available silicon oxide particles may be used after being subjected to purification treatment and pulverization treatment. The silicon oxide particles may be produced by subjecting silicon oxide particles having a large particle size to mechanical energy treatment using a ball mill or the like described later and washing the particles with an alkaline washing solution for a short period of time.

In addition, although the production method is not particularly limited, silicon oxide particles produced by the method described in Japanese Patent No. 3952118, for example, can also be used.
For example, SiO ₂ powder and metal Si powder are mixed in a specific ratio, and after filling this mixture into a reactor, the pressure is reduced to normal pressure or a specific pressure, and the temperature is raised to 1000 ° C. or higher and held. Silicon oxide particles can be obtained by generating SiOx gas and cooling and depositing it (sputtering process). The precipitate can also be made into particles by applying a pulverization treatment (dynamic energy treatment) and used.

In the production of the silicon oxide particles of the present invention, when the pulverization step is performed, if the pulverization is performed in a wet process, impurities are likely to be mixed in through the medium. can't get
For this reason, dry pulverization is preferably used for the pulverization.

In the dry pulverization process, for example, using an apparatus such as a ball mill, a vibrating ball mill, a planetary ball mill, a rolling ball mill, a bead mill, etc., a raw material filled in a reactor and a moving body that does not react with the raw material are placed, and vibrated, It can be done by a method that imparts motion by rotation or a combination thereof.

Dry pulverization treatment time is usually 3 minutes or more, preferably 5 minutes or more, more preferably 10 minutes or more, still more preferably 15 minutes or more, usually 5 hours or less, preferably 4 hours. or less, more preferably 3 hours or less, and still more preferably 1 hour or less. When the dry pulverization treatment time is within the above range, both improvement in productivity and stability of product properties can be achieved.
The dry pulverization treatment temperature is preferably above the freezing point and below the boiling point of the solvent in view of the process.

<Nitriding Treatment of Silicon Oxide Particles>
Since the silicon oxide particles have bonds with nitrogen atoms on their surfaces, the presence of oxides of the silicon oxide particles that cannot contribute to charging and discharging is suppressed, and the capacity per weight of the silicon oxide particles is improved. It is preferable to form a bond between the silicon oxide particles and the nitrogen atoms in order to reduce the reactivity of the surface of the silicon oxide particles and improve the charge/discharge efficiency.
Bonds between silicon oxide particles and nitrogen atoms can be analyzed by methods such as XPS, IR, XAFS, and the like.
In order to form bonds between silicon oxide particles and nitrogen atoms, there is a method of mixing a gas containing nitrogen atoms during the above-described sputtering treatment or dry pulverization treatment.

[particle]
The particles of the present invention are particles containing silicon oxide particles having a _d50 of 1 μm or less and graphite, wherein the total content of zirconium, yttrium, hafnium and manganese is 600 ppm or less.

Particles containing silicon oxide particles having a _d50 of 1 μm or less and graphite, and having a total content of zirconium, yttrium, hafnium and manganese of 600 ppm or less have an excellent effect in improving battery characteristics, particularly in suppressing electrode swelling. Although the details of the mechanism are not clear, it is presumed as follows.
When the total content of zirconium, yttrium, hafnium and manganese exceeds 600 ppm, the above elements tend to exist locally non-uniformly within the particles. Locations in the particles where the above elements exist non-uniformly impede charging and discharging reactions in the battery, and induce non-uniform volumetric changes in the particles. As a result, irreversible changes occur in the particles within the electrode, such as cracking of the particles and no reduction in the volume of the increased particles, resulting in swelling of the electrode. When the total content of zirconium, yttrium, hafnium and manganese is 600 ppm or less, the above 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, still more preferably 60 ppm or less.
When 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, and in particular, the occurrence of electrode swelling can be suppressed.
There is no particular lower limit for the total content of zirconium, yttrium, hafnium and manganese, and the lower the better. The total content of zirconium, yttrium, hafnium and manganese in the particles of the invention is usually 6 ppm or more.

As described above, as a method for producing the particles of the present invention having a low total content of zirconium, yttrium, hafnium and manganese, the silicon oxide particles of the present invention having a low total content of zirconium, yttrium, hafnium and manganese can be used. and the silicon oxide particles of the present invention are combined with graphite. In particular, in the step of combining the silicon oxide particles and graphite, a method of mixing the silicon oxide particles and graphite and then performing a spheroidizing treatment is preferred.

<Zirconium content>
In the particles of the present invention, the content of each metal element is not particularly limited as long as the total content of zirconium, yttrium, hafnium and manganese is 600 ppm or less. It is preferably 300 ppm or less, more preferably 60 ppm or less, still more preferably 30 ppm or less. When the zirconium content is equal to or less than the above upper limit, there is a tendency to suppress the generation of deposits within the battery.
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 invention is usually 0.06 ppm or more.

<Yttrium content>
In the particles of the present invention, the content of each metal element is not particularly limited as long as the total content of zirconium, yttrium, hafnium and manganese is 600 ppm or less, but among these metal elements, the yttrium content is It is preferably 60 ppm or less, more preferably 6 ppm or less, and still more preferably 0.06 ppm or less. When the yttrium content is equal to or less than the above upper limit, there is a tendency to suppress the generation of deposits within the battery.
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 of the particles of the invention is usually 0.006 ppm or more.

<Hafnium content>
In the particles of the present invention, the content of each metal element is not particularly limited as long as the total content of zirconium, yttrium, hafnium and manganese is 600 ppm or less, but among these metal elements, the hafnium content is It is preferably 60 ppm or less, more preferably 6 ppm or less, and still more preferably 0.6 ppm or less. When the hafnium content is equal to or less than the above upper limit, there is a tendency to suppress the generation of deposits within the battery.
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 of the particles of the invention is usually 0.006 ppm or more.

<Manganese content>
In the particles of the present invention, the content of metal elements is not particularly limited as long as the total content of zirconium, yttrium, hafnium and manganese is 600 ppm or less, but among these metal elements, the manganese content is preferably is 180 ppm or less, more preferably 120 ppm or less, and still more preferably 60 ppm or less. When the manganese content is equal to or less than the above upper limit, there is a tendency to suppress the generation of deposits within the battery.
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 invention is usually 0.06 ppm or more.

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

<Graphite>
Graphite, which is one of the constituents of the particles of the present invention, is shown below as an example. A publicly known product or a commercially available product may be used as the graphite.

(type of graphite)
As graphite, for example, scale-like, block-like or plate-like natural graphite, petroleum coke, coal pitch coke, coal needle coke, mesophase pitch, etc. are heated to 2500 ° C. or higher to produce scale-like, block-like or plate-like artificial graphite. Graphite can be obtained by removing impurities, pulverizing, sieving, and classifying, if necessary. Among these graphites, natural graphite in the form of flakes, lumps or plates is preferred, and natural graphite in the form of flakes is more preferred, because of its low cost and high capacity.

Natural graphite is classified into Flake Graphite, Crystal Line (Vein) Graphite, and Amorphous Graphite according to its properties ("Powder and Granule Process Technology Shusei" (Sangyo Co., Ltd.) Technical Center, published in 1974) and "Handbook of Carbon, Graphic, Diamond and Full Renes" (published by Noyes Publications)). The degree of graphitization is highest for flake graphite at 100%, followed by flake graphite at 99.9%. Therefore, it is preferable to use these graphites.

　Flake graphite, which is natural graphite, is produced in Madagascar, China, Brazil, Ukraine, Canada, etc. Sri Lanka is the main source of flake graphite. The main production areas of earthy graphite are the Korean Peninsula, China, Mexico, etc.

Among these natural graphites, flake graphite and flake graphite have advantages such as a high degree of graphitization and a low amount of impurities, and therefore can be preferably used in the present invention.
As a visual method for confirming that graphite is scale-like, particle surface observation by a scanning electron microscope; A cross-section of the coating film is prepared by a cross-section polisher, the cross-section of the particle is cut out, and then the cross-section of the particle is observed with a scanning electron microscope;
Flaky graphite and flaky graphite include natural graphite that has been highly purified so as to exhibit nearly perfect crystallinity, and artificially formed graphite. Of these, natural graphite is preferable because it is soft and easy to produce a folded structure.

