WO2014027845A1 - Silicon composite anode active material for lithium secondary batteries, method for preparing same, and lithium secondary batteries including same - Google Patents

Abstract

The present invention relates to a nanosilicon-based compound graphene/carbon fiber composite, to a method for preparing same, and to lithium secondary batteries including an anode active material containing the composite, wherein the composite is prepared by reacting lithium powder with silica powder so as to form a nanosilicon-based compound powder through a single displacement reaction of oxygen in which the oxygen in silica is transferred to lithium, and allowing the nanosilicon-based compound powder to include the graphene and carbon fibers.

Description

 【Specification】

 [Name of invention]

 Silicon composite negative electrode active material for lithium secondary battery, manufacturing method thereof and lithium secondary battery comprising same

 Technical Field

 The present invention relates to a lithium composite negative electrode active material for a lithium secondary battery, a manufacturing method thereof, and a lithium secondary battery including the same.

 Background Art

 <2> Among the negative electrode materials for lithium secondary batteries, silicon has a theoretical capacity larger than that of a commercially available flammable material as a material that can replace a carbon material. However, silicon has a problem in that capacity decreases rapidly because the electrode deteriorates due to a large volume change in the alloying and de-alloying process with lithium.

In order to prevent the deterioration of the electrode due to the volume change, a method of using a porous silicon to have a buffering effect against the volume change has been studied. In addition, efforts are being made to minimize the absolute volume change of the electrode by preparing the size of the particles to a nano size.

<4> Silicon oxide (SiO) is more stable than silicon because lithium oxide (Li ₂ 0) and lithium silicate (Li _a Si _b 0 _c ) formed by reaction with lithium have a moderate effect on the volume change of silicon. Charge and discharge performance can be obtained, but there is a problem that the capacity and electrical conductivity is lower than silicon (Si). In order to solve this problem, efforts are being made to develop SiO-carbon composites or carbon coated SiO materials.

 As a method of preparing the silicon nanopowder, a method of etching a silicon wafer by a chemical or electrochemical method has been reported. In addition, as another method of synthesizing nano-sized silicon particles, a method of synthesizing using an organo-metallic precursor or a method of reducing a liquid precursor is known. However, organo-metallic precursors or liquid precursors are semi-strong and very toxic and have the disadvantage of being synthesized in the absence of oxygen or moisture.

 In addition, the manufacturing method of the silicon nano powder includes a method of ultrasonically treating porous silicon particles, a colloid synthesis method, a vacuum deposition method, etc., but the methods are required to have a high cost process. ， The precursor or etching solution has a toxic problem.

<7> Korean Patent Publication No. 10-2004-0082876 discloses a silicon precursor and an alkali metal or an al A method of preparing silicon particles through heat treatment of carito metal and manufacturing silicon nanoparticles using ultrasonic waves has been disclosed. However, when applied to an active material for a lithium secondary battery negative electrode, stability can be improved from volume expansion and peeling. However, there is a problem that the charge / discharge performance is not sufficient and cycle characteristics are poor.

 On the other hand, the use of conductive materials such as graphene and carbon nanotubes as battery electrode materials has been continuously studied. Korean Patent Publication No. 10-2011-0059130 discloses a composite composition in which carbon nanotubes and graphene are mixed and a method of using the same as an electrode material, but it does not use silicon or silicon suboxide nanopowder. As an electrode material, it simply describes various applications such as carbon fiber, graphene, etc., and applies them to a battery. Therefore, physicochemical characteristics such as particle size, processability, and electrical conductivity of electrode material including silicon-based nano powder phase are described. There is a limit to improvement. .

 Therefore, it is economically inexpensive yet simple to produce nano silicon-based particles at room temperature, and by adding a conductive material to them, by controlling physicochemical properties such as size, surface area, pore size, nano structure of secondary battery anode material There is a need for research and development on how to significantly improve the performance as an active material.

 [Detailed Description of the Invention]

 [Technical problem]

 The present invention has been made to solve the above problems, synthesizes a nano silicon-based compound powder using a low-cost silica, and includes the nano-silicon compound, graphene and carbon fiber to reduce the cost An object of the present invention is to provide a negative electrode active material for a secondary battery that can improve electrode characteristics while reducing costs.

 In addition, an object of the present invention is to provide a negative active material for a lithium secondary battery comprising the nano-silicon compound-graphene ᅳ carbon fiber composite material and a secondary battery comprising the same.

