Negative electrode active material, method of manufacturing negative electrode active material, and negative electrode including negative electrode active material

Abstract

The present disclosure relates to a negative electrode active material, a method of manufacturing a negative electrode active material, and a negative electrode including the negative electrode active material. The negative electrode active material includes: a core formed of agglomerated first silicon particles; a shell formed of agglomerated second silicon particles; and an amorphous carbon coating layer surrounding the first silicon particles and the second silicon particles.

Description

[0001] This application claims priority and benefit to Korean Patent Application No. 10-2024-0172673, filed on November 27, 2024, with the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference. Technical Field

[0002] This disclosure relates to a negative electrode active material, a method for manufacturing the negative electrode active material, and a negative electrode including the negative electrode active material. Background Technology

[0003] With the rapid proliferation of battery-powered electronic devices such as mobile phones, laptops, and electric vehicles, the demand for rechargeable batteries with high energy density and large capacity has increased. Therefore, extensive research and development efforts have been undertaken to enhance the performance of rechargeable lithium batteries.

[0004] Rechargeable lithium-ion batteries typically consist of a positive electrode, a negative electrode, and an electrolyte. Both the positive and negative electrodes contain active materials capable of inserting and deintercalating lithium ions. As lithium ions move between the electrodes during charging and discharging, electrical energy is generated through oxidation and reduction reactions. Summary of the Invention

[0005] This disclosure provides a negative electrode active material with excellent capacity, efficiency and cycle life characteristics, as well as a method for manufacturing the negative electrode active material.

[0006] This disclosure provides a negative electrode with high structural stability.

[0007] This disclosure provides a rechargeable lithium battery with high energy density, excellent efficiency and long cycle life.

[0008] According to embodiments of the present disclosure, the negative electrode active material includes: a core formed of aggregated first silicon particles; a shell formed of aggregated second silicon particles; and an amorphous carbon coating surrounding the first and second silicon particles, wherein the shell is disposed on the core, wherein the average particle size (D50) of the first silicon particles is greater than the average particle size (D50) of the second silicon particles, wherein the average particle size (D50) of the first silicon particles is about 100 nm to about 140 nm, and wherein the average particle size (D50) of the second silicon particles is about 40 nm to about 100 nm.

[0009] According to embodiments of this disclosure, a method for manufacturing a negative electrode active material includes: grinding a silicon precursor using a bead mill to manufacture first silicon particles and second silicon particles; preparing an aggregate of the first silicon particles; forming a negative electrode active material precursor by coating the surface of the aggregate with second silicon particles; and forming an amorphous carbon coating on the negative electrode active material precursor, wherein the average particle size (D50) of the first silicon particles is greater than the average particle size (D50) of the second silicon particles, wherein the average particle size (D50) of the first silicon particles is about 100 nm to about 140 nm, and wherein the average particle size (D50) of the second silicon particles is about 40 nm to about 100 nm.

[0010] According to embodiments of the present disclosure, the negative electrode includes a negative electrode current collector and a negative electrode active material layer on the negative electrode current collector, wherein the negative electrode active material layer includes: a core formed by aggregated first silicon particles; a shell formed by aggregated second silicon particles; and an amorphous carbon coating surrounding the first and second silicon particles, wherein the shell is disposed on the core, wherein the average particle size (D50) of the first silicon particles is greater than the average particle size (D50) of the second silicon particles; wherein each of the first silicon particles includes a first silicon oxide layer on its surface, wherein each of the second silicon particles includes a second silicon oxide layer on its surface, and wherein the thickness of the first silicon oxide layer and the thickness of the second silicon oxide layer are each about 1 nm to about 10 nm. Attached Figure Description

[0011] Figure 1 This is a conceptual diagram of a rechargeable lithium battery according to an embodiment of the present disclosure.

[0012] Figures 2 to 5 This is a cross-sectional view of a rechargeable lithium battery according to an embodiment. Figure 2 A cylindrical battery is shown. Figure 3 A prismatic battery is shown. Figure 4 and Figure 5 A pouch-type battery is shown.

[0013] Figure 6 The negative electrode active material according to an embodiment of the present disclosure is shown.

[0014] Figure 7 A first silicon particle according to an embodiment of the present disclosure is shown.

[0015] Figure 8 A second silicon particle according to an embodiment of the present disclosure is shown.

[0016] Figure 9 This is a flowchart of a method for manufacturing a negative electrode active material according to an embodiment of the present disclosure.

[0017] Figure 10An exemplary method for manufacturing a precursor of a negative electrode active material is shown. Detailed Implementation

[0018] To fully understand the structure and effects of this disclosure, some embodiments will be described with reference to the accompanying drawings. However, this disclosure is not limited to the following exemplary embodiments and can be implemented in various forms. Exemplary embodiments are provided merely to illustrate this disclosure and to enable those skilled in the art to fully understand its scope.

[0019] In this specification, when an element is described as being "on" another element, it may be directly on said other element, or one or more intervening elements may be present. In the drawings, certain thicknesses may be exaggerated to better illustrate technical details. Throughout the specification, the same reference numerals indicate the same elements. Cross-sectional views and / or plan views may be used to illustrate embodiments presented herein as idealized examples of this disclosure. For clarity, the thickness of layers and regions in the drawings may be exaggerated. The regions shown in the drawings are for illustrative purposes and should not be construed as limiting the scope of this disclosure. Although terms such as "first," "second," and "third" may be used to describe various elements, these terms are used only for distinction and do not imply any particular order or hierarchy. The embodiments described and illustrated herein include complementary variations.

[0020] The terminology used in this specification is for illustrative purposes only and is not intended to limit this disclosure. Unless expressly stated otherwise, the singular form may also include the plural form. The term "comprising / including" and variations thereof do not exclude the presence or addition of one or more other components. The phrases "A or B," "at least one of A and B," "at least one of A or B," "A, B or C," "at least one of A, B and C," and "at least one of A, B or C" encompass any combination or all possible combinations of the listed elements.

[0021] In this specification, the phrase "combinations thereof" may refer to mixtures, stacks, complexes, copolymers, alloys, blends, or reaction products.

