KR101371555B1 - Method for manufacturing silicon-carbon nano composite for anode active material of lithium secondary batteries - Google Patents

Abstract

Disclosed is a production method of a silicon-carbon nanocomposite powder for a negative electrode active material of a lithium secondary battery. The production method of the silicon-carbon nanocomposite powder, according to an embodiment of the present invention, comprises the following steps: a step for forming an inert atmosphere by supplying inert gas into a reaction chamber; a step for generating a RF plasma inside the reaction chamber; a step for inserting a silicon powder inside the reaction chamber with the RF plasma; a step for evaporating the silicon powder using the plasma; a step for pyrolyzing by flowing hydrocarbon gas into the chamber; and a step for condensing the carbon pyrolyzed from the hydrocarbon and the evaporated silicon. [Reference numerals] (S10) Step for forming inert atmosphere; (S20) Step for generating plasma; (S30) Step for inserting silicon powder; (S40) Step for evaporating the silicon powder; (S50) Step for pyrolyzing hydrocarbon; (S60) Step for condensing silicon-carbon nanocomposite powder

Description

Method for manufacturing silicon-carbon composite nano powder for lithium secondary battery negative active material {Method for manufacturing silicon-carbon nano composite for anode active material of lithium secondary batteries}

The present invention relates to a method for preparing a silicon-carbon composite nanopowder for a lithium secondary battery negative electrode active material, and more particularly, to produce a silicon nanopowder by RF plasma pyrolysis and grow a carbon secondary on a surface thereof. A method for producing a silicon-carbon composite nanopowder for a negative electrode active material.

As the functions of portable electronic devices such as mobile phones and laptops are diversified and highly functional, Li-ion secondary batteries, which are widely used as portable energy sources, are required for high capacity and high output by expanding the secondary battery market in the field of energy storage and electric vehicles. Is rising.

Since the graphite lithium ion secondary battery developed by Sony in the early 1990s appeared on the market, the energy density of the battery has developed dramatically, more than three times than the initial development. However, there is still a demand for high capacity batteries, and there is a need for developing a negative electrode material having excellent high efficiency charge and discharge characteristics.

Since the capacity of the battery is controlled by the charge and discharge characteristics of the positive electrode material and the negative electrode material, the improvement of the negative electrode active material is of great interest to battery developers. Recently, carbon graphite, which is a negative electrode material of a secondary battery, has been studied through surface modification of various negative electrode active materials such as inorganic coating, crystalline carbon coating, pyro carbonaceous coating, carbon nanofibers or carbon nanotubes and surface coating on negative electrode materials. Research is ongoing to improve the electrochemical properties of. The method described above is known to play a role of preventing the crystal structure from being destroyed while lithium is inserted / released in the secondary battery. In addition, a product having improved charge / discharge characteristics by coating a surface of a natural graphite active material, which is a negative electrode of a lithium secondary battery, with crystalline carbon has been developed.

Meanwhile, in the study of carbon anode material modification using metal, Tsutomu Takamura et al. Coated metal thin films such as Ag, Au, Bi, I, Zn on the surface of graphite-based anode active material by using metal heating evaporation method to improve charge and discharge characteristics. Reported. Journal of Power Source 81-82 pp 368-372 (1999). US Patent No. 6,797,434 discloses a method of coating a graphite-based active material with tin oxide, which is an amorphous metal. Korean Unexamined Patent Publication No. 2004-100058 discloses a method of manufacturing a carbon / metal composite using a carbon material and a metal precursor in a negative electrode active material for a lithium secondary battery and a method for manufacturing the same. Republic of Korea Patent No. 536,247 'Negative active material for lithium secondary battery and lithium secondary battery comprising the same' method for forming an inorganic oxide film or hydroxide film such as Al, Ag, B, Zn, Zr on the surface of the graphite carbon material through a heat treatment process Is starting.

