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

Abstract

To improve the performance.SOLUTION: A negative electrode material is a negative electrode material of a battery, and includes carbon, tungsten trioxide, 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 is 3 or more on an atomic concentration basis when 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 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, tungsten trioxide, 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, tungsten trioxide, 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 flowchart illustrating an example of a method for manufacturing a battery according to this embodiment. [Figure 11] FIG. 11 is a table showing the manufacturing conditions, properties of silicon particles, and evaluation results 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, tungsten trioxide, and a silicon material. In the negative electrode material of this embodiment, tungsten trioxide is provided on the surface of carbon, and a silicon material is provided on the surface of the carbon. However, the positional relationship between the carbon, tungsten trioxide, and silicon material is not limited to this and may be any. More specifically, the negative electrode material of the negative electrode material layer 22 includes carbon particles 30, WO3 (tungsten trioxide) particles 32, and silicon particles 33, which are particles containing silicon. Note that the shape of the particles here is not limited to spherical shapes, and may be any shape, such as linear or sheet-like.

[0017] The tungsten trioxide provided on the carbon surface includes at least one of the following: tungsten trioxide directly adhering to carbon; tungsten trioxide indirectly adhering to carbon via silicon adhering to carbon; silicon indirectly adhering to carbon via tungsten trioxide adhering to carbon; and composite particles of tungsten trioxide and silicon directly adhering to carbon, directly or indirectly adhering to carbon. The negative electrode material of this embodiment preferably includes at least carbon and a silicon material to which tungsten trioxide is adhering. The negative electrode material of this embodiment may also be composed of carbon, tungsten trioxide, and a silicon material, and may contain, except for unavoidable impurities, only carbon, tungsten trioxide, 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 tungsten trioxide on the surface. Therefore, these functional groups allow tungsten trioxide to be appropriately trapped on the surface of the amorphous carbon, allowing tungsten trioxide to be appropriately disposed on the surface. Furthermore, since these functional groups fix tungsten trioxide to the surface of the amorphous carbon, the adhesion of tungsten trioxide to the amorphous carbon surface can be increased, and tungsten trioxide can be prevented from being separated from the carbon surface. In particular, since 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 tungsten trioxide 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 includes a plurality of WO3 particles 32 and silicon particles (silicon material) 33. More specifically, a plurality of WO3 particles 32 and silicon particles 33 are provided for each carbon particle 30. One of the plurality of WO3 particles 32 is provided on the surface of the carbon particle 30. Another of the plurality of WO3 particles 32 is provided on the surface of a silicon particle 33. More specifically, the silicon particle 33 is in close contact with (adheres to) the surface of the carbon particle 30, and the WO3 particle 32 is in close contact with (adheres to) the surface of the silicon particle 33. The carbon particle 30, the WO3 particle 32, and the silicon particle 33 may be composited. Alternatively, the carbon particle 30 and the silicon particle 33 may be composited, and the carbon particle 30 and the WO3 particle 32 may be composited. Therefore, the negative electrode material of the negative electrode material layer 22 is a composite of carbon particles 30, WO3 particles 32, and silicon particles 33, but may further include at least one of a composite of carbon particles 30 and silicon particles 33 and a composite of carbon particles 30 and WO3 particles 32.

[0023] Here, "composite" refers to a state in which, at least when no external force is applied, it is impossible to separate the silicon particles 33 from the carbon particles 30, the silicon particles 33 from the WO3 particles 32, and the WO3 particles 32 from the carbon particles 30. For example, the external force refers to the force exerted when a solid electrolyte interphase (SEI) film is formed to cover the entire surface and expands and contracts when a battery using the negative electrode material is operated.

[0024] For example, the composite formation includes at least one of forming a composite in which silicon particles 33 are arranged on the surface of carbon particles 30 and WO3 particles 32 are arranged on the surface of silicon particles 33, forming a composite in which WO3 particles 32 are arranged on the surface of carbon particles 30 and silicon particles 33 are arranged on the surface of WO3 particles 32, forming a composite in which silicon particles 33 are arranged on the surface of carbon particles 30, forming a composite in which WO3 particles 32 are arranged on the surface of carbon particles 30, forming a composite in which WO3 particles 32 are arranged on the surface of silicon particles 33, and forming WO3 particles 32 and silicon particles 33 on the surface of carbon particles 30 and the WO3 particles 32 and silicon particles 33 are also in close contact with each other.

