Lithium-ion battery negative electrode material or negative electrode manufacturing device and manufacturing method thereof

Abstract

To provide a lithium ion battery negative electrode material that can produce a lithium ion battery with little change in charge / discharge capacity even after repeated charging and discharging, and a lithium ion battery, a negative electrode material manufacturing device, and a negative electrode material manufacturing method.SOLUTION: One lithium ion battery negative electrode material according to the present invention is formed using silicon fine particles, which has a volume distribution with a mode diameter and a median diameter of less than 50 nm, and whose surface is at least partially covered with carbon, or an aggregate or a collection thereof. In addition, another lithium ion battery negative electrode material according to the present invention is formed using silicon fine particles whose surface is at least partially covered with carbon, or an aggregate or a collection thereof, and also includes the aggregate or the collection of the silicon fine particles folded in a multi-layered petal-like or scale-like state.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a negative electrode material for a lithium ion battery, a lithium ion battery, a method for manufacturing a negative electrode or a negative electrode material for a lithium ion battery, and an apparatus for manufacturing the same. [Background technology]

[0002] Conventional lithium-ion batteries have a negative electrode with a composite layer made by mixing graphite (e.g., natural graphite or artificial graphite) and anode material with a binder on the negative electrode side. The positive electrode has a composite layer made by mixing lithium (Li) oxide powder (e.g., LiCoO2, LiNiO2, LiMnO2) and conductive graphite (mainly carbon black) with a binder (e.g., PVDF: polyvinylidene fluoride) on the positive electrode side. The cell container of a lithium-ion battery is filled with electrolyte, and a separator (mainly a porous polyolefin or porous polypropylene sheet) is placed between the negative and positive electrode materials.

[0003] The separator is provided to allow the electrolyte to pass through and the lithium ions to move, and to separate the electrodes to prevent electrical short circuits.

[0004] Charging and discharging of lithium-ion batteries is carried out by the movement of lithium ions between the negative and positive electrode materials in the electrolyte. During charging, lithium ions move to the negative electrode side, and during discharging, lithium ions move to the positive electrode side. Charging is carried out through an externally connected power supply, and discharging is carried out through an externally connected resistance (load).

[0005] Recently, in the field of lithium-ion batteries, a technology has been disclosed that uses silicon particles as an alternative to graphite as the negative electrode active material. For example, one example of silicon particles is a powder with a diameter of approximately 38 microns (μm) or less, formed by crushing single-crystal silicon in a mortar and classifying it using a mesh. The powder is heated to 150°C (ultimate temperature) at a heating rate of 30°C / min in an argon atmosphere (see Patent Document 1). Another example involves supplying liquid silicon tetrachloride to high-temperature, high-concentration zinc gas and reacting it 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 temperatures below 1000°C, particularly 500-800°C, after which the particle size of the formed silicon particles is adjusted and collected in an aqueous zinc chloride solution. This process produces high-purity silicon particles with a particle size of approximately 1-100 μm, and its use has been disclosed (see Patent Document 2). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-032733 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-101998 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the prior art, when silicon particles are used as a negative electrode material, the electrical capacity during charging and discharging can be increased, but on the other hand, lithium is absorbed and released into the silicon particles, causing the silicon particles to change in volume or even be destroyed, resulting in the problem that the charge-discharge cycle characteristics cannot be maintained.

[0008] Furthermore, the silicon particles disclosed in the above-mentioned prior art documents require high-temperature synthesis and collection processes, making the manufacturing process for obtaining silicon particles as a negative electrode material extremely complicated. As a result, productivity declines and manufacturing costs are unavoidable. Therefore, the silicon particles disclosed so far have major issues, such as poor negative electrode properties for lithium-ion batteries and insufficient industrial applicability. In other words, the development of lithium-ion batteries using silicon particles is still in its infancy. [Means for solving the problem]

[0009] The present invention can greatly contribute to the provision of a high-performance negative electrode material for lithium ion batteries, a lithium ion battery, a negative electrode for lithium ion batteries, or a method and apparatus for manufacturing a negative electrode material, by solving at least some of the problems associated with conventional negative electrode materials using silicon particles, such as problems related to charge / discharge cycle characteristics.

[0010] Furthermore, one negative electrode material for a lithium ion battery of the present invention is formed using silicon fine particles or aggregates or aggregates thereof, which have a volume distribution in which the mode diameter and median diameter are less than 50 nm and at least a portion of the surface of which is covered with carbon.

[0011] Another negative electrode material for a lithium ion battery of the present invention is formed using silicon fine particles, at least a portion of whose surfaces are covered with carbon, or aggregates or conglomerates thereof, and includes the aggregates or conglomerates of the silicon fine particles in a state where they are folded into multi-layered petal-like or scale-like shapes.

[0012] By adopting the above-mentioned negative electrode materials, it is possible to realize a lithium ion battery that exhibits little change in charge / discharge capacity even after repeated charge / discharge, in other words, has good charge / discharge cycle characteristics, or can realize an increase in charge / discharge capacity.

[0013] It is also worth noting that the silicon fine particles or their aggregates or conglomerates that form each of the above-mentioned negative electrode materials can be prepared from, for example, chips or shavings that are typically treated as industrial waste and are produced by cutting a molten and solidified silicon block or ingot with a fixed abrasive wire. Furthermore, the silicon fine particles or their aggregates or conglomerates formed by pulverizing the chips or shavings with a ball mill and / or a bead mill are a suitable embodiment for maintaining a high level of charge / discharge cycle performance of a lithium-ion battery and / or improving these performances.

[0014] Furthermore, one lithium-ion battery of the present invention includes a negative electrode material formed using silicon fine particles or aggregates or aggregates thereof, the silicon fine particles having a volume distribution in which the mode diameter and median diameter are less than 50 nm and at least a portion of the surface of the silicon fine particles is covered with carbon.

[0015] Another lithium-ion battery of the present invention comprises a negative electrode material formed using silicon fine particles or aggregates or aggregates thereof, at least a portion of the surfaces of which are covered with carbon, and containing the aggregates or aggregates of the silicon fine particles in a state where they are folded into multi-layered petal-like or scale-like shapes.

[0016] The lithium ion battery described above can reduce the change in charge / discharge capacity even when repeatedly charged and discharged, or can maintain and / or improve the charge / discharge cycle characteristics at a high level, and can also realize an increase in charge / discharge capacity.

[0017] Furthermore, one of the present inventions provides an apparatus for manufacturing a negative electrode material for a lithium-ion battery, which includes a crushing unit that crushes crystalline silicon to form silicon fine particles or aggregates or assemblies thereof having a volume distribution in which the mode diameter and median diameter are less than 50 nm, and a coating forming unit that forms carbon that covers at least a portion of the surface of the silicon fine particles or the aggregates or assemblies.

[0018] Another manufacturing apparatus for a lithium-ion battery negative electrode material of the present invention includes a crushing unit that crushes crystalline silicon, which is chips or shavings cut out by a fixed abrasive wire, to form silicon microparticles containing agglomerates or aggregates of silicon microparticles folded into multi-layered petal-like or scale-like shapes, and a coating forming unit that forms carbon to cover at least a portion of the surface of the silicon microparticles or the agglomerates or aggregates.

