JP7525191B2 - Anode material for lithium ion battery, lithium ion battery, method for manufacturing anode material for lithium ion battery and manufacturing device thereof - Google Patents

Description

The present invention relates to a negative electrode material for lithium ion batteries, lithium ion batteries, a method for manufacturing a negative electrode material for lithium ion batteries, and an apparatus for manufacturing the same.

A conventional lithium ion battery has a negative electrode on its negative electrode side, which has a mixture layer made by mixing a graphite (natural graphite, artificial graphite, etc.) of a negative electrode active material (hereinafter also referred to as "negative electrode material") and a negative electrode material using a binder. The positive electrode side has a positive electrode with a mixture layer formed by mixing a lithium (Li) oxide powder (LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , etc.) of a positive electrode active material and a conductive graphite (mainly carbon black, etc.) using a binder (PVDF: polyvinylidene fluoride, etc.) and applying the mixture layer. The cell container of the lithium ion battery is filled with an electrolyte, and a separator (mainly a polyolefin-based porous material or a porous polypropylene sheet, etc.) is provided between the negative electrode material and the positive electrode material.

The separator is provided to allow the electrolyte to pass through and the movement of lithium ions to occur, separating the electrodes to prevent electrical short circuits.

Lithium-ion batteries are charged and discharged by the movement of lithium ions between the negative and positive electrode materials in the electrolyte. When charging, the lithium ions move to the negative electrode side, and when discharging, the lithium ions move to the positive electrode side. Charging is performed through an externally connected power source, and discharging is performed through an externally connected resistance (load).

In the field of lithium ion batteries, a technology has been recently disclosed that uses silicon particles as an alternative material to the graphite in the negative electrode active material. For example, a silicon particle is formed by crushing single crystal silicon in a mortar and classifying it using a mesh, and the powder is heated to 150°C (attained temperature) at a heating rate of 30°C/min in an argon atmosphere (see Patent Document 1). Another example is a method in which liquid silicon tetrachloride is supplied to high-temperature, high-concentration zinc gas and reacted at a high temperature of 1050°C or higher to reduce the silicon tetrachloride and form silicon particles. The fine silicon is then crystallized and aggregated at 1000°C or lower, particularly 500 to 800°C, after which the particle size of the formed silicon particles is adjusted and collected in an aqueous zinc chloride solution. It has been disclosed that this process produces high-purity silicon particles with a particle size of about 1 to 100 μm, and that the particles can be used (see Patent Document 2).

JP 2005-032733 A JP 2012-101998 A International Publication No. WO2015/189926 International Publication No. WO2013/027686

However, in conventional technology, when silicon particles are used as the negative electrode material, the electrical capacity during charging and discharging can be increased, but at the same time, lithium is absorbed and released into the silicon particles, causing the silicon particles to change in volume or be destroyed. As a result, there is a problem in that the charge and discharge cycle characteristics cannot be maintained.

For example, in the case of the silicon particles disclosed in the above-mentioned Patent Documents 1 and 2, high-temperature synthesis and collection processes are required, making the manufacturing process for obtaining silicon particles as a negative electrode material extremely complicated. As a result, it is inevitable that productivity will decrease and manufacturing costs will increase. In addition, the technology disclosed in Patent Document 3 is effective in that it takes care not to electrically isolate some of the silicon particles due to, for example, expansion and contraction, but there is still room for improvement. In other words, the development of lithium-ion batteries using silicon particles is still in progress.

In light of the above technical issues, the inventors of the present application have conducted extensive research and analysis to find a higher performance negative electrode material that can be adapted to the mechanism of lithium ion batteries, without being limited to silicon particles as the material used as the negative electrode material.

As a result, the inventors of the present application have discovered that, in a unique manner, by incorporating certain characteristic fine silicon particles into an internal space formed by using graphite, surrounding and internalizing them, and, so to speak, integrating or combining them (hereinafter, also referred to as "composite formation"), it is possible to realize a higher performance anode material that significantly enhances the usefulness of the characteristic fine silicon particles. The present invention was created based on the above-mentioned perspective.

The present invention solves at least some of the problems with charge/discharge cycle characteristics that existed with conventional anode materials using silicon particles, and is expected to contribute greatly to the realization of higher performance anode materials and manufacturing methods for lithium ion batteries, which are also expected to reduce carbon dioxide emissions.

The negative electrode material of one lithium ion battery of the present invention is silicon microparticles and/or aggregates or assemblies of the silicon microparticles having a volume distribution with a mode diameter and a median diameter of 30 nm or less, and includes the aggregates or assemblies in a state where the aggregates or assemblies are folded into at least a multi-layered petal shape or a scale shape, and graphite surrounds at least a portion of the silicon microparticles and/or the aggregates or assemblies.

The above-mentioned negative electrode material contains a composite in which at least a part of the silicon fine particles and/or the aggregates or assemblies of the silicon fine particles in a state where they are folded in a multi-layered petal-like or scale-like shape is surrounded by graphite. In addition, the silicon fine particles and/or the aggregates or assemblies are very fine aggregates or assemblies having a volume distribution with a mode diameter and a median diameter of 30 nm or less. Therefore, although the detailed mechanism is not yet clear, the silicon fine particles and/or the aggregates or assemblies are surrounded by graphite, in combination with the specificity of the multi-layered petal-like or scale-like shape of the aggregates or assemblies, which suppresses the degree of freedom of the silicon fine particles and/or the aggregates or assemblies to a certain extent, which leads to an increase in the cooperation between the graphite and the silicon fine particles and/or the graphite and the aggregates or assemblies. As a result, by adopting this negative electrode material, a lithium ion battery with little change in charge/discharge capacity even when charging and discharging are repeated, in other words, with good charge/discharge cycle characteristics, can be realized. Alternatively, an increase in charge/discharge capacity can be achieved.

In addition, one of the lithium ion battery negative electrode material manufacturing devices of the present invention includes a crushing section that crushes crystalline silicon to form silicon fine particles and/or agglomerates or aggregates of the silicon fine particles having a volume distribution with a mode diameter and a median diameter of 30 nm or less, the agglomerates or aggregates being in a state where the agglomerates or aggregates are at least folded in a multi-layered petal-like or scale-like shape, and a composite forming section that forms a composite containing the graphite and the silicon fine particles, or a composite containing the graphite and the agglomerates or aggregates, by surrounding at least a portion of the silicon fine particles and/or the agglomerates or aggregates with graphite.

According to this manufacturing device for lithium-ion battery negative electrode material, the grinding unit forms very fine silicon microparticles and/or agglomerates or aggregates of the silicon microparticles having a volume distribution with a mode diameter and a median diameter of 30 nm or less. Here, the agglomerates or aggregates are formed in a state where they are folded at least in a multi-layered petal shape or scale shape. In addition, this manufacturing device further includes a composite forming unit that surrounds at least a portion of the silicon microparticles and/or agglomerates or aggregates with graphite to form a composite containing the graphite and the silicon microparticles, or a composite containing the graphite and the agglomerates or aggregates. Therefore, although the detailed mechanism is not yet clear, the silicon fine particles and/or the agglomerates or the aggregates, combined with the uniqueness of the multi-layered petal-like or scale-like shape of the agglomerates or the aggregates described above, are surrounded by graphite, which suppresses the degree of freedom of the silicon fine particles and/or the agglomerates or the aggregates to a certain extent, which leads to increased cooperation between the graphite and the silicon fine particles and/or the graphite and the agglomerates or the aggregates. As a result, this manufacturing device can contribute to the production of a lithium ion battery negative electrode material that has little change in charge/discharge capacity even when charging and discharging are repeated, in other words, has good charge/discharge cycle characteristics, or a lithium ion battery negative electrode material that can increase the charge/discharge capacity.

