Method of manufacturing negative electrode active material, negative electrode active material manufactured using same, and rechargeable lithium battery including same

Abstract

Disclosed are a method of manufacturing a negative electrode active material, a negative electrode active material manufactured using the method, and a rechargeable lithium battery including the negative electrode active material. The method of manufacturing a negative electrode active material includes the steps of: mixing together a silicon-iron alloy and a hard carbon raw material to prepare a first mixture; subjecting the first mixture to graphitization at about 1,000 DEG C to about 1,500 DEG C to produce a second mixture; and washing the second mixture with an acid.

Description

[0001] This application claims priority to and the benefit of Korean Patent Application No. 10-2024-0049309 filed on April 12, 2024, in the Korean Intellectual Property Office, the entire contents of which are incorporated herein by reference. Technical Field

[0002] Embodiments of the present disclosure relate to a method of manufacturing a negative electrode active material, a negative electrode active material manufactured using the method, and a rechargeable lithium battery including the negative electrode active material. Background Art

[0003] Recently, with the rapid popularization of electronic devices using batteries (such as mobile phones, laptop computers and electric vehicles), the demand for rechargeable batteries with high energy density and high capacity has rapidly increased. Therefore, intensive research has been conducted on improving the performance of rechargeable lithium batteries.

[0004] The rechargeable lithium battery includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode and the negative electrode include active materials in which lithium ions can be intercalated and deintercalated, and if the lithium ions are intercalated and deintercalated, electric energy is generated due to oxidation and reduction reactions. Summary of the Invention

[0005] Embodiments of the present disclosure provide a method for manufacturing a negative electrode active material, which can easily shrink, maintain its structure despite volume changes during charge and discharge, and has low resistance (e.g., low electronic resistance), and a negative electrode active material manufactured using the method.

[0006] Embodiments of the present disclosure provide a rechargeable lithium battery having excellent capacity and a long lifespan.

[0007] According to an embodiment of the present disclosure, a method for manufacturing a negative electrode active material may include the following steps: mixing a silicon-iron alloy and a hard carbon raw material together to prepare a first mixture; subjecting the first mixture to graphitization at about 1,000°C to about 1,500°C (graphitizing the first mixture at about 1,000°C to about 1,500°C) to prepare a second mixture; and washing the second mixture with an acid.

[0008] According to an embodiment of the present disclosure, a negative electrode active material may include: a core comprising first crystalline carbon and porous silicon particles; and a shell on the core. The core may have a size ranging from about 1 μm to about 20 μm. The shell may include: a first shell on the core; and a second shell on the first shell. The first shell may include amorphous carbon. The second shell may include second crystalline carbon.

[0009] According to an embodiment of the present disclosure, a rechargeable lithium battery may include the negative electrode active material. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The drawings, together with the specification, illustrate embodiments of the presently disclosed subject matter, and, together with the description, serve to explain principles of the embodiments of the presently disclosed subject matter.

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

[0012] Figures 2 to 5 is a simplified diagram illustrating a rechargeable lithium battery according to an embodiment of the present disclosure, wherein Figure 2 shows a cylindrical battery, Figure 3 A prismatic cell is shown, and Figure 4 、 Figure 5 A pouch-type battery is shown.

[0013] Figure 6 is a cross-sectional view illustrating a negative electrode for a rechargeable lithium battery according to an embodiment of the present disclosure.

[0014] Figure 7 is a cross-sectional view illustrating a negative electrode active material according to an embodiment of the present disclosure.

[0015] Figure 8 is a cross-sectional view illustrating a porous silicon particle according to an embodiment of the present disclosure.

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

[0017] Figures 10 to 12 is a diagram illustrating a method of manufacturing a negative electrode active material according to an embodiment of the present disclosure.

[0018] Figure 13 is a SEM image showing the negative electrode active material according to Example 1.

[0019] Figure 14 is a SEM image showing a negative electrode active material according to Comparative Example 1.

[0020] Figure 15 is a SEM image showing a negative electrode active material according to Comparative Example 2.

[0021] Figure 16 is a SEM image showing a negative electrode active material according to Comparative Example 3.

[0022] Figure 17 is a SEM image showing a negative electrode active material according to Comparative Example 5.

[0023] Figure 18is a SEM image showing a negative electrode active material according to Comparative Example 6. DETAILED DESCRIPTION

[0024] In order to fully understand the structure and effect of the subject matter of the present disclosure, some embodiments of the present disclosure will be described with reference to the accompanying drawings. However, it should be noted that the present disclosure is not limited to the following example embodiments and can be implemented in various suitable forms. On the contrary, the example embodiments are provided here only to disclose the subject matter of the present disclosure and to allow those of ordinary skill in the art to fully understand the scope of the present disclosure.

[0025] In this specification, it will be understood that if an element is referred to as being on another element, the element may be directly on the other element, or there may be an intervening element between them. In the accompanying drawings, the thickness of some components may be exaggerated to effectively explain the technical content of this disclosure. Throughout the specification, the same reference numerals refer to the same elements.

[0026] Unless otherwise specified in this specification, expressions in the singular may include expressions in the plural. In an embodiment, unless otherwise specified, the phrase "A or B" may mean "A but not B," "B but not A," and "A and B." The term "includes" and / or its variations used in this specification do not exclude the presence or addition of one or more other components.

[0027] As used herein, the term "combinations thereof" may refer to mixtures, stacks, composites, copolymers, alloys, blends, and / or reaction products.

[0028] Unless otherwise specifically defined in this specification, the particle size may be an average particle size. In the embodiment, the particle size refers to the average particle size (D 50 Average particle size (D 50 ) can be measured by any suitable method commonly used in the art (e.g., by a particle size analyzer, a transmission electron microscope (TEM) image, and / or a scanning electron microscope (SEM) image). In an embodiment, a dynamic light scattering measurement device is used for data analysis, and the number of particles in each particle size range is counted, and the average particle size (D) can be calculated from this. 50 ) value. In an embodiment, the average particle size (D 50 In the laser scattering method, target particles are dispersed in a dispersion solvent, introduced into a laser scattering particle measuring device (e.g., MT3000 commercially available from Microtrac, Inc.), irradiated with 28 kHz ultrasonic waves at a power of 60 W, and then the average particle size (D) is calculated based on the 50% standard of the particle size distribution in the measuring device. 50 ).

