Apparatus and method for growing sic nanocrystals

Abstract

The present invention relates to an apparatus and a method for growing SiC nanocrystals. The apparatus for growing SiC nanocrystals comprises: a reaction tube; a reaction boat disposed in the reaction tube; a halogenation gas supply tube for supplying a halogenation gas to the reaction boat; a nitridation gas supply tube for supplying a nitridation gas to the reaction boat; and a heating unit for heating the reaction tube. In this case, a substrate is disposed on a part or the entirety of the bottom surface of the reaction boat, a mixed raw material is disposed on the substrate, the mixed raw material includes graphite, silicon, aluminum, and gallium in a solid state, and the mixing ratio of graphite:silicon:aluminum:gallium in the mixed raw material is 2:1-3:1-2:1-2.

Description

SiC nanocrystal growth apparatus and method

[0001] The present invention relates to an apparatus and method for growing SiC nanocrystals, and more specifically, to an apparatus and method for growing SiC nanocrystals using a mixed raw material hydrogen vapor phase growth (HVPE) method.

[0002] Silicon carbide (SiC) has become a very important material in high-temperature and high-power electronic device applications due to its unique material properties, such as a wide energy bandgap, high critical electric field, and high thermal conductivity [1,2]. Natural mineral SiC is a type of gemstone named moissanite. Moissanite is a rare mineral composed of silicon carbide (SiC), which is found in very small quantities in nature. In 1904, Henri Moissan discovered crystals composed of 6H-SiC while studying minerals found in the Canyon Diablo meteorite crater in Arizona, USA, in 1892. Meanwhile, the first synthetic SiC was produced by Acheson et al. in 1884, before it was discovered as a natural mineral [3]. The SiC powder synthesis method known as the Acheson process first synthesized SiC using clay and graphite, and SiC ingots are produced, ground, and refined to be used as various industrial raw materials such as abrasives [4]. Recently, SiC is attracting attention for its stability at high temperatures and in extreme environments, its lack of raw material depletion, and its energy conservation, leading to an increase in its use. SiC can exist in various crystal forms (polytypes) due to the stacking order of double layers of C and Si.

[0003] 4H-SiC and 6H-SiC with hexagonal structures can be grown as single crystals and used as SiC substrates, and can also be grown as SiC epitaxially, expanding into various application fields. In addition, interest has increased further due to Round, who first discovered the electroluminescence phenomenon in which light is emitted when an electric current is applied to a SiC solid material [5]. Lely et al. and Tairov et al. made significant advancements in SiC crystal growth technology through a high-temperature sublimation process for SiC single crystal growth [6-12]. The physical vapor transport (PVT) process has been firmly established as a standard method for producing SiC bulk materials for many years, and the growth of bulk SiC crystals for manufacturing large-diameter, high-quality substrates is one of the key topics in semiconductor technology.

[0004] Meanwhile, nanotechnology is accelerating the development of optoelectronics, nanodevices, nanostructured catalysts, and nanoporous materials in relation to applications such as adsorption and catalysis. Furthermore, unlike bulk materials, nanoscale materials exhibit unique electrical, magnetic, optical, and mechanical properties, enabling the development of innovative technologies in various industrial fields. Single-walled carbon nanotubes (SiC single-walled carbon nanotubes, SWNTs) were first analyzed by Mavrandonakis et al. and Ivanov et al. [13,14]. Subsequently, they were synthesized by Hu et al. and Borowiak-Palen et al. in 2001 [15,16]. Recently, due to the unique physical and chemical properties of SiC nanostructures, their applications in high-voltage / current fields have increased, attracting the attention of many theoretical and experimental researchers [17-31]. SiC possesses various crystal structures, and hexagonal 4H-SiC and 6H-SiC have wider band gaps than 3C-SiC. 4H-SiC has an energy band of 3.26 eV, 6H-SiC has 3.02 eV, and 3C-SiC has 2.39 eV [32-34]. In particular, 6H-SiC has the highest breakdown voltage and thermal conductivity among various SiC structures [34,35]. Most general SiC nanocrystals are 3C-SiC structures, and the synthesis of SiC nanocrystals, along with 6H-SiC, remains a challenging task. These SiC nanocrystals are promising alternative nanostructures to carbon and exhibit improved properties compared to carbon nanotubes (CNT) [36,37]. Therefore, SiC nanocrystals are being synthesized by various methods such as arc discharge

[0038] , catalytic pyrolysis

[0039] , and chemical vapor deposition (CVD)

[0040] , and much research is needed to obtain high-yield and high-quality SiC nanocrystals.

[0005] Meanwhile, the hydride vapor phase epitaxy (HVPE) method has the advantage of a very fast growth rate compared to other equipment, with a growth rate of tens of μm or hundreds of μm per hour compared to the metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE) methods [41-47]. However, there have been no reports of SiC nanocrystal growth using the HVPE method, and a new growth method is needed to improve yield in the field of SiC crystal growth.

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[0055] The object of the present invention is to provide an apparatus and method for growing SiC nanocrystals capable of growing SiC nanocrystals using an HVPE method having a high growth rate.

[0056] Another objective of the present invention is to provide an apparatus and method for growing SiC nanocrystals using graphite in a fragment form rather than a powder form, which offers excellent economic efficiency in growing SiC nanocrystals using graphite in a powder or fragment form.

[0057] Another objective of the present invention is to provide an apparatus and method for growing a large amount of SiC nanocrystals regardless of the type of substrate.

[0058] Another objective of the present invention is to provide a method for manufacturing a secondary battery negative electrode by manufacturing a negative electrode material for a secondary battery using SiC nanocrystals.

