Anode material, battery, method for manufacturing anode material, and method for manufacturing a battery

Abstract

To provide a negative electrode material improved in performance, a battery, a method for producing a negative electrode material, and a method for producing a battery.SOLUTION: Provided is a negative electrode material for batteries, which contains carbon, sodium tungstate, and silicon particles 33 containing silicon. In the silicon particles 33, the ratio of the amount of Si in Si2p derived from elemental silicon to the amount of Si in Si2p derived from SiO2 in a surface layer is 3 or more on an atomic concentration basis as measured by X-ray photoelectron spectroscopy.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an anode material, a battery, a method for producing an anode material, and a method for producing a battery. [Background technology]

[0002] Carbon is sometimes used as the negative electrode material for lithium-ion secondary batteries. For example, Patent Document 1 describes a negative electrode in which tungsten trioxide is disposed on the surface of graphite. By disposing tungsten trioxide on the surface of graphite, it becomes possible to improve the diffusibility of lithium ions, thereby improving the performance of the battery. Furthermore, for example, Patent Document 2 describes a negative electrode containing silicon particles, tungsten, and carbon. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-45904 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-125816 Summary of the Invention [Problem to be solved by the invention]

[0004] In the case of negative electrode materials, the performance can be improved by providing a tungsten compound such as tungsten trioxide or silicon, but there is still room for improvement in performance.

[0005] The present invention has been made in view of the above, and an object of the present invention is to provide an anode material, a battery, a method for manufacturing an anode material, and a method for manufacturing a battery with improved performance. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems and achieve the object, the negative electrode material according to the present disclosure is a negative electrode material for a battery, comprising carbon, sodium tungstate, and a silicon material containing silicon, wherein the silicon material has a ratio of the amount of Si in Si2p derived from elemental silicon to the amount of Si in Si2p derived from SiO2 in a surface layer, as measured by X-ray photoelectron spectroscopy, on an atomic concentration basis, of 3 or more.

[0007] To solve the above problems and achieve the objectives, the battery according to the present disclosure includes the above-described negative electrode material and a positive electrode material.

[0008] In order to solve the above-mentioned problems and achieve the object, the method for producing an anode material according to the present disclosure is a method for producing an anode material for a battery, comprising the steps of preparing a silicon raw material in an atmosphere having an oxygen concentration of 5% or less, and using the silicon raw material to produce an anode material containing carbon, sodium tungstate, and a silicon material, wherein the silicon material has a ratio of the amount of Si in Si2p derived from elemental silicon to the amount of Si in Si2p derived from SiO2 in a surface layer, as measured by X-ray photoelectron spectroscopy, on an atomic concentration basis, of 3 or more.

[0009] In order to solve the above-mentioned problems and achieve the objectives, the method for manufacturing a battery according to the present disclosure includes the method for manufacturing the negative electrode material and a step of manufacturing a positive electrode material. [Effects of the Invention]

[0010] According to the present invention, the performance of the negative electrode material can be improved. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic partial cross-sectional view of a battery according to this embodiment. [Figure 2] FIG. 2 is a schematic cross-sectional view of an example of the negative electrode according to this embodiment. [Figure 3] FIG. 3 is a schematic cross-sectional view of a silicon material. [Figure 4]FIG. 4 is a diagram showing an example of a survey spectrum showing the results of XPS measurement of a silicon material. [Figure 5] FIG. 5 is a diagram showing an example of a narrow spectrum of Si2p showing the measurement result of a silicon material by XPS. [Figure 6] FIG. 6 is a diagram showing an example of peak separation of a narrow spectrum of Si2p, showing the results of measurement of a silicon material by XPS. [Figure 7] FIG. 7 is a diagram showing an example of an O1s narrow spectrum showing the results of measurement of a silicon material by XPS. [Figure 8] FIG. 8 is a flow chart illustrating the steps of preparing a silicon source material. [Figure 9] FIG. 9 is a flowchart illustrating an example of a method for manufacturing a battery according to this embodiment. [Figure 10] FIG. 10 is a table showing the manufacturing conditions and properties of the silicon material for each example. [Figure 11] FIG. 11 is a table showing the identification results of the negative electrode materials for each example. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be described in detail below with reference to the drawings. Note that the present invention is not limited to the following modes for carrying out the invention (hereinafter referred to as embodiments). Furthermore, the components in the following embodiments include those that can be easily imagined by a person skilled in the art, those that are substantially the same, and those that are within the so-called equivalent range. Furthermore, the components disclosed in the following embodiments can be combined as appropriate.

[0013] (battery) FIG. 1 is a schematic partial cross-sectional view of a battery according to this embodiment. The battery 1 according to this embodiment is a lithium-ion secondary battery. The battery 1 includes a casing 10, an electrode group 12, and an electrolyte (not shown). The casing 10 is a case that houses the electrode group 12 and the electrolyte. In addition to the electrode group 12, the casing 10 may also include wiring and terminals connected to the electrode group 12.

[0014] The electrode group 12 includes a negative electrode 14, a positive electrode 16, and a separator 18. The electrode group 12 is configured such that the separator 18 is disposed between the negative electrode 14 and the positive electrode 16. In the example of FIG. 1 , the electrode group 12 has a so-called stacked electrode group structure in which rectangular negative electrodes 14 and rectangular positive electrodes 16 are alternately stacked with a rectangular separator 18 sandwiched therebetween. However, the electrode group 12 is not limited to a stacked electrode group structure. For example, the electrode group 12 may have a wound electrode group structure in which strip-shaped negative electrodes 14 and strip-shaped positive electrodes 16 are stacked with a strip-shaped separator 18 sandwiched therebetween and then wound.

[0015] (Negative electrode) FIG. 2 is a schematic cross-sectional view of an example of a negative electrode according to this embodiment. As shown in FIG. 2, the negative electrode 14 includes a current collecting layer 20 and a negative electrode material layer 22. The current collecting layer 20 is a layer made of a conductive material. An example of the conductive material of the current collecting layer 20 is copper. The negative electrode material layer 22 is a layer containing the negative electrode material according to this embodiment. The negative electrode material layer 22 is provided on the surface of the current collecting layer 20. The thickness of the current collecting layer 20 may be, for example, approximately 15 μm to 40 μm, and the thickness of the negative electrode material layer 22 may be, for example, approximately 20 μm to 200 μm. The negative electrode 14 may include the negative electrode material layer 22 on both sides of the current collecting layer 20.

[0016] The negative electrode material layer 22 includes a negative electrode material. The negative electrode material includes carbon, sodium tungstate, and a silicon material (silicon particles). The sodium tungstate is Na x WO y where x and y are numbers greater than 0. x WO yThe details of this will be described later. In the negative electrode material of this embodiment, sodium tungstate is provided on the surface of carbon, and a silicon material is provided on the surface of the carbon, but the positional relationship between the carbon, sodium tungstate, and silicon material is not limited to this and may be arbitrary. More specifically, the negative electrode material of the negative electrode material layer 22 is composed of carbon particles 30, which are carbon particles, and Na x WO y The particles include (sodium tungstate) particles 32 and silicon particles 33, which are particles containing silicon. Note that the shape of the particles is not limited to spherical shapes, but may be any shape, such as linear or sheet-like. Furthermore, the particle surface may be smooth or uneven.

[0017] The sodium tungstate provided on the carbon surface includes at least one of the following: sodium tungstate directly adhering to carbon; sodium tungstate indirectly adhering to carbon via silicon adhering to carbon; silicon indirectly adhering to carbon via sodium tungstate adhering to carbon; and composite particles of sodium tungstate and silicon directly or indirectly adhering to carbon. The negative electrode material of this embodiment preferably contains at least carbon and a silicon material to which sodium tungstate is adhering. The negative electrode material of this embodiment may also be composed of carbon, sodium tungstate, and a silicon material, and may contain, except for unavoidable impurities, only carbon, sodium tungstate, and a silicon material. The negative electrode material of this embodiment may also contain unavoidable impurities as the remainder.

[0018] The negative electrode material of the negative electrode layer 22 includes a plurality of carbon particles 30. The carbon particles 30 include amorphous carbon or graphite.

[0019] Amorphous carbon is non-crystalline carbon that does not have a crystalline structure. Amorphous carbon is also called amorphous carbon or diamond-like carbon, and can be said to be carbon with a mixture of sp2 bonds and sp3 bonds. Amorphous carbon particles are composed entirely of amorphous carbon, and preferably contain no components other than amorphous carbon, except for unavoidable impurities. Specifically, amorphous carbon particles preferably do not contain graphite. Furthermore, amorphous carbon can contain functional groups (e.g., hydroxyl groups, carboxyl groups) on its surface during the treatment to dispose sodium tungstate on the surface. Therefore, these functional groups enable appropriate trapping of sodium tungstate on the surface of the amorphous carbon, allowing sodium tungstate to be appropriately disposed on the surface. Furthermore, because sodium tungstate is fixed to the surface of the amorphous carbon by these functional groups, the adhesion of sodium tungstate to the amorphous carbon surface can be increased, and separation of sodium tungstate from the carbon surface can be suppressed. In particular, because hard carbon raw materials are produced at lower temperatures than, for example, graphite, the functional groups are more likely to remain without being removed, allowing sodium tungstate and silicon to be appropriately disposed on the surface.

[0020] Graphite is carbon with a planar crystalline structure.

[0021] The carbon particles 30 preferably have an average particle size of 1 μm or more and 50 μm or less, and more preferably 1 μm or more and 20 μm or less. When the average particle size is in this range, the strength of the electrode film can be maintained.

[0022] The negative electrode material of the negative electrode material layer 22 further contains a plurality of Na x WO y The carbon particles 30 include a plurality of Na particles 32 and silicon particles (silicon material) 33. x WO yThe silicon particles 32 and the silicon particles 33 are provided. x WO y One of the particles 32 is Na x WO y The particles 32 are provided on the surface of the carbon particles 30. x WO y The other Na of particle 32 x WO y The particles 32 are provided on the surfaces of the silicon particles 33. More specifically, the silicon particles 33 are in close contact with the surfaces of the carbon particles 30, and Na x WO y The carbon particles 30 and Na x WO y The particles 32 and the silicon particles 33 may be composited. Alternatively, the carbon particles 30 and the silicon particles 33 may be composited, and the carbon particles 30 and the Na x WO y The negative electrode material of the negative electrode material layer 22 may be a composite of the carbon particles 30 and the Na x WO y The carbon particles 30 and the silicon particles 33 are composited together, and the carbon particles 30 and the Na x WO y The particle 32 may be composited with the particle 32. Furthermore, sodium tungstate has a crystal structure containing Na x WO y Not only in the form of Na2WO4 and Na5W 14 O 44 In addition, Na2WO4 has a valence of 2 for Na, 1 for W, and 4 for O, so Na x WO y It can be said that it is expressed by the chemical formula Na5W 14 O 44 When the valence of W is converted to 1, Na 5 / 14 WO 44 / 14(That is, the valence of Na is 5 / 14, the valence of W is 1, and the valence of O is 44 / 14), so Na x WO y It can be said that it is expressed by the chemical formula: Na x WO y Sodium tungstate represented by the chemical formula above can be said to refer to sodium tungstate in which the ratio of the valence of Na, the valence of W, and the valence of O is X:1:Y.