In addition, one method for producing a negative electrode material for a lithium ion battery of the present invention includes a crushing step of crushing crystalline silicon to form silicon fine particles and/or aggregates or aggregates of the silicon fine particles having a volume distribution with a mode diameter and a median diameter of 30 nm or less, the aggregates or aggregates being in a state where the aggregates or aggregates are folded at least in a multi-layered petal shape or scale shape, and a composite formation step of forming a composite containing the graphite and the silicon fine particles, or a composite containing the graphite and the aggregates or aggregates by surrounding at least a portion of the silicon fine particles and/or the aggregates or aggregates with graphite.

According to this method for producing a negative electrode material for a lithium ion battery, a grinding step is performed to form very fine silicon microparticles and/or agglomerates or aggregates of the silicon microparticles having a volume distribution with a mode diameter and a median diameter of 30 nm or less. Here, the agglomerates or aggregates are formed in a state where they are folded at least in a multi-layered petal-like or scale-like shape. In addition, this production method further includes a composite formation step in which graphite surrounds at least a portion of the silicon microparticles and/or agglomerates or aggregates to form a composite containing the graphite and the silicon microparticles, or a composite containing the graphite and the agglomerates or aggregates. Therefore, although the detailed mechanism is not yet clear, the silicon fine particles and/or the agglomerates or the aggregates, combined with the uniqueness of the multi-layered petal-like or scale-like shape of the agglomerates or the aggregates described above, are surrounded by graphite, which suppresses the degree of freedom of the silicon fine particles and/or the agglomerates or the aggregates to a certain extent, which leads to increased cooperation between the graphite and the silicon fine particles and/or the graphite and the agglomerates or the aggregates. As a result, this manufacturing device can contribute to the production of a lithium ion battery negative electrode material that has little change in charge/discharge capacity even when charging and discharging are repeated, in other words, has good charge/discharge cycle characteristics, or a lithium ion battery negative electrode material that can increase the charge/discharge capacity.

The crystalline silicon in each of the above-mentioned inventions includes not only single crystal silicon but also polycrystalline silicon. Metallic silicon can also be selected as the crystalline silicon in each of the above-mentioned inventions. The crystalline silicon in each of the above-mentioned inventions is silicon chips, cutting waste, or polishing waste, which is usually treated as waste in the cutting process of silicon in the production process of silicon wafers, for example. This is a very suitable embodiment from various viewpoints such as reducing manufacturing costs, reducing the burden on the environment, and reusing resources.

Therefore, from the viewpoint of reducing manufacturing costs, easiness of procuring raw materials, reducing environmental burden, and/or utilization of resources, a negative electrode material for a lithium ion battery containing crystalline silicon chips or cutting chips and graphite surrounding at least a part of the chips or cutting chips is another aspect that can be adopted. Also, a manufacturing device for a negative electrode material for a lithium ion battery including a complex forming part in which graphite surrounds at least a part of the crystalline silicon chips or cutting chips to form a complex containing the graphite and the chips or cutting chips is another aspect that can be adopted. In addition, a manufacturing method for a negative electrode material for a lithium ion battery including a complex forming step in which graphite surrounds at least a part of the crystalline silicon chips or cutting chips to form a complex containing the graphite and the chips or cutting chips is another aspect that can be adopted.

Furthermore, in each of the above-mentioned inventions, in order to make it easier or more certain for the above-mentioned aggregates or aggregates in a multi-layered petal-like or scale-like state to store and release lithium ions, it is another preferred embodiment to adopt a negative electrode material for a lithium ion battery in which at least a part of the surface of the above-mentioned aggregates or aggregates, or the above-mentioned chips or cutting chips, is covered with carbon. From the viewpoint of ease of storing or releasing lithium ions, it is another preferred embodiment to adopt a manufacturing device for a negative electrode material for a lithium ion battery that includes a coating forming part that forms carbon that covers at least a part of the surface of the above-mentioned aggregates or aggregates, or the above-mentioned chips or cutting chips. Similarly, it is another preferred embodiment to adopt a manufacturing method for a negative electrode material for a lithium ion battery that includes a coating forming step that forms carbon that covers at least a part of the surface of the above-mentioned aggregates or aggregates, or the above-mentioned chips or cutting chips.

In addition, in each of the above-mentioned inventions, graphite, or more positively expressed as a "layer" of graphite (e.g., graphene or graphene sheets), surrounds the above-mentioned very fine aggregates or aggregates having a unique shape. However, the graphite does not necessarily completely surround the silicon microparticles and/or the aggregates or aggregates. Therefore, the above-mentioned composite can be said to be one in which the aggregates or aggregates are surrounded by graphite, rather than one in which the aggregates or aggregates are encapsulated within the graphite.

According to one of the lithium ion battery anode materials of the present invention, it is possible to realize a lithium ion battery with little change in charge/discharge capacity even when charging/discharging is repeated, in other words, with good charge/discharge cycle characteristics. Alternatively, it is possible to realize an increase in charge/discharge capacity. In addition, according to one of the lithium ion battery anode material manufacturing apparatuses of the present invention, it is possible to contribute to the manufacture of a lithium ion battery anode material with little change in charge/discharge capacity even when charging/discharging is repeated, in other words, with good charge/discharge cycle characteristics, or a lithium ion battery anode material that can increase charge/discharge capacity. In addition, according to one of the lithium ion battery anode material manufacturing methods of the present invention, it is possible to contribute to the manufacture of a lithium ion battery anode material with little change in charge/discharge capacity even when charging/discharging is repeated, in other words, with good charge/discharge cycle characteristics, or a lithium ion battery anode material that can increase charge/discharge capacity.

FIG. 2 is a flow diagram showing a manufacturing process of the negative electrode material of the lithium ion battery according to the first embodiment. FIG. 1 is a schematic diagram showing a manufacturing apparatus and a manufacturing process for a negative electrode material for a lithium ion battery according to a first embodiment. FIG. 2 is a diagram showing a TEM (transmission electron microscope) image of an example of silicon fine particles and/or their aggregates or conglomerates that have been subjected to the coating formation step (S4) of the first embodiment. 1 is a SEM image of an example of silicon fine particles and/or aggregates or aggregates thereof according to the first embodiment. 4 is a SEM image of an example of enlarged silicon microparticles and/or aggregates or clusters thereof in the first embodiment. 5A is an SEM image of another example of an aggregate or conglomerate of silicon fine particles in the first embodiment, and FIG. 5B is an enlarged view of a portion of FIG. 5A. FIG. 2 is a diagram showing a TEM image of a silicon microparticle of the first embodiment. 1 is a graph showing (a) the crystallite size distribution in number distribution and (b) the crystallite size distribution in volume distribution with respect to the crystallite size of silicon fine particles or the like of the first embodiment. 5 is a graph showing the results of X-ray diffraction measurement of silicon fine particles and/or their aggregates or conglomerates of the first embodiment ((a) wide range, (b) limited range). FIG. 11 is a schematic configuration diagram of a lithium ion battery according to a second embodiment. FIG. 1 is a schematic diagram showing a manufacturing apparatus and a manufacturing process for a negative electrode material for a lithium ion battery according to another embodiment.

Embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this description, common parts are given common reference symbols throughout all the drawings unless otherwise specified. In addition, the elements of each embodiment are not necessarily shown to scale in the drawings. In addition, some symbols may be omitted to make each drawing easier to see.

First Embodiment
Fig. 1 is a flow diagram showing the manufacturing process of the negative electrode material for the lithium ion battery of this embodiment. Also, Fig. 2 is a schematic diagram showing the manufacturing apparatus and manufacturing process of the negative electrode material for the lithium ion battery of this embodiment.

