Patent Application
20160016143
This application claims the benefit of Korean Patent Applications No. 10-2014-0090084 and No. 10-2014-0090085, filed on Jul. 16, 2014 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Technical Field
The present disclosure relates to an apparatus for manufacturing Si-based nanoparticles such as Si—C composite and SiOx using plasma.
2. Description of the Related Art
Silicon nano-powders are known as materials widely applicable to various advanced electronic or optical fields. For example, in printable electronics, a nano-ink composition comprising silicon nano-powders is used in environmentally friendly process for forming a semiconductor layer for electrical or optical function. Recently, many studies have been made on silicon having a high theoretical capacity as a negative electrode active material for a high capacity lithium-ion battery (4200 mAh/g) for replacing carbon. In particular, nano-sized silicon is one of the solutions to mitigate a large volume expansion (300 to 400%) of a silicon-based negative electrode occurring during charging and discharging of the battery, which causes a reduced service life. This is because nanoparticles are able to more efficiently withstand stresses and strains than microparticles.
However, sufficient buffering effect on the volume changes that occur during charging and discharging of the battery with nano-sized silicon alone cannot be obtained. Therefore, an appropriate mixing ratio and a uniform structural arrangement with carbon which is electrically conductive and has a structural buffering effect are required for the silicon nano-powders. When the silicon nano-powders are coated with a porous/amorphous carbon in a continuous process, an oxidation of a surface of the silicon can be prevented, whereby the initial irreversible capacity can be minimized while at the same time due to the buffering effect on the volume expansion of the silicon occurring during charging and discharging of the battery, the cycle life characteristics of the battery can be improved. For this particular purpose, there remains the need to prepare Si—C nanoparticles, SiOx nanoparticles, and the like.
In general, a method of producing silicon nano-powders includes solid phase synthesis, liquid phase synthesis, and a vapor phase synthesis. However, among these methods, the vapor phase synthesis, since therefrom a high reaction rate and a high purity of particles can be obtained, is preferred. More specifically, most preferred is such vapor phase synthesis using plasmas that can obtain nano-powders regardless of the phase of starting materials.
A further relevant reference to the present disclosure is made to a plasma nano-powder synthesis and a coating device and a method thereof disclosed in the Korean Laid-open Patent Publication No. 2012-0130039 (publication date: Nov. 28, 2012).
One object of the present disclosure is to provide a manufacturing apparatus capable of uniformly producing silicon-based nanoparticles, more specifically Si—C composite nanoparticles, in a continuous process using a plasma torch.
Another object of the present disclosure is to provide a manufacturing apparatus capable of producing silicon-based nanoparticles, more specifically SiOx nanoparticles, using a plasma torch.
An apparatus for manufacturing silicon-based nanoparticles in accordance with one aspect of the present disclosure comprises a reaction chamber for providing a reaction space; a plasma torch for generating plasma to decompose silicon precursors and produce Si particles, provided on an upper portion of the reaction chamber; a cooling part for cooling Si particles supplied into the reaction chamber, provided within the reaction chamber; and a carbon material supplying part for supplying carbonaceous materials into the reaction chamber, wherein in the plasma torch, the Si precursors injected with plasma are dissociated and bonded to form Si particles through particle nucleation and nuclear growth, and wherein in the reaction chamber, the Si particles and the carbonaceous materials are complexed.
According to some embodiments, the carbon material supplying part is connected to the cooling part, such that the carbonaceous materials can be supplied through the cooling part.
According to some embodiments, this apparatus further comprises a particle trap for trapping silicon-based nanoparticles, provided at a lower portion of the reaction chamber. According to some embodiments, this apparatus further comprises a scrubber for treating an acid exhaust gas, provided at a lower portion of the particle trap.
Further, an apparatus for manufacturing silicon-based nanoparticles in accordance with another aspect of the present disclosure comprises a reaction chamber for providing a reaction space; and a plasma torch using a microwave as a plasma source, comprising a precursor gas inlet for injecting a silicon precursor gas, provided on an upper portion of the reaction chamber, and a swirl gas inlet for injecting a plasma gas in the form of swirl, wherein the plasma gas and an oxidizing gas are supplied into the swirl gas inlet to allow a source gas and the oxidizing gas to react along a vortex flow.
