York-shell structured silicon-carbon composite, process for preparing the same, and negative electrode active material comprising the same

Abstract

This invention relates to a silicon-carbon composite with an eggshell-like structure, its preparation method, and a negative electrode active material comprising the same. The silicon-carbon composite with an eggshell-like structure according to embodiments of the invention can be prepared without the use of strong acids. Uniform pores are formed by using a uniformly thick inorganic layer as a sacrificial layer, thereby accommodating the volume expansion of silicon when used as a negative electrode active material, thus suppressing the peeling of the outermost carbon film. As a result, the reduction in battery performance and lifespan can be suppressed.

Description

Technical Field

[0001] This invention relates to a silicon-carbon composite with an egg yolk and eggshell structure, and more specifically, to a silicon-carbon composite with an egg yolk and eggshell structure, its preparation method, and a negative electrode active material including the composite. Prior Technology

[0002] In recent years, with the development of the information and communication industry, the demand for electronic devices has increased rapidly, the electric vehicle market has become significantly more active, and the demand for batteries used in these electronic devices or electric vehicles has also continued to increase.

[0003] Secondary batteries, such as lithium-ion batteries containing liquid electrolytes and all-solid-state batteries, have high energy density and low self-discharge when not in use, making them the most widely used for this purpose. Secondary batteries mainly consist of a positive electrode, a negative electrode, and an electrolyte (liquid or solid), with carbon materials such as graphite widely used as the negative electrode active material.

[0004] Recently, silicon-based anode active materials have been explored to improve the capacity of secondary batteries. Theoretically, silicon has a very high energy density, thus attracting attention as a next-generation battery anode active material to replace graphite. However, during charging and discharging, it reacts with lithium, increasing in volume by up to 300%, leading to problems such as silicon breaking down as the charging and discharging process progresses, resulting in very poor mechanical stability.

[0005] To address the aforementioned issues, a silicon-carbon composite with a yolk-shell structure was proposed, formed by using porous silicon particles with pores capable of accommodating the volume expansion of silicon and forming a carbon film on them. To prepare this composite, the surface of the silicon particles, which serve as the yolk, needs to be coated with an inorganic material, followed by etching with a strong acid such as hydrofluoric acid.

[0006] Therefore, there is a need to develop new materials that can be used as sacrificial layers in a more environmentally friendly and convenient way. Existing technical documents Patent documents (Patent Document 0001) Japanese Patent Application Publication No. 2016-502253 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] The purpose of this invention is to provide a silicon-carbon composite with an egg yolk and eggshell structure. The silicon-carbon composite with the egg yolk and eggshell structure can form uniform pores by using an inorganic layer of uniform thickness as a sacrificial layer, thereby suppressing the reduction in battery performance caused by the volume expansion of silicon when used as a negative electrode active material.

[0009] Another object of the present invention is to provide a method for effectively preparing the silicon-carbon composite with the above-mentioned egg yolk and eggshell structure.

[0010] Another object of the present invention is to provide a negative electrode active material containing the above-mentioned egg yolk and eggshell structure of silicon-carbon composite. Technical means to solve the problem

[0011] The present invention provides a method for preparing a silicon-carbon composite with an egg yolk shell structure, comprising: (1) supplying silicon particles in a reactor; (2) forming an inorganic layer on the silicon particles by atomic layer deposition (ALD) to prepare a silicon-inorganic layer composite; (3) forming a carbon film on the silicon-inorganic layer composite to obtain a silicon-inorganic layer-carbon composite; and (4) removing at least part of the inorganic layer from the silicon-inorganic layer-carbon composite to prepare a silicon-carbon composite with an egg yolk shell structure; wherein step (3) is performed by heat-treating the silicon-inorganic layer composite in the presence of a gaseous carbon supply source, or by mixing a solution containing a carbon supply source and a solvent with the silicon-inorganic layer composite and then drying and heat-treating it.

[0012] According to an embodiment of the present invention, step (2) above can be performed as a cycle, including step (2-1) of supplying a first precursor to the reactor to form a first precursor multilayer on the silicon particles with at least a portion of the first precursor adsorbed thereon; step (2-2) of purging the inside of the reactor to remove unadsorbed first precursor from the first precursor multilayer to form a first precursor monolayer; step (2-3) of supplying a second precursor to the reactor and causing the first precursor monolayer to react with at least a portion of the second precursor to form a composite layer; and step (2-4) of purging the inside of the reactor to remove unreacted second precursor from the composite layer to form an inorganic layer. The cycle can be performed one or more times.

[0013] Furthermore, the time for supplying the first precursor and the time for supplying the second precursor can each be independently from 1 second to 600 seconds.

[0014] In addition, the aforementioned first precursor may include at least one selected from the group consisting of trimethylaluminum, diethylzinc, zinc acetate, tetra(dimethylamino)tin(IV), butoxytri(ethylmethylamino)hafnium, titanium isopropoxide, and diisopropylaminosilane.

[0015] In addition, the aforementioned second precursor may include at least one selected from the group consisting of H2O, O3, H2O plasma, O3 plasma and O2 plasma.

[0016] In addition, the gas used for purging in at least one of the above steps (2-2) and (2-4) may include nitrogen (N2) or argon (Ar).

[0017] In addition, the above cycle can be performed 1 to 300 times.

[0018] Furthermore, during the aforementioned cycle, the temperature of the silicon particles can be maintained between 90°C and 400°C.

[0019] Furthermore, step (4) above can be performed by etching the inorganic layer in the silicon-inorganic layer-carbon composite.

[0020] Furthermore, the present invention provides a silicon-carbon composite with an egg yolk and eggshell structure, comprising: silicon particles; and a carbon film formed in such a way as to form predetermined pores on the silicon particles.

[0021] According to one embodiment of the present invention, the average particle size of the silicon particles can be from 10 nm to 50 mm, and the average thickness of the carbon film can be from 1 nm to 1 mm.

[0022] Furthermore, the porosity of the silicon-carbon composite in the aforementioned egg yolk and eggshell structure can be from 10% to 80%.

[0023] In addition, the present invention provides a negative electrode active material comprising the silicon-carbon composite of the above-mentioned egg yolk and eggshell structure.

