JP7465672B2 - Negative electrode materials for power storage devices - Google Patents

Description

The present invention relates to a material suitable for the negative electrode of an electricity storage device involving the movement of lithium ions during charging and discharging, such as a lithium ion secondary battery, an all-solid-state lithium ion secondary battery, and a hybrid capacitor.

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

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

Carbonaceous materials such as natural graphite, artificial graphite, and coke are used as the active material in the negative electrode. The theoretical capacity of these carbonaceous materials for lithium ions is only 372 mAh/g. Active materials with a larger capacity are desired.

As an active material in the negative electrode, Si has been attracting attention. Si reacts with lithium ions. This reaction forms a compound. A typical compound is Li ₂₂ Si _5. This reaction causes a large amount of lithium ions to be absorbed in the negative electrode. Si can increase the storage capacity of the negative electrode.

When the active material layer containing Si absorbs lithium ions, the active material layer expands due to the formation of the aforementioned compound. The expansion rate of the active material is approximately 400%. When lithium ions are released from the active material layer, the active material layer contracts. Repeated expansion and contraction causes the active material to fall off the current collector. This falling off reduces the storage capacity. Repeated expansion and contraction can also impede conductivity between active materials.

The repeated expansion and contraction creates new interfaces in the active material, so that the SEI is continuously formed on the surface of the active material. The formation of the SEI is accompanied by a decomposition reaction of the electrolyte, which causes the electrolyte to be depleted. The decomposition reaction of the electrolyte is accompanied by the formation of a resistive film, which increases the internal resistance of the battery. The life span of conventional lithium-ion secondary battery negative electrodes containing Si is short.

The storage capacity of silicon oxide is smaller than that of silicon, but is sufficiently larger than that of carbon-based materials. Furthermore, the volume change when silicon oxide absorbs lithium ions is smaller than that of silicon. From the viewpoint of cycle life, the application of silicon oxide to lithium ion secondary batteries is being considered.

When silicon oxide absorbs lithium ions, a reaction occurs to produce lithium silicate. This reaction is irreversible. This lithium silicate reduces the initial capacity reversibility rate. Furthermore, if a large amount of lithium silicate is produced and a coating is formed, this coating acts as resistance and causes a decrease in capacity during cycling.

JP 2018-41702 A discloses an anode material whose composition is composed of Si, Si oxide, and a carbon-based material. In this anode material, the carbon-based material improves the initial capacity reversibility rate. JP 2019-508842 A discloses an anode material with a similar composition.

JP 2018-41702 A Patent Publication No. 2019-508842

Conventional lithium-ion secondary batteries cannot meet all of the requirements of a large storage capacity, a long cycle life, and a sufficient initial capacity reversibility rate. Similar problems also occur in various power storage devices other than lithium-ion secondary batteries.

The object of the present invention is to provide a negative electrode material that can provide an electricity storage device with excellent storage capacity, cycle life, and initial capacity reversibility.

The negative electrode material for an electric storage device according to the present invention is composed of a large number of particles. The material of each particle is an alloy having a metal structure in which a plurality of Si phases are dispersed in a matrix of Si oxide. This matrix is
The sample includes (1) a _SiO2 phase and (2) _{a SiOX} phase obtained by replacing a part of O in the _SiO2 phase with Si. The crystallite size of the Si phase is 80 nm or less. In X-ray diffraction, the half-width A of the diffraction peak intensity I of the (101) plane, which is the main peak of _SiO2 , is 0.20° or more and 1.30° or less. In X-ray diffraction, the half-width B of the diffraction peak intensity II of the (111) plane, which is the main peak of Si, is 0.30° or more and 1.50° or less.

Preferably, in this alloy, the area fraction of the Si phase is 5.0% or more and 10.0% or less, the area fraction of the SiO _X phase is 80.0% or more and 90.0% or less, and the area fraction of the SiO ₂ phase is 5.0% or more and 10.0% or less.

