Silicon-carbon composite with yolk-shell structure, method for producing the same, and negative electrode active material containing the same

Abstract

The present invention relates to a yoke-shell silicon-carbon composite, a manufacturing method thereof, and an anode active material including the same. The yoke-shell silicon-carbon composite according to an embodiment of the present invention can be manufactured without an etching process using strong acid, and can form uniform pores by using a polymer layer of uniform thickness as a sacrificial layer. This allows the composite to absorb the volume expansion of silicon when used as an anode active material, thereby preventing peeling of the outermost carbon thin film. As a result, deterioration of battery performance and lifespan can be prevented.

Description

[Technical Field]

[0001] The present invention relates to a silicon-carbon composite having a yoke-shell structure, and more particularly to a silicon-carbon composite having a yoke-shell structure, a method for producing the same, and a negative electrode active material including the same. [Background technology]

[0002] In recent years, with the development of the information and communications industry, demand for electronic devices has been increasing rapidly, and as the market for electric vehicles has become significantly more active, demand for the batteries used in these electronic devices and electric vehicles has also increased.

[0003] Secondary batteries, such as lithium secondary batteries and all-solid-state batteries, containing liquid electrolytes, are the most widely used for such applications due to their high energy density and low self-discharge when not in use. Secondary batteries are broadly composed of a positive electrode, a negative electrode, and an electrolyte (liquid or solid), and carbon materials such as graphite are widely used as the negative electrode active material for secondary batteries.

[0004] Recently, attempts to use silicon-based anode active materials have been progressing to improve the capacity of secondary batteries. Silicon theoretically has a very high energy density and is attracting attention as a next-generation battery anode active material to replace graphite. However, it reacts with lithium during charging and discharging, increasing its volume by up to 300%. Repeated charging and discharging causes the silicon as an anode active material to break down, resulting in a significant decrease in mechanical stability.

[0005] To solve this problem, a silicon-carbon composite with a yolk-shell structure was proposed, which involves using porous silicon particles with pores that can absorb the volume expansion of silicon and forming a thin carbon film on top of them. To manufacture this composite, the surface of the silicon particles that will become the yoke must be coated with an inorganic material and then etched with a strong acid such as hydrofluoric acid.

[0006] Therefore, there is a need to develop a material that can be used as a sacrificial layer in a more environmentally friendly and convenient manner. Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a silicon-carbon composite with a yoke-shell structure that can be prepared without using a strong acid and that can form uniform pores by using a polymer layer of uniform thickness as a sacrificial layer, thereby suppressing a decrease in battery performance due to volume expansion of silicon when used as a negative electrode active material.

[0008] Another object of the present invention is to provide a method for efficiently producing the above-mentioned silicon-carbon composite having a yoke-shell structure.

[0009] A further object of the present invention is to provide a negative electrode active material containing the silicon-carbon composite with the yolk-shell structure. [Means for solving the problem]

[0010] The present invention relates to a method for polymerizing silicon particles by (1) supplying silicon particles into a reactor, (2) supplying a monomer and an initiator to the reactor, and (3) activating the initiator to polymerize the monomer. Therefore, the present invention provides a method for manufacturing a silicon-carbon composite having a yoke-shell structure, the method including: (1) forming a thin polymer film on the surface of the silicon particles to obtain a silicon-polymer composite; and (2) forming a thin carbon film on the silicon-polymer composite to form pores between the silicon particles and the formed thin carbon film, thereby manufacturing a silicon-carbon composite having a yoke-shell structure.

[0011] According to one embodiment of the present invention, the silicon particles may have an average particle size of 10 nm to 50 μm.

[0012] The polymer thin film may have a thickness of 1 nm to 10 μm.

[0013] In step (2), the monomer may be supplied at a flow rate of 0.1 sccm to 10 sccm, and the initiator may be supplied at a flow rate of 0.1 sccm to 5 sccm.

[0014] The initiator can be activated by a predetermined heat treatment, and the heat treatment can be carried out at a temperature of 135 to 350°C.

[0015] Also, the step (3) may be carried out in a vacuum state at a pressure of 50 to 1,000 mTorr for 10 minutes to 6 hours.

[0016] The silicon particles may be located in a mounting section within the reactor, and the temperature of the mounting section in the step (3) may be 10 to 50°C.

[0017] Step (4) can be performed by supplying a monomer and an initiator to the reactor, activating the initiator to polymerize the monomer, thereby forming a thin polymer film on the surface of the silicon-polymer composite, and then heat-treating the resulting silicon-polymer composite at a temperature of 400 to 1,400°C.

[0018] Also, the step (4) can be carried out by heat treatment at a temperature of 400 to 1,400° C. in the presence of a carbon source.

[0019] The carbon thin film may have a thickness of 1 nm to 1 μm.

[0020] The present invention also provides a silicon-carbon composite having a yoke-shell structure, which includes silicon particles and a carbon thin film formed on the silicon particles with a predetermined pore size.

[0021] According to one embodiment of the present invention, the yolk-shell structured silicon-carbon composite may have a porosity of 10 to 80%.

[0022] The present invention also provides a negative electrode active material containing the silicon-carbon composite with the yolk-shell structure.

[0023] The present invention also provides an all-solid-state battery including an SEI (Solid Electrolyte Interphase) film containing the silicon-carbon composite with the above-mentioned yolk-shell structure. [Effects of the Invention]