[0029] Figure 1 is a simplified conceptual diagram illustrating a rechargeable lithium battery according to an embodiment of the present disclosure. Figure 1 , a rechargeable lithium battery may include a positive electrode 10, a negative electrode 20, a separator 30, and an electrolyte ELL.

[0030] The positive electrode 10 and the negative electrode 20 may be spaced apart from each other via a separator 30. The separator 30 may be between the positive electrode 10 and the negative electrode 20. The positive electrode 10, the negative electrode 20, and the separator 30 may be in contact with the electrolyte ELL. The positive electrode 10, the negative electrode 20, and the separator 30 may be immersed in the electrolyte ELL.

[0031] The electrolyte ELL may be a medium through which lithium ions are transferred between the positive electrode 10 and the negative electrode 20. In the electrolyte ELL, the lithium ions may move toward one of the positive electrode 10 or the negative electrode 20 through the separator 30.

[0032] The following will refer to Figure 6 The negative electrode 20 is discussed further.

[0033] 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 COL1. 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 (eg, an electrically conductive material).

[0034] For example, the positive electrode 10 may further include additives that may function as a sacrificial positive electrode.

[0035] The amount of the positive electrode active material may be about 90 wt % to about 99.5 wt % relative to 100 wt % of the positive electrode active material layer AML1. The amount of each of the binder and the conductive material may be about 0.5 wt % to about 5 wt % relative to 100 wt % of the positive electrode active material layer AML1.

[0036] The binder can be used to improve the adhesion of the positive electrode active material particles to each other and can also be used to improve the adhesion of the positive electrode active material to the current collector COL1. The binder may include, for example, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, an ethylene oxide-containing polymer, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and / or nylon, but the present disclosure is not limited thereto.

[0037] Conductive materials can be used to provide conductivity (e.g., electrical conductivity) to the electrodes, and any suitable conductive material that does not cause chemical changes in the battery (e.g., does not cause undesirable chemical changes in a rechargeable lithium battery) can be used as the conductive material constituting the battery. Conductive materials may include, for example: carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers, and / or carbon nanotubes (e.g., SWCNTs or multi-walled CNTs); metal powders and / or metal fibers including one or more of copper, nickel, aluminum, and / or silver; conductive polymers (e.g., electrically conductive polymers) such as polyphenylene derivatives; or mixtures thereof.

[0038] Aluminum (Al) may be used as the current collector COL1 , but the present disclosure is not limited thereto.

[0039] For example, the current collector COL1 may have an area substantially the same as that of the positive electrode active material layer AML1. In this specification, the term "substantially the same area" may mean that the difference between the two areas is less than 10%. For another example, the current collector COL1 may have an area different from that of the positive electrode active material layer AML1. In this specification, the term "different area" may mean that the difference between the two areas is greater than 10%. For example, the current collector COL1 may have an area larger than that of the positive electrode active material layer AML1.

[0040] Positive electrode active material The positive electrode active material in the positive electrode active material layer AML1 may include a compound that can reversibly intercalate and deintercalate lithium (e.g., a lithiated intercalation compound). For example, the positive electrode active material may include at least one composite oxide containing lithium and a metal selected from the group consisting of cobalt, manganese, nickel, and combinations thereof.

[0041] The composite oxide may include a lithium transition metal composite oxide, for example, a lithium nickel-based oxide, a lithium cobalt-based oxide, a lithium manganese-based oxide, a lithium iron phosphate-based compound, a cobalt-free lithium nickel manganese-based oxide, or a combination thereof.

[0042] For example, the positive electrode active material may include a compound represented by one selected from the following chemical formulas: Li a A 1-b X b O 2-c D c (where 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(where 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 D α (where 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 (where 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 (where 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 (where 0.90≤a≤1.8 and 0.001≤b≤0.1); Li a CoG b O2 (where 0.90≤a≤1.8 and 0.001≤b≤0.1); Li a Mn 1-b G b O2 (where 0.90≤a≤1.8 and 0.001≤b≤0.1); Li a Mn2G b O4 (where 0.90≤a≤1.8, and 0.001≤b≤0.1); Li a Mn 1-g G g PO4 (where 0.90≤a≤1.8, and 0≤g≤0.5); Li (3-f) Fe2(PO4)3 (where 0≤f≤2); and Li a FePO4 (where 0.90≤a≤1.8).

[0043] 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, a rare earth element 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 1It is Mn, Al or a combination thereof.

[0044] For example, the positive electrode active material may be a high-nickel positive electrode active material having a nickel content of approximately 80 mol% or greater, approximately 85 mol% or greater, approximately 90 mol% or greater, approximately 91 mol% or greater, or approximately 94 mol% or greater and approximately 99 mol% or less relative to 100 mol% of metal in the lithium transition metal composite oxide excluding lithium. The high-nickel positive electrode active material can achieve high capacity and thus can be applied to high-capacity and high-density rechargeable lithium batteries (e.g., high-capacity and high-energy-density rechargeable lithium batteries).

[0045] Diaphragm 30 Depending on the type (or kind) of the rechargeable lithium battery, the separator 30 may be present between the positive electrode 10 and the negative electrode 20. The separator 30 may include one or more selected from polyethylene, polypropylene, and polyvinylidene fluoride, and may have a multilayer separator thereof (such as a polyethylene / polypropylene double-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, and / or a polypropylene / polyethylene / polypropylene three-layer separator).

[0046] The separator 30 may include a porous substrate and a coating layer on one surface or opposite surfaces (eg, two opposite surfaces) of the porous substrate, the coating layer including an organic material, an inorganic material, or a combination thereof.

[0047] The porous substrate may be a polymer layer comprising one selected from polyolefins (such as polyethylene and polypropylene), polyesters (such as polyethylene terephthalate and polybutylene terephthalate), polyacetals, polyamides, polyimides, polycarbonates, polyetherketones, polyaryletherketones, polyetherimides, polyamideimides, polybenzimidazoles, polyethersulfones, polyphenylene oxides, cyclic olefin copolymers, polyphenylene sulfide, polyethylene naphthalate, glass fibers, Teflon, and polytetrafluoroethylene, or may be a copolymer or a mixture comprising two or more selected from the foregoing materials.