[0025] The WO particles 32 include those with a hexagonal crystal structure and those with monoclinic, triclinic, and orthorhombic crystal structures. That is, the negative electrode material includes tungsten trioxide with a hexagonal crystal structure and tungsten trioxide with monoclinic and triclinic crystal structures. However, the negative electrode material may include at least one of tungsten trioxide with a hexagonal crystal structure, tungsten trioxide with a monoclinic crystal structure, and tungsten trioxide with a triclinic crystal structure. In summary, the negative electrode material preferably includes at least one of tungsten trioxide with a hexagonal, monoclinic, and triclinic crystal structure, more preferably tungsten trioxide with a hexagonal crystal structure and tungsten trioxide with a monoclinic or triclinic crystal structure, and even more preferably tungsten trioxide with a hexagonal, monoclinic, and triclinic crystal structure. In addition, when the negative electrode material contains tungsten trioxide of other crystal structures, such as monoclinic or triclinic, in addition to hexagonal tungsten trioxide, it is preferable that the content of hexagonal tungsten trioxide be the largest among the tungsten trioxide of each crystal structure. However, the crystal structure of the tungsten trioxide contained in the negative electrode material is not limited to this, and for example, tungsten trioxide of other crystal structures may be contained. Furthermore, the negative electrode material may also contain amorphous tungsten trioxide.

[0026] The average particle size of the WO3 particles 32 is smaller than that of the carbon particles 30. The average particle size of the WO3 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.

[0027] In this way, the negative electrode material has a structure in which particulate tungsten trioxide (WO3 particles 32) and silicon (silicon particles 33) are provided on the surface of carbon particles 30, but is not limited to this. The negative electrode material may have a structure in which tungsten trioxide and silicon material are provided on the surface of carbon, and the shapes of the tungsten trioxide and silicon material provided on the surface of carbon may be arbitrary. In this embodiment, tungsten trioxide is used as the tungsten compound or tungsten oxide. Furthermore, in this embodiment, silicon is used as the silicon particles 33, but a silicon compound may also be used.

[0028] The negative electrode material layer 22 may contain a substance other than the negative electrode material (carbon particles 30, WO3 particles 32, and silicon particles 33). The negative electrode material layer 22 may contain, for example, a binder. Any binder material may be used, 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.

[0029] Carbon, tungsten trioxide, and silicon can be identified by X-ray diffraction. For 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 a known graphite structure is broad, the object can be determined to be amorphous carbon. Also, for example, if the position (angle) of the peak in the X-ray diffraction analysis of the object to be analyzed matches the position of the peak in known tungsten trioxide, the object to be analyzed can be determined to contain tungsten trioxide. Furthermore, for example, if the position (angle) of the peak in the X-ray diffraction analysis of the object to be analyzed matches the position of the peak in known silicon, the object to be analyzed can be determined to contain silicon.

[0030] Furthermore, the arrangement of the WO3 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 an SEM (Scanning Electron Microscope) or a TEM (Transmission Electron Microscope).

[0031] Furthermore, the element ratios of carbon, tungsten trioxide, and silicon in the negative electrode material in this embodiment can be measured by optical emission spectrometry.

[0032] For the negative electrode material of this embodiment, the chemical components of silicon, tungsten, and oxygen may be measured, with the remaining amount being carbon. Silicon and tungsten can be measured using an ICP-OES (Inductively Coupled Plasma Optical Emission Spectrometer) (manufacturer: Agilent, product name: 720-ES), and oxygen can be measured using an inert gas fusion-infrared absorption method (manufacturer: LECO, product name: ONH836). In the resulting negative electrode material, the silicon content is preferably 1% to 10% by weight, more preferably 1% to 8% by weight, or 2% to 8% by weight, and even more preferably 1.5% to 7% by weight, or 1.8% to 7% by weight. In the negative electrode material product, when the total of the three elements of silicon material, tungsten trioxide, and carbon is taken as 100% by weight, the tungsten trioxide content is preferably 1% by weight or more and 10% by weight or less, more preferably 2% by weight or more and 8% by weight or less, and even more preferably 3% by weight or more and 5% by weight or less.

[0033] Furthermore, when the total of the three elements of silicon material, tungsten trioxide, and carbon in the product negative electrode material is taken as 100% by weight, the ratio of the silicon material content (% by weight) to the tungsten trioxide content (% by weight) is preferably 0.2 or more and 2.5 or less, more preferably 0.2 or more and 2.0 or less, or 0.5 or more and 2.0 or less, and even more preferably 0.3 or more and 1.8 or less, or 0.4 or more and 1.7 or less.

