KR101612603B1 - Carbon-silicon complex, negative active material for secondary battery including the same and method for preparing the same - Google Patents

Abstract

There is provided a carbon-silicon composite including a first carbon matrix and a first carbon-silicon composite particle and a second carbon particle which are trapped in the first carbon matrix and include dispersed silicon particles.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a carbon-silicon composite, a negative electrode active material for a secondary battery including the same, and a method for manufacturing the carbon-

The present invention relates to a carbon-silicon composite, a negative electrode active material for a secondary battery comprising the carbon-silicon composite, and a method for producing the carbon-silicon composite.

In order to be used as an IT device and an automobile battery, a cathode material of a lithium secondary battery capable of realizing a high capacity is required. Accordingly, silicon has attracted attention as a cathode material of a high capacity lithium secondary battery. For example, pure silicon is known to have a high theoretical capacity of 4200 mAh / g.

However, since the cycle characteristics are lower than those of the carbon-based materials, they are still obstacles to commercialization because inorganic particles such as silicon are used as lithium intercalation and deintercalation materials as negative electrode active materials, The conductivity between the active materials deteriorates or the negative electrode active material peels off from the negative electrode collector. That is, the inorganic particles such as silicon contained in the negative electrode active material occlude lithium by charging and expand to a volume of about 300 to 400%. When lithium is discharged by discharging, the inorganic particles shrink. When such a charge and discharge cycle is repeated, electrical insulation may occur due to a void space generated between the inorganic particles and the anode active material, And thus has a serious problem for use in a lithium secondary battery.

An embodiment of the present invention is to provide a carbon-silicon composite capable of improving the capacity and life characteristics of a secondary battery.

Another embodiment of the present invention is to provide a negative electrode active material for a secondary battery comprising the carbon-silicon composite.

Another embodiment of the present invention is to provide a method for producing the carbon-silicon composite.

In one embodiment of the invention,

A first carbon-silicon composite particle comprising a first carbon matrix and the dispersed silicon particles entrapped in the first carbon matrix; And

The second carbon particles

≪ / RTI >

The silicon particles may be present throughout the entire interior of the carbon-silicon composite.

The carbon-silicon composite may include silicon agglomerated particles formed by aggregating the silicon grains, and the diameter of the silicon agglomerates in the first carbon matrix may be less than 20 탆.

The carbon-silicon composite may be formed by sintering together the first carbon-silicon composite particle and the second carbon particle.

The carbon-silicon composite may include voids formed between the carbon-silicon composite particles and the second carbon particles.

The first carbon matrix may include at least one selected from the group consisting of pitch carbide, polymer carbide, and combinations thereof.

The second carbon particles may include at least one selected from the group consisting of natural graphite, artificial graphite, soft carbon, hard carbon, pitch carbide, calcined cokes, graphene, carbon nanotubes, and combinations thereof .

The silicon particles may be contained in an amount of 1 to 30 wt% of the entire carbon-silicon composite particles.

The first carbon matrix may be contained in an amount of 0.05 to 50 wt% of the entire carbon-silicon composite particles.

The carbon-silicon composite may further include an amorphous carbon coating layer as an outermost layer of the carbon-silicon composite.

In another embodiment of the present invention, there is provided a negative electrode active material for a secondary battery comprising the carbon-silicon composite.

In another embodiment of the present invention,

Preparing a silicon slurry solution;

Preparing a mixed solution obtained by mixing the silicon slurry solution, the first carbon material, and the second carbon material;

Performing a carbonization process on the mixed solution to carbonize the mixed solution to produce a carbon-silicon composite; And

Spheroidizing the carbon-silicon composite;

Lt; / RTI >

Wherein the 90% cumulative mass particle size distribution diameter is D90, and the 50% cumulative mass particle size distribution diameter is D50, the silicon slurry solution is a slurry containing silicon particles and a dispersion medium, &Lt; D90 / D50 < / = 2.5, and 2 nm &lt;

To provide a method for producing a carbon-silicon composite.

The mixed solution dissolves the first carbon source in the silicon slurry solution, and the second carbon source may be insoluble in the dispersion medium of the silicon slurry solution.

The first carbon source and the second carbon source may be conductive or non-conductive.

The dispersion medium may be selected from the group consisting of N-methyl-2-pyrrolidone (NMP), tetrahydrofuran (THF), water, ethanol, methanol, cyclohexanol, cyclohexanone, methyl ethyl ketone, acetone, Diethyl carbonate, dimethyl sulfoxide (DMSO), and combinations thereof.

The silicon slurry solution may be prepared by mixing the silicon particle powder and the dispersion medium, followed by ultrasonic treatment.

The ultrasonic treatment may be performed by a method of ultrasonically treating the entire silicon slurry solution at the same time or by continuously circulating the silicon slurry solution to partially ultrasonic wave the silicon slurry solution .