[0024] In addition, the present invention provides an all-solid-state battery comprising a solid electrolyte interphase (SEI) membrane of a silicon-carbon composite containing the above-mentioned egg yolk and eggshell structure. Compared with the efficacy of previous technologies

[0025] The yolk-shell structured silicon-carbon composite according to an embodiment of the present invention is prepared based on an inorganic layer formed using atomic layer deposition, thus allowing for precise adjustment of the sacrificial layer thickness. Furthermore, since uniform pores can be formed by using a uniformly thick inorganic layer as the sacrificial layer, the volume expansion of silicon can be accommodated when the yolk-shell structured silicon-carbon composite is used as the negative electrode active material, thereby suppressing the peeling of the outermost carbon film. As a result, the reduction in battery performance and lifespan can be suppressed. Simple Explanation of the Diagram

[0026] Figure 1 is a TEM (transmission electron microscope) image of a silicon-inorganic layer composite, which is an intermediate of a silicon-carbon composite (Example 1) according to an embodiment of the present invention.

[0027] Figure 2 is a TEM-EDS (energy dispersive spectrometer) image of a silicon-inorganic layer composite, which is an intermediate of a silicon-carbon composite (Example 1) according to an embodiment of the present invention.

[0028] Figure 3 is a TEM (transmission electron microscope) image of a silicon-inorganic layer-carbon composite, which is an intermediate of a silicon-carbon composite (Example 1) according to an embodiment of the present invention.

[0029] Figure 4 is a TEM-EDS image of a silicon-inorganic layer-carbon composite, which is an intermediate of a silicon-carbon composite (Example 1) according to an embodiment of the present invention.

[0030] Figure 5 is a TEM image of a silicon-carbon composite (Example 1) according to an embodiment of the present invention.

[0031] Figure 6 is a TEM-EDS image of a silicon-carbon composite (Example 1) according to an embodiment of the present invention.

[0032] Figure 7 is an atomic distribution curve of a silicon-carbon composite (Example 1) according to an embodiment of the present invention.

[0033] Figure 8 is a TEM image of a silicon-inorganic layer composite, which is an intermediate of a silicon-carbon composite (Example 2) according to an embodiment of the present invention. Implementation

[0034] This invention is not limited to the contents disclosed below, but can be modified into various forms as long as the essence of the invention is not changed.

[0035] Unless otherwise stated, in this specification, "including" means that other components may also be included.

[0036] Unless otherwise stated, all figures and expressions relating to the amount of components, reaction conditions, etc., used in this specification shall be understood to be modified by the term “about”.

[0037] In this specification, any description of a component being formed above / below another component or connected or combined with each other includes cases where these components are directly or indirectly formed, connected or combined with other components.

[0038] The invention will be described in more detail below. Silicon-carbon complex in egg yolk and eggshell structure

[0039] This invention provides a silicon-carbon composite with an egg yolk and eggshell structure. The aforementioned silicon-carbon composite with an egg yolk and eggshell structure is achieved by comprising silicon particles and a carbon film formed by leaving predetermined pores on the silicon particles.

[0040] The silicon-carbon composite of the egg yolk and eggshell structure according to an embodiment of the present invention is obtained by using a silicon-inorganic layer-carbon composite as an intermediate. The silicon-inorganic layer-carbon composite includes: a silicon-inorganic layer composite comprising silicon particles and an inorganic layer formed on the silicon particles; and a carbon film formed on the silicon-inorganic layer composite.

[0041] Therefore, in the following text, the silicon-inorganic layer composite and the silicon-inorganic layer-carbon composite as intermediates will be described, and the silicon-carbon composite of the egg yolk shell structure according to an embodiment of the present invention will also be described. Silicon particles

[0042] In one embodiment of the present invention, the silicon-inorganic layer composite and silicon-inorganic layer-carbon composite as intermediates, and the silicon-carbon composite of the egg yolk shell structure as the final product, comprise silicon particles.

[0043] Since the silicon particles in the silicon-carbon composite with egg yolk and eggshell structure according to the embodiment of the present invention play a role in lithium charging, when the silicon-carbon composite with egg yolk and eggshell structure according to the embodiment of the present invention is used as a negative electrode active material, the silicon particles can function as the main negative electrode active material.

[0044] The aforementioned silicon particles can be crystalline or amorphous. Regarding expansion / contraction and battery performance during charging and discharging of the secondary battery, an amorphous state or a similar phase is preferred. When the silicon particles are crystalline, the smaller the crystallite size, the denser the composite material, thereby enhancing the matrix strength and preventing cracking. Therefore, the initial efficiency or cycle life characteristics of the secondary battery can be improved. On the other hand, when the silicon particles are amorphous or a similar phase, the expansion or contraction during charging and discharging of the secondary battery is smaller, and battery performance such as capacity characteristics can be improved.

[0045] The size of the silicon particles can be selected to make the silicon-carbon composite with the yolk-shell structure according to embodiments of the present invention suitable for use as a negative electrode active material. Specifically, the average particle size of the silicon particles can be from 10 nm to 50 mm, preferably from 10 nm to 25 mm. When the silicon particles meet the above-mentioned average particle size range, it is more advantageous to achieve the purpose of the present invention.

[0046] The aforementioned silicon particles may further include silicon oxide compounds. The general formula for silicon oxide compounds can be represented by SiOx (0.5 ≤ x ≤ 2). Wherein, if the value of x is less than 0.5, it may lead to increased expansion and contraction during the charging and discharging of the secondary battery, resulting in deterioration of the lifetime characteristics. If the value of x exceeds 2, the inert oxides may increase, leading to a decrease in the initial efficiency of the secondary battery.

[0047] Based on the total weight of the silicon particles, the content of silicon oxide compounds in the silicon particles can be less than 50% by weight. If the content of silicon oxide compounds in the silicon particles exceeds 50% by weight, the initial efficiency of the secondary battery may decrease.

