WO2022202357A1

WO2022202357A1 - Active material and method for producing same

Info

Publication number: WO2022202357A1
Application number: PCT/JP2022/010555
Authority: WO
Inventors: 大輔鷲田
Original assignee: 三井金属鉱業株式会社
Priority date: 2021-03-23
Filing date: 2022-03-10
Publication date: 2022-09-29
Also published as: JPWO2022202357A1

Abstract

This active material comprises a silicon-based material containing Si and B. The ratio P2/P1 of the intensity P2 of the diffraction peak observed in the range of 2θ = 30º-45º with respect to the intensity P1 of the diffraction peak observed in the range 2θ = 27.5º-29.5º in an XRD pattern is 0.1 or less. The active material has a cubic crystal structure with a lattice constant of 0.5390-0.5420 nm. The ratio D₅₀/CS of the volume-cumulative particle size D₅₀ to the crystallite size CS in the active material is 8 or more.

Description

Active material and manufacturing method thereof

The present invention relates to an active material that can be used for a negative electrode and a method for producing the same. The present invention also relates to a battery containing the active material.

Carbonaceous materials are mainly used as negative electrode active materials for lithium-ion secondary batteries. However, since the carbonaceous material has a low theoretical discharge capacity, it is difficult to cope with the increase in power consumption due to the multi-functionalization of small electric and electronic devices, and the use as a vehicle battery. Therefore, as a negative electrode active material to replace the carbonaceous material, a material containing silicon, which has a higher capacity than the carbonaceous material, has been proposed.

For example, Patent Document 1 described below is known as a conventional technology related to silicon-containing active materials. This document proposes an electrode material composed of solid-state alloy particles in which microcrystalline or amorphous elements other than silicon are dispersed in microcrystalline silicon or amorphous silicon. there is The document describes that this electrode material has low resistance, high charge-discharge efficiency, and high capacity.

US2006/040182A1

However, the improvement of battery performance is related not only to charge/discharge efficiency and capacity, but also to various factors such as cycle characteristics, and the electrode material described in Patent Document 1 cannot provide sufficiently satisfactory battery performance. Accordingly, an object of the present invention is to provide an active material having good battery performance.

The present invention provides an active material made of a silicon-based material containing silicon (Si) element and boron (B) element,
In the X-ray diffraction pattern measured by an X-ray diffraction device (XRD) using Cukα1 rays, the diffraction peak intensity P1 observed in the range of 2θ = 27.5 ° or more and 29.5 ° or less is 2θ = 30 The ratio P2/P1 of the intensity P2 of the diffraction peaks observed in the range of 45° or less is 0.1 or less,
Having a cubic crystal structure with a lattice constant of 0.5390 nm or more and 0.5420 nm or less,
An active material having a ratio D ₅₀ /CS of a volume cumulative particle size D ₅₀ in a cumulative volume of 50% by volume measured by a laser diffraction scattering particle size distribution measurement method to a crystallite size CS calculated from the X-ray diffraction pattern is 8 or more. It provides

The present invention also provides a method for producing an active material made of a silicon-based material containing silicon (Si) element and boron (B) element,
A step of applying an external force to the raw material powder, which is an aggregate of particles containing the silicon (Si) element and the boron (B) element,
In the above step, an external force is applied to the raw material powder so that the particles are pulverized and the fine particles generated by the pulverization are simultaneously bonded.

1 is a diagram showing an X-ray diffraction pattern of the negative electrode active material obtained in Example 1. FIG. 2 is a diagram showing an X-ray diffraction pattern of the negative electrode active material obtained in Comparative Example 1. FIG. 3 is a diagram showing a Raman spectrum of the negative electrode active material obtained in Example 1. FIG. 4 is a diagram showing the Raman spectrum of the negative electrode active material obtained in Example 2. FIG. 5 is a diagram showing the Raman spectrum of the negative electrode active material obtained in Example 3. FIG. 6 is a diagram showing a Raman spectrum of the negative electrode active material obtained in Comparative Example 2. FIG. 7 is a diagram showing a Raman spectrum of the negative electrode active material obtained in Comparative Example 3. FIG. 8 is a diagram showing a Raman spectrum of the negative electrode active material obtained in Comparative Example 4. FIG.

The present invention will be described below based on its preferred embodiments. The present invention relates to active materials. The active material of the present invention consists of a silicon-based material. "Composed of a silicon-based material" means that the active material of the present invention is a single-phase material containing silicon (Si) and other elements. As another element, boron (B) element is used in the present invention. The active material of the present invention is preferably a single-phase material containing silicon and boron elements. Silicon-containing alloys containing titanium and iron (such as TiSi ₂ and FeSi), which are conventionally known active materials, and active materials containing pure silicon do not have a single phase. different. Similarly, a mixture of pure silicon and pure boron, for example, is not a single phase, and thus differs from the active material of the present invention.