[0048] The organic material may include a polyvinylidene fluoride-based copolymer and / or a (meth)acrylic acid copolymer.

[0049] The inorganic material may include inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, or a combination thereof, but the present disclosure is not limited thereto.

[0050] The organic material and the inorganic material may be mixed together and exist in one coating layer, or may exist as a stack of a coating layer including an organic material and a coating layer including an inorganic material.

[0051] Electrolyte ELL The electrolyte ELL for a rechargeable lithium battery may include a non-aqueous organic solvent and a lithium salt.

[0052] The non-aqueous organic solvent may serve as a medium for transporting ions participating in the electrochemical reaction of the battery.

[0053] The non-aqueous organic solvent may include a carbonate solvent, an ester solvent, an ether solvent, a ketone solvent, an alcohol solvent, an aprotic solvent, or a combination thereof.

[0054] The carbonate-based solvent may include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), ethylmethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and / or butylene carbonate (BC).

[0055] The ester solvent may include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanoic acid lactone, mevalonolactone, valerolactone and / or caprolactone.

[0056] Ether solvents may include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and / or tetrahydrofuran. Ketone solvents may include cyclohexanone. Alcohol solvents may include ethanol or isopropanol. Aprotic solvents may include: nitriles, such as R-CN (wherein R is a C2 to C20 linear, branched, or cyclic hydrocarbon group, and may include a double bond, an aromatic ring, and / or an ether group); amides, such as dimethylformamide; dioxolanes, such as 1,3-dioxolane and / or 1,4-dioxolane; and / or sulfolane.

[0057] The non-aqueous organic solvent may be used alone or as a mixture of two or more species.

[0058] In an embodiment, if a carbonate-based solvent is used, a cyclic carbonate and a chain carbonate may be mixed together for use, and the cyclic carbonate and the chain carbonate may be mixed together in a volume ratio of about 1:1 to about 1:9.

[0059] The lithium salt may be a material dissolved in a non-aqueous organic solvent to serve as a supply source of lithium ions in a battery, and plays a role in enabling the basic operation of a rechargeable lithium battery and promoting the movement of lithium ions between a positive electrode and a negative electrode. The lithium salt may include, for example, a material selected from LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide, LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (wherein x and y are integers of 1 to 20), at least one of lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFBOP) and lithium bis(oxalato)borate (LiBOB).

[0060] Rechargeable lithium battery Rechargeable lithium batteries may be classified into cylindrical, prismatic, pouch type(s), and / or coin type(s) based on their shapes. Figures 2 to 5 is a simplified diagram illustrating a rechargeable lithium battery according to an embodiment, wherein Figure 2 shows a cylindrical battery, Figure 3 A prismatic cell is shown, and Figure 4 、 Figure 5 Shows a pouch type battery. Figures 2 to 5 , the rechargeable lithium battery 100 may include an electrode assembly 40 in which a separator 30 is interposed between a positive electrode 10 and a negative electrode 20, and may further include a case 50 in which the electrode assembly 40 is housed. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte. Figure 2 As shown in FIG, the rechargeable lithium battery 100 may include a sealing member 60 that seals the housing 50. In an embodiment, as shown in FIG. Figure 3 As shown in , the rechargeable lithium battery 100 may include a positive electrode lead tab 11, a positive electrode terminal 12, a negative electrode lead tab 21, and a negative electrode terminal 22. Figure 4 、 Figure 5 As shown in FIG, the rechargeable lithium battery 100 may include an electrode tab 70 ( Figure 5 ), or the positive electrode tab 71 and the negative electrode tab 72 ( Figure 4 ), the electrode tabs 70 / 71 / 72 serve as an electrical path for inducing current generated in the electrode assembly 40 to the outside.

[0061] The rechargeable lithium battery according to an embodiment of the present disclosure may be applied to automobiles, mobile phones, and / or any other suitable electronic devices, but the present disclosure is not limited thereto.

[0062] Figure 6 is a cross-sectional view showing the negative electrode 20 according to an embodiment of the present disclosure. Figure 6 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).

[0063] For example, the negative electrode active material layer AML2 may include about 90 wt % to about 99 wt % of a negative electrode active material, about 0.5 wt % to about 5 wt % of a binder, and about 0 wt % to about 5 wt % of a conductive material (eg, an electrically conductive material).

[0064] The binder can be used to improve the adhesion of the negative electrode active material particles to each other and to the current collector COL 2. The binder can include a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0065] The non-aqueous binder may include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0066] The aqueous binder may include styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinyl pyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinyl pyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, or a combination thereof.

[0067] If an aqueous binder is used as the negative electrode binder, a cellulose compound that can provide or increase viscosity may be further included. The cellulose compound may include one or more selected from carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, and alkali metal salts thereof. The alkali metal may include Na, K, and / or Li.

[0068] The dry binder may include a fibrillable polymeric material, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or combinations thereof.

[0069] Conductive materials can be used to provide conductivity (e.g., electrical conductivity) to the electrodes. As the conductive material constituting the battery, any suitable conductive material that does not cause chemical changes in the battery (e.g., does not cause undesirable chemical changes in a rechargeable lithium battery) can be used. For example, the conductive material may include: carbon materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers, and / or carbon nanotubes; metal powders and / or metal fibers including one or more selected from copper, nickel, aluminum, and silver; conductive polymers (e.g., electrically conductive polymers) such as polyphenylene derivatives; or mixtures thereof.

[0070] The current collector COL2 may include a copper foil, a nickel foil, a stainless steel foil, a titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal (eg, an electrically conductive metal), or a combination thereof.

[0071] For example, the current collector COL2 may have an area substantially the same as that of the negative electrode active material layer AML2. In an embodiment, the current collector COL2 may have an area different from that of the negative electrode active material layer AML2. For example, the current collector COL2 may have an area larger than that of the negative electrode active material layer AML2.