[0034] Furthermore, in the negative electrode material of the negative electrode material layer 22, the silicon particles 33 may be in close contact with the surfaces of the carbon particles 30, and the WO3 particles 32 may be in close contact with the surfaces of the carbon particles 30. In this case, the carbon particles 30 and the silicon particles 33 may be composited, and the carbon particles 30 and the WO3 particles 32 may be composited.

[0035] In this way, the negative electrode material has a structure in which particulate tungsten trioxide (WO3 particles 32) and silicon particles 33 are provided on the surface of carbon particles 30, but is not limited to this. The negative electrode material may have a structure in which tungsten trioxide and silicon material are provided on the surface of carbon, and the shapes of the tungsten trioxide and silicon material provided on the surface of carbon may be arbitrary.

[0036] (silicon particles) FIG. 3 is a schematic cross-sectional view of a silicon particle. 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.

[0037] (Silicon particle characteristics 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

[0038] (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, as 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 particles 33 are 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 of 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 particles, 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.

[0039] 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 waveform 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.

[0040] 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.

[0041] (Si concentration ratio derived from Si) 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 (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 particles, which makes it possible to improve the capacity of the negative electrode material while suppressing a decrease in productivity.

[0042] (Si concentration ratio derived from SiO2) 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 23% 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 silicon particles, and it is possible to improve the capacity of the negative electrode material while suppressing a decrease in productivity.

[0043] (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 1.2 or more, more preferably 1.3 or more, and even more preferably 1.4 or more, on an atomic concentration basis. The O in O1s refers to an O atom that has had its 1s orbital electron ejected, 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 not necessary to prepare excessively pure Si, thereby improving the capacity of the negative electrode material and suppressing a decrease in productivity. Thus, when silicon particles 33 are measured by X-ray photoelectron spectroscopy, the ratio of Si in Si2p to the amount of O in O1s in the surface layer is preferably 1.2 or more and 4 or less, more preferably 1.2 or more and 9 or less, and even more preferably 1.2 or more and 99 or less, on an atomic concentration basis. When silicon particles 33 are measured by 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.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 1.4 or more and 4 or less, more preferably 1.4 or more and 9 or less, and even more preferably 1.4 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.

[0044] 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 the narrow spectrum of Si2P, and Figure 7 shows the 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 11. 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 concentration ratio Si / O.

[0045] (Si concentration) The Si concentration is preferably 50 at% or more, more preferably 55 at% or more, and even more preferably 60 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 silicon particles, and it is possible to improve the capacity of the negative electrode material while suppressing a decrease in productivity.

[0046] (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 negative electrode material. Furthermore, the O concentration is preferably 20 at% or more, more preferably 10 at% or more, and even more preferably 1 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 silicon particles, and it is possible to improve the capacity of the negative electrode material while suppressing a decrease in productivity.

[0047] (thickness of oxide layer) The thickness of the oxide layer 33B of the silicon particles 33 is preferably 2.1 angstroms or less, more preferably 1.8 angstroms or less, and even more preferably 1.3 angstroms or less. Having the thickness of the oxide layer 33B within this range reduces the amount of oxide near the surface, thereby improving the capacity of the negative electrode material. Furthermore, 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 the thickness of the oxide layer 33B within this range eliminates the need to prepare excessively pure Si, thereby improving the capacity of the negative electrode material and suppressing a decrease in productivity. The thickness of the oxide layer 33B is calculated by multiplying the ratio of the amount of Si in Si2p derived from SiO2 to the amount of Si in 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 Si2p derived from SiO2 to the amount of Si in Si2p derived from elemental silicon), by the photoelectron escape depth of Si in Si2p, 6 angstroms.

[0048] (Silicon particle characteristics based on volume average particle size) Next, the characteristics of the silicon particles 33 based on the volume average particle size will be described.

[0049] (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.

[0050] (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 volume is calculated using the volume average particle diameter assuming that the silicon particles 33 are spherical. In this case, the volume ratio of the oxide layer 33B based on the volume average particle diameter is preferably 0.05% or less, more preferably 0.04% or less, and even more preferably 0.035% or less. A volume ratio within this range reduces the amount of oxide near the surface, thereby improving the capacity of the negative electrode material. 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. A volume ratio within this range eliminates the need for equipment or processes to prevent excessive oxidation of the silicon particles, thereby improving the capacity of the negative electrode material and suppressing a decrease in productivity.

[0051] 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.

[0052] (Silicon particle characteristics based on D50) Next, the characteristics of silicon particles 33 based on D50 will be described.

