CN111755689A

CN111755689A - Negative electrode material for lithium ion battery, method for producing negative electrode or negative electrode material for lithium ion battery, and apparatus for producing negative electrode or negative electrode material for lithium ion battery

Info

Publication number: CN111755689A
Application number: CN202010436052.9A
Authority: CN
Inventors: 小林光; 肥后徹; 金谷弥生
Original assignee: Nisshin Kasei KK
Current assignee: Nisshin Kasei KK
Priority date: 2014-06-11
Filing date: 2014-06-11
Publication date: 2020-10-09
Also published as: KR20210071110A; JP5866589B1; KR102280508B1; CN106415897B; JPWO2015189926A1; KR20170018350A; WO2015189926A1; TW201545979A; KR102476118B1; CN106415897A

Abstract

The negative electrode material of a lithium ion battery of the present invention has silicon particles obtained by pulverizing crystalline silicon. The cathode material of another lithium ion battery of the invention is as follows: the intensity of a diffraction peak ascribed to Si (111) in the vicinity of 28.4 ° to a plurality of silicon fine particles formed of crystalline silicon was measured by X-ray diffraction, and was larger than the intensities of the other diffraction peaks. By using the above-described various negative electrode materials, a lithium ion battery can be obtained in which the charge/discharge capacity is less likely to change even when charge/discharge is repeated.

Description

Negative electrode material for lithium ion battery, method for producing negative electrode or negative electrode material for lithium ion battery, and apparatus for producing negative electrode or negative electrode material for lithium ion battery

The present application is a divisional application of chinese invention patent application entitled "negative electrode material for lithium ion battery, method and apparatus for manufacturing negative electrode or negative electrode material for lithium ion battery" based on application No. 201480079578.9,

application date

2014, 6, and 11. The Chinese invention patent application is a Chinese national phase application of International application No. PCT/JP 2014/065432.

Technical Field

The present invention relates to a negative electrode material for a lithium ion battery, a method for producing a negative electrode or a negative electrode material for a lithium ion battery, and a device for producing the same.

Background

A lithium ion battery that has been widely used so far has a negative electrode on its negative electrode side, the negative electrode having a negative electrode current collector and a mixture layer obtained by mixing graphite (natural graphite, artificial graphite, or the like) as a negative electrode active material (hereinafter also referred to as "negative electrode material") with a binder for the mixture layer; the lithium ion battery has a positive electrode on the positive electrode side, the positive electrode having a positive electrode current collector and a mixture layer, a binder (PVdF or the like) for the mixture layer and an oxide powder of lithium (Li) (LiCoO) as a positive electrode active material₂、LiNiO₂、LiMnO₂Etc.) and conductive graphite (mainly carbon black, etc.) are mixed and coated. A cell container of a lithium ion battery is filled with an electrolyte, and a separator (mainly, a polyolefin porous film, a porous polypropylene film, or the like) is provided between a negative electrode current collector and a positive electrode current collector.

The separator is capable of allowing an electrolyte to pass therethrough and moving lithium ions, and is provided to separate electrodes to prevent an electrical short circuit.

Lithium ions move between the negative electrode current collector and the positive electrode current collector through the electrolyte, thereby performing charge and discharge of the lithium ion battery. During charging, lithium ions move to the negative electrode side; during discharge, lithium ions move to the positive electrode side. The power is charged through an external power supply and discharged through an external resistor (load).

In recent years, in the field of lithium ion batteries, the following technologies are disclosed: silicon particles are used as a material of a negative electrode active material of a lithium ion battery instead of the graphite. For example, an example of silicon particles is obtained by the following method: the silicon particles are obtained by crushing single crystal silicon in a mortar, classifying the crushed silicon with a sieve to form powder having a diameter of about 38 micrometers (μm) or less, and heating the powder to 150 ℃ (reached temperature) at a temperature rise rate of 30 ℃/min in argon (see patent document 1). Another example of silicon particles can also be obtained by the following method: the silicon particles are obtained by adding liquid silicon tetrachloride to gaseous zinc at a high temperature and a high concentration, reacting the gaseous zinc at a high temperature of 1050 ℃ or higher to reduce the silicon tetrachloride to form silicon particles, growing and aggregating the silicon fine particle crystals at a temperature of 1000 ℃ or lower (particularly 500 to 800 ℃) to form silicon particles, adjusting the particle size of the silicon particles, and concentrating the silicon particles in an aqueous zinc chloride solution. Patent document 2 discloses the following: through the above operations, high purity silicon particles having a particle diameter of about 1 to 100 μm and a method for using the silicon particles can be obtained.

Patent document 1: japanese laid-open patent publication No. 2005-032733

Patent document 2: japanese laid-open patent publication No. 2012-101998

Disclosure of Invention

Technical problems to be solved by the invention

However, in the conventional technology, when silicon particles are used as a negative electrode material, the capacity during charge and discharge can be increased, but on the other hand, the silicon particles are destroyed by the absorption and desorption of lithium from the silicon particles. As a result, the charge-discharge cycle characteristics of the lithium ion battery cannot be maintained.

Since the silicon particles disclosed in the above-mentioned prior art documents require high-temperature synthesis and collection processes, it is necessary to carry out extremely complicated production processes for obtaining silicon particles to be used as a negative electrode material. As a result, productivity is inevitably lowered and manufacturing cost is inevitably increased. Therefore, the silicon particles disclosed so far have a large problem: not only the negative electrode characteristics of the lithium ion battery are poor, but also there is still insufficient industrial applicability. That is, lithium ion batteries manufactured using silicon particles are still in the development stage.

Technical solution for solving technical problem

The present invention solves at least some of the problems associated with charge-discharge cycle characteristics and the like of conventional negative electrode current collectors made of silicon particles, and is extremely useful for providing a negative electrode material for a high-performance lithium ion battery, a method for producing a negative electrode for a lithium ion battery or a negative electrode material, and an apparatus for producing the same.

The negative electrode material for a lithium ion battery according to an aspect of the present invention includes silicon fine particles obtained by pulverizing crystalline silicon.

