Carbon-silicon / carbon composite and processes for preparing the same

Abstract

This invention relates to a carbon-silicon / carbon composite and its preparation method, wherein the carbon-silicon / carbon composite forms a silicon / carbon composite matrix in the pores and / or surface of a porous carbon support with controlled pore characteristics. When the carbon-silicon / carbon composite of the embodiments of this invention is used as a negative electrode active material, the overall silicon size can be suppressed to a small size, and the formation of intermediate phase crystals -LixSiy (e.g., Li15Si4 or Li3.75Si) that affect battery performance degradation can be suppressed, thereby mitigating battery performance degradation during repeated charge and discharge.

Description

Carbon-silicon / carbon composites and their preparation methods This invention relates to a carbon-silicon / carbon composite, and more specifically, to a carbon-silicon / carbon composite and a method for preparing the same. Carbon materials are materials made from carbon, one of the most abundant resources on Earth. Carbon materials are very light, strong, and possess excellent electrical and thermal conductivity, making them core materials widely used in hydrogen fuel cell vehicles, aerospace, rechargeable batteries, and high-end consumer materials. Carbon materials can be made from a variety of raw materials such as palm shells, polyacrylonitrile, rayon and pitch. Among them, the molecular weight and composition of carbon materials made from solid raw materials such as palm shells are difficult to control (Korean Patent Application Publication 10-2019-0093960). Conversely, pitch, a viscoelastic solid polymer extracted from crude oil or plants, has a high yield when converted into carbon materials, is inexpensive, and has a molecular structure that is closer to that of graphite than other raw materials. Therefore, it has the advantage of reducing the energy required for heat treatment (US Patent Nos. 4,242,196 and 4,340,464). In particular, asphalt prepared from pyrolysis fuel oil (PFO), naphtha cracking bottom oil (NCB), vacuum residue (VR), and fluid catalytic cracking decant oil (FCC-DO), which are byproducts of petroleum refining processes, has a high content of aromatic compounds and low content of impurities such as sulfur and nitrogen. On the other hand, silicon-based anode active materials are being explored to improve the capacity of secondary batteries. Silicon has a very high theoretical energy density and has attracted much attention as a next-generation battery anode active material to replace graphite. However, its volume can increase by up to 300% during charge and discharge, resulting in a significant decrease in mechanical stability, such as silicon breakage, as an anode active material. Therefore, research has been conducted to address this problem. However, existing negative electrode active materials still suffer from insufficient resolution of issues such as breakage due to volume expansion and reduced electrochemical performance. Prior art literature includes: Patent Document 0001 Korean Patent Application Publication 10-2019-0093960; Patent Document 0002 US Patent No. 4242196; Patent Document 0003 US Patent No. 4340464. The technical problem to be solved by the present invention is to provide a carbon-silicon / carbon composite, wherein a silicon / carbon composite matrix is ​​formed in the pores and / or surface of a porous carbon support having controlled pore characteristics. Another object of the present invention is to provide a method for preparing the carbon-silicon / carbon composite. Another object of the present invention is to provide a negative electrode active material comprising the aforementioned carbon-silicon / carbon composite. Technical Solution The present invention provides a carbon-silicon / carbon composite, comprising: a porous carbon support, wherein the volume ratio of mesopores with a pore size of 2nm to 50nm is 5% to 80% based on the total pore volume; and a silicon / carbon composite matrix located on the surface and inside the pores of the porous carbon support. According to one embodiment of the present invention, the BET specific surface area in the porous carbon support can be 300 m². 2 / g~3000m 2 / g, tap density can be 0.05g / ml~0.5g / ml, and average particle size can be 1μm~20μm. In addition, the silicon content in the total weight of the carbon-silicon / carbon composite can be 20% to 70% by weight. In addition, the silicon / carbon composite matrix accounts for 10% to 90% by weight of the total weight of the carbon-silicon / carbon composite. In addition, the average size of the silicon crystals in the silicon / carbon composite matrix can be less than 10 nm. In addition, the c / a peak ratio of the carbon-silicon / carbon composite can be 0 to 1.5. In addition, the present invention provides a method for preparing a carbon-silicon / carbon composite, the method comprising the following steps: forming a silicon / carbon composite matrix on the surface and inside the pores of a porous carbon support to prepare a carbon-silicon / carbon composite. According to an embodiment of the present invention, prior to the step of preparing the carbon-silicon / carbon composite, the method may further include: step 1, synthesizing asphalt by pyrolysis and polycondensation of petroleum feedstock; step 2, obtaining granular asphalt by solidifying and granulating the asphalt, or obtaining powdered asphalt by solidifying, granulating and pulverizing the asphalt; step 3, stabilizing the granular asphalt or powdered asphalt; step 4, carbonizing the stabilized asphalt to obtain carbides; and step 5, initiating the carbides to obtain a porous carbon support. In addition, the silicon / carbon composite matrix can be formed by composite CVD of silicon source and carbon source on the porous carbon support. In addition, the gas flow rate ratio of the silicon source to the carbon source can be 1:0.1 to 1:2. In addition, the present invention provides a negative electrode active material comprising the above-mentioned carbon-silicon / carbon composite. Furthermore, this invention provides an all-solid-state battery comprising a solid electrolyte interphase (SEI) membrane, wherein the solid electrolyte interphase membrane comprises the aforementioned carbon-silicon / carbon composite. Beneficial effects In embodiments of the present invention, a silicon / carbon composite matrix is ​​formed on the pores and / or surface of a porous carbon support with a high mesopore ratio in the overall pore structure. When this carbon-silicon / carbon composite is used as a negative electrode active material, the overall silicon size can be suppressed to a small size, and the intermediate phase crystal-Li that affects battery performance degradation can be suppressed. x Si y (For example, Li) 15 Si 4 or Li 3.75 The formation of Si can alleviate the degradation of battery performance during repeated charging and discharging. Furthermore, the preparation method of