KR102096547B1 - Silicon-encapsulated carbon composite material for secondary battery anode material and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a carbon composite material encapsulated in silicon for a secondary battery negative electrode material and a method for manufacturing the same. The silicon-carbon composite of the present invention encapsulates silicon in carbon, prevents bulk expansion of silicon, improves electrical conductivity, and provides a negative electrode material for lithium secondary batteries and capacitors with high and low charge / discharge life characteristics and high capacity at high currents. Can provide.

Description

Silicon-encapsulated carbon composite material for secondary battery anode material and manufacturing method thereof

The present invention relates to a carbon composite material encapsulated in silicon for a secondary battery negative electrode material and a method for manufacturing the same.

In the early 2000s, the market for lithium-ion secondary batteries expanded rapidly due to the expansion of smart IT devices such as mobile phones and notebooks, and is expected to grow rapidly to over 30 trillion won by 2020 with the industrialization of electric vehicles and ESS. In general, a lithium secondary battery is made by assembling a positive electrode material, a negative electrode material, an electrolyte, and a separator, and four materials of a positive electrode material, a negative electrode material, an electrolyte, and a separator account for 50% of the total production cost.

Among these, carbon-based materials are mainly used in the anode material, and the carbon-based anode materials include crystalline carbon graphite, amorphous carbon hard carbon and soft carbon. Graphite currently used is no longer high-capacity, and is looking for new materials to improve and replace carbon materials.

As a new material to replace the carbon material, silicon having a high theoretical capacity of 4200 mAh / g as well as a very low lithium reaction potential has been actively studied. However, silicon does not maintain capacity due to volume expansion up to 400% when lithium ions are inserted (charged), and has problems of formation of an unstable SEI layer and low electrical conductivity.

Accordingly, carbon has high electrical conductivity and prevents direct contact between silicon and electrolyte, thereby generating stable SEI, and thus studies on coating carbon on silicon have been conducted. However, since the thin carbon coating layer does not completely control the volume change of silicon, in order to solve this, a method of manufacturing a silicon-carbon composite for negative electrode active material of a lithium secondary battery capable of encapsulating silicon in carbon and continuously maintaining high capacity and energy density Should provide

Korean Registered Patent No. 10-1500983 Korean Registered Patent No. 10-1580039

An object of the present invention is to provide a silicon-carbon composite capable of improving the electrical conductivity of an electrode and solving the volume change problem of silicon by encapsulating silicon in carbon by forming micelles using starch and a surfactant.

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

In order to achieve the above object, the present invention is a spherical carbon structure containing carbon; And silicon nanoparticles enclosed in the spherical carbon structure.

The silicon-carbon composite may have a diameter of 5 to 300 μm and a tap density of 0.7 to 1 g / cm 3.

The silicon nanoparticles may have an average diameter of 10 to 100 nm.

The silicon-carbon composite may have a weight ratio of carbon to silicon of 65:35 to 35:65.

The silicon-carbon composite may be synthesized using a microemulsion method.

The carbon structure may be a carbide of starch.

In addition, the present invention comprises: 1) preparing a precursor solution by mixing silicone, starch and surfactant in a solvent selected from water, C _1-5 alcohol or a mixture thereof; 2) preparing a mixture by mixing oil in the precursor solution; And 3) heat-treating the mixture at a temperature of 500 to 1000 ° C. for 3 to 10 hours.

The weight ratio of the starch and the surfactant may be 1: 3.5 to 1:10.

The weight ratio of the starch and the silicone may be 5: 1 to 10: 1.

The starch concentration of the precursor solution in step 1) may be 0.1 to 5 M.

The starch may be any one or a mixture of two or more selected from the group consisting of potato starch, sweet potato starch, corn starch, 칡 starch and tapioca starch.

In step 1), the concentration of silicon nanoparticles in the precursor solution may be 0.01 to 2 M.

The surfactant concentration of the precursor solution in step 1) may be 0.01 to 3 M.

The surfactant may be selected from anionic surfactants, nonionic surfactants, cationic surfactants and amphoteric surfactants.