 Technical Solution

 In order to achieve the above object, the present invention provides a nano silicon-based compound-graphene-carbon fiber composites selected from nano silicon, nano silicon suboxide, and mixtures thereof.

<13> In the nano-silicon compound-graphene-carbon fiber composite according to an embodiment of the present invention, the nano silicon suboxide is 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 nano-silicon compound-graphene-carbon fiber composite selected from nano silicon, nano silicon suboxide, and mixtures thereof.

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

 <16>

 <17> The present invention is (a) oxygen exchange reaction of lithium powder and silica powder,

 Preparing a nano silicon-based compound powder selected from cone nano silicon suboxides and mixtures thereof; and (b) mixing the prepared nano silicon-based compound powders with graphene and carbon fibers. Provides a method for producing graphene-carbon fiber composites.

 <] 8> In the method for producing a nano silicon compound-graphene-carbon fiber composite according to an embodiment of the present invention, step (a) is a step of separating and purifying the prepared nano silicon compound powder from lithium oxide It may further include.

In the method of preparing a nano silicon compound-graphene-carbon fiber composite according to an embodiment of the present invention, step (b) comprises dispersing the nano silicon compound powder, graphene and carbon fiber in a solvent, respectively. After mixing the slurry may further comprise the step of removing the solvent and then drying.

 <20> In the method for producing a nano-silicon compound-graphene-carbon fiber composite according to an embodiment of the present invention, the silica powder is any one selected from the group silica, microporous silica, mesoporous silica and macroporous silica or It may be two or more combinations.

<21> The exemplary nano silicon-based compound according to an embodiment of the invention - graphene - a method of manufacturing a carbon fiber composite material, silica powder is not limited, for example ⁱ may be a diameter of 2 ran ~ 30 ^.

 In the method for producing a nano-silicon compound-graphene ᅳ carbon fiber composite material according to an embodiment of the present invention, the graphene is not particularly limited, for example, the diameter may be ΙΟηπι ~ / m.

 In the method of preparing a nano-silicon compound-graphene-carbon fiber composite according to an embodiment of the present invention, the carbon fiber is not particularly limited, but may be, for example, a thickness of lnm to im and a length of 50 to 200j¾m.

<24> Nano silicon compound-graphene-carbon fiber composite according to an embodiment of the present invention In the production method of, the molar ratio of lithium and silica (Si0 ₂ ) can be adjusted and used within the scope of the present invention, for example, may be from 2 to 6: 1.

 In the method of preparing a nano-silicon compound-graphene-carbon fiber composite according to an embodiment of the present invention, step (a) is carried out in an inert atmosphere, followed by a slicing time, for example, 1 Ball milling can be performed for 20 hours.

In the method for preparing a nano-silicon compound-graphene-carbon fiber composite according to an embodiment of the present invention, the oxygen exchange reaction in step (a) is not limited as long as the reaction reaction can proceed sufficiently. For example, it can be carried out in the temperature range of 0 ~ 300 ^° C.

 In the method of manufacturing a nano silicon compound-graphene-carbon fiber composite according to an embodiment of the present invention, the carbon fiber of step (b) may be surface oxidized by acid treatment.

 <28> In the method for producing a nano-silicon compound-graphene-carbon fiber composite according to an embodiment of the present invention, in step (b), the weight mixture ratio of the nano-silicon compound powder, the mixture of graphene and carbon fiber Is not particularly limited, but may preferably be 1: 9-9: 1.

 In the method for preparing a nano-silicon compound-graphene-carbon fiber composite according to an embodiment of the present invention, in the step (b), the graphene and the carbon fiber are not greatly limited, but preferably the weight mixing ratio. 1: 10 to 10: 1 can be.

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

 In the nano-silicon compound-graphene-carbon fiber composite according to an embodiment of the present invention, carbon fiber is not particularly limited as long as it is a normal carbon fiber, for example, carbon fiber, single wall carbon nanotube, It may be any one selected from among multi-walled carbon nanotubes and carbon nanowires, and may be modified.

 The present invention can provide a nano-silicon compound-graphene-carbon fiber composite prepared by the above production method.

 Advantageous Effects

The present invention is a nano-silicon compound -graphene-carbon fiber composites and composites that can improve the secondary battery electrochemical properties while reducing costs by synthesizing nano-silicon compound powder using a low-cost silica Cathode active material for lithium secondary battery Can provide quality.

