JP6974007B2 - Method for manufacturing negative electrode material for lithium ion battery, lithium ion battery, negative electrode or negative electrode material for lithium ion battery, and manufacturing equipment thereof - Google Patents

Description

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 a manufacturing apparatus thereof.

Conventionally adopted lithium ion batteries use a binder material on the negative electrode side of the negative electrode active material (hereinafter, also referred to as “negative electrode material”) graphite (natural graphite, artificial graphite, etc.) and the negative electrode material. It has a negative electrode with a mixed mixture layer. _{Further, on the positive electrode side, a binder material (PVDF) is bonded with lithium (Li) oxide powder (LiCoO 2} , LiNiO ₂ , LiMnO _2, etc.) of the positive electrode material and the positive electrode active material, and conductive graphite (mainly carbon black, etc.). : Polyvinylidene fluoride, etc.) is mixed and coated to form a positive electrode having a mixture layer. Further, the cell container of the lithium ion battery is filled with an electrolytic solution, and a separator (mainly a polyolefin-based porous material or a porous polypropylene sheet or the like) is provided between the negative electrode material and the positive electrode material. Has been done.

The above-mentioned separator is provided so as to allow the electrolytic solution to pass through and cause the movement of lithium ions, and to separate the electrodes so that an electrical short circuit does not occur.

Charging and discharging of a lithium ion battery is performed by moving lithium ions between a negative electrode material and a positive electrode material in an electrolytic solution. During charging, lithium ions move to the negative electrode side, and during discharging, lithium ions move to the positive electrode side. Charging is done through an externally connected power source and discharging is done through an externally connected resistor (load).

By the way, in the field of lithium ion batteries, in recent years, a technique of using silicon particles as a material in place of the above-mentioned graphite as the negative electrode active material has been disclosed. For example, as an example of silicon particles, a powder having a diameter of about 38 microns (μm) or less formed by crushing single crystal silicon in a mortar and classifying using a mesh is raised at 30 ° C./min in an argon atmosphere. Some are heated to 150 ° C. (reached temperature) at a temperature rate (see Patent Document 1). Further, as another example, by supplying liquid silicon tetrachloride into high-temperature and high-concentration zinc gas and reacting at a high temperature of 1050 ° C. or higher, silicon tetrachloride is reduced to form silicon particles. After crystal growth and aggregation of fine silicon at 1000 ° C. or lower, particularly 500 to 800 ° C., the particle size of the formed silicon particles is adjusted and collected in a zinc chloride aqueous solution. It is disclosed that high-purity silicon particles having a particle size of about 1 to 100 μm can be obtained by this work, and that they can be used (see Patent Document 2).

Japanese Unexamined Patent Publication No. 2005-032733 Japanese Unexamined Patent Publication No. 2012-101998

However, in the prior art, when silicon particles are used as the negative electrode material, the electric capacity in charging and discharging can be increased, but on the other hand, lithium is occluded and released into the silicon particles, and the volume of the silicon particles fluctuates. Or will be destroyed. As a result, there is a problem that the charge / discharge cycle characteristics cannot be maintained.

Further, in the case of the silicon particles disclosed in the above-mentioned prior art document, since it is necessary to perform a high-temperature synthesis and collection process, the manufacturing process until the silicon particles as the negative electrode material are obtained becomes extremely complicated. As a result, it is inevitable that productivity will decrease and manufacturing costs will increase. Therefore, the silicon particles conventionally disclosed have a big problem that the negative electrode characteristics of the lithium ion battery are poor and the industrial usability is not yet sufficient. That is, the development of lithium-ion batteries using silicon particles is still in progress.

INDUSTRIAL APPLICABILITY The present invention solves at least a part of various problems related to charge / discharge cycle characteristics of a negative electrode material using conventional silicon particles, thereby providing a negative electrode material for a high-performance lithium ion battery, a lithium ion battery, and the like. It can greatly contribute to the provision of a method for manufacturing a negative electrode or a negative electrode material of a lithium ion battery and a manufacturing apparatus thereof.

Further, the negative electrode material of one lithium ion battery of the present invention has a volume distribution having a mode diameter and a median diameter of less than 50 nm, and silicon fine particles or aggregates thereof having at least a part covered with carbon on the surface. It is formed using an aggregate.

Further, the negative electrode material of another lithium ion battery of the present invention is formed by using silicon fine particles or aggregates or aggregates thereof having at least a part of the surface covered with carbon, and has a multi-layered petal shape or. It contains the agglomerates or aggregates of the silicon fine particles in a scaly folded state.

By adopting each of the above-mentioned negative electrode materials, it is possible to realize a lithium ion battery in which the charge / discharge capacity does not change much even if charging / discharging is repeated, in other words, the charging / discharging cycle characteristics are good. Alternatively, an increase in charge / discharge capacity can be realized.

Further, the silicon fine particles or aggregates or aggregates thereof, which are the above-mentioned negative electrode materials, are, for example, treated as industrial waste obtained by cutting out a molten and solidified mass or ingot of silicon by a fixed abrasive wire. It is worth noting that the chips or cutting chips that have been cut can be used as the starting material. In addition, the silicon fine particles or aggregates or aggregates thereof formed by crushing the chips or cutting chips with a ball mill machine and / or a bead mill machine have a high level of charge / discharge cycle characteristics of a lithium ion battery. This is a preferred embodiment for maintaining and / or improving the characteristics thereof.

Further, one lithium ion battery of the present invention has a volume distribution having a mode diameter and a median diameter of less than 50 nm, and silicon fine particles or aggregates or aggregates thereof having at least a part of the surface covered with carbon. It comprises a negative electrode material formed using.

In addition, another lithium ion battery of the present invention is formed by using silicon fine particles or aggregates or aggregates thereof, at least a part of which is covered with carbon on the surface, and has a multi-layered petal shape or a scale shape. It comprises a negative electrode material containing the agglomerates or aggregates of the silicon fine particles in a folded state.

According to the above-mentioned lithium ion battery, it is possible to reduce the change in charge / discharge capacity even if charging / discharging is repeated. Alternatively, it is possible not only to maintain a high level of charge / discharge cycle characteristics and / or to improve the characteristics, but also to realize an increase in charge / discharge capacity.

Further, in the apparatus for producing a negative electrode material of one lithium ion battery of the present invention, silicon fine particles having a volume distribution having a mode diameter and a median diameter of less than 50 nm or aggregates or aggregates thereof are obtained by pulverizing crystalline silicon. It is provided with a pulverized portion for forming the silicon fine particles or a coating forming portion for forming carbon covering at least a part on the surface of the aggregate or the aggregate.

Further, the apparatus for producing a negative electrode material of another lithium ion battery of the present invention is formed by crushing crystalline silicon, which is chips or cutting chips cut out by a fixed abrasive grain wire, into a multi-layer petal shape or a scale shape. A crushed portion that forms the silicon fine particles so as to contain an agglomerate or an aggregate of the silicon fine particles in a folded state, and at least a part of the silicon fine particles or the agglomerate or the aggregate on the surface. It comprises a coating forming portion that forms a covering carbon.

According to the above-mentioned equipment for manufacturing a negative electrode material of a lithium-ion battery, a lithium-ion battery having a small change in charge capacity and / or discharge capacity even after repeated charge / discharge, in other words, having good charge / discharge cycle characteristics is realized. It can contribute to the production of lithium-ion batteries that can be obtained or can realize an increase in charge / discharge capacity.

Further, in the negative electrode manufacturing apparatus of one lithium ion battery of the present invention, silicon fine particles serving as a negative electrode material having a volume distribution having a mode diameter and a median diameter of less than 50 nm by pulverizing crystalline silicon or agglomeration thereof. It comprises a pulverized portion that forms an object or an aggregate, and a coating forming portion that forms carbon covering at least a part of the surface of the silicon fine particles or the aggregate or the aggregate.

