Silicon-polymer composite, method for producing the same, negative electrode active material including the same, and all-solid-state battery including the same

Abstract

The present invention relates to a silicon-polymer composite, a method for manufacturing the same, and an anode active material including the same. The silicon-polymer composite according to an embodiment of the present invention has excellent thickness uniformity in the polymer thin film, and the existing shape of the silicon particles is preserved. The polymer thin film has little effect on electrical conductivity and lithium ion conductivity. When used as an anode active material, the silicon-polymer composite maintains the high specific power and coulombic efficiency of silicon, which is the main anode active material, while functioning as a stable solid electrolyte interfacial layer between the silicon and the electrolyte, thereby suppressing deterioration of battery performance and lifespan.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a silicon-polymer composite, and more particularly to a silicon-polymer composite, a method for manufacturing the same, and an anode 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 more active, demand for the batteries used in these electronic devices and electric vehicles has also increased significantly.

[0003] Secondary batteries, such as lithium secondary batteries and all-solid-state batteries, containing liquid electrolytes are the most widely used for such applications because of their high energy density and low self-discharge when not in use. Secondary batteries generally consist of a positive electrode, a negative electrode, and an electrolyte (liquid or solid), and carbon-based 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%, which causes the silicon as an anode active material to break down with repeated charging and discharging, resulting in a significant decrease in mechanical stability.

[0005] To solve these problems, Japanese Patent No. 4393610 discloses an anode active material in which silicon is composited with carbon through a mechanical processing process and the surface of the silicon particles is coated with a carbon layer using chemical vapor deposition (CVD). However, this method has limitations in suppressing volume expansion and contraction during charge and discharge.

[0006] In addition, silicon-based anode active materials have the problem that the solid electrolyte interphase (SEI) layer that is generated in excess during the process of crushing and pulverizing silicon raw materials is unstable, causing a decrease in battery stability and electrical performance. Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a silicon-polymer composite that has excellent thickness uniformity in the polymer thin film, preserves the original shape of silicon particles, and can suppress deterioration of battery performance and lifespan when used as a negative electrode active material.

[0008] Another object of the present invention is to provide a method for producing the above silicon-polymer composite.

[0009] It is still another object of the present invention to provide a negative electrode active material containing the above silicon-polymer composite. [Means for solving the problem]

[0010] The present invention provides a method for producing a silicon-polymer composite, which comprises forming a thin polymer film on the surface of silicon particles using initiator-based chemical vapor deposition (iCVD).

[0011] According to one embodiment of the present invention, the step of forming the polymer thin film may include the steps of: (1) supplying silicon particles into a reactor; (2) supplying a monomer and an initiator to the reactor containing the silicon particles; and (3) activating the initiator to polymerize the monomer, thereby forming a polymer thin film on the surface of the silicon particles.

[0012] The silicon particles may also be non-porous silicon particles.

[0013] The silicon particles may have an average particle size of 10 nm to 50 μm.

[0014] The polymer thin film may have a thickness of 1 nm to 10 μm.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] Also, after the step of forming the polymer thin film, the method may further include the step of forming a carbon thin film on the surface of the polymer thin film.

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

[0020] The present invention also provides a silicon-polymer composite produced by the above-described method for producing a silicon-polymer composite.

[0021] The present invention also provides a negative electrode active material comprising the above-mentioned silicon-polymer composite and a carbon-based negative electrode material.

[0022] The present invention also provides an all-solid-state battery comprising an SEI (Solid Electrolyte Interphase) film containing the aforementioned silicon-polymer composite. [Effects of the Invention]