[0019] The above-described manufacturing apparatus for a lithium-ion battery negative electrode material can contribute to the production of a lithium-ion battery in which the charge capacity and / or discharge capacity change little even after repeated charge and discharge, in other words, a lithium-ion battery with good charge and discharge cycle characteristics, or in which an increased charge and discharge capacity can be realized.

[0020] Furthermore, one lithium-ion battery negative electrode manufacturing apparatus of the present invention includes a crushing unit that crushes crystalline silicon to form silicon fine particles or aggregates or assemblies thereof that serve as a negative electrode material, the silicon fine particles or aggregates or assemblies having a volume distribution in which the mode diameter and median diameter are less than 50 nm, and a coating forming unit that forms carbon that covers at least a portion of the surface of the silicon fine particles or the aggregates or assemblies.

[0021] Another lithium-ion battery negative electrode manufacturing apparatus of the present invention includes a crushing unit that crushes crystalline silicon, which is chips or shavings cut out by a fixed abrasive wire, to form silicon fine particles that will become the negative electrode material so that the silicon fine particles contain agglomerates or aggregates of silicon fine particles that are folded into multi-layered petal-like or scale-like shapes, and a coating formation unit that forms carbon to cover at least a portion of the surface of the silicon fine particles or the agglomerates or aggregates.

[0022] The above-described manufacturing apparatus for a lithium ion battery negative electrode can contribute to the production of a lithium ion battery that exhibits little change in charge capacity and / or discharge capacity even after repeated charge and discharge, in other words, has good charge and discharge cycle characteristics, or can increase the charge and discharge capacity.

[0023] Furthermore, one method for producing a negative electrode material for a lithium-ion battery according to the present invention includes a crushing step of crushing crystalline silicon to form silicon fine particles or aggregates or conglomerates thereof having a volume distribution in which the mode diameter and median diameter are less than 50 nm, and a coating step of forming carbon to cover at least a portion of the surface of the silicon fine particles or the aggregates or conglomerates.

[0024] Another method of the present invention for producing a negative electrode material for a lithium-ion battery includes a grinding step in which crystalline silicon, which is chips or shavings cut out by a fixed abrasive wire, is ground to form silicon fine particles containing agglomerates or aggregates of silicon fine particles folded into multi-layered petal-like or scale-like shapes, and a coating step in which carbon is formed to cover at least a portion of the surface of the silicon fine particles or the agglomerates or aggregates.

[0025] The above-described method for producing a negative electrode material for a lithium ion battery can contribute to the production of a lithium ion battery that exhibits little change in charge capacity and / or discharge capacity even after repeated charge and discharge, in other words, has good charge and discharge cycle characteristics, or can increase the charge and discharge capacity.

[0026] Furthermore, one method for producing a negative electrode for a lithium ion battery according to the present invention includes a crushing step of crushing crystalline silicon to form silicon fine particles or aggregates or assemblies thereof as a negative electrode material, the silicon fine particles or aggregates or assemblies having a volume distribution in which the mode diameter and median diameter are less than 50 nm, and a coating step of forming carbon to cover at least a portion of the surface of the silicon fine particles or the aggregates or assemblies.

[0027] Another method of manufacturing a negative electrode for a lithium ion battery according to the present invention includes a grinding step in which crystalline silicon, which is chips or shavings cut out by a fixed abrasive wire, is ground to form silicon fine particles that will serve as a negative electrode material so that the silicon fine particles contain agglomerates or aggregates of silicon fine particles that are folded into multi-layered petal-like or scale-like structures; and a coating step in which carbon is formed to cover at least a portion of the surface of the silicon fine particles or the agglomerates or aggregates.

[0028] The above-described method for manufacturing a negative electrode of a lithium ion battery can contribute to the manufacture of a lithium ion battery that not only increases the charge / discharge capacity but also exhibits little change in charge capacity and / or discharge capacity even after repeated charge / discharge, in other words, has good charge / discharge cycle characteristics.

[0029] The means for covering at least a portion of the surface of each of the silicon fine particles or their aggregates or aggregates with carbon is not particularly limited. Typical examples of such means include a means using a carbon film formed by thermal decomposition of a hydrocarbon such as acetylene, a means using a carbon film formed by a furnace method, a means using a carbon film formed by a channel method, or a means using a carbon film formed by plasma treatment.

[0030] The crystalline silicon in the above-mentioned inventions includes not only single crystal silicon but also polycrystalline silicon. Also, metallic silicon can be selected as the crystalline silicon in the above-mentioned inventions. [Effects of the Invention]

[0031] According to one lithium-ion battery anode material of the present invention, not only can a lithium-ion battery with little change in charge / discharge capacity even after repeated charging / discharging, in other words, with good charge / discharge cycle characteristics be realized, but also an increase in charge / discharge capacity can be realized. Furthermore, according to one lithium-ion battery of the present invention, not only can a change in charge / discharge capacity be reduced even after repeated charging / discharging, in other words, with good charge / discharge cycle characteristics be realized, but also an increase in charge / discharge capacity can be realized. In addition, according to one lithium-ion battery manufacturing apparatus and one lithium-ion battery manufacturing method of the present invention, not only can a lithium-ion battery with little change in charge / discharge capacity even after repeated charging / discharging, in other words, with good charge / discharge cycle characteristics be realized, but also a lithium-ion battery with an increase in charge / discharge capacity can be realized. [Brief explanation of the drawings]

[0032] [Figure 1] FIG. 1 is a flow chart showing a manufacturing process of a negative electrode material for a lithium ion battery according to a first embodiment. [Figure 2] FIG. 1 is a schematic diagram showing a manufacturing apparatus and manufacturing process for a negative electrode material for a lithium ion battery according to a first embodiment. [Figure 3] FIG. 10 is a diagram showing a TEM (transmission electron microscope) image of an example of silicon fine particles or their aggregates or aggregates that have been subjected to the coating formation step (S4) of the first embodiment. [Figure 4A] 1 is an SEM image of an example of silicon fine particles or aggregates or aggregates thereof according to the first embodiment. [Figure 4B] FIG. 2 is a diagram showing an SEM image of an example of enlarged silicon fine particles or their aggregates or aggregates in the first embodiment. [Figure 4C] 5A is a view showing an SEM image of another example of an aggregate or agglomerate of silicon fine particles in the first embodiment, and FIG. 5B is an enlarged view of a part of FIG. 5A. [Figure 5] FIG. 2 is a diagram showing a TEM image of silicon microparticles according to the first embodiment. [Figure 6]2 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 of the first embodiment. [Figure 7] 2 is a graph showing the results of X-ray diffraction measurement of silicon fine particles or their aggregates or aggregates according to the first embodiment ((a) wide range, (b) limited range). [Figure 8] FIG. 1 is a schematic configuration diagram of a lithium ion battery according to a second embodiment. [Figure 9] 10 is a graph showing an example of charging cycle characteristics of the lithium ion battery of the second embodiment. [Figure 10] 10 is a graph showing an example of discharge cycle characteristics of the lithium ion battery of the second embodiment. [Figure 11] 1 is a graph showing the charging cycle characteristics of a lithium ion battery as a reference example. [Figure 12] 1 is a graph showing the discharge cycle characteristics of a lithium ion battery as a reference example. [Figure 13] 10 is a TEM image of silicon microparticles or aggregates or aggregates thereof in the lithium ion battery of the second embodiment after 100 charge / discharge cycles. [Figure 14] FIG. 10 is a schematic diagram showing a manufacturing apparatus and manufacturing process for a negative electrode material for a lithium ion battery according to another embodiment. [Figure 15A] 10 is a graph showing the charging cycle characteristics of a lithium ion battery according to another embodiment when the amount of FEC in the electrolyte is changed. [Figure 15B] 10 is a graph showing the discharge cycle characteristics of a lithium ion battery according to another embodiment when the amount of FEC in the electrolyte is changed. [Figure 16A] 10 is a graph showing the charging cycle characteristics of a lithium ion battery according to another embodiment when the weight ratio of silicon (Si) to carbon (C) is changed. [Figure 16B]10 is a graph showing the discharge cycle characteristics of a lithium ion battery according to another embodiment when the weight ratio of silicon (Si) to carbon (C) is changed. [Explanation of symbols]

