Silicon oxide-based negative electrode materials

Abstract

To provide a negative electrode material by which a power storage device superior in cycle life can be obtained.SOLUTION: A lithium ion secondary battery 2 has a tank 4, an electrolyte solution 6, a separator 8, a positive electrode 10 and a negative electrode 12. The negative electrode 12 has an active material layer. The active material layer contains many particles. The particles include a Si-based material. The Si-based material has a metal structure including a matrix of SiO2, Si crystalline dispersed in the matrix, and Sn, B, In or Bi dispersed in the matrix.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to an energy storage device that involves the movement of cations such as lithium ions and sodium ions during charging or discharging. More specifically, this invention relates to an improvement of the negative electrode of this energy storage device. [Background technology]

[0002] In recent years, mobile phones, portable music players, and other portable devices have become widespread. These portable devices contain lithium-ion rechargeable batteries. Electric vehicles and hybrid vehicles also contain lithium-ion rechargeable batteries. Furthermore, lithium-ion rechargeable batteries and hybrid capacitors are used as stationary energy storage devices for home use.

[0003] In lithium-ion secondary batteries, the negative electrode absorbs lithium ions during discharge. During charging, lithium ions are released from the negative electrode. The negative electrode consists of a current collector and an active material fixed to the surface of the current collector.

[0004] Carbon-based materials such as natural graphite, artificial graphite, and coke are used as active materials in the negative electrode. The theoretical capacity of these carbon-based materials for lithium ions is only 372 mAh / g. Active materials with higher capacity are desired.

[0005] Si is attracting attention as an active material in the negative electrode. Si reacts with lithium ions. This reaction forms compounds. Typical compounds include Li 3.75 This reaction involves the absorption of a large amount of lithium ions into the negative electrode. Si can increase the energy storage capacity of the negative electrode.

[0006] When an active material layer containing Si absorbs lithium ions, the formation of the aforementioned compounds causes this active material layer to expand. The expansion rate of the active material is approximately 400%. When lithium ions are released from the active material layer, this layer contracts. Repeated expansion and contraction causes the active material to detach from the current collector. This detachment reduces the energy storage capacity. Repeated expansion and contraction can also inhibit conductivity between active materials. Furthermore, the formation of new interfaces in the active material due to repeated expansion and contraction leads to excessive decomposition reactions of the electrolyte caused by SEI formation on the surface of the active material. The excess resistive film produced by this reaction increases the battery resistance. Moreover, this reaction causes electrolyte depletion. The lifespan of conventional lithium-ion secondary battery negative electrodes containing Si is not long.

[0007] Japanese Patent Publication No. 2018-41702 discloses a negative electrode material whose composition consists of Si, SiO2, and a carbon-based material. In this negative electrode material, the SiO2 relieves the stress caused by the volume change of Si. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2018-41702 [Overview of the project] [Problems that the invention aims to solve]

[0009] Conventional lithium-ion rechargeable batteries have insufficient cycle life. Similar problems occur in other energy storage devices where cations such as lithium ions and sodium ions are responsible for electrical conduction.

[0010] The objective of the present invention is to provide an anode material that enables the creation of energy storage devices with excellent cycle life. [Means for solving the problem]

[0011] The negative electrode material for an energy storage device according to the present invention consists of a plurality of particles. The material of these particles is a Si-based material. The metallic structure of this Si-based material includes an SiO2 matrix, Si crystals dispersed in this matrix, and Sn, B, In, or Bi dispersed in this matrix.

[0012] From another perspective, the negative electrode of the energy storage device according to the present invention comprises a current collector and a plurality of particles fixed to the surface of the current collector. The material of these particles is a Si-based material. The microstructure of this Si-based material comprises an SiO2 matrix, Si crystals dispersed in this matrix, and Sn, B, In, or Bi dispersed in this matrix.