[0059] To achieve these and other purposes, a SiC nanocrystal growth apparatus according to one feature of the present invention comprises a reaction tube; a reaction boat disposed within the reaction tube; a halogenation reaction gas supply pipe for supplying a halogenation reaction gas to the reaction boat; a nitridation reaction gas supply pipe for supplying a nitridation reaction gas to the reaction boat; and a heating unit for heating the reaction tube. At this time, a substrate is disposed on part or all of the bottom surface of the reaction boat, and a mixed raw material is disposed on the substrate, wherein the mixed raw material comprises solid graphite, silicon, aluminum, and gallium, and the mixing ratio of graphite:silicon:aluminum:gallium of the mixed raw material is 2:1~3:1~2:1~2, and most preferably 1:1.5:1:1.

[0060] Graphite from the mixed raw materials is placed directly above the substrate to ensure direct contact between the substrate and the graphite. Graphite can be used in either powder or flake form, but the flake form is advantageous for separation from the mixed raw materials after SiC nanocrystal growth.

[0061] The substrate can be used regardless of type, and preferably selected from the group consisting of SiC substrates, AlN substrates, sapphire substrates, and graphite substrates. In particular, the SiC substrate can be used regardless of the type of SiC substrate, such as 3c-SiC, 4H-SiC, and 6H-SiC.

[0062] A method for growing SiC nanocrystals according to another feature of the present invention comprises the steps of: placing a substrate on the bottom surface of a reaction boat; placing a mixed raw material, which is a mixture of solid graphite, silicon, aluminum, and gallium, on top of the substrate, wherein graphite is placed directly above the substrate; placing the reaction boat inside a reaction tube; heating the reaction tube to a temperature in the range of 1100-1250°C; supplying a halogenation reaction gas and a nitridation reaction gas to the reaction boat; reacting the mixed raw material and the halogenation reaction gas to produce carbon tetrachloride (CCl4) gas, trichlorosilane gas, and metal chloride gas; introducing the generated carbon tetrachloride gas into the contact surface between the graphite and the substrate to form a seed; and the carbon tetrachloride gas reacting with the trichlorosilane gas to grow SiC nanocrystals centered on the seed.

[0063] The step of placing the substrates is to place one or more substrates on the entire or part of the bottom surface of the reaction boat without overlapping each other.

[0064] The mixed raw material placement step consists of a step of evenly placing graphite in the form of pieces directly on the substrate; a step of placing aluminum after the graphite placement step; and a step of mixing and placing silicon and gallium after the aluminum placement step.

[0065] The mixing ratio of graphite:silicon:aluminum:gallium of the mixed raw materials is 2:1~3:1~2:1~2, and most preferably 1:1.5:1:1.

[0066] The substrate can be used regardless of type, and preferably selected from the group consisting of SiC substrates, AlN substrates, sapphire substrates, and graphite substrates. In particular, the SiC substrate can be used regardless of the type of SiC substrate, such as 3c-SiC, 4H-SiC, and 6H-SiC.

[0067] A method for manufacturing a secondary battery negative electrode containing lithium ions according to another feature of the present invention comprises the steps of: growing SiC nanocrystals according to the method described above; grinding the grown SiC nanocrystals; mixing the ground SiC nanocrystals with a conductive material and a binder to form a composite material; and forming an electrode using the composite material.

[0068] According to the present invention, high-quality SiC nanocrystals can be grown at a high growth rate using the HVPE method, which utilizes a mixed raw material composed of solid-state graphite, silicon, aluminum, and gallium on various substrates. Furthermore, by using graphite in powder or fragment form as a raw material, the material can be supplied at a low cost and is easy to handle.

[0069] According to the SiC nanocrystal growth apparatus and method of the present invention, SiC nanocrystals can be grown at a lower cost than conventional growth methods, and since these SiC nanocrystals can be used in various application fields, economic efficiency is improved.

[0070] Furthermore, these SiC nanocrystals can be utilized as materials for fabricating negative electrodes for secondary batteries and solar cells, and can be applied to nanoelectronics, nanophotonics, and composite materials. Their excellent hydrogen storage capacity gives them high application value. Moreover, the SiC nanocrystals grown according to the present invention can revitalize new industrial and technological fields related to the power semiconductor-based industry, such as solar cells, secondary batteries, power semiconductors, and optoelectronic devices. In particular, they are useful materials for various mechanical applications, such as electronic device applications like semiconductor field-effect transistors, as well as for blue light-emitting diode applications. Additionally, 3C-SiC and 6H-SiC are applied to high-temperature, high-power, and high-frequency devices due to their unique properties. Therefore, the present invention is crucial for securing source technology and leading positions in related fields by presenting a novel crystal growth method for these SiC nanocrystals using an HVPE device.

[0071] FIG. 1 is a drawing illustrating a SiC nanocrystal growth apparatus according to one embodiment of the present invention.

[0072] FIGS. 2a to 2d are schematic diagrams of the process of growing SiC nanocrystals according to a SiC nanocrystal growth method according to one embodiment of the present invention.

[0073] Figure 3 is a photograph of the surface of a graphite piece of mixed raw material.

[0074] Figure 4a is a photograph showing the arrangement of graphite on a substrate.

[0075] Figure 4b shows the state in which aluminum, silicon, and gallium are placed on graphite.

[0076] Figure 5 is a photograph of the inside of the reaction boat after SiC nanocrystal growth.

[0077] Figure 6 is a photograph of the surface of a graphite piece after SiC nanocrystal growth.

[0078] Figures 7a to 7c show photographs of SiC nanocrystals formed on a substrate on which a graphite piece was placed.

[0079] Fig. 8a is an enlarged photograph of a point in Fig. 7c.

[0080] Figure 8b is an enlarged photograph of section “A” of Figure 8a.

[0081] Figures 9 to 13 are photographs of various forms of grown SiC nanocrystals.

[0082] Figure 14 is a photograph showing the surface of the upper side of the graphite source that is not in contact with the SiC substrate after SiC nanocrystal growth.

[0083] Fig. 15 is a magnified photograph of a point in Fig. 14.

[0084] Figures 16a to 16d are the results of EDS measurements at each point of the SiC nanocrystal in Figure 8a.

[0085] Figure 17 is a graph showing the change in the ratio of each element according to each point of the SiC nanocrystals in Figures 16a to 16d.