[0053] (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.

[0054] (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. A volume ratio within this range reduces the amount of oxide near the surface, 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. A volume ratio within this range eliminates the need for equipment or processes to prevent excessive oxidation of the silicon particles, thereby improving the capacity of the negative electrode material and suppressing a decrease in productivity.

[0055] 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.

[0056] (positive electrode) The positive electrode 16 shown in FIG. 1 includes a current collector layer and a positive electrode material layer. The current collector layer of the positive electrode 16 is a layer composed of a conductive member, and examples of the conductive member here include aluminum. The positive electrode material layer is a layer of a positive electrode material and is provided on the surface of the current collector layer of the positive electrode 16. The thickness of the current collector layer of the positive electrode may be, for example, about 10 μm or more and 30 μm or less, and the thickness of the positive electrode material layer may be, for example, about 10 μm or more and 100 μm or less.

[0057] The positive electrode material layer contains a positive electrode material. The positive electrode material contains particles of a lithium compound, which is a compound containing lithium. Examples of the lithium compound may include lithium-containing metal oxides and lithium-containing phosphates. 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 include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PAA, etc. The binder may be used alone or in combination of two or more.

[0058] (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. Further, 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.

[0059] (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).

[0060] (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, using the silicon raw material to manufacture an anode material by providing tungsten trioxide and a silicon material on the surface of carbon, and manufacturing a cathode material.

[0061] (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.

[0062] 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. The oxygen concentration is preferably 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.

[0063] (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.

[0064] 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.

[0065] (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.

[0066] 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.

[0067] (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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] (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 S28.

[0074] Specifically, the WO3 raw material is added to the dissolving solution, and the WO3 raw material is dissolved in the dissolving solution (step S10; dissolving step). The WO3 raw material is tungsten trioxide, which is used as a raw material for negative electrode materials. The dissolving solution is a solution capable of dissolving the WO3 raw material, i.e., tungsten trioxide. For example, an alkaline solution is used as the dissolving solution, and in this embodiment, an aqueous ammonia solution is used. The dissolving solution preferably has an ammonia concentration of 5% or more and 30% or less by weight relative to the total amount of the dissolving solution.

[0075] In this embodiment, dissolution is not limited to a state in which everything is dissolved, but also includes a state in which some of the material remains. Dissolution also includes dissolving by mixing.

[0076] The WO3 raw material can be produced by, for example, reacting CaWO4 with hydrochloric acid, dissolving it in ammonia, and calcining the crystallized ammonium paratungstate, but it can also be produced by any method. WO3 is tungsten trioxide, tungsten (VI) oxide, or tungstic anhydride.

[0077] In step S10, the ratio of the amount of WO3 raw material added to the amount of ammonia contained in the dissolving solution is preferably set to 1% or more and 10% or less in mole percent. Setting the ratio of the WO3 raw material added to 1% or more ensures a sufficient amount of tungsten trioxide in the dissolving solution, while setting the ratio of the WO3 raw material added to 10% or less reduces the amount of tungsten trioxide remaining undissolved. In step S10, the WO3 raw material is added to the dissolving solution and stirred for a predetermined time to dissolve the WO3 raw material in the dissolving solution. This predetermined time is preferably set to 6 hours or more and 24 hours or less. Setting the predetermined time to 6 hours or more ensures that the WO3 raw material is adequately dissolved in the dissolving solution, while setting the predetermined time to 24 hours or less prevents excessively long manufacturing times. Note that step S10 may be a preparation step in which a dissolving solution containing the WO3 raw material is prepared in advance before proceeding to step S12, which will be described later.

[0078] Next, the silicon raw material is added to and dissolved in the dissolving solution (here, an ammonium tungstate solution) in which the WO3 raw material has been dissolved (step S12; adding step).

[0079] In step S12, the dissolving solution in which the WO3 raw material is dissolved is stirred to disperse the silicon raw material in the dissolving solution. In step S12, a surfactant may be added to the dissolving solution in which the silicon raw material and WO3 are dispersed in order to improve the affinity between the silicon raw material and WO3. As the surfactant, sodium dodecyl sulfate (SDS) may be used, or a surfactant that does not contain Na may be used. Examples of surfactants that do not contain sodium include poly(oxyethylene) alkyl ethers and polyoxyethylene nonylphenyl ethers. As the poly(oxyethylene) alkyl ethers, those having an alkyl group with 12 to 15 carbon atoms are preferably used, 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. may be used. The amount of surfactant added is preferably 2% to 8% by weight of the amount of WO3 raw material added to the dissolving solution, which appropriately improves the affinity between the silicon raw material and WO3.