the embodiments of the present invention can easily prepare carbon-silicon / carbon composites having the above-mentioned characteristics. This invention is not limited to the contents disclosed below. It can be modified in various ways as long as the spirit of the invention is not changed. In this specification, unless otherwise stated, "comprising" means may also include other constituent elements. Unless otherwise stated, in all cases, all figures and expressions representing the amounts of components and reaction conditions described in this specification shall be understood to be modified by the term "about". The present invention will now be described in more detail. Carbon-silicon / carbon composite According to one embodiment of the present invention, a carbon-silicon / carbon composite is provided, comprising: a porous carbon support, wherein the volume ratio of mesopores with a pore size of 2 nm to 50 nm is 5% to 80% based on the total pore volume; and a silicon / carbon composite matrix located on the surface and inside the pores of the porous carbon support. The constituent elements of a carbon-silicon / carbon composite according to an embodiment of the present invention will be described below. Porous carbon support The carbon-silicon / carbon composite of an embodiment of the present invention comprises a porous carbon support. Based on the total pore volume, the volume ratio of mesopores with a pore size of 2nm to 50nm in the porous carbon support can be 5% to 80%, preferably 30% to 60%, and more preferably 40% to 50%. When the mesopore volume ratio of the porous carbon support is less than 5%, there are too many micropores, which can form a relatively large amount of silicon / carbon composite matrix on the outside of the particles. When the mesopore volume ratio of the porous carbon support exceeds 80%, due to insufficient particle hardness, if it is used to prepare electrodes, there is a risk of electrode structure collapse. In addition, the porous carbon support may have a diameter of 300m. 2 / g~3000m 2 The BET specific surface area is 300 m² / g. Preferably, the porous carbon support has a specific surface area of ​​300 m² / g. 2 / g~1500m 2 The BET specific surface area per g, more preferably, can be 500 m² / g. 2 / g~1500m 2 / g BET specific surface area. When the BET specific surface area of ​​porous carbon support is less than 300m². 2 At a density of / g, excessive macropores can lead to insufficient effective pores. When the BET specific surface area of ​​the porous carbon support exceeds 3000m², this can cause problems. 2 At / g, excessive micropores allow for the deposition of a relatively large amount of silicon / carbon composite matrix on the outside of the particles. Furthermore, the porous carbon support may have a tap density of 0.05 g / ml to 0.5 g / ml. Preferably, the porous carbon support may have a tap density of 0.05 g / ml to 0.3 g / ml, and more preferably, it may have a tap density of 0.1 g / ml to 0.3 g / ml. When the tap density of the porous carbon support is less than 0.05 g / ml, the yield may decrease due to difficulty in controlling the process during the formation of the silicon / carbon composite matrix. When the tap density of the porous carbon support exceeds 0.5 g / ml, it may be difficult to uniformly form the matrix during the formation of the silicon / carbon composite matrix. Furthermore, the porous carbon support can have an average particle size of 1 μm to 20 μm. Preferably, the porous carbon support can have an average particle size of 3 μm to 20 μm, and more preferably, it can have an average particle size of 3 μm to 10 μm. When the average particle size of the porous carbon support is less than 1 μm, the silicon / carbon composite matrix cannot fully penetrate into the pores and only forms in large quantities on the outside of the particles. When the average particle size of the porous carbon support exceeds 20 μm, the silicon / carbon composite matrix is ​​difficult to form sufficiently within the pores. The carbon-silicon / carbon composite of the present invention comprises a porous carbon support having the above-described properties. When used as a negative electrode active material, this carbon-silicon / carbon composite exhibits excellent electrical conductivity and can alleviate stress caused by silicon volume expansion. Silicon / carbon composite matrix The carbon-silicon / carbon composite of an embodiment of the present invention comprises a silicon / carbon composite matrix located on the surface and inside the pores of the porous carbon support. In this invention, the silicon / carbon composite matrix can refer to a continuous phase consisting of a silicon portion formed by Si-Si bonding and a silicon carbide portion formed by Si-C bonding (Si... x C y ). In a specific embodiment of the present invention, as described below, silicon and carbon sources can be composite CVD on a porous carbon support to obtain a carbon-silicon / carbon composite. In a specific embodiment of the present invention, the silicon / carbon composite matrix may contain crystalline silicon particles. In this case, the size of the silicon crystals can be at the nanometer level. Specifically, the average size of the silicon crystals in the silicon / carbon composite matrix can be less than 10 nm. Preferably, the average size of the silicon crystals in the silicon / carbon composite matrix can be less than 8 nm, less than 5 nm, less than 3 nm, or less than 1 nm. When the average size of the silicon crystals in the silicon / carbon composite matrix meets the above range, the stress due to silicon volume expansion decreases, thus improving the lifetime characteristics of the negative electrode active material. On the other hand, the fact that the average particle size of the silicon crystals meets the above range may be because Si-Si bonding is preferred over Si-C bonding. On the other hand, since the carbon-silicon / carbon composite contains the silicon / carbon composite matrix, the silicon content in the total weight of the carbon-silicon / carbon composite can be 20% to 70% by weight, preferably 25% to 65% by weight. If the silicon content in the total weight of the carbon-silicon / carbon composite is less than 20% by weight, the capacitance can be reduced; if it exceeds 70% by weight, the problem caused by silicon volume expansion during charging and discharging cannot be solved, which can lead to structural damage to the negative electrode material and reduced cycle characteristics. Furthermore, the silicon / carbon composite matrix may account for 10% to 90% by weight of the total weight of the carbon-silicon / carbon composite, preferably 15% to 85% by weight. If the silicon / carbon composite matrix accounts for less than 10% by weight of the total weight of the carbon-silicon / carbon composite, the capacitance may be reduced. If it exceeds 90% by weight, the problem caused by silicon volume expansion during charging and discharging cannot be solved, which may lead to structural damage to the negative electrode