KR100762796B1 - Manufacturing Method of Negative Active Material For Lithium Secondary Battery And Lithium Secondary Battery Comprising The Same - Google Patents

Abstract

The present invention provides a method of manufacturing a lithium secondary battery negative electrode active material coated with silicon by mixing a high capacity silicon (Si) material and a conductive polymer, in particular polyaniline (PAn) and carbonizing in an inert atmosphere. In addition, by including the negative electrode active material in the negative electrode, the electronic conductivity is smooth by the carbon network of the carbon sponge, the conduction of lithium ions by the pores smoothly, and buffer the volume expansion of the silicon material to buffer the performance of the battery Provided is an improved lithium secondary battery.

Lithium secondary battery, negative electrode active material, silicon, conductive polymer, polyaniline

Description

Manufacturing method of negative electrode active material for lithium secondary battery and lithium secondary battery having same {Manufacturing Method of Negative Active Material For Lithium Secondary Battery And Lithium Secondary Battery Comprising The Same}

1 is a block diagram of a lithium secondary battery according to an embodiment of the present invention,

2a to 2d are distribution charts for the particle size analysis of the negative electrode active material according to an embodiment of the present invention,

3 is a change in particle size due to the synthesis and carbonization of the negative electrode active material according to an embodiment of the present invention,

Figure 4a and 4b is an XRD diffraction analysis of the negative electrode active material according to an embodiment of the present invention,

5A through 5D are FESEM results of the negative active material according to the exemplary embodiment of the present invention.

6A to 6C are views illustrating specific capacity and life characteristics of a lithium secondary battery according to an embodiment of the present invention;

7A to 7C are diagrams illustrating initial charge and discharge characteristics of a rechargeable lithium battery according to one embodiment of the present invention;

8A to 8D are diagrams illustrating initial charge and discharge characteristics by de-doping and adding FEC of a lithium secondary battery according to one embodiment of the present invention;

9A to 9C are diagrams illustrating potential characteristics through a GISOC test of a lithium secondary battery according to one embodiment of the present invention;

10a to 10c is a view of the irreversible specific capacity characteristics according to the discharge capacity of the lithium secondary battery according to an embodiment of the present invention,

11A to 11C are diagrams for specific resistance characteristics according to charge capacity of a rechargeable lithium battery according to one embodiment of the present invention;

12A to 12F are diagrams illustrating GISOC test characteristics by de-doping and adding FEC of a lithium secondary battery according to one embodiment of the present invention.

** Description of the main symbols in the drawings *

1: lithium secondary battery 2: negative electrode

3: anode 4: separator

5: battery container 6: sealing member

The present invention relates to a method for manufacturing a negative electrode active material for a lithium secondary battery and a lithium secondary battery having the same. More specifically, a conductive polymer, preferably a thermosetting polymer, in particular polyaniline (PAn) and silicon is mixed and carbonized The present invention relates to a method for producing a negative electrode active material having excellent physical and electrochemical properties, and to a lithium secondary battery including the negative electrode active material.

 Recently, the development of the electronic and information communication industry is showing rapid growth through the portable, miniaturized, lightweight, and high-performance electronic devices. Therefore, high-performance lithium secondary batteries are employed as power sources for these portable electronic devices, and demand is increasing rapidly. Secondary batteries used with repeated charging and discharging are essential as power sources for portable electronic devices, electric bicycles, and electric vehicles for information and communication. In particular, since their product performance depends on batteries, which are core components, the demand for high performance batteries is very large. The characteristics required for the battery include various aspects such as charge and discharge characteristics, lifespan, high rate characteristics, and stability at high temperatures, and lithium secondary batteries are most commonly used.

Lithium secondary batteries are the ones that are attracting the most attention because they have high voltage and high energy density. They are liquid type batteries using liquids according to electrolytes, gel polymer batteries using a mixture of liquids and polymers, and solid polymer batteries using pure polymers. It can also be distinguished.

The lithium secondary battery is mainly composed of a positive electrode, a negative electrode, an electrolyte, a separator, a packaging material, and the like. The positive electrode is formed by binding a mixture of a positive electrode active material, a conductive agent, and a binder to a current collector. As the positive electrode active material, lithium transition metal compounds such as LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , and LiMnO ₂ are mainly used. These materials have a high electrochemical reaction potential that proceeds as intercalation / deintercalation of lithium ions into the crystal structure occurs.