[0033] 1 Chips etc. 2. Silicon microparticles 10 Washing machine (washing and pre-crushing machine) 11 Ball Types 13a Pot 13b Lid 15 Rotation axis 20 Crusher 21 Introduction 22 Processing Room 24 Outlet 25 filters 30 Dryer 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 Mixing section 100 Lithium-ion battery negative electrode material and negative electrode manufacturing equipment 500 Lithium-ion battery 510 Container 512 Negative electrode 514 Anode materials and negative electrode materials 516 Positive electrode 518 Cathode materials and cathode materials 520 Separator 530 Electrolyte 540 Power supply 550 Resistor DETAILED DESCRIPTION OF THE INVENTION

[0034] Embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this description, common parts are designated by common reference numerals throughout the drawings unless otherwise specified. In addition, in the drawings, elements of each embodiment are not necessarily shown to scale. In addition, some reference numerals may be omitted to make each drawing easier to understand.

[0035] First Embodiment Fig. 1 is a flow diagram showing the manufacturing process of the negative electrode material for lithium ion batteries of this embodiment, and Fig. 2 is a schematic diagram showing the manufacturing apparatus and manufacturing process of the negative electrode material for lithium ion batteries of this embodiment.

[0036] The negative electrode material for a lithium-ion battery according to the present embodiment, a lithium-ion battery including the negative electrode material, and their manufacturing methods include various steps using, as a starting material, silicon chips, silicon cutting waste, or silicon grinding waste (hereinafter also referred to as "silicon chips, etc." or "chips, etc."), which are typically discarded during silicon cutting processing in the production of silicon wafers used in semiconductor products such as solar cells. The chips, etc. also include fine chips obtained by pulverizing discarded silicon wafers using a known pulverizer. As shown in FIG. 1 , the manufacturing method for a lithium-ion battery according to the present embodiment includes the following steps (1), (2), (4), and (5). Furthermore, the manufacturing method for a lithium-ion battery according to the present embodiment may include the following step (3) as another possible embodiment. (1) Cleaning process (S1) (2) Grinding process (S2) (3) Oxide film removal process (S3) (4) Covering formation process (S4) (5) Negative electrode formation process (S5)

[0037] 2, the lithium-ion battery anode material and anode manufacturing apparatus 100 of this embodiment mainly includes a washer (washing and pre-crushing machine) 10, a crusher 20, a dryer (not shown), a rotary evaporator 40, a coating forming unit 60 that forms carbon to cover at least a portion of the surface of silicon microparticles or their aggregates or aggregates (hereinafter collectively referred to as "silicon microparticles"), and a mixing unit 70 that plays a part in forming the lithium-ion battery anode. The lithium-ion battery anode material and anode manufacturing apparatus 100 of this embodiment may also include an oxide film removal tank 50 and a centrifuge 58 as another possible embodiment. The crusher 20 alone, or the washer 10 and the crusher 20, are referred to as the crushing unit in this embodiment.

[0038] (1) Cleaning process (S1) In the cleaning step (S1) of this embodiment, silicon chips and the like formed during the cutting process of, for example, monocrystalline or polycrystalline silicon, i.e., a crystalline silicon chunk or ingot (an n-type crystalline silicon chunk or ingot), are cleaned. Typical silicon chips and the like are chips and the like formed when a silicon ingot is cut using a known wire or the like (typically, a fixed abrasive wire). Therefore, in this embodiment, silicon chips and the like, which have traditionally been considered waste material, are used as the starting material to form silicon microparticles that constitute the negative electrode material of a lithium-ion battery, which is advantageous in terms of production cost and / or ease of procurement of raw materials and resource utilization.

[0039] The cleaning step (S1) of this embodiment is primarily intended to remove organic matter adhering during the formation 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, the chips, etc. 1 to be cleaned are first 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, two cylindrical rotors 15 of a ball mill, which is a cleaning machine (cleaning and preliminary crushing machine) 10, are rotated to rotate the pot 13a on the rotors 15. As a result, the chips, etc. 1 to be cleaned are dispersed in the first liquid within the pot 13a, thereby cleaning the chips, etc. 1 and performing preliminary crushing.

[0040] The ball mill of this embodiment is a mill that applies physical impact force to balls 11 (milling media) such as steel balls, magnetic balls, boulders, and the like housed in a pot 13a and a lid 13b by rotating the pot 13a and the lid 13b. A preferred example of the first liquid is acetone. In a more specific example, 300 milliliters (mL) of acetone was added to 100 grams (g) of silicon chips or the like, and the mixture was 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 Corporation) to disperse the silicon chips or the like in the acetone. The balls used in the ball mill were alumina balls with a diameter of 10 millimeters (mm) and alumina balls with a diameter of 20 mm. In the cleaning step (S1) of this embodiment, the silicon chips or the like were pre-pulverized and stirred in the first liquid in the ball mill to disperse the silicon chips or the like. Therefore, the cleaning efficiency is significantly improved compared to a process in which the particles 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 the charge-discharge cycle characteristics.

[0041] After the cleaning step (S1), the lid 13b is opened to discharge the silicon particles together with the first liquid, and then the first liquid is removed by suction filtration using a known vacuum filtration means to become 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 by 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).

[0042] (2) Grinding process (S2) Then, in the pulverization step (S2), a predetermined second liquid is added to the washed silicon particles, and the silicon particles are pulverized in a bead mill. Therefore, in this embodiment, the silicon particles that have been through the washing step (S1) are further pulverized by the bead mill used after the ball mill, in other words, after pulverization by the ball mill.

[0043] A suitable example of the second liquid in this embodiment is IPA (isopropyl alcohol). As a pretreatment for the pulverization process, the second liquid and the silicon particles obtained in the cleaning process (S1) are placed in a pot 13a in a weight ratio of 95% second liquid to 5% silicon particles, and then a pre-pulverization process is performed by rotating a washer (cleaning and pre-pulverizer) 10. The pre-pulverized slurry containing silicon particles is passed through a mesh with an opening of 180 microns to remove relatively coarse particles, and the resulting slurry containing silicon particles is then further pulverized using a bead mill (in this embodiment, a Star Mill LMZ015 manufactured by Ashizawa Fining Co., Ltd.) in the pulverizer 20. More specifically, the slurry containing silicon particles from which silicon chips with particle diameters of 180 microns or larger have been removed is introduced into the inlet 21 of the pulverizer 20, and the slurry is circulated using a pump 28 while being pulverized in the processing chamber 22 of the bead mill. An example of a specific type of bead used in the bead mill is zirconia beads with a diameter of 0.5 mm. After recovering the slurry containing the pulverized silicon particles, the second liquid is removed using a rotary evaporator 40 that automatically performs vacuum distillation, thereby obtaining silicon fine particles as the result of the pulverization process.

