KR20160098653A - A method of preparing silicon based anode active materials and lithium secondary battery using the same - Google Patents

Abstract

Provided in the present invention are a method for manufacturing a silicon nanowire for a lithium secondary battery coated with a metal on a surface, and a silicon nanowire for a lithium secondary battery manufactured therefrom. The method comprises the steps of: (a) forming a silicon nanowire by a metal-catalyst etching method; (b) removing the randomly electrodeposited metal on the surface of the etched silicon nanowire; and (c) carrying the silicon nanowire in a diluted solution of strong acid and precipitating metal particles on the surface of the silicon nanowire. Provided is the lithium secondary battery, which has high capacity and can perform charging and discharging at a high speed.

Description

[0001] The present invention relates to a method for preparing a silicon-based anode active material and a lithium secondary battery using the same,

The present invention relates to a silicon-based negative electrode active material for a secondary battery and a lithium secondary battery using the same.

2. Description of the Related Art Demand for lithium secondary batteries has been greatly increased as a power source for electric vehicles such as personal portable terminal devices such as smart phones and tablet PCs, hybrid electric vehicles and plug-in electric vehicles, High-power and high-energy-density active materials capable of replacing the anode and cathode materials have been actively developed 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 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 material on the metal current collector.

On the other hand, in order to solve the mechanical damage of the electrode due to the volume expansion and shrinkage caused by charging and discharging, and the rapid shortening of the service life due to the charging and discharging, as well as most metal and metal oxide materials in which an alloy is electrochemically alloyed with lithium, Improvement in performance through the combination of lithium and active / inactive lithium materials has been pursued. As one of these methods, many researches have been made to use silicon as a negative electrode active material in the form of nanowires, which can prevent cracking of silicon due to a considerable buffering force against volume expansion and shrinkage of silicon.

However, when the negative electrode active material using such a silicon nanowire is used in a lithium secondary battery, the non-capacity and cycle characteristics are deteriorated due to the solid electrolyte interface formed on the silicon surface during high-speed charge and discharge.

Patent Reference:

Korean Patent Publication No. 10-2010-0127990

Korean Patent Publication No. 10-2011-0123578

DISCLOSURE Technical Problem The present invention aims to solve the above problems and to improve the cycle characteristics and the capacity characteristics by suppressing the solid electrolyte interface formed on the surface when the silicon nanowires are used as the negative electrode active material. To this end, the present invention provides a lithium secondary battery capable of realizing a high-capacity and high-speed charge-discharge by providing a cathode material with a silicon nanowire whose surface is coated with metal particles. .

One embodiment of the present invention includes the steps of (a) forming a silicon nanowire by metal catalyst etching; (B) removing randomly electrodeposited metal on the etched silicon nanowire surface; And (c) depositing metal particles on the surface of the silicon nanowire by supporting the silicon nanowires in a dilution liquid of a strong acid. The present invention also provides a method of manufacturing a silicon nanowire for a lithium secondary battery.

In one embodiment of the present invention, step (a) comprises supporting a silicon substrate on an etchant, wherein the etchant comprises an aqueous solution of hydrofluoric acid (HF) and a molten metal.

In one embodiment of the present invention, the concentration of the aqueous solution of hydrofluoric acid is 4M to 5M.

In one embodiment of the present invention, the diluent of the strong acid in step (c) has a concentration of 0.01M to 1M.

In one embodiment of the present invention, the metal is at least one selected from silver, gold, copper, lead, tin, nickel, cobalt, cadmium, iron, chromium and zinc.

In one embodiment of the invention, the metal comprises silver.

In one embodiment of the present invention, the concentration of the metal in the aqueous solution of hydrofluoric acid is 0.01M to 0.05M.

In one embodiment of the present invention, step (b) is carried out by supporting a silicon nanowire in a nitric acid etching solution.

Is In one embodiment, (c) the strong acid in step hydrofluoric acid (HF), hydrochloric acid (HCl), sulfuric acid (H ₂ SO ₄₎ or nitric acid (HNO _3).

