KR20140107926A - Manufacturing of nitrogen doped carbon coated Silicon based anode materials and lithium secondary battery comprising the same - Google Patents

Abstract

Provided are a silicon-based anode material including a nitrogen-doped carbon coating and a lithium secondary battery including the same. According to the present invention, the silicon-based anode material including a nitrogen-doped carbon coating is manufactured by a mixing process with 1-ethyl-3-methylimidazolium dicynamide, which is an ionic liquid containing a large quantity of nitrogen; and by a carbonizing process. Through this method, a lithium secondary battery having excellent discharging capacity and high output properties can be manufactured.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a silicon-based anode active material containing a nitrogen-doped carbon coating and a lithium secondary battery comprising the same,

The present invention relates to a method for producing a silicon-based anode active material including a nitrogen-doped carbon coating layer having excellent electrical conductivity, and a lithium secondary battery comprising the same. More particularly, the present invention relates to a method of forming a carbon-doped carbon coating layer on a surface of a silicon-based particle by mixing a silicon-based particle having a high capacity and an ionic liquid containing a large amount of nitrogen, followed by a carbonization process by heat treatment The present invention relates to a method for producing a silicon-based anode active material, and a silicon-based anode active material thus prepared is applied to a lithium secondary battery to realize a high output characteristic and a high capacity.

The lithium secondary battery is a battery that generates electrical energy by changing the chemical potential when the lithium ions are intercalated / deintercalated in the positive and negative electrodes. Such a lithium secondary battery is manufactured by using a material capable of reversible intercalation / deintercalation of lithium ions as a positive electrode and a negative electrode active material, and filling an organic electrolyte or a polymer electrolyte between the positive electrode and the negative electrode. As the cathode active material of the lithium secondary battery, a lithium composite metal compound is used. Examples of the lithium composite metal compound include LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiNi _1-x Co _x O ₂ (0 <x <1), LiMnO ₂ Metal oxides are being studied.

As an anode active material of a lithium secondary battery, graphite capable of intercalation / deintercalation of lithium has been typically used. However, since the graphite-based electrode has a low charge capacity of 365 mAh / g (theoretical value: 372 mAh / g), there is a limit in providing a lithium secondary battery exhibiting excellent capacity characteristics.

Accordingly, inorganic active materials such as silicon (Si), germanium (Ge), and antimony (Sb) have been studied. Such a mineral-based active material, in particular, a silicon-based negative electrode active material, can exhibit a very large amount of lithium bonding (theoretical maximum: Li _4.4 Si), approaching a theoretical capacity of about 4200 mAh / g.

However, the silicon based negative electrode active material may cause pulverization of the active material due to intercalation / deintercalation of lithium, that is, a large volume change occurs during charging and discharging of the battery. As a result, the disruptions of the negative electrode active material can be electrically decoupled from the current collector, which can result in irreversible capacity loss under long cycles. Another disadvantage of the silicon based negative electrode active material is low electric conductivity. As a result, there is a problem that the output characteristic of the silicon-based anode active material is inferior to that of the conventional carbon-based anode active material, and this problem must be solved in the development of the next generation lithium secondary battery. In order to solve these problems, attempts were made to improve cycle characteristics and output characteristics of a silicon anode active material by incorporating a carbonaceous material having excellent electrical conductivity and excellent mechanical properties and a silicon anode material or a carbon surface coating.

Korean Patent Laid-Open Publication No. 10-2011-0134793 discloses carbon-coated silicon nanoparticles and a method for producing the same. More specifically, the present invention relates to carbon-coated nanoparticles synthesized by immersing in a solution of a hydrofluoric acid solution, immersing in a chloroform solution, and ultrasonication, and a method for producing the same. However, when such carbon-coated silicon nanoparticles are used as an anode active material, the capacity and output characteristics are insufficient. Accordingly, the present inventors have completed the present invention in order to solve such a problem.

It is an object of the present invention to solve the above problems by using a silicon-based particle containing a nitrogen-doped carbon coating layer treated through carbonization of a nitrogen-containing ionic liquid as an anode active material of a lithium secondary battery, To secure stable cycle characteristics and to obtain improved output characteristics due to excellent electrical conductivity.

In order to accomplish the above object, the present invention provides a method of manufacturing a semiconductor device, Mixing the silicon-based particles with a nitrogen-doped carbon precursor; And a nitrogen-doped carbon coating layer including a step of heat-treating the mixture. The present invention also provides a method for producing a silicon-based negative electrode active material.

The silicon-based particles may include at least one of Si, SiO, and SiOx (1 < x < 2). The silicon-based particles may have an average diameter of 20 nm to 20 mu m.