Preferably, the average particle diameter D50 of the negative electrode material is 1.0 μm or more and 12.0 μm or less.

Another negative electrode material for an electricity storage device according to the present invention is composed of a large number of coated particles. Each coated particle has a core particle and a conductive coating layer that covers a part or all of the surface of the core particle. The material of the core particle is an alloy having a metal structure in which a Si phase is dispersed in a matrix of Si oxide. The matrix is
The sample includes (1) a _SiO2 phase and (2) _{a SiOX} phase obtained by replacing a part of O in the _SiO2 phase with Si. The crystallite size of the Si phase is 80 nm or less. In X-ray diffraction, the half-width A of the diffraction peak intensity I of the (101) plane, which is the main peak of _SiO2 , is 0.20° or more and 1.30° or less. In X-ray diffraction, the half-width B of the diffraction peak intensity II of the (111) plane, which is the main peak of Si, is 0.30° or more and 1.50° or less.

Preferably, the material of the coating layer is one or more selected from the group consisting of acetylene black, ketjen black, carbon nanofibers, and carbon nanotubes.

Preferably, the coating layer content is 10% by mass or less.

The method for producing the negative electrode material according to the present invention comprises the steps of:
The method includes (1) preparing a raw material whose material is Si and a raw material whose material is _SiO2 , and (2) milling these raw materials to replace some of the O in the _SiO2 phase with Si to form a _SiOX phase.

In an electricity storage device using the negative electrode material according to the present invention, the Si phase mainly contributes to the electricity storage capacity and the initial capacity reversibility rate, and the SiO ₂ phase and the SiO _X phase mainly contribute to the cycle life.

FIG. 1 is a TEM photograph showing a part of the metal structure of a negative electrode material according to one embodiment of the present invention. FIG. 2 is a TEM photograph showing another portion of the metal structure of FIG. FIG. 3 is a graph showing the results of powder X-ray diffraction of the negative electrode material of FIG.

The present invention will now be described in detail based on a preferred embodiment, with reference to the drawings as appropriate.

This embodiment is a negative electrode material for a lithium ion secondary battery. This lithium ion secondary battery is an example of an electricity storage device that involves the movement of lithium ions during charging and discharging. The negative electrode of a lithium ion secondary battery has a current collector, an active material, a conductive material, and a binder. The active material, conductive material, and binder are mixed together and attached to the current collector. The conductive material assists the conductivity of the active material. The binder fixes the active material particles to other active material particles. The binder further fixes the active material particles to the current collector. The negative electrode material according to the present invention can be used as this active material.

The negative electrode material consists of a large number of particles. The collection of particles is a powder. The material of these particles is an alloy.

FIG. 1 shows a TEM photograph of the metal structure of the negative electrode material. FIG. 1 shows a plurality of Si phases and a _SiO2 phase. FIG. 2 is a TEM photograph showing another part of the metal structure of FIG. 1. FIG. 2 shows a _SiOX phase. This metal structure has a plurality of Si phases, a _SiO2 phase, and a SiOX phase. The _SiO2 phase and _{the SiOX} phase are a matrix. In other words, this metal structure has a matrix which is a Si oxide. In this metal structure, the Si phase is dispersed in the matrix.

The alloy may contain other phases in addition to the Si, _SiO2 and _SiOX phases. Preferably, the alloy consists of only the Si, _SiO2 and _SiOX phases. Preferably, the composition of the alloy includes Si and O, with the balance being unavoidable impurities.

Each Si phase is fine. In this lithium ion battery, the Si phase is electrically connected to the electrolyte through the matrix. The Si phase is not electrically isolated. The Si phase reacts with lithium ions. This reaction forms a compound. A typical compound is Li ₂₂ Si _5. This reaction causes a large amount of lithium ions to be absorbed into the Si phase. The Si phase can increase the storage capacity of the negative electrode. This absorption causes the Si phase to expand. Lithium ions can be released from the Si phase. This release causes the Si phase to shrink.