material and reduced cycle characteristics. On the other hand, the silicon can be crystalline or amorphous, preferably amorphous or a similar phase. When the silicon is crystalline, the smaller the crystallites, the denser the composite material, thus strengthening the matrix and preventing cracking. Therefore, the initial efficiency or cycle life characteristics of the secondary battery can be improved. The silicon may further comprise silicon oxide compounds. Silicon oxide compounds may be derived from the general formula SiO₂. x (0.5≦x≦2) indicates that when x is less than 0.5, expansion and contraction can increase and lifespan characteristics can deteriorate during the charging and discharging of the secondary battery. When x exceeds 2, the initial efficiency of the secondary battery can be reduced with the increase of inactive oxides. Based on the total weight of the silicon, the content of silicon oxide compounds in the silicon can be less than 50% by weight. When the content of silicon oxide compounds in the silicon exceeds 50% by weight, the initial efficiency of the secondary battery can be reduced. On the other hand, the c / a peak ratio of the carbon-silicon / carbon composite can be 0~1.5, preferably 0~1.3, more preferably 0~1.2, further preferably 0~1.18, and most preferably 0~1.15. As the c / a peak ratio of the carbon-silicon / carbon composite satisfies the above range, it is more advantageous to achieve the objectives of the present invention (such as maintaining stable electrochemical performance during lifetime evaluation). Here, the c / a peak ratio represents the peak ratio of the crystalline (c) to the amorphous (a) form. Preparation method of carbon-silicon / carbon composite. An embodiment of the present invention provides a carbon-silicon / carbon composite prepared by a method comprising the following steps: forming a silicon / carbon composite matrix on the surface and inside the pores of a porous carbon support to prepare the carbon-silicon / carbon composite. On the other hand, according to an embodiment of the present invention, prior to the step of preparing the carbon-silicon / carbon composite, the method may further include: step 1, synthesizing asphalt by pyrolysis and polycondensation of petroleum feedstock; step 2, obtaining granular asphalt by solidifying and granulating the asphalt, or obtaining powdered asphalt by solidifying, granulating and pulverizing the asphalt; step 3, stabilizing the granular asphalt or powdered asphalt; step 4, carbonizing the stabilized asphalt to obtain carbides; and step 5, activating the carbides to obtain a porous carbon support. The following describes the steps of a method for preparing a carbon-silicon / carbon composite according to an embodiment of the present invention. Step 1 In step 1, asphalt can be synthesized by pyrolysis and condensation of petroleum-based raw materials. In specific embodiments of the present invention, the petroleum feedstock may include at least one selected from the group consisting of pyrolysis fuel oil (PFO), naphtha cracking residue (NCB), ethylene cracker bottom oil (EBO), vacuum residue (VR), deasphalted oil (DAO), atmospheric residue (AR), fluidized bed catalytic cracking decant oil (FCC-DO), residue fluid catalytic cracking decant oil (RFCC-DO), and heavy aromatic oil. In a preferred embodiment of the present invention, the petroleum feedstock may include pyrolysis fuel oil. In a specific embodiment of the present invention, the petroleum-based feedstock may contain aromatic compounds at a content of 10% to 90% by weight. Preferably, the petroleum-based feedstock may contain aromatic compounds at a content of 20% to 80% by weight, and more preferably, at a content of 30% to 70% by weight. When the content of aromatic compounds in the petroleum-based feedstock meets the above range, a porous carbon support with controlled pore characteristics can be obtained even if the solid-phase asphalt particles described later are stabilized, carbonized, and started without separate pulverization. In specific embodiments of the present invention, the aromatic compound may be a compound having one to four aromatic rings. Specifically, the aromatic compound may contain at least one selected from the group consisting of substituted or unsubstituted benzene, naphthalene, phenanthrene, indene, biphenyl, anthracene, tetrahydronaphthalene, and fluorene. In this case, even if the solid pitch particles described later are stabilized, carbonized, and started without being individually pulverized, a porous carbon support with controlled pore characteristics can be obtained. In specific embodiments of the present invention, the pyrolysis and polycondensation of petroleum-based raw materials can be carried out at a temperature of 350°C to 500°C. In preferred embodiments of the present invention, the pyrolysis and polycondensation of petroleum-based raw materials can be carried out at a temperature of 400°C to 500°C. In even more preferred embodiments of the present invention, the pyrolysis and polycondensation of petroleum-based raw materials can be carried out at a temperature of 430°C to 470°C. When the pyrolysis and polycondensation temperature of the petroleum-based raw materials is 350°C to 500°C, asphalt containing a large amount of relatively low molecular weight components can be prepared. During the initiation process of step 5 described later, the relatively low molecular weight components are first vaporized, and mesopores can be fully formed on the carbon support. If the pyrolysis and polycondensation temperature of the petroleum-based raw materials is below 350°C, it is difficult to prepare solid asphalt at room temperature. When the temperature exceeds 500°C, it is difficult to prepare a carbon support with mesopores because the asphalt contains a large amount of relatively high molecular weight components. In specific embodiments of the present invention, the pyrolysis and polycondensation of petroleum feedstocks can be carried out in an atmosphere of oxidizing gas, inert gas, or a mixture thereof. In preferred embodiments of the present invention, the oxidizing gas can be oxygen, ozone, or a combination thereof, the inert gas can be nitrogen, helium, neon, argon, or a combination thereof, and the mixture thereof can be air, but is not particularly limited thereto. When oxidizing gases are used in the pyrolysis and polycondensation of petroleum feedstocks, asphalt with a high softening point can be produced, but pyrolysis and polycondensation are difficult to achieve at high temperatures. When inert gases are used in the pyrolysis and polycondensation of petroleum feedstocks, pyrolysis and polycondensation can be carried out at high temperatures, but it is difficult to produce asphalt with a relatively high softening point. When a mixture of oxidizing and inert gases is used in the pyrolysis and polycondensation of petroleum feedstocks, asphalt with a relatively high softening point can be produced by carrying out pyrolysis and polycondensation at relatively high