Wherein the silicone slurry solution further comprises an additive, wherein the additive is selected from the group consisting of polyacrylic acid, polyacrylate, polymethacrylic acid, polymethylmethacrylate, polyacrylamide, carboxymethylcellulose, polyvinylacetate, polymaleic acid, polyethylene glycol, A polyvinyl resin, a copolymer thereof, a block copolymer having a high affinity with Si and a block copolymer having a low affinity with Si, and a combination thereof.

In the method for producing the carbon-silicon composite, the carbonization process may be performed on the mixed solution by performing a heat treatment at 400 to 1400 ° C for 1 to 24 hours.

The method of fabricating the carbon-silicon composite may further include forming an amorphous carbon coating layer obtained by coating the spheroidized carbon-silicon composite with an amorphous carbon precursor to carbonize the spherical carbon-silicon composite.

The carbon-silicon composite of the present invention contains nano-sized silicon particles dispersed in a very uniform manner, thereby improving the capacity and life characteristics of the secondary battery when used as a negative electrode active material for a secondary battery.

1 is a graph showing the distribution characteristics of silicon particles by dynamic light scattering (measuring instrument: ELS-Z2, manufactured by Otsuka Electronics) with respect to the silicon slurry solution used for producing the carbon-silicon composite of Example 1 As shown in FIG.
FIG. 2 is a scanning electron microscope (SEM) image of a cut surface obtained by cutting the silicon-carbon composite of Example 1 with a FIB (Focus Ion Bean).
3 is an EDS image of carbon in the silicon-carbon composite of Example 1 obtained using Energy-dispersive spectroscopy.
4 is an EDS image of silicon in the silicon-carbon composite of Example 1 obtained using Energy-dispersive spectroscopy.
FIG. 5 is a graph showing a result of measuring a specific capacity according to a cycle for the secondary battery manufactured in the example. FIG.
6 is a graph showing the post-capacity retention ratio of the secondary battery manufactured in the example in terms of cycle, in terms of the initial capacity, in terms of cycles.

Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited thereto, and the present invention is only defined by the scope of the following claims.

In one embodiment of the present invention, a first carbon-silicon composite particle comprising a first carbon matrix and a silicon particle entrapped in the first carbon matrix and dispersed therein; And carbon-silicon composite including second carbon particles.

The carbon-silicon composite includes a first carbon-silicon composite particle formed in a well-dispersed state in the first carbon matrix without forming a large aggregation of silicon particles during the process of forming a composite of silicon with carbon. And a second carbon particle together with the first carbon-silicon composite particle. Thus, the silicon particles may be dispersed in the first carbon matrix of the carbon-silicon composite and dispersed evenly throughout the carbon-silicon composite. Such a carbon-silicon composite can improve the lifetime characteristics of the secondary battery by effectively utilizing the silicon characteristic of a high capacity when applied to the anode active material of the secondary battery, and alleviating the volume expansion problem during charging and discharging.

A carbon-silicon composite in which silicone particles are more evenly dispersed can realize a better capacity even if it contains the same amount of silicon. For example, about 80% or more of the silicon theoretical capacity.

The first carbon-silicon composite particle is formed into a spherical or nearly spherical particle shape, and is sphered together with the second particle to form the carbon-silicon composite.

Various known methods and devices for spheronizing the first carbon-silicon composite particles and the second particles can be used.

The carbon-silicon composite formed by sphering the first carbon-silicon composite particle and the second particle may include voids formed between the first carbon-silicon composite particle and the second carbon particle.

Since the silicon particles are uniformly dispersed in the first carbon-silicon composite particle and the first carbon-silicon composite particle is formed while being distributed throughout the carbon-silicon composite, The silicon particles are evenly dispersed throughout the carbon-silicon composite.

Since the silicon-silicon composite is formed by uniformly dispersing the silicon uniformly throughout the carbon-silicon composite, it is possible to effectively exhibit silicon characteristics in a high capacity when applied to the anode active material of the secondary battery and alleviate the volume expansion problem during charging and discharging, Can be improved.

More evenly dispersed carbon-silicon composites can achieve even better capacity, even if they contain the same amount of silicon. For example, about 80% or more of the silicon theoretical capacity.

As described above, in the carbon-silicon composite, the silicon particles are uniformly dispersed throughout the entire interior region of the carbon-silicon composite through the first carbon-silicon composite particle, do. Means that the silicon particles are trapped in a depth of 1% or more of the radius of the carbon-silicon composite, that is, 1% to 100% of the radius of the carbon-silicon composite Silicon complexes in which silicon is distributed only on the surface side corresponding to a depth of less than 1% of the radius in that the silicon particles are present even at a depth corresponding to 100%. Naturally, the meaning that the silicon particles are present at a depth corresponding to 1% to 100% of the radius of the carbon-silicon composite does not mean that it exists at a depth corresponding to 0% to 1% of the radius of the carbon-silicon composite It is not.