Further, the device for manufacturing the negative electrode of another lithium ion battery of the present invention is formed into a multi-layer petal shape or a scale shape by crushing crystalline silicon which is a chip or cutting chip carved by a fixed abrasive grain wire. A crushed portion that forms the silicon fine particles as a negative electrode material, and the silicon fine particles or the aggregate or the aggregate on the surface so as to include the aggregate or the aggregate of the silicon fine particles in the folded state. It comprises a coating forming portion that forms carbon covering at least a part thereof.

According to the above-mentioned lithium-ion battery negative electrode manufacturing apparatus, it is possible to realize a lithium-ion battery having a small change in charge capacity and / or discharge capacity even if charging / discharging is repeated, in other words, having good charging / discharging cycle characteristics. Alternatively, it can contribute to the production of a lithium ion battery that can realize an increase in charge / discharge capacity.

Further, in the method for producing a negative electrode material of one lithium ion battery of the present invention, silicon fine particles having a volume distribution having a mode diameter and a median diameter of less than 50 nm or aggregates or aggregates thereof are obtained by pulverizing crystalline silicon. It comprises a pulverization step of forming the silicon fine particles or a coating forming step of forming carbon covering at least a part on the surface of the aggregate or the aggregate.

In addition, another method for producing a negative electrode material for a lithium ion battery of the present invention is a multi-layer petal-like or scaly shape by crushing crystalline silicon, which is chips or cutting chips cut out by a fixed abrasive grain wire. A pulverization step of forming the silicon fine particles so as to contain an agglomerate or an aggregate of the silicon fine particles in a folded state, and at least a part of the silicon fine particles or the agglomerate or the aggregate on the surface. It comprises a coating forming step of forming a covering carbon.

According to the above-mentioned method for manufacturing a negative electrode material for a lithium-ion battery, a lithium-ion battery having a small change in charge capacity and / or discharge capacity even after repeated charge / discharge, in other words, having good charge / discharge cycle characteristics is realized. It can contribute to the production of lithium-ion batteries that can be obtained or can realize an increase in charge / discharge capacity.

Further, in one method of manufacturing a negative electrode of a lithium ion battery of the present invention, by pulverizing crystalline silicon, silicon fine particles serving as a negative electrode material having a volume distribution having a mode diameter and a median diameter of less than 50 nm or aggregation thereof. It comprises a pulverization step of forming an object or an aggregate and a coating forming step of forming carbon covering at least a part on the surface of the silicon fine particles or the aggregate or the aggregate.

Further, another method for manufacturing a negative electrode of a lithium ion battery of the present invention is to crush crystalline silicon, which is chips or cutting chips cut out by a fixed abrasive grain wire, into a multi-layer petal shape or a scale shape. A pulverization step of forming the silicon fine particles to be a negative electrode material so as to include aggregates or aggregates of silicon fine particles in an folded state, and on the surface of the silicon fine particles or the aggregates or aggregates. It comprises a coating forming step of forming carbon covering at least a part thereof.

According to the above-mentioned method for manufacturing a negative electrode of a lithium-ion battery, the charge / discharge capacity does not change much even if the charge / discharge capacity is increased and the charge / discharge capacity is repeated. In other words, the charge / discharge cycle characteristics are good. It can contribute to the manufacture of lithium-ion batteries.

The means for covering at least a part of the surface of each of the above-mentioned silicon fine particles or their aggregates or aggregates with carbon is not particularly limited. Typical examples of the means were formed by 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, and a channel method. It is a means for utilizing a carbon film or a means for utilizing a carbon film formed by plasma treatment.

The crystalline silicon in each of the above-mentioned inventions includes not only single crystal silicon but also polycrystalline silicon. Further, metallic silicon can be selected as the crystalline silicon in each of the above-mentioned inventions.

According to the negative electrode material of one lithium ion battery of the present invention, it is only possible to realize a lithium ion battery having a small change in charge / discharge capacity even if charge / discharge is repeated, in other words, a lithium ion battery having good charge / discharge cycle characteristics. However, it is possible to increase the charge / discharge capacity. Further, according to one lithium-ion battery of the present invention, it is possible not only to reduce the change in charge / discharge capacity even if charge / discharge is repeated, in other words, to improve the charge / discharge cycle characteristics, but also to improve charge / discharge. Increased capacity can be achieved. In addition, according to the one lithium-ion battery manufacturing apparatus of the present invention and the one lithium-ion battery manufacturing method of the present invention, the change in charge / discharge capacity is small even if charging / discharging is repeated, in other words, charging. It can contribute to the production of not only lithium-ion batteries having good discharge cycle characteristics but also lithium-ion batteries that can increase the charge / discharge capacity.

It is a flow chart which shows the manufacturing process of the negative electrode material of the lithium ion battery of 1st Embodiment. It is a schematic diagram which shows the manufacturing apparatus and manufacturing process of the negative electrode material of the lithium ion battery of 1st Embodiment. It is a figure which shows the TEM (transmission electron microscope) image of an example of silicon fine particles or aggregates or aggregates thereof which went through the coating formation step (S4) of 1st Embodiment. It is an SEM image of an example of silicon fine particles or aggregates or aggregates thereof of 1st Embodiment. It is a figure which shows the SEM image of an example of the enlarged silicon fine particle or the aggregate or aggregate thereof in 1st Embodiment. 1 is a diagram showing (a) an SEM image of another example of an aggregate or aggregate of silicon fine particles in the first embodiment, and (b) a partially enlarged view of (a). It is a figure which shows the TEM image of the silicon fine particle of 1st Embodiment. It is a graph which shows (a) the crystallite diameter distribution in the number distribution, and (b) the crystallite diameter distribution in the volume distribution with respect to the crystallite diameter of the silicon fine particles of 1st Embodiment. It is a graph which shows the result ((a) wide range, (b) limited range) of the X-ray diffraction measurement of the silicon fine particle or the aggregate or aggregate thereof of 1st Embodiment. It is a schematic block diagram of the lithium ion battery of 2nd Embodiment. It is a graph which shows an example of the cycle characteristic of the charge of the lithium ion battery of 2nd Embodiment. It is a graph which shows an example of the discharge cycle characteristic of the lithium ion battery of 2nd Embodiment. It is a graph which shows the cycle characteristic of the charge of the lithium ion battery as a reference example. It is a graph which shows the discharge cycle characteristic of a lithium ion battery as a reference example. For the lithium ion battery of the second embodiment, it is a TEM image of silicon fine particles or aggregates or aggregates thereof after 100 charge / discharge cycles have been performed. It is a schematic diagram which shows the manufacturing apparatus and manufacturing process of the negative electrode material of the lithium ion battery of another embodiment. It is a graph which shows the cycle characteristic of the charge of the lithium ion battery when the amount of FEC in the electrolytic solution is changed in the lithium ion battery of another embodiment. It is a graph which shows the cycle characteristic of the discharge of the lithium ion battery when the amount of FEC in the electrolytic solution is changed in the lithium ion battery of another embodiment. It is a graph which shows the charge cycle characteristic of a lithium ion battery when the weight ratio of silicon (Si) and carbon (C) is changed in the lithium ion battery of another embodiment. It is a graph which shows the discharge cycle characteristic of a lithium ion battery when the weight ratio of silicon (Si) and carbon (C) is changed in the lithium ion battery of another embodiment.