[0023] The silicon-polymer composite according to an embodiment of the present invention has excellent thickness uniformity of the polymer thin film, preserves the existing shape of the silicon particles, and has little effect on the electrical conductivity and lithium ion conductivity. Therefore, when used as an anode active material, the silicon-polymer composite acts as a stable solid electrolyte interfacial layer between the silicon and the electrolyte while maintaining the high specific power and coulombic efficiency of silicon as a main anode active material, thereby suppressing deterioration of battery performance and lifespan. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 1 is a schematic diagram illustrating a process for forming a polymer thin film on a silicon particle surface by initiator-based chemical vapor deposition (iCVD) according to 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 a silicon-polymer composite according to one embodiment of the present invention. [Figure 5b] FIG. 5b is an energy dispersive spectroscopy (EDS) image of a silicon-polymer composite according to one embodiment of the present invention. [Figure 6] FIG. 6 is a TEM image of a silicon-polymer composite (Example 2) according to one embodiment of the present invention. [Figure 7] FIG. 7 is a graph comparing the nitrogen atom content of bare silicon particles and a silicon-polymer composite according to one embodiment of the present invention (Example 2). [Figure 8] FIG. 8 is a TEM image of a silicon-polymer composite (Example 3) according to one embodiment of the present invention. [Figure 9] FIG. 9 is a TEM image of a silicon-polymer composite (Example 4) according to one embodiment of the present invention. [Figure 10] FIG. 10 shows TEM images of bare silicon particles, a silicon-polymer composite according to one embodiment of the present invention (Example 4), and a silicon-polymer composite that has been polymer-coated in liquid form (Comparative Example 1). [Figure 11] FIG. 11 is a graph showing the measurement results of the initial charge / discharge efficiency and capacity retention of a battery using bare silicon particles and a battery using a silicon-polymer composite according to one embodiment of the present invention (Example 1) (Production Example 1). DETAILED DESCRIPTION OF THE INVENTION

[0025] 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.

[0026] In this specification, the word "comprise" means that other components may be further included, unless otherwise specified.

[0027] All numbers and expressions expressing quantities 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.

[0028] 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.

[0029] The present invention will be described in more detail below.

[0030] Silicon-polymer composite

[0031] The present invention provides a silicon-polymer composite manufactured by the method for manufacturing a silicon-polymer composite described below. The silicon-polymer composite includes silicon particles and a polymer thin film formed on the surface of the silicon particles.

[0032] Silicon particles

[0033] A silicon-polymer composite according to one embodiment of the present invention comprises silicon particles.

[0034] The silicon particles play a role in charging lithium, and therefore, when the silicon-polymer composite according to an embodiment of the present invention is used as a negative electrode active material, the silicon particles play a role in charging lithium. It can act as an electrode active material.

[0035] The silicon particles may be one or more of porous silicon particles and non-porous silicon particles, but are preferably non-porous silicon particles, which may be advantageous in terms of excellent thickness uniformity of the polymer thin film, preserving the original shape of the silicon particles, and suppressing deterioration of battery performance and lifespan when used as a negative electrode active material.

[0036] The silicon particles may be crystalline or amorphous, and are preferably amorphous or a similar phase in terms 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 improves 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, improving battery performance such as capacity characteristics.

[0037] The size of the silicon particles may be selected so that the silicon-polymer composite according to the embodiment of the present invention is suitable for use as a negative electrode active material. Specifically, the average particle size of the silicon particles may be 10 nm to 50 μm, preferably 10 nm to 25 μm. When the silicon particles satisfy this average particle size range, it may be more advantageous to achieve the object of the present invention.

[0038] The silicon particles may further comprise a silicon oxide compound having 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.

[0039] 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.

[0040] 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-polymer composite is 1 to 80 wt %, preferably 5 to 50 wt %. If the total silicon content in the silicon-polymer 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-polymer 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.

[0041] polymer thin film

[0042] A silicon-polymer composite according to one embodiment of the present invention includes a thin polymer film formed on the surface of silicon particles.

[0043] In the silicon-polymer composite according to the embodiment of the present invention, the polymer thin film on the surface of the silicon particle can be formed by the initiator-based chemical vapor deposition method described below. It is formed by chemical vapor deposition (iCVD).

[0044] 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 lithium ion 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, and an aromatic hydrocarbon group.

[0045] 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 (1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane (V4D4), 1,3,5-trimethyl-1,3,5-trivinylcyclotrisiloxane (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, 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-pentadecafluoro Nonyl 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-trichotofluorotridecyl 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, and one or more monomers 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-pentacosafluorotetradecyl acrylate, dimethylaminoethyl methacrylate, dimethylaminoethyl acrylate, diethylaminoethyl methacrylate, and diethylaminoethyl acrylate. It may also be something that

[0046] 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, 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.

