KR101589458B1 - A method for manufacturing silicon nanowire and a method for manufacturing silicon anode material and lithium secondary battery using the same - Google Patents

Abstract

The present invention provides a method of manufacturing a silicon-based anode active material using the silicon nanowire and a method of manufacturing a lithium secondary battery using the same. In the case of a lithium secondary battery including a negative electrode active material manufactured using silicon nanowires coated with metal particles according to the present invention, high capacity charge and discharge can be realized as well as high capacity maintenance and cycle life improvement effect . According to the present invention, there is provided a method of manufacturing metal nanoparticles coated with metal particles, comprising the steps of: (a) forming first metal particles spaced from each other on a silicon substrate; (b) selectively etching the silicon substrate to form silicon nanowires; (c) removing the first metal particles; (d) forming second metal particles spaced apart from each other on the surface of the silicon nanowire; And (e) separating the silicon nanowires having the second metal particles formed thereon from the silicon substrate.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method for manufacturing a silicon nanowire, a silicon anode active material using the same, and a method for manufacturing a lithium secondary battery,

The present invention relates to a method of manufacturing a silicon nanowire, a silicon anode active material using a silicon nanowire, and a method of manufacturing a lithium secondary battery, and more particularly, to a method of manufacturing a silicon nanowire coated with metal particles having excellent electrical conductivity, To a method for manufacturing a silicon-based negative electrode active material and a lithium secondary battery.

Demand for lithium secondary batteries has been greatly increased as power sources for electric vehicles such as personal portable terminal devices such as smart phones and tablet PCs, hybrid electric vehicles and plug-in electric vehicles, Development of high-power and high-energy density active materials capable of replacing the anode and cathode materials of the secondary battery has been actively conducted all over the world.

In the case of the cathode, since the theoretical capacity of graphite used in most commercial lithium secondary batteries is 372 mAh / g, it is impossible to realize a high capacity battery. As an active material for overcoming this problem, a silicon based anode active material having a theoretical capacity of 4,200 mAh / g has attracted much attention. The silicon-based anode active material is generally prepared by mixing a conductive material (carbon) and an adhesive (binder) with a silicone material to prepare a slurry and then coating the metal current collector.

On the other hand, as with most metals and metal oxide materials in which an alloy is electrochemically formed with lithium, silicon also has a problem of mechanical damage of the electrode due to volume expansion and shrinkage due to charging and discharging and shortening of life time thereof rapidly. , There is a demand for improvement of performance by nano-sizing of particles and complexing with lithium active / inactive dissimilar materials. In one of these methods, many studies have been made to use a nanowire type of silicon as a negative electrode active material, which has a considerable buffering capacity against the volume expansion and contraction of silicon, thereby preventing cracking of the silicon (Korean Patent Laid- 2010-0127990 and 10-2011-0123578).

However, when the anode active material using such a silicon nanowire is used in a lithium secondary battery, there is a disadvantage that the capacity and cycle characteristics are deteriorated due to the solid electrolyte interface formed on the silicon surface during high-speed charge and discharge. Therefore, it is necessary to manufacture a silicon nanowire that can suppress the formation of a solid electrolyte interface on the surface of a silicon nanowire to improve cycle characteristics and maintain a high capacity when the silicon nanowire is used as an anode active material of a lithium secondary battery. .

The present invention relates to a method for producing a silicon-based anode active material having metal particles having excellent electrical conductivity on its surface and a method for producing the same, a method for producing a silicon-based anode active material capable of realizing a high capacity and high charge / discharge rate by using the silicon nanowire, And a method for manufacturing a secondary battery.

The present invention provides, as one means for solving the above problems,

(a) forming first metal particles spaced apart from each other on a silicon substrate;

(b) selectively etching the silicon substrate to form silicon nanowires;

(c) removing the first metal particles;

(d) forming second metal particles spaced apart from each other on the surface of the silicon nanowire; And

(e) separating the silicon nanowires formed with the second metal particles on the surface from the silicon substrate.

The present invention also provides, as another means for solving the above problems,

Silicon nanowires; And metal particles formed on the surface of the silicon nanowire, the metal particles being spaced apart from each other.

Further, the present invention provides, as still another means for solving the above problems,

There is provided a method for producing a silicon-based anode active material, which comprises mixing a silicon nanowire prepared according to the present invention or coated with metal particles according to the present invention with a conductive material and a binder to prepare a slurry.