The surfactant may be selected from cetyltrimethylammonium bromide, brominated dodecyltrimethylammonium bromide, polyvinylirolidone, aliphatic polyol block copolymer, sodium dodecyl sulfate, polyethylene oxide, and polyvinyl alcohol.

The method of manufacturing the silicon-carbon composite may further include; 2-1) subjecting the mixture of step 2) to homogenizer treatment for 1 to 10 minutes and sonication for 5 to 30 minutes at a power of 105 to 250 Watts; You can.

The volume ratio of the solvent and the oil may be 1: 1 to 1:10.

The oil may be any one selected from the group consisting of edible oil and silicone oil, or a mixture of two or more of them.

The method for preparing the silicon-carbon composite may further include 2-2) heating and drying the mixture at 100 to 500 ° C. for 8 to 24 hours.

The method for preparing the silicon-carbon composite may further include 2-3) washing the mixture with acetone.

The present invention provides a negative electrode active material comprising a silicon-carbon composite prepared by the manufacturing method according to the above.

The present invention provides a negative electrode for a secondary battery comprising the negative electrode active material, a conductive material and a binder.

The conductive material may be any one or a mixture of two or more selected from the group consisting of acetylene black, carbon black and ketjen black.

The binder may be any one selected from the group consisting of polyacrylic acid, polyamide, styrene-butadiene rubber, carboxymethyl cellulose, polyvinylidene fluoride-hexafluoropropylene copolymer, or a mixture of two or more of them.

The present invention provides a lithium secondary battery comprising a negative electrode for a secondary battery, a positive electrode containing a lithium metal, and an electrolyte.

The electrolyte is an ethylene carbonate (EC; ethylene carbonate), ethylmethyl carbonate (EMC), diethyl carbonate (DEC) in which LiPF ₆ salt, LiBF ₄ salt, LiClO ₄ salt, etc. are dissolved. It may be any one or a mixture of two or more selected from the group consisting of a mixture and a mixture of fluoroethylene carbonate (FEC; Fluoroethylene carbonate), a solution of vinylene carbonate (VC) and mixtures thereof. have.

In the lithium secondary battery, when lithium metal is used as a counter electrode, the initial discharge capacity is 1000 mAh / g to 2500 mAh / g at 0.05 C (0.2 A / g) in the charge / discharge test, and 0.2 C (0.8 A / g), the discharge capacity is 500 mAh / g to 2000 mAh / g, and the retention rate of the discharge capacity of 0.2 C (0.8 A / g) may be 80 to 95%.

The silicon-carbon composite of the present invention encapsulates silicon in carbon, prevents bulk expansion of silicon, improves electrical conductivity, and provides a negative electrode material for lithium secondary batteries and capacitors with high and low charge / discharge life characteristics and high capacity at high currents. Can provide