When the SiO2 phase reacts with lithium ions, lithium silicate, an irreversible compound, is produced. When _{the SiO2 phase} reacts with lithium ions, a small amount of a reversible compound is also produced. This reaction causes the _SiO2 phase to expand. When the lithium ions leave the reversible compound, the _SiO2 phase contracts. The volume change rate of the _SiO2 phase during expansion and contraction is extremely small compared to that of the Si phase.

The SiO _X phase is derived from the SiO ₂ phase. The SiO _X phase is formed by substituting a part of the O atoms contained in the SiO ₂ phase with Si atoms. Therefore, the value X is less than 2.0. The preferred value X is 0.2 or more and 1.8 or less.

In the SiO _X phase, the Si introduced by substitution reacts with lithium ions. This reaction causes lithium ions to be absorbed in the negative electrode. The Si introduced by substitution can increase the charge storage capacity of the negative electrode.

When the Si introduced by substitution reacts with lithium ions, the SiO _X phase expands. When the lithium ions are released, the SiO _X phase contracts. The stress caused by the expansion or contraction is relieved by the O-Si-O bonds present around the Si introduced by substitution. This relaxation suppresses electrical isolation of Si. This relaxation suppresses the falling off of particles from the current collector. This negative electrode has an excellent cycle life.

The SiO _X phase has intermediate properties between the Si phase and the SiO ₂ phase. The volume change rate of the SiO _X phase during expansion and contraction is smaller than that of the Si phase and larger than that of the SiO ₂ phase. The difference between the volume change rate of the SiO _X phase and the volume change rate of the Si phase is not very large. In this negative electrode, the stress caused by the expansion or contraction of the Si phase is alleviated by the SiO _X phase and further alleviated by the SiO ₂ phase. This alleviation suppresses electrical isolation of the Si phase. This alleviation suppresses the falling off of particles from the current collector. This negative electrode has excellent cycle life.

In a conventional negative electrode made of a Si phase, the interface of the Si phase comes into contact with the electrolyte, and a decomposition reaction of the electrolyte occurs. This reaction forms an SEI. The SEI peels off due to the subsequent expansion and contraction of the Si phase. Furthermore, the SEI is formed again, and a new SEI is formed at the interface that appears due to cracks during expansion and contraction. In a conventional negative electrode, an excessive and non-uniform SEI is generated. The generation of this SEI causes an increase in the internal resistance of the battery and depletion of the electrolyte. In the negative electrode material of the present invention, the Si phase is dispersed in the matrix, so it does not come into contact with the electrolyte much. In this negative electrode, the formation of the SEI can be suppressed. This negative electrode has excellent cycle life.

When the _SiO2 phase reacts with lithium ions, lithium silicate is produced. This reaction is irreversible. This lithium silicate leads to a decrease in the initial capacity reversibility rate. The negative electrode material according to the present invention has a small amount of oxygen because the _SiOX phase is formed. Therefore, the production of lithium silicate is suppressed. This lithium ion secondary battery has an excellent initial capacity reversibility rate.

The area ratio of the Si phase is preferably 5.0% or more and 10.0% or less. A negative electrode with this area ratio of 5.0% or more has excellent storage capacity. From this viewpoint, the area ratio is more preferably 6.0% or more, and particularly preferably 7.0% or more. A negative electrode with this area ratio of 10.0% or less has small stress due to expansion and contraction. Therefore, this negative electrode has excellent cycle life. From this viewpoint, the area ratio is more preferably 9.0% or less, and particularly preferably 8.5% or less.

The area ratio of the SiO _X phase is preferably 80.0% or more and 90.0% or less. In a negative electrode with an area ratio within this range, cracks at the interface between the Si phase and other phases are suppressed, and cracks at the interface between the SiO ₂ phase and other phases are also suppressed. This negative electrode has excellent cycle life. From this viewpoint, this area ratio is more preferably 81.0% or more, and particularly preferably 82.0% or more. From this viewpoint, this area ratio is more preferably 89.0% or less, and particularly preferably 88.0% or less.