In addition, since the silicon particles used as raw materials are generally aggregated together as a raw material in the carbonization process, the carbon-silicon composite may include silicon agglomerates formed by the silicon particles being clustered together.

In this specification, the dispersion of the silicon particles is well-balanced means that the silicon particles are uniformly distributed in the first carbon matrix while the silicon particles are small and uniformly formed and the deviation value is small in terms of statistical analysis of the particle diameter of each silicon ingot , Meaning that the maximum value of the particle diameter of the silicon ingot can be obtained at a certain level or less.

That is, since the silicon particles are well dispersed in the carbon-silicon composite, the particles of the silicon particles also become relatively small. Specifically, the diameter of the silicon agglomerates in which the silicon grains are formed in the first carbon matrix may be 20 탆 or less. In one embodiment, the diameter of the silicon ingot particles in the first carbon-silicon composite particles may be 2 nm to 15 탆 or less. In another embodiment, the diameter of the silicon ingot particles in the first carbon-silicon composite particles may be 2 nm to 10 탆 or less.

In addition, for example, the average diameter of the silicon ingot particles in the first carbon-silicon composite particles may be from 1 탆 to 10 탆.

The silicon particles may be contained in an amount of 1 to 30 wt% of the entire carbon-silicon composite particles. The numerical range is a range including a case where the silicon content is high, meaning that the carbon-silicon composite has an advantage that it can contain silicon in a high content, and furthermore, Since the particles are well dispersed, the problem of volume expansion upon charge and discharge, which is problematic when using a negative electrode active material of a silicon material, can be improved.

The first carbon matrix may be contained in an amount of 0.05 to 50 wt% of the entire carbon-silicon composite particles. The carbon-silicon composite containing the first carbon matrix as the above content can improve the lifetime characteristics of the secondary battery by effectively exerting high-capacity silicon characteristics when applied as an anode active material of the secondary battery, while alleviating the volume expansion problem during charging and discharging .

The carbon-silicon composite may be formed as spherical or spherical particles, and the carbon-silicon composite may have a particle diameter of 0.5 to 50 탆. The carbon-silicon composite having the particle size within the above range can improve the lifetime characteristics of the secondary battery by effectively exerting high-capacity silicon characteristics when applied as an anode active material of the secondary battery, while alleviating the volume expansion problem during charging and discharging.

The first carbon matrix may include at least one selected from the group consisting of pitch carbide, polymer carbide, and combinations thereof.

The second carbon particles may include at least one selected from the group consisting of natural graphite, artificial graphite, soft carbon, hard carbon, pitch carbide, calcined cokes, graphene, carbon nanotubes, and combinations thereof .

In one embodiment, in the carbon-silicon composite, the first carbon matrix may be amorphous carbon and the second carbon particles may be crystalline carbon. For example, when the second carbon particles are graphite, the second carbon particles may have a plate shape or a shape of a slice. The second carbon particles may be sphered together with the first carbon-silicon composite particles formed in a spherical shape, Silicon composite particles may be formed in a spherical state in which the first carbon-silicon composite particles are dispersed.

When the second carbon particles are graphite, it may be in the form of a plate or a slice having an average diameter in a flat plane of 0.1 to 500 m and a thickness of 0.01 to 10 m.

The first carbon-silicon composite particle may be specifically 0.05 to 50 탆.

The average diameter of the silicon particles included in the carbon-silicon composite may be 2 nm to 180 nm. As described above, when forming the complex with carbon, the silicon particles having the above-mentioned range size are not enlarged and enlarged, and when the carbon-silicon composite is used as the negative electrode active material of the secondary battery, a high capacity silicon characteristic is effectively exhibited, The lifetime characteristics of the secondary battery can be improved.

The carbon-silicon composite has a very low oxygen content because it hardly contains oxides which may degrade the performance of the secondary battery, for example. Specifically, the carbon-silicon composite may have an oxygen content of 0 to 1 wt%. In addition, the first carbon matrix may be substantially free of other impurities and by-products, and may be composed only of carbon. Specifically, the content of the carbon material in the first carbon matrix may be 70 to 100% by weight.

In the present specification, the diameter of a particle can mean a distance between two points defined by a straight line passing through the center of gravity of the particle meeting with the surface of the particle.

The diameter of the particles can be measured by various methods according to known methods and can be measured, for example, by using X-ray diffraction analysis (XRD) or by scanning electron microscope (SEM) images.

The carbon-silicon composite may further include an amorphous carbon coating layer as an outermost layer.

In another embodiment of the present invention, there is provided a negative electrode active material for a secondary battery comprising the carbon-silicon composite.

The negative electrode active material for a secondary battery of the present invention can be produced by a method known to a person skilled in the art.