[0024] The silicon-carbon composite with a yoke-shell structure according to an embodiment of the present invention can be manufactured based on a polymer layer formed using an iCVD method, without an etching process using strong acid, and the thickness of the sacrificial layer can be precisely controlled. In addition, a polymer layer with a uniform thickness can be used as the sacrificial layer, allowing for the formation of uniform pores. This allows the silicon-carbon composite with a yoke-shell structure to absorb the volume expansion of silicon when used as a negative electrode active material, thereby preventing the outermost carbon thin film from peeling off, thereby preventing a decrease in battery performance and lifespan. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 1 is a schematic diagram illustrating a process for producing an intermediate silicon-polymer composite by forming a polymer thin film on the surface of silicon particles using initiator-based chemical vapor deposition (iCVD) in accordance with one embodiment of the present invention. [Figure 2] FIG. 2 is a TEM image of bare silicon particles before forming a thin polymer film on the surface of the silicon particles according to one embodiment of the present invention. [Figure 3] FIG. 3 is a photograph showing the degree to which silicon particles disperse in water before and after forming a thin polymer film on the surface of the silicon particles (Example 1) according to one embodiment of the present invention. [Figure 4] FIG. 4 is a TEM image of a silicon-polymer composite (Example 1) according to one embodiment of the present invention. [Figure 5a] FIG. 5a is an energy dispersive spectroscopy (EDS) image of an intermediate silicon-polymer composite according to one embodiment of the present invention. [Figure 5b]FIG. 5b is an energy dispersive spectroscopy (EDS) image of an intermediate silicon-polymer composite according to one embodiment of the present invention. [Figure 6] FIG. 6 is a TEM image of an intermediate silicon-polymer composite (Example 2) according to one embodiment of the present invention. [Figure 7] FIG. 7 is a comparative graph of nitrogen atom content between bare silicon particles and an intermediate silicon-polymer composite (Example 2) according to one embodiment of the present invention. [Figure 8] FIG. 8 is a TEM image of an intermediate silicon-polymer composite (Example 3) according to one embodiment of the present invention. [Figure 9] FIG. 9 shows TEM images of bare silicon particles, an intermediate silicon-polymer composite according to one embodiment of the present invention (Example 3), and an intermediate silicon-polymer composite coated with a polymer in liquid form (Comparative Example 1). [Figure 10] FIG. 10 is a TEM image of an intermediate silicon-polymer composite (Example 4) according to one embodiment of the present invention. [Figure 11] FIG. 11 is a graph showing the resistance of a silicon-polymer composite (Example 4) as an intermediate according to an embodiment of the present invention at different carbonization (heat treatment) temperatures. [Figure 12] FIG. 12 shows a TEM image (FIG. 12a), a TEM-EDS image (FIG. 12b), and an EDS result graph image (FIG. 12c) of a silicon-polymer-periphery polymer composite (production example) as an intermediate according to one embodiment of the present invention. [Figure 13] FIG. 13 shows a TEM image (FIG. 13a), a TEM-EDS image (FIG. 13b), and an EDS result graph image (FIG. 13c) of a silicon-carbon composite (production example) according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0026] The present invention is not limited to the contents described below, and can be modified into various forms as long as the gist of the invention is not changed.

[0027] In this specification, the word "comprise" means that other components may be further included, unless otherwise specified.

[0028] All numbers and expressions expressing amounts of components, reaction conditions, and the like described herein should be understood to be modified in all instances by the term "about," unless otherwise specified.

[0029] As used herein, it is understood that one component may be formed above / below another component or may be attached to another component. When it is stated that something is connected or coupled, it includes all of the elements that are formed, connected, or coupled directly between these elements or indirectly through other elements.

[0030] The present invention will be described in more detail below.

[0031] Silicon-carbon composite with yolk-shell structure

[0032] The present invention provides a silicon-carbon composite having a yoke-shell structure, which includes silicon particles and a carbon thin film having a predetermined pore space formed on the silicon particles.

[0033] The silicon-carbon composite having a yoke-shell structure according to an embodiment of the present invention is obtained using a silicon-polymer composite as an intermediate, which includes silicon particles and a polymer thin film formed on the surface of the silicon particles.

[0034] Therefore, in the following, a silicon-carbon composite having a yoke-shell structure according to an embodiment of the present invention will be described, while a silicon-polymer composite as an intermediate will be described.

[0035] Silicon particles

[0036] In an embodiment of the present invention, the intermediate silicon-polymer composite and the final product silicon-carbon composite with a yolk-shell structure contain silicon particles.

[0037] The silicon particles in the yoke-shell structured silicon-carbon composite according to an embodiment of the present invention serve to charge lithium. Therefore, when the yoke-shell structured silicon-carbon composite according to an embodiment of the present invention is used as an anode active material, the silicon particles can act as a main anode active material.

[0038] The silicon particles may be crystalline or amorphous, and are preferably amorphous or a similar phase from the viewpoint of expansion / contraction during charge / discharge of the secondary battery and battery performance. When the silicon particles are crystalline, the smaller the crystal grain size, the denser the composite, which strengthens the matrix and prevents cracks. This can improve the initial efficiency and cycle life characteristics of the secondary battery. Furthermore, when the silicon particles are amorphous or a similar phase, expansion or contraction during charge / discharge of the secondary battery is small, and battery performance such as capacity characteristics can be improved.

[0039] The size of the silicon particles can be selected so that the yolk-shell structured silicon-carbon composite according to an embodiment of the present invention is suitable for use as a negative electrode active material. Specifically, the average particle size of the silicon particles can be 10 nm to 50 μm, preferably 10 nm to 25 μm. When the silicon particles satisfy this average particle size range, it can be more advantageous to achieve the object of the present invention.

[0040] The silicon particles may further comprise a silicon oxide compound, which has the general formula SiO x(0.5≦x≦2). If the value of x is less than 0.5, the secondary battery may expand and contract significantly during charging and discharging, resulting in a deterioration in its lifespan. If x is greater than 2, the amount of inactive oxides increases, resulting in a decrease in the initial efficiency of the secondary battery.

[0041] The content of the silicon oxide compound in the silicon particles may be 50 wt % or less based on the total weight of the silicon particles. If the content of the silicon oxide compound in the silicon particles exceeds 50 wt %, the initial efficiency of the secondary battery may decrease.

[0042] The silicon particles may further contain elements such as carbon and magnesium in addition to silicon and oxygen. The silicon content in the silicon particles can be selected so that the total silicon content in the silicon-carbon composite is 1 to 80 wt %, preferably 5 to 50 wt %. If the total silicon content in the silicon-carbon composite is less than 1 wt %, the amount of active material that absorbs and releases lithium may be insufficient, resulting in a decrease in the charge / discharge capacity of the secondary battery. If the total silicon content in the silicon-carbon composite exceeds 80 wt %, the charge / discharge capacity of the secondary battery may increase, but the electrode may expand and contract excessively during charge / discharge, further pulverizing the negative electrode active material powder and reducing the cycle characteristics of the secondary battery.