[0072] Negative electrode active material Figure 7 is a cross-sectional view illustrating a negative electrode active material according to an embodiment of the present disclosure. Figure 8 is a cross-sectional view illustrating a porous silicon particle of a negative electrode active material according to an embodiment of the present disclosure.

[0073] Reference Figure 7 , the negative electrode active material according to an embodiment of the present disclosure may include a core COR and a shell SHL on the core COR.

[0074] The core COR may have a size in the range of about 1 μm to about 20 μm or about 1 μm to about 10 μm. For example, the size of the core COR may refer to the diameter obtained by measuring 30 or more core CORs randomly selected from an electron microscope image of the negative electrode active material. For example, the diameter may include the major axis length and / or the minor axis length.

[0075] The core COR may include first crystalline carbon MTR and porous silicon particles PSN.

[0076] The first crystalline carbon MTR may include at least one selected from natural graphite and artificial graphite. For example, the first crystalline carbon MTR may be natural graphite, artificial graphite, or any combination thereof. The first crystalline carbon MTR may have a lower resistance than that of amorphous carbon. Therefore, electrons can easily move between the first crystalline carbon MTR and the porous silicon particles PSN.

[0077] For example, the first crystalline carbon MTR may have a D / G value equal to or less than about 0.2. For example, the first crystalline carbon MTR may have a D / G value in the range of about 0.02 to about 0.2. The D / G value may be defined as a ratio representing the D-band peak intensity area to the G-band peak intensity area in a Raman spectrum.

[0078] The porous silicon particles PSN may include a plurality of porous silicon particles. For example, the plurality of porous silicon particles may be dispersed in the first crystalline carbon MTR. The first crystalline carbon MTR may surround each of the plurality of porous silicon particles.

[0079] The porous silicon particles PSN may include iron (Fe). For example, the porous silicon particles PSN may include an alloy of silicon (Si) and iron (Fe). For example, the silicon-iron alloy may include ferrosilicon.

[0080] The concentration of iron (Fe) in the porous silicon particles PSN may be equal to or less than about 13 at%. The concentration of iron (Fe) may be defined as the ratio of the number of iron atoms in the porous silicon particles PSN to the total number of silicon atoms and iron atoms. For example, the concentration of iron (Fe) in the porous silicon particles PSN may be in the range of about 2 at% to about 13 at%. In an embodiment, the porous silicon particles PSN according to the present invention may substantially not include iron (Fe). If the porous silicon particles PSN have the above-mentioned concentration of iron (Fe), it may be possible to provide a negative electrode active material with excellent capacity.

[0081] The porous silicon particles PSN may have a particle size in the range of about 5 nm to about 15 nm. For example, the porous silicon particles PSN may have a nanometer-sized particle size. In this specification, the term "particle size" may refer to the diameter obtained by measuring 30 or more porous silicon particles PSN randomly selected from an electron microscope image of a negative electrode active material. The particle size of the porous silicon particles PSN may be uniform (e.g., substantially uniform) and within the above range.

[0082] The porous silicon particles PSN may have an amount in a range of about 15 wt % to about 65 wt %, about 15 wt % to about 60 wt %, about 20 wt % to about 55 wt %, about 35 wt % to about 55 wt %, about 40 wt % to about 55 wt %, or about 43 wt % to about 53 wt %, relative to the total weight of the negative electrode active material.

[0083] If the porous silicon particles PSN have a particle size and an amount satisfying the above ranges, it is possible to provide a negative electrode active material that can maintain its structure while having excellent charge and discharge capacity.

[0084] The porous silicon particles PSN may include pores POR. For example, the porous silicon particles may have a porous structure. The porous silicon particles PSN may include a plurality of pores POR.

[0085] The porous silicon particles PSN can have a 2 / g to about 760m 2 The BET (Brunauer-Emmett-Teller) specific surface area of ​​porous silicon particles (PSN) can be determined by BET analysis of the porous silicon particles (PSN) remaining after treating a negative electrode active material at high temperature and then oxidizing and removing carbon from the negative electrode active material.

[0086] If the porous silicon particles PSN have their above-described structure, it may be possible to reduce volume changes occurring during alloying / de-alloying of silicon and lithium during charge and discharge, and maintain the structure of the negative electrode active material.

[0087] Reference Figure 8 In an embodiment of the present disclosure, the porous silicon particle PSN may include a region RG, the region RG including a first region RG1 and a second region RG2, the second region RG2 surrounding the first region RG1. The second region RG2 may be defined as representing a region having a thickness in a range of about 2 nm to about 5 nm in a direction from the outermost edge toward the center of the porous silicon particle PSN. The first region RG1 may be defined as representing a region in the porous silicon particle PSN excluding the second region RG2.

[0088] The distribution of pores POR in the porous silicon particles PSN may vary. For example, the distribution of pores POR per unit area (or the distribution of pores POR per unit area) may be greater in the second region RG2 than in the first region RG1.

[0089] The concentration of iron (Fe) in the porous silicon particles PSN may vary. For example, the concentration of iron (Fe) in the porous silicon particles PSN may be lower in the second region RG2 than in the first region RG1.

[0090] Return to reference Figure 7The shell SHL may include a plurality of shells. The shell SHL may include a first shell SHL1 and a second shell SHL2. The first shell SHL1 may include a plurality of first shells. The second shell SHL2 may include a plurality of second shells. The plurality of first shells and the plurality of second shells may be arranged alternately. For example, one of the plurality of first shells may be between the core COR and one of the plurality of second shells.

[0091] The first shell SHL1 may include amorphous carbon. For example, the amorphous carbon may include at least one selected from non-graphitizable carbon (hard carbon) and graphitizable carbon (soft carbon).

[0092] The amorphous carbon may have a D / G value equal to or greater than about 0.3. For example, the D / G value of the amorphous carbon may be in the range of about 0.3 to about 1.5.

[0093] The first shell SHL1 may suppress or reduce a volume change of the core COR.The first shell SHL1 may allow lithium ions to easily move at an interface between the negative electrode active material and the electrolyte.