In the active material of the present invention, diffraction peaks are observed in the range of 2θ = 27.5° or more and 29.5° or less in an X-ray diffraction pattern measured by an X-ray diffraction device (XRD) using Cukα1 rays. is preferred. In particular, the fact that the diffraction peak observed in this angle range is derived from a boron-silicon alloy, which is a compound of silicon and boron, can suppress the volume change of the active material caused by the absorption and release of lithium ions. preferred from

Because boron-silicon alloys have electronic conductivity, they have better reactivity with lithium ions than pure silicon. As a result, unlike other silicon-containing alloys, the boron-silicon alloy can absorb and release lithium ions, and the boron-silicon alloy can be used alone as an active material. Boron-silicon alloys have better reactivity with lithium ions than pure silicon, so lithium occlusion and desorption tend to occur uniformly within the particles, and expansion due to lithium ions occlusion is uniform. likely to occur. As a result, when the active material of the present invention is used together with, for example, a solid electrolyte, the stress generated in the electrode can be made uniform, and as a result, there is the advantage that the life of the electrode is extended. Further, when the active material of the present invention is used together with an electrolytic solution, there is an advantage that the active material itself is suppressed from pulverizing, and the reaction with the electrolytic solution caused by the generation of a highly reactive new surface can be suppressed.

By the way, silicon-containing alloys other than boron-silicon alloys (such as TiSi ₂ and FeSi) do not absorb and release lithium ions, so they cannot be used alone as active materials and must be used together with pure silicon. Even if a silicon-containing alloy other than a boron-silicon alloy is used in combination with pure silicon, the expansion of pure silicon itself is not alleviated at all. Moreover, when the proportion of pure silicon in the entire active material is relatively low, the charge/discharge capacity tends to be small.
On the other hand, the active material of the present invention has an X-ray diffraction pattern measured by XRD using Cukα1 rays, in which the diffraction peak intensity P1 , the ratio P2/P1 of the intensity P2 of the diffraction peak observed in the range of 2θ=30° to 45° is 0.1 or less. Here, the diffraction peaks observed in the range of 2θ=30° or more and 45° or less are presumed to be derived from silicon-containing alloys other than boron-silicon alloys. In the present invention, the above problem can be solved by setting P2/P1 to 0.1 or less. Specifically, it is possible to suppress the volume change of the active material caused by the intercalation and deintercalation of lithium ions. From the viewpoint of making the volume change suppressing effect even more remarkable, the P2/P1 is, for example, more preferably 0.05 or less, and even more preferably 0.02 or less.

Examples of silicon-containing alloys other than boron-silicon alloys include titanium silicide (TiSi ₂ ), manganese silicide (MnSi ₂ ), niobium silicide (NbSi ₂ ), aluminum silicide, tin silicide, and carbon silicide.

The active material of the present invention has a crystal structure similar to that of pure silicon. The stable phase of pure silicon at room temperature and pressure is cubic, and the active material of the present invention also has a stable phase of cubic at room temperature and pressure. Since the active material of the present invention contains boron in addition to silicon, its lattice constant is smaller than that of pure silicon (0.543 nm). As a result of studies by the present inventors, the lattice constant of the active material of the present invention is, for example, preferably 0.5390 nm or more, more preferably 0.5395 nm or more, and even more preferably 0.5400 nm or more. preferable. On the other hand, the lattice constant is, for example, preferably 0.5420 nm or less, more preferably 0.5415 nm or less, and even more preferably 0.5410 nm or less. As a result, it is possible to effectively suppress the volume change of the active material caused by the absorption and release of lithium ions while exhibiting charge/discharge capacity equivalent to that of pure silicon.

The content of element B in the active material of the present invention is preferably, for example, 1 atomic % or more. On the other hand, the content is, for example, preferably 5 at % or less, more preferably 4 at % or less, and even more preferably 3 at % or less. When the content of the B element is within the above range, the above P2/P1 can be set within the desired range, and the lattice constant can be set within the desired range.

The active material of the present invention may contain a carbon (C) element. The content of C element in the active material is, for example, preferably less than 5% by mass, particularly preferably less than 3% by mass. This is because the decrease in capacity can be suppressed.

The content of Si element in the active material of the present invention is, for example, preferably 80% by mass or more, more preferably 85% by mass or more, and even more preferably 90% by mass or more. Moreover, the active material of the present invention is preferably a single phase composed of Si element, B element and the balance of unavoidable impurities. Here, the unavoidable impurities are, for example, unavoidable impurities derived from raw materials. Examples of unavoidable impurities derived from raw materials include metalloid elements and metal elements other than Si element and B element. The content of the remaining unavoidable impurities in the active material of the present invention is, for example, preferably less than 2% by mass, more preferably less than 1% by mass, and more preferably less than 0.5% by mass. This is because the decrease in capacity can be suppressed.