The method for producing the negative electrode material of the lithium ion battery of the present embodiment and the method for producing the lithium ion battery including the negative electrode material include various steps using silicon chips, silicon cutting chips, or polishing chips (hereinafter also referred to as "silicon chips, etc." or "chips, etc.") that are usually waste materials in the cutting process of silicon in the production process of silicon wafers used in semiconductor products such as solar cells as an example of a starting material. The chips, etc. also include fine chips obtained by pulverizing silicon wafers to be discarded with a known pulverizer. As shown in FIG. 1, the method for producing the lithium ion battery of the present embodiment includes the following steps (1), (2), (5), and (6), or the following steps (1), (2), (4), (5), and (6). The method for producing the lithium ion battery of the present embodiment may further include the following step (3) as another aspect that may be adopted.
(1) Cleaning step (S1)
(2) Crushing step (S2)
(3) Oxide film removal process (S3)
(4) Covering formation step (S4)
(5) Complex formation step (S5)
(6) Negative electrode formation step (S6)

As shown in FIG. 2, the manufacturing apparatus 100 for the negative electrode material (or negative electrode) of the lithium ion battery of this embodiment mainly includes a washer (cleaning and preliminary crusher) 10, a crusher 20, a dryer (not shown), a rotary evaporator 40, a coating forming section 60 that forms carbon to cover at least a part of the surface of silicon fine particles and/or their aggregates or conglomerates (hereinafter also referred to as "silicon fine particles, etc."), a complex forming section 70 that forms a complex containing graphite and silicon fine particles, etc. by surrounding at least a part of the silicon fine particles, etc. with graphite, and a mixing section 80 that is responsible for part of the negative electrode formation process of the lithium ion battery. Of the above-mentioned configurations, the manufacturing apparatus 100 for the negative electrode material (or negative electrode) of the lithium ion battery that does not include the coating forming section 60 is also another aspect that can be adopted.

In addition, the manufacturing apparatus 100 for the lithium ion battery negative electrode material (or negative electrode) of this embodiment can be equipped with an oxide film removal tank 50 and a centrifuge 58 as another embodiment that can be adopted. Note that only the crusher 20, or the washer 10 and the crusher 20, are referred to as the crushing section in this embodiment.

(1) Cleaning step (S1)
In the cleaning step (S1) of this embodiment, for example, silicon chips formed in the cutting process of single crystal or polycrystalline silicon, that is, a lump or ingot of crystalline silicon (a lump or ingot of n-type crystalline silicon), are cleaned. Representative silicon chips are chips formed by cutting a silicon ingot with a known wire or the like (typically, a fixed abrasive wire). Therefore, in this embodiment, silicon chips, which have conventionally been considered to be waste materials, are used as a starting material to form silicon fine particles constituting the negative electrode material of a lithium ion battery, which is excellent in terms of reducing manufacturing costs, facilitating procurement of raw materials, reducing the burden on the environment, and/or utilizing resources.

The cleaning step (S1) of this embodiment is mainly intended to remove organic matter that adheres during the formation process of the silicon chips, etc., typically organic matter such as coolants and additives used in the cutting process. In this embodiment, as shown in FIG. 2, first, the chips, etc. 1 to be cleaned are weighed, and then the chips, etc. 1, a predetermined first liquid, and balls 11 are introduced into a cylindrical pot 13a with a bottom. After sealing the pot 13a with a lid 13b, the pot 13a on the rotors 15 is rotated by rotating two cylindrical rotors 15 of the ball mill machine, which is the cleaning machine (cleaning and preliminary crushing machine) 10. As a result, the chips, etc. 1 to be cleaned are dispersed in the first liquid in the pot 13a, whereby cleaning and preliminary crushing of the chips, etc. 1 is performed.

Here, the ball mill of this embodiment is a grinding machine that applies physical impact force by rotating the pot 13a and the lid 13b to balls 11 (grinding media) such as steel balls, porcelain balls, boulders, and the like housed in the pot 13a and the lid 13b. A suitable example of the first liquid is acetone. In a more specific embodiment, for example, 300 milliliters (mL) of acetone is added to 100 grams (g) of silicon chips, etc., and the mixture is stirred for about one hour in the pot 13a and the lid 13b placed on the rotor 15 of the ball mill (Universal BALL MILL, manufactured by MASUDA Co., Ltd. in this embodiment), thereby dispersing the silicon chips, etc. in the acetone. The ball types of the ball mill were alumina balls with a particle diameter of φ10 millimeters (mm) and alumina balls with a particle diameter of φ20 mm. In the cleaning process (S1) of this embodiment, silicon chips and the like are pre-pulverized and stirred in the first liquid in a ball mill to perform a dispersion process. This significantly improves the cleaning efficiency compared to a process in which the chips are simply immersed in the first liquid, making it possible to obtain silicon particles that are suitable for improving the negative electrode characteristics of lithium ion batteries, particularly in terms of improving the charge/discharge cycle characteristics.

After the cleaning step (S1), the lid 13b is opened to discharge the silicon particles together with the first liquid, and the first liquid is then removed by suction filtration using a known reduced pressure filtration means to produce waste liquid. Meanwhile, the remaining silicon particles are dried in a known dryer. If necessary, the silicon particles obtained after the drying process are pre-crushed and washed again in the washer (cleaning and pre-crushing machine) 10 in the same process. Examples of other cleaning methods that can be used in the cleaning step (S1) include cleaning using the RCA cleaning method, or cleaning using water (including pure water).

(2) Crushing step (S2)
Then, in the crushing step (S2), a predetermined second liquid is added to the washed silicon particles, and the silicon particles are crushed in a bead mill. Therefore, in this embodiment, the silicon particles that have been subjected to the washing step (S1) are crushed further finely by the bead mill used after the ball mill, in other words, after the crushing by the ball mill.

A suitable example of the second liquid in this embodiment is IPA (isopropyl alcohol). As a pretreatment for the grinding process, the second liquid and the silicon particles obtained in the cleaning process (S1) are placed in the pot 13a so that the weight ratio of the second liquid is 95% and the silicon particles is 5%, and then the pot 13a and the lid 13b of the cleaning machine (cleaning and preliminary grinding machine) 10 are rotated to perform a preliminary grinding process. The slurry containing the pre-ground silicon particles is passed through a mesh with an opening of 180 microns to remove relatively coarse particles, and the obtained slurry containing the silicon particles is further finely ground using a bead mill (in this embodiment, Star Mill LMZ015, manufactured by Ashizawa Finding Co., Ltd.) of the grinder 20. More specifically, the slurry containing silicon chips from which silicon chips with a particle diameter of 180 microns or more have been removed is introduced into the inlet 21 of the grinder 20, and is guided to the filter 25 on the outlet 24 side while or after the fine grinding process is being performed by the grinder 20. Furthermore, if this process does not produce sufficient pulverization, the slurry can be circulated using pump 28 back to the inlet 21 of the pulverizer 20 so that it can be pulverized again. A specific example of the type of beads used in the bead mill is zirconia beads with a diameter of φ0.5 mm. After collecting the slurry containing the pulverized silicon particles, the second liquid is removed using a rotary evaporator 40 that automatically performs reduced pressure distillation, thereby obtaining silicon fine particles and the like as the result of the pulverization process.

In this embodiment, about 450 g of zirconia beads having a particle diameter of φ0.5 mm are introduced, and the fine grinding process is performed at a rotation speed of 2900 rpm for 4 hours, thereby obtaining silicon fine particles and the like. In addition, in the grinding process (S2), grinding process may be performed by any one of the grinders consisting of a ball mill, a bead mill, a jet mill, and a shock wave grinder, or a combination of two or more of them other than those described above. In addition, as the grinder used in the grinding process (S2), not only an automatic grinder but also a manual grinder may be used. However, from the viewpoint of forming agglomerates or aggregates of silicon fine particles in a state of being folded into a multi-layered petal shape or scale shape as described later with high accuracy, it is preferable to adopt the grinding process (S2) consisting of processing by a bead mill, or the grinding process (S2) including processing by a bead mill.