The area ratio of the _SiO2 phase is preferably 5.0% or more and 10.0% or less. In a negative electrode having this area ratio of 5.0% or more, the stress caused by the expansion or contraction of the Si phase is alleviated. Therefore, this negative electrode has excellent cycle life. From this viewpoint, the area ratio is more preferably 6.0% or more, and particularly preferably 7.0% or more. A negative electrode having this area ratio of 10.0% or less has excellent storage capacity. From this viewpoint, the area ratio is more preferably 9.0% or less, and particularly preferably 8.5% or less.

The area ratio of each phase is measured by TEM EDS analysis. Measurements are taken at 10 randomly selected locations on the negative electrode, and the average value is calculated.

Fig. 3 is a graph showing the results of powder X-ray diffraction of the negative electrode material of Fig. 1. In Fig. 3, the horizontal axis is 2θ (deg.) and the vertical axis is intensity (a.u.). Fig. 3 shows the diffraction peak intensity I of the (101) plane, which is the main peak of _SiO2 , and the diffraction peak intensity II of the (111) plane, which is the main peak of Si.

In this X-ray diffraction, CuKα radiation with a wavelength of 1.54059 angstroms is used as the X-ray source. Measurements are performed with 2θ in the range of 20° to 80°. This results in a diffraction spectrum. From this diffraction spectrum, diffraction peak intensity I and diffraction peak intensity II are selected.

The half width A of the diffraction peak intensity I preferably satisfies the following formula.
0.20≦A≦1.30
In other words, the half-width A is preferably 0.20° or more and 1.30° or less. In a negative electrode material with a half-width A of 0.20° or more, the crystallinity of the SiO ₂ phase is low. In this negative electrode, there are many SiO ₂ grain boundaries as diffusion paths for lithium ions. This negative electrode is excellent in storage capacity and initial capacity reversibility. From this viewpoint, the half-width A is more preferably 0.30° or more, and particularly preferably 0.35° or more. A negative electrode material with a half-width A of 1.30° or less can be obtained at low cost. From this viewpoint, the half-width A is more preferably 1.15° or less, and particularly preferably 1.05° or less. The half-width A is the width of the peak when the intensity is half the maximum value I of the peak in the X-ray diffraction chart.

The half width B of the diffraction peak intensity II preferably satisfies the following formula.
0.30≦B≦1.50
In other words, the half-width B is preferably 0.30° or more and 1.50° or less. In a negative electrode material having a half-width B of 0.30° or more, the crystallinity of the Si phase is low. In this negative electrode material, the Si phase is not easily broken even by the volume change during the absorption and release of lithium ions. This negative electrode material has excellent cycle life. From this viewpoint, the half-width B is more preferably 0.40° or more, and particularly preferably 0.50° or more. In a negative electrode material having a half-width B of 1.50° or less, the crystallinity of the Si phase is not too low. In this negative electrode material, the number of paths to the Si phase of lithium ions is not excessive. Therefore, even if the path is slightly blocked, the performance does not decrease significantly. Furthermore, in this negative electrode material, even if the Si crystal size varies to some extent, local electrode expansion is not likely to occur. This negative electrode has excellent cycle life. From these viewpoints, the half-width B is more preferably 1.40° or less, and particularly preferably 1.30° or less. The half-width B is the width of a peak when the intensity is half the maximum value II of the peak in an X-ray diffraction chart.

The crystallite size of the Si phase is preferably 80 nm or less. In a Si phase with a crystallite size of 80 nm or less, the stress caused by expansion during charging is small. This negative electrode has excellent cycle life. From this viewpoint, the crystallite size is more preferably 50 nm or less, and particularly preferably 30 nm or less. The crystallite size is preferably 3 nm or more. It is preferable that the crystallite size of all Si phases contained in the negative electrode material is within the above range.