1 Chips, etc. 2 Silicon fine particles 10 Cleaning machine (cleaning and pre-crushing machine)
11 Ball type 13a Pot 13b Lid 15 Rotating shaft 20 Crusher 21 Introducing port 22 Processing room 24 Discharge port 25 Filter 30 Dryer 40 Rotary evaporator 50 Oxide film removal tank 55 Hydrofluoric acid or ammonium fluoride aqueous solution 57 Stirrer 58 Centrifugal Separator 60 Coating forming part 70 Mixing part 100 Negative electrode material and negative electrode manufacturing equipment for 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 supply 550 resistance

Embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this description, common reference numerals are given to common parts throughout the drawings unless otherwise specified. Further, in the figure, each of the elements of each embodiment is not necessarily shown while maintaining the scale ratio of each other. In addition, some reference numerals may be omitted in order to make each drawing easier to see.

<First Embodiment>
FIG. 1 is a flow chart showing a manufacturing process of a negative electrode material for the lithium ion battery of the present embodiment. Further, FIG. 2 is a schematic view showing a manufacturing apparatus and a manufacturing process of the negative electrode material of the lithium ion battery of the present embodiment.

The negative electrode material of the lithium ion battery of the present embodiment, the lithium ion battery provided with the negative electrode material, and the manufacturing method thereof are silicon cutting processing in the production process of a silicon wafer used for a semiconductor product such as a solar cell, for example. Various processes using silicon chips, silicon cutting chips, or polishing chips (hereinafter, also referred to as "silicon chips, etc." or "chips, etc."), which are usually regarded as waste, as an example of starting material. To prepare for. In addition, the chips and the like also include fine chips obtained by crushing a silicon wafer to be discarded by a known crusher. As shown in FIG. 1, the method for manufacturing a lithium ion battery of the present embodiment includes the following steps (1), (2), (4) and (5). In addition, the method for manufacturing a lithium ion battery of the present embodiment can include the following step (3) as another aspect that can be adopted.
(1) Cleaning step (S1)
(2) Crushing step (S2)
(3) Oxide film removing step (S3)
(4) Coating forming step (S4)
(5) Negative electrode forming step (S5)

Further, as shown in FIG. 2, the negative electrode material of the lithium ion battery and the negative electrode manufacturing apparatus 100 of the present embodiment mainly include a washing machine (cleaning and pre-crushing machine) 10, a crushing machine 20, and a dryer (not shown). , A rotary evaporator 40, a coating forming portion 60 that forms carbon covering at least a part on the surface of silicon fine particles or aggregates or aggregates thereof (hereinafter, also collectively referred to as “silicon fine particles”), and lithium. A mixing unit 70 is provided, which is responsible for forming a part of the negative electrode of the ion battery. Further, the negative electrode material of the lithium ion battery and the negative electrode manufacturing apparatus 100 of the present embodiment may include an oxide film removing tank 50 and a centrifuge 58 as another aspect that can be adopted. Only the above-mentioned crusher 20, or the washing machine 10 and the crusher 20 are referred to as a crushing unit in the present embodiment.

(1) Cleaning step (S1)
In the cleaning step (S1) of the present embodiment, for example, it is formed in the cutting process of single crystal or polycrystalline silicon, that is, a crystalline silicon mass or an ingot (n-type crystalline silicon mass or ingot). Silicon chips and the like are washed. Typical silicon chips and the like are chips and the like that are machined by a wire or the like (typically, a fixed abrasive grain wire) for which a silicon ingot is known. Therefore, in the present embodiment, in order to form silicon fine particles constituting the negative electrode material of the lithium ion battery, using silicon chips and the like, which have been conventionally regarded as waste materials, as a starting material, the manufacturing cost and / or the raw material It is excellent in terms of ease of procurement and resource utilization.

The cleaning step (S1) of the present embodiment is mainly aimed at removing organic substances such as coolants and additives used in the cutting process, which are mainly attached to the above-mentioned organic substances such as silicon chips and the like. And. In the present embodiment, as shown in FIG. 2, first, the chips and the like 1 to be cleaned are weighed, and then the chips and the like 1, the predetermined first liquid, and the ball 11 have a bottomed cylindrical shape. It is introduced into the pot 13a. After the inside of the pot 13a is sealed using the lid 13b, the two cylindrical rotating bodies 15 of the ball mill machine, which is the washing machine (cleaning and pre-crushing machine) 10, are rotated on the rotating body 15. Rotate the pot 13a. As a result, in the pot 13a, the chips and the like 1 to be cleaned are dispersed in the first liquid to perform the cleaning of the chips and the like 1 and the preliminary pulverization treatment.

Here, in the ball mill machine of the present embodiment, steel balls, magnetic balls, balls and the like contained in the pot 13a and the lid 13b are used as the ball type 11 (crushing medium), and the pot 13a and the lid 13b are rotated. It is a crusher that gives a physical impact force. Further, a suitable example of the above-mentioned first liquid is acetone. Further, in a more specific embodiment, for example, 300 ml (mL) of acetone is added to 100 g (g) of silicon chips or the like, and a ball mill machine (in this embodiment, manufactured by MASUDA) is used. Silicon chips and the like were dispersed in acetone by stirring in the pot 13a and the lid 13b placed on the rotating body 15 of Universal BALL MILL) for about 1 hour. The ball types of the ball mill were an alumina ball having a particle size of φ10 mm (mm) and an alumina ball having a particle size of φ20 mm. In the cleaning step (S1) of the present embodiment, the dispersion treatment is performed by pre-grinding and stirring silicon chips and the like in the first liquid in the ball mill machine. Therefore, since the cleaning efficiency is significantly improved as compared with the treatment of simply immersing in the first liquid, silicon particles suitable for improving the negative electrode characteristics of the lithium ion battery, particularly the charge / discharge cycle characteristics, can be used. It will be possible to obtain.

After the cleaning step (S1), the lid 13b is opened and the silicon particles are discharged together with the first liquid, and then the first liquid is removed by suction filtration by a known vacuum filtration means to become a waste liquid. On the other hand, the remaining silicon particles are dried in a known dryer. If necessary, the silicon particles obtained after the drying treatment are pre-ground and washed again in the washing machine (washing and pre-crushing machine) 10 by the same step. An example of another cleaning method that can be adopted in the cleaning step (S1) is cleaning using an RCA cleaning method or cleaning using water (including pure water).

(2) Crushing step (S2)
After that, in the crushing step (S2), a predetermined second liquid is added to the washed silicon particles, and the silicon particles are crushed in the bead mill machine. Therefore, in the present embodiment, after the above-mentioned ball mill machine, in other words, the silicon particles that have undergone the cleaning step (S1) are further finely pulverized by the bead mill machine used after the pulverization by the above-mentioned ball mill machine. Become.

A preferred example of the second liquid of this embodiment is IPA (isopropyl alcohol). As a pretreatment for the crushing step, the second liquid and the silicon particles obtained in the washing step (S1) are placed in the pot 13a so that the weight ratio of the second liquid is 95% and the silicon particles are 5%. After storing, the pre-crushing process is performed by rotating the washing machine (washing and pre-crushing machine) 10. After the relatively coarse particles are removed by passing the slurry containing the pre-ground silicon particles through a mesh having an opening of 180 microns, the obtained slurry containing the silicon particles is subjected to a bead mill of the crusher 20 (the present embodiment). In, the star mill LMZ015) manufactured by Ashizawa Finding Co., Ltd. is used for further fine pulverization treatment. More specifically, the slurry containing the silicon particles from which silicon chips having a particle diameter of 180 microns or more have been removed is charged into the introduction port 21 of the crusher 20, and the slurry is circulated using the pump 28 in the processing chamber of the bead mill. The fine pulverization treatment is performed at 22. An example of a specific bead type of a bead mill machine is zirconia beads having a particle size of φ0.5 mm. After recovering the slurry containing the finely pulverized silicon particles, the second liquid is removed using a rotary evaporator 40 that automatically performs vacuum distillation, whereby silicon fine particles as a result of the finely pulverized treatment are obtained. Be done.