The nitrogen-doped carbon precursor may be a nitrogen-containing ionic liquid. The nitrogen-containing ionic liquid may be an imidazolium-based ionic liquid. The imidazolium-based ionic liquid may comprise a 1-ethyl-3-methylimidazolium ion. The imidazolium-based ionic liquid may be 1-ethyl-3-methylimidazolium dicyanamide.

The heat treatment step may be for carbonizing the nitrogen-doped carbon precursor to coat the nitrogen-doped carbon with the silicon-based particles. The heat treatment step may be performed at a temperature of 300 ° C to 1000 ° C.

In the mixing step, the nitrogen-doped carbon precursor may be added in an amount of 50 to 300 parts by weight based on 100 parts by weight of the silicon-based particles. In the mixing step, 1 to 100 parts by weight of one kind of organic solvent selected from the group consisting of acetone and ethanol may be added to 100 parts by weight of the silicone-based particles.

The present invention also provides a silicon-based anode active material produced by the method for producing the silicon-based anode active material of the present invention.

In order to achieve the above object, the present invention also provides an anode active material for a lithium secondary battery, wherein the anode active material comprises a silicon-based particle including a nitrogen-doped carbon coating layer. The silicon-based particles may include at least one of Si, SiO, and SiOx (1 < x < 2). The silicon-based particles may have an average diameter of 20 nm to 20 mu m.

The present invention also provides a negative electrode comprising the negative active material of the present invention in order to achieve the above object.

The present invention also provides a lithium secondary battery comprising a cathode including a cathode active material, a cathode including the anode active material, an electrolyte, and a separator, wherein the anode active material comprises lithium Thereby providing a secondary battery.

The present invention uses a silicon-based particle including a nitrogen-doped carbon coating layer treated through carbonization of a nitrogen-containing ionic liquid as an anode active material of a lithium secondary battery. As a result, stable cycle characteristics can be secured while having the advantages of a high-capacity silicon anode, and output characteristics can be improved due to excellent electrical conductivity.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic diagram of a method for producing nitrogen-doped carbon-coated silicon-based particles using an ionic liquid.
Fig. 2 shows an FE-SEM photograph (a), a TEM photograph (b) and an XPS analysis result (c) of silicon-based particles coated with nitrogen doped carbon.
3 shows the initial charge-discharge curve (a), the cycle characteristics (b) at 1-C (1500 mA / g), and the discharge capacity comparison (c) according to current conditions of the examples and comparative examples according to the present invention.
Fig. 4 shows impedance results (a) after initial charging and discharging and impedance results (b) after 200 cycles in Examples and Comparative Examples according to the present invention.

The following examples are intended to illustrate the present invention and should not be construed as limiting the scope of the present invention. Accordingly, equivalent inventions performing the same functions as the present invention are also within the scope of the present invention.

In addition, in adding reference numerals to the constituent elements of the drawings, it is to be noted that the same constituent elements are denoted by the same reference numerals even though they are shown in different drawings. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

In describing the components of the present invention, terms such as first, second, A, B, (a), and (b) may be used. These terms are intended to distinguish the constituent elements from other constituent elements, and the terms do not limit the nature, order or order of the constituent elements. When a component is described as being "connected", "coupled", or "connected" to another component, the component may be directly connected or connected to the other component, Quot; may be "connected," "coupled," or "connected. &Quot;

In order to solve the above-mentioned problems, the present inventors have conducted extensive studies to improve the output characteristics and the discharge capacity of the lithium secondary battery, and to expand the application range of the lithium secondary battery, A carbon-coated silicon based negative electrode active material is provided.

In order to accomplish the above object, the present invention provides a method of manufacturing a semiconductor device, Mixing the silicon-based particles with a nitrogen-doped carbon precursor; And a nitrogen-doped carbon coating layer including a step of heat-treating the mixture. The present invention also provides a method for producing a silicon-based negative electrode active material.

In the present invention, the silicon-based particles may include at least one of Si, SiO, and SiOx (1 <x <2), and the silicon-based particles may have an average diameter of 20 nm to 20 μm.

In the present invention, the nitrogen-doped carbon precursor may be a nitrogen-containing ionic liquid. The nitrogen-containing ionic liquid may be an imidazolium-based ionic liquid. The imidazolium-based ionic liquid preferably contains 1-ethyl-3-methylimidazolium ion, more preferably 1-ethyl-3-methylimidazolium dicyanamide.

In the present invention, the heat treatment step is for carbonizing the nitrogen-doped carbon precursor to coat the nitrogen-doped carbon with the silicon-based particles, and the heat treatment step may be performed at a temperature of preferably 300 ° C. to 1000 ° C. have. If the heat treatment is performed outside the above range, the coating layer is not formed well on the surface of the silicon-based particles, and a desired effect can not be obtained.