Another suitable embodiment that can be adopted is to further crush the silicon microparticles obtained by the above-mentioned crushing step (S2) using a known crushing machine (a representative crushing machine is Model 20D manufactured by Ishikawa Factory Co., Ltd.). This crushing process improves the dispersibility when forming the negative electrode of the lithium ion battery, and therefore has the effect of highly reliably preventing or suppressing the destruction of the negative electrode due to the absorption and release of lithium.

(3) Oxide film removal process (S3)
In this embodiment, the oxide film removing step (S3) is performed as a preferred embodiment. However, even if this oxide film removing step (S3) is not performed, at least a part of the effect of this embodiment can be achieved. is played.

In the oxide film removal step (S3) of this embodiment, the silicon fine particles, etc. 2 obtained in the pulverization step (S2) are brought into contact with hydrofluoric acid or an aqueous ammonium fluoride solution. The silicon fine particles, etc. 2 obtained in the pulverization step (S2) are dispersed by immersing them in hydrofluoric acid or an aqueous ammonium fluoride solution. Specifically, in the oxide film removal tank 50, the silicon fine particles, etc. 2 are dispersed in hydrofluoric acid or an aqueous ammonium fluoride solution 55 using an agitator 57, thereby removing oxides (mainly silicon oxide) on the surfaces of the silicon fine particles, etc. 2.

Then, the silicon microparticles, etc. from which some or all of the surface oxides have been removed are separated from the hydrofluoric acid solution by a centrifuge 58. The silicon microparticles, etc. are then immersed in a third liquid, such as an ethanol solution. By removing the third liquid, silicon microparticles, etc. from which some or all of the oxides (or oxide film) originally formed on the surface have been removed are obtained. If the process of removing oxides that may be present on the surface of the silicon microparticles, etc. 2 is not performed, the silicon microparticles, etc. are processed in the coating formation process (S4), composite formation process (S5), and negative electrode formation process (S6) described below.

In the oxide film removal step (S3) of this embodiment, the silicon fine particles, etc. are brought into contact with hydrofluoric acid by immersing the silicon fine particles, etc. in hydrofluoric acid or an aqueous solution of ammonium fluoride. However, a step of bringing the silicon fine particles, etc. into contact with hydrofluoric acid or an aqueous solution of ammonium fluoride by other methods may also be employed. For example, spraying the aqueous solution of hydrofluoric acid onto the silicon fine particles, etc., in the manner of a so-called shower, is another embodiment that may be employed.

(4) Covering formation step (S4)
In this embodiment, the coating formation step (S4) is performed as a preferred embodiment. However, even if the coating formation step (S4) is not performed, at least a part of the effects of this embodiment can be achieved. Therefore, as already described, after the crushing step (S2) or the oxide film removing step (S3), the coating forming step (S4) is not carried out, and the following (5) complex forming step is carried out. Another aspect that can be adopted is that (S5) is performed.

In this embodiment, a coating formation process is performed in which a part or all of the surface of silicon fine particles, etc., which have undergone or have not undergone the oxide film removal process (S3), is coated with a carbon film. Therefore, the silicon fine particles, etc., which have undergone the coating formation process (S4) of this embodiment have at least a part of their surface covered with carbon, so that they are thicker than silicon fine particles, etc., which are not covered with carbon. In addition, since the carbon of this embodiment has conductivity, a conductive negative electrode material can be formed. In addition, by covering the silicon fine particles, etc. with carbon having a film thickness of, for example, several nm to several μm, not only a thin negative electrode is formed, but also a relatively thick negative electrode is easily formed. In addition, FIG. 3 is a TEM (transmission electron microscope) image of an example of silicon fine particles, etc. (partially enlarged view) and/or their aggregates or aggregates (partially enlarged view) which have undergone the coating formation process (S4) of this embodiment. The crystalline silicon shown in FIG. 3 was observed to have mainly a crystal plane orientation (111) (also referred to simply as "Si(111)" or "(111)". The same applies to other plane orientations).

In addition, for example, covering silicon microparticles with carbon can contribute to alleviating internal stress in the negative electrode as a whole, and more microscopically, to alleviating internal stress in individual silicon microparticles. As a result, it can make lithium-ion batteries easier to manufacture and can also contribute to improving the performance of lithium-ion batteries (for example, charge/discharge cycle characteristics).

In addition, by forming the negative electrode material of a lithium ion battery using silicon fine particles, etc., at least a portion of whose surface is covered with carbon, it is possible to increase the charge capacity value and discharge capacity value compared to silicon fine particles, etc., that are not covered with carbon. For example, according to research by the present inventors, in the case of silicon fine particles, etc., that are not covered with carbon, for example, when the thickness of the negative electrode material is about 30 μm, the charge capacity value and discharge capacity value are less than 500 (mAh/g). However, by using silicon fine particles, etc., at least a portion of whose surface is covered with carbon, the charge capacity value and discharge capacity value can be increased by more than two times (typically about 3 to about 5 times).

In the coating formation step (S4) of this embodiment, the means for coating part or all of the surface of the silicon fine particles, etc. (in other words, at least a part of the surface) with a carbon film is not particularly limited. For example, a method of covering at least a part of the surface of the silicon fine particles, etc. 2 with carbon by a thermal CVD method, which is an example of a chemical vapor deposition method, can be adopted. Specifically, at least a part of the surface of the silicon fine particles, etc. 2 can be coated with a carbon film by heating the silicon fine particles, etc. 2 at about 600°C or higher and about 1200°C or lower in an atmosphere containing an organic gas and/or its vapor. Therefore, a thermal CVD device, which is an example of a chemical vapor deposition device, is one aspect of the coating formation unit 60 that can be adopted in the coating formation step (S4) of this embodiment. Examples of materials (or raw materials) that can be used in the thermal CVD method include one or more hydrocarbons selected from the group consisting of methane, ethane, acetylene, ethylene, propane, butane, butene, pentane, isobutane, and hexane, and/or one or more known aromatic hydrocarbons. By using copper or a copper alloy as a catalyst, acetylene can be thermally decomposed even at about 400°C, which can contribute to lowering the processing temperature.

As described above, typically, a hydrocarbon gas is pyrolyzed on or near the heated silicon microparticles 2 to carbonize them, thereby covering at least a portion of the surface of the silicon microparticles 2 with a carbon film, which is an example of a suitable carbon film in this embodiment and is a method with excellent productivity and industrial applicability. Note that reduced pressure thermal CVD or plasma CVD, which are other examples of chemical vapor deposition methods, may also be used as appropriate.

Another example of a method for covering at least a portion of the surface of silicon fine particles, etc. 2 with a carbon film is as follows. First, a known organic compound (such as chlorinated polyethylene elastomer) or a mixture of the organic compound and graphite powder is attached or adsorbed to silicon fine particles, etc. 2 that have been treated at least by the cleaning step (S1) and the crushing step (S2) of this embodiment in the coating forming section 60. Thereafter, the organic compound is heated to a temperature at which it pyrolyzes, and the organic compound is carbonized to form silicon fine particles, etc. 2 whose surfaces are at least partially covered with carbon (typically graphene, graphite, and/or amorphous carbon). In addition, a step of baking the silicon fine particles, etc. 2 once formed in a nitrogen atmosphere or a hydrogen atmosphere at, for example, 400°C to 1200°C can also be additionally and/or previously performed, which is one aspect of a modified example of this embodiment. From the viewpoint of being able to reliably prevent, suppress, or remove the formation of an oxide film on the surface of the silicon microparticles, etc. 2, it is preferable to heat the silicon microparticles, etc. 2 in a hydrogen atmosphere.

