JP6711475B1 - Composite particle group, negative electrode active material particle group, negative electrode, battery, and exposed convex composite particle contained in composite particle group - Google Patents

Abstract

A composite particle group capable of achieving both excellent rapid charge performance and initial charge/discharge efficiency. The plurality of composite particles constituting the composite particle group have a plurality of convex portions, and in the plurality of composite particles having a particle diameter of not less than the median diameter (d50), the average of the amorphous carbon film on the surface of the active material particles When the area where the coverage is 50 to 90 area% and the surface of the active material particle in the composite particle is 1 μm 2 or more is defined as the exposed area, the number density of the exposed area with respect to the total surface area of the plurality of composite particles is It is 0.0010 to 0.0500 pieces/μm 2.

Description

TECHNICAL FIELD The present invention relates to a composite particle group that can be used as a negative electrode active material particle group for non-aqueous electrolyte secondary battery applications, represented by a lithium secondary battery, and more specifically, a composite particle group, a negative electrode active material particle group, and a negative electrode. , A battery, and a convex-part exposed composite particle contained in the composite particle group.

In recent years, small electronic devices such as home video cameras, notebook computers, and smartphones have become widespread. Non-aqueous electrolyte secondary batteries typified by lithium-ion batteries are used in these small electronic devices. Along with further miniaturization and higher performance of small electronic devices, nonaqueous electrolyte secondary batteries are required to have improved charge/discharge capacity and rapid charge performance.

International Publication No. 2015/041186 (Patent Document 1), International Publication No. 2006/075552 (Patent Document 2), JP-A-2016-162548 (Patent Document 3), and JP-A-2008-235252 (Patent Document 4). ), JP-A-2008-159446 (Patent Document 5), JP-A-2018-73611 (Patent Document 6), JP-A-2001-68096 (Patent Document 7), and JP-A-2016-154061 (Patent). Document 8) and Japanese Patent Laid-Open No. 2013-69564 (Patent Document 9) propose electrode active material particles coated with a coating material in order to enhance the performance of the battery.

In the coating active material for a lithium ion battery disclosed in Patent Document 1, at least a part of the surface of the battery active material is coated with a coating agent containing a coating resin and a conductive additive. The method for producing a battery active material in this document includes a step of mechanically coating the battery active material with a coating resin and a conductive additive. At this time, the ratio (D2/D1) of the average particle diameter D2 (μm) of the coating resin to the average particle diameter D1 (μm) of the battery active material is 1/5 or less. Furthermore, the ratio (D3/D1) of the average particle diameter D3 (μm) of the conductive additive to the average particle diameter D1 (μm) of the battery active material is 1/10 or less. It is described in Patent Document 1 that the coated active material for a lithium-ion battery having the above-described structure has increased conductivity.

The negative electrode material for lithium secondary batteries disclosed in Patent Document 2 is either an A phase mainly composed of silicon or a mixed phase of B phase and A phase composed of an intermetallic compound of a transition metal element and silicon. Including or. The phase A and the mixed phase are base material particles that are either microcrystalline or amorphous, a carbon material attached to a part of the surface of the base material particles, and a carbon material among the surfaces of the base material particles. And a film containing silicon oxide formed on the surface other than the surface on which the silicon oxide is attached. It is described in Patent Document 2 that the negative electrode material for a lithium secondary battery having the above-described structure can have high conductivity and low irreversible capacity.

The electrode active material proposed in Patent Document 3 is an electrode active material coated with a carbonaceous material. The carbonaceous materials are carbon black and hydrocarbons, and carbon black has a ratio “PPA/d” of 8 or more of the number PPA (the number) of primary particles forming the aggregate and the primary particle size d (nm). Is. It is described in Patent Document 3 that the electrode active material having the above-described structure has increased conductivity.

The active material particles for an electrode disclosed in Patent Document 4 include an active material main body and a conductive auxiliary agent having electron conductivity that partially covers the surface of the active material main body. A protrusion made of a conductive additive is formed on the surface of the active material body. The height of the protrusions from the surface of the active material body is 5 to 30% of the particle diameter of the active material body. It is described in Patent Document 4 that the active material particles for an electrode having the above-mentioned configuration enhance the rapid charging performance.

The active material particles for electrodes disclosed in Patent Document 5 include an active material main body and a conductive auxiliary agent having electron conductivity that partially covers the surface of the active material main body. The active material particles for an electrode have a continuous layer of a conductive additive that covers the surface of the active material main body by 10 to 80%. It is described in Patent Document 5 that the electrode active material particles having the above configuration enhance the rapid charging performance.

The silicon-containing alloy disclosed in Patent Document 6 is coated with a carbon coating layer formed of a carbon-based material. The negative electrode for an electric device proposed in this document includes a silicon-containing alloy coated with the above carbon coating layer, a conductive additive for a negative electrode, and a binder for a negative electrode. The ratio of the specific surface area of the carbon-based material to the specific surface area of the conductive additive for the negative electrode is 7 or more. Patent Document 6 describes that the negative electrode having the above structure has improved charge/discharge efficiency and cycle durability.

Patent Document 7 proposes a negative electrode active material material for a non-aqueous electrolyte secondary battery, which is composed of composite particles. The composite particles include active material particles consisting of a phase containing at least Sn as a constituent element that occludes lithium, and a phase that does not occlude lithium, and a conductive material that covers a part or all of the surface of the active material particles. Consists of. With the composite particles having the above structure, even if the expansion and contraction associated with the electrochemical storage and release of lithium are repeated, miniaturization hardly occurs. Therefore, it is described in Patent Document 7 that the contact between the active material particles and the conductive agent can be maintained and the charge/discharge cycle life characteristics can be improved.

The negative electrode active material disclosed in Patent Document 8 contains graphite that is coated with amorphous carbon and is not scale-like. Patent Document 8 describes that the negative electrode active material having the above structure can prevent the graphite and the electrolytic solution from reacting with each other during charging and discharging of the battery.

The electrode material of Patent Document 9 is an aggregate formed by aggregating electrode active material particles having a carbonaceous film formed on the surface thereof. The average particle size of the aggregate is 1.0 μm or more and 100 μm or less. The volume density of the aggregate is 50% by volume or more and 80% by volume or less of the volume density when the aggregate is solid. The pore distribution of the pores contained in the aggregate is unimodal, and the average pore diameter in the pore distribution is 0.3 μm or less. It is described in Patent Document 9 that the above-mentioned configuration makes it possible to reduce the unevenness in the amount of the carbonaceous film carried and to improve the electronic conductivity.

International Publication No. 2015/041186 International Publication No. 2006/075552 JP, 2016-162548, A JP, 2008-235252, A JP, 2008-159446, A JP, 2008-73611, A JP, 2001-68096, A JP, 2016-154061, A JP, 2013-69564, A

High initial charge/discharge efficiency is required as an index of excellent charge/discharge efficiency. The initial charge/discharge efficiency is lower than the charge/discharge efficiency of the second and subsequent times. The reason why the initial charge/discharge efficiency is low is considered to be due to the reaction between the electrode surface and the electrolytic solution. If the initial charge/discharge efficiency is low, the charge/discharge efficiency is unlikely to increase when the charge/discharge is repeated thereafter. If the charge/discharge efficiency is high from the first time, the high charge/discharge efficiency can be maintained even if the charge/discharge is repeated thereafter. For the above reasons, high initial charge/discharge efficiency is required.

In the above-mentioned Patent Document 1 and Patent Documents 3 to 9, the decomposition reaction of the electrolytic solution due to the reaction between the electrode active material and the electrolytic solution is not considered. When the reactivity between the electrode active material and the electrolytic solution is high, the decomposition reaction of the electrolytic solution is likely to occur. Due to this decomposition reaction, decomposition products are deposited on the electrode surface or decomposition gas is generated. Therefore, the irreversible capacity increases and the initial charge/discharge efficiency decreases.

In Patent Document 2, the decomposition reaction between the electrode active material and the electrolytic solution is considered. However, in order to suppress the decomposition reaction of the electrolytic solution, a film containing silicon oxide is formed on the surface of the electrode active material. The conductivity of silicon oxide is low. Therefore, when a film of silicon oxide is formed on the surface of the electrode active material, the decomposition reaction of the electrolytic solution is suppressed, but the conductivity may be low. If the conductivity is low, the quick charging performance is deteriorated.

An object of the present disclosure is to achieve both excellent initial charge/discharge efficiency and excellent rapid charge performance, a composite particle group, a negative electrode active material particle group, a negative electrode, a battery, and a convex-part exposed composite particle included in the composite particle group. Is to provide.

The composite particle group according to the present disclosure,
With multiple composite particles,
The composite particles are
Active material particles containing a metal active material that occludes and/or releases metal ions;
An amorphous carbon coating made of amorphous carbon, which covers the surface of the active material particles,
The plurality of composite particles have a plurality of convex portions,
In a plurality of the composite particles having a median diameter (d50) or more, the average coverage of the amorphous carbon coating on the surface of the active material particles is 50 to 90 area %,
In the composite particles, when a region in which the surface of the active material particles is exposed by 1 μm ² or more is defined as an exposed region, a plurality of the composite particles having the particle diameter of the median diameter (d50) or more are The number density of the exposed regions with respect to the total surface area of the composite particles is 0.0010 to 0.0500/μm ² .

The negative electrode active material particle group according to the present disclosure,
Equipped with a plurality of negative electrode active material,
A plurality of the negative electrode active material,
Including the composite particle group described above,
The ratio of the composite particle group is 70% or more among the plurality of negative electrode active material materials having a particle diameter of not less than the median diameter (d50).

The negative electrode according to the present disclosure is
A thin film-shaped or plate-shaped active material supporting member,
A negative electrode material mixture layer formed on the surface of the active material supporting member,
The negative electrode mixture layer,
The negative electrode active material particle group,
And a binder having the negative electrode active material particles dispersed therein.

The battery according to the present disclosure is
The negative electrode,
The positive electrode,
A separator,
And an electrolyte.

The convex-exposed composite particles according to the present disclosure,
Active material particles containing a metal active material that occludes and/or releases metal ions;
A surface of the active material particles, comprising an amorphous carbon coating of amorphous carbon,
The coverage of the amorphous carbon coating on the surface of the active material particles is 50 to 90 area %,
The protrusion-exposed composite particles have a plurality of protrusions,
At least one exposed region in which the surface of the active material particle is exposed by 1 μm ² or more exists in the plurality of convex portions.

The composite particle group, the negative electrode active material particle group, the negative electrode, the battery, and the convex portion exposed composite particle according to the present disclosure can achieve both excellent rapid charging performance and excellent initial charge/discharge efficiency.

FIG. 1 is a diagram showing the relationship between the average coverage of the amorphous carbon coating and the initial charge/discharge efficiency in the composite particle group. FIG. 2 is a diagram showing the relationship between the average coverage of the amorphous carbon coating and the reaction resistance, which is an index of the rapid charging performance, in the composite particle group. FIG. 3 is a perspective view of the convex-part exposed composite particles of the present embodiment. FIG. 4 is a perspective view of the active material particles in FIG. FIG. 5 is an image of a secondary electron image of the active material particles of this embodiment at a magnification of 5000 using a scanning electron microscope. FIG. 6 is an SEM image of the composite particles of this embodiment. FIG. 7 is a quaternary image of the SEM image of FIG. FIG. 8 is a SEM image of the composite particle group of the present embodiment at 1000 times magnification. FIG. 9 is a schematic diagram of an apparatus for producing a metal active material of active material particles according to this embodiment. FIG. 10 shows the peripheral speed Y (m/sec) of the rotor of the dry particle composite apparatus, the processing time X (minutes) in the composite processing step, and the median diameter under the manufacturing conditions of the composite particle group according to the present embodiment. The average coverage of the amorphous carbon coating of the plurality of composite particles having a particle size of (d50) or more is 50 to 90%, and the number density of exposed regions is 0.0010 to 0.0500/μm ^2. FIG. 3 is a diagram showing a relationship with whether or not the composite particle group of the present embodiment which is is manufactured.

The present inventors have studied a composite particle group that achieves both rapid charge performance and initial charge/discharge efficiency. As a result, the present inventors have obtained the following findings.

The inventors of the present invention first studied to improve the initial charge/discharge efficiency. In order to improve the initial charge/discharge efficiency, it is sufficient to suppress the decomposition reaction of the electrolytic solution due to the reaction between the active material particles containing the metal active material and the electrolytic solution. By suppressing the decomposition reaction of the electrolytic solution due to the reaction between the active material particles and the electrolytic solution, it is possible to suppress the decomposition product generated by the decomposition reaction from being deposited on the surface of the active material particles, and the decomposition gas is generated. Can be suppressed. As a result, the initial charge/discharge efficiency is increased.

Therefore, the present inventors have proposed to coat the active material particles containing a metal active material with an amorphous carbon coating made of amorphous carbon in order to suppress the reaction between the active material particles and the electrolytic solution. Thought.

Here, "amorphous carbon" is also called amorphous carbon, and means carbon having a structure in which fine crystals are randomly connected and having no regular crystal structure. In the present embodiment, “amorphous carbon” refers to a broad intensity peak near 2θ=20 to 30° in the X-ray diffraction profile obtained by the X-ray diffraction performed on the amorphous carbon film. Means a carbon having a crystallite diameter Lc of 50 nm or less calculated by Scherrer's formula described later.

In amorphous carbon, the development of a crystallite called a hexagonal mesh plane of carbon is smaller than that of graphite. In the case of amorphous carbon, the reactivity of the hexagonal net surface edge is lower than that of graphite, and the side reaction (irreversible capacity) accompanying the decomposition of the electrolyte is smaller than that of graphite. Therefore, the amorphous carbon coating has a higher charge acceptability of metal ions represented by lithium ions than the graphite coating. That is, when an amorphous carbon coating film made of amorphous carbon is formed on the surface of the active material particles, metal ions pass through the amorphous carbon coating and are occluded in the active material particles, and the metal ions are not The particles pass through the amorphous carbon coating and are released into the electrolyte. As a result, it is considered that the initial charge/discharge efficiency is increased.

The active material particles coated with the amorphous carbon coating contain a metal active material. Here, the “metal active material” is a material that occludes and/or releases metal ions. The metal active material contains one or two or more kinds selected from the group consisting of metal elements and metalloid elements in a total amount of 80 at% or more. The metal element is one or more selected from the group consisting of copper (Cu), tin (Sn), aluminum (Al), and zinc (Zn). The metalloid element is, for example, silicon (Si). The metal active material may be a simple metal, an alloy, a metal oxide, or an intermetallic compound. The intermetallic compound is, for example, Cu ₆ Sn ₅ , Cu ₃ Sn, or the like. The metal active material consists of one or more selected from the group consisting of metals, alloys, intermetallic compounds, and metal oxides, and the balance consists of impurities.

The “metal ion” is, for example, lithium ion, magnesium ion, sodium ion or the like. A preferred metal ion is lithium ion.

Here, a particle including an active material particle containing a metal active material and an amorphous carbon coating film coating the surface of the active material particle is defined as a “composite particle”. In a composite particle group including a plurality of composite particles, it is considered that the initial charge/discharge efficiency is increased based on the above mechanism.

However, in the above-mentioned composite particle group, although the initial charge/discharge efficiency is increased, the rapid charge performance may be significantly deteriorated, and it has been clarified by the study by the present inventors. Therefore, the present inventors have investigated and examined the factors that reduce the rapid charging performance. As a result, the following factors were considered as the factors that deteriorate the rapid charging performance.

When the surface of the active material particles is covered with the amorphous carbon film, contact between the surface of the active material particles and the electrolytic solution is suppressed. Therefore, the initial charge/discharge efficiency is increased. However, if the coverage of the amorphous carbon coating on the surface of the active material particles is too high, metal ions must enter and exit the active material particles through the amorphous carbon coating. Although the amorphous carbon coating is permeable to metal ions, the amorphous carbon coating can be resistive as the metal ions pass. That is, the amorphous carbon coating becomes resistant to the entry and exit of metal ions into and from the active material particles.