[0086] Figure 18 shows the XRD 2θ / ω measurement results for grown SiC nanocrystals.

[0087] Figures 19a to 19e are HRTEM results of grown SiC nanocrystals.

[0088] Figures 20 and 21 are the EDS measurement results for SiC nanocrystals grown in different forms.

[0089] Figures 22 and 23 are the results of EDS measurements on the surface of graphite pieces after SiC nanocrystal growth.

[0090] Figure 24 shows the Raman shift results for the grown SiC nanocrystals.

[0091] Figure 25 shows the results of Raman analysis measured by changing the output of the incident laser.

[0092] Figures 26 to 28 are graphs of the charge-discharge characteristics of the first 3 cycles for a general graphite sample, a graphite piece of mixed raw material, and SiC nanocrystals, respectively.

[0093] The present invention is described below in detail with reference to the attached drawings so that those skilled in the art can easily implement it. In the drawings, elements indicated by the same reference numerals indicate the same elements.

[0094] FIG. 1 is a drawing illustrating a SiC nanocrystal growth apparatus according to an embodiment of the present invention. The SiC nanocrystal growth apparatus according to the present invention is an apparatus that grows SiC nanocrystals at an ultra-high growth rate by the HVPE method. Referring to FIG. 1, the SiC nanocrystal growth apparatus mainly comprises a reaction tube (100), a reaction boat (200) disposed within the reaction tube (100), a gas supply unit (300) that supplies various reaction gases within the reaction tube (100), and a heating unit (400) that heats the inside of the reaction tube (100).

[0095] It is preferable to use a quartz tube for the reaction tube (100). It is preferable to use a hot wall furnace consisting of three general heater furnaces for the heating section (400), but it is not limited to this and an RF furnace may be used.

[0096] The reaction boat (200) is a cylindrical shape having a bottom surface. In one embodiment of the present invention, the reaction boat (200) is illustrated as a rectangular cylindrical shape, but is not limited thereto and may be formed as a rectangular or other shaped cylindrical shape having a bottom surface, and it is preferable that the material be made of quartz. Additionally, although not illustrated, a cover may be formed on the reaction boat as needed.

[0097] A substrate (240) is placed on the bottom surface of a reaction boat (200), and a mixed raw material (230) is placed on the substrate (240).

[0098] The substrate (240) may have a size that covers part or all of the bottom surface of the reaction boat (200). Additionally, the substrate (240) may be formed as one or multiple substrates and arranged to cover the entire or part of the bottom surface, and when multiple substrates are arranged, they are arranged so as not to overlap each other.

[0099] There is. The substrate (240) can be used regardless of type and can preferably be selected from the group consisting of SiC substrates, AlN substrates, sapphire substrates, and graphite substrates, and most preferably, a SiC substrate can be used. In addition, the SiC substrate can be used regardless of the type of SiC substrate, such as 3c-SiC, 4H-SiC, and 6H-SiC.

[0100] The mixed raw material (230) is placed on the substrate (240) so that SiC nanocrystals may grow on the substrate (240). When the substrate (240) is placed with a size that covers only a portion of the bottom surface of the reaction boat (200), the mixed raw material (230) may be placed only on the portion where the substrate (240) is placed, or the mixed raw material (230) may be placed on the entire portion where the substrate (240) is placed and the portion where it is not placed. The mixed raw material (230) consists of solid graphite (231), silicon (233), aluminum (232), and gallium (234). The graphite (231) may be graphite in powder or fragment form, and preferably graphite in fragment form. Graphite in fragment form is not only economical as it is readily available as a raw material such as pencil lead, for example, and is also very inexpensive, but it also has the advantage of being easy to separate from the substrate (240) after SiC crystal growth.

[0101] At this time, the mixing ratio of graphite:silicon:aluminum:gallium of the mixed raw materials is 2:1~3:1~2:1~2, and preferably 1:1.5:1:1.

[0102] As shown in FIG. 1, the mixed raw materials (230) are arranged such that graphite (231) is placed on a substrate (240), aluminum (232) is placed on top of it, and silicon (233) and gallium (234) are mixed and placed on top of the aluminum (232). Through this arrangement of the mixed raw materials (230), the graphite (231) and the substrate (240) can come into direct contact. Therefore, as shown in FIG. 1, the mixed raw materials (230) are arranged approximately in the order of graphite (231) - aluminum (232) - silicon (233) and gallium (234) starting from the substrate (240).

[0103] The gas supply unit (300) is equipped with an atmosphere gas supply unit (310) that supplies an atmosphere gas such as nitrogen, a nitrification reaction gas supply unit (320) that supplies a nitrification reaction gas such as ammonia (NH3), and a halogenation reaction gas supply unit (330) that supplies a halogenation reaction gas such as hydrogen chloride (HCl), and each gas supply unit supplies gas to the reaction tube (100) through supply pipes (311, 321, 331).

[0104] The atmosphere gas supply unit (310) supplies an atmosphere gas, such as nitrogen, to the reaction tube (100) and the reaction boat (200) through the atmosphere gas supply pipe (311), thereby not only creating a nitrogen atmosphere inside the reaction tube (100) and the reaction boat (200), but also trichlorosilane and metal chloride gas (AlCl₂) generated by the mixed raw materials and the halogenation reaction gas. n , GaCl n It is possible to move the gas flow within the reaction tube (100) to the substrate (240) and maintain it stably.

[0105] The halogenation reaction gas supply pipe (331) connected to the halogenation reaction gas supply unit (330) supplies halogenation reaction gas to the reaction boat (200). The supplied halogenation reaction gas reacts with the mixed raw material (230) to produce carbon tetrachloride (CCl4) gas, trichlorosilane and metal chloride gas (AlCl4). n , GaCl n It promotes the production of ).

[0106] The nitriding reaction gas supply pipe (321) connected to the nitriding reaction gas supply unit (320) supplies nitriding reaction gas to the reaction boat (200).

[0107] A method for growing SiC nanocrystals using a SiC nanocrystal growth apparatus according to one embodiment of the present invention is described. FIGS. 2a to 2d are schematic diagrams of SiC nanocrystal growth.