Another embodiment of the present invention provides a silicon nanowire for a lithium secondary battery manufactured by the above method, wherein metal particles are uniformly distributed on the surface of the silicon nanowire.

Another embodiment of the present invention provides an anode active material comprising the silicon nanowire.

Another embodiment of the present invention provides a lithium secondary battery using the negative electrode active material.

The present invention provides a lithium secondary battery improved in capacity characteristics and cycle characteristics by a method of coating metal particles on the surface of a silicon nanowire and a negative electrode active material obtained therefrom. Further, by using the lithium secondary battery according to the present invention, it becomes possible to realize an electric vehicle and a large energy storage device.

1 is a schematic view of a process of forming a silicon nanowire with metal particles coated thereon.
2 shows SEM images of silicon nanowires coated with metal particles and silicon nanowires not attached, respectively. (a) and (c): silicon nanowires coated with metal particles of the examples, and (b) and (d): metallic silicon nanowires not coated with metal particles of the comparative example.
FIG. 3 shows the XRD spectrum of silicon nanowires coated with metal particles and silicon nanowires not adhered thereto.
FIG. 4 shows a TEM image and EDX mapping image of a silicon nanowire coated with metal particles (left) and a silicon nanowire coated with EDX image (right) metal particles. FIG.
FIG. 5 shows impedance measurement results of a coin cell fabricated using the silicon nanowires manufactured in Examples and Comparative Examples, respectively.

One embodiment of the present invention provides a method of manufacturing a silicon nanowire for a lithium secondary battery having a surface coated with a metal and a silicon nanowire produced therefrom.

 In one embodiment of the present invention, the method includes: (a) forming a silicon nanowire by metal catalyst etching; (b) removing a metal electrodeposited on the surface of the etched silicon nanowire; And (c) supporting the silicon nanowires in a diluted solution of strong acid to precipitate the metal particles on the surface of the silicon nanowires.

In another embodiment of the present invention, the silicon nanowires obtained by the above-described method are separated from a substrate, mixed with a conductive material and a binder to prepare a slurry, and then coated on a metal current collector to produce an anode material Thereby providing a method for finally manufacturing a lithium secondary battery.

Another embodiment of the present invention provides a lithium secondary battery produced by the above method.

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

(a)

First, in step (a), the silicon nanowires are etched using a metal catalyst etching method. In one embodiment, the silicon substrate is supported on an etchant containing an aqueous solution of hydrofluoric acid (HF) and a molten metal to form silicon nanowires as shown in FIG. 1A. Wherein the etchant comprises a hydrofluoric acid (HF) solution in the range of 4 to 5 M, preferably in the range of 4.6 to 5 M.

The metal functions as a catalyst for oxidizing the silicon substrate to form silicon oxide, and the silicon nanowire is formed by etching the silicon oxide in the hydrofluoric acid aqueous solution. At this time, the metal may be at least one selected from silver, gold, copper, lead, tin, nickel, cobalt, cadmium, iron, chromium and zinc. The metal particles and the particles must be controlled to be spaced apart from each other, and preferably the size of the metal particles may be in the range of tens to hundreds of nanometers. When this condition is satisfied, a uniform coating can be formed on the surface of the silicon nanowire formed through step (c). The concentration of the metal dissolved in the aqueous solution of hydrofluoric acid may be in the range of 0.01M to 0.05M, preferably 0.03M to 0.04M. Typically, when silver (Ag) particles are used, the redox reaction that occurs during the etching reaction of silicon is as follows.

4Ag ⁺ + 4e ^- = > 4Ag (s) (1) (reduction reaction)

Si + 6HF = > SiF ₆ ^{2 -} + 6H ⁺ + 4e ^- (2) (Oxidation reaction)

^{Si (s) + 4Ag + +} 6HF => 4 Ag (s) + SiF 6 2 - + 6H + (3) ( oxidation-reduction reaction)

As shown in the oxidation-reduction reaction (3), during the etching reaction, silver (Ag) is reduced and silver is randomly deposited between the top, bottom, surface and / or nanowire of the silicon nanowire. Therefore, the silver particles are non-uniformly present on the silicon nanowire, and the following step (b) is performed to remove the silver.