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

・Volume average particle size (d ₅₀ )
The _d50 of graphite is usually 1 μm or more and 120 μm or less, preferably 3 μm or more and 100 μm or less, more preferably 5 μm or more and 90 μm or less. When _d50 is within the above range, particles with high properties can be produced by combining with silicon oxide particles. When the _d50 of graphite is equal to or higher than the above lower limit, it is possible to produce particles having a particle size within a range that allows an electrode to be formed with an appropriate amount of binder. If the _d50 of graphite is equal to or less than the above upper limit, streaks and unevenness caused by large particles are eliminated in the process of adding a binder, water, and an organic solvent to the particles and applying them as a slurry in the production of a secondary battery. You can prevent it from happening.

・Particle size (d ₉₀ )
The _d90 of graphite is usually 1.5 to 150 μm, preferably 4 to 120 μm, more preferably 6 to 100 μm. If the _d90 of the graphite is equal to or higher than the above lower limit, the silicon oxide particles and graphite can be combined efficiently. When the _d90 of graphite is equal to or less than the above upper limit, it is possible to suppress the formation of coarse particles when silicon oxide particles and graphite are combined.

・Average aspect ratio The average aspect ratio, which is the ratio of the length of the major axis to the minor axis of graphite, is usually 2.1 or more and 10 or less, preferably 2.3 or more and 9 or less, and more preferably 2.5 or more. 8 or less. When the aspect ratio is within the above range, it is possible to efficiently produce spherical particles, and minute voids are formed in the obtained particles, which alleviates volume expansion due to charging and discharging, and improves cycle characteristics. can contribute to improvement.

In the present specification, the aspect ratio is defined by A/B, which is the longest diameter A of the particles when observed three-dimensionally using a scanning electron microscope, and the shortest diameter B among the diameters perpendicular to it. It is calculated 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 or more and 1.0 g/cm ³ or less, preferably 0.13 g/cm ³ or more and 0.8 g/cm ³ or less, more preferably 0 .15 g/cm ³ or more and 0.6 g/cm ³ or less. When the tap density is within the above range, minute voids are likely to be formed in the obtained particles.

In this specification, the tap density is measured by filling a cylindrical tap cell with a diameter of 1.5 cm and a volume capacity of 20 cm ³ to the end using a powder density measuring instrument, then tapping with a stroke length of 10 mm 1000 times. is the density calculated from the volume of the sample and the mass of the sample.

- Specific surface area by BET method The specific surface area of graphite by the BET method is usually 1 m ² /g or more and 40 m 2 /g or less, preferably 2 m ² ^/ g or more and 35 m ² /g or less, more preferably 3 m ² /g. g or more and 30 m ² /g or less. The specific surface area of graphite determined by the BET method is reflected in the specific surface area of the obtained particles.
When the specific surface area of the graphite is at least the above lower limit value, the battery output can be improved due to the increased lithium ion absorption capacity of the particles. When the specific surface area of graphite is equal to or less than the above upper limit, it is possible to prevent a decrease in battery capacity due to an increase in the irreversible capacity of the particles.

・Plane spacing (d ₀₀₂ ) and Lc of (002) plane
The interplanar spacing (d ₀₀₂ ) of the (002) plane of graphite by wide-angle X-ray diffraction is usually 0.335 nm or more and 0.337 nm or less. Lc of graphite measured by wide-angle X-ray diffraction is usually 90 nm or more, preferably 95 nm or more. When the interplanar spacing (d ₀₀₂ ) of the (002) plane is 0.337 nm or less, the crystallinity of the graphite is high, and a high-capacity secondary battery negative electrode active material particle can be obtained. When Lc is 90 nm or more, the crystallinity of graphite is high, and a negative electrode active material with high capacity can be obtained.

In the present specification, the interplanar spacing of the (002) plane and Lc are values measured by the X-ray wide-angle diffraction method.

-Length of major axis and minor axis The length of the major axis of graphite is usually 100 µm or less, preferably 90 µm or less, and more preferably 80 µm or less. The minor axis length of graphite is usually 0.9 μm or more, preferably 1.0 μm or more, and more preferably 1.2 μm or more. When the major axis and minor axis of graphite are within the above range, microscopic voids are likely to be formed in the obtained particles, and volume expansion due to charging and discharging can be alleviated, and cycle characteristics can be improved. .

<Content Ratio of Graphite and Silicon Oxide Particles>
The content ratio of graphite and silicon oxide particles in the particles of the present invention is 10 to 95% by mass of the total 100% by mass of the graphite, silicon oxide particles, and carbonaceous material used as necessary. , the content of silicon oxide particles is preferably 3 to 60% by mass, the content of graphite is 30 to 90% by mass, and the content of silicon oxide particles is more preferably 5 to 50% by mass, More preferably, the content of graphite is 50 to 85% by mass and the content of silicon oxide particles is 8 to 40% by mass. When the content of graphite is at least the lower limit and the content of silicon oxide particles is at most the upper limit, it is easy to form a composite of graphite and silicon oxide particles. When the graphite content is equal to or less than the above upper limit and the silicon oxide particle content is equal to or more than the above lower limit, the particles of the present invention can have a high capacity.

<Carbonaceous material>
The particles of the present invention may contain carbonaceous substances other than graphite. When the particles of the present invention contain a carbonaceous material other than graphite, it is possible to reduce the influence of the size and shape of the graphite and silicon oxide particles when the graphite and silicon oxide particles are combined, which is preferable. In this case, amorphous carbon is preferable as the carbonaceous material because of its excellent ability to accept lithium ions.

Specifically, the carbonaceous material can be obtained by heat-treating the carbon precursor as described later. As the carbon precursor, the carbon materials described in (i) and/or (ii) below are preferable.
(i) coal-based heavy oil, DC heavy oil, cracked petroleum heavy oil, aromatic hydrocarbons, N-ring compounds, S-ring compounds, polyphenylenes, organic synthetic polymers, natural polymers, thermoplastic resins and A carbonizable organic substance selected from the group consisting of thermosetting resins (ii) A carbonizable organic substance dissolved in a low-molecular-weight organic solvent

When the particles of the present invention contain a carbonaceous material, the content of the carbonaceous material is preferably 2 to 30% by mass, preferably 5 to 25% by mass, based on the total 100% by mass of graphite, silicon oxide particles and carbonaceous material. is more preferable, and 7 to 20% by mass is even more preferable. When the content of the carbonaceous material is at least the above lower limit, the specific surface area of the particles of the present invention is reduced, and the initial charge/discharge efficiency is improved. When the content of the carbonaceous material is equal to or less than the above upper limit, the particles of the present invention can have a high capacity.

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

・Plane spacing (d ₀₀₂ ) between (002) planes of particles
The interplanar spacing (d ₀₀₂ ) of the (002) plane of the graphite (A) contained in the particles of the present invention is usually 0.335 nm or more and 0.337 nm or less as determined by wide-angle X-ray diffraction. The Lc of the particles of the present invention determined by wide-angle X-ray diffraction is usually 90 nm or more, preferably 95 nm or more. When the interplanar spacing (d ₀₀₂ ) of the (002) plane and Lc by the X-ray wide-angle diffraction method are within the above ranges, the particles for a secondary battery negative electrode active material become a high-capacity electrode.

- Tap density of particles The tap density of the particles of the present invention is usually 0.5 g/cm ³ or more, preferably 0.6 g/cm ³ or more, and more preferably 0.8 g/cm ³ or more.
When the tap density of the particles of the present invention is at least the above lower limit, the particles are spherical, sufficient continuous gaps are secured in the electrode, and the mobility of Li ions in the electrolytic solution held in the gaps is improved. Increase. This tends to improve rapid charge/discharge characteristics.