[0048] In addition to silicon and oxygen, the aforementioned silicon particles may also contain elements such as carbon and magnesium. However, the silicon content in the silicon particles can be selected such that the total silicon content in the silicon-carbon composite is from 1% to 80% by weight, preferably from 5% to 50% by weight. If the total silicon content in the silicon-carbon composite is less than 1% by weight, the amount of active material for adsorbing and releasing lithium is insufficient, resulting in a decrease in the charge and discharge capacity of the secondary battery. If the total silicon content in the silicon-carbon composite exceeds 80% by weight, the charge and discharge capacity of the secondary battery can be improved. However, the expansion and contraction of the electrodes during charge and discharge become excessive, and the negative electrode active material powder becomes finer, thus potentially deteriorating the cycle characteristics of the secondary battery. Inorganic layer

[0049] In embodiments of the present invention, the silicon-inorganic layer composite, as an intermediate, comprises an inorganic layer formed on the surface of silicon particles. This inorganic layer is formed by atomic layer deposition (ALD), as described below.

[0050] As the aforementioned inorganic layer, it is possible to prepare a silicon-carbon composite with an egg yolk and eggshell structure by forming it as a sacrificial layer for forming a carbon film through ALD and then removing it completely by the etching process described below. The type of material is not particularly limited.

[0051] In embodiments of the present invention, the inorganic layer may include at least one selected from the group consisting of alumina (Al2O3), zinc oxide (ZnO), tin oxide (SnO2), hafnium oxide (HfO), zirconium oxide (ZrO2), titanium oxide (TiO2), and silicon oxide (SiO2), but is not particularly limited thereto. In a preferred embodiment of the present invention, the inorganic layer may include alumina (Al2O3).

[0052] In embodiments of the present invention, the thickness of the inorganic layer can be from 1 nm to 10 mm, preferably from 1 nm to 1 mm, and more preferably from 1 nm to 100 nm. When the thickness of the inorganic layer is within the above range, the inorganic layer is appropriately used as a sacrificial layer in the etching steps described below, thereby appropriately forming pores between the silicon particles and the carbon film.

[0053] In embodiments of the present invention, in the etching step described below, at least a portion, preferably 10% to 100% by weight, more preferably 50% to 100% by weight, of the inorganic layer on the surface of the silicon particles in the silicon-inorganic layer composite as an intermediate is removed, thereby serving to appropriately form pores between the silicon particles and the carbon film.

[0054] Residues of the inorganic layer left after etching removal can exist between the silicon particles and the carbon film of the silicon-carbon composite of the yolk-shell structure, which is the final product according to an embodiment of the present invention. Therefore, the silicon-carbon composite of the yolk-shell structure according to an embodiment of the present invention can include residues of the inorganic layer between the silicon particles and the carbon film. However, the present invention is not limited thereto; when all inorganic layers are removed by etching, the silicon-carbon composite of the yolk-shell structure may not contain residues of the inorganic layer between the silicon particles and the carbon film. carbon thin film

[0055] The silicon-carbon composite of the egg yolk and eggshell structure according to one embodiment of the present invention includes a carbon film formed on the silicon particles.

[0056] The silicon-carbon composite with an egg yolk and eggshell structure according to embodiments of the present invention can ensure appropriate conductivity by including a carbon film, and its specific surface area can be appropriately adjusted. Therefore, when used as a negative electrode active material for a secondary battery, the life characteristics and capacity of the secondary battery can be further improved.

[0057] The conductivity of the negative electrode active material is an important factor in promoting electron movement during electrochemical reactions. The silicon-carbon composite with an eggshell-like structure according to embodiments of the present invention includes the aforementioned carbon film, thereby improving the charge / discharge capacity, initial charging efficiency, and capacity retention of the secondary battery, providing excellent conductivity, suppressing electrolyte side reactions, and further enhancing the performance of the secondary battery.

[0058] In the silicon-carbon composite with an egg yolk and eggshell structure according to an embodiment of the present invention, the thickness of the carbon film can be from 1 nm to 1 mm, preferably from 3 nm to 150 nm, and more preferably from 5 nm to 100 nm. When the thickness of the carbon film is within the above range, the conductivity can be improved while suppressing the reduction in the capacity of the secondary battery.

[0059] The aforementioned carbon thin film may include at least one selected from graphene, carbon nanotubes, carbon nanofibers, and graphite. Specifically, the carbon thin film may include graphene, and may also include graphite, but is not particularly limited thereto. Pores

[0060] In the silicon-carbon composite of the egg yolk and eggshell structure according to one embodiment of the present invention, there are pores between the silicon particles and the carbon film.

[0061] As described above, in the silicon-inorganic layer composite used as an intermediate for preparing the silicon-carbon composite structure of the egg yolk shell according to an embodiment of the present invention, the inorganic layer on the surface of the silicon particles is used as a sacrificial layer. In the etching step described below, at least a portion, preferably 10% to 100% by weight, more preferably 50% to 100% by weight, of the inorganic layer is removed, thereby forming pores between the silicon particles and the carbon film.

[0062] In the silicon-carbon composite with an egg yolk shell structure according to an embodiment of the present invention, the pores existing between the silicon particles and the carbon film accommodate the volume expansion of silicon when the silicon-carbon composite with an egg yolk shell structure is used as a negative electrode active material, thereby suppressing the phenomenon of the outermost carbon film being peeled off.

[0063] The silicon-carbon composite of the yolk-shell structure according to embodiments of the present invention can have a porosity of 10% to 80%, preferably 10% to 50%, and more preferably 20% to 50%. The porosity can be measured using the Brunauer-Emmett-Teller (BET) method, but the present invention is not particularly limited to this method. When the silicon-carbon composite of the yolk-shell structure meets the above-mentioned porosity range, it is more advantageous to achieve the objectives of the present invention. Preparation method of silicon-carbon complex in egg yolk and eggshell structure

[0064] The silicon-carbon composite with an egg yolk shell structure according to an embodiment of the present invention is prepared by the following preparation method, which includes: (1) supplying silicon particles in a reactor; (2) forming an inorganic layer on the silicon particles by atomic layer deposition (ALD) to prepare a silicon-inorganic layer composite; (3) forming a carbon film on the silicon-inorganic layer composite to obtain a silicon-inorganic layer-carbon composite; and (4) removing at least part of the inorganic layer from the silicon-inorganic layer-carbon composite to prepare a silicon-carbon composite with an egg yolk shell structure; wherein step (3) is performed by heat-treating the silicon-inorganic layer composite in the presence of a gaseous carbon supply source, or by mixing a solution containing a carbon supply source and a solvent with the silicon-inorganic layer composite and then drying and heat-treating it.