[0023] The term "composite" used here means, at least when no external force is applied, separating the silicon particles 33 from the carbon particles 30 and separating the silicon particles 33 from the Na x WO y Separating from particle 32, and Na x WO y This refers to a state in which it is impossible to separate the particles 32 from the carbon particles 30. For example, the external force refers to the force that occurs when a battery using the negative electrode material is operated and an SEI (Solid Electrolyte Interphase) coating is formed to cover the entire surface and expands and contracts.

[0024] For example, the composite is formed by disposing silicon particles 33 on the surface of carbon particles 30 and disposing Na on the surface of the silicon particles 33. x WO y forming a composite in which the carbon particles 32 are arranged; x WO y Particle 32 is arranged in Na x WO y forming a composite in which silicon particles 33 are arranged on the surface of the particle 32; forming a composite in which silicon particles 33 are arranged on the surface of the carbon particle 30; x WO y The silicon particles 33 are arranged on the surface of the silicon particles 33 to form a complex. x WO y The carbon particles 30 are formed on the surface thereof. x WO y The particles 32 and silicon particles 33 are arranged.x WO y The particles 32 and the silicon particles 33 are also in close contact with each other.

[0025] Na contained in the negative electrode material of the negative electrode material layer 22 x WO y The particles 32 preferably have y (valence of O) of 3, in other words, Na x The negative electrode material of the negative electrode material layer 22 is preferably WO3. x WO y In the particles 32, it is preferable that x (the valence of Na) is greater than 0 and is equal to or less than 1, and y (the valence of O) is equal to or greater than 2 and is equal to or less than 4. x WO y In the particles 32, the valence of x is more preferably 0.1 or more and 0.95 or less, and y is more preferably 2.5 or more and 3.5 or less, and the valence of x is even more preferably 0.3 or more and 0.7 or less, and y is more preferably 2.8 or more and 3.2 or less. When x and y are within these ranges, Na is formed on the surface of the carbon particles 30. x WO y The negative electrode material of the negative electrode material layer 22 is a single type of Na x WO y It may contain only particles 32 or multiple types of Na x WO y It may contain particles 32. The negative electrode material of the negative electrode material layer 22 is Na x WO y As particle 32, Na 0.78 WO3, Na 0.48 WO3, Na 0.72 WO3, Na 0.44 WO3, Na 0.49 WO3, Na 0.33 WO3, NaNa2WO4, and Na5W 14 O 44 It is preferable to include at least one of the following. Also, Na2WO4 and Na5W 14 O 44 As described above, the negative electrode material of the negative electrode material layer 22 in this embodiment may contain at least one of the following as sodium tungstate: Na0.78 WO3, Na 0.48 WO3, Na 0.72 WO3, Na 0.44 WO3, Na 0.49 WO3, Na 0.33 WO3, Na 0.58 WO3, Na2WO4, and Na5W 14 O 44 It is preferable to include at least one of the following.

[0026] Na x WO y The compounds contained in the negative electrode material, such as the particles 32, can be measured by XRD (X-ray diffraction). The measurement conditions for XRD may be, for example, as follows. Measurement equipment: Rigaku Corporation Ultima IV ·Tube used: Cu Tube voltage: 40kV ·Tube current: 40mA Scanning range: 5°~80° Scanning speed: 2° / min As a database for identifying compounds, the powder diffraction and crystal structure database ICDD (PDF2.DAT), i.e., PDF2.DAT from the ICDD (International Center for Diffraction Data), may be used. Then, for the crystal peaks detected by XRD, the integrated powder X-ray diffraction software PDXL2 may be used to identify the compounds contained in the measurement sample (here, the negative electrode material). Specifically, the software may be used to extract compounds whose FOM (figure of merit) is below a threshold, and the compounds whose FOM is below the threshold may be identified as compounds contained in the measurement sample (here, the negative electrode material). The FOM takes a value between 0 and 100, with the smaller the value, the higher the degree of match. The threshold for the FOM may be set to 10. For example, the diffraction peak of the negative electrode material may be identified as Na in ICDD. 0.3 When the FOM for the diffraction peak of WO3 is below a threshold value (e.g., 10), the negative electrode material contains Na. 0.3For example, if the peak waveform in the X-ray diffraction analysis of the object to be analyzed shows the peak waveform of carbon, but the (002) peak waveform in the known graphite structure becomes broad, it can be determined that the object is amorphous carbon.

[0027] Na x WO y The particles 32 preferably include at least one of a cubic crystal structure, a tetragonal crystal structure, and a triclinic crystal structure. x WO y The particles 32 may be of cubic crystal type only, tetragonal crystal type only, triclinic crystal type only, both cubic and tetragonal crystal type, both cubic and triclinic crystal type, both tetragonal and triclinic crystal type, or all of cubic, tetragonal, and triclinic crystal type. x WO y If both cubic and tetragonal crystals are included as particles 32, cubic Na x WO y Tetragonal Na than particle 32 x WO y It may contain a large number of grains 32. Furthermore, when triclinic crystals and other crystal structures are contained, the content of triclinic crystals may be less than that of the other crystal structures. Cubic Na x WO y For example, Na 0.3 WO3, Na 0.78 WO3, Na 0.72 WO3, Na 0.44 WO3, Na 0.49 WO3, Na 0.58 WO 3、 Na2WO4 is one example, and tetragonal Na x WO y For example, Na 0.1 WO3, Na 0.48 WO3, Na 0.33 WO3, triclinic Na x WO y For example, Na5W14 O 44 However, the crystal structure of the tungsten trioxide contained in the negative electrode material is not limited to this, and for example, the negative electrode material may contain tungsten trioxide with a different crystal structure. Furthermore, the negative electrode material may contain amorphous tungsten trioxide. In addition, Na x WO y The crystal structure of the particles 32 can be identified in the same manner as in the identification of the compounds contained in the negative electrode material. For example, the diffraction peak of the negative electrode material is identified as cubic Na in ICDD. 0.3 When the FOM with the diffraction peak of WO3 is below a threshold value (for example, 10), the negative electrode material contains cubic Na. 0.3 It is determined that WO3 is included.

[0028] Na x WO y The average particle size of the particles 32 is preferably smaller than the average particle size of the carbon particles 30. x WO y The average particle size of the particles 32 is preferably 100 nm or more and 20 μm or less, and more preferably 100 nm or more and 1 μm or less.

[0029] In this way, the negative electrode material is formed by disposing particulate sodium tungstate (Na x WO y The negative electrode material has a structure in which sodium tungstate and a silicon material (silicon particles 32) are provided on the surface of carbon, but is not limited thereto. The negative electrode material may have a structure in which sodium tungstate and a silicon material are provided on the surface of carbon, and the shape of the sodium tungstate and the silicon material provided on the surface of carbon may be arbitrary. In this embodiment, silicon fine particles are used as the silicon particles 33, but a silicon compound may also be used.

[0030] Sodium tungstate (Na x WO yThe content of particles 32) can be confirmed by measuring the contents of Na, W, and O by fluorescent X-ray analysis. That is, at least a part of the total amount of Na, W, and O detected by fluorescent X-ray analysis is sodium tungstate (Na x WO y Since the particles 32) are composed of sodium tungstate, the content of sodium, tungstate, and tungsten can be confirmed by the content of sodium, tungsten, and tungsten. The negative electrode material preferably has a Na content of 0.01% to 0.5% by mass, a W content of 0.5% to 20% by mass, and an O content of 1% to 15% by mass, as measured by X-ray fluorescence analysis. Furthermore, the negative electrode material more preferably has a Na content of 0.02% to 0.4% by mass, a W content of 0.7% to 17% by mass, and an O content of 2% to 13% by mass, as measured by X-ray fluorescence analysis. Furthermore, the negative electrode material more preferably has a Na content of 0.03% to 0.3% by mass, a W content of 1% to 15% by mass, and an O content of 3% to 12% by mass, as measured by X-ray fluorescence analysis. When the contents of Na, W, and O are within these ranges, an appropriate amount of sodium tungstate is contained, and the tungsten compound can be appropriately arranged on the surface of the carbon.

[0031] The negative electrode material preferably has a C content of 60% to 95%, more preferably 65% ​​to 95%, and even more preferably 70% to 92%, by mass, as measured by X-ray fluorescence analysis. When the C content is within this range, the tungsten compound can be appropriately arranged on the carbon surface.

[0032] The negative electrode material preferably has a mass ratio of Na / W, which is the ratio of Na to W, measured by X-ray fluorescence analysis, of 0.001 to 0.2, more preferably 0.005 to 0.15, and even more preferably 0.007 to 0.15. Furthermore, the negative electrode material preferably has a mass ratio of W / C, which is the ratio of W to C, measured by X-ray fluorescence analysis, of 0.005 to 0.3, more preferably 0.008 to 0.25, and even more preferably 0.01 to 0.2. By ensuring that the content ratios fall within these ranges, the tungsten compound can be appropriately arranged on the carbon surface.

[0033] The content of silicon particles 33 in the negative electrode material can be confirmed by measuring the content of Si by fluorescent X-ray analysis. That is, at least a portion of the total amount of Si detected by fluorescent X-ray analysis constitutes silicon particles 33. The negative electrode material preferably has a Si content of 1% to 15%, more preferably 2% to 12%, and even more preferably 3% to 10%, by mass, as measured by X-ray fluorescence analysis. When the Si content is within this range, silicon particles 33 can be appropriately arranged on the surface of the carbon.