 In addition, the present invention has the advantage of providing a method of producing a nano silicon-based compound-graphene-carbon fiber composite having excellent productivity, economical efficiency and environmental friendliness due to the simple reaction process.

 In addition, the present invention can use a variety of silica, secondary to the particle size, porosity, and electrical conductivity of the nano silicon-based compound—graphene-carbon fiber composite by controlling the physical properties and content of graphene and carbon fiber There is an advantage that can be applied to the battery negative electrode optimized.

 [Brief Description of Drawings]

 1 illustrates a TEM image and an electron diffraction pattern of a nano silicon powder obtained from nano silica in an embodiment of the present invention.

 Figure 2 shows a TEM image of the nano silicon-graphene ᅳ carbon fiber composite powder in one embodiment of the present invention.

 3 is a graph showing a constant voltage circulation curve of a lithium secondary battery including a nano silicon composite anode according to an embodiment of the present invention.

Figure 4 is a graph showing the charge and discharge profile of the nano silicon-graphene-carbon fiber composite anode according to an embodiment of the present invention.

5 is a graph showing a capacity profile of the nano silicon-graphene-carbon fiber composite anode according to an embodiment of the present invention.

 FIG. 6 is a graph illustrating a cycle performance comparison between a nano silicon-graphene-carbon fiber composite anode and a silicon cathode according to an embodiment of the present invention.

<42> Figure 7 shows the TEM image and elemental mapping images of one embodiment of a nano-silicon suboxide produced by (Si0 _{0. 37)} powders of the present invention.

<43> Figure 8 is nano-silicon suboxide (Si0 _{0 37.)} In accordance with one embodiment of the present invention - a graph showing the dose profile of the carbon fiber composite cathode-graphene.

 [Best form for implementation of the invention]

Hereinafter, a negative active material for a nano-silicon compound-graphene-carbon fiber composite lithium lithium battery of the present invention, a method of manufacturing the same, and a lithium secondary battery including the same will be described in detail. The following embodiments are provided as examples to ensure that the spirit of the present invention can be fully conveyed to those skilled in the art. In addition, unless there is another definition in the technical terminology and scientific terminology used, it has the meaning commonly understood by one of ordinary skill in the art to which this invention belongs, The description of well-known functions and configurations that may unnecessarily obscure the subject matter of the present invention will be omitted.

 The inventors of the present invention have studied to develop a negative electrode active material for a lithium secondary battery, to provide a nano-silicon compound-graphene-carbon fiber composite material selected from nano silicon, nano silicon suboxide, and mixtures thereof, Surprisingly, while reducing the cost of the negative electrode active material for a lithium secondary battery including the same, the present inventors have found that the electrochemical properties of the lithium secondary battery can be improved dramatically, thereby completing the present invention.

The present invention can provide a nano silicon-based compound-graphene-carbon fiber composites selected from nano silicon, nano silicon suboxide, and mixtures thereof. In this case, the nano-silicon is a nano-sized silicon (Si), the nano silicon suboxide has a SiO _x to X range of 0 <X <0.9, preferably 0 <X <0.5, more preferably 0.2 <X <0.4. In the above range, the electrical conductivity of the electrode is more excellent, and the charge and discharge reversibility and capacity of the lithium secondary battery may be excellent.

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

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

 The present invention is the step of (a) oxygen exchange reaction of lithium powder and silica powder to prepare a nano silicon-based compound powder selected from nano silicon, nano silicon suboxide and a mixture thereof and (b) the It provides a method for producing a nano silicon-based compound ᅳ graphene carbon fiber composite comprising the step of mixing the prepared nano silicon-based compound powder, graphene and carbon fiber.

Specifically, the nano-silicon compound-graphene-carbon fiber composite manufacturing method of the present invention by reacting the lithium powder and silica (Si0 ₂ ) powder to the oxygen exchange reaction of the oxygen of the silica is transferred to lithium (single di spl acement) ) To produce a nano silicon-based compound powder, and may then uniformly mix the resulting nano silicon-based compound powder, graphene and carbon fibers.

The nano silicon-based compound powder may be any one selected from nano silicon, nano silicon suboxide, and mixtures thereof.