In the present invention, in the mixing step, the nitrogen-doped carbon precursor may be added in an amount of 50 to 300 parts by weight based on 100 parts by weight of the silicon-based particles. When the silicon-based particles are mixed with the carbon precursor in the range out of the above-mentioned range, the coating layer is not formed well on the surface of the silicon-based particles, and a desired effect can not be obtained.

In the present invention, in the mixing step, 1 to 100 parts by weight of one kind of organic solvent selected from acetone and ethanol may be added to 100 parts by weight of the silicone-based particles. This is to appropriately control the degree of dispersion and viscosity of the mixture of the carbon precursor and the silicon-based particles.

An embodiment of the present invention will be described in detail with reference to Fig.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic diagram of the preparation of silicon monoxide (SiO) comprising a nitrogen-doped carbon coating layer using an ionic liquid.

In the present embodiment, commercially available silicone-based particles (SiO, manufactured by Sigma Aldrich) were prepared as conducting cone-based particles. An ionic liquid (IL: ionic liquid) containing a large amount of nitrogen as a nitrogen-doped carbon precursor, specifically, 1-ethyl-3-methylimidazolium dicyanamide (manufactured by Merck) was prepared. 0.6 g of the SiO particles and 1.4 g of IL were mixed and stirred to mix well. The mixture was heat-treated at 300 ° C for 1 hour in the presence of nitrogen gas, and then carbonized at 1000 ° C for 1 hour to prepare a silicon-based negative active material (N-C-SiO) coated with SiO 2 on carbon doped with nitrogen.

In the examples of the present invention, the preparation and characterization of silicon-based particles coated with nitrogen-doped carbon prepared using an ionic liquid were carried out. The lithium-ion secondary battery was fabricated and applied to the anode material to analyze the electrochemical characteristics.

In Comparative Example 1, a lithium secondary battery was produced using commercially available silicon-based particles (SiO, Sigma Aldrich) without carbon coating.

In Comparative Example 2, a silicon-based negative electrode active material coated with carbon which was obtained by mixing commercial silicon-based particles and sucrose, followed by carbonization, which was not doped with nitrogen, was prepared. In the case of Comparative Example 2, 0.6 g of commercial silicone-based particles and 7.0 g of sucrose (manufactured by Sigma Aldrich) were mixed and heat-treated at 1000 ° C for 1 hour in the presence of nitrogen gas to prepare silicon- Respectively.

FIG. 2 (a) is a scanning electron microscope (SEM) image of a silicon-based particle (an embodiment of the present invention) containing a nitrogen-doped carbon coating layer.

Referring to FIG. 2 (a), it can be seen that the micro-sized particle morphology remains after the carbonization process.

FIG. 2 (b) is an image observed through a transmission electron microscope (TEM) to clearly observe the thickness of the nitrogen-doped carbon coating layer.

Referring to FIG. 2 (b), it was confirmed that a coating layer of 20 to 30 nm was formed.

2 (c) was analyzed using an X-ray photoelectron microscope (XPS) to more clearly illustrate the chemical properties of the nitrogen-doped carbon coating layer.

Referring to FIG. 2 (c), in order to explain the presence or absence of nitrogen doping, the present inventor paid attention to the N1s spectrum. As shown in Fig. 1 (c), the existence of nitrogen-doped carbon was confirmed through a peak of 400.6 eV (C = N) and a peak of CN of 398.3 eV (CN).

The electrochemical performance of the silicon-based negative active material in Examples of the present invention and Comparative Examples 1 and 2 was measured by preparing a coin-shaped unit cell. To prepare a silicon-based anode, silicon-based anode particles including the silicon-based anode active material, Super-P and polyacrylic acid (PAA, Mw = 3,000,000, Sigma Aldrich) were mixed at a weight ratio of 60:20:20 and dispersed in deionized water The slurry was cast on a copper foil and dried at 120 ° C for at least 2 hours to prepare an electrode.

1 M of lithium hexafluorophosphate (LiPF ₆ ) was added to a mixed solution of ethylene carbonate (EC) and diethylcarbonate (DEC) (1) containing 5% by weight of fluoroethylene carbonate (PANAX E-TEC, : 1 = v / v) and a polypropylene separator (Celgard 2400) were used as an electrolytic solution and a separator, respectively. Lithium foil (Hosen, Japan) was used as a counter electrode. The typical loading of active material for all electrodes was 1 mg / cm ² .

The electrochemical characteristics of the single cells produced according to the above-mentioned contents were analyzed through a galvanostatic method.

As shown in FIG. 3 (a), the initial charge and discharge were driven under a constant current of 0.1 C (150 mA / g). As a result, the initial discharge capacities of Examples, Comparative Examples 1 and 2 were 1258, 1429 and 1495 mAh / g. Also, the initial charge / discharge efficiency was 51.0, 71.4, and 72.9%, respectively. It is considered that the nitrogen-doped carbon according to the present invention has excellent discharge capacity and efficiency due to excellent electrical conduction.