As described above, in pure silicon, the stable phase at normal temperature and pressure is a cubic crystal, and it has the property of easily absorbing and releasing lithium from a certain orientation in the cubic crystal. Due to this, pure silicon tends to expand anisotropically due to absorption of lithium ions, which is one of the factors that deteriorate the cycle characteristics of the battery. As a result of investigations by the present inventors from this point of view, it was found that low crystallization of the active material of the present invention made of a silicon-based material containing silicon and boron is effective from the viewpoint of suppressing anisotropic expansion. did. Specifically, the low crystallization of the active material of the present invention makes it difficult for lithium to be absorbed from a specific crystal orientation. In other words, the absorption of lithium ions tends to occur isotropically. As a result, the expansion caused by the absorption of lithium ions also tends to occur isotropically. As a result, the cycle characteristics of the battery are less likely to deteriorate. As described above, the active material of the present invention preferably has low crystallinity from the viewpoint of isotropically causing expansion due to absorption of lithium ions.

The degree of crystallinity of the active material can be evaluated based on the relationship between crystallite size and particle size. In the present invention, the crystallite size CS of the active material calculated from the X-ray diffraction pattern measured by XRD using CuKα1 rays is measured by a laser diffraction scattering particle size distribution measurement method, and the active material at a cumulative volume of 50% by volume The ratio D ₅₀ /CS of the volume cumulative particle size D ₅₀ of is 8 or more, for example, 9 or more is more preferable, and 10 or more is even more preferable. On the other hand, D ₅₀ /CS is preferably 30 or less. When D ₅₀ /CS is within the above range, for example, in the case of a battery using an electrolytic solution, many new surfaces are likely to occur on the particles, resulting in a resistance layer that hinders smooth exchange of lithium ions. However, it is possible to suppress the occurrence of the problem that the particles are likely to be formed at the interface between the particles and the electrolytic solution. Further, in the case of a battery using a solid electrolyte, by reducing the particle size of the active material particles, the degree of contact between the particles and the solid electrolyte particles is reduced, thereby hindering the conduction of lithium ions. It is possible to suppress the occurrence of problems such as
In order to make the D ₅₀ /CS value of the active material equal to or higher than the above value, the active material may be produced, for example, by the method described later. However, it is not limited to this manufacturing method.

The particle diameter _D50 of the active material particles is, for example, preferably 5 μm or less, more preferably 4 μm or less, and even more preferably 3 μm or less. By setting the particle size _D50 in this manner, the effect of volume change when the active material absorbs and releases lithium ions can be reduced. Moreover, the reactivity between the active material and the electrolytic solution can be enhanced, and sufficient contact with the solid electrolyte can be ensured.
Further, the particle diameter _D50 of the active material is, for example, preferably 0.1 μm or more, more preferably 0.2 μm or more, still more preferably 0.3 μm or more, and 0.4 μm or more. is even more preferred. By setting the particle size _D50 of the active material in this way, it is possible to suppress an excessive increase in the number of contact points with the solid electrolyte due to an excessive increase in the specific surface area of the active material, thereby increasing the contact resistance. can be suppressed.
The crystallite size CS of the silicon-based material in the active material is preferably, for example, 10 nm or more from the viewpoint of reducing the crystallinity of the silicon-based material. On the other hand, the crystallite size CS is, for example, preferably 100 nm or less, more preferably 80 nm or less, even more preferably 70 nm or less, and even more preferably 60 nm or less.
The method for measuring the particle size _D50 of the active material and the crystallite size CS of the silicon-based material will be described in the examples below.

In the present invention, due to the low crystallinity of the silicon-based material in the active material, when Raman spectroscopic analysis is performed on the active material, a characteristic peak is observed. As a result of examination, it became clear. Specifically, the active material of the present invention has a peak in a wavenumber range of 450 cm ^-1 to 500 cm ^-1 in a Raman spectrum obtained by measuring a wavenumber range of 400 cm ^{-1 to 600 cm -1} ^by Raman spectroscopy. Observation is preferred. An active material having a peak in this wavenumber range has the advantage that the silicon-based material has low crystallinity, and expansion due to absorption of lithium ions tends to occur isotropically. From the viewpoint of making this advantage even more remarkable, it is more preferable that the active material of the present invention has a peak observed in the wave number range of 455 cm ^{−1 to 500 cm −1} ⁱⁿ the Raman spectrum, and 455 cm ⁻¹ to 495 cm It is more preferable that a peak is observed in the wavenumber range of ^-1 or less.
Depending on the type of active material, a plurality of peaks may be observed when the wave number range of 400 cm ⁻¹ to 600 cm ⁻¹ is measured by Raman spectroscopy. In that case, the highest intensity peak is preferably observed in the wavenumber range of 450 cm ⁻¹ to 500 cm ⁻¹ .
Moreover, it is not prevented that a plurality of peaks are observed in the wave number range of 450 cm ⁻¹ to 500 cm ⁻¹ .
A method for measuring the Raman spectrum will be described later in Examples.