Lithium metal, carbon or graphite is mainly used as the negative electrode active material and has a low electrochemical reaction potential as opposed to the positive electrode active material. The electrolyte is mainly composed of LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ , LiPF ₆ , LiBF ₄ , LiClO ₄ , LiN ( A salt containing lithium ions such as SO ₂ C ₂ F ₅ ) ₂ is dissolved and used.

As the separator which electrically insulates the positive electrode and the negative electrode and provides a passage of ions, a polyoletin-based polymer such as porous polyethylene is mainly used. As an exterior material that protects the contents of the battery and provides an electrical passage to the outside of the battery, a metal can or a packaging material composed of aluminum and several layers of polymer layers is mainly used.

Lithium-ion secondary batteries that use liquids as electrolytes present a risk of fire or explosion due to overcharging or other careless use. In order to manufacture such a safety problem and a thinner and free battery, there are many developments of a lithium ion polymer battery using a polymer as an electrolyte. The lithium ion polymer battery is constructed by impregnating a liquid electrolyte in a matrix of polymer materials such as polyvinylidene fluoride, polyethylene oxide, and polyacrylonitrile. Therefore, there is less risk of leakage of the liquid electrolyte, and instead of a metal can, a packaging material composed of aluminum foil and polymer layers can be used, thereby having an advantage of being thin and free of shapes.

BACKGROUND OF THE INVENTION A lithium secondary battery is used as a battery that stores DC power by repetitive operations of charging and discharging and can supply DC to the outside as needed. Such a secondary battery has a configuration in which a positive electrode and a negative electrode are positioned in the same casing with an electrolyte therebetween, and these electrodes are connected to an external load so that current can flow. To this end, the positive electrode and the negative electrode are coated or cast with a so-called active material which functions as a chemical substance for generating and exporting electrical energy to an external circuit. Since the active material may be uniformly applied to the electrode member to improve the performance of the battery, the application of the active material has a great effect on the performance of the battery and active research is being conducted.

Significant improvements in the specific amount of the cathode material have been made. The current graphite material has a theoretical specific capacity of 372 mAh / g and a density of 2.62 g / ml. However, in the case of silicon under development, the graphite material has a significantly higher value of 4200 mAh / g and has a density of 2.33 g / ml. Lithium intercalation potential also shows similar characteristics as graphite.

However, when silicon is used as a negative electrode active material, the electrical conductivity is low as ˜10 ⁻⁴ s / cm, which is a semiconductor region, and has a problem that volume expansion occurs up to 297% (Li ₂₁ Si ₅ ) due to lithium insertion.

In addition, recently, as a negative electrode material of a lithium secondary battery, a material in which graphite is simply mixed with a silicon compound powder has been proposed, but since the graphite and silicon compound are not necessarily in close contact with each other, the charge and discharge cycle proceeds. Therefore, when the graphite expands and contracts, the silicon compound is released from the graphite, and since the silicon compound itself has low electron conductivity, the silicon compound is not sufficiently used as a negative electrode active material, and the cycle characteristics of the lithium secondary battery are deteriorated. have.

The present invention is to solve the above problems,

Lithium secondary battery negative electrode active material coated with silicon by mixing a high capacity silicon (Si) material with a conductive polymer, preferably a thermosetting polymer, particularly polyaniline (PAn) and silicon and carbonizing in an inert atmosphere It is an object to provide a method for producing a.

In addition, by including the negative electrode active material in the negative electrode, the electronic conductivity is smooth by the carbon network of the carbon sponge, the conduction of lithium ions by the pores smoothly, and buffer the volume expansion of the silicon material to buffer the performance of the battery It is an object to provide an improved lithium secondary battery.

The present invention for achieving the above object,

Preparing a mixture of conductive polymer and silicon; And a carbonization step of carbonizing the mixture in a carbonization furnace to apply carbon to the silicon surface.

In addition, the conductive polymer provides a method for producing a negative electrode active material for a lithium secondary battery, characterized in that the thermosetting polymer.

In addition, the conductive polymer provides a method for producing a negative active material for a lithium secondary battery, characterized in that the doped with hydrochloric acid.

The preparing of the mixture may include preparing a mixed solution including the monomer and the silicon of the conductive polymer, polymerizing and drying the monomer to prepare a mixture of the conductive polymer and the silicon. It provides a method of manufacturing.