[0022] Unless otherwise specifically defined, the term "particle size" refers to the average particle size. Particle size can be expressed as the median particle size (D50) corresponding to the diameter of particles at 50% volume of the cumulative particle size distribution. The average particle size (D50) can be measured using widely known methods, such as by particle size analyzer, transmission electron microscopy (TEM) imaging, or scanning electron microscopy (SEM) imaging. Alternatively, dynamic light scattering can be used, in which particle counts across a size range are analyzed to calculate the average particle size (D50). Additionally, laser scattering can be employed, in which target particles are dispersed in a solvent, introduced into a laser scattering particle measurement device (e.g., the MT3000 from Microtrac), irradiated with ultrasound at 28 kHz and 60 W, and subsequently analyzed to determine the D50 value based on the 50% cumulative particle size distribution.

[0023] Figure 1 This is a cross-sectional view of a rechargeable lithium battery according to an embodiment of the present disclosure. (Refer to...) Figure 1 A rechargeable lithium battery may include a positive electrode 10, a negative electrode 20, a separator 30, and an electrolyte ELL.

[0024] The positive electrode 10 and the negative electrode 20 can be separated from each other by a diaphragm 30. That is, the diaphragm 30 can be disposed between the positive electrode 10 and the negative electrode 20. The positive electrode 10, the negative electrode 20 and the diaphragm 30 can be in contact with the electrolyte ELL. In particular, the positive electrode 10, the negative electrode 20 and the diaphragm 30 can be immersed in the electrolyte ELL.

[0025] The electrolyte ELL can be a medium for the transfer of lithium ions between the positive electrode 10 and the negative electrode 20. In the electrolyte ELL, lithium ions can move toward the positive electrode 10 or the negative electrode 20 through the membrane 30.

[0026] The following will refer to Figure 6 Describe the negative electrode 20.

[0027] Positive electrode 10 The positive electrode 10 for a rechargeable lithium battery may include a current collector COL1 and a positive electrode active material layer AML1 on the current collector. The positive electrode active material layer AML1 may include a positive electrode active material and may also include a binder and / or a conductive material (e.g., an electrically conductive material). The positive electrode 10 may also include additives that can be used as a sacrificial positive electrode.

[0028] Based on a 100 wt% positive electrode active material layer AML1, the amount of positive electrode active material can be from about 90 wt% to about 99 wt%. Based on a 100 wt% positive electrode active material layer AML1, the amounts of binder and conductive material can be from about 0.5 wt% to about 10 wt%, respectively.

[0029] The binder is used to adhere the positive electrode active material particles to each other, and also to adhere the positive electrode active material to the current collector COL1. Non-limiting examples of binders may include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylate resin, polyester resin, nylon, etc.

[0030] Conductive materials can be used to impart conductivity (e.g., electrical conductivity) to electrodes. Any material that does not cause chemical changes (e.g., does not cause undesirable chemical changes in rechargeable lithium batteries) and conducts electrons can be used. Examples of conductive materials include: carbon-based materials such as natural graphite, synthetic graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers, and carbon nanotubes; metallic materials containing copper, nickel, aluminum, silver, etc., in the form of metal powders or metal fibers; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0031] Aluminum can be used as a current collector COL1, but this disclosure is not limited thereto.

[0032] Positive electrode active material The positive electrode active material may include compounds capable of intercalating and deintercalating lithium (lithium-intercalating compounds). In some examples, at least one of lithium and a composite oxide of a metal selected from cobalt, manganese, nickel, and combinations thereof may be used.

[0033] The composite oxide can be a lithium transition metal composite oxide. Specific examples of composite oxides may include lithium nickel oxides, lithium cobalt oxides, lithium manganese oxides, lithium iron phosphate compounds, cobalt-free lithium nickel manganese oxides, or combinations thereof. As an example, compounds represented by any of the following chemical formulas may be used. Li a A 1-b X b O 2-c D c (0.90≤a≤1.8, 0≤b≤0.5, and 0≤c≤0.05); Li a Mn 2-b X b O 4-c D c (0.90≤a≤1.8, 0≤b≤0.5, and 0≤c≤0.05); Li a Ni 1-b-c Co b X c O 2-α Dα (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, and 0<α<2); Li a Ni 1-b-c Mn b X c O 2-α D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, and 0<α<2); Li a Ni b Co c L 1 d G e O2 (0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5, and 0≤e≤0.1); Li a NiG b O2 (0.90≤a≤1.8, and 0.001≤b≤0.1); Li a CoG b O2 (0.90≤a≤1.8, and 0.001≤b≤0.1); Li a Mn 1-b G b O2 (0.90≤a≤1.8, and 0.001≤b≤0.1); Li a Mn2G b O4 (0.90≤a≤1.8, and 0.001≤b≤0.1); Li a Mn 1-g G g PO4 (0.90 ≤ a ≤ 1.8, and 0 ≤ g ≤ 0.5); Li (3-f) Fe2(PO4)3 (0≤f≤2); and Li a FePO4 (0.90≤a≤1.8). In the above chemical formula, A is Ni, Co, Mn or a combination thereof; X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements or a combination thereof; D is O, F, S, P or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V or a combination thereof; and L 1 It is Mn, Al, or a combination thereof.

[0034] The positive electrode active material can be, for example, a high-nickel positive electrode active material, based on 100 mol% of metals other than lithium in a lithium transition metal composite oxide. The high-nickel positive electrode active material has a nickel content greater than or equal to about 80 mol%, greater than or equal to about 85 mol%, greater than or equal to about 90 mol%, greater than or equal to about 91 mol%, or greater than or equal to about 94 mol% and less than or equal to about 99 mol%. High-nickel positive electrode active materials can provide high capacity and can be used in high-capacity, high-density rechargeable lithium batteries.

[0035] Diaphragm 30 Depending on the type of rechargeable lithium battery, the separator 30 may be present between the positive electrode 10 and the negative electrode 20. The separator 30 may include a multilayer membrane of polyethylene, polypropylene, polyvinylidene fluoride, or two or more layers thereof, such as a mixed multilayer membrane, such as a polyethylene / polypropylene bilayer separator, a polyethylene / polypropylene / polypropylene trilayer separator, a polypropylene / polypropylene / polypropylene trilayer separator, etc.

[0036] The diaphragm 30 may include a porous substrate and a coating on one or both surfaces of the porous substrate, including organic materials, inorganic materials, or combinations thereof.