temperatures. In a specific embodiment of the present invention, during the pyrolysis and polycondensation of petroleum feedstocks, the aforementioned gas can be supplied at a flow rate of 10 ml / min to 800 ml / min. In a preferred embodiment of the present invention, during the pyrolysis and polycondensation of petroleum feedstocks, the aforementioned gas can be supplied at a flow rate of 100 ml / min to 500 ml / min. When the flow rate of the aforementioned gas is less than 10 ml / min, although the yield of asphalt increases, there is an excessive amount of low molecular weight components, which is therefore detrimental to subsequent processes (e.g., stabilization). When the flow rate of the aforementioned gas exceeds 800 ml / min, the yield of asphalt may decrease. In specific embodiments of the present invention, the pyrolysis and polycondensation of petroleum-based raw materials can be carried out for 1 to 10 hours. In preferred embodiments of the present invention, the pyrolysis and polycondensation of petroleum-based raw materials can be carried out for 2 to 8 hours. In even more preferred embodiments of the present invention, the pyrolysis and polycondensation of petroleum-based raw materials can be carried out for 2 to 7 hours. When the pyrolysis and polycondensation time of petroleum-based raw materials is less than 1 hour, it is difficult to prepare asphalt with a high softening point; when the pyrolysis and polycondensation time of petroleum-based raw materials exceeds 10 hours, an excessive amount of quinoline-insoluble components may be generated. In a specific embodiment of the present invention, the pyrolysis and polycondensation of petroleum feedstocks can be carried out under stirring conditions. There are no particular limitations on the stirring conditions for the petroleum feedstocks; for example, a stirrer rotating at 10 rpm to 500 rpm can be used. In a specific embodiment of the present invention, the asphalt synthesized in step 1 may have a softening point of 200°C to 350°C. In a preferred embodiment of the present invention, the asphalt may have a softening point of 200°C to 330°C. In a more preferred embodiment of the present invention, the asphalt may have a softening point of 200°C to 300°C. The asphalt prepared according to the present invention has a high softening point, and when used as a precursor for preparing a carbon support, it is easy to perform the stabilization process, and a high yield can be obtained after carbonization and start-up. In a specific embodiment of the present invention, the yield of the synthesized asphalt in step 1 can be 10% to 50% by weight. In a preferred embodiment of the present invention, the yield of asphalt can be 10% to 40% by weight. In a more preferred embodiment of the present invention, the yield of asphalt can be 20% to 30% by weight. In a specific embodiment of the present invention, a pretreatment step for petroleum-based raw materials may be performed before step 1 described above. This pretreatment step removes low-boiling-point components from the petroleum-based raw materials, thereby enabling the preparation of asphalt with a higher softening point. In a specific embodiment of the present invention, the pretreatment step can be carried out at a temperature that is the same as or lower than the pyrolysis and polycondensation temperature of the petroleum-based raw materials in step 1, but is not particularly limited to this condition. Specifically, the pretreatment step can be carried out at a temperature of 250°C to 450°C, preferably 250°C to 400°C, and more preferably 300°C to 400°C. In a specific embodiment of the present invention, the pretreatment step may be carried out for the same or shorter time as the pyrolysis and polycondensation time of the petroleum-based raw material in step 1, but is not particularly limited to this condition. Specifically, the pretreatment step may be carried out for 1 hour to 8 hours, preferably 1 hour to 6 hours, and more preferably 1 hour to 5 hours. In addition, in step 2, granular asphalt can be obtained by solidifying and granulating the asphalt, or powdered asphalt can be obtained by solidifying, granulating and pulverizing the asphalt. First, regarding granular asphalt, for example, the asphalt (liquid phase) obtained in step 1 is solidified and granulated to the desired size to obtain solid asphalt particles (granular asphalt). The process of obtaining solid asphalt particles by extruding, cooling, and granulating liquid asphalt can be carried out using commercially available equipment. For example, this process can be carried out using IPCO's dual-belt cooler and flaker, but is not particularly limited to this equipment. The asphalt particles (granular asphalt) obtained in step 2 have an average particle size of 1 mm to 30 mm, preferably 5 mm to 25 mm. When the average particle size of the asphalt particles (granular asphalt) is within this range, the porous carbon support can be prepared by stabilizing, carbonizing and activating the asphalt particles (granular asphalt) as described later, without the need for separate pulverization. Furthermore, regarding powdered asphalt, the asphalt particles (granular asphalt) can be further decomposed, pulverized, and classified. Decomposition or pulverization can further micronize the asphalt particles (granular asphalt), and classification can ensure a uniform particle size distribution. Classification can utilize dry classification, wet classification, or sieve-based classification. Through decomposition, pulverization, and classification, powdered asphalt with an average particle size of 50 μm to 500 μm can be obtained. Furthermore, in step 3, a step of stabilizing the granular or powdered asphalt can be performed. First, the granular or powdered asphalt obtained in step 2 is subjected to a first oxidation process to stabilize the carbon structure of the asphalt. In a specific embodiment of the invention, the stabilization can be carried out in an oxidizing gas atmosphere. In a preferred embodiment of the invention, the stabilization can be carried out in an air atmosphere, but is not particularly limited thereto. In a specific embodiment of the present invention, the stabilization can be carried out at a temperature of 100°C to 500°C, preferably 150°C to 300°C. When the stabilization is carried out at this temperature, the carbon structure in the granular or powdered asphalt can change from thermoplastic to thermosetting, and the structure can be stably maintained during subsequent carbonization. At this time, the heating rate can be 2°C / min to 10°C / min. If the heating rate is too slow, the productivity may be poor; if the heating rate is too fast, it may be difficult to achieve uniform stabilization. In a specific embodiment of the present invention, the stabilization can be carried out under pressure conditions of 0.1 bar to 10 bar, preferably 0.5 bar to 5 bar. When the stabilization is carried out under these pressure conditions, the structural stabilization of the carbon inside the granular or powdered