[0034] The negative electrode material preferably has a mass ratio of Si / C, which is the ratio of Si content to C content, measured by X-ray fluorescence analysis, of 0.01 to 0.3, more preferably 0.02 to 0.25, and even more preferably 0.03 to 0.15. Furthermore, the negative electrode material preferably has a mass ratio of Si / W, which is the ratio of Si content to W content, measured by X-ray fluorescence analysis, of 0.1 to 15, more preferably 0.15 to 12, and even more preferably 0.2 to 10. Furthermore, the negative electrode material preferably has a mass ratio of Si / O, which is the ratio of Si content to O content, measured by X-ray fluorescence analysis, of 0.1 to 2, more preferably 0.2 to 1.5, and even more preferably 0.3 to 1.3. By ensuring that the content ratios fall within these ranges, the tungsten compound can be appropriately arranged on the carbon surface.

[0035] The X-ray fluorescence analysis may be carried out using a wavelength dispersive X-ray fluorescence analyzer, and the measurement conditions may be as follows. Measuring device: Rigaku ZSX PrimusIV Tube voltage: 30kV ·Tube current: 100mA The measurement method is the standardless fundamental parameter method, and the analysis can be performed using Rigaku's SQX scattered ray FP method.

[0036] The negative electrode material layer 22 is made of a negative electrode material (carbon particles 30, Na x WO yThe negative electrode material layer 22 may contain a material other than the carbon particles 32 and the silicon particles 33. The negative electrode material layer 22 may contain, for example, a binder. Any material may be used for the binder, and examples thereof include polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), and polyacrylic acid (PAA). Only one type of binder may be used, or two or more types may be used in combination. However, when the carbon particles 30 are amorphous carbon, it is preferable that the negative electrode material layer 22, in other words, the negative electrode material, does not contain graphite.

[0037] Also, Na x WO y The arrangement of the particles 32 and silicon particles 33 on the surface of the carbon particles 30 can be confirmed by observing with an electron microscope such as a SEM (Scanning Electron Microscope) or a TEM (Transmission Electron Microscope).

[0038] In addition, the negative electrode material of the negative electrode material layer 22 is such that the silicon particles 33 are in close contact with the surfaces of the carbon particles 30, and Na x WO y The particles 32 may be in close contact with (contact with) the surface of the carbon particles 30. In this case, the carbon particles 30 and the silicon particles 33 are composited, and the carbon particles 30 and the Na x WO y The particles 32 may be composited.

[0039] In this way, the negative electrode material is formed by disposing particulate sodium tungstate (Na x WO y The negative electrode material has a structure in which sodium tungstate and silicon particles 32 are provided on the surface of carbon, but is not limited thereto. The negative electrode material may have a structure in which sodium tungstate and silicon material are provided on the surface of carbon, and the shape of the sodium tungstate and silicon material provided on the surface of carbon may be arbitrary.

[0040] (silicon material) FIG. 3 is a schematic cross-sectional view of the silicon material before it is added. As shown in FIG. 3, the silicon particle 33 includes a Si layer 33A and an oxide layer 33B. The Si layer 33A is a layer made of Si, and can be said to be the core of the silicon particle 33. The Si layer 33A preferably does not contain any elements other than Si, except for unavoidable impurities. The oxide layer 33B is a layer formed on the surface of the Si layer 33A, and preferably covers the entire surface of the Si layer 33A. The oxide layer 33B can be said to be the layer that forms the outermost surface of the silicon particle 33. The oxide layer 33B is made of silicon oxide (SiO x ) is a layer composed of. The oxide layer 33B contains SiO2 as a silicon oxide, but may contain silicon oxide other than SiO2, for example, SiO. The oxide layer 33B preferably does not contain elements other than elements constituting the oxide of silicon, except for unavoidable impurities.

[0041] (Silicon material properties based on XPS) Next, the characteristics of the silicon particles 33 measured using X-ray photoelectron spectroscopy (XPS) will be described. Unless otherwise specified, the measurement conditions for X-ray photoelectron spectroscopy are as follows. Measurement equipment: PHI5000 Versa Probe II (ULVAC-PHI) Excitation X-ray: Monochrome AlKα ray Output: 50W Pass energy: 187.85 eV (Survey), 46.95 eV (Narrow) Measurement interval: 0.8 eV / step (Survey), 0.1 eV / step (Narrow) Photoelectron take-off angle relative to the sample surface: 45° X-ray diameter: 200 μm

[0042] (Ratio of the amount of Si derived from elemental silicon to the amount of Si derived from SiO2) When measured by X-ray photoelectron spectroscopy, the silicon particles 33 have a ratio of the amount of Si in Si2p derived from elemental silicon to the amount of Si in Si2p derived from SiO2 in the surface layer, expressed in atomic concentration, of 3.0 or more, preferably 3.5 or more, and more preferably 4 or more. The surface layer here refers to the range from the surface to the depth at which photoelectrons can escape from the sample, and is described, for example, in Figure 5 of the paper by JD Lee et al., Journal Surface Analysis Vol. 16, No. 1 (2009) pp. 42-63. Furthermore, when silicon particle 33 is measured by X-ray photoelectron spectroscopy under the above measurement conditions, the depth range at which photoelectrons can be observed may be referred to as the surface layer. Because the photoelectron take-off angle with respect to the sample surface is 45°, in the case of a flat surface such as a Si wafer, the measurement depth of the detected photoelectrons, d' = dcosθ (θ is the photoelectron take-off angle with respect to the sample surface, d is the photoelectron escape depth), is 0.71 times that when θ = 90°. However, because measurements were taken with granular silicon spread over a flat plate, photoelectrons from the surfaces of individual particles facing the detector are thought to be the majority, and so no correction for the photoelectron take-off angle with respect to the sample surface was made. Additionally, the Si in Si2p refers to a Si atom from which an electron in the 2p orbital has been ejected as determined by X-ray photoelectron spectroscopy. The Si in SiO2-derived Si2p refers to the Si that makes up SiO2 from which an electron in the 2p orbital has been ejected as determined by X-ray photoelectron spectroscopy, and the Si in elemental silicon-derived Si2p refers to the Si that makes up elemental silicon (metallic silicon) from which an electron in the 2p orbital has been ejected as determined by X-ray photoelectron spectroscopy. The ratio of the amount of Si in Si2p derived from elemental silicon to the amount of Si in Si2p derived from SiO2 in the surface layer refers to the ratio of the atomic concentration of Si (Si atoms) derived from elemental silicon from which electrons in the 2p orbital have been released to the atomic concentration of Si (Si atoms) derived from SiO2 from which electrons in the 2p orbital have been released in the surface layer (here, for example, from the outermost surface of silicon particle 33 to a position approximately 6 angstroms deeper than the outermost surface). When the ratio of the amount of Si in Si2p derived from elemental silicon to the amount of Si in Si2p derived from SiO2 falls within this range (3.0 or greater), the amount of oxide near the surface of silicon particle 33 is reduced, thereby improving the capacity of the anode material. Furthermore, because the surface oxide layer is thinner, it becomes easier for Li ions to penetrate and desorb, reducing impedance. Furthermore, when silicon particles 33 are measured by X-ray photoelectron spectroscopy, the ratio of the amount of Si in Si2p derived from elemental silicon to the amount of Si in Si2p derived from SiO2 in the surface layer is preferably 9 or less, more preferably 19 or less, and even more preferably 99 or less, on an atomic concentration basis. When the ratio of the amount of Si to the amount of SiO2 in silicon particles 33 is within this range (99 or less), there is no need to prepare equipment or processes to prevent excessive oxidation of the silicon material, and it is possible to improve the capacity of the negative electrode material while suppressing a decrease in productivity. Thus, when silicon particles 33 are measured using X-ray photoelectron spectroscopy, the ratio of the amount of Si in Si2p derived from elemental silicon to the amount of Si in Si2p derived from SiO2 in the surface layer is preferably 3 or more and 9 or less, more preferably 3 or more and 19 or less, and even more preferably 3 or more and 99 or less, on an atomic concentration basis. Furthermore, when silicon particles 33 are measured using X-ray photoelectron spectroscopy, the ratio of the amount of Si in Si2p derived from elemental silicon to the amount of Si in Si2p derived from SiO2 in the surface layer is preferably 3.5 or more and 9 or less, more preferably 3.5 or more and 19 or less, and even more preferably 3.5 or more and 99 or less, on an atomic concentration basis.Furthermore, when silicon particles 33 are measured using X-ray photoelectron spectroscopy, the ratio of the amount of Si in Si2p derived from elemental silicon to the amount of Si in Si2p derived from SiO2 in the surface layer is preferably 4 or more and 9 or less, more preferably 4 or more and 19 or less, and even more preferably 4 or more and 99 or less, on an atomic concentration basis. For example, when the amount of Si in Si2p derived from SiO2 is 1%, the amount of Si in Si2p derived from elemental silicon is 99%, so taking this ratio, the ratio of the amount of Si in Si2p derived from elemental silicon to the amount of Si in Si2p derived from SiO2 in the surface layer is 99. Similarly, when the amount of Si in Si2p derived from SiO2 is 5%, the amount of Si in Si2p derived from elemental silicon is 95%, so taking this ratio, the ratio of the amount of Si in Si2p derived from elemental silicon to the amount of Si in Si2p derived from SiO2 in the surface layer is 19.

[0043] Here, we will explain how to calculate the ratio of the amount of Si in SiO2-derived Si2p to the amount of Si in elemental silicon-derived Si2p when measured by X-ray photoelectron spectroscopy. Figure 4 shows an example of a survey spectrum representing the results of XPS measurement of a silicon material. Figure 5 shows an example of a narrow spectrum of Si2p representing the results of XPS measurement of a silicon material. Figure 6 shows an example of peak separation in the narrow spectrum of Si2p representing the results of XPS measurement of a silicon material. Figure 7 shows an example of a narrow O1s spectrum representing the results of XPS measurement of a silicon material. Figure 4 shows an example of a peak waveform P of a silicon particle 33 in a wide scan analysis. The peak waveform P1 near a binding energy of 100 eV indicates the Si2p peak. Figure 5 shows an example of a narrow spectrum of a silicon particle 33 in a narrow scan analysis near the peak waveform P1. The background has been removed to extract the Si2p peak. The Si in SiO2-derived Si2p and the Si in elemental silicon-derived Si2p have different binding energies due to differences in their bonding states. Therefore, as shown in Figure 6, peak waveform P1 can be separated into peak waveform P1A, which represents Si2p derived from elemental silicon, and peak waveform P1B, which represents Si2p derived from SiO2. Peak waveform P1A has one peak near a binding energy of 99 eV, and peak waveform P1B has one peak near a binding energy of 103 eV. Background removal from the peak waveforms was performed using Multipak version 9.9.0.8 software, which comes with the X-ray photoelectron spectrometer, and baseline correction was mainly performed using the Shirley method.