[0037] Porous substrates can be made of polymers such as polyolefins (e.g., polyethylene and polypropylene), polyesters (e.g., polyethylene terephthalate and polybutylene terephthalate), polyacetals, polyamides, polyimides, polycarbonates, polyetherketones, polyaryletherketones, polyetherimides, polyamideimides, polybenzimidazoles, polyethersulfones, polyphenylene ethers, cyclic olefin copolymers, polyphenylene sulfide, polyethylene naphthalate, glass fibers, and polytetrafluoroethylene (e.g., TEFLON). ® Polymer films formed from copolymers or mixtures of two or more of them.

[0038] Organic materials may include polymers such as polyvinylidene fluoride or (meth)acrylic acid polymers.

[0039] Inorganic materials may include inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof. However, this disclosure is not limited to these examples.

[0040] Organic and inorganic materials can be mixed in a coating, or coatings containing organic materials and coatings containing inorganic materials can be stacked.

[0041] Electrolyte ELL Electrolytes (ELLs) used in rechargeable lithium batteries may include non-aqueous organic solvents and lithium salts.

[0042] Non-aqueous organic solvents can be used as a medium for transporting ions that participate in the electrochemical reactions of a battery.

[0043] Non-aqueous organic solvents can be carbonates, esters, ethers, ketones, alcohols, aprotic solvents, or combinations thereof.

[0044] Carbonate solvents can include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), fluoroethylene carbonate (FEC), etc.

[0045] Ester solvents can include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanoic acid lactone, mevalonate lactone, caprolactone, etc.

[0046] Ether solvents may include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. Ketone solvents may include cyclohexanone, etc. Alcohol solvents may include ethanol, isopropanol, etc. Aprotic solvents may include: nitriles, such as R-CN, where R is a C2 to C20 straight-chain, branched, or cyclic hydrocarbon group, and may include double bonds, aromatic rings, or ether bonds, etc.; amides, such as dimethylformamide; dioxolane, such as 1,3-dioxolane, 1,4-dioxolane, etc.; sulfolane, etc.

[0047] Non-aqueous organic solvents can be used alone or in combination of two or more.

[0048] In addition, when using carbonate solvents, cyclic carbonates and chain carbonates can be mixed and used, and cyclic carbonates and chain carbonates can be mixed in a volume ratio of about 1:1 to about 1:9.

[0049] Lithium salts dissolved in organic solvents supply lithium ions in batteries, enabling basic operation of rechargeable lithium batteries and improving lithium ion transport between the positive and negative electrodes. Examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide, LiFSI), LiC4F9SO3, and LiN(C x F 2x+1 SO2)(Cy F 2y+1 Lithium trifluoromethane sulfonate (where x and y are integers from 1 to 20), lithium tetrafluoroethane sulfonate, lithium difluoro(oxalate)borate (LiDFOB), lithium difluorobis(oxalate)phosphate (LiDFBOP), and lithium bis(oxalate)borate (LiBOB).

[0050] Negative electrode active material and method for manufacturing negative electrode active material Figure 6 This is a schematic cross-sectional view of the negative electrode active material according to an embodiment of the present invention. (Refer to...) Figure 6 The negative electrode active material PTC may include a first silicon particle CP, a second silicon particle SP, and an amorphous carbon coating CC. Additionally, the negative electrode active material PTC may include a core COR and a shell SHL disposed on the core COR.

[0051] Specifically, the negative electrode active material PTC may include a core COR formed by aggregated first silicon particles CP, a shell SHL formed by aggregated second silicon particles SP, and an amorphous carbon coating CC surrounding the first silicon particles CP and the second silicon particles SP. The core COR of the negative electrode active material PTC may include the first silicon particles CP and the amorphous carbon coating CC surrounding the first silicon particles CP. The shell SHL of the negative electrode active material PTC may include the second silicon particles SP and the amorphous carbon coating CC surrounding the second silicon particles SP.

[0052] The negative electrode active material PTC can include first silicon particles CP and second silicon particles SP of different sizes. The average particle size (D50) of the first silicon particles can be larger than that of the second silicon particles. When the average particle size (D50) of the first silicon particles CP located in the core COR is larger than that of the second silicon particles SP located in the shell SHL, the core COR can have a higher porosity than the shell SHL. In such a configuration, the volume expansion that occurs during charging and discharging can be mitigated due to the porosity in the core COR. In addition, the shell SHL can densely surround the core COR, thereby suppressing side reactions with the electrolyte.

[0053] The average particle size (D50) of the first silicon particle CP can be, for example, about 100 nm to about 140 nm, about 105 nm to about 135 nm, or about 110 nm to about 130 nm. The average particle size (D50) of the second silicon particle SP can be, for example, about 40 nm to about 100 nm, about 45 nm to about 95 nm, or about 50 nm to about 90 nm. When the average particle size D50 of the first silicon particle CP and the second silicon particle SP are within these ranges, the core COR can have a larger interparticle space than the shell SHL due to the relatively large first silicon particle CP, thereby mitigating the problem of volume expansion that may occur during charging and discharging. In addition, the relatively small second silicon particle SP densely coats the surface of the negative electrode active material PTC, thereby suppressing side reactions with the electrolyte. When the average particle size (D50) of the first silicon particle CP and the second silicon particle SP are not within the above ranges, side reactions with the electrolyte may increase, and silicon may expand during charging and discharging, leading to structural instability.

[0054] The average particle size (D50) of the first silicon particle CP and the second silicon particle SP can be measured by a particle size analyzer or by transmission electron microscopy or scanning electron microscopy.

[0055] For example, before manufacturing the negative electrode active material PTC, when the first silicon particle CP and the second silicon particle SP may be separated from each other, the average particle size (D50) can be measured using a particle size analyzer. The average particle size (D50) measured using a particle size analyzer refers to the diameter of particles that constitute 50% of the total volume.

[0056] As another example, after being manufactured as a negative electrode or negative electrode active material PTC, the average particle size (D50) of the first silicon particle CP and the second silicon particle SP can be measured using scanning electron microscopy (SEM) images. However, when measuring using SEM images, and the silicon particles are not spherical, measurements from a large number of cross-sections can be obtained and averaged. The average particle size (D50) measured using SEM can be based on the projected area equivalent diameter. In this case, the projected area equivalent diameter can be calculated based on the projected area seen in the 2D cross-section of the particle, using a method that calculates the diameter of an equivalent spherical particle with the same area.