[0065] Atomic layer deposition (ALD) is a deposition method that grows thin films on an atomic layer basis. In conventional chemical vapor deposition (CVD), each reactant is injected simultaneously, allowing surface reactions to occur concurrently with the gas-phase reaction. However, in ALD, reactants are injected sequentially to suppress the gas-phase reaction, inducing a surface reaction on the deposition target surface through a self-limited adsorption process. Since the overall thickness of the deposited film is adjustable by the number of deposition cycles, it offers the advantage of easily adjusting thickness on an atomic layer basis. Furthermore, due to its versatility, excellent film properties, and ability to be processed even at relatively low temperatures, it is primarily used in semiconductor dielectrics and magnetic materials. In recent years, with the development of nanotechnology, the application of inorganic atomic layer deposition is expanding into various fields, moving away from the previous research focus centered on traditional integrated circuit devices.

[0066] The preparation method of silicon-carbon composites of egg yolk and eggshell structures using atomic layer deposition (ALD) will be explained step by step below. Step (1)

[0067] In step (1) above, silicon particles are supplied to the reactor.

[0068] The specific details of the silicon particles used in step (1) are as described above in the section on silicon-carbon complexes for the structure of the egg yolk and eggshell.

[0069] The reactor used in the method for preparing the silicon-carbon composite with egg yolk and eggshell structure according to an embodiment of the present invention can be used as long as it can form an inorganic layer on the surface of silicon particles by atomic layer deposition (ALD), and its structure is not particularly limited. Step (2)

[0070] In step (2) above, an inorganic layer is formed on the silicon particles by atomic layer deposition (ALD) to prepare a silicon-inorganic layer composite.

[0071] At this point, step (2) above can be performed as a cycle, including step (2-1) of supplying a first precursor to the reactor to form a first precursor multilayer on the silicon particles with at least a portion of the first precursor adsorbed; step (2-2) of purging the inside of the reactor to remove the unadsorbed first precursor from the first precursor multilayer to form a first precursor monolayer; step (2-3) of supplying a second precursor to the reactor and causing the first precursor monolayer to react with at least a portion of the second precursor to form a composite layer; and step (2-4) of purging the inside of the reactor to remove the unreacted second precursor from the composite layer to form an inorganic layer. This cycle can be performed one or more times.

[0072] First, in step (2-1), a first precursor may be supplied to the reactor to form a first precursor multilayer on which at least a portion of the first precursor is adsorbed on the silicon particles.

[0073] In embodiments of the present invention, the first precursor may include at least one selected from the group consisting of trimethylaluminum, diethylzinc, zinc acetate, tetra(dimethylamino)tin(IV), butoxytris(ethylmethylamino)hafnium, titanium isopropoxide, and diisopropylaminosilane. In a preferred embodiment of the present invention, the first precursor may include trimethylaluminum.

[0074] In embodiments of the present invention, the supply time of the first precursor can be from 1 second to 600 seconds. In a preferred embodiment of the present invention, the supply time of the first precursor is 1 second or more, 2 seconds or more, 5 seconds or more, 10 seconds or more, or 15 seconds or more and less than 600 seconds, 300 seconds or less, 100 seconds or less, 50 seconds or less, or 20 seconds or less. When the supply time of the first precursor meets the above ranges, a layer of the first precursor can be appropriately formed on the silicon particles. However, if the supply time of the first precursor is less than 1 second, it may be difficult to form an inorganic layer of uniform thickness due to incomplete atomic layer deposition. If the supply time exceeds 600 seconds, the inorganic layer thickness may become too thick, and the purging time will also increase, resulting in a longer overall process time.

[0075] Secondly, in step (2-2), the supply of the first precursor is stopped, the inside of the reactor is purged, and the unadsorbed first precursor is removed from the above-mentioned first precursor multilayer, thereby forming a first precursor monolayer.

[0076] In an embodiment of the present invention, an inert gas may be used for purging in step (2-2), and the inert gas may include nitrogen (N2) or argon (Ar).

[0077] In embodiments of the present invention, the purging time in step (2-2) can be from 1 second to 300 seconds. In preferred embodiments of the present invention, the purging time can be more than 1 second, more than 2 seconds, more than 5 seconds, more than 10 seconds, or more than 15 seconds but less than 300 seconds, less than 200 seconds, less than 100 seconds, less than 50 seconds, or less than 20 seconds. If the purging time is too short, residues of the first precursor may remain, potentially forming an inorganic oxide film thicker than expected; if the purging time is too long, the process efficiency may decrease.

[0078] Secondly, in step (2-3), a second precursor is supplied to the reactor, and the first precursor monolayer reacts with at least a portion of the second precursor to form a composite layer.

[0079] In embodiments of the present invention, the second precursor may include at least one selected from the group consisting of H2O, O3, H2O plasma, O3 plasma, and O2 plasma. In a preferred embodiment of the present invention, the second precursor may include H2O.

[0080] The first precursor reacts with the second precursor to form an inorganic layer on the particles, comprising at least one selected from the group consisting of alumina (Al2O3), zinc oxide (ZnO), tin oxide (SnO2), hafnium oxide (HfO), zirconium oxide (ZrO2), titanium oxide (TiO2), and silicon oxide (SiO2).

[0081] In embodiments of the present invention, the supply time of the second precursor can be from 1 second to 600 seconds. In a preferred embodiment of the present invention, the supply time of the second precursor is 1 second or more, 2 seconds or more, 5 seconds or more, 10 seconds or more, or 15 seconds or more and less than 600 seconds, 300 seconds or less, 100 seconds or less, 50 seconds or less, or 20 seconds or less. When the supply time of the second precursor meets the above ranges, an inorganic layer can be appropriately formed on the silicon particles. However, if the supply time of the second precursor is less than 1 second, it may be difficult to form an inorganic layer of uniform thickness due to incomplete atomic layer deposition; if the supply time exceeds 600 seconds, the inorganic layer thickness may become too thick, and the purging time will also increase, resulting in a longer overall process time.

[0082] Secondly, in step (2-4), the supply of the second precursor is stopped, and the inside of the reactor is purged to remove the unreacted second precursor from the composite layer, thereby forming an inorganic layer.