 FIG. 3 (b) shows the cycle characteristics at a constant current of 1 C (1500 mA / g). In the case of the example, the discharge capacity was the highest and the cycle holding characteristics were excellent.

As shown in FIG. 3 (c), the current density was increased from 0.2 C to 2 C, and the discharge capacity was measured. As a result, it was found that the discharge capacity of 732.3 mAh / g at the high driving current condition of 2C (3000 mA / Has been implemented. This is twice as high as the discharge capacity of a commercial graphite anode.

FIG. 4 (d) is a result of impedance analysis performed to confirm the interfacial stability characteristics of the silicon-based anode including the nitrogen-doped carbon coating layer according to the present invention. In the case of the embodiment, it can be seen that the size of the semicircle indicating the interface resistance of the electrode did not greatly increase after the initial charge-discharge and after 200 cycles. On the other hand, in the case of Comparative Example 2, the interfacial resistance value greatly increased after 200 cycles, and the interfacial resistance was larger than that of the Example. It is considered that the introduction of the nitrogen-doped carbon coating layer according to the present invention stabilizes the interface of the silicon-based anode.

According to the present invention, the silicon-based particles containing the nitrogen-doped carbon coating layer obtained through the carbonization process of the ionic liquid have superior discharge capacity and improved output characteristics compared to the particles made of the non- Lt; / RTI &gt; Especially, high discharge capacity of 732.3mAh / g can be realized even at high charge / discharge drive current of 2C-rate (3000mA / g).

This is an advantage of the present invention that a high capacity of the silicon anode active material can be realized by introducing a nitrogen-doped carbon coating layer having excellent electrical conductivity. Accordingly, the present invention enables the production of a silicon-based anode active material having improved discharge capacity characteristics and output characteristics through a simple mixing process and a carbonization process, thereby suggesting the possibility of a next-generation lithium secondary battery material.

It is to be understood that the terms "comprises", "comprising", or "having" as used in the foregoing description mean that the constituent element can be implanted unless specifically stated to the contrary, But should be construed as further including other elements. All terms, including technical and scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs, unless otherwise defined. Commonly used terms, such as predefined terms, should be interpreted to be consistent with the contextual meanings of the related art, and are not to be construed as ideal or overly formal, unless expressly defined to the contrary.

The foregoing description is merely illustrative of the technical idea of the present invention, and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas falling within the scope of the same shall be construed as falling within the scope of the present invention.

Claims (17)

Preparing silicon-based particles;
Mixing the silicon-based particles with a nitrogen-doped carbon precursor;
Heat treating the mixture;
And a carbon-doped carbon coating layer containing a nitrogen-doped carbon coating layer.
The method of producing a silicon-based anode active material according to claim 1, wherein the silicon-based particles comprise at least one of Si, SiO, and SiOx (1 <x <2).
The method of producing a silicon based negative active material according to claim 1, wherein the silicon-based particles have an average diameter of 20 nm to 20 μm.
The method of claim 1, wherein the nitrogen-doped carbon precursor is a nitrogen-containing ionic liquid.
5. The method of claim 4, wherein the nitrogen-containing ionic liquid is an imidazolium-based ionic liquid.
6. The method of claim 5, wherein the imidazolium-based ionic liquid comprises 1-ethyl-3-methylimidazolium ions.
6. The method of producing a silicon-based anode active material according to claim 5, wherein the imidazolium-based ionic liquid is 1-ethyl-3-methylimidazolium dicyanamide.
The method of claim 1, wherein the heat treatment step comprises carbonizing the nitrogen-doped carbon precursor to coat nitrogen-doped carbon on the silicon-based particles.
The method of claim 1, wherein the annealing step is performed at a temperature of 300 ° C to 1000 ° C.
The method of claim 1, wherein in the mixing step, the nitrogen-doped carbon precursor is added in an amount of 50 to 300 parts by weight based on 100 parts by weight of the silicon-based particles.
The method of claim 1, wherein 1 to 100 parts by weight of one kind of organic solvent selected from the group consisting of acetone and ethanol is added to 100 parts by weight of the silicon-based particles in the mixing step.
A silicon-based negative electrode active material produced by the method according to any one of claims 1 to 11.
In the negative electrode active material of the lithium secondary battery,
Wherein the negative electrode active material comprises silicon-based particles including a nitrogen-doped carbon coating layer.
14. The negative electrode active material according to claim 13, wherein the silicon-based particles comprise at least one of Si, SiO, and SiOx (1 < x <
14. The negative electrode active material according to claim 13, wherein the silicon-based particles have an average diameter of 20 nm to 20 mu m.
An anode comprising the anode active material according to any one of claims 13 to 15.
1. A lithium secondary battery including a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, an electrolyte, and a separator,
The negative electrode active material according to any one of claims 13 to 15.

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