The negative electrode material of the lithium ion battery of another aspect of the present invention is as follows: the intensity of a diffraction peak ascribed to Si (111) in the vicinity of 2 θ of 28.4 ° was measured by X-ray diffraction, and the intensity was larger than that of the other diffraction peaks.

By using the above negative electrode materials, a lithium ion battery can be obtained in which the charge/discharge capacity is less likely to change even when charge/discharge is repeated. In other words, the lithium ion battery has good charge-discharge cycle characteristics.

In particular, it is proposed that, for example, cutting powder or chips (usually disposed as industrial waste) obtained by cutting an ingot or block formed by melting and solidifying silicon by a fixed-abrasive wire saw can be used as a starting material of the silicon fine particles constituting each of the above-described negative electrode materials. Preferably, in order to maintain and/or improve the charge-discharge cycle characteristics of the lithium ion battery at a high level, the cutting powder or chips are pulverized by a ball mill and/or a sand mill to form silicon fine particles.

A lithium ion battery according to an aspect of the present invention has a negative electrode material having silicon fine particles obtained by pulverizing crystalline silicon.

A lithium ion battery of another aspect of the invention is as follows: the intensity of a diffraction peak ascribed to Si (111) in the vicinity of 2 θ of 28.4 ° was measured by X-ray diffraction, and the intensity was larger than that of the other diffraction peaks.

According to the above lithium ion battery, the charge/discharge capacity is less likely to change even if charge/discharge is repeated. In other words, it is possible to maintain a higher level of charge-discharge cycle characteristics and/or improve the characteristics.

An apparatus for manufacturing a negative electrode material for a lithium ion battery according to an aspect of the present invention includes a pulverization unit configured to pulverize crystalline silicon to form silicon microparticles.

Another aspect of the present invention is directed to an apparatus for producing a negative electrode material for a lithium ion battery, the apparatus including a pulverization unit for forming silicon fine particles, wherein the silicon fine particles formed of crystalline silicon have an intensity of a diffraction peak attributed to Si (111) in the vicinity of 28.4 ° 2 θ, which is higher than intensities of other diffraction peaks, as measured by X-ray diffraction.

According to the apparatus for producing a negative electrode material for a lithium ion battery, the charge capacity and/or the discharge capacity are less likely to change even when the lithium ion battery is repeatedly charged and discharged. In other words, it is helpful to manufacture a lithium ion battery having good charge-discharge cycle characteristics.

An apparatus for manufacturing a negative electrode for a lithium ion battery according to an aspect of the present invention includes a pulverization portion that pulverizes crystalline silicon to form silicon fine particles, which are used as a negative electrode material.

Another aspect of the present invention is a device for manufacturing a negative electrode for a lithium ion battery, the device including a pulverization unit for forming silicon fine particles, the silicon fine particles formed of crystalline silicon having an intensity of a diffraction peak attributed to Si (111) in the vicinity of 2 θ of 28.4 ° that is higher than intensities of other diffraction peaks, the silicon fine particles being used as a negative electrode material, as measured by X-ray diffraction.

According to the apparatus for producing a negative electrode for a lithium ion battery, the charge capacity and/or the discharge capacity are less likely to change even when the lithium ion battery is repeatedly charged and discharged. In other words, it is helpful to manufacture a lithium ion battery having good charge-discharge cycle characteristics.

A method for producing a negative electrode material for a lithium ion battery according to one aspect of the present invention includes a pulverization step of pulverizing crystalline silicon to form silicon fine particles.

A method for producing a negative electrode material for a lithium ion battery according to another aspect of the present invention includes a pulverization step for forming silicon fine particles, and the intensity of a diffraction peak attributed to Si (111) in the vicinity of 2 θ of 28.4 ° is measured by X-ray diffraction, and is greater than the intensities of other diffraction peaks.

According to the method for producing a negative electrode material for a lithium ion battery, the charge/discharge capacity is less likely to change even when the lithium ion battery is repeatedly charged and discharged. In other words, it is helpful to manufacture a lithium ion battery having good charge-discharge cycle characteristics.

A method for manufacturing a negative electrode for a lithium ion battery according to an aspect of the present invention includes a pulverization step of pulverizing crystalline silicon to form silicon fine particles, which are used as a negative electrode material.

A method for producing a negative electrode for a lithium ion battery according to another aspect of the present invention includes a pulverization step of forming silicon fine particles, and the silicon fine particles formed of crystalline silicon are measured by X-ray diffraction to have an intensity attributed to a diffraction peak of Si (111) in the vicinity of 2 θ of 28.4 °, which is larger than intensities of other diffraction peaks, and are used as a negative electrode material.

According to the method for producing a negative electrode for a lithium ion battery, the charge capacity and/or the discharge capacity are less likely to change even when the lithium ion battery is repeatedly charged and discharged. In other words, it is helpful to manufacture a lithium ion battery having good charge-discharge cycle characteristics.

In the above inventions, the crystalline silicon includes not only single crystal silicon but also polycrystalline silicon. Further, metal silicon can be selected as the crystalline silicon in each of the above inventions.

Effects of the invention

According to the negative electrode material for a lithium ion battery of one aspect of the present invention, the charge/discharge capacity is less likely to change even when charge/discharge of the lithium ion battery is repeated. In other words, a lithium ion battery having good charge-discharge cycle characteristics can be obtained. According to the lithium ion battery of one aspect of the present invention, the charge/discharge capacity is less likely to change even if charge/discharge is repeated. In other words, the charge-discharge cycle characteristics can be improved. Further, according to the apparatus for manufacturing a lithium ion battery of one aspect of the present invention and the method for manufacturing a lithium ion battery of one aspect of the present invention, the charge/discharge capacity is less likely to change even if charge/discharge of the lithium ion battery is repeated. In other words, it is helpful to manufacture a lithium ion battery having good charge-discharge cycle characteristics.

Drawings

Fig. 1 is a flowchart illustrating a manufacturing process of a negative electrode material of a lithium ion battery according to a first embodiment.