The carbon-silicon composite may be produced by a method for producing a carbon-silicon composite described below. Hereinafter, a method for producing the carbon-silicon composite will be described in detail.

In another embodiment of the present invention,

Preparing a silicon slurry solution;

Preparing a mixed solution obtained by mixing the silicon slurry solution, the first carbon material, and the second carbon material;

Performing a carbonization process on the mixed solution to carbonize the mixed solution to produce a carbon-silicon composite; And

Spheroidizing the carbon-silicon composite;

Silicon composite, wherein the carbon-silicon composite comprises a carbon-

Wherein the 90% cumulative mass particle size distribution diameter is D90, and the 50% cumulative mass particle size distribution diameter is D50, the silicon slurry solution is a slurry containing silicon particles and a dispersion medium, ? D90 / D50? 2.5, and 2 nm <D50 <180 nm.

The first carbon material in the mixed solution is dissolved in the dispersion medium of the silicon slurry solution and the second carbon material is insoluble. Therefore, when the carbonization process is performed on the mixed solution, the silicon particles dispersed in the 1 carbon matrix Silicon composite particles are formed, and the second carbon raw material forms second carbon particles as separate particles. As a result, the carbon-silicon composite having the above-described structure can be formed.

By the method of producing the carbon-silicon composite, nano-sized silicon particles are evenly dispersed throughout the first carbon matrix to the inside of the carbon-silicon composite, and as a result, the silicon particles are uniformly distributed throughout the carbon- A carbon-silicon composite implementing the dispersed effect can be produced.

The method for producing the carbon-silicon composite may further comprise preparing the silicon slurry solution separately prepared before the silicon particles are mixed with the first carbon material and the second carbon material to prepare the first carbon matrix and the finally produced carbon -Silicon composite in which nano-sized silicon particles are evenly distributed and distributed over the entire silicon composite.

The silicon slurry solution has a uniform distribution with a small D50 and a small inter-particle size variation. The carbon-silicon composite prepared from the silicon slurry solution containing the silicon particles having uniformly dispersed nanosized particles can alleviate the volume expansion problem during charging and discharging when used as a negative electrode active material of the secondary battery, The lifetime characteristics of the battery can be improved.

Since the silicon slurry solution is used as a slurry state in which silicon particles evenly dispersed in the dispersion medium are dispersed in the dispersion medium, unlike the silicon powder state exposed to the atmosphere, the silicon particles are not exposed to the air, There is an advantage that it can be. By suppressing the oxidation of silicon, it is possible to further improve the capacity when applied to the secondary battery anode active material, thereby further improving the electrical characteristics of the secondary battery.

Hereinafter, the silicon slurry solution will be described in detail.

The silicon slurry solution may contain silicon particles in a high content and may satisfy the dispersion conditions as described above, about 1? D90 / D50? 2.5 and about 2 nm <D50 <180 nm. In addition, when used in a slurry state, a uniform dispersion state can be maintained while the silicon particles are contained in a high content and the average particle size is small.

Various methods for improving the dispersion can be used to realize the above-described dispersion conditions, about 1? D90 / D50? 2.5 and about 2 nm <D50 <180 nm. In particular, in order to realize a silicon slurry solution satisfying the dispersion conditions using a silicon powder having a relatively large average particle diameter, various methods can be combined or applied.

As an example of a method for improving dispersion, an additive for adjusting the kind of the dispersion medium or improving the dispersion may be added to the slurry slurry, or a method of ultrasonically treating the silicon slurry solution may be used. As a method for improving dispersion, various known methods other than those exemplified above may be applied, or may be applied in combination.

In one embodiment, by further improving dispersion using the methods described above, the silicon slurry can form a silicon particle distribution of about 1? D90 / D50? 2.0 and about 2 nm <D50 <160 nm.

In another embodiment, the dispersion can be further improved to form a silicon particle distribution of about 1? D90 / D50? 1.75 and about 2 nm <D50 <120 nm.

The dispersion medium may be selected from the group consisting of N-methyl-2-pyrrolidone (NMP), tetrahydrofuran (THF), water, ethanol, methanol, cyclohexanol, cyclohexanone, methyl ethyl ketone, acetone, Diethyl carbonate, dimethyl sulfoxide (DMSO), and combinations thereof.

By using the above-described type of dispersion medium, the silicon slurry solution can be well dispersed.

The silicon slurry solution may further include an additive to allow the silicon particles to be well dispersed.

The additive is selected from the group consisting of polyacrylic acid, polyacrylate, polymethylmethacrylic acid, polymethylmethacrylate, polyacrylamide, carboxymethylcellulose, polyvinyl acetate, polymaleic acid, polyethylene glycol, polyvinyl resin, A block copolymer including a block having a high affinity to Si and a block having a low affinity to Si, and a combination thereof.

The additive can help suppress the aggregation of the silicon particles.

