KR101751787B1 - Anodes active material containing Si composite for lithium secondary batteries and its preparation method and lithium secondary batteries comprising the same - Google Patents

Abstract

The present invention relates to a process for producing nanosilicone compound powder by reacting a lithium powder with a silica powder to form a nanosilicone compound powder through an oxygen exchange reaction in which oxygen of silica is transferred to lithium, To a lithium secondary battery comprising a silicon compound-graphene-carbon fiber composite material, a method for producing the same, and a negative electrode active material containing the composite material.

Description

TECHNICAL FIELD The present invention relates to a silicon composite anode active material for a lithium secondary battery, a method of manufacturing the same, and an anode active material containing the same,

The present invention relates to a silicon composite anode active material for a lithium secondary battery, a method for producing the same, and a lithium secondary battery comprising the same.

Among the anode materials for lithium secondary batteries, silicon has a theoretical capacity larger than the theoretical capacity of commercialized graphite materials as a substitute for carbon materials. However, silicon has a problem in that the capacity is rapidly reduced because the electrode is deteriorated due to a large volume change during alloying and de-alloying with lithium.

In order to prevent degeneration of the electrode due to the volume change, a method of using a porous silicon to have a buffering effect on the volume change has been studied. Efforts have also been made to minimize the absolute volume change of the electrode by making the particle size nano-sized.

Lithium oxide (Li ₂ O) and lithium silicate (Li _a Si _b O _c ) formed by the reaction with lithium in silicon oxide (SiO) have the effect of alleviating the volume change of silicon, However, there is a problem that capacitance and electric conductivity are lower than that of silicon (Si). In order to solve this problem, efforts are being made to develop a SiO-carbon composite material or a carbon-coated SiO 2 material.

As a method of producing the silicon nano powder, a method of etching a silicon wafer by a chemical or electrochemical method has been reported. As another method for synthesizing nano-sized silicon particles, there is known a method of synthesizing using an organo-metallic precursor or a method of reducing a liquid precursor. However, organic-metal precursors or liquid precursors are very reactive and highly toxic and must be synthesized in the absence of oxygen or moisture.

The silicon nanopowder may be manufactured by a method of ultrasonically treating porous silicon particles, a colloid synthesis method, a vacuum deposition method, or the like. However, these methods require a high-cost process, There is a problem that the solution is toxic.

Korean Patent Laid-Open No. 10-2004-0082876 (Patent Document 1) discloses a method for producing silicon particles by heat treatment of a silicon precursor and an alkali metal or alkaline earth metal, and preparing silicon nanoparticles by using ultrasonic waves, When applied to an anode active material for a lithium secondary battery, stability can be improved due to volume expansion and peeling, but the charge / discharge performance is not sufficient and cycle characteristics are deteriorated.

On the other hand, the use of conductive materials such as graphene and carbon nanotubes as electrode materials for batteries has been continuously studied. Korean Patent Laid-open Publication No. 10-2011-0059130 (Patent Document 2) discloses a composite composition in which carbon nanotubes and graphene are mixed and a method of using the same as an electrode material. However, this method uses a silicon or silicon oxide nano powder And it is described only about the application of various components such as carbon fiber and graphene as an electrode material to a battery so that the physical properties such as particle size, porosity, and electric conductivity of the electrode material including the silicon- There is a limit to improving the characteristics.

Therefore, the performance as an active material can be remarkably improved by adjusting the particle size, surface area, porosity and nanostructure of the secondary battery anode material by adding nano silicon particles at a low cost economically at room temperature and adding a conductive material thereto The researchers need to research and develop methods that can improve them.

Korean Patent Publication No. 10-2004-0082876 (September 30, 2004) Korean Patent Publication No. 10-2011-0059130 (June 2, 2011)

Disclosure of Invention Technical Problem [8] Accordingly, the present invention has been made in order to solve the above-mentioned problems, and it is an object of the present invention to provide a nanosilicon compound powder using low cost silica, And a negative electrode active material for a secondary battery.