(b)

In step (b), randomly electrodeposited metal is removed between the top, bottom, and / or nanowires of the etched silicon nanowires.

In one embodiment, the silicon nanowires are carried on an etchant to remove electrodeposited metal. In this case, as shown in FIG. 1B, the metal existing between the top, bottom, surface and / or the nanowire of the silicon nanowire is removed. Typically, when the metal is silver, the oxidation-reduction reaction that takes place in step (b) is as follows.

3Ag (s) + 4HNO ₃ => 3 AgNO ₃ + NO + 2H ₂ O (4)

At this time, nitric acid is used as an etchant, and silicon nitride is carried on nitric acid to remove electrodeposited metal. Thus, in step (c), metal such as silver is uniformly deposited on the surface of the nanowire.

(c)

In step (c), the silicon nanowires are carried in a dilute solution of strong acid to precipitate metal particles on the surface of the silicon nanowires. The silicon nanowire having the surface of the precipitated metal particles coated thereon can provide a lithium secondary battery in which the solid electrolyte interface (SEI) is controlled and the electrical conductivity is improved. In addition, in the present invention, since the etching solution such as hydrofluoric acid used in step (a) can be diluted with distilled water without preparing a separate solution, it is also excellent in terms of cost reduction. As the strong acid, hydrochloric acid (HCl), sulfuric acid (H ₂ SO ₄ ), or nitric acid (HNO ₃ ) may be used in addition to hydrofluoric acid.

The concentration of the diluted solution of the strong acid may be 0.01M to 1M, preferably 0.4M to 0.5M. On the other hand, the silver (Ag) precipitated in the step (c) is uniformly distributed not only in the size of the grain size but also on the surface of the silicon nanowire. Therefore, when used as a negative electrode active material, The effect is very excellent, and thus it is possible to provide a lithium secondary battery capable of realizing a high capacity and high charge / discharge rate.

Another embodiment of the present invention provides a negative active material comprising the silicon nanowire and a lithium secondary battery using the negative active material. Such a lithium secondary battery has excellent capacity characteristics, cycle characteristics and stability. The method of manufacturing the lithium secondary battery is generally the same as the known method, and a detailed description thereof will be omitted.

Example

Step 1: Metal catalytic etching  Used silicon Nanowire  formation

0.68 g of AgNO ₃ and 16.8 mL of HF (48 to 52%) were added to 200 mL of distilled water, and the mixture was stirred for about 10 minutes to prepare an aqueous solution of hydrofluoric acid. At this time, the concentration of the aqueous solution of hydrofluoric acid was 4.6 M and the concentration of dissolved silver was 0.04 M. After 200 mL of the aqueous solution of hydrofluoric acid was added to the reactor, the silicon substrate was carried thereon. Silicon substrates were etched to produce silicon nanowires.

Step 2: Silicone On the nanowire Electrodeposited  silver( Ag Removal of Particles

In order to improve the electrical conductivity of the negative electrode active material by coating metal particles on the surface of the silicon nanowire, the silicon substrate was supported on nitric acid. Thus, silver (Ag) particles generated in step 1 randomly formed between the top, bottom, surface and nanowires of the silicon nanowires were removed.

Step 3: Silicone Nanowire  Surface coating

A diluted hydrofluoric acid aqueous solution of 0.45 M was prepared, 500 mL of the diluted hydrofluoric acid aqueous solution was added to the reactor, and the silicon substrate after step 2 was carried thereon. As a result, a silicon nanowire having silver particles precipitated on its surface was obtained.

Comparative Example :

Silicon nanowires were obtained in the same manner as in the above example except that the above step 3 was not performed.

