KR101718367B1 - Anode material for lithium ion secondary battery which is composed of carbon and nanosilicon diffused on the conducting material and the manufacturing method thereof - Google Patents

Abstract

The anode active material for a lithium ion secondary battery composed of a composite of nanosilicon and carbon dispersed in a conductive material according to the present invention comprises a nanosilicon 2, a conductive material 3 and a coke 4, Is dispersed in the conductive material (3), and the relative weight ratio of the nanosilicone (2) and the conductive material (3) is in the range of 1: 0.3 to 1: 5. The method for manufacturing an anode active material for a lithium ion secondary battery according to the present invention comprises dispersing nanosilicon in a conductive carbon black or a carbon nanotube, mixing the mixture in a pitch, and heat-treating the composite at a temperature of 600 to 1500 ^° C to form a composite of nanosilicon and carbon There is an effect that the nanosilicon in the composite is surrounded by the conductor and the lifetime shortening due to the volume expansion is remarkably improved.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anode active material for a lithium ion secondary battery comprising a composite of nanosilicon and carbon dispersed in a conductive material and an anode active material for a lithium ion secondary battery,

The present invention relates to a negative electrode active material for a lithium ion secondary battery comprising a composite of nanosilicon and carbon dispersed in a conductive material and a method of manufacturing the same, and is intended to solve the deterioration of the service life of a silicon negative electrode according to the volume expansion of silicon. Particularly, the present invention relates to a novel effect of dispersing nanosilicon in a conductive material and complexing the dispersion by heat treatment with carbon to thereby reduce the unusable portion of silicon due to volume expansion and structural collapse due to the conductors present in the nanosilicon- .

Lithium ion secondary batteries have been widely used as power sources for portable devices since they appeared in 1991 as small-sized, lightweight, and large-capacity batteries. 2. Description of the Related Art In recent years, with the rapid development of the electronics, communication, and computer industries, camcorders, mobile phones, notebook PCs, and the like have been remarkably developed and demand for lithium ion secondary batteries as power sources for driving these portable electronic information communication devices .

In recent years, the global eco-friendly automobile market has grown rapidly in response to instability of global oil prices and global environmental regulations due to global warming. In addition to the existing centralized, distributed power generation system that relies on large power plants, Smart Grid) system, the development of rechargeable batteries for energy storage, especially the development of high energy density electrode materials, has become very important.

In addition, portable electronic devices such as mobile phones, tablet PCs, notebook PCs, PDAs, and the like are becoming more diverse, and miniaturization trends are required to increase the energy density of batteries used as power sources.

Graphite has been continuously used as an anode material for lithium secondary batteries for mobile devices. In particular, natural graphite has recently been replacing artificial graphite because of its price advantage. However, graphite has a theoretical capacity limit of 371 mAh / g. In order to overcome this capacity limit and achieve high energy density, research on silicon material having a large theoretical capacity of 4200 mAh / g has been concentrated, Has a disadvantage in that although the theoretical capacity is large, the volume increases up to four times at the time of filling, and the stress inside the silicon is cracked to cause the structure to collapse. This structural collapse of the silicon prevents the electron transfer of the electrode, resulting in a space that can not be used in the electrode, resulting in a decrease in the capacity of the silicon and a reduction in the life span.

A technique for coating silicone on the surface of graphite as a method for overcoming the disadvantages of such a silicon material and utilizing its advantages has been disclosed in Korean Patent No. 1219171 (Patent Application No. 10-2006-0061064). However, As the resistance increases, the thickness must be reduced. As a result, there is a problem that the capacity limit of 500 mAh / g or less is required for maintaining the life.

The composite of silicon and amorphous carbon is disclosed in Korean Patent No. 595896, Patent No. 1365112, Patent No. 830612, Patent Application No. 10-2011-0097597, and Patent Application No. 10-2012-0048236, A small amount of silicon should be included in order to suppress the expansion and maintain the life-span characteristics, which is due to the conductive drop in silicon.