[0094] The second shell SHL2 may include a second crystalline carbon. The second crystalline carbon may include at least one selected from natural graphite and artificial graphite. For example, the second crystalline carbon may be natural graphite, artificial graphite, or any combination thereof. The second crystalline carbon may be the same as or different from the first crystalline carbon MTR.

[0095] The second crystalline carbon may have a D / G value equal to or less than about 0.2. For example, the D / G value of the second crystalline carbon may be in the range of about 0.02 to about 0.2.

[0096] The second shell SHL2 may have superior mechanical ductility to that of the first shell SHL1. For example, the second shell SHL2 may be easily deformed by external forces, easily shrink, and buffer volume changes of silicon. In some embodiments, the second shell SHL2 may have a lower resistance (e.g., electronic resistance) than that of the first shell SHL1.

[0097] The shell SHL may have a thickness in the range of about 500 nm to about 6 μm. The shell SHL may have a maximum thickness in the range of about 1 μm to about 6 μm, about 1.5 μm to about 5 μm, or about 2 μm to about 4 μm. For example, the maximum thickness of the shell SHL may represent a value obtained by randomly selecting 100 or more negative electrode active materials from an electron microscope image of the negative electrode active material and measuring the thickness of the thickest part of the shell included in each negative electrode active material. The thickness may be defined as the distance between a first point on the outermost edge of the shell SHL and a second point at the boundary where the core COR and the shell SHL meet. The first point may be a contact point where the outermost edge of the shell SHL meets the tangent. The second point may be the point where a straight line intersects the boundary if the straight line is drawn from the contact point in a direction perpendicular to the tangent.

[0098] Since the shell SHL has the above structure, it is possible to provide a negative electrode active material that can be easily shrunk, maintains its structure even if the volume changes during charge and discharge, has low resistance (eg, low electronic resistance), and excellent capacity.

[0099] The shell SHL may have a D / G value in the range of about 0.2 to about 0.3. For example, the shell SHL including the first shell SHL1 and the second shell SHL2 may have a D / G value in the range of about 0.2 to about 0.3. In an embodiment, the shell including both amorphous carbon and second crystalline carbon may have a D / G value in the range of about 0.2 to about 0.3. If the D / G value of the shell SHL satisfies the above range, a negative electrode active material having a suitable or desired structure and composition of the shell SHL may be manufactured.

[0100] The core COR and the shell can be distinguished from each other in terms of composition, amount, D / G value, etc. For example, the amount of porous silicon particles PSN in the core COR can be greater than the amount of porous silicon particles PSN in the shell. The amount of crystalline carbon in the core COR can be greater than the amount of crystalline carbon in the first shell SHL1. The amount of amorphous carbon in the core COR can be less than the amount of amorphous carbon in the first shell SHL1.

[0101] The negative electrode active material and the rechargeable lithium battery including the same according to some embodiments of the present disclosure may have the following characteristics. The negative electrode active material may have a 2 / g to about 10m 2 For example, the BET specific surface area of ​​the negative electrode active material can be about 5.2 m 2 / g. The negative electrode active material may have a porosity in the range of about 5% to about 20%. The negative electrode active material may have a true density in the range of about 2 g / cc to about 5 g / cc. According to some embodiments of the present disclosure, the negative electrode active material may be easily compressible and thus can be easily used to manufacture a negative electrode.

[0102] Rechargeable lithium batteries according to some embodiments of the present disclosure may have low resistance (e.g., low electronic resistance), high capacity, increased charge rate, and long life. For example, the rechargeable lithium battery may have a discharge rate equal to or greater than approximately 1,850 mAh / g. The rechargeable lithium battery may have a charge rate equal to or greater than approximately 60%. The rechargeable lithium battery may have a lifespan equal to or greater than approximately 80%.

[0103] Production of negative electrode active material Figure 9 is a flowchart illustrating a method of manufacturing a negative electrode active material according to an embodiment of the present disclosure. Figures 10 to 12 A diagram illustrating a method of manufacturing a negative electrode active material is shown.

[0104] Reference Figure 9 , a method of manufacturing a negative electrode active material according to some embodiments of the present disclosure may include the following steps: mixing a silicon-iron alloy and a hard carbon raw material together to prepare a first mixture (S100); subjecting the first mixture to graphitization to prepare a second mixture (S300); and washing the second mixture with an acid (S500).

[0105] Reference Figure 10 , the silicon-iron alloy SFA and the hard carbon raw material HCS may be mixed together to prepare a first mixture MXR1 ( S100 ).

[0106] For example, the silicon-iron alloy SFA may include ferrosilicon.

[0107] For example, the hard carbon raw material HCS may include at least one selected from the group consisting of lignin, phenolic resin, petroleum-based coal tar pitch, and coal-based coal tar pitch.

[0108] The silicon-iron alloy SFA and the hard carbon raw material HCS may have a weight ratio of about 1:1.5 to about 1:11.

[0109] A mixer can be used to perform a mixing process. For example, the mixer can include a centrifugal mixer of the revolution-autogenous type. A centrifugal mixer of the revolution-autogenous type can be a mixer in which both rotation and revolution occur simultaneously (e.g., concurrently) with or without vacuum conditions. For example, the rotation stirring speed and the revolution stirring speed can each independently be equal to or less than 2,000 rpm or equal to or less than about 1,000 rpm. The centrifugal mixer of the revolution-autogenous type can include a planetary mixer or a planetary distributing mixer. The rotation stirring speed and the revolution stirring speed can be appropriately or properly adjusted to alternately stir and degas and mix the components uniformly (e.g., substantially uniformly).

[0110] For example, step S100 may include mixing the silicon-iron alloy SFA, the hard carbon raw material HCS, and a solvent, and evaporating the solvent of the mixture. For example, the solvent may include water. In an embodiment, a dough-like first mixture MXR1 may be prepared.

[0111] Reference Figure 11 , the first mixture MXR1 may be subjected to graphitization to prepare a second mixture MXR2 ( S300 ).

