JP2023012417A - Silicon oxide-based negative electrode material - Google Patents

Abstract

Kind Code: A1 An object of the present invention is to provide a negative electrode material with which an electricity storage device having excellent cycle life can be obtained. A lithium ion secondary battery (2) has a tank (4), an electrolytic solution (6), a separator (8), a positive electrode (10) and a negative electrode (12). The negative electrode 12 has an active material layer. This active material layer contains a large number of particles. The material of these particles is a Si-based material. The metal structure of this Si-based material contains a matrix of SiO2, Si crystals dispersed in this matrix, and Sn, B, In or Bi dispersed in this matrix. [Selection drawing] Fig. 1

Description

TECHNICAL FIELD The present invention relates to an electricity storage device that accompanies movement of positive ions such as lithium ions and sodium ions during charging or discharging. Specifically, the present invention relates to improvement of the negative electrode of this electricity storage device.

In recent years, mobile phones, mobile music players, mobile terminals, etc. have rapidly spread. These portable devices have lithium ion secondary batteries. Electric vehicles and hybrid vehicles also have lithium-ion secondary batteries. Furthermore, lithium ion secondary batteries and hybrid capacitors are used as stationary power storage devices for home use.

In a lithium ion secondary battery, the negative electrode absorbs lithium ions during discharge. During charging of the lithium ion secondary battery, lithium ions are released from the negative electrode. The negative electrode has a current collector and an active material adhered to the surface of this current collector.

Carbon-based materials such as natural graphite, artificial graphite, and coke are used as active materials in negative electrodes. The theoretical capacity of this carbon-based material for lithium ions is only 372 mAh/g. An active material with a large capacity is desired.

Si has attracted attention as an active material for negative electrodes. Si reacts with lithium ions. This reaction forms a compound. A typical compound is Li _3.75 Si. Due to this reaction, a large amount of lithium ions are occluded in the negative electrode. Si can increase the storage capacity of the negative electrode.

When the active material layer containing Si absorbs lithium ions, the active material layer expands due to the formation of the aforementioned compounds. The expansion rate of the active material is about 400%. When lithium ions are released from the active material layer, the active material layer contracts. The active material drops from the current collector due to repeated expansion and contraction. This shedding reduces the storage capacity. Repeated expansion and contraction may hinder electrical conductivity between active materials. Furthermore, due to the formation of a new interface of the active material due to repeated expansion and contraction, the decomposition reaction of the electrolytic solution due to the formation of SEI on the surface layer of the active material occurs excessively. The excess resistive coating produced by this reaction increases the cell resistance. In addition, this reaction causes electrolyte depletion. The life of conventional lithium-ion secondary battery negative electrodes containing Si is not long.

Japanese Patent Application Laid-Open No. 2018-41702 discloses a negative electrode material whose composition is Si, SiO ₂ and a carbonaceous material. In this negative electrode material, SiO ₂ relieves the stress caused by the volume change of Si.

Japanese Patent Application Laid-Open No. 2018-41702

Conventional lithium-ion secondary batteries have insufficient cycle life. A similar problem occurs in other electric storage devices in which cations such as lithium ions and sodium ions are responsible for electric conduction.

SUMMARY OF THE INVENTION An object of the present invention is to provide a negative electrode material with which an electricity storage device having excellent cycle life can be obtained.

A negative electrode material for an electricity storage device according to the present invention is composed of a plurality of particles. The material of these particles is a Si-based material. The metallographic structure of this Si-based material includes a matrix of _SiO2 , Si crystals dispersed in this matrix, and Sn, B, In or Bi dispersed in this matrix.

According to another aspect, a negative electrode of an electricity storage device according to the present invention has a current collector and a plurality of particles adhered to the surface of the current collector. The material of these particles is a Si-based material. The metallographic structure of this Si-based material includes a matrix of _SiO2 , Si crystals dispersed in this matrix, and Sn, B, In or Bi dispersed in this matrix.

According to still another aspect, an electricity storage device according to the present invention has a positive electrode and a negative electrode. This negative electrode has a current collector and a plurality of particles adhered to the surface of this current collector. The material of these particles is a Si-based material. The metallographic structure of this Si-based material includes a matrix of _SiO2 , Si crystals dispersed in this matrix, and Sn, B, In or Bi dispersed in this matrix.