[0080] Next, the liquid components of the dissolving solution are removed to generate a primary intermediate material (primary intermediate material generation step). In this embodiment, steps S14 and S16 are executed as the primary intermediate material step. Specifically, the dissolving solution is dried to generate a primary intermediate (step S14; drying step). In step S14, the dissolving solution is dried in air or in an inert gas at 80°C for 12 hours to remove, i.e., evaporate, the liquid components contained in the dissolving solution. The use of an inert gas can suppress oxidation of Si. The primary intermediate can be said to contain the solid components remaining after the liquid components of the dissolving solution have been removed.

[0081] Next, the dried primary intermediate is heat-treated to produce a primary intermediate material (step S16; heating step). By heating the primary intermediate, a primary intermediate material is formed in which WO3 particles 32 are provided on the surfaces of silicon particles 33. The temperature at which the primary intermediate is heated is preferably 500°C or higher and 900°C or lower in an inert gas. By heating the primary intermediate to a temperature within this range, the primary intermediate material can be properly formed. Furthermore, the heating time for the primary intermediate is preferably 1 hour or higher and 10 hours or lower. By heating the primary intermediate for a time within this range, the primary intermediate material can be properly formed. Note that steps S12 to S16 may be a preparation step in which the above-mentioned primary intermediate material (or primary intermediate) is prepared in advance before proceeding to step S18, which will be described later.

[0082] Next, the primary intermediate and the carbon raw material (here, hard carbon) are mixed and dispersed in a liquid (here, water) (step S18; adding step). The carbon raw material is hard carbon used as a raw material.

[0083] 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.

[0084] Here, when adding a WO3 raw material, a silicon raw material, and a carbon raw material to a dissolving solution, the ratio of the amount of silicon raw material added to the total amount of the WO3 raw material, the silicon raw material added, and the carbon raw material added is referred to as the silicon raw material addition ratio, and the ratio of the amount of WO3 raw material added to the total amount of the WO3 raw material added is referred to as the WO3 raw material addition ratio. In this manufacturing method, the silicon raw material addition ratio is set to 1% by weight or more and 10% by weight or less, preferably 2% by weight or more and 8% by weight or less, and more preferably 5% by weight or more and 8% by weight or less. By setting the silicon raw material addition ratio within this range, silicon particles 33 can be appropriately formed on the surfaces of carbon particles 30, which can be used as a negative electrode to increase the capacity of the battery. Furthermore, in this manufacturing method, the WO3 raw material addition ratio is preferably set to 1% by weight or more and 10% by weight or less, preferably 2% by weight or more and 8% by weight or less, and more preferably 5% by weight or more and 8% by weight or less. By setting the WO3 raw material addition ratio within this range, WO3 particles 32 can be appropriately formed on the surface of the carbon particles 30, and the resulting negative electrode can increase the capacity of the battery.

[0085] In step S18, the liquid (here, water) is stirred to disperse the primary intermediate material and the carbon raw material in the liquid. Also, in step S18, a surfactant may be added to the liquid to improve the affinity between the carbon raw material, silicon, and WO3. As the surfactant, sodium dodecyl sulfate (SDS) may be used, or a surfactant that does not contain Na may be used. The amount of surfactant added is preferably 2% to 8% by weight of the amount of carbon raw material added to the liquid. By setting the amount within this numerical range, the affinity between the carbon raw material, silicon, and WO3 is appropriately improved.

[0086] Next, the liquid component of the solution in which the primary intermediate material and the carbon raw material are dispersed in the liquid is removed to produce the negative electrode material (negative electrode material production step). In this embodiment, steps S20 and S22 are executed as the negative electrode material production step. Specifically, the solution is dried to produce a negative electrode intermediate (step S20; drying step). In step S20, the solution is dried in the air or in an inert gas at 80°C for 12 hours to remove, i.e., evaporate, the liquid component contained in the solution. The negative electrode intermediate can be said to contain the solid component remaining after the liquid component of the solution has been removed.

[0087] Next, the negative electrode intermediate is heated to produce a negative electrode material (step S22; heating step). By heating the negative electrode intermediate, a negative electrode material is formed in which WO3 particles 32 and silicon particles 33 are provided on the surfaces of carbon particles 30. The temperature at which the negative electrode intermediate is heated is preferably 500°C or higher and 900°C or lower in an inert gas. By setting the temperature at which the negative electrode intermediate is heated within this range, the negative electrode material can be properly formed. Furthermore, the time for which the negative electrode intermediate is heated is preferably 1 hour or higher and 10 hours or lower. By setting the heating time of the negative electrode intermediate within this range, the negative electrode material can be properly formed.