Therefore, the present inventors considered that a part of the amorphous carbon film covering the surface of the active material particles is intentionally peeled off to expose a part of the surface of the active material particles. While covering the surface of the active material particles with the amorphous carbon film, and if part of the surface of the active material particles is exposed, the amorphous carbon film suppresses contact between the active material particles and the electrolytic solution. At the same time, metal ions easily enter and leave the active material particles through the exposed areas of the active material particles. When the metal ions can enter and leave, it becomes possible to alloy the metal active material in the active material particles with the metal ions. Therefore, it is considered that the quick charging performance is enhanced.

Therefore, the present inventors have examined a method of adjusting the coverage of the amorphous carbon coating on the surface of the active material particles. As a result, if the shape of the active material particles is not spherical but has a shape having a plurality of convex portions, the amorphous carbon coating film once coated on the plurality of convex portions can be peeled off, and as a result, the active material particles It is thought that the exposed area of can be formed. Here, the plurality of convex portions of the active material particles may be, for example, corner portions or ridge portions in the particle shape. Further, the convex portion may be a convex portion other than the corners and ridges of the particles.

Based on the above findings, the present inventors have used an active material particle having a plurality of protrusions to coat the surface of the active material particle with an amorphous carbon coating, and further coat the amorphous carbon coating. A plurality of composite particle groups with adjusted rates were prepared. Then, the relationship between the average coverage rate of the amorphous carbon coating and the initial charge/discharge efficiency and the quick charge performance in a plurality of composite particles having a particle diameter of the median diameter (d50) or more in the composite particle group was investigated. ..

FIG. 1 shows a composite particle group composed of a plurality of composite particles including active material particles and an amorphous carbon film coated on the surface of the active material particles, and a plurality of composite particles having a median diameter (d50) or more. It is a figure which shows the average coverage of the amorphous carbon film in a particle|grain, and the relationship of initial charge/discharge efficiency. FIG. 2 is a diagram showing the relationship between the average coverage of the amorphous carbon coating and the rapid charging performance in the composite particle group described above. The reaction resistance (Ω) corresponding to the vertical axis in FIG. 2 is an index of rapid charging performance. The lower the reaction resistance, the higher the rapid charging performance.

Referring to FIG. 1, when the average coverage of the amorphous carbon coating is increased, the initial charge/discharge efficiency is rapidly increased. When the average coverage of the amorphous carbon coating is 50 area% or more, the initial charge/discharge efficiency is not so high and is constant even if the average coverage is high.

On the other hand, referring to FIG. 2, when the average coverage of the amorphous carbon coating increases, the reaction resistance decreases and the rapid charging performance increases. However, when the average coverage of the amorphous carbon coating exceeds 90% by area, the reaction resistance sharply rises and the rapid charging performance rapidly declines. Therefore, the present inventors have a composite particle group consisting of a plurality of composite particles in which an active carbon particle having a plurality of protrusions is coated with an amorphous carbon film, and have a particle size of not less than the median diameter (d50). It was found that when the average coverage of the amorphous carbon coating of the plurality of composite particles is 50 to 90 area %, not only excellent initial charge/discharge efficiency can be obtained, but also rapid charge performance is improved.

However, even if the average coverage of the amorphous carbon coating of the plurality of composite particles having a particle diameter of the median diameter (d50) or more is 50 to 90 area %, the rapid charging performance may still be low. Therefore, the inventors have made further studies. As a result, in the composite particles, not only the average coverage of the amorphous carbon coating film in the plurality of composite particles having a median diameter (d50) or more is set to 50 to 90 area %, but also in the composite particles, the amorphous carbon coating is amorphous. It has been found that it is important that there is at least one exposed region where the surface of the active material particles is exposed by 1 μm ² or more without being covered with the carbonaceous film. As a result of further investigation, in a plurality of composite particles having a median diameter (d50) or more, the average coverage of the amorphous carbon coating is 50 to 90 area %, and the total surface area of the plurality of composite particles is It has been found that if the number density of exposed regions is 0.0010 to 0.0500/μm ² , both excellent initial charge/discharge efficiency and excellent rapid charge performance can be achieved.

The composite particle group, the negative electrode active material particle group, the negative electrode, the battery, and the convex-part exposed composite particles of the present embodiment completed based on the above findings have the following configurations.

[1]
A composite particle group,
With multiple composite particles,
The composite particles are
Active material particles containing a metal active material that occludes and/or releases metal ions;
An amorphous carbon coating made of amorphous carbon, which covers the surface of the active material particles,
The plurality of composite particles have a plurality of convex portions,
In a plurality of the composite particles having a median diameter (d50) or more, the average coverage of the amorphous carbon coating on the surface of the active material particles is 50 to 90 area %,
In the composite particles, when a region in which the surface of the active material particles is exposed by 1 μm ² or more is defined as an exposed region, a plurality of the composite particles having the particle diameter of the median diameter (d50) or more are The number density of the exposed areas with respect to the total surface area of the composite particles is 0.0010 to 0.0500 pieces/μm ² .
Composite particle group.

[2]
The composite particle group according to [1],
The Vickers hardness of the active material particles is HV20 to 500,
Composite particle group.

[3]
The composite particle group according to [1] or [2],
The specific surface area is 1.0 to 5.0 m ² /g,
Composite particle group.

[4]
The composite particle group according to any one of [1] to [3],
The metal active material is
Contains one or more selected from the group consisting of Cu, Sn, and Si,
Composite particle group.

[5]
The composite particle group according to [4],
The metal active material is
Sn: 10 to 40 at %,
Cu: containing 50 to 90 at %,
Composite particle group.

[6]
The composite particle group according to [5],
The metal active material further comprises
Sn: 10 to 35 at %,
Ti: 9 at% or less, V: 49 at% or less, Cr: 49 at% or less, Mn: 9 at% or less, Fe: 49 at% or less, Co: 49 at% or less, Ni: 9 at% or less, Zn: 29 at% or less, Al: 49 at% or less, Si: 49 at% or less, B: 5 at% or less, and C: 5 at% or less, and one or more selected from the group consisting of,
The balance consists of Cu and impurities,
Composite particle group.

[7]
The composite particle group according to any one of [1] to [6],
The plurality of composite particles includes a plurality of convex-part exposed composite particles,
The convex-part exposed composite particles have a plurality of convex parts,
In the protrusion-exposed composite particles, the coverage of the amorphous carbon film is 50 to 90 area %, and in the plurality of protrusions, the surface of the active material particles is exposed by 1 μm ² or more. There is at least one exposed area,
Of the plurality of composite particles having a particle diameter of the median diameter (d50) or more, the number ratio of the convex-exposed composite particles is 80% or more.
Composite particle group.

[8]
A negative electrode active material particle group,
Equipped with a plurality of negative electrode active material,
A plurality of the negative electrode active material,
Including the composite particle group according to any one of [1] to [7],
The ratio of the composite particle group is 70% or more among the plurality of negative electrode active material materials having a particle diameter of not less than the median diameter (d50).
Negative electrode active material particle group.

[9]
The negative electrode,
A thin film-shaped or plate-shaped active material supporting member,
A negative electrode material mixture layer formed on the surface of the active material supporting member,
The negative electrode mixture layer,
A negative electrode active material particle group according to [8],
A binder having the negative electrode active material particles dispersed therein,
Negative electrode.

[10]
The negative electrode according to [9],
The negative electrode active material particle group includes the composite particle group according to any one of [1] to [7].
Negative electrode.

[11]
The negative electrode according to [9] or [10],
The positive electrode,
A separator,
With an electrolyte,
battery.

[12]
The convex-exposed composite particles,
Active material particles containing a metal active material that occludes and/or releases metal ions;
A surface of the active material particles, comprising an amorphous carbon coating of amorphous carbon,
The coverage of the amorphous carbon coating on the surface of the active material particles is 50 to 90 area %,
The protrusion-exposed composite particles have a plurality of protrusions,
In the plurality of convex portions, there is at least one exposed region in which the surface of the active material particles is exposed by 1 μm ² or more.
Convex exposed composite particles.

[13]
The convex-part exposed composite particle according to [12],
The Vickers hardness of the active material particles is HV20 to 500,
Convex exposed composite particles.

[14]
The convex-part exposed composite particle according to [12] or [13],
The metal active material is
Contains one or more selected from the group consisting of Cu, Sn, and Si,
Convex exposed composite particles.

[15]
The convex-part exposed composite particle according to [14],
The metal active material is
Sn: 10 to 40 at %,
Cu: containing 50 to 90 at %,
Convex exposed composite particles.

[16]
The convex-part exposed composite particle according to [15],
The metal active material further comprises
Sn: 10 to 35 at %,
Ti: 9 at% or less, V: 49 at% or less, Cr: 49 at% or less, Mn: 9 at% or less, Fe: 49 at% or less, Co: 49 at% or less, Ni: 9 at% or less, Zn: 29 at% or less, Al: 49 at% or less, Si: 49 at% or less, B: 5 at% or less, and C: 5 at% or less, and one or more selected from the group consisting of,
The balance consists of Cu and impurities,
Convex exposed composite particles.

Hereinafter, the composite particle group, the negative electrode active material particle group, the negative electrode, the battery, and the convex-part exposed composite particles of the present embodiment will be described in detail.

[Composite particle group]
The composite particle group of the present embodiment is composed of a plurality of composite particles.

FIG. 3 is a perspective view showing an example of the composite particles. Composite particle 1 includes active material particle 10 and amorphous carbon coating 30. In FIG. 3, the amorphous carbon film 30 is a hatched region. The active material particles 10 contain a metal active material. The metal active material is a material that occludes and/or releases metal ions. The amorphous carbon film 30 is made of amorphous carbon and covers the surface of the active material particles 10.

FIG. 4 is a perspective view of the active material particles 10 in FIG. Referring to FIG. 4, active material particle 10 is not spherical, but has a shape having a plurality of convex portions 11 (11A to 11C). The convex portion 11 includes a corner portion 11A, a ridge line portion 11B, and a convex portion 11C formed on a flat surface. In short, the convex portion 11 means a portion of the surface of the active material particle 10 that protrudes to the outside.

FIG. 5 is an image of a secondary electron image of the active material particles 10 of the present embodiment using a scanning electron microscope (hereinafter, also referred to as SEM image). FIG. 6 is an SEM image of the composite particle 1 of this embodiment. The SEM images in FIGS. 5 and 6 are images obtained by observing at 5000 times.

Referring to FIG. 5, active material particle 10 is not spherical, but has a shape having a plurality of convex portions 11. Referring to FIG. 6, composite particle 1 has a plurality of convex portions 11 as in active material particle 10. Then, the surface of the active material particles 10 is covered with the black amorphous carbon film 30 on the SEM image. Then, in the plurality of convex portions 11 of the composite particle 1, there is a region in which a part of the surface of the active material particle 10 is exposed. Of the exposed areas, the areas where the surface of the active material particles 10 is exposed by 1 μm ² or more are defined as “exposed areas” 20.

Hereinafter, the active material particles 10 and the amorphous carbon coating film 30 constituting the composite particle 1 will be described in detail.

[Active material particles 10]
Active material particles 10 contain a metal active material. The metal active material occludes and/or releases metal ions. Preferably, active material particles 10 are composed of a metal active material and impurities.

In the present embodiment, the metal active material contains at least 80 at% or more in total of one or more selected from the group consisting of metal elements and metalloid elements. In the metal active material, the element other than the metal element and the metalloid element is, for example, oxygen or carbon. The metal element is, for example, one or more selected from the group consisting of copper (Cu), tin (Sn), aluminum (Al), and zinc (Zn). The metalloid element is, for example, silicon (Si).

Preferably, the metal active material contains one or more selected from the group consisting of metals, semimetals, alloys, intermetallic compounds, and metal oxides, and the balance is impurities. More preferably, the metal active material is made of one or more selected from the group consisting of metals, semimetals, alloys, and intermetallic compounds, with the balance being impurities.

The “metal ion” is, for example, lithium ion, magnesium ion, sodium ion or the like. A preferred metal ion is lithium ion.

The active material particles 10 may contain a substance other than the above metal active material. Preferably, the metal active material is the main component (main phase) of the active material particles 10. The "main component" means a component that accounts for 50% by volume or more. The component other than the metal active material in the active material particles 10 is, for example, carbon (graphite). Preferably, the metal active material occupies 90% by volume or more of the active material particles 10. More preferably, active material particles 10 are made of a metal active material. The metal active material may contain impurities as long as the gist of the present invention is not impaired.

[Preferable Component (1) of Metal Active Material]
Preferably, the metal active material contains at least one selected from the group consisting of Cu, Sn and Si.

[Preferred Component (2) of Metal Active Material]
More preferably, the metal active material contains Sn, and the balance is Cu and impurities. More preferably, the metal active material contains 10 to 40 at% Sn and 50 to 90 at% Cu, and the balance is impurities.

Sn: 10 to 40 at%
Tin (Sn) increases the discharge capacity per volume. If the Sn content is 10 at% or more, this effect can be effectively obtained. When the Sn content is 40 at% or less, the initial charge/discharge efficiency is further enhanced. Therefore, the preferable Sn content is 10 to 40 at %. The more preferable lower limit of the Sn content is 13 at%, more preferably 18.5 at%, and further preferably 21 at%. A more preferable upper limit of the Sn content is 35 at%, and further preferably 30 at%.

Cu: 50 to 90 at%
Copper (Cu) enhances charge/discharge efficiency. When the Cu content is 50 at% or more, the initial charge/discharge efficiency is further increased. When the Cu content is 90 at% or less, the discharge capacity per volume is increased. Therefore, the Cu content is 50 to 90 at %. The more preferable lower limit of the Cu content is 55 at%, more preferably 60 at%. The more preferable upper limit of the Cu content is 80 at%, and more preferably 70 at%.

[Preferred Component (3) of Metal Active Material]
The metal active material also contains at least one selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Al, Si, B, and C, and the balance Cu. And may be impurities.

The metal active material contains Sn and at least one selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Al, Si, B and C, and the balance Cu and impurities. Preferably, the metal active material comprises Sn: 10 to 35 at%, Ti: 9 at% or less, V: 49 at% or less, Cr: 49 at% or less, Mn: 9 at% or less, Fe: 49 at% or less, Co: 49 at% or less, Ni: 9 at% or less, Zn: 29 at% or less, Al: 49 at% or less, Si: 49 at% or less, B: 5 at% or less, and C: 5 at% or less, selected from the group consisting of: One or more of them are contained, and the balance consists of Cu and impurities.

The preferable upper limit of the Ti content is 9 at% as described above. The more preferable upper limit of the Ti content is 6 at %, and more preferably 5 at %. The preferable lower limit of the Ti content is 0.1 at%, more preferably 0.5 at%, and further preferably 1 at%. Ti can suppress excessive oxidation of Cu and Sn, and can further improve the initial charge/discharge efficiency.

The preferable upper limit of the V content is 49 at% as described above. The more preferable upper limit of the V content is 30 at %, more preferably 15 at %, and further preferably 10 at %. The preferable lower limit of the V content is 0.1 at%, more preferably 0.5 at%, and further preferably 1 at%. V can suppress excessive oxidation of Cu and Sn, and can further improve initial charge/discharge efficiency.

The preferable upper limit of the Cr content is 49 at% as described above. The more preferable upper limit of the Cr content is 30 at %, more preferably 15 at %, and further preferably 10 at %. The preferable lower limit of the Cr content is 0.1 at%, more preferably 0.5 at%, and further preferably 1 at%. Cr can suppress excessive oxidation of Cu and Sn, and can further improve the initial charge/discharge efficiency.

The preferable upper limit of the Mn content is 9 at% as described above. The more preferable upper limit of the Mn content is 6 at %, and more preferably 5 at %. The preferable lower limit of the Mn content is 0.1 at %, more preferably 0.5 at %, and further preferably 1 at %. Mn can suppress excessive oxidation of Cu and Sn, and can further improve the initial charge/discharge efficiency.

The preferable upper limit of the Fe content is 49 at% as described above. The more preferable upper limit of the Fe content is 30 at %, more preferably 15 at %, and further preferably 10 at %. The preferable lower limit of the Fe content is 0.1 at %, more preferably 0.5 at %, and further preferably 1 at %. Fe can suppress excessive oxidation of Cu and Sn, and can further improve the initial charge/discharge efficiency.