Test Example  1: Silicon Nanowire SEM  Measure

SEM photographs of the silicon nanowires prepared in Examples and Comparative Examples were measured and shown in Fig. 2 (a) and 2 (c) show SEM images of the silver-coated silicon nanowires of the embodiment, and FIGS. 2 (b) and 2 .

Test Example  2. Silicon Nanowire XRD  Measure

The XRD of the silicon nanowires prepared in Examples and Comparative Examples was measured and shown in FIG. Fig. 3 shows that the silicon nanowires of the embodiment were precipitated by silver (Ag).

Test Example  3: Silicon Nanowire TEM  Measure

TEM photographs of the silicon nanowires prepared in Examples and Comparative Examples were measured and shown in FIG. FIG. 4 shows a TEM image and EDX mapping image of a silicon nanowire coated with metal particles of the embodiment (left) and an EDX image (right) coated with metal particles, and a silicon nanowire having a metal particle of the comparative example precipitated on its surface.

Test Example  4: Silicon Nanowire  Impedance measurement

The silicon nanowires prepared in Examples and Comparative Examples were separated from the silicon substrate using an ultrasonic grinder and mixed with a carbon conductive material and a binder to prepare slurries and then coated on a metal current collector to form a negative electrode Prepared as ashes. The negative electrode material was fabricated from a lithium secondary cell in the form of a coin cell, and the impedance was measured. The results are shown in FIG.

Specifically, the lithium secondary battery using the silicon nanowires of the examples and comparative examples was charged at a charging rate of 0.5 C-rate until the voltage reached 1 V (vs. Li), and then the voltage was changed to 0.01 V (vs. Li). ≪ / RTI > Subsequently, charging and discharging were repeated 30 times in the same current and voltage section, and impedance analysis was performed in a voltage range of 10 mV in the frequency range of 1 to 1000 Hz.

As shown in FIG. 5, it was confirmed that the silicon nanowires of the example in which the metal particles were coated had lower coin cell resistance than the silicon nanowires of the comparative example. As a result, the electrical conductivity is improved when the metal particles are coated on the surface of the silicon nanowire.

Claims (12)

(A) forming a silicon nanowire by a metal catalyst etching method;
(B) removing randomly electrodeposited metal on the etched silicon nanowire surface; And
(C) step of depositing metal particles on the surface of the silicon nanowire by supporting the silicon nanowires in a dilution liquid of strong acid
Wherein the silicon nanowire is a silicon nanowire. The method according to claim 1,
(a) comprises supporting a silicon substrate on an etchant,
Characterized in that the etchant comprises an aqueous solution of hydrofluoric acid (HF) and a molten metal. 3. The method of claim 2,
Characterized in that the concentration of the hydrofluoric acid aqueous solution is from 4 M to 5 M. The method according to claim 1,
wherein the diluted solution of strong acid in step (c) has a concentration of 0.01M to 1M. 3. The method of claim 2,
Wherein the metal is at least one selected from silver, gold, copper, lead, tin, nickel, cobalt, cadmium, iron, chromium and zinc. 6. The method of claim 5,
Wherein the metal comprises silver. 3. The method of claim 2,
Wherein the concentration of the metal in the aqueous solution of hydrofluoric acid is 0.01M to 0.05M. The method according to claim 1,
(b) is carried out by supporting the silicon nanowires in a nitric acid etching solution. Method according to claim 1, wherein the strong acid, characterized in that hydrofluoric acid (HF), hydrochloric acid (HCl), sulfuric acid (H ₂ SO ₄₎ or nitric acid (HNO _3),. 10. A silicon nanowire for a lithium secondary battery, wherein metal nanoparticles are uniformly distributed on a surface of the silicon nanowire produced by the manufacturing method according to any one of claims 1 to 9. An anode active material comprising the silicon nanowire for a lithium secondary battery according to claim 10. A lithium secondary battery using the negative electrode active material according to claim 11.

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