[0112] Graphitization refers to a process in which a carbonaceous material is converted into graphite. This process produces crystalline carbon. Graphitization is typically performed at high temperatures of approximately 3,000°C. However, at these temperatures, the carbonaceous material and pure silicon may chemically react with each other to form silicon carbide (SiC). Silicon carbide (SiC) may be an irreversible compound (e.g., it may be formed irreversibly) and may not be suitable for use as a negative electrode in rechargeable lithium batteries.

[0113] Iron (Fe) included in the silicon-iron alloy SFA can graphitize the carbon raw material at low temperatures. For example, iron (Fe) can be used as a catalyst to graphitize the hard carbon raw material HCS at low temperatures.

[0114] In an embodiment, graphitization may be performed at a temperature less than about 3,000° C. For example, the graphitization temperature may be in a range of about 1,000° C. to about 1,500° C. Silicon-iron alloy SFA including iron (Fe) may be used to prepare crystalline carbon even at low temperatures.

[0115] Graphitization may be maintained at the above temperature range (eg, about 1,000° C. to about 1,500° C.) for 20 minutes to about 3 hours. For example, graphitization may be maintained at about 1,000° C. to about 1,500° C. for about 20 minutes to about 3 hours (this may be referred to as graphitization duration).

[0116] The rate at which the temperature is raised to the graphitization temperature (about 1,000°C to about 1,500°C) (e.g., a heating rate or a temperature increase rate) may be in the range of about 5°C / min to about 20°C / min. The time for which the temperature is raised to the graphitization temperature (about 1,000°C to about 1,500°C) (e.g., a heating time or a temperature increase time) may be in the range of about 1 hour to about 4 hours. For example, graphitization may include heating to about 1,000°C to about 1,500°C for a heating time of about 1 hour to about 4 hours at a heating rate of about 5°C / min to about 20°C / min.

[0117] If the temperature rising rate, the temperature rising time, and the graphitization duration satisfy the above ranges, it may be possible to produce a negative electrode active material having a suitable or desired maximum shell thickness.

[0118] The iron (Fe) in the first mixture MXR1 rapidly graphitizes the hard carbon raw material HCS. Consequently, a core COR is formed comprising the first crystalline carbon MTR and nanometer-sized silicon-containing particles SNP. The silicon-containing particles SNP may include not only silicon (Si) but also iron (Fe). The silicon-containing particles SNP may include a plurality of silicon-containing particles. For example, the plurality of silicon-containing particles may be dispersed within the first crystalline carbon MTR.

[0119] After forming the core COR, the first mixture MXR1 may be graphitized to form a shell SHL on the core COR. The first mixture MXR1 may have a portion without iron (Fe), and this portion may be formed into the first shell SHL1 comprising amorphous carbon. The first mixture MXR1 may have a predetermined or specific portion containing iron (Fe), and this predetermined or specific portion may be formed into the second shell SHL2 comprising second crystalline carbon. The type of the second crystalline carbon may be as described above.

[0120] The first shell SHL1 may include a plurality of first shells. The second shell SHL2 may include a plurality of second shells. The plurality of first shells and the plurality of second shells may be arranged alternately. For example, one of the plurality of first shells may be between the core COR and one of the plurality of second shells.

[0121] Reference Figure 12 , the second mixture MXR2 may be washed with acid ( S500 ).

[0122] For example, the acid may include at least one selected from hydrochloric acid, nitric acid, acetic acid, formic acid, succinic acid, citric acid, malic acid, maleic acid, oxalic acid, and any mixture thereof.

[0123] The acid dissolves the iron (Fe) in the second mixture MXR2. The acid enters the second mixture MXR2 to dissolve the iron (Fe) in the second mixture MXR2. This dissolves the iron (Fe) that does not participate in charge and discharge, forming pores in the silicon-containing particles SNP. This results in the formation of porous silicon particles PSN. The pores in the porous silicon particles PSN remain as empty spaces in the final negative electrode active material, buffering the volume changes that occur during the alloying and dealloying of silicon and lithium during charge and discharge, and maintaining the structure of the negative electrode active material.

[0124] The acid can enter the second mixture MXR2 to form Figure 8 The porous silicon particles PSN shown in FIG. The distribution of pores in the porous silicon particles PSN may vary. For example, the number of pores per unit area may be greater in the second region RG2 than in the first region RG1. In embodiments, the iron (Fe) concentration in the porous silicon particles PSN may vary. For example, the iron (Fe) concentration in the porous silicon particles PSN may be lower in the second region RG2 than in the first region RG1.

[0125] In an embodiment, it is possible to manufacture Figure 7 、 Figure 8 The negative electrode active material shown in FIG. The negative electrode active material can reduce structural fracture caused by volume change during charging, has low resistance (eg, low electronic resistance), and high capacity per unit material.

[0126] After step S300 is completed, step S500 may be performed to allow the negative electrode active material to have excellent discharge capacity and superior charge rate. In an embodiment, the negative electrode active material may have a low expansion rate and a long lifespan.

[0127] Here, the subject matter of the present disclosure will be described in more detail with reference to examples.The following examples are provided for illustrative purposes only and are not to be construed as limiting the scope of the present disclosure.

[0128] Example 1 A negative electrode active material having a core-shell structure was manufactured, in which the core includes crystalline carbon and a plurality of porous silicon particles, and the shell includes a first shell including amorphous carbon and a second shell including crystalline carbon. The maximum thickness of the shell is about 1 μm to about 6 μm.

[0129] Ferrosilicon (FeSi), lignin, and water are mixed together to prepare a first mixture (S100). The weight ratio of ferrosilicon (FeSi) to lignin is about 1:1.7, and the solid content in the first mixture is about 60 wt%. Mixing is performed using a high-speed stirrer at about 1,500 rpm for about 1 hour.

[0130] The first mixture is graphitized to prepare a second mixture ( S300 ). Graphitization is performed under a N 2 environment. The temperature is first increased to approximately 1200° C. at a heating rate of approximately 10° C. / min over approximately 2 hours, maintained at approximately 1200° C. for approximately 1 hour, and then cooled to room temperature.

[0131] The second mixture is added to a 35% hydrochloric acid (HCl) solution to perform an acid washing process (S500). Thereafter, the washed second mixture is washed three times with distilled water and dried (eg, in an infrared (IR) oven) to obtain a negative electrode active material.