In the present embodiment, silicon fine particles can be obtained by introducing about 450 g of zirconia beads having a particle size of φ0.5 mm and performing a fine pulverization treatment at a rotation speed of 2908 rpm for 4 hours. Further, in the crushing step (S2), it is also adopted to perform the crushing process by any one of the crushers consisting of a ball mill, a bead mill, a jet mill, and a shock wave crusher other than the above, or a combination of two or more kinds. It is another aspect that can be done. Further, as the crusher used in the crushing step (S2), not only an automatic crusher but also a manual crusher may be adopted. However, from the viewpoint of forming agglomerates or aggregates of silicon fine particles in a state of being folded into multi-layer petals or scales, which will be described later with high accuracy, a crushing step (S2) consisting of treatment with a bead mill or a bead mill. It is preferable that the crushing step (S2) including the treatment according to the above method is adopted.

Further, the silicon fine particles obtained by the above-mentioned crushing step (S2) can be further crushed by using a known raikai machine (as a typical raikai machine, manufactured by Ishikawa Factory Co., Ltd., model 20D type). , Another preferred embodiment that can be adopted. Since this crushing treatment improves the dispersibility when forming the negative electrode of the lithium ion battery, it is possible to obtain the effect of preventing or suppressing the destruction of the negative electrode by the occlusion / release of lithium with high accuracy. ..

(3) Oxide film removing step (S3)
In the present 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 effects of the present embodiment can be achieved.

In the oxide film removing step (S3) of the present embodiment, a treatment is performed in which the silicon fine particles 2 obtained in the pulverization step (S2) are brought into contact with hydrofluoric acid or an aqueous solution of ammonium fluoride. The silicon fine particles 2 obtained in the pulverization step (S2) are dispersed by immersing them in an aqueous solution of hydrofluoric acid or ammonium fluoride. Specifically, in the oxide film removing tank 50, the silicon fine particles 2 are dispersed in the hydrofluoric acid or the ammonium fluoride aqueous solution 55 using a stirrer 57 to obtain an oxide on the surface of the silicon fine particles 2. Mainly silicon oxide) is removed.

Then, the centrifuge 58 separates the silicon fine particles from which some or all of the oxides on the surface have been removed and the hydrofluoric acid aqueous solution. Then, the silicon fine particles are immersed in a third liquid such as an ethanol solution. By removing the third liquid, silicon fine particles in which a part or all of the initially formed surface oxide (or oxide film) is removed can be obtained. When the oxides that may be present on the surface of the silicon fine particles 2 are not removed, the silicon fine particles are treated by the coating forming step (S4) and the negative electrode forming step (S5) described later.

In the oxide film removing step (S3) of the present embodiment, hydrofluoric acid is brought into contact with the silicon fine particles by immersing the silicon fine particles in hydrofluoric acid or an aqueous solution of ammonium fluoride. The step of contacting the silicon fine particles with hydrofluoric acid or an aqueous solution of ammonium fluoride can also be adopted. For example, spraying the hydrofluoric acid aqueous solution on the silicon fine particles as in a so-called shower is another aspect that can be adopted.

(4) Coating forming step (S4)
In the present embodiment, a coating forming step is performed in which a part or all of the surface of the silicon fine particles that has undergone or has not passed the oxide film removing step (S3) is covered with a carbon film. Therefore, since at least a part of the silicon fine particles that have undergone the coating forming step (S4) of the present embodiment are covered with carbon, the thickness of the silicon fine particles is increased as compared with the silicon fine particles that are not covered with carbon. It will be. Since the carbon of the present embodiment has conductivity, it is possible to form a negative electrode material having conductivity. Further, for example, by covering the silicon fine particles with carbon having a film thickness of several nm to several μm, not only a thin negative electrode can be formed but also a relatively thick negative electrode can be easily formed. Note that FIG. 3 shows a TEM (transmission type) of an example of silicon fine particles (partially enlarged view) or aggregates or aggregates thereof (partially enlarged view) that have undergone the coating forming step (S4) of the present embodiment. (Electron microscope) image. The crystalline silicon shown in FIG. 3 mainly has a crystal plane orientation (111) (also simply referred to as “Si (111)” or “(111)”; the same applies to other plane orientations). Observed.

In addition, for example, it may contribute to the relaxation of the internal stress of the entire negative electrode by covering the silicon fine particles with carbon, and more microscopically, the relaxation of the internal stress of the individual silicon fine particles. As a result, the production of the lithium ion battery can be facilitated, and the performance of the lithium ion battery (for example, the cycle characteristics of charge / discharge) can be improved.

Further, by forming the negative electrode material of the lithium ion battery using silicon fine particles whose surface is at least partially covered with carbon, the charge capacity value and the discharge capacity are compared with those of the silicon fine particles not covered with carbon. It is also possible to increase the value. For example, according to the research by the inventors of the present application, in the case of silicon fine particles not covered with carbon, for example, when the thickness of the negative electrode material is about 30 μm, the charge capacity value and the discharge capacity value are 500 (mAh). / G) or less. However, by using silicon fine particles whose surface is at least partially covered with carbon, the charge capacity value and the discharge capacity value are increased more than twice (typically, about 3 to about 5 times). be able to.

By the way, in the coating forming step (S4) of the present embodiment, the means for coating a part or all (in other words, at least a part on the surface of the silicon fine particles) 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 2 with carbon by the thermal CVD method, which is an example of the chemical vapor deposition method, can be adopted. Specifically, by heating the silicon fine particles 2 at about 600 ° C. or higher and about 1200 ° C. or lower in an atmosphere containing an organic gas and / or its vapor, at least a part of the silicon fine particles 2 on the surface is carbonized. Can be covered with a film of. Therefore, the thermal CVD apparatus, which is an example of the chemical vapor deposition apparatus, is one aspect of the coating forming portion 60 that can be adopted in the coating forming step (S4) of the present embodiment. Further, examples of the material (or raw material) that can be adopted in the thermal CVD method are one or more selected from the group of methane, ethane, acetylene, ethylene, propane, butane, butane, pentane, isobutane, and hexane. Hydrocarbons 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 treatment temperature.

As described above, typically, at least a part of the surface of the silicon fine particles 2 is carbonized by thermally decomposing the hydrocarbon gas on or in the vicinity of the heated silicon fine particles 2 to carbonize the hydrocarbon gas. It can be said that coating with the above-mentioned film realizes an example of an appropriate carbon film in the present embodiment and is excellent in productivity and industriality. In addition, a reduced pressure thermal CVD method or a plasma CVD method, which is another example of the chemical vapor deposition method, can also be appropriately adopted.

Further, another example of a method of coating at least a part of the surface of the silicon fine particles 2 with a carbon film is as follows. First, a known organic compound (chlorinated polyethylene elastomer or the like) or a mixture of the organic compound and graphite powder is placed in the coating forming portion 60 at least in the cleaning step (S1) and the pulverization step (S1) of the present embodiment. It adheres to or is adsorbed on the silicon fine particles 2 treated by S2). Then, by heating the organic compound to a temperature at which it is thermally decomposed and carbonizing the organic compound, at least a part of the surface is covered with carbon (typically graphene, graphite, and / or amorphous carbon). The broken silicon fine particles 2 can be formed. In addition, it is also present embodiment that the step of firing the once formed silicon fine particles 2 in a nitrogen atmosphere or a hydrogen atmosphere, for example, at 400 ° C. to 1200 ° C. is additionally and / or in advance. It is one aspect of the modification of. From the viewpoint of preventing, suppressing, or removing the formation of an oxide film on the surface of the silicon fine particles 2 or their aggregates or aggregates with high accuracy, the silicon fine particles 2 are heated in a hydrogen atmosphere. It is preferable to do so.