According to some embodiments, this apparatus further comprises an oxidizing gas supplying part for supplying the oxidizing gas into the swirl gas inlet.
According to some embodiments, this apparatus further comprises a cooling part for cooling particles produced in the reaction chamber, provided within the reaction chamber.
According to some embodiments, it is preferred that the swirl gas inlet is radially disposed around the precursor gas inlet, and is configured in such a way that the swirl gas can be injected toward the center of the plasma zone in a direction inclined inside at an angle of 25 to 45 degrees with respect to a vertical direction.
According to some embodiments, it is more preferred that the swirl gas inlet is allowed for the swirl gas to be injected at an angle of 5 to 15 degrees inside toward the center of a circle with respect to a planar tangential direction.
According to some embodiments, this apparatus further comprises a particle trap for trapping silicon-based nanoparticles, provided at a lower portion of the reaction chamber, and a scrubber for treating an acid exhaust gas, provided at a lower portion of the particle trap.
According to some embodiments, a Si nanoparticle forming process and a Si—C complexing process are performed in an integral reaction chamber, and the characteristics of Si nanoparticles and Si—C composite can be controlled based on a source input method and process conditions, such as a plasma power, a gas type, a flow rate, and a cooling gas. In this embodiment, advantageous is that a vacuum unit is not required, and thus the cost of the equipment can be reduced.
According to some embodiments, a larger volume of a high density plasma zone can be obtained and a residence time of reactive gas remaining in the plasma can be increased by concentrating the plasma on the reactor center by swirling the gas. By concentrating the plasma as such, an outer wall of the reactor can be protected from overheating, and the contamination of reagents caused by this outer wall can be prevented.
According to some embodiments, in the process of manufacturing SiOx nanoparticles, the x value may be varied in a range of 0.4 to 2.0 by controlling the flow rate of the oxidizing gas, where the x value indicates oxygen content.
Still another aspect of the present disclosure is to the use of the SiOx nanoparticles produced by the process according to the present disclosure in a negative electrode active material for a lithium secondary battery. In this embodiment, advantage of an excellent capacity retention rate can be provided.
The above and other objects or aspects, features and advantages of the present disclosure will become apparent from the following descriptions of the exemplary embodiments with reference to the accompanying drawings, in which:
Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Prior to the description, it should be understood that the terms used in the specification and the appended claims should not be construed as limited to general and dictionary meanings, but interpreted based on the meanings and concepts corresponding to technical aspects of the present disclosure based on the principle that the inventor is allowed to define terms. Therefore, the description proposed herein is just a preferable example for the purpose of illustration only, and is not intended to limit the scope of the disclosure, so it should be understood that other equivalents and modifications could be made thereto without departing from the spirit and scope of this disclosure.
As depicted, an apparatus for manufacturing Si—C composite according to the present disclosure includes a reaction chamber 110 for providing a reaction space, a plasma torch 120 for generating plasma to decompose silicon precursors and produce Si particles, a cooling part 130 for cooling the Si particles supplied thereto, provided within the reaction chamber 110, and a carbon material supplying part 140 for supplying carbonaceous materials into the reaction chamber 110.
The plasma torch 120 is provided on an upper portion of the reaction chamber 110, and the cooling part 130 is provided on a lower portion of the plasma torch 120.
Carbon material supplying part 140 is connected to the cooling part 130, and therefore carbonaceous materials can be supplied together with a cold gas.
In addition, at a lower portion of the reaction chamber 110, further provided are a particle trap 150 for trapping the Si—C particles, and a scrubber 160 for treating to neutralize an acid exhaust gas, connected to a lower portion of the particle trap 150.
The present disclosure is characterized in that the reaction chamber 110 is configured integrally with the plasma torch 120, such that Si—C composites can be produced uniformly in a continuous manner.