- Raman R value of particles The Raman R value of the particles of the present invention is generally 0.05 or more and 0.4 or less, preferably 0.1 or more and 0.35 or less. When the Raman R value of the particles of the present invention is within the above range, the surface crystallinity of the particles is in order and a high capacity can be expected.

In this specification, the Raman R value is obtained by measuring 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, and measuring the intensity ratio ( It is a value calculated as IB/IA). “Around 1580 cm ⁻¹ ” means the range of 1580 to 1620 cm ⁻¹ , and “around 1360 cm ⁻¹ ” means the range of 1350 to 1370 cm ⁻¹ .

Raman spectra can be measured with a Raman spectrometer. Specifically, the particles to be measured are allowed to fall freely into the measurement cell to fill the sample, and while the measurement cell is irradiated with argon ion laser light, the measurement cell is rotated in a plane perpendicular to the laser light. take measurements.

- Specific surface area of particles by BET method The specific surface area of the particles of the present invention by the BET method is usually 0.1 m ² /g or more and 40 m 2 /g or less, preferably 0.7 ^{m 2} ^/ g or more and 35 m ² /g or less and more preferably 1 m ² /g or more and 30 m ² /g or less. When the specific surface area of the particles according to the present invention as determined by the BET method is at least the above lower limit, there is a tendency that the acceptability of lithium ions during charging when used as an active material for a negative electrode is improved. If the specific surface area of the particles of the present invention as determined by the BET method is equal to or less than the above upper limit, the area of contact between the particles and the non-aqueous electrolytic solution can be suppressed when used as a negative electrode active material, resulting in reduced reactivity. As a result, the generation of gas tends to be suppressed, and a favorable battery tends to be obtained.

・Particle volume average particle diameter (d ₅₀ )
The _d50 of the particles of the present invention is usually 1 μm to 50 μm, preferably 4 μm to 40 μm, more preferably 6 μm to 30 μm.
When the _d50 of the particles of the present invention is at least the above lower limit, it is possible to produce particles having a particle size within a range that allows an electrode to be formed with an appropriate amount of binder. If the _d50 of the particles of the present invention is equal to or less than the above upper limit, streaking due to large particles may occur in the step of applying the particles in a slurry form by adding a binder, water, or an organic solvent in the production of a secondary battery. It is possible to suppress the occurrence of unevenness and unevenness.

[Method for producing particles of the present invention]
The particles of the present invention can be produced according to the method of producing particles of the present invention, preferably by mixing graphite and silicon oxide particles and then subjecting the mixture to a spheronization treatment to form a composite. Here, when the graphite and the silicon oxide particles are mixed, the carbonaceous material described above may be further mixed.

The mixing ratio of graphite, silicon oxide particles, and optionally used carbonaceous material may be set according to the aforementioned content ratio.

A preferred method for producing the particles of the present invention includes at least steps 1 and 2 below.
Step 1: Obtaining a mixture containing at least graphite and silicon oxide particles Step 2: Applying mechanical energy to the mixture of Step 1 to spheroidize it

The manufacturing method of the present invention will be described in detail below.

(Step 1: Step of obtaining a mixture containing at least graphite and silicon oxide particles)
The mixture obtained in this step may be in the form of powder, solidification, mass, slurry, etc., but the mass is preferred from the viewpoint of ease of handling.

In this step, the method of mixing graphite and silicon oxide particles is not particularly limited as long as a mixture containing at least graphite and silicon oxide particles is obtained. As a mixing method, graphite and silicon oxide particles may be added together and mixed, or may be mixed while adding each of them successively.

A preferred method for obtaining the mixture is, for example, a method of using wet silicon oxide particles and mixing them with graphite so as not to dry the silicon oxide particles.

As the wet silicon oxide particles, the silicon oxide particles obtained while the above-described silicon oxide particles are produced in a wet process may be used, or the silicon oxide particles produced in a dry process are mixed with graphite before being mixed. It may be dispersed in a dispersion solvent and wetted.
The silicon oxide particles that are wet in this way suppress aggregation of the silicon oxide particles, so that they can be uniformly dispersed during mixing, and the silicon oxide particles can be easily fixed on the surface of the graphite, which is preferable.

From the viewpoint of facilitating uniform dispersion of the silicon oxide particles on the surface of the graphite, an excess amount of the dispersing solvent used in the wet pulverization of the silicon oxide particles may be added during mixing.
In this specification, when the silicon oxide particles are mixed as a slurry when the silicon oxide particles are mixed with the graphite, 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 15% by mass or more and 85% by mass or less, more preferably 20% by mass or more and 80% by mass or less. When the solid content of the silicon oxide particles is at least the above lower limit, there is a tendency that the process is easy to handle. When the solid content of the silicon oxide particles is equal to or less than the above upper limit, the fluidity of the slurry is excellent, and the silicon oxide particles tend to be easily dispersed in the graphite.

After mixing, it is preferable to evaporate and remove the dispersion solvent using an evaporator, a dryer, or the like, and to fix the silicon oxide particles on the graphite.
Alternatively, without adding an excessive amount of the dispersing solvent, it is preferable to mix while heating in a high-speed stirrer while evaporating the dispersing solvent to immobilize the silicon oxide particles on the graphite.

At this time, a carbon precursor or the like, which will be described later, may be mixed in order to suppress the reactivity between the silicon oxide particles and the electrolytic solution.
Furthermore, at this time, a resin or the like may be mixed as a pore-forming material in order to reduce the breakage of the silicon oxide particles due to the expansion and contraction of the particles.

Examples of resins that can be used as the void-forming material in step 1 include polyvinyl alcohol, polyethylene glycol, polycarbosilane, polyacrylic acid, and cellulose-based polymers. Polyvinyl alcohol and polyethylene glycol are preferred because they have a small amount of residual carbon during firing and a relatively low decomposition temperature.

Mixing is usually carried out under normal pressure, but can also be carried out under reduced pressure or increased pressure. Mixing can be carried out either batchwise or continuously. In any case, the mixing efficiency can be improved by combining a device suitable for coarse mixing and a device suitable for precise mixing. Alternatively, a device that performs mixing and fixing (drying) at the same time may be used.
Drying is usually carried out under reduced pressure or increased pressure. Drying under reduced pressure is preferred.

The drying time is usually 5 minutes or more and 2 hours or less, preferably 10 minutes or more and 1.5 hours or less, more preferably 20 minutes or more and 1 hour or less.
Although the drying temperature varies depending on the solvent, it is preferable that the drying temperature is a time that can achieve the above time. Moreover, it is preferable that the temperature is below the temperature at which the resin is not denatured.

As a batch system mixing device, a mixer with a structure in which two frames revolve while rotating; A device with a structure for stirring and dispersing; a so-called kneader type device that has a structure in which stirring blades such as a sigma type rotate along the side of a semi-cylindrical mixing tank; a trimix type device with three stirring blades a device of the so-called bead mill type having a rotating disk and a dispersing medium in a vessel; and the like.

The container has a paddle inside which is rotated by a shaft, the inner wall surface of the container is preferably formed in a long catamaran substantially along the outermost line of rotation of the paddle, and the paddles slide on opposite sides. A device with a structure in which many pairs are arranged in the axial direction of the shaft so as to be movably engaged (for example, KRC reactor manufactured by Kurimoto Iron Works, SC processor, TEM manufactured by Toshiba Machine Cermac, TEX-K manufactured by Japan Steel Works, etc. ); has a single shaft inside, and a container in which a plurality of plow-shaped or saw-toothed paddles fixed to the shaft are arranged in different phases, the inner wall surface of which is substantially on the outermost line of rotation of the paddles. along the (external heating) device (e.g. Loedige mixer manufactured by Loedige, Flowshare mixer manufactured by Pacific Machinery Co., Ltd., DT dryer manufactured by Tsukishima Kikai Co., Ltd., etc.) preferably formed in a cylindrical shape. can also be used.
For continuous mixing, a pipeline mixer, a continuous bead mill, or the like may be used. It is also possible to homogenize by means such as ultrasonic dispersion.
The mixture obtained in this step may be appropriately subjected to powder processing such as pulverization, pulverization, and classification.