[0088] Next, the negative electrode 14 is formed using the formed negative electrode material (step S24). 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.

[0089] This manufacturing method also forms the positive electrode 16 (step S26). In step S26, the positive electrode material is formed in the same manner as steps S10 to S24, except that a lithium compound raw material, which is a lithium compound, is used instead of the carbon 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.

[0090] 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 S28). 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.

[0091] As described above, in this embodiment, as shown in steps S10 to S24, silicon is added to a dissolving solution containing tungsten trioxide, the liquid component is removed to produce a primary intermediate material, and then the primary intermediate material and hard carbon are added to the liquid, followed by the removal of the liquid component, thereby producing a negative electrode material. Hereinafter, this method of producing a negative electrode material will be referred to as a solution method, where appropriate. Furthermore, the above-described method using SDS as a surfactant will be referred to as a first production method.

[0092] In step S18, a surfactant may be added to the solution to improve the affinity between the carbon raw material, silicon, and WO. A surfactant that does not contain sodium may be used as the surfactant. Using the surfactant, silicon is added to a dissolving solution containing tungsten trioxide, and the liquid component is removed to produce a primary intermediate material, as shown in steps S10 to S24. The primary intermediate material and hard carbon are then added to the liquid, and the liquid component is then removed, thereby producing a negative electrode material. Hereinafter, this method of producing a negative electrode material will be referred to as the solution method, where appropriate. The above-described method of production will also be referred to as the second production method.

[0093] (Modification of Battery Manufacturing Method) Next, another example of a method for manufacturing the battery 1 according to this embodiment will be described. Fig. 10 is a flowchart illustrating one example of a method for manufacturing the battery according to this embodiment. As shown in Fig. 10, in this manufacturing method, the negative electrode 14 is formed in steps S30 to S44. Steps S30, S32, S40, S42, and S44 are similar to steps S10, S12, S24, S26, and S28.

[0094] Next, the carbon raw material is added to the dissolving solution in which the WO3 raw material and the silicon raw material have been dissolved, and dissolved (step S34; adding step). The carbon raw material is hard carbon used as a raw material.

[0095] In step S34, the dissolving solution is stirred to mix and disperse the WO3 raw material, silicon raw material, and carbon raw material in the solution. In step S34, a surfactant may be added to the solution to improve the affinity between the carbon raw material, silicon, and WO3.

[0096] Next, the liquid components of the dissolving solution are removed to produce the negative electrode material (negative electrode material production step). In this embodiment, steps S36 and S38 are performed as the negative electrode material production step. Specifically, the dissolving solution is dried to produce a negative electrode intermediate (step S36; drying step). In step S36, the dissolving solution is dried in air or in an inert gas at 80°C for 12 hours to remove, i.e., evaporate, the liquid components contained in the dissolving solution. The negative electrode intermediate can be said to contain the solid components remaining after the liquid components of the dissolving solution have been removed.

[0097] Next, the negative electrode intermediate is heated to produce a negative electrode material (step S38; heating step). By heating the negative electrode intermediate, a negative electrode material is formed in which WO3 particles 32 and silicon particles 33 are provided on the surfaces of carbon particles 30. The temperature at which the negative electrode intermediate is heated is preferably 500°C or higher and 900°C or lower in an inert gas. By setting the temperature at which the negative electrode intermediate is heated within this range, the negative electrode material can be properly formed. Furthermore, the time for which the negative electrode intermediate is heated is preferably 1 hour or higher and 10 hours or lower. By setting the heating time of the negative electrode intermediate within this range, the negative electrode material can be properly formed.

[0098] As described above, in this embodiment, as shown in steps S30 to S44, a negative electrode material is produced by adding silicon and hard carbon to a dissolving solution containing tungsten trioxide, and then removing the liquid component. Hereinafter, this method of producing a negative electrode material will also be referred to as a solution method, as appropriate. The above-described method of production will also be referred to as a third production method.

[0099] 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.

[0100] (effect) As described above, the negative electrode material according to this embodiment is a battery negative electrode material and includes carbon, tungsten trioxide, 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.

[0101] Here, the addition of tungsten trioxide 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 Si oxides inhibit capacity improvement. In contrast, in the negative electrode material according to this embodiment, 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 3 or more, based on atomic concentration. Therefore, according to this embodiment, the amount of silicon oxide can be reduced, thereby improving battery performance.