[0044] In this embodiment, the ratio of the area of ​​the peak waveform P1A to the area of ​​the peak waveform P1B is calculated as the ratio of the amount of Si in Si2p derived from elemental silicon to the amount of Si in Si2p derived from SiO2 on an atomic concentration basis.

[0045] (Si-derived Si concentration ratio) The ratio of the atomic concentration of Si in the Si2p derived from elemental silicon to the atomic concentration of Si in all Si2p (all Si with electrons from the 2p orbitals ejected) in the surface layer of the silicon particle 33 is defined as the Si concentration ratio derived from Si (first Si concentration). The Si concentration ratio derived from Si can be calculated as the ratio of the area of ​​peak waveform P1A to the area of ​​peak waveform P1. The Si concentration ratio derived from Si is preferably 75% or more, more preferably 77% or more, and even more preferably 80% or more. When the Si concentration ratio derived from Si is within this range, the amount of oxide near the surface is reduced, thereby improving the capacity of the negative electrode material. The Si concentration ratio derived from Si is preferably 90% or less, more preferably 95% or less, and even more preferably 99% or less. When the Si concentration ratio derived from Si is within this range, there is no need to prepare equipment or processes to prevent excessive oxidation of the silicon material, and it is possible to improve the capacity of the negative electrode material while suppressing a decrease in productivity.

[0046] (SiO2-derived Si concentration ratio) The ratio of the Si atomic concentration of Si2p derived from SiO2 to the Si atomic concentration of all Si2p in the surface layer of silicon particle 33 is defined as the Si concentration ratio derived from SiO2. The Si concentration ratio derived from SiO2 can be calculated as the ratio of the area of ​​peak waveform P1B to the area of ​​peak waveform P1. The Si concentration ratio derived from SiO2 is preferably 25% or less, more preferably 24% or less, and even more preferably 20% or less. When the Si concentration ratio derived from SiO2 is within this range, the amount of oxide near the surface is reduced, thereby improving the capacity of the negative electrode material. The Si concentration ratio derived from SiO2 is preferably 10% or more, more preferably 5% or more, and even more preferably 1% or more. When the Si concentration ratio derived from SiO2 is within this range, there is no need to prepare equipment or processes to prevent excessive oxidation of the silicon material, and it is possible to improve the capacity of the negative electrode material while suppressing a decrease in productivity.

[0047] (Ratio of Si to O) When silicon particles 33 are measured by X-ray photoelectron spectroscopy, the ratio of the amount of Si in Si2p to the amount of O in O1s in the surface layer is preferably 1.0 or more, more preferably 1.1 or more, and even more preferably 1.3 or more, on an atomic concentration basis. The O in O1s refers to an O atom that has lost an electron in the 1s orbital as determined by X-ray photoelectron spectroscopy. The ratio of the amount of Si in Si2p to the amount of O in O1s in the surface layer refers to the ratio of the atomic concentration of O in O1s (O atoms with electrons in the 1s orbital popped out) in the surface layer of silicon particle 33 (e.g., from the outermost surface to a position approximately 10 angstroms deeper than the outermost surface) to the atomic concentration of Si in Si2p (Si atoms with electrons in the 2p orbital popped out) in the surface layer of silicon particle 33 (e.g., from the outermost surface to a position approximately 10 angstroms deeper than the outermost surface). When the ratio of Si in Si2p to the amount of O in O1s in silicon particle 33 falls within this range, the amount of oxide near the surface is reduced, thereby improving the capacity of the negative electrode material. In particular, silicon oxides other than SiO2 (e.g., SiO2) may also act as a factor inhibiting capacity improvement. In such cases, when the ratio of Si to O falls within the above range, the amount of silicon oxides other than SiO2 is also reduced, thereby appropriately improving capacity. Furthermore, when silicon particles 33 are measured by X-ray photoelectron spectroscopy, the ratio of the amount of Si in Si2p to the amount of O in O1s in the surface layer is preferably 4 or less, more preferably 9 or less, and even more preferably 99 or less, on an atomic concentration basis. When the ratio of the amount of Si to the amount of O in silicon particles 33 is within this range, it is no longer necessary to prepare excessively pure Si, and it is possible to improve the capacity of the negative electrode material while suppressing a decrease in productivity. Thus, when silicon particles 33 are measured using X-ray photoelectron spectroscopy, the ratio of the amount of Si in Si2p to the amount of O in O1s in the surface layer is preferably 1.0 or more and 4 or less, more preferably 1.0 or more and 9 or less, and even more preferably 1.0 or more and 99 or less, on an atomic concentration basis. Furthermore, when silicon particles 33 are measured using X-ray photoelectron spectroscopy, the ratio of the amount of Si in Si2p to the amount of O in O1s in the surface layer is preferably 1.1 or more and 4 or less, more preferably 1.1 or more and 9 or less, and even more preferably 1.1 or more and 99 or less, on an atomic concentration basis.Furthermore, when silicon particles 33 are measured using X-ray photoelectron spectroscopy, the ratio of Si in Si2p to the amount of O in O1s in the surface layer is preferably 1.3 or more and 4 or less, more preferably 1.3 or more and 9 or less, and even more preferably 1.3 or more and 99 or less, on an atomic concentration basis. For example, when the O concentration is 20 at% and the Si concentration is 80%, the ratio of Si in Si2p to the amount of O in O1s in the surface layer is 4, and when the O concentration is 5 at% and the Si concentration is 95%, the ratio of Si in Si2p to the amount of O in O1s in the surface layer is 19.

[0048] Here, we explain how to calculate the ratio of Si in Si2p to O in O1s measured by X-ray photoelectron spectroscopy. A qualitative analysis called a survey spectrum (Figure 4) is performed. Next, narrow spectra of binding energies corresponding to the orbital levels specific to each element are measured for elements whose presence is confirmed in the survey spectrum. For example, Figure 5 shows a narrow spectrum of Si2p, and Figure 7 shows a narrow spectrum of O1s. If trace amounts of other elements are present, narrow spectra of those elements are measured in the same way. A background correction is performed for each narrow spectrum, and the peak area is calculated. This peak area is multiplied by the sensitivity coefficient corresponding to the orbital level of each element to determine the concentration of that element. This series of concentration calculations can be performed using Multi Pack, the analysis software included with the PHI5000 Versa Probe II. The results obtained in this way are the Si concentration (secondary Si concentration) and O concentration shown in Figure 10. The Si / O ratio was calculated from these concentrations. That is, the ratio of the Si concentration to the O concentration obtained as described above is the Si / O ratio, that is, the ratio of the amount of Si in Si2p to the amount of O in O1s.

[0049] (Si concentration) The Si concentration is preferably 50 at% or more, more preferably 52 at% or more, and even more preferably 55 at% or more. By keeping the Si concentration within this range, the amount of oxide near the surface is reduced, thereby improving the capacity of the negative electrode material. Furthermore, the Si concentration is preferably 80 at% or less, more preferably 90 at% or less, and even more preferably 99 at% or less. By keeping the Si concentration within this range, there is no need to prepare equipment or processes to prevent excessive oxidation of the silicon material, and it is possible to improve the capacity of the negative electrode material while suppressing a decrease in productivity.

[0050] (O concentration) The O concentration is preferably 46 at% or less, more preferably 40 at% or less, and even more preferably 30 at% or less. By keeping the O concentration within this range, the amount of oxide near the surface is reduced, thereby improving the capacity of the anode material. Furthermore, the O concentration is preferably 1 at% or more, more preferably 10 at% or more, and even more preferably 20 at% or more. By keeping the O concentration within this range, there is no need to prepare equipment or processes to prevent excessive oxidation of the silicon material, and it is possible to improve the capacity of the anode material while suppressing a decrease in productivity.

[0051] (thickness of oxide layer) The thickness of the oxide layer 33B of the silicon particles 33 is preferably 2.3 angstroms or less, more preferably 2.0 angstroms or less, more preferably 1.5 angstroms or less, and even more preferably 1.3 angstroms or less. When the thickness of the oxide layer 33B is within this range, the amount of oxide near the surface is reduced, and the capacity of the negative electrode material can be improved. Furthermore, the carbon particles 30 and Na x WO yThis reduces the contact resistance with the particles 32, improving charge mobility. The thickness of the oxide layer 33B is preferably 0.7 angstroms or more, more preferably 0.3 angstroms or more, and even more preferably 0.06 angstroms or more. Having a thickness of the oxide layer 33B within this range eliminates the need to prepare excessively pure Si, improving the capacity of the negative electrode material while suppressing a decrease in productivity. The thickness of the oxide layer 33B is calculated by multiplying the ratio of the amount of Si in the Si2p derived from SiO2 to the amount of Si in the Si2p derived from elemental silicon in the surface layer, as measured by X-ray photoelectron spectroscopy (the reciprocal of the ratio of the amount of Si in the Si2p derived from SiO2 to the amount of Si in the Si2p derived from elemental silicon), by the photoelectron escape depth of Si in the Si2p, 6 angstroms.

[0052] (Silicon material properties based on volume average particle size) Next, the characteristics of the silicon particles 33 based on the volume average particle size will be described.

[0053] (Volume average particle size) The volume average particle diameter (volume-based average particle diameter) of the silicon particles 33 measured by a laser diffraction scattering method will be referred to as the volume average particle diameter hereinafter.

[0054] (Volume ratio of the oxide layer based on the volume average particle size) The volume ratio of the oxide layer 33B based on the volume average particle diameter is the ratio of the volume of the oxide layer 33B to the total volume of the silicon particles 33 when the silicon particles 33 are assumed to be spherical and the volume is calculated using the volume average particle diameter. In this case, the volume ratio of the oxide layer 33B based on the volume average particle diameter is preferably 0.06% or less, more preferably 0.05% or less, and even more preferably 0.04% or less. When the volume ratio is within this range, the amount of oxide near the surface is reduced, and the capacity of the negative electrode material can be improved. Furthermore, when the carbon particles 30 and Na x WO yThis reduces the contact resistance with the particles 32, improving charge mobility. Furthermore, the volume ratio of the oxide layer 33B based on the volume average particle diameter is preferably 0.015% or more, more preferably 0.01% or more, and even more preferably 0.001% or more. Having a volume ratio within this range eliminates the need for equipment or processes to prevent excessive oxidation of the silicon material, and can improve the capacity of the negative electrode material while suppressing a decrease in productivity.