According to still another aspect, the method for producing a negative electrode material for an electricity storage device according to the present invention comprises:
(1) a step of preparing a raw material whose main component is _SiO2 , a raw material whose main component is Si, and a raw material whose material is Sn, B, In or Bi;
and,
(2) These raw materials are subjected to mechanical milling to disperse Si crystals in a matrix of SiO ₂ and to disperse Sn, B, In or Bi in this matrix.

In the negative electrode according to the present invention, the matrix having excellent electronic conductivity promotes uniform reaction between Si and cations. An electricity storage device having this negative electrode has excellent cycle life.

FIG. 1 is a conceptual diagram showing a lithium ion secondary battery as an electricity storage device according to one embodiment of the present invention. 2 is a cross-sectional view showing a portion of the negative electrode of the battery of FIG. 1. FIG. FIG. 3 is a transmission electron micrograph showing particles of the negative electrode of FIG. FIG. 4 is a transmission electron micrograph showing the particles of FIG. 3 enlarged. FIG. 5 is a scanning electron microscope image showing particles of a negative electrode material according to an example of the present invention. FIG. 6 is a chart showing the results of X-ray diffraction of negative electrode materials according to examples of the present invention. FIG. 7 is a chart showing the results of X-ray diffraction of negative electrode materials according to examples of the present invention. FIG. 8 is a schematic diagram showing a metal structure of a negative electrode material according to an example of the present invention. FIG. 9 is a graph showing electrical conductivity of negative electrode materials according to examples of the present invention. FIG. 10 is a graph showing measurement results of cycle life of negative electrode materials according to examples of the present invention. FIG. 11 is a graph showing measurement results of cycle life of negative electrode materials according to examples of the present invention. FIG. 12 is a scanning electron microscope image showing particles of a negative electrode material according to an example of the present invention. FIG. 13 is a chart showing the results of X-ray diffraction of negative electrode materials according to examples of the present invention. FIG. 14 is a graph showing electrical conductivity of negative electrode materials according to examples of the present invention. FIG. 15 is a graph showing measurement results of cycle life of negative electrode materials according to examples of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

A lithium ion secondary battery 2 conceptually shown in FIG. A tank 4 stores an electrolytic solution 6 . This electrolytic solution 6 contains lithium ions. This lithium ion is responsible for electrical conduction. The electrolyte solution 6 may contain other ions. Other ions are exemplified by sodium ions. In the electrolytic solution 6 containing sodium ions, the sodium ions are responsible for electrical conduction. A battery containing a sodium ion electrolyte is called a "sodium ion secondary battery".

The separator 8 partitions the tank 4 into a positive electrode chamber 14 and a negative electrode chamber 16 . The separator 8 prevents contact between the positive electrode 10 and the negative electrode 12 . Although not shown, this separator 8 has a large number of holes. Lithium ions can pass through this hole. The positive electrode 10 is immersed in the electrolytic solution 6 in the positive electrode chamber 14 . The negative electrode 12 is immersed in the electrolytic solution 6 in the negative electrode chamber 16 .

A portion of the negative electrode 12 is shown in FIG. This negative electrode 12 has a current collector 18 and an active material layer 20 . Active material layer 20 includes a large number of particles 22 . A particle 22 is fixed with another particle 22 that abuts this particle 22 . The particles 22 contacting the current collector 18 are adhered to this current collector 18 . Active material layer 20 is porous.

The aggregate (that is, powder) of the particles 22 of the active material layer 20 is referred to as "negative electrode material" in the present invention. The material of this negative electrode material is a Si-based material. This Si-based material contains Si and O. This alloy further contains one or more selected from the group consisting of Sn, B, In and Bi. Preferably, the balance is unavoidable impurities.

The metal structure of this Si-based material is
(1) a matrix of SiO ₂ (2) Si crystals and (3) Sn, B, In or Bi
contains.

FIG. 3 is a transmission electron micrograph showing particles of the negative electrode of FIG. 2, and FIG. 4 is an enlarged photograph thereof. A matrix and a plurality of spots are shown in FIG. These spots are dispersed in a matrix. The matrix shows a halo pattern. According to EDS analysis, the main components of the matrix are Si and O. The composition of this matrix is _SiO2 . This matrix is amorphous. According to electron beam analysis, each speck is a single phase of Si. These spots are Si crystals. In Figures 3 and 4, Sn and B are not identified. The reason is that the Sn and B phases are fine. Sn and B are dispersed in a matrix, as will be detailed later. In a preferred embodiment, Sn and B are in solid solution in the matrix.