Fig. 2 is a schematic diagram illustrating a manufacturing apparatus and a manufacturing process of a negative electrode material of a lithium ion battery according to a first embodiment.

Fig. 3A is an SEM image showing an example of the silicon fine particles or the aggregate thereof according to the first embodiment.

Fig. 3B is an SEM image showing an example of the silicon fine particles or the aggregate thereof in the first embodiment in an enlarged manner.

Fig. 3C is a diagram showing the first embodiment: (a) a SEM image of another example of the aggregate of the silicon fine particles; (b) (a) enlarged view of a part thereof.

Fig. 4 is a view showing a TEM image of the silicon fine particle of the first embodiment.

Fig. 5 is a graph showing the crystallite diameter of the silicon fine particles of the first embodiment: (a) a crystallite particle size distribution diagram showing a number distribution; (b) the volume distributed crystallite size distribution plot is shown.

Fig. 6 is a graph showing the results of X-ray diffraction measurement of the silicon fine particles or the aggregates thereof of the first embodiment ((a) wide angle range, (b) limited angle range).

Fig. 7 is a schematic configuration diagram showing a lithium ion battery according to a second embodiment.

Fig. 8 is a graph showing the charge cycle characteristics of the lithium ion battery of the second embodiment.

Fig. 9 is a graph showing the discharge cycle characteristics of the lithium ion battery of the second embodiment.

Fig. 10 is a graph showing the charge cycle characteristics of the lithium ion battery of the comparative example.

Fig. 11 is a graph showing the discharge cycle characteristics of the lithium ion battery of the embodiment of the comparative example.

Fig. 12 is a schematic diagram showing a manufacturing apparatus and a manufacturing process of a negative electrode material of a lithium ion battery according to another embodiment.

-description of symbols-

1 cutting powder and the like

2 silicon microparticles

10 cleaning machine (cleaning and pre-crusher)

11 grinding balls

13a storage tank

13b Top cover

15 rotating shaft

20 disintegrator

21 introduction port

22 process chamber

24 discharge port

25 filter

30 drier

40 rotary evaporator

50 oxidation film removing tank

55 hydrofluoric acid or ammonium fluoride aqueous solution

57 stirrer

58 centrifugal separator

60 mixing section

Negative electrode material for 100 lithium ion battery and apparatus for producing negative electrode

500 lithium ion battery

510 Container

512 negative electrode

514 negative electrode current collector and negative electrode material

516 positive electrode

518 positive electrode current collector and positive electrode material

520 diaphragm

530 electrolyte

540 Power supply

550 resistance

Detailed Description

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In the following description, the same reference numerals are used to designate the same parts throughout the drawings unless otherwise specified. Moreover, each element of the embodiments in the drawings is not necessarily shown in actual scale. Some symbols may be omitted to make the drawings easily visible.

< first embodiment >

Fig. 1 is a flowchart illustrating a manufacturing process of a negative electrode material of a lithium ion battery according to the present embodiment. Fig. 2 is a schematic diagram showing a manufacturing apparatus and a manufacturing process of the negative electrode material of the lithium ion battery according to the present embodiment.

The negative electrode material for a lithium ion battery of the present embodiment, the lithium ion battery having the negative electrode material, and the manufacturing methods thereof include various steps, and for example, in the cutting of silicon in the production process of a silicon wafer used for a semiconductor product such as a solar battery, silicon cutting powder, silicon cutting chips, or grinding dust (hereinafter, also referred to as "silicon cutting powder or the like" or "cutting powder or the like") generated in the cutting process of silicon is generally treated as a waste material. The cutting powder or the like contains fine particles obtained by pulverizing a silicon wafer to be processed by a known pulverizer. As shown in fig. 1, the method for manufacturing a lithium ion battery according to the present embodiment includes the following steps (1), (2), and (4). Other possible solutions that can be adopted in the method for manufacturing a lithium ion battery of the present embodiment are: comprising the following step (3).

(1) Cleaning process (S1)

(2) Grinding step (S2)

(3) Oxide film removal step (S3)

(4) Negative electrode Forming Process (S4)

As shown in fig. 2, the apparatus 100 for manufacturing a negative electrode material and a negative electrode of a lithium ion battery according to the present embodiment mainly includes a washing machine (washing and pre-grinding machine) 10, a grinding machine 20, a drying machine (not shown), a rotary evaporator 40, and a mixing unit 60 that is responsible for a part of a negative electrode forming process of the lithium ion battery. Other possible configurations that can be adopted by the negative electrode material for lithium ion batteries and the negative electrode manufacturing apparatus 100 according to the present embodiment are: the apparatus may include an oxide film removing tank 50 and a centrifugal separator 58.

(1) Cleaning process (S1)

In the cleaning step (S1) of the present embodiment, silicon chips formed, for example, during the cutting of an ingot or block of crystalline silicon (ingot or block of n-type crystalline silicon), which is single crystal silicon or polycrystalline silicon, are cleaned. Typical silicon cutting powder and the like are cutting powder and the like obtained by cutting a silicon ingot with a known wire saw or the like (which is typically a fixed abrasive wire saw). Therefore, in the present embodiment, since the silicon fine particles constituting the negative electrode material of the lithium ion battery are formed using the silicon cutting powder or the like, which has been conventionally treated as a scrap, as a starting material, the cleaning step (S1) of the present embodiment is preferable from the viewpoints of production cost, ease of starting of raw materials, and effective utilization of resources.

The main purpose of the cleaning step (S1) in the present embodiment is to remove organic substances adhering to the formation of the silicon cutting powder and the like, which are typically organic substances such as cutting fluid and additives used in the cutting process. In the present embodiment, as shown in fig. 2, first, the cut powder or the like 1 to be cleaned is weighed, and then the cut powder or the like 1, a predetermined first liquid, and the grinding ball 11 are introduced into a bottomed cylindrical tank 13 a. After the reservoir 13a is closed by the top cover 13b, the reservoir 13a on the rotary body 15 is rotated by rotating the two cylindrical rotary bodies 15 of the ball mill, which is the cleaning machine (cleaning and pre-pulverizing machine) 10. As a result, the cut powder or the like 1 to be cleaned is dispersed in the first liquid, whereby the cleaning and the preliminary pulverization of the cut powder or the like 1 are performed in the tank 13 a.