[0108] First, a substrate (240) for growing SiC nanocrystals is mounted on the bottom surface of the reaction boat (200). The substrate can be selected from the group consisting of a SiC substrate, an AlN substrate, a sapphire substrate, and a graphite substrate, and a SiC substrate is most preferred. When using multiple substrates (240), the multiple substrates are arranged so that they do not overlap each other.

[0109] Next, a mixed raw material (230) comprising solid graphite (231), silicon (233), aluminum (232), and gallium (234) is placed on a substrate (240). For graphite (231), it is preferable to use graphite in powder or fragment form, and the mixing ratio of graphite:silicon:aluminum:gallium is 2:1~3:1~2:1~2, and preferably 1:1.5:1:1.

[0110] In particular, when arranging the mixed raw materials, graphite (231) is evenly and uniformly placed directly on the substrate (240) so that the seeds of the SiC nanocrystals can be well formed, and the substrate (240) and the graphite (231) are in direct contact, and any arrangement shape is acceptable as long as it is evenly arranged. Next, aluminum (232) is placed after the graphite (231), and after the aluminum (232) is placed, silicon (233) and gallium (234) are mixed and placed.

[0111] FIG. 3 is a photograph of the surface of a graphite (231) piece in a mixed raw material (230). The shape of the graphite piece may be any shape, but in order for the reaction gases to diffuse to the contact surface between the substrate (240) and the graphite (231) in the subsequent reaction, a piece with a curved surface toward the substrate (240), such as a cylinder, is preferred. For example, a graphite piece made by cutting a pencil lead into a certain length in the longitudinal direction can be used.

[0112] FIG. 4a shows a state in which graphite (231) is placed on a substrate (240), and FIG. 4b shows a state in which aluminum (232), silicon (233), and gallium (234) are placed on the graphite (231). In FIG. 4a and FIG. 4b, the substrate (240) is exposed to show the presence of the substrate (240), but during actual SiC crystal growth, the substrate (240) is covered by a mixed raw material (230), so the substrate (240) is not exposed.

[0113] Next, the heater (400) is operated to heat the reaction tube (100) to a temperature range of 1100-1250°C. At this time, nitrogen, which is an atmosphere gas, is flowed before the temperature of the reaction boat (200) is raised, and when the temperature of the reaction tube (100) is stabilized, a certain amount of hydrogen chloride, which is a halogenation reaction gas, and ammonia, which is a nitrification reaction gas, are supplied to the reaction boat (200).

[0114] The supplied hydrogen chloride reacts with the mixed raw materials, graphite (231), silicon (233), aluminum (232), and gallium (234), respectively. Specifically, graphite (231) reacts with hydrogen chloride to produce carbon tetrachloride (CCl4) series gas, silicon (233) reacts with hydrogen chloride to produce silane trichloride (Si + 3HCl → SiHCl3 + H2), aluminum (232) reacts with hydrogen chloride to produce AlCl, and gallium (234) reacts with hydrogen chloride to produce GaCl n (n=1, 2, 3...) occurs. At this time, gallium diffuses from the surfaces of aluminum and silicon among the mixed raw materials, removing most of the oxide and nitride films formed on the surfaces of the aluminum and silicon. In other words, although oxidation and nitride occur on silicon and aluminum in a high-temperature atmosphere, the diffusion of a small amount of gallium onto these surfaces removes the oxide and nitride films during the heating process, thereby activating them. Therefore, gallium activates aluminum, promoting its reaction with hydrogen chloride and facilitating the formation of AlCl. In addition, gallium suppresses the formation of oxide and nitride films on the surface of silicon, thereby promoting the reaction between silicon and hydrogen chloride gas and facilitating the formation of trichlorosilane (SiHCl3). If gallium is not mixed into the raw materials, it is difficult for a reaction with hydrogen chloride to occur due to the oxide and nitride films on the silicon surface.

[0115] Next, carbon tetrachloride (CCl4) gas generated by the reaction of graphite (231) and hydrogen chloride is introduced into the interface between the graphite (231) in contact with the substrate (240) on the substrate (240) and the substrate (240), and reacts with trichlorosilane gas at this interface of the substrate (240) to form SiC nanocrystal seeds. At this time, AlCl reacts together with CCl4 to form hexagonal seeds containing Al on the substrate (240).

[0116] In the schematic diagram of FIG. 2a, a piece of graphite (231) is placed on a substrate (240). The placement form is irrelevant. In FIG. 2b, gallium, aluminum, graphite, and silicon each react with HCl gas at 1100-1250°C to form GaCl3, AlCl3, CCl4, and SiCl4. n After generating, these gases diffuse into the contact surface between the substrate (240) and the graphite (231) piece to form seeds of pure SiC nanocrystals. At this time, Ga diffuses over the surfaces of Al, graphite, and Si, and reacts with AlCl and CCl4 to form seeds containing Al on the substrate (240). In the absence of gallium, silicon does not easily react with HCl gas due to the oxide and nitride layers on its surface, but this problem is resolved by using gallium. That is, Ga reacts with AlCl, CCl4, and SiCl n It promotes the formation of. As a result, a kind of seed is formed, and SiC nanocrystals grow on the substrate (240) around it as shown in FIG. 2c. Subsequently, CCl4 and SiCl n Al becomes an essential component of the SiC nanostructure, and a stable SiC nanostructure with a C-to-Si ratio of 50:50 is grown as shown in Fig. 2d. Fig. 2d is an enlarged view of a portion of the SiC nanocrystal. The same reaction can occur on the surface of a graphite fragment, forming a hairy caterpillar-like nanostructure with a high Si content. The nanostructure formed on the surface of this graphite fragment is a nanomaterial containing C, Al, and Si; although it is not a pure SiC nanocrystal, it can be usefully utilized when fabricating solar cells or secondary batteries (composites) as SiC nanocrystals containing various impurities.