The matrix _SiO2 has a _tetrahedral network derived from SiO4. Si crystals are fine. As will be detailed later, neither Sn nor B is dispersed in the Si crystal. Si crystals have a cluster shape. In this negative electrode material, Si exists as SiO ₂ and as Si crystals. This composition is referred to herein as "SiO _x ". X is a positive number less than 2.0.

Si crystals react with lithium ions. This reaction forms a compound. A typical compound is Li _3.75 Si. Due to this reaction, a large amount of lithium ions can be occluded by the negative electrode. The Si crystal absorbs lithium ions during discharge. The Si crystal releases lithium ions during charging. Si crystals can contribute to the power storage performance of the battery.

When the Si crystal absorbs lithium ions, the crystal expands. When the Si crystal releases lithium ions, the crystal contracts. During expansion, stress is generated. Stress is also generated during shrinkage. The _SiO2 matrix follows the expansion and contraction of the Si crystal and relieves the stress caused by this expansion and contraction. This matrix prevents the particles from falling off from the current collector.

SiO ₂ is inherently insulating. In the matrix of the anode material according to the invention Sn, B, In or Bi is dispersed in _SiO2 . Sn, B, In and Bi enhance the electronic conductivity of the matrix. This matrix facilitates the reaction of each Si crystal with lithium ions. In this negative electrode material, many Si crystals uniformly react with lithium ions.

When Si absorbs lithium ions, the reaction represented by the following formula (1) occurs.

When Li _2.00 Si further absorbs lithium ions, the reaction represented by the following formula (2) occurs.

The volume expansion coefficient of Si due to the reaction of the above formula (1) is 240%. When the Li _2.00 Si produced by the above formula (1) proceeds to the reaction of the formula (2), the volume expansion coefficient of Si reaches 380%. The volume expansion rate when proceeding to the above formula (2) is larger than the volume expansion rate due to the reaction of formula (1). As described above, in a negative electrode material in which Sn, B, In or Bi is dispersed in a matrix, Si crystals uniformly react with lithium ions. Therefore, the local occurrence of the reaction leading to the above formula (2) is suppressed, and the local volumetric expansion is suppressed. In this battery, Sn, B, In, or Bi suppresses particles from falling off from the current collector. This battery has excellent cycle life.

From the viewpoint of storage capacity and cycle life, it is preferable that none of Sn, B, In and Bi form a solid solution in the Si crystal.

The content of SiO ₂ in this negative electrode material is preferably 31.0% by mass or more and 49.0% by mass or less. In a negative electrode material having a content of 31.0% by mass or more, the matrix sufficiently contributes to stress relaxation. From this point of view, the content is more preferably 32.0% by mass or more, and particularly preferably 35.0% by mass or more. A negative electrode material with a content of 49.0% by mass or less can contain sufficient amounts of Si crystals, Sn, B, In and Bi.

The content of Si crystals in this negative electrode material is preferably 49.0% by mass or more and 66.0% by mass or less. A battery with a content of 49.0% by mass or more has a large power storage capacity. From this point of view, the content is more preferably 50.0% by mass or more, and particularly preferably 51.0% by mass or more. A negative electrode material having a content of 66.0% by mass or less can contain sufficient amounts of SiO ₂ , Sn, B, In and Bi.

The total content of Sn, B, In and Bi in this negative electrode material is preferably 0.1% by mass or more and 10.0% by mass or less. In a battery with a content of 0.1% by mass or more, Sn or B can contribute to the storage capacity and cycle life. From this point of view, the content is more preferably 1.0% by mass or more, and particularly preferably 1.5% by mass or more. A negative electrode material whose content is 10.0% by mass or less can contain sufficient amounts of SiO ₂ and Si crystals.

The crystallite size of the Si crystal is preferably 20 nm or less. A battery with a crystallite size of 20 nm or less is excellent in storage capacity and cycle life. From these points of view, the crystallite size is more preferably 15 nm or less, and particularly preferably 12 nm or less. All Si crystals contained in the negative electrode material preferably have a crystallite size within the above range.