[0055] The volume ratio of the oxide layer 33B based on the volume average particle diameter can be calculated as follows. That is, assuming that the silicon particles 33 are spherical (true spheres), the volume of the silicon particles 33 is calculated using the volume average particle diameter as the diameter of the silicon particles 33. Then, the thickness of the oxide layer 33B calculated as above is subtracted from the volume average particle diameter to calculate the diameter of the Si layer 33A. Then, assuming that the Si layer 33A is spherical (true spheres), the diameter of the Si layer 33A is used to calculate the volume of the Si layer 33A. The value obtained by subtracting the volume of the Si layer 33A from the volume of the silicon particles 33 calculated in this manner is defined as the volume of the oxide layer 33B. The ratio of the volume of the oxide layer 33B to the volume of the silicon particles 33 is defined as the volume ratio of the oxide layer 33B based on the volume average particle diameter.

[0056] (Silicon material properties based on D50) Next, the characteristics of silicon particles 33 based on D50 will be described.

[0057] (D50) In the volume-based particle size distribution measured by laser diffraction scattering, the particle diameter at which the cumulative frequency is 50% by volume is defined as D50.

[0058] (Volume ratio of oxide layer based on D50) Here, the volume ratio of the oxide layer 33B based on D50 is the ratio of the volume of the oxide layer 33B to the total volume of the silicon particle 33 when the volume is calculated using D50 assuming that the silicon particle 33 is spherical. In this case, the volume ratio of the oxide layer 33B based on D50 is preferably 0.4% or less, more preferably 0.3% or less, and even more preferably 0.25% or less. When the volume ratio is within this range, the amount of oxide near the surface is reduced, thereby improving the capacity of the negative electrode material. Furthermore, the volume ratio of the oxide layer 33B based on D50 is preferably 0.13% or more, more preferably 0.05% or more, and even more preferably 0.01% or more. When the volume ratio is within this range, there is no need to prepare equipment or processes to prevent excessive oxidation of the silicon material, and it is possible to improve the capacity of the negative electrode material while suppressing a decrease in productivity.

[0059] The volume ratio of the oxide layer 33B based on D50 can be calculated as follows. That is, assuming that the silicon particles 33 are spherical (true spheres), D50 is used as the diameter of the silicon particles 33 to calculate the volume of the silicon particles 33. Then, the thickness of the oxide layer 33B calculated as above is subtracted from D50 to calculate the diameter of the Si layer 33A. Then, assuming that the Si layer 33A is spherical (true spheres), the diameter of the Si layer 33A is used to calculate the volume of the Si layer 33A. The value obtained by subtracting the volume of the Si layer 33A from the volume of the silicon particles 33 calculated in this way is defined as the volume of the oxide layer 33B. The ratio of the volume of the oxide layer 33B to the volume of the silicon particles 33 is defined as the volume ratio of the oxide layer 33B based on D50.

[0060] (positive electrode) The positive electrode 16 shown in FIG. 1 includes a current collecting layer and a positive electrode material layer. The current collecting layer of the positive electrode 16 is a layer made of a conductive material, such as aluminum. The positive electrode material layer is a layer of a positive electrode material and is provided on the surface of the current collecting layer of the positive electrode 16. The thickness of the positive electrode current collecting layer may be, for example, about 10 μm to 30 μm, and the thickness of the positive electrode material layer may be, for example, about 10 μm to 100 μm.

[0061] The positive electrode material layer contains a positive electrode material. The positive electrode material includes particles of a lithium compound, which is a compound containing lithium. The lithium compound may be, for example, a lithium-containing metal oxide or a lithium-containing phosphate. More specifically, the lithium compound may be LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi a Co b Mn c O2 (where 0 < a < 1, 0 < b < 1, 0 < c < 1, and a + b + c = 1), LiFePO4, etc. The lithium compound may contain only one type of material or may contain two or more types of materials. Further, the positive electrode material layer may contain substances other than the positive electrode material, for example, it may contain a binder. The material of the binder may be arbitrary, and examples thereof include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PAA, etc. The binder may be used alone or two or more binders may be combined and used.

[0062] (Separator) The separator 18 shown in FIG. 1 is an insulating member. In this embodiment, the separator 18 is, for example, a porous membrane made of resin, and examples of the resin include polyethylene (PE), polypropylene (PP), etc. Further, the separator 18 may have a structure in which membranes of different materials are laminated. Also, the separator 18 may have a heat-resistant layer. The heat-resistant layer is a layer containing a substance with a high melting point. The heat-resistant layer may contain, for example, particles of an inorganic material such as alumina.

[0063] (Electrolyte) The electrolyte provided in the battery 1 is a nonaqueous electrolyte. The electrolyte is impregnated into the voids in the electrode group 12. The electrolyte contains, for example, a lithium salt and an aprotic solvent. The lithium salt is dispersed or dissolved in the aprotic solvent. Examples of the lithium salt include LiPF6, LiBF4, Li[N(FSO2)2], Li[N(CF3SO2)2], Li[B(C2O4)2], and LiPO2F2. The aprotic solvent may be, for example, a mixture of a cyclic carbonate and a chain carbonate. Examples of the cyclic carbonate include EC, PC, and butylene carbonate. Examples of the chain carbonate include dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC).

[0064] (Battery manufacturing method) Next, an example of a method for manufacturing the battery 1 according to this embodiment will be described. This manufacturing method includes the steps of preparing a silicon raw material in an atmosphere with an oxygen concentration of 5% or less, manufacturing a negative electrode material by providing sodium tungstate and a silicon material on the surface of carbon using the silicon raw material, and manufacturing a positive electrode material.

[0065] (Step of Preparing Silicon Raw Material) Fig. 8 is a flowchart illustrating steps for preparing a silicon raw material. The silicon raw material is a raw material for silicon particles 33. As shown in Fig. 8, the steps for preparing the silicon raw material include a crushing step S1, a coarse crushing step S2, and a crushing step S3.

[0066] The silicon raw material preparation step preferably involves crushing a silicon base material in an atmosphere with an oxygen concentration of 5% or less, more preferably 3% or less, even more preferably 1% or less, and even more preferably 0.1% or less. Such a low oxygen concentration suppresses oxidation of the newly formed silicon surface after crushing and further thickening of the oxide layer formed on the surface before crushing, thereby suppressing capacity loss. The oxygen concentration can be measured using an oxygen monitor OM-25MF01 manufactured by Taiei Engineering Co., Ltd., or, when the oxygen concentration is lower than 1%, using a low-concentration oxygen monitor JKO-O2LJD3 manufactured by Ichinenjiko Co., Ltd. Furthermore, it is preferable to maintain the oxygen concentration within the above range in the coarse crushing step S2 and the crushing step S3. It is more preferable to maintain the oxygen concentration within the above range in all steps, including the crushing step S1, the coarse crushing step S2, and the crushing step S3.

[0067] (Crushing process) The crushing step S1 is a step of crushing silicon blocks to obtain crushed silicon. There are no particular limitations on the size of the silicon blocks. There are no particular limitations on the shape of the silicon blocks, and they may be, for example, columnar, plate-like, or granular. Examples of silicon blocks that can be used include silicon chunks, polycrystalline silicon other than chunks, lumps of single crystal silicon and columnar silicon ingots, monitor silicon wafers, dummy silicon wafers, and granular silicon.

[0068] The crushing device for crushing the silicon lumps is not particularly limited, and for example, a hammer crusher, jaw crusher, gyrectly crusher, cone crusher, roll crusher, or impact crusher can be used. The size of the crushed silicon particles obtained by crushing the silicon lumps preferably has a longest diameter in the range of more than 1 mm and not more than 5 mm.

[0069] (coarse grinding process) The coarse pulverization step S2 is a step in which the crushed silicon material is coarsely pulverized to obtain coarse silicon particles. The coarse silicon particles obtained in the coarse pulverization step S2 preferably have a maximum particle size of 1000 μm or less when separated by a sieve. For this reason, the coarse pulverization step S2 preferably includes a step of classifying the coarsely pulverized material obtained by the coarse pulverization using a sieve with a mesh size of 1000 μm and recovering coarse particles with a maximum particle size of 1000 μm or less. If the size of the coarse silicon particles exceeds 1000 μm, the coarse silicon particles may not be sufficiently pulverized in the subsequent pulverization step S3, and these particles may become mixed in. It is particularly preferable that the maximum particle size of the coarse silicon particles is 500 μm or less.

[0070] The coarse pulverization may be carried out by either a dry method or a wet method, but is preferably carried out by a dry method. The pulverization apparatus for coarsely pulverizing the crushed silicon material is not particularly limited, and for example, a ball mill (planetary ball mill, vibration ball mill, tumbling ball mill, stirring ball mill), a jet mill, or a three-dimensional ball mill can be used.

[0071] (Crushing process) The pulverization step S3 is a step of pulverizing the silicon coarse particles to obtain silicon raw material (silicon fine particles). In the pulverization step S3, for example, a ball mill (planetary ball mill, vibration ball mill, tumbling ball mill, stirring ball mill), a jet mill, or a three-dimensional ball mill can be used. As the pulverization device, it is preferable to use a three-dimensional ball mill manufactured by Nagao System Co., Ltd.

[0072] Zirconia (ZrO2) balls or alumina (Al2O3) balls can be used as the hard balls. The particle diameter of the hard balls is preferably in the range of 0.1 mm to 20 mm. When the particle diameter of the hard balls is within this range, the coarse silicon particles can be efficiently pulverized. The amount of hard balls used is preferably in the range of 500 parts by mass to 2500 parts by mass relative to 100 parts by mass of the coarse silicon particles. When the amount of hard balls used is within this range, the coarse silicon particles can be efficiently pulverized. The amount of hard balls used is more preferably in the range of 1000 parts by mass to 2000 parts by mass, and particularly preferably in the range of 1100 parts by mass to 1500 parts by mass.

[0073] The filling rate of the silicon coarse particles and hard balls in the container of the three-dimensional ball mill is preferably in the range of 3% to 35% in terms of the total volume of the silicon coarse particles and hard balls relative to the capacity of the container. If the filling rate is too low, the milling efficiency may decrease, resulting in higher production costs. On the other hand, if the filling rate is too high, milling may be difficult to proceed, resulting in a larger average particle size of the resulting silicon raw material, or the silicon coarse particles may not be sufficiently milled and remain. The filling rate of the silicon coarse particles and hard balls is more preferably in the range of 15% to 30%, and particularly preferably in the range of 20% to 30%. Note that the filling rate is the volume assuming that the interior of the container is filled with the raw material and balls without any gaps, which is 100%. For example, if the raw material and hard balls are filled up to half the height of a spherical container without any gaps, the filling rate is 50%, and if the raw material and hard balls are filled up to half the height of a spherical container without any gaps, the filling rate is 15.6%. However, the term "without gaps" used here refers to macroscopic gaps, meaning a state in which multiple balls have been removed, and not gaps formed between the balls.