[0057] The amorphous carbon coating CC may include amorphous carbon. The amorphous carbon may surround a first silicon particle CP and a second silicon particle SP. Specifically, the amorphous carbon may be positioned between the first silicon particle CP and the second silicon particle SP, or between the first silicon particles CP and the second silicon particle SP. The amorphous carbon coating CC may be disposed on the first silicon particle CP and the second silicon particle SP. Furthermore, the amorphous carbon coating CC may surround the first silicon particle CP and the second silicon particle SP.

[0058] Amorphous carbon can include at least one of non-graphitizable carbon (hard carbon), graphitizable carbon (soft carbon), and combinations thereof. For example, amorphous carbon can be at least one of soft carbon, hard carbon, mesophase pitch carbides, calcined coke, and combinations thereof. Amorphous carbon can possess excellent hardness and electrical conductivity.

[0059] Amorphous carbon coatings (CC) can exhibit a D band (peak position: 1350 ± 50 cm⁻¹) in Raman spectra obtained by Raman spectroscopy. -1 (near) and G band (peak position: at 1580±50cm) -1 (Nearby). Here, the D / G ratio can be defined as the ratio of the maximum peak intensity of the D band to the maximum peak intensity of the G band.

[0060] The D / G ratio of the amorphous carbon coating CC can be, for example, about 0.5, about 0.6, about 0.7, about 0.8, or about 0.9 or greater. For instance, the D / G ratio of the amorphous carbon coating CC can be from about 0.5 to about 1.5, from about 0.6 to about 1.4, from about 0.7 to about 1.3, from about 0.8 to about 1.2, or from about 0.9 to about 1.1. When the D / G ratio of the amorphous carbon coating CC is within these ranges, the conductivity of the negative electrode active material can be excellent.

[0061] Based on the total weight of the negative electrode active material PTC, the amount of amorphous carbon coating CC can be, for example, about 20 wt% to about 50 wt%, about 25 wt% to about 50 wt%, or about 30 wt% to about 45 wt%. When the amount of amorphous carbon coating CC is within these ranges, rechargeable lithium batteries with excellent cycle life characteristics and capacity can be provided. When the amount of amorphous carbon coating CC is less than these ranges, conductivity may be insufficient and cycle characteristics may be poor. When the amount of amorphous carbon coating CC exceeds these ranges, capacity and efficiency may decrease.

[0062] The average particle size (D50) of the negative electrode active material PTC can be approximately 6 μm to approximately 12 μm, approximately 7 μm to approximately 11 μm, or approximately 8 μm to approximately 10 μm. The average particle size (D50) of the negative electrode active material PTC refers to the diameter of the particles that constitute 50% of the total volume in the particle size distribution. The average particle size (D50) of the negative electrode active material PTC can be measured using a particle size analyzer, transmission electron microscopy (TEM) images, or scanning electron microscopy (SEM) images. When the average particle size (D50) of the negative electrode active material PTC is within these ranges, side reactions with the electrolyte during battery charging and discharging can be reduced, and mechanical stability can be excellent, thereby improving the cycle life characteristics of rechargeable lithium batteries.

[0063] The weight ratio of the first silicon particle CP to the second silicon particle SP in the negative electrode active material PTC can be, for example, from about 1:4 to about 7:3, or from about 1:4 to about 3:2. When the weight ratio of the first silicon particle CP to the second silicon particle SP is within these ranges, the structural stability during the charging and discharging of the rechargeable lithium battery can be excellent, and the energy density can be increased. When the weight ratio of the first silicon particle CP to the second silicon particle SP is outside these ranges, side reactions may not be effectively prevented, and the cycle characteristics may be poor.

[0064] As described above, the negative electrode active material PTC may include a core COR and a shell SHL disposed on the core COR. The shell SHL may be coated with the core COR. The core COR of the negative electrode active material PTC may include a first silicon particle CP and an amorphous carbon coating CC surrounding the first silicon particle CP. The shell SHL of the negative electrode active material PTC may include a second silicon particle SP and an amorphous carbon coating CC surrounding the second silicon particle SP.

[0065] The core-to-shell (COR) thickness ratio of the negative electrode active material (PTC) can be, for example, from about 6:4 to about 9:1. When the core-to-shell thickness ratio meets this range, energy efficiency can be improved due to the combined advantages of the core-to-shell COR, which exhibits high efficiency and high capacity during charging and discharging, and the shell-to-shell SHL, which provides excellent cycling characteristics. The thickness of the core-to-shell COR and the shell-to-shell SHL of the negative electrode active material (PTC) can vary depending on the respective amounts of the first silicon particle (CP) and the second silicon particle (SP) in the negative electrode active material (PTC).

[0066] Here, the thickness of the core COR refers to the distance from the center of the negative electrode active material PTC to the boundary between the core COR and the shell SHL. When the negative electrode active material PTC is not spherical, the thickness is the average of the distances from the center of the negative electrode active material PTC to the boundary between the core COR and the shell SHL. The thickness of the shell SHL can be obtained by subtracting the thickness of the core COR from the distance from the center of the negative electrode active material PTC to its outermost edge. Alternatively, it can refer to the distance from the outermost edge of the negative electrode active material PTC to the boundary between the core COR and the shell SHL. When the negative electrode active material PTC is not spherical, the thickness of the SHL can refer to the average of the aforementioned distances.

[0067] According to this disclosure, "silicon particle" refers to a first silicon particle CP and a second silicon particle SP. The silicon particle may include a silicon oxide layer and a silicon core composed of pure silicon. The silicon oxide layer may be formed on the surface of the silicon core and may be positioned on the silicon core.

[0068] The shape of the silicon particles is not limited in this disclosure. According to an example embodiment, the first silicon particle CP and the second silicon particle SP are plate-shaped, oblate, or spherical.

[0069] According to an embodiment, the silicon particles can be crystalline silicon. Crystalline silicon can improve the capacity and efficiency of the negative electrode active material.

[0070] Figure 7 A first silicon particle CP according to an embodiment of the present disclosure is shown. Figure 8 A second silicon particle SP according to an embodiment of the present disclosure is shown.

[0071] Reference Figure 7 and Figure 8 The first silicon particle CP may include a first silicon oxide layer SOX1 and a first silicon core CRS1. The second silicon particle SP may include a second silicon oxide layer SOX2 and a second silicon core CRS2. That is, the first silicon oxide layer SOX1 may be positioned on the first silicon core CRS1, and the second silicon oxide layer SOX2 may be positioned on the second silicon core CRS2. The first silicon core CRS1 and the second silicon core CRS2 may be crystalline silicon.