The present invention has been proposed in order to solve the deterioration of the service life of a silicon-based anode according to the above-mentioned volume expansion. The present invention relates to a method of dispersing nanosilicon in a conductive material and heat- To reduce the unusable part of the silicon due to volume expansion and structural collapse due to the conductors present in the cavity.

In addition, the present invention makes it possible to serve as a buffer for suppressing the structural collapse due to volume expansion due to the amorphous carbon existing in the conductor and the composite. Particularly, the nanosilicon is mixed with carbon black or carbon nanotubes, Nanosilicon is dispersed in the conductor, mixed with pitch, and annealed at 500 to 1400 ^o C to produce a carbon-nanosilicon composite.

It is an object of the present invention to provide a negative electrode material for a lithium secondary battery with remarkably improved life characteristics, and a method for manufacturing such a negative electrode active material for a lithium secondary battery.

In order to achieve the above object, a negative electrode active material for a lithium ion secondary battery composed of a composite of nanosilicon and carbon dispersed in a conductive material provided by the present invention includes nanosilicon (2), a conductive material (3), and a coke Wherein the nanosilicon particles are dispersed in the conductive material 3 and the relative weight ratio of the nanosilicon 2 and the conductive material 3 is in the range of 1: 0.3 to 1: 5 do.

In order to achieve the above object, the present invention also provides a method for manufacturing a negative electrode active material for a lithium ion secondary battery comprising a composite of nanosilicon and carbon dispersed in a conductive material provided by the present invention, comprising mixing a nanosilicon (2) and a conductive material Thereby forming a first mixture in which the particles of the nanosilicon (2) are dispersed homogeneously in the conductive material (3); And a second step of mixing the first mixture with a pitch material and then heat-treating the mixture in an inert atmosphere at 500 to 1400 ° C to produce a composite (1) of nanosilicon and carbon.

In order to accomplish the above object, the present invention provides a method for manufacturing a negative electrode active material for a lithium ion secondary battery comprising a composite of nanosilicon and carbon dispersed in a conductive material provided by the present invention, which comprises mixing nanosilicon (2) and a conductive material A first step of making particles of the nanosilicon (2) to be homogeneously dispersed in the conductive material (3); And a second step of mixing the first mixture with a polymer material and then heat-treating the composite material in an inert atmosphere at 500 to 1400 ° C to produce a composite material (1) of nanosilicon and carbon.

In addition, a method for manufacturing a negative electrode active material for a lithium ion secondary battery comprising a composite of nanosilicon and carbon dispersed in a conductive material according to the present invention is characterized in that natural graphite is added to the composite of nanosilicon and carbon produced in the second step 3: 7 to 7: 3 by weight.

In the method for manufacturing a negative electrode active material for a lithium ion secondary battery comprising a composite of nanosilicon and carbon dispersed in a conductive material according to the present invention, the nanosilicon (2) has a particle size in a range of 10 to 500 nm, The conductive material 3 is characterized by including at least one material selected from the group consisting of carbon nanotubes, carbon black, graphene sheet, ground carbon, and the like.

According to the negative electrode active material for a lithium ion secondary battery comprising a composite of nanosilicon and carbon dispersed in the conductive material according to the present invention, the composite of nanosilicon and carbon dispersed in the conductive material maintains the conductivity of silicon well, By acting as a space buffering agent, the lifetime of the lithium ion secondary battery can be remarkably improved.