[0074] The container is preferably filled with a non-oxidizing gas. By using a container filled with a non-oxidizing gas, it is possible to suppress particle aggregation due to moisture absorption of the silicon microparticles and oxidation of the silicon microparticles. Examples of the non-oxidizing gas that can be used include argon, nitrogen, and carbon dioxide.

[0075] In the method for producing a silicon raw material according to the present embodiment, coarse silicon particles having a maximum particle size of 1000 μm or less as measured by a sieving method are prepared in a coarse crushing step S2, and the coarse silicon particles are crushed under predetermined conditions using a three-dimensional ball mill in the subsequent crushing step S3. This makes it possible to industrially advantageously produce a silicon raw material that is fine and does not easily form coarse agglomerates, and that has high dispersibility when mixed with other raw material particles.

[0076] Although the method for producing the silicon raw material has been described above, the production method is not limited to the above and may be any method.

[0077] (Steps for producing negative and positive electrode materials) Fig. 9 is a flowchart illustrating an example of a method for manufacturing a battery according to this embodiment. As shown in Fig. 9, in this manufacturing method, the negative electrode 14 is formed in steps S10 to S20.

[0078] Specifically, a surfactant is dissolved in a solvent to produce a first solution (step S10). The first solution is a solution in which the surfactant is dissolved and which contains Na (Na in an ionic state). The surfactant is used to disperse amorphous carbon. Any surfactant capable of dispersing amorphous carbon may be used, but in this embodiment, a surfactant containing Na is used. For example, sodium dodecyl sulfate (SDS) may be used as a surfactant containing Na. The solvent of the first solution may be any solvent capable of dissolving the surfactant, but for example, water may be used. The surfactant is not limited to one containing Na. In this case, for example, a surfactant not containing Na and a compound containing Na may be dissolved in a solvent to produce the first solution. As the surfactant not containing Na, for example, poly(oxyethylene) alkyl ether, polyoxyethylene nonylphenyl ether, etc. may be used. As the poly(oxyethylene) alkyl ether, it is preferable to use one having an alkyl group with 12 to 15 carbon atoms, for example, C 12 H 25 O(C2H4) n H(poly(oxyethylene) dodecyl ether), C 13 H 27 O(C2H4) n H(poly(oxyethylene) tridecyl ether), C 13 H 27 O(C2H4) n H(poly(oxyethylene) isotridecyl ether), C 14 H 25 O(C2H4) n H(poly(oxyethylene)tetradecyl ether), C 155 H 25 O(C2H4) n H(poly(oxyethylene)pentadecyl ether), etc., may be used. Here, n is an integer of 1 or more. Examples of polyoxyethylene nonylphenyl ether include CH 19 C6(CH2CH2O)8H, C9H 19 C6(CH2CH2O) 10 H, C9H 19 C6(CH2CH2O) 12 H, etc. Examples of compounds containing Na include sodium sulfate, sodium stearate, sodium hyaluronate, and sodium hypochlorite.

[0079] The content of the surfactant in the first solution, i.e., the amount of surfactant added, is preferably 0.1% to 10% by mass, more preferably 0.5% to 7% by mass, and even more preferably 1% to 5% by mass, relative to the amount of carbon raw material added in the subsequent step S12. x WO y It is possible to appropriately improve the affinity with

[0080] Next, a carbon raw material and a silicon raw material are added to the first solution to produce a second solution (step S12). The carbon raw material is carbon used as a raw material for carbon particles 30. The carbon raw material preferably has an average particle size of 1 μm or more and 50 μm or less, and more preferably 1 μm or more and 20 μm or less. By setting the average particle size of the carbon raw material within this range, it is possible to increase the capacity of the battery. In step S12, the first solution to which the carbon raw material and the silicon raw material have been added, i.e., the second solution, is stirred to disperse the amorphous carbon raw material and the silicon raw material in the first solution. In other words, the second solution can be said to be the first solution in which the amorphous carbon raw material and the silicon raw material are dispersed. In this step, the order in which the silicon source and the carbon source are added to the first solution may be arbitrary. For example, the silicon source may be added to the first solution first and stirred, and then the carbon source may be added and stirred. Alternatively, for example, the carbon source may be added to the first solution first and stirred, and then the silicon source may be added and stirred. Alternatively, for example, the carbon source and the silicon source may be added to the first solution simultaneously and stirred.

[0081] The carbon raw material may be produced, for example, by an oil furnace method. In the oil furnace method, for example, a raw material oil is sprayed into a high-temperature atmosphere to cause thermal decomposition, and then rapidly cooled to produce a particulate carbon raw material. However, the method for producing the carbon raw material is not limited to this and may be any method.

[0082] Next, the second solution and the tungsten solution are mixed to generate a third solution (step S14). The tungsten solution is a solution containing W and O. The tungsten solution is, for example, a solution generated by dissolving a tungsten oxide raw material in a solvent. The tungsten oxide raw material here is Na x WO y The raw material of the particles 32 is, for example, tungsten trioxide. As the solvent, for example, an alkaline liquid is used, and in this embodiment, an aqueous ammonia solution is used. Therefore, in this embodiment, the tungsten solution is an alkaline solution containing W and O, or more specifically, ammonium tungstate. However, the tungsten solution may be any solution containing W and O.

[0083] The content of W in the tungsten solution added to the second solution, i.e., the amount of W added, is preferably 0.5% or more and 20% or less, more preferably 1% or more and 15% or less, and even more preferably 1.3% or more and 10% or less, by mass ratio relative to the amount of carbon raw material added in step S12. By setting it within this range, the amount of W added to the tungsten solution is reduced. x WO y It is possible to appropriately improve the affinity with

[0084] Next, the liquid component of the third solution is removed to produce a negative electrode material (negative electrode material production step). In this embodiment, steps S16 and S18 are performed as the negative electrode material production step. Specifically, the third solution is dried to produce a negative electrode intermediate (step S16; drying step). In step S16, for example, the third solution is dried in the atmosphere at 80°C for 12 hours to remove, i.e., evaporate, the liquid component contained in the additive solution. However, the drying conditions may be arbitrary. It can be said that the negative electrode intermediate contains the solid component remaining after the liquid component of the third solution has been removed.

[0085] Next, the negative electrode intermediate is heated to produce a negative electrode material (step S18; heating step). By heating the negative electrode intermediate, Na is formed on the surface of the carbon particles 30. x WOy The negative electrode material is formed by dissolving the carbon particles 32 and silicon particles 33 on the surface of the carbon particles 30 dispersed in the third solution. That is, Na, W, and O in the ionic state contained in the third solution are dissolved in Na x WO y It precipitates as particles 32 to form the negative electrode material.

[0086] The conditions for heating the negative electrode intermediate in the heating step may be arbitrary, but are preferably performed as follows: That is, the heating step preferably includes a step of placing the negative electrode intermediate in a furnace and creating an inert atmosphere inside the furnace, a first heating step of heating the negative electrode intermediate to a first temperature at a first heating rate, and a second heating step of heating the negative electrode intermediate heated to the first temperature to a second temperature at a second heating rate.

[0087] The inert atmosphere in the step of creating an inert atmosphere inside the furnace may be, for example, a nitrogen atmosphere or a rare gas atmosphere such as Ar, and the inert atmosphere may be created by, for example, replacing oxygen in the furnace with nitrogen or a rare gas. Note that this step is not essential.

[0088] The first heating step is a step for removing metals, organic substances, and the like contained in the negative electrode intermediate. The first heating temperature in the first heating step is, for example, 550°C, but is not limited thereto. The first heating temperature is preferably 150°C to 625°C, more preferably 175°C to 600°C, and more preferably 200°C to 575°C. The first heating rate may be any rate, but is, for example, preferably 45°C / hour to 75°C / hour, more preferably 50°C / hour to 70°C / hour, and even more preferably 55°C / hour to 65°C / hour. By setting the first heating temperature and the first heating rate within these ranges, metals, organic substances, and the like contained in the negative electrode intermediate can be appropriately removed.

[0089] The second heating step is performed after the first heating step. x WO yIn the second heating step, the second heating temperature is higher than the first heating temperature, for example, 700°C, but is not limited thereto, and is preferably 680°C or higher and 750°C or lower, preferably 685°C or higher and 740°C or lower, and more preferably 690°C or higher and 730°C or lower. The second heating rate may be any rate, but is preferably higher than the first heating rate, for example, preferably 165°C / hour or higher and 195°C / hour or lower, more preferably 170°C / hour or higher and 190°C / hour or lower, and even more preferably 175°C / hour or higher and 185°C / hour or lower. By setting the second heating temperature and the second heating rate within these ranges, it is possible to shorten the time required for the process while increasing the amount of Na. x WO y can be generated properly.

[0090] In the second heating step, the negative electrode intermediate heated to the second heating temperature is preferably held at the second heating temperature for a predetermined time, preferably from 1.25 hours to 2.75 hours, more preferably from 1.5 hours to 2.5 hours, and even more preferably from 1.75 hours to 2.25 hours.

[0091] Note that, prior to the first heating step (and in this embodiment, after the step of creating an inert atmosphere), a step of heating the negative electrode intermediate to a third temperature at a third heating rate and holding the negative electrode intermediate at the third temperature for a predetermined time may be provided. The third temperature is lower than the first temperature, for example, 100°C, but is not limited thereto. It is preferably 80°C to 120°C, more preferably 85°C to 115°C, and more preferably 90°C to 110°C. The third heating rate may also be any rate, for example, preferably 165°C / hour to 195°C / hour, more preferably 170°C / hour to 190°C / hour, and even more preferably 175°C / hour to 185°C / hour. The predetermined time for holding the negative electrode intermediate at the third heating temperature may also be any rate, for example, preferably 0.5 hours to 1.75 hours, more preferably 0.75 hours to 1.5 hours, and even more preferably 1.0 hour to 1.25 hours. By providing this step, moisture can be appropriately removed.

[0092] Next, the negative electrode 14 is formed using the formed negative electrode material (step S20). That is, the negative electrode 14 is formed by forming a negative electrode material layer 22 containing the negative electrode material on the surface of the current collecting layer 20.

[0093] This manufacturing method also includes forming the positive electrode 16 (step S22). In step S22, the positive electrode material may be formed by the same method as steps S10 to S20, except that a lithium compound raw material, which is a lithium compound, is used instead of the carbon raw material and the silicon raw material. Then, a positive electrode material layer containing the positive electrode material is formed on the surface of the current collecting layer for the positive electrode 16, thereby forming the positive electrode 16.