[0072] In the example, the first silicon oxide layer SOX1 can be positioned discontinuously, in an island-like or dot-like manner on the surface of the first silicon core CRS1, which is crystalline silicon. Similarly, the second silicon oxide layer SOX2 can be positioned discontinuously, in an island-like or dot-like manner on the surface of the second silicon core CRS2, which is crystalline silicon. In other examples, the first silicon oxide layer SOX1 can be continuously positioned on the surface of the crystalline first silicon core CRS1 or can exist as a layer on the surface of the crystalline first silicon core CRS1, and the second silicon oxide layer SOX2 can be continuously positioned on the surface of the crystalline second silicon core CRS2 or can exist as a layer on the surface of the crystalline second silicon core CRS2. Silicon oxide layers such as the first silicon oxide layer SOX1 or the second silicon oxide layer SOX2 can effectively suppress the volume expansion of crystalline silicon that may occur in the first silicon core CRS1 and the second silicon core CRS2 during charging and discharging. In addition, the silicon oxide layer can prevent structural collapse. Furthermore, the silicon oxide layer can reduce the area of ​​crystalline silicon exposed to the electrolyte, thereby preventing side reactions of the electrolyte.

[0073] The first silicon oxide layer SOX1 and the second silicon oxide layer SOX2 can be formed, for example, in processes such as silicon particle manufacturing, silicon particle storage, PTC (Polydioxanone) manufacturing, negative electrode manufacturing, and charging and discharging processes of rechargeable lithium batteries. In a specific embodiment, the first silicon oxide layer SOX1 and the second silicon oxide layer SOX2 can be formed during the process of grinding the individual particles.

[0074] The thicknesses of the first silicon oxide layer SOX1 and the second silicon oxide layer SOX2 can each be, for example, about 1 nm to about 10 nm, about 1 nm to about 8 nm, about 1 nm to about 5 nm, or about 2 nm to about 5 nm. When the first silicon oxide layer SOX1 and the second silicon oxide layer SOX2 are of such thicknesses, the silicon oxide layers can have excellent mechanical strength and can reduce side reactions with the electrolyte. When the thickness is greater than these ranges, the capacity of the rechargeable lithium battery may decrease.

[0075] The thicknesses of the first silicon oxide layer SOX1 and the second silicon oxide layer SOX2 can vary depending on the manufacturing process. The thickness of the first silicon oxide layer SOX1 can be equal to or less than the thickness of the second silicon oxide layer SOX2. This thickness difference may be due to a shorter grinding time during the production of the first silicon particle CP to produce the first silicon particle CP with a larger average particle size (D50) than the second silicon particle SP. When the thickness of the first silicon oxide layer SOX1 is less than the thickness of the second silicon oxide layer SOX2, the volume of the first silicon core CRS1 of the first silicon particle CP present in the core COR can be increased, thereby producing improved capacity characteristics. In addition, irreversible reactions caused by the silicon oxide layer can be reduced, thereby producing improved initial efficiency characteristics. Furthermore, a thicker second silicon oxide layer SOX2 can increase the mechanical stability of the second silicon particle SP located on the periphery of the negative electrode active material PTC.

[0076] Here, the thickness of the first silicon oxide layer SOX1 can refer to the distance from the outermost edge of the first silicon particle CP to the boundary line between the first silicon oxide layer SOX1 and the first silicon core CRS1. When the first silicon particle CP is not spherical, the thickness can refer to the average value of the distance. The thickness of the second silicon oxide layer SOX2 can refer to the distance from the outermost edge of the second silicon particle SP to the boundary line between the second silicon oxide layer SOX2 and the second silicon core CRS2. When the second silicon particle SP is not spherical, the thickness can refer to the average value of the distance.

[0077] The average thickness of the first silicon oxide layer SOX1 or the second silicon oxide layer SOX2 can refer, for example, to the average value measured by arbitrarily selecting about 100 first silicon particles CP and second silicon particles SP in a cross-section of the negative electrode active material PTC in an electron micrograph. The thickness of the first silicon oxide layer SOX1 and the second silicon oxide layer SOX2 can be measured using transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), etc. However, this disclosure is not limited to these examples, and those skilled in the art can appropriately choose the method for measurement.

[0078] Figure 9A flowchart illustrating a method for manufacturing a negative electrode active material according to an embodiment of the present disclosure is shown. Figure 9 A method for manufacturing a negative electrode active material PTC may include the following steps: grinding a silicon precursor with a bead mill to manufacture a first silicon particle CP and a second silicon particle SP (S100); preparing an aggregate of the first silicon particle CP (S300); forming a negative electrode active material precursor by coating the surface of the aggregate with the second silicon particle (S500); and forming an amorphous carbon coating CC on the negative electrode active material precursor (S700).

[0079] A first silicon particle (CP) can be manufactured by grinding a silicon precursor using a bead mill. A second silicon particle (SP) can be manufactured by grinding the silicon precursor using a bead mill. The silicon precursor can be crystalline silicon. The first silicon particle (CP) and the second silicon particle (SP) can be formed from silicon precursors of the same size or from silicon precursors of different sizes.

[0080] During the grinding of the silicon precursor, the grinding time for the first silicon particle and the grinding time for the second silicon particle can differ. In an embodiment, a silicon precursor with a diameter of approximately 1 μm can be ground using a bead mill to manufacture the first silicon particle CP and the second silicon particle SP. When the first silicon particle CP and the second silicon particle SP are formed from silicon precursors of the same size, the grinding time for manufacturing the first silicon particle CP can be shorter than the grinding time for manufacturing the second silicon particle SP.

[0081] The thickness of the first silicon oxide layer SOX1 in the first silicon particle CP and the second silicon oxide layer SOX2 in the second silicon particle SP can vary depending on the polishing time. The longer the polishing time, the more oxidation occurs on the surface of the silicon particles, and the thicker the silicon oxide layer can be.

[0082] The first silicon particles CP can be aggregated to prepare an aggregate (S300). The aggregate can be formed, for example, by preparing a slurry including the first silicon particles CP using a spray drying process.