The silicon precursor supplied into the plasma torch 120 includes a solid-phase micro-Si particle, a liquid-phase SiCl4, a gas-phase SiH4, and the like.
The precursors are sufficiently and uniformly fined or gasified and then injected into the plasma torch with a plasma forming gas, such as argon or nitrogen. In addition, H2 gas may be introduced together with the Si precursors as a carrier gas or reactive gas.
The plasma torch 120 can use a variety of plasma source. For example, the plasma source that can be used includes, but not limited to, an electron cyclotron resonance (ECR) plasma source, a reactive ion etching (RIE) source, a capacitively coupled plasma (CCP) source, and an inductively coupled plasma (ICP) source.
The ECR source is also known as microwave plasma, since in general the microwave is an energy source for plasma generation. ICP source can be operated in an electrodeless discharge mode that induces an electric field in the chamber by supplying a RF power to an induction coil, to thereby generate plasma. On the other hand, CCP source generates plasma in the chamber by an electric field generated by supplying a RF power to electrode plates.
The cooling part 130 is provided in the interior of the reaction chamber 110 for controlling, for example, the Si nanoparticles reaction and formation.
In the plasma torch 120, plasma is formed by a plasma source and a plasma forming gas (e.g., Ar and N2), and silicon precursors injected therewith are dissociated and combined to form Si nanoparticles through the process of nucleation and nuclear growth. The Si nanoparticles grow between the plasma torch 120 and the cooling part 130, and microstructure such as grain size is controlled in the cooling part 130 into which a cooling gas is injected.
Further, carbonaceous materials are introduced into the cooling part 130 where a Si—C complexing process may be continuously performed.
The carbonaceous materials are supplied from the carbon material supplying part 140 to the cooling part 130.
The carbon material supplying part 140 can supply the carbonaceous materials, such as carbon nanotubes (CNT), carbon nanofibers (CNF), and graphite, to the cooling part 130. In addition, the carbon material supplying part 140 may supply a carbon precursor gas. The carbon precursor gas that may be used is an alcohol or a hydrocarbon-based gas.
A process for manufacturing Si—C composite according to another aspect of the present disclosure using the apparatus as mentioned above, comprises: supplying a Si precursor gas with a plasma forming gas into the reaction chamber 110, such that Si precursors injected with plasma may be dissociated and combined to form Si nanoparticles through the process of nucleation and nuclear growth, and supplying carbonaceous materials with a cooling gas to the cooling part 130 in the reaction chamber 110, thereby complexing the Si nanoparticles and the carbonaceous materials.
In this embodiment, the carbon precursor gas is further supplied to the cooling part, such that carbon coating over the Si—C composite can be achieved.
According to some embodiments of the apparatus and process for manufacturing Si—C composite of the present disclosure, the Si nanoparticle forming process and the Si—C complexing process are performed in an integral reaction chamber 110, and the characteristics of Si nanoparticles and the Si—C composite can be controlled following a source input method and process conditions, such as a plasma power, a gas type, a flow rate, and a cooling gas.
Referring to
The cooling part 130 is configured to inject the cooling gas and the carbonaceous materials into a lower portion of the plasma zone.
The cooling part 130 is substantially ring-shaped, and has spraying holes 132 formed on an inner surface thereof.
The spraying holes have a diameter range of 1 to 3 mm, and are formed at uniform intervals.
The cooling part 130 may be made of a suitable chemical resistant metal.
The cooling gas that can be injected through the cooling part 130 includes, but not limited to, nitrogen (N2), argon (Ar), helium (He), hydrogen (H2), air, and mixtures thereof.
Table 1 below indicates the characteristics of nanoparticles produced according to plasma source power, plasma forming gas, flow rate of injection gas, kinds of particle precursors, and flow rate of the precursors.