There are no particular restrictions on the equipment used for crushing and crushing. Examples of coarse pulverizers include shear mills, jaw crushers, impact crushers, cone crushers and the like. Examples of intermediate pulverizers include roll crushers and hammer mills. Examples of fine pulverizers include ball mills, vibration mills, pin mills, stirring mills, jet mills, and the like.

As for the device used for classification, in the case of dry sieving, rotary sieves, rocking sieves, turning sieves, vibrating sieves, etc. can be used. In the case of dry airflow classification, a gravity classifier, an inertial force classifier, or a centrifugal force classifier (classifier, cyclone, etc.) can be used. Wet sieving, mechanical wet classifier, hydraulic classifier, sedimentation classifier, centrifugal wet classifier and the like can be used.

(Step 2: Step of applying mechanical energy to the mixture of Step 1 to spheronize)
Through this step 2, the degree of compositing of graphite and silicon oxide particles is greatly improved, and the particles of the present invention can be produced.
In the production method for obtaining the particles of the present invention, a mixture (also referred to herein as a mixture) in which silicon oxide particles are mixed on the surface of the graphite obtained in the above step 1 is subjected to a spheronization treatment. However, particularly in the present invention, it is preferable to appropriately set the manufacturing conditions as described later so that silicon oxide particles within a predetermined range are present in the gaps within the graphite structure.

The spheroidization process is basically a process that uses mechanical energy (mechanical actions such as impact compression, friction, and shear force). Specifically, treatment using a hybridization system is preferred. The system has a rotor with many blades that exert mechanical actions such as impact compression, friction and shear, and rotation of the rotor generates a large airflow. As a result, a large centrifugal force is applied to the graphite in the mixture obtained in the above step 1, and the graphite in the mixture obtained in the above step 1 and the graphite in the mixture obtained in the above step 1 collide with the walls and blades. By doing so, the graphite and silicon oxide particles in the mixture obtained in the above step 1 can be efficiently combined.

The apparatus used for the spheronization treatment has, for example, a rotor with a large number of blades installed inside the casing, and the rotor rotates at a high speed so that the graphite in the mixture obtained in the step 1 introduced into the interior is A device or the like can be used to apply a mechanical action such as impact compression, friction, shear force, etc., to surface treatment.
For example, Hybridization System (manufactured by Nara Machinery Co., Ltd.), Cryptotron, Crypton Orb (manufactured by Earthtechnica), CF Mill (manufactured by Ube Industries), Mechanofusion System, Nobilta, Faculty (manufactured by Hosokawa Micron), Theta Composer (manufactured by Tokuju Kosakusho Co., Ltd.), COMPOSI (manufactured by Nippon Coke Kogyo Co., Ltd.), and the like. Among these, the hybridization system manufactured by Nara Machinery Co., Ltd. is preferable.

When processing using the apparatus described above, the peripheral speed of the rotating rotor is usually 30 to 100 m/sec, preferably 40 to 100 m/sec, and more preferably 50 to 100 m/sec. The treatment can be carried out by simply passing the carbonaceous material through, but it is preferable to circulate or retain the carbonaceous material in the apparatus for 30 seconds or more, and more preferably to circulate or retain the carbonaceous material in the apparatus for 1 minute or more. .

- Granulating agent The spheronization treatment may be performed in the presence of a granulating agent. The use of a granulating agent increases the adhesion between carbon materials, making it possible to manufacture a spherical carbon material in which the carbon materials are more strongly adhered.

The granulating agent used in the present embodiment does not contain an organic solvent, or if it contains an organic solvent, at least one of the organic solvents does not have a flash point, or if it has a flash point, the flash point is 5. °C or higher is preferred. As a result, it is possible to prevent the risk of ignition, fire and explosion of the organic compound induced by impact or heat when granulating the carbon material in the subsequent process. Therefore, the manufacturing can be stably and efficiently carried out.

Examples of granulating agents include coal tar, heavy petroleum oils, paraffinic oils such as liquid paraffin, synthetic oils such as olefinic oils, naphthenic oils, and aromatic oils; vegetable oils and fats, and animal fats. Natural oils such as family oils, esters, and higher alcohols; organic compounds such as resin binder solutions in which a resin binder is dissolved in an organic solvent having a flash point of 5°C or higher, preferably 21°C or higher; aqueous systems such as water solvents; mixtures thereof;

Organic solvents with a flash point of 5°C or higher include alkylbenzenes such as xylene, isopropylbenzene, ethylbenzene and propylbenzene; alkylnaphthalenes such as methylnaphthalene, ethylnaphthalene and propylnaphthalene; allylbenzenes such as styrene; Hydrogens; aliphatic hydrocarbons such as octane, nonane and decane; ketones such as methyl isobutyl ketone, diisobutyl ketone and cyclohexanone; esters such as propyl acetate, butyl acetate, isobutyl acetate and amyl acetate; , butanol, isopropyl alcohol, isobutyl alcohol, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, glycerin; 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 ethyl methyl ether, triethylene glycol dimethyl ether, tri Glycol derivatives such as propylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol monophenyl ether; ethers such as 1,4-dioxane, dimethylformamide, pyridine, 2-pyrrolidone, N-methyl-2-pyrrolidone nitrogen-containing compounds; sulfur-containing compounds such as dimethylsulfoxide; halogen-containing compounds such as dichloromethane, chloroform, carbon tetrachloride, dichloroethane, trichloroethane and chlorobenzene; and mixtures thereof. For example, substances with low flash points such as toluene are not included. These organic solvents can also be used alone as a granulating agent.
As used herein, the flash point can be measured by a known method.

Examples of resin binders include cellulose-based resin binders such as ethyl cellulose, methyl cellulose, and salts thereof; acrylic resin binders such as polymethyl acrylate, polyethyl acrylate, polybutyl acrylate, polyacrylic acid, and salts thereof; Methacrylic resin binders such as methyl methacrylate, polyethyl methacrylate and polybutyl methacrylate; phenolic resin binders and the like.
As the granulating agent, coal tar, heavy petroleum oil, paraffinic oils such as liquid paraffin, alcohols, and aromatic oils are preferable because they can produce a spherical carbon material with high circularity and little fine powder.

The granulating agent preferably has properties that can be removed efficiently and that do not adversely affect battery characteristics such as capacity, output characteristics, storage and cycle characteristics. Specifically, when heated to 700° C. in an inert atmosphere, it is usually 50% by mass or more, preferably 80% by mass or more, more preferably 95% by mass or more, still more preferably 99% by mass or more, and particularly preferably 99% by mass. It is possible to select one that reduces the mass by 9% by mass or more.

The graphite (A) in the mixture obtained in Step 1 above, which is subjected to spheronization treatment, may have already undergone a certain spheronization treatment under the conditions of a conventional method. Moreover, the composite obtained in the above step 1 may be subjected to repeated mechanical action by circulating or passing through this step multiple times.

During the spheronization treatment, the rotation speed of the rotor is usually 2000 rpm to 9000 rpm, preferably 4000 rpm to 8000 rpm, more preferably 5000 rpm to 7500 rpm, still more preferably 6000 rpm to 7200 rpm, for usually 30 seconds to 60 minutes. , preferably 1 minute or more and 30 minutes or less, more preferably 1 minute and 30 seconds or more and 10 minutes or less, still more preferably 2 minutes or more and 5 minutes or less.

If the rotation speed of the rotor is too low, the spherical processing is weak and the tapping density may not increase sufficiently. If the number of rotations of the rotor is too high, the pulverization effect becomes stronger than the spheroidizing treatment, and the particles may collapse and the tapping density may decrease. If the spheronization treatment time is too short, a high tapping density cannot be achieved while sufficiently reducing the particle size. If the spheronization treatment time is too long, the graphite in the mixture obtained in the above step 1 will be shattered, possibly failing to achieve the object of the present invention.