[0013] From yet another perspective, the energy storage device according to the present invention has a positive electrode and a negative electrode. The negative electrode has a current collector and a plurality of particles fixed to the surface of the current collector. The material of these particles is a Si-based material. The metallic structure of this Si-based material includes an SiO2 matrix, Si crystals dispersed in this matrix, and Sn, B, In, or Bi dispersed in this matrix.

[0014] From another perspective, the method for manufacturing a negative electrode material for an energy storage device according to the present invention is: (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) A process of mechanically milling these raw materials to disperse Si crystals in an SiO2 matrix and to disperse Sn, B, In, or Bi in this matrix. Includes. [Effects of the Invention]

[0015] In the negative electrode according to the present invention, a matrix with excellent electronic conductivity promotes a uniform reaction between Si and cations. Energy storage devices having this negative electrode have excellent cycle life. [Brief explanation of the drawing]

[0016] [Figure 1] Figure 1 is a conceptual diagram showing a lithium-ion secondary battery as a power storage device according to an embodiment of the present invention. [Figure 2] Figure 2 is a cross-sectional view showing a part of the negative electrode of the battery in Figure 1. [Figure 3] Figure 3 is a transmission electron microscope photograph showing the particles of the negative electrode in Figure 2. [Figure 4] Figure 4 is a transmission electron microscope photograph showing the particles in Figure 3 enlarged. [Figure 5] Figure 5 is a scanning electron microscope image showing the particles of the negative electrode material according to an example of the present invention. [Figure 6] Figure 6 is a chart showing the results of X-ray diffraction of the negative electrode material according to an example of the present invention. [Figure 7] Figure 7 is a chart showing the results of X-ray diffraction of the negative electrode material according to an example of the present invention. [Figure 8] Figure 8 is a schematic diagram showing the metal structure of the negative electrode material according to an example of the present invention. [Figure 9] Figure 9 is a graph showing the electrical conductivity of the negative electrode material according to an example of the present invention. [Figure 10] Figure 10 is a graph showing the measurement results of the cycle life of the negative electrode material according to an example of the present invention. [Figure 11] Figure 11 is a graph showing the measurement results of the cycle life of the negative electrode material according to an example of the present invention. [Figure 12] Figure 12 is a scanning electron microscope image showing the particles of the negative electrode material according to an example of the present invention. [Figure 13] Figure 13 is a chart showing the results of X-ray diffraction of the negative electrode material according to an example of the present invention. [Figure 14] Figure 14 is a graph showing the electrical conductivity of the negative electrode material according to an example of the present invention. [Figure 15] Figure 15 is a graph showing the measurement results of the cycle life of the negative electrode material according to an example of the present invention.

Mode for Carrying Out the Invention

[0017] The present invention will be described in detail below based on preferred embodiments, with reference to drawings as appropriate.

[0018] The lithium-ion secondary battery 2 conceptually shown in Figure 1 has a cell 4, an electrolyte 6, a separator 8, a positive electrode 10, and a negative electrode 12. The cell 4 stores the electrolyte 6. This electrolyte 6 contains lithium ions. These lithium ions are responsible for electrical conduction. The electrolyte 6 may also contain other ions. Sodium ions are an example of other ions. In an electrolyte 6 containing sodium ions, these sodium ions are responsible for electrical conduction. A battery containing a sodium ion electrolyte is called a "sodium-ion secondary battery."

[0019] The separator 8 divides 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, the separator 8 has numerous pores. Lithium ions can pass through these pores. The positive electrode 10 is immersed in the electrolyte 6 in the positive electrode chamber 14. The negative electrode 12 is immersed in the electrolyte 6 in the negative electrode chamber 16.

[0020] Figure 2 shows a portion of the negative electrode 12. This negative electrode 12 has a current collector 18 and an active material layer 20. The active material layer 20 contains a large number of particles 22. The particles 22 are fixed to other particles 22 that are in contact with them. The particles 22 that are in contact with the current collector 18 are fixed to the current collector 18. The active material layer 20 is porous.

[0021] In this invention, the aggregate (i.e., powder) of particles 22 in the active material layer 20 is referred to as the "negative electrode material." 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 remainder is an unavoidable impurity.