In the study of the high capacity negative electrode active material, it is known that metal silicon exhibits an energy density of 10 or more higher than that of the graphite-based negative electrode active material. In lithium secondary batteries, lithium ions are repeatedly inserted / released, and the crystal structure of the negative electrode active material expands and contracts and crystals are destroyed, resulting in degradation of cycle characteristics of the battery. It can no longer be utilized as a negative electrode active material.

That is, volume expansion due to alloying of lithium and silicon, such as charge and discharge when Li _{1 .71 ~ 4.4} Si is increased more than four times that of the silicon itself, and eventually the discharge capacity of silicon electrode structure kkaejimyeonseo while charging and discharging the duration of the initial capacity It is rapidly lowered to 20% or less and loses the function as an electrode active material.

Many research and developments have been conducted to improve the stability of the silicon electrode structure, such as nano-sizing of silicon particles, alloying with transition metals such as nickel and copper, carbon / silicon composites, changing oxygen content of silicon, and improving electrode binders. Although this attempt was made, the result is that the capacity of 1000mAh / g or more of the silicon active material does not make use of the capacity reduction problem due to the progress of the cycle is still not overcome.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and an object of the present invention is to precisely control the complexation of silicon metal nanopowder and carbon in order to suppress the volume expansion of the negative electrode active material and maintain long-term high rate charge / discharge cycle characteristics. The present invention provides a method for producing a silicon-carbon composite nanopowder for a lithium secondary battery negative electrode active material, which resists volume expansion of a negative electrode active material crystal structure generated while ions are repeatedly inserted and released.

Method of manufacturing a silicon-carbon composite nanopowder for a lithium secondary battery negative electrode active material according to an embodiment of the present invention is to supply an inert gas into the reaction chamber to form an inert atmosphere, to generate an RF plasma inside the reaction chamber A step of charging silicon powder into the reaction chamber, vaporizing the silicon powder into the plasma, pyrolyzing the hydrocarbon compound by flowing the hydrocarbon compound into the chamber, and pyrolyzing the vaporized silicon and the hydrocarbon compound Condensing carbon.

The RF plasma may be due to the plasma generator output with a capacity of 15 ~ 200kW.

The silicon-carbon nanocomposite powder condensation step may be performed by cooling with a quenching gas supplied.

The inert gas may be argon (Ar) or nitrogen (N ₂ ).

The? Ching gas may be argon (Ar) or nitrogen (N ₂ ).

The hydrocarbon compound may be flowed into the sheath gas inlet of the plasma torch unit in the pyrolysis step by flowing the hydrocarbon gas into the chamber.

The hydrocarbon compound may flow into the powder input unit of the plasma torch unit in the pyrolysis step by flowing hydrocarbon gas into the chamber.

The hydrocarbon compound may be flowed into the quenching gas part of the reaction chamber in the pyrolysis step by flowing the hydrocarbon gas into the chamber.

Hydrocarbon gas may be flowed into the chamber to pyrolyze the hydrocarbon compound from the bottom of the reaction chamber to the top of the torch.

The hydrocarbon compound may be at least one selected from hydrocarbon compounds composed of carbon and hydrogen, and the hydrocarbon compound composed of carbon and hydrogen may be any one or more selected from ethylene, acetylene, methane, propane, propylene, ethane and butylene. have.

The hydrocarbon compound may be any one or more selected from volatile alcohol or ketone, and the volatile alcohol or ketone may be any one or more selected from methanol, ethanol, propanol, butanol, acetone and methylethyl ketone.

According to an embodiment of the present invention has the following effects.

First, a silicon-carbon composite nanopowder, which is advantageous for high output and high capacity, may be prepared as compared with a complexation process by mechanical mixing of silicon powder and carbon powder.

Second, the RF plasma can be used to simplify the manufacturing process of several stages than before, and the productivity can be improved to reduce the manufacturing cost.