Further, the present invention provides, as still another means for solving the above problems,

There is provided a method of manufacturing a lithium secondary battery comprising the step of coating a silicon negative electrode active material prepared according to the present invention on a metal current collector to prepare a negative electrode active material layer.

When a negative electrode active material for a lithium secondary battery is manufactured using a silicon nanowire coated with metal particles and a lithium secondary battery is manufactured using the same, a solid electrolyte interface is controlled on the surface of the silicon nanowire A high capacity and a cycle characteristic can be improved, and a lithium secondary battery capable of realizing fast charge / discharge can be provided.

1 is a flowchart illustrating a method of manufacturing a silicon nanowire with metal particles coated thereon according to the present invention.
Fig. 2 is a schematic diagram of a process for producing silicon nanowires coated with metal particles according to the present invention.
3 to 5 are cross-sectional views of a process for producing silicon nanowires coated with metal particles, according to the present invention.
6 is a scanning electron microscope (SEM) photograph of a silicon nanowire coated with gold (Au) particles according to the present invention, wherein (a) is an enlarged view at 1,000x and (b) is an enlarged view at 100,000x.
7 is a transmission electron microscope (TEM) photograph of a silicon nanowire coated with gold (Au) particles according to the present invention.
FIG. 8 is a photograph of energy dispersive x-ray spectroscopy (EDX) of gold nanowires coated with gold (Au) particles according to the present invention.
9 is a cross-sectional view of one embodiment of a lithium secondary battery according to the present invention.
Fig. 10 is a graph showing the relationship between the battery cycle (measured at a discharging current of 0.5 C) and the lithium secondary battery using a lithium secondary battery using a silicon nanowire as a negative active material and a lithium secondary battery using a silicon nanowire coated with gold cycle and capacity.
Fig. 11 is a graph showing the results of a comparison between a lithium secondary battery using a silicon nanowire as a negative electrode active material and a lithium secondary battery using a silicon nanowire coated with gold (Au) particles as a negative electrode active material, at 0.2C, 0.5C, 1C and 2C A graph showing the battery cycle and capacity measured at the discharge current.
12 is a graph showing the results of impedance measurement of a lithium secondary battery using a silicon nanowire as a negative electrode active material and a lithium secondary battery using a silicon nanowire coated with gold (Au) particles as a negative electrode active material, using a Nyquist plot nyquist plot).

(A) forming first metal particles spaced apart from each other on a silicon substrate; (b) selectively etching portions of the silicon substrate to form silicon nanowires; (c) removing the first metal particles; (d) forming second metal particles spaced apart from each other on the surface of the silicon nanowire; And (e) separating the silicon nanowires having the second metal particles formed thereon from the silicon substrate.

Hereinafter, with reference to FIGS. 1 to 5, a method of manufacturing a silicon nanowire having metal particles coated thereon according to an embodiment of the present invention will be described in detail.

FIG. 1 is a flow chart for explaining a method of manufacturing a silicon nanowire having metal particles coated thereon according to the present invention, and FIG. 2 is a view for explaining a method of manufacturing silicon nanowires coated with metal particles according to the present invention. And FIGS. 3 to 5 are cross-sectional views illustrating a method for manufacturing a silicon nanowire having metal particles coated thereon according to the present invention.

Referring to Figures 1 to 3, a method of manufacturing metal nanoparticles coated with metal particles, according to the present invention, comprises the steps of: (a) forming first metal particles spaced from each other on a silicon substrate; have.

 The silicon substrate of step (a) may have a thickness of 50 [mu] m to 500 [mu] m. The silicon substrate may be doped with a p-type dopant or an n-type dopant, or may not be doped.

Referring to FIG. 1, the silicon substrate used in step (a) may be cleaned before forming the first metal particles on the surface thereof. The cleaning step of the silicon substrate may be a process for removing organic matter on the silicon substrate and forming a hydrophilic surface.

The cleaning step of the silicon substrate may include a step of immersing the silicon substrate in the cleaning solution, or the cleaning solution may be provided on one surface of the silicon substrate to clean only one surface of the silicon substrate. The type of the cleaning solution for the silicon substrate is not particularly limited and may be any one generally used in the art.

Referring to FIGS. 1 to 3, first metal particles are formed on the silicon substrate. The first metal particles may be formed on one or both surfaces of the silicon substrate. Wherein the first metal particles are spaced apart from one another on a silicon substrate and the first metal particles are noble metal or preferably selected from the group consisting of silver (Ag), gold (Au), platinum (Pt) .