Another possible embodiment is to form silicon fine particles, etc., 2, at least a part of which is covered with carbon, using other known means. For example, it is also possible to use a carbon film formed by a known carbon black manufacturing method (furnace method or channel method). The furnace method is a method in which creosote oil obtained by distilling coal tar is partially burned in a specified chamber in a state in which the creosote oil is turbulently diffused, and then the droplets are water-cooled. The channel method is a method in which carbon is precipitated by colliding a flame formed by burning natural gas, for example, with the cooling surface of a channel steel. However, since sulfur components derived from petroleum are included, it is more preferable to adopt the above-mentioned thermal CVD method, which is a method in which such impurity components are less likely to be mixed in. In addition, when employing each of the above-mentioned methods, for example, a method of coating at least a part of the surface of the silicon fine particles, etc. 2 and/or their aggregates or conglomerates with a carbon film by applying kinetic energy to the silicon fine particles, etc. by appropriately employing a known mechanical structure is a preferred embodiment, since it is possible to form a carbon film more uniformly (for example, with good uniformity in thickness and/or density) on the surface of the silicon fine particles, etc. 2 and/or their aggregates or conglomerates. More specifically, while rotating the chamber or tube containing the silicon fine particles, etc. 2 and/or applying ultrasonic vibration to the silicon fine particles, etc. 2 and/or their aggregates or conglomerates, it is a preferred embodiment to employ a method of coating at least a part of the surface of the silicon fine particles, etc. 2 and/or their aggregates or conglomerates with a carbon film, since it is possible to form a carbon film more uniformly on the surface of the silicon fine particles, etc. 2 and/or their aggregates or conglomerates.

In the first embodiment in which the coating formation process (S4) is performed, the weight ratio of carbon (C) in the silicon fine particles etc. 2 that constitute the negative electrode material or part of the negative electrode is 0.1 when silicon (Si) is taken as 1. However, if the weight ratio of carbon (C) when silicon (Si) is taken as 1 is 0.05 or more and less than 0.37, a stable lithium ion battery with high charge capacity value and discharge capacity value can be obtained.

Furthermore, as a result of further detailed analysis by the inventor, the film thickness of the portion where carbon (C) adheres to silicon (Si) was about 2 nm to about 3 nm when the weight ratio of carbon (C) to silicon (Si) was 0.1 when the weight ratio of carbon (C) to silicon (Si) was 1 was about 5 nm to about 10 nm when the weight ratio of carbon (C) to silicon (Si) was 0.16. The film thickness of the portion where carbon (C) adheres to silicon (Si) was also about 5 nm to about 10 nm when the weight ratio of carbon (C) to silicon (Si) was 0.21 when the weight ratio of carbon (C) to silicon (Si) was 1. In addition, the film thickness of the portion where carbon (C) adheres to silicon (Si) was about 50 nm to about 90 nm when the weight ratio of carbon (C) to silicon (Si) was 0.37 when the weight ratio of carbon (C) to silicon (Si) was 1. Therefore, if the thickness of the carbon (C) film attached to the silicon (Si) is 1 nm or more and less than 50 nm, and in particular, if the thickness is 2 nm or more and 10 nm or less, a stable lithium ion battery with high charge capacity and discharge capacity values can be obtained.

Furthermore, the charge capacity and discharge capacity of a lithium-ion battery in which at least a portion of the surface of silicon microparticles and/or their aggregates or assemblies is not covered with carbon (i.e., has not been subjected to the coating formation process (S4)) can be at least two times (typically about three times) higher.

(5) Complex formation step (S5)
As described above, after the crushing step (S2) or the oxide film removing step (S3), the composite forming step (S5) is performed via the coating forming step (S4) or without the coating forming step (S4). In the composite formation step (S5) of the present embodiment, a composite containing the graphite and the silicon fine particles 2 is formed by surrounding at least a part of the silicon fine particles 2 with the graphite. It is a process.

Specifically, first, silicon microparticles etc. 2 and graphite (typically, flake graphite or expanded graphite) are introduced into the composite forming section 70. The flake graphite or expanded graphite of this embodiment can be formed by a method disclosed in a publicly known method.

In addition, in this embodiment, since the grinding step (S2) is performed, a very fine aggregate or aggregate of silicon fine particles (silicon fine particles, etc. 2) having a volume distribution with a mode diameter and a median diameter of 30 nm or less is formed. In addition, the aggregate or aggregate is an aggregate or aggregate of silicon fine particles in a state of being folded in a multi-layered petal shape or scale shape. Since such very fine silicon fine particles, etc. 2 are used, a bead mill machine similar to the bead mill machine used in the grinder 20 can be used as an example of a complex forming section 70 in which the silicon fine particles, etc. 2 and graphite are mixed, the silicon fine particles, etc. 2 are taken into the internal space formed using graphite, and the silicon fine particles, etc. 2 are surrounded and internalized, so to speak, and integrated or combined. Other examples of the complex forming section 70 are equipment groups that use a known dry process or a known wet process in combination with a grinder, represented by a high-speed rotary impact grinder. However, from the viewpoint of reducing the actual number of steps, when compounding silicon fine particles etc. 2 with graphite, it is preferable to use, as the composite forming section 70, the above-mentioned bead mill machine alone or a composite processing device that includes at least a bead mill machine, or a composite processing device that includes a high-speed rotary impact grinder.

In particular, the scaly silicon fine particles and/or their aggregates or aggregates are advantageous for compositing the graphite and the silicon fine particles 2 when the graphite and the silicon fine particles 2 are introduced into the composite forming section 70 because the silicon fine particles 2 are easily taken in between layers of graphite (particularly expanded graphite) having a moderate distance due to the specific shape, and/or are easily surrounded by the graphite. In addition, it is preferable to adopt the scaly silicon fine particles and/or their aggregates or aggregates that have undergone the coating formation process (S4) because the silicon fine particles 2 are more easily taken in between layers of graphite (particularly expanded graphite) having a moderate distance, and/or the silicon fine particles 2 are more easily surrounded by the graphite. Also, as described above, from the viewpoint of having a higher charge capacity value and discharge capacity value, it is a preferable embodiment to adopt the scaly silicon fine particles and/or their aggregates or aggregates that have undergone the coating formation process (S4).

By carrying out the composite formation step (S5), it is possible to form a state in which the extremely fine silicon microparticles, etc. 2, which have the above-mentioned agglomerates or aggregates in a state of being folded into a multi-layered petal-like or scale-like shape, are surrounded by graphite. In this embodiment, it is not necessarily necessary to go through a process (representatively, "spheroidization") in which the edges of the graphite are folded so that the silicon microparticles, etc. 2 are, so to speak, captured by the sheet-like graphite, but it is also possible to adopt an embodiment in which the silicon microparticles, etc. 2 are surrounded by graphite after going through such a process.

(6) Negative electrode formation step (S6)
The manufacturing apparatus 100 for manufacturing the negative electrode material (or negative electrode) of the lithium ion battery of this embodiment is for crushing the lithium ion battery material (or negative electrode) after the crushing step (S2) or after the oxide film removing step (S3), and for forming a coating (S4). The untreated negative electrode material, which is at least partly surrounded by graphite, is bound to a component (e.g., copper foil) that constitutes a part of the negative electrode by a binder (e.g., ammonium carboxylate). The mixing section 80 mixes methyl cellulose (CMC) and styrene butadiene rubber (SBR), or ammonium carboxymethyl cellulose (CMC) and polyvinyl alcohol (PVA). The layer is used to form the negative electrode.

<Other processes>
The silicon fine particles etc. obtained by the following steps (A) to (D) can be classified, for example, in order to reduce the variation in the number distribution and/or volume distribution of the crystallite diameter of each silicon fine particle etc.
(A) Washing step (S1), crushing step (S2), and composite forming step (S5)
(B) Cleaning step (S1), crushing step (S2), oxide film removal step (S3), and composite forming step (S5)
(C) Cleaning step (S1), crushing step (S2), coating forming step (S4), and composite forming step (S5)
(D) Cleaning step (S1), crushing step (S2), oxide film removal step (S3), coating forming step (S4), and composite forming step (S5)

<Analysis results of silicon fine particles etc. obtained in the first embodiment>
1. Analysis of silicon microparticles using SEM and TEM images

Figure 4A is a SEM (scanning electron microscope) image of an example of silicon fine particles and/or their aggregates or conglomerates after the crushing step (S2) of the first embodiment. Also, Figure 4B is a diagram showing an enlarged SEM image of an example of silicon fine particles and/or their aggregates or conglomerates after the crushing step (S2) of the first embodiment. Also, Figure 4C is a diagram showing (a) an SEM image of another example of an aggregate or conglomerate of silicon fine particles in the first embodiment, and (b) an enlarged view of a part of (a). In addition, Figure 5 is a diagram showing a transmission electron microscope (TEM) image of silicon fine particles of the first embodiment.