The preferable upper limit of the Co content is 49 at% as described above. The more preferable upper limit of the Co content is 30 at%, more preferably 15 at%, and further preferably 10 at%. The preferable lower limit of the Co content is 0.1 at%, more preferably 0.5 at%, and further preferably 1 at%. Co can suppress excessive oxidation of Cu and Sn, and can further improve the initial charge/discharge efficiency.

The preferable upper limit of the Ni content is 9 at% as described above. The more preferable upper limit of the Ni content is 5 at%, and more preferably 2 at%. The preferable lower limit of the Ni content is 0.1 at %, more preferably 0.5 at %, and further preferably 1 at %. Ni can suppress excessive oxidation of Cu and Sn, and can further improve the initial charge/discharge efficiency.

The preferable upper limit of the Zn content is 29 at% as described above. The more preferable upper limit of the Zn content is 27 at %, and more preferably 25 at %. The preferable lower limit of the Zn content is 0.1 at %, more preferably 0.5 at %, and further preferably 1 at %. Zn can suppress excessive oxidation of Cu and Sn, and can further improve the initial charge/discharge efficiency.

The preferable upper limit of the Al content is 49 at% as described above. The more preferable upper limit of the Al content is 30 at %, more preferably 15 at %, and further preferably 10 at %. The lower limit of the Al content is preferably 0.1%, more preferably 0.5 at%, and further preferably 1 at%. Al can suppress excessive oxidation of Cu and Sn, and can further improve the initial charge/discharge efficiency.

The preferable upper limit of the Si content is 49 at% as described above. The more preferable upper limit of the Si content is 30 at %, more preferably 15 at %, and further preferably 10 at %. The lower limit of the Si content is preferably 0.1 at%, more preferably 0.5 at%, and further preferably 1 at%. Si can increase the discharge capacity per volume.

The preferable upper limit of the B content is 5 at %. The preferable lower limit of the B content is 0.01 at %, more preferably 0.1 at %, further preferably 0.5 at %, further preferably 1 at %. B can suppress excessive oxidation of Cu and Sn, and can further improve the initial charge/discharge efficiency.

The preferable upper limit of the C content is 5 at %. The lower limit of the C content is preferably 0.01 at%, more preferably 0.1 at%, further preferably 0.5 at%, further preferably 1 at%. C can reduce the volume expansion coefficient of the metal active material (when occluding metal ions).

[Preferred component of metal active material (4)]
The metal active material may further contain Sn and a Group 2 element and/or a rare earth element (REM) for the purpose of increasing the discharge capacity, and the balance may be Cu and impurities. The Group 2 element is, for example, magnesium (Mg), calcium (Ca), or the like. REM is, for example, lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), or the like.

[Preferable Vickers hardness of active material particles 10]
Preferably, the Vickers hardness of the active material particles 10 is HV20-500. The Vickers hardness of the active material particles 10 affects the coverage of the amorphous carbon coating 30 that covers the surface of the active material particles 10. When the Vickers hardness of the active material particles 10 is HV 20 or more, it becomes easy to form the active material particles 10 having the plurality of convex portions 11 when the composite particle group is manufactured by the below-described composite treatment. On the other hand, if the Vickers hardness of the active material particles 10 is HV 500 or less, the entire surface of the active material particles 10 having the plurality of protrusions 11 is coated when the composite particle group is manufactured by the below-described composite treatment. Of the amorphous carbon coating 30, the amorphous carbon coating 30 that covers the convex portion 11 is easily peeled off. As a result, it is easy to form at least one exposed region 20 in which the surface of the active material particles 10 is exposed by 1 μm ² or more among the plurality of convex portions 11, and a plurality of particles having a particle diameter of the median diameter (d50) or more are formed. In the composite particles, the average coverage of the amorphous carbon coating 30 is likely to be 50 to 90 area %. The lower limit of the Vickers hardness of the active material particles 10 is preferably HV30, more preferably HV50, and further preferably HV80. The preferable upper limit of the Vickers hardness of the active material particles 10 is HV480, more preferably HV460, and further preferably HV450.

Vickers hardness depends on the chemical composition of the metal active material. For example, when the metal active material contains 10 to 40 at% Sn and 50 to 90 at% Cu, the Vickers hardness of the active material particles 10 becomes HV 20 to 500.

[Method of measuring Vickers hardness of active material particles 10]
The Vickers hardness of the active material particles 10 is measured by the following method. A liquid epoxy resin precursor, a curing agent, and a plurality of composite particles 1 are mixed to obtain a mixture. The curing agent may be a commercially available epoxy resin curing agent. This mixture is poured into a mold and cured to obtain a cured product. The surface of the cured product taken out from the mold (hereinafter referred to as the measurement surface) is wet-polished using sandpaper to form a measurement surface including the cross section of the composite particle 1. Further, the measurement surface including the cross section of the composite particle 1 is mirror-polished with aluminum oxide powder. In the mirror polishing, the particle size of the aluminum oxide powder is gradually reduced (for example, 0.3 μm and 0.06 μm in this order), and the polishing is performed so that the cross section of the composite particle 1 in the measurement plane becomes flat. After polishing, the Vickers hardness in the cross section of the active material particles 10 in the cross section of the composite particle 1 in the measurement surface is measured using a micro Vickers hardness meter. Specifically, the Vickers hardness is measured by aligning the indenter with the substantially central portion of the cross section of the active material particle 10 using an optical microscope. The test load is 50 gf. A diamond indenter is used as the indenter. The micro Vickers hardness meter is not particularly limited. The micro Vickers hardness meter is, for example, MVK-G2 manufactured by Akashi Seisakusho. The Vickers hardness of the active material particles 10 of the 10 composite particles 1 in the measurement plane is measured. The arithmetic average value of 10 Vickers hardnesses is defined as the Vickers hardness HV of the active material particles 10.

[Preferred Median Diameter of Active Material Particles 10 (d50)]
The median diameter (d50) of the plurality of active material particles 10 forming the composite particle group is not particularly limited. The median diameter (d50) of the active material particles 10 is, for example, 1 to 50 μm. When the median diameter (d50) of the active material particles 10 is 1 μm or more, it is easy to adjust the coverage of the amorphous carbon coating 30 to 50 to 90 area %. If the median diameter (d50) of the active material particles 10 is 50 μm or less, it is easy to adjust the coverage of the amorphous carbon coating 30 to 50 area% or more. The lower limit of the median diameter (d50) of the active material particles 10 is preferably 3 μm, more preferably 5 μm. The preferable upper limit of the median diameter (d50) of the active material particles 10 is 45 μm, more preferably 40 μm, and further preferably 35 μm.

[Method of measuring median diameter (d50) of active material particles 10]
The median diameter (d50) of the active material particles 10 is obtained by the following method. A part of the plurality of active material particles 10 serving as a raw material of the plurality of particle groups is scooped and collected. With respect to the plurality of collected active material particles 10, the median diameter of the active material particles 10 was measured by a laser diffraction/scattering method using a laser diffraction/scattering type particle size distribution meter in accordance with JIS Z 8825 (2013). d50) is measured. The dispersion medium in the measurement is water containing 0.1% by mass of a surfactant containing alkylglycoxide. The dispersion method is ultrasonic waves for 5 minutes. The particle size (volume average particle size by laser diffraction scattering method) when the cumulative volume of all particles is 50% is defined as the average particle size (median size (d50)) of the active material particles 10.

[Amorphous carbon coating 30]
The amorphous carbon film 30 is made of amorphous carbon. Here, "amorphous carbon" is carbon that has a structure in which fine crystals are randomly connected and does not have a regular crystal structure. Amorphous carbon has a short-range order (several atoms to a dozen or so atomic order), and does not have a long-range order (several hundreds to thousands atomic order). Therefore, in amorphous carbon, the development of a crystallite called a hexagonal mesh plane of carbon is smaller than that of graphite. Therefore, in the case of amorphous carbon, the reactivity of the hexagonal mesh surface end (edge) in the electrolytic solution is lower than that of graphite, and the side reaction (irreversible capacity) accompanying decomposition of the electrolytic solution is smaller than in graphite. Therefore, the amorphous carbon film 30 has higher charge acceptance of metal ions represented by lithium ions, as compared with the graphite film. When the amorphous carbon coating film 30 is formed on the surface of the active material particles 10, metal ions pass through the amorphous carbon coating film 30 and are occluded in the active material particles 10, and the active material particles 10 form the amorphous carbon. It passes through the coating 30 and is released into the electrolyte. As a result, the initial charge/discharge efficiency is increased.

[Determination Method of Amorphous Carbon Film 30]
In this embodiment, the amorphous carbon film 30 is determined as follows. In the X-ray diffraction profile of the amorphous carbon film 30 obtained using the X-ray diffraction method, a broad intensity peak is obtained near 2θ=20 to 30°. Note that in the X-ray diffraction profile of highly crystalline graphite, a sharp intensity peak is obtained near 2θ=26 to 27°. Regarding the broad peak at 2θ=20 to 30° in the X-ray diffraction profile, when the crystallite diameter Lc calculated by the Scherrer equation is 50 nm or less, it is determined to be the amorphous carbon film 30.

Specifically, the amorphous carbon film 30 is confirmed by the following X-ray diffraction method. An arbitrary part of the plurality of composite particles 1 is scooped with a medicine spoon and collected. A plurality of the collected composite particles 1 are placed (deposited) on a non-reflective sample plate (a plate cut out so that a specific crystal plane of a silicon single crystal is parallel to the measurement surface). Then, the surface of the deposit of the plurality of composite particles 1 is flattened with a slide glass to obtain a sample. The above sample is set in an X-ray diffractometer and X-ray diffraction measurement is performed to obtain an X-ray diffraction profile. At this time, X-rays are incident on the amorphous carbon coating 30 covering the surface of the composite particle 1, and an X-ray diffraction profile of the amorphous carbon coating 30 is obtained.

Further, when the battery is disassembled and the presence or absence of the amorphous carbon film 30 is determined by X-ray diffraction measurement, the following method is performed. The battery before charging, or in the case of the used battery, after discharging, is disassembled in a glove box in an argon atmosphere, and the negative electrode to which the plurality of composite particles 1 are attached is taken out from the battery. Wrap the extracted negative electrode in mylar foil. Then, the periphery of the mylar foil is sealed with a thermocompression bonding machine. The negative electrode sealed with Myra foil is taken out of the glove box. The inside of the glove box is filled with an argon atmosphere using argon gas supplied from an ultra-high purity argon gas cylinder having a purity of 99.9999% or more. Further, an argon gas is passed through a purifying device using a catalyst or the like to prevent impurities such as nitrogen from being mixed out of the system. Thereby, the dew point is controlled to be -60°C or lower, and the deterioration of the composite particles 1 due to nitrogen or water is prevented. Subsequently, the negative electrode is attached to a non-reflective sample plate with a hair spray to prepare a sample. The sample is set in the X-ray diffractometer, and the X-ray diffraction measurement of the sample is performed. In this case, X-rays are incident on the amorphous carbon coating 30 that covers the surface of the negative electrode composite particle 1, and an X-ray diffraction profile of the amorphous carbon coating 30 is obtained.

The measurement conditions of the X-ray diffraction measurement for identifying the amorphous carbon film 30 are as follows.
・Device: Smart Lab manufactured by Rigaku
・X-ray tube: Cu-Kα line ・X-ray output: 45 kV, 200 mA
・Inlet side monochromator: Johansson element (Cu-Kα ₂ line and Cu-Kβ line are cut)
・Optical system: Focusing method ・Injection parallel slit: 5.0° ・Injection slit: 1/2° ・Longitudinal restriction slit: 10.0 mm
・Light receiving slit 1: 8.0 mm
・Light receiving slit 2: 13.0 mm
・Parallel light receiving slit: 5.0 degrees ・Goniometer: SmartLab goniometer ・X-ray source-mirror distance: 90.0 mm
* Distance between X-ray source and selected slit: 114.0 mm
・X-ray source-sample distance: 300.0 mm
・Distance between sample and light-receiving slit 1: 187.0 mm
・Distance between sample and light receiving slit 2: 300.0 mm
・Distance between light receiving slit 1 and light receiving slit 2: 113.0 mm
・Sample-detector distance: 331.0 mm
・Detector: D/Tex Ultra
-Measurement range: 10-120 degrees-Data collection angle interval: 0.02 degrees-Scan method: Continuous-Scan speed: 2.0 degrees/minute

The Scherrer formula for calculating the crystallite diameter Lc is as follows.
Lc=(K·λ)/{B·cos θ}
Lc: Crystallite size (nm)
K: Scherrer constant (dimensionless)
λ: X-ray wavelength (nm)
B: Full width at half maximum (radian) derived from the material
θ: Diffraction angle (radian) during X-ray diffraction measurement by the θ-2θ method
In this specification, the Scherrer constant K of Scherrer's formula uses K=0.94. The wavelength (λ) of the X-ray is measured by converting it into monochrome of Cu-Kα ₁ . As a value corresponding to the wavelength, λ=0.15401 nm.

The obtained X-ray diffraction profile is analyzed using a commercially available X-ray analysis software, and the crystallite diameter Lc is calculated from the full width at half maximum of the broad peak near 2θ=20 to 30°. The X-ray analysis software is, for example, PDXL software built in Rigaku's SmartLab, but is not limited to this as long as an equivalent result can be obtained. If the crystallite diameter Lc is 50 nm or less, it is determined that the coating film covering the active material particles 10 is the amorphous carbon coating film 30.

[About Raw Material (Carbon Source) of Amorphous Carbon Film 30]
The amorphous carbon film 30 is formed by subjecting the carbon source, which is a raw material, and the active material particles 10 to a composite treatment using a dry particle composite apparatus described later. In this embodiment, the carbon source is an organic substance. The organic material serving as a carbon source is, for example, one or more selected from the group consisting of carbon black, hard carbon, soft carbon, mesoporous carbon, and activated carbon. Among these, carbon black is particularly preferable.

Carbon black generally has a small primary particle size, and the carbon structure is crushed by the composite treatment described below. Therefore, the carbon black easily covers the active material particles. Therefore, the carbon source that is the raw material of the amorphous carbon coating 30 is preferably carbon black. Carbon black is amorphous carbon. In carbon black, primary particles of several to several hundreds nm form a structure to form secondary particles. Representative carbon blacks are conductive carbon blacks, acetylene blacks and Ketjen blacks. Carbon black having a primary particle size of 5 to 200 nm is preferred. In this case, the carbon source (carbon black) easily adheres to the surface of the active material particles 10 during the composite treatment process.

The specific surface area of the carbon source that is the raw material of the amorphous carbon film 30 is not particularly limited. The specific surface area of the carbon source is, for example, 5 to 500 m ² /g. When the specific surface area of the carbon source is 5 m ² /g or more, the active material particles 10 can be appropriately covered. When the specific surface area of the carbon source is 500 m ² /g or less, the coverage with the amorphous carbon coating 30 is likely to be 90 area% or less. When the specific surface area of the carbon source exceeds 500 m ² /g, the coverage rate and the specific surface area of the composite particles 1 become too high in the composite treatment step described later depending on the composite treatment conditions. The more preferable lower limit of the specific surface area of the carbon source is 10 m ² /g, and the more preferable upper limit thereof is 100 m ² /g.

[Type of composite particles 1 in composite particle group]
As described above, the composite particle group of the present embodiment is composed of a plurality of composite particles 1. Here, “comprising a plurality of composite particles 1 ”allows mixing of impurities. Specifically, 99% or more in the mass% of the composite particle group of the present embodiment is the plurality of composite particles 1.