[0022] The microstructure of this 4-system material is (1) SiO2 matrix (2)Si crystal and (3) Sn, B, In or Bi It includes.

[0023] Figure 3 is a transmission electron microscope image showing the negative electrode particles in Figure 2, and Figure 4 is a magnified image thereof. Figure 3 shows the matrix and several spots. These spots are dispersed in the matrix. The matrix exhibits 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 spot is a single phase of Si. These spots are Si crystals. Sn and B are not visible in Figures 3 and 4. This is because the phases of Sn and B are fine. As will be explained in detail later, Sn and B are dispersed in the matrix. In a preferred embodiment, Sn and B are solid-dissolved in the matrix.

[0024] The matrix, SiO2, has a tetrahedral network structure derived from SiO4. The Si crystals are fine. As will be explained in detail later, neither Sn nor B is dispersed in the Si crystals. The Si crystals have a cluster shape. In this negative electrode material, Si exists both as SiO2 and as Si crystals. This composition is referred to herein as "SiO x This is expressed as , where X is a positive number less than 2.0.

[0025] Si crystals react with lithium ions. This reaction forms compounds. Typical compounds include Li 3.75 This is silicon (Si). This reaction allows for the absorption of a large amount of lithium ions into the negative electrode. During discharge, the Si crystal absorbs lithium ions. During charging, the Si crystal releases lithium ions. The Si crystal can contribute to the battery's energy storage performance.

[0026] When a Si crystal absorbs lithium ions, it expands. When the Si crystal releases lithium ions, it contracts. Stress is generated during expansion. Stress is also generated during contraction. The SiO2 matrix follows the expansion and contraction of the Si crystal and relieves the stress caused by this expansion and contraction. This matrix suppresses the detachment of particles from the current collector.

[0027] SiO2 is inherently an insulating material. In the matrix of the negative electrode material according to the present invention, Sn, B, In, or Bi are dispersed in SiO2. Sn, B, In, and Bi enhance the electronic conductivity of the matrix. This matrix promotes the reaction of each Si crystal with lithium ions. In this negative electrode material, many Si crystals react uniformly with lithium ions.

[0028] When Si intercalates lithium ions, the reaction shown in equation (1) below occurs.

number

[0029] Li 2.00 When Si further absorbs lithium ions, the reaction shown in equation (2) below occurs.

number

[0030] The volume expansion coefficient of Si due to the reaction in equation (1) above is 240%. The Li produced in equation (1) above... 2.00If the reaction proceeds further from Si to the reaction shown in equation (2), the volume expansion coefficient of Si reaches 380%. The volume expansion coefficient when the reaction proceeds to equation (2) is greater than the volume expansion coefficient due to the reaction in equation (1). As mentioned above, in a negative electrode material in which Sn, B, In, or Bi are dispersed in the matrix, the Si crystals react uniformly with lithium ions. Therefore, the local occurrence of the reaction leading to equation (2) is suppressed, and local volume expansion is suppressed. In this battery, Sn, B, In, or Bi suppresses the detachment of particles from the current collector. This battery has excellent cycle life.

[0031] From the viewpoint of energy storage capacity and cycle life, it is preferable that none of Sn, B, In, and Bi are solid-solved in the Si crystal.

[0032] The SiO2 content in this negative electrode material is preferably 31.0% by mass or more and 49.0% by mass or less. In negative electrode materials with a SiO2 content of 31.0% by mass or more, the matrix contributes sufficiently to stress relaxation. From this viewpoint, a SiO2 content of 32.0% by mass or more is more preferable, and 35.0% by mass or more is particularly preferable. Negative electrode materials with a SiO2 content of 49.0% by mass or less may contain sufficient amounts of Si crystals, Sn, B, In, and Bi.