[0043] polymer thin film

[0044] In an embodiment of the present invention, the silicon-polymer composite as an intermediate includes a polymer thin film formed on the surface of a silicon particle. The silicon-polymer composite may further include an outer polymer thin film on the polymer thin film. The polymer thin film and the outer polymer thin film may be formed by an initiator-based chemical vapor deposition method as described below. It is formed by vapor deposition (iCVD).

[0045] The polymer thin film is formed by iCVD and is not particularly limited in type as long as it does not substantially affect the electrical conductivity and ionic conductivity of the negative electrode active material. Specifically, the polymer thin film may be formed by polymerizing or copolymerizing at least one of vinyl or acrylate monomers containing at least one of a siloxane group, an amine group, a fluorine group, a glycidyl group, a carboxyl group, and an aromatic hydrocarbon group.

[0046] In a specific example of the present invention, the polymer thin film is made of 4-vinylpyridine (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-trimethyl-1,3,5-trivinylcyclotrisiloxane (V3D3), hexavinyldisiloxane (HVDS), glycidyl methacrylate, divinylbenzene, diethylene glycol divinyl Ether, diethylene glycol diacrylate (DEGDA), ethylene glycol dimethacrylate, dimethylaminoethyl methacrylate, methacrylic acid and 1,3-diethenyl-1,1,3,3-tetramethyl-disiloxane, 1H,1H,2H,2H-perfluorodecyl acrylate, perfluorodecyl methacrylate, dodecafluoroheptyl acrylate, pentafluorophenyl methacrylate, 3,3,4,4,5,5,6,6,7,7,8,8,9,9,9-pentadecafluorononyl acrylate, 2-methyl-3,3,4,4,5,5,6,6 ,7,7,8,8,9,9,9-Pentadecafluorononyl acrylate, 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl acrylate, 2-methyl-3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl acrylate, 3,3,4,4,5,5,6,6,7,7,7-undecafluoroheptyl acrylate, 2-methyl-3,3,4,4,5,5,6,6,7,7,7-undecafluoroheptyl acrylate, 3 ,3,4,4,5,5,6,6,6-nonafluorohexyl acrylate, 2-methyl-3,3,4,4,5,5,6,6,6-nonafluorohexyl acrylate, 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,11-nonadecafluoroundecyl acrylate, 2-methyl-3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,11-nonadecafluoroundecyl acrylate, 3,3,4,4,5,5, 6,6,7,7,8,8,9,9,10,10,11,11,12,12,12-heneicosafluorododecyl acrylate, 2-methyl-3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,12-heneicosafluorododecyl acrylate, 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,13,13,13-tricosafluorotridecyl 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-tricosafluorotridecyl 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-pentacosafluorotetradecyl acrylate, and 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,It may be polymerized from one or more monomers selected from the group consisting of 14-pentacosafluorotetradecyl acrylate, dimethylaminoethyl methacrylate, dimethylaminoethyl acrylate, diethylaminoethyl methacrylate, and diethylaminoethyl acrylate.

[0047] In a preferred embodiment of the present invention, the polymer thin film may be polymerized from one or more monomers selected from the group consisting of 1H,1H,2H,2H-perfluorodecyl acrylate, dimethylaminomethylstyrene, divinylbenzene, glycidyl methacrylate, acrylic acid, 1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane, 1,3,5-trivinyl-1,3,5-trimethylcyclotrisiloxane, and hexavinyldisiloxane, but is not particularly limited thereto.

[0048] In a specific example of the present invention, the thickness of the polymer thin film may be 1 nm to 10 μm, preferably 1 nm to 1 μm, and more preferably 10 to 100 nm. When the thickness of the polymer thin film is within this range, the polymer thin film can properly function as a sacrificial layer in the carbon thin film formation step described below, and pores can be properly formed between the silicon particles and the carbon thin film.

[0049] In an embodiment of the present invention, the polymer thin film on the surface of the silicon particle in the intermediate silicon-polymer composite is at least partially, preferably 10 to 100 wt %, and more preferably 50 to 100 wt %, removed in the carbon thin film formation step described below, thereby appropriately forming pores between the silicon particle and the carbon thin film. For example, in the silicon-polymer composite, the outer polymer thin film is carbonized and converted into a carbon thin film, and the polymer thin film located in the interior is at least partially removed to form pores.

[0050] Residues of the polymer thin film remaining after removal in the carbon thin film formation step may be present between the silicon particles and the carbon thin film in the yoke-shell structured silicon-carbon composite as the final product according to an embodiment of the present invention. The silicon-carbon composite of the present invention may include a residue of the polymer thin film between the silicon particles and the carbon thin film. However, the present invention is not limited thereto, and if the polymer thin film is completely removed by the heat treatment described below, the silicon-carbon composite of the yoke-shell structure may not include a residue of the polymer thin film between the silicon particles and the carbon thin film.

[0051] carbon thin film

[0052] A silicon-carbon composite having a yoke-shell structure according to an embodiment of the present invention includes a carbon thin film formed on the silicon particles.

[0053] The yoke-shell silicon-carbon composite according to an embodiment of the present invention includes a carbon thin film, which can ensure appropriate electrical conductivity and appropriately control the specific surface area. Therefore, when used as an anode active material for a secondary battery, the life characteristics and capacity of the secondary battery can be further improved.

[0054] The electrical conductivity of a negative electrode active material is an important factor for facilitating electron transfer during an electrochemical reaction. By including the carbon thin film in a yolk-shell silicon-carbon composite according to an embodiment of the present invention, the charge / discharge capacity, initial charge efficiency, and capacity retention of a secondary battery can be improved, and excellent electrical conductivity can be provided, thereby suppressing side reactions in the electrolyte, thereby further improving the performance of the secondary battery.

[0055] In the silicon-carbon composite with a yoke-shell structure according to the embodiment of the present invention, the carbon thin film may have a thickness of 1 nm to 5 μm, preferably 10 nm to 1 μm, and more preferably 10 to 500 nm. When the carbon thin film has a thickness within this range, the electrical conductivity can be improved and a decrease in the capacity of the secondary battery can be suppressed.

[0056] The 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 further include graphite, but is not particularly limited thereto.

[0057] pore space

[0058] In the silicon-carbon composite with a yoke-shell structure according to one embodiment of the present invention, pores exist between the silicon particles and the carbon thin film.