In the step (a), forming the first metal particles spaced apart from each other on the silicon substrate may be performed by a method including spin coating, dip coating, electroless deposition, physical vapor deposition, chemical vapor deposition, thermal vapor deposition, electron beam vapor deposition, sputtering, drop coating drop-coating, spray aerosol, or a combination thereof, but may preferably be performed by a drop coating using a solution comprising the first metal particles, a spray aerosol or a combination thereof .

In the step (a), first metal particles spaced apart from each other may be formed on a silicon substrate, and then heat-treated. The heat treatment in the step (a) may be performed within a temperature range of 200 ° C to 500 ° C. By performing the heat treatment within the temperature range, the first metal particles can be attached to the surface of the silicon substrate.

Referring to FIGS. 1, 2 and 4, a method for fabricating silicon nanowires coated with metal particles according to the present invention includes the steps of: (b) selectively etching a portion of the silicon substrate to form silicon nanowires Step < / RTI >

The step (b) may be performed by dipping the silicon substrate obtained in the step (a) in an etching solution, i.e., by a wet etching process.

Specifically, as shown in FIG. 4, the silicon nanowires can be formed by selectively etching portions of the first metal particles spaced apart from each other on the silicon substrate in contact with the silicon substrate.

The wet etch process may include dipping the silicon substrate obtained in step (a), for example, in an etching solution comprising hydrofluoric acid (HF), hydrogen peroxide (H ₂ O ₂ ) and deionized water . In one embodiment of the present invention, in the etching solution, the concentration of hydrofluoric acid is 4 M to 5 M, preferably 4.6 M, and the concentration of hydrogen peroxide may be 0.4 M to 0.5 M.

When an etching solution containing hydrofluoric acid, hydrogen peroxide and deionized water is used in the etching process of the step (b), the portion of the silicon substrate which is in contact with the first metal particles is selectively Can be etched.

[Reaction Scheme 1]

Si + 2H ₂ O ₂ + 6HF? H ₂ SiF ₆ + 4H ₂ O

Upon etching the silicon substrate, the first metal particles may act as an etch catalyst. Accordingly, the etching rate at the portion of the silicon substrate that contacts the first metal particles may be higher than the etching rate at the portion of the silicon substrate that is not in contact with the first metal particles. Accordingly, the portion of the silicon substrate which contacts the first metal particles can be selectively etched. As shown in FIG. 4, by selective etching of the silicon substrate, silicon nanowires can be formed.

5, the length h1, the thickness w1 and the interval d1 of the silicon nanowires formed on the silicon substrate satisfy the conditions of the wet etching process, the forming conditions of the first metal particles, Can be easily adjusted by controlling the combination thereof.

For example, the length h1 of the silicon nanowires can be adjusted by adjusting the time of the etching process, the concentration of the etching solution, or a combination thereof.

As another example, when forming the first metal particles on the silicon substrate, the interval of the first metal particles can be adjusted by adjusting the concentration of the first metal particles in the solution containing the first metal particles. Accordingly, the distance d1 between the silicon nanowires can be adjusted.

As another example, when the first metal particles are formed on the silicon substrate, the first metal particles of the solution containing the first metal particles may be adjusted in size to adjust the thickness w1 of the silicon nanowires .

In one embodiment of the present invention, the size of the first metal particles may be between 10 nm and 500 nm, and the length h1 of the silicon nanowires may be between 5 and 50, preferably between 10 and 20, And the thickness w1 of the silicon nanowires may be 10 nm to 500 nm, preferably 20 nm to 50 nm, and the distance d1 between the silicon nanowires may be 10 nm to 100 nm, May be between 20 nm and 30 nm.

Referring to FIGS. 1 and 2, a method of manufacturing a silicon nanowire with metal particles coated thereon according to the present invention may include (c) removing the first metal particles.

The step (c) may be carried out by a wet process. The first metal particles remaining on the silicon substrate obtained in step (b), preferably a nitric acid solution, a KI / I ₂ mixed solution, a royal water, molten sulfur, sulfur, or combinations thereof, the remaining first metal particles can be removed from the silicon substrate.

Referring to FIGS. 1 and 2, a method for fabricating a metal-coated silicon nanowire according to the present invention includes the steps of (d) forming second metal particles spaced apart from each other on a surface of the silicon nanowire, .