[0033] The Si crystal content in this negative electrode material is preferably 49.0% by mass or more and 66.0% by mass or less. Batteries with a Si content of 49.0% by mass or more have a large energy storage capacity. From this viewpoint, a Si content of 50.0% by mass or more is more preferable, and 51.0% by mass or more is particularly preferable. A negative electrode material with a Si content of 66.0% by mass or less may contain sufficient amounts of SiO2, Sn, B, In, and Bi.

[0034] 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 batteries where this content is 0.1% by mass or more, Sn or B may contribute to the energy storage capacity and cycle life. From this viewpoint, this content is more preferably 1.0% by mass or more, and particularly preferably 1.5% by mass or more. A negative electrode material with a content of 10.0% by mass or less may contain a sufficient amount of SiO2 and Si crystals.

[0035] The crystallite size of the Si crystal is preferably 20 nm or less. Batteries with a crystallite size of 20 nm or less exhibit excellent energy storage capacity and cycle life. From these viewpoints, a crystallite size of 15 nm or less is more preferable, and 12 nm or less is particularly preferable. It is preferable that the crystallite size of all Si crystals contained in the negative electrode material is within the above range.

[0036] Crystallite size can be measured by X-ray diffraction. The X-ray source used in X-ray diffraction is CuKα radiation with a wavelength of 1.54059 angstroms. From the full width at half maximum (FMAX) of the peaks obtained by this X-ray diffraction analysis, the crystallite size can be determined using Scherrer's equation, as shown below. D = (K × λ) / (β × cosθ) In this formula, D represents the crystallite size (angstrom), K represents Scherrer's constant, λ represents the wavelength of the X-ray tube, β represents the broadening of the diffraction line due to the crystallite size, and θ represents the diffraction angle.

[0037] The aggregate of numerous particles applied to the active material layer is in the form of a powder. The average particle size D50 of this powder is preferably between 1.0 μm and 6.0 μm. Batteries with an average particle size D50 exhibit excellent cycle life. From the viewpoint of cycle life, an average particle size D50 of 2.0 μm or more is more preferable, and 2.5 μm or more is particularly preferable. From the viewpoint of cycle life, an average particle size D50 of 5.0 μm or less is more preferable, and 4.5 μm or less is particularly preferable.

[0038] The average particle diameter D50 is the particle diameter when the cumulative volume is 50% in the cumulative curve of the powder volume. The average particle diameter D50 is measured by a laser diffraction / scattering particle size distribution measuring device.

[0039] Hereinafter, an example of a method for manufacturing a negative electrode material according to the present invention will be described. 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) A step of subjecting these raw materials to mechanical milling to disperse Si crystals in the SiO2 matrix and disperse Sn, B, In or Bi in this matrix. is included.

[0040] The SiO2 raw material used for milling can be produced by a liquid phase synthesis method, a gas phase synthesis method, a melting method, etc. The properties of this SiO2 raw material are powdery, flaky,块状 (blocky), etc. The Si raw material used for milling can be produced by an atomization method, a melting method, a reduction method, etc. The properties of this Si raw material are powdery, flaky,块状 (blocky), etc. The raw materials of Sn, B, In or Bi used for milling can be produced by an atomization method, a melting method, a reduction method, etc. The properties of these raw materials of Sn, B, In or Bi are powdery, flaky,块状 (blocky), etc.

[0041] The reaction Gibbs energy (ΔrG 0 ) of B2O3 is 181.25 kJ mol -1 The reaction Gibbs energy (ΔrG 0 ) of SnO2 is 340.93 kJ mol -1 When B or Sn is added, ΔrG 0Since the threshold is >0, SiO2 is more stable than B2O3 and SnO2. For this reason, Si and B2O3 may be used as raw materials instead of SiO2, or Si and SnO2 may be used. These raw materials for B2O3 and SnO2 can be produced by liquid-phase synthesis, gas-phase synthesis, melting, etc. Furthermore, the properties of these raw materials for B2O3 and SnO2 can be powder, flake, or lump.