[0047] In a specific example of the present invention, the polymer thin film may have a thickness of 1 nm to 10 μm, preferably 1 nm to 1 μm, and more preferably 10 to 100 nm. When the polymer thin film has a thickness within this range, it acts as a stable solid electrolyte interfacial layer between the silicon and the electrolyte without substantially affecting the electrical conductivity and lithium ion conductivity of the negative electrode active material, thereby preventing a decrease in battery life.

[0048] carbon thin film

[0049] The silicon-polymer composite according to one embodiment of the present invention may further include a carbon thin film formed on the surface of the polymer thin film to produce a silicon-polymer-carbon composite.

[0050] When the silicon-polymer composite according to an embodiment of the present invention further comprises a carbon thin film to form a silicon-polymer-carbon composite, the silicon-polymer-carbon composite can ensure appropriate electrical conductivity and appropriately control its specific surface area. When the silicon-polymer-carbon composite is used as an anode active material for a secondary battery, the life characteristics and capacity of the secondary battery can be further improved.

[0051] The electrical conductivity of a negative electrode active material is an important factor in facilitating the transfer of electrons during an electrochemical reaction. If the carbon content in the silicon-polymer composite used as the negative electrode active material is insufficient, the electrical conductivity of the negative electrode active material may be insufficient. In this case, by forming a carbon thin film on the surface of the silicon-polymer composite to produce a silicon-polymer-carbon, the charge / discharge capacity, initial charge efficiency, and capacity retention of the secondary battery can be improved, and excellent electrical conductivity can be provided, suppressing side reactions in the electrolyte, thereby further improving the performance of the secondary battery.

[0052] In the silicon-polymer-carbon composite according to the present invention, the carbon thin film may have a thickness of 1 nm to 1 μm, preferably 3 to 150 nm, and more preferably 5 to 100 nm. When the carbon thin film has a thickness within this range, the conductivity can be improved and a decrease in the capacity of the secondary battery can be suppressed.

[0053] 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.

[0054] Method for manufacturing silicon-polymer composites

[0055] A silicon-polymer composite according to one embodiment of the present invention is fabricated by a method including forming a thin polymer film on the surface of silicon particles using initiator-based chemical vapor deposition (iCVD).

[0056] 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.

[0057] According to one embodiment of the present invention, the step of forming the polymer thin film may include the steps of: (1) supplying silicon particles into a reactor; (2) supplying a monomer and an initiator to the reactor containing the silicon particles; and (3) activating the initiator to polymerize the monomer, thereby forming a polymer thin film on the surface of the silicon particles.

[0058] 1 is a schematic diagram illustrating a process for forming a polymer thin film on the surface of silicon particles by initiator-based chemical vapor deposition (iCVD) according to an embodiment of the present invention. A method for manufacturing a silicon-polymer composite according to an embodiment of the present invention will be described with reference to FIG.

[0059] Stage (1)

[0060] In the above step (1), silicon particles are fed into the reactor.

[0061] The reactor used in the method for producing a silicon-polymer composite according to one embodiment of the present invention is not particularly limited in structure, as long as it can form a polymer thin film on the surface of silicon particles using the initiator-based chemical vapor deposition (iCVD) method described below.

[0062] 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 .

[0063] 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 arranged with as little overlap as possible. More specifically, a silicon substrate (wafer) may be used as the mounting part for accommodating the silicon particles, but is not particularly limited thereto.

[0064] 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.

[0065] Stage 2

[0066] In step (2) above, the monomers and initiator are fed to the reactor.

[0067] 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 .

[0068] 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 silicon-polymer composites.

[0069] The initiator I is a substance that decomposes under heat or light to form free radicals, and the type is not particularly limited 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 particularly limited thereto. Most preferably, the initiator is di-t-butyl peroxide.

[0070] 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.

[0071] 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.

[0072] Stage 3

[0073] In the above step (3), the initiator is activated and polymerizes the monomer, thereby forming a polymer thin film on the surface of the silicon particles.

[0074] First, the initiator I supplied in a vaporized state to the chamber 100 of the reactor 10 is activated by contact with the heating unit 500 to form free radicals I *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, but is preferably in the range of 135 to 350°C, more preferably 140 to 340°C, which can be advantageous from the viewpoint of preventing changes in the properties of the reactants.