As a specific example, the block copolymer of the additive may form Si-block copolymer core-shell nanoparticles with the silicon particles in the slurry. Wherein the Si-block copolymer core-shell nanoparticles comprise Si core; And a block copolymer shell including a block having high affinity with Si and a block having low affinity with Si form a spherical micelle structure around the Si core.

The block having a high affinity with Si is associated with the surface of the Si core by a van der Waals force or the like. At this time, the block having a high affinity with Si may be a polyacrylic acid, But are not limited to, polyacrylate, poly methacrylic acid, poly methyl methacrylate, poly acryamide, carboxymethyl cellulose, poly vinyl acetate ) Or polymaleic acid, but is not limited thereto.

The block having a low affinity to Si is assembled toward the outside by a van der Waals force or the like. At this time, the block having a low affinity with Si may be a block material such as polystyrene, poly acrylonitrile ), Polyphenol, poly ethylene glycol, poly lauryl acrylate, and poly vinyl difluoride. However, the present invention is not limited thereto.

Most preferably, the block copolymer shell is a polyacrylic acid-polystyrene block copolymer shell. The number average molecular weight (Mn) of the polyacrylic acid is preferably about 100 g / mol to about 100,000 g / mol, and the polystyrene has a number average molecular weight (Mn) of about 100 g / mol to about 100,000 g / mol But is not limited thereto.

The additive may be included in the silicone slurry solution in an amount of about 0.1 to about 50 parts by weight based on 100 parts by weight of the silicon. The silicone slurry solution may help to achieve the above-described dispersion characteristics, including the aforementioned additives, in the above range of contents.

The silicon slurry solution may be subjected to ultrasonic treatment, fine mill treatment, ball mill treatment, fine mill treatment, three roll mill treatment, stamping Various treatment methods such as stamp mill treatment, eddy mill treatment, homomixer treatment, planetary centrifugal mixer treatment, homogenizer treatment or vibration shaker treatment Can be performed.

In one embodiment, the silicon slurry solution may be sonicated to implement the above-described dispersion characteristics.

The ultrasonic treatment may be performed by a method of ultrasonically treating the whole silicon slurry solution simultaneously in a batch type, or by continuously circulating the silicon slurry solution to partially ultrasonically treat the silicon slurry solution .

In general, a tip is formed in an apparatus for performing an ultrasonic process, and the silicon particles are dispersed by using the ultrasonic energy emitted from the tip end, so that there is a limit in the area in which the ultrasonic energy is transmitted. Therefore, if ultrasonic treatment is to be performed on a large amount of the silicon slurry solution, ultrasonic treatment is performed as a continuous circulation type in which the silicon slurry solution is continuously circulated rather than the batch type so that a part of the silicon slurry solution is continuously subjected to ultrasonic treatment The efficiency can be increased. That is, a larger amount of the silicon slurry solution can be treated by ultrasonic treatment in a continuous cycle type within the same time for the same power.

For example, when the ultrasonic treatment is performed in a batch type, 100 to 500 Watt power may be supplied to 1000 ml or less of the silicon slurry solution for 30 seconds to 1 hour.

For example, in the case of performing the ultrasonic treatment in the above-described continuous circulation type, 500 Watt electric power may be supplied and ultrasonic treatment may be performed for 30 seconds to 1 hour to treat an amount of about 3600 ml / hr of the silicon slurry solution.

For example, ultrasonic treatment may be performed using ultrasonic waves of 10 kHz to 100 kHz, but is not limited thereto.

Since the silicon slurry solution prepared by simply mixing the silicon powder with the dispersion medium forms a lump by the aggregation of the silicon particles, the average particle diameter of the silicon particles constituting the silicon slurry solution increases, and the slurry in which the silicon particles are not uniformly dispersed .

On the other hand, the silicone slurry solution can be prepared by, for example, allowing the dispersion to proceed well by, for example, selecting an appropriate type of dispersion medium, including an additive, or further processing to improve dispersion such as ultrasonic treatment, D90 / D50 &amp;le; 2.5 and about 2 nm < D50 &lt; 180 nm in a silicon slurry solution using a silicon powder having an average particle size of 2 nm to about 200 nm. That is, even if a powder having an average particle diameter of about 2 nm to about 200 nm, specifically about 10 nm to about 150 nm is used as the silicon powder, a silicon slurry solution in a state of being uniformly dispersed in the dispersion medium can be obtained.

As described above, the silicon slurry solution is prepared and then mixed with the first carbon source and the second carbon source to prepare a mixed solution in which the first carbon source is dissolved in the silicon slurry solution. The dispersion medium of the silicon slurry solution may dissolve the first carbon material, and the second carbon material is insoluble and insoluble in the dispersion medium of the silicon slurry solution.

Since the first carbon material is dissolved in the silicon slurry solution, carbon-silicon composite particles containing the silicon particles, which are carbonized while being trapped in the carbonization step and captured in the first carbon matrix, may be formed .

