Negative electrode active material for lithium secondary battery and lithium secondary battery comprising same

Abstract

A negative electrode active material for a lithium secondary battery according to an embodiment of the present invention comprises composite particles, the composite particles comprising: carbon-based particles comprising pores; and a silicon-containing coating layer formed on a surface of the carbon-based particle, in which a crystal grain size of silicon contained in the silicon-containing coating layer, measured by X-ray diffraction (XRD) analysis, after heat treatment of the composite particle at 900 DEG C to 1200 DEG C for 6 hours to 9 hours, is 10 nm or less.

Description

Technical Field

[0001] The present invention relates to a negative electrode active material for a lithium secondary battery and a lithium secondary battery containing the negative electrode active material. Background Art

[0002] Secondary batteries are batteries that can be repeatedly charged and discharged. With the development of the information communications and display industries, secondary batteries are widely used as power sources for portable electronic communication devices such as camcorders, mobile phones, and laptop computers. Furthermore, battery packs containing secondary batteries are being developed in recent years and used as power sources for environmentally friendly vehicles such as electric vehicles.

[0003] Examples of secondary batteries include lithium secondary batteries, nickel-cadmium batteries, and nickel-metal hydride batteries. Among them, lithium secondary batteries have high operating voltage and energy density per unit weight, and are advantageous in terms of charging speed and weight reduction, and therefore are being actively developed and used.

[0004] In recent years, as the applications of lithium secondary batteries have expanded, lithium secondary batteries with higher capacity and power have been developed. For example, high-capacity silicon and carbon can be combined and used as negative electrode active materials.

[0005] However, due to the large differences in volume expansion rates of silicon-carbon composite negative electrode active materials, repeated charge and discharge may cause cracks in the negative electrode active material and expose it to the electrolyte. Summary of the Invention

[0006] (1) Technical issues to be resolved

[0007] According to one aspect of the present invention, a negative electrode active material for a lithium secondary battery having improved lifespan characteristics can be provided.

[0008] According to another aspect of the present invention, a lithium secondary battery having improved lifespan characteristics can be provided.

[0009] (2) Technical solution

[0010] A negative electrode active material for a lithium secondary battery according to an embodiment of the present invention includes composite particles comprising: carbon-based particles containing pores; and a silicon-containing coating formed on the surface of the carbon-based particles. After the composite particles are heat-treated at 900° C. to 1200° C. for 6 to 9 hours, the silicon contained in the silicon-containing coating has a crystallite size of 10 nm or less as measured by X-ray diffraction (XRD) analysis.

[0011] In some embodiments, the grain size of silicon contained in the silicon-containing coating layer may be measured by the following Formula 1.

[0012] [Formula 1]

[0013]

[0014] In Formula 1, L represents the crystallite size (nm), λ represents the X-ray wavelength (nm), β represents the full width at half maximum of the peak of the (111) plane of silicon contained in the silicon-containing coating (radians (rad)), and θ represents the diffraction angle (radians).

[0015] In some embodiments, the heat treatment may be performed on 1 g to 5 g of the composite particles in an inert atmosphere.

[0016] In some embodiments, the grain size of silicon contained in the silicon-containing coating layer after the heat treatment may be 8 nm or less as measured by XRD analysis.

[0017] In some embodiments, the silicon contained in the silicon-containing coating after the heat treatment may include an amorphous structure.

[0018] In some embodiments, the pores of the carbon-based particles may have a size of 0.1 nm to 10 nm.

[0019] In some embodiments, the pores of the carbon-based particles may have a size of 1 nm to 5 nm.

[0020] In some embodiments, the composite particles after the heat treatment may further contain silicon carbide (SiC).

[0021] In some embodiments, the composite particles after the heat treatment may satisfy the following Formula 2.

[0022] [Formula 2]

[0023] I(Si(220)) / I(SiC)<1.0

[0024] In Formula 2, I(Si(220)) is the maximum peak intensity within the 2θ range of 46° to 48° measured by XRD analysis, and I(SiC) is the maximum peak intensity within the 2θ range of 34° to 36° measured by XRD analysis, where 2θ represents a diffraction angle (°).

[0025] In some embodiments, the composite particles may further include a carbon coating formed on the silicon-containing coating.