[0083] In an embodiment of the present invention, an inert gas may be used for purging in steps (2-4), and the inert gas may include nitrogen (N2) or argon (Ar).

[0084] In embodiments of the present invention, the purging time in steps (2-4) can be from 1 second to 300 seconds. In preferred embodiments of the present invention, the purging time can be more than 1 second, more than 2 seconds, more than 5 seconds, more than 10 seconds, or more than 15 seconds but less than 300 seconds, less than 200 seconds, less than 100 seconds, less than 50 seconds, or less than 20 seconds. If the purging time is too short, residues of the second precursor may remain, potentially forming an inorganic oxide film thicker than expected; if the purging time is too long, the process efficiency may decrease.

[0085] In embodiments of the present invention, the temperature of the silicon particles can be maintained between 90°C and 400°C during the above-described cycle. In a preferred embodiment of the present invention, the temperature of the silicon particles can be maintained between 120°C and 300°C during the above-described cycle. If the temperature of the silicon particles is below 90°C, defects may occur in the formed inorganic layer due to incomplete reaction; if the temperature exceeds 400°C, there may be a problem of excessive formation of inorganic thin films on the silicon particles.

[0086] In embodiments of the invention, the above-described cycle can be performed at a pressure of 0.5 Torr to 10 Torr. In a preferred embodiment of the invention, the above-described cycle can be performed at a pressure of 1 Torr to 5 Torr.

[0087] In embodiments of the present invention, the above-described cycle can be repeated from 1 to 300 times. In a preferred embodiment of the present invention, the above-described cycle can be repeated from 50 to 300 times. If the above-described cycle is performed more than 300 times, excessive inorganic films may be formed on the silicon particles, and the process time may be prolonged. Step (3)

[0088] In step (3) above, a carbon film is formed on the silicon-inorganic layer composite to obtain a silicon-inorganic layer-carbon composite.

[0089] The step of forming a carbon film on the aforementioned silicon-inorganic layer composite particles, which serve as intermediates, can be performed using apparatus and methods known in the art to which this invention pertains, such as chemical pyrolysis deposition, but is not particularly limited thereto. For example, the aforementioned carbon film can be formed by carbonizing a polymer film formed using initiator-based chemical vapor deposition (iCVD).

[0090] In an embodiment of the present invention, the step of forming a carbon film on the silicon-inorganic layer composite, which serves as an intermediate, can be performed by heat-treating the silicon-inorganic layer composite at a temperature of 400°C to 1,400°C in the presence of a gaseous carbon source.

[0091] In a preferred embodiment of the present invention, 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.

[0092] The step of forming a carbon film on the aforementioned silicon-inorganic layer composite as an intermediate can be carried out in the presence of at least one inert gas selected from the group consisting of hydrogen, nitrogen, helium and argon, in addition to the aforementioned carbon source.

[0093] The reaction time (heat treatment time) for forming the carbon film can be appropriately adjusted according to the heat treatment temperature, the pressure during heat treatment, the composition of the gas mixture, and the required amount of carbon coating. For example, the reaction time can be from 10 minutes to 100 hours, specifically from 30 minutes to 90 hours, and more specifically from 50 minutes to 40 hours, but is not particularly limited to this range.

[0094] In an embodiment of the present invention, the step of forming a carbon film on the aforementioned silicon-inorganic layer composite as an intermediate can be performed by mixing the silicon-inorganic layer composite with a solution in which a carbon source is dispersed in a solvent as needed, then drying it and heat-treating it at a temperature of 400°C to 1,400°C.

[0095] In a preferred embodiment of the present invention, the carbon source can be selected from the group consisting of asphalt, hydrocarbon-based materials, and petroleum-based materials. More specifically, the asphalt can be petroleum-based asphalt, coal-based asphalt, or a mixture thereof; the hydrocarbon-based material can be furfuryl alcohol or phenolic resin; and the petroleum-based material can be pyrolysis fuel oil (PFO), naphtha cracking bottom oil (NCB), ethylene cracker bottom oil (EBO), vacuum residue (VR), deasphalted oil (DAO), atmospheric residue (AR), fluid catalytic cracking decant oil (FCC-DO), residue fluid catalytic cracking decant oil (RFCC-DO), or heavy aromatic oil. The solvent can be tetrahydrofuran (THF) or an alcohol.

[0096] In addition, when the above-mentioned carbon film is formed by carbonizing the polymer film, the monomer, which is a volatile substance that can be activated by an initiator to form a polymer, can be activated by an initiator and polymerized to form a polymer film, and then the formed polymer film is carbonized.

[0097] At this time, the monomer can be at least one of vinyl and acrylate monomers containing at least one of siloxane, amine, fluorine and aromatic hydrocarbon groups.

[0098] Furthermore, for example, the polymer film formed by polymerizing the above monomers can be made from a polymer selected from 4-vinyl pyridine (4VP), 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane, 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecyl methacrylate. methacrylate (PFDMA), 1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane (V4D4), 1,3,5-trivinyl-1,3,5-trimethylcyclotrisiloxane (V3D3), hexavinyldisiloxane (HVDS), glycidyl methacrylate, divinylbenzene, diethylene glycol divinyl ether, diethylene glycol diacrylate (DEGDA), ethylene glycol dimethacrylate, dimethylamino methacrylate Ethyl acrylate, methacrylic acid, 1,3-divinyl-1,1,3,3-tetramethylsiloxane, 1H,1H,2H,2H-perfluorodecyl acrylate, perfluorodecyl methacrylate, dodecylfluoroheptyl acrylate, pentafluorophenyl methacrylate, 3,3,4,4,5,5,6,6,7,7,8,8,9,9,9-pentadecylfluorononyl acrylate, 2-methyl-3,3,4,4,5,5,6,6,7,7,8,8,9,9 9-Pentadecylfluorononyl acrylate, 3,3,4,4,5,5,6,6,7,7,8,8,8-Tetrafluorooctyl acrylate, 2-Methyl-3,3,4,4,5,5,6,6,7,7,8,8,8-Tetrafluorooctyl acrylate, 3,3,4,4,5,5,6,6,7,7,7-Undecylfluoroheptyl acrylate, 2-Methyl-3,3,4,4,5,5,6,6,7,7,7-Undecylfluoroheptyl acrylate, 3,3,4,4,5,5,6,6,6-Nonfluorohexyl acrylate, 2-Methyl-3,3,4,4,5,5,6,6,6-Nonfluorohexyl acrylate, 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,11-Ninedecylfluoroundecyl acrylate, 2-Methyl-3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,11-Ninedecylfluoroundecyl acrylate, 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,12-Ticosicododecyl acrylate, 2- Methyl-3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,12-teicosicofluorododecyl acrylate, 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,13,13,13-teicosicofluorotridecyl acrylate, 2-methyl-3, 3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,13,13,13-Ticosicosyltridecyl acrylate, 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,13,13,14,14,14-Ticosicosyltetradecyl acrylate, It is polymerized from at least one monomer selected from the group consisting of 2-methyl-3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,13,13,14,14,14-tetrafluorotetradecyl acrylate, dimethylaminoethyl methacrylate, dimethylaminoethyl acrylate, diethylaminoethyl methacrylate, and diethylaminoethyl acrylate.