FIG. 1 is a flowchart illustrating a method for manufacturing a negative electrode active material for a lithium ion secondary battery and a method for testing the same, the composite comprising nanosilicon and carbon dispersed in a conductive material according to the present invention.
2 is an anomaly of a carbon-nanosilicon composite.
FIG. 3 is a table summarizing the types of conductor materials used in Examples of the present invention (Examples 1 to 4) and Comparative Examples, and the composition ratio, efficiency, capacity, and service life between the mixed materials.
4 is a scanning electron microscope (SEM) photograph of a nanosilicone 2 dispersed in a carbon nanotube 3 as a conductive material in Example 1 of the present invention.
5 is a scanning electron micrograph (SEM) photograph of a nanosilicon-carbon composite material 1 in which nanosilicon particles 2 are dispersed in a carbon nanotube 3 as a conductive material in Example 1 of the present invention to be.
6 is an SEM photograph of nanosilicon (2) and nanosilicon-carbon composite (1) dispersed in a conductive material in Example 3 of the present invention.
7 is an SEM photograph showing a state in which nanosilicon 2 is dispersed in a carbon black 3a as a conductive material in Example 4 of the present invention.
8 is an SEM photograph of a nanosilicon and carbon composite 1 in which nanosilicon 2 is dispersed in carbon black 3a as a conductive material in Example 4 of the present invention.
9 is an SEM photograph of the nanosilicon (2) and the carbon composite material (100) according to Comparative Example 1.
10 is a graph showing the capacity curves of Examples 1, 2, 3, 4 and Comparative Example 1 in comparison with the capacity curves of Examples 1, 2, 3 and 4. FIG.
11 is a graph showing life curves of Examples 1, 2, 3, 4 and Comparative Example 1 of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The negative electrode active material for a lithium ion secondary battery comprising a composite of nanosilicon and carbon dispersed in a conductive material according to the present invention and a manufacturing method thereof will be described in detail with reference to the accompanying drawings.

FIG. 1 is a flowchart illustrating a method for manufacturing a negative electrode active material for a lithium ion secondary battery and a method for testing the same, the composite comprising nanosilicon and carbon dispersed in a conductive material according to the present invention. 1, the structure of a negative electrode active material manufacturing method of the present invention will be described.

1. Preparation of precursor (step S1)

First, the nanosilicon and the conductive material are mixed with a ball mill to uniformly disperse the nanosilicon in the conductive material as a whole. Ball milling is performed by mixing a mixture of active material and ball in a soft container in a ratio of 1: 1 to 1:50, the diameter of the ball is 0.1 to 3 mm, and the rotation speed of the ball mill is 50 to 300 rpm.

The nanosilicon has a size of 10 to 500 nm and is not limited to a manufacturing method and a form. Examples of the conductive material include carbon black, carbon nanotube, graphene sheet, ground carbon, and the like .

As the ball mill container, soft material such as HDPE, PE, PP, TEFLON and PTFE can be applied.

After the ball mill, the nanosilicon particles must be uniformly adsorbed in the conductive material, and the nanosilicon particles are coagulated in the conductive material with a certain size.

2. Preparation of nanosilicon, conductor mixture and carbon composite (S2)

The mixture of nanosilicon and conductor is mixed with pitch or polymer and heat treated at 500 ~ 1400 ^o C in inert atmosphere to produce nanosilicon and carbon composite.

The above-mentioned pitch type includes coal tar pitch, petroleum pitch, PVA, PVC, PVdF, PS, and the like.

The precursor and the pitch or polymer may be mixed with the precursor in the solid phase or the liquid phase, and water, alcohols, NMP, benzene, quinoline or the like may be used as the solvent for the liquid phase mixing.

3. Preparation of electrode and test cell (step S3)

The prepared nanosilicon and carbon composite were used as a negative electrode active material, PVdF as a binder and carbon black (Super-P) as a conductive agent, and their mixing ratios were set at a weight ratio of 60:25:15 to prepare a negative electrode. Lithium metal was used as a counter electrode in the prepared cathode, a separator was used between both electrodes, and an electrolyte was injected to manufacture a pouch type cell.

Examples of the solvent of the electrolytic solution usable as the above include esters such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) and vinyl (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and di (methyl ethyl ketone) Aliphatic carboxylic acid esters such as noncyclic carbonate such as propylene carbonate (DPC), methyl formate, methyl acetate (MA), methyl propionate (MP) and ethyl propionate (MA) And cyclic carboxylic acid esters such as butylolactone (GBL) and the like. In particular, a mixture of a cyclic carbonate of ethylene carbonate (EC), propylene carbonate (PC) and a cyclic carbonate of dimethyl carbonate (DMC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) is preferred.