1 is a scanning electron microscope (SEM; Scanning Electron Microscope) photograph of starch according to Example 1 of the present invention.
Figure 2a is a SEM photograph of a silicon-carbon composite (starch: surfactant = 2: 1) encapsulated in silicone according to the ratio of starch and surfactant in Example 1 of the present invention.
Figure 2 'is a SEM photograph of a silicon-carbon composite (starch: surfactant = 1: 1) encapsulated in silicone according to the ratio of starch and surfactant in Example 1 of the present invention.
FIG. 2C is a SEM photograph of a silicon-carbon composite (starch: surfactant = 1: 2) in which silicone is encapsulated according to the ratio of starch and surfactant in Example 1 of the present invention.
FIG. 2d is a SEM photograph of a silicon-carbon composite (starch: surfactant = 1: 4) in which silicon is encapsulated according to the ratio of starch and surfactant in Example 1 of the present invention.
FIG. 3 is an SEM photograph of a silicon-carbon composite encapsulated with silicon prepared without using silicone oil in Example 1 of the present invention.
FIG. 4 is a graph showing X-ray diffraction (XRD) of a silicon-carbon composite in which silicon is encapsulated according to the ratio of starch and surfactant in Example 1 of the present invention.
5A is a SEM photograph of a silicon-carbon composite (starch: silicon = 10: 1) in which silicon is encapsulated according to the ratio of starch and silicon in Example 1 of the present invention.
5B is a SEM photograph of a silicon-carbon composite (starch: silicon = 5: 1) in which silicon is encapsulated according to the ratio of starch and silicon in Example 1 of the present invention.
6 is a graph showing the XRD of a silicon-carbon composite encapsulated with silicon according to the ratio of starch and silicon in Example 1 of the present invention.
7A is a graph showing thermogravimetric analysis (TGA) of a silicon-carbon composite (starch: silicon = 10: 1) in which silicon is encapsulated according to the ratio of starch and silicon in Example 1 of the present invention.
7B is a graph showing TGA of a silicon-carbon composite (starch: silicon = 5: 1) encapsulated in silicon according to the ratio of starch and silicon in Example 1 of the present invention.
7C is a graph showing TGA of a silicon-carbon composite (starch: silicon = 3.33: 1) in which silicon is encapsulated according to the ratio of starch and silicon in Example 1 of the present invention.
8A is a graph showing a charge / discharge voltage curve of a lithium secondary battery prepared from Example 2 and Comparative Example 2 of the present invention.
8B is a graph showing charge / discharge cycle performance at room temperature of a lithium secondary battery prepared from Example 2 and Comparative Example 2 of the present invention.

As described above, silicon has a low electrical conductivity and has a disadvantage that the volume expands during charging and discharging of the electrode. The present invention is characterized in that starch and silicon are formed into micelles through microemulsion method to form a carbon structure using starch, encapsulating silicon inside the carbon structure to prevent bulk expansion of silicon, and to increase electrical conductivity.

Hereinafter, the present invention will be described in detail.

The present invention is a spherical carbon structure containing carbon; And silicon nanoparticles enclosed in the spherical carbon structure.

The silicon-carbon composite may have a diameter of 5 to 300 μm and a tap density of 0.7 to 1 g / cm 3.

The silicon-carbon composite prepared by the conventional hydrothermal synthesis method has a uniform particle diameter of about 2 μm, while the silicon-carbon composite of the present invention has various particle diameters of 5 to 300 μm. Due to the diameter of various sizes, the tap density is high, and when the tap density is increased, the energy density of the finished battery is increased. Conventionally developed silicon-carbon composites exhibit a tap density of about 0.6 g / cm 3, while the silicon-carbon composites of the present invention exhibit improved tap densities of 0.7 to 1 g / cm 3 due to various particle diameters.

The silicon nanoparticles may have an average diameter of 10 to 100 nm. If the size of the silicon nanoparticles is less than the above range, dispersion is not easy, and if it exceeds the above range, the volume change due to insertion and desorption of lithium ions may be rough, and thus cycle stability may deteriorate, which is not preferable.

The silicon-carbon composite may have a weight ratio of carbon to silicon of 65:35 to 35:65. In the case of the existing composite material of silicon and carbon, compared to the maximum weight ratio of carbon to silicon of 65:35, the content ratio of silicon is dramatically increased, and the capacity of the battery can be significantly increased, thereby saving electric vehicles and power. It is applicable to medium and large-sized lithium secondary batteries.

The silicon-carbon composite may be synthesized using a microemulsion method.

The carbon structure may be a carbide of starch, the starch may be any one or a mixture of two or more selected from the group consisting of potato starch, sweet potato starch, corn starch, 칡 starch and tapioca starch, fructose in which glucose is polymerized Any starch made of sugar is possible.

In addition, the present invention 1) preparing a precursor solution by mixing the silicone, starch and surfactant in a solvent selected from C _1-5 alcohol or a mixture thereof; 2) adding oil to the precursor solution and preparing a mixture by homogenizer treatment and sonication; And 3) heat-treating the resultant product at a temperature of 500 to 1000 ° C. for 3 to 10 hours; to provide a method of manufacturing a silicon-carbon composite.