Here, the ball mill of the present embodiment is a pulverizer that applies physical impact force by rotating the pot 13a and the top cover 13b using steel balls, magnetic balls, small stones, and the like enclosed by the pot 13a and the top cover 13b as the balls 11 (pulverizing media). A preferred example of the first liquid is acetone. In a more specific embodiment, for example, 300 milliliters (mL) of acetone is added to 100 grams (g) of silicon chips, etc., and the mixture is stirred for about one hour in a storage tank 13a and a top cover 13b on a rotary body 15 of a BALL MILL (Universal BALL MILL manufactured by MASUDA, inc., in the present embodiment), thereby dispersing the silicon chips, etc., in the acetone. The grinding balls of the ball mill used were alumina balls having a particle diameter of 10 millimeters (mm) and alumina balls having a particle diameter of 20 mm. In the cleaning step (S1) of the present embodiment, the silicon chips and the like are pre-pulverized and stirred in the first liquid, and thereby dispersed in the ball mill. Therefore, since the cleaning efficiency is significantly improved as compared with a treatment method in which silicon chips or the like are simply immersed in the first liquid, the silicon particles that can be obtained are preferable from the viewpoint of improving the negative electrode characteristics of the lithium ion battery, particularly the charge-discharge cycle characteristics.

After the washing step (S1), the top lid 13b is opened to discharge the silicon particles together with the first liquid, and the first liquid is filtered off by a known vacuum distillation apparatus to be a waste liquid. On the other hand, the remaining silicon particles are dried in a known dryer. The silicon particles obtained by the drying process are subjected to the preliminary grinding and washing again in the washing machine (washing and preliminary grinding machine) 10 in the same step as necessary.

(2) Grinding step (S2)

Then, in the grinding step (S2), a predetermined second liquid is added to the washed silicon particles, and thereafter, the silicon particles are ground in a grinder.

A preferred example of the second liquid of the present embodiment is IPA (isopropyl alcohol). The second liquid and the silicon particles obtained in the cleaning step (S1) were put in the tank 13a at a ratio of 95% by weight of the second liquid and 5% by weight of the silicon particles, and the cleaning machine (cleaning and pre-pulverizing machine) 10 was rotated to perform pre-pulverization, i.e., pre-processing in the pulverizing step. The slurry containing the silicon particles after the preliminary pulverization treatment was filtered by a filter having a mesh size of 180 μm to remove coarse particles, and the slurry was further subjected to a fine pulverization treatment by a pulverizer 20, i.e., a sand Mill (in the present embodiment, Star Mill LMZ015 manufactured by Ashizawa Finetech ltd. More specifically, a slurry containing silicon particles obtained by removing silicon chips having a particle size of 180 μm or more is poured into an inlet 21 of a pulverizer 20, and the slurry is subjected to a micro-pulverization treatment in a treatment chamber 22 of a sand mill while being circulated and flowed by a pump 28. A specific example of the beads of the sand mill is zirconia beads having a particle diameter of 0.5 mm. After the slurry containing the finely pulverized silicon particles is recovered, the second liquid is removed by a rotary evaporator 40 which automatically performs vacuum distillation, and as a result of the fine pulverization, fine silicon particles are obtained.

In this embodiment, about 450g of zirconia beads having a particle diameter of 0.5mm were introduced and subjected to a fine pulverization treatment at a peripheral speed of 2908rpm for four hours, whereby silicon fine particles were obtained. Other solutions that can be employed are: in the pulverizing step (S2), one type of pulverizer other than the above-mentioned one type or a combination of two or more types of pulverizers is selected from a group consisting of a ball mill, a sand mill, a jet mill, and a shock wave pulverizer, and the pulverization is performed. As the pulverizer used in the pulverizing step (S2), a manual pulverizer may be used in addition to the automatic pulverizer.

Other solutions that can be employed are: the silicon fine particles obtained in the Grinding step (S2) were further dispersed in a known Grinding Mixer (typically, model 20D Grinding Mixer manufactured by shichuan corporation). When the negative electrode of a lithium ion battery is formed by this dispersion treatment, the dispersibility is improved, and therefore, the negative electrode can be prevented or suppressed from being damaged by the absorption and desorption of lithium with high reliability.

(3) Oxide film removal step (S3)

In the present embodiment, it is one preferable to perform the oxide film removing step (S3). However, even if this oxide film removal step (S3) is not performed, at least some of the effects of the present embodiment can be obtained.

In the oxide film removal step (S3) of the present embodiment, the following processes are performed: the silicon fine particles 2 obtained in the grinding step (S2) are brought into contact with an aqueous solution of hydrofluoric acid or ammonium fluoride. The silicon fine particles 2 obtained in the grinding step (S2) are dispersed by immersing the silicon fine particles 2 in an aqueous solution of hydrofluoric acid or ammonium fluoride. 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 by the stirrer 57, whereby the oxide (mainly silicon oxide) on the surfaces of the silicon fine particles 2 is removed.

The silicon particles with surface oxides partially or completely removed are then separated from the aqueous hydrofluoric acid solution by a centrifuge 58. Next, the fine silicon particles are immersed in a third liquid such as an ethanol solution. The oxide (or oxide film) is originally formed on the surface of the silicon fine particles 2, and the third liquid is removed to obtain silicon fine particles in which the oxide (or oxide film) is partially or completely removed. If the oxide possibly present on the surface of the silicon fine particles 2 is not removed, the silicon fine particles are treated in the negative electrode forming step (S4) described later.

In the oxide film removal step (S3) of the present embodiment, the silicon microparticles are brought into contact with hydrofluoric acid by immersing the silicon microparticles in a hydrofluoric acid or ammonium fluoride aqueous solution, but a step of bringing the silicon microparticles into contact with hydrofluoric acid or an ammonium fluoride aqueous solution by another method may be employed. Other solutions that can be used are, for example: the silicon particles are sprayed with an aqueous hydrofluoric acid solution in a so-called shower manner.