It is another object of the present invention to provide a negative electrode active material for a lithium secondary battery comprising the nanosilicone compound-graphene-carbon fiber composite material and a secondary battery comprising the same.

In order to achieve the above object, the present invention provides a nanosilicon compound-graphene-carbon fiber composite material which is prepared by including a nanosilicone compound selected from a nanosilicon, a nanosilicon, and a mixture thereof, Lt; / RTI >

In the nanosilicone compound-graphene-carbon fiber composite according to one embodiment of the present invention, the nanosilicone suboxide (SiO _x ) satisfies 0 <x <0.9, preferably 0 <x <0.5, more preferably 0.2 < x < 0.4.

The present invention can provide a negative electrode active material for a lithium secondary battery comprising a nanosilicone compound-graphene-carbon fiber composite material selected from a nanosilicon, a nanosilicon oxide, and a mixture thereof.

The present invention can provide a lithium secondary battery comprising the negative electrode active material containing the nanosilicone compound-graphene-carbon fiber composite material.

(A) preparing a nanosilicone compound powder selected from a nanosilicon, a nanosilicon oxide, and a mixture thereof by an oxygen exchange reaction between a lithium powder and a silica powder; and (b) And a step of mixing the graphene and the carbon fiber to obtain a nanosilicone compound-graphene-carbon fiber composite material.

In the method of manufacturing a nanosilicone compound-graphene-carbon fiber composite material according to an embodiment of the present invention, the step (a) may further include a step of separating and purifying the prepared nanosilicone compound powder from lithium oxide .

In step (b), the nanosilicone compound powder, the graphene and the carbon fiber are dispersed in a solvent, and the slurry is mixed. And then removing the solvent before drying.

In the method for producing a nanosilicone compound-graphene-carbon fiber composite material according to an embodiment of the present invention, the silica powder may be any one or more selected from among fumed silica, microporous silica, mesoporous silica, Lt; / RTI &gt;

In the method for producing a nanosilicone compound-graphene-carbon fiber composite material according to an embodiment of the present invention, the silica powder is not limited, but may be, for example, 2 nm to 30 μm in diameter.

In the method for producing a nanosilicone compound-graphene-carbon fiber composite material according to an embodiment of the present invention, graphene is not particularly limited, but may be, for example, 10 nm to 5 μm in diameter.

In the method for producing a nanosilicone compound-graphene-carbon fiber composite material according to an embodiment of the present invention, the carbon fiber is not particularly limited, but may be, for example, 1 nm to 5 μm in thickness and 50 to 200 μm in length.

The molar ratio of lithium to silica (SiO ₂ ) in the method of preparing a nanosilicone compound-graphene-carbon fiber composite material according to an embodiment of the present invention can be adjusted within the scope of the present invention, For example, 2 to 6: 1.

In the method for producing a nanosilicone compound-graphene-carbon fiber composite material according to an embodiment of the present invention, the step (a) may be carried out in an inert atmosphere for a sufficient time, for example, 1 to 20 hours Ball milling can be performed to perform solid-state reaction.

In the method for preparing a nanosilicone compound-graphene-carbon fiber composite material according to an embodiment of the present invention, the oxygen exchange reaction in the step (a) is not limited as long as the exchange reaction can proceed sufficiently, Lt; 0 &gt; C to 300 &lt; 0 &gt; C.

In the method for producing a nanosilicone compound-graphene-carbon fiber composite material according to an embodiment of the present invention, the carbon fiber in step (b) may be surface-oxidized through acid treatment.

In the method for producing a nanosilicone compound-graphene-carbon fiber composite material according to an embodiment of the present invention, the weight mixing ratio of the mixture of the nanosilicone compound powder and the graphene and the carbon fiber in the step (b) But not as good as 1: 9 to 9: 1.

In the method of producing a nanosilicone compound-graphene-carbon fiber composite material according to an embodiment of the present invention, graphene and carbon fiber are not limited to a wide range in the step (b) : May be one.

In the method for producing a nanosilicone compound-graphene-carbon fiber composite material according to an embodiment of the present invention, step (b) is not particularly limited, but may be carried out at 0 to 100 ° C, for example.