A lithium salt dissolved in this solvent is _{LiClO₄, LiBF₄, LiPF 6, LiAlCl} 4, LiSbF 6, LiSCN, LiCF 3 SO₃, LiCF 3 CO₂, Li (CF3SO₂) ₂, LiAsF 6, LiN (CF 3 SO₂) ₂, LiB ₁₀ Cl _10, lower aliphatic carboxylic acid lithium (lithium), chloroborane lithium (chloro borane lithium), four-phenyl lithium borate, or _{LiN (CF 3 SO 2) (} C 2 F 5 SO 2), LiN (CF 3 SO 2 ), LiN (C ₂ F ₅ SO ₂ ) ₂ and LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ). These may be used alone or in any combination insofar as the effects of the present invention are not impaired. Of these, it is particularly preferable to include LiPF ₆ .

The separator (separator) is mainly made of a polyethylene-based or polypropylene-based polymer such as porous polyethylene.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to these Examples.

≪ Example 1 >

(1) Preparation of a ball mill mixture

5 g of nanosilicon having a size of 100 nm and 5 g of carbon nanotubes were mixed, and 200 g of balls were put into a 1 L HDPE vessel and ball milled in a ball miller at a speed of 100 rpm. The shape after mixing with the ball mill is shown in Fig. It can be confirmed that nanosilicon (2) particles are evenly adsorbed on the surface of the carbon nanotubes (3).

(2) Production of nanosilicon and carbon composite

20 g of the coal tar pitch was dissolved in an appropriate amount of N-methylpyrrolidone (NMP), 10 g of the ball mill mixture prepared above was put into the dissolved solution, and the mixture was placed in a quartz tube. The temperature was elevated to 1100 ^° C, 4 ^° C and maintained for 1 hour. Through these processes, nanosilicon and carbon composites were fabricated. The shape of the composite thus prepared is shown in FIG. 5, wherein the <b> drawing of FIG. 5 shows that the carbon mixture 4 is entirely covered with the ball mill mixture.

(3) Electrochemical evaluation of nanosilicon and carbon composites

The prepared nanosilicon and carbon composite were used as a negative electrode active material, and PVDF as a binder and carbon black (Super-P) as a conductive material were mixed at a weight ratio of 60:25:15 to prepare a negative electrode.

To the thus prepared negative electrode and lithium foil as a counter electrode, a porous polyethylene membrane (Celgard 2300, thickness: 25 mu m) was used as a separator, and a mixture of ethylene carbonate and diethyl carbonate in a volume ratio of 1: 2 was added LiPF ₆ Was dissolved in a concentration of 1 mol, a pouch battery was manufactured according to a conventional manufacturing process.

When the battery was discharged using a charge-discharge device, the battery was discharged at a constant current of 0.2 C to 0.01 V, at a constant voltage of 0.01 V to 0.05 C, and then charged to a constant current of 2.0 V The battery capacity and efficiency at 25 [deg.] C were evaluated.

The lifetime characteristics were the same as above except that 0.5C was used as a constant current during discharging and charging. The charging / discharging curve is shown in Fig. 10 and the life curve is shown in Fig. 11. It can be seen that the capacity of the battery is maintained at 733 mAh, the efficiency is 72.6%, and the lifetime is 92.3% up to 30 cycles.