The obtained particles may be classified. If the obtained particles do not fall within the specified range of physical properties of the present invention, they are subjected to classification treatment repeatedly (usually 2 to 10 times, preferably 2 to 5 times) to bring the physical properties into the desired range. can be done. Examples of classification include dry classification (air classification, sieve), wet classification, and the like. Dry classification, particularly air classification, is preferred from the viewpoint of cost and productivity.

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

<Method for producing carbonaceous material-coated particles>
The particles of the present invention obtained as described above preferably contain a carbonaceous material. As a more specific embodiment, it is more preferable to coat at least part of the surface of the particles with a carbonaceous material (hereinafter also referred to as "carbonaceous material-coated particles" or "carbonaceous material-coated particles of the present invention").

The carbonaceous material-coated particles can be produced by performing the following step 3 after step 2 described above.
Step 3: Step of Coating the Particles Spheronized in Step 2 with a Carbonaceous Material Step 3 will be described in detail below.

(Step 3: Step of coating the particles spheroidized in Step 2 with a carbonaceous material)
-Carbonaceous material Examples of the carbonaceous material include amorphous carbon and graphitized material depending on the difference in heating temperature in the manufacturing method described below. Among these, amorphous carbon is preferable from the viewpoint of lithium ion acceptance.

Specifically, the carbonaceous material can be obtained by heat-treating the carbon precursor as described later. As the carbon precursor, the carbon material described in (i) and/or (ii) above is preferable.

- Coating treatment In the coating treatment, a carbon precursor for obtaining a carbonaceous material is used as a coating raw material for the particles obtained in step 2 described above, and these are mixed and fired to obtain coated particles. .
When the firing temperature is usually 600° C. or higher, preferably 700° C. or higher, more preferably 900° C. or higher, and usually 2000° C. or lower, preferably 1500° C. or lower, more preferably 1200° C. or lower, amorphous carbon is produced as the carbonaceous material. can get. Graphitized carbon can be obtained as a carbonaceous material by performing heat treatment at a firing temperature of usually 2000° C. or higher, preferably 2500° C. or higher, and usually 3200° C. or lower.
The amorphous carbon is carbon with low crystallinity. The graphitized carbon is carbon with high crystallinity.
In the coating treatment, the particles described above are used as the core material, and the carbon precursor for obtaining the carbonaceous material is used as the coating raw material, and these are mixed and fired to obtain the carbonaceous material-coated particles.

- Mixing with Metal Particles and Carbon Microparticles Metal particles and carbon microparticles that can be alloyed may be contained in the coating layer. The shape of the fine carbon particles is not particularly limited, and may be granular, spherical, chain-like, needle-like, fibrous, plate-like, scale-like, or the like.

Carbon fine particles are not particularly limited, but specific examples include coal fine powder, vapor phase carbon powder, carbon black, ketjen black, and carbon nanofiber. Among these, carbon black is particularly preferred. Carbon black has the advantage that it has high input/output characteristics even at low temperatures and is readily available at low cost.

The volume average particle diameter (d ₅₀ ) of the carbon fine particles is usually 0.01 μm or more and 10 μm or less, preferably 0.05 μm or more and 8 μm or less, more preferably 0.07 μm or more and 5 μm or less, still more preferably 0 .1 μm or more and 1 μm or less.

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

-Other Steps Particles that have undergone the above steps may be subjected to powder processing such as pulverization, pulverization, and classification described in Step 1.
The carbonaceous material-coated particles of the present invention can be produced by the production method as described above.

<Application>
By using the particles of the present invention as a negative electrode active material for a secondary battery, a secondary battery with excellent battery characteristics can be realized. Therefore, the particles of the present invention are useful as a negative electrode active material for secondary batteries.

[Secondary battery]
A secondary battery of the present invention includes a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode includes a current collector and a negative electrode active material layer formed on the current collector. The active material layer contains the particles of the present invention. The secondary battery of the present invention is generally manufactured by the method for manufacturing a secondary battery of the present invention, which includes the step of forming a negative electrode active material layer containing the particles of the present invention on a current collector to obtain a negative electrode.

<Negative Electrode>
In order to prepare a negative electrode using the particles of the present invention (hereinafter sometimes referred to as "negative electrode of the present invention"), the particles of the present invention mixed with a binder (binder resin) are dispersed in a dispersion medium. to form a slurry, which is applied to a current collector and dried to form a negative electrode active material layer on the current collector.

As the binder, use one that has an olefinic unsaturated bond in the molecule. The type is not particularly limited. Specific examples include styrene-butadiene rubber, styrene/isoprene/styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, and ethylene/propylene/diene copolymer. By using a binder having such an olefinically unsaturated bond, swelling of the negative electrode active material layer with respect to the electrolytic solution can be reduced. Among them, styrene-butadiene rubber is preferable because of its easy availability.

As the binder having olefinic unsaturated bonds in the molecule, it is desirable to have a large molecular weight or a high proportion of unsaturated bonds.
A binder having a high molecular weight preferably has a weight-average molecular weight of usually 10,000 or more, preferably 50,000 or more, and usually 1,000,000 or less, preferably 300,000 or less. As a binder with a high proportion of unsaturated bonds, 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, and usually 5 x10 ^-6 or less, preferably 1 x 10 ^-6 or less.

The binder should satisfy at least one of the regulations regarding the molecular weight and the regulations regarding the ratio of unsaturated bonds, but it is more preferable to satisfy both regulations at the same time. If the molecular weight of the binder having olefinically unsaturated bonds is too small, the mechanical strength is poor. If the molecular weight of the binder is too large, the flexibility is poor. On the other hand, if the proportion of olefinic unsaturated bonds in the binder is too low, the effect of improving the strength will be weak, and if it is too high, the flexibility will be poor.

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

In the present invention, binders having no olefinic unsaturated bonds can also be used in combination with binders having the above-mentioned olefinic unsaturated bonds as long as the effects of the present invention are not lost. The mixing ratio of the binder having no olefinically unsaturated bonds to the amount of the binder having olefinically unsaturated bonds is usually 150% by mass or less, preferably 120% by mass or less.
By using a binder that does not have an olefinic unsaturated bond, coatability can be improved.

Examples of binders having no olefinic unsaturated bonds include polysaccharides such as methylcellulose, carboxymethylcellulose and starch; thickening polysaccharides such as carrageenan, pullulan, guar gum and xanthan gum; polyethylene oxide, polypropylene oxide and the like. Polyethers; vinyl alcohols such as polyvinyl alcohol and polyvinyl butyral; polyacids such as polyacrylic acid and polymethacrylic acid, or metal salts of these polymers; fluorine-containing polymers such as polyvinylidene fluoride; alkane polymers such as polyethylene and polypropylene and copolymers thereof.

The mass ratio (the particles of the present invention / binder) is usually 90/10 or more, preferably 95/5 or more, usually 99.9/0.1 or less, preferably 99.5/0.5 It is below.
If the proportion of the binder is too high, the capacity tends to decrease and the resistance increases. If the proportion of the binder is too small, the strength of the negative electrode plate will deteriorate.

An organic solvent such as alcohol or water can be used as a dispersion medium for forming a slurry in which the particles of the present invention and the binder are dispersed.
Optionally, a conductive agent may be added to the slurry. Examples of the conductive agent include carbon black such as acetylene black, ketjen black, and furnace black, and fine powders of Cu, Ni, or alloys thereof having an average particle size of 1 μm or less. The amount of the conductive agent added is usually 10% by mass or less relative to the particles of the present invention.

A conventionally known current collector can be used as the current collector to which the slurry is applied. Specific examples include metal thin films such as rolled copper foil, electrolytic copper foil, and stainless steel foil. The thickness of the current collector is usually 4 μm or more, preferably 6 μm or more, and usually 30 μm or less, preferably 20 μm or less.