[0044] In this embodiment, silicon microparticles are obtained by introducing approximately 450 g of zirconia beads with a particle diameter of 0.5 mm and performing a fine pulverization process at a rotation speed of 2908 rpm for 4 hours. In another embodiment, the pulverization process in the pulverization step (S2) can be performed using any one of the following pulverizers, or a combination of two or more of them, selected from the group consisting of a ball mill, a bead mill, a jet mill, and an impact wave pulverizer. In addition, not only automatic pulverizers but also manual pulverizers may be used in the pulverization step (S2). However, from the viewpoint of highly accurately forming agglomerates or aggregates of silicon microparticles in a multi-layered petal-like or scale-like state, as described below, it is preferable to use a pulverization step (S2) consisting of treatment with a bead mill or a pulverization step (S2) including treatment with a bead mill.

[0045] Another suitable embodiment that can be adopted is to further crush the silicon fine particles obtained in the above-mentioned crushing step (S2) using a known crusher (a representative crusher is Model 20D manufactured by Ishikawa Kogyo Co., Ltd.). This crushing treatment improves dispersibility when forming the negative electrode of a lithium ion battery, thereby providing the effect of highly reliably preventing or suppressing damage to the negative electrode due to the absorption and release of lithium.

[0046] (3) Oxide film removal process (S3) In this embodiment, the oxide film removing step (S3) is performed as a preferred aspect, but at least some of the effects of this embodiment can be achieved even if this oxide film removing step (S3) is not performed.

[0047] In the oxide film removal step (S3) of this embodiment, the silicon fine particles 2 obtained in the pulverization step (S2) are brought into contact with hydrofluoric acid or an aqueous ammonium fluoride solution. The silicon fine particles 2 obtained in the pulverization step (S2) are dispersed by immersing them in the hydrofluoric acid or ammonium fluoride aqueous solution. Specifically, in the oxide film removal tank 50, the silicon fine particles 2 are dispersed in the hydrofluoric acid or ammonium fluoride aqueous solution 55 using a stirrer 57, thereby removing oxides (mainly silicon oxide) on the surfaces of the silicon fine particles 2.

[0048] Thereafter, the silicon microparticles from which some or all of the surface oxides have been removed are separated from the hydrofluoric acid aqueous solution by a centrifuge 58. The silicon microparticles are then immersed in a third liquid such as an ethanol solution. By removing the third liquid, silicon microparticles from which some or all of the oxides (or oxide films) originally formed on the surfaces have been removed are obtained. If the process of removing oxides that may be present on the surfaces of the silicon microparticles 2 is not performed, the silicon microparticles are subjected to the coating formation process (S4) and the anode formation process (S5) described below.

[0049] In the oxide film removal step (S3) of this embodiment, the silicon fine particles are brought into contact with hydrofluoric acid by immersing the silicon fine particles in hydrofluoric acid or an aqueous ammonium fluoride solution, but other methods for bringing the silicon fine particles into contact with hydrofluoric acid or an aqueous ammonium fluoride solution may also be employed. For example, spraying the aqueous hydrofluoric acid solution onto the silicon fine particles in a shower-like manner is another embodiment that may be employed.

[0050] (4) Covering formation process (S4) In this embodiment, a coating step is performed in which a carbon film is applied to cover part or all of the surface of silicon fine particles that have or have not undergone the oxide film removal step (S3). Therefore, the silicon fine particles that have undergone the coating step (S4) of this embodiment have at least a portion of their surface covered with carbon, resulting in an increased thickness compared to silicon fine particles that are not covered with carbon. The carbon of this embodiment is conductive, allowing for the formation of a conductive anode material. Furthermore, by covering silicon fine particles with carbon having a thickness of, for example, several nanometers to several micrometers, not only can a thin anode be formed, but also a relatively thick anode can be easily formed. FIG. 3 shows a TEM (transmission electron microscope) image of an example of silicon fine particles (partially enlarged) or their aggregates or aggregates (partially enlarged) that have undergone the coating step (S4) of this embodiment. The crystalline silicon shown in FIG. 3 was observed to have a crystal plane orientation (111) (also simply referred to as "Si(111)" or "(111)". The same applies to the notations for other plane orientations).

[0051] In addition, for example, covering silicon fine particles 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 fine particles, which can facilitate the production of lithium ion batteries and also contribute to improving the performance (e.g., charge / discharge cycle characteristics) of lithium ion batteries.

[0052] Furthermore, by forming a negative electrode material for a lithium ion battery using silicon fine particles at least partially covered with carbon, it is possible to increase the charge capacity and discharge capacity compared to silicon fine particles not covered with carbon. For example, according to research by the present inventors, in the case of silicon fine particles not covered with carbon, when the thickness of the negative electrode material is, for example, about 30 μm, the charge capacity and discharge capacity are less than 500 (mAh / g). However, by using silicon fine particles at least partially covered with carbon, the charge capacity and discharge capacity can be increased by more than two times (typically about 3 to about 5 times).

[0053] In the coating formation step (S4) of this embodiment, the means for coating part or all of the surface of the silicon microparticles (in other words, at least a portion of the surface) with a carbon film is not particularly limited. For example, a method of covering at least a portion of the surface of the silicon microparticles 2 with carbon by thermal CVD, which is an example of chemical vapor deposition, can be used. Specifically, at least a portion of the surface of the silicon microparticles 2 can be coated with a carbon film by heating the silicon microparticles 2 at a temperature of about 600°C to about 1200°C in an atmosphere containing an organic gas and / or its vapor. Therefore, a thermal CVD apparatus, which is an example of a chemical vapor deposition apparatus, is one aspect of the coating formation unit 60 that can be used in the coating formation step (S4) of this embodiment. In addition, 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. Furthermore, 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 treatment temperature.

[0054] As described above, typically, a hydrocarbon gas is thermally decomposed on or near the heated silicon microparticles 2 to carbonize the gas, thereby coating 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 low-pressure thermal CVD or plasma CVD, which are other examples of chemical vapor deposition methods, may also be used as appropriate.

[0055] Another example of a method for coating at least a portion of the surface of silicon microparticles 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 microparticles 2 that have been treated at least by the cleaning step (S1) and the pulverization step (S2) of this embodiment in the coating formation unit 60. The organic compound is then heated to a temperature at which it pyrolyzes to carbonize the organic compound, thereby forming silicon microparticles 2 at least a portion of whose surface is covered with carbon (typically, graphene, graphite, and / or amorphous carbon). A variation of this embodiment also includes additionally and / or beforehand performing a step of baking the formed silicon microparticles 2 in a nitrogen or hydrogen atmosphere, for example, at 400°C to 1200°C. 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 2 or their aggregates or aggregates, it is preferable to heat the silicon microparticles 2 in a hydrogen atmosphere.