In the nanosilicone compound-graphene-carbon fiber composite material according to an embodiment of the present invention, the carbon fiber is not limited as long as it is ordinary carbon fiber, and examples thereof include carbon fiber, single wall carbon nanotube, A tube, and a carbon nanowire, and may be modified.

The present invention can provide a nanosilicone compound-graphene-carbon fiber composite material produced by the above-described manufacturing method.

The present invention relates to a nanosilicon compound-graphene-carbon fiber composite material and a negative electrode active material for a lithium secondary battery including the nanosilicone compound-graphene-carbon fiber composite material, which can improve the electrochemical characteristics of a secondary battery while reducing costs by synthesizing a nanosilicone compound powder using low- Can be provided.

In addition, the present invention has an advantage of being able to provide a method of manufacturing a nanosilicon compound-graphene-carbon fiber composite material which is simple in the reaction process and excellent in productivity and economy and is environment-friendly.

In addition, the present invention can use various kinds of silica. By controlling the physical properties and content of graphene and carbon fiber, the particle size, porosity and electric conductivity of the nanosilicone compound-graphene-carbon fiber composite material There is an advantage that it can be applied optimally.

1 shows TEM images and electron diffraction patterns of nanosilicon powders obtained from nanosilica in one embodiment of the present invention.
FIG. 2 is a TEM image of a nanosilicon-graphene-carbon fiber composite material powder according to an embodiment of the present invention.
3 is a graph showing a constant voltage circulation curve of a lithium secondary battery including a nanosilicon composite anode according to an embodiment of the present invention.
FIG. 4 is a graph illustrating a charging / discharging profile of a nanosilicon-graphene-carbon fiber composite anode according to an embodiment of the present invention.
FIG. 5 is a graph illustrating a capacity profile of a nanosilicon-graphene-carbon fiber composite anode according to an embodiment of the present invention.
FIG. 6 is a graph illustrating a comparison of cycle performance between a nanosilicon-graphene-carbon fiber composite negative electrode and a silicon negative electrode according to an embodiment of the present invention.
7 shows the TEM image and elemental mapping images of the nano-silicon suboxide (SiO _{0 .37)} powders prepared by one example embodiment of the present invention.
Figure 8 is nano-silicon suboxide (SiO _{0 .37)} in accordance with one embodiment of the present invention - a graph showing the dose profile of the carbon fiber composite cathode-graphene.

Hereinafter, the nanosilicone compound-graphene-carbon fiber composite material, the negative electrode active material for a lithium secondary battery, the method for producing the same, and the lithium secondary battery comprising the same will be described in detail. The following embodiments are provided by way of example so that those skilled in the art can fully understand the spirit of the present invention. Further, it is to be understood that, unless otherwise defined, technical terms and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Descriptions of known functions and configurations that may be unnecessarily blurred are omitted.

The inventors of the present invention have made studies on developing an anode active material for a lithium secondary battery, and as a result, they have found that a nanosilicon compound-containing compound prepared by incorporating a nanosilicon compound selected from a nanosilicon, a nanosilicon oxide, The present invention has been accomplished based on the discovery that it is possible to remarkably improve the electrochemical characteristics of a lithium secondary battery while reducing the cost of a negative electrode active material for a lithium secondary battery including the graphite-carbon fiber composite material.

The present invention can provide a nanosilicon compound-graphene-carbon fiber composite material comprising nanosilicone compounds selected from nanosilicones, nanosilicon oxides, and mixtures thereof, and graphene and carbon fibers. In this case, the nano-silicon is silicon (Si) nano-sized, nano-silicon suboxide is the x range of SiO _x 0 <x <0.9, preferably from 0 <x <0.5, more preferably 0.2 <x <0.4 Lt; / RTI &gt; In the above range, the electrode has better electric conductivity, and the lithium secondary battery has excellent characteristics such as reversibility of charging / discharging and capacity.

The present invention can provide an anode active material for a lithium secondary battery including the nanosilicone compound-graphene-carbon fiber composite material.