The composite particle group may include the following three types of composite particles 1. Specifically, the composite particle group includes type 1 composite particles (projection-exposed composite particles), and may include type 2 and/or type 3 composite particles.
Type 1: Convex exposed particle. That is, the active material particles 10 and the amorphous carbon coating film 30 that covers the surface of the active material particles 10 are included, and the coverage of the amorphous carbon coating film 30 is 50 to 90 area %, and the plurality of convex portions are provided. In the part 11, the surface of the active material particles 10 is exposed to at least 1 μm ² or more, and at least one exposed region 20 is present in the composite particles Type 2: Active material particles 10 and the surface of the active material particles 10 are coated. Composite particles including the amorphous carbon coating 30 and the coverage of the amorphous carbon coating 30 is less than 50 area% or more than 90 area% Type 3: Active material particles 10 and the surface of the active material particles 10 The amorphous carbon coating 30 for coating the amorphous carbon coating 30 has a coverage of 50 to 90 area %, but the exposed region 20 where the surface of the active material particle is exposed by 1 μm ² or more is 1 No composite particles

[About exposed composite particles]
The convex-exposed composite particles are composite particles 1 which are the main constituent of the composite particle group. In the convex-part exposed composite particles, the coverage of the amorphous carbon film 30 on the surface of the active material particles 10 is 50 to 90 area %. In the protrusion-exposed composite particles, at least one exposed region 20 in which the surface of the active material particle 10 is exposed by 1 μm ² or more is present in the plurality of protrusions 11. FIG. 3 is a schematic diagram of type 1 composite particles, that is, convex-part exposed composite particles, of the composite particles 1. As shown in FIG. 3, in the protrusion-exposed composite particles, among the plurality of protrusions 11, there are one or more exposed regions 20 where the surface of the active material particles 10 is exposed by 1 μm ² or more. Most of the exposed region 20 is formed on the convex portion 11. FIG. 6 is an SEM image of the convex-part exposed composite particles among the composite particles. In the convex exposed composite particles (composite particle 1) of FIG. 6, the white region 20 corresponds to the exposed region 20, and the black region 30 corresponds to the amorphous carbon coating film 30. As is clear from FIG. 6, at least one exposed region 20 is formed in the convex portion 11.

As described above, the main constituent of the composite particle group of the present embodiment is the plurality of convex-part exposed composite particles. As a result, in the composite particle group of the present embodiment, the average coverage of the amorphous carbon coating 30 on the surface of the active material particles 10 is 50 to 50 in the composite particles 1 having a particle diameter of not less than the median diameter (d50). 90% by area. Further, in the plurality of composite particles 1 having a particle diameter of not less than the median diameter (d50), the number density of the exposed regions 20 in which the surface of the active material particles 10 is exposed at 1 μm ² or more is 0.0010 to 0.0500. /Μm ² . Hereinafter, this point will be described.

[Average Coverage of Amorphous Carbon Coating 30: 50 to 90 Area%]
In the composite particle group of the present embodiment, the average coverage of the amorphous carbon coating 30 on the surface of the active material particle 10 is 50 to 90 area% in the plurality of composite particles 1 having a particle diameter of not less than the median diameter (d50). Is.

FIG. 1 is a diagram showing the relationship between the average coverage of the amorphous carbon coating 30 and the initial charge/discharge efficiency. FIG. 2 is a diagram showing the relationship between the average coverage of the amorphous carbon coating 30 and the rapid charging performance. The reaction resistance on the vertical axis of FIG. 2 shows a negative correlation with the rapid charging performance. That is, the higher the reaction resistance, the lower the rapid charging performance.

Referring to FIGS. 1 and 2, when the average coverage of amorphous carbon coating 30 is less than 50% by area, initial charge/discharge efficiency and rapid charge performance are low. When the coverage of the amorphous carbon coating 30 is less than 50 area %, the exposed area of the surface of the active material particles 10 is large. Therefore, the surface of the active material particles 10 comes into contact with the electrolytic solution during the charging reaction, and the decomposition reaction proceeds. As a result, a film (SEI: solid electrolyte interface) derived from the decomposition reaction is thickly deposited on the surface of the active material particles 10. Since the SEI is formed thickly, it is considered that the initial charge/discharge efficiency is lowered and the quick charge performance is also lowered.

On the other hand, when the average coverage of the amorphous carbon coating 30 exceeds 90 area %, as shown in FIGS. 1 and 2, the initial charging/discharging efficiency is maintained, but the rapid charging performance is sharply reduced. When the average coverage of the amorphous carbon coating 30 is high, contact between the active material particles 10 and the electrolytic solution can be suppressed. Therefore, the decomposition reaction between the active material particles 10 and the electrolytic solution can be suppressed. However, if the average coverage of the amorphous carbon coating 30 is too high, it becomes difficult for metal ions to enter and leave the active material particles 10. Therefore, the alloying reaction between the metal active material in the active material particles 10 and the metal ion does not easily proceed, and the reaction resistance increases. As a result, the quick charge performance is reduced. Therefore, in the plurality of composite particles 1 having a particle diameter of not less than the median diameter (d50), the average coverage of the amorphous carbon coating 30 is 50 to 90 area %.

The preferable lower limit of the average coverage of the amorphous carbon coating 30 is 55 area %, more preferably 60 area %, further preferably 65 area %, further preferably 70 area %. The preferable upper limit of the average coverage of the amorphous carbon coating 30 is less than 90 area %, more preferably 88 area %, further preferably 85 area %, further preferably 80 area %.

[Method of Measuring Average Coverage of Amorphous Carbon Film 30]
The average coverage of the amorphous carbon coating 30 in the composite particle group is measured as follows. First, the median diameter (d50) of the composite particle group is measured by the following method. Collect any part of the complex particle group with a spoonful. The median diameter (d50) of the composite particle group is measured for the collected composite particles 1 by a laser diffraction scattering method according to JIS Z 8825 (2013).

Further, the plurality of composite particles 1 collected above are observed with a scanning electron microscope (Scanning Electron Microscope: SEM) at an acceleration voltage of 1.5 kV and a magnification of 5000 times to obtain a secondary electron image (hereinafter, SEM). Image). The longest diameter Dmax and the shortest diameter Dmin are measured for each composite particle in the SEM image. Then, the arithmetic mean value (=(Dmax+Dmin)/2) of the longest diameter Dmax and the shortest diameter Dmin is defined as the particle diameter (μm) of the composite particle.

Of the plurality of observed composite particles 1, 30 composite particles 1 having a particle size not less than the median diameter (d50) are arbitrarily selected. In each composite particle 1, the exposed region 20 has a lower conductivity than the amorphous carbon coating 30. Therefore, in the SEM image, the exposed region 20 is brighter than the amorphous carbon coating 30 and the amorphous carbon coating 30 is darker than the exposed region 20. Therefore, the coverage of the amorphous carbon coating 30 on each composite particle 1 is calculated based on the contrast in the SEM image.

Specifically, a grayscale SEM image of each composite particle is generated. The SEM image is composed of a plurality of pixels and has a plurality of gradations of brightness. The number of pixels of the SEM image is not particularly limited, but is, for example, 1.2 to 1.5 million pixels and the number of gradations of luminance is 256. From the gray scale SEM image, 30 composite particles 1 having a median diameter (d50) or more are selected. The outer edge of each selected composite particle 1 is surrounded by a line, and the area surrounded by the line (that is, the composite particle 1) is trimmed. The area of each trimmed composite particle 1 is calculated.

Next, the trimmed composite particle 1 is binarized to obtain the total area of the exposed region of the surface of the composite particle 1. Specifically, for the trimmed composite particle 1, a brightness histogram is created in which the horizontal axis represents gray scale brightness of 0 to 255 and the vertical axis represents the number of pixels. A well-known flattening process is performed on the luminance histogram to convert the trimmed composite particles 1 (SEM image) into gradation. Based on the brightness histogram, the trimmed composite particles 1 are separated into a black area (class 1) and a white area (class 2). More specifically, an arbitrary brightness value is provisionally determined as a threshold value and classified into classes. An average value, the number of pixels, and a variance value are obtained for each class. The degree of separation is obtained from the obtained average value, the number of pixels, and the variance value. The operation of obtaining the degree of separation is repeated with different threshold values. Find the threshold that maximizes the resolution. The threshold value (luminance value) when the degree of separation is maximum is defined as a binarization threshold value. Binarization processing is performed on the SEM image based on the obtained threshold value, and a binarized image is generated from the trimmed SEM image of the composite particle 1.

In the binarized image of the composite particles, the total area of the region exposed (exposed area is less than 1 [mu] m ² area, and an area of 1 [mu] m total area of ² or more exposed regions 20) obtained. The total area of the exposed region is the total area of pixels classified into the white region (class 2) in the binarized image. That is, the pixels classified into class 1 correspond to the amorphous carbon film 30. In each composite particle 1, using the area of the composite particle 1 and the total area of the exposed region, the coverage (area%) of the amorphous carbon film of each composite particle 1 is obtained by the following formula. ..
Coverage of amorphous carbon coating=(area of composite particle 1−total area of exposed region)/area of composite particle 1×100

The arithmetic average value of the coverages of the obtained 30 amorphous carbon coatings 30 is defined as the average coverage (area%) of the amorphous carbon coatings of the composite particle group.

[Number Density of Exposed Area 20 of Composite Particle Group]
In the composite particle group, the number density of the exposed regions 20 in which the surface of the active material particles 10 is exposed at 1 μm ² or more in the plurality of composite particles 1 having a particle size of not less than median diameter (d50) is 0.0010. 0.0500 pieces/μm ² .

When the number density of the exposed regions 20 is 0.0010 to 0.0500/μm ² or more, in the composite particles 1, the exposed regions 20 are often formed in the convex portions 11 where metal ions easily enter and leave. Therefore, the metal ions easily enter and leave the active material particles 10. As a result, the rapid charge performance can be improved while maintaining the high initial charge/discharge efficiency.

Specifically, when the number density of the exposed regions 20 in the plurality of composite particles 1 having a median diameter (d50) or more is 0.0010/μm ² or more, the rapid charging performance is sufficiently improved. Furthermore, if the number density of the exposed regions is 0.0500/μm ² or less, the decomposition reaction of the electrolytic solution due to contact between the active material particles 10 and the electrolytic solution can be suppressed, and as a result, the initial charge/discharge efficiency is improved. Is sufficiently high.

[Method of measuring number density of exposed region 20 of composite particle group]
The number density of the exposed regions 20 in the plurality of composite particles 1 having a particle diameter not less than the median diameter (d50) is measured by the following method. First, the median diameter (d50) of the composite particle group is measured by the following method. Collect any part of the complex particle group with a spoonful. The median diameter (d50) of the composite particle group is measured for the collected composite particles 1 by a laser diffraction scattering method according to JIS Z 8825 (2013). Further, the plurality of collected composite particles 1 are observed with an SEM at an accelerating voltage of 1.5 kV and a magnification of 5000 times to obtain an SEM image. For each composite particle 1 in the SEM image, the longest diameter Dmax and the shortest diameter Dmin are measured. Then, the arithmetic mean value (=(Dmax+Dmin)/2) of the longest diameter Dmax and the shortest diameter Dmin is defined as the particle diameter (μm) of the composite particle. Of the plurality of observed composite particles 1, 30 composite particles 1 having a particle size not less than the median diameter (d50) are arbitrarily selected.

In the SEM image, the outer edge of each selected composite particle 1 is surrounded by a line, and the area surrounded by the line (that is, the composite particle 1) is trimmed. The area of each trimmed composite particle 1 is obtained. Calculate the diameter of the circle (equivalent circle diameter) when the calculated area is converted to a circle. The value obtained by substituting the equivalent circle diameter into 4πr ² which is the formula of the surface area of the sphere is defined as the total surface area of each composite particle 1. That is, the total surface area of the composite particles 1 used to calculate the number density of the exposed regions 20 is the total surface area of the composite particles 1 alone. Well-known image processing software is used to enclose the outer edge of the composite particle 1 with a line, to trim the composite particle 1 surrounded by the line, to calculate the area of the trimmed composite particle 1, and to calculate the equivalent circle diameter. Can be obtained using. Well-known image processing software is, for example, trade name: imageJ.

Further, a grayscale SEM image of the trimmed composite particle 1 is prepared. Of the luminance values of each pixel of the grayscale SEM image of the trimmed composite particle 1, the difference between the highest luminance value and the lowest luminance value is equally divided into four, and a four-valued process is performed. In the quaternarization process, a plurality of pixels of the grayscale SEM image of the trimmed composite particle 1 are classified (leveled) into a highest area, a high area, a low area, and a lowest area in the order of high brightness value. Then, a region that belongs to the highest area and has a total area of a plurality of pixels that are continuously arranged is 1 μm ² or more is identified as an “exposed region 20”. When one or more certified exposed regions 20 are present, it is determined that at least one exposed region 20 is present in the composite particle 1. In addition, in the composite particle of the present embodiment, most of the exposed region 20 is formed in the convex portion 11. The upper limit of the area of the exposed region 20 is not particularly limited, but is less than 1/2 of the area of the trimmed composite particle 1.

Specifically, the determination of the exposed area 20 by the four-valued process is performed as follows. A grayscale SEM image of trimmed composite particle 1 is prepared. The number of pixels of the SEM image is 1.2 to 1.5 million, and the number of gradations of luminance is 256. From the trimmed gray scale SEM image of the composite particle 1, a gray scale luminance gradation is taken from 0 to 255 on the horizontal axis and a pixel number is taken on the vertical axis to create a luminance histogram. A well-known flattening process is performed on the luminance histogram to convert the grayscale SEM image of the trimmed composite particle 1 into gradation. In the luminance histogram of the grayscale SEM image whose gradation has been converted, a four-valued process is performed by dividing the difference between the highest luminance value and the lowest luminance value into four equal parts and dividing them into four areas. A quaternarized image in which a plurality of pixels of the grayscale SEM image of the composite particle 1 that has been trimmed by the quaternarization treatment are classified (level-divided) into a highest area, a high area, a low area, and a lowest area in descending order of luminance value. To generate.

FIG. 7 is a quaternary image of the SEM image of FIG. The white area 20 in FIG. 7 is the highest area and is an exposed area 20 having an area of 1 μm ² or more. Therefore, in FIG. 7, it is determined that at least one exposed region 20 exists in the plurality of convex portions.

As shown in an example in FIG. 7, in the plurality of convex portions 11 of the composite particle 1, at least one exposed region 20 in which the surface of the active material particle 10 is exposed by 1 μm ² or more is present.

With respect to 30 composite particles 1, the total surface area and the number of exposed regions 20 in each composite particle 1 are obtained. Then, a value obtained by dividing the total number of exposed regions 20 in 30 composite particles 1 by the total total surface area of 30 composite particles 1 is the number density of exposed regions 20 in the composite particle group (units/μm ² ) Is defined.

A preferable lower limit of the number density of the exposed regions 20 of the composite particle group is 0.0020/μm ² , more preferably 0.0030/μm ² , and further preferably 0.0050/μm ² . The number is more preferably 0.0100/μm ² , and even more preferably 0.0150/μm ² . A preferable upper limit of the number density of the exposed region 20 of the composite particle group is 0.0490 particles/μm ² , more preferably 0.0450 particles/μm ² , and further preferably 0.0440 particles/μm ² . The number is more preferably 0.0400 pieces/μm ² , and further preferably 0.0350 pieces/μm ² .

[Preferable specific surface area of composite particle group: 1.0 to 5.0 m ² /g]
The specific surface area of the composite particle group of the present embodiment is preferably 1.0 to 5.0 m ² /g. When the specific surface area is 1.0 m ² /g or more, the contact area with the electrolytic solution is sufficiently large and the reaction resistance decreases. As a result, the quick charging performance is improved. On the other hand, when the specific surface area is 5.0 m ² /g or less, the contact area with the electrolytic solution can be set within an appropriate range. Therefore, the electrolytic solution decomposition reaction can be suppressed. Therefore, in this embodiment, the specific surface area of the composite particle group is preferably 1.0 to 5.0 m ² /g. The preferable lower limit of the specific surface area is 1.2 m ² /g, and more preferably 1.5 m ² /g. The preferable upper limit of the specific surface area is 4.5 m ² /g, more preferably 4.0 m ² /g, further preferably 3.5 m ² /g, further preferably 3.0 m ² /g. is there. In the composite treatment step described below, the specific surface area of the composite particle group is 1.0 to 5. If the ratio of the carbon source mixed with the active material particles 10 is adjusted or the treatment time in the composite treatment step is adjusted. It can be 0 m ² /g.