asphalt can be fully achieved. In a specific embodiment of the present invention, the stabilization can be carried out under oxidizing gas conditions of 0.1 ml / min to 500 ml / min, preferably 1 ml / min to 300 ml / min, and more preferably, under air flow conditions. When the stabilization is carried out under these oxidizing gas flow conditions, the carbon structure within granular or powdered asphalt can be sufficiently stabilized. In a specific embodiment of the present invention, the stabilization process can be carried out for 1 to 10 hours, preferably 2 to 8 hours. When the stabilization is carried out within this time period, the carbon structure within the granular or powdered asphalt can be sufficiently stabilized. Furthermore, in step 4, the stabilized asphalt is carbonized to obtain carbides. Through the carbonization of the stabilized asphalt, other functional groups contained in the asphalt can be removed, and carbides that are actually composed of pure carbon can be obtained. In a specific embodiment of the invention, the carbonization can be carried out under an inert gas atmosphere. In a preferred embodiment of the invention, the carbonization can be carried out under a nitrogen or argon atmosphere, but is not particularly limited thereto. In a specific embodiment of the present invention, the carbonization can be carried out at a temperature exceeding 700°C but below 1000°C, preferably 800°C to 900°C. When the carbonization temperature is below this range, carbonization may not be sufficiently achieved, and when the carbonization temperature is above this range, the carbonization yield may decrease. In a specific embodiment of the present invention, the carbonization can be carried out under inert gas conditions of 0.1 ml / min to 30 ml / min, preferably 0.1 ml / min to 10 ml / min, and more preferably, under nitrogen flow conditions. When the carbonization is carried out under these inert gas flow conditions, the stabilized asphalt can be fully carbonized. In a specific embodiment of the present invention, the carbonization can be carried out for 0.5 hours to 5 hours, preferably 1 hour to 3 hours. When the carbonization is carried out within this time period, the stabilized asphalt can be fully carbonized. Furthermore, in step 5, the carbide is activated to obtain a porous carbon support. Pores can be formed on the carbide through activation, thereby obtaining a porous carbon support. In a specific embodiment of the invention, the initiation of the carbide can be carried out in an oxidizing gas atmosphere. In a preferred embodiment of the invention, the initiation of the carbide can be carried out in a water vapor atmosphere, but is not particularly limited thereto. In a specific embodiment of the present invention, the initiation of the carbide can be carried out at a temperature exceeding 700°C but below 1000°C, preferably 800°C to 900°C. When the initiation of the carbide is carried out under this temperature condition, a porous carbon support with sufficiently formed micropores and mesopores can be obtained. In a specific embodiment of the present invention, the initiation of the carbide can be carried out under a pressure of 0.1 bar to 10 bar, preferably 0.1 bar to 5 bar. When the initiation of the carbide is carried out under this pressure condition, a porous carbon support with sufficient micropores and mesopores can be obtained. In a specific embodiment of the present invention, the initiation of the carbide can be carried out under oxidizing gas conditions with a flow rate of 0.1 ml / min to 100 ml / min, preferably 0.1 ml / min to 50 ml / min, and more preferably under water vapor flow conditions. When the initiation of the carbide is carried out under these oxidizing gas flow conditions, a porous carbon support with sufficiently formed micropores and mesopores can be obtained. In a specific embodiment of the present invention, the initiation of the carbide can be carried out for 0.5 hours to 5 hours, preferably 1 hour to 3 hours. When the initiation of the carbide is carried out within this time period, a porous carbon support with sufficient micropores and mesopores can be obtained. In a specific embodiment of the present invention, the stabilization, carbonization, and start-up in steps 3 to 5 above can be performed in a microwave heating furnace. In a preferred embodiment of the present invention, the stabilization, carbonization, and start-up in steps 3 to 5 above can all be performed in a microwave heating furnace. Using a microwave heating furnace is preferred because it can increase the temperature of the asphalt itself without increasing the external temperature of the asphalt, but it is not particularly limited thereto. In a specific embodiment of the present invention, steps 3 to 5 can be performed continuously in one apparatus. In a preferred embodiment of the present invention, steps 3 to 5 can be performed continuously in a rotary kiln, but are not particularly limited to this apparatus. The continuous performance of steps 3 to 5 in one apparatus optimizes the process. In a specific embodiment of the present invention, the porous carbon support obtained in step 5 can be further decomposed or pulverized and classified. The porous carbon support can be further micronized through decomposition or pulverization, and the particle size distribution of the porous carbon support can be made uniform through classification. Classification can be performed using dry classification, wet classification, or classification using sieves. Through decomposition or pulverization and classification, an average particle size of 1μm~20μm and a BET specific surface area of ​​300m² can be obtained. 2 ~3000m 2 / g and a tap density of 0.05g / ml to 0.5g / ml. In addition, in the porous carbon support powder, based on the total pore volume, the volume ratio of mesopores with a pore size of 2nm to 50nm is 5% to 80%. On the other hand, when stabilizing, carbonizing and starting the granular asphalt in step 2 above to obtain a porous carbon support without further pulverizing the asphalt, the carbon support can be pulverized (or further classified) to make it have an average particle size of 1μm to 20μm, but is not limited thereto. Next, a silicon / carbon composite matrix is ​​formed on the surface and inside the pores of the porous carbon support to prepare a carbon-silicon / carbon composite. At this point, the formation of the silicon / carbon composite matrix can be carried out using apparatus (e.g., rotary kiln) and methods (e.g., chemical vapor deposition, CVD) known in the art to which this invention pertains. Specifically, the silicon / carbon composite matrix can be formed on the surface and inside the pores of the porous carbon support by performing a composite CVD that simultaneously supplies silicon and carbon sources to the porous carbon support and performs CVD. In a specific embodiment of the present invention, the silicon source may comprise silane (SiH₂O) selected from silanes. 