[0056] Another possible embodiment is to form silicon microparticles 2 whose surfaces are at least partially covered with carbon using other known means. For example, a carbon film formed by a known carbon black manufacturing method (furnace method or channel method) can be used. The furnace method involves partially burning creosote oil obtained by distilling coal tar in a specified chamber where the creosote oil is turbulently diffused, and then water-cooling the resulting droplets. The channel method involves depositing carbon by impinging a flame formed by burning natural gas, for example, on the cooling surface of a channel steel. However, because the resulting product contains sulfur components derived from petroleum, it is more preferable to use the thermal CVD method described above, which is a method that is less likely to introduce such impurities. Furthermore, when employing each of the above-mentioned methods, for example, employing a method in which kinetic energy is applied to the silicon fine particles or their agglomerates or aggregates using a known mechanical structure as appropriate, thereby coating at least a portion of the surface of the silicon fine particles 2 or their agglomerates or aggregates with a carbon film, is a preferred embodiment, since this enables a more uniform (e.g., uniform in thickness and / or density) carbon film to be formed on the surface of the silicon fine particles 2 or their agglomerates or aggregates. More specifically, employing a method in which at least a portion of the surface of the silicon fine particles 2 or their agglomerates or aggregates is coated with a carbon film while rotating a chamber or tube containing the silicon fine particles or their agglomerates or aggregates and / or while applying ultrasonic vibrations to the silicon fine particles 2 or their agglomerates or aggregates, is a preferred embodiment, since this enables a more uniform carbon film to be formed on the surface of the silicon fine particles 2 or their agglomerates or aggregates.

[0057] (4) Negative electrode formation process (S5) The lithium-ion battery negative electrode material and negative electrode manufacturing apparatus 100 of this embodiment includes a mixing section 70 that mixes silicon fine particles as the negative electrode material processed in the coating formation step (S4) with a member (e.g., copper foil) that constitutes a part of the negative electrode using a binder (e.g., ammonium carboxyl methyl cellulose (CMC) and styrene butadiene rubber (SBR), or ammonium carboxyl methyl cellulose (CMC) and polyvinyl alcohol (PVA)). A negative electrode is formed using a mixture layer formed by this mixing section 70.

[0058] <Other processes> The silicon microparticles obtained by the above-mentioned cleaning step (S1), pulverization step (S2), and (4) coating formation step (S4), or by the cleaning step (S1), pulverization step (S2), oxide film removal step (S3), and (4) coating formation step (S4), may be classified, for example, to reduce variations in the number distribution and / or volume distribution of the crystallite diameter of each silicon microparticle.

[0059] <Analysis results of silicon fine particles obtained in the first embodiment> 1. Analysis of silicon microparticles using SEM and TEM images

[0060] Fig. 4A is an SEM (scanning electron microscope) image of an example of silicon microparticles or their aggregates or conglomerates after the pulverization step (S2) of the first embodiment. Fig. 4B is a diagram showing an enlarged SEM image of an example of silicon microparticles or their aggregates or conglomerates after the pulverization step (S2) of the first embodiment. Fig. 4C is (a) a diagram showing an SEM image of another example of an aggregate or conglomerate of silicon microparticles in the first embodiment, and (b) an enlarged view of a portion of (a). In addition, Fig. 5 is a diagram showing a transmission electron microscope (TEM) image of silicon microparticles of the first embodiment.

[0061] As shown in Figure 4A, not only individual silicon microparticles but also silicon microparticles or their aggregates or conglomerates shown in Y1 and Y2 were confirmed. Interestingly, upon more detailed analysis, as shown in Figure 4B and the Z portion of Figures 4C(a) and (b), it was confirmed that the silicon microparticles or their aggregates were aggregates or conglomerates in which thin-layer silicon microparticles were folded into multi-layered petal-like or scale-like shapes. Furthermore, upon closer observation, for example, when the width (minor axis) of one or a group of scale-like silicon microparticles was taken as 1, the range of the length (major axis) was 3.3 to 12.9.

[0062] 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 indicated by 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 approximately 2 nm to approximately 10 nm in size in cross-sectional view. In Figure 5, the crystal plane orientation is indicated in each area surrounded by white lines.

[0063] 2. Analysis of crystallite size distribution of silicon microparticles by X-ray diffraction 6A and 6B are graphs showing (a) the crystallite size distribution showing the number distribution and (b) the crystallite size distribution showing the volume distribution of the crystallite size in the Si(111) direction of the silicon microparticles of the first embodiment. Fig. 6 shows the results obtained by analyzing the crystallite size distribution of the silicon microparticles after the pulverization step (S2) using X-ray diffraction. In both Fig. 6A and Fig. 6B, the horizontal axis represents the crystallite size (nm) and the vertical axis represents the frequency.

[0064] 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, in the number distribution, it was confirmed that both the mode diameter and the median diameter were 5 nm or less, more specifically, 3 nm or less. It is noteworthy that in the volume distribution, it was confirmed that both the mode diameter and the median diameter were at least 50 nm or less, and particularly 30 nm or less. Furthermore, in Figure 6, it was confirmed that an extremely small value of 10 nm or less was achieved.

[0065] 6(a) and 6(b), it was confirmed that the silicon microparticles obtained after the pulverization step (S2) using the bead mill method have an average crystallite diameter of approximately 20 nm or less, more specifically, approximately 9.8 nm, which achieves an average crystallite diameter of 10 nm or less. The crystallite diameter distribution of the silicon microparticles after the oxide film removal step (S3) is also similar to that shown in FIG.

[0066] Therefore, by analyzing the results of Fig. 6 together with the results of each diagram in Fig. 4, it can be said that the aggregates or aggregates of silicon microparticles at least after the pulverization step (S2) or the oxide film removal step (S3) are in a state in which thin-layer silicon microparticles with a major axis of about 100 nm or less are folded into multi-layered petal-like or scale-like shapes. Furthermore, as can be seen from Figs. 5 and 6, the silicon microparticles are mainly composed of crystallites with a major axis of 10 nm or less.

[0067] Furthermore, 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 approximately 10 nm. This value can be said to be very small. Furthermore, as mentioned above, further investigation confirmed that the apparent volume diameter of the silicon microparticles is in the range of approximately 100 nm or less. In particular, by containing a large number of ultrafine silicon particles with a crystallite diameter of 5 nm or less, the charge / discharge cycle characteristics derived from the silicon microparticles used as the negative electrode material for lithium-ion batteries, as described below, are more reliably improved. Furthermore, because at least a portion of the surface of the ultrafine silicon particles is covered with carbon, higher charge capacity values and discharge capacity values, as well as excellent charge / discharge cycle characteristics, can be achieved.