[0132] Comparative Example 1 Except that step S500 was omitted, a negative electrode active material was manufactured according to substantially the same method as Example 1. Thus, a negative electrode active material in which the core included silicon-containing particles instead of porous silicon particles was obtained.

[0133] Comparative Example 2 A negative electrode active material was manufactured according to substantially the same method as in Example 1, except that silicon was added instead of ferrosilicon in step S100 and step S500 was omitted. Thus, a negative electrode active material was obtained in which the core included silicon-containing particles instead of porous silicon particles and the shell included only amorphous carbon.

[0134] Comparative Example 3 First, ferrosilicon was added to a 35% hydrochloric acid (HCl) solution to perform an acid washing process, washed three times with distilled water, and then dried to prepare porous silicon particles.

[0135] A negative electrode active material was produced according to substantially the same method as in Example 1, except that the prepared porous silicon particles were added in step S100 and step S500 was omitted. For example, graphitization was performed after the preparation of the porous silicon particles. Thus, a negative electrode active material was obtained in which the core comprised porous silicon particles and the shell comprised only amorphous carbon.

[0136] Comparative Example 4 The ferrosilicon was added to a 35% hydrochloric acid (HCl) solution to perform an acid washing process, washed three times with distilled water, and then dried to prepare a negative electrode active material including porous silicon particles.

[0137] Comparative Example 5 A negative electrode active material including a shell having a maximum thickness of about 9 μm was produced.

[0138] A negative electrode active material was manufactured according to substantially the same method as Example 1, except that in step S300 , the temperature was increased to about 900° C. at a heating rate of about 30° C. / min for about 0.5 hours and then immediately cooled to room temperature.

[0139] Comparative Example 6 A negative electrode active material including a shell having a maximum thickness of about 381 nm was produced.

[0140] A negative electrode active material was manufactured according to substantially the same method as in Example 1, except that in step S300, the temperature was increased to about 1550° C. at a heating rate of about 4° C. / min for about 6 hours, maintained at about 1550° C. for about 5 hours, and then cooled to room temperature.

[0141] Manufacturing of rechargeable lithium batteries 98 wt% of the prepared negative electrode active material, 1 wt% of carboxymethyl cellulose, and 1 wt% of styrene-butadiene rubber were mixed with distilled water to prepare a slurry. The slurry was coated on a copper (Cu) film, dried, and then roll-pressed to produce a negative electrode.

[0142] 96 wt% of LiCoO2, 2 wt% of polyvinylidene fluoride (PVdF), and 2 wt% of carbon black were mixed together with N-methyl-2-pyrrolidone (NMP) to prepare a slurry, which was coated on an aluminum (Al) film and dried, and then roll-pressed to manufacture a positive electrode.

[0143] A rechargeable lithium battery was manufactured using a negative electrode, a positive electrode, a polyethylene separator, and an electrolyte. 1.5M LiPF6 was mixed in an organic solvent containing ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) mixed together in a volume ratio of 2:1:7, and 3 parts by weight of fluoroethylene carbonate (FEC) was added relative to 100 parts by weight of the organic solvent to obtain an electrolyte.

[0144] Evaluation Example 1: Analysis of Negative Electrode Active Material Figures 13 to 18 is an SEM image showing the negative electrode active material according to Example 1 and Comparative Examples 1 to 3, 5 and 6. The silicon amount, specific surface area, porosity and true density of the negative electrode active materials according to the examples and comparative examples were measured, and the measurement results are listed in Table 1 below. The silicon amount is expressed as a percentage of the total weight of the negative electrode active material. The silicon amount was measured using energy dispersive X-ray analysis (EDX). The specific surface area was measured using a gas adsorption method based on the Brunauer-Emmett-Teller (BET) model. The porosity was measured using a mercury intrusion method. The porosity measuring device is a MicroActive AutoPore V 9600 commercially available from Micrometrics Instrument Corporation. For the examples and comparative examples, if mercury is squeezed, the porosity is evaluated by measuring the volume of mercury that changes with pressure.

[0145] Reference Figure 13 The negative electrode active material according to Example 1 has a core-shell structure. The core includes crystalline carbon (dark gray) and a plurality of porous silicon particles. The porous silicon particles amount to 53 wt % relative to the total weight of the negative electrode active material. The core has a size of approximately 3 μm to approximately 8 μm. The shell includes a first shell and a second shell. The first and second shells are arranged alternately. The first shell includes amorphous carbon (light gray). The second shell includes crystalline carbon (dark gray). The maximum shell thickness is approximately 1 μm to approximately 6 μm.

[0146] Reference Figure 14 , the negative electrode active material according to Comparative Example 1 includes silicon-containing particles instead of porous silicon particles. For example, it was determined that the acid washing process in step S500 causes the silicon-containing particles to have pores and forms porous silicon particles.

[0147] Reference Figure 15 The negative electrode active material according to Comparative Example 2 included only silicon-containing particles and amorphous carbon. For example, when silicon was used instead of the silicon-iron alloy, no crystalline carbon was formed within the graphitization temperature in step S300. It was confirmed that no crystalline carbon was formed within this temperature range without a catalyst.

[0148] Reference Figure 16 , it was observed that the negative electrode active material according to Comparative Example 3 included only porous silicon particles and amorphous carbon. For example, it was determined that if porous silicon particles were first prepared and then graphitized, crystalline carbon was not formed due to the absence of a silicon-iron alloy as a catalyst.

[0149] Reference Figure 17 , the maximum thickness of the shell in the negative electrode active material according to Comparative Example 5 is greater than the maximum thickness of the shell in the negative electrode active material according to Example 1. The maximum thickness of the shell according to Comparative Example 5 is 9 μm. Figure 18 , the maximum thickness of the shell in the negative electrode active material according to Comparative Example 6 is less than the maximum thickness of the shell in the negative electrode active material according to Example 1. The maximum thickness of the shell according to Comparative Example 6 is 381 nm. For example, it is confirmed that if the heating rate, heating time, and graphitization duration meet the above ranges in step S300, a negative electrode active material having a suitable or desired maximum shell thickness can be manufactured.