[0117] Figure 5 is a photograph of the inside of the reaction boat after SiC nanocrystal growth, and Figure 6 is a photograph of the surface of the graphite piece after SiC nanocrystal growth. When comparing Figure 3 and Figure 6, it can be seen that the surface of the graphite piece before SiC nanocrystal growth has changed as shown in Figure 6.

[0118] Figures 7a to 7c are photographs showing SiC nanocrystals formed on a substrate on which a graphite piece was placed. Figure 7b is an enlarged view of section "A" in Figure 7a, and Figure 7c is an enlarged view of section "B" in Figure 7b, showing the surface of the substrate.

[0119] Figure 8a is a further enlarged view of a portion of Figure 7c, showing SiC nanocrystals grown according to an embodiment of the present invention. Figure 8b is an enlarged view of the “A” portion of Figure 8a, showing hexagonal seeds. These hexagonal seeds are formed when AlCl reacts with CCl4 to form Al-containing seeds in a hexagonal shape, meaning that a hexagonal structure containing Al, N components, and C is formed under the influence of Al.

[0120] Afterwards, SiCl n Silver is an important component of SiC nanocrystals, and a very stable SiC nanocrystal structure is grown when the ratio of C to Si is 50:50 [13,19,36].

[0121] According to an embodiment of the present invention, the SiC nanocrystal growth conditions and experimental data are as shown in Table 1 below.

[0122] Experimental Conditions Reaction Tube Temperature: 1100-1250℃ 1250℃ Hydrogen Chloride: 20-1000 sccm 500 sccm Growth Time: 20 min - 2 hours 60 min Amount of Mixed Raw Material Graphite: 10-100g 20g Amount of Mixed Raw Material Silicon: 10-200g 30g Amount of Mixed Raw Material Aluminum: 10-100g or less 20g Amount of Mixed Raw Material Gallium: 10-100g or less 20g Growth Rate (Diameter): 500 nm / h 500 nm / 60 min Growth Rate (Length ℓ): ℓ > 1 μm / h ℓ > 1 μm / 60 min Ammonia: 300-500 sccm 300 sccm Nitrogen: 500-1000 sccm 500 sccm

[0123] The results of growing SiC nanocrystals under the experimental conditions of Table 1 are explained as follows. Figure 3 is a photograph showing the surface of a graphite piece to be used in the mixed raw material. It shows the surface of the graphite piece before growth, which resembles a typical pencil lead.

[0124] FIG. 4a is a photograph showing graphite (231) placed on a substrate (240), and FIG. 4b is an optical image showing 20 g of graphite pieces, 30 g of Si, 20 g of Al, and 20 g of Ga as mixed raw materials (230) mounted on a substrate (240) placed in a reaction boat (200). The substrate (240) used a SiC substrate, the gallium used was 7N (99.99999%) high-purity Ga, and the aluminum used was 4N (99.99%) high-purity Al. This 7N high-purity Ga is adsorbed onto the surface of metallic Al, Si, and graphite pieces, allowing them to react well with HCl. The 4N metallic Al contributes to the growth of SiC nanostructures by adsorbing Si and C elements through the initial synthesis of AlN-based nanostructures. Cylindrical graphite with an average diameter of 2 mm and a length of 8 mm was used for the graphite pieces. For the Si raw material, an n-type Si substrate was cut into small pieces and used as the group 5 element N, which was nitriding reaction gas NH3 gas. N2, NH3, and HCl gases were supplied at constant rates of 5,000 sccm, 1,000 sccm, and 200 sccm, respectively, into a reaction tube (100) made of quartz along respective supply pipes (311, 321, 331). The growth temperature was set to 1,200℃ and the growth time to 60 minutes.

[0125] FIG. 5 is a photograph showing the interior of a graphite boat after SiC nanocrystal growth according to one embodiment of the present invention.

[0126] Figure 6 is a photograph showing the surface changes of the graphite fragments of the mixed raw material after growth. As can be seen in Figure 6, a large amount of nanostructures were formed on the remaining surface of the graphite fragments in addition to the contact surface between the substrate (240) and the graphite (231). Since the graphite has a high density, it is not completely consumed in the HCl reaction, and carbon nanostructures containing a large amount of Al or C are formed on the surface of the graphite fragments.

[0127] Figures 7a to 7c show photographs of SiC nanocrystals formed on a substrate on which graphite pieces were placed. Figure 7a is an image of the SiC substrate surface after the growth of SiC nanocrystals. The marks where cylindrical graphite pieces were placed can be clearly seen.

[0128] Figure 7b is a magnified surface photograph of the SiC substrate at point “A” where the graphite piece of Figure 7a is placed after growth of the SiC nanocrystal growth device, and Figure 7c is a magnified view of part “B” of Figure 7b, showing that crystals have been formed on the surface of the SiC substrate.

[0129] Figure 8a is an FE-SEM result of a grown SiC nanocrystal magnified at a point in Figure 7c, and Figure 8b is an FE-SEM image magnified at section “A” of Figure 8a. As can be seen in Figure 8a, the grown SiC nanocrystal can have various shapes. Figure 8b is a further magnification of section “A” of Figure 8a, showing hexagonal seeds. In other words, it is clear that in the present invention, AlN-based nanostructures contribute to the growth of SiC nanocrystals by adsorbing Si and C elements. This can be confirmed by the fact that in some nanocrystals in Figure 8b, hexagonal seeds are formed and the nanocrystals are growing, as seen in section “A”.

[0130] In Figures 9 to 13, it can be seen that the grown SiC nanocrystals have various shapes, and Figures 9 to 13 are FE-SEM images magnified at different points of Figure 7c. It can be seen that the SiC nanocrystal in Figure 9 is hollow, and in Figure 10, nodes of the grown SiC nanocrystal can be seen. In addition, Figure 11 is a photograph of SiC nanocrystals with a diameter of approximately 0.20 μm to 0.69 μm, Figure 12 is a photograph of SiC nanocrystals with a diameter of approximately 0.49 μm, and Figure 13 is a photograph showing different shapes of grown SiC nanocrystals.