In the manufacturing method of the nano-silicon compound-graphene-carbon fiber composite, when the nano-silicon compound powder is nanosilicon (Si), the reaction formula is the same as the following formula 1 below. <53>

<54> 4 Li + Si0 ₂ → Si + 2Li ₂ 0 (Scheme 1)

 <55>

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

In the method of preparing the nano-silicon compound-graphene-carbon fiber composite material, when the nano-silicon compound powder is nano silicon suboxide (SiO), the reaction formula is the same as in the following formula ( ²⁾ .

In this case, the nano silicon suboxide (SiO _x ) powder is formed by the incomplete reduction of silica, X in the silicon suboxide (Si) 0 <X <0.9, preferably 0 <X <0.5, more preferably Preferably 0.2 <X <0.4. The silicon suboxide nanopowder may be partially reduced by adjusting oxygen exchange reaction time of the lithium powder and the silica powder or by reducing the molar ratio of lithium and silica to form a partial oxide. For example, when the ball mill process of the lithium powder and the silica powder is within 3 hours, or when the lithium and the reacting lithium are 4 moles or less, the reduction of the silica is not sufficiently performed, thereby forming a suboxide.

 <59>

<60> (4-2x) Li + Si0 ₂ → (2-x) Li ₂ 0 + SiO _x (Ref. 2)

 <61>

The silica (Si0 ₂ ) powder used in the present invention may be composed of fumed silica,

⁰ 1Crophorus Sili? ^It can be any one or two or more combinations selected from ^" Hjnicroporous silica, mesoporous silica" and macroporous silica, and can be used without being limited to the type, size or pore size of silica. have.

 The silica powder may be preferably used having a diameter of 2 ran to 30, and more preferably 10 ran to 100 ran. If the particle diameter of the silica powder exceeds the above range, lithium diffusion may not be easy. If the particle diameter is less than the particle size, particle aggregation may occur due to high specific surface area and surface energy.

The graphene may have a diameter of 10 nm to 5, and the carbon fiber may have a thickness of lnm to 5Λη and a length of 50 to 200. Also the carbon The fiber may be any one selected from carbon fiber, single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanorubbers (M NT), and carbon nano ires.

The molar ratio of the lithium to silica (Si0 ₂ ) may be 2 to 6: 1, and when lithium has a ratio of greater than 6, the amount of acid used to remove lithium remaining after the reaction and the increase of wastewater result. When the ratio is less than 2, an oxide having a high oxygen content (SiO _y> l <y <2) is obtained, thereby reducing the charge and discharge reversibility and capacity of the lithium secondary battery.

The forming of the nano silicon-based compound powder may be performed by, for example, mixing the lithium powder and the silica powder in a glove box and performing ball milling for 1 to 20 hours. At this time, the glove box may be an inert gas atmosphere such as nitrogen or argon, the oxygen exchange reaction temperature through the ball mill of the lithium and silica may be 0 ~ 300 ° C. If the reaction temperature is more than 30CTC, it is not preferable that non-uniform particles having a large and small particle size may be obtained. If the reaction temperature is less than 0 ^° C, the exchange reaction rate of oxygen may be lowered.

 After preparing the nano silicon-based compound powder in the present invention, the method may further include separating and purifying the prepared nano silicon-based compound powder from lithium oxide.

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

 <69>

<70> Li ₂ 0 + ¾0 → 2LiOH (3 reactions)

<7i> Li ₂ 0 + 2HC1 → 2LiCl + ¾0 (Ref. 4)

 <72>

 The acid used in the acid treatment process may include inorganic acids such as sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid, but is not limited thereto.

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

<75-The nano-silicon compound powder 사 according to the present invention is mixed with graphene and carbon fiber The process may further include a step of mixing the nano silicon-based compound powder, a slurry in which graphene and carbon fibers are dispersed in a solvent, and then removing the solvent and drying it.

 The solvent may be used as long as it can uniformly disperse the nano silicon-based compound powder, graphene and carbon fiber, and preferably selected from alcohols having 1 to 5 carbon atoms, water or a mixture thereof. It can be either.

The carbon fiber may improve surface dispersibility by inducing surface oxidation through acid treatment. At this time, 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.

After the acid treatment, water, ethanol, isopropanol and a mixed solvent thereof may further include drying the product after the acid treatment several times.

In the present invention, the mixed weight ratio of the nano silicon-based compound powder, graphene, and carbon fiber may be 1/9 to 9/1. If the above range is insignificant effect of mixing graphene and carbon fiber in the nano silicon-based compound powder, if less than the silicon content having an electrochemical activity may be lowered and the capacity may be reduced.