The first carbon material may include at least one selected from the group consisting of pitch, polymer, and combinations thereof.

The second carbon material may include at least one selected from the group consisting of natural graphite, artificial graphite, soft carbon, hard carbon, pitch, coke, graphene, carbon nanotubes, and combinations thereof.

When pitch is used as the first carbon raw material or the second carbon raw material, generally coal-based coal tar pitch or petroleum pitch can be commercially obtained and used.

In one embodiment, an amorphous carbon source may be used as the first carbon source, and a crystalline carbon source may be used as the second carbon source.

The carbon raw material is carbonized by the subsequent carbonization process to form the first carbon matrix and the second carbon particles, respectively. At this time, since the first carbon material is dissolved in the mixed solution, the first carbon material is formed as the first carbon-silicon composite particle by dispersing the silicon particles therein.

The first carbon material and the second carbon material may be used both in conductive and non-conductive cases without discrimination.

Specific examples of the dispersion medium are as described above.

The content of silicon, the first carbon and the second carbon in the mixed solution may be appropriately mixed with the silicon slurry solution, the first carbon source and the second carbon source so that the carbon-silicon composite can be formed in the above-mentioned content.

As described above, the mixed solution is prepared, and then the mixed solution is carbonized by performing a carbonization process to prepare the first carbon-silicon composite particle and the second carbon particles as a mixture.

The term 'carbonization process' means a process in which a carbon material is calcined at a high temperature to leave carbon as an inorganic material. The first carbon material forms a first carbon matrix by the carbonization process, and the second carbon The raw material forms the second carbon particles.

The carbonization process may be performed by heat-treating the mixed solution at a temperature of 400 to 1400 DEG C, and the pressure process may be performed at a low pressure to a high pressure condition of 1 bar to 15 bar, To 24 hours.

The carbonization process may be performed in one step or multiple steps depending on the intended use.

For example, the carbonization yield of the carbonization process may be 40 to 80 wt%. By increasing the carbonization yield of the carbonization process in the method of producing such a carbon-silicon composite, generation of volatile matter can be reduced and the process can be facilitated, which can be an eco-friendly process.

Subsequently, the first carbon-silicon composite particles and the second carbon particles, which are prepared by mixing in a mixture state, are sphered. The sphering process may use a variety of known methods and apparatuses. The spherical carbon-silicon composite may include voids formed between the first carbon-silicon composite particle and the second carbon particle. In addition, the carbon-silicon composite may include voids formed by volatilizing the solvent in the carbonization process described above.

And forming an amorphous carbon coating layer by carbonizing the spheroidized carbon-silicon composite with an amorphous carbon precursor.

Hereinafter, specific embodiments of the present invention will be described. It should be noted, however, that the embodiments described below are only intended to illustrate or explain the present invention, and thus the present invention should not be limited thereto.

( Example )

Example  One

A slurry prepared by mixing silicone powder having an average particle diameter of 50 nm and NMP and having a silicon content of 10% by weight was subjected to continuous wave circulation for 30 minutes at an electric power of 500 Watt and an ultrasonic wave of 20 kHz for 30 minutes to obtain 1? D90 / D50? 2.5 and 2 nm <D50 <180 nm A silicon slurry solution satisfying dispersion conditions was prepared.

1 is a graph showing the results of measurement of distribution characteristics of silicon particles by dynamic light scattering (measuring instrument: ELS-Z2, manufactured by Otsuka Electronics) for the silicon slurry solution.

The measurement result is D50 = 140.8 and D90 / D50 = 203.7 / 140.8 = 1.45.

The carbonaceous pitch as the first carbon source and graphite as the second carbon source were mixed in the silicon slurry solution and stirred for about 30 minutes to prepare a mixed solution in which the coal pitch was dissolved in the NMP dispersion medium. The mixing ratio was 10 parts by weight of silicon, 30 parts by weight of pitch and 60 parts by weight of graphite. Under vacuum conditions, the NMP was evaporated at a temperature of about 125 &lt; 0 &gt; C.

Subsequently, carbonization was carried out at a temperature of 900 ° C for 1 hour at a pressure of 1 bar to obtain a carbide. Subsequently, the carbide was introduced into a sphering device and sphered at 3500 rpm for 2 hours to obtain spherical powder. The powders were subjected to classification to obtain powders having only particles having a particle diameter of 50 μm or less.

The selected particles were sintered together with the pitch powder at 3500 rpm for 1 hour, and the selected particles were coated with a pitch to obtain a final silicon-carbon composite.

FIG. 2 is a scanning electron microscope (SEM) image of a cut surface obtained by cutting the obtained silicon-carbon composite with a FIB (Focus Ion Bean), and FIG. 3 is a graph showing the SEM image obtained by using the energy-dispersive spectroscopy FIG. 4 is an EDS image of silicon among the silicon-carbon composites obtained using energy-dispersive spectroscopy. FIG.