[0131] As can be seen in FIG. 9, the SiC nanocrystals grown according to one embodiment of the present invention have a hollow tube shape. This confirms that SiC nanocrystals with a crystal structure different from the conventional method of impregnating fibrous carbon with a liquid precursor and coating (e.g., Patent No. 10-2208517 SiC nanotubes and methods for manufacturing the same) have been grown. In addition, in FIG. 10, a nanocrystal shape having nodes, similar to a typical bamboo shape, was observed [48-55]. This is similar to the properties of carbon nanotubes and is a characteristic also obtained in SiC nanocrystals. At a growth temperature of 1100-1250°C, HCl gas reacts with Ga, Al, graphite, and Si sources to form GaCl3, AlCl4, CCl4, and SiCl4. nThese gases are generated. These gases diffuse into the interface between the SiC substrate and the graphite source, and CCl4 reacts with AlCl to first form an Al-containing seed on the substrate. Subsequently, as the growth time increases, the SiC nanocrystals have tube diameters ranging from 200 nm to 700 nm, which are larger than those of typical SiC nanocrystals as shown in Fig. 11; when the growth time is set to 60 minutes, SiC nanocrystals with an average diameter of approximately 500 nm can be obtained as shown in Fig. 12. Therefore, according to the present invention, the maximum growth rate of the SiC nanocrystals is 150 nm / h in the diameter direction and up to several hundred μm / h in the length direction, resulting in a length of several mm. Thus, according to one embodiment of the present invention, pure SiC nanocrystals with a Si-to-C ratio of 50:50 can be formed. Here, Ga diffuses over the surfaces of Al, graphite, and Si; furthermore, if Ga is not used, Si does not easily react with HCl gas due to the oxide and nitride layers on the surface. The arrangement of the mixed raw materials can be any form, but it is important to arrange them so that the Al and graphite sources are well mixed across the entire surface of the substrate so that SiC nanocrystal seeds can be well formed.

[0132] FIG. 14 is an FE-SEM result observing the surface of the upper surface of a graphite source that is not in contact with the substrate (240) after SiC nanocrystal growth, wherein the surface of the graphite piece is exposed to HCl gas, AlCl, and SiCl n As it is directly exposed, the same reaction occurs on the surface of the graphite piece as on the contact surface between the graphite (231) and the substrate (240). FIG. 15 is an enlarged photograph of a point in FIG. 14, showing that a large number of hairy caterpillar-shaped structures are formed. That is, it shows that nanostructures with a high Si content are grown on the surface of the graphite piece, and that AlN-based nanostructures are acting as absorbers for various elements

[0067] .

[0133] Figures 16a to 16d show the results of EDS measurements at each point of the SiC nanocrystal in Figure 8a, observing changes in composition at each point (1 to 4) of the SiC nanocrystal. Figure 16a shows the results measured at the hexagonal seed portion at point 1, where the elemental ratios related to C, Si, and AlN were measured as 31.26 at%, 38.82 at%, and 29.91 at%, respectively, confirming that each element is distributed similarly. Figure 16b shows the results measured at point 2, which can be viewed as the seed surface and the starting point of nanocrystal growth. It can be seen that the elemental ratios of C and Si are increasing similarly, with C at 39.17 at% and Si at 38.71 at%, while the elemental ratio related to AlN is decreasing to 22.12 at%. This indicates that there is a contribution from AlN-based nanostructures during the initial growth of the SiC nanocrystal. Figure 16c shows the results measured at point 3, where the nanostructure begins to grow, and it can be seen that C (47.95 at%) and Si (46.20 at%) account for the majority. Figure 16d shows the results measured at point 4, where the growth of SiC nanocrystals continues, and it can be seen that the C component is gradually increasing to 55.28 at%. This is because the formation of CCl4 by the graphite source in the mixed raw materials becomes dominant over time.

[0134] Figure 17 is a graph showing the change in the elemental ratios according to each point of the SiC nanocrystals in Figures 16a to 16d. As the SiC nanocrystals grow, the elemental ratios of C and Si increase together. These results clearly show that SiC nanocrystals different from the growth of carbon nanotubes have been formed, and it can be considered that AlN-based nanostructures play a role in the initial growth.

[0135] Figure 18 shows the XRD 2θ / ω results measured for SiC nanocrystals grown according to the present invention in the range of 2θ values ​​from 20° to 80°. Measurement and analysis were performed using a high-resolution X-ray diffraction (HR-XRD) device from Rigaku's Smartlab. In the case of graphite carbon (JCPDS file no: 26-1079), two diffraction peaks were observed at 26.4° and 43.3°, corresponding to the (003) and (101) lattice planes, and in the case of 3C-SiC, a peak near 33.6° (JCPDS file no: 75-0254) appeared in the (111) lattice plane. However, unlike these, the results obtained in the present invention showed diffraction peaks at 26.8° and 35.6°. The peak at 26.8° corresponds to the (002) diffraction plane of hexagonal graphite (JCPDS file no: 41-1487), and the peak at 35.6° corresponds to the (004) lattice plane of the crystal phase in the case of 4H-SiC nanostructures (JCPDS file no: 22-1317) and can be assigned to the (102) lattice plane of the crystal phase in the case of 6H-SiC (JCPDS file no: 29-1128) [32, 38, 50, 56-60]. Therefore, it is determined that 4H-SiC or 6H-SiC nanostructures and carbon nanostructures were grown in the grown nanocrystals, respectively, and that they are mixed.

[0136] Figures 19a to 19e show HRTEM results of grown SiC nanocrystals. Figure 19a shows an HRTEM image of a typical very thin SiC nanocrystal. Figure 19b is an HRTEM image of the edge portion of the SiC nanocrystal with a diameter of 382 nm in Figure 19a. Figure 19c is an enlarged view of region “A” in Figure 19b. Figure 19d is an enlarged view of region “B” in Figure 19c. Figure 19e is an enlarged view of region “C” in Figure 19d, and the nanostructure in the HRTEM lattice image shows a periodic lattice structure. The d-spacing between two adjacent lattice fringes is 0.25 nm, which corresponds well to the inter-plane spacing in the (111) plane or (102) plane direction of SiC [32, 61-66]. Thus, it can be confirmed that crystalline SiC nanocrystals can be grown by the HVPE method.