Crystallite size can be measured by X-ray diffraction. The X-ray source in X-ray diffraction is CuKα rays with a wavelength of 1.54059 angstroms. From the half width of the peak obtained by this X-ray diffraction analysis, the following Scherrer equation can be used to determine the crystallite size.
D = (K x λ) / (β x cos θ)
In this formula, D represents the crystallite size (angstroms), K represents Scherrer's constant, λ represents the wavelength of the X-ray tube, and β represents the spread of the diffraction line due to the crystallite size. , θ represents the diffraction angle.

The mass of particles applied to the active material layer is powder. The average particle diameter D50 of this powder is preferably 1.0 μm or more and 6.0 μm or less. A battery having an average particle diameter of D50 is excellent in cycle life. From the viewpoint of cycle life, the average particle diameter D50 is more preferably 2.0 µm or more, particularly preferably 2.5 µm or more. From the viewpoint of cycle life, the average particle diameter D50 is more preferably 5.0 μm or less, particularly preferably 4.5 μm or less.

The average particle size D50 is the particle diameter when the cumulative volume is 50% in the powder volume cumulative curve. The average particle size D50 is measured with a laser diffraction/scattering particle size distribution analyzer.

An example of the method for producing a negative electrode material according to the present invention will be described below. This manufacturing method
(1) a step of preparing a raw material whose main component is _SiO2 , a raw material whose main component is Si, and a raw material whose material is Sn, B, In or Bi;
and,
(2) These raw materials are subjected to mechanical milling to disperse Si crystals in a matrix of SiO ₂ and to disperse Sn, B, In or Bi in this matrix.

The raw material of SiO ₂ to be milled can be produced by a liquid phase synthesis method, a vapor phase synthesis method, a melting method, or the like. The properties of this SiO ₂ raw material are powder, flakes, lumps, and the like. The Si raw material to be milled can be produced by an atomizing method, a melting method, a reduction method, or the like. The properties of this Si raw material are powder, flakes, lumps, and the like. Raw materials of Sn, B, In, or Bi to be milled can be produced by an atomizing method, a melting method, a reduction method, or the like. The properties of the Sn, B, In, or Bi raw material are powder, flake, block, and the like.

The reaction Gibbs energy (ΔrG ⁰ ) of B ₂ O ₃ is 181.25 kJ mol ⁻¹ . The reaction Gibbs energy (ΔrG ⁰ ) of SnO ₂ is 340.93 kJ mol ⁻¹ . Since ΔrG ⁰ >0 when B or Sn is added, it is more stable to exist as SiO ₂ than B ₂ O ₃ and SnO ₂ . For this reason, Si and B ₂ O ₃ may be used as raw materials instead of SiO ₂ , and Si and SnO ₂ may be used. The B ₂ O ₃ and SnO ₂ raw materials can be produced by a liquid phase synthesis method, a gas phase synthesis method, a melting method, or the like. The properties of the B ₂ O ₃ and SnO ₂ raw materials are powder, flakes, lumps, and the like.

These raw materials are put into the pot together with the media. Zirconia, SUS304 and SUJ2 are exemplified as media materials. Examples of the pot material include zirconia, SUS304 (austenitic stainless steel specified by JIS), and SUJ2 (high carbon chromium bearing steel specified by JIS). The interior of the pot is filled with inert gas and the pot is sealed. The pot is placed on a milling device and agitated. Examples of milling methods include ball mills, bead mills, planetary ball mills, attritors and vibrating ball mills. Various mechanical grinding processes capable of achieving the objectives of the present invention, including techniques called "mechanical grinding", "mechanical alloying", etc., are collectively referred to herein as "mechanical milling". This milling disperses Si crystals in a matrix of _SiO2 . This milling disperses the Sn or B in the _SiO2 matrix. Milling reduces the crystallinity of _SiO2 .

The effects of the present invention will be clarified by examples below, but the present invention should not be construed in a limited manner based on the description of these examples.