The present invention can provide a lithium secondary battery comprising the negative electrode active material containing the nanosilicone compound-graphene-carbon fiber composite material.

(A) preparing a nanosilicone compound powder selected from a nanosilicon, a nanosilicon oxide, and a mixture thereof by an oxygen exchange reaction between a lithium powder and a silica powder; and (b) And a step of mixing the graphene and the carbon fiber to obtain a nanosilicone compound-graphene-carbon fiber composite material.

Specifically, in the method of producing a nanosilicone compound-graphene-carbon fiber composite material of the present invention, an oxygen exchange reaction (single displacement) is performed in which lithium oxide is reacted with lithium (SiO ₂ ) And then uniformly mixing the resulting nanosilicone compound powder, graphene, and carbon fiber.

The nanosilicone compound powder may be any one selected from a nanosilicon, a nanosilicon, and a mixture thereof.

When the nanosilicone compound powder is nanosilicon (Si) in the method of producing the nanosilicone compound-graphene-carbon fiber composite material, the reaction formula is as shown in the following reaction formula 1.

4 Li + SiO ₂ ? Si + ₂ Li ₂ O (Reaction Scheme 1)

That is, the nanosilicon is produced by reducing silica while lithium metal powder is oxidized to lithium oxide.

When the nanosilicone compound powder is a nanosilicone suboxide (SiO _x ) in the method for producing a nanosilicone compound-graphene-carbon fiber composite material, the reaction formula is as shown in the following reaction formula 2.

In this case, the nanocrystalline silicon oxide (SiO _x ) powder is formed by incomplete reduction of silica. In the silicon oxides (SiO _x ), x satisfies 0 <x <0.9, preferably 0 <x <0.5, 0.2 < x < 0.4. The silicon oxynitone nano powder may not be sufficiently reduced by controlling the time of oxygen exchange reaction between the lithium powder and the silica powder or the molar ratio of lithium and silica, so that some oxygen may remain to form the acid. For example, when the ball milling process of the lithium powder and the silica powder is performed within 3 hours, or when the amount of lithium reacting with the silica is 4 mol or less, the reduction of the silica is not sufficiently performed and the acid can be formed.

(4-2x) Li + SiO ₂ ? (2-x) Li ₂ O + SiO _x (Reaction Scheme 2)

The silica (SiO ₂ ) powder used in the present invention may be any one or more selected from among fumed silica, microporous silica, mesoporous silica and macroporous silica Mixture and can be used without being limited by the type, size or pore size of the silica.

The silica powder preferably has a diameter of 2 nm to 30 μm, more preferably 10 nm to 100 nm. If the particle size of the silica powder exceeds the above range, lithium diffusion may not be easy, and if it is less than the above range, particle aggregation may occur due to high specific surface area and surface energy, so that the particle dispersing ability required for cathode production may be lowered.

The graphene may have a diameter of 10 nm to 5 mu m, and the carbon fiber may have a thickness of 1 nm to 5 mu m and a length of 50 mu m to 200 mu m. The carbon fiber may be any one selected from a carbon fiber, a single wall carbon nanotube (SWCNT), a multiwall carbon nanotube (MWCNT), and a carbon nanowire.

The molar ratio of lithium to silica (SiO ₂ ) may be 2 to 6: 1. If the ratio of lithium is greater than 6, the amount of acid used to remove lithium remaining after the reaction is increased and the wastewater increase result is obtained (SiO _y , 1 < y < 2) having a high oxygen content can be obtained at a ratio smaller than 2, so that the reversibility and capacity of the lithium secondary battery can be reduced.

The forming of the nanosilicone compound powder may be performed, for example, by mixing the lithium powder and the silica powder in a glove box followed by ball milling for 1 to 20 hours. At this time, the glove box may be an inert gas atmosphere such as nitrogen or argon, and the oxygen exchange reaction temperature through the ball mill of lithium and silica may be 0 to 300 ° C. If the reaction temperature is higher than 300 ° C, undesirable particles having a large particle size and a small particle size can be obtained. If the reaction temperature is lower than 0 ° C, the exchange reaction rate of oxygen may be lowered.