[Method of measuring specific surface area of composite particle group]
The specific surface area of the composite particle group is determined by the BET (Brunauer, Emmet and Teller) method. Specifically, an arbitrary part of the composite particle group is scooped with a spoon and collected. Nitrogen (N ₂ ) gas molecules are adsorbed to the collected plurality of composite particles 1. The specific surface area (m ² /g) of the composite particle group is measured from the amount of adsorbed gas molecules.

Specifically, first, the single molecule adsorption amount (V _m ) is obtained from the relationship between the pressure (P) and the adsorption amount (V) by using the BET formula (Brunauer, Emmet and Teller's equation). Vm is the volume (mL) of gas molecules adsorbed on the surfaces of the plurality of composite particles 1. Then, the specific surface area of the plurality of composite particles 1 is obtained using the adsorption cross-sectional area (A _m ) of the gas molecule. A _m means the occupied area (nm ² ) per molecule. The specific surface area is calculated by the equation (3).
Specific surface area=(V _m ×N/M)×A _m /w (3)
Here, N is Avogadro's number (6.02×10 ²³ /mol), M is the molecular weight of gas molecule (mass of one gas molecule×N), and w is sample weight (g). In the case of nitrogen (N ₂ ), Am is 0.162 nm ² .

The obtained specific surface area (m ² /g) is defined as the specific surface area of the composite particle group.

[Number Density of Exposed Convex Composite Particles in Composite Particle Group]
As described above, in the composite particle group of the present embodiment, in the plurality of composite particles 1 having a particle diameter of the median diameter (d50) or more, the average coverage of the amorphous carbon coating 30 on the surface of the active material particles 10 is 50. In the plurality of composite particles 1 having a particle diameter of not less than 90 area% and a median diameter (d50) or more, the number density of the exposed regions 20 with respect to the total surface area of the plurality of composite particles is 0.0010 to 0.0500/ μm ² .

In the composite particle group, when the average coverage of the amorphous carbon coating 30 is 50 to 90 area% and the number density of the exposed regions 20 is 0.0010 to 0.0500/μm ^2, it is more preferable. In the composite particle group, among the plurality of composite particles 1 having a particle size not less than the median diameter (d50) of the composite particle group, the number ratio of the convex-exposed exposed composite particles is 80% or more.

The preferable lower limit of the number ratio of the convex-exposed exposed composite particles among the plurality of composite particles 1 having a particle size of the composite particle group median diameter (d50) or more is 85%, more preferably 88%, and further preferably Is 90%.

[Measurement method of number ratio of exposed convex composite particles in composite particle group]
The number ratio of the convex-part exposed composite particles can be measured by the following method. Collect any part of the complex particle group with a spoonful. The median diameter (d50) of the composite particle group is measured for the collected composite particles by a laser diffraction scattering method according to JIS Z 8825 (2013). Further, a part of the composite particle group (a plurality of composite particles 1) is observed with an SEM at an acceleration voltage of 1.5 kV and a magnification of 1000 times to obtain an SEM image. For each composite particle 1 in the SEM image, the longest diameter and the shortest diameter are measured. Then, the arithmetic mean value of the longest diameter and the shortest diameter is defined as the particle diameter (μm) of the composite particle 1.

From the plurality of composite particles 1 in the SEM secondary electron image, 30 composite particles 1 having a particle size not less than the median diameter (d50) are selected. With respect to each of the selected 30 composite particles 1, the coverage of the amorphous carbon coating 30 is obtained by the method described above. Further, the number of exposed regions 20 in each composite particle 1 is obtained by the above-described method of measuring the number density of exposed regions 20. Then, in each of the 30 composite particles, particles having a coverage of the amorphous carbon film 30 of 50 to 90 area% and having the exposed region 20 in one or more locations among the plurality of convex portions 11, It is certified as "exposed convex composite particle". The number of convex-part exposed composite particles in the 30 composite particles 1 is counted. The number ratio (%) of the convex-exposed composite particles in the composite particle group is calculated based on the obtained number of convex-exposed composite particles and the number (30) of the composite particles 1 to be measured.

FIG. 8 is an SEM image at 1000× of a composite particle group according to an embodiment of the present invention. Reference numeral 1 in FIG. 8 is a convex-part exposed composite particle. In FIG. 8, the number ratio of the convex-part exposed composite particles is 80%.

[Preferred median diameter of composite particle group (d50)]
The median diameter of the composite particle group is not particularly limited. The preferable median diameter (d50) of the composite particle group is 1 to 50 μm. When the median diameter (d50) is 1 μm or more, the specific surface area does not become too large. In this case, the exposed region 20 can be easily formed appropriately. Therefore, the quick charging performance is further enhanced. On the other hand, when the median diameter (d50) of the composite particle group is 50 μm or less, a flat and thin negative electrode can be manufactured.

The more preferable lower limit of the median diameter (d50) of the composite particle group is 3 μm, and more preferably 5 μm. The more preferable upper limit of the median diameter (d50) of the composite particle group is 45 μm, more preferably 40 μm, further preferably 35 μm, and further preferably 30 μm.

[Measurement method of median diameter (d50) of composite particle group]
The median diameter (d50) of the composite particle group is obtained by the following method. Collect any part of the complex particle group with a spoonful. The median diameter (d50) of the composite particle group is measured by a laser diffraction scattering method based on JIS Z 8825 (2013) for the collected composite particles. The dispersion medium in the measurement is water containing 0.1% by mass of a surfactant containing alkylglycoxide. The dispersion method is ultrasonic waves for 5 minutes. The average particle size (median size) of the composite particle group is defined as the particle size (volume average particle size by the laser diffraction scattering method) when the cumulative volume of all particles is 50%.

[Uses of composite particle group]
The composite particle group of the present embodiment can be used as an electrode, especially as a negative electrode active material particle group constituting a negative electrode of a non-aqueous electrolyte secondary battery. Further, in the non-aqueous electrolyte secondary battery, the negative electrode active material forming the negative electrode may be metallic lithium, and the composite particle group of the present embodiment may be used as the positive electrode active material particle group.

[Negative electrode active material particle group]
The negative electrode active material particle group of the present embodiment is composed of a plurality of negative electrode active material materials. Here, "comprising a plurality of negative electrode active material materials" allows the mixing of impurities. Specifically, 99% or more in the mass% of the negative electrode active material particle group of the present embodiment is a plurality of negative electrode active material materials.

The negative electrode active material particle group of the present embodiment contains the composite particle group described above. The negative electrode active material particle group may contain a plurality of negative electrode active material materials other than the composite particle group. The negative electrode active material other than the composite particle group is, for example, one or more kinds selected from the following first to sixth groups.
First group: at least one selected from the group consisting of graphite, amorphous carbon, and a fired polymer compound (for example, one obtained by firing and carbonizing a phenol resin, a furan resin, etc.) Second group: Cokes (for example, One or more selected from the group consisting of pitch coke, needle coke and petroleum coke)
Group 3: Carbon fiber Group 4: Conductive polymer (for example, one or more selected from the group consisting of polyacetylene and polypyrrole)
Fifth group: metal particles (for example, one or more selected from the group consisting of tin, silicon, lithium-tin alloy, lithium-silicon alloy, lithium-aluminum alloy, and lithium-aluminum-manganese alloy).
Group 6: Complex oxide of lithium and transition metal (for example, Li ₄ Ti ₅ O ₁₂ ).

That is, the negative electrode active material particle group of the present embodiment may be composed of the composite particle group and one or more kinds selected from the first group to the sixth group, and the balance may be impurities.

In the negative electrode active material particle group of the present embodiment, preferably, in a plurality of negative electrode active material materials having a particle size of median diameter (d50) or more, the ratio of the above-mentioned composite particle group is 70% or more. In this case, the negative electrode active material particle group has high initial discharge efficiency and excellent rapid charging performance. The preferable lower limit of the ratio of the composite particle group in the negative electrode active material particle group is 80%, more preferably 85%, further preferably 90%, further preferably 95%, most preferably 100%. (That is, the negative electrode active material particle group=the above-mentioned composite particle group).

[Method of measuring ratio of composite particle group in negative electrode active material particle group]
The ratio of the composite particle group in the negative electrode active material particle group can be measured by the following method. Scoop and collect any part of the negative electrode active material particles. The median diameters (d50) of the plurality of negative electrode active material materials are measured by a laser diffraction/scattering method based on JIS Z 8825 (2013) for the plurality of collected negative electrode active material materials. Further, a part of the negative electrode active material particle group (a plurality of negative electrode active material materials) is observed with an SEM at an acceleration voltage of 1.5 kV and a magnification of 1000 times to obtain an SEM image. The longest diameter and the shortest diameter of each negative electrode active material in the SEM image are measured. Then, the arithmetic mean value of the longest diameter and the shortest diameter is defined as the particle diameter (μm) of the negative electrode active material.

At least 30 negative electrode active material materials having a particle diameter of the median diameter (d50) or more are selected from the plurality of negative electrode active material materials in the SEM image. The composite particles 1 are specified from the selected negative electrode active material by the following method. A point analysis of the negative electrode active material is performed by energy dispersive X-ray analysis (EDS). When carbon (C), which is an element contained in the composite particles 1, and elements (Cu, Sn, Si, etc.) contained in the active material particles are detected as the measurement element species, the negative electrode active material is combined with The particle 1 is specified.

Further, the average coverage rate of the amorphous carbon coating 30 and the number density of the exposed regions 20 are obtained by the above-mentioned method for the identified plurality of composite particles 1. Then, whether or not the specified plurality of composite particles 1 correspond to a composite particle group, that is, a plurality of composite particles having a particle size of the median diameter (d50) or more among the specified plurality of composite particles 1 It is judged whether the coverage of the amorphous carbon of No. 1 is 50 to 90 area% and the number density of the exposed region 20 is 0.0010 to 0.0500 pieces/μm ² .

Of the plurality of specified composite particles 1, the coverage of the amorphous carbon coating 30 of the plurality of composite particles 1 having a particle size of the median diameter (d50) or more is 50 to 90 area %, and the exposed region When the number density of 20 is 0.0010 to 0.0500/μm ² , the plurality of composite particles 1 are recognized as a composite particle group. Then, a value obtained by dividing the number of the composite particles 1 constituting the composite particle group by 30 negative electrode active material is defined as a ratio (%) of the composite particle group.

[Negative electrode]
The negative electrode of the present embodiment contains an active material supporting member and a negative electrode mixture layer. The negative electrode mixture layer contains a negative electrode active material particle group and a binder in which the negative electrode active material particle group is dispersed. The negative electrode active material particle group contains a composite particle group.

[Negative electrode mixture layer]
The negative electrode mixture layer contains the above-mentioned negative electrode active material particle group and a binder.

A negative electrode active material particle group is dispersed in the binder. That is, a plurality of negative electrode active material materials are dispersed inside the binder. The binder may have a known configuration. The binder is, for example, one or more selected from the group consisting of water-insoluble resins that are insoluble in the solvent used for the non-aqueous electrolyte of batteries, water-soluble resins, and styrene-butadiene rubber (SBR). Consists of. Non-water-soluble resins that are insoluble in the solvent used for the non-aqueous electrolyte of the battery include, for example, polyimide (PI), polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA), and polytetrafluoroethylene. It is one or more selected from the group consisting of (PTFE). The water-soluble resin is, for example, one or more selected from the group consisting of carboxymethyl cellulose (CMC) and polyvinyl alcohol (PVA).

The active material support member is a thin film-shaped or plate-shaped support. A negative electrode mixture layer is formed on the surface of the active material supporting member. The active material support member is made of metal. The active material support member is made of a well-known material such as Cu, Ni, and stainless steel. In the case of the negative electrode for lithium ion secondary battery use, the active material supporting member is preferably made of Cu. This is because Cu does not easily form an alloy with lithium and is easily formed into a thin film.

The negative electrode mixture layer is formed by applying a negative electrode mixture slurry prepared by adding a solvent such as water to the negative electrode mixture to the active material supporting member and drying it.

The negative electrode active material material (composite particles, convex portion exposed composite particles) used for the negative electrode can be taken out by shaving the negative electrode material mixture layer adhering to the surface of the active material supporting member using a spatula. .. In the composite particles, peeling of the amorphous carbon coating 30 from the active material particles 10 due to shaving is negligibly small.

The negative electrode active material particle group in the negative electrode mixture layer may be a composite particle group. In this case, in the composite particle group (a plurality of composite particles 1), of the plurality of composite particles having a median diameter (d50) or more, the preferable number ratio of the convex-exposed composite particles is 80% or more, and It is preferably 90% or more.

When the negative electrode active material particle group in the negative electrode mixture layer contains not only the composite particle group but also the composite particle group and another negative electrode active material material, the composite particle group of the negative electrode active material particle group is preferable. The ratio is 70% or more, more preferably 80% or more, and further preferably 90% or more.

[battery]
The battery of this embodiment is a non-aqueous electrolyte secondary battery. The battery of this embodiment includes the above-mentioned negative electrode, positive electrode, separator, and electrolyte.

The shape of the battery of the present embodiment may be cylindrical, prismatic, coin-shaped, sheet-shaped or the like.

The positive electrode need only have a known configuration. Preferably, the positive electrode contains a transition metal compound containing a metal ion as an active material. More preferably, the positive electrode contains a lithium (Li)-containing transition metal compound as an active material. The Li-containing transition metal compound is, for example, LiM ₁ -xM′ _x O ₂ and/or LiM ₂ yM′O ₄ . Here, in the formula, 0≦x and y≦1, and M and M′ are barium (Ba), cobalt (Co), nickel (Ni), manganese (Mn), chromium (Cr), titanium ( Ti), vanadium (V), iron (Fe), zinc (Zn), aluminum (Al), indium (In), tin (Sn), scandium (Sc) and yttrium (Y). That is all.

The battery according to the present embodiment has, as the positive electrode having the above-described configuration, a transition metal chalcogenide, a vanadium oxide and a lithium (Li) compound thereof, a niobium oxide and a lithium compound thereof, a conjugated polymer using an organic conductive material, and Cheprel. Other well known positive electrodes such as phase compounds, activated carbon, activated carbon fibers and the like may be included.

When the electrolyte is an electrolytic solution, the electrolytic solution is generally a non-aqueous electrolytic solution in which a lithium salt as a supporting electrolyte is dissolved in an organic solvent. Examples of the lithium salt include lithium perchlorate (LiClO ₄ ), lithium borofluoride (LiBF ₄ ), lithium hexafluorophosphate (LiPF ₆ ), LiAsF ₆ , LiB(C ₆ H ₅ ), LiCF ₃ SO ₃ , and LiCH _{3. SO 3, Li (CF 3 SO} 2) 2 N, LiC 4 F 9 SO 3, Li (CF 2 SO 2) 2, LiCl, LiBr, and a LiI or the like. These may be used alone or in combination. As the organic solvent, carbonic acid esters such as propylene carbonate, ethylene carbonate, ethylmethyl carbonate, dimethyl carbonate and diethyl carbonate are preferable. However, various other organic solvents such as carboxylic acid ester and ether can also be used. These organic solvents may be used alone or in combination. When the electrolyte is a solid electrolyte, the battery of this embodiment is, for example, a polymer battery or an all-solid battery.

The separator is installed between the positive electrode and the negative electrode. The separator acts as an insulator. The separator also contributes significantly to the retention of the electrolyte. The separator may have a known configuration. The separator is, for example, a polyolefin material such as polypropylene, polyethylene, a mixture of both, or a porous body such as a glass filter.

The composite particles 1 can be taken out as described above by disassembling the battery, taking out the negative electrode, and scraping the negative electrode with a spatula. Peeling of the amorphous carbon coating 30 from the active material particles 10 due to shaving is negligibly small.

[Method for producing composite particle group]
An example of the method for producing the composite particle group of the present embodiment will be described. The composite particle group of the present embodiment is not limited to the manufacturing method described below. An active material particle 10 having a plurality of convex portions 11 and an amorphous carbon coating 30 are provided, and the average coverage of the amorphous carbon coating 30 on the surface of the active material particle 10 is 50 to 90 area %. If the number density of the exposed regions 20 is 0.0010 to 0.0500 particles/μm ² , the composite particle group of the present embodiment may be manufactured by a method other than the manufacturing method described below.