[0083] A negative electrode active material precursor can be formed by coating second silicon particles SP onto the surface of the aggregate (S500). The negative electrode active material precursor may have a structure in which multiple layers of second silicon particles SP surround the surface of the aggregated first silicon particles CP. The negative electrode active material precursor may refer to a structure having a core composed only of first silicon particles CP and a shell structure formed by second silicon particles SP surrounding the core.

[0084] The negative electrode active material precursor can be manufactured, for example, by coating a second silicon particle SP onto the surface of an aggregate of first silicon particles CP. This can be accomplished, for example, via a spray drying process.

[0085] Figure 10An exemplary method for manufacturing a precursor for a negative electrode active material is shown. (Refer to...) Figure 10 A slurry containing first silicon particles CP can be prepared, and an aggregate of the first silicon particles CP can be formed using a spray drying process (S300). Then, a slurry containing the aggregates and second silicon particles SP can be prepared, and a precursor of the negative electrode active material can again be formed using a spray drying process (S500). When the spray drying process is performed with a slurry containing aggregates of large-sized first silicon particles CP and second silicon particles SP, the negative electrode active material precursor can be manufactured with a structure in which the second silicon particles SP are coated on the periphery of the aggregates of first silicon particles CP. However, this may only be an exemplary method for manufacturing a negative electrode active material precursor, and this disclosure is not limited to the above method, as long as a negative electrode active material precursor as described herein is formed.

[0086] The negative electrode active material can be manufactured by coating the negative electrode active material precursor with amorphous carbon (S700). The amorphous carbon may include at least one of, for example, soft carbon, hard carbon, mesophase pitch carbide, calcined coke, and combinations thereof.

[0087] Amorphous carbon can form an amorphous carbon coating CC. The amorphous carbon coating CC can surround a first silicon particle CP and a second silicon particle SP. The amorphous carbon coating CC can fill the space between the first silicon particle CP and the second silicon particle SP. More specifically, the amorphous carbon coating CC can fill the space between the first silicon particle CP and the second silicon particle SP, thereby increasing the mechanical stability of the negative electrode active material PTC.

[0088] Amorphous carbon coating (CC) can be formed, for example, by mixing a negative electrode active material precursor with pitch and then heat-treating it.

[0089] negative electrode 20 The negative electrode 20 for a rechargeable lithium battery may include a current collector COL2 and a negative electrode active material layer AML2 on the current collector COL2. The negative electrode active material layer AML2 may include a negative electrode active material and may also include a binder and / or a conductive material (e.g., an electrically conductive material). For example, the negative electrode active material layer AML2 may include about 80 wt% to about 99 wt% of the negative electrode active material, about 0.5 wt% to about 10 wt% of the binder, and about 0.5 wt% to about 10 wt% of the conductive material.

[0090] The binder can be used to adhere the negative electrode active material particles to each other, and also to adhere the negative electrode active material to the current collector COL2. The binder may include non-aqueous binders, aqueous binders, dry binders, or combinations thereof.

[0091] Non-aqueous adhesives may include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene-propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyimide, or combinations thereof.

[0092] Waterborne adhesives can be styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepoxychloropropane, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0093] When using an aqueous binder as the negative electrode binder, it may also include a cellulose compound capable of imparting viscosity. The cellulose compound may include at least one of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, and their alkali metal salts. The alkali metal may include Na, K, or Li.

[0094] Dry adhesives can be polymeric materials capable of forming fibers. For example, dry adhesives can be polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or combinations thereof.

[0095] Conductive materials can be used to impart conductivity (e.g., electrical conductivity) to electrodes. Any material that does not cause chemical changes (e.g., does not cause undesirable chemical changes in rechargeable lithium batteries) and conducts electrons can be used in batteries. Non-limiting examples of conductive materials include: carbon-based materials such as natural graphite, synthetic graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers, and carbon nanotubes; metallic materials comprising copper, nickel, aluminum, silver, etc., in the form of metal powders or metal fibers; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0096] The negative electrode current collector COL2 may include copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or a combination thereof.

[0097] Rechargeable lithium batteries Rechargeable lithium batteries can be cylindrical, prismatic, pouch-shaped, or coin-shaped, depending on their shape. Figures 2 to 5 This is a schematic diagram of a rechargeable lithium battery according to an embodiment of the present disclosure. Figure 2 A cylindrical battery is shown. Figure 3 A prismatic battery is shown. Figure 4 and Figure 5 A pouch-type battery is shown. (See reference) Figures 2 to 5The rechargeable lithium battery 100 may include an electrode assembly 40 and a housing 50 therein housing the electrode assembly 40. The electrode assembly 40 includes a positive electrode 10, a negative electrode 20, and a separator 30 between the positive electrode 10 and the negative electrode 20. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte (not shown). Figure 2 As shown, the rechargeable lithium battery 100 may include a sealing member 60 of the sealed housing 50. Figure 3 In the example depicted, the rechargeable lithium battery 100 includes a positive electrode lead connector 11, a positive electrode terminal 12, a negative electrode lead connector 21, and a negative electrode terminal 22. For example... Figure 4 and Figure 5 As shown, the rechargeable lithium battery 100 may include electrode terminals 70 forming an electrical path for guiding current formed in the electrode assembly 40 to the outside of the battery 100. The electrode terminals 70 may be, for example, a positive electrode terminal 71 and a negative electrode terminal 72.

[0098] As a non-limiting example, the rechargeable lithium battery according to the embodiments can be used in automobiles, mobile phones and / or various types of electronic devices.

[0099] The following examples and comparative examples are provided to highlight the features of one or more embodiments; however, it will be understood that the examples and comparative examples do not limit the scope of this disclosure, nor are they necessarily outside the scope of this disclosure. Furthermore, it will be understood that the embodiments are not limited to the specific details described in the examples and comparative examples.

[0100] Example 1 (Manufacturing of the first and second silicon particles) The silicon precursor with an average diameter of approximately 1 μm was milled using a bead mill (Labstar, NETZSCH). Beads of approximately 100 nm in size were used, with a bead-to-silicon precursor volume ratio of approximately 8:2. Milling was continued until the average particle size (D50) of the first and second silicon particles, as measured by a particle size analyzer, became 120 nm and 70 nm, respectively.