It is also another aspect that can be adopted to form silicon fine particles 2 having at least a part of the surface covered with carbon by using other known means. For example, it is also possible to use a carbon film formed by a known carbon black production method (furness method or channel method). The furnace method is a method in which the creosote oil obtained by distilling coal tar is partially burned in a predetermined chamber in a state where the creosote oil is turbulently diffused, and then the droplets are water-cooled. Further, the channel method is a method of precipitating carbon by, for example, colliding a flame formed by burning natural gas with the cooling surface of the channel steel. However, since a sulfur component derived from petroleum is contained, it is more preferable to adopt the above-mentioned thermal CVD method, which is a method in which such an impurity component is less likely to be mixed. Further, when each of the above methods is adopted, for example, silicon fine particles 2 or their aggregates or aggregates thereof are given kinetic energy by appropriately adopting a known mechanical structure to give the silicon fine particles 2 or the aggregate thereof. Adopting a method of coating at least a part on the surface of the agglomerate or aggregate with a carbon film is more homogeneous (eg, for example) on the surface of the silicon fine particles 2 or the agglomerate or aggregate thereof. This is a preferred embodiment because it enables the formation of a carbon film (with good uniformity in thickness and / or density). More specifically, while rotating a chamber or tube containing silicon fine particles or aggregates or aggregates thereof, and / or applying ultrasonic vibration to silicon fine particles 2 or aggregates or aggregates thereof. However, by adopting a method of coating at least a part of the surface of the silicon fine particles 2 or the aggregate or the aggregate thereof with a carbon film, it is possible to adopt the method of coating the silicon fine particles 2 or the aggregate or the aggregate thereof on the surface of the silicon fine particles 2 or the aggregate or the aggregate thereof. In addition, it is possible to form a carbon film more uniformly, which is a preferable embodiment.

(4) Negative electrode forming step (S5)
The negative electrode material of the lithium ion battery and the negative electrode manufacturing apparatus 100 of the present embodiment include silicon fine particles as the negative electrode material processed by the coating forming step (S4) and a member (for example, a copper foil) constituting a part of the negative electrode. ) Is mixed with a binder (for example, ammonium carboxylmethyl cellulose (CMC) and styrene butadiene rubber (SBR), or ammonium carboxylmethyl cellulose (CMC) and polyvinyl alcohol (PVA)). .. A negative electrode is formed using the mixture layer formed by the mixing portion 70.

<Other processes>
It should be noted that by the above-mentioned cleaning step (S1), crushing step (S2) and (4) coating forming step (S4), or by the cleaning step (S1), crushing step (S2), oxide film removing step (S3) and ( 4) The silicon fine particles obtained in the coating forming step (S4) can be classified, for example, in order to reduce variations in the number distribution and / or volume distribution of the crystallite diameter of each silicon fine particle.

<Analysis result of silicon fine particles obtained in the first embodiment>
1. 1. Analysis of silicon fine particles by SEM image and TEM image

FIG. 4A is an SEM (scanning electron microscope) image of an example of silicon fine particles or aggregates or aggregates thereof after the pulverization step (S2) of the first embodiment. Further, FIG. 4B is a diagram showing an SEM image of an example of enlarged silicon fine particles or aggregates or aggregates thereof after the crushing step (S2) of the first embodiment. Further, FIG. 4C is a diagram showing (a) an SEM image of another example of agglomerates or aggregates of silicon fine particles in the first embodiment, and (b) a partially enlarged view of (a). be. In addition, FIG. 5 is a diagram showing a transmission electron microscope (TEM) image of the silicon fine particles of the first embodiment.

As shown in FIG. 4A, not only individual silicon fine particles but also silicon fine particles shown in Y1 and Y2 or aggregates or aggregates thereof were confirmed. Very interestingly, when analyzed in more detail, as shown in FIGS. 4B and the Z portion of FIGS. 4C (a) and 4C (b), the silicon fine particles or their aggregates are, so to speak, thin layered silicon fine particles. It was confirmed that it was an agglomerate or an aggregate in a state of being folded in a multi-layered petal shape or a scale shape. If observed in more detail, for example, the range of length (major axis) when the width (minor axis) of one or a group of scaly silicon fine particles is 1, is 3.3 to 12.9. there were.

In addition, another interesting finding was obtained from the TEM image shown in FIG. 5, which focused on individual silicon fine particles. Specifically, it was confirmed that the individual silicon fine particles indicated by the region surrounded by the white line in FIG. 5 are crystalline, that is, single crystal silicon. In addition, it was confirmed that at least a part of the silicon fine particles were amorphous polygonal crystals having a size of about 2 nm to about 10 nm in a cross-sectional view. In FIG. 5, the plane orientation of the crystal is shown in each region surrounded by the white line.

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

From the results of FIGS. 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 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, and more specifically, a value of 3 nm or less was realized. It is worth noting that it was confirmed that the volume distribution was at least 50 nm or less, and particularly 30 nm or less, regardless of whether the mode diameter or the median diameter was used. Further, in FIG. 6, it was confirmed that an extremely small value of 10 nm or less was realized.

From the results of FIGS. 6 (a) and 6 (b), the silicon fine particles obtained after the pulverization step (S2) using the bead mill method have an average crystallite diameter of about 20 nm or less, more specifically, 10 nm. It was confirmed that the diameter was about 9.8 nm, which realizes the following. The crystallite diameter distribution of the silicon fine particles after the oxide film removing step (S3) is also substantially the same as in FIG.

Therefore, when the results of FIG. 6 and the results of each of the figures of FIG. 4 are combined and analyzed, at least the aggregates or aggregates of the silicon fine particles after the pulverization step (S2) or the oxide film removing step (S3) are obtained. It can be said that the so-called thin layered silicon fine particles having a major axis of about 100 nm or less are folded into a multi-layer petal shape or a scale shape. Further, as can be seen from FIGS. 5 and 6, the silicon fine particles are mainly composed of crystals having a major axis of 10 nm or less.

Further, as shown in FIG. 6, it can be seen that the silicon fine particles of the present embodiment contain silicon fine particles having 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 fine particles of the present embodiment was about 10 nm. It can be said that this value is a very small value. Further, as described above, further investigation confirmed that the apparent volume diameter of the silicon fine particles was in the range of about 100 nm or less. In particular, by containing a large number of ultrafine silicon particles having a major axis of 5 nm or less, the charge / discharge cycle characteristics derived by the silicon fine particles used as the negative electrode material of the lithium ion battery described later are improved with higher accuracy. It is a thing. Further, since at least a part of the surface is covered with carbon in the above-mentioned ultrafine silicon particles, higher charge capacity value and discharge capacity value, and excellent charge / discharge cycle characteristics can be realized.

3. 3. Analysis of the plane orientation of the crystallites of the silicon fine particles by the X-ray diffraction method FIG. 7 (a) shows the X-ray diffraction of the silicon fine particles or their aggregates or aggregates before the pulverization step (S2) of the first embodiment. This is the result of analyzing the measurement result (P) and the X-ray diffraction measurement result (Q) of the silicon fine particles or their aggregates or aggregates after the pulverization step (S2) in a wide angle range. Further, FIG. 7 (b) is an enlargement of a part of the result (P) of FIG. 7 (a), and is a silicon fine particle or an agglomerate thereof after the crushing step (S2) of the first embodiment. It is the result (R) which analyzed the result of the X-ray diffraction measurement of an aggregate in a limited angle range. The peak intensities of the C (002) plane and the C (003) plane shown in FIG. 7 (b) are such that the graphite fine particles of about 1 wt% to about 3 wt% are silicon fine particles or silicon fine particles. It indicates that it is contained in an agglomerate or an aggregate. As an example, the size of the graphite fine particles on the C (002) plane is about 50 nm or less, more specifically, about 35 nm, and the size of the graphite fine particles on the C (003) plane is about 100 nm. Hereinafter, more specifically, it was about 75 nm.