Table 2 below indicates the characteristics of the nanoparticles produced based on plasma source power, plasma forming gas, flow rate of injection gas, kinds of particle precursors, and flow rates of the precursors. As shown from the XRD patterns, Si nanoparticles produced using a plasma torch can be controlled as amorphous or crystalline Si nanoparticles depending on the process conditions (e.g., plasma density, gas partial pressure, residence time, etc.).
The left Raman spectrum indicates Si nanoparticles produced in a plasma reactor, where a peak corresponding to the crystalline Si nanoparticles at about 520 cm−1 (Si—Si stretching mode, Transverse Optical (TO)), a peak corresponding to Longitudinal Acoustic (LA) of Si particles at 280 to 290 cm−1, and a peak corresponding to a second Transverse Optical (TO) of Si particles at 900 to 930 cm−1 are shown. The right Raman spectrum indicates Si—C composite produced in a plasma reactor, where a peak corresponding to crystalline Si nanoparticles is observed at about 520 cm−1, and a peak corresponding to low crystallinity carbon at 1350 cm−1 (D band; amorphous graphitic material) and a peak corresponding to high crystallinity carbon at 1570 cm−1 (G band; crystalline graphite) are shown.
According to the evaluation of the charging and discharging of a negative electrode active material for a secondary battery, in the case of crystalline Si nanoparticles (particle sizes of 80-120 nm), the initial charge capacity was about 2,561 mAh/g, and the initial coulombic efficiency (ICE) was 88.1%. Capacity retention rate after 100 cycles was about 8.1%. In the case of carbon-coated Si—C composite (100˜150 nm), the initial reversible capacity was 2,139 mAh/g, ICE was 85.3%, and the capacity retention rate after 100 cycles was 68.6%, where the initial reversible capacity, ICE and capacity retention rate were all remarkably improved compared to the non-carbon-coated Si nanoparticles (NPs).
The apparatus of manufacturing silicon-based nanoparticles depicted in
As depicted, the apparatus for manufacturing SiOx nanoparticles according to an embodiment of the present disclosure includes a reaction chamber 110 for providing a reaction space, a microwave plasma torch 120 for generating plasma using a microwave to decompose silicon precursors and produce Si particles, and a cooling part 130 for cooling SiOx nanoparticles so formed, provided within the reaction chamber 110.
The plasma torch 120 is provided on an upper portion of the reaction chamber 110, comprising a precursor gas inlet 122 and a swirl gas inlet 124 for injecting a plasma gas in the form of swirl.
The precursor gas inlet 122 is configured to inject a gas in a vertical direction towards the plasma center, and the swirl gas inlet 124 is configured to inject a swirl gas in a spiral form.
Through the precursor gas inlet 122, silicon precursor, such as solid phase of micro-Si particles or liquid phase of SiCl4, may be sprayed or gasified, or silicon precursor, such as SiH4 gas, may be supplied alone or in mixture with a carrier gas, such as argon (Ar) or hydrogen (H2).
Through the swirl gas inlet 124, plasma gas, such as N2 or Ar, may be injected, or in mixture with an oxidizing gas.
The oxidizing gas that can be used includes, but not limited to, a mixed gas of hydrogen and oxygen, or air.
Preferably, the plasma gas for forming plasma, such as N2 or Ar gas, is injected in the form of swirl to the microwave plasma torch 120. When the plasma renders the gas to be injected in the form of swirl, the plasma may be concentrated on the center of the reactor, obtaining a larger volume of high-density plasma zone.
In addition, a particle trap 150 for trapping SiOx particles is provided at a lower portion of the reaction chamber 110, and a scrubber 160 for neutralizing an acid exhaust gas is connected to a lower portion of the particle trap 150.
Referring to
In addition, the vortex flow acts to concentrate the plasma towards the center of the reaction chamber to reduce the contact between the plasma and an inner wall of the torch, such that the contamination of the inner wall of the torch from reagents can be prevented and the overheating of the outer wall of the torch can be protected.
In this embodiment, plasma flame edge can be further reliably controlled, and the plasma gas itself can also be stabilized.