The weight mixing ratio of the graphene and the carbon fiber may be 1/10 to 10/1, and the step of uniformly mixing and dispersing the nano-silicon compound powder and graphene and carbon fiber

It can be carried out at 0 ~ 100 ^° C.

The present invention can provide a nano-silicon compound-graphene-carbon fiber composite material obtained by the above production method and a lithium secondary battery comprising the same as a negative electrode active material. In one embodiment of the lithium secondary battery according to the present invention, the positive electrode active material is LKMn, Ni,

Co) 0 _{2 type} , LiMn ₂ - _x M _x 0 ₄ (M = Li, Al, Zn, Zr, Cr, Co, Ni, Fe) Spinel type, LiMP0 ₄ (M = Fe,

Mn, Co, Ni), and any one selected from the group consisting of LiPF ₆ lithium salt and a non-aqueous 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 current collector made of metal; And (ii) it can provide a lithium secondary battery comprising the nano-silicon compound-graphene-carbon fiber composite material as a negative electrode active material to be applied to the current collector.

 <84>

 Hereinafter, a method for preparing a nano-silicon compound-graphene-carbon fiber composite according to the present invention will be described through a preferred embodiment.

<86> Example 1 Preparation of Nano Silicon Powders from Nano Silica by Oxygen Substitution Solid Phase Reaction and Preparation of Nano Silicon-Graphene-Carbon Fiber Composites

<88> silica (Si0 ₂ ᅳ average particle diameter 15nm) powder and lithium metal powder (average particle diameter 25) 1:

At 4 molar ratios, the argon atmosphere and the phases were mixed at (25 ^° C), followed by ball milling at room temperature for 6 hours, and the reaction of solid phase (sol id-state) to induce oxygen substitution reaction.

<89> Lithium oxide was separated to separate the silicon oxide synthesized from the lithium oxide, which is an auxiliary reaction product.

 Wash with 0.5M hydrochloric acid solution and mix with ethanol and 1M HC1 aqueous solution (ethanol and 1M

The mixture was washed sequentially with a mixture ratio of HC1 aqueous solution 1: 1).

In the above process, LiCl salt, which is easily soluble in water, was formed by reaction of acid and lithium oxide as shown in Equations 1 and 2 below.

After washing several times with water to remove LiCl, the finally obtained dark brown nano silicon powder (SiO, average particle diameter: 50 nm) was dried in a vacuum oven.

FIG. 1 shows a TEM image and electron diffraction pattern of a nano silicon (SiO) powder obtained from the nano silica of the present invention. Primary particles of spherical nano silicon powder having a diameter of about 50 nm are observed, and since no specific ring shape or regular electron arrangement is observed in the electron diffraction pattern, it can be confirmed that the manufactured silicon powder is amorphous. there was.

 The slurry prepared by uniformly dispersing the prepared nano silicon powder 100 mg in water ΙΟΟι, and dispersing 50 mg of graphene powder (average particle diameter 2.5 / m) and 50 mg of carbon fiber powder (thickness 100 nm) in water 200 ^ After mixing with nano silicon powder solution dispersed in. Dispersion was performed using ultrasonic waves to prepare a composite dispersion solution. In this case, the composite dispersion solution includes a nano silicon-graphene-carbon fiber composite having a ratio of 50:25:25 wt. That is, nano silicon / (graphene + carbon fiber) weight ratio is 1/1, and the graphene / carbon fiber weight ratio is 1/1 to prepare a powder solution. Next, water was removed through centrifugation and dried in a vacuum oven to obtain a silicon composite anode active material.

 Figure 2 shows a TEM image of the nano silicon-graphene-carbon fiber composite powder. Three components of the silicon composite anode active material were uniformly mixed and good contact between the particles was confirmed.

 <95>

 Example 2 Investigation of the Low-Chemical Characteristic of Relop Secondary Judges Comprising a Cathode Made of Nano Silicon-Graphene-Carbon Fiber Cathode Active Material of Example 1

<97> Nano silicon-graphene-carbon fiber composite prepared from nano silica in Example 1 The negative electrode was prepared by mixing the weight ratio of the re-cathode active material: super P: polyacryl ic acid binder to 75: 15:10 (^%). At this time, polyacrylic acid was dissolved in NMP (N-methyl pyrrol idinone) to prepare a binder solution, and a silicon composite negative electrode active material and super P were added thereto to prepare a slurry for negative electrode coating. The slurry was coated on a copper current collector foil in a conventional manner. Next, it was dried for 12 hours at 1K C using a vacuum oven. After drying, a negative electrode was produced by passing through a roll press maintained at a pressure of 40 kg / otf.