[0075] Free radical I generated from the initiator * The monomer M moves to the bottom of the chamber and is adsorbed onto the surface of the silicon particles accommodated in the mounting part 200. The monomer adsorbed onto the surface of the silicon particles is converted into free radicals I * Activated by M * Polymerization then occurs, forming a thin polymer film on the surface of the silicon particles.

[0076] 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.

[0077] In the above step (3), in order to increase the adsorption rate of the monomer and free radicals, It is preferable to maintain the surface temperature of the silicon particles low. Specifically, the surface temperature of the silicon particles is preferably in the range of 10 to 50°C, and more 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.

[0078] 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 in step (3) may 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 satisfies this range, a polymer thin film of the desired thickness can be formed uniformly.

[0079] 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.

[0080] Additional Stages

[0081] The method for manufacturing a silicon-polymer composite according to an embodiment of the present invention may further include, after the step of forming the polymer thin film, forming a carbon thin film on the surface of the polymer thin film.

[0082] The step of forming a carbon thin film on the surface of the polymer thin film of the silicon-polymer composite may be performed using an apparatus and method known in the art to which the present invention belongs, for example, a chemical pyrolysis deposition method, but is not limited thereto.

[0083] In a specific example of the present invention, the step of forming a carbon thin film on the surface of the polymer thin film of the silicon-polymer composite can be performed by heat-treating the silicon-polymer composite at a temperature of 400 to 1,200°C in the presence of a gaseous carbon source.

[0084] 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.

[0085] The step of forming a carbon thin film on the surface of the polymer thin film of the silicon-polymer composite 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.

[0086] 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 may 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.

[0087] In a specific example of the present invention, the step of forming a carbon thin film on the surface of the polymer thin film of the silicon-polymer composite can 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.

[0088] 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 tetrahydrofuran (THF) or alcohol.

[0089] The carbon thin film formation step can produce a silicon-polymer-carbon composite in which the carbon thin film is uniformly formed over the entire surface of the polymer thin film of the silicon-polymer composite. When forming the carbon thin film on the surface of the polymer thin film of the silicon-polymer composite, the type of monomer, the process conditions for forming the polymer thin film, the type of carbon source, and the process conditions for forming the carbon thin film can be appropriately controlled to form the carbon thin film on the surface without substantially damaging the polymer thin film. That is, when the carbon thin film is formed on the surface of the polymer thin film of the silicon-polymer composite, 10 to 100 wt %, preferably 50 to 100 wt %, and more preferably 80 to 100 wt % of the polymer thin film may remain on the silicon particle surface. When the silicon-polymer-carbon composite obtained in this manner is used as an anode active material, the electrical conductivity of the anode active material can be improved without structural change.

[0090] In the method for manufacturing a silicon-polymer composite or silicon-polymer-carbon composite according to an embodiment of the present invention, the obtained silicon-polymer composite or silicon-polymer-carbon composite may be crushed or pulverized and classified. Classification can make the particle size distribution of the composite uniform. Here, classification can be performed by dry classification, wet classification, classification using a sieve, or the like.

[0091] negative electrode active material

[0092] According to yet another embodiment of the present invention, there is provided a negative electrode active material comprising the silicon-polymer composite.

[0093] 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 silicon-polymer composite or silicon-polymer-carbon composite. For example, the negative electrode active material may include a silicon-polymer composite or silicon-polymer-carbon composite according to an embodiment of the present invention and a carbon-based negative electrode material, for example, a graphite-based negative electrode material. It is obtained by mixing.

[0094] Here, examples of the carbon-based negative electrode material include natural graphite, artificial graphite, soft carbon, hard carbon, mesocarbon, carbon fiber, carbon nanotube, pyrolytic carbon, carbon The material may contain at least one selected from the group consisting of sintered organic polymer compounds, fired organic polymer compounds, and carbon black, but is not particularly limited to these.

[0095] 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.

[0096] 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.

[0097] all solid state battery

[0098] According to yet another embodiment of the present invention, there is provided an all-solid-state battery including a solid electrolyte interphase (SEI) film containing the silicon-polymer composite.

[0099] 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. The negative electrode may include a negative electrode active material layer, and at least a portion of the negative electrode active material particles in the negative electrode active material layer may include an SEI (Solid Electrolyte Interphase) film containing the silicon-polymer composite.

[0100] 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.

[0101] 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]

[0102] 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.