In addition, the carbonization step provides a method for producing a negative electrode active material for a lithium secondary battery, characterized in that performed in an inert gas atmosphere.

In addition, the inert gas provides a method for producing a negative electrode active material for a lithium secondary battery, characterized in that the argon (Ar) gas.

In addition, the carbonization step provides a method for producing a negative electrode active material for a lithium secondary battery, characterized in that performed in the range of 900 ~ 1100 ℃.

In addition, after the carbonization step, it provides a method for producing a negative electrode active material for a lithium secondary battery, characterized in that it further comprises a grinding step of finely pulverizing the carbon coated silicon.

In addition, the weight ratio of the conductive polymer and the silicon is in the range of 20 to 70: 80 to 30, more preferably in the range of 40 to 60: 60 to 40 provides a method for producing a negative electrode active material for a lithium secondary battery do.

In addition, the silicon provides a method for producing a negative electrode active material for a lithium secondary battery, characterized in that the average particle diameter is 40㎛ or less.

In addition, the conductive polymer provides a method for producing a negative electrode active material for a lithium secondary battery, characterized in that the polyaniline (PAn).

The present invention also provides a lithium secondary battery having a negative electrode including a negative electrode active material and a positive electrode and an ion conductor including a positive electrode active material, wherein the negative electrode active material is any one of claims 1 to 10 using a conductive polymer. It provides a lithium secondary battery comprising a negative electrode active material prepared according to the manufacturing method described in.

In addition, the conductive polymer provides a lithium secondary battery, characterized in that the polyaniline (PAn).

In addition, the negative electrode provides a lithium secondary battery, further comprising carbon black (Super P Black) as a conductive material.

In addition, the negative electrode provides a lithium secondary battery, characterized in that the binder further comprises a carboxymethyl cellulose (CMC) and a copper current collector.

In addition, the ion conductor provides a lithium secondary battery, characterized in that the electrolyte or polymer electrolyte.

Hereinafter, the present invention will be described in more detail.

First, the manufacturing method of the negative electrode active material for lithium secondary batteries according to the present invention will be described.

Method for producing a negative electrode active material for a lithium secondary battery according to the invention, the step of preparing a conductive polymer, preferably a thermosetting polymer, in particular a mixture of polyaniline (PAn) and silicon, and carbonizing the mixture in a carbonization furnace on the surface of the silicon Characterized in that it comprises a; carbonization step to be applied to the carbon.

The conductive polymer is not limited but is preferably a thermosetting polymer. In particular, polyaniline (PAn) is preferable. The thermosetting polymer has a feature of forming a more porous form when carbonizing than the thermoplastic polymer. Since there is no melting of the polymer during carbonization, no agglomeration occurs between particles, and thus no separate grinding process is required. There is an advantage.

Examples of the conductive polymer may include polyaniline (PAn), polyacetylene (Polyacetylene), polypyrrole (polypyrrole), polythiophene (Polythiophene) and the like. The conductive polymer may be a conductive polymer doped with hydrochloric acid or the like.

The method of evenly mixing the conductive polymer and the silicon is not limited and may be mixed by the following method.

First, the conductive polymer is added and stirred until completely dissolved. The solvent is not limited and is preferably an organic solvent, in particular water or acetone. The stirring time is not limited and preferably 20 minutes to 2 hours.

The weight ratio of the conductive polymer and the silicon is not limited, but is preferably in the range of 20 to 70: 80 to 30, particularly preferably in the range of 40 to 60: 60 to 40. According to the experimental results to be described later, the best at a composition ratio of about 50:50.

Thereafter, silicon is added to the solution, stirred, and dried to obtain a mixture. Although the average particle diameter of a silicon particle is not restrict | limited, 40 micrometers, More preferably, 1-20 micrometers is preferable. The stirring time is not limited and preferably 20 minutes to 2 hours.

More preferably, after preparing a mixed solution containing the monomer and silicon of the conductive polymer, the monomer is polymerized and dried to prepare a mixture of the conductive polymer and silicon. The mixed solution may include hydrochloric acid for doping.