The above slurry is applied onto a current collector using a doctor blade or the like, dried, and then pressed using 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 amount of the particles of the present invention attached to the current collector is 5 to 15 mg/cm ² .

The drying after coating the slurry on the current collector is usually carried out at a temperature of 60°C or higher, preferably 80°C or higher, and usually 200°C or lower, preferably 195°C or lower, in dry air or an inert atmosphere.

The thickness of the negative electrode active material layer obtained by coating and drying the slurry is usually 5 μm or more, preferably 20 μm or more, more preferably 30 μm or more, and usually 200 μm or less in the state after pressing. , preferably 100 μm or less, more preferably 75 μm or less. If the negative electrode active material layer is too thin, it lacks practicality as a negative electrode active material layer due to the balance with the particle diameter of the particles of the present invention which are the negative electrode active material. If the negative electrode active material layer is too thick, it is difficult to obtain a sufficient Li ion intercalation/deintercalation function for a high-density current value.

The density of ^the particles of the present invention in the negative electrode active material layer varies depending on the application ^. ³ or more, and particularly preferably 1.7 g/cm ³ or more. If the density is too low, the battery capacity per unit volume is not necessarily sufficient. If the density is too high, the rate characteristics deteriorate, so the density of graphite is preferably 1.9 g/cm ³ or less.

When the negative electrode of the present invention is produced using the particles of the present invention described above, the method and selection of other materials are not particularly limited.
When a secondary battery is produced using this negative electrode, there are no particular restrictions on the selection of members necessary for the battery configuration, such as the positive electrode and the electrolytic solution that constitute the secondary battery.

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

The basic configuration of the secondary battery of the present invention, particularly a lithium ion secondary battery, is the same as that of conventionally known lithium ion secondary batteries, and usually includes a positive electrode and a negative electrode capable of intercalating and deintercalating lithium ions, and an electrolyte. . As the negative electrode, the negative electrode of the present invention described above is used.

The positive electrode is formed by forming a positive electrode active material layer containing a positive electrode active material and a binder on a current collector.

Examples of positive electrode active materials include metal chalcogen compounds capable of intercalating and deintercalating alkali metal cations such as lithium ions during charging and discharging. Metal chalcogen compounds include transition metal oxides such as vanadium oxide, molybdenum oxide, manganese oxide, chromium oxide, titanium oxide, tungsten oxide; vanadium sulfide, molybdenum sulfide transition metal sulfides such as sulfides, titanium sulfides, _and CuS; transition metal phosphorus-sulfur compounds such as NiPS ₃ and FePS ₃ ; transition metal selenium compounds such as VSe ₂ and NbSe ₃ _; transition metal composite oxides such as ₇₅ S ₂ and Na _0.1 CrS ₂ ; transition metal composite sulfides such as LiCoS ₂ and LiNiS ₂ ;

Among these: _V2O5 _, _V5O13 _, _VO2 , _Cr2O5 , _MnO2 _, TiO _, _MoV2O8 _, _LiCoO2 _, _LiNiO2 , _LiMn2O4 , _TiS2 , _V2S5 , Cr _0.25 V _0.75 S ₂ , Cr _0.5 V _0.5 S ₂ and the like are preferable, and LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ and a part of these transition metals are particularly preferable. It is a lithium transition metal composite oxide substituted with other metals. These positive electrode active materials may be used singly or in combination.

As the binder that binds the positive electrode active material, any known binder can be selected and used. Examples thereof include inorganic compounds such as silicate and water glass, and resins having no unsaturated bonds such as Teflon (registered trademark) and polyvinylidene fluoride. Among these, resins having no unsaturated bonds are preferred. If a resin having an unsaturated bond is used as the resin that binds the positive electrode active material, it may decompose during an oxidation reaction (during charging). The weight average molecular weight of these resins is usually 10,000 or more, preferably 100,000 or more, and usually 3,000,000 or less, preferably 1,000,000 or less.

A conductive agent may be contained in the positive electrode active material layer in order to improve the conductivity of the electrode. The conductive agent is not particularly limited as long as it can be mixed with the active material in an appropriate amount to impart conductivity. Examples of conductive agents generally include carbon powders such as acetylene black, carbon black, and graphite, and fibers, powders, and foils of various metals.

The positive electrode plate is formed by slurrying the positive electrode active material and binder with a dispersant, applying it on the current collector, and drying it, in the same manner as in the manufacturing of the negative electrode of the present invention described above. Aluminum, nickel, stainless steel (SUS), or the like is used as the current collector of the positive electrode, but is not limited at all.

As the electrolyte, a non-aqueous electrolytic solution obtained by dissolving a lithium salt in a non-aqueous solvent, or a non-aqueous electrolytic solution made into a gel, rubber, or solid sheet by using an organic polymer compound or the like is used.

The non-aqueous solvent used in the non-aqueous electrolyte is not particularly limited, and can be appropriately selected and used from known non-aqueous solvents that have been conventionally proposed as solvents for non-aqueous electrolytes. For example, chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate; cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate; chain ethers such as 1,2-dimethoxyethane; tetrahydrofuran, 2-methyl Cyclic ethers such as tetrahydrofuran, sulfolane and 1,3-dioxolane; chain esters such as methyl formate, methyl acetate and methyl propionate; and cyclic esters such as γ-butyrolactone and γ-valerolactone.

Any one of these non-aqueous solvents may be used alone, or two or more may be used in combination. In the case of a mixed solvent, a combination of a mixed solvent containing a cyclic carbonate and a chain carbonate is preferred. It is particularly preferable that the cyclic carbonate is a mixed solvent of ethylene carbonate and propylene carbonate, since high ionic conductivity can be expressed even at low temperatures and low-temperature charging load characteristics are improved.

Among them, the content of propylene carbonate is preferably in the range of 2% by mass to 80% by mass, more preferably 5% by mass to 70% by mass, and 10% by mass to 60% by mass with respect to the entire non-aqueous solvent. A range is more preferred. If the content of propylene carbonate is lower than the above lower limit, the ionic conductivity at low temperatures decreases. If the content of propylene carbonate is higher than the above upper limit, propylene carbonate solvated with Li ions co-inserts between the graphite phases of the negative electrode, causing delamination and deterioration of the graphite-based negative electrode active material, resulting in insufficient capacity. I have a missing problem.

The lithium salt used in the non-aqueous electrolytic solution is also not particularly limited, and can be appropriately selected and used from known lithium salts known to be usable for this purpose. For example, Li
halides such as Cl, LiBr; perhalogenates such as _LiClO4 , _LiBrO4 , _LiClO4 ; inorganic lithium salts such as inorganic fluoride salts such _as _LiPF6 , _LiBF4 , _LiAsF6 ; _LiCF3SO3 , _LiC4 perfluoroalkanesulfonate such as F ₉ SO ₃ ; fluorine-containing organic lithium salt such as perfluoroalkanesulfonimide salt such as Li trifluorosulfonimide ((CF ₃ SO ₂ ) ₂ NLi); Among these, LiClO ₄ , LiPF ₆ and LiBF ₄ are preferred.

The lithium salt may be used alone or in combination of two or more. The concentration of the lithium salt in the non-aqueous electrolytic solution is usually in the range of 0.5 mol/L or more and 2.0 mol/L or less.

When the non-aqueous electrolytic solution described above 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 poly(ethylene oxide, polypropylene oxide, etc.). Ether-based polymer compound; Crosslinked polymer of polyether-based polymer compound; Vinyl alcohol-based polymer compound such as polyvinyl alcohol and polyvinyl butyral; Insolubilized vinyl alcohol-based polymer compound; Polyepichlorohydrin; vinyl-based polymer compounds such as polyvinylpyrrolidone, polyvinylidene carbonate, and polyacrylonitrile; poly(ω-methoxyoligooxyethylene methacrylate), poly(ω-methoxyoligooxyethylene methacrylate-co-methyl methacrylate), poly(hexafluoropropylene) -vinylidene fluoride) and the like.