[0150] Table 1

[0151] Evaluation Example 2: Battery Characteristics The characteristics of rechargeable lithium batteries manufactured using the corresponding negative electrode active materials of Examples and Comparative Examples were evaluated.

[0152] The rechargeable lithium battery was initially charged under constant current (0.2C) and, after standing for 10 minutes, initially discharged under constant current (0.2C) until the voltage reached 2.5V to evaluate the discharge capacity. The lifespan was evaluated as the ratio of the discharge capacity measured after 500 cycles under the same charge and discharge conditions to the discharge capacity measured at the first cycle. In addition, the charge rate was evaluated as the ratio of the charge capacity measured after charging at 2.0C to the charge capacity measured after charging at 0.2C. The battery was charged at 0.2C under the same conditions and disassembled to measure the thickness of the negative electrode, and the expansion rate was evaluated as the ratio of the measured thickness of the negative electrode to the thickness of the negative electrode before charging. The evaluation results of the battery characteristics are shown in Table 2 below.

[0153] Table 2

[0154] Referring to Table 2, the rechargeable lithium battery including the negative electrode active material according to Example 1 had excellent discharge capacity and excellent charge rate, compared with the rechargeable lithium batteries including the negative electrode active materials according to Comparative Examples 1 to Comparative Examples 6. In addition, the rechargeable lithium battery including the negative electrode active material according to Example 1 had a reduced expansion rate and an increased lifespan, compared with the rechargeable lithium batteries including the negative electrode active materials according to Comparative Examples 1 to Comparative Examples 6.

[0155] Therefore, if the method of manufacturing a negative electrode active material according to some embodiments of the present disclosure is used, it is possible to easily manufacture a negative electrode, prepare a negative electrode active material with low resistance (e.g., low electronic resistance), excellent capacity and long life, and provide a rechargeable lithium battery including the negative electrode active material.

[0156] If the method of manufacturing a negative electrode active material according to some embodiments of the present disclosure is used, the negative electrode can be easily manufactured because the negative electrode easily shrinks, and a negative electrode active material having low resistance (e.g., low electronic resistance) and reduced structural changes caused by volume changes during charge and discharge is provided.

[0157] Furthermore, the rechargeable lithium battery according to an embodiment of the present disclosure may have excellent capacity and lifespan characteristics.

[0158] Although some embodiments of the present disclosure have been discussed with reference to the accompanying drawings, it will be understood that various suitable changes in form and details can be made therein without departing from the spirit and scope of the present disclosure. Therefore, it will be understood that the above embodiments are illustrative in all aspects and not restrictive.

Claims

1. A method for producing a negative electrode active material, the method comprising the following steps: mixing together a silicon-iron alloy and a hard carbon raw material to prepare a first mixture; subjecting the first mixture to graphitization at 1,000° C. to 1,500° C. to prepare a second mixture; as well as The second mixture is washed with acid.

2. The method according to claim 1, wherein The silicon-iron alloy includes ferrosilicon.

3. The method according to claim 1, wherein The hard carbon raw material includes at least one selected from lignin, phenolic resin, petroleum-based coal tar pitch, and coal-based coal tar pitch.

4. The method according to claim 1, wherein The graphitization is maintained at 1,000° C. to 1,500° C. for 20 minutes to 3 hours.

5. The method according to claim 1, wherein The graphitization includes heating to 1,000° C. to 1,500° C. at a heating rate of 5° C. / min to 20° C. / min for a heating time of 1 hour to 4 hours.

6. The method according to claim 1, wherein The acid includes at least one selected from hydrochloric acid, nitric acid, acetic acid, formic acid, succinic acid, citric acid, malic acid, maleic acid, oxalic acid and any mixture thereof.

7. A negative electrode active material, comprising: a core comprising first crystalline carbon and porous silicon particles; as well as a shell, on said core, wherein the size of the core is in the range of 1 μm to 20 μm, The shell comprises: a first shell on the core; and a second shell on the first shell. wherein the first shell comprises amorphous carbon, and Wherein, the second shell comprises second crystalline carbon.

8. The negative electrode active material according to claim 7, wherein The porous silicon particles include a plurality of porous silicon particles, The plurality of porous silicon particles are dispersed in the first crystalline carbon.

9. The negative electrode active material according to claim 7, wherein The porous silicon particles include iron, Wherein, the concentration of iron in the porous silicon particles is equal to or less than 13 at %.

10. The negative electrode active material according to claim 7, wherein The porous silicon particles include: First Region; and a second region surrounding the first region, The second region has a thickness of 2 nm to 5 nm in a direction from the outermost edge toward the center of the porous silicon particle.

11. The negative electrode active material according to claim 10, wherein The porous silicon particles include a plurality of pores, The distribution of the plurality of holes per unit area is greater in the second region than in the first region.

12. The negative electrode active material according to claim 10, wherein The porous silicon particles include iron, The concentration of iron in the porous silicon particles is lower in the second region than in the first region.

13. The negative electrode active material according to claim 7, wherein The particle size of the porous silicon particles is in the range of 5 nm to 15 nm.

14. The negative electrode active material according to claim 7, wherein The amount of the porous silicon particles is in the range of 15 wt % to 65 wt % relative to the total weight of the negative electrode active material.

15. The negative electrode active material according to claim 7, wherein The first shell includes a plurality of first shells, The second shell includes a plurality of second shells, and The plurality of first shells and the plurality of second shells are alternately disposed with each other.

16. The negative electrode active material according to claim 7, wherein The D / G value of the shell is in the range of 0.2 to 0.

3.

17. The negative electrode active material according to claim 7, wherein The maximum thickness of the shell is in the range of 1 μm to 6 μm.

18. The negative electrode active material according to claim 7, wherein Each of the first crystalline carbon and the second crystalline carbon includes at least one selected from natural graphite and artificial graphite.

19. The negative electrode active material according to claim 7, wherein The amorphous carbon includes at least one selected from non-graphitizable carbon and graphitizable carbon. The non-graphitizable carbon is hard carbon, and the graphitizable carbon is soft carbon. 20 . A rechargeable lithium battery comprising the negative electrode active material according to claim 7 .

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