The method may further include a step of separating and purifying the produced nanosilicone compound powder from the lithium oxide after the step of preparing the nanosilicone compound powder.

The separation and purification process may include a step of removing lithium oxide, which is a side reaction, through an acid treatment. The obtained lithium oxide reacts with an acid as shown in the following Reaction Schemes 3 and 4 to produce lithium chloride (LiCl).

Li ₂ O + H ₂ O? 2LiOH (scheme 3)

Li ₂ O + 2HCl - &gt; 2LiCl + H ₂ O (scheme 4)

The acid used in the acid treatment may be inorganic acid such as sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, etc., but is not limited thereto.

After the acid treatment, the acid-treated product is washed several times with water, ethanol, isopropanol, and a mixed solvent thereof to dry the finally obtained nanosilicone compound powder.

In the process of mixing the nanosilicone compound powder, graphene and carbon fiber in the present invention, a slurry in which a nanosilicone compound powder, graphene and carbon fiber are respectively dispersed in a solvent is mixed, and then the solvent is removed and dried May be further included.

The solvent may be any solvent as long as it can uniformly disperse the nanosilicone compound powder, graphene and carbon fiber, and may be any one selected from among alcohols having 1 to 5 carbon atoms, water, and mixtures thereof .

The carbon fiber can induce surface oxidation through acid treatment to improve dispersibility. The acid may be an inorganic acid such as sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, or an organic acid having a carboxyl group.

The acid treatment may further include the step of drying the acid-treated product several times with water, ethanol, isopropanol, and a mixed solvent thereof, followed by drying.

In the present invention, the mixing weight ratio of the nanosilicone compound powder to graphene and carbon fiber may be 1/9 to 9/1. If the above range is exceeded, the effect of mixing the graphene and the carbon fiber into the nanosilicone compound powder is insignificant. If it is less than this range, the silicon content having the electrochemical activity may be lowered and the capacity may be lowered.

The weight mixing ratio of the graphene and carbon fiber may be 1/10 to 10/1, and the step of uniformly mixing and dispersing the nanosilicone compound powder, graphene and carbon fiber may be performed at 0 to 100 ° C.

The present invention can provide a nanosilicone compound-graphene-carbon fiber composite material obtained by the above-described production method, and a lithium secondary battery comprising the same as an anode active material.

In one embodiment of the lithium secondary battery according to the present invention, the positive electrode active material includes Li (Mn, Ni, Co) O ₂ , LiMn _{2 - x} M _x O ₄ (M = Li, Al, Zn, Zr, Ni, Fe) spinel type, and LiMPO ₄ (M = Fe, Mn, Co, Ni), and the electrolyte may include LiPF ₆ lithium salt and a non-water soluble carbonate solvent.

The present invention provides a lithium secondary battery including a positive electrode, a negative electrode and a separator, wherein the negative electrode comprises: (i) a metallic current collector; And (ii) a lithium secondary battery comprising the nanosilicone compound-graphene-carbon fiber composite material as the negative electrode active material coated on the current collector.

Hereinafter, a method for producing a nanosilicone compound-graphene-carbon fiber composite material according to the present invention will be described with reference to a preferred embodiment.

(Example 1) Production of nanosilicon powder from nanosilica by oxygen substitution solid phase reaction and production of nanosilicon -graphene-carbon fiber composite material

The powder was mixed with silica (SiO ₂ , average particle diameter 15 nm) and lithium metal powder (average particle diameter 25 μm) in a 1: 4 molar ratio in an argon atmosphere at room temperature (25 ° C.), ball milled at room temperature for 6 hours, solid-state reaction to induce oxygen substitution reaction.

Lithium oxide was washed with a 0.5 M hydrochloric acid solution and washed sequentially with a mixed solution of ethanol and 1 M aqueous HCl solution (mixing ratio of ethanol and 1 M aqueous HCl solution 1: 1) to separate lithium oxide and synthesized silicon powder, I got it.