[0059] As described above, in the silicon-polymer composite serving as an intermediate for producing a silicon-carbon composite with a yolk-shell structure according to an embodiment of the present invention, the polymer thin film on the surface of the silicon particles acts as a sacrificial layer and is removed at least partially, preferably 10 to 100 wt %, and more preferably 50 to 100 wt %, in the carbon thin film formation step described below, thereby forming pores between the silicon particles and the carbon thin film.

[0060] In the yoke-shell silicon-carbon composite according to an embodiment of the present invention, the pores present between the silicon particles and the carbon thin film absorb the volumetric expansion of the silicon when the yoke-shell silicon-carbon composite is used as a negative electrode active material, thereby preventing the outermost carbon thin film from peeling off.

[0061] The yolk-shell structured silicon-carbon composite according to an embodiment of the present invention may have a porosity of 10 to 80%, preferably 10 to 50%, and more preferably 20 to 50%. Here, the porosity can be measured by the Brunauer-Emmett-Teller (BET) method, but is not particularly limited to this method. If the composite-carbon material satisfies the above porosity range, it may be more advantageous to achieve the object of the present invention.

[0062] Manufacturing method for yolk-shell structured silicon-carbon composite

[0063] A yoke-shell silicon-carbon composite according to one embodiment of the present invention is produced by a method for producing a yoke-shell silicon-carbon composite, the method including: (1) supplying silicon particles into a reactor; (2) supplying a monomer and an initiator into the reactor; (3) activating the initiator to polymerize the monomer to form a polymer thin film on the surface of the silicon particles, thereby obtaining a silicon-polymer composite; and (4) forming a carbon thin film on the silicon-polymer composite, thereby forming pores between the silicon particles and the formed carbon thin film, thereby producing a yoke-shell silicon-carbon composite.

[0064] Initiator-based chemical vapor deposition (iCVD) refers to a process in which a vapor-phase initiator is decomposed into radicals to polymerize the resulting monomer. Initiator-based chemical vapor deposition (iCVD) deposits polymer thin films by supplying energy from a heat source such as a heated filament or UV light. While this process may not appear significantly different from conventional CVD processes for depositing inorganic thin films, the iCVD process activates the initiator at low temperatures, typically in the range of 135-350°C, and preferably in the range of 140-340°C. Furthermore, the surface temperature of the silicon particles on which the polymer thin film is deposited is maintained low, typically in the range of 10-50°C, and preferably in the range of 13-45°C. Due to this low surface temperature, iCVD is useful for depositing polymer thin films on various substrates that are vulnerable to mechanical or chemical shock. Furthermore, iCVD is performed under vacuum conditions of 50-1,000 mTorr, preferably 60-900 mTorr, eliminating the need for high-vacuum equipment.

[0065] 1 is a schematic diagram illustrating a process for fabricating an intermediate silicon-polymer composite by forming a polymer thin film on the surface of silicon particles using initiator-based chemical vapor deposition (iCVD) according to an embodiment of the present invention. A method for fabricating a silicon-carbon composite with a yolk-shell structure according to an embodiment of the present invention will now be described with reference to FIG. 1.

[0066] Stage (1)

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

[0068] The specific content of the silicon particles used in step (1) is as explained above in the section on the silicon-carbon composite with a yolk-shell structure.

[0069] The reactor used in the method for producing a yolk-shell silicon-carbon composite according to an embodiment of the present invention is not particularly limited in structure, as long as it is capable of forming a polymer thin film on the surface of silicon particles using an initiator-based chemical vapor deposition (iCVD) method described below.

[0070] In an embodiment of the present invention, the reactor 10 may include a chamber 100 , a mounting section 200 , an inlet 300 , an outlet 400 and a heating section 500 .

[0071] The silicon particles may be placed in a mounting part 200 provided at the lower end of the chamber 100 of the reactor 10. The shape, size, and material of the mounting part are not particularly limited as long as it can accommodate the silicon particles. Specifically, the mounting part may be flat so that the silicon particles can be spread out and placed without overlapping with each other as much as possible. More specifically, In addition, a silicon substrate (wafer) can be used as a mounting part for accommodating the silicon particles, but is not particularly limited thereto.

[0072] The mounting unit may be connected to a position changing means (not shown) that can change the position of the silicon particles. The position changing means may vibrate or move the mounting unit, which may be a silicon substrate, to change or rotate the positions of the silicon particles arranged on the silicon substrate, thereby enabling a polymer thin film to be uniformly formed on the surface of the silicon particles in step (3), which will be described later, but is not limited thereto.

[0073] Stage 2

[0074] In step (2) above, the monomers and initiator are fed to the reactor.

[0075] At this time, the monomer M and the initiator I may be vaporized and supplied to the chamber 100 through the inlet 300 of the reactor 10 .

[0076] The monomer M is a volatile material that can be activated by the initiator I to form a polymer. Details of the monomer are as described above in the section on the yolk-shell silicon-carbon composite.

[0077] The initiator I is a substance that decomposes under heat or light to form free radicals. There are no particular limitations on the type of initiator as long as it is a substance that can activate the monomers to form a polymer. Preferably, the initiator is a peroxide. Specifically, the initiator may include at least one selected from the group consisting of di-t-butyl peroxide, t-butyl peroxybenzoate, benzoyl peroxide, methyl ethyl ketone peroxide, lauryl peroxide, and benzophenone, but is not limited thereto. Most preferably, the initiator is di-t-butyl peroxide.

[0078] In this case, the flow rate of the monomer in the reactor may be 0.1 sccm to 10 sccm. Specifically, the flow rate of the monomer may 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.

[0079] The flow rate of the initiator in the reactor may be 0.1 sccm to 5 sccm. Specifically, the flow rate of the initiator may be 0.1 sccm or more and 5 sccm or less, 3 sccm or less, or 2 sccm or less.

[0080] Stage 3

[0081] In the above step (3), the initiator is activated and the monomer is polymerized to form a polymer thin film on the surface of the silicon particles, thereby obtaining a silicon-polymer composite.