[0102] 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 of 1.2 or more, as measured by X-ray photoelectron spectroscopy, on an atomic concentration basis. 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.

[0103] 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 0.05% 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.

[0104] 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.

[0105] Furthermore, when the total content of carbon, tungsten trioxide, 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.

[0106] 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, tungsten trioxide, 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 at a low oxygen concentration can suppress oxidation of silicon, thereby improving battery performance.

[0107] (Example) Next, an example will be described.

[0108] 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 a container that could be divided into one container and the other container 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 rate of the crushed silicon material and hard balls in the container was 28%. The container filled with the crushed silicon material and hard balls was removed from the glove box and placed in a three-dimensional ball mill. The material was coarsely crushed under the following conditions: a first rotating shaft rotation speed of 300 rpm, a second rotating shaft rotation speed of 300 rpm, and a crushing time of 0.33 hours. The coarsely crushed silicon material and hard balls were dry-classified using a sieve with 1000 μm openings 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 container filled with the silicon coarse particles and hard balls was removed from the glove box and placed in a three-dimensional ball mill. The silicon raw material was obtained by milling under the following conditions: first rotation speed: 300 rpm, second rotation speed: 300 rpm, and milling time: 3 hours.

[0109] (Preparation of negative electrode material) In Example 1, a negative electrode material was produced using hard carbon, tungsten trioxide, and silicon by the first manufacturing method using the solution method described in the embodiment. Specifically, 5 ml of a 28 wt % ammonia solution and 0.05 g of WO3 raw material were added to a 50 ml beaker and stirred at 40 °C for 12 hours to dissolve the WO3 raw material in the ammonia solution. 0.05 g of SDS was then added to the ammonia solution so that the weight ratio with respect to the WO3 raw material was 1:1, and the mixture was stirred at room temperature for 4 hours to dissolve the SDS in the ammonia solution. 0.05 g of silicon raw material was then added to the ammonia solution so that the weight ratio with respect to the WO3 raw material was 1:1, and the mixture was stirred at room temperature for 4 hours to dissolve the silicon raw material in the ammonia solution. After stirring, the ammonia solution was heated at 80 °C for 12 hours and dried to produce a primary intermediate material. This primary intermediate material was then introduced into a tubular furnace and heated under a nitrogen atmosphere at room temperature for two hours. Subsequently, while still in the nitrogen atmosphere, it was continuously heated at a rate of 3°C / min to 200°C, 1°C / min to 550°C, and 3°C / min to 700°C, and held for two hours to produce a primary intermediate material. The resulting primary intermediate material was then added, in order, to 5 ml of pure water, 0.053 g of SDS, and 0.95 g of carbon raw material. The liquid was stirred for four hours until the carbon raw material was dispersed in the pure water, and then heated and dried at 80°C for 12 hours to produce a negative electrode intermediate. This negative electrode intermediate was then introduced into a tubular furnace and heated under a nitrogen atmosphere at room temperature for two hours. Subsequently, while still in the nitrogen atmosphere, it was continuously heated at a rate of 3°C / min to 200°C, 1°C / min to 550°C, and 3°C / min to 700°C, and held for two hours to produce a negative electrode material.

[0110] In Example 1, the silicon raw material ratio, i.e., the amount of silicon raw material added relative to the total amount of carbon raw material, WO3 raw material, and silicon raw material, was set to 5% by weight. In Example 1, the amount of WO3 raw material added was 0.05 g, the amount of silicon raw material added was 0.05 g, and the amount of carbon raw material added was 0.95 g.

[0111] Example 2 In Example 2, a negative electrode material was produced in the same manner as in Example 1, except that the final crushing time in obtaining the silicon raw material was set to 6 hours.

[0112] Example 3 In Example 3, the surfactant was a poly(oxyethylene) alkyl ether (C 12 H 25 O(C2H4) n The amount of hard carbon, tungsten trioxide, silicon raw material, and surfactant additive was the same as in Example 1.

[0113] Example 4 In Example 4, the surfactant was polyoxyethylene nonylphenyl ether (CH 19 A negative electrode material was produced in the same manner as in Example 3, except that the final grinding time in obtaining the silicon raw material was 6 hours using C6(CH2CH2O)8H).

[0114] (Comparative Example 1) In Comparative Example 1, a negative electrode material was produced in the same manner as in Example 1, except that when obtaining the silicon raw material, air was filled indoors and the final crushing time was set to one hour.