The method for manufacturing a composite particle group according to the present embodiment includes a step of preparing active material particles 10 having a plurality of convex portions 11 and a carbon source that is a raw material of the amorphous carbon coating film 30 (preparing step), and an active material. And a step of mixing and compositing the particles 10 and the carbon source with a dry particle compositing device (composite treatment step). Hereinafter, each step will be described in detail.

[Preparation process]
In the preparation step, a plurality of active material particles 10 and a carbon source which is a raw material of the amorphous carbon film 30 are prepared.

[Preparation of Active Material Particles 10]
The plurality of active material particles 10 may be those supplied by a third party or may be manufactured. When manufacturing, the active material particles 10 are manufactured by, for example, quenching a molten metal. The method of quenching the molten metal is, for example, a roll cooling method, a gas atomizing method, a rotating submerged spinning method, a melt spinning method, or the like.

Preferably, the active material particles 10 are manufactured by the following method. A molten metal having the components of the metal active material described above is produced. The molten metal is produced by melting the raw materials by a known melting method such as arc melting or resistance heating melting.

A metal active material is manufactured using the molten metal. The method for producing the metal active material is, for example, an ingot casting method, a strip casting method and a melt spin method. When the metal active material is manufactured by quenching, the metal ribbon 600 is manufactured by using the manufacturing apparatus 100 shown in FIG. 9 in consideration of production efficiency. FIG. 9 is a schematic view of an apparatus 100 for producing a metal active material of active material particles 10. The manufacturing apparatus 100 includes a cooling roll 200, a tundish 300, and a blade member 400.

The cooling roll 200 has an outer peripheral surface, and cools and solidifies the molten metal 500 on the outer peripheral surface while rotating. The cooling roll 200 rotates around the central axis of the cooling roll 200 by the drive source. RD shown in FIG. 9 is the rotation direction of the cooling roll 200. When manufacturing the metal ribbon 600, the cooling roll 200 rotates in the rotation direction RD. As a result, in FIG. 9, the molten metal 500 in contact with the cooling roll 200 is partially solidified on the outer peripheral surface of the cooling roll 200 and moves as the cooling roll 200 rotates. The tundish 300 can store the molten metal 500 and supplies the molten metal 500 onto the outer peripheral surface of the cooling roll 200.

The blade member 400 is arranged downstream of the tundish 300 in the rotation direction of the cooling roll 200 with a gap provided between the blade member 400 and the outer peripheral surface of the cooling roll 200. The blade member 400 is a member separate from the tundish 300, and is arranged downstream of the tundish 300 in the rotation direction RD of the cooling roll 200. The blade member 400 regulates the thickness of the molten metal 500 on the outer peripheral surface of the cooling roll 200 to the thickness of the gap between the outer peripheral surface of the cooling roll 200 and the blade member 400 to manufacture the metal ribbon 600. .. The thickness of the molten metal 500 is limited to the thickness of the gap between the blade member 400 and the cooling roll 200, and the molten metal 500 is cooled by the cooling roll 200 and the blade member 400. Thereby, the molten metal 500 is rapidly cooled and the metal ribbon 600 is manufactured.

Mechanical alloying treatment (MA treatment) is performed on the manufactured metal ribbon 600 to manufacture active material particles 10 having a plurality of convex portions 11. The mechanical alloying device is, for example, a high speed planetary mill. An example of the high-speed planetary mill is a product name, HIZY BX, manufactured by Kurimoto Iron Works Co., Ltd. At the time of MA treatment, the active material particles 10 are formed into a shape having a plurality of convex portions 11 without spheroidizing the active material particles 10.

[Preparation of carbon source]
In the preparation step, not only the active material particles 10 but also a carbon source is prepared. The amount of carbon source to be prepared (the amount of carbon source added) is selected according to the carbon source. The preferable addition amount of the carbon source is 0.01 to 15.00% by mass with the active material particles 10 as 100% by mass. When the addition amount of the carbon source is 0.01% by mass or more, the amorphous carbon film 30 can sufficiently cover the active material particles 10. That is, the coverage of the amorphous carbon coating 30 is 50 area% or more. When the amount of the carbon source added is 15.00% by mass or less, it is possible to obtain the amorphous carbon coating film 30 in a sufficient amount so that the coverage is 90% by area or less. Therefore, the preferable amount of carbon source added to the active material particles 10 is 0.01 to 15.00 mass% with the active material particles as 100 mass %. A more preferable lower limit of the amount of carbon source added to active material particles 10 is 0.10% by mass, and more preferably 1.00% by mass. A more preferable upper limit of the amount of carbon source added to active material particles 10 is 12.00% by mass, and more preferably 10.00% by mass.

[Complexing process step]
In the composite treatment step, the prepared active material particles 10 and the carbon source are mixed and composited using a dry particle composite device. Here, the term “compositing” refers to particles that are different from the core particles (matrix particles: active material particles 10 in the present embodiment) and are smaller than the mother particles (child particles. : In the present embodiment, the mixture with the carbon source) is subjected to mechanical energy such as compression, shearing, friction and impact to coat the mother particles with a large number of child particles without using a binder to form a composite. Means producing particles.

The dry particle compounding device is a device for performing compounding. In other words, the dry particle compounding apparatus is a mixture of particles of a substance serving as a core (hereinafter referred to as mother particles) and particles different from the mother particles and smaller than the mother particles (hereinafter referred to as child particles). Is a device for producing composite particles by applying mechanical energy such as compression, shearing, friction and impact to the mother particles to coat them with a large number of child particles without using a binder. The dry particle composite device is, for example, Nobilta Mini NOB-MINI (trademark), Nobilta NOB (registered trademark) or Nobilta NOB (registered trademark) manufactured by Hosokawa Micron Corporation.

Conventionally, a film is formed on the active material particles by a mechanofusion method, a mechanical alloying method, a mechanical grinding method, or a two-step firing method. The mechanofusion method is performed using, for example, Mechanofusion (trademark) manufactured by Hosokawa Micron Corporation. The mechanical alloying method uses, for example, a vibration mill. The mechanical grinding method uses, for example, a planetary ball mill. In these conventional methods, the amorphous carbon coating film 30 is not formed on the entire active material particles 10, but the amorphous carbon coating film 30 is partially formed on the surface of the active material particles 10. Therefore, it is difficult to selectively expose the convex portions 11 of the active material particles 10.

On the other hand, in the composite treatment step of the present embodiment, the amorphous carbon film 30 is once formed on the entire surface of the active material particles 10. After that, the amorphous carbon film 30 once formed on the convex portion 11 of the active material particle 10 is shaved to form the exposed region 20. More specifically, when the compounding treatment is performed using the dry particle compounding device, the amorphous carbon film 30 is once formed on the entire surface of the active material particles 10. In this embodiment, the compounding process is continued thereafter. In this case, the projections 11 of the composite particles have a larger number of collisions than the parts other than the projections 11. Therefore, the collision causes the amorphous carbon coating 30 on the protrusion 11 to be peeled off. As a result, the exposed region 20 can be formed.

It is known that dry particle compounding devices such as the Nobilta Mini NOB-MINI® or Nobilta NOB® have a special rotor shape. Due to this special rotor shape, the number of collisions of the composite particles 1 with each other becomes larger than in the conventional method. Therefore, if a dry particle compounding apparatus is used, the amorphous carbon coating film of the convex portion 11 of the composite particle 1 once coated with the amorphous carbon coating film 30 can be obtained by setting the manufacturing conditions in the compounding treatment as follows. 30 can be selectively shaved.

In the compounding process step, when the processing time at the compounding process step is defined as X (minutes) and the peripheral speed of the rotor of the dry particle compounding device is defined as Y (m/sec), the formula (1) is defined as Under the conditions that satisfy the conditions, the composite treatment is performed on the active material particles 10 having the plurality of convex portions 11 and the carbon source.
-1.0X+20≤Y≤-1.0X+50 (1)

It is defined as F1=-1.0X+20. F1 is the left side of Expression (1). If the rotor peripheral speed Y of the dry particle composite apparatus is less than F1, the rotor peripheral speed of the dry particle composite apparatus is too slow, or the processing time X in the composite processing step is too short. In this case, the average coverage of the amorphous carbon coating 30 becomes less than 50 area% or exceeds 90 area %. Further, the amorphous carbon coating film 30 coated on the convex portion 11 of the composite particle 1 may not be sufficiently peeled off, and no exposed region 20 may be generated. As a result, the composite particle group of this embodiment is not manufactured.

It is defined as F2=-1.0X+50. F2 is the right side of equation (1). If the rotor peripheral speed Y of the dry particle composite apparatus exceeds F2, the rotor peripheral speed of the dry particle composite apparatus is too fast, or the processing time X in the composite processing step is too long. In this case, the number of collisions between particles becomes excessively large. As a result, the average coverage of the amorphous carbon coating 30 becomes less than 50 area %.

FIG. 10 shows the peripheral speed Y (m/sec) of the rotor of the dry particle composite apparatus, the processing time X (minutes) in the composite processing step, and the median diameter under the manufacturing conditions of the composite particle group according to the present embodiment. The average coverage of the amorphous carbon coatings 30 of the plurality of composite particles 1 having a particle size of (d50) or more is 50 to 90 area %, and the number density of the exposed regions 20 is 0.0010 to 0.0500. It is a figure which shows the relationship with whether the composite particle group of this embodiment which is a piece/micrometer ² was manufactured. The mark "●" in FIG. 10 means that the composite particle group of the present embodiment was manufactured. The “x” mark in FIG. 10 means that the composite particle group of the present embodiment could not be manufactured. A broken line F1 is a straight line showing F1=−1.0X+20 when the processing time in the composite processing step is X (minutes) and the peripheral speed of the dry particle composite apparatus is Y (m/sec). .. The broken line F2 is a straight line indicating F2=-1.0X+50. With reference to FIG. 10, if the rotor peripheral speed Y is F1 or more and F2 or less, the composite particle group of the present embodiment can be manufactured.

Therefore, in the compounding process step, the compounding process is performed under the condition that the processing time X (minute) at the compounding process step and the peripheral speed Y (m/sec) of the rotor of the dry particle compounding device satisfy the formula (1). The conversion process is carried out.
-1.0X+20≤Y≤-1.0X+50 (1)

The preferable lower limit of the treatment time X in the complexing treatment step is 5 minutes, more preferably 7 minutes, and further preferably 10 minutes. The preferable upper limit of the treatment time X is 30 minutes, more preferably 25 minutes, further preferably 20 minutes.

A preferable lower limit of the rotor peripheral speed Y of the dry particle compounding device is 10 m/sec, more preferably 12 m/sec, and further preferably 14 m/sec. The preferable upper limit of the rotor peripheral speed Y is 35 m/sec, more preferably 30 m/sec, further preferably 25 m/sec, and further preferably 20 m/sec.

A composite particle group is manufactured by the above manufacturing process. By adjusting the manufacturing conditions, the average coverage of the amorphous carbon coating 30 in the composite particle group and the number density of the exposed regions 20 can be adjusted.

[Method for producing negative electrode active material particle group]
A negative electrode active material particle group is manufactured using the composite particle group or by mixing with a negative electrode active material material other than the composite particle group. As described above, the negative electrode active material particle group includes the composite particle group, the negative electrode active material particle group may be composed of only the composite particle group, or the composite particle group and a plurality of other than the composite particle group. It may be a group consisting of the negative electrode active material.

[Negative electrode manufacturing method]
An example of the method of manufacturing the negative electrode of this embodiment is as follows. The negative electrode active material particles are mixed with a binder to produce a negative electrode mixture.

A solvent such as water is added to the negative electrode mixture to produce a negative electrode mixture slurry. Specifically, the mixture obtained by mixing the negative electrode mixture and the solvent is sufficiently stirred using a homogenizer or glass beads as necessary to produce a negative electrode mixture slurry. This negative electrode material mixture slurry is applied onto the surface of the active material supporting member and dried to form a negative electrode material mixture layer on the active material supporting member. Further, if necessary, the active material supporting member and the negative electrode mixture layer after drying are pressed. The negative electrode is manufactured through the above steps.

[Battery manufacturing method]
A known method is used to produce a laminate in which the above-described negative electrode, separator, and positive electrode are laminated. The laminate is put in a case to manufacture a battery.

The effects of the composite particle group of the present embodiment will be described more specifically by way of examples. The conditions in the following examples are one example of conditions adopted to confirm the feasibility and effects of the composite particle group of the present embodiment. Therefore, the composite particle group of the present embodiment is not limited to this one condition example.

[Preparation of composite particle group]
[Preparation process]
[Preparation of active material particles]
Active material particles having the composition shown in Table 1 were prepared. Specifically, regarding Test No. 1 to Test No. 28, Test No. 31 to Test No. 36, and Test No. 38, the molten metal was added so that the active material particles have the chemical composition shown in “Composition” in Table 1. Manufactured. For example, in “Cu-20Sn-8Si” in the “Composition (at %)” column of the “Active material particles” column in Table 1, the active material particles of the corresponding test number are made of a metal active material, and are 20 at% Sn. , 8 at% Si, and the balance is Cu and impurities. “Cu-18Sn-17Si” in the “Composition (at %)” column of the “Active material particles” column of Table 1 indicates that the active material particles of the corresponding test number are made of a metal active material, and 18 at% Sn and 17 at % Si and the balance consists of Cu and impurities. Test number 29 means that the active material particles are made of Si. Test No. 30 means that the active material particles consist of In. Test No. 37 means that the active material particles consist of Sn. The active material particles of all test numbers were particles made of a metal active material.

The molten metal temperature was maintained at 1200°C. Then, the molten metal of 1200 degrees was rapidly cooled by a strip casting method to cast a metal ribbon having a thickness of 75 μm. In strip casting, the manufacturing apparatus 100 shown in FIG. 9 was used. Specifically, a water-cooled copper cooling roll 200 was used. The rotation speed of the cooling roll 200 was 300 m/min in terms of the peripheral speed of the roll surface. The above-mentioned molten metal 500 was supplied to a rotating cooling roll 200 through a horizontal tundish 300 (made of alumina) in an argon atmosphere. The molten metal 500 was placed on the surface of the rotating cooling roll 200 and sandwiched between the cooling roll 200 and the blade member 400 to rapidly solidify the molten metal 500. The width of the gap between the blade member 400 and the cooling roll 200 was 80 μm. The blade member 400 was made of alumina.

The obtained metal ribbon was further crushed to produce active material particles having a plurality of protrusions. A high-speed planetary mill (Kurimoto Iron Works Co., Ltd., trade name Heidi BX) was used for the pulverization process. In order to control the particle size, the grinding time was adjusted as follows. The rotation speed was 500 rpm. After the pulverization, a coarse powder having a particle size exceeding the following particle size was further removed using a stainless steel sieve.

Specifically, in test numbers 1 to 7, 16 to 24, 26, 31 to 35, and 38, the crushing time was set to 1 hour. Furthermore, a sieve having an opening of 45 μm was used. As a result, the average particle diameter (median diameter d50) of the active material particles of these test numbers was 20 μm.

In Test Nos. 11, 12, 15 and 27, the grinding time was set to 2 hours. Further, a sieve having an opening of 20 μm was used. As a result, the average particle diameter (median diameter d50) of the active material particles of these test numbers was 12 μm.

In test numbers 8 to 10, 13, 14, 25 and 28, the crushing time was 5 hours. Further, a sieve having an opening of 20 μm was used. As a result, the average particle diameter (median diameter d50) of the active material particles of these test numbers was 8 μm.

In test number 29, active material particles made of Si were used. The crushing time was 5 hours, and a sieve having an opening of 45 μm was used. As a result, the average particle diameter (median diameter d50) of the active material particles of Test No. 29 was 20 μm.

In Test No. 30, production of active material particles made of In was attempted. However, since the Vickers hardness (HV) of In was too low, active material particles could not be generated.

In Test No. 36, the grinding time was 0.5 hours. Furthermore, a sieve having an opening of 100 μm was used. As a result, the average particle diameter (median diameter d50) of the active material particles of Test No. 36 was 35 μm.