As shown in Figure 4A, not only individual silicon microparticles but also silicon microparticles and/or their aggregates or conglomerates shown in Y1 and Y2 were confirmed. Interestingly, a more detailed analysis confirmed that the silicon microparticles or their aggregates were aggregates or conglomerates of thin-layer silicon microparticles folded into a compound petal-like or scale-like shape, as shown in Figure 4B and the Z portion of Figures 4C (a) and (b). Furthermore, a more detailed observation revealed that, for example, when the width (minor axis) of one or a group of scale-like silicon microparticles was taken as 1, the length (major axis) ranged from 3.3 to 12.9.

Another interesting finding was obtained from the TEM image shown in Figure 5, which focuses on individual silicon microparticles. Specifically, it was confirmed that the individual silicon microparticles shown in the areas surrounded by white lines in Figure 5 are crystalline, i.e., single crystal silicon. In addition, it was confirmed that at least a portion of the silicon microparticles are irregular polygonal crystallites measuring about 2 nm to about 10 nm in size when viewed in cross section. Note that in Figure 5, the crystal plane orientation is shown in each area surrounded by white lines.

2. Analysis of crystallite size distribution of silicon fine particles by X-ray diffraction method Figure 6 is a graph showing (a) the crystallite size distribution in number distribution and (b) the crystallite size distribution in volume distribution for the crystallite size of silicon fine particles of the first embodiment in the Si (111) direction. Figure 6 shows the results obtained by analyzing the crystallite size distribution of silicon fine particles after the pulverization step (S2) using X-ray diffraction. In both Figure 6 (a) and Figure 6 (b), the horizontal axis represents the crystallite size (nm) and the vertical axis represents the frequency.

From the results of Figures 6(a) and 6(b), in the number distribution, the mode diameter was 1.6 nm and the median diameter (50% crystallite diameter) was 2.6 nm. In addition, in the volume distribution, the mode diameter was 6.3 nm and the median diameter was 9.9 nm. Therefore, it was confirmed that in the number distribution, both the mode diameter and the median diameter were 5 nm or less, and more specifically, a value of 3 nm or less was realized. It is noteworthy that in the volume distribution, both the mode diameter and the median diameter were confirmed to be at least 50 nm or less, particularly 30 nm or less, and more narrowly 20 nm or less. Furthermore, in Figure 6, it was confirmed that an extremely small value of 10 nm or less was realized.

From the results of Figures 6(a) and 6(b), it was confirmed that the silicon microparticles obtained after the grinding process (S2) using the bead mill method have an average crystallite diameter of about 20 nm or less, more specifically, about 9.8 nm, which achieves a crystallite diameter of 10 nm or less. The crystallite diameter distribution of the silicon microparticles after the oxide film removal process (S3) is also almost the same as that shown in Figure 6.

Therefore, by analyzing the results of FIG. 6 together with the results of each diagram in FIG. 4, it can be said that at least after the crushing step (S2) or the oxide film removal step (S3), the aggregates or conglomerates of silicon microparticles, etc. are in a state in which thin-layered silicon microparticles, etc. with a major axis of about 100 nm or less are piled up in a multi-layered petal-like or scale-like shape. Furthermore, as can be seen from FIG. 5 and FIG. 6, the silicon microparticles, etc. are mainly composed of crystallites with a major axis of 10 nm or less.

As shown in FIG. 6, the silicon microparticles of this embodiment contain silicon microparticles with a crystallite diameter of 1 nm or less. Interestingly, it was also confirmed that the average crystallite diameter in the volume distribution of the silicon microparticles of this embodiment is about 10 nm. This value can be said to be a very small value. As described above, further investigation confirmed that the apparent volume diameter of the silicon microparticles is in the range of about 100 nm or less. In particular, by containing a large number of extremely fine silicon particles with a crystallite diameter of 5 nm or less, the charge and discharge cycle characteristics derived from the silicon microparticles used as the negative electrode material of the lithium ion battery described later can be improved with a higher degree of accuracy. In addition, since at least a portion of the surface of the extremely fine silicon particles described above is covered with carbon, it is possible to realize higher charge capacity values and discharge capacity values, as well as excellent charge and discharge cycle characteristics.

3. Analysis of crystallite plane orientation of silicon fine particles by X-ray diffraction method FIG. 7(a) shows the results of X-ray diffraction measurement (P) of silicon fine particles and/or their aggregates or aggregates before the crushing step (S2) of the first embodiment and the results of X-ray diffraction measurement (Q) of silicon fine particles and/or their aggregates or aggregates after the crushing step (S2) in a wide angle range. FIG. 7(b) shows an enlarged view of a part of the result (P) of FIG. 7(a), and shows the results of X-ray diffraction measurement (R) of silicon fine particles and/or their aggregates or aggregates after the crushing step (S2) of the first embodiment in a limited angle range. The peak intensities of the C(002) and C(003) planes shown in FIG. 7(b) indicate that about 1 wt % to about 3 wt % of graphite particles are contained in the silicon fine particle group or the aggregates or aggregates of silicon fine particles. As an example, the size of the graphite particles on the C(002) plane was about 50 nm or less, more specifically, about 35 nm, and the size of the graphite particles on the C(003) plane was about 100 nm or less, more specifically, about 75 nm.

7(a) and (b), it was confirmed that the diffraction peak attributable to Si (111) after the grinding step (S2) had a larger half-width than the diffraction peak attributable to the crystal plane (111) of Si around 2θ = 28.4° before the grinding step (S2) of the first embodiment. The average crystallite size calculated using Scherrer's formula from the half-width of the Si (111) peak after the grinding step (S2) was 9.8 nm. Interestingly, it was revealed that the intensity of the diffraction peak attributable to Si (111) around 2θ = 28.4° after the grinding step (S2) was larger than the intensity of other diffraction peaks (for example, the peak intensity of Si (220) or Si (311)). The arrangement interval of Si (111) in the crystal lattice of the silicon microparticles after the grinding step (S2) is 0.31 nm (3.1 Å), as shown in FIG. 5.

Considering the above analytical results, the silicon microparticles after the crushing step (S2) of this embodiment can be said to be aggregates or conglomerates in which crystalline silicon microparticles, mainly with a (111) plane orientation, are multi-layered and petal- or scale-like.

In this way, by using the silicon fine particles and/or their agglomerates or aggregates after the crushing step (S2) or the oxide film removal step (S3) of this embodiment as part of the negative electrode material of a lithium ion battery, a unique effect can be achieved in which when lithium ions (Li ⁺ ) ionized from the positive electrode material of the lithium ion battery reach the negative electrode, the lithium ions (Li ⁺ ) can easily enter and exit the gaps in the folds of the agglomerates or aggregates, which are in a multi-folded, petal-like or scale-like state.

In addition, in this embodiment, at least a part of the aggregates or aggregates of silicon fine particles in the above-mentioned multi-layered petal-like or scale-like folded state is surrounded by graphite. Therefore, due to the presence of the aggregates or aggregates in the multi-layered petal-like or scale-like folded state, a negative electrode material or negative electrode in which lithium ions are easily stored and released is obtained. In addition, combined with the specificity of the multi-layered petal-like or scale-like shape of the aggregates or aggregates, the degree of freedom of the aggregates or aggregates is suppressed to a certain extent by being surrounded by graphite, which leads to increased cooperation between the graphite and the aggregates or aggregates, and therefore a high degree of stability in the movement state of lithium ions can be realized. As a result, by adopting this negative electrode material, a lithium ion battery with little change in charge/discharge capacity even when charging/discharging is repeated, in other words with good charge/discharge cycle characteristics, can be realized. Alternatively, an increase in charge/discharge capacity can be realized.