[0068] 3. Analysis of crystallite orientation of silicon microparticles using X-ray diffraction Figure 7(a) shows the results of X-ray diffraction measurement (P) of silicon fine particles or their aggregates or aggregates before the pulverization step (S2) of the first embodiment, and the results of X-ray diffraction measurement (Q) of silicon fine particles or their aggregates or aggregates after the pulverization step (S2), analyzed over a wide angle range. Figure 7(b) is an enlarged view of the results (P) of Figure 7(a), showing the results of X-ray diffraction measurement (R) of silicon fine particles or their aggregates or aggregates after the pulverization step (S2) of the first embodiment, analyzed over a limited angle range. The peak intensities of the C(002) and C(003) planes shown in Figure 7(b) indicate that approximately 1 wt% to approximately 3 wt% of graphite particles are contained in the silicon fine particle groups or silicon fine particle aggregates or aggregates. As an example, the size of the graphite particles on the C(002) plane was approximately 50 nm or less, more specifically, approximately 35 nm, and the size of the graphite particles on the C(003) plane was approximately 100 nm or less, more specifically, approximately 75 nm.

[0069] As shown in Figures 7(a) and 7(b), it was confirmed that the diffraction peak attributable to the Si (111) crystal plane near 2θ = 28.4° before the milling step (S2) of the first embodiment had a larger half-width than the diffraction peak attributable to the Si (111) crystal plane near 2θ = 28.4° before the milling step (S2). The average crystallite diameter calculated using the Scherrer equation from the half-width of the Si (111) peak after the milling step (S2) was 9.8 nm. Interestingly, it was also revealed that the intensity of the diffraction peak attributable to Si (111) near 2θ = 28.4° after the milling step (S2) was greater than the intensity of other diffraction peaks (e.g., the peak intensity of Si (220) or Si (311)). The arrangement spacing of Si (111) in the crystal lattice of the silicon microparticles after the milling step (S2) was 0.31 nm (3.1 Å), as shown in Figure 5.

[0070] Taking the above analytical results into consideration, it can be said that the silicon microparticles obtained after the pulverization step (S2) of this embodiment are aggregates or aggregates of crystalline silicon microparticles, mainly having a (111) plane orientation, which are multi-layered and petal-like or scale-like in shape.

[0071] In this case, by using the silicon fine particles or their aggregates or aggregates after the pulverization step (S2) or the oxide film removal step (S3) of this embodiment as the negative electrode material of a lithium ion battery, the ionized lithium ions (Li + ) reaches the negative electrode, lithium ions (Li + ) can easily penetrate into and escape from the gaps between the folds of the aggregates or aggregates that are in a state of being multi-folded in a compound petal-like or scale-like state.

[0072] <Second embodiment> The lithium-ion battery of this embodiment uses, as the negative electrode material, silicon microparticles at least partially covered with carbon, as prepared in the first embodiment. Note that the configuration other than the negative electrode material is the same as that of a conventional CR2032 coin cell lithium-ion battery.

[0073] 8 is a schematic diagram of a lithium-ion battery 500 of this embodiment. The lithium-ion battery 500 of this embodiment includes, in a CR2032 coin cell container 510, a negative electrode 512 electrically connected to a negative electrode material 514, a positive electrode 516 electrically connected to a 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. The lithium-ion battery 500 of this embodiment also includes an external circuit that includes a power source 540 and a resistor 550 connected to the negative electrode 512 and the positive electrode 516 to realize charging and discharging.

[0074] The lithium ion battery 500 of this embodiment is manufactured as follows.

[0075] Regarding the method for producing the negative electrode, first, about 0.3 g of silicon fine particles, at least a portion of whose surface is covered with carbon, produced in the first embodiment, are dispersed in about 10 mL (milliliters) of a solution consisting of a 1 wt % CMC binder aqueous solution and an SBR binder aqueous dispersion (TRD2001, manufactured by JSR Corporation).

[0076] In this embodiment, the silicon microparticles, carbon black, CMC binder aqueous solution, and SBR binder aqueous dispersion are blended in a dry weight ratio of 67:11:13:9 or 50:25:20:5, in that order. In one variation of this embodiment, the silicon microparticles, carbon black, CMC binder aqueous solution, and PVA binder aqueous dispersion are blended in a dry weight ratio of 50:25:20:5, in that order.

[0077] Next, the slurry prepared by mixing using an agate mortar is applied to one side of a 15 μm-thick copper foil measuring approximately 9 cm (length) × 10 cm (width) so that the thickness after drying is approximately 30 μm to approximately 200 μm, and then dried on a hot plate in the atmosphere at 80°C for approximately 1 hour. The copper foil and the dried slurry are then punched into a circle with a diameter of 11.3 mm, corresponding to a CR2032 coin cell battery standard, to form a working electrode. After measuring the weight of this working electrode, it is again dried by vacuum heating at 120°C for 6 hours in a glove box, and then attached to the inner surface of the copper foil negative electrode 512, thereby producing the negative electrode of this embodiment.

[0078] 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 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.

[0079] The separator 520 of this embodiment is a porous polypropylene sheet. The electrolyte 530 of this embodiment is an electrolyte solution in which 1 mole of lithium hexafluorophosphate (LiPF6) is dissolved in a solvent (1 L) of a 1 / 1 volumetric mixture of ethylene carbonate (EC) and diethyl carbonate (DEC), or an electrolyte solution to which fluoroethylene carbonate (FEC) has been added. The amount of the electrolyte solution is sufficient to fill the internal volume (approximately 1 mL) of a CR2032 coin cell.

[0080] 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 were placed in a CR2032 coin cell container 510. Thereafter, in an argon atmosphere glove box, the components of separator 520 and electrolyte 530 were sealed in container 510 while insulating positive electrode 516 and negative electrode 512 of the outer frame of the coin cell, thereby producing a prototype CR2032 coin cell lithium ion battery 500.

[0081] In this embodiment, examples of the electrolytic solvent constituting the electrolytic solution 530 include a mixed solvent 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). Supporting salts such as lithium hexafluorophosphate (LiPF) and lithium tetrafluoroborate (LiBF) can be dissolved in the electrolytic solvent and used.

[0082] <Charge and discharge cycle characteristics of lithium-ion battery 500> By employing the lithium ion battery 500 having the above-described configuration, the charge capacity value and discharge capacity value can be increased by more than two times (typically about three to five times) compared to less than about 500 (mAh / g) when silicon fine particles whose surfaces are not covered with carbon are employed. Furthermore, even after 100 or more charge / discharge cycles, it is possible to achieve extremely good charge / discharge cycle characteristics, in which neither the charge capacity value nor the discharge capacity value decreases significantly. A specific comparison is as follows.

[0083] Fig. 9 is a graph showing the charge cycle characteristics of the lithium-ion battery 500 of this embodiment. Fig. 10 is a graph showing the discharge cycle characteristics of the lithium-ion battery 500 of this embodiment. In each figure, circles indicate examples in which CMC and PVA are used as binders, and filled squares indicate examples in which CMC and SBR are used as binders.

[0084] As shown in Figures 9 and 10, in both the example using CMC and PVA and the example using CMC and SBR, the charge capacity and discharge capacity values were stably maintained at high values up to at least 60 charge / discharge cycles. Furthermore, a slight decrease in the charge capacity and discharge capacity values was observed up to 100 charge / discharge cycles. However, it was also found that both the example using CMC and PVA and the example using CMC and SBR maintained high charge capacity values (approximately 1400 to 1500 mAh / g) and discharge capacity values (approximately 1400 to 1500 mAh / g) even after 100 charge / discharge cycles.

[0085] Interestingly, it was confirmed that the example using CMC and PVA was able to maintain higher charge and discharge capacity values than the example using CMC and SBR. This is thought to be because when SBR is used, it is more difficult to mix uniformly with CMC or silicon fine particles than with PVA.