In the active material of the present invention, controlling the degree of oxidation on the surface of the particles also contributes to improving the performance of batteries containing the active material. In particular, it is advantageous to reduce the degree of oxidation on the surface of the particles of active material. When the degree of oxidation on the surface of a particle is expressed as a value normalized by the specific surface area of the particle, the active material of the present invention has a ratio of the content of oxygen (O) element to the specific surface area SSA of the particle, O/SSA is, for example, 0.1 (mass%/(m ² /g)) or more. On the other hand, O/SSA is, for example, preferably 0.3 (mass%/(m ² /g)) or less, more preferably 0.2 (mass%/(m ² /g)) or less. .
In order to set the value of O/SSA in the active material within the above range, the active material may be produced by, for example, the above method. However, it is not limited to this manufacturing method.

The value of the specific surface area SSA in the active material is preferably, for example, 3 m ² /g or more, more preferably 8 m ² /g or more, from the viewpoint of setting the particle size of the active material particles within an appropriate range. , 15 m ² /g or more. On the other hand, the specific surface area SSA is preferably 50 m ² /g or less, for example.
In addition, the content of oxygen element in the active material is preferably 7 mass% or less, for example, from the viewpoint of suppressing deterioration of charge-discharge capacity and charge-discharge efficiency and improving battery performance including the active material, and 6 mass%. is more preferably 5 mass % or less. The smaller the oxygen element content, the better.
A method for measuring the specific surface area SSA of the active material and the content of the oxygen element will be described in Examples described later.

Next, a suitable method for producing the active material of the present invention will be described. However, the method described below is an example of the method for producing the active material of the present invention, and the method for producing the active material of the present invention is not limited to the method described below.

First, silicon and boron, which are raw materials for the active material, are prepared. A molten metal is obtained by melting silicon and boron in a crucible. From this molten metal, a silicon solid solution, that is, raw material powder, which is an aggregate of particles of a silicon-based material containing elemental silicon and elemental boron, is produced. In order to produce raw material powder in this step, for example, an atomizing method can be used. Alternatively, a method of pulverizing a ribbon obtained using a roll casting method can be used.
In the raw material powder thus obtained, the silicon-based material has high crystallinity. Therefore, an operation is performed to reduce the crystallinity of the silicon-based material in this raw material powder. Such an operation includes, for example, an operation of applying a high-energy external force to pulverize the particles constituting the raw material powder of the silicon-based material. Of course, if the silicon-based material is simply pulverized, the crystallinity of the silicon-based material is lowered, but the particle size of the particles is also reduced. Therefore, in the present production method, it is advantageous to apply an external force to the raw material powder so that the pulverization of the particles and the bonding of the fine particles generated by the pulverization occur simultaneously. By applying such an external force, the crystallite size and grain size of the silicon-based material can be set within desired ranges.

For the purpose of applying the above-described external force to the raw material powder, in the present production method, for example, a pulverizer equipped with rotating blades is used in the reaction vessel, and the grinding media to be introduced into the reaction vessel include, for example, grains of the raw material powder. It is preferable to use those having a particle size of 1500 to 4000 times the diameter _D50 . The diameter of the grinding media is, for example, preferably 4 mm or more and 10 mm or less, more preferably 5 mm or more and 8 mm or less, and even more preferably 5 mm or more and 7 mm or less.
Materials for the grinding media include, for example, alumina, zirconia, silicon nitride, and tungsten carbide.
The ratio of the grinding media to the raw material powder is 2 parts by mass or more and 15 parts by mass or less, particularly 5 parts by mass or more and 10 parts by mass or less, especially 6 parts by mass or more and 8 parts by mass or less for 100 parts by mass of the grinding media. Setting is preferable from the viewpoint of efficiently reducing the crystallization of the silicon-based material.

From the viewpoint of improving battery performance, it is preferable to perform the pulverization of the raw material powder using the pulverizer in a non-oxidizing atmosphere. Examples of non-oxidizing atmospheres include inert gas atmospheres such as argon and nitrogen, and reducing atmospheres containing hydrogen below the explosive concentration limit.

After the pulverization of the raw material powder is completed by the above procedure, it is preferable to bring the powder obtained by pulverization into contact with the atmosphere gradually from the viewpoint of suppressing excessive oxidation of the active material particles. Since the oxidation reaction caused by the contact of the powder obtained by pulverization with oxygen is an exothermic reaction, when the powder is brought into contact with the air for a very short time, the oxidation reaction rapidly generates heat, and the heat generated causes the oxidation reaction. is further accelerated, and the powder is excessively oxidized. Therefore, in the present production method, the powder obtained by pulverization is brought into contact with the atmosphere gradually to suppress the rapid oxidation reaction and to prevent the powder surface from being oxidized as much as possible. By performing such an operation, it becomes possible to keep the oxygen content per specific surface area SSA in the particles of the active material at a low level.