4) Dichlorosilane (SiH) 2Cl 2) Silicon tetrafluoride (SiF) 4) Silicon tetrachloride (SiCl) 4) Methylsilane (CH4) 3SiH 3) and silane (Si) 2H At least one of 6), but not particularly limited thereto. Additionally, the carbon source may include at least one selected from the group consisting of methane, ethane, propane, butane, methanol, ethanol, propanol, propylene glycol, butane glycol, ethylene, propylene, butene, butadiene, cyclopentene, acetylene, benzene, toluene, xylene, ethylbenzene, naphthalene, anthracene, and dibutylhydroxytoluene, but is not particularly limited thereto. Furthermore, the composite CVD can be performed at temperatures ranging from 300°C to 600°C, preferably from 450°C to 550°C. The composite CVD can also be performed under atmospheric pressure, and, if necessary, under a low vacuum of approximately 10 Torr. In the composite CVD, based on a charge of 10g to 100g, the silicon source can be supplied at a charge flow rate of 100sccm to 1000sccm, and the silicon source to carbon source can be supplied at a weight ratio of 1:0.1 to 2, preferably 1:0.15 to 1:1.9. If the weight ratio of silicon source to carbon source exceeds 1:2 (silicon source less than 1, carbon source more than 2), then with the formation of a relatively large amount of SiC... x The capacitance and cycle characteristics can decrease if the weight ratio is less than 1:0.1 (silicon source greater than 1, carbon source less than 0.1), because a relatively small amount of SiC can be formed. x Furthermore, the formation of a relatively large amount of Si means that the problem caused by silicon volume expansion during charging and discharging cannot be resolved, potentially leading to structural damage to the negative electrode material. (Negative electrode active material) According to another embodiment of the present invention, a negative electrode active material comprising the carbon-silicon / carbon composite is provided. The negative electrode active material in an embodiment of the present invention may comprise a carbon-silicon / carbon composite. In addition to carbon-silicon / carbon composites, the negative electrode active material of embodiments of the present invention may further include carbon-based negative electrode materials, specifically graphite-based negative electrode materials. For example, the negative electrode active material can be obtained by mixing the carbon-silicon / carbon composite of embodiments of the present invention with a carbon-based negative electrode material (e.g., a graphite-based negative electrode material). For example, carbon-based anode materials may include at least one selected from the group consisting of natural graphite, artificial graphite, soft carbon, hard carbon, mesophase carbon, carbon fiber, carbon nanotubes, pyrolytic carbon, coke, sintered organic polymer compounds, and carbon black, but are not particularly limited thereto. In the negative electrode active material of the present invention, the content of carbon-based negative electrode material relative to the total weight of the negative electrode active material can be 2% to 80% by weight, preferably 5% to 70% by weight, and more preferably 30% to 70% by weight. The negative electrode active material of the embodiments of the present invention can be effectively used in the preparation of secondary batteries, specifically as the negative electrode of lithium secondary batteries and the negative electrode of all-solid-state batteries. All-solid-state battery According to another embodiment of the present invention, an all-solid-state battery is provided, the all-solid-state battery comprising a solid electrolyte interphase (SEI) membrane containing the carbon-silicon / carbon composite. The all-solid-state battery may be an all-solid-state battery comprising a positive electrode, a negative electrode, and a solid electrolyte between the positive electrode and the negative electrode. The negative electrode may comprise a negative electrode active material layer, and at least a portion of the negative electrode active material particles in the negative electrode active material layer may comprise a solid electrolyte interphase (SEI) film comprising a carbon-silicon / carbon composite. On the other hand, the negative electrode active material particles can be carbon-based negative electrode materials. In this case, their contents can be the same as those described in the above description of negative electrode active materials, so the relevant descriptions will be omitted. Furthermore, apart from the negative electrode active material particles and SEI film of the all-solid-state battery, the negative electrode structure, positive electrode structure, and solid electrolyte structure can be adapted from conventional all-solid-state battery structures, and therefore are not particularly limited in this invention. [Example] The present invention will now be described in more detail through embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. <Embodiment 1> 300g of petroleum residue oil (YNCC, HTC PFO (pyrolysis fuel oil)) was added to a reactor equipped with a stirrer, and nitrogen was supplied at a flow rate of 100ml / min. The mixture was pyrolyzed and polycondensed at 450°C for 3 hours. During this time, the stirrer was rotated at 200rpm (step 1) to mix the reactants. The polymerized asphalt was solidified and granulated to obtain solid asphalt particles with an average particle size of 1mm~30mm. The solid asphalt particles obtained above were pulverized and prepared into asphalt particles with an average particle size of 200 μm (step 2). They were then fed into a rotary kiln with three zones and subjected to stabilization (step 3), carbonization (step 4), and start-up (step 5) in sequence. The conditions for stabilization, carbonization, and start-up are shown in Table 1 below. The specific surface area of ​​the carbon support was determined using a Belserp mini II according to ASTM D4820-93. The tap density of the carbon support was determined using a tap density analyzer (Electrolab ETD-1020x) according to ASTM B527. The average particle size of the carbon support was determined using a particle size analyzer (Horiba, Japan, laser particle size analyzer, LA-960V2) according to ASTM E112. The results are shown in Table 1. Table 1 The porous carbon support of the reference example was pulverized using a pulverizer (NETSCH, Germany, air jet mill) to obtain porous carbon support micropowder with an average particle size of 7 μm. Then, 15 g of this porous carbon support micropowder was loaded into a rotary CVD (rotating CVD) device and subjected to an inactive atmosphere (N2). 