(4) Negative electrode Forming Process (S4)

The negative electrode material and negative electrode manufacturing apparatus 100 of the lithium ion battery of the present embodiment includes the mixing section 60. The silicon fine particles, i.e., the negative electrode active material, are formed in the pulverization step (S2) or in the pulverization step (S2) and the oxide film removal step (S3). The mixing section 60 mixes the fine silicon particles with a negative electrode current collector (e.g., copper foil) using a binder (e.g., carboxymethyl cellulose (CMC) and Styrene Butadiene Rubber (SBR)). A mixture layer is formed by the mixture portion 60, and a negative electrode is formed by the mixture layer.

< other Process >

The silicon fine particles obtained in the grinding step (S2) or in the grinding step (S2) and the oxide film removal step (S3) may be classified, for example, in order to reduce variation in the number distribution and/or volume distribution of the crystallite diameters of the silicon fine particles.

< analysis result of silicon microparticles obtained in the first embodiment >

Silicon particle analysis of SEM and TEM images

Fig. 3A is an SEM (scanning electron microscope) image of an example of the silicon fine particles or the aggregates thereof after the pulverization step (S2) in the first embodiment. Fig. 3B is an enlarged view of an SEM image of an example of the silicon fine particles or the aggregates thereof after the pulverization step (S2) in the first embodiment. Fig. 3C is a diagram showing the first embodiment: (a) a SEM image of another example of the aggregate of the silicon fine particles; (b) (a) enlarged view of a part thereof. Fig. 4 is a view showing a Transmission Electron Microscope (TEM) image of the silicon fine particles of the first embodiment.

As shown in fig. 3A, not only individual silicon particles but also silicon particles shown by Y1 and Y2 or aggregates thereof can be observed. It is extremely interesting to note that, as shown in the Z-sections (a), (B) of FIGS. 3B and 3C, the silicon fine particles or aggregates thereof are aggregates or aggregates in which silicon fine particles, which may be lamellar, are superposed in a multi-layered petal-like or scaly state.

The TEM image shown in fig. 4 focuses on individual silicon microparticles from which another interesting finding can be derived. Specifically, it can be observed that the individual silicon fine particles shown by the region indicated by the white line in fig. 4 are crystalline silicon, i.e., single crystal silicon. Further, at least a part of the silicon fine particles can be observed as crystallites having a cross section of an irregular polygon shape having a size of about 2nm to about 10 nm. In fig. 4, the regions indicated by the white circles show crystal plane orientations.

2. Analysis of crystallite size distribution of silicon microparticles by X-ray diffraction method

Fig. 5 shows the crystallite diameter in the (111) direction of the silicon fine particles of the first embodiment: (a) a distribution diagram of the number distribution of the crystallite grain sizes; (b) volume distribution of crystallite size distribution. Fig. 5 shows the results of analyzing the crystallite size distribution of the silicon fine particles after the grinding step (S2) by X-ray diffraction. In fig. 5(a) and 5(b), the horizontal axis represents the crystallite diameter (nm) and the vertical axis represents the frequency.

From the results of fig. 5(a) and 5(b), it is understood that the number distribution has a mode particle diameter of 1.6nm and a median particle diameter (50% crystallite diameter) of 2.6 nm. In the volume distribution, the mode particle diameter was 6.3nm and the median particle diameter was 9.9 nm. Therefore, it is found that the number distribution has a value of 5nm or less in both the mode particle diameter and the median particle diameter, and more specifically, a value of 3nm or less in both the mode particle diameter and the median particle diameter. It is also known that the volume distribution of the particles has a value of 10nm or less in both the mode particle diameter and the median particle diameter.

From the results of fig. 5(a) and 5(b), it is understood that the silicon fine particles obtained after the grinding step (S2) was carried out by the sand mill grinding method had an average crystallite diameter of about 9.8 nm. The crystallite size distribution of the silicon fine particles after the oxide film removal step (S3) is also substantially the same as that in fig. 5.

Therefore, when the results of fig. 5 and the results of the respective graphs of fig. 3 are combined and analyzed, it can be said that at least the aggregate or the collection of silicon fine particles after the pulverization step (S2) or after the oxide film removal step (S3) is formed by overlapping silicon fine particles, which can be said to have a long diameter of about 100nm or less, in a multi-layer petal-like or scaly state. As is clear from FIGS. 4 and 5, the silicon fine particles are mainly composed of fine crystals having a major axis of 10nm or less.

As shown in fig. 5, it is understood that the silicon fine particles of the present embodiment contain silicon fine particles having a crystallite diameter of 1nm or less. Interestingly, it is also found that the average crystallite diameter in the volume distribution of the silicon fine particles of the present embodiment is about 10 nm. This value can be said to be very small. As described above, further studies have revealed that the apparent volume diameter of the silicon fine particles is in the range of about 100nm or less. In particular, the silicon fine particles used as a negative electrode material for a lithium ion battery described later contain a large amount of ultrafine silicon particles having a crystallite size of 5nm or less in length, and thus the charge-discharge cycle characteristics derived from the silicon fine particles can be more reliably improved.

3. Analysis of crystal plane orientation of crystallites of silicon fine particles based on X-ray diffraction method

Fig. 6(a) is a result of analyzing the result (P) of the X-ray diffraction measurement of the silicon fine particles or the aggregates thereof before the pulverization step (S2) and the result (Q) of the X-ray diffraction measurement of the silicon fine particles or the aggregates thereof after the pulverization step (S2) in a wide angle range. Fig. 6(b) is a partially enlarged view of the result (P) of fig. 6(a), and is a result (R) of analyzing the result of the X-ray diffraction measurement of the silicon fine particles or the aggregates thereof after the pulverization step (S2) of the first embodiment within a limited angle range. The intensities of the respective peaks of the C (002) plane and the C (003) plane shown in fig. 6(b) are shown as follows: about 1 wt% to about 3 wt% of the graphite fine particles are contained in the silicon fine particle group or the aggregate of silicon fine particles. For example, the graphite particle size of the C (002) plane is about 35nm, and the graphite particle size of the C (003) plane is about 75 nm.

