KR101365112B1 - Preparing method of uniform carbon/silicon composite - Google Patents

Abstract

The present invention relates to a method of improving the performance of a composite of silicon and carbon (Si / C), which is a negative electrode for a lithium ion secondary battery, according to the present invention, comprising the steps of: A) isostatic pressing of carbon powder (Cold Isostatic Pressing); B) grinding the pressurized carbon into fine powder using a high speed mill; C) complexing the nano-size silicon dispersed by the pulverized fine carbon powder and a dispersant; And D) provides a method for producing a carbon / silicon composite negative electrode material for a lithium secondary battery comprising the step of spherical carbon / silicon composite. After pressurizing the carbon, it is pulverized into fine powder using a blade type high speed grinder, and the pulverized carbon is well dispersed in nanosilicone using a planetary mill, which is a ball-rotating machine, and spray sprayer is used as a spray dryer. By preparing a spherical homogeneous composite, it was possible to minimize the volume expansion of the composite and increase the mixture density.

Description

Method of producing uniform carbon / silicone composite using carbon milling by equal pressure / fast milling and pulverized carbon {PREPARING METHOD OF UNIFORM CARBON / SILICON COMPOSITE}

The present invention relates to a technology for improving the performance of the composite of silicon and carbon (Si / C), which is a negative electrode material for a lithium ion secondary battery, and specifically, pulverizes the carbon to form fine powder, which is then dispersed well with silicon. The present invention relates to the production of a carbon / silicon composite negative electrode material for lithium secondary batteries that is spherically complexed and then spherical.

Recently, as commercialization of electric vehicles has progressed rapidly, a lithium ion secondary battery having high capacity, high stability, and long life performance is required. Components that influence the performance of the lithium ion secondary battery include a positive electrode, a negative electrode, an electrolyte, a separator, and the like, in particular, depending on the performance of the positive electrode and negative electrode material greatly affects the battery characteristics. Although lithium cobalt oxide is mainly used as a cathode material and graphite is used as a cathode material in small lithium ion secondary batteries that are currently used, the graphite material, which is a cathode material, has a theoretical capacity of 372 mAh / g, which is low in capacity for use in electric vehicles. have.

As a material that can replace graphite, silicon materials have been highlighted. Silicon is a cathode and has a high capacity of 4000 mAh / g. However, these inserts have not been practically applied. The main reason for this is because the volume expansion during the lithium insertion is severe, causing decomposition of the electrode, which results in poor cycle characteristics. Therefore, studies on carbon / silicon composites are being conducted in order to supplement stable cycle characteristics of carbon and high capacity of silicon.

Many researchers have reported electrochemical properties of different complexation methods and starting materials, and it has been demonstrated that the properties vary with methods and starting materials. For example, when silicon and carbon were mixed by mechanical milling, they could have a high capacity in the first cycle, but thereafter, a sharp decrease in capacity occurred during the cycle.

The present inventors studied their effective compounding methods, and when the carbon is pulverized and then composited with nano-sized silicon and granulated into spherical particles, the volume expansion of the silicon is alleviated, side reactions are suppressed, and the mixture density is improved. The present invention has been found to have an effect.

Accordingly, an object of the present invention is to provide a method for producing a carbon / silicon composite for a lithium secondary battery in which volume expansion of silicon is alleviated, side reactions are suppressed, and the mixture density is improved.

In addition, another object of the present invention is to provide a method for producing a negative electrode using the carbon / silicon composite.

According to the present invention to achieve the above object, A) isostatic pressing the carbon powder (Cold Isostatic Pressing); B) grinding the pressurized carbon into fine powder using a high speed mill; C) complexing the nano-size silicon dispersed by the pulverized fine carbon powder and a dispersant; And D) provides a method for producing a carbon / silicon composite negative electrode material for a lithium secondary battery comprising the step of spherical carbon / silicon composite.

The carbon powder in step A) is preferably a coarse powder of 10 ~ 30㎛. The equivalent pressure molding can be carried out for 1 to 2 hours at a pressure of 1500 ~ 2500barr. In the step B), the high-speed grinding is preferably performed at a speed of 10000 rpm or more. In the step C), the fine carbon powder and the nano-sized silicon are preferably mixed in a weight ratio of 90:10 to 70:30. As the dispersant, EG, PEG or HPC may be used. The compounding is preferably carried out by a planetary mill. In step D), the spheronization of the carbon / silicon composite is preferably performed by spray drying. The carbon / silicon composite has a size of 5 ~ 15㎛, characterized in that it has a compact spherical shape.