In the present invention, micelles are formed using a microemulsion method that is different from the conventional method. In the microemulsion method, particles having a desired size can be obtained by forming a space between interfaces using a surfactant and causing polymer polymerization within the space. The method of manufacturing the silicon-carbon composite of the present invention does not undergo any treatment on silicon or starch, and has a merit that the process is very simple and simple for mass production by simple mixing and heating and drying.

First, a precursor solution is prepared and stirred by mixing silicone, starch and surfactant in a solvent.

The weight ratio of the starch and the surfactant may be 1: 3.5 to 1:10, and preferably 1: 4 by weight. Outside the above range, the silicon-carbon composite is not preferable because it cannot form a spherical model. Within the above range, the weight ratio of starch and surfactant can be appropriately adjusted according to the desired particle size and shape. The amount of silicon nanoparticles encapsulated, the silicon content of the silicon-encapsulated carbon sphere, porosity, capacity characteristics of the secondary battery, and long-term cycle characteristics can be determined according to the weight ratio of the starch and surfactant of the precursor solution.

The weight ratio of the starch and the silicone may be 5: 1 to 10: 1.

The solvent may be a polar solvent such as water, C _1-5 alcohol or a mixture thereof.

The starch may be any one or a mixture of two or more selected from the group consisting of potato starch, sweet potato starch, corn starch, 칡 starch, and tapioca starch, and may be any starch composed of fructose with a large amount of glucose. Preferably, 490 glucose may be polymerized corn starch, but is not limited thereto.

The starch concentration of the precursor solution in step 1) may be 0.1 to 5 M. When the concentration of starch is less than the above range, the yield of the silicon-carbon composite to be produced is low and there is no economical efficiency. If it exceeds the above range, there is a problem that the capacity is lowered because the specific surface area of the resulting silicon-carbon composite is low.

Starch is a natural polymer in which a number of α-glucose molecules are polymerized by glycosidic bonds to a carbohydrate of the molecular formula (C ₆ H ₁₂ O ₆ ) _n and is contained in many seeds, roots, etc. of plants. This material not only has a high viscosity at the molecular size of a micrometer, but also has excellent gel-forming ability, so there is no difficulty in encapsulating silicone particles, and it contains a large amount of phosphate to maintain evenly dispersed form due to its weak repulsive force to ensure structural stability. can do.

In step 1), the concentration of silicon nanoparticles in the precursor solution may be 0.01 to 2 M. When the concentration of the silicon nanoparticles is less than the above range, the amount of the silicon nanoparticles entrapped inside the carbon precursor is too small to decrease the charge / discharge capacity, and if it exceeds the above range, dispersion is not easy, and cycle stability is lowered. You can. The tap density of the silicon-carbon composite prepared according to the concentration of silicon nanoparticles in the precursor solution may vary, and capacity characteristics, long-term cycle characteristics, and rate characteristics of the secondary battery using the composite as a negative electrode active material may be determined.

In step 1), the surfactant in the precursor solution may be 0.01 to 3 M, and the surfactant may be selected from anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants. In addition, the surfactant may be selected from cetyl trimethylammonium bromide, brominated dodecyl trimethylammonium bromide, polyvinylirolidone, aliphatic polyol block copolymer, sodium dodecyl sulfate, polyethylene oxide and polyvinyl alcohol.

The method of manufacturing the silicon-carbon composite may further include; 2-1) subjecting the mixture of step 2) to homogenizer treatment for 1 to 10 minutes and sonication for 5 to 30 minutes at a power of 105 to 250 Watts; You can. The homogenizer and ultrasonic treatment further improve the dispersibility of the starch and silicon nanoparticles, so that the silicon nanoparticles are uniformly contained within the starch, thereby reducing the volume change and increasing the capacity.

The volume ratio of the oil and the solvent may be 1: 1 to 1:10, and the oil may be any one selected from the group consisting of edible oil and silicone oil, or a mixture of two or more of them.