[0082] The initiator can be activated by a predetermined heat treatment. For example, the initiator, which is first supplied in a vaporized state into the chamber 100 of the reactor 10, is activated upon contact with the heating unit 500 to form free radicals. The heating unit may be, for example, a number of electrically heated filaments, but is not particularly limited thereto. The temperature of the heating unit is not limited as long as it can decompose and activate the initiator. However, a temperature in the range of 135 to 350°C, preferably 140 to 340°C, can be advantageous from the viewpoint of preventing changes in the properties of the reactants.

[0083] The free radicals and monomers generated from the initiator move together to the bottom of the chamber and are adsorbed onto the surface of the silicon particles housed in the mounting part 200. The monomers adsorbed onto the surface of the silicon particles are polymerized by the free radicals to form a polymer thin film on the surface of the silicon particles.

[0084] The vapor phase initiator and monomer remaining after being used in the reaction in step (3) above can be discharged out of the reactor using outlet 400.

[0085] In step (3), it is preferable to maintain a low surface temperature of the silicon particles in order to increase the adsorption rate of the monomer and free radicals. Specifically, the surface temperature of the silicon particles is preferably in the range of 10 to 50°C, and preferably in the range of 13 to 45°C, but is not particularly limited to this range. In order to maintain the surface temperature of the silicon particles within the above range, the reactor 10 may further include a cooling unit (not shown) disposed below the mounting unit 200. The cooling method and structure of the cooling unit (not shown) are not particularly limited as long as it can control the surface temperature of the silicon particles within the above range.

[0086] The above step (3) may be carried out under a vacuum condition of 50 to 1,000 mTorr, preferably 60 to 900 mTorr. This vacuum range can be achieved using a simple rotary pump rather than a high vacuum pump. Furthermore, the reaction time in step (3) may be 10 minutes to 6 hours, preferably 30 minutes to 2 hours, but is not limited thereto. However, by ensuring that the reaction time satisfies the above range, a polymer thin film of the desired thickness can be uniformly formed.

[0087] Furthermore, the reaction in step (3) can be carried out for 10 minutes to 6 hours, preferably 30 minutes to 2 hours, but is not limited thereto. However, by ensuring that the reaction time is within the above range, a polymer thin film of the desired thickness can be formed uniformly.

[0088] The physical properties of the polymer thin film formed in step (3) can be easily adjusted by controlling the process variables of iCVD, such as the pressure and temperature in the chamber, reaction time, flow rate of the initiator and monomer, and surface temperature of the heating element and silicon particles, thereby easily adjusting the molecular weight, thickness, composition, and deposition rate of the polymer thin film.

[0089] Stage (4)

[0090] In the above step (4), a carbon thin film is formed on the silicon-polymer composite, and pores are formed between the silicon particles and the formed carbon thin film, thereby producing a silicon carbon composite with a yoke-shell structure.

[0091] The steps of forming a carbon thin film on the silicon-polymer composite particles as an intermediate and forming pores between the silicon particles and the carbon thin film may be performed using an apparatus and method known in the art to which the present invention pertains, for example, a chemical pyrolysis deposition method, but are not limited thereto.

[0092] According to a preferred embodiment of the present invention, the carbon thin film may be formed by carbonizing a peripheral polymer thin film formed on the silicon-polymer composite using an initiator-based chemical vapor deposition (iCVD) method. At this time, the initiator-based chemical vapor deposition (iCVD) method is the same as that described in step (3), and therefore, the description thereof will be omitted below. At this time, the peripheral polymer thin film is carbonized, and the silicon Pores can be formed by removing the polymer thin film on the silicon particles. The carbonization can be carried out at a temperature of 400 to 1,400°C, preferably 500 to 1,400°C, more preferably 600 to 1,400°C, and even more preferably 650 to 1,400°C. If the temperature is below this range, the carbon thin film may not be formed to the desired level, and if the temperature is above this range, the silicon-carbon composite may be damaged.

[0093] In another embodiment of the present invention, the step of forming a carbon thin film on the intermediate silicon-polymer composite and forming pores between the silicon particles and the carbon thin film may be performed by heat-treating the intermediate silicon-polymer composite in the presence of a gaseous carbon source at a temperature of 400 to 1,400° C., preferably 500 to 1,400° C., more preferably 600 to 1,400° C., and even more preferably 650 to 1,400° C. If the temperature is below this range, the carbon thin film may not be formed to the desired level, and if the temperature is above this range, the silicon-carbon composite may be damaged.

[0094] 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, propanediol, butanediol, ethylene, propylene, butylene, butadiene, cyclopentene, acetylene, benzene, toluene, xylene, ethylbenzene, naphthalene, anthracene, and dibutylhydroxytoluene, but is not particularly limited thereto.

[0095] The step of forming a carbon thin film on the silicon-polymer composite as an intermediate may 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 carbon source described above.

[0096] The reaction time (heat treatment time) for forming the carbon thin film can be appropriately adjusted depending on the heat treatment temperature, the pressure during the heat treatment, the composition of the gas mixture, and the desired carbon coating amount. For example, the reaction time can be 10 minutes to 100 hours, specifically 30 minutes to 90 hours, and more specifically 50 minutes to 40 hours, but is not particularly limited to this range.

[0097] In an embodiment of the present invention, the step of forming a carbon thin film on the silicon-polymer composite as an intermediate may be performed by mixing the silicon-polymer composite with a solution in which a carbon source is dispersed in a solvent as needed, followed by drying and heat-treating the mixture at a temperature of 400 to 1,400°C.

[0098] In a preferred embodiment of the present invention, the carbon source can be selected from the group consisting of pitch, hydrocarbon-based materials, and petroleum-based materials. More specifically, the pitch can be petroleum-based pitch, coal-based pitch, or a mixture thereof. The hydrocarbon-based material can be furfuryl alcohol or a phenolic resin. 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 a tetrahydrofuran (TFO) or a tetrahydrofuran (TCC ... It may be tetrahydrofuran (THF) or an alcohol.

[0099] When the intermediate silicon-polymer composite is heat-treated in the presence of a carbon source, at least a portion, preferably 10 to 100 wt %, and more preferably 50 to 100 wt %, of the polymer thin film is removed, thereby appropriately forming pores between the silicon particles and the carbon thin film. In this case, the silicon-polymer composite may further include an outer polymer thin film, as described above. The outer polymer thin film may be carbonized and converted into a carbon thin film, and at least a portion of the inner polymer thin film may be removed to form pores. Residue of the polymer thin film remaining after removal during the carbon thin film formation step may be present between the silicon particles and the carbon thin film in the yolk-shell silicon-carbon composite as a final product according to an embodiment of the present invention. However, this is not limited thereto. If the polymer thin film is completely removed by the heat treatment, or if the yolk-shell silicon-carbon composite is completely removed, the yolk-shell silicon-carbon composite may not include any polymer thin film residue between the silicon particles and the carbon thin film.