[0103] Example 1

[0104] Fabrication of Silicon-Polymer Composites

[0105] A silicon-polymer composite was 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 into 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 1 are as follows:

[0106] -Non-porous silicon particles: average particle size 20μm and 2μm (REC Silicon)

[0107] Monomer: 1H,1H,2H,2H-perfluorodecyl acrylate (Aldrich, 97%)

[0108] Initiator: di-t-butyl peroxide (Aldrich, 98%)

[0109] -Average initiator feed flow rate: 0.26 sccm

[0110] -Average monomer feed flow rate: 0.425sccm

[0111] - Filament temperature: 140℃

[0112] -Pressure in reactor chamber: 80mTorr

[0113] -Surface temperature of reactor mounting part (silicon wafer): 38℃

[0114] <Experimental Example 1>

[0115] (1) X-ray photoelectron spectroscopy

[0116] 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.

[0117] [Table 1]

[0118] 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.

[0119] (2) Water dispersibility

[0120] 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.

[0121] 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.

[0122] (3) Transmission electron microscope-energy dispersive spectrometer

[0123] Transmission electron microscope (TEM) - Energy analysis of silicon particles with an average diameter of 20 μm on which a polymer thin film was formed The TEM analysis results were shown in Figure 4, and the EDS analysis results were shown in Figure 5 and Tables 2 and 3.

[0124] [Table 2]

[0125] [Table 3]

[0126] 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 of the fluorine, a component of the monomer, was observed, whereas in the areas where the silicon-polymer composite was not present, no fluorine, a component of the monomer, was 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.

[0127] <Example 2>

[0128] 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. -Non-porous silicon particles: average particle size 20μm (REC Silicon)

[0129] -Monomer: dimethylaminomethylstyrene styrene) (Acros, 90%)

[0130] -Pressure in reactor chamber: 160mTorr

[0131] -Surface temperature of reactor mounting part (silicon wafer): 35℃

[0132] <Experimental Example 2>

[0133] (1) Transmission electron microscope-energy dispersive spectrometer 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. 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.

[0134] 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.

[0135] Example 3

[0136] 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.

[0137] -Non-porous silicon particles: average particle size 20μm (REC Silicon)

[0138] Monomer: Divinylbenzene (Aldrich, 80%)

[0139] -Pressure in reactor chamber: 450mTorr

[0140] -Surface temperature of reactor mounting part (silicon wafer): 23℃

[0141] <Experimental Example 3>

[0142] (1) Transmission electron microscope analysis

[0143] 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.

[0144] 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.

[0145] Example 4

[0146] A silicon-polymer composite was prepared in the same manner as in Example 1, with the following changes: A thin polymer film (pGMA) was formed on the surface of silicon particles to produce a silicon-polymer composite.

[0147] -Non-porous silicon particles: average particle size 20μm (REC Silicon)

[0148] Monomer: Glycidyl methacrylate (Alcrich, 97%)

[0149] -Pressure in reactor chamber: 300mTorr

[0150] -Surface temperature of reactor mounting part (silicon wafer): 30℃

[0151] <Experimental Example 4>

[0152] (1) Transmission electron microscope analysis

[0153] Silicon particles (Example 4) with an average particle size of 20 μm on which a polymer thin film was formed were observed using a transmission electron microscope (TEM). The TEM analysis results are shown in FIG.

[0154] As a result, from the bare silicon particles in Figure 2 and the TEM photograph in Figure 9, 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.

[0155] <Comparative Example 1>

[0156] Fabrication of Silicon-Polymer Composites

[0157] 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.

[0158] <Experimental Example 5>

[0159] (1) Comparative transmission electron microscope analysis

[0160] The bare silicon particles (FIGS. 10a-10d), the silicon-polymer composite obtained in Example 4 (FIGS. 10e-10h), and the liquid-coated silicon-polymer composite obtained in Comparative Example 1 (FIGS. 10i-10l) were observed using a transmission electron microscope (TEM). The TEM analysis results are shown in FIG. 10.

[0161] As a result, in the case of the silicon-polymer composite according to Example 4 (Figs. 10e to 10h), it was confirmed that the shape of the bare silicon particles (Figs. 10a to 10d) was maintained and a polymer coating of uniform thickness was formed.