Silicone oil is very stable chemically, and the viscosity does not deteriorate even at high temperatures because the change in viscosity with temperature changes is small. This property of the silicone oil holds the model when forming the micelle so that the silicone-composite has a spherical shape. It can be confirmed from the following examples that a spherical model is not formed when silicone oil is not added.

The method for preparing the silicon-carbon composite may further include 2-2) heating and drying the mixture at 100 to 500 ° C. for 8 to 24 hours.

The method for preparing the silicon-carbon composite may further include 2-3) washing the mixture with acetone. It is possible to separate the oil and powder through the above steps.

In particular, although not explicitly described in the following Examples or Comparative Examples, in the method for preparing the silicone-carbon composite according to the present invention, for various types of starch, surfactant types, solvent types, oil types , Weight ratio of starch and surfactant, weight ratio of starch and silicone, volume ratio of oil and solvent, 2) whether to perform homogenizer treatment and ultrasonic treatment of the mixture of the stage, whether to perform the heating and drying stage of the mixture, washing the mixture with acetone By changing the condition of whether or not, a silicon-carbon composite was prepared, and its shape was confirmed through a scanning electron microscope (SEM). In addition, an electrode including the composite was prepared, and electrochemical characteristics and charge / discharge voltage characteristics were confirmed through a half cell including the electrode.

As a result, unlike in other conditions and other numerical ranges, when all of the following conditions were satisfied, the silicon-carbon composite confirmed that a spherical composite encapsulated with silicon was formed, and silicon was completely exposed to the carbon structure without being exposed to the outside. It was observed.

(I) starch is corn starch, (ii) surfactant is cetyltrimethylammonium bromide, (i) solvent is water, (i) oil is silicone oil, (i) starch and surfactant are in a weight ratio of 1: 4 to 1: 5, (i) the weight ratio of starch and silicone is 9: 1 to 10: 1, (v) the volume ratio of solvent and oil is 1: 3 to 1: 4, and (v) the mixture is homogenized for 1 to 10 minutes and 105 Sonication for 5 to 30 minutes at a power of 250 Watts, (i) washing the mixture with acetone.

However, when any one of the above conditions is not satisfied, it was confirmed that a spherical composite is not generated or silicon is not completely covered by the carbon structure and is exposed to the outside.

The present invention provides a negative electrode active material comprising a silicon-carbon composite prepared by the manufacturing method according to the above.

The present invention provides a negative electrode for a secondary battery comprising the negative electrode active material, a conductive material and a binder.

The conductive material may be any one or a mixture of two or more selected from the group consisting of acetylene black, carbon black and ketjen black.

The binder may be any one selected from the group consisting of polyacrylic acid, polyamide, styrene-butadiene rubber, carboxymethyl cellulose, polyvinylidene fluoride-hexafluoropropylene copolymer, or a mixture of two or more of them.

The present invention provides a lithium secondary battery comprising a negative electrode for a secondary battery, a positive electrode containing a lithium metal, and an electrolyte.

The electrolyte is an ethylene carbonate (EC; ethylene carbonate), ethylmethyl carbonate (EMC), diethyl carbonate (DEC) in which LiPF ₆ salt, LiBF ₄ salt, LiClO ₄ salt, etc. are dissolved. It may be any one or a mixture of two or more selected from the group consisting of a mixture and a mixture of fluoroethylene carbonate (FEC; Fluoroethylene carbonate), a solution of vinylene carbonate (VC) and mixtures thereof. have.

In the lithium secondary battery, when lithium metal is used as a counter electrode, the initial discharge capacity is 1000 mAh / g to 2500 mAh / g at 0.05 C (0.2 A / g) in the charge / discharge test, and 0.2 C (0.8 A / g), the discharge capacity is 500 mAh / g to 2000 mAh / g, and the retention rate of the discharge capacity of 0.2C (0.8 A / g) may be 80 to 95%.