[0101] (Manufacturing of negative electrode active material) A first slurry was prepared by mixing first silicon particles with ethanol at a weight ratio of approximately 1:9. The first slurry was then treated with a spray-drying process at 150°C to produce aggregates in which the first silicon particles were aggregated.

[0102] The aggregates and second silicon particles are mixed in an ethanol solvent to prepare a second slurry. The second slurry is then treated with a spray dryer at 150°C to form a precursor for the negative electrode active material. At this point, the aggregates become nuclei, and the second silicon particles aggregate in a manner that forms a coating on the surface of the aggregates. Thus, the precursor for the negative electrode active material is formed.

[0103] The negative electrode active material precursor was mixed with pitch and heat-treated at approximately 950°C in a N2 atmosphere to produce the negative electrode active material. The weight ratio of the first silicon particles to the second silicon particles in the negative electrode active material was approximately 5:5. Based on the total weight of the negative electrode active material, the amount of carbon was approximately 40 wt%. The average particle size (D50) of the produced negative electrode active material was approximately 9 μm.

[0104] Example 2 Except that the average particle size (D50) of the first silicon particle is about 120 nm and the average particle size (D50) of the second silicon particle is about 40 nm, the negative electrode active material of Example 2 is manufactured in the same manner as in Example 1.

[0105] Example 3 Except that the average particle size (D50) of the first silicon particle is about 140 nm and the average particle size (D50) of the second silicon particle is about 40 nm, the negative electrode active material of Example 3 is manufactured in the same manner as in Example 1.

[0106] Example 4 The negative electrode active material is manufactured in the same manner as in Example 1, except that the amount of carbon is approximately 25 wt% based on the total mass weight of the negative electrode active material.

[0107] Example 5 Except that the weight ratio of the first silicon particle to the second silicon particle in the negative electrode active material is about 3:7, the negative electrode active material of Example 5 is prepared in the same manner as in Example 1.

[0108] Comparison Example 1 The negative electrode active material is manufactured in the same manner as in Example 1, except that it is formed only from silicon particles with an average particle size of about 100 nm.

[0109] Comparison Example 2 The negative electrode active material is manufactured in the same manner as in Example 1, except that it is formed only from silicon particles with an average particle size of about 120 nm.

[0110] Comparison Example 3 Except that the average particle size (D50) of the first silicon particle is about 150 nm and the average particle size (D50) of the second silicon particle is about 70 nm, the negative electrode active material of Comparative Example 3 is manufactured in the same manner as in Example 1.

[0111] Compare Example 4 Except that the average particle size (D50) of the first silicon particle is about 70 nm and the average particle size (D50) of the second silicon particle is about 120 nm, the negative electrode active material of Comparative Example 4 is manufactured in the same manner as in Example 1.

[0112] Compare Example 5 Except that the average particle size (D50) of the first silicon particle is about 40 nm and the average particle size (D50) of the second silicon particle is about 140 nm, the negative electrode active material of Comparative Example 5 is manufactured in the same manner as in Example 1.

[0113] Comparison Example 6 Except that the average particle size (D50) of the first silicon particle is about 40 nm and the average particle size (D50) of the second silicon particle is about 120 nm, the negative electrode active material of Comparative Example 6 is manufactured in the same manner as in Example 1.

[0114] Table 1 below summarizes the various examples and comparison examples.

[0115] Table 1

[0116] *The dimensions of the first and second silicon particles refer to the average particle size (D50).

[0117] The amount of carbon is based on the total weight of the active material of the negative electrode.

[0118] negative electrode preparation Approximately 6 g of the negative electrode active material prepared by Examples 1 to 5 and Comparative Examples 1 to 6 above, approximately 2 g of carboxymethyl cellulose, and approximately 2 g of styrene-butadiene rubber were mixed to prepare a negative electrode slurry. The negative electrode slurry was coated onto a Cu foil, dried, and rolled to prepare a negative electrode.

[0119] Manufacturing of rechargeable lithium batteries A slurry was prepared by mixing approximately 96 wt% LiCoO2, approximately 2 wt% polyvinylidene fluoride (PVdF), and approximately 2 wt% carbon black in N-methylpyrrolidone. This slurry was then coated onto an Al foil, dried, and rolled to prepare the positive electrode. Weight percentages (wt%) are based on the total weight of solids in the slurry.

[0120] A coin cell is manufactured using a negative electrode, a positive electrode, a separator made of polyethylene, and an electrolyte. The electrolyte is a solution obtained by dissolving approximately 1.5 M LiPF6 in an organic solvent and adding approximately 3.5 parts by weight of fluoroethylene carbonate (FEC) to 100 parts by weight of the organic solvent, wherein the organic solvent is obtained by mixing ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) in a volume ratio of approximately 2:1:7.

[0121] In addition, a coin half-cell was manufactured by replacing the positive electrode in a coin full cell with a 0.5 mm lithium metal counter electrode.

[0122] Evaluation Example 1 - Evaluation of Battery Characteristics The evaluation includes the characteristics of rechargeable lithium batteries based on the negative electrode active materials of Examples 1 to 5 and Comparative Examples 1 to 6.

[0123] A coin cell (as described above) was charged to 0.01V under constant current (0.1C), and then charged under constant voltage until the current decreased to 0.01C. After resting for 10 minutes, the coin cell was discharged to 1.5V under constant current (0.1C) to perform the initial charge and discharge process, and the initial charge and discharge capacity was evaluated. The ratio of the measured initial discharge capacity to the measured initial charge capacity was calculated, and this ratio was expressed as the initial efficiency.

[0124] The coin cell was charged to 4.2V under constant current (0.1C), and then charged under constant voltage until the current dropped to 0.01C. After resting for 10 minutes, the coin cell was discharged to 2.5V under constant current (0.1C) to stably form the initial SEI film, and then further charged to 4.0V under constant current (1.0C), and then charged under constant voltage until the current dropped to 0.01C. After resting for another 10 minutes, the coin cell was repeatedly charged and discharged under constant current (1.0C) until 2.5V was reached, and the point at which the cycle life rapidly decreased was identified. The results are shown in Table 2.

[0125] Table 2

[0126] Referring to Table 2, when silicon particles of the same size are used as in Comparative Example 1 and Comparative Example 2, there is insufficient space to mitigate volume expansion, and surface side reactions may not be effectively suppressed, potentially leading to poor cycling characteristics. However, when the size of the first silicon particle forming the core, as in the examples, is larger than the size of the second silicon particle forming the shell, excellent capacity and cycle life characteristics are observed.