In the lithium cell, lithium metal was used as a counter electrode and a reference electrode, and a manufactured silicon anode was used as a working electrode. Ethylene carbonate with 1M LiPF ₆ dissolved in electrolyte

(EC) and ethylmethyl carbonate (EMC) were prepared by mixing 5 wt% ° l of a silane additive (t r i s (2-mehtoxy e t hoxy) vinylsilane) in a mixed solution (mixture ratio 3: 7).

 <99> The constant voltage circulation curve of the lithium secondary battery including the negative electrode containing the nano silicon-graphene-carbon fiber composite was 0.05 to 1.5 vs. It is shown in Figure 3 measured at 0.1 mV / s sweep rate in / potential range.

The peak of about 0.2 V observed in the cathodic process (charging, 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). This is due to lithium desorption from Li _x Si amorphous silicon, with a peak of about 0.5 V due to a process in which lithium is desorbed from the Li ₁₅ Si ₄ phase to regenerate the silicon. Nano silicon-graphene-carbonaceous oil composite according to an embodiment of the present invention is electrochemically active in the lithium cell, it can be seen that the insertion-desorption of lithium reversibly.

Next, look at the charge and discharge profiles of the nano-silicon-graphene-carbon fiber composite anodes at 0.1-1.5 V vs. 150 / crf current density (approximately 0.02C). Charging and discharging were performed in a constant current-constant voltage (CC-CV) method in the Li / Li ⁺ period. Figure 4 shows the charge and discharge profile accordingly, it was confirmed that the flat surface by the Li _x Si formation by lithium insertion, desorption reaction into amorphous silicon.

In addition, the result of converting the capacity (catacity) of the negative electrode into a specific gravimetric capacity is shown in FIG.

103> An anode including a nano silicon-graphene-carbon fiber composite according to an embodiment of the present invention has an initial layer charge (lithium insertion) capacity of 1700 mAh / g and an initial discharge (lithium desorption) capacity of At 606 mAh / g, the initial efficiency was about 36 ¾>, but it maintained a discharge capacity of 734-635 mAh / g up to 20 cycles after 5 cycles and an efficiency of about 95% or more.

In addition, the particle breakdown phenomenon during lithium insertion-desorption increases the surface area of the silicon particles (interface contacting with the electrolyte), which leads to active electrolytic reductive decomposition, resulting in additional charge capacity, resulting in high initial charge capacity. Could get.

 In addition, lithium ions may be irreversibly adsorbed on the surface of the graphene particles to increase only the layer charge capacity.

 6 is a comparison of the cycle performance of the nano silicon-graphene-carbon fiber composite negative electrode and the silicon negative electrode according to an embodiment of the present invention, in the negative electrode made of nano silicon powder only after three cycles rapidly The discharge capacity was reduced. This is because the graphene and carbon fibers of the nano-nano-silicon compound-graphene-carbon fiber composite anode accommodate the volume change of silicon generated when reacting with lithium and increase the electrical conductivity of the cathode, thereby significantly improving cycle performance. can confirm.

 <107>

 (Example 3) Nano silicon nitrous acid from nano silica by oxygen-substituted solid phase reaction

 Preparation of Carbide (SiOx) Powders and Nano Silicon Nitrous Graphene-Carbon Fiber Composites

<109> Silica (Si0 ₂ , average particle diameter 15ran) powder and lithium metal powder (average particle diameter 25 / m) 1:

After mixing in an argon atmosphere at room temperature (25 ^° C.) at 4 molar ratio, the ball-milling at room temperature for 3 hours and solid-state reaction to induce oxygen substitution reaction.

<iio> (4-2x) Li + Si0 ₂ → (2-χ) Li-20 + Si0 _x (Ref. 4)

<m> Lithium oxide was washed with a 0.5M hydrochloric acid solution to separate the sub-acupuncture lithium oxide and the synthesized silicon nitrite powder in the same manner as in Example 1, and a mixed solution of ethanol and 1M HC1 aqueous solution (ethanol and 1M HC1 The mixture was washed sequentially with a mixing ratio of 1: 1). After removing LiCl, a brown nano silicon nitrite powder (SiO.37, average particle size: 50 nm) was finally obtained and dried in a vacuum oven.