[0042] These raw materials are placed in a pot along with media. Examples of media materials include zirconia, SUS304, and SUJ2. Examples of pot materials include zirconia, SUS304 (austenitic stainless steel as defined by JIS), and SUJ2 (high-carbon chromium bearing steel as defined by JIS). The inside of the pot is filled with inert gas and sealed. The pot is placed on a milling device and stirred. Examples of milling methods include ball mills, bead mills, planetary ball mills, attritors, and vibrating ball mills. Various mechanical grinding processes that can achieve the objectives of the present invention, including methods referred to as "mechanical gliding" and "mechanical alloying," are collectively referred to as "mechanical milling" in this specification. This milling disperses Si crystals in the SiO2 matrix. This milling disperses Sn or B in the SiO2 matrix. Milling reduces the crystallinity of SiO2. [Examples]

[0043] The effects of the present invention will be demonstrated below by the examples, but the present invention should not be interpreted restrictively based on the description in these examples.

[0044] [Example 1] Flake-shaped Si raw material was heated by high-frequency induction in an alumina crucible to obtain a molten alloy. The 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 refined the molten metal and rapidly cooled it, forming a powder. This powder was classified using a sieve with a mesh size of 300 μm to obtain Si powder. Numerous balls made of high-carbon chromium bearing steel were placed in 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 SiO2 powder (purity: 99.9%), and 1.8 g of Sn powder (purity: 99.0%) were added to this container. The ratio of the total mass of these powders to the total mass of the balls was 1:200. This container was sealed, and the pressure inside was reduced to 0.1 MPa. Argon gas was then sealed into this container. The container was placed in a vibrating ball mill. Mechanical milling was performed under the following conditions. Frequency: 1200 rpm Time: 14 hours After this mechanical milling, the mass ratio of powder to balls was set to 1:300, and mechanical milling was performed for another 14 hours to obtain alloy powder.

[0045] This alloy powder was subjected to crushing under the following conditions. Equipment: Jet mill Type of gas: Nitrogen gas Gas pressure: 0.7 MPa This crushing process yielded a negative electrode material with a particle size of 10 μm or less. The Sn content in this negative electrode material was 3% by mass.

[0046] [Example 2] The negative electrode material for Example 2 was obtained in the same manner as in Example 1, except that B powder (purity: 99.9%) was added to the container instead of Sn powder.

[0047] [Comparative Example 1] The negative electrode material for Comparative Example 1 was obtained in the same manner as in Example 1, except that Al powder (purity: 99.9%) was added to the container instead of Sn powder.

[0048] [Comparative Example 2] The negative electrode material for Comparative Example 2 was obtained in the same manner as in Example 1, except that the Sn powder was not added to the container.

[0049] [exterior] The particles contained in the powder were photographed using a scanning electron microscope. The results are shown in Figure 5. The arrangement of each image in Figure 5 is as follows: Top left: Comparative example 2 Top right: Comparative Example 1 Bottom left: Example 2 Bottom right: Example 1 Secondary particles with a size of approximately 5 μm were observed in each image. This suggests that Sn and B have little influence on the size and shape of the secondary particles. Primary particles could not be clearly identified in any of the images. Therefore, the size of the primary particles is estimated to be several hundred nanometers or less.

[0050] [X-ray diffraction] The powders were subjected to X-ray diffraction at 2θ = 20-60 degrees. The results are shown in Figure 6. As is clear from Figure 6, diffraction peaks of Si ((111), (220), and (311)) were observed in each powder. The crystallite size of Si was calculated using Scherrer's formula and found to be approximately 8-12 nm. No diffraction peaks of SiO2 were observed in any of the powders. It is thought that the SiO2 was almost completely transformed into an amorphous state by high-energy grinding using mechanical milling. No peaks originating from Sn were observed in the powder of Example 1. No peaks originating from B were observed in the powder of Example 2. No peaks originating from Al were observed in the powder of Comparative Example 1.