As shown in FIGS. 7 (a) and 7 (b), compared with the diffraction peak attributable to the crystal plane (111) of Si near 2θ = 28.4 ° before the pulverization step (S2) of the first embodiment. It was confirmed that the diffraction peak attributed to Si (111) after the pulverization step (S2) had a large half-value width. The average crystallite diameter calculated using Scherrer's equation from the half width of the Si (111) peak after the pulverization step (S2) was 9.8 nm. Also, very interestingly, the intensity of the diffraction peak attributed to Si (111) near 2θ = 28.4 ° after the pulverization step (S2) is the intensity of other diffraction peaks (eg, Si (220) or Si). It became clear that it was larger than the peak intensity of (311). The arrangement interval of Si (111) in the crystal lattice of the silicon fine particles after the pulverization step (S2) is 0.31 nm (3.1 Å) as shown in FIG.

Based on the above analysis results, with respect to the silicon fine particles after the crushing step (S2) of the present embodiment, the crystalline silicon fine particles having a plane orientation of (111) are mainly multi-layered petals or scaly. It can be said that it is an agglomerate or an aggregate in a state of being folded multiple times.

Then, by using the silicon fine particles or their aggregates or aggregates after the crushing step (S2) or the oxide film removing step (S3) of the present embodiment as the negative electrode material of the lithium ion battery, the positive electrode material of the lithium ion battery is used. When the lithium ion (Li ⁺ ) ionized from the inside reaches the negative electrode, the lithium ion (Li ⁺ ) forms a multi-layered petal-like or scaly multi-folded aggregate or aggregate in the fold gap. The unique effect of being easy to enter and easy to get out can be achieved.

<Second embodiment>
The lithium ion battery of the present embodiment uses silicon fine particles having at least a part of the surface covered with carbon, which are produced in the first embodiment, as a negative electrode material. The configuration other than the negative electrode material is the same as the configuration of the conventional CR2032 type coin cell structure lithium ion battery.

FIG. 8 is a schematic configuration diagram of the lithium ion battery 500 of the present embodiment. The lithium ion battery 500 of the present embodiment has a negative electrode 512 electrically connected to the negative electrode material and the negative electrode material 514 and a positive electrode electrically connected to the positive electrode material and the positive electrode material 518 in the container 510 of the CR2032 type coin cell. 516, a separator 520 that electronically insulates the negative electrode material and the negative electrode material 514, and the positive electrode material and the positive electrode material 518, and an electrolytic solution 530 are provided. Further, the lithium ion battery 500 of the present embodiment has an external circuit including a power supply 540 and a resistor 550 connected to a negative electrode 512 and a positive electrode 516 in order to realize charging / discharging.

Further, the method for manufacturing the lithium ion battery 500 of the present embodiment is as follows.

Regarding the method for manufacturing the negative electrode, first, about 0.3 g of silicon fine particles whose surface is at least partially covered with carbon, which was prepared in the first embodiment, is mixed with a 1 wt% CMC binder aqueous solution and an SBR binder aqueous dispersion. Disperse in a solution of about 10 mL (milliliter) consisting of (TRD2001, manufactured by JSR Corporation).

In the present embodiment, the dry weight ratio is 67: 11: 13: 9 or 50:25: 20: 5 in the order of silicon fine particles, carbon black, CMC binder aqueous solution, and SBR binder aqueous dispersion. To be mixed with. Further, in one modification of the present embodiment, the dry weight ratio is 50:25:20: 5 in the order of silicon fine particles, carbon black, CMC binder aqueous solution, and PVA binder aqueous dispersion. ..

Next, the slurry mixed and prepared using an agate mortar was placed on one surface of a copper foil having a thickness of 15 μm and about 9 cm (length) × 10 cm (horizontal) so as to have a thickness of about 30 μm to about 200 μm after drying. After coating on a hot plate, it is dried in the air at 80 ° C. for about 1 hour. Then, the above-mentioned copper foil is punched together with the dried slurry into a circle having a diameter of 11.3 mm corresponding to the battery standard CR2032 type coin cell to form a working electrode. After measuring the weight of this working electrode, a product that has been dried again by vacuum heating at 120 ° C. for 6 hours in a glow box is attached to the inner surface of a negative electrode 512 made of copper foil to obtain the present embodiment. The negative electrode is manufactured.

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

Further, the separator 520 of the present embodiment is a porous polyprolene sheet. In addition, the electrolytic solution 530 of the present embodiment contains 1 mol of lithium hexafluorophosphate (1 L) in a solvent (1 L) in which ethylene carbonate (EC) / diethyl carbonate (DEC) is mixed at a volume ratio of 1/1. An electrolytic solution in which LiPF ₆ ) is dissolved, or a solution in which fluoroethylene carbonate (FEC) is added to the electrolytic solution, and an amount within the amount satisfying the internal volume (about 1 mL) of the CR2032 type coin cell is injected. be.

The above-mentioned positive electrode material and positive electrode material 518, positive electrode 516, negative electrode material and negative electrode material 514, negative electrode 512, separator 520 and electrolytic solution 530 are arranged in the container 510 of the CR2032 type coin cell. Then, in a glove box having an argon atmosphere, each component of the separator 520 and the electrolytic solution 530 is sealed in the container 510 in a state where the positive electrode 516 and the negative electrode 512 of the outer frame of the coin cell are insulated from each other. As a result, a lithium-ion battery 500 of a CR2032 type coin cell was prototyped.

Examples of the electrolytic solvent constituting the electrolytic solution 530 in the present embodiment include ethylene carbonate (EC), propylene carbonate (PC) (polyprolene sheet) cyclic carbonate, dimethyl carbonate (DMC), and diethyl carbonate (DEC). ) Is a mixed solvent of a chain carbonate organic solvent. Further, a supporting salt such as lithium hexafluorophosphate (LiPF) or lithium tetrafluoroborate (LiBF) can be used by dissolving it in the above-mentioned electrolytic solvent.

<Charge / discharge cycle characteristics of lithium-ion battery 500>
By adopting the lithium ion battery 500 having the above configuration, the charge capacity value and the discharge capacity value are compared with the case where silicon fine particles whose surface is not covered with carbon are adopted (less than about 500 (mAh / g)). Therefore, it can be increased twice or more (typically about 3 to about 5 times). Further, even when the number of charge / discharge cycles reaches 100 or more, the charge capacity value and the discharge capacity value can be increased. In either case, it is possible to realize extremely good charge / discharge cycle characteristics that are not significantly reduced. Specific comparisons are as follows.

FIG. 9 is a graph showing the charging cycle characteristics of the lithium ion battery 500 of the present embodiment. Further, FIG. 10 is a graph showing the discharge cycle characteristics of the lithium ion battery 500 of the present embodiment. The circles in each figure indicate an example in which CMC and PVA are used as the binder, and the filled square marks indicate an example in which CMC and SBR are used as the binder.

As shown in FIGS. 9 and 10, in both the example in which CMC and PVA are adopted and the example in which CMC and SBR are adopted, the charge capacity value and the discharge capacity value are stably charged and discharged up to at least 60 times. It can be seen that is maintaining a high value. Further, by the time the number of charge / discharge cycles reaches 100, the charge capacity value and the discharge capacity value tend to decrease slightly. However, both the example in which CMC and PVA are adopted and the example in which CMC and SBR are adopted have a high charge capacity value (about 1400 to about 1500 mAh / g) and a discharge capacity value (about 1400 to about 1500 mAh / g) even when the number of charge / discharge cycles is 100. It was also found that it maintained about 1400 to about 1500 mAh / g).