Gradually bringing the powder obtained by pulverization into contact with the atmosphere means that when the non-oxidizing atmosphere is returned to the atmosphere, the amount of air introduced is limited, and the atmosphere is returned to the atmosphere in several steps. , refers to contacting both by limiting the amount of air introduced per unit time. Specifically, it is preferable that the obtained powder is brought into contact with the air while maintaining a temperature of 60° C. or less. Oxidation can be suppressed by setting the temperature of the obtained powder to 60° C. or lower when returning to the air atmosphere.

When the powder obtained by pulverization is brought into contact with the air, it is preferable to contact the air with a dew point of preferably -10°C or less from the viewpoint of minimizing oxidation of the powder surface. From this point of view, the dew point of the atmosphere is preferably −20° C. or less, more preferably −40° C. or less.

The active material of the present invention thus obtained can be used alone. Alternatively, the active material of the present invention can be used in combination with other active materials or substances other than active materials. For example, the active material of the present invention can be used in combination with Si oxide. Examples of Si oxide include SiOA (0<a≦2). Specifically, SiO, SiO ₂ and the like can be mentioned.

The active material of the present invention can be used, for example, in the form of an electrode mixture containing the active material and a solid electrolyte. The active material of the present invention can be suitably used as a negative electrode active material for batteries, particularly solid batteries, especially solid lithium batteries. However, there is nothing to prevent the application of the active material of the present invention to a battery having an electrolytic solution.
Preferably, the battery has a positive electrode layer, a negative electrode layer, and an electrolyte layer positioned between the positive electrode layer and the negative electrode layer, the negative electrode layer containing the active material of the present invention. The battery may be a primary battery or a secondary battery, preferably a secondary battery, especially a solid lithium secondary battery. For example, the active material of the present invention can be suitably used as a negative electrode active material of a solid battery containing a sulfide solid electrolyte as the solid electrolyte. Examples of the shape of the battery include laminate type, cylindrical type, square type, coin type, and the like.

A solid battery preferably has a positive electrode layer, a negative electrode layer, and a solid electrolyte layer positioned therebetween, and the negative electrode layer preferably contains the active material of the present invention described above. A solid battery can be produced, for example, by laminating a positive electrode layer, a solid electrolyte layer, and a negative electrode layer in this order and then press-molding them. "Solid battery" means a solid battery that does not contain any liquid or gel material as an electrolyte, or a solid battery that contains, for example, 50% by mass or less, 30% by mass or less, or 10% by mass or less of liquid or gel material as an electrolyte. Aspects are also included.

The solid electrolyte can be similar to solid electrolytes used in general solid batteries. Examples include sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, halide solid electrolytes, etc. Among them, sulfide solid electrolytes containing sulfur (S) are preferred. The sulfide solid electrolyte may contain, for example, Li and S and have lithium ion conductivity. The sulfide solid electrolyte may be any of crystalline material, glass ceramics, and glass. The sulfide solid electrolyte may have an aldirodite crystal structure. Examples of such sulfide solid electrolytes include Li ₂ SP ₂ S ₅ , Li ₂ SP ₂ S ₅ -LiX ("X" represents one or more halogen elements), Li ₂ S- _P2S5 _- _P2O5 _, _Li2S _- _Li3PO4 _- _P2S5 _, _Li3PS4 _, _Li4P2S6 _, _Li10GeP2S12 _, _Li3.25Ge0 _. _{_} _25P0.75S4 , _Li7P3S11 _, _{Li3.25P0.95S4} _{, LiaPSbXc} ₍ _X _is at least one _halogen element, _a is 3.0 _or more and ₆ represents a number of 0.0 or less, b represents a number of 3.5 or more and 4.8 or less, and c represents a number of 0.1 or more and 3.0 or less. In addition, for example, sulfide solid electrolytes described in International Publication No. 2013/099834 and International Publication No. 2015/001818 are included.

The present invention will be described in more detail below with reference to examples. However, the scope of the invention is not limited to such examples.

[Example 1]
A silicon ingot and a boron ingot were heated and melted so that the composition was B _0.02 Si _0.98 , and the melt heated to 1700° C. was rapidly cooled using a liquid rapid solidification apparatus (single roll type). , a quenched ribbon alloy was obtained. The obtained quenched ribbon alloy is further subjected to particle size adjustment using a dry pulverizer under a nitrogen atmosphere (less than 1 vol% of air, the remainder being vaporized nitrogen from liquid nitrogen (purity of 99.999 vol% or more)) to obtain an alloy powder. got

The obtained raw material powder was subjected to a low crystallization treatment using a nanoparticle surface modification device (product name: “Nanomec Reactor CMJ-20SS” manufactured by Techno-I Co., Ltd.). Specifically, 20 kg of stabilized zirconia beads and 1,500 g of the raw material powder were placed in a container having a capacity of 22.4 L, and the treatment was performed at 800 rpm for 135 minutes and at 400 rpm for 45 minutes. At this time, the inside of the surface modification apparatus was set to an argon atmosphere. After the low crystallization treatment, air having a dew point of −60° C. was gradually introduced into the surface modification apparatus, and the pulverized powder was gradually oxidized while maintaining the temperature at 60° C. or less, and then taken out. This powder was then classified with a 75 μm mesh screen.
The powder obtained by classification was pulverized using a wet pulverizer to adjust the particle size, and then classified with a sieve having an opening of 45 μm. Chemical analysis of the obtained powder revealed that the boron content was 0.66% by mass.