[0051] The powder was subjected to X-ray diffraction at 2θ = 25-32 degrees. The results are shown in Figure 7. It was found that the peak position at 2θ = 28 degrees for Examples 1 and 2 did not shift from the peak position for Comparative Example 2. From these results, it was found that the Si crystal lattice did not expand or contract, and therefore Sn or B was not solid-dissolved in Si.

[0052] [Metal structure] From the above findings, it was found that the powders of each example have the metallic structure shown in Figure 8. This metallic structure is (1) Amorphous SiO2 matrix (2) Si crystals dispersed in this matrix and (3) Amorphous Sn or B dispersed in this matrix It has the following properties. Sn and B are substantially absent in Si.

[0053] [Experiment 1] [Electrical conductivity] Each powder was pressurized to obtain a molded body. The electrical conductivity of this molded body was measured. The results are shown in the graph in Figure 9. In this graph, the horizontal axis represents the pressurizing pressure, and the vertical axis represents the electrical conductivity. The electrical conductivity of the negative electrode material in 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 in Comparative Example 1 is equivalent to that of Comparative Example 2. The reason why no improvement in conductivity was observed in the negative electrode material of Comparative Example 1 is presumed to be because Al2O3, an insulator, was formed by the oxidation of Al.

[0054] [Cycle life] A composition was obtained by kneading 70% by mass of powder (negative electrode material), 15% by mass of acetylene black, 10% by mass of carboxymethylcellulose, and 5% by mass of styrene-butadiene copolymer. This composition was coated onto copper foil to obtain a negative electrode. A coin cell having this negative electrode was prepared. In this coin cell, the anode was lithium, and the separator was a glass fiber filter. In this coin cell, the electrolyte was a propylene carbonate solution of lithium bis(trifluoromethanesulfonyl)amide. The concentration of this solution was 1 mol / dm³ -3The value was M. Charging and discharging cycles were repeatedly performed with this coin cell, and the discharge capacity was measured. The results are shown in the graph in Figure 10. In this graph, the horizontal axis represents the number of cycles, and the vertical axis represents the discharge capacity. As is clear from Figure 10, the negative electrode material in each embodiment has a longer lifespan compared to the negative electrode material in Comparative Example 2.

[0055] [Experiment 2] [Cycle life] Sodium-ion secondary batteries were fabricated using each negative electrode material. The cycle life of these negative electrode materials was measured in the same manner as in Experiment 1. The results are shown in the graph in Figure 11. In this graph, the horizontal axis represents the number of cycles, and the vertical axis represents electrical conductivity. As is clear from Figure 11, the negative electrode materials of each example have a longer lifespan than the negative electrode material of Comparative Example 2.

[0056] [Example 3] The negative electrode material for Example 3 was obtained in the same manner as in Example 1, except that the amount of Sn powder added to the aforementioned container was 0.6 g. The Sn content in this negative electrode material was 1% by mass.

[0057] [Example 4] The negative electrode material for Example 4 was obtained in the same manner as in Example 1, except that the amount of Sn powder added to the aforementioned container was 3.0 g. The Sn content in this negative electrode material was 5% by mass.

[0058] [exterior] The particles contained in the powder were photographed using a scanning electron microscope. The results are shown in Figure 12. The arrangement of each image in Figure 12 is as follows: Top left: Comparative example 2 Top right: Example 3 Bottom left: Example 1 Bottom right: Example 4 Secondary particles with a size of approximately 5 μm were observed in each image. This suggests that Sn has little influence on the size and shape of secondary particles. Primary particles could not be clearly identified in any of the images. Therefore, the size of primary particles is estimated to be several hundred nanometers or less.

[0059] [X-ray diffraction] The powders were subjected to X-ray diffraction at 2θ = 20-60 degrees. The results are shown in Figure 13. As is clear from Figure 13, diffraction peaks of Si ((111), (220), and (311)) were observed in each powder. The crystallite size of Si was calculated using Scherrer's formula and found to be approximately 8-12 nm. No diffraction peaks of SiO2 were observed in any of the powders. It is thought that the SiO2 was almost completely transformed into an amorphous state by high-energy grinding using mechanical milling. Furthermore, no peaks originating from Sn were observed in any of the powders.