In the above process, an acid and a lithium oxide reacted to form a LiCl salt which is easily dissolved in water as shown in the following formulas 1 and 2.

Thereafter, the resultant was washed several times with water to remove LiCl, and then finally obtained dark brown nanosilicon powder (SiO, average particle diameter: 50 nm) was dried in a vacuum oven.

1 shows TEM images and electron diffraction patterns of nanosilicon (SiO) powder obtained from nanosilica of the present invention. Primary particles of spherical nanosilicon powder having a diameter of about 50 nm were observed, and no specific ring shape or regular electronic arrangement was observed in the electron diffraction pattern, so that the produced silicon powder was found to be amorphous there was.

100 mg of the thus-prepared nanosilicon powder was uniformly dispersed in 100 ml of water, and a slurry in which 50 mg of graphene powder (average particle diameter 2.5 탆) and 50 mg of carbon fiber powder (100 nm in thickness) were dispersed in 200 ml of water was dispersed in water After mixing with nanosilicon powder solution. And dispersed using ultrasonic waves to prepare a composite material dispersion solution. At this time, the composite material dispersion solution includes a nanosilicon-graphene-carbon fiber composite material having a ratio of 50: 25: 25 wt%. That is, a powdery liquid having a weight ratio of nano silicon / (graphene + carbon fiber) of 1/1 and graphene / carbon fiber weight ratio of 1/1 is prepared. Next, water was removed by centrifugation and dried in a vacuum oven to obtain a silicon composite anode active material.

2 is a TEM image of a nanosilicon-graphene-carbon fiber composite powder. It was confirmed that the three components constituting the anode active material of the silicon composite were uniformly mixed and the contact between the particles was good.

(Example 2) Electrochemical characteristics of a lithium secondary battery including a negative electrode made of the nanosilicone - graphene -carbon fiber negative electrode active material of Example 1

(Weight ratio of a carbon conductive material (super P): polyacrylic acid binder) of 75: 15: 10 (wt%) was mixed with the nanosilicon-graphene-carbon fiber composite anode active material prepared from nanosilica in Example 1 To prepare a negative electrode. At this time, a binder solution was prepared by dissolving polyacrylic acid in NMP (N-methyl pyrrolidinone), and then a silicon composite anode active material and a carbon conductive material (super P) were added thereto to prepare an anode coating slurry. The slurry was coated on copper foil in a conventional manner. Next, it was dried in a vacuum oven at 110 DEG C for 12 hours. After drying, the mixture was passed through a roll press maintained at a pressure of 40 kg / cm &lt; 2 &gt; to prepare a negative electrode.

In the lithium cell, lithium metal was used as a counter electrode and a reference electrode, and the produced silicon negative electrode was used as a working electrode. (Tris (2-mehtoxyethoxy) vinylsilane) of 5 wt% was added to a mixed solution of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in which 1 M LiPF ₆ was dissolved as an electrolyte (mixed solution ratio 3: 7).

A constant voltage circulation curve of a lithium secondary battery including a negative electrode containing a nano-silicon-graphene-carbon fiber composite material is 0.05 to 1.5 vs. And measured at a sweep rate of 0.1 mV / s in the Li / Li ⁺ potential range and is shown in FIG.

The peak of about 0.2 V observed in the cathodic process (charge, lithium insertion) is the process of lithium insertion into amorphous silicon, and the peak of about 0.3 V observed in the anodic process (discharge, lithium desorption) is from Li _x Si amorphous silicon And a peak of about 0.5 V is attributed to a process in which lithium is desorbed from the Li ₁₅ Si ₄ phase to regenerate the silicon. The nanosilicon-graphene-carbon fiber composite according to an embodiment of the present invention exhibits electrochemical activity in the lithium cell and reversibly inserts and desorbs lithium.