1 is a process flowchart of a method of manufacturing a silicon-carbon composite nanopowder for a lithium secondary battery negative electrode active material according to an embodiment of the present invention.
Figure 2 is a schematic view showing a device for manufacturing a silicon-carbon composite nanopowder for a lithium secondary battery negative electrode active material according to an embodiment of the present invention.
3 is an X-ray diffraction graph of a silicon-carbon composite nanopowder for a lithium secondary battery negative electrode active material prepared according to an embodiment of the present invention.
4 is an electron scanning microscope (SEM) photograph of a silicon-carbon composite nanopowder for a lithium secondary battery negative electrode active material prepared according to an embodiment of the present invention.

Advantages and features of the present invention and methods for achieving them will be apparent with reference to the embodiments described below in detail with the accompanying drawings. However, it is to be understood that the present invention is not limited to the disclosed embodiments, but may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. It is intended that the disclosure of the present invention be limited only by the terms of the appended claims. Like reference numerals refer to like elements throughout the specification.

Hereinafter, a method of manufacturing a silicon-carbon composite nanopowder for a lithium secondary battery negative electrode active material according to a preferred embodiment of the present invention will be described.

1 is a process flowchart of a method of manufacturing a silicon-carbon composite nanopowder for a lithium secondary battery negative electrode active material according to an embodiment of the present invention.

Figure 2 is a schematic view showing a device for manufacturing a silicon-carbon composite nanopowder for a lithium secondary battery negative electrode active material according to an embodiment of the present invention.

Referring to Figure 1, an embodiment of the present invention is to supply an inert gas into the reaction chamber to form an inert atmosphere (S10), generating an RF plasma in the reaction chamber (S20), the reaction chamber Charging silicon powder therein (S30), vaporizing the silicon powder into the plasma (S40), flowing a hydrocarbon gas into the chamber to pyrolyze (S50) and from the vaporized silicon and the hydrocarbon Condensing the pyrolyzed carbon (S60).

In addition, in an embodiment of the present invention, the method may further include filtering the condensed silicon-carbon composite nanopowder and collecting it.

In addition, referring to FIG. 2, the metal nano powder manufacturing apparatus 100 using the RF plasma includes a powder supplier 120, a plasma generator 130, a reaction chamber 110, a cyclone 140, and a vacuum pump 145. , A filter 151, and a nano powder collector 150.

According to an embodiment of the present invention, silicon (Si) is heated and evaporated in the reaction chamber 110 using an RF plasma to produce vapor phase silicon, and a carbon source is provided through pyrolysis of hydrocarbon gas to condense on the surface of the silicon nanopowder. To prepare a silicon-carbon composite nanopowder.

First, the inert atmosphere composition step (S10) forms a vacuum in the reaction chamber 110 in a state where the silicon powder is put into the powder injector, and supplies the inert gas to form the reaction chamber 110 in an inert atmosphere. This process may be repeated two or more times.

Next, the plasma generation step (S20) is made in the reaction chamber 110. The plasma generator 130 may be mounted on the reaction chamber 110 to communicate with the inside of the reaction chamber 110, and the plasma generator 130 may generate an RF plasma using argon (Ar) gas. . At this time, the power used in the plasma generation unit 130 may be 15 ~ 200kW.

Silicon powder is charged into the reaction chamber 110 to vaporize the silicon. (S30) Here, the silicon powder is applied to the RF plasma generator by applying a transfer force of a predetermined size at the same time as the vibration is in the powder feeder 120. It may be introduced into the reaction chamber 110 through the 130. The frequency of the vibration may be 90 ~ 120Hz, the feed force can be adjusted to 0 ~ 100% of the device capacity to adjust the input amount. At this time, the silicon powder introduced into the reaction chamber 110 by the powder feeder 120 may be transferred by the transfer gas, the transfer gas may be an inert gas such as argon (Ar) and the flow rate is 5 ~ 40slpm Can be controlled.

The charged silicon powder is vaporized through the RF plasma generated by the plasma generator 130 (S40). The RF plasma used to vaporize the silicon powder is formed from the plasma generator 130, and the final temperature is about It can be 5,000 ~ 10,000K. The final temperature corresponds to a temperature above the break point of the silicon.