The crystallite size of the Si phase can be confirmed by the above-mentioned powder X-ray diffraction. In the diffraction spectrum, the smaller the crystallite size, the broader the diffraction peak observed. The crystallite size can be calculated from the half-width of the peak obtained by powder X-ray diffraction analysis using the following Scherrer formula.
D = (K × λ) / (β × cosθ)
In this formula, D represents the crystallite size (Angstroms), K represents the Scherrer constant, λ represents the wavelength of the X-ray tube, β represents the broadening of the diffraction lines due to the crystallite size, and θ represents the diffraction angle.

The average particle diameter D50 of the powder of the negative electrode material is preferably 1.0 μm or more and 12.0 μm or less. In a negative electrode material having an average particle diameter D50 of 1.0 μm or more, the amount of SEI formed on the surface layer of the particles is suppressed. Therefore, the resistance is less likely to increase and the electrolyte is less likely to run short. This negative electrode material has excellent cycle life. From this viewpoint, the average particle diameter D50 is more preferably 1.2 μm or more, and particularly preferably 1.5 μm or more. In a negative electrode material having an average particle diameter D50 of 12.0 μm or less, cracks due to volume changes during absorption and release of lithium ions are suppressed. This negative electrode material has excellent cycle life. From this viewpoint, the average particle diameter D50 is more preferably 10.0 μm or less, and particularly preferably 8.0 μm or less.

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

An example of a method for producing a negative electrode material according to the present invention will now be described.
The method includes (1) a step of preparing a raw material whose material is Si and a raw material whose material is _SiO2 , and (2) a step of milling these raw materials to obtain a mixture.

The Si raw material to be milled can be produced by an atomizing method, a melting method, a reduction method, etc. The Si raw material can be in the form of powder, flakes, or lumps. The SiO ₂ raw material to be milled can be produced by a liquid phase synthesis method, a gas phase synthesis method, a melting method, etc. The SiO ₂ raw material can be in the form of powder, flakes, or lumps. These raw materials are put into a pot together with media. Examples of the media material include zirconia, SUS304, and SUJ2. Examples of the pot material include zirconia, SUS304, and SUJ2. The inside of the pot is filled with an inert gas, and the pot is sealed. The pot is placed on a milling device and stirred. Examples of the milling method include a ball mill, a bead mill, a planetary ball mill, an attritor, and a vibration ball mill. The crystallinity of the Si phase and the SiO ₂ phase is reduced by milling. The high energy of the milling forces some of the O in _SiO2 to be replaced by Si, resulting in a negative electrode material having a Si phase, a _SiO2 phase, and a _SiOX phase. Excessive milling leads to the disappearance of the _SiO2 phase. The milling conditions are adjusted so that an appropriate amount of the _SiOX phase is produced and an appropriate amount of the _SiO2 phase remains.

The negative electrode using the negative electrode material according to the present invention is excellent in storage capacity, cycle life, and initial capacity reversibility rate.
The present invention comprises (1) a current collector and (2) a large number of particles fixed to the surface of the current collector. The material of each particle is an alloy having a metal structure in which a plurality of Si phases are dispersed in a matrix of Si oxide. The matrix is
(2-1) _SiO2 phase and (2-2) _SiOX phase obtained by replacing some of the O in the _SiO2 phase with Si. In X-ray diffraction, the half-width A of the diffraction peak intensity I of the (101) plane, which is the main peak of _SiO2 , is 0.20° or more and 1.30° or less. In X-ray diffraction, the half-width B of the diffraction peak intensity II of the (111) plane, which is the main peak of Si, is 0.30° or more and 1.50° or less.

An electricity storage device using the negative electrode material according to the present invention is excellent in electricity storage capacity, cycle life, and initial capacity reversibility rate.
The battery includes (1) a positive electrode and (2) a negative electrode. The negative electrode includes
The current collector (2-1) and the multiple particles (2-2) are attached to the surface of the current collector. The material of each particle is an alloy having a metal structure in which multiple Si phases are dispersed in a matrix of Si oxide. The matrix is
The (2-2-1) _SiO2 phase and the (2-2-2) _SiOX phase are obtained by replacing some of the O in the _SiO2 phase with Si. In X-ray diffraction, the half-width A of the diffraction peak intensity I of the (101) plane, which is the main peak of _SiO2 , is 0.20° or more and 1.30° or less. In X-ray diffraction, the half-width B of the diffraction peak intensity II of the (111) plane, which is the main peak of Si, is 0.30° or more and 1.50° or less.