Hereinafter, the present invention will be described in more detail with reference to preferred embodiments. However, these examples are intended to illustrate the present invention in more detail, and it will be apparent to those skilled in the art that the scope and contents of the present invention may not be reduced or interpreted. In addition, if it is based on the disclosure of the present invention including the following examples, it is obvious that a person skilled in the art can easily implement the present invention in which experimental results are not specifically provided, and such modifications and modifications are attached to the patent. Naturally, it is within the scope of the claims.

Example 1. Preparation of carbon anode material encapsulated in silicon

Example 1-1

As a carbon-based material, 2.5 g of cetyltrimethyl ammonium bromide (CTAB) and 0.5 g of C & Vision's silicon nanopowder (silicon purity ≥99.9%) using 5 g of corn starch in starch are used. The mixture dispersed in 10 ml of water is added to 30 ml of silicone oil, and the resultant mixture stirred at 1150 rpm is homogeneously mixed with a Homogenizer for 3 minutes at a power of 105 watts through an ultra sonicate for 10 minutes. The mixture was heated and dried in an air atmosphere at 180 ° C. for 12 hours, and then washed with acetone to separate the silicone oil and powder. Finally, the resultant was heat-treated, or carbonized, at 700 ° C. for 6 hours to prepare a silicon-carbon composite.

Example 1-2

A silicon-carbon composite was prepared in the same manner as in Example 1-1, except that 5 g of corn starch, 5 g of cetyltrimethylammonium bromide, and 0.5 g of silicon were used.

Example 1-3

A silicon-carbon composite was prepared in the same manner as in Example 1-1, except that 5 g of corn starch, 10 g of cetyltrimethylammonium bromide, and 0.5 g of silicon were used.

Example 1-4

A silicon-carbon composite was prepared in the same manner as in Example 1-1, except that 5 g of corn starch, 20 g of cetyltrimethylammonium bromide, and 0.5 g of silicon were used.

Example 1-5

A silicon-carbon composite was prepared in the same manner as in Example 1-1, except that 5 g of corn starch, 20 g of cetyltrimethylammonium bromide, and 1 g of silicon were used.

Example 1-6

A silicon-carbon composite was prepared in the same manner as in Example 1-1, except that 5 g of corn starch, 20 g of cetyltrimethylammonium bromide, and 1.5 g of silicon were used.

Example 1-7

A silicone-carbon composite was prepared in the same manner as in Example 1-1, except that 40 ml of water was used without adding silicone oil.

Example 2. Electrode comprising silicon-carbon composite encapsulated in silicon

The carbon anode material encapsulated in silicon prepared in Example 1-4, Example 1-5 and Example 1-6, a conductive material (Super P), and a binder (PAA; polyacylic acid) of 60:20:20 After mixing in a weight ratio, a slurry was prepared by uniformly stirring with stirrer using ethanol (Ethylene alcohol) as a dispersant. The slurry was applied to a copper foil, dried at 60 ° C. for 12 hours, and then pressed using a rolling press. After punching the pressed electrode to a diameter of 14 mm, the content was measured using a fine balance, and only the mass of the silicon-carbon composite containing silicon except for the conductive material, binder, and foil was obtained. The compressed electrode was dried in a vacuum oven at 80 ° C. for 12 hours to prepare a composite electrode. A button cell (Coin cell) was assembled using the dried electrode, and lithium metal was used as a counter electrode.

Example 3. Half cell including the electrode of Example 2

The electrode prepared from Example 2 was used as a working electrode of a half cell, lithium metal was used as a counter electrode, and the electrolyte was wetted as a separator. ) Polypropylene (PP; poly-propylene) was used.

Here, ethylene carbonate (EC; ethylene carbonate) and diethyl carbonate (DEC) in which 1.2 M LiPF ₆ salt is dissolved are 10 wt% in a 1: 1 volume ratio of fluoroethylene carbonate (FEC; Fluoroethylene). carbonate) was used.

The half cell was made of Coin 2032 type, and all processes of battery assembly were performed in a glove box in which the relative humidity and oxygen are always maintained at less than 0.1 ppm.

Comparative Example 1. Silicon nanoparticles

Silicon nanoparticles without any treatment were used to examine the difference between the silicon-encapsulated silicon-carbon composite.