[Example 2]
In Example 1, _D50 was adjusted by shortening the pulverization time when pulverizing using a wet pulverizer. A negative electrode active material was obtained in the same manner as in Example 1 except for this.

[Example 3]
The pulverization time when pulverizing using a wet pulverizer was made shorter than in Example 2. A negative electrode active material was obtained in the same manner as in Example 1 except for this.

[Comparative Example 1]
In this comparative example, an active material made of pure silicon that is not low-crystallized was manufactured.
A molten metal of 1700° C. obtained by heating and melting a silicon ingot was rapidly cooled using a liquid rapid cooling and solidification apparatus (single roll type) to obtain a rapidly solidified ribbon alloy. The obtained quenched ribbon alloy is subjected to particle size adjustment using a dry pulverizer under a nitrogen atmosphere (less than 1% by volume of air, the remainder being vaporized nitrogen from liquid nitrogen (purity of 99.999% by volume or more)), and then jetted. The particle size was adjusted using a mill pulverizer to obtain a silicon powder. This silicon powder was classified with a 25 μm mesh screen without being subjected to a low crystallization treatment to obtain a negative electrode active material composed of pure silicon.

[Comparative Example 2]
In this comparative example, an active material composed of pure silicon that is not low-crystallized was manufactured.
In Comparative Example 1, instead of the pulverization by the jet mill pulverizer, the particle size was adjusted using a wet pulverizer. A negative electrode active material composed of pure silicon was obtained in the same manner as in Comparative Example 1 except for this.

[Comparative Example 3]
In this comparative example, an active material composed of low-crystallized pure silicon was produced.
In Comparative Example 2, after low crystallization treatment was performed using a nanoparticle surface modification device (product name “Nanomek Reactor CMJ-20SS” Chuko Seiki Co., Ltd.), the particle size was adjusted using a wet pulverizer. A negative electrode active material composed of pure silicon was obtained in the same manner as in Example 2. Specifically, in the low crystallization treatment, 20 kg of stabilized zirconia beads and 1500 g of raw material powder were placed in a container with a capacity of 22.4 L, and treated at 800 rpm for 135 minutes and 400 rpm for 45 minutes. At this time, the inside of the surface modification apparatus was set to an argon atmosphere. After the low crystallization treatment, air having a dew point of −60° C. was gradually introduced into the surface modification apparatus, and the pulverized powder was slowly oxidized and taken out.

[Comparative Example 4]
In this comparative example, an active material made of a silicon-based material with low crystallinity was produced.
A silicon ingot and a boron ingot were heated and melted so as to have a composition of B _0.02 Si _0.98 , and rapidly cooled using the same apparatus as in Example 1 to obtain a quenched ribbon alloy. Further, the particle size was adjusted using a dry pulverizer under a nitrogen atmosphere (less than 1 vol% in air, the remainder being vaporized nitrogen from liquid nitrogen (purity of 99.999 vol% or more)) to obtain a raw material powder. This raw material powder was not subjected to a low crystallization treatment, but was subjected to particle size adjustment using a wet pulverizer and classified with a 45 μm mesh screen to obtain a negative electrode active material containing silicon and boron.

〔evaluation〕
The negative electrode active materials obtained in Examples and Comparative Examples were subjected to XRD measurement by the following method to measure peak intensities P1 and P2, lattice constants, and crystallite sizes CS. XRD patterns of the negative electrode active materials obtained in Example 1 and Comparative Example 1 are shown in FIGS.
Also, the particle size D ₅₀ , the specific surface area SSA and the oxygen element content were measured by the following methods.
Furthermore, the Raman spectrum was measured by the following method, and the peak position was identified. Raman spectra of the negative electrode active materials obtained in Examples 1-3 and Comparative Examples 2-4 are shown in FIGS. 3-8.
Further, batteries were produced using the negative electrode active materials obtained in Examples and Comparative Examples, and the charge capacity, discharge capacity, efficiency and cycle characteristics (capacity retention rate) of the batteries were measured by the following methods.
These results are shown in Table 1 below.