[0137] Figures 20 and 21 are the EDS measurement results for SiC nanocrystals grown in different forms.

[0138] Figure 20 shows the results of performing EDS on SiC nanocrystals grown in different forms to confirm SiC nanocrystals. Specifically, the EDS results for the SiC nanocrystals of Figure 8a (indicated point, diameter 75 nm) show that the elemental ratios related to C and Si are composed of 43.33 at% and 53.69 at%, respectively.

[0139] Figure 21 shows the EDS results for a SiC nanocrystal with a diameter of 1300 nm at the marked point in the crystal of Figure 10, with the elemental ratios of C and Si being 48.16 at% and 51.43 at%, respectively. This confirms that a very stable SiC nanocrystal is maintained when the ratio of C to Si is 50:50 during SiC nanocrystal growth [13,19,36].

[0140] Figures 22 and 23 are the results of EDS measurements on the surface of graphite pieces after SiC nanocrystal growth.

[0141] Figure 22 shows the EDS results for the hairy caterpillar-shaped carbon nanostructure in Figure 15. An elemental ratio associated with AlN was measured at 33.05 at% with C 12.26 at% and Si 53.90 at%, and Figure 23 shows the EDS results for the surface of the graphite fragment remaining after SiC nanocrystal growth. A rather small elemental ratio was detected with C 2.45 at% and Si 12.80 at%, and an elemental ratio associated with AlN was 81.38 at%, which means that AlN-based nanostructures, along with the graphite source in the mixed source, are contributing significantly to the growth of SiC nanocrystals as element absorbers

[0067] .

[0142] Figure 24 shows the Raman shift results for the grown SiC nanocrystals. Raman shift measurements were performed by attaching the grown SiC nanocrystals to carbon tape for FE-SEM measurement. For comparison, a SiC substrate, a standard graphite block, graphite fragments added as a mixed material, and the grown SiC nanocrystals were subjected to comparative measurements by irradiating them with a 5 mW laser at a wavelength of 532 nm. For the SiC substrate, the values ​​were 527, 614 (LT), 777 (TO), 798 (TO), and 980 (LO) cm⁻¹. -1 A mode was observed. This is a typical Raman peak of 4H-SiC bulk crystals [68-73]. In graphite blocks and graphite fragments, the 1354 and 1581 cm⁻¹ modes, which are major features of the Raman spectrum, were observed. -1 The so-called D and G peaks in [74-76] were observed.

[0143] Figure 25 shows the Raman analysis results measured by varying the output of the incident laser. The peaks for SiC nanocrystals are at 504, 613, 780, 798, 980, 1356, 1516, 1582, 1710, and 2693 cm⁻¹. -1 A mode was observed. The bulk 6H-Si Raman peaks were at 767, 789, and 797 cm⁻¹. -1In 3 TO phonon modes and 889 and 965 cm -1 It has two LO modes. Therefore, at the measured peak, it is at 504 cm⁻¹. -1 It is associated with the TA mode of 6H-SiC, and 613 cm⁻¹ -1 is the LT mode of 4H-SiC, 780 cm -1 TO mode of 4H-SiC, 798 cm -1 TO mode of 6H-SiC and 4H-SiC, 980 cm⁻¹ -1 It is related to the LO mode of 4H-SiC and is considered to have different Raman characteristics from 4H-Si substrates and bulk 6H-Si [77-80]. Also, 1356, 1516, 1582, 1710, 2693 cm⁻¹ -1 Although it is fundamentally related to SiC nanostructures and carbon structures, it is difficult to distinguish between them, so the peak associated with SiC nanocrystals is at 1000 cm⁻¹. -1 It is deemed reasonable to limit the range to the following peaks. Therefore, the measurement results confirm the coexistence of SiC nanocrystals and carbon nanostructures in the specimen.

[0144] Next, a method for manufacturing a negative electrode of a secondary battery containing lithium ions using SiC nanocrystals according to the present invention will be described.

[0145] First, SiC nanocrystals are ground to make a secondary battery. When grinding, the grinding can be performed manually or appropriately by using any one of known grinders, including ball mills, bead mills, jet mills, and shock wave grinders, or a combination of two or more types.

[0146] The crushed SiC nanocrystalline powder serves as the negative electrode active material for a secondary battery. A composite is formed by mixing it with a conductive material and a binder, and then the negative electrode is formed using this composite. Acetylene black was used as the conductive material. Polyvinylidene Fluoride (PVDF) was used as the binder. The SiC nanocrystalline powder, which is the negative electrode active material, the conductive material, and the binder are mixed using a ball mill in a ratio of 80:10:10. Next, using a doctor blade device, the composite is applied to a copper foil attached to a flat glass plate to a desired thickness, for example, 20 to 100 μm, and dried at a temperature of 50 °C to 80 °C for 10 to 12 hours.

[0147] The characteristics of a lithium-ion battery (LIB) manufactured using SiC nanocrystals grown according to one embodiment of the present invention are as shown in FIGS. 26 to 28. For comparison, i) a sample of crushed graphite used in a general lithium-ion battery, ii) a sample of crushed graphite fragments added as a mixed raw material, and iii) a sample of crushed SiC nanocrystals were applied to the negative electrode of a lithium-ion battery under the same conditions to compare the charge / discharge profiles of the cycles. In the case of sample iii), the amount of SiC nanocrystals was insufficient during the test, so the nanostructure on the graphite surface shown in FIG. 15 after SiC nanocrystal growth was added and used as a sample.