That is, silicon (2-5 μm Atlantic equipment engineers) and a conductive polymer monomer are added to a beaker containing a solvent containing hydrochloric acid and stirred, and according to a polymerization method of a conductive polymer known in the art, a polymerization initiator or A polymerization catalyst is added and polymerization is carried out by irradiating heat or ultraviolet rays as necessary. After completion of the reaction, the mixture is washed several times with distilled water and acetone and dried in a vacuum oven at 100 ° C. for 24 hours to prepare a conductive polymer-silicon mixture. Through this method, the mixture can be formed more evenly. Although the weight ratio of the conductive polymer and the silicon is not limited, it is preferable to be in the range of 20 to 70: 80 to 30, particularly preferably in the range of 40 to 60: 60 to 40. According to the experimental results to be described later, the best at a composition ratio of about 50:50. In addition, a hydrochloric acid dedoped conductive polymer may be used using a solvent that does not contain hydrochloric acid, or the hydrochloric acid dedoped conductive polymer may be used by removing the hydrochloric acid by washing until it is neutral with an aqueous ammonia solution.

Next, the conductive polymer-silicon mixture prepared by the above process is put into a carbonization furnace and carbonized to prepare a negative electrode active material coated with carbon on the silicon surface by a simple method. In the above method, since the chemical vapor deposition method has to blow carbon material into an electric furnace including silicon material in the gas phase, deposition is not uniform, it is difficult to process in large quantities, and the process is complicated. The method is characterized in that the material is uniformly mixed before carbonization and carbonized, so that the material is uniformly applied, easy to manufacture in large quantities, and simple to manufacture, which is easy to manufacture.

The carbonization step is preferably carried out in an atmosphere of inert gas, it is particularly preferable to use argon gas as the inert gas. In addition, the carbonization time is not limited, but is preferably 1 to 3 hours, the carbonization temperature is preferably carried out at 900 ~ 1100 ℃, especially about 1000 ℃.

After the carbonization step, it may further include the fine grinding of the negative electrode active material coated with carbon on the silicon surface obtained by using a mortar.

Physical properties of the negative electrode active material according to an embodiment of the present invention prepared by the above process was measured and the measurement results will be described in more detail in Example 1 and Experimental Example 1 which will be described later.

Hereinafter, a lithium secondary battery having a negative electrode active material according to an embodiment of the present invention will be described in detail.

A lithium secondary battery having a negative electrode active material according to the present invention is a lithium secondary battery having a negative electrode including a negative electrode active material and a positive electrode and an ion conductor including a positive electrode active material, wherein the negative electrode active material is prepared according to the above-described manufacturing method It characterized by comprising a negative electrode active material. Except for the negative active material manufactured according to the above-described manufacturing method, the remaining components can be selected and applied without limiting the configurations known in the art. Preferably, the negative electrode may further include carbon black (Super P Black) as a conductive material, and the negative electrode may further include a carboxymethyl cellulose (CMC) and a copper current collector as a binder. In addition, the ion conductor may be an electrolyte solution or a polymer electrolyte.

The lithium secondary battery according to an embodiment of the present invention may further include a negative electrode active material known in the art, in addition to the above-described negative electrode active material. That is, although not limited, it may further include lithium metal, carbon or graphite. Since the negative electrode active material has been described above in detail, a description thereof will be omitted.

1 shows a lithium secondary battery 1 which is an embodiment of the present invention. The lithium secondary battery 1 includes a negative electrode 2, an electrode 3, a separator 4 disposed between the negative electrode 2 and the positive electrode 3, the negative electrode 2, the positive electrode 3, and the separator 4. ), The ion conductor impregnated in the ()), the battery container (5), and the sealing member (6) for sealing the battery container (5) as a main portion. The shape of the lithium secondary battery illustrated in FIG. 1 may be in a cylindrical shape, but in addition, various shapes such as a cylindrical shape, a square shape, a coin shape, a sheet shape, and the like.

The positive electrode 3 is provided with a positive electrode mixture composed of a positive electrode active material, a conductive material and a binder. The positive electrode active material is a compound capable of reversibly intercalating / deintercalating lithium, such as LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , LiFeO ₂ , V ₂ O ₅ , TiS, MoS, and the like.

As the separator, an olefin porous film such as polyethylene or polypropylene can be used.