It can be seen from FIG. 4 that silicon among the silicon-carbon composites is uniformly dispersed throughout the entire silicon-carbon composite.

Comparative Example  One

First, a silicon slurry solution was prepared so as to have a silicon content of 10% by weight in the same manner as in Example 1.

The graphite was mixed with the silicon slurry solution so as to have a mixing ratio of 10 parts by weight of silicon and 90 parts by weight of graphite, and the mixture was stirred for about 30 minutes to prepare a mixed solution. Under vacuum conditions, the NMP was evaporated at a temperature of about 125 &lt; 0 &gt; C.

Subsequently, carbonization was carried out at a temperature of 900 ° C for 1 hour at a pressure of 1 bar to obtain a carbide. Subsequently, the carbide was introduced into a sphering device and sphered at 3500 rpm for 2 hours to obtain spherical powder. The powders were subjected to classification to obtain powders having only particles having a particle diameter of 50 μm or less.

The selected particles were sintered together with the pitch powder at 3500 rpm for 1 hour, and the selected particles were coated with a pitch to obtain a final silicon-carbon composite.

Experimental Example  One

A silicon-carbon composite powder of Example 1 and Comparative Example 1 was used as a negative electrode active material to prepare secondary batteries, respectively. First, a coating composition for forming an anode active material layer was prepared by mixing the mixture in water at a weight ratio of an anode active material: carboxyl methyl cellulose (CMC): styrene butadiene (SBR) = 96: 2: 2. The coating composition for forming the anode active material layer was coated on a copper current collector and dried in an oven at 110 캜 for about 20 minutes and rolled to prepare a negative electrode.

A 1.0 M LiPF _{6 was} added as a mixed solvent of the prepared negative electrode, separator and electrolyte (ethylene carbonate: dimethyl carbonate (1: 1 weight ratio)) and a lithium electrode were stacked in this order to form a coin- .

Separately, a comparative secondary battery was manufactured in the same manner as in the above-mentioned secondary battery manufacturing process except that silicon was not used but only soft carbon was used as an anode active material. Since the control secondary cell does not contain silicon, there is no problem of a capacitance drop due to the cycle due to silicon. Therefore, the capacity according to the cycle of the secondary battery manufactured in Example 1 and Comparative Example 1 can be evaluated in comparison with the secondary battery.

Charging and discharging tests were carried out on the secondary battery under the following conditions.

Assuming that 300 mA per 1 g weight is 1C, the charging condition was controlled from 0.2C to 0.01V at a constant current and from 0.01V to 0.01C at a constant voltage. The discharging condition was 0.2C at a constant current of 1.5V.

FIG. 5 is a graph showing the results of measuring the specific capacity according to the cycle under the above conditions.

FIG. 6 is a graph showing the post-capacity retention ratio in% converted to the initial capacity according to a cycle.

5, the initial capacity of the secondary battery of Example 1 containing silicon and the secondary battery of Comparative Example 1 was higher than that of the control secondary battery. In the case of the secondary battery of Comparative Example 1, The capacity decrease problem became serious as the cycle continued. On the other hand, in the case of the secondary battery of Example 1, it was confirmed that the problem of the capacity decrease due to the cycle was solved according to the silicon content, and the excellent initial capacity was maintained. Likewise, according to the cycle in FIG. 6, the capacity retention ratio of the control secondary battery and the secondary battery of Example 1 is almost 100% even when the cycle continues, and in Comparative Example 1, the capacity retention rate is remarkably lowered as the cycle continues.

The first discharge capacity, the initial cycle efficiency and the post-20 cycle retention rate of the secondary battery of Example 1, the secondary battery of Comparative Example 1, and the control secondary battery are shown in Table 1 below.

Contrast secondary battery The secondary battery prepared from Example 1 The secondary battery prepared from Comparative Example 1 The first discharge capacity, mAh / g 318 397 438 Initial cycle efficiency,% 92.2 84.4 85.7 Capacity retention after 20 cycles,% 87.0 88.0 5.7

In Table 1, it is also confirmed that the secondary battery of Example 1 exhibits a higher first discharge capacity than the control secondary battery, and that the capacity retention ratio is excellent. Thus, the secondary battery of Example 1 has a problem of capacity reduction It was confirmed that the secondary battery manufactured from Comparative Example 1 improved the supercharger capacity by using silicon. However, the capacity of the secondary battery manufactured by using Comparative Example 1 was lower than that of the control secondary battery.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, And falls within the scope of the invention.