<Modification of the first embodiment>
In the first embodiment, silicon chips or the like (more specifically, chips or cutting chips of crystalline silicon) obtained as a result of performing only the cleaning step (S1) are subjected to a process of forming a composite by a composite forming step (S5) using a composite forming unit 70, for example, without performing a crushing step (S2). As in the first embodiment, an oxide film removing step (S3) may be performed after the cleaning step (S1). As in the first embodiment, a coating forming step (S4), i.e., a coating forming step using a coating forming unit 60, for example, for forming carbon that covers at least a part of the surface of the chips or cutting chips, may be performed after the cleaning step (S1) or after the cleaning step (S1) and the oxide film removing step (S3).

In this modified example, as described above, graphite surrounds at least a portion of the silicon chips, etc. obtained only by the cleaning step (S1). In addition, in this modified example, the silicon chips, etc. and graphite (typically, flaky graphite or expanded graphite) are introduced into the composite forming section 70 used in the first embodiment. Thereafter, a process similar to the composite forming step (S5) in the first embodiment is performed to form a composite in which at least a portion of the silicon chips, etc. are surrounded by graphite.

Even if this modified example is adopted, the same effects as those of the first embodiment, or at least some of the effects, can be achieved.

Second Embodiment
The lithium ion battery of this embodiment uses silicon chips or silicon fine particles surrounded by graphite as the negative electrode material in the following forms (1) to (3). The configuration other than the negative electrode material is the same as that of a conventional CR2032 type coin cell lithium ion battery.
(1) Silicon fine particles and/or aggregates or clusters of silicon fine particles in a multi-layered petal-like or scale-like folded state, at least partially surrounded by graphite.
(2) In (1), at least a portion of the surface of the silicon fine particles and/or the aggregates or conglomerates is covered with carbon.
(3) At least a portion of crystalline silicon chips or cutting waste is surrounded by graphite.

Figure 8 is a schematic diagram of the lithium ion battery 500 of this embodiment. The lithium ion battery 500 of this embodiment includes a negative electrode 512 electrically connected to the negative electrode material 514, a positive electrode 516 electrically connected to the positive electrode material 518, a separator 520 that electronically insulates the negative electrode material 514 from the positive electrode material 518, and an electrolyte 530 in a container 510 of a CR2032 type coin cell. In addition, the lithium ion battery 500 of this embodiment has an external circuit including a power source 540 and a resistor 550 connected to the negative electrode 512 and the positive electrode 516 to realize charging and discharging.

The manufacturing method for the lithium ion battery 500 of this embodiment is as follows.

Regarding the method of manufacturing the negative electrode, first, about 0.3 g of the silicon fine particles, etc., at least partially surrounded by graphite, or the silicon fine particles, etc., at least partially covered on the surface with carbon, at least partially surrounded by graphite, as produced in the first embodiment (hereinafter collectively referred to as "negative electrode active material") is dispersed in about 10 mL (milliliters) of a solution consisting of a 1 wt % aqueous CMC binder solution and an aqueous SBR binder dispersion (TRD2001, manufactured by JSR Corporation).

In this embodiment, the silicon fine particles, etc., carbon black, CMC binder aqueous solution, and SBR binder aqueous dispersion are mixed in the order of 67:11:13:9 or 50:25:20:5 in dry weight ratio. In one modified example of this embodiment, the silicon fine particles, etc., carbon black, CMC binder aqueous solution, and PVA binder aqueous dispersion are mixed in the order of 50:25:20:5 in dry weight ratio.

Next, the slurry mixed and prepared using an agate mortar is applied to one side of a copper foil measuring 9 cm (length) x 10 cm (width) with a thickness of 15 μm so that the thickness after drying will be about 30 μm to about 200 μm, and then dried on a hot plate in air at 80°C for about 1 hour. The copper foil and the dried slurry are then punched out into a circle with a diameter of 11.3 mm, which corresponds to the battery standard CR2032 type coin cell, to form a working electrode. After measuring the weight of this working electrode, it is dried again by vacuum heating at 120°C for 6 hours in a glove box, and then attached to the inner surface of the negative electrode 512 made of copper foil, thereby producing the negative electrode of this embodiment.

Next, for the positive electrode, in order to evaluate the characteristics of the negative electrode material using a lithium ion battery with a half-cell structure, a lithium substrate was punched out into a circle with a diameter of 13 mm and used as the positive electrode 516. Note that for the positive electrode of the lithium ion battery, a known positive electrode can be used instead of the above-mentioned positive electrode 516.

The separator 520 of this embodiment is a porous polypropylene sheet. In addition, the electrolyte 530 of this embodiment is an electrolyte in which 1 mole of lithium hexafluorophosphate (LiPF ₆ ) is dissolved in a solvent (1 L) of ethylene carbonate (EC)/diethyl carbonate (DEC) mixed at a volume ratio of 1/1, or the electrolyte to which fluoroethylene carbonate (FEC) has been added, and is injected in an amount that is within the amount that fills the internal volume (about 1 mL) of a CR2032 coin cell.

The above-mentioned positive electrode material and cathode material 518, positive electrode 516, negative electrode material and anode material 514, negative electrode 512, separator 520, and electrolyte 530 are placed in a container 510 of a CR2032 type coin cell. After that, in a glove box with an argon atmosphere, the components of the separator 520 and electrolyte 530 are sealed in the container 510 while insulating the positive electrode 516 and negative electrode 512 of the outer frame of the coin cell, thereby producing a prototype lithium-ion battery 500 of a CR2032 type coin cell.

In addition, examples of the electrolytic solvent constituting the electrolytic solution 530 in this embodiment are mixed solvents of cyclic carbonates such as ethylene carbonate (EC) and propylene carbonate (PC) (polypropylene sheet), and chain carbonate organic solvents such as dimethyl carbonate (DMC) and diethyl carbonate (DEC). In addition, supporting salts such as lithium hexafluorophosphate (LiPF) and lithium tetrafluoroborate (LiBF) can be dissolved in the electrolytic solvent and used.

By adopting the above-mentioned structure, the presence of the above-mentioned silicon fine particles, or the unique multi-layered petal-like or scale-like shape of the agglomerates or aggregates, combined with the fact that they are surrounded by graphite, suppresses the degree of freedom of the above-mentioned silicon fine particles and/or the agglomerates or aggregates to a certain extent, which leads to increased cooperation between the graphite and the silicon fine particles and/or the graphite and the agglomerates or aggregates. As a result, by adopting this negative electrode material, it is possible to realize a lithium ion battery with little change in charge/discharge capacity even when charging and discharging are repeated, in other words, with good charge/discharge cycle characteristics. Alternatively, it is possible to realize an increase in charge/discharge capacity.

<Other embodiment (1)>
Incidentally, in each of the above-mentioned embodiments, silicon chips formed in the cutting process of a single crystal or polycrystalline silicon lump or ingot are exemplified as the starting material, but other forms of silicon chips can also be used as the starting material. Specifically, silicon chips are not limited to those inevitably formed in the cutting process of a silicon ingot in the production process of semiconductor products, but can also be produced by cutting a pre-selected crystalline silicon ingot uniformly or randomly with a cutting machine. In addition, so-called silicon waste materials such as silicon chips and silicon polishing chips, which are usually considered waste, can be the starting material for the silicon fine particles, etc. of each of the above-mentioned embodiments, but the silicon waste materials can also include fine chips obtained by crushing wafer fragments, waste wafers, etc. Furthermore, silicon fine particles, etc. using materials such as metallic silicon chips, metallic silicon polishing chips, or metallic other particulate silicon as the starting material can also be adopted.