Referring to FIGS. 1 and 2, second metal particles may be formed on the surface of the silicon nanowire. The second metal particles are spaced apart from each other on the surface of the silicon nanowire. The second metal particles may be a metal having excellent electrical conductivity or preferably copper (Cu), aluminum (Al), zinc (Zn) ), Lead (Pb), silver (Ag), gold (Au), and combinations thereof.

In the step (d), the formation of the second metal particles spaced apart from each other on the surface of the silicon nanowire can be performed by any one of spin coating, dip coating, electroless deposition, physical vapor deposition, chemical vapor deposition, thermal vapor deposition, electron beam vapor deposition, sputtering, Coating, spray aerosol or a combination thereof, but may preferably be performed by a drop coating using a solution comprising the second metal particles, a spray aerosol or a combination thereof.

In the step (d), the second metal particles spaced apart from each other on the surface of the silicon nanowire may be formed and then heat-treated. The heat treatment in the step (d) may be performed within a temperature range of 200 ° C to 500 ° C. By performing the heat treatment within the temperature range, the second metal particles can be attached to the surface of the silicon nanowires.

In the step (d), the entire surface of the silicon nanowire is not coated with the second metal particles, but the second metal particles formed on the surface of the silicon nanowire are controlled to have a predetermined gap therebetween, When the silicon nanowire having the second metal particles formed thereon is used as the negative electrode active material of the lithium secondary battery, the movement of lithium ions is facilitated and high-speed charge / discharge can be efficiently performed.

As shown in Fig. 2d), the spacing of the second metal particles formed on the surface of the silicon nanowire can be easily adjusted by controlling the formation conditions of the second metal particles.

For example, when forming the second metal particles on the surface of the silicon nanowire, the interval of the second metal particles can be adjusted by adjusting the concentration of the second metal particles in the solution containing the second metal particles . Accordingly, second metal particles spaced apart from each other on the surface of the silicon nanowire may be formed.

In one embodiment of the present invention, the size of the second metal particles may be between 10 nm and 500 nm, and the spacing of the second metal particles on the silicon nanowire surface may be between 10 nm and 1 μm, preferably 100 nm To 200 nm. By controlling the interval of the second metal particles within the above range, it is possible to facilitate the movement of lithium ions when using the silicon nanowires coated with the metal particles according to the present invention as the negative electrode active material of the lithium secondary battery, Can be efficiently implemented.

Referring to FIGS. 1 and 2, a method of manufacturing a silicon nanowire having metal particles coated thereon according to the present invention includes the steps of: (e) separating silicon nanowires having the second metal particles formed thereon from the silicon substrate .

In the step (e), the method of separating the silicon nanowires is not particularly limited, and for example, an ultrasonicator or the like may be used, but the ultrasonic wave pulverizer may be preferably used.

The present invention also relates to a nanowire comprising: a silicon nanowire; And metal particles formed on the surface of the silicon nanowires spaced apart from each other.

The silicon nanowires may be conventional silicon nanowires known in the art, but may preferably be silicon nanowires manufactured according to the method of the present invention described above. The above-described silicon nanowires are as described above in the method for producing silicon nanowires coated with metal particles.

The metal particles separated from each other on the surface of the silicon nanowire may be a metal having excellent electrical conductivity or may be a metal such as copper (Cu), aluminum (Al), zinc (Zn), iron (Fe), lead (Pb) Ag), gold (Au), and combinations thereof.

The metal particles formed on the surface of the silicon nanowire are spaced apart at a predetermined interval, and preferably, the interval of the metal particles may be 10 nm to 1 탆, preferably 100 nm to 200 nm. By controlling the intervals of the metal particles to the above range, it is possible to facilitate the movement of lithium ions when using the silicon nanowires coated with the metal particles according to the present invention as the negative electrode active material of the lithium secondary battery, It can be implemented efficiently.

6 is a scanning electron microscope (SEM) photograph of a silicon nanowire coated with gold (Au) particles according to the present invention, wherein (a) is an enlarged view at 1,000x, (TEM) photograph of a silicon nanowire coated with gold (Au) particles according to the present invention, and FIG. 8 is an EDX photograph of a silicon nanowire coated with gold (Au) particles according to the present invention .

As shown in FIGS. 6 to 8, it can be seen that metal particles, for example, gold (Au) particles are formed on the surface of the silicon nanowire at predetermined intervals.