Comparative Example 2. Silicon nanoparticle electrode

Using the silicon nanoparticles of Comparative Example 1 as a negative electrode material for a lithium battery, the same procedure as in Example 2 was performed to prepare an electrode.

Comparative Example 3. Half cell including the electrode of Comparative Example 2

A lithium secondary battery was manufactured in the same manner as in Example 3, except that the electrode prepared from Comparative Example 2 was used instead of the electrode prepared from Example 2.

Test Example 1. Scanning electron microscope observation of starch

A scanning electron microscope (SEM; Scanning Electron Microscope) picture of corn starch, which is a starch used as a carbon material according to Example 1 of the present invention, is shown in FIG. 1. 1 shows a 5 μm image of corn starch, and the average diameter of corn starch in FIG. 1 is 5 μm to 10 μm.

Test Example 2. Silicon-carbon composite according to starch and surfactant ratio

Scanning electron microscope observation

Scanning Electron Microscope (SEM) pictures of silicon-carbon composites prepared according to Examples 1-1 to 1-4 of the present invention are shown in FIG. 2. Figure 2 is a photograph of Example 1-1 (starch: surfactant = 2: 1 weight ratio) according to the weight ratio of the starch and the surfactant according to the weight ratio of the starch and surfactant in Figure 2a, Example 1-2 (starch: interface Activator = 1: 1 weight ratio) Picture in FIG. 2B, Example 1-3 (starch: surfactant = 1: 2 weight ratio) Picture in FIG. 2C, Example 1-4 (starch: surfactant = 1: 4 weight ratio) ) Pictures are shown in FIG. 2D. In FIG. 2, when the surfactant was prepared at a ratio of 4 times the starch, it was confirmed that the optimal condition was observed by observing that a model of the sphere was produced.

In addition, Figure 3 is a SEM photograph of a silicon-carbon composite prepared according to Examples 1-7. When silicone oil was not added, it was confirmed that a spherical model was not generated.

X-ray diffraction analysis

FIG. 4 shows that the silicon-carbon composites prepared according to Examples 1-1 to 1-4 of the present invention cannot be confirmed through the photograph of FIG. 2 whether silicon is encapsulated in carbon, X-ray diffraction analysis (XRD; XX-ray diffraction) is a graph measuring silicon-carbon complex according to the ratio of starch and surfactant. As a result of the measurement, since silicon peaks were detected in the silicon-carbon composites of Examples 1-1 to 1-4, it was confirmed that silicon was encapsulated in carbon.

Test Example 3. Silicon-carbon composite according to starch and silicon ratio

Scanning electron microscope observation

Scanning Electron Microscope (SEM) pictures of silicon-carbon composites prepared according to Examples 1-4 and 1-5 of the present invention are shown in FIG. 5. Figure 5 is a photograph of Example 1-4 (starch: silicon = 10: 1 weight ratio) as a photograph of a silicon-carbon composite according to the weight ratio of starch and silicone. In Figure 5a, Example 1-5 (starch: silicon = 5 : 1 weight ratio) The photograph is shown in Fig. 5B. In the complex of FIG. 5, the weight of the surfactant was 4 times the starch, and in FIG. 5, it was confirmed that a model of a sphere was generated when the weight of silicone was 10% and 20% of the weight of the starch. Could.

X-ray diffraction analysis

FIG. 6 shows that the silicon-carbon composites prepared according to Examples 1-4 and 1-5 of the present invention cannot be confirmed through the photograph of FIG. 5 whether silicon is encapsulated in carbon, and thus X-ray diffraction analysis (XRD; It is a graph measured by XX-ray diffraction) device. As a result of the measurement, silicon peaks were detected in the silicon-carbon composites of Examples 1-4 and 1-5, and it was confirmed that silicon was encapsulated in carbon.