As shown in fig. 6(a) and 6(b), it is understood that the half-width of the diffraction peak attributed to Si (111) after the pulverization step (S2) is larger than the diffraction peak attributed to the crystal plane (111) of Si (hereinafter also abbreviated as "Si (111)", other crystal plane orientations are also the same) in the vicinity of 28.4 ° 2 θ before the pulverization step (S2) in the first embodiment. The average crystallite diameter was 9.8nm, calculated from the half-value width of the diffraction peak of Si (111) after the pulverization step (S2) using the scherrer equation. It is extremely interesting that the intensity of the diffraction peak attributed to Si (111) in the vicinity of 28.4 ° after the pulverization step (S2) is significantly greater than the intensity of other diffraction peaks (for example, the intensity of the peak of Si (220) or Si (311)). As shown in fig. 4, the lattice spacing of Si (111) in the lattice of the silicon fine particles after the pulverization step (S2) was 0.31nm (

). From the above results, it is considered that the silicon particles cut by the fixed abrasive grain process and the silicon microparticles formed from the silicon particles are cut out with Si (111) whose bonding force of Si is considered to be the weakest as a fracture surface.

From the above analysis results, it can be said that the silicon fine particles after the pulverization step (S2) of the present embodiment are mainly aggregates in which crystalline silicon fine particles having a crystal plane orientation of (111) are stacked in a multi-layer petal-like or scaly state.

As described above, when the silicon fine particles or the aggregates thereof after the pulverization step (S2) or after the oxide film removal step (S3) of the present embodiment are used for the negative electrode current collector of the lithium ion battery, the following unique effects can be exhibited: lithium ions when ionized from the positive electrode material of a lithium ion battery(Li⁺) After reaching the negative electrode, lithium ions (Li)⁺) Easily enter the folded part gap of the aggregate overlapped in a multi-layer petal-shaped or scaly state, and easily exit from the folded part gap.

< second embodiment >

The lithium ion battery of the present embodiment employs the silicon fine particles prepared in the first embodiment as a negative electrode material. The structure other than the negative electrode material is the same as that of the conventional CR2032 button-type lithium ion battery.

Fig. 7 is a schematic configuration diagram showing a lithium ion battery 500 according to the present embodiment. The lithium ion battery 500 of the present embodiment includes a negative electrode 512 electrically connected to a negative electrode current collector and a negative electrode material 514, a positive electrode 516 electrically connected to a positive electrode current collector and a positive electrode material 518, a separator 520 for electrically insulating the negative electrode current collector and the negative electrode material 514 from the positive electrode current collector and the positive electrode material 518, and an electrolyte 530 in a container 510 of a CR2032 type button cell. To achieve charging and discharging, the lithium ion battery 500 of the present embodiment has an external circuit including a power supply 540 and a resistor 550 connected to the negative electrode 512 and the positive electrode 516.

The following is a method of manufacturing the lithium ion battery 500 of the present embodiment.

The method of manufacturing the negative electrode is specifically as follows. First, about 0.3g of the silicon microparticles prepared in the first embodiment were dispersed in about 10mL (milliliter) of a solution made of a 1 wt% CMC binder aqueous solution and an SBR binder aqueous dispersion (TRD 2001 manufactured by JSR CORPORATION). At this time, the ratio of silicon fine particles, carbon black, CMC binder aqueous solution, and SBR binder aqueous dispersion was changed in the order of 67: 11: 13: 9 by dry weight ratio. Next, a slurry was prepared by mixing with an agate mortar, and the slurry was applied to one surface of a copper foil having a thickness of about 9cm (width) × 10cm (length) of 15 μm so that the thickness became about 100 μm to about 200 μm after drying, followed by drying treatment in air on a hot plate at 80 ℃ for about one hour. The copper foil was then punched with the dry paste into a circular shape of 15.95mm diameter corresponding to a battery standard CR2032 button cell to form the working electrode. The weight of the working electrode was measured, and then the electrode was heated in a glove box under vacuum at 120 ℃ for 6 hours, dried again, and then attached to the inner surface of a negative electrode 512 made of copper foil, thereby producing a negative electrode according to the present embodiment.

Then, as for the positive electrode, since the characteristics of the negative electrode material were evaluated with a lithium ion battery of a half cell structure, a lithium substrate was punched out in a circular shape with a diameter of 13mm and used as the positive electrode 516. Note that, the positive electrode 516 of the lithium ion battery may be replaced by a known positive electrode.

The separator 520 of the present embodiment is a polypropylene porous membrane. The electrolyte 530 of the present embodiment is prepared by mixing Ethylene Carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of 1/1 and adding 1 mol of lithium hexafluorophosphate (LiPF)₆) Dissolved in the mixed solvent (1L), and the amount of the electrolyte 530 injected does not exceed the internal volume (about 1mL) of the CR2032 button cell.

The positive current collector and material 518, positive electrode 516, negative current collector and material 514, negative electrode 512, separator 520, and electrolyte 530 described above are disposed into a container 510 of a CR2032 type button cell. After that, in a glove box filled with argon gas, constituent materials of the separator 520 and the electrolyte 530 were sealed in the container 510 in a state where insulation was maintained between the positive electrode 516 and the negative electrode 512 on the outer frame of the button cell, and thereby a lithium ion battery 500 as a CR2032 type button cell was produced in a trial.

The electrolyte solvent constituting the electrolyte 530 in the present embodiment is, for example, a mixed solvent of a cyclic carbonate including Ethylene Carbonate (EC) and Propylene Carbonate (PC) (polypropylene film) and a chain carbonate including dimethyl carbonate (DMC), diethyl carbonate (DEC), and the like, and an organic solvent. An inorganic salt such as lithium hexafluorophosphate (LiPF) or lithium tetrafluoroborate (LiBF) can be dissolved as a supporting electrolyte in the electrolyte solution solvent.