The silicon nanowires coated with metal particles and the method of manufacturing the same according to the present invention can be applied to various fields to which a silicon nanostructure can be applied. For example, in the manufacture of a negative active material layer of a lithium secondary battery Lt; / RTI >

The present invention also relates to a method for producing a silicon-based anode active material, comprising the step of mixing a silicon nanowire coated with metal particles with a conductive material and a binder to prepare a slurry, which is produced according to the present invention.

The conductive material is not particularly limited and may be any conductive material generally used in the art. For example, carbon black, Nanotubes, hard carbon, soft carbon, graphite, or a combination thereof.

The type of the binder is not particularly limited and the binder commonly used in the art can be used without limitation. Examples of the binder include polyimide, polyamide imide, polyamide, Polyacrylonitrile, polyacrylic acid, polyvinyl alcohol, polyurethane, polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), polyvinylidene fluoride , Styrene butadiene rubber (SBR), or a combination thereof.

The silicon-based anode active material of the present invention can be produced in the form of a slurry by mixing the silicon nanowires coated with the metal particles prepared according to the present invention with a conductive material and a binder.

The present invention also relates to a process for producing a lithium secondary battery, comprising the step of coating a silicon negative electrode active material prepared according to the present invention onto a metal current collector to prepare a negative electrode active material layer.

Referring to FIG. 9, the above-described silicon nanowires coated with metal particles, a lithium secondary battery to which the method is applied, and a method of manufacturing the same will be described in detail.

9, a cathode 110 and an anode 140 facing each other, a separator 130 between the cathode 110 and the anode 140, and a separator 130 between the cathode 110 and the anode 140 There is provided a lithium secondary battery 100 according to the present invention, which includes an electrolyte 160.

The anode 140 includes a cathode current collector 141; And a cathode active material layer 150 between the cathode current collector 141 and the separator 130.

The cathode 110 includes an anode current collector 111; And a negative electrode active material layer 120 between the negative electrode collector 111 and the separator 130. The anode active material layer 120 includes silicon nanowires 123 having second metal particles 125 formed on the surface thereof according to the present invention. And a conductive material and a binder 126 filled between the silicon nanowires 123.

The types of the cathode current collector 141, the anode current collector 111, the separator 130, and the cathode active material layer 150 are not particularly limited and those commonly used in the art can be used without limitation. The types of the conductive material and the binder 126 are as described above.

The method for manufacturing a lithium secondary battery according to the present invention includes the step of coating a silicon based negative electrode active material prepared according to the present invention on an anode current collector 111 to manufacture a negative electrode active material layer 120 for a lithium secondary battery , Other process steps may be employed without limitation in the manufacturing processes generally used in the art.

[ Example ]

In the following Examples, the present invention will be described in more detail with reference to Examples according to the present invention and Comparative Examples not based on the present invention, but the scope of the present invention is not limited by the following Examples.

Example  One

(1) Cleaning of silicon substrate

The silicon substrate was immersed in a mixed solution of sulfuric acid (H ₂ SO ₄ ) and hydrogen peroxide (H ₂ O ₂ ) (mixed solution of 400 ml of an aqueous sulfuric acid solution of about 60 vol% and 100 ml of an aqueous hydrogen peroxide solution of about 30 vol% Lt; 0 > C for about 30 minutes to remove organic matter on the silicon substrate and to form a hydrophilic surface.

(2) First metal particle formation and heat treatment on a silicon substrate

A solution containing silver (Ag) particles (49 wt% silver ion-containing solution) was diluted to 1/100 on the cleaned silicon substrate and coated with silver particles by a drop coating method. Thereafter, the silicon substrate having the silver particles formed on its surface was heat-treated at a temperature of 200 ° C to 500 ° C.

(3) Silicon nanowire formation through selective etching of silicon substrate

The heat-treated silicon substrate was immersed in an etching solution containing hydrofluoric acid, hydrogen peroxide and deionized water (a solution containing 4.6 M of hydrofluoric acid and 0.5M of hydrogen peroxide) to perform a wet etching process. The wet etching process was performed at room temperature for about 1 hour.

(4) Removal of first metal particles from the silicon substrate

After the wet etching process, the silicon substrate on which the silicon nanowires were formed was immersed in a nitric acid solution to remove silver particles remaining on the silicon substrate.