[0060] [Experiment 3] [Electrical conductivity] Each powder was pressurized to obtain a molded body. The electrical conductivity of this molded body was measured. The results are shown in the graph in Figure 14. In this graph, the horizontal axis represents the pressurizing pressure, and the vertical axis represents the electrical conductivity. The electrical conductivity of the negative electrode material in each example is greater than that of Comparative Example 2.

[0061] [Cycle life] The discharge capacity was measured in the same manner as in Experiment 2. The results are shown in the graph in Figure 15. In this graph, the horizontal axis represents the number of cycles, and the vertical axis represents the discharge capacity. As is clear from Figure 15, the anode material in each embodiment has a longer lifespan than the anode material in Comparative Example 2.

[0062] The advantages of the present invention are clear from the results of Experiments 1-3.

[0063] [Disclosure items] Each of the following items is a disclosure of a preferred embodiment.

[0064] [Item 1] A negative electrode material for an energy storage device consisting of multiple particles, The material of these particles is a Si-based material. This Si-based material has a microstructure comprising an SiO2 matrix, Si crystals dispersed in the matrix, and Sn, B, In, or Bi dispersed in the matrix, making it a negative electrode material.

[0065] [Item 2] The negative electrode material according to item 1, wherein the above-mentioned Sn, B, In, or Bi is solidly dissolved in the above-mentioned matrix.

[0066] [Item 3] The negative electrode material according to item 1 or 2, wherein the SiO2 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 total content of Sn, B, In, and Bi is 0.1% by mass or more and 10.0% by mass or less.

[0067] [Item 4] The negative electrode material described in any of items 1 to 3, wherein the crystallite size of the above Si crystal is 20 nm or less.

[0068] [Item 5] The negative electrode material described in any of items 1 to 4, wherein none of Sn, B, In, and Bi are solid-dissolved in the above Si crystal.

[0069] [Item 6] The negative electrode material described in any of items 1 to 5, wherein the average particle size D50 is 1.0 μm or more and 6.0 μm or less.

[0070] [Item 7] It comprises a current collector and multiple particles fixed to the surface of this current collector, The material of these particles is a Si-based material. The negative electrode of an energy storage device, wherein the microstructure of this Si-based material includes an SiO2 matrix, Si crystals dispersed in the matrix, and Sn, B, In, or Bi dispersed in the matrix.

[0071] [Item 8] It has a positive electrode and a negative electrode, The above-mentioned negative electrode comprises a current collector and a plurality of particles fixed to the surface of the current collector. The material of these particles is a Si-based material. This Si-based material has a microstructure comprising an SiO2 matrix, Si crystals dispersed in the matrix, and Sn, B, In, or Bi dispersed in the matrix, making it an energy storage device.

[0072] [Item 9] A process of preparing raw materials whose main component is SiO2, raw materials whose main component is Si, and raw materials whose material is Sn, B, In, or Bi. and, The process involves mechanically milling these raw materials to disperse Si crystals in an SiO2 matrix, and then dispersing Sn, B, In, or Bi in this matrix. A method for manufacturing a negative electrode material for energy storage devices, comprising the features described above. [Industrial applicability]

[0073] The negative electrode material according to the present invention can be applied to various energy storage devices such as lithium-ion secondary batteries, sodium-ion secondary batteries, all-solid-state lithium-ion secondary batteries, all-solid-state sodium-ion secondary batteries, and hybrid capacitors. [Explanation of symbols]

[0074] 2. Lithium-ion rechargeable battery 4...tank 6...Electrolyte 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

[Claim 1] Its main component is SiO ２ A process of preparing raw materials, a raw material whose main component is Si, and a raw material whose material is Sn or B, and, These raw materials are subjected to mechanical milling, SiO ２ A process of dispersing Si crystals in a matrix and dispersing Sn or B in this matrix. A method for manufacturing a negative electrode material for energy storage devices.

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