&Lt; Example 2 >

(1) Manufacture of batteries

m 천연흑연을 50:50으로 음극 혼합하여 음극 활물질로 하고, 바인더로 PVDF, 도전제로 카본블랙(Super-P)를 사용하여 80:20으로 음극을 제조하였다. 제조된 음극을 상기의 실시예1의 전지 제조와 동일하게 용량 및 수명을 측정하여, 도10 및 도11에 표시하였다. Manufactured nanosilicon and carbon composite and size 10

m natural graphite was mixed with the negative electrode at a ratio of 50:50 to prepare a negative electrode active material, and a negative electrode was prepared at 80:20 using PVDF as a binder and carbon black (Super-P) as a conductive agent. The prepared negative electrode was measured for capacity and lifetime in the same manner as in the preparation of the battery of Example 1, and shown in Figs. 10 and 11. Fig.

By mixing natural graphite together, the capacity of the battery was reduced to 480mAh / g, but the life span was maintained at 94.8% up to 30 cycles.

&Lt; Example 3 >

(1) Preparation of a ball mill mixture

Was prepared in the same manner as in Example 1 except that 2.5 g of the carbon nanotubes was used instead of 5.0 g of the carbon nanotubes.

(2) Production of nanosilicon and carbon composite

The carbon composite material was prepared in the same manner as in Example 1 except that 12.5 g of coal tar pitch was used. The particle shape of the carbon composite material was shown in Fig. It can be seen that the carbon 4 uniformly covers the ball mill 1.

(3) Electrochemical evaluation of nanosilicon and carbon composites

The battery was manufactured and evaluated in the same manner as in Example 1, and the charging / discharging curve was shown in FIG. 10 and the life curve was shown in FIG. 11, where the capacity of the battery was 949 mAh and the efficiency was 78.1% , And the life span was maintained at 79.8% up to 30 cycles.

<Example 4>

(1) Preparation of a ball mill mixture

Except that 10 g of carbon black (Super P) was used instead of 5.0 g of the carbon nanotubes. As can be seen from Fig. 7, the carbon black 3a and the nanosilicon 2 are uniformly dispersed in the surface shape of the composite.

(2) Production of nanosilicon and carbon composite

15 g of a coal tar pitch and 15 g of a ball mill complex were used in place of the carbon composite material of Example 1. The shape of the carbon composite material at this time is shown in Fig. 8, it can be seen that the carbon 4 uniformly covers the ball-and-tube mixture 1.

(3) Electrochemical evaluation of nanosilicon and carbon composites

A battery was manufactured and evaluated in the same manner as in Example 1, and the charging / discharging curve was shown in FIG. 10, and the life curve was shown in FIG. The capacity of the battery is 685 mAh, the efficiency is 74.5%, and the life span is maintained at 77.6% up to 30 cycles.

&Lt; Comparative Example 1 &

(1) Production of nanosilicon and carbon composite

25 g of a coal tar pitch was dissolved in NMP without mixing a ball mill of nano silicon and a carbon nanotube, and then 5 g of nanosilicon was added thereto, followed by heat treatment in the same manner as in Example 1. Fig. 9 shows the surface shape thereof. In this photograph, the structure of the common coke was completely the same as that of the ordinary coke mixed with the nanosilicon in the carbon structure.

(2) Electrochemical evaluation of nanosilicon and carbon composites

A battery was manufactured and evaluated in the same manner as in Example 1, and the charging / discharging curve was shown in FIG. 10, and the life curve was shown in FIG. The capacity of this battery was 699 mAh, the efficiency was 72.7%, and the lifetime was between 30 and 63.7%.

As can be seen in Table 1, when the ball mill is mixed with the nanosilicon, the carbon nanotube and the carbon black, the lifetime characteristics are remarkably improved. This is because the carbon nanotube keeps the conductivity of the silicon material continuously and acts as a buffer It is because.