The particles described above (hereinafter also referred to as "core particles") may be covered with a coating layer. The core particle and the coating layer form a coated particle. The electrical conductivity of the coating layer is higher than that of the core particle. The coating layer is formed from a large number of fine powders. These fine powders adhere to the surface of the core particle. The coating layer covers a part or the entire surface of the core particle. A negative electrode material having a coating layer has excellent initial capacity reversibility and cycle life. This negative electrode material is particularly excellent in rate characteristics.

The coating layer prevents direct contact between the core particles and the electrolyte. This coating layer therefore prevents the reaction between Si and the electrolyte. In this negative electrode, the formation of a resistive coating is suppressed, and the depletion of the electrolyte is suppressed. This negative electrode has an excellent cycle life.

Examples of the material for the coating layer include carbon-based materials. Examples of preferred carbon-based materials include acetylene black, ketjen black, other carbon blacks, carbon nanofibers, carbon nanotubes, and amorphous carbon powders. Acetylene black, ketjen black, carbon nanofibers, and carbon nanotubes are particularly preferred. Two or more powders may be used in combination. There is substantially no reaction between the C contained in these carbon-based materials and the Si contained in the core particles.

It is preferable that 50% or more of the surface of the core particle is covered with the coating layer. This negative electrode material has excellent electrical conductivity. Furthermore, this negative electrode material suppresses the reaction between Si and the electrolyte. From this viewpoint, the coverage is more preferably 55% or more, and particularly preferably 60% or more.

From the viewpoint of storage capacity, the content of the coating layer in the coated particles is preferably 10% by mass or less, more preferably 8% by mass or less, and particularly preferably 7% by mass or less.

The effects of the present invention will be explained below by way of examples, but the present invention should not be interpreted in a restrictive manner based on the description of these examples.

[Example 1]
Si powder was obtained by atomization. _SiO2 powder was obtained by liquid phase synthesis. A predetermined amount of Si powder and a predetermined amount of _SiO2 powder were put into a pot made of SUS304, and the inside of the pot was filled with nitrogen gas. This pot was placed in a ball mill device and the powder was stirred to obtain the negative electrode material of Example 1. The properties of this negative electrode material are shown in Table 1 below.

[Examples 2 to 23 and Comparative Examples 24 to 31]
Except for changing the ratio of the two types of powders put into the pot and the stirring time, the negative electrode materials of Examples 2 to 23 and Comparative Examples 24 to 31 were obtained in the same manner as in Example 1. In some of the negative electrode materials, the surfaces of the core particles were covered with fine powder of a carbon-based material to form a coating layer.

[evaluation]
A negative electrode material, a conductive material (acetylene black or ketjen black), a binder (polyimide or polyvinylidene fluoride), and a dispersion liquid (N-methylpyrrolidone) were mixed to obtain a slurry. This slurry was applied onto a copper foil current collector. This slurry was dried under reduced pressure in a vacuum dryer. The drying temperature was 200°C or higher when polyimide was the binder, and 160°C or higher when polyvinylidene fluoride was the binder. The solvent was evaporated by this drying, and an active material layer was obtained. This active material layer and copper foil were pressed with a roll. This active material layer and copper foil were punched into a shape suitable for a coin-shaped cell to obtain a negative electrode.

A mixed solvent of ethylene carbonate and dimethyl carbonate was prepared as the electrolyte. The mass ratio of the two was 3:7. Furthermore, lithium hexafluorophosphate (LiPF ₆ ) was prepared as the supporting electrolyte. The amount of this supporting electrolyte was 1 mole per 1 liter of the electrolyte. This supporting electrolyte was dissolved in the electrolyte.