After the silicon powder is vaporized, hydrocarbon gas is included in the gas introduced into the reaction chamber 110 and flowed to the hydrocarbon gas by the high-temperature RF plasma generated by the plasma generator 130. ₂ ) Pyrolyzed to gas (S50) As the carbon source used here, one or more selected from ethylene, acetylene, methane, propane, propylene, ethane, butylene, etc. may be used, and methanol, ethanol, propanol, butanol Volatile alcohols such as acetone, methylethyl ketone, ketones and the like can also be used. In this case, the hydrocarbon gas may be injected from the gas or the quenching gas, the powder injection gas, the reaction chamber lower portion, or the like, injected into the plasma torch unit.

Finally, the silicon-carbon nanocomposite powder condensation step (S60) may condense and quench the vaporized silicon and carbon to obtain a silicon-carbon composite nanopowder surrounded by the carbon nanopowder around the silicon nanopowder. Here, the condensation or quenching of the silicon-carbon powder may be performed by injecting a quenching gas into the reaction chamber 110, and the quenching gas used may be an inert gas such as argon (Ar). At this time, the flow rate may be 10 ~ 600slpm.

The silicon-carbon composite nanopowders prepared by condensation and quenching can be collected by filtration. Here, the silicon-carbon composite nanopowder, argon (Ar) gas, and hydrogen (H ₂ ) gas are transported together by the vacuum pump 145 and passed through the cyclone 140 to collect the nanopowder 150 with the temperature lowered. Flows into). The nano-powder collecting unit 150 is provided with a filter 151 to adsorb the silicon-carbon composite nano-powder introduced into the outer wall and the gas can be discharged through a separate pipe.

When a predetermined amount of the silicon-carbon composite nanopowder is adsorbed on the outer wall of the filter 151, the back-flushing is performed inside the filter 151 to desorb the adsorbed silicon-carbon composite nanopowder, and the desorbed silicon-carbon The composite nanopowder can be recovered. Since the recovered silicon-carbon composite nanopowder has a large specific surface area in contact with the reactive gas, attention must be paid to recovery and treatment.

Table 1 below shows the process conditions of the method for producing a silicon-carbon composite nanopowder for a lithium secondary battery negative electrode active material according to an embodiment of the present invention.

division Condition Plasma output 15 ~ 200kW gas Sheath gas Ar: 100 ~ 120slpm
CH4: 5 ~ 10slpm Central gas Ar: 5 ~ 40slpm Quenching gas Ar: 10 ~ 600slpm Carrier gas Ar: 5 ~ 40slpm

In order to prepare a silicon powder into a silicon-carbon composite nanopowder using an RF plasma, a silicon powder having a size of 10 to 100 μm was used as a precursor.

First, the process of forming the inside of the reaction chamber 110 in a vacuum state and supplying argon (Ar) gas to form an argon (Ar) gas atmosphere inside the reaction chamber 110 was repeated twice. In addition, argon (Ar) and hydrogen (H ₂ ) gas were supplied as the plasma composition gas, and the output of the plasma generator was adjusted to 20 to 60 kW to generate an RF plasma.

The silicon powder was placed in the powder feeder 120 and the silicon powder was supplied to the reaction chamber 110 by applying a feeding force of a predetermined size at the same time as the vibration of 90 Hz. At this time, methane gas was supplied and used as a carbon source. Thereafter, argon gas was injected into the reaction chamber 110 to condense the vaporized silicon-carbon composite nanopowder and then collected.

X-ray diffraction analysis was performed to analyze the components of the collected powder. 3 is an X-ray diffraction graph of a silicon-carbon composite nanopowder prepared according to an embodiment of the present invention.