The ion conductor may be propylene carbonate (hereinafter referred to as PC), ethylene carbonate (hereinafter referred to as EC), butylene carbonate, benzonitrile, acetonitrile, tetrahydrofuran, 2-methyl tetrahydrofuran, γ-butyrolactone, dioxane, and the like. Solan, 4-methyldioxolane, N, N-dimethylformamide, dimethylacetoamide, dimethyl sulfoxide, dioxane, 1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, dimethyl carbonate ( Hereinafter, DMC), ethyl methyl carbonate (hereinafter EMC), diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, ethyl butyl carbonate, dipropyl carbonate, diisopropyl carbonate, dibutyl carbonate, diethylene glycol, dimethyl ether LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ , LiPF ₆ , LiBF ₄ , LiClO ₄ , LiN (S) in an aprotic solvent such as or a mixed solvent of two or more of these solvents mixed. O ₂ C ₂ F ₅₎ may be used that prepared by dissolving a mixture of the electrolyte alone or in combination of two or more made of a lithium salt of _2, and so on.

In addition, a polymer solid electrolyte may be used instead of the electrolyte solution. In this case, it is preferable to use a polymer having high ion conductivity with respect to lithium ions, and polyethylene oxide, polypropylene oxide, polyethyleneimine and the like can be used. The solvent and the solute may be added to the polymer of to form a gel.

Hereinafter, preferred examples and comparative examples of the present invention are described. However, the following examples are only one preferred embodiment of the present invention and the present invention is not limited to the following examples.

<Example 1>

In order to prepare the negative electrode active material, a beaker containing distilled water and hydrochloric acid mixed solution was added with a single molecule of silicon (2-5 μm Atlantic equipment engineers) and aniline (C ₆ H ₇ N, Aldrich), followed by stirring for about 10 minutes. Then, a mixture of distilled water and sulfuric acid prepared in advance was added and stirred for about 10 minutes. Then, a solution in which ammonium persulfate ((NH ₄ ) ₂ S ₂ O ₈ , Aldrich) was dissolved in distilled water was added dropwise for about 7 hours. To react. At this time, it was maintained at -5 ℃ ~ 0 ℃ using ice. After the reaction was completed, washed several times with distilled water and acetone and dried for 24 hours in a vacuum oven at 100 ℃ to prepare a silicone-polyaniline complex. The weight ratio of silicone and polyaniline was prepared in 70/30 and 50/50. In addition, some of the silicon-polyaniline composites prepared at a weight ratio of 70/30 were washed with distilled water several times until the filtrate was neutralized with 28% aqueous ammonia solution (NH ₄ OH), followed by de-doping of hydrochloric acid. The mixture thus prepared was carbonized and cooled at 1000 ° C. for about 2 hours in an argon gas atmosphere carbonized furnace, and finely ground using mortar.

Experimental Example 1

To measure the physical properties of the negative electrode active material prepared by the above method, the average particle size of the prepared active material particles was analyzed (mastersizer, 0.3 to 300 μm, malvern, UK), and XRD (Philips, PW1830, 0.04 2θ / sec, 10 to 120 °), FESEM (Hitachi, s-4800) was measured to confirm the physical properties of the composition and form of the active material.

As a result, the negative electrode active material according to the present invention has an average particle size increased to about 1.2㎛, 10㎛ according to the content of PAn as shown in Figures 2a to 2d and the particle size of about 10㎛, 12㎛ depending on the presence or absence of doping The difference is shown. In addition, as shown in FIG. 3, it was confirmed that PAn is coated on the silicon at a content of 70/30, and thus the particle size is increased, and the PAn shrinks slightly while undergoing carbonization again.

XRD diffraction analysis results shown in Figures 4a and 4b can confirm the characteristic peaks of the crystalline silicon. However, when the intensity value of the figure is expressed on a log scale, the coexistence of the carbon material can be easily confirmed as shown in FIG. 4B. It can be seen that low crystalline carbon appears with the characteristic peak of Si in the region where the 2θ value is 20 degrees. The average interplanar spacing was 4.037Å when the lambda value of 1.54056Å was applied, indicating low crystallinity of zero graphitization degree.

As shown in the SEM analysis results shown in FIGS. 5A to 5D, it was confirmed that carbon was applied to the silicon surface regardless of PA doping or not, and the amount of carbon increased as the content was increased. 5A shows the formation of non-carbonized silicon. 5b and 5c show silicon surface shapes with and without de-doping of materials using 30 wt% PAn, and FIG. 5d shows silicon surface shapes of materials using 50 wt.% PAn. As shown, it can be seen that the carbon material surrounds the silicon surface.