[0086] As a reference example, the charge / discharge cycle characteristics of a lithium ion battery manufactured in the same manner as lithium ion battery 500 using silicon microparticles of this embodiment before treatment in the coating formation step (S4) are described below. FIG. 11 is a graph showing the charge cycle characteristics of the lithium ion battery of the reference example. FIG. 12 is a graph showing the discharge cycle characteristics of the lithium ion battery of the reference example. This reference example uses CMC and PVA as binders.

[0087] As shown in FIGS. 11 and 12, the charge capacity value and the discharge capacity value are relatively low, less than 500 (mAh / g).

[0088] Therefore, it was confirmed that the use of the silicon microparticles and / or their aggregates (including aggregates) of the first embodiment described above can realize a lithium-ion battery with high capacity and excellent charge / discharge cycle characteristics. It is particularly noteworthy that, compared to the results of the reference lithium-ion battery, the lithium-ion battery 500 of the second embodiment, which employs silicon microparticles and / or their aggregates (including aggregates) whose surfaces are at least partially covered with carbon by the coating formation step (S4), can increase the charge and discharge capacities by more than two times (typically about three to five times). Additionally, covering part or all of the silicon microparticles with carbon facilitates the formation of a thick anode material, thereby making the lithium-ion battery 500 easier to manufacture. Even after more than 100 charge / discharge cycles (e.g., several hundred to 1,000), the lithium-ion battery 500 can be said to have significantly better charge and discharge capacities and / or charge / discharge cycle characteristics than a lithium-ion battery employing the silicon microparticles of the present embodiment before the coating formation step (S4).

[0089] As shown in FIG. 13, a TEM (transmission electron microscope) image of the silicon microparticles or their aggregates or conglomerates constituting the negative electrode material of the lithium-ion battery 500 of this embodiment after 100 charge-discharge cycles was observed. As shown in the "A" area in the figure, approximately circular crystals (microcrystals) with a diameter of approximately 4 nm were observed. Therefore, another interesting fact is that a negative electrode material using silicon microparticles or their aggregates or conglomerates obtained by crushing crystalline silicon can maintain a partial crystalline state even after at least 100 charge-discharge cycles. The example of the lithium-ion battery 500 shown in FIG. 13 uses CMC and PVA as binders, with approximately 5 wt% of fluoroethylene carbonate (FEC), described below, added. The crystalline silicon in the "A" area in FIG. 13 is believed to primarily have a Si(111) surface.

[0090] <Other embodiment (1)> In the above-described embodiments, silicon chips formed during the cutting process of a single-crystal or polycrystalline silicon block or ingot are used as starting materials. However, other forms of silicon chips may also be used as starting materials. Specifically, silicon chips are not limited to those inevitably formed during the cutting process of a silicon ingot in the semiconductor product production process. They may also be produced by uniformly or randomly cutting a preselected crystalline silicon ingot with a cutting machine. Furthermore, so-called silicon waste, such as silicon chips and silicon grinding shavings, which are usually considered waste, can be used as starting materials for the silicon microparticles of the above-described embodiments. However, such silicon waste can also include fine chips obtained by crushing wafer fragments, discarded wafers, etc. Furthermore, silicon microparticles using metallic silicon chips, metallic silicon grinding shavings, or other metallic silicon particles as starting materials can also be used.

[0091] <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. Furthermore, not only n-type but also p-type crystalline silicon can be used. Furthermore, crystalline silicon, which is an intrinsic semiconductor, can also be used as the crystalline silicon in each of the above-mentioned embodiments. Since the movement of electrons within the negative electrode material of a lithium ion battery is important, it is more preferable to use crystalline silicon containing n-type impurities. Furthermore, since approximately 1 wt % to approximately 3 wt % of graphite particles, as indicated by the peak intensities of the C(002) plane and the C(003) plane shown in FIG. 7(b) above, are contained within the silicon fine particle group or silicon fine particle aggregate, it should be noted that some or all of this graphite can contribute to improving the conductivity of the negative electrode material.

[0092] <Other embodiment (3)> Furthermore, the silicon microparticles and lithium ion batteries including the same according to the above-described embodiments are not limited to application to the coin cell structure introduced in the second embodiment. Therefore, they can be applied to various devices or apparatuses that include or use lithium ion batteries with a larger electric capacity than those of the coin cell structure. Another possible embodiment is to use a negative electrode material obtained by mixing graphite (typically, graphite) with the silicon mixed powder according to the above-described embodiments.

[0093] <Other embodiment (4)> As an alternative to the lithium-ion battery anode material and anode manufacturing apparatus 100 shown in FIG. 2 in the first embodiment described above, a lithium-ion battery anode manufacturing apparatus 200 shown in FIG. 14 may be employed. Specifically, from the viewpoint of simplifying the equipment and / or reducing manufacturing costs, the lithium-ion battery anode manufacturing apparatus 200 includes a washer 10 that cleans silicon chips and the like formed during the silicon cutting process, and a pulverizer 20 that pulverizes the cleaned silicon chips and the like to form silicon microparticles. Therefore, in the apparatus / method shown in FIG. 14 , 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 pulverization process to obtain silicon microparticles for use as a lithium-ion battery anode material. However, to obtain the silicon microparticles described in the first embodiment with a higher degree of accuracy, it is preferable to form silicon microparticles using a bead mill after processing using a ball mill, as in the first embodiment.

[0094] <Other embodiment (5)> Furthermore, the inventors' analysis revealed that the amount of fluoroethylene carbonate (FEC) added to the electrolyte solution 530 in the second embodiment can affect the charge capacity, discharge capacity, and charge / discharge cycle characteristics. FIG. 15A is a graph showing the charge cycle characteristics of a lithium-ion battery when the amount of FEC in the electrolyte solution 530 is changed. FIG. 15B is a graph showing the discharge cycle characteristics of a lithium-ion battery when the amount of FEC in the electrolyte solution 530 is changed. The amounts of FEC measured were 5 wt%, 10 wt%, and 15 wt%, respectively. For reference, a lithium-ion battery without added FEC was also measured. In FIGS. 15A and 15B, the weight ratio of silicon (Si) to carbon (C) was 1:0.1. 15A and 15B, the charge-discharge cycles were performed at a current value of 180 mA / g up to 5 times, and at a current value of 1800 mA / g for 6 or more times, in order to form a good (e.g., low-resistance and / or thin) solid electrolyte interface (SEI) on the surface of the negative electrode material.

[0095] As shown in Figures 15A and 15B, when the amount of FEC added (wt%) is in the range of more than 5% and not more than 15%, the charge capacity and discharge capacity values are stably maintained at high values (typically about 1500 mAh / g) even after 100 charge / discharge cycles. In particular, it was found that adding about 10% FEC stably maintains very high charge capacity and discharge capacity values. Therefore, it was found that adding FEC can achieve high charge capacity and discharge capacity values, especially after 100 charge / discharge cycles.