[XRD measurement]
Using "Ultima IV" manufactured by Rigaku Corporation, measurement was performed under the following conditions to obtain an XRD pattern. Based on the obtained XRD pattern, the peak intensity ratio P2/P1 was calculated using those displayed in the peak list as peaks. The crystallite size CS and the lattice constant were determined by checking the diffraction peak position and the number of diffraction peaks in comparison with the card information of ICDD card number: 00-005-0565 (chemical formula: Si). The crystallite size was calculated by analyzing using the Hall method.
・ Radiation source: CuKα1 (line focus)
・Operation axis: 2θ/θ, measurement method: continuous, counting unit: cps
・Start angle: 15.0°, End angle: 120.0°, Number of times of accumulation: 1 ・Sampling width: 0.01°, Scan speed: 1.0°/min
・Voltage: 40 kV, current: 40 mA
・Divergence slit: 0.2 mm, vertical divergence limiting slit: 10 mm
・Scattering slit: open, light receiving slit: open ・Offset angle: 0°
・Goniometer radius: 285mm, optical system: focusing method ・Attachment: ASC-48
・Slit: D/teX Ultra slit ・Detector: D/teX Ultra
・Incident Monochrome: CBO
・Ni-Kβ filter: None ・Rotational speed: 50 rpm

[Particle size D ₅₀ ]
Using an automatic sample feeder for a laser diffraction particle size distribution measuring device ("Microtrac SDC" manufactured by Microtrac Bell Co., Ltd.), powder of the negative electrode active material was put into ion-exchanged water to which 20 vol% ethanol was added, and ultrasonic wave was applied. Set it in a homogenizer (Homogenizer US-150E manufactured by Nippon Seiki Seisakusho Co., Ltd., using a tip of φ20), adjust the dial level so that AMPLITUDE is 80%, irradiate ultrasonic waves for 5 minutes, and immerse the sample in the liquid. to obtain a dispersion. Next, the particle size distribution was measured using a laser diffraction particle size distribution measuring machine "MT3000II" manufactured by Microtrack Bell Co., Ltd., and the volume cumulative particle size _D50 was measured from the obtained volume-based particle size distribution chart.
In addition, the water-soluble solvent at the time of measurement is passed through a 60 μm filter, the “solvent refractive index” is 1.33, the particle permeability condition is “reflection”, the measurement range is 0.221 μm or more and 2000 μm or less, and the measurement time is 10 seconds. and

[Specific surface area SSA]
The specific surface area SSA of the negative electrode active material powder was measured using a fully automatic specific surface area measuring device Macsorb (manufactured by Mountec Co., Ltd.). 1.0 g of a sample (powder) was weighed into a glass cell (standard cell), and after replacing the inside of the glass with nitrogen gas, heat treatment was performed at 250° C. for 15 minutes in the nitrogen gas atmosphere. After that, cooling was performed for 4 minutes while flowing a nitrogen/helium mixed gas. After cooling, the samples were measured by the BET single point method. A mixed gas of 30 vol % nitrogen and 70 vol % helium was used as the adsorbed gas during cooling and measurement.

[Content of oxygen element]
The oxygen element content was measured using an oxygen/nitrogen analyzer manufactured by LECO.

[Raman spectrum]
When measuring the Raman spectrum, the less uneven the sample surface and the higher the particle density, the more particles are present in the space where the excitation light and Raman scattered light are focused, and the lower the excitation power of the laser. High Raman light intensity can be obtained. Therefore, using a Specac mini hydraulic press and a φ7 mm pellet forming die, 1 ton of pressure was applied to each of the negative electrode active material powders obtained in Examples and Comparative Examples to form pellets.

The Raman spectrum measurement conditions are as follows. The Raman spectrum was obtained by averaging all spectra obtained by mapping measurements and calculating the average spectrum for each sample.
・ Apparatus: NRS5200 (manufactured by JASCO Corporation)
・Excitation wavelength: 532 nm
・Excitation power: 0.9 mW
・Detector: DU970P-FI
・Attenuation filter: 10%
・Grating: 1800gr/mm
・Aperture diameter: 4000 μm
・Exposure time: 20 sec
・Objective lens: MPLFLN × 20
・Mapping area: 10 μm×10 μm
・Measurement interval: 10 μm
・Accumulation count: 1

Wavenumber calibration was performed by measuring Si, which is a standard sample, and adjusting the main peak to 520.0 cm ⁻¹ . A laser excitation wavelength of 532 nm was adopted.