Referring to FIG. 3, it can be seen that the X-ray diffraction pattern of the prepared silicon-carbon composite nanopowder is consistent with the X-ray diffraction pattern of silicon, carbon and silicon carbide based on JCPDS. As the carbon grew on the main surface of the silicon nanopowder, silicon carbide was formed at the interface, and it was confirmed that the composite nanopowder was well surrounded by the carbon around the silicon nanoparticle.

4 is an electron scanning microscope (SEM) photograph of a silicon-carbon composite nanopowder prepared according to an embodiment of the present invention.

As shown in FIG. 4, the average particle size of the prepared silicon-carbon composite nanopowder was about 10 nm, and carbon was surrounded by a spherical silicon nanopowder.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the exemplary embodiments or constructions. It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. will be.

It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. The scope of the present invention is defined by the appended claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be interpreted as being included in the scope of the present invention .

100: nano-powder manufacturing apparatus 110: reaction chamber
120: powder feeder 130: RF plasma generator
140: cyclone 145: vacuum pump
150: nano powder collection unit 151: filter

Claims (12)

Supplying an inert gas into the reaction chamber to create an inert atmosphere;
Generating an RF plasma inside the reaction chamber;
Charging silicon powder into the reaction chamber;
Vaporizing the silicon powder with the plasma;
Flowing a hydrocarbon compound into the chamber to pyrolyze it; And
Condensing pyrolyzed carbon from the vaporized silicon and the hydrocarbon compound;
Method for producing a silicon-carbon composite nanopowder for a lithium secondary battery negative electrode active material comprising a. In claim 1,
The RF plasma is a manufacturing method of the negative electrode active material silicon-carbon composite nanopowder for lithium secondary dust, characterized in that by the plasma generator output with a capacity of 15 ~ 200kW. In claim 1,
The silicon-carbon nano composite powder condensation step is a method of manufacturing a negative active material silicon-carbon composite nano powder for a lithium secondary electrode, characterized in that the cooling by the supplied quenching gas. 4. The method of claim 3,
The? Ching gas is a method for producing a silicon-carbon composite nanopowder for a lithium secondary battery negative electrode active material, characterized in that argon (Ar) or nitrogen (N ₂ ). The method of claim 1,
The method of manufacturing a silicon-carbon composite nanopowder for a lithium secondary battery negative electrode active material, characterized in that the hydrocarbon compound flows into the sheath gas inlet of the plasma torch in a step of flowing pyrolyzed hydrocarbon gas into the chamber. The method of claim 1,
The method of manufacturing a silicon-carbon composite nanopowder for a lithium secondary battery negative electrode active material, characterized in that the hydrocarbon compound flows into the powder injection unit of the plasma torch in the step of flowing pyrolyzed hydrocarbon gas into the chamber. The method of claim 1,
The method of manufacturing a silicon-carbon composite nanopowder for a lithium secondary battery negative electrode active material, characterized in that the hydrocarbon compound flows into the? Ching gas portion of the reaction chamber in the step of pyrolysis by flowing a hydrocarbon gas into the chamber. The method of claim 1,
The method of manufacturing a silicon-carbon composite nanopowder for a lithium secondary battery negative electrode active material, characterized in that the hydrocarbon compound flows from the lower part of the reaction chamber to the upper part of the torch in the step of pyrolysis by flowing a hydrocarbon gas into the chamber. In claim 1,
The hydrocarbon compound is a method for producing a silicon-carbon composite nanopowder for a lithium secondary battery negative electrode active material, characterized in that at least one selected from a hydrocarbon compound consisting of carbon and hydrogen. The method of claim 9,
The hydrocarbon compound composed of carbon and hydrogen is any one or more selected from ethylene, acetylene, methane, propane, propylene, ethane and butylene. In claim 1,
The hydrocarbon compound is a volatile alcohol or ketone, a method for producing a silicon-carbon composite nanopowder for a lithium secondary battery negative electrode active material. 12. The method of claim 11,
The volatile alcohol or ketone is any one or more selected from among methanol, ethanol, propanol, butanol, acetone and methyl ethyl ketone.

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