< Charge-discharge cycle characteristics of lithium ion Battery 500 >

The charge-discharge cycle characteristics of the lithium ion battery 500 having the above-described structure were measured, and the results will be described below. Fig. 8 is a graph showing the charge cycle characteristics of the lithium ion battery 500 of the second embodiment. Fig. 9 is a graph showing the discharge cycle characteristics of the lithium ion battery 500 of the second embodiment.

In each drawing, the horizontal axis indicates the number of times the charge and discharge process is repeated. The a to g shown in the upper part of each figure represent the current density (mA/g) and the charging time during charging. Thus, for example, show: during the time a, the current density was 200(mA/g), and the charging process was performed relatively slowly; the current density was 5000(mA/g) during the time d, and the charging process was rapidly performed.

As shown in fig. 8 and 9, excellent results were obtained in the charge-discharge cycle under the condition of about 1500 (mAh/g): even if the number of cycles reaches 100 times, the charge capacity value and the discharge capacity value are hardly decreased. It was also found that even if the current density varied from 200(mA/g) to 5000(mA/g), the charge capacity value and the discharge capacity value were not substantially affected by the variation. In particular, according to the present embodiment, it is proposed that the charge-discharge cycle characteristics with extremely high stability can be obtained: the lithium ion battery 500 was repeatedly charged and discharged 30 times under the condition that a current density of 5000(mA/g) was applied to the negative electrode of the lithium ion battery 500, and the charge capacity (mAh/g) at the 30 th time was lower than the charge capacity at the 1 st time by 0.5% or less.

As a comparative example, the above charge/discharge cycle characteristics of the lithium ion battery were examined under the same conditions as in the second embodiment, except that the negative electrode was formed using commercially available silicon particles (particle diameter of 1 μm to 2 μm, purity 99.9%, manufactured by soekawa chemical co., ltd.) as a negative electrode active material. As a result, as shown in fig. 9 and 10, it is understood that both the charge capacity value and the discharge capacity value are rapidly (inversely proportional curve-like) deteriorated from the 20 th cycle. More specifically, the charge capacity value and the discharge capacity value decreased from about 1500(mAh/g) to about 800(mAh/g) from the 20 th cycle to the 30 th cycle. The above results show that the lithium ion battery 500 of the second embodiment is significantly superior to the comparative example described above.

In the prior art, graphite is used as a negative electrode active material to form a negative electrode, and the theoretical capacity of a lithium ion battery having the negative electrode is about 370 mAh/g. Therefore, it is apparent that the lithium ion battery 500 of the second embodiment can not only realize a charge and discharge capacity of about 1500mAh/g, which is several times higher than 370mAh/g, but also have a charge and discharge cycle characteristic with extremely high stability. And it has been proved that by employing the silicon fine particles and/or the aggregates thereof of the above-described first embodiment, unlike commercially available silicon particles, a lithium ion battery having a large capacity and excellent charge-discharge cycle characteristics can be realized.

< other embodiment >

In the above embodiments, silicon cutting powder formed during cutting of an ingot or a block of single crystal silicon or polycrystalline silicon is given as an example of a starting material, but other means can be adopted: the silicon cutting powder or the like of the other embodiments is used as a starting material. Specifically, the silicon cutting powder and the like are not limited to those that are inevitably formed in the cutting process of a silicon ingot in the production process of a semiconductor product, and may be those prepared by selecting a silicon ingot of crystalline silicon in advance and uniformly or randomly cutting the silicon ingot by a cutting machine. Silicon chips such as silicon cutting powder and silicon grinding dust which are generally treated as scraps may be used as the starting material of the silicon fine particles in the above embodiments, but the silicon chips may contain fine scraps obtained by pulverizing wafer fragments, waste wafers, and the like. Further, silicon microparticles using a material such as metal silicon cutting powder or silicon abrasive dust as a starting material may be used.

The impurity concentration of the n-type crystalline silicon in each of the above embodiments is not limited. Not only n-type crystalline silicon but also p-type crystalline silicon can be used. The crystalline silicon in each of the above embodiments may be crystalline silicon of an intrinsic semiconductor. Since it is important that electrons move in the negative electrode material of a lithium ion battery, crystalline silicon containing an n-type impurity is preferably used. As shown in fig. 6(b), about 1 wt% to about 3 wt% of the graphite fine particles expressed by the intensity of each peak of the C (002) plane and the C (003) plane are contained in the silicon fine particle group or the aggregate of the silicon fine particles, and therefore, a part or all of the graphite is advantageous for improving the conductivity of the negative electrode material.

The application of the silicon microparticles and the lithium ion battery having the silicon microparticles of the above embodiments is not limited to the button cell structure described in the second embodiment. And thus may also be applied to various devices or apparatuses having or using a lithium ion battery having a larger capacity than the button cell structure. Other schemes of negative electrode materials can also be adopted: a material obtained by mixing graphite (typically graphite) with the silicon mixed powder of each of the above embodiments.

As an alternative to the negative electrode material and negative electrode manufacturing apparatus 100 of the lithium ion battery shown in fig. 2 of the first embodiment, a negative electrode manufacturing apparatus 200 of the lithium ion battery shown in fig. 12 may be used. Specifically, in the apparatus 200 for manufacturing a negative electrode of a lithium ion battery, the cleaning machine 10 for cleaning silicon chips and the like formed during the cutting of silicon also functions as the crusher 20, and the cleaned silicon chips and the like are crushed to form silicon fine particles, from the viewpoint of facility simplification and/or production cost reduction. Therefore, in the apparatus/method shown in fig. 12, for example, by selecting large-diameter beads in the washing step and small-diameter beads in the pulverizing step, silicon fine particles used as a negative electrode material of a lithium ion battery can be obtained.

The embodiments disclosed above are described only for the purpose of illustrating the embodiments, and are not described for the purpose of limiting the present invention. Further, modifications that include other combinations of the embodiments and are within the scope of the present invention also belong to the scope of the claims of the present invention.