[Production of battery and measurement of charge capacity, discharge capacity, efficiency and cycle characteristics]
Lithium secondary batteries were produced using the negative electrode active materials obtained in Examples and Comparative Examples. The details of the procedure for producing the battery are as described below.
Negative electrode active material powder: conductive material: binder = 80: 10: 10 (% by mass), and these were mixed to obtain a negative electrode mixture by suspending them in N-methylpyrrolidone. . Acetylene black was used as the conductive material. Polyimide was used as the binder. This negative electrode mixture was applied onto an electrolytic copper foil having a thickness of 16 μm. After the coating film was dried, it was heat-treated at 350° C. for 1 hour in a nitrogen atmosphere to form a negative electrode active material layer to obtain a negative electrode.
A circle having a diameter of 16 mmφ was punched from the negative electrode obtained as described above, and vacuum-dried at 160° C. for 6 hours. Then, an electrochemical evaluation cell TOMCEL (registered trademark) was assembled in a glove box under an argon atmosphere. Metallic lithium was used as the counter electrode. As the electrolytic solution, an electrolytic solution obtained by dissolving LiPF ₆ in a carbonate-based mixed solvent so as to have a concentration of 1 mol/L was used. A polypropylene porous film was used as the separator.

Using the electrochemical evaluation cell TOMCEL (registered trademark) prepared as described above, initial activation was performed by the method described below. The prepared electrochemical evaluation cell TOMCEL (registered trademark) was left to stand for 6 hours, and then charged at 0.1 C at 25° C. with a constant current of 0.001 V (charged when the current value reached 0.01 C). end), and discharged at a constant current of 0.1C to 1.0V. This was repeated for 3 cycles. Incidentally, the actually set current value was calculated from the content of the negative electrode active material in the negative electrode. After that, the cell was placed in a constant temperature bath at 45° C. and allowed to stand for 5 hours until the cell reached the ambient temperature. After that, in a voltage range of 0.001 to 1 V, one charge/discharge cycle was performed at 0.1C, and then 50 charge/discharge cycles were performed at 1C. After that, one charge/discharge cycle was performed at 0.1C.
In addition, the capacity retention rate was calculated by dividing the discharge capacity at the 52nd charge/discharge at 45° C. by the initial discharge capacity in the above charge/discharge cycles, and this value was used as a measure of the cycle characteristics.

As is clear from the results shown in Table 1, the batteries comprising the negative electrode active materials obtained in Examples exhibit better cycle characteristics than the batteries comprising the negative electrode active materials obtained in Comparative Examples. .

According to the active material of the present invention, a battery with good performance can be obtained. Moreover, according to the method of the present invention, such an active material can be easily produced.

Claims

An active material made of a silicon-based material containing a silicon (Si) element and a boron (B) element,
In the X-ray diffraction pattern measured by an X-ray diffraction device (XRD) using Cukα1 rays, the diffraction peak intensity P1 observed in the range of 2θ = 27.5 ° or more and 29.5 ° or less is 2θ = 30 The ratio P2/P1 of the intensity P2 of the diffraction peaks observed in the range of 45° or less is 0.1 or less,
Having a cubic crystal structure with a lattice constant of 0.5390 nm or more and 0.5420 nm or less,
An active material having a ratio D 50 /CS of a volume cumulative particle size D 50 in a cumulative volume of 50% by volume measured by a laser diffraction scattering particle size distribution measurement method to a crystallite size CS calculated from the X-ray diffraction pattern is 8 or more. .
The active material according to claim 1, wherein the content of the boron (B) element is 1 at% or more and 5 at% or less.
The Raman spectrum obtained by measuring a wavenumber range of 400 cm -1 or more and 600 cm -1 or less by Raman spectroscopy, wherein a peak is observed in a wavenumber range of 450 cm -1 or more and 500 cm -1 or less. active material.
The ratio O/SSA of the oxygen (O) element content to the specific surface area SSA is 0.1 (mass%/(m 2 /g)) or more and 0.3 (mass%/(m 2 /g)) or less 4. The active material according to any one of claims 1 to 3.
The active material according to any one of claims 1 to 4, wherein the volume cumulative particle size D50 is 0.1 µm or more and 5 µm or less.
The active material according to any one of claims 1 to 5, wherein the crystallite size CS is 10 nm or more and 100 nm or less.
7. The active material according to any one of claims 1 to 6, which is a single phase composed of the silicon (Si) element, the boron (B) element, and the balance of inevitable impurities.
A method for producing an active material made of a silicon-based material containing silicon (Si) element and boron (B) element,
A step of applying an external force to the raw material powder, which is an aggregate of particles containing the silicon (Si) element and the boron (B) element,
In the above step, an external force is applied to the raw material powder so that the particles are pulverized and the fine particles generated by the pulverization are bonded together.
The manufacturing method according to claim 8, wherein the steps are performed in a non-oxidizing atmosphere.
The manufacturing method according to claim 9, wherein the powder obtained by the process is brought into contact with the atmosphere.
The manufacturing method according to claim 10, wherein the contact is made with the atmosphere having a dew point of -10°C or less.
A negative electrode comprising the active material according to any one of claims 1 to 7.
A positive electrode layer, a negative electrode layer, and an electrolyte layer positioned between the positive electrode layer and the negative electrode layer, wherein the negative electrode layer comprises the active material according to any one of claims 1 to 7, battery.