[0096] <Other embodiment (6)> The inventors of the present application also investigated the correlation between the weight ratio of carbon (C) to silicon (Si) in the negative electrode material employed in the second embodiment and the charge capacity, discharge capacity, and charge / discharge cycle characteristics. Fig. 16A is a graph showing the charge cycle characteristics of a lithium ion battery when the weight ratio of silicon (Si) to carbon (C) is changed. Fig. 16B is a graph showing the discharge cycle characteristics of a lithium ion battery when the weight ratio of silicon (Si) to carbon (C) is changed. The weight ratios of silicon (Si) to carbon (C) measured were the following four examples (1) to (4). (1) Carbon (C):Silicon (Si) = 0.1:1 (2) Carbon (C):Silicon (Si) = 0.16:1 (3) Carbon (C):Silicon (Si) = 0.21:1 (4) Carbon (C):Silicon (Si) = 0.37:1

[0097] 16A and 16B, the charge-discharge cycles were performed at a current value of 180 mA / g for up to five charge-discharge cycles, and at a current value of 1800 mA / g for six or more charge-discharge cycles. This is to form a good (e.g., low-resistance and / or thin) solid electrolyte interface (SEI) on the surface of the negative electrode material. Note that FIGS. 16A and 16B show an example in which approximately 10 wt% of fluoroethylene carbonate (FEC) was added.

[0098] As shown in Figures 16A and 16B, the charge capacity and discharge capacity values of the example with the highest carbon (C) ratio ((4) above) are somewhat low, but the other three examples all maintain stable high charge capacity and discharge capacity values. Therefore, it was revealed that, when the carbon (C) ratio (weight ratio) is 0.1 or more and 0.21 or less, assuming silicon (Si) to be 1, particularly high charge capacity and discharge capacity values (typically, about 1500 mAh / g) can be stably maintained even after 100 charge / discharge cycles. However, the charge capacity and discharge capacity values of the example (4) above are more than two times (typically, about three times) higher than those of a lithium-ion battery in which at least a portion of the surface of the silicon fine particles or their aggregates or aggregates is not covered with carbon.

[0099] In this embodiment, the weight ratio of carbon (C) was 0.1 when silicon (Si) was taken as 1, but if the weight ratio of carbon (C) is 0.05 or more when silicon (Si) is taken as 1, effects substantially equivalent to the results of (1) to (3) above can be achieved. Therefore, if the ratio of carbon (C) is 0.05 or more and less than 0.37 when silicon (Si) is taken as 1, a stable lithium ion battery with high charge capacity and discharge capacity can be obtained.

[0100] Furthermore, as a result of further detailed analysis by the present inventors in this embodiment, TEM (transmission electron microscope) images showed that the film thickness of the portion where carbon (C) adhered to silicon (Si) in the above-mentioned case (1) was about 2 nm to about 3 nm. Furthermore, the film thickness of the portion where carbon (C) adhered to silicon (Si) in the above-mentioned case (2) was about 5 nm to about 10 nm. Furthermore, the film thickness of the portion where carbon (C) adhered to silicon (Si) in the above-mentioned case (3) was also about 5 nm to about 10 nm. Additionally, the film thickness of the portion where carbon (C) adhered to silicon (Si) in the above-mentioned case (4) was about 50 nm to about 90 nm. Therefore, if the film thickness of the carbon (C) adhered to silicon (Si) is 1 nm or more and less than 50 nm, and particularly if the film thickness is 2 nm or more and 10 nm or less, a stable lithium-ion battery with high charge capacity and discharge capacity can be obtained.

[0101] The disclosure of each of the above-mentioned embodiments has been described for the purpose of explaining those embodiments, and is not intended to limit the present invention. In addition, modifications within the scope of the present invention, including other combinations of the embodiments, are also included in the scope of the claims. [Industrial Applicability]

[0102] The silicon microparticles of the present invention and lithium ion batteries comprising 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 power storage systems), smartphones, personal digital assistants, portable electronic devices (mobile phones, portable music players, laptop computers, digital cameras and videos), electric vehicles, hybrid electric vehicles (HEVs) or plug-in hybrid electric vehicles (PHEVs), motor-powered motorcycles, motor-powered tricycles, other transportation machines or vehicles, and the like.

Claims

1. a crushing section for crushing silicon waste using a ball mill and a bead mill used after the ball mill to form aggregates or aggregates of silicon fine particles having a volume distribution in which the mode diameter and median diameter of the silicon fine particles are 50 nm or less, the aggregates or aggregates being in a state of being folded into a multi-layered petal-like or scale-like shape; a coating forming unit that forms carbon to cover at least a portion of the surface of the aggregate or the collection; The silicon waste material is at least one selected from the group consisting of silicon cutting chips, silicon polishing chips, wafer fragments, fine chips obtained by crushing waste wafers, and metallic silicon particles. Equipment for manufacturing negative electrode materials for lithium-ion batteries.

2. The coating formation unit is a chemical vapor deposition apparatus. The apparatus for producing a negative electrode material for a lithium ion battery according to claim 1.

3. a crushing section for crushing silicon waste using a ball mill and a bead mill used after the ball mill to form aggregates or aggregates of silicon fine particles that become a negative electrode material, the aggregates or aggregates being in a state of being folded into a multi-layered petal-like or scale-like shape, the aggregates or aggregates having a volume distribution in which the mode diameter and median diameter of the silicon fine particles are 50 nm or less; a coating forming unit that forms carbon to cover at least a portion of the surface of the aggregate or the collection; The silicon waste material is at least one selected from the group consisting of silicon cutting chips, silicon polishing chips, wafer fragments, fine chips obtained by crushing waste wafers, and metallic silicon particles. Lithium-ion battery negative electrode manufacturing equipment.

4. The coating formation unit is a chemical vapor deposition apparatus. The apparatus for manufacturing a negative electrode for a lithium ion battery according to claim 3.

5. a crushing step of crushing the silicon waste material with a ball mill and then with a bead mill to form aggregates or aggregates of silicon fine particles having a volume distribution in which the mode diameter and median diameter of the silicon fine particles are 50 nm or less, the aggregates or aggregates being in a state of being folded into a multi-layered petal-like or scale-like shape; a coating formation step of forming carbon that covers at least a portion of the surface of the aggregates or the conglomerates, The silicon waste material is at least one selected from the group consisting of silicon cutting chips, silicon polishing chips, wafer fragments, fine chips obtained by crushing waste wafers, and metallic silicon particles. A method for manufacturing negative electrode materials for lithium-ion batteries.

6. The coating formation step is a step of forming the carbon by chemical vapor deposition. The method for producing the negative electrode material of a lithium ion battery according to claim 5.

7. a crushing step of crushing the silicon waste material using a ball mill and then using a bead mill to form aggregates or aggregates of silicon fine particles that will become a negative electrode material, the aggregates or aggregates being in a multi-layered petal-like or scale-like state and having a volume distribution in which the mode diameter and median diameter of the silicon fine particles are 50 nm or less; a coating formation step of forming carbon that covers at least a portion of the surface of the aggregates or the conglomerates, The silicon waste material is at least one selected from the group consisting of silicon cutting chips, silicon polishing chips, wafer fragments, fine chips obtained by crushing waste wafers, and metallic silicon particles. A method for manufacturing the negative electrode of a lithium-ion battery.

8. The coating formation step is a step of forming the carbon by chemical vapor deposition. The method for producing the negative electrode of the lithium ion battery according to claim 7.

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