In test number 37, active material particles made of Sn were used. The crushing time was 5 hours, and a sieve having an opening of 45 μm was used. As a result, the average particle diameter (median diameter d50) of the active material particles of Test No. 37 was 20 μm.

The average particle size of the active material particles of each test number was measured by the following method. The laser diffraction scattering method based on JIS Z 8825 (2013) was adopted for the measurement of the average particle diameter. The dispersion medium in the measurement was water containing 0.1% by mass of a surfactant containing alkylglycoxide. The dispersion method was ultrasonic waves for 5 minutes. The particle size (volume average particle size by laser diffraction scattering method) when the cumulative volume of all the active material particles was 50% was defined as the average particle size (median size) of the active material particles.

[Vickers hardness measurement]
The Vickers hardness of the active material particles was measured by the following method. The active material material was mixed with the liquid epoxy resin precursor and the curing agent to obtain a mixture. As the curing agent, a commercially available epoxy resin curing agent was used. This mixture was poured into a mold and cured to obtain a cured product. The surface of the cured product taken out from the mold (hereinafter referred to as the measurement surface) was wet-polished using sandpaper to form a measurement surface including the cross section of the active material particles. The measurement surface including the cross section of the active material particles was polished and finished with aluminum oxide powder to obtain a measurement sample. In the polishing finish, the particle size of the aluminum oxide powder was gradually reduced (0.3 μm and 0.06 μm in this order), and the active material particles in the measurement plane were polished to have a flat cross section. After polishing, the Vickers hardness of the cross section of the active material particles in the measurement plane was measured using a micro Vickers hardness meter. Specifically, the Vickers hardness was measured by aligning the indenter with the approximate center of the cross section of the active material particle using an optical microscope. The test load was 50 gf. A diamond indenter was used as the indenter. As the micro Vickers hardness meter, MVK-G2 manufactured by Akashi Seisakusho was used. The obtained Vickers hardness is shown in Table 1.

[Preparation of carbon source]
In order to form an amorphous carbon film, the carbon sources shown in the column "carbon source at the time of producing composite particles" in Table 1 were prepared. The term "carbon source during the production of composite particles" means that the following products were used.
(A) Conductive carbon black Product name: SuperC65 (manufactured by Imerys Graphite & Carbon Co., specific surface area: 63 m ² /g)
(B) Acetylene black Product name: HS-100 (manufactured by Denka Co., specific surface area: 39 m ² /g)
(C) Resin Product name: Polyethylene glycol 20000 (manufactured by Wako Pure Chemical Industries, Ltd.)
(D) Ketjen Black Product name: Carbon ECP600JD (manufactured by Lion Specialty Chemicals, specific surface area: 1300 m ² /g)
(E) Carbon fiber Product name: VGCF-H (Showa Denko KK, specific surface area: 13 m ² /g)

Test No. 18 means that a mixture of conductive carbon black and resin was used as the carbon source. Test number 19 means that a mixture of acetylene black and resin was used. Test number 20 means that a mixture of Ketjen black and resin was used. In Test Nos. 26 to 28, it means that the carbon source was not used (indicated by "-" in Table 1).

[Complexing process step]
A composite treatment was carried out using the prepared active material particles and carbon source to produce a composite particle group. Specifically, in Test Nos. 1 to 25, 29 to 31, and 35 to 38, the carbon source addition amount (% by mass) relative to 100% by mass of the active material particles was adjusted to the amount shown in Table 2.

In Test Nos. 1 to 25, 29 to 31, and 36 to 38, Novirta Mini NOB-MINI (registered trademark) manufactured by Hosokawa Micron Co., Ltd. was used as a dry particle composite device. Using the dry particle compounding apparatus, 20 g of the active material particles and the carbon source having the addition amount shown in Table 2 (mass% when the mass of the active material particles was 100) were charged into the dry particle compounding apparatus. .. In addition, in the test numbers 18 to 20 in which the resin was used as the carbon source, the addition amount of the resin was 5% by mass with respect to the total mass of the active material particles, the carbon source and the resin. A composite particle group was manufactured by performing the composite processing at the rotor peripheral speed Y (m/sec) and the processing time X (minutes) shown in Table 2. The manufactured composite particle group was vacuum packed and stored. The "rotor speed (rpm)" in Table 2 indicates the rotor speed. The “F1” column shows the F1 value. The F2 value is shown in the "F2" column.

In test number 35, active material particles and a carbon source were physically mixed using a high-speed planetary mill device (trade name: HYGY BX manufactured by Kurimoto Iron Works Co., Ltd.) without performing the composite treatment. The manufactured particle group was vacuum packed and stored.

In test number 32, the composite particle group of test number 1 and the composite particle group of test number 31 were mixed at a mass ratio of 80:20. In Test No. 33, the composite particle group of Test No. 1 and Si particles (median diameter d50: 20 μm) were mixed at a mass ratio of 75:25. In Test No. 34, the composite particle group of Test No. 1 and Si particles (median diameter d50 is 20 μm) were mixed at a mass ratio of 50:50. The manufactured particle group was vacuum packed and stored.

[Measurement of median diameter (d50) of composite particle group]
The median diameter (d50) of the obtained composite particle group was measured by the following method. The laser diffraction scattering method based on JIS Z 8825 (2013) was adopted for the measurement. The dispersion medium in the measurement was water containing 0.1% by mass of a surfactant containing alkylglycoxide. The dispersion method was ultrasonic waves for 5 minutes. The particle size (volume average particle size by laser diffraction scattering method) when the cumulative volume to the volume of all the composite particles was 50% was defined as the median diameter (d50) of the composite particle group. A particle size distribution measuring device (trade name: Microtrac FRA) manufactured by Microtrac Bell was used for the measurement. As a result of the measurement, the median diameter (d50) was 1 to 50 μm in any of the composite particle groups having any test number.

[Measurement of specific surface area of composite particle group]
The specific surface area of the composite particle group was measured by the BET method. Specifically, gas molecules of nitrogen (N ₂ ) were adsorbed on the composite particles. The specific surface area of the composite particle group was measured from the amount of adsorbed gas molecules. The specific surface area was calculated by the formula (3).
Specific surface area=(V _m ×N/M)×A _m /w (3)
Here, Vm is the volume (mL) of gas molecules adsorbed on the surface of the composite particles, N is Avogadro's number (6.02×10 ²³ /mol), and M is the molecular weight of gas molecules (mass of one gas molecule× N) and w were sample weights (g). A _m is the area occupied per one molecule, was 0.162nm ^2. For the measurement, a product name Kantosorb manufactured by Yuasa Ionics Co., Ltd. was used. The measurement conditions were nitrogen gas adsorption, degassing temperature of 200° C., and 1 hour.

[Measurement of Average Coverage of Amorphous Carbon Film of Composite Particle Group]
The average coverage of the amorphous carbon coating in the composite particle group was measured as follows. An arbitrary part of the composite particle group was scooped with a spoon and collected. The median diameter (d50) of the composite particle group was measured by the method described above for the plurality of collected composite particles. Further, the plurality of composite particles collected above were observed using an SEM (VE-9800 type manufactured by Keyence Corporation) at an acceleration voltage of 1.5 kV and a magnification of 5000 times to obtain an SEM image. The number of pixels of the SEM image was 1228800 (1280x960). The longest diameter Dmax and the shortest diameter Dmin of each composite particle in the SEM image were measured. Then, the arithmetic mean value (=(Dmax+Dmin)/2) of the longest diameter Dmax and the shortest diameter Dmin was defined as the particle diameter (μm) of the composite particles. Of the plurality of observed composite particles, 30 composite particles having a particle size not less than the median diameter (d50) were arbitrarily selected. In the SEM image, the outer edge of each selected composite particle 1 is surrounded by a line, and the area surrounded by the line (that is, the composite particle) is trimmed. The area of each trimmed composite particle was calculated.

Next, the trimmed composite particles were binarized to obtain the total area of the exposed regions on the surface of the composite particles. Specifically, with respect to the trimmed composite particles, a brightness histogram was created in which the horizontal axis represents gray scale brightness of 0 to 255 and the vertical axis represents the number of pixels. A well-known flattening process was performed on the brightness histogram, and the trimmed composite particles (SEM image) were subjected to gradation conversion. Based on the brightness histogram, the trimmed composite particles were separated into a black area (class 1) and a white area (class 2). More specifically, an arbitrary brightness value is tentatively set as a threshold value and classified into classes. The average value, the number of pixels, and the variance value were obtained for each class. The degree of separation was calculated from the calculated average value, the number of pixels, and the dispersion value. The operation of obtaining the degree of separation was repeated with different thresholds. We have found a threshold that maximizes the degree of separation. The threshold value (luminance value) when the degree of separation is maximum is defined as the threshold value for binarization. Binarization processing was performed on the SEM image based on the obtained threshold value, and a binarized image was generated from the SEM image of the trimmed composite particles.

In the binarized image of the composite particles, the total area of the region exposed (exposed area is less than 1 [mu] m ² area, and an area of 1 [mu] m total area of ² or more exposed regions 20) was determined. The total area of the exposed region is the total area of pixels classified into the white region (class 2) in the binarized image. That is, the pixels classified into class 1 correspond to the amorphous carbon film 30. In each composite particle, using the area of the composite particle and the total area of the exposed region, the coverage (area%) of the amorphous carbon film of each composite particle was obtained by the following formula.
Coverage of amorphous carbon film=(area of composite particles-total area of exposed regions)/area of composite particles×100

The arithmetic average value of the coverage of the obtained 30 amorphous carbon coatings 30 was defined as the average coverage (area%) of the amorphous carbon coating of the composite particle group.

[Confirmation of amorphous carbon film]
Whether or not the coating of the composite particles was an amorphous carbon coating was confirmed by the following method. The above X-ray diffraction measurement was performed on the coating film of the composite particles to obtain an X-ray diffraction profile. In the X-ray diffraction profile, the crystallite diameter Lc was calculated from the Scherrer formula for a broad peak at 2θ=20 to 30° obtained in the case of amorphous carbon. When the crystallite size was 50 nm or less, the coating of the composite particles was judged to be an amorphous carbon coating.

[Measurement of number density of exposed region of composite particle group]
The presence or absence of the exposed area was determined as follows. The SEM image used in the measurement of the average coverage of the amorphous carbon coating of the composite particle group was used. Among the plurality of composite particles in the SEM image, 30 composite particles having a particle diameter not less than the median diameter (d50) were arbitrarily selected.

In the SEM image, the outer edge of each selected composite particle was surrounded by a line, and the area surrounded by the line (that is, the composite particle) was trimmed. The area of each trimmed composite particle was determined. The diameter of the circle (circle equivalent diameter) when the calculated area was converted to a circle was calculated. The value obtained by substituting the equivalent circle diameter into 4πr ² which is the formula of the surface area of the sphere was defined as the total surface area of each composite particle 1. Well-known image processing software (trade name: imageJ) is used to enclose the outer edge of the composite particle with a line, to trim the composite particle surrounded by the line, to calculate the area of the trimmed composite particle, and to calculate the equivalent circle diameter. ) Was used.

A grayscale SEM image of the trimmed composite particles was prepared. The number of pixels of the SEM image before trimming was 1228800 (1280×960), and the number of luminance gradations was 256. From the grayscale SEM image of the trimmed composite particles, a luminance histogram in which the horizontal axis represents grayscale luminance gradation from 0 to 255 and the vertical axis represents the number of pixels was created. A well-known flattening process was performed on the luminance histogram, and the grayscale SEM image of the trimmed composite particles was subjected to gradation conversion. In the luminance histogram of the grayscale SEM image whose gradation has been converted, a four-valued process was performed in which the difference between the highest luminance value and the lowest luminance value was equally divided into four areas. By the quaternarization treatment, a plurality of pixels of the grayscale SEM image of the trimmed composite particles are classified (leveled) into a highest area, a high area, a low area, and a lowest area in the order of high luminance value to obtain a quaternary image. Generated. Then, a region that belongs to the highest area and has a total area of a plurality of pixels arranged continuously of 1 μm ² or more was identified as an “exposed region”.

When the coverage of the amorphous carbon film is 50 to 90 area% in the composite particles and one or more exposed regions are present in the plurality of convex portions, the composite particle is referred to as “projection exposed composite”. Certified as "particles". For 30 composite particles, it was determined whether or not the composite particles were exposed convex portions. Among the 30 composite particles, the number of convex-part exposed composite particles was counted. Then, the ratio (%) obtained by dividing the number of convex-exposed composite particles by the number of composite particles (30) was defined as the number-proportion (%) of exposed convex composite particles.

Furthermore, for 30 composite particles, the total surface area and the number of exposed regions in each composite particle were determined. Then, a value obtained by dividing the total number of exposed regions of the 30 composite particles by the total of the total surface areas of the 30 composite particles was defined as the number density (units/μm ² ) of the exposed regions of the composite particle group. ..

[Preparation of negative electrode active material particle group]
The negative electrode active material particle group shown in Table 3 was prepared. In Test No. 32, the composite particle group of Test No. 1 and the composite particle group of Test No. 31 were physically mixed at a mass ratio of 80:20 to obtain a negative electrode active material particle group. In Test No. 33, the composite particle group of Test No. 1 and Si were physically mixed in a mass ratio of 75:25 to obtain a negative electrode active material particle group. In Test No. 34, the composite particle group of Test No. 1 and Si were physically mixed at a mass ratio of 50:50 to obtain a negative electrode active material particle group. For other test numbers, the composite particle group was used as the negative electrode active material particle group. The ratio of the composite particle group in the negative electrode active material particle group was measured as described above.

[Manufacturing of battery (coin cell) (for initial charge/discharge efficiency measurement)]
A coin cell was manufactured using the negative electrode active material particles obtained above, and the initial charge/discharge efficiency was evaluated. More specifically, as described below, a coin cell was manufactured using the negative electrode using the negative electrode active material particle group obtained above, the counter electrode, the electrolytic solution, and the separator.

[Manufacture of negative electrode for coin cell]
A negative electrode mixture slurry containing negative electrode active material particles of each test number was manufactured. Specifically, a negative electrode active material particle group, acetylene black (AB) as a conduction aid, styrene butadiene rubber (SBR) as a binder (2-fold dilution liquid), and carboxymethyl cellulose (CMC) as a thickener. : Daicel Fine Chemical Co., Ltd. product number 1160) were mixed in a mass ratio of 97:1:1:1 to prepare a mixture. Distilled water was added to the mixture using a kneader to produce a negative electrode mixture slurry.

The negative electrode mixture slurry was thinly applied on one side of a 17 μm thick electrolytic copper foil using an applicator (75 μm) and dried at 100° C. for 20 minutes to form a coating film. The dried copper foil had a coating film composed of a negative electrode mixture layer on the surface. The copper foil on which the negative electrode mixture layer was formed was punched to produce a disk-shaped copper foil having a diameter of 13 mm. The punched copper foil was pressed with a pressing pressure of 500 kgf/cm ² to manufacture a plate-shaped negative electrode.

[Counter electrode (positive electrode) for coin cell]
Li metal foil was used for the positive electrode.

[Electrolyte for coin cell]
A non-aqueous solution was used as the electrolytic solution. The non-aqueous solution contains lithium hexafluorophosphate (LiPF ₆ ):dimethyl carbonate (DMC):ethylene carbonate (EC):ethyl methyl carbonate (EMC):vinylene carbonate (VC):fluoroethylene carbonate (FEC) 16:48: A composition having a mass ratio of 23:4:1:8 was used.

[Separator for coin cell]
A polyolefin separator (φ19 mm) was used as the separator.

[Manufacture of coin cell]
A coin-type non-aqueous test cell (coin cell) was manufactured using the prepared negative electrode, positive electrode, electrolytic solution, and separator. A separator, a negative electrode, and a counter electrode were placed in a stainless steel coin cell can containing an electrolytic solution to obtain a coin cell.

In the evaluation of the positive electrode Li, the doping of Li into the negative electrode is treated as discharge. However, since the negative electrode material is evaluated in this example, the “charge capacity” and the “discharge capacity”, which are not described below, mean the capacity on the doped side and the capacity on the dedoped side, respectively.