[0100] In step (4) above, when a carbon thin film is formed on the silicon-polymer composite particles and pores are formed between the silicon particles and the carbon thin film, the degree of pore formation and the degree of polymer thin film remaining can be appropriately controlled depending on the type of monomer, process conditions for forming the polymer thin film, type of carbon source, process conditions for forming the carbon thin film, etc. When the silicon-carbon composite having a yoke-shell structure obtained in this manner is used as an anode active material, the electrical conductivity of the anode active material can be improved without changing the structure.

[0101] negative electrode active material

[0102] According to yet another embodiment of the present invention, there is provided an anode active material comprising the silicon-carbon composite having a yolk-shell structure.

[0103] The negative electrode active material according to an embodiment of the present invention may further include a carbon-based negative electrode material, specifically, a graphite-based negative electrode material, in addition to the yoke-shell silicon-carbon composite. For example, the negative electrode active material may be obtained by mixing the yoke-shell silicon-carbon composite according to an embodiment of the present invention with a carbon-based negative electrode material, for example, a graphite-based negative electrode material.

[0104] Here, the carbon-based negative electrode material may include, for example, at least one selected from the group consisting of natural graphite, artificial graphite, soft carbon, hard carbon, mesocarbon, carbon fiber, carbon nanotube, pyrolytic carbons, cokes, fired organic polymer compounds, and carbon black, but is not particularly limited to these.

[0105] The content of the carbonaceous negative electrode material in the negative electrode active material according to an embodiment of the present invention may be 2 to 80 wt %, preferably 5 to 70 wt %, more preferably 30 to 70 wt %, based on the total weight of the negative electrode active material.

[0106] The negative electrode active material according to an embodiment of the present invention can be effectively used to manufacture a secondary battery, specifically, a negative electrode of a lithium secondary battery and a negative electrode of an all-solid-state battery.

[0107] all solid state battery

[0108] According to yet another embodiment of the present invention, there is provided an all-solid-state battery including a solid electrolyte interphase (SEI) film including the silicon-carbon composite with the yolk-shell structure.

[0109] The all-solid-state battery may be an all-solid-state battery including a positive electrode, a negative electrode, and a solid electrolyte between the positive electrode and the negative electrode, and the negative electrode may include a negative electrode active material layer, and may include an SEI (Solid Electrolyte Interphase) film including the silicon-carbon composite with the yolk-shell structure on at least a portion of the negative electrode active material particles of the negative electrode active material layer.

[0110] The negative electrode active material particles may be a carbon-based negative electrode material. In this case, the negative electrode active material is the same as that described above with respect to the negative electrode active material, and therefore, the related description will be omitted.

[0111] In addition, in addition to the negative electrode active material particles and the SEI film of the all-solid-state battery, the configuration of the negative electrode, the configuration of the positive electrode, the configuration of the solid electrolyte, and the like can be any known configuration of an all-solid-state battery, and therefore, the present invention is not particularly limited thereto. [Example]

[0112] Example

[0113] The present invention will be described in more detail below with reference to examples. The following examples are merely illustrative of the present invention and are not intended to limit the scope of the present invention.

[0114] Example 1

[0115] Manufacturing of silicon-polymer composites (intermediates)

[0116] Silicon-polymer composites were produced using the reactor shown generally in Figure 1. Five grams of silicon powder with average particle sizes of 20 μm and 2 μm were evenly spread on a circular silicon wafer. Vaporized monomer and initiator were supplied to the reactor chamber through an inlet to form a thin polymer film (pPFDA) on the silicon particle surface. The materials and process conditions used in this example are as follows:

[0117] -Silicon particles: average particle size 20μm and 2μm (REC Silicon)

[0118] Monomer: 1H,1H,2H,2H-perfluorodecyl acrylate (Aldrich, 97%)

[0119] Initiator: di-t-butyl peroxide (Aldrich, 98%)

[0120] -Average initiator feed flow rate: 0.26 sccm

[0121] -Average monomer feed flow rate: 0.425sccm

[0122] - Filament temperature: 140℃

[0123] -Pressure in reactor chamber: 80mTorr

[0124] -Surface temperature of reactor mounting part (silicon wafer): 38℃

[0125] <Experimental Example 1>

[0126] (1) X-ray photoelectron spectroscopy

[0127] The silicon particles before and after the polymer thin film was formed were analyzed for elements on the particle surface using X-ray photoelectron spectroscopy (Multilab 2000, Thermo). The results are shown in Table 1.

[0128] [Table 1]

[0129] As is clear from Table 1, almost no fluorine was measured on the surface of the silicon particles before the polymer thin film was formed, but a considerable amount of fluorine was measured after the polymer thin film was formed on the silicon particles by the manufacturing method of the present invention. Therefore, it can be seen that the manufacturing method of the present invention produced a silicon-polymer composite in which a fluorine-containing polymer thin film was formed on the surface of the silicon particles.

[0130] (2) Water dispersibility

[0131] 0.3 g of the silicon particles before the polymer thin film was formed and 0.3 g of the silicon-polymer composite obtained in Example 1 were each dispersed in 10 ml of water for 10 minutes. The results are shown in Figure 3.

[0132] Silicon particles before the polymer thin film was formed were sufficiently dispersed in water (Figure 3a), indicating their hydrophilicity. On the other hand, silicon-polymer composites with the polymer thin film formed on them did not disperse in water but formed a layer on the water surface (Figure 3b), indicating that their surfaces had been modified to be hydrophobic. This demonstrates that the manufacturing method of the present invention produced silicon-polymer composites with a fluorine-containing polymer thin film formed on the surface of silicon particles.