Interestingly, it was confirmed that the example in which CMC and PVA were adopted could maintain a higher charge capacity value and discharge capacity value than the example in which CMC and SBR were adopted. It is considered that this is because when SBR is adopted, it is more difficult to mix uniformly with PVA when mixed with CMC or silicon fine particles.

Further, as a reference example, the charge / discharge cycle characteristics of the lithium ion battery manufactured in the same manner as the lithium ion battery 500 were measured using the silicon fine particles of the present embodiment before the treatment by the coating forming step (S4). The results will be described. FIG. 11 is a graph showing the charging cycle characteristics of the lithium-ion battery of the above-mentioned reference example. Further, FIG. 12 is a graph showing the discharge cycle characteristics of the lithium ion battery of the above-mentioned reference example. In addition, this reference example is an example which adopted CMC and PVA as a binder.

As shown in FIGS. 11 and 12, it can be seen that the charge capacity value and the discharge capacity value are relatively low values of less than 500 (mAh / g).

Therefore, by using the silicon fine particles and / or their aggregates (including the case of aggregates) of the first embodiment described above, a lithium ion battery having a high capacity and excellent charge / discharge cycle characteristics. It was confirmed that can be realized. In particular, as compared with the result of a lithium ion battery as a reference example, silicon fine particles and / or aggregates thereof (aggregates) whose surface is at least partially covered with carbon by the coating forming step (S4). It is worth noting that the lithium-ion battery 500 of the second embodiment adopting (including) can increase the charge capacity value and the discharge capacity value more than twice (typically about 3 to about 5 times). .. In addition, by covering a part or all of the silicon fine particles with carbon, the formation of a thick negative electrode material is facilitated, so that the production of the lithium ion battery 500 can be facilitated. Even when the charge / discharge cycle is performed more than 100 times (for example, several hundred times to 1000 times), the lithium ion battery 500 is the present embodiment before the treatment by the coating forming step (S4) is performed. It can be said that it has a charge capacity value, a discharge capacity value, and / or charge / discharge cycle characteristics that are significantly superior to those of the lithium ion battery in which the silicon fine particles of the above are adopted.

As shown in FIG. 13, in the lithium ion battery 500 of the present embodiment, after 100 charge / discharge cycles have been performed, TEM (transmission) of silicon fine particles or aggregates or aggregates thereof constituting the negative electrode material. When the image (type electron microscope) was confirmed, as shown by the region "A" in the figure, a substantially circular crystal (microcrystal) having a diameter of about 4 nm was confirmed. Therefore, if a negative electrode material using silicon fine particles obtained by pulverizing crystalline silicon or aggregates or aggregates thereof is adopted, a part of the crystalline state can be obtained even after at least 100 charge / discharge cycles. It is another interesting fact that it has become clear that it will be maintained. The example of the lithium ion battery 500 shown in FIG. 13 is an example in which CMC and PVA are used as the binder and about 5 wt% of fluoroethylene carbonate (FEC), which will be described later, is added. Further, it is considered that the crystalline silicon in the region "A" in FIG. 13 mainly has Si (111).

<Other Embodiment (1)>
By the way, in each of the above-described embodiments, as a starting material, a single crystal or polycrystalline silicon block, silicon chips formed in the cutting process of an ingot, or the like is exemplified, but other forms of silicon are exemplified. It is another embodiment that can be adopted by using chips or the like as a starting material. Specifically, silicon chips and the like are not limited to those that are inevitably formed in the cutting process of silicon ingots in the production process of semiconductor products, and preselected crystalline silicon ingots are uniformly formed by a cutting machine. It can also be manufactured by cutting in or randomly. Further, so-called silicon waste materials such as silicon chips and silicon polishing chips, which are usually regarded as waste, can be a starting material for the silicon fine particles of each of the above-described embodiments, and the silicon waste materials include wafer fragments. It may also contain fine debris obtained by crushing waste wafers and the like. Further, silicon fine particles using a material such as metallic silicon chips or metallic silicon abrasive chips, or metallic other particulate silicon as a starting material can also be adopted.

<Other Embodiment (2)>
Further, the impurity concentration of the n-type crystalline silicon in each of the above-mentioned embodiments is not particularly limited. Further, not only n-type but also p-type crystalline silicon can be adopted. Further, crystalline silicon, which is an intrinsic semiconductor, can also be adopted as crystalline silicon in each of the above-described 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 an n-type impurity. Further, the graphite fine particles of about 1 wt% to about 3 wt% indicated by the peak intensities of the C (002) plane and the C (003) plane shown in FIG. 7B described above are the silicon fine particles or the silicon fine particles. It is added that a part or all of these graphites can contribute to the improvement of the conductivity of the negative electrode material because they are contained in the aggregate.

<Other Embodiment (3)>
Further, the silicon fine particles of each of the above-described embodiments and the lithium ion battery provided with the silicon fine particles are not limited to the application to the coin cell type structure introduced in the second embodiment. Therefore, it can be applied to various devices or devices having or using a lithium ion battery having a larger electric capacity than the coin cell type structure. Further, as the negative electrode material, it is also another aspect that a material obtained by mixing graphite (typically graphite) with the silicon mixed powder of each of the above-described embodiments can be adopted.

<Other Embodiment (4)>
Further, as an alternative device to the device 100 for manufacturing the negative electrode material and the negative electrode of the lithium ion battery shown in FIG. 2 in the first embodiment described above, the device 200 for manufacturing the negative electrode of the lithium ion battery shown in FIG. 14 is adopted. Is also good. Specifically, from the viewpoint of simplifying the equipment and / or reducing the manufacturing cost, in the negative electrode manufacturing apparatus 200 of the lithium ion battery, a washing machine for cleaning silicon chips and the like formed in the silicon cutting process. 10 is an embodiment that also serves as a crusher 20 that forms silicon fine particles by crushing washed silicon chips and the like. Therefore, in the apparatus / method shown in FIG. 14, for example, beads having a relatively large diameter are used in the cleaning step, and beads having a relatively small diameter are used in the pulverization step, so that they are used as a negative electrode material for a lithium ion battery. You will get silicon fine particles. However, in order to obtain the silicon fine particles described in the first embodiment with higher accuracy, the silicon fine particles are formed by a bead mill machine after processing with a ball mill machine as in the first embodiment. It is preferable to do so.

<Other Embodiment (5)>
Further, according to the analysis by the inventors of the present application, the amount of fluoroethylene carbonate (FEC) added to the electrolytic solution 530 in the second embodiment determines the charge capacity value, the discharge capacity value, and the characteristics of the charge / discharge cycle. It became clear that it could have an impact. FIG. 15A is a graph showing the charging cycle characteristics of the lithium ion battery when the amount of FEC in the electrolytic solution 530 is changed. Further, FIG. 15B is a graph showing the discharge cycle characteristics of the lithium ion battery when the amount of FEC in the electrolytic solution 530 is changed. The amount of FEC to be measured is 5 wt%, 10 wt%, and 15 wt%, respectively. For reference, a lithium ion battery to which FEC was not added was also measured. Further, in FIGS. 15A and 15B, the weight ratio of carbon (C) was 0.1 when silicon (Si) was 1. In addition, in FIGS. 15A and 15B, the charge / discharge cycle is performed under the condition of a current value of 180 mA / g up to 5 times of charge / discharge, and the current of 1800 mA / g is performed when the number of charge / discharge times is 6 or more. The charge / discharge cycle is performed under the condition of the value. This is to form a good (eg, low resistance and / or thin) SEI (solid electrolyte interface) on the surface of the negative electrode material.