[0094] After the negative electrode 14 and the positive electrode 16 are formed, the negative electrode 14 and the positive electrode 16 are used to manufacture the battery 1 (step S24). Specifically, the negative electrode 14, the separator 18, and the positive electrode 16 are stacked together to form the electrode group 12, and the electrode group 12 and the electrolyte are housed in the casing 10 to manufacture the battery 1.

[0095] Although the manufacturing methods of the negative electrode material and the positive electrode material have been described above, the manufacturing methods are not limited to the above and may be any methods.

[0096] (effect) As described above, the negative electrode material according to this embodiment is a battery negative electrode material and includes carbon, sodium tungstate, and silicon particles 33 containing silicon. When measured by X-ray photoelectron spectroscopy, the silicon particles 33 have a surface layer in which the ratio of the amount of Si in Si2p derived from elemental silicon to the amount of Si in Si2p derived from SiO2 is 3 or more on an atomic concentration basis.

[0097] Here, adding a tungsten compound or Si to the negative electrode material can improve battery performance. However, further performance improvements are required, and the inventors have discovered through extensive research that the oxide of Si in the raw material inhibits capacity improvement. In contrast, in the negative electrode material according to this embodiment, the ratio of the amount of Si in the Si2p derived from elemental silicon to the amount of Si in the Si2p derived from SiO2 in the surface layer is 3 or more, based on atomic concentration. Therefore, according to this embodiment, it is possible to reduce the amount of silicon oxide and improve battery performance.

[0098] Furthermore, the silicon particles 33 preferably have a ratio of the amount of Si in Si2p to the amount of O in O1s in the surface layer, as measured by X-ray photoelectron spectroscopy, of 1.0 or more, based on atomic concentration. In the negative electrode material according to this embodiment, when the ratio of the amount of Si in Si2p to the amount of O in O1s of the silicon particles 33 is within this range, the amount of oxide near the surface is reduced, thereby improving battery performance. In particular, silicon oxides other than SiO2 (e.g., SiO) may also act as a factor inhibiting capacity improvement. In such cases, when the ratio of the amount of Si in Si2p to the amount of O in O1s is within the above range, the amount of silicon oxides other than SiO2 can also be reduced, thereby appropriately improving battery performance.

[0099] Furthermore, silicon particle 33 includes Si layer 33A made of Si and oxide layer 33B made of silicon oxide formed on the surface of Si layer 33A, and when silicon particle 33 is assumed to be spherical and the volume of silicon particle 33 is calculated using the volume average particle diameter, the volume of oxide layer 33B is preferably 0.06% or less of the total volume of silicon particle 33. When the volume ratio of oxide layer 33B is in this range, the amount of oxide near the surface is reduced, and battery performance can be improved.

[0100] Furthermore, silicon particle 33 includes Si layer 33A made of Si and oxide layer 33B made of silicon oxide formed on the surface of Si layer 33A, and when silicon particle 33 is assumed to be spherical and the volume of silicon particle 33 is calculated using a particle diameter D50 at a cumulative frequency of 50 volume % in a volume-based particle size distribution measured by a laser diffraction scattering method, the volume of oxide layer 33B is preferably 0.4% or less of the total volume of silicon particle 33. When the volume ratio of oxide layer 33B falls within this range, the amount of oxide near the surface is reduced, thereby improving battery performance.

[0101] Furthermore, when the total content of carbon, sodium tungstate, and silicon particles 33 in the negative electrode material is taken as 100% by weight, the content of silicon particles 33 is preferably 1% by weight or more and 10% by weight or less. By setting the content of silicon particles 33 within this range, the performance of the battery can be improved.

[0102] In the negative electrode material according to this embodiment, sodium tungstate is Na x WO y It is preferable that x is greater than 0 and less than or equal to 1, and y is greater than or equal to 2 and less than or equal to 4. By including sodium tungstate of this chemical formula, it is possible to appropriately arrange sodium tungstate on the surface of the carbon.

[0103] Furthermore, the negative electrode material according to this embodiment preferably has a sodium content of 0.01% to 0.5% by mass, a tungsten content of 0.5% to 20% by mass, and an oxygen content of 1% to 15% by mass, as measured by X-ray fluorescence analysis. When Na, W, and O are within these ranges, sodium tungstate is contained in appropriate amounts, allowing the sodium tungstate to be appropriately arranged on the carbon surface.

[0104] Furthermore, the negative electrode material according to this embodiment preferably has a ratio of sodium to tungsten, Na / W, of 0.001 to 0.2, as measured by fluorescent X-ray analysis. When Na / W is in this range, an appropriate amount of sodium tungstate is contained, and the sodium tungstate can be appropriately arranged on the surface of the carbon.

[0105] The method for producing an anode material according to this embodiment includes the steps of preparing a silicon raw material in an atmosphere with an oxygen concentration of 5% or less, and using the silicon raw material to produce an anode material containing carbon, sodium tungstate, and silicon particles 33. The silicon particles 33 preferably have a ratio of the amount of Si2p of elemental silicon to the amount of Si2p of Si resulting from SiO2 in the surface layer, as measured by X-ray photoelectron spectroscopy, of 3 or more, on an atomic concentration basis. Preparing the silicon raw material in this manner under a low oxygen concentration can suppress oxidation of silicon, thereby improving battery performance.

[0106] (Example) Next, an example will be described.

[0107] Example 1 (Preparation of silicon raw materials) Scaly polycrystalline silicon chunks (purity: 99.999999999% by mass, length: 5 to 15 mm, width: 5 to 15 mm, thickness: 2 to 10 mm) were crushed using a hammer mill. The crushed material was then dry-classified using a sieve with 5 mm openings to obtain crushed silicon material that fell under the sieve. The obtained crushed silicon material, hard balls (zirconia balls, diameter: 10 mm), and an 80 mm diameter ZrO2 spherical container that could be divided into one container and the other were each placed in a glove box filled with Ar gas. Inside the glove box, 30 parts by mass of crushed silicon material and 380 parts by mass of hard balls were placed in one of the containers. Next, one container containing the crushed silicon material and hard balls was combined with the other container, and the two containers were screwed together and sealed inside the glove box filled with Ar gas. The mating surfaces of the two containers were ground to maintain airtightness. The filling ratio of the crushed silicon material and hard balls in the container was 28%. The 80mm diameter ZrO2 sphere container filled with crushed silicon and hard balls was removed from the glove box and placed in a three-dimensional ball mill. The mixture was coarsely crushed under the following conditions: a first rotational speed of 300 rpm, a second rotational speed of 300 rpm, and a crushing time of 0.33 hours. The coarsely crushed silicon and hard balls were dry-classified using a 1000 μm mesh sieve to obtain coarse silicon particles with a maximum particle size of 1000 μm or less. The obtained coarse silicon particles, hard balls (zirconia balls, diameter: 10 mm), and a hemispherical container were each placed in a glove box filled with Ar gas. Next, in the glove box, 15 parts by mass of crushed silicon material and 200 parts by mass of hard balls were placed in one of the hemispherical containers (the amount of hard balls per 100 parts by mass of coarse silicon particles was 1,333 parts by mass). Next, one hemispherical container containing the crushed silicon material and hard balls was combined with the other hemispherical container to form a spherical container, and the two containers were screwed together and sealed in the glove box filled with Ar gas. The filling ratio of the crushed silicon material and hard balls in the container was 15%. The 80 mm diameter ZrO2 spherical container filled with silicon coarse particles and hard balls was taken out of the glove box and set in a three-dimensional ball mill. Then, the silicon raw material was obtained by milling under the conditions of a first rotational axis rotation speed of 300 rpm, a second rotational axis rotational speed of 300 rpm, and a milling time of 6 hours.

[0108] (Preparation of negative electrode material) In Example 1, a negative electrode material was manufactured using the method described in the embodiment. Specifically, a solution containing water as a solvent and SDS dissolved as a surfactant was prepared as a first solution. The concentration of SDS in the first solution was set to 3%. Then, amorphous carbon raw material and silicon raw material were added to the first solution so that the mass ratio of SDS in the first solution relative to the amorphous carbon raw material added was 3%, and the mixture was stirred with a stirring propeller (360 rpm) to prepare a second solution. The amount of silicon added was 4 wt% relative to the amount of carbon added. Then, ammonium tungstate (tungsten solution) was added to the second solution so that the amount of W contained in the ammonium tungstate (tungsten solution) relative to the amorphous carbon raw material in the second solution was 5% by mass, to prepare a third solution. The third solution was then stirred with a stirring propeller (180 rpm), and then heated to evaporate the water and dry, producing a negative electrode intermediate. This negative electrode intermediate was then placed in a tubular furnace (sintering furnace) and heated to 550°C (first heating temperature) at a first heating rate of 60°C / hour under an argon atmosphere. After reaching the first heating temperature, the temperature was increased to 700°C (second heating temperature) at a second heating rate of 180°C / hour and held for 2 hours. After holding for 2 hours, heating was stopped and the temperature was allowed to naturally decrease to 50°C to produce the negative electrode material.

[0109] Example 2 In Example 2, a negative electrode material was produced in the same manner as in Example 1, except that the grinding time was 3 hours and the amounts of silicon, tungsten, and SDS added were 5 wt%, 5 wt%, and 3 wt%, respectively.

[0110] Example 3 In Example 3, a negative electrode material was produced in the same manner as in Example 1, except that the grinding time was 4 hours and the amounts of silicon, tungsten, and SDS added were 5 wt%, 5 wt%, and 3 wt%, respectively.

[0111] Example 4 In Example 4, a negative electrode material was produced in the same manner as in Example 1, except that the shape of the container used for pulverization was an 80 mmΦ SUS long-bodied container, the pulverization time was 2 hours, and the amounts of silicon, tungsten, and SDS added were 5 wt%, 5 wt%, and 3 wt%, respectively.

[0112] Example 5 In Example 5, a negative electrode material was produced in the same manner as in Example 1, except that the shape of the container used for grinding was an 80 mmΦ SUS long-bodied container, the grinding time was 1 hour, and the amounts of silicon, tungsten, and SDS added were 10 wt%, 5 wt%, and 3 wt%, respectively.

[0113] Example 6 In Example 6, a negative electrode material was produced in the same manner as in Example 1, except that the shape of the container used for pulverization was an 80 mmΦ SUS long-bodied container, the pulverization time was 3 hours, and the amounts of silicon, tungsten, and SDS added were 10 wt%, 5 wt%, and 3 wt%, respectively.