[Evaluation of initial charge/discharge efficiency]
The initial charging/discharging efficiency of the battery of each test number was evaluated by the following method. A charge/discharge device manufactured by Electrofield was used for the measurement of the initial charge/discharge efficiency. The temperature at the time of measurement was measured at room temperature (23°C).

Constant current charging was performed on the coin type non-aqueous test cell with a current value of 0.15 mA until the potential difference became 0.005 V with respect to the counter electrode. After that, while maintaining 0.005 V, the counter electrode was continuously charged with a constant voltage until the current reached 0.005 mA, and the charge capacity was measured.

Next, discharge was performed at a current value of 0.15 mA until the potential difference became 1.5 V, and the discharge capacity was measured. The initial charge/discharge efficiency was calculated as (initial discharge capacity)/(initial charge capacity)×100. Those having an initial charge/discharge efficiency of 80.0% or more were evaluated as being excellent in initial charge/discharge efficiency.

[Manufacture of battery (laminate cell) (for measuring reaction resistance (rapid charging performance)])
A laminate cell was manufactured using the obtained negative electrode active material particle group, and reaction resistance was measured in order to evaluate rapid charging performance.

[Manufacture of negative electrode for laminate cell]
A negative electrode for a laminated cell was manufactured in the same manner as the negative electrode for a coin cell described above, and a negative electrode plate of 2.5 cm×2.5 cm was cut out.

[Manufacture of positive electrode for laminated cell]
Lithium cobalt oxide (LiCoO ₂ ) was used as an active material for the positive electrode for the laminate cell. The positive electrode was manufactured as follows.

A mixture was prepared by mixing 10 parts by mass of acetylene black (AB) powder with 80 parts by mass of the positive electrode active material (powder). Further, 10 parts by mass of polyvinylidene fluoride (PVdF) dispersion was added to the mixture and then stirred to prepare a positive electrode mixture slurry. The compounding ratio was a mass ratio, and the positive electrode active material:acetylene black:PVDF=80:10:10 (the compounding amount was 0.8 g:0.1 g:0.1 g).

The produced positive electrode mixture slurry was thinly applied on one surface of an aluminum foil having a thickness of 17 μm using an applicator (150 μm) and dried at 100° C. for 20 minutes to form a coating film. 2.3 cm×2.3 cm was cut out from the aluminum foil having the coating film. The cut aluminum foil was pressed by a press molding machine to manufacture a positive electrode plate. The pressure applied by the press molding machine was adjusted to be 500 kgf/cm ² .

[Manufacture of laminated cells]
A laminated cell battery was manufactured using the manufactured negative electrode plate and positive electrode plate. A non-aqueous solution was used as the electrolytic solution. The non-aqueous solution used had a composition such that LiPF ₆ :DMC:EC:EMC:VC:FEC had a mass ratio of 16:48:23:4:1:8. Celgard 2100 was used as a separator. A laminated cell was manufactured using a negative electrode plate, an electrolytic solution, a separator, a positive electrode plate, and an aluminum laminate sheet. Two separators were sandwiched between the negative electrode plate and the positive electrode plate, and an aluminum wire (0.25 mmφ) was placed between the two separators. An aluminum wire (0.25 mmφ) was used as a reference electrode.

[Pre-treatment of laminate cell (pre-treatment before calculation of reaction resistance)]
As a pretreatment for calculating the reaction resistance, a charge/discharge test was carried out at room temperature (23° C.) so that the laminate cell had a state of charge (SOC) of 50%. The charging/discharging device used was manufactured by Electrofield.

The specific processing method is described below. The charging conditions were constant current charging and then constant potential charging. After constant current charging at 0.1 mA/cm ² to 4.2 V, constant potential charging was performed at 4.2 V until the current value became 0.01 mA/cm ² . The discharge conditions were constant current discharge. Specifically, constant current discharge was performed at 0.1 mA/cm ² to 3.0 V. The above charging/discharging was repeated for 2 cycles. After that, constant current charging was performed so that the SOC became 50%.

[Production of reference electrode]
The positive electrode and the reference electrode (aluminum wire (0.25 mmφ)) of the pre-processed laminate cell are connected by the terminal of the charging/discharging device, and the potential and current are controlled using the charging/discharging device. As a result, lithium was alloyed with the aluminum wire (0.25 mmφ) installed between the two separators. Specifically, it was charged at a constant current of 0.03 mA so that the amount of electricity charged was 0.3 mAh.

[Evaluation of rapid charging performance]
The laminated cell for which the pretreatment and the production of the reference electrode were completed was kept at a set temperature of -30°C for 3 hours or more in a constant temperature bath. After that, AC impedance measurement was performed using a product name modulab manufactured by Solartron. At this time, the impedance between the negative electrode and the reference electrode was measured with the negative electrode as the working electrode. The measurement conditions were an amplitude of 5 mV and a frequency range of 0.1 Hz to 10 kHz. ZPlot (registered trademark) (manufactured by Scribner Associates, Inc.) was used as the analysis software. From the arc component obtained by the Nyquist plot of the AC impedance measurement, the reaction resistance was determined by fitting with an equivalent circuit (Instant fit Rs (CPE-Rp)) with ZPlot (registered trademark) built-in. When the reaction resistance was 600Ω or less, it was evaluated as excellent in rapid charging performance.

[Measurement result]
The results are shown in Table 3.

With reference to Tables 1 to 3, the coatings of the composite particles and the composite particle groups of test numbers 1 to 15, 33, and 37 were amorphous carbon coatings. Furthermore, the average coverage of the amorphous carbon coatings of the composite particle groups of Test Nos. 1 to 15, 33 and 37 was 50 to 90 area %. Furthermore, the number density of the exposed regions was 0.0010 to 0.0500/μm ² . Furthermore, in Test Nos. 1 to 15, 33 and 37, the number ratio of exposed convex composite particles in the composite particle group was 80% or more, and the number ratio of composite particles in the negative electrode active material particle group was 70% or more. there were. As a result, the reaction resistance was less than 600Ω and the initial charge/discharge efficiency was 80.0% or more, and both excellent rapid charge performance and initial charge/discharge efficiency could be achieved.

On the other hand, the test number 16 did not satisfy the formula (1) because the processing time at the time of the composite processing step was short. Therefore, the average coverage of the amorphous carbon coating was less than 50 area %. Further, the number density of exposed regions exceeded 0.0500/μm ² . As a result, the quick charge performance was low and the initial charge/discharge efficiency was low.

Test No. 17 did not satisfy the formula (1) because the peripheral speed of the dry particle composite device was low. Therefore, the average coverage of the amorphous carbon coating exceeded 90% by area. As a result, the quick charging performance was low. It is considered that since the peripheral speed was slow, the rate at which the coating of the convex portions was mechanically peeled off decreased, and the average coverage of the amorphous carbon coating exceeded 90 area %.

Test number 18 contained resin as the carbon source. Therefore, the average coverage of the amorphous carbon coating exceeded 90% by area due to the adhesive effect of the resin. Therefore, the quick charging performance was low. It is considered that the inclusion of the resin facilitates adhesion due to the amphipathic effect (adhesive-like effect) due to the functional group contained in the resin, and thus the coverage of the amorphous carbon film is increased.

Test number 19 contained resin as the carbon source. Therefore, the average coverage of the amorphous carbon coating exceeded 90% by area due to the adhesive effect of the resin. Therefore, the quick charging performance was low. It is considered that the inclusion of the resin facilitates adhesion due to the amphipathic effect (adhesive-like effect) due to the functional group contained in the resin, and therefore the average coverage of the amorphous carbon film is increased.

Test No. 20 contained a resin as a carbon source, and further contained Ketjen Black. Since the specific surface area of Ketjen Black was as high as 1300 m ² /g, the specific surface area of the composite particles became high, and the average coverage of the amorphous carbon coating exceeded 90 area %. Furthermore, the number density of the exposed regions was less than 0.0010/μm ² . As a result, the quick charging performance was low.

In Test Nos. 21 to 23, carbon fiber was used as the carbon source. Therefore, the average coverage of the amorphous carbon coating was less than 50 area %. Further, the number density of exposed regions exceeded 0.0500/μm ² . As a result, the initial charge/discharge efficiency was low. Since the carbon fibers are fibrous, they have a mesh-like coating form, and as a result, it is considered that the coverage of the amorphous carbon coating was low. Further, it is considered that the coverage is lowered because the fibers are cut (broken) by the mechanical coating.

Test No. 24 did not satisfy the formula (1) because the peripheral speed of the dry particle composite device was slow. In addition, it contained Ketjen Black. Therefore, the exposed area was hardly confirmed, and the number density of the exposed area was less than 0.0010 pieces/μm ² . As a result, the quick charging performance was low.

In Test No. 25, since the specific surface area of Ketjen Black was as high as 1300 m ² /g, the specific surface area of the composite particles became high, and the average coverage of the amorphous carbon coating exceeded 90 area %. Furthermore, the number density of the exposed regions was less than 0.0010/μm ² . As a result, the quick charge performance was low and the initial charge/discharge efficiency was low.

In Test Nos. 26 to 28, the active material particles were not covered with the amorphous carbon film. As a result, the quick charge performance was low and the initial charge/discharge efficiency was low. It is considered that since the active material particles have a large exposed area, a coating film (SEI: solid electrolyte interface) derived from decomposition of the electrolytic solution becomes thick during the charging reaction.

In test number 29, the average coverage of the amorphous carbon coating exceeded 90 area %. Furthermore, the number density of the exposed regions was less than 0.0010/μm ² . As a result, the quick charging performance was low. It is considered that the exposed region could not be sufficiently formed because the Vickers hardness of Si, which is the composition of the active material particles, was too high.

In Test No. 30, the composition of the active material particles was In. Since the Vickers hardness of In was too low, powder could not be formed. Therefore, the subsequent evaluation was not conducted.

In test number 31, the peripheral speed of the dry particle compounding apparatus was too high. Therefore, the average coverage of the amorphous carbon coating was less than 50 area %. Further, the number density of exposed regions exceeded 0.0500/μm ² . As a result, the quick charge performance was low and the initial charge/discharge efficiency was low.

In test number 32, the composite particle group of test number 1 and the composite particle group of test number 31 were physically mixed so that the mass ratio was 80:20. Since the number ratio of the convex-exposed exposed composite particles in the composite particle group was less than 80%, the initial charge/discharge efficiency was slightly low.

In Test No. 34, the composite particle group of Test No. 1 and Si were physically mixed in a mass ratio of 50:50. Therefore, the ratio of the composite particle group in the negative electrode active material particle group was less than 70%. As a result, the initial charge/discharge efficiency was low.

Test No. 35 did not use the dry particle compounding apparatus used in the embodiment of the present invention. Therefore, the average coverage of the amorphous carbon coating was less than 50 area %. Further, the number density of exposed regions exceeded 0.0500/μm ² . As a result, the initial charge/discharge efficiency was low.

In test number 36, the specific surface area of the composite particle group was too low. Therefore, the quick charging performance was low. This is probably because the contact area with the electrolyte was small and the reaction resistance increased.

In the test number 38, the peripheral speed of the dry particle composite device was too high. Therefore, the average coverage of the amorphous carbon coating was less than 50 area %. Further, the number density of exposed regions exceeded 0.0500/μm ² . As a result, the quick charge performance was low and the initial charge/discharge efficiency was low.

The embodiments of the present invention have been described above. However, the above-described embodiment is merely an example for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiments, and can be implemented by appropriately modifying the above-described embodiments without departing from the spirit of the invention.

Claims (16)

A composite particle group,
With multiple composite particles,
The composite particles are
Active material particles containing a metal active material that occludes and/or releases metal ions;
An amorphous carbon coating made of amorphous carbon, which covers the surface of the active material particles,
The plurality of composite particles have a plurality of convex portions,
In a plurality of the composite particles having a median diameter (d50) or more, the average coverage of the amorphous carbon coating on the surface of the active material particles is 50 to 90 area %,
In the composite particles, when a region in which the surface of the active material particles is exposed by 1 μm ² or more is defined as an exposed region, a plurality of the composite particles having the particle diameter of the median diameter (d50) or more are The number density of the exposed areas with respect to the total surface area of the composite particles is 0.0010 to 0.0500 pieces/μm ² .
Composite particle group. The composite particle group according to claim 1, wherein
The Vickers hardness of the active material particles is HV20 to 500,
Composite particle group. The composite particle group according to claim 1 or 2, wherein
The specific surface area is 1.0 to 5.0 m ² /g,
Composite particle group. The composite particle group according to any one of claims 1 to 3,
The metal active material is
Contains one or more selected from the group consisting of Cu, Sn, and Si,
Composite particle group. The composite particle group according to claim 4, wherein
The metal active material is
Sn: 10 to 40 at %,
Cu: containing 50 to 90 at %,
Composite particle group. The composite particle group according to claim 5, wherein
The metal active material further comprises
Sn: 10 to 35 at %,
Ti: 9 at% or less, V: 49 at% or less, Cr: 49 at% or less, Mn: 9 at% or less, Fe: 49 at% or less, Co: 49 at% or less, Ni: 9 at% or less, Zn: 29 at% or less, Al: 49 at% or less, Si: 49 at% or less, B: 5 at% or less, and C: 5 at% or less, and one or more selected from the group consisting of,
The balance consists of Cu and impurities,
Composite particle group. The composite particle group according to any one of claims 1 to 6,
The plurality of composite particles includes a plurality of convex-part exposed composite particles,
The convex-part exposed composite particles have a plurality of convex parts,
In the protrusion-exposed composite particles, the coverage of the amorphous carbon film is 50 to 90 area %, and in the plurality of protrusions, the surface of the active material particles is exposed by 1 μm ² or more. There is at least one exposed area,
Of the plurality of composite particles having a particle diameter of the median diameter (d50) or more, the number ratio of the convex-exposed composite particles is 80% or more.
Composite particle group. A negative electrode active material particle group,
Equipped with a plurality of negative electrode active material,
A plurality of the negative electrode active material,
Comprising the composite particle group according to any one of claims 1 to 7,
The ratio of the composite particle group is 70% or more among the plurality of negative electrode active material materials having a particle diameter of not less than the median diameter (d50).
Negative electrode active material particle group. The negative electrode,
A thin film-shaped or plate-shaped active material supporting member,
A negative electrode material mixture layer formed on the surface of the active material supporting member,
The negative electrode mixture layer,
A negative electrode active material particle group according to claim 8,
A binder having the negative electrode active material particles dispersed therein,
Negative electrode. The negative electrode according to claim 9,
The negative electrode active material particle group includes the composite particle group according to any one of claims 1 to 7.
Negative electrode. A negative electrode according to claim 9 or 10,
The positive electrode,
A separator,
With an electrolyte,
battery. The convex-exposed composite particles,
Active material particles containing a metal active material that occludes and/or releases metal ions;
A surface of the active material particles, comprising an amorphous carbon coating of amorphous carbon,
The coverage of the amorphous carbon coating on the surface of the active material particles is 50 to 90 area %,
The protrusion-exposed composite particles have a plurality of protrusions,
In the plurality of convex portions, there is at least one exposed region in which the surface of the active material particles is exposed by 1 μm ² or more.
Convex exposed composite particles. The convex-part exposed composite particle according to claim 12,
The Vickers hardness of the active material particles is HV20 to 500,
Convex exposed composite particles. The convex-part exposed composite particle according to claim 12 or 13,
The metal active material is
Contains one or more selected from the group consisting of Cu, Sn, and Si,
Convex exposed composite particles. The convex-part exposed composite particle according to claim 14, wherein
The metal active material is
Sn: 10 to 40 at %,
Cu: containing 50 to 90 at %,
Convex exposed composite particles. The convex-part exposed composite particle according to claim 15,
The metal active material further comprises
Sn: 10 to 35 at %,
Ti: 9 at% or less, V: 49 at% or less, Cr: 49 at% or less, Mn: 9 at% or less, Fe: 49 at% or less, Co: 49 at% or less, Ni: 9 at% or less, Zn: 29 at% or less, Al: 49 at% or less, Si: 49 at% or less, B: 5 at% or less, and C: 5 at% or less, and one or more selected from the group consisting of,
The balance consists of Cu and impurities,
Convex exposed composite particles.

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