(5) Formation of second metal particles on the surface of silicon nanowires

After the removal of the silver particles, a solution containing gold (Au) particles (a solution containing 49% by weight of gold ions) was diluted to 1/100 on the silicon substrate and coated with gold particles by a drop coating method. Thereafter, the silicon substrate of the silicon nanowire having gold particles formed on its surface was heat-treated at a temperature of 300 캜.

(6) Separation of silicon nanowires having second metal particles formed on their surfaces from a silicon substrate

A silicon substrate of silicon nanowires having gold particles formed on the surface thereof was placed in an ultrasonic mill and an ultrasonic mill was operated to separate the silicon nanowires formed on the surface of the gold particles from the silicon substrate.

The surface morphology of the silicon nanowires coated with gold particles on the surface was confirmed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive x-ray spectroscopy (EDX) Respectively. FIG. 6 is a scanning electron micrograph of the gold nanoparticle-coated silicon nanowire fabricated according to Example 1, and FIG. 7 is a transmission electron micrograph of the gold nanoparticle-coated silicon nanowire fabricated according to Example 1 , And FIG. 8 is an EDX photograph of the gold nanoparticle-coated silicon nanowire fabricated according to Example 1. 6 to 8, silicon nanowires having a predetermined thickness and spacing are formed by the above-described manufacturing method, and gold particles are formed on the surfaces of the silicon nanowires at predetermined intervals Can be confirmed.

Example  2

20 wt% of silicon nanowires having gold particles formed on the surface thereof, prepared in Example 1, were mixed with 70 wt% of a conductive material and 10 wt% of a binder to prepare a silicon-based negative active material in the form of a slurry. To prepare a slurry having an appropriate viscosity at this time, pure water as a solvent was added at a half of the total weight of the silicon nanowire, the conductive material and the binder, and the mixture was stirred at 5,000 rpm for 30 minutes at high speed to obtain a slurry- . Super-P was used as the conductive material, and carboxymethyl cellulose (CMC) was used as the binder.

Example  3

The silicon anode active material prepared in Example 2 was coated on a negative electrode current collector (copper thin film) to a thickness of 40 탆 by a doctor blade method to prepare a negative electrode. The prepared negative electrode was rolled, and then dried in a vacuum oven for 12 hours. Thereafter, a dried negative electrode, a polypropylene separator, and a lithium metal counter electrode were laminated. Subsequently, a solution 1 (1: 1) in which LiPF ₆ was dissolved in EC: DMC M LiPF ₆ solution) was injected as an electrolyte to prepare a lithium secondary battery in the form of a coin cell.

Comparative Example  One

Silicon nanowires without the second metal particles were prepared in the same manner as in Example 1, except that step (5) of Example 1 was omitted.

Comparative Example  2

A silicon-based negative active material was prepared in the same manner as in Example 2, except that the silicon nanowire in which the second metal particles were not coated, according to Comparative Example 1 was used.

Comparative Example  3

A lithium secondary battery was produced in the same manner as in Example 3, except that the silicone-based negative active material of Comparative Example 2 was used.

Test Example  One

Charge-discharge experiments were carried out for 30 cycles using the lithium secondary batteries prepared in Example 3 and Comparative Example 3 to measure the capacity change. The charge and discharge conditions were such that a constant current was applied to the Li electrode at a current of 100 mA per 1 g of the negative electrode active material until the voltage reached 0 V, and the battery was discharged at a constant current until it reached 1 V.

Fig. 10 is a graph showing the results of a comparison between a lithium secondary battery (Comparative Example 3) using a silicon nanowire as a negative electrode active material and a lithium secondary battery (Example 3) using a silicon nanowire coated with gold (Au) C " and " capacity " measured at the discharging current of " C ".

10, it can be seen that the lithium secondary battery of Example 3 is improved in comparison with the cycle life of the lithium secondary battery of Comparative Example 3. [

Test Example  2

Charge-discharge experiments were carried out for 25 cycles using the lithium secondary batteries prepared in Example 3 and Comparative Example 3 to measure the capacity change. The charge and discharge conditions were charged with a constant current until the voltage reached 0 V at a rate of 0.5 C and discharged at a constant current until the voltage reached 1 V. [

Fig. 11 is a graph showing the results of a comparison between a lithium secondary battery using a silicon nanowire as a negative electrode active material (Comparative Example 3) and a lithium secondary battery using a silicon nanowire coated with gold (Au) particles as a negative electrode active material (Example 3) 0.2 C, 0.5 C, 1 C, and 2 C, respectively.