2) After heating to 475℃, SiH 4:C 2H Composite CVD was performed for 1 hour at a gas flow rate of 450 sccm:144 sccm (silicon source to carbon source gas flow rate ratio of 1:0.32) to form a silicon / carbon composite matrix on the surface and inside the pores of a porous carbon support, thereby preparing a carbon-silicon / carbon composite. <Example 2> Implemented in the same manner as in Example 1, and SiH 4:C 2H The gas flow rate of 4 = 450 sccm: 144 sccm is changed to SiH 4:C 2H A gas flow rate of 450 sccm:108 sccm (gas flow rate ratio of silicon source to carbon source is 1:0.24) was used to prepare carbon-silicon / carbon composites. <Example 3> Implemented in the same manner as in Example 1, and SiH 4:C 2H The gas flow rate of 4 = 450 sccm: 144 sccm is changed to SiH 4:C 2H A gas flow rate of 150 sccm:450 sccm (silicon source to carbon source gas flow rate ratio of 1:3) was used to prepare carbon-silicon / carbon composites. <Comparative Example> The procedure was carried out in the same manner as in Example 1, but without composite CVD, at 450 sccm in SiH After deposition for 1 hour at a gas flow rate of 4 and a temperature of 475°C, the deposition was changed to a gas flow rate of C2H4:Ar = 100 sccm: 900 sccm and a temperature of 700°C for 1 hour to prepare a carbon-silicon / carbon composite. <Experimental Example 1> (1) Scanning Electron Microscopy (SEM) Analysis The carbon-silicon / carbon composite prepared according to Example 1 was observed using a scanning electron microscope (SEM). The SEM analysis results are shown in Figure 1. The results confirm that, as shown in Figure 1, a uniform silicon / carbon composite matrix is ​​formed on the surface and inside the pores of the porous carbon support. (2) Electrochemical evaluation Electrochemical evaluations were performed after half-button batteries were prepared using the composites from Examples 1, 2, 3, and the comparative examples. The preparation conditions for the half-button batteries are shown in Table 2, and the evaluation results are shown in Tables 3-4 and Figure 2. In Table 2, AM, CM, and BM represent the active material (carbon-silicon / carbon composite), conductor (Super P carbon black), and binder (styrene-butadiene rubber / carboxymethyl cellulose 5:5), respectively; EC, EMC, DMC, FEC, VC, and PS represent ethylene carbonate, methyl ethyl carbonate, dimethyl carbonate, vinyl fluorocarbonate, vinylene carbonate, and propane sulpholone, respectively. Table 2 Table 3 Table 4 From Tables 3-4 and Figure 2 above, it can be confirmed that Examples 1 and 2 exhibit a reversible capacity of approximately 2000 mAh / g, and the peak near 0.45V of the suSi phase is significantly lower, indicating that a high CE of over 99.6% is achieved after 25 cycles. In contrast, regarding Example 3 (1:3), which exceeds the gas flow ratio range of silicon source to carbon source during composite CVD, it can be confirmed that in the silicon / carbon composite matrix, carbon is more dominant than silicon, resulting in a lower capacity and a lower ICE. Furthermore, it can be confirmed that since the comparative example is not a composite matrix in which silicon and carbon are bonded together, the cycle retention rate is significantly reduced. (3) dq / dV determination (determination related to c-LiSi phase) For Examples 1, 2, and Comparative Example 1, formation (CC-CV) was performed using a charge-discharge rate (C-rate) calculated based on the Si loading of the negative electrode material, with cut-off (CV) conditions of 0.1C-0.1C and 0.005V / 0.01C. Then, dQ / dV (d(Q-Qo) / dE) was exported using the collected data. In this invention, dQ / dV is calculated and exported using the analysis process of EC-Lab. This is shown in Figure 3. The results showed that the c / a peak ratio of Example 1 was 0.66, that of Example 2 was 0.64, and that of the comparative example was 2.72. Compared with Comparative Example 1, Examples 1 and 2 formed less c-LiSi phase, which is expected to result in stable electrochemical performance retention during lifetime evaluation. (4) XRD analysis The carbon-silicon / carbon composite of Example 1 was analyzed by XRD under the following conditions, shown in Figure 4. - Equipment: D-MAX 2200 (RIGAKU) - Angle: 20°~70° - Sampling W.: 0.01 - X-ray: 40kV / 30mA - DivSlit: 1 / 2 deg. - DivH.L.Slit: 10mm - SctSlit: 1 / 2 deg - RecSlit: 0.15mm. The results showed that the carbon-silicon / carbon composite in Example 1 did not have a Si crystalline peak, nor a SiC peak. <Examples 1-1 to Examples 1-3> The composite from Example 1 was heat-treated at 600°C (Example 1-1), 700°C (Example 1-2), and 900°C (Example 1-3), respectively. Experimental Example 2 (1) XRD Analysis XRD analysis was performed on the complexes of Example 1, Examples 1-1 to 1-3 and the comparative examples. Specifically, the composite of Example 1, the heat-treated composites of Examples 1-1 to 1-3, and the composite of the comparative example were analyzed by XRD under the following conditions. These are shown in Figure 5. - Equipment: D-MAX 2200 (RIGAKU) - Angle: 20°~70° - Sampling W.: 0.01 - X-ray: 40kV / 30mA - DivSlit: 1 / 2 deg. - DivH.L.Slit: 10 mm - SctSlit: 1 / 2 deg. - RecSlit: 0.15 mm The results show that, in the comparative example, at a temperature of 700 °C, a distinct Si peak (Si peak) was observed in the carbon-coated crystals according to the attachment, as mentioned above, which resulted in poor lifetime assessment. In addition, regarding the heat-treated composite, no clear Si and SiC peaks were observed even when heat-treated to 700℃, and broad amorphous peaks were observed between 28℃ and 32℃. Furthermore, during heat treatment at 900℃, peaks of SiC(111), SiC(220), and Si(111) were observed. The crystallite size was then calculated using these peaks, yielding the following results: - SiC(111): 1.1 nm - SiC(220): 2.4 nm - Si(111): 4.8 nm The above results confirm that a silicon-carbon composite matrix is ​​formed on a porous carbon support, thereby controlling the size of the Si crystals. The above describes one embodiment of the present invention. However, the concept of the present invention is not limited to the embodiment presented in this specification. Those skilled in the art who understand the concept of the present invention can easily propose other embodiments by adding, changing, deleting, and adding constituent elements within the same conceptual scope, but this also falls within the conceptual scope of the present invention. none Figure 1 is a SEM image of a carbon-silicon / carbon composite (Example 1) according to an embodiment of the present invention. Figure 2 is a graph showing the electrochemical evaluation results (charge-discharge efficiency, ICE, and capacity retention) of Examples 1, 2, and Comparative Example 1 of the present invention. Figure 3 is a graph showing the dQ / dV measurement curves of Examples 1, 2 and Comparative Example 1 of the present invention. Figure 4 is an XRD analysis result image of a carbon-silicon / carbon composite (Example 1) according to an embodiment of the present invention. Figure 5 shows the XRD analysis results of the carbon-silicon / carbon composite (Example 1) of the comparative example and an embodiment of the present invention at each heat treatment temperature (Examples 1-1 to Examples 1-3). Domestic storage information (please note in order of storage institution, date, and number): None Overseas storage information (please note in the order of storage country, institution, date, and number): None