[Example 1]
A flaky Si raw material was heated by high-frequency induction in an alumina crucible to obtain a molten alloy. A molten alloy was dropped from a nozzle formed at the bottom of the crucible, and high-pressure nitrogen gas was injected into it. This injection atomized and quenched the molten metal to form a powder. This powder was classified with a sieve having an opening of 300 μm to obtain Si powder. A large number of balls made of high-carbon chromium bearing steel were put into a container made of austenitic stainless steel. The total mass of these balls was 12 kg. 31.4 g of Si powder, 26.8 g of SiO ₂ powder (purity: 99.9%) and 1.8 g of Sn powder (purity: 99.0%) were charged into the container. The ratio of the total weight of these powders to the total weight of the balls was 1:200. The container was sealed and the pressure inside the container was reduced to 0.1 MPa. Argon gas was sealed in this container. The container was set in a vibrating ball mill apparatus. Mechanical milling was performed under the following conditions.
Frequency: 1200rpm
Time: 14 hours After this mechanical milling, the mass ratio of the powder to the balls was set to 1:300, and mechanical milling was further performed for 14 hours to obtain an alloy powder.

This alloy powder was pulverized under the following conditions.
Apparatus: Jet mill Gas type: Nitrogen gas Gas pressure: 0.7 MPa
By this pulverization, a negative electrode material having a particle size adjusted to 10 μm or less was obtained. The Sn content in this negative electrode material was 3% by mass.

[Example 2]
A negative electrode material of Example 2 was obtained in the same manner as in Example 1, except that B powder (purity: 99.9%) was put into the container instead of the Sn powder.

[Comparative Example 1]
A negative electrode material of Comparative Example 1 was obtained in the same manner as in Example 1, except that Al powder (purity: 99.9%) was put into the container instead of Sn powder.

[Comparative Example 2]
A negative electrode material of Comparative Example 2 was obtained in the same manner as in Example 1, except that the Sn powder was not put into the container.

[exterior]
The particles contained in the powder were photographed with a scanning electron microscope. The results are shown in FIG. The arrangement of each image in FIG. 5 is as follows.
Upper left: Comparative example 2
Upper right: Comparative example 1
Lower left: Example 2
Lower right: Example 1
In each image, secondary particles with a size of about 5 μm were confirmed. From this result, it is considered that Sn and B have little effect on the size and shape of secondary particles. Primary particles could not be clearly identified in each image. From this result, the size of the primary particles is estimated to be several hundred nm or less.

[X-ray diffraction]
2θ=20-60 deg. was subjected to X-ray diffraction. The results are shown in FIG. As is clear from FIG. 6, Si diffraction peaks ((111), (220) and (311)) were observed in each powder. The crystallite size of Si was calculated from Scherrer's formula and found to be about 8-12 nm. No SiO ₂ diffraction peak was observed in each powder. It is believed that the high-energy pulverization of mechanical milling changed the _SiO2 to almost amorphous. In the powder of Example 1, no peak derived from Sn was observed. In the powder of Example 2, no peak derived from B was observed. In the powder of Comparative Example 1, no peak derived from Al was observed.

2θ=25-32 deg. was subjected to X-ray diffraction. The results are shown in FIG. 2θ=28 deg. did not shift from the peak position of Comparative Example 2. From this result, it was found that the crystal lattice of Si did not expand or contract, and therefore Sn or B did not form a solid solution in Si.

[Metal structure]
From the above study results, it was found that the powder of each example had the metallographic structure shown in FIG. This metallographic structure is
(1) a matrix of amorphous _SiO2 , (2) Si crystals dispersed in this matrix and (3) amorphous Sn or B dispersed in this matrix.
have. Sn and B are substantially absent in Si.

[Experiment 1]
[Electrical conductivity]
Each powder was pressed to obtain a compact. The electrical conductivity of this compact was measured. The results are shown in the graph of FIG. In this graph, the horizontal axis is the applied pressure and the vertical axis is the electrical conductivity. The electrical conductivity of the negative electrode material of each example is 1.5 times or more that of Comparative Example 2. On the other hand, the electrical conductivity of the negative electrode material of Comparative Example 1 is equivalent to that of Comparative Example 2. The reason why the conductivity of the negative electrode material of Comparative Example 1 is not improved is presumed to be that Al ₂ O ₃ , which is an insulator, was formed by oxidation of Al.