A separator and positive electrode of a shape suitable for a coin-type cell were prepared. The positive electrode was punched out from lithium foil. The separator was immersed in electrolyte under reduced pressure and left for 5 hours to allow the electrolyte to fully permeate the separator.

The negative electrode, separator, and positive electrode were assembled into a coin-type cell. The coin-type cell was filled with electrolyte. Note that the electrolyte must be handled in an inert atmosphere with a controlled dew point. Therefore, the cell was assembled in an inert atmosphere glove box.

In a coin-type cell, charging was performed at a temperature of 25°C and under conditions of a constant current and constant voltage of 0.3 C until the potential difference between the positive and negative electrodes reached 0.010 V. Then, discharging was performed under a constant current condition of 0.3 C until the potential difference reached 1.5 V. The initial efficiency of this charging and discharging (initial discharge capacity/initial charge capacity x 100) was measured. This charging and discharging was repeated for 50 cycles. The discharge capacity after the 50 cycles was measured. The results are shown in Tables 1 and 2 below.

As shown in Tables 1 and 2, the negative electrode materials of each embodiment achieve an initial efficiency of 75.0% or more and an initial discharge capacity of 1,400 mAh/g or more. Furthermore, the discharge capacity after 50 cycles of the negative electrode materials of each embodiment is greater than the initial discharge capacity of 372 mAh/g of the negative electrode material made of graphite. From these evaluation results, the superiority of the present invention is clear.

The negative electrode described above can be applied not only to lithium ion secondary batteries, but also to various power storage devices such as all-solid-state lithium ion secondary batteries and hybrid capacitors.

Claims (6)

A negative electrode material for an electricity storage device, comprising a large number of particles,
Each particle has a structure in which a plurality of Si phases are dispersed in a matrix of Si oxide,
The above matrix is
(1) The _SiO2 phase and (2) the _SiOX phase obtained by replacing some of the O in the _SiO2 phase with Si,
The crystallite size of the Si phase is 80 nm or less,
In X-ray diffraction, the half-value width A of the diffraction peak intensity I of the (101) plane, which is the main peak of _SiO2 , is 0.20° or more and 1.30° or less;
A negative electrode material in which the half-value width B of the diffraction peak intensity II of the (111) plane, which is the main peak of Si in X-ray diffraction, is 0.30° or more and 1.50° or less. 2. The negative electrode material according to claim 1, wherein the area ratio of the Si phase in the particles is 5.0% or more and 10.0% or less, the area ratio of the SiO _X phase is 80.0% or more and 90.0% or less, and the area ratio of the SiO ₂ phase is 5.0% or more and 10.0% or less. The negative electrode material according to claim 1 or 2, whose average particle diameter D50 is 1.0 μm or more and 12.0 μm or less. A negative electrode material for an electricity storage device, comprising a large number of coated particles,
Each of the coated particles has a core particle and a conductive coating layer that covers a part or all of the surface of the core particle,
the core particle has a structure in which a Si phase is dispersed in a matrix of Si oxide,
The above matrix is
(1) The _SiO2 phase and (2) the _SiOX phase obtained by replacing some of the O in the _SiO2 phase with Si,
The crystallite size of the Si phase is 80 nm or less,
In X-ray diffraction, the half-value width A of the diffraction peak intensity I of the (101) plane, which is the main peak of _SiO2 , is 0.20° or more and 1.30° or less;
A negative electrode material in which the half-value width B of the diffraction peak intensity II of the (111) plane, which is the main peak of Si in X-ray diffraction, is 0.30° or more and 1.50° or less. The negative electrode material according to claim 4, wherein the material of the coating layer is one or more selected from the group consisting of acetylene black, ketjen black, carbon nanofibers, and carbon nanotubes. The negative electrode material according to claim 4 or 5, wherein the coating layer has a content of 10% by mass or less.

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