[0099] Furthermore, for example, the initiator described above can be a peroxide. Specifically, the initiator may include at least one selected from the group consisting of di-tert-butyl peroxide, tert-butyl peroxide, benzoyl peroxide, methyl ethyl ketone peroxide, lauryl peroxide, and benzophenone, but the present invention is not particularly limited thereto.

[0100] At this time, the flow rate of the aforementioned unit supplied to the reactor can be from 0.1 sccm to 10 sccm. Specifically, the unit flow rate can be 0.1 sccm or more, or 0.2 sccm or more and 10 sccm or less, 5 sccm or less, or 4 sccm or less.

[0101] Furthermore, the flow rate of the initiator supplied to the reactor can be from 0.1 sccm to 5 sccm. Specifically, the initiator flow rate can be 0.1 sccm or more and 5 sccm or less, 3 sccm or less, or 2 sccm or less.

[0102] In addition, the initiator can be activated by a predetermined heat treatment, which can be carried out at a temperature of 135°C to 350°C, preferably 140°C to 340°C. Meeting the above temperature conditions has advantages in preventing the occurrence of the properties of the reactants.

[0103] On the other hand, in order to improve the adsorption rate of the aforementioned monomers and free radicals, it is preferable to keep the surface temperature of the silicon-inorganic layer composite low. Specifically, the surface temperature of the aforementioned silicon-inorganic layer composite is in the range of 10°C to 50°C, preferably in the range of 13°C to 45°C, but the present invention is not particularly limited to the above range. Step (4)

[0104] In step (4) above, a silicon-carbon composite with an egg yolk shell structure is prepared by removing at least a portion of the inorganic layer from the silicon-inorganic layer-carbon composite.

[0105] At this point, step (4) above can be performed by etching the inorganic layer in the silicon-inorganic layer-carbon composite. The etching can be performed by immersing the silicon-inorganic layer-carbon composite in an alkaline or acidic aqueous solution and treating it at a temperature of room temperature to 80°C for 1 minute to 1 hour.

[0106] In embodiments of the present invention, the alkali may include at least one selected from the group consisting of sodium hydroxide (NaOH), potassium hydroxide (KOH), and calcium hydroxide (Ca(OH)2), but is not particularly limited thereto. The concentration of the alkali aqueous solution may be from 0.1M to 3M, but is not particularly limited to this range.

[0107] In embodiments of the present invention, the acid may include at least one selected from the group consisting of hydrofluoric acid (HF), hydrochloric acid, sulfuric acid, and nitric acid, but is not particularly limited thereto. The concentration of the aqueous acid solution may be from 0.1M to 2M, but is not particularly limited to the above range.

[0108] By etching the silicon-inorganic layer-carbon composite as described above, at least a portion, preferably 10% to 100% by weight, more preferably 50% to 100% by weight, of the inorganic layer is removed, thereby appropriately forming pores between the silicon particles and the carbon film. The residue of the inorganic layer remaining after removal in step (4) may exist between the silicon particles and the carbon film of the silicon-carbon composite in the yolk-shell structure of the embodiment of the present invention.

[0109] In step (4) above, when pores are formed between the silicon particles and the carbon film, the degree of pore formation and the degree of inorganic layer residue can be appropriately adjusted by changing the size of the silicon particles, the etching time and temperature of the alkaline aqueous solution, etc. When the silicon-carbon composite with the egg yolk and eggshell structure obtained in this way is used as a negative electrode active material, the conductivity of the negative electrode active material can be improved without changing the structure. Additional steps

[0110] In the method for preparing a silicon-carbon complex with an egg yolk and eggshell structure according to an embodiment of the present invention, the obtained silicon-carbon complex with an egg yolk and eggshell structure can be crushed or pulverized and graded. Grading can make the particle size distribution of the complex uniform. Grading can be performed using dry grading, wet grading, or grading using a sieve, etc. Negative electrode active materials

[0111] According to another embodiment of the present invention, a silicon-carbon composite containing the above-described egg yolk and eggshell structure is provided as a negative electrode active material.

[0112] In addition to the silicon-carbon composite with an egg yolk and eggshell structure, the negative electrode active material according to embodiments of the present invention may also include a carbon-based negative electrode material, specifically a graphite-based negative electrode material. For example, the negative electrode active material can be obtained by mixing the silicon-carbon composite with an egg yolk and eggshell structure according to embodiments of the present invention with a carbon-based negative electrode material, such as a graphite-based negative electrode material.

[0113] The carbon-based anode material may include, for example, 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 is not particularly limited thereto.

[0114] The content of carbon-based anode material in the anode active material according to the embodiments of the present invention can be from 2% to 80% by weight relative to the total weight of the anode active material, preferably from 5% to 70% by weight, and more preferably from 30% to 70% by weight.

[0115] The negative electrode active material according to embodiments of the present invention can be effectively used in the manufacture of secondary batteries, especially negative electrodes for lithium secondary batteries and negative electrodes for all-solid-state batteries. All-solid-state batteries

[0116] According to another embodiment of the present invention, an all-solid-state battery is provided, comprising a solid electrolyte interphase (SEI) membrane of a silicon-carbon composite containing the above-described egg yolk and eggshell structure.