[Cycle life]
70% by mass of powder (negative electrode material), 15% by mass of acetylene black, 10% by mass of carboxymethyl cellulose and 5% by mass of styrene-butadiene copolymer were kneaded to obtain a composition. This composition was applied to a copper foil to obtain a negative electrode. A coin cell having this negative electrode was produced. In this coin cell, the anode was lithium and the separator was a glass fiber filter. In this coin cell, the electrolyte was a solution of lithium bis(trifluoromethanesulfonyl)amide in propylene carbonate. The concentration of this solution was 1 mol/dm ⁻³ M. This coin cell was repeatedly subjected to charge and discharge cycles, and the discharge capacity was measured. The results are shown in the graph of FIG. In this graph, the horizontal axis is the number of cycles, and the vertical axis is the discharge capacity. As is clear from FIG. 10 , the negative electrode material of each example has a longer life than the negative electrode material of Comparative Example 2.

[Experiment 2]
[Cycle life]
A sodium ion secondary battery was produced using each negative electrode material. As in Experiment 1, the cycle life of this negative electrode material was measured. The results are shown in the graph of FIG. In this graph, the horizontal axis is the number of cycles and the vertical axis is the electrical conductivity. As is clear from FIG. 11 , the negative electrode material of each example has a longer life than the negative electrode material of Comparative Example 2.

[Example 3]
A negative electrode material of Example 3 was obtained in the same manner as in Example 1, except that 0.6 g of Sn powder was put into the container. The Sn content in this negative electrode material was 1% by mass.

[Example 4]
A negative electrode material of Example 4 was obtained in the same manner as in Example 1, except that 3.0 g of the Sn powder was put into the aforementioned container. The Sn content in this negative electrode material was 5% by mass.

[exterior]
The particles contained in the powder were photographed with a scanning electron microscope. The results are shown in FIG. The arrangement of each image in FIG. 12 is as follows.
Upper left: Comparative example 2
Upper right: Example 3
Lower left: Example 1
Lower right: Example 4
In each image, secondary particles with a size of about 5 μm were confirmed. From this result, it is considered that Sn has little effect on the size and shape of secondary particles. Primary particles could not be clearly identified in each image. From this result, the size of the primary particles is estimated to be several hundred nm or less.

[X-ray diffraction]
2θ=20-60 deg. was subjected to X-ray diffraction. The results are shown in FIG. As is clear from FIG. 13, Si diffraction peaks ((111), (220) and (311)) were observed in each powder. The crystallite size of Si was calculated from Scherrer's formula and found to be about 8-12 nm. No SiO ₂ diffraction peak was observed in each powder. It is believed that the high-energy pulverization of mechanical milling changed the _SiO2 to almost amorphous. Furthermore, no peak derived from Sn was observed in each powder.

[Experiment 3]
[Electrical conductivity]
Each powder was pressed to obtain a compact. The electrical conductivity of this compact was measured. The results are shown in the graph of FIG. In this graph, the horizontal axis is the applied pressure and the vertical axis is the electrical conductivity. The electrical conductivity of the negative electrode material of each example is greater than that of Comparative Example 2.

[Cycle life]
The discharge capacity was measured in the same manner as in Experiment 2. The results are shown in the graph of FIG. In this graph, the horizontal axis is the number of cycles, and the vertical axis is the discharge capacity. As is clear from FIG. 15, the negative electrode material of each example has a longer life than the negative electrode material of Comparative Example 2.

The superiority of the present invention is clear from the results of Experiments 1-3.

[Disclosure items]
Each of the following items is a disclosure of a preferred embodiment.

[Item 1]
A negative electrode material for an electricity storage device comprising a plurality of particles,
The material of these particles is a Si-based material,
A negative electrode material in which the metallic structure of this Si-based material includes a matrix of _SiO2 , Si crystals dispersed in the matrix, and Sn, B, In or Bi dispersed in the matrix.

[Item 2]
2. The negative electrode material according to item 1, wherein the Sn, B, In or Bi is dissolved in the matrix.

[Item 3]
The SiO ₂ content is 31.0% by mass or more and 49.0% by mass or less, the Si crystal content is 49.0% by mass or more and 66.0% by mass or less, and the Sn, B, In 3. The negative electrode material according to item 1 or 2, wherein the total content of Bi and Bi is 0.1% by mass or more and 10.0% by mass or less.