Next, the charging / discharging profile of the nanosilicon-graphene-carbon fiber composite anode was found to be 0.1 to 1.5 V vs. 150 μA / cm 2 current density (corresponding to about 0.02C). Charge / discharge was performed in a constant current-constant voltage (CC-CV) manner in the Li / Li ^{+ region} . FIG. 4 shows the charging / discharging profile. As a result, it was confirmed that a flat surface due to Li _x Si formation due to lithium insertion and desorption reaction into amorphous silicon was confirmed.

The result of conversion of the capacity of the cathode into the specific gravimetric capacity is shown in FIG.

The anode including the nanosilicon-graphene-carbon fiber composite according to an embodiment of the present invention has an initial charge (lithium insertion) capacity of 1700 mAh / g and an initial discharge (lithium desorption) capacity of 606 mAh / The efficiency was about 36%, but the discharge capacity of 734 ~ 635 mAh / g and the efficiency of about 95% or more were maintained up to 20 cycles after 5th cycle.

Also, the surface area of the silicon particles (the interface area with the electrolyte) increases due to the particle crushing phenomenon occurring during the lithium insertion-desorption, and thereby the electrolyte reduction decomposition is actively performed, and an additional charging capacity is generated, .

Further, lithium ions are irreversibly adsorbed on the surface of the graphene particles, so that only the charging capacity can be increased.

FIG. 6 is a graph comparing the cycle performance of a nano silicon-graphene-carbon fiber composite negative electrode and a silicon negative electrode according to an embodiment of the present invention. In a negative electrode made of only nano silicon powder, the discharge capacity rapidly decreases after three cycles. Respectively. This improves the cycle performance by accommodating changes in the volume of silicon generated by the reaction between the graphene and carbon fibers of the nano-nanosilicon compound-graphene-carbon fiber composite anode and lithium and increasing the electrical conductivity of the negative electrode. can confirm.

(Example 3) Preparation of Nanosilicon Suboxide (SiOx) Powder from Nano Silica by Oxygen Substitution Solid Phase Reaction and Production of Nano Silicon Substrate-Graphene-Carbon Fiber Composite Material

The powder was mixed with silica (SiO ₂ , average particle diameter 15 nm) and lithium metal powder (average particle diameter 25 μm) in a 1: 4 molar ratio in an argon atmosphere at room temperature (25 ° C.), ball milled for 3 hours at room temperature, solid-state reaction to induce oxygen substitution reaction.

(4-2x) Li + SiO ₂ → (2-x) Li 2 O + SiO _x (Reaction Scheme 4)

Lithium oxide was washed with a 0.5 M hydrochloric acid solution to separate lithium oxide and synthesized silicon oxide powder in the same manner as in Example 1, and a mixed solution of ethanol and 1 M aqueous HCl solution (a mixture of ethanol and 1 M aqueous HCl solution Ratio 1: 1). After removal of LiCl, finally a brown nanosilicon oxide powder (SiO _0.37 , average particle diameter 50 nm) was obtained and dried in a vacuum oven.

FIG. 7 is a TEM image and elemental mapping image of nanosilicon oxide powder obtained from nanosilica according to an embodiment of the present invention. Secondary particles having a diameter of about 200 to 300 nm of silicon oxide having a diameter of about 50 nm could be confirmed. From the Si: O = 1: 0.37 ratio obtained by the elemental mapping analysis, it can be seen that the formula of the produced silicon oxides is SiO _0.37 .

Example 1, a nano-silicon suboxide in the same manner (SiO _{0 .37)} 100mg powder uniformly dispersed in water 100㎖, and graphene powder (average particle size 2.5㎛) 12.5mg and carbon fiber powder (100nm thickness) 12.5mg Was dispersed in 50 ml of water was mixed with the nanosilicon oxide powder solution dispersed in the above water and dispersed by using ultrasonic waves to prepare a composite material dispersion solution. At this time, the composite material dispersion solution is 80: 10: 10 wt% nano-silicon suboxide having the ratio (SiO _{0 .37)} - comprises a carbon fiber composite material-graphene. That is, a powder solution having a weight ratio of nanocrystalline silicon oxide / (graphene + carbon fiber) of 4/1 and a graphene / carbon fiber weight ratio of 1/1 is produced. Next, water was removed by centrifugation and dried in a vacuum oven to obtain a silicon composite anode active material.