The non-aqueous electrolytic solution described above may further contain a film-forming agent. Specific examples of film-forming agents include carbonate compounds such as vinylene carbonate, vinyl ethyl carbonate and methylphenyl carbonate; alkene sulfides such as ethylene sulfide and propylene sulfide; sultone compounds such as 1,3-propanesultone and 1,4-butanesultone. and acid anhydrides such as maleic anhydride and succinic anhydride.
Furthermore, the non-aqueous electrolytic solution may contain an overcharge inhibitor such as diphenyl ether or cyclohexylbenzene.

When using these additives, the content in the non-aqueous electrolytic solution is usually 10% by mass or less, preferably 8% by mass or less, more preferably 5% by mass or less, and particularly preferably 2% by mass or less. If the content of the additive is too large, other battery characteristics may be adversely affected, such as an increase in initial irreversible capacity, deterioration in low-temperature characteristics and rate characteristics.

As the electrolyte, a polymer solid electrolyte, which is a conductor of alkali metal cations such as lithium ions, can also be used. Examples of polymer solid electrolytes include those obtained by dissolving Li salts in the aforementioned polyether-based polymer compounds, and polymers in which terminal hydroxyl groups of polyethers are substituted with alkoxides.

A porous separator such as a porous membrane or non-woven fabric is usually interposed between the positive electrode and the negative electrode to prevent a short circuit between the electrodes. In this case, the non-aqueous electrolytic solution is used by impregnating a porous separator. As a material for the separator, polyolefin such as polyethylene and polypropylene, polyethersulfone, and the like are used, and polyolefin is preferable.

The form of the lithium ion secondary battery to which the present invention is applied is not particularly limited. Examples include a cylinder type in which a sheet electrode and a separator are formed in a spiral shape, a cylinder type in which a pellet electrode and a separator are combined to form an inside-out structure, and a coin type in which a pellet electrode and a separator are laminated.
By enclosing the battery of these forms in an arbitrary external case, it can be used in an arbitrary shape such as a coin shape, a cylindrical shape, a rectangular shape, and the like.

There are no particular restrictions on the procedure for assembling the lithium-ion secondary battery, and it may be assembled in an appropriate procedure according to the structure of the battery. For example, a negative electrode is placed on an exterior case, an electrolytic solution and a separator are provided thereon, a positive electrode is placed so as to face the negative electrode, and a gasket and a sealing plate are crimped together to form a battery.

<Secondary battery performance>
Since the secondary battery of the present invention uses the particles of the present invention containing the silicon oxide particles of the present invention and graphite as a negative electrode active material, the secondary battery is excellent in battery characteristics, particularly in the effect of suppressing electrode swelling.
Specifically, it is preferable that the discharge capacity at the 50th cycle measured by the method described in Examples below is 400 mAh/g or more and the charge/discharge efficiency is 99.8% or more.
The secondary battery of the present invention preferably has an electrode swelling of 1.4 or less as measured by the method described in Examples below.

Next, specific embodiments of the present invention will be described in more detail by way of examples. The invention is not limited by these examples.

[Measuring method]
Methods for measuring physical properties of materials used in the following examples and comparative examples are as follows.

<Zirconium, Yttrium, Hafnium and Manganese Contents in Silicon Oxide Particles>
The contents of zirconium (Zr), yttrium (Y), hafnium (Hf), and manganese (Mn) in silicon oxide particles were measured by the following method.
The sample was dissolved by heating with a mixed acid (hydrofluoric acid, nitric acid) to volatilize the silicon oxide particles, and after dissolving in sulfuric acid, water was added to a constant volume. The metal impurities in the decomposed solution were quantified by the acid matrix matching calibration curve method using ICP-AES (iCAP7600DuO manufactured by Thermo Fisher Scientific).
Detection limits in this measurement method are zirconium: 0.1 ppm, yttrium: 0.1 ppm, hafnium: 0.3 ppm, and manganese: 0.1 ppm.

<Zirconium, Yttrium, Hafnium and Manganese Contents in Negative Electrode Active Material Particles>
The content of zirconium, yttrium, hafnium and manganese in the particles is calculated from the content of zirconium, yttrium, hafnium and manganese in the silicon oxide particles used in the production of the particles and the content of silicon oxide particles in the particles. asked.

<Volume average particle size ( _d50 )>
About 20 mg of particles were added to about 1 ml of a 2% by volume aqueous solution of polyoxyethylene (20) sorbitan monolaurate and dispersed in about 200 ml of deionized water. The volume particle size distribution was measured using a model name "LA-920") to determine the median diameter (d ₅₀ ). 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 size ( _d90 )>
The particle diameter (d ₉₀ ) was defined as the particle diameter corresponding to cumulative 90% from the small particle side in the particle size distribution obtained by the measurement of the volume average particle diameter (d ₅₀ ).

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

<Value of x in SiOx>
The value of x in SiOx of the silicon oxide particles was calculated from the value measured by impulse furnace heat extraction under an inert gas atmosphere-IR detection method and ICP emission spectrometry.
Specifically, the sample was alkali-fused, and after constant volume, the amount of silicon in the diluted sample solution was measured using ICP-AES (manufactured by Thermo Fisher Scientific, model name “iCAP7600Duo”). Separately, the oxygen content of the sample was measured using an oxygen nitrogen hydrogen analyzer (manufactured by LECO, model name "TCH600"). The amount of oxygen relative to silicon was calculated and used as the value of x in SiOx.

<Specific surface area by BET method>
Using a specific surface area measuring device (manufactured by Mountech, model name "Macsorb HM Model-1210"), the sample is filled in a dedicated cell and heated to 150 ° C. for pretreatment, and then cooled to liquid nitrogen temperature. Accurately adjusted about 30% nitrogen and helium balance gas was saturated and adsorbed, then heated to room temperature, the amount of desorbed gas was measured, and the specific surface area was calculated from the obtained adsorption amount by BET one-point analysis.

<Tap density>
Using a powder density measuring instrument (model name "Tap Denser KYT-5000", manufactured by Seishin Enterprise Co., Ltd.), a cylindrical tap cell with a diameter of 1.5 cm and a volume capacity of 20 cm ³ is passed through a sieve with an opening of 300 μm, and the sample is dropped. to allow the cell to fill to the brim. After that, tapping with a stroke length of 10 mm was performed 1000 times, and the density calculated from the volume at that time and the mass of the sample was taken as the tap density.

[Example 1-1]
Silicon and silicon dioxide are used as raw materials, and after being synthesized by a reduced-pressure vapor deposition method, the silicon oxide powder obtained through a coarse pulverization process is dry-pulverized in a jet mill for fine pulverization (manufactured by Aisin Nano Technologies) equipped with a classifier. According to the results, silicon oxide particles No. 1 having a value of x in SiOx of 0.9, d ₅₀ , d _max , and the content of each metal element having the values shown in Table 1 are obtained. 1 was produced.

[Comparative Example 1-1]
In Example I-1, instead of dry pulverization, wet pulverization was performed using a bead mill (manufactured by Asada Iron Works Co., Ltd.) using 2-propanol as a dispersion medium. Silicon _oxide particle _no . 2 was produced.

[Examples II-1 and 2, Comparative Example II-1]
<Production of particles>
As the graphite, graphite having the following physical properties was used.
(Physical properties of graphite No. 1)
_d50 : 11.1 μm
_d90 : 21.1 μm
Specific surface area by BET method: 9.9 m ² /g
Tap density: 0.44g/ ^cm3
(Physical properties of graphite No. 2)
_d50 : 7.8 μm
_d90 : 14.1 μm
Specific surface area by BET method: 12.3 m ² /g
Tap density: 0.45g/ ^cm3

In Examples II-1 and 2, the silicon oxide particles No. 2 synthesized in Example I-1 were used as the silicon oxide particles. 1, and the silicon oxide particles No. 1 synthesized in Comparative Example I-1 in Comparative Example II-1. 2 was used.
As graphite, graphite No. 2 was used in Example II-1 and Comparative Example II-1. 1 was replaced with graphite No. 1 in Example II-2. 2 was used.