According to the present invention to achieve the above another object, A) isostatic pressing the carbon powder (Cold Isostatic Pressing); B) grinding the pressurized carbon into fine powder using a high speed mill; C) complexing the nano-size silicon dispersed by the pulverized fine carbon powder and a dispersant; D) spheronizing the carbon / silicon composite; And E) provides a method for producing a carbon / silicon composite negative electrode for a lithium secondary battery comprising the step of preparing a negative electrode using the carbon / silicon composite negative electrode material as a negative electrode active material.

According to the manufacturing method of the negative electrode material of the present invention, it is possible to reduce the problem of silicon volume expansion by dispersing silicon well on the surface of carbon, and also to improve the electrode density by spherical composites to produce a material having high energy density. In addition, it can improve the electrochemical properties by inhibiting side reactions. By manufacturing the carbon / silicon composite material, which is a negative electrode active material, it is possible to develop a negative electrode material having a mixture density, cycle characteristics, and high capacity, and as a result, it is applied to automobile batteries as a negative electrode material to replace graphite, which is difficult to use in electric vehicles requiring high capacity. This has the advantage of being possible.

1 is a scanning microscope photograph of an isostatically formed carbon powder according to an embodiment of the present invention.
2 is a scanning microscope photograph of carbon powder pulverized into fine powder according to an embodiment of the present invention.
3 is a scanning micrograph and X-ray diffraction graph of nano silicon dispersed in a dispersant according to one embodiment of the present invention.
Figure 4 is a scanning micrograph and X-ray diffraction analysis graph of the nano carbon / silicon composite prepared according to an embodiment of the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

According to one embodiment of the invention, A) isostatic pressing the carbon powder (Cold Isostatic Pressing); B) grinding the pressurized carbon into fine powder using a high speed mill; C) complexing the nano-size silicon dispersed by the pulverized fine carbon powder and a dispersant; And D) spheronizing the carbon / silicon composite to produce the carbon / silicon composite.

In general, carbon as a negative electrode active material has a low capacity and, in the case of silicon, has a large volume expansion and thus worses cycle characteristics, thereby causing decomposition of the electrode, thereby causing safety problems. Combining the two materials is desirable because it can complement the low capacity of carbon and high capacity of silicon, and the good cycle characteristics of carbon and the bad cycle characteristics of silicon.

The carbon powder in step A) is preferably a coarse powder of 10 ~ 30㎛. The present invention is characterized in that the carbon powder is first subjected to cold isostatic pressing and then pulverized to produce finely divided carbon. Specifically, the carbon of the crude powder which is pulverized only in the horizontal direction and difficult to pulverize in the vertical direction is cracked in the vertical direction by applying an equal pressure (Cold Isostatic Press), and granulated, and the carbon is pulverized by a high-speed grinder. . First of all, it is important to prepare pulverized carbon in small size, and for this purpose, an equal pressure was applied to the surface of the carbon before pulverization. When carbon is pulverized after applying an equal pressure in the vertical direction, it is pulverized well. Acetone, ethanol, and anhydrous alcohol can be used as the solvent during isostatic pressing. Since the degree of pressure on the surface of the carbon varies depending on the amount of powder, the pressure and the amount of carbon can be appropriately controlled to form the equivalent pressure. . The equivalent pressure molding may be carried out for 1 hour or more, preferably 1 to 2 hours at a pressure of 1500 ~ 2500barr.

After the equivalent pressure molding of the carbon powder, it is pulverized with a high speed mill to prepare fine powder. In the step B), the high-speed grinding is preferably performed at a speed of 10000 rpm or more. Subsequently, the carbon powder of the fine powder prepared in the above step and the nano-sized silicon are mixed and complexed. At this time, the fine carbon powder and the nano-sized silicon are preferably mixed in a weight ratio of 90:10 to 70:30. In this case, the nano-sized silicon is preferably used dispersed in a dispersant. When dispersing the silicone with the addition of a dispersant, the dispersant should not exceed 3% of the total amount. If it is more than 3%, it may interfere with future electrochemical properties. In this case, as the dispersant, ethylene glycol, polyethylene glycol, or hydroxy poly cellulose may be used. The compounding is preferably carried out by a planetary mill.

Then it is spherical form using a spray drier to improve the mixture density of the composite. In step D), the spheronization of the carbon / silicon composite is preferably performed by spray drying. When using a spray dryer to spheronize, the rate of slurry injection is preferably slowly injected, and the slurry is preferably added while stirring continues on the stirrer. In addition, after preparing the slurry and stirred for 24 hours it is good to spray drying. The spherical carbon silicon composite prepared by the present invention was analyzed by the scanning electron microscope, and the result was a range of 5-15 μm, showing a dense spherical shape in which fine particles were firmly agglomerated.