[0115] (Comparative Example 2) In Comparative Example 2, a negative electrode material was produced in the same manner as in Example 1, except that air was filled indoors when obtaining the silicon raw material and the final crushing time was 1.5 hours.

[0116] In Examples 1 to 4, the glove box was filled with argon, and the oxygen concentration when the silicon raw material was obtained was 5% or less. However, in Comparative Examples 1 and 2, the glove box was filled with air, and the oxygen concentration when the silicon raw material was obtained was higher than 5%.

[0117] (Characteristics of silicon particles) FIG. 11 is a table showing the manufacturing conditions, silicon particle characteristics, and evaluation results for each example. As shown in FIG. 11, the characteristics of the silicon particles for each example were measured based on XPS measurement. The Si concentration in FIG. 11 corresponds to the Si concentration described in this embodiment, the O concentration in FIG. 11 corresponds to the O concentration described in this embodiment, the SiO2-derived Si concentration ratio in FIG. 11 corresponds to the SiO2-derived Si concentration ratio described in this embodiment, the Si-derived Si ratio in FIG. 11 corresponds to the Si-derived Si ratio described in this embodiment, the Si / SiO2 in FIG. 11 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 in FIG. 11 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, and the oxide film thickness in FIG. 11 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. 11, the characteristics based on the volume average particle diameter and D50 were measured for each silicon particle. Silicon particles were added to a surfactant aqueous solution and ultrasonically dispersed to prepare a silicon particle dispersion. The particle size distribution of the silicon particles in the resulting silicon particle dispersion was then measured using a laser diffraction / scattering particle size distribution analyzer (MT3300EX II, manufactured by Microtrack Bell Corporation). The volume average particle diameter and D50 were calculated from the resulting particle size distribution. The SiO volume in FIG. 11 corresponds to the volume of the oxide layer 33B calculated using the volume average particle diameter (or D50) in this embodiment. The particle volume in FIG. 11 corresponds to the volume of the silicon particles 33 calculated using the volume average particle diameter (or D50) in this embodiment. The SiO volume / particle volume in FIG. 11 corresponds to the volume ratio of the oxide layer 33B based on the volume average particle diameter (or D50) in this embodiment.

[0118] (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 0.2 hours. In addition, to evaluate the negative electrode material of each example, we also checked whether lithium flowed into the Si of the negative electrode or whether lithium was released from the Si of the negative electrode. If lithium flowed into the Si of the negative electrode, it was marked with a ◯, if it did not flow, it was marked with an ×, and if lithium was released from the Si of the negative electrode, it was marked with a ◯, if it was not released, it was marked with an ×. The evaluation results are shown in Figure 11. As shown in Figure 11, in Examples 1 and 2 where the Si / SiO2 is 3 or more, the amount of silicon oxide is small, so the current value is sufficiently maintained when the C rate is 0.2, and when the C rate is 3.2, the current value is sufficiently maintained, and lithium flows into the negative electrode and is released from the negative electrode, which improves the battery performance. On the other hand, in Comparative Examples 1 and 2 where the Si / SiO2 is less than 3, the amount of silicon oxide increases, resulting in a low current value at a C rate of 3.2, and lithium is not released from the Si in the negative electrode, making it impossible to adequately improve the battery performance.

[0119] 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]

[0120] 1 battery 14 Negative electrode 22 Negative electrode material layer 30 carbon particles 32 WO3 particles 33 Silicon particles

Claims

1. A battery negative electrode material, a silicon material provided on the surface of the carbon, the silicon material including silicon, and a carbon material provided on the surface of the carbon; 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, When the total content of the silicon material, the tungsten trioxide, and the carbon is taken as 100% by weight, the content of the silicon material is 1% by weight or more and 10% by weight or less, and the content of the tungsten trioxide is 1% by weight or more and 10% by weight or less. Anode 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. A battery comprising the negative electrode material according to any one of claims 1 to 4 and a positive electrode material.

6. 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 raw material to produce an anode material including carbon, tungsten trioxide provided on a surface of the carbon, and a silicon material provided on a surface of the carbon, wherein the content of the silicon material is 1% by weight or more and 10% by weight or less, and the content of the tungsten trioxide is 1% by weight or more and 10% by weight or less, when the total content of the silicon material, the tungsten trioxide, and the carbon is taken as 100% by weight; 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; A method for producing anode materials.

7. A method for manufacturing a battery, comprising the method for manufacturing the negative electrode material of claim 6 and a step of manufacturing a positive electrode material.

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