Λ '\ 2> FIG. 7 shows ΤΕΜ image and elemental mapping image of the nano silicon nanooxide powder obtained from nano silica according to an embodiment of the present invention. Secondary particles having a diameter of about 200 to 300 nm of silicon suboxide having a diameter of about 50 nm could be identified. From the Si: 0 = 1: 0.37 ratio obtained by elemental mapping analysis, the formula of the prepared silicon suboxide is Si0 ₀ . It can be seen that ₃₇ . <Π3> Examples 1 and nano-silicon suboxide in the same manner (Si0 _{0. 37)} of the powder lOOmg water

A nanosilicon suboxide powder solution dispersed in water, which was uniformly dispersed in 100 m, and a slurry obtained by dispersing 12.5 mg of graphene powder (average particle diameter 2.5 卿) and 12.5 mg of carbon fiber powder (100 nm thick) in 50 ^ After mixing with, dispersion was prepared using ultrasonic waves to prepare a composite dispersion solution. At this time, the composite material dispersion solution is 80: 10: nano silicon suboxide having a 10 wt% ratio (Si0 _{0 37.)} - includes a carbon fiber composite material-graphene. In other words, nano silicon nitrite / (graphene + carbon fiber) weight ratio is 4/1, graphene / carbon fiber weight ratio of 1/1 to prepare a powder solution. Next, water was removed by centrifugation and dried in a vacuum oven to obtain a silicon composite anode active material.

 <114>

 <Example 5> (Example 4) Investigation of the electrochemical characteristics of the reflow secondary battery comprising a negative electrode composed of a nano silicon suboxide (SiO) -graphene-carbon fiber negative electrode active material of Example 3

<ιΐ6> Example 3 the nano silicon suboxide produced from nanosilica in (Si0 _{0 37.)} - graphene-carbon fiber cathode active material: super P: the ratio by weight of the binder of 75: 10: combined common to 15 (wt¾>) A negative electrode was prepared. At this time, sodium carboxymethyl cellulose and polyacrylic acid were mixed at a weight ratio of 1: 1 to prepare a binder solution dissolved in water, and then a silicon composite anode active material and super P were added thereto. Put to prepare a slurry for negative electrode coating. The slurry was coated on a copper current foil in a conventional manner. Next, using a vacuum oven was dried for 12 hours at 110 ° C. After drying, a pressure of 40 kg / cu was maintained through a press (roll press) to prepare a negative electrode.

Lithium cell is a pullulo ethylene carbonate (FEC) and diethyl carbonate (1M LiPF ₆ dissolved in an electrolyte solution using lithium metal as a counter electrode and a reference electrode, and a prepared silicon cathode as a working electrode). It was prepared using a mixed solution of DEC) (mixture ratio 5: 5). Charging and discharging were performed in 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 (Si0 _{0 37.)} - graphene - was shows the results in terms of negative electrode capacity (capacity) of the lithium secondary battery comprising the carbon fiber composite material as a capacity (specific gravimetric capacity) per weight in Fig.

118> The negative electrode including the nano silicon suboxide (Si0 _0.37 ) -graphene-carbon fiber composite according to an embodiment of the present invention has an initial charge (lithium insertion) capacity of 1965 mAh / g, the initial discharge (li Lithium desorption capacity was 1579 mAh / g, the initial coolant efficiency was about 80 ¾>, but after two cycles, the keg efficiency increased to 97% or more, and the capacity retention rate up to 50 cycles was 80%.

This is an improved charge and discharge performance than the negative electrode made of the nanosilicon composite of Example 2. This silicon suboxide (. Si0 _{0 37)} oxygen of the initial charge Li ₂ 0, lithium to form a silicate improved the volume change of the silicon capacity (accomodate) nano-silicon suboxide (Si0 _{0 37.)} In- This is because the interfacial reaction with the electrolyte was suppressed by layer discharge of the graphene-carbon fiber composite anode in an electrolyte consisting of FEC: DEC, which is known to have a negative reaction.

 <120>

 As described above, the present invention has been described by a limited embodiment, but this is only provided to help a more general understanding of the present invention, and the present invention is not limited to the above embodiments. Those skilled in the art can make various modifications and variations from this description.