[0148] Figure 26 illustrates the charge / discharge curve characteristics of the initial 3 cycles of a lithium secondary battery manufactured by forming a cathode with the sample of i), Figure 27 illustrates the charge / discharge curve characteristics of the initial 3 cycles of a lithium secondary battery manufactured by forming a cathode with the sample of ii), and Figure 28 illustrates the charge / discharge curve characteristics of the initial 3 cycles of a lithium secondary battery manufactured by forming a cathode with the sample of iii). In Figure 26, 349 mAh g -1 At the point, the 1st, 2nd, and 3rd curves coincide, indicating stable charge / discharge curve characteristics. In the case of the charge / discharge curve characteristics of the initial 3 cycles of a lithium secondary battery manufactured using the sample of ii) as the cathode, Figure 27 shows that the capacity increases in the 2nd curve compared to the 1st, and in the 3rd curve compared to the 2nd, with an initial value of 155 mAh g -1 It shows a very low value. In Fig. 28, the initial first-order curve shows 462 mAh g -1 Although it shows a large value, it exhibits very stable characteristics with the graphs almost matching in the second and third orders.

[0149] Conventional silicon anodes are high-energy-density active materials that can replace carbon-based anodes (360 mAh / g), which have reached their capacity limit with the recent development of electric vehicles, as anodes for lithium secondary batteries. However, conventional silicon anodes have difficulty being used for a long life due to large volume expansion and low conductivity during charging and discharging. The anode material containing SiC nanocrystals of the present invention can be used as a secondary battery anode active material with maximized high capacity, long life, and high power performance based on excellent conductivity while suppressing life degradation due to volume expansion and shrinkage [84, 85].

[0150] In addition, as can be seen in FIGS. 26 to 28, for sample i), the capacity during the lithiation and delithiation processes is 444 mAh g⁻¹, respectively. -1and 349 mAh g -1 and, in the case of sample ii), 248 mAh g -1 and 155 mAh g -1 They have very low values, and in the case of sample iii), 462 mAh g each. -1 and 268 mAh g -1 The first Coulombic efficiency was found to be 58%. Table 2 below shows a comparison of the characteristics of the results for samples i) to iii). When comparing the profile of sample iii) with that of sample i), it can be seen that the profile shape is very different [81-83]. Therefore, when SiC nanocrystals grown according to the present invention are used as a negative electrode active material, the efficiency of secondary batteries can be improved as a new material.

[0151] Primary lithiation capacity (mAh g) -1 )1st Delithiation Capacity (mAh g -1 ) Sample with 1st-order Coulombic efficiency (%) i) 444 mAh g -1 349 mAh g -1 Sample of 79%ii) 248 mAh g -1 155 mAh g -1 63%iii) of the sample 462 mAh g -1 268 mAh g -1 58%

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Claims

1. As a SiC nanocrystal growth device, Reaction tube; A reaction boat disposed within the above reaction tube; A halogenation reaction gas supply pipe for supplying halogenation reaction gas to the above reaction boat; A nitriding reaction gas supply pipe for supplying nitriding reaction gas to the above reaction boat; and A heating unit that heats the above reaction tube including A substrate is placed on part or all of the bottom surface of the above reaction boat, and A mixed raw material is placed on the above substrate, and The above mixed raw material comprises solid graphite, silicon, aluminum, and gallium, and the mixing ratio of graphite:silicon:aluminum:gallium of the above mixed raw material is 2:1~3:1~2:1~2, and A SiC nanocrystal growth apparatus in which graphite among the mixed raw materials is disposed directly above the substrate, and the substrate and graphite come into contact.

2. In Paragraph 1, SiC nanocrystal growth apparatus in which the mixing ratio of graphite:silicon:aluminum:gallium of the above mixed raw materials is 1:1.5:1:

1.

3. In Paragraph 1, The above graphite is a SiC nanocrystal growth device in the form of fragments.

4. In Paragraph 1, The above substrate is a SiC nanocrystal growth apparatus selected from the group consisting of SiC substrates, AlN substrates, sapphire substrates, and graphite substrates.

5. As a method for growing SiC nanocrystals, Step of placing a substrate on the bottom surface of the reaction boat; A mixed material placement step comprising placing a mixed material comprising solid graphite, silicon, aluminum, and gallium on the upper side of the substrate, wherein graphite is placed directly above the substrate; Step of placing the above reaction boat inside the reaction tube; A step of heating the above reaction tube to a temperature in the range of 1100-1250℃; A step of supplying halogenation reaction gas and nitrification reaction gas to the above reaction boat; A step of reacting the above mixed raw materials with a halogenation reaction gas to produce carbon tetrachloride (CCl4) gas, trichlorosilane gas, and metal chloride gas; The step of introducing the generated carbon tetrachloride gas into the contact surface between the graphite and the substrate to form a seed; and A step in which the carbon tetrachloride gas reacts with the trichlorosilane gas to grow SiC nanocrystals centered on the seed. A method for growing SiC nanocrystals including 6. In Paragraph 5, A method for growing SiC nanocrystals in which the mixing ratio of graphite:silicon:aluminum:gallium of the above-mentioned mixed raw materials is 2:1~3:1~2:1~2.

7. In Paragraph 5, The above substrate is a SiC nanocrystal growth method selected from the group consisting of SiC substrates, AlN substrates, sapphire substrates, and graphite substrates.

8. In Paragraph 5, The step of placing the substrates is a SiC nanocrystal growth method in which one or more substrates are placed on all or part of the bottom surface of the reaction boat without overlapping each other.

9. In Paragraph 5, The above mixed raw material batching step A step of evenly distributing graphite in the form of pieces directly on the substrate; Step of placing aluminum after the graphite placement step; and Step of mixing and placing silicon and gallium after the aluminum placement step A method for growing SiC nanocrystals including 10. A method for manufacturing a secondary battery negative electrode containing lithium ions, A step of growing SiC nanocrystals according to any one of claims 5 to 9; A step of grinding the grown SiC nanocrystals; and A step of forming a composite material by mixing the above-mentioned crushed SiC nanocrystals, a conductive material, and a binder; and Step of forming an electrode using the above composite material A method for manufacturing a secondary battery negative electrode including

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