[Item 4]
4. The negative electrode material according to any one of items 1 to 3, wherein the Si crystal has a crystallite size of 20 nm or less.

[Item 5]
5. The negative electrode material according to any one of items 1 to 4, wherein none of Sn, B, In and Bi is dissolved in the Si crystal.

[Item 6]
6. The negative electrode material according to any one of items 1 to 5, which has an average particle diameter D50 of 1.0 μm or more and 6.0 μm or less.

[Item 7]
comprising a current collector and a plurality of particles adhered to the surface of the current collector;
The material of these particles is a Si-based material,
A negative electrode of an electric storage device, wherein the metallographic structure of this Si-based material comprises a matrix of SiO ₂ , Si crystals dispersed in the matrix, and Sn, B, In or Bi dispersed in the matrix.

[Item 8]
comprising a positive electrode and a negative electrode,
The negative electrode comprises a current collector and a plurality of particles adhered to the surface of the current collector,
The material of these particles is a Si-based material,
A power storage device in which the metallographic structure of the Si-based material includes a matrix of SiO ₂ , Si crystals dispersed in the matrix, and Sn, B, In or Bi dispersed in the matrix.

[Item 9]
preparing a raw material whose main component is _SiO2 , a raw material whose main component is Si, and a raw material whose material is Sn, B, In or Bi;
and,
A method for producing a negative electrode material for an electric storage device, comprising a step of subjecting these raw materials to mechanical milling to disperse Si crystals in a matrix of SiO ₂ and disperse Sn, B, In or Bi in this matrix.

The negative electrode material according to the present invention can be applied to various power storage devices such as lithium ion secondary batteries, sodium ion secondary batteries, all solid lithium ion secondary batteries, all solid sodium ion secondary batteries, hybrid capacitors and the like.

DESCRIPTION OF SYMBOLS 2... Lithium ion secondary battery 4... Tank 6... Electrolyte solution 8... Separator 10... Positive electrode 12... Negative electrode 14... Positive electrode chamber 16... Negative electrode chamber 18... Current collector 20... Active material layer 22... Particles (negative electrode material)

Claims (9)

A negative electrode material for an electricity storage device comprising a plurality of particles,
The material of these particles is a Si-based material,
A negative electrode material in which the metallic structure of this Si-based material includes a matrix of _SiO2 , Si crystals dispersed in the matrix, and Sn, B, In or Bi dispersed in the matrix. 2. The negative electrode material according to claim 1, wherein said Sn, B, In or Bi is dissolved in said matrix. The SiO ₂ content is 31.0% by mass or more and 49.0% by mass or less, the Si crystal content is 49.0% by mass or more and 66.0% by mass or less, and the Sn, B, In 3. The negative electrode material according to claim 1, wherein the total content of Bi and Bi is 0.1% by mass or more and 10.0% by mass or less. 3. The negative electrode material according to claim 1, wherein the Si crystal has a crystallite size of 20 nm or less. 3. The negative electrode material according to claim 1, wherein none of Sn, B, In and Bi is dissolved in the Si crystal. 3. The negative electrode material according to claim 1, wherein the average particle diameter D50 is 1.0 [mu]m or more and 6.0 [mu]m or less. comprising a current collector and a plurality of particles adhered to the surface of the current collector;
The material of these particles is a Si-based material,
A negative electrode of an electric storage device, wherein the metallographic structure of this Si-based material comprises a matrix of SiO ₂ , Si crystals dispersed in the matrix, and Sn, B, In or Bi dispersed in the matrix. comprising a positive electrode and a negative electrode,
The negative electrode comprises a current collector and a plurality of particles adhered to the surface of the current collector,
The material of these particles is a Si-based material,
A power storage device in which the metallographic structure of the Si-based material includes a matrix of SiO ₂ , Si crystals dispersed in the matrix, and Sn, B, In or Bi dispersed in the matrix. preparing a raw material whose main component is _SiO2 , a raw material whose main component is Si, and a raw material whose material is Sn, B, In or Bi;
and,
A method for producing a negative electrode material for an electric storage device, comprising a step of subjecting these raw materials to mechanical milling to disperse Si crystals in a matrix of SiO ₂ and disperse Sn, B, In or Bi in this matrix.

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