 Therefore, the spirit of the present invention should not be limited to the described embodiments, and all the things equivalent to or equivalent to the scope of the claims as well as the claims to be described below are within the scope of the spirit of the present invention. Will belong.

 <123>

Claims

[Range of request]

 [Claim 1]

 Nano silicon-based compound-graphene-carbon fiber composites selected from nano silicon, nano silicon suboxide, and mixtures thereof.

[Claim 2]

 The method of claim 1,

The nano silicon suboxide is SiO _x (0 <X <0.5) nano silicon compound-graphene ᅳ carbon fiber composite.

[Claim 3]

 The negative electrode active material for a lithium secondary battery comprising the nano-silicon compound ᅳ graphene-carbon fiber composite of any one of claims 1 and 2.

[Claim 4]

 A lithium secondary battery comprising the negative electrode active material for lithium secondary battery of claim 3.

[Claim 5]

 (a) oxygen exchange reaction of lithium powder and silica powder to produce a nano silicon-based compound powder selected from nano silicon, nano silicon suboxide and mixtures thereof; and

 (B) a method for producing a nano-silicon compound-graphene-carbon fiber composite comprising the step of mixing the prepared nano-silicon compound powder, graphene and carbon fiber.

[Claim 6]

 The method of claim 5,

 The step (a) is a method for producing a nano silicon-based compound-graphene ᅳ carbon fiber composite further comprising the step of separating and purifying the prepared nano silicon-based compound powder from lithium oxide.

[Claim 7] The method of claim 5,

 Step (b) is a nano silicon compound-graphene-graphene-carbon fiber composites further comprising the step of mixing the nano silicon compound powder, a slurry of graphene and carbon fibers dispersed in a solvent, and then removing the solvent and drying How to make it.

[Claim 8]

 The method of claim 5,

 The silica powder is any one or two or more combinations selected from the group silica, microporous silica, mesoporous silica and macroporous silica nano-silicon compound-graphene-carbon fiber composite manufacturing method.

[Claim 9]

 The method of claim 5,

 The silica powder is a method for producing a nano-silicon compound-graphene pentane small fiber composite having a diameter of 2 nm ~ 30.

[Claim 10]

 The method of claim 5,

 The graphene is a method for producing a nano-silicon compound-graphene-carbon fiber composite having a diameter of lOran ~ 5 卿.

[Claim 11]

 According to claim 15,

 The carbon fiber is a nano-silicon compound of lnm ~ 5, length 50 ~ 200-graphene-carbon fiber composite manufacturing method.

[Claim 12]

 The method of claim 5,

A method of producing a nano-silicon compound-graphene-carbon fiber composite material, wherein the molar ratio of the lithium and silica (Si0 ₂ ) is 2 to 6: 1.

[Claim 13] The method of claim 5,

 The step) is a method for producing a nano-silicon compound-graphene-carbon fiber composites which are carried out by a ball milling process for 1 to 20 hours after mixing in an inert atmosphere.

[Claim 14]

 The method of claim 5,

Oxygen exchange reaction in step (a) is a method for producing a nano silicon-based compound-graphene-carbon fiber composite material is carried out at a temperature range of 0 ~ 300 ^° C.

[Claim 15]

 The method of claim 5,

 The carbon fiber of step (b) is surface-oxidized by acid treatment method for producing a nano silicon-based compound—graphene-carbon fiber composite.

[Claim 16]

 The method of claim 5,

 The method of producing a nano-silicon compound—graphene-carbon fiber composite material having a weight mixing ratio of the nano silicon-based compound powder and the graphene and carbon fiber mixture in the step (b) is from 1: 9 to 9: 1.

[Claim 17]

6. The method of claim 5, ^■

 Graphene and carbon fibers in the step (b) is a method of producing a nano silicon compound-graphene-carbon fiber composite having a weight mixing ratio of 1: 10 ~ 10: 1.

[Claim 18]

 The method of claim 5,

Step (b) is a method for producing a nano silicon-based compound-graphene-carbon fiber composite is carried out at 0 ~ 100 ^° C.

[Claim 19] According to claim 15,

 The carbon fiber is any one selected from carbon fiber, single-walled carbon nanotubes, multi-walled carbon nanotubes and carbon nanowires nano-silicon compound-graphene-carbon fiber composite manufacturing method.