When the plasma gas is injected in the form of swirl, the moving path of the gas in the plasma is formed in the swirl shape, and the residence time of the reactive gas in the plasma gets longer. As a result, it is possible to achieve a sufficient reaction time of the particles, whereby the reaction efficiency can be enhanced.
As depicted in
Further, the plasma gas, in plan view as shown in
The plasma gas that can be used includes, but not limited to, nitrogen or argon gas, and may be supplied together with an oxidizing gas.
The oxidizing gas that can be used includes, but not limited to, air, water vapor (H2O) or a mixture of these gases.
Plasma gas (or the plasma gas mixed with oxidizing gas) is injected with an inclination to form plasma in the swirl shape, and the source gas moves along this path. As a result, the source gas can have a relatively longer reaction time than non-swirl type of plasma is injected.
Table 3 compares the reaction efficiencies between the case of injecting the plasma gas in the normal mode (vertical direction) and the case of injecting the plasma gas in the swirl mode.
As used herein, the “reaction efficiency” indicates the relative mass percentage of the particles actually obtained, based on the mass where the injected source materials are completely converted into the nanoparticles is taken as 100%.
Plasma power (15 kW) and other process conditions were the same through all the experiments.
Referring to Table 3, it can be seen that when injected in the swirl mode, particle production yields greatly increase compared to those injected in the vertical mode. It is believed due to the increased residence time of the source gas in the plasma.
The left image shows the particles produced when the plasma gas was injected in the swirl mode, and the right image shows the particles when the plasma gas was injected in the normal mode (vertical direction).
The particles synthesized when the plasma gas was injected in the swirl mode show a substantially uniform spherical shape, while the particles synthesized when the plasma gas was injected in the normal mode show aggregates of small particles, rather than have a particular shape. It is believed that the particles were passed through the plasma zone with a wide energy distribution due to microwave plasma having a thermal plasma characteristic.
However, since in the swirl mode the plasma zone was concentrated on the center as depicted in
In
According to the temperature distributions, the temperature at a position spaced 60 cm from the plasma was below 500° C., and the temperature at a position spaced 5 cm from the plasma was 1225° C. Due to the measurement limits of the temperature sensor, further measurements at a higher temperature were not possible. However, it can be expected from the temperature changes relative to the plasma power that when forming plasmas at 6.0 kW power, a temperature higher than 3000° C. will be formed at a position spaced 5 from the plasma. The temperature at a maximum density area in a typical microwave plasma was known to be around 3000 to 6000° C.
When each of the plasma gas flow rates of the swirl type of plasma was supplied at 20 slm and 25 slm, the temperature at a position spaced 5 m from the center of the plasma was 550° C. Considering that the internal temperature was 1223° C. at the same position, the temperature difference between the inside and the outside of the reactor amounts to 673° C. Accordingly, it can be seen that since the heat transferred to the reactor can be reduced by concentrating the plasma as the swirl shape, the reactor can be protected from overheating.
The plasma shapes and lengths are varied by the types of the plasma gas and the reactive gas, and the flow rates thereof. The plasma gas supplied as swirl mode concentrates the plasma on the center.
Further, the plasma shapes and lengths can be determined by the ratios of the flow rates of the reactive gas (or a mixed gas of reactive gas and carrier gas) and the flow rates of plasma gas supplied as swirl mode.
In
In the case of (a), nitrogen was used as the swirl mode of plasma gas, and 1.5 kW of microwave output was applied at a flow rate of 1 slm.
In the case of (b), the same swirl mode of plasma gas as in (a) was used, and 100 sccm of argon, 1 mL of SiCl4, and 200 sccm of air were injected as a reactive gas at the output set.
In the case of (C), the same swirl mode of plasma gas as in (a) was used, and the optimal ratio of reactive gas at the output set (Ar:50 sccm, SiCl4(I):1.5 mL, air:15 sccm) was injected.
SiOx can be produced by employing silicon precursors (e.g., SiCl4 or SiHCl3) and oxidizing gas, such as H2, O2, air or water vapor (H2O), alone or in combinations thereof.