[0162] On the other hand, in the case of the liquid-coated silicon-polymer composite obtained in Comparative Example 1 (Figs. 10i to 10l), the shape of the bare silicon particles (Figs. 10a to 10d) was not maintained, and the bare silicon It was confirmed that the polymer was coated in an irregular shape that was unrelated to the shape of the particles.

[0163] Overall, it can be seen that the iCVD method must be used to coat a polymer with a uniform thickness on silicon particles.

[0164] <Production Example 1>

[0165] A half coin cell was manufactured using the silicon-polymer composite manufactured in Example 1. The manufacturing conditions for the half coin cell are shown below.

[0166] - Composition (AM:CM:BM) = 8:1:1 (where AM, CM, and BM represent the active material (silane-deposited porous carbon support), conductor (Super P carbon black), and binder (styrene butadiene rubber / carboxymethyl cellulose 5:5), respectively.)

[0167] -area capacity(mAh / cm 2 ):4.5

[0168] Electrolyte: 1.3M LiPF6EC / EMC / DMC 3:5:2, FEC 10%, LiBF4 0.2%, VC 0.5%, PS 1% (where EC, EMC, DMC, FEC, VC, and PS represent ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, fluoroethylene carbonate, vinylene carbonate, and propane sultone, respectively.)

[0169] <Experimental Example 6>

[0170] (1) Electrochemical evaluation

[0171] The lithium secondary battery manufactured in Manufacturing Example 1 was measured for the initial charge-discharge efficiency, initial coulombic efficiency (ICE) and capacity retention rate (capacity retention rate at the 14th cycle) under the following conditions. (%)) were measured and are shown in Table 4 below and FIG.

[0172] -Cut-off voltage (V): Formation 0.005-1.5, Cycle test 0.005-1.5

[0173] -C Rate (C): Formation 0.1-0.1, 0.005V at 0.01C cut-off (CV)

[0174] [Table 4]

[0175] As a result, it can be seen from Table 4 and Figure 11 that the initial discharge efficiency and ICE were similar, while the capacity retention rate increased. Specifically, in Preparation Example 1, compared to the bare Si application example, the decrease in charge / discharge capacity that occurs when a specific material is coated on the bare Si surface was minimized, while the relative ratio of the capacity retention rate was significantly increased by more than 10%.

[0176] 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. A method for producing a silicon-polymer composite, comprising: forming a thin polymer film on the surface of silicon particles using initiator-based chemical vapor deposition (iCVD).

2. The step of forming the polymer thin film comprises: (1) providing silicon particles into a reactor; (2) feeding a monomer and an initiator into the reactor containing the silicon particles; and 3. The method for producing a silicon-polymer composite according to claim 1, further comprising: (3) activating the initiator to polymerize the monomer, thereby forming a polymer thin film on the surface of the silicon particle.

3. The method for producing a silicon-polymer composite according to claim 1, wherein the silicon particles are non-porous silicon particles.

4. The method for producing a silicon-polymer composite according to claim 1, wherein the silicon particles have an average particle size of 10 nm to 50 μm.

5. The method for producing a silicon-polymer composite according to claim 1, wherein the polymer thin film has a thickness of 1 nm to 10 μm.

6. In the step (2), the monomer is supplied at a flow rate of 0.1 sccm to 10 sccm; The method for producing a silicon-polymer composite according to claim 2, wherein the initiator is supplied at a flow rate of 0.1 sccm to 5 sccm.

7. The initiator is activated by a predetermined heat treatment, The method for producing a silicon-polymer composite according to claim 2, wherein the heat treatment is carried out at a temperature of 135 to 350°C.

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

9. After forming the polymer thin film, The method for producing a silicon-polymer composite according to claim 1, further comprising the step of forming a carbon thin film on the surface of the polymer thin film.

10. The method for producing a silicon-polymer composite according to claim 9, wherein the carbon thin film has a thickness of 1 nm to 1 μm.

11. A silicon-polymer composite produced by the method for producing a silicon-polymer composite according to any one of claims 1 to 10.

12. The silicon-polymer composite of claim 11; and a carbon-based negative electrode material; and an anode active material comprising the carbon-based negative electrode material.

13. An all-solid-state battery comprising: an SEI (Solid Electrolyte Interphase) film comprising the silicon-polymer composite of claim 11.

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