Industrial applicability-

The silicon fine particles and the lithium ion battery having the same according to the present invention can be applied to various devices or apparatuses as follows: various power generation or storage devices (including small-sized power storage devices for home use and large-sized power storage systems), smart phones, portable information terminals, portable electronic devices (mobile phones, portable music players, notebook computers, digital cameras, and digital video cameras), electric vehicles, Hybrid Electric Vehicles (HEV), plug-in hybrid electric vehicles (PHEV), motorcycles that use motors as power sources, tricycles that use motors as power sources, other transportation machines, vehicles, and the like.

Claims

1. A negative electrode material for a lithium ion battery has silicon fine particles obtained by pulverizing crystalline silicon.

2. The negative electrode material of the lithium ion battery according to claim 1, wherein the crystalline silicon is cutting powder or cutting chips cut by a fixed abrasive wire saw.

3. The negative electrode material for a lithium ion battery according to claim 1 or 2, wherein the silicon fine particles are formed by pulverizing the crystalline silicon by a sand mill.

4. The negative electrode material for a lithium ion battery according to any one of claims 1 to 3, wherein the intensity of a diffraction peak attributed to Si (111) in the vicinity of 28.4 ° with respect to 2 θ of silicon fine particles formed from crystalline silicon is higher than the intensities of other diffraction peaks, as measured by X-ray diffraction.

5. The negative electrode material for a lithium ion battery according to any one of claims 1 to 4, comprising crystallites, which are observable on an image of a transmission electron microscope, form the silicon fine particles and have irregular polygonal shapes.

6. A lithium ion battery has a negative electrode material having silicon fine particles obtained by pulverizing crystalline silicon.

7. The lithium ion battery of claim 6, wherein the crystalline silicon is cutting powder or swarf cut by a fixed-abrasive wire saw.

8. The lithium ion battery of claim 6 or 7, wherein the silicon particles are formed by crushing the crystalline silicon by a sand mill.

9. The lithium ion battery according to any one of claims 6 to 8, wherein the intensity of a diffraction peak attributed to Si (111) in the vicinity of 28.4 ° with respect to 2 θ of silicon fine particles formed from crystalline silicon is measured by X-ray diffraction and is greater than the intensities of other diffraction peaks.

10. The lithium ion battery according to any one of claims 6 to 9, the negative electrode material comprising crystallites, which are observable on an image of a transmission electron microscope, form the silicon microparticles and have irregular polygonal shapes.

11. The lithium ion battery according to any one of claims 6 to 10, which is repeatedly charged and discharged 30 times under a condition that a current density of 5000(mA/g) is provided to a negative electrode having the negative electrode material, and a charge capacity (mAh/g) of the 30 th time is lower than a charge capacity of the 1 st time by 0.5% or less.

12. A device having the lithium ion battery of any of claims 6-11.

13. A device for producing a negative electrode material for a lithium ion battery has a pulverization unit for pulverizing crystalline silicon to form silicon microparticles.

14. The apparatus for manufacturing a negative electrode material for a lithium ion battery according to claim 13, wherein the crystalline silicon is cutting powder or cutting chips cut by a fixed abrasive wire saw.

15. The apparatus for manufacturing an anode material for a lithium ion battery according to claim 13 or 14, wherein the silicon fine particles are formed by pulverizing the crystalline silicon by a sand mill.

16. The apparatus for producing a negative electrode material for a lithium ion battery according to any one of claims 13 to 15, which has a pulverization portion for forming silicon fine particles, wherein the intensity of a diffraction peak attributed to Si (111) in the vicinity of 2 θ ═ 28.4 ° can be measured by X-ray diffraction, and the intensity is larger than the intensities of other diffraction peaks.

17. A device for manufacturing a negative electrode of a lithium ion battery has a pulverization portion for pulverizing crystalline silicon to form silicon fine particles, and the silicon fine particles are used as a negative electrode material.

18. The apparatus for manufacturing a negative electrode of a lithium ion battery according to claim 17, wherein the crystalline silicon is cutting powder or cutting chips cut by a fixed abrasive wire saw.

19. The apparatus for manufacturing a negative electrode of a lithium ion battery according to claim 17 or 18, wherein the silicon fine particles are obtained by pulverizing the crystalline silicon with a sand mill.

20. The apparatus for producing a negative electrode for a lithium ion battery according to any one of claims 17 to 19, which has a pulverization portion for forming silicon fine particles, and which is capable of measuring, by X-ray diffraction, the intensity of a diffraction peak attributed to Si (111) in the vicinity of 28.4 ° with respect to 2 θ, which is larger than the intensities of other diffraction peaks, and which is used as a negative electrode material.

21. A method for producing a negative electrode material for a lithium ion battery includes a pulverization step for pulverizing crystalline silicon to form silicon fine particles.

22. The method for manufacturing the negative electrode material of the lithium ion battery according to claim 21, wherein the crystalline silicon is cutting powder or cutting chips cut by a fixed abrasive wire saw.

23. The method for manufacturing an anode material for a lithium ion battery according to claim 21 or 22, wherein the silicon fine particles are obtained by pulverizing the crystalline silicon with a sand mill.

24. The method for producing a negative electrode material for a lithium ion battery according to any one of claims 21 to 23, which comprises a pulverization step for forming silicon fine particles, wherein the intensity of a diffraction peak attributed to Si (111) in the vicinity of 2 θ ═ 28.4 ° can be measured by X-ray diffraction, and the intensity is larger than the intensities of other diffraction peaks.

25. A method for manufacturing a negative electrode for a lithium ion battery includes a pulverization step for pulverizing crystalline silicon to form silicon fine particles, which are used as a negative electrode material.

26. A method for producing a negative electrode for a lithium ion battery, comprising a pulverization step for forming silicon fine particles, wherein the intensity of a diffraction peak attributed to Si (111) in the vicinity of 28.4 DEG 2 theta of the silicon fine particles can be measured by X-ray diffraction and is greater than the intensities of other diffraction peaks, and the silicon fine particles are used as a negative electrode material.