According to one embodiment of the invention A) isostatic pressing the carbon powder (Cold Isostatic Pressing); B) grinding the pressurized carbon into fine powder using a high speed mill; C) complexing the nano-size silicon dispersed by the pulverized fine carbon powder and a dispersant; D) spheronizing the carbon / silicon composite; And E) there is provided a method for producing a carbon / silicon composite negative electrode for a lithium secondary battery comprising the step of preparing a negative electrode using the carbon / silicon composite negative electrode material as a negative electrode active material. In the case where the negatively-dispersed spherical carbon silicon composite was prepared as a negative electrode active material for a lithium ion secondary battery and used in the battery, an excellent battery was obtained due to high capacity and excellent cycle characteristics.

[Example]

Hereinafter, the present invention will be described in detail by way of the following examples and test examples, but the present invention is not limited to these examples.

Example  1: carbon Equivalent pressure  Molding

100 ml of acetone and 1 g of carbon having a size of 10 to 30 μm were placed in a vial, and the carbon was dispersed for 1 hour using sonic. In order to perform cold isostatic press, carbon dispersed in a yellow rubber container and a solvent are added and the pressure is applied at 2000 barr for 1 hour. After the end of the operation is dried for 24 hours at 80 ℃ using a dryer to obtain a carbon powder. A scanning electron micrograph of the equivalent pressure carbon is shown in FIG. 1.

Example  2: Preparation of Carbon Fines

The carbon powder dried in the method of grinding the carbon precursor prepared in Example 1 by using a high speed mixer corresponding to 10000rpm or more was ground using a high speed mixer. The obtained carbon powder has an average particle diameter of 10 μm, and a scanning electron micrograph of the pulverized carbon is shown in FIG. 2.

Example  3: Preparation of Carbon / Silicon Composite

First, nano-sized silicon was dispersed using a dispersant. 100 ml of acetone and 1 g of nanosilicon were added thereto, followed by sonication for 1 hour, followed by addition of 2% ethylene glycol (Ethylene glycol). The zeta potentials of the dispersed and undispersed silicon were measured, and high zeta potential values were determined by adding a dispersant. Scanning electron micrographs and X-ray diffraction analysis of the dispersed silicon are shown in FIG. 3.

The finely divided carbon prepared in Example 2 and the dispersed nano-sized silicon were mixed and complexed. The pulverized carbon and the dispersed silicon were mixed in acetone solvent for 2 hours at 200 rpm using a planetary mill.

Example  4: of carbon / silicon composite Sphericalization

After stirring the carbon / silicon composite in distilled water, the binder PVA was added and stirred for 24 hours. After that, the spray dryer was carried out when the inlet 200 degrees outlet 120 degrees. In this case, the scanning electron microscope of the spherical carbon / silicon composite is shown in FIG. 4.

As a result of fabricating a battery including a negative electrode prepared using the spherical carbon / silicon composite prepared in Example 4, the battery showed a stable cycle characteristic of 80% even after 50 cycles, and the capacity was 680 mAh / g. I got it.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the scope of the present invention is not limited to the disclosed embodiments, but various changes and modifications may be made without departing from the spirit and scope of the present invention. And this is also within the scope of the present invention.

Claims (8)

A) cold isostatic pressing the carbon powder;
B) pulverizing the pressurized carbon into fine powder using a high speed mill;
C) complexing by mixing the pulverized carbon powder and the nano-sized silicon dispersed by a dispersant in a weight ratio of 90:10 to 70:30; And
D) spheronizing the carbon / silicon composite
Method of producing a carbon / silicon composite. The method of claim 1,
The carbon powder in the step A is a coarse powder of 10 ~ 30㎛ characterized in that the equivalent pressure molding for 1 to 2 hours at a pressure of 1500 ~ 2500barr
Method of producing a carbon / silicon composite. 3. The method of claim 2,
The equivalent pressure molding is characterized by using acetone, ethanol, anhydrous alcohol as a solvent
Method of producing a carbon / silicon composite. The method of claim 1,
The high speed grinding in step B) is performed at a speed of 10000 rpm or more.
Method of producing a carbon / silicon composite. delete The method of claim 1,
In the step C), the dispersing agent is ethylene glycol, polyethylene glycol, or hydroxy poly cellulose.
Method of producing a carbon / silicon composite. The method of claim 1,
The complexing is characterized in that the wet mixing is carried out for 2 hours at 200rpm using a planetary mill (Planetary mill)
Method of producing a carbon / silicon composite. The method of claim 1,
The carbon / silicon composite is a method of producing a carbon / silicon composite, characterized in that the sphere of 5 ~ 15㎛ size.

Images