Graphite and silicon oxide particles were mixed at a ratio of 70% by mass of graphite and 16% by mass of silicon oxide particles, 9% by mass of liquid oil was added as a granulating agent, and the mixture was stirred and mixed with a stirring granulator. The obtained mixture was put into a hybridization system, and granulated and spheroidized by mechanical action for 5 minutes at a rotor peripheral speed of 85 m/sec. Furthermore, the liquid oil used as a granulating agent was removed by heat treatment to obtain spherical composite particles. The resulting spheroidized composite particles were mixed with pitch having an ash content of 0.02% by mass, a metal impurity amount of 20% by mass, and a Qi of 1% by mass as a graphite material precursor, and heat-treated at 1000°C in an inert gas. to obtain a baked product. By pulverizing and classifying the fired product, negative electrode active material particles in which graphite, silicon oxide particles, and amorphous carbon were combined in the proportions shown in Table 2A were obtained.

<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 particles obtained in each example and comparative example, 2.5% by mass of acetylene black as a conductive material, 1.5% by mass of carboxymethyl cellulose (CMC) and 48% by mass of styrene-butadiene rubber (SBR) as binders 3.1% by mass of the aqueous dispersion was kneaded in a hybrid mixer to form a slurry. This slurry was applied to a rolled copper foil having a thickness of 20 μm by a blade method so as to have a basis weight of 7 to 8 mg/cm ² and dried.
Thereafter, the negative electrode active material layer was roll-pressed with a 250 mφ roll press equipped with a load cell so that the density of the negative electrode active material layer was 1.6 to 1.7 g/cm ³ , and punched into a circular shape with a diameter of 12.5 mm, at 90° C. for 8 hours. It was vacuum-dried and used as a negative electrode for evaluation.

This negative electrode and a Li foil serving as a counter electrode were stacked via a separator impregnated with an electrolytic solution to prepare a battery for a charge/discharge test. The electrolytic solution used was prepared by dissolving LiPF ₆ in a mixed solution of ethylene carbonate/ethylmethyl carbonate/monofluoroethylene carbonate=3/6/1 (volume ratio) so as to be 1 mol/liter.

<Evaluation of battery characteristics>
The obtained lithium secondary battery was evaluated for battery characteristics by the following method, and the results are shown in Table 2B. Table 2B shows the total content of zirconium, yttrium, hafnium, and manganese in the silicon oxide particles used (referred to as "total metal content" in Table 2B) and the content of each metal element in the negative electrode active material particles. The content rate and the total content rate of these are written together.

(discharge capacity/charge/discharge efficiency)
First, the positive electrode and the negative electrode of the battery for the charge/discharge test were charged to 5 mV at a current density of 0.08 mA/cm ² , and then charged at a constant voltage of 5 mV until the current value reached 0.03 mA. After doping with lithium, the positive electrode and the negative electrode were discharged to 1.5 V at a current density of 0.2 mA/cm ² (initial first cycle). Thereafter, charging and discharging were repeated four times under the same conditions as above except that the current density during charging was 0.2 mA/cm ² and the current density during discharging was 0.3 mA/cm ² (initial 2 cycle to initial 5th cycle). Flowing current in the direction of lithium doping to the negative electrode for evaluation was described as "charging", and flowing current in the direction of dedoping lithium from the negative electrode for evaluation was described as "discharging".
The initial discharge capacity was determined as follows.
First, the mass of the negative electrode active material is obtained by subtracting the mass of a copper foil punched into the same area as the negative electrode from the mass of the negative electrode. asked for capacity.

The charge/discharge efficiency was determined by the following formula. The mass of the negative electrode active material was determined by subtracting the mass of a copper foil punched into the same area as the negative electrode from the mass of the negative electrode.
Charge-discharge efficiency (%) = {Discharge capacity of initial 3rd cycle (mAh / g) / (Charge capacity of initial 1st cycle (mAh / g) + Charge capacity of initial 2nd cycle (mAh / g) - Initial 2 Cycle discharge capacity (mAh / g) + initial 3rd cycle charge capacity (mAh / g) - initial 3rd cycle discharge capacity (mAh / g)} × 100

(electrode swelling)
After the initial charging and discharging, the battery was further charged and discharged 50 times (1st cycle to 50th cycle). However, except for the 25th and 50th cycles, the conditions were the same as those for the initial 1st cycle, except that the current density during charging was 0.2 mA/cm ² and the current density during discharging was 0.3 mA/cm ² . was used. In the 25th and 50th cycles, the same conditions as in the initial 2nd cycle were used.
After repeating 50 cycles of charging and discharging, the battery is disassembled, the negative electrode is taken out, the thickness of the negative electrode is measured with a thickness measuring instrument (manufactured by Mitutoyo), and the thickness of the copper foil punched into the same area as the negative electrode is subtracted from this. Thus, the thickness of the negative electrode was obtained and divided by the value of the thickness of the negative electrode at the time of battery fabrication to obtain an index value of electrode swelling.

From Tables 2A and 2B, the present invention having a total content of zirconium, yttrium, hafnium and manganese of 600 ppm or less, containing graphite and silicon oxide particles of the present invention having a total content of zirconium, yttrium, hafnium and manganese of 1000 ppm or less. As a negative electrode active material, it is possible to provide a secondary battery having excellent battery characteristics, particularly an excellent effect of suppressing electrode swelling.

Although the present invention has been described in detail using specific embodiments, it will be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the invention.
This application is based on Japanese Patent Application No. 2021-175656 filed on October 27, 2021, which is incorporated by reference in its entirety.

Claims

Silicon oxide particles having a total content of zirconium, yttrium, hafnium and manganese of less than or equal to 1000 ppm and a d50 of less than or equal to 1 μm.
The silicon oxide particles according to claim 1, wherein the zirconium content is 500 ppm or less.
The silicon oxide particles according to claim 1 or 2, wherein the yttrium content is 100 ppm or less.
The silicon oxide particles according to any one of claims 1 to 3, wherein the hafnium content is 100 ppm or less.
The silicon oxide particles according to any one of claims 1 to 4, wherein the manganese content is 300 ppm or less.
Silicon oxide particles according to any one of claims 1 to 5, wherein d max /d 50 is 2-10.
The silicon oxide particles according to any one of claims 1 to 6, which are used in secondary batteries.
The method for producing silicon oxide particles according to any one of claims 1 to 7, comprising a step of dry pulverizing the silicon oxide particles.
Particles containing silicon oxide particles having a d50 of 1 μm or less and graphite,
Particles having a total content of zirconium, yttrium, hafnium and manganese of 600 ppm or less.
The particles according to claim 9, wherein the zirconium content is 300 ppm or less.
The particles according to claim 9 or 10, wherein the yttrium content is 60 ppm or less.
The particles according to any one of claims 9 to 11, wherein the hafnium content is 60 ppm or less.
The particles according to any one of claims 9 to 12, wherein the manganese content is 180 ppm or less.
The method for producing particles according to any one of claims 9 to 13, comprising a step of combining silicon oxide particles and graphite.
The method for producing particles according to claim 14, wherein the method of combining silicon oxide particles and graphite is a method of mixing the silicon oxide particles and graphite and then performing a spheroidizing treatment.
A secondary battery comprising a positive electrode, a negative electrode and an electrolyte,
the negative electrode includes a current collector and a negative electrode active material layer formed on the current collector;
A secondary battery, wherein the negative electrode active material layer comprises the particles according to any one of claims 9 to 13.
A method for manufacturing a secondary battery including a positive electrode, a negative electrode and an electrolyte,
A method for producing a secondary battery, comprising the step of forming a negative electrode active material layer containing the particles according to any one of claims 9 to 13 on a current collector to obtain a negative electrode.