It can be seen from Fig. 11 that the lithium secondary battery of Example 3 is improved in comparison with the cycle life of the lithium secondary battery of Comparative Example 3 in both cases where the discharge current amount (or discharge current rate) is high and low.

Test Example  3

In the lithium secondary battery manufactured in Example 3 and Comparative Example 3, the internal impedance of the negative electrode was measured.

12 is a graph showing a relationship between a voltage applied to a lithium secondary battery (Example 3) in which a lithium secondary battery (Comparative Example 3) using silicon nanowires as a negative electrode active material and a silicon nanowire coated with gold (Au) particles as a negative electrode active material (Z ') represents the real part of the impedance, and the y-axis (Z ") represents the imaginary part of the impedance.

12, the size of the real part of the impedance is smaller than that of the lithium secondary battery of the comparative example 3, so that the lithium secondary battery of the example 3 is smaller than that of the lithium secondary battery of the comparative example 3 It can be confirmed that the resistance is smaller. This is because when a silicon nanowire coated with gold particles is used as a negative electrode active material, a solid electrolyte interface is formed on the surface of the silicon nanowire, compared with a case where silicon nanowires not coated with any metal particles are included as an anode active material Which can be suppressed more effectively.

As described above, in the case where the metal nanopowder coated with metal particles was used as the negative electrode active material of the lithium secondary battery (Example 3), the silicon nanowires without the metal particles were applied to the lithium secondary battery It can be confirmed that not only the high capacity of the battery can be maintained but also the cycle life is improved as compared with the case of using as the negative electrode active material (Comparative Example 3).

100: lithium secondary battery 110: cathode
111: negative electrode collector 120: negative electrode active material layer
121: Silicon substrate 123: Silicon nanowire
124: first metal particle 125: second metal particle
126: conductive material and binder 130: separator
140: positive electrode 141: positive electrode collector
150: positive electrode active material layer 160: electrolyte
h1: length of silicon nanowire
w1: thickness of silicon nanowire
d1: spacing between silicon nanowires

Claims (13)

(a) forming first metal particles spaced apart from each other on a silicon substrate;
(b) selectively etching the silicon substrate to form silicon nanowires;
(c) removing the first metal particles;
(d) forming second metal particles spaced apart from each other on the surface of the silicon nanowire; And
(e) separating the silicon nanowires having the second metal particles formed thereon from the silicon substrate. The method according to claim 1,
Wherein the first metal particles of step (a) are selected from the group consisting of silver (Ag), gold (Au), platinum (Pt), and combinations thereof. The method according to claim 1,
The formation of the first metal particles of step (a) is carried out by drop-coating, spray aerosol or a combination thereof using a solution comprising the first metal particles, Method for manufacturing silicon nanowires. The method according to claim 1,
Wherein the heat treatment of step (a) is carried out within a temperature range of 200 ° C to 500 ° C. The method according to claim 1,
Wherein the etching of step (b) is performed through a wet etching process. 6. The method of claim 5,
A wet etching process is performed using an etching solution comprising hydrofluoric acid (HF), hydrogen peroxide (H ₂ O ₂ ) and deionized water. The method according to claim 1,
The second metal particles of step (d) may be made of copper (Cu), aluminum (Al), zinc (Zn), iron (Fe), lead (Pb), silver (Ag) ≪ / RTI > wherein the metal nanoparticles are coated with metal particles. The method according to claim 1,
The formation of the second metal particles of step (d) may be carried out by drop-coating, spray aerosol or a combination thereof using a solution comprising the second metal particles, Method for manufacturing silicon nanowires. The method according to claim 1,
Wherein the separation of the silicon nanowires in step (e) is performed using an ultrasonicator. Silicon nanowires; And metal particles formed on the surface of the silicon nanowire, wherein the metal particles are formed at an interval of 10 nm to 1 탆, and the metal particles are aluminum (Al), zinc (Zn), iron (Fe ), Lead (Pb), silver (Ag), gold (Au), and combinations thereof. delete 9. A method for producing a silicon-based anode active material, comprising the steps of: mixing a silicon nanowire coated with metal particles with a conductive material and a binder to prepare a slurry according to any one of claims 1 to 9. A method for manufacturing a lithium secondary battery, comprising the step of coating a silicon negative electrode active material prepared according to claim 12 onto a metal current collector to produce a negative electrode active material layer.

Images