When the plasma gas is injected as the swirl mode, it allows for the plasma to be concentrated toward the center. When the plasma is concentrated on the center, the plasma is isolated from an outer wall of the plasma torch, and the outer wall can be prevented from being deformed, etched or damaged due to the overheating. Further, the reactants may be prevented from the contamination by the outer wall of the torch. Moreover, the residence time of the source gas in the plasma can be increased, and the reaction efficiency can be improved. Besides, it is possible to manufacture nanoparticles with a uniform shape and particle size due to the concentrated plasma shape.
Referring to
The present disclosure provides a method and apparatus capable of producing SiOx nanoparticles having various oxidation numbers. Further, when SiOx nanoparticles produced by the method and apparatus according to the present disclosure are used as a negative electrode active material for a lithium-based secondary battery, the electrical characteristics of the secondary battery can be improved.
In this embodiment, silicon precursor, such as solid Si particles or liquid SiCl4 is sprayed or gasified, or silicon precursor, such as SiH4 gas is injected alone or in combination with a carrier gas into the plasma reactor, and oxidizing gas, such as hydrogen, oxygen, and/or water vapor is injected to condense SiOx (x=0.4˜2.0) gas, thereby obtaining nanoparticles.
When only oxygen is used as the oxidizing gas, most of the x values of the particles are close to 2 depending on the injection volume, or unreacted silicon precursor may remain, while when only hydrogen is used as the oxidizing gas, a large amount of trichlorosilane (SiHCl3) and hydrochloric acid are generated depending on the injection volume, or unreacted silicon precursor may remain.
When injecting a mixture of constant ratio of hydrogen and oxygen, the x values of SiOx nanoparticles can be controlled in a range of 0.4 to 2.0.
Further, even though water vapor (H2O) is injected, the x values of SiOx nanoparticles can be varied based on the injection volume.
In accordance with the present disclosure, SiOx nanoparticles can be produced to have a variety of crystallinity from a high crystalline phase to a pure amorphous phase.
When the amorphous SiOx nanoparticles are applied to a negative electrode active material for a lithium secondary battery, it can act as a buffer for volume expansion of the silicon occurring during charging and discharging of the battery, thereby obtaining a high charge-discharge capacity and a maintenance performance.
In these embodiments, the air was used as the oxidizing gas, and as shown in the figure, it can be seen that the oxidation numbers of SiOx were varied based on the amount of the air. Further, it can be seen that as the amounts of the air in the total feed gas were varied at 0.15 vol %, 1.00 vol %, 5.00 vol %, and 10.00 vol % from the left, respectively, the resulting oxidizing numbers were changed.
Table 4 shows the oxidation numbers (x value) of SiOx nanoparticles according to the kinds of oxidizing gas and the injection volume.
As can be seen from Table 4, the oxidation numbers can be controlled to vary by adjusting the injection volume of the oxidizing gas.
In a negative electrode active material for a secondary battery, silicon has high theoretical capacity of 4200 mAh/g, but due to a rapid volume changes during charging and discharging of the battery, cracks and thick nonconductive films of the cell electrode (solid electrolyte interphase, SEI) are generated (resistance increases sharply), and disrupted away from a current collector, thereby significantly reducing the cycle life characteristics. However, the nano-sized particles of the negative electrode active material and the controlled oxidation number (x value) of SiOx can serve as an effective buffer against the large volume changes of Si-based negative electrode, and lead to improved cycle properties.
It is considered that these excellent capacity retention rates are due to the buffering effect of the amorphous SiOx phase against the large volume changes of Si-based negative electrode, as previously mentioned.
Although some embodiments have been provided to illustrate the present disclosure, it will be apparent to those skilled in the art that the embodiments are given by way of illustration, and that various modifications and equivalent embodiments can be made without departing from the spirit and scope of the present disclosure. Accordingly, the scope of the present disclosure should be limited only by the accompanying claims and equivalents thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2014-0090084 | Jul 2014 | KR | national |
| 10-2014-0090085 | Jul 2014 | KR | national |