As shown in FIGS. 15A and 15B, if the amount of FEC added (wt%) is in the range of more than 5% and 15% or less, stable charging is performed even when 100 charge / discharge cycles are performed. It can be seen that the capacity value and the discharge capacity value maintain high values (typically, about 1500 mAh / g). In particular, it has been clarified that by adding about 10% of FEC, the charge capacity value and the discharge capacity value can be stably maintained at very high values. Therefore, it was found that by adding FEC, a high charge capacity value and a high discharge capacity value can be obtained even when 100 charge / discharge cycles are performed.

<Other Embodiment (6)>
Further, the inventor of the present application describes the weight ratio of carbon (C) and silicon (Si), the charge capacity value and the discharge capacity value, and the characteristics of the charge / discharge cycle in the negative electrode material adopted in the second embodiment. Correlation was investigated. FIG. 16A is a graph showing the charging cycle characteristics of a lithium ion battery when the weight ratio of silicon (Si) and carbon (C) is changed. Further, FIG. 16B is a graph showing the discharge cycle characteristics of the lithium ion battery when the weight ratio of silicon (Si) and carbon (C) is changed. The weight ratios of silicon (Si) and carbon (C) as measurement targets are the four examples shown in (1) to (4) below.
(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

Further, in FIGS. 16A and 16B, the charge / discharge cycle is performed under the condition of a current value of 180 mA / g up to 5 times of charge / discharge, and the current value of 1800 mA / g is performed when the number of charge / discharge times is 6 or more. The charge / discharge cycle is performed under the conditions of. This is to form a good (eg, low resistance and / or thin) SEI (solid electrolyte interface) on the surface of the negative electrode material. Note that FIGS. 16A and 16B are examples in which about 10 wt% of fluoroethylene carbonate (FEC) is added.

As shown in FIGS. 16A and 16B, the charge capacity value and the discharge capacity value of one example having the largest ratio of carbon (C) ((4) above) are slightly low values, but the other three examples have a slightly lower value. It can be seen that in each case, the charge capacity value and the discharge capacity value are stably maintained at high values. Therefore, when the ratio (weight ratio) of carbon (C) is 0.1 or more and 0.21 or less when silicon (Si) is 1, even when 100 charge / discharge cycles are performed, It has been clarified that the charge capacity value and the discharge capacity value can be stably maintained at particularly high values (typically, about 1500 mAh / g). However, the above example (4) is more than the charge capacity value and the discharge capacity value of the lithium ion battery in which at least a part on the surface of the silicon fine particles or their aggregates or aggregates is not covered with carbon. It has a charge capacity value and a discharge capacity value that are more than twice as high (typically about three times).

In this embodiment, the weight ratio of carbon (C) was 0.1 when silicon (Si) was 1, but the weight of carbon (C) when silicon (Si) was 1. When the ratio is 0.05 or more, almost the same effect as the above-mentioned results (1) to (3) can be obtained. Therefore, when the ratio of carbon (C) is 0.05 or more and less than 0.37 when silicon (Si) is 1, the lithium ion is stable and has a high charge capacity value and discharge capacity value. You can get a battery.

Further, in this embodiment, as a result of further detailed analysis by the present inventor, a portion where carbon (C) in the above-mentioned case (1) is attached to silicon (Si) by a TEM (transmission electron microscope) image. The film thickness was about 2 nm to about 3 nm. Further, in the case of (2) described above, the film thickness of the portion where the carbon (C) was attached to the silicon (Si) was about 5 nm to about 10 nm. Further, the film thickness of the portion where the carbon (C) adheres to the silicon (Si) in the case of the above-mentioned (3) was also about 5 nm to about 10 nm. In addition, in the case of (4) described above, the film thickness of the portion where the carbon (C) was attached to the silicon (Si) was about 50 nm to about 90 nm. Therefore, if the film thickness of carbon (C) in the portion adhering to silicon (Si) is 1 nm or more and less than 50 nm, particularly if the film thickness is 2 nm or more and 10 nm or less, it is stable and has a charging capacity. A lithium ion battery having a high value and a high discharge capacity value can be obtained.

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

The silicon fine particles of the present invention and the lithium ion battery provided with the silicon fine particles are, for example, various power generation or power storage devices (including small household power storage devices and large power storage systems), smartphones, mobile information terminals, and portable electronic devices (portable). Phones, portable music players, laptops, digital cameras / videos), electric vehicles, hybrid electric vehicles (HEV) or plug-in hybrid electric vehicles (PHEV), motor-powered motorcycles, motor-powered vehicles Can be suitable for a wide variety of devices or devices, including motorized vehicles, other transport machines or vehicles, etc.

Claims (9)

The binding-crystalline silicon, ball mill, and by grinding with a bead mill machine used after the ball mill, the mode diameter and median diameter in aggregates or aggregate of silicon micro particles having the volume distribution 30nm A crushed portion that forms the aggregate or aggregate in a multi-layered petal-like or scaly-like folded state.
Forming a carbon covering at least a portion of the surface of the aggregates or the aggregate, e Bei and a coating forming portion,
The crystalline silicon, Ru chips or shavings der are carved by a fixed abrasive wire,
Equipment for manufacturing negative electrode materials for lithium-ion batteries. The coating forming portion is a chemical vapor deposition apparatus.
The apparatus for manufacturing a negative electrode material for a lithium ion battery according to claim 1. The intensity of the diffraction peak attributed to Si (111) near 2θ = 28.4 ° by the X-ray diffraction measurement of the silicon fine particles or the aggregate or the aggregate is larger than the intensity of the other diffraction peaks.
The apparatus for manufacturing a negative electrode material for a lithium ion battery according to any one of claims 1 and 2. The binding-crystalline silicon, ball mill, and by grinding with a bead mill machine used after the ball mill, the mode diameter and median diameter having the following volume distribution 30 nm, agglomeration of silicon fine particles as the negative electrode material A crushed portion that is an object or an aggregate and forms the aggregate or the aggregate in a state of being folded in a multi-layered petal shape or a scale shape.
Forming a carbon covering at least a portion of the surface of the aggregates or the aggregate, e Bei and a coating forming portion,
The crystalline silicon, Ru chips or shavings der are carved by a fixed abrasive wire,
Negative electrode manufacturing equipment for lithium-ion batteries. The coating forming portion is a chemical vapor deposition apparatus.
The apparatus for manufacturing a negative electrode of a lithium ion battery according to claim 4. By milling by a bead mill machine forming-crystalline silicon after trituration with ball mill machine, a agglomerate or aggregate of silicon micro particles mode diameter and median diameter having the following volume distribution 30 nm, multilayer petaloid Alternatively, a pulverization step of forming the agglomerates or aggregates in a state of being folded in a scaly shape, and
Forming a carbon covering at least a portion of the surface of the aggregates or the aggregate, the coating formation step, only including,
The crystalline silicon is chips or cutting chips machined by a fixed abrasive wire.
A method for manufacturing a negative electrode material for a lithium ion battery. The coating forming step is a step of forming the carbon by a chemical vapor deposition method.
The method for manufacturing a negative electrode material for a lithium ion battery according to claim 6. The binding-crystalline silicon, ball mill, and by grinding with a bead mill machine used after the ball mill, the mode diameter and median diameter having the following volume distribution 30 nm, agglomeration of silicon fine particles as the negative electrode material A crushing step of forming the aggregate or the aggregate in a state of being folded into a multi-layered petal-like or scaly shape, which is an object or an aggregate.
Forming a carbon covering at least a portion of the surface of the aggregates or the aggregate, the coating formation step, only including,
The crystalline silicon is chips or cutting chips machined by a fixed abrasive wire.
A method for manufacturing a negative electrode of a lithium ion battery. The coating forming step is a step of forming the carbon by a chemical vapor deposition method.
The method for manufacturing a negative electrode of a lithium ion battery according to claim 8.

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