[0117] The aforementioned all-solid-state battery may be an all-solid-state battery comprising a positive electrode, a negative electrode, and a solid electrolyte located between the positive electrode and the negative electrode. The negative electrode may include a negative electrode active material layer, and at least a portion of the negative electrode active material particles of the negative electrode active material layer may contain a solid electrolyte interface (SEI) film containing the aforementioned egg yolk and eggshell structure of silicon-carbon composite.

[0118] On the other hand, the aforementioned negative electrode active material particles can be carbon-based negative electrode materials. In this case, since they can be the same as those described in the content about the aforementioned negative electrode active materials, the relevant descriptions will be omitted.

[0119] In addition to the negative electrode active material particles and SEI film of the all-solid-state battery mentioned above, the composition of known all-solid-state batteries can be used as the negative electrode composition, positive electrode composition and solid electrolyte composition, etc., and the present invention does not particularly limit this. Example

[0120] The invention is described in more detail below by way of examples. These examples are merely illustrative and the scope of the invention is not limited thereto. <Example 1> Preparation of silicon-inorganic layer composite (intermediate)

[0121] Silicon-inorganic layer composites were prepared using a conventional ALD reactor. 5 g of silicon powder with an average particle size of 20 mm and 5 g of silicon powder with an average particle size of 2 mm were uniformly spread on circular silicon wafers in the reactor. The silicon-inorganic layer composites were prepared by forming an inorganic layer on the surface of the silicon particles under the following conditions. The specific conditions of the materials and processes used in Example 1 are as follows. - Silicon particles: average particle sizes of 20 mm and 2 mm (REC silicon) - First precursor: Trimethylaluminum (EG Chem) - Second precursor: H2O (Merck Millipore, Milli-Q) - Precursor carrier gas: N2 300 sccm - Average supply flow rate and time of first precursor: 2 seconds - Purge gas and time after supplying the first precursor: N2, 60 seconds - Average supply flow rate and time of the second precursor: 2 seconds - Purge gas and time after supplying the second precursor: N2, 60 seconds - Pressure within the reactor chamber: 1.2 Torr - Surface temperature of reactor mounting section (silicon wafer): 150℃ - Number of loops: 100 - The inorganic layer formed: Al2O3 Experimental Example 1-1 (1) X-ray photoelectron spectroscopy

[0122] The elemental composition of silicon particles before and after the formation of the inorganic layer was analyzed using X-ray photoelectron spectroscopy (Multilab 2000, Thermo Scientific). The results are shown in Table 1. Table 1 Silicon particle size carbon aluminum oxygen Silicon 20mg Before the formation of the inorganic layer 18.19 0 27.59 53.62 After the inorganic layer is formed 27.73 22.34 40.76 9.17 2 mm Before the formation of the inorganic layer 41.38 0 27.63 30.98 After the inorganic layer is formed 34.15 24.64 40.17 1.05

[0123] As shown in Table 1, almost no aluminum was measured on the surface of the silicon particles before the formation of the inorganic layer. However, after the inorganic layer was formed on the silicon particles using the preparation method of the present invention, a significant amount of aluminum was measured. Therefore, the preparation method of the present invention successfully prepared a silicon-inorganic layer composite with an alumina inorganic layer on the surface of silicon particles. (2) Transmission electron microscopy-energy dispersive optics analysis

[0124] Silicon particles with an average diameter of 20 mm and an Al2O3 inorganic layer were observed using a transmission electron microscope (TEM) and energy dispersive spectrometer (EDS) (Tecnai G2 F30 S-Twin, FEI). The TEM analysis results are shown in Figure 1, and the EDS analysis results are shown in Figure 2 and Table 2. Table 2 atom% Si 69.06 C 13.27 F 3.34 Al 14.33 O 69.06

[0125] As can be seen from the TEM images in Figures 1a and 1b, the silicon-inorganic layer composite obtained in Example 1 formed an inorganic layer with a uniform thickness of about 5 nm without problems such as severe agglomeration or particle breakage, and essentially maintained its original shape.

[0126] Figures 2a and 2b and Table 2 show the EDS analysis results of the silicon-inorganic layer composite. As shown in Figures 2a, 2b and Table 2, aluminum, as a component of the inorganic layer, was observed on the silicon-inorganic layer composite. Therefore, it can be qualitatively seen that a silicon-inorganic layer composite with an inorganic layer formed on the surface of silicon particles was prepared by the preparation method of the present invention. Preparation of silicon-inorganic layer-carbon composite

[0127] Then, 5g of the silicon-inorganic layer composite (intermediate) prepared above was uniformly spread onto a circular silicon wafer in the reactor. Vaporized monomers and initiators were supplied into the reaction chamber through the inlet to form a polymer film (pDVB) on the silicon-inorganic layer composite, thereby preparing the silicon-inorganic layer-polymer composite. The specific conditions of the materials and processes used in this embodiment are as follows. - Monomer: Divinylbenzene (Sigma-Aldrich, 80%) - Initiator: Di-tert-butyl peroxide (Sigma-Aldrich, 98%) - Average initiator supply flow rate: 0.26 sccm - Average supply flow rate per unit: 0.425 sccm - Wire temperature: 140℃ - Pressure inside the reactor chamber: 450 mTorr - Surface temperature of reactor mounting section (silicon wafer): 23°C

[0128] Then, the prepared silicon-inorganic layer-polymer composite was carbonized at 700°C for 30 minutes to carbonize the polymer film, thereby preparing the silicon-inorganic layer-carbon composite. Experimental Examples 1-2 (1) Transmission electron microscopy-energy dispersive optics analysis

[0129] The silicon-inorganic layer-carbon composite prepared above was observed using transmission electron microscopy (TEM) with energy-dispersive spectroscopy (EDS) (Tecnai G2 F30 S-Twin, FEI). The TEM analysis results are shown in Figure 3, and the EDS analysis results are shown in Figure 4.