(Example 4) Example 3 nano silicon suboxide (SiO _{0 .37)} of the-graphene-electrochemical properties of the lithium secondary battery comprising a negative electrode made of a carbon fiber anode active material irradiated

Exemplary nano silicon suboxide produced from nanosilica in Example 3 (SiO _{0 .37)} - graphene-carbon fiber cathode active material: a 15 (wt%): carbon conductive agent (super P): the weight ratio of the binder is 75: 10 Were mixed to prepare a negative electrode. At this time, sodium carbonate carboxymethyl cellulose and polyacrylic acid were mixed at a mixing ratio of 1: 1 by weight to prepare a binder solution which was dissolved in water. Then, a silicon composite anode active material and a carbon conductive material (super P) To prepare an anode coating slurry. The slurry was coated on copper foil in a conventional manner. Next, it was dried in a vacuum oven at 110 DEG C for 12 hours. After drying, the mixture was passed through a roll press maintained at a pressure of 40 kg / cm &lt; 2 &gt; to prepare a negative electrode.

The lithium cell uses a lithium metal as a counter electrode and a reference electrode, uses the produced silicon negative electrode as a working electrode, and mixes a mixture of a fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) in which 1 M LiPF ₆ is dissolved as an electrolyte Solution (mixed liquid ratio 5: 5). And charged and discharged by a constant current-constant voltage (CC-CV) method at a voltage range of 0.05 to 1.5 V at about 0.2C. The nano-silicon suboxide (SiO _{0 .37)} - graphene - was expressed in terms of the effect of the negative electrode capacity of the lithium secondary battery comprising the carbon fiber composite material (capacity) in a dose (specific gravimetric capacity) per weight in Fig.

Nano-silicon suboxide according to one embodiment of the present invention (SiO _{0 .37)} - graphene-anode including a carbon fiber composite material is initially charged (lithium insertion) capacity is 1965 mAh / g, an initial discharge (lithium desorption) Capacity Was 1579 mAh / g. The initial coulombic efficiency was about 80%, but after 2 cycles, the coulombic efficiency was increased to 97% or more, and the capacity retention rate up to 50 cycles was 80%.

This is because the charge / discharge performance is improved in the negative electrode made of the nanosilicon composite material of Example 2. This silicon suboxide (SiO _{0 .37)} oxygen of the initial charge Li ₂ O, to form a lithium silicate improved the volume change of the silicon capacity (accomodate) nano silicon suboxide in (SiO _{0 .37)} - graphene This is because the interfacial reaction with the electrolyte is suppressed by charging / discharging the carbon fiber composite anode with an electrolyte consisting of FEC: DEC, which is known to have a side reaction inhibiting effect.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, Various modifications and variations are possible in light of the above teachings.

Accordingly, the spirit of the present invention should not be construed as being limited to the embodiments described, and all of the equivalents or equivalents of the claims, as well as the following claims, belong to the scope of the present invention .

Claims (4)

A nanosilicone compound powder having a diameter of 10 nm to 100 nm selected from among silicon (Si) and silicon oxides (SiOx (0 < x < 0.9)
Carbon nanotube, carbon fiber, single-wall carbon nanotube, multi-wall carbon nanotube, and carbon nanowire,
Obtained by mixing a slurry obtained by dispersing the nanosilicone compound powder, graphene and carbon fiber in a solvent, and removing the solvent and drying the mixture,
Wherein the nanosilicone compound powder is uniformly dispersed and mixed with graphene and carbon fiber.
The method according to claim 1,
The nano-silicon suboxide is _{SiO x (0 <x <0.5} ) the nano-silicon based compound-graphene-carbon fiber composite material.
A negative electrode active material for a lithium secondary battery comprising a nanosilicone compound-graphene-carbon fiber composite material according to any one of claims 1 and 2.
A lithium secondary battery comprising the negative active material for a lithium secondary battery according to claim 3.

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