[0133] (3) Transmission electron microscope-energy dispersive spectrometer

[0134] The silicon particles with an average diameter of 20 μm on which the polymer thin film was formed were observed using a transmission electron microscope (TEM) and energy dispersive spectrometer (EDS) (Tecnai G2 F30 S-Twin, FEI company). The TEM analysis results are shown in Figure 4, and the EDS analysis results are shown in Figure 5 and Tables 2 and 3.

[0135] [Table 2]

[0136] [Table 3]

[0137] As a result, from the bare silicon particles in FIG. 2 and the TEM photograph in FIG. 4, it can be seen that the silicon-polymer composite obtained in Example 1 formed a uniform thin film of approximately 5 nm without any problems such as particle fracture, and essentially maintained its original shape. FIG. 5 and Tables 2 and 3 show the EDS analysis results for the areas where the silicon-polymer composite was present (areas marked A and B in FIG. 5a and areas marked D and E in FIG. 5b) and the areas where the silicon-polymer composite was not present (area marked C in FIG. 5a). In the areas where the silicon-polymer composite was present, all fluorine, a component of the monomer, was observed, whereas in the areas where the silicon-polymer composite was not present, fluorine, a component of the monomer, was not observed. Therefore, it can be qualitatively confirmed that a silicon-polymer composite with a polymer thin film formed on the surface of silicon particles was produced using the manufacturing method of the present invention.

[0138] <Example 2> A silicon-polymer composite was produced in the same manner as in Example 1, except for the following changes: a thin polymer film (pDMAMS) was formed on the surface of silicon particles to produce the silicon-polymer composite.

[0139] -Non-porous silicon particles: average particle size 20μm (REC Silicon)

[0140] -Monomer: dimethylaminomethylstyrene styrene) (Acros, 90%)

[0141] -Pressure in reactor chamber: 160mTorr

[0142] -Surface temperature of reactor mounting part (silicon wafer): 35℃

[0143] <Experimental Example 2>

[0144] (1) Transmission electron microscope-energy dispersive spectrometer

[0145] Silicon particles with an average particle size of 20 μm (Example 2) on which a polymer thin film was formed were observed using a transmission electron microscope (TEM) and energy dispersive spectrometer (EDS) (Tecnai G2 F30 S-Twin, FEI company). The TEM analysis results are shown in FIG. 6, and the EDS analysis results are shown in FIG. 7.

[0146] As a result, from the bare silicon particles in Figure 2 and the TEM photograph in Figure 6, it was found that the silicon-polymer composite obtained in Example 2 formed a uniform thin film with a thickness of about 5 nm and essentially maintained its original shape.

[0147] Furthermore, as shown in FIG. 7, the silicon-polymer composite obtained in Example 2 was confirmed to contain the desired nitrogen atoms, and it was qualitatively confirmed that a silicon-polymer composite in which a polymer thin film was formed on the surface of silicon particles was produced by the manufacturing method of the present invention.

[0148] Example 3

[0149] A silicon-polymer composite was produced in the same manner as in Example 1, except for the following changes: a thin polymer film (pGMA) was formed on the surface of silicon particles to produce the silicon-polymer composite.

[0150] -Non-porous silicon particles: average particle size 20μm (REC Silicon)

[0151] Monomer: Glycidyl methacrylate (Alcrich, 97%)

[0152] -Pressure in reactor chamber: 300mTorr

[0153] -Surface temperature of reactor mounting part (silicon wafer): 30℃

[0154] <Comparative Example 1>

[0155] Fabrication of Silicon-Polymer Composites

[0156] 0.5 g of silicon powder with an average particle size of 20 μm was added to 10 ml of a 3 wt% solution of polydivinylbenzene (pDVB) dissolved in toluene solvent, and liquid coating was carried out at a speed of 40 rpm and room temperature (25°C) for 120 minutes. The liquid-coated silicon powder was then removed and dried at room temperature (25°C) for 12 hours to produce a liquid-coated silicon-polymer composite.

[0157] <Experimental Example 3>

[0158] (1) Transmission electron microscope analysis

[0159] The silicon particles (Example 3) having an average particle size of 20 μm on which the polymer thin film was formed were observed using a transmission electron microscope (TEM). The TEM analysis results are shown in FIG.

[0160] As a result, from the bare silicon particles in Figure 2 and the TEM photograph in Figure 8, it was found that the silicon-polymer composite obtained in Example 3 formed a uniform thin film with a thickness of about 10 nm and essentially maintained its original shape.

[0161] (2) Comparative transmission electron microscope analysis

[0162] The bare silicon particles (FIGS. 9a-9d), the silicon-polymer composite obtained in Example 3 (FIGS. 9e-9h), and the liquid-coated silicon-polymer composite obtained in Comparative Example 1 (FIGS. 9i-9l) were observed using a transmission electron microscope (TEM). The TEM analysis results are shown in FIG. 9. As a result, in the case of the silicon-polymer composite of Example 3 (Figures 9e to 9h), it was confirmed that the shape of the bare silicon particles (Figures 9a to 9d) was maintained and a polymer coating of uniform thickness was formed.

[0163] On the other hand, in the case of the liquid-coated silicon-polymer composite obtained in Comparative Example 1 (FIGS. 9i to 9l), the shape of the bare silicon particles (FIGS. 9a to 9d) was not maintained, and it was confirmed that the polymer was coated in an irregular shape unrelated to the shape of the bare silicon particles.

[0164] Overall, it can be seen that the iCVD method must be used to coat a polymer with a uniform thickness on silicon particles.

[0165] Example 4

[0166] A silicon-polymer composite was produced in the same manner as in Example 1, except that the following changes were made to form a polymer thin film (pDVB) on the surface of silicon particles to produce the silicon-polymer composite.

[0167] -Non-porous silicon particles: average particle size 20μm (REC Silicon)

[0168] Monomer: Divinylbenzene (Aldrich, 80%)

[0169] -Pressure in reactor chamber: 450mTorr

[0170] -Surface temperature of reactor mounting part (silicon wafer): 23℃

[0171] <Experimental Example 4>

[0172] (1) Transmission electron microscope analysis

[0173] The silicon particles (Example 4) having an average particle size of 20 μm on which the polymer thin film was formed were observed using a transmission electron microscope (TEM). The TEM analysis results are shown in FIG.

[0174] As a result, from the bare silicon particles in Figure 2 and the TEM photograph in Figure 10, it was found that the silicon-polymer composite obtained in Example 4 formed a uniform thin film with a thickness of about 10 nm and essentially maintained its original shape.