<Example 2>

Preparation of a lithium secondary battery according to the present invention is as follows. The electrode was prepared by first mixing 92 wt% of the negative electrode active material prepared in Example 1 with 4 wt% of a binder (CMC (carboxymethyl cellulose 1.2 wt% solution), followed by high speed stirring (6000 rpm), and then 40 wt% solution of styrene butadiene rubber (SBR). 4% by weight was added and stirred again at 9000 rpm to prepare a negative electrode mixture, which was applied to a copper current collector and dried in a 110 ° C. dryer for 30 minutes. The prepared negative electrode was pressed at an electrode density of 1.5 to 1.6 g / cm ³ using a twin roller, and used in an experiment after vacuum drying at 60 ° C. for 24 hours. The fabrication of the test cell used Si-C electrode plate as the working electrode, A coin cell was fabricated using lithium metal as a counter electrode. Electrolyte is 1.0 M LiPF ₆ + Electrolyte solution to which EC: DMC: EMC: PC (4: 3: 3: 1 volume ratio) and 5% by weight of Fluoro Ethylene Carbonate (FEC) was added was used. The prepared lithium secondary battery was aged at room temperature for 24 hours.

Comparative Example

 In order to compare the negative electrode active material and the pure silicon active material according to the present invention, a Si / Li cell was manufactured using silicon alone as an active material, and a cycle test and a GISOC test were performed. The battery was manufactured by the method of Example 2 described above.

Experimental Example 2

The lithium secondary batteries prepared according to Experimental Example 2 and Comparative Example were analyzed for change in potential over time, capacity characteristics, and initial charge / discharge characteristics through cycle tests and GISOC tests. Cycle characteristics were determined using Si | active material manufactured by Si alone and Si-PAn. Li and Si-C | A Li battery was prepared and charged and discharged 20 times over a voltage range of 0 to 3 V at a current of C / 10 hours.

6a to 6c for Si alone and polyaniline (PAn) content | Li and Si-C | Li battery cycle characteristics are shown. When the capacity change was confirmed from the charge and discharge test results, it was confirmed that the capacity of the battery was slightly increased as the content of polyaniline (PAn) increased.

As shown in FIGS. 7A to 7C, the initial charge and discharge capacity of the polyaniline (PAn) content was analyzed. As a result, the initial charge specific capacity was 2.25 to 1949 mAh / g, and the discharge capacity was 0.46 to. A specific capacity value of 204.87 mAh / g was shown.

8A to 8D show test results for active materials having a composition of 70/30 to confirm the effects of dedoping and addition of fluorine-substituted EC (hereinafter referred to as FEC) in the electrolyte. Changes in charge and discharge capacity due to de-doping resulted in an initial charge cost of 1337 mAh / g and a discharge cost of 370 mAh / g, and changes in charge and discharge capacity when FEC was added and an initial charge cost of 1759 mAh / g and 127 mAh. The discharge specific capacity of / g appeared, but rather the cycle characteristics were confirmed to be lowered.

Si with increasing content of Si and PAn through GISOC test | Li and Si-C | The results of analyzing the initial charge and discharge characteristics of the Li battery are shown in FIGS. 9A to 11C. Each figure shows the potential-time gradient, the relationship between the charge and discharge capacities and the irreversible specific capacities, and the specific resistance change with the specific capacities. In the results of FIG. 10, the reversible specific capacity of the test battery was about 49.3 mAh / g for Si 100 wt%, about 148 mAh / g for 30 wt% PAn, and about 414 mAh / g 50 wt% PAn. Showed the results. The initial intercalation efficiency (IIE) of initial charge and discharge for each reversible range was 27.8%, 55.08%, 75.73%, and the initial irreversible capacity by the surface (IICs) was 1.41 mAh / g, 46.61 mAh / g and 35.35 mAh / g. When the weight ratio of Si and PAn is 70/30, the content of carbon material is lower than that of 50/50, and carbon and silicon are charged during the filling process, and the material particles are conductive path due to the expansion of silicon. Are likely to be separated from This assumption can be confirmed from the GISOC charge and discharge results described above. In the case of 50/50 ratio of Si and PAn, the reversible charge / discharge area of carbon material and silicon material appears respectively. Reversible capacity tended to decrease compared to the progress of charging. Si | Li and Si-C | Specific resistances obtained from the end of charging for each step in the GISOC test of the Li battery are shown in FIGS. 11A to 11C. In the initial stage of charging, the resistivity was high, but as the lithium insertion progressed, the resistance rapidly decreased and converged. The average resistivity of each battery according to the content of silicon and PAn of 100/0, 70/30, 50/50 wt% was maintained at 3.01 ohm * g, 2.61 ohm * g, and 2.72 ohm * g.