[0114] Example 7 In Example 7, the grinding time was 2 hours, and the C of the surfactant in the first solution 12 H 25 O(C2H4) n A negative electrode material was produced in the same manner as in Example 1, except that H(poly(oxyethylene) dodecyl ether) was added at a concentration of 4% and sodium stearate was added at a concentration of 1%.

[0115] (Comparative Example 1) In Comparative Example 1, only amorphous carbon was used as the negative electrode material.

[0116] (Comparative Example 2) In Comparative Example 2, the negative electrode material was produced in the same manner as in Example 1, except that the shape of the container used for pulverization was an 80 mmΦ SUS long-bodied container, the atmosphere inside the container was air, the pulverization time was 1 hour, and the amounts of silicon, tungsten, and SDS added were 10 wt%, 4 wt%, and 2 wt%, respectively.

[0117] (Comparative Example 3) In Comparative Example 3, the negative electrode material was produced in the same manner as in Example 1, except that the container shape used for grinding was an 80 mmΦZrO2 spherical container, the atmosphere inside the container was air, the grinding time was 3 hours, and the amounts of silicon, tungsten, and SDS added were 10 wt%, 8 wt%, and 2 wt%, respectively.

[0118] (Silicon material properties) FIG. 10 is a table showing the manufacturing conditions and characteristics of the silicon material for each example. As shown in FIG. 10, the characteristics of the silicon material for each example were measured based on XPS measurement. The Si concentration in FIG. 10 corresponds to the Si concentration described in this embodiment. The O concentration in FIG. 10 corresponds to the O concentration described in this embodiment. The SiO2-derived Si concentration ratio in FIG. 10 corresponds to the SiO2-derived Si concentration ratio described in this embodiment. The Si concentration ratio in FIG. 10 corresponds to the Si concentration ratio described in this embodiment. The Si concentration ratio in FIG. 10 corresponds to the Si concentration ratio described in this embodiment. The Si / Si(SiO2) concentration ratio in FIG. 10 corresponds to the ratio of the amount of Si in the Si2p derived from elemental silicon to the amount of Si in the SiO2-derived Si2p in the surface layer described in this embodiment. The Si / O concentration ratio in FIG. 10 corresponds to the ratio of the amount of Si in the Si2p derived from elemental silicon to the amount of O in the O1s in the surface layer described in this embodiment. The oxide film thickness in FIG. 10 corresponds to the thickness of the oxide layer 33B described in this embodiment. X-ray photoelectron spectroscopy in each example was performed using the apparatus and conditions described in this embodiment. Furthermore, as shown in FIG. 10, the characteristics based on the volume average particle size and D50 were measured for each silicon material. The silicon material was introduced into a surfactant aqueous solution, and silicon microparticles were dispersed by ultrasonic treatment to prepare a silicon microparticle dispersion. The particle size distribution of the silicon microparticles in the resulting silicon microparticle dispersion was then measured using a laser diffraction / scattering particle size distribution analyzer (MT3300EX II, manufactured by Microtrack Bell Corporation). The volume average particle size and D50 were calculated from the obtained particle size distribution. The SiO volume in FIG. 10 corresponds to the volume of the oxide layer 33B calculated using the volume average particle size (or D50) in this embodiment. The particle volume in FIG. 10 corresponds to the volume of the silicon particles 33 calculated using the volume average particle size (or D50) in this embodiment. The SiO volume / particle volume in FIG. 10 corresponds to the volume ratio of the oxide layer 33B based on the volume average particle size (or D50) in this embodiment.

[0119] (Identification of negative electrode material) FIG. 11 is a table showing the identification results of the negative electrode material for each example. Fluorescent X-ray analysis was performed on the negative electrode material produced in each example to measure the elemental content and Na / W, Si / C, W / C, Si / W, and Si / O contained in the negative electrode material. The measurement results of the elemental content are shown in FIG. 11. The measurement conditions for fluorescent X-ray analysis were the same as those described in the above embodiment. The negative electrode materials of Examples 1 to 7 contain elements (here, S) other than C derived from amorphous carbon, Si derived from silicon material, and Na, W, and O derived from sodium tungstate, which are impurities. Furthermore, the negative electrode materials may contain unavoidable impurities other than the elements listed in FIG. 11.

[0120] XRD was performed on the negative electrode material produced in each example to identify the chemical formula and crystal structure of sodium tungstate contained in the negative electrode material. The identification results are shown in Figure 11. The XRD measurement conditions were the same as those described in the above embodiment.

[0121] (Evaluation results) To evaluate the negative electrode material of each example, the capacity of the negative electrode using the negative electrode material was measured. Specifically, the current value per 1g (mAh / g) was measured when the C rate was 0.2, and the current value per 1g (mAh / g) was measured when the C rate was 3.2. For example, the current value per 1g of the negative electrode when the C rate was 0.2 refers to the current value that consumes the rated capacity in 5 hours. In addition, to evaluate the negative electrode material of each example, we also checked whether lithium flows into the Si of the negative electrode or whether lithium is released from the Si of the negative electrode. Cases where lithium flows into the Si of the negative electrode were marked as "yes," and cases where it does not flow were marked as "no." The evaluation results are shown in Figure 11. As shown in Figure 11, in Example 1-7, in which the Si / SiO2 ratio was 3 or more and sodium tungstate was provided on the surface of the carbon, the battery characteristics at 0.2 C were improved compared to Comparative Example 1, which did not contain sodium tungstate. Furthermore, it was found that the battery characteristics at 3.2 C of Example 1-7 also maintained sufficient values.

[0122] Although the embodiments of the present invention have been described above, the embodiments are not limited to the contents of these embodiments. Furthermore, the above-described components include those that can be easily imagined by a person skilled in the art, those that are substantially the same, and those that are within the scope of what is called equivalents. Furthermore, the above-described components can be combined as appropriate. Furthermore, various omissions, substitutions, or modifications of the components can be made without departing from the spirit of the above-described embodiments. [Explanation of symbols]

[0123] 1 battery 14 Negative electrode 22 Negative electrode material layer 30 carbon particles 32 Na x WO y particle 33 Silicon particles

Claims

1. A battery negative electrode material, a silicon material including carbon, sodium tungstate, and silicon, The silicon material has a surface layer of SiO when measured by X-ray photoelectron spectroscopy. ２ the ratio of the amount of Si in Si2p derived from elemental silicon to the amount of Si in Si2p derived from elemental silicon is 3 or more on an atomic concentration basis, The sodium tungstate is represented by the chemical formula Na x WO y , where x is greater than 0 and less than or equal to 1, and y is greater than or equal to 2 and less than or equal to 4. Negative electrode material.

2. 2. The negative electrode material according to claim 1, wherein the silicon material has a ratio of the amount of Si in Si2p to the amount of O in O1s in the surface layer of 1.2 or more on an atomic concentration basis, as measured by X-ray photoelectron spectroscopy.

3. 3. The negative electrode material according to claim 1, wherein the silicon material includes a Si layer made of Si and an oxide layer made of an oxide of silicon formed on a surface of the Si layer, and when the silicon material is assumed to be spherical and the volume of the silicon material is calculated using a volume average particle diameter, the volume of the oxide layer is 0.04% or less of the total volume of the silicon material.

4. 4. The negative electrode material according to claim 1, wherein the silicon material includes a Si layer formed of Si and an oxide layer formed on a surface of the Si layer and containing Si and O, and when the silicon material is assumed to be spherical and the volume of the silicon material is calculated using a particle diameter D50 at which a cumulative frequency of 50 volume % is measured in a volume-based particle size distribution measured by a laser diffraction scattering method, the volume of the oxide layer is 0.4% or less of the total volume of the silicon material.

5. 5. The negative electrode material according to claim 1, wherein the sodium content is, by mass, from 0.01% to 0.5%, the tungsten content is, by mass, from 0.5% to 20%, and the oxygen content is, by mass, from 1% to 15% when measured by fluorescent X-ray analysis.

6. 6. The negative electrode material according to claim 1, wherein a content ratio of sodium to tungsten, Na / W, is 0.001 or more and 0.2 or less in mass ratio when measured by fluorescent X-ray analysis.

7. The sodium tungstate may be Na ０．７８ WO ３ , Na ０．４８ WO ３ , Na ０．７２ WO ３ , Na ０．４４ WO ３ , Na ０．４９ WO ３ , Na ０．３３ WO ３ , Na ０．５８ WO ３ , Na ２ WO ４ , and Na ５ W １４ O ４４ The negative electrode material according to claim 1 , comprising at least one of:

8. A battery anode material, comprising: a silicon material including carbon, sodium tungstate, and silicon, the silicon material has a ratio of the amount of Si in Si2p derived from elemental silicon to the amount of Si in Si2p derived from SiO 2 in a surface layer, measured by X-ray photoelectron spectroscopy, of 3 or more on an atomic concentration basis; the ratio of sodium to tungsten, Na / W, is a mass ratio of 0.001 or more and 0.2 or less, as measured by fluorescent X-ray analysis; Negative electrode material.

9. A battery anode material, comprising: a silicon material including carbon, sodium tungstate, and silicon, the silicon material has a ratio of the amount of Si in Si2p derived from elemental silicon to the amount of Si in Si2p derived from SiO 2 in a surface layer, measured by X-ray photoelectron spectroscopy, of 3 or more on an atomic concentration basis; The sodium tungstate includes at least one of Na0.78WO3, Na0.48WO3, Na0.72WO3, Na0.44WO3, Na0.49WO3, Na0.33WO3, Na0.58WO3, Na2WO4, and Na5W14O44; Negative electrode material.

10. A battery comprising the negative electrode material according to any one of claims 1 to 9 and a positive electrode material.

11. A method for producing a negative electrode material for a battery, comprising: preparing a silicon source material in an atmosphere having an oxygen concentration of 5% or less; using the silicon feedstock to produce an anode material including carbon, sodium tungstate, and a silicon material; The silicon material has a surface layer of SiO when measured by X-ray photoelectron spectroscopy. ２ the ratio of the amount of Si of Si2p derived from elemental silicon to the amount of Si of Si2p derived from elemental silicon is 3 or more on an atomic concentration basis, The sodium tungstate is represented by the chemical formula Na x WO y , where x is greater than 0 and less than or equal to 1, and y is greater than or equal to 2 and less than or equal to 4. A method for producing anode materials.

12. A method for manufacturing a battery, comprising the method for manufacturing the negative electrode material of claim 11 and manufacturing a positive electrode material.

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