Claims (20)

Preparing a silicon slurry solution;
Preparing a mixed solution obtained by mixing the silicon slurry solution, the first carbon material, and the second carbon material;
Performing a carbonization process on the mixed solution to carbonize the mixed solution to produce a carbon-silicon composite; And
And sintering the carbon-silicon composite, wherein the carbon-silicon composite is a carbon-
Wherein the 90% cumulative mass particle size distribution diameter is D90, and the 50% cumulative mass particle size distribution diameter is D50, the silicon slurry solution is a slurry containing silicon particles and a dispersion medium, ? D90 / D50? 2.5, 2 nm <D50 <180 nm,
A first carbon-silicon composite particle comprising a first carbon matrix and the dispersed silicon particles entrapped in the first carbon matrix; And
The second carbon particles
Lt; / RTI &gt;
Wherein the first carbon matrix is amorphous carbon,
Wherein the first carbon matrix comprises at least one selected from the group consisting of pitch carbide, polymer carbide, and combinations thereof
Carbon-silicon composite.
The method according to claim 1,
Wherein the silicon particles are present in the entire region inside the carbon-silicon composite
Carbon-silicon composite.
The method according to claim 1,
Wherein the silicon lump particles have a diameter of 20 占 퐉 or less in the first carbon matrix
Carbon-silicon composite.
The method according to claim 1,
The first carbon-silicon composite particle and the second carbon particle are sintered together to form
Carbon-silicon composite.
The method according to claim 1,
And a gap formed between the carbon-silicon composite particle and the second carbon particles
Carbon-silicon composite.
delete The method according to claim 1,
Wherein the second carbon particles comprise at least one selected from the group consisting of natural graphite, artificial graphite, soft carbon, hard carbon, pitch carbide, calcined coke, graphene, carbon nanotubes and combinations thereof
Carbon-silicon composite.
The method according to claim 1,
The silicon particles may be contained in an amount of 1 to 30 wt% of the entire carbon-silicon composite particles.
Carbon-silicon composite.
The method according to claim 1,
The first carbon matrix is contained in an amount of 0.05 to 50% by weight based on the entire carbon-silicon composite particles.
Carbon-silicon composite.
The method according to claim 1,
Further comprising an amorphous carbon coating layer as an outermost layer of said carbon-silicon composite
Carbon-silicon composite.
A negative active material for a secondary battery comprising the carbon-silicon composite according to any one of claims 1 to 5 and 7 to 10.
Preparing a silicon slurry solution;
Preparing a mixed solution obtained by mixing the silicon slurry solution, the first carbon material, and the second carbon material;
Performing a carbonization process on the mixed solution to carbonize the mixed solution to produce a carbon-silicon composite; And
Spheroidizing the carbon-silicon composite;
Lt; / RTI &gt;
Wherein the 90% cumulative mass particle size distribution diameter is D90, and the 50% cumulative mass particle size distribution diameter is D50, the silicon slurry solution is a slurry containing silicon particles and a dispersion medium, &Lt; D90 / D50 &lt; / = 2.5, and 2 nm &lt;
Carbon composite.
13. The method of claim 12,
Wherein the mixed solution dissolves the first carbon material in the silicon slurry solution and the second carbon material is insoluble in the dispersion medium of the silicon slurry solution
Carbon composite.
13. The method of claim 12,
The first and second carbon materials may be conductive or non-
Carbon composite.
13. The method of claim 12,
The dispersion medium may be selected from the group consisting of N-methyl-2-pyrrolidone (NMP), tetrahydrofuran (THF), water, ethanol, methanol, cyclohexanol, cyclohexanone, methyl ethyl ketone, acetone, Diethyl carbonate, dimethyl sulfoxide (DMSO), and combinations thereof.
Carbon composite.
13. The method of claim 12,
Mixing the powder of the silicon particles with the dispersion medium, and then subjecting the resultant mixture to ultrasonic treatment to prepare the silicon slurry solution
Carbon composite.
17. The method of claim 16,
The ultrasonic treatment may be performed by ultrasonic treatment of the entire silicon slurry solution at the same time or by continuously circulating the silicon slurry solution so that a part of the silicon slurry solution is continuously ultrasonically treated
Carbon composite.
13. The method of claim 12,
Wherein the silicon slurry solution further comprises an additive,
Wherein the additive is selected from the group consisting of polyacrylic acid, polyacrylate, polymethacrylic acid, polymethylmethacrylate, polyacrylamide, carboxymethylcellulose, polyvinylacetate, polymaleic acid, polyethylene glycol, And at least one selected from the group consisting of a block copolymer having high affinity and a block having low affinity for Si, and combinations thereof
Carbon composite.
13. The method of claim 12,
The mixed solution is subjected to a carbonization process by heat treatment at a temperature of 400 to 1400 ° C and for 1 to 24 hours
Carbon composite.
13. The method of claim 12,
Further comprising the step of forming an amorphous carbon coating layer by carbonizing the spheroidized carbon-silicon composite with an amorphous carbon precursor
Carbon composite.

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