[0175] <Example 5>

[0176] A silicon-polymer composite was produced in the same manner as in Example 1, except that the following changes were made to form a thin polymer film (pAA) on the surface of the silicon particles.

[0177] -Non-porous silicon particles: average particle size 20μm (REC Silicon)

[0178] -Monomer: acrylic acid (Aldrich)

[0179] -Pressure in reactor chamber: 500mTorr

[0180] -Surface temperature of reactor mounting part (silicon wafer): 23℃

[0181] <Production example>

[0182] Fabrication of yolk-shell structured silicon-carbon composites

[0183] Five grams of the silicon-polymer composite prepared in Example 5 was evenly spread on a circular silicon wafer. Vaporized monomer and initiator were supplied into the reactor chamber through an inlet to form a thin peripheral polymer film (pDVB) on the silicon-polymer composite, thereby forming a silicon-polymer-peripheral polymer composite. The specific materials and process conditions used in this example are as follows:

[0184] -Silicon particles: average particle size 20μm and 2μm (REC Silicon)

[0185] Monomer: Divinylbenzene (Aldrich, 80%)

[0186] Initiator: di-t-butyl peroxide (Aldrich, 98%)

[0187] -Average initiator feed flow rate: 0.26 sccm

[0188] -Average monomer feed flow rate: 0.425sccm

[0189] - Filament temperature: 140℃

[0190] -Pressure in reactor chamber: 450mTorr

[0191] -Surface temperature of reactor mounting part (silicon wafer): 23℃

[0192] 5 g of the silicon-polymer-periphery polymer composite (intermediate) was then evenly spread on a circular silicon wafer in a reactor. It was then oxidized in an air atmosphere at 250°C for 50 minutes to improve the stability of the outermost pDVB polymer. It was then carbonized at 700°C for 30 minutes to remove the polymer thin film and replace the outer polymer thin film with a carbon thin film, producing a silicon-carbon composite with a yoke-shell structure.

[0193] As a result, as shown in Figure 11, it can be seen that the resistance of the manufacturing example in which carbonization was performed at a temperature of 700°C was significantly lower, and a carbonized thin film was produced (compared to the same conditions performed at temperatures of 500°C and 600°C).

[0194] <Experimental Example 5>

[0195] (1) Transmission electron microscope-energy dispersive spectrometer

[0196] The silicon-polymer-periphery polymer composite (intermediate) and the silicon-carbon composite with a yolk-shell structure according to the Preparation Example were observed using a transmission electron microscope (TEM) and energy dispersive spectrometer (EDS) (Tecnai G2 F30 S-Twin, FEI company). The TEM analysis results are shown in Figures 12a and 13a, respectively, and the EDS analysis results are shown in Figures 12b and 13b, and Figures 12c and 13c, respectively.

[0197] As a result, it was confirmed from the TEM image of FIG. 12 that a silicon-polymer-periphery polymer composite was formed, and from the EDS analysis result image, it was confirmed that certain atoms were detected in all parts. It was confirmed from the TEM image of FIG. 13 that the silicon-carbon composite was formed with a yoke-shell structure having uniform pores, and from the EDS analysis result image, it was confirmed that certain pores were formed by the presence of regions where no atoms were detected between regions where carbon atoms and silicon atoms were detected.

[0198] Although the embodiments of the present invention have been described above, the concept of the present invention is not limited to the embodiments 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, or adding components within the same concept, and these can also be said to fall within the concept of the present invention.

Claims

1. (1) providing silicon particles into a reactor; (2) feeding monomers and an initiator to the reactor; (3) activating an initiator to polymerize the monomer to form a polymer thin film on the surface of the silicon particles, thereby obtaining a silicon-polymer composite; (4) forming a carbon thin film on the silicon-polymer composite and forming pores between the silicon particles and the formed carbon thin film, thereby producing a silicon-carbon composite with a yoke-shell structure.

2. 2. The method for producing a silicon-carbon composite having a yoke-shell structure according to claim 1, wherein the silicon particles have an average particle size of 10 nm to 50 μm.

3. The method for producing a silicon-carbon composite with a yoke-shell structure according to claim 1, wherein the polymer thin film has a thickness of 1 nm to 10 μm.

4. In the step (2), the monomer is supplied at a flow rate of 0.1 sccm to 10 sccm; 2. The method for producing a silicon-carbon composite having a yoke-shell structure according to claim 1, wherein the initiator is supplied at a flow rate of 0.1 sccm to 5 sccm.

5. The initiator is activated by a predetermined heat treatment, The method for producing a silicon-carbon composite having a yoke-shell structure according to claim 1, wherein the heat treatment is carried out at a temperature of 135 to 350°C.

6. 2. The method of claim 1, wherein step (3) is performed in a vacuum state at a pressure of 50 to 1,000 mTorr for 10 minutes to 6 hours.

7. The silicon particles are located in a reactor mounting portion; 2. The method of claim 1, wherein the temperature of the mounting portion in the step (3) is 10 to 50°C.

8. 10. The method of claim 1, wherein step (4) is performed by supplying a monomer and an initiator to the reactor, activating the initiator, and polymerizing the monomer to form a thin polymer film on the surface of the silicon-polymer composite, followed by heat treatment at a temperature of 400 to 1,400°C.

9. 2. The method for producing a silicon-carbon composite having a yoke-shell structure according to claim 1, wherein step (4) is performed by heat treatment at a temperature of 400 to 1,400° C. in the presence of a carbon source.

10. 2. The method for producing a silicon-carbon composite having a yoke-shell structure according to claim 1, wherein the carbon thin film has a thickness of 1 nm to 1 μm.

11. Silicon particles; a carbon thin film formed on the silicon particles with a predetermined pore space; and

12. 12. The silicon-carbon composite of claim 11, wherein the silicon-carbon composite of said yoke-shell structure has a porosity of 10 to 80%.

13. A negative electrode active material comprising the silicon-carbon composite with a yolk-shell structure according to claim 11 or 12.

14. An all-solid-state battery comprising: an SEI (Solid Electrolyte Interphase) film comprising the silicon-carbon composite with a yolk-shell structure according to claim 11 or 12.

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