12A to 12F illustrate the relationship between charge and discharge specific amounts and irreversible specific amounts according to de-doping and addition of FEC to an active material of 70/30 composition. The reversible specific capacity range after undoping was about 169 mAh / g, and the reversible specific capacity range was about 194.8 mAh / g when FEC addition electrolyte was used. The intercalation efficiency IIE of initial charge and discharge for the reversible range was 70.9% after dedoping and 71.42% after FEC addition. The surface irreversible specific capacities were 11.3 mAh / g and 30.2 mAh / g, respectively. The average resistivity for charging was 1.99 ohm * g after undoping and 2.98 ohm * g after FEC addition. The GISOC characteristics according to Si and PAn contents are summarized in Table 1 below. As shown, the negative electrode active material and the battery according to the present invention can be seen that the properties are significantly improved compared to the silicon single material.

Table 1. Si-C | GISOC Characteristics of Li Cell

 PAn t content in Si-PAn (wt%) Electrolyte Doping Reversible Specific Capacity (mAh / g) Initial Intercalation Efficiency (IIE) (%) Initial irreversible specific capacities (IICs) (mAh / g) Resistivity (ohm * g) 0 E 49 27.80 1.41 3.01 30 E D 148 55.08 46.61 2.61 30 E U 169 70.90 11.29 1.99 30 E-F D 195 71.42 30.16 2.98 50 E D 414 75.73 35.35 2.72 [E]: 1M LiPF6 / EC: EMC: DMC: PC (4: 3: 3: 1), [EF]: 1M LiPF6 / EC: EMC: DMC: PC (4: 3: 3: 1) with FEC ( 5% by weight) [D]: doping, [U]: non-doping

According to the present invention, a negative electrode active material was developed using conductive polymers such as silicone and polyaniline (PAn), and physical and electrochemical properties were analyzed. It was confirmed that the negative electrode active material was coated with silicon through XRD diffraction analysis, and the electrochemical experiments showed that the negative electrode active material was excellent as a negative electrode active material of a lithium secondary battery.

In addition, the lithium secondary battery having the negative electrode active material according to the present invention has a smooth electron conduction by the carbon network of the carbon sponge, the conduction of lithium ions by the pores smoothly, and buffer the volume expansion of the silicon material to buffer the battery The performance is significantly improved.

Claims (17)

Preparing a mixture of a conductive polymer monomer and silicon, and then polymerizing and drying the monomer to prepare a mixture of the conductive polymer and silicon; And And carbonizing the mixture in a carbonization furnace so that carbon is coated on the surface of the silicon. The method of claim 1, wherein the conductive polymer is a thermosetting polymer. The method of claim 1, wherein the conductive polymer is doped with hydrochloric acid. delete The method of claim 1, wherein the carbonization step is performed in an inert gas atmosphere. The method of claim 1, wherein the inert gas is an argon (Ar) gas. The method of claim 1, wherein the carbonization step is performed in a range of 900 to 1100 ° C. 6. The method of claim 1, further comprising a grinding step of grinding the carbon-coated silicon finely after the carbonization step. The method of claim 1, wherein the weight ratio of the conductive polymer: silicon is in the range of 20 to 70:80 to 30. The method of claim 1, wherein the weight ratio of the conductive polymer and the silicon is in the range of 40 to 60: 60 to 40. The method of claim 1, wherein the silicon has an average particle diameter of 40 μm or less. 12. The method of claim 1, wherein the conductive polymer is polyaniline (PAn). 13. In a lithium secondary battery provided with a negative electrode containing a negative electrode active material and a positive electrode containing a positive electrode active material and an ion conductor, The negative electrode active material is a lithium secondary battery comprising a negative electrode active material prepared according to the manufacturing method of any one of claims 1 to 10 using a conductive polymer. The lithium secondary battery of claim 13, wherein the conductive polymer is polyaniline (PAn). The lithium secondary battery of claim 13, wherein the anode further comprises carbon black (Super P Black) as a conductive material. The lithium secondary battery of claim 13, wherein the anode further comprises a carboxymethyl cellulose (CMC) and a copper current collector as a binder. The lithium secondary battery of claim 13, wherein the ion conductor is an electrolyte or a polymer electrolyte.

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