Claims

1. A carbon-silicon / carbon composite comprising: a porous carbon support having a mesopore volume ratio of 5% to 80% with a pore size of 2 nm to 50 nm based on the total pore volume; and a silicon / carbon composite matrix comprising a continuous phase consisting of a silicon portion formed by Si-Si bonding and a silicon carbide portion formed by Si-C bonding, located on the surface and inside the pores of the porous carbon support.

2. The carbon-silicon / carbon composite of claim 1, wherein the porous carbon support has a BET specific surface area of ​​300 m² / g to 3000 m² / g, a tap density of 0.05 g / ml to 0.5 g / ml, and an average particle size of 1 μm to 20 μm.

3. The carbon-silicon / carbon composite of claim 1, wherein the silicon content in the total weight of the carbon-silicon / carbon composite is 20% to 70% by weight.

4. The carbon-silicon / carbon composite of claim 1, wherein the silicon / carbon composite matrix accounts for 10% to 90% by weight of the total weight of the carbon-silicon / carbon composite.

5. The carbon-silicon / carbon composite of claim 1, wherein the average size of the silicon crystals in the silicon / carbon composite matrix is ​​less than 10 nm.

6. The carbon-silicon / carbon composite of claim 1, wherein the c / a peak ratio of the carbon-silicon / carbon composite is 0 to 1.5, and the c / a peak ratio is the peak ratio of crystalline (c) to amorphous (a).

7. A method for preparing a carbon-silicon / carbon composite, comprising the following steps: forming a silicon / carbon composite matrix by composite CVD with a silicon source and a carbon source on the surface and inside the pores of a porous carbon support, thereby preparing the carbon-silicon / carbon composite.

8. The method for preparing the carbon-silicon / carbon composite as claimed in claim 7, further comprising, prior to the step of preparing the carbon-silicon / carbon composite: Step 1: Synthesize asphalt by pyrolysis and polycondensation of petroleum feedstock; Step 2: Obtain granular asphalt by solidification and granulation, or obtain powdered asphalt by solidification, granulation and pulverization; Step 3: Stabilize the granular or powdered asphalt; Step 4: Carbonize the stabilized asphalt to obtain carbides; and Step 5: Initiate the formation of pores in the carbides to obtain a porous carbon carrier.

9. The method for preparing the carbon-silicon / carbon composite as claimed in claim 9, wherein the gas flow rate ratio (sccm) of the silicon source to the carbon source is 1:0.1 to 1:

2.

10. A negative electrode active material comprising a carbon-silicon / carbon composite as described in any one of claims 1 to 6.

11. An all-solid-state battery, comprising a solid electrolyte interface membrane, said solid electrolyte interface membrane comprising a carbon-silicon / carbon composite as described in any one of claims 1 to 6.

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