[0130] As a result, the TEM image in Figure 3 confirms that the silicon-inorganic layer-carbon composite obtained in the example forms a uniform thin film with a thickness of approximately 20 nm on the silicon particles. Analysis results in Figures 4a, 4b, and 4c confirm that both aluminum and carbon are observed in a uniform region of the silicon-inorganic layer-carbon composite prepared above. Therefore, it can be qualitatively seen that the preparation method of the present invention successfully prepared a silicon-inorganic layer-carbon composite with an inorganic layer and a carbon thin film formed on the surface of silicon particles. Preparation of silicon-carbon complexes in egg yolk and eggshell structure

[0131] The inorganic layer of the silicon-inorganic layer-carbon composite (intermediate) prepared on the above is etched by immersing it in H3PO4 (85%, Sigma-Aldrich) at 50°C for 100 seconds, thereby preparing a silicon-carbon composite with an egg yolk shell structure. Experimental Examples 1-3 (1) Transmission electron microscopy-energy dispersive optics analysis

[0132] The silicon-carbon complex of the egg yolk and eggshell structure prepared above was observed using transmission electron microscopy (TEM)-energy dispersive spectroscopy (EDS) (Tecnai G2 F30 S-Twin, FEI). The TEM analysis results are shown in Figure 5, and the EDS analysis results are shown in Figures 6 and 7.

[0133] As a result, the TEM image in Figure 5 confirms that the silicon-carbon composite forms a yolk-shell structure with uniform pores. The results in Figures 6 and 7 confirm that a carbon film is formed on the silicon particles. In particular, in Figure 7, there is a region (around 110 nm) where no atoms were detected between the locations where carbon atoms were detected and the locations where silicon atoms were detected, which confirms that the predetermined pores were formed. <Example 2> Preparation of silicon-inorganic layer composite (intermediate)

[0134] Except for the following changes, the silicon-inorganic layer composite was prepared in the same manner as in Example 1 above. - Silicon particles: average particle size 20 mm (REC silicon) - First precursor: Titanium isopropoxide (IV) (TTIP) - Second precursor: H2O (Millpore, Milli-Q) - Precursor carrier gas: N2 300 sccm - Average supply flow rate and time of the first precursor: 15 seconds - Purge gas and time after supplying the first precursor: N2, 600 seconds - Average supply flow rate and time of the second precursor: 15 seconds - Purge gas and time after supplying the second precursor: N2, 600 seconds - Pressure within the reactor chamber: 1.2 Torr - Surface temperature of reactor mounting section (silicon wafer): 150℃ - Number of loops: 100 - The formed inorganic layer: TiO2 Experimental Example 2 (1) Transmission electron microscopy analysis

[0135] Transmission electron microscopy (TEM) analysis was performed on silicon particles with TiO2 inorganic layers. The TEM analysis results are shown in Figure 8.

[0136] As can be seen from the TEM images in Figures 8a and 8b, the silicon-inorganic layer composite obtained in Example 2 formed an inorganic layer with a uniform thickness of about 6 nm without problems such as severe agglomeration or particle breakage, and essentially maintained its original shape.

[0137] none

[0138] 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 method for preparing a silicon-carbon composite with an egg yolk and eggshell structure, comprising: (1) the step of supplying silicon particles into a reactor; (2) the step of forming an inorganic layer on the silicon particles by atomic layer deposition (ALD) to prepare a silicon-inorganic layer composite; (3) the step of forming a carbon film on the silicon-inorganic layer composite to obtain a silicon-inorganic layer-carbon composite; and (4) the step of at least partially removing the inorganic layer from the silicon-inorganic layer-carbon composite to prepare a silicon-carbon composite with an egg yolk and eggshell structure. The above step (2) includes: (2-1) supplying a first precursor to the reactor for less than 600 seconds to form a first precursor multilayer on the silicon particles having at least a portion of the first precursor adsorbed thereon; (2-2) purging the inside of the reactor for more than 1 second to remove unadsorbed first precursor from the first precursor multilayer to form a first precursor monolayer; (2-3) supplying a second precursor to the reactor for less than 600 seconds to cause the first precursor monolayer to react with at least a portion of the second precursor to form a composite layer; and (2-4) purging the inside of the reactor for more than 1 second to remove unreacted second precursor from the composite layer to form an inorganic layer; the above steps are performed as one cycle, and the above cycles are repeated one or more times. The above step (3) is performed by heat-treating the silicon-inorganic layer composite in the presence of a gaseous carbon supply source. Alternatively, the process can be performed by mixing a solution containing a carbon supply source and a solvent with the aforementioned silicon-inorganic layer composite, followed by drying and heat treatment. The first precursor includes at least one selected from the group consisting of trimethylaluminum, diethylzinc, zinc acetate, tetra(dimethylamino)tin(IV), butoxytri(ethylmethylamino)hafnium, titanium isopropoxide, and diisopropylaminosilane. The second precursor includes at least one selected from the group consisting of H2O, O3, H2O plasma, O3 plasma, and O2 plasma.

2. A method for preparing the silicon-carbon composite with the egg yolk and eggshell structure as described in claim 1, wherein, The time for supplying the first precursor and the time for supplying the second precursor are each independently between 1 second and 600 seconds.

3. A method for preparing the silicon-carbon composite with the egg yolk and eggshell structure as described in claim 1, wherein, The gas used for purging in at least one of the above steps (2-2) and (2-4) includes nitrogen (N2) or argon (Ar).

4. A method for preparing the silicon-carbon composite with the egg yolk and eggshell structure as described in claim 1, wherein, Repeat the above cycle 1 to 300 times.

5. A method for preparing the silicon-carbon composite with the egg yolk and eggshell structure as described in claim 1, wherein, During the above cycle, the temperature of the silicon particles is maintained between 90°C and 400°C.

6. A method for preparing the silicon-carbon composite with the egg yolk and eggshell structure as described in claim 1, wherein, The above step (4) is performed by etching the inorganic layer of the silicon-inorganic layer-carbon composite.

7. A silicon-carbon composite with an egg yolk and eggshell structure, comprising: Silicon particles with an average particle size of 10 nm to 50 μm; and a carbon film formed by forming predetermined pores on the silicon particles and having an average thickness of 1 nm to 1 μm; wherein the porosity of the silicon-carbon composite of the egg yolk and eggshell structure is 10% to 80%.

8. A negative electrode active material comprising a silicon-carbon composite with the egg yolk and eggshell structure as claimed in claim 7.

9. An all-solid-state battery comprising a solid electrolyte interface (SEI) membrane of a silicon-carbon composite containing the yolk-shell structure of claim 7.

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