1: nano silicon-carbon composite 2: nano silicon
3: carbon nanotube 3a: carbon black
4: Coke
10: a mixture of nano-silicon and carbon nanotubes
100: composite particle of nanosilicon and carbon

Claims (7)

A first step of mixing the nanosilicon 2 and the conductive material 3 to form a first mixture in which particles of the nanosilicon 2 are uniformly dispersed in the conductive material 3; And
And a second step of mixing the first mixture with a pitch material and then heat-treating the mixture in an inert atmosphere at 500 to 1400 ° C to produce a composite (1) of nanosilicon and carbon,
In the first step, the nanosilicon 2 and the conductive material 3 are mixed by a ball mill. In the ball mill operation, the nanosilicon and the conductive material are introduced into a container made of synthetic resin, (2) and the conductive material (3) at a weight ratio of 1 to 50 times,
In this case, the size of the nanosilicon (2) is in the range of 10 to 500 nm, the conductive material (3) is carbon nanotube or carbon black,
The diameter of the balls in the ball mill is 0.1 to 3 mm, the rotation speed of the ball mill is 50 to 300 rpm,
After the ball milling operation in the first step, nanosilicon is evenly adsorbed on the conductive material, nanosilicon particles are aggregated in the conductive material to a certain size,
Wherein the pitch material is at least one selected from the group consisting of coal tar pitches and petroleum pitches. The method for producing a negative electrode active material for a lithium ion secondary battery according to claim 1, wherein the mixture of nanosilicon and carbon is dispersed in a conductive material. A first step of mixing the nanosilicon 2 and the conductive material 3 to form a first mixture in which particles of the nanosilicon 2 are uniformly dispersed in the conductive material 3; And
And a second step of mixing the first mixture with a polymer material and then heat-treating the mixture in an inert atmosphere at 500 to 1400 ° C to produce a composite (1) of nanosilicon and carbon,
In the first step, the nanosilicon 2 and the conductive material 3 are mixed by a ball mill. In the ball mill operation, the nanosilicon and the conductive material are introduced into a container made of synthetic resin, (2) and the conductive material (3) at a weight ratio of 1 to 50 times,
In this case, the size of the nanosilicon (2) is in the range of 10 to 500 nm, the conductive material (3) is carbon nanotube or carbon black,
The diameter of the balls in the ball mill is 0.1 to 3 mm, the rotation speed of the ball mill is 50 to 300 rpm,
After the ball milling operation in the first step, nanosilicon is evenly adsorbed on the conductive material, nanosilicon particles are aggregated in the conductive material to a certain size,
Wherein the polymer material is at least one material selected from the group consisting of polyvinyl alcohol (PVA), polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), and polystyrene (PS) , A composite of nanosilicon and carbon dispersed in a conductive material, for producing a negative electrode active material for a lithium ion secondary battery. The method according to claim 1 or 2, further comprising a third step of mixing natural graphite in a weight ratio of 3: 7 to 7: 3 to the composite (1) of nanosilicon and carbon produced in the second step Wherein the negative electrode active material is composed of a composite of nanosilicon and carbon dispersed in a conductive material. delete delete And a coke (4), wherein the nanosilicone particles are dispersed in the conductive material (3), and the coke (4) comprises a composite of the nanosilicon and the conductive material Surrounding,
The relative weight ratio of the nanosilicon (2) to the conductive material (3) is in the range of 1: 0.3 to 1: 5,
Wherein the nanosilicon (2) has a particle size in the range of 10 to 500 nm, the conductive material (3) is a carbon nanotube or carbon black,
Wherein the nanosilicon is uniformly adsorbed to the conductive material, the nanosilicon particles are present in a coherent form in the conductive material with a predetermined size,
The coke 4 is formed by mixing a mixture of the nanosilicon and a conductive material with a pitch material or a high molecular material and then heat-treating the mixture in an inert atmosphere at a temperature of 500 to 1400 ° C,
Wherein the pitch material is at least one material selected from the group consisting of coal tar pitch and petroleum pitch, and the polymer material is selected from the group consisting of polyvinyl alcohol (PVA), polyvinyl chloride (PVC), polyvinylidene fluoride , PVdF), and polystyrene (PS). The negative electrode active material for a lithium ion secondary battery according to any one of claims 1 to 7, wherein the negative active material is a composite of nanosilicon and carbon dispersed in a conductive material. delete

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