[0127] Even when there is a size difference between the silicon particles in the shell and the core, as can be seen in Comparative Example 3, an excessively large first silicon particle leads to a deterioration in cycling characteristics.

[0128] When the first silicon particle is smaller than the second silicon particle, as in Comparative Examples 4 to 6, it can be seen that the separation of the core and shell occurs due to the difference in volume expansion between the core and shell during charging and discharging, resulting in a deterioration in efficiency, capacity and cycle life characteristics.

[0129] In summary, it has been confirmed that the batteries of Examples 1 to 5 can be driven for 400 cycles or more, with an initial discharge capacity of 1600 mAh / g or greater, and an initial efficiency of 86% or greater. Therefore, all of these characteristics—efficiency, capacity, and cycle life—are excellent. In other words, when the average particle size (D50) of the first silicon particle is greater than that of the second silicon particle (D50), the particle size is neither too large nor too small, and both the weight ratio and carbon content of the first and second silicon particles are appropriate, the efficiency, capacity, and cycle life characteristics are all excellent.

[0130] By using the negative electrode active material according to this disclosure, a structurally stable negative electrode can be manufactured, and a rechargeable lithium battery with excellent capacity and cycle life characteristics can be produced. By using the method for manufacturing the negative electrode active material according to this disclosure, a negative electrode active material with excellent capacity, efficiency, and cycle life characteristics can be manufactured.

[0131] While this disclosure has been described with reference to preferred embodiments, these embodiments are provided for illustrative purposes only and are not intended to limit the scope of this disclosure. Various modifications and equivalent arrangements can be made. The described embodiments should be considered as examples and not as limitations on this disclosure.

Claims

1. A negative electrode active material, said negative electrode active material comprising: The core is formed by the aggregation of the first silicon particles; The shell is formed by aggregated second silicon particles; as well as An amorphous carbon coating surrounds the first silicon particle and the second silicon particle. The shell is disposed on the core. The average particle size D50 of the first silicon particle is greater than the average particle size D50 of the second silicon particle. Wherein, the average particle size D50 of the first silicon particle is 100nm to 140nm, and The average particle size D50 of the second silicon particle is 40 nm to 100 nm.

2. The negative electrode active material according to claim 1, wherein, Based on the total weight of the negative electrode active material, the amount of the amorphous carbon coating is 20 wt% to 50 wt%.

3. The negative electrode active material according to claim 1, wherein, The average particle size D50 of the negative electrode active material is 6 μm to 12 μm.

4. The negative electrode active material according to claim 1, wherein, The weight ratio of the first silicon particles to the second silicon particles in the negative electrode active material is 1:4 to 7:

3.

5. The negative electrode active material according to claim 1, wherein, The thickness ratio of the core to the shell is 6:4 to 9:

1.

6. The negative electrode active material according to claim 1, wherein, Each of the first silicon particles includes a first silicon oxide layer on its surface. Each of the second silicon particles includes a second silicon oxide layer on its surface, and The thickness of the first silicon oxide layer and the second silicon oxide layer is 1 nm to 10 nm, respectively.

7. The negative electrode active material according to claim 6, wherein, The thickness of the first silicon oxide layer is less than the thickness of the second silicon oxide layer.

8. The negative electrode active material according to claim 1, wherein, The amorphous carbon coating has a D / G ratio of 0.5 to 1.5, whereby the D / G ratio is expressed as the ratio of the maximum peak intensity of the D band to the maximum peak intensity of the G band in the Raman spectrum.

9. A method for manufacturing a negative electrode active material, the method comprising the following steps: The silicon precursor was ground using a bead mill to produce first and second silicon particles; Prepare aggregates of the first silicon particles; A negative electrode active material precursor is formed by coating the second silicon particles onto the surface of the aggregate. as well as An amorphous carbon coating is formed on the negative electrode active material precursor. The average particle size D50 of the first silicon particle is greater than the average particle size D50 of the second silicon particle. Wherein, the average particle size D50 of the first silicon particle is 100nm to 140nm, and The average particle size D50 of the second silicon particle is 40 nm to 100 nm.

10. The method according to claim 9, wherein, The amorphous carbon coating surrounds the first silicon particle and the second silicon particle.

11. The method according to claim 9, wherein, Based on the total weight of the negative electrode active material, the amount of the amorphous carbon coating is 20 wt% to 50 wt%.

12. The method according to claim 9, wherein, During the step of grinding the silicon precursor, the grinding time of the first silicon particle and the grinding time of the second silicon particle are different.

13. The method according to claim 9, wherein, During the step of grinding the silicon precursor, the grinding time of the first silicon particle is shorter than that of the second silicon particle.

14. The method according to claim 9, wherein, The silicon precursor is crystalline silicon.

15. The method according to claim 9, wherein, The weight ratio of the first silicon particles to the second silicon particles in the negative electrode active material is 1:4 to 7:

3.

16. The method according to claim 9, wherein, The average particle size D50 of the negative electrode active material is 6 μm to 12 μm.

17. The method according to claim 9, wherein, The amorphous carbon coating has a D / G ratio of 0.5 to 1.5, whereby the D / G ratio is expressed as the ratio of the maximum peak intensity of the D band to the maximum peak intensity of the G band in the Raman spectrum.

18. A negative electrode, the negative electrode comprising: Negative electrode current collector; as well as The negative electrode active material layer is located on the negative electrode current collector. The negative electrode active material in the negative electrode active material layer comprises: a core formed by aggregated first silicon particles; a shell formed by aggregated second silicon particles; and an amorphous carbon coating surrounding the first and second silicon particles. The shell is disposed on the core. The average particle size D50 of the first silicon particle is greater than the average particle size D50 of the second silicon particle. Each of the first silicon particles includes a first silicon oxide layer on its surface. Each of the second silicon particles includes a second silicon oxide layer on its surface, and The thickness of the first silicon oxide layer and the second silicon oxide layer is 1 nm to 10 nm, respectively.

19. The negative electrode according to claim 18, wherein, The average particle size D50 of the first silicon particle is 100 nm to 140 nm, and The average particle size D50 of the second silicon particle is 40 nm to 100 nm.

20. The negative electrode according to claim 18, wherein, The average particle size D50 of the negative electrode active material is 6 μm to 12 μm.

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