<Other embodiment (2)>
In addition, the impurity concentration of the n-type crystalline silicon in each of the above-mentioned embodiments is not particularly limited. In addition, not only n-type but also p-type crystalline silicon can be adopted. Furthermore, crystalline silicon, which is a true semiconductor, can also be adopted as the crystalline silicon in each of the above-mentioned embodiments. Since the movement of electrons in the negative electrode material of the lithium ion battery is important, it is more preferable to use crystalline silicon containing n-type impurities. In addition, since about 1 wt % to about 3 wt % of graphite particles indicated by the peak intensities of the C(002) plane and the C(003) plane shown in the above-mentioned FIG. 7(b) are contained in the group of silicon fine particles or the aggregate of silicon fine particles, it is added that a part or all of these graphite particles can contribute to improving the conductivity of the negative electrode material.

<Other embodiment (3)>
Furthermore, the silicon microparticles and the lithium ion batteries including the same in the above-described embodiments are not limited to application to the coin cell type structure introduced in the second embodiment, and can therefore be applied to various devices or apparatuses that include or use lithium ion batteries with a larger electric capacity than those in the coin cell type structure.

<Other embodiment (4)>
In addition, as an alternative to the lithium ion battery negative electrode material (or negative electrode) manufacturing apparatus 100 shown in FIG. 2 in the first embodiment described above, a lithium ion battery negative electrode material (or negative electrode) manufacturing apparatus 200 shown in FIG. 9 may be adopted. Specifically, from the viewpoint of simplifying the equipment and/or reducing manufacturing costs, in the lithium ion battery negative electrode material (or negative electrode) manufacturing apparatus 200, a cleaning machine 10 for cleaning silicon chips formed in the silicon cutting process also serves as a crusher 20 for forming silicon fine particles 2 by crushing the cleaned silicon chips. Therefore, in the apparatus/method shown in FIG. 9, for example, beads with a relatively large diameter are used in the cleaning process and beads with a relatively small diameter are used in the crushing process to obtain silicon fine particles 2 to be used as a lithium ion battery negative electrode material. However, in order to obtain the silicon fine particles 2 described in the first embodiment with a higher degree of accuracy, it is preferable to form the silicon fine particles 2 by a bead mill machine after processing using a ball mill machine as in the first embodiment.

<Other embodiment (5)>
Furthermore, the inventors' analysis revealed that the amount of fluoroethylene carbonate (FEC) added to the electrolyte 530 in the second embodiment can affect the charge capacity value, the discharge capacity value, and the charge/discharge cycle characteristics, because a good (e.g., low-resistance and/or thin) solid electrolyte interface (SEI) is formed on the surface of the negative electrode material.

The disclosure of each of the above-mentioned embodiments is provided for the purpose of explaining those embodiments, and is not provided to limit the present invention. In addition, modifications within the scope of the present invention, including other combinations of each embodiment, are also included in the scope of the claims.

The negative electrode material for the lithium ion battery of the present invention and the lithium ion battery equipped with the same can be suitable for a wide variety of devices or apparatuses, including, for example, various power generation or storage devices (including small home power storage devices and large storage systems), smartphones, personal digital assistants, portable electronic devices (mobile phones, portable music players, notebook computers, digital cameras and videos), electric vehicles, hybrid electric vehicles (HEVs) or plug-in hybrid electric vehicles (PHEVs), motorcycles powered by motors, three-wheeled vehicles powered by motors, and other transport machinery or vehicles.

1. Cutting chips, etc. 2. Silicon fine particles, etc. 10. Cleaning machine (cleaning and preliminary crushing machine)
11 Bowl 13a Pot 13b Lid 15 Rotor 20 Crusher 21 Inlet 22 Treatment chamber 24 Outlet 25 Filter 40 Rotary evaporator 50 Oxide film removal tank 55 Hydrofluoric acid or ammonium fluoride aqueous solution 57 Stirrer 58 Centrifuge 60 Coating forming section 70 Composite forming section 80 Mixing section 100 Manufacturing device for negative electrode material (or negative electrode) of lithium ion battery 500 Lithium ion battery 510 Container 512 Negative electrode 514 Negative electrode material and negative electrode material 516 Positive electrode 518 Positive electrode material and positive electrode material 520 Separator 530 Electrolyte 540 Power source 550 Resistor

Claims (15)

The silicon fine particles include an aggregate or agglomerate of the silicon fine particles in which thin-layer silicon fine particles are stacked in a scale-like manner,
The agglomerates or aggregates are trapped between layers of graphite, so that the graphite surrounds at least a portion of the agglomerates or aggregates; and
The crystallites of the silicon fine particles have a volume distribution in which the mode diameter and the median diameter are 30 nm or less.
A negative electrode material for lithium-ion batteries. The aggregates or conglomerates contain 1 wt % to 3 wt % of graphite particles;
The negative electrode material for a lithium ion battery according to claim 1. The silicon fine particles have a volume distribution in which the mode diameter and the median diameter are 20 nm or less.
The negative electrode material for a lithium ion battery according to claim 1 or 2. In an X-ray diffraction measurement of the aggregate or the assembly, the intensity of a diffraction peak attributable to Si (111) near 2θ = 28.4° is greater than the intensities of other diffraction peaks.
The negative electrode material for a lithium ion battery according to any one of claims 1 to 3. The graphite is expanded graphite.
The negative electrode material for a lithium ion battery according to any one of claims 1 to 4. The negative electrode material of a lithium ion battery according to any one of claims 1 to 5 is provided.
Lithium-ion battery. A device comprising the lithium ion battery of claim 6. a grinding section for grinding crystalline silicon to form a thin-layer aggregate or aggregate of silicon fine particles having a volume distribution in which the mode diameter and median diameter of the crystallites of the silicon fine particles are 30 nm or less, the aggregate or aggregate being composed of at least the silicon fine particles overlapping in a scale-like manner;
and a composite forming section in which the agglomerates or the aggregates are taken in between layers of graphite, so that the graphite surrounds at least a part of the agglomerates or the aggregates, thereby forming a composite containing the graphite and the agglomerates or the aggregates.
Equipment for manufacturing negative electrode materials for lithium-ion batteries. A coating forming unit that forms carbon to cover at least a portion of the surface of the aggregate or the conglomerate,
The apparatus for producing a negative electrode material for a lithium ion battery according to claim 8. The crystalline silicon is chips or shavings cut by a fixed abrasive wire.
An apparatus for producing a negative electrode material for a lithium ion battery according to claim 8 or 9. The grinding unit includes a ball mill and a bead mill used after the ball mill.
An apparatus for producing a negative electrode material for a lithium ion battery according to any one of claims 8 to 10. a grinding step of grinding crystalline silicon to form a thin-layer aggregate or aggregate of silicon fine particles having a volume distribution in which the mode diameter and median diameter of the crystallites of the silicon fine particles are 30 nm or less, the aggregate or aggregate being composed of at least the silicon fine particles stacked in a scale-like shape;
and a composite forming step in which the agglomerates or the aggregates are incorporated between layers of graphite, so that the graphite surrounds at least a portion of the agglomerates or the aggregates, thereby forming a composite containing the graphite and the agglomerates or the aggregates.
A method for producing negative electrode materials for lithium-ion batteries. A coating forming step of forming carbon covering at least a portion of the surface of the aggregate or the conglomerate is further included.
A method for producing the negative electrode material of a lithium ion battery according to claim 12. The crystalline silicon is chips or shavings cut by a fixed abrasive wire.
A method for producing the negative electrode material of a lithium ion battery according to claim 12 or 13. In the pulverization step, the crystalline silicon is pulverized by a ball mill and then pulverized by a bead mill to form the aggregates or the conglomerates.
A method for producing the negative electrode material of a lithium ion battery according to any one of claims 12 to 14.

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