Test Example 4. Thermogravimetric analysis

7 is a graph measured by a thermogravimetric analysis (TGA) device to determine the silicon content of the silicon-carbon composites prepared according to Examples 1-4, 1-5, and 1-6 of the present invention. As a result of measuring from 100 ° C. to 900 ° C. in an oxygen atmosphere, 10% of the weight of silicon was used in Example 1-4 (10% silicon-carbon composite). 38.92% by weight of silicon and 20% of silicon by weight Example 1-5 (20% silicon-carbon composite) used was 54.36% by weight of silicone and 30% of the weight of silicone was used. Example 1-6 (30% silicon-carbon composite) was 62.09% by weight of silicone. %.

Test Example 4. Evaluation of half cell electrochemical properties

8A is a view showing the electrochemical characteristics of a lithium half cell according to Example 3 of the present invention, and the cut-off voltage was charged / discharged in a region of 0.01 V to 1.5 V.

The charge / discharge current was 0.05 C (0.2 A / g), and the same current intensity was used, and the unit C was the speed of the current, meaning the theoretical capacity divided by the discharge time.

The silicon-carbon composite electrode of Example 3 prepared from Example 1-4 of the present invention (starch: silicon = 10: 1 weight ratio) confirmed the first discharge capacity of 1250 mAh / g.

The silicon-carbon composite electrode of Example 3 prepared from Example 1-5 (starch: silicon = 5: 1 weight ratio) of the present invention confirmed the first discharge capacity of 1830 mAh / g.

The silicon-carbon composite electrode of Example 3 prepared from Example 1-6 of the present invention (starch: silicon = 3.33: 1 weight ratio) confirmed the first discharge capacity of 1970 mAh / g.

As shown in the above results, it was confirmed that the capacity increased as the silicon content increased, and compared to the existing silicon-carbon composite electrode having an initial discharge capacity of about 800 mAh / g, it was confirmed that the initial discharge capacity was significantly increased. Did.

Figure 8b is a view showing the electrochemical properties of the electrode with a cut-off voltage of 0.01 V ~ 1.5 V of the present invention, charge and discharge in the case of a charge and discharge current of 0.2 C-rate (0.8A / g) The discharge storage capacity is changed according to the number of cycles. Basically, to test the cycle performance, the c-rate of charge / discharge was kept constant at 0.2 C.

The silicon-carbon composite electrode of Example 3 prepared from Example 1-4 of the present invention (starch: silicon = 10: 1 weight ratio) confirmed a cycle retention rate of 93% at 50 cycles.

The silicon-carbon composite electrode of Example 3 prepared from Example 1-5 (starch: silicon = 5: 1 weight ratio) of the present invention confirmed a cycle retention rate of 90% at 50 cycles.

The silicon-carbon composite electrode of Example 3 prepared from Example 1-6 of the present invention (starch: silicon = 3.33: 1 weight ratio) confirmed a cycle retention rate of 93% at 50 cycles.

The silicon nanoparticle electrode according to Comparative Example 3 confirmed a very low cycle retention rate of 17% at 50 cycles.

As shown in the above results, it was confirmed that the electrode of the present invention has a significantly higher cycle retention rate than the comparative example, and thus has excellent durability.

Claims (28)

delete delete delete delete delete delete 1) preparing a precursor solution by mixing silicone, starch and surfactant in a solvent selected from water, C _1-5 alcohol or mixtures thereof;
2) preparing a mixture by mixing oil in the precursor solution; And
3) heat-treating the mixture at a temperature of 500 to 1000 ° C. for 3 to 10 hours.
The starch is corn starch;
The surfactant is cetyltrimethylammonium bromide;
The solvent is water;
The oil is silicone oil;
The weight ratio of the starch and the surfactant is 1: 4 to 1: 5;
The weight ratio of the starch and the silicone is 9: 1 to 10: 1;
The volume ratio of the solvent and the oil is 1: 3 to 1: 4;
Further comprising the step of homogenizing the mixture of step 2) for 1 to 10 minutes and sonication for 5 to 30 minutes at a power of 105 to 250 Watts;
Washing the mixture with acetone; Method for producing a silicon-carbon composite further comprising. delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete

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