[0026] In some embodiments, the pores of the carbon-based particles may include a shape that curves from the outermost portion of the carbon-based particles toward the interior of the carbon-based particles.

[0027] A lithium secondary battery according to an embodiment of the present invention includes: a negative electrode including the negative electrode active material for a lithium secondary battery as described above; and a positive electrode disposed opposite to the negative electrode.

[0028] According to the method for preparing a negative electrode active material for a lithium secondary battery according to an embodiment of the present invention, carbon-based particles containing pores can be prepared. The carbon-based particles and a silicon-containing gas can be calcined together to form composite particles, wherein the composite particles include a silicon-containing coating formed on the surface of the carbon-based particles. After the composite particles are heat-treated at 900° C. to 1200° C. for 6 to 9 hours, the grain size of silicon contained in the silicon-containing coating measured by X-ray diffraction (XRD) analysis is 10 nm or less.

[0029] In some embodiments, the silicon-containing gas may include silane gas, and the volume of the silane gas may be 10 volume % to 70 volume % relative to the total volume of the silicon-containing gas.

[0030] In some embodiments, the volume of the silane gas may be 30 volume % to 50 volume % relative to the total volume of the silicon-containing gas.

[0031] (3) Beneficial effects

[0032] According to one embodiment of the present invention, generation of gas caused by a side reaction between a negative electrode active material and an electrolyte solution can be suppressed.

[0033] According to one embodiment of the present invention, lifespan characteristics of a secondary battery can be improved.

[0034] According to one embodiment of the present invention, the lifespan characteristics of a secondary battery under a high temperature environment or when charge and discharge are repeated can be improved.

[0035] The negative electrode active material for lithium secondary batteries and lithium secondary batteries containing the negative electrode active material of the present invention can be widely used in electric vehicles, battery charging stations, and other green technology fields such as solar power generation and wind power generation using batteries. The negative electrode active material for lithium secondary batteries and lithium secondary batteries containing the negative electrode active material of the present invention can be used in eco-friendly electric vehicles and hybrid vehicles that prevent climate change by suppressing air pollution and greenhouse gas emissions. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is a schematic cross-sectional view illustrating a composite particle according to an exemplary embodiment.

[0037] Figure 2 and Figure 3 1 and 2 are respectively a schematic plan view and a schematic cross-sectional view illustrating a lithium secondary battery according to an exemplary embodiment.

[0038] Figure 4 3 are X-ray diffraction (XRD) analysis charts of Example 1, Comparative Example 1, and Comparative Example 3. DETAILED DESCRIPTION

[0039] Embodiments of the present invention provide a negative electrode active material for a lithium secondary battery (hereinafter referred to as "negative electrode active material") comprising composite particles. Furthermore, a lithium secondary battery (hereinafter referred to as "secondary battery") comprising the negative electrode active material is provided.

[0040] The following describes the embodiments of the present invention in detail, but these are merely exemplary embodiments, and the present invention is not limited to the specific embodiments described exemplarily.

[0041] Figure 1 is a schematic cross-sectional view illustrating a composite particle according to an exemplary embodiment.

[0042] For ease of explanation, Figure 1 The shape of the composite particles is schematically shown in FIG. , but the structure / shape of the composite particles of the present invention is not limited to Figure 1 For example, the cross-section of the carbon-based particles may be randomly changed from a circular shape. In addition, the silicon-containing coating may be partially formed on the pores and surfaces of the carbon-based particles and may also be formed as a discontinuous plurality of islands or patterns.

[0043] Reference Figure 1 , the composite particles 50 may include carbon-based particles 60 and a silicon (Si)-containing coating 70 .

[0044] In an exemplary embodiment of the present invention, the carbon-based particles 60 may include pores 65. For example, the carbon-based particles 60 may be porous particles including a plurality of pores.

[0045] In some embodiments, the carbon-based particles 60 may include activated carbon, carbon nanotubes, carbon nanowires, graphene, carbon fibers, carbon black, graphite, porous carbon, pyrolysis cryogel, pyrolysis xerogel, pyrolysis aerogel, etc. These may be used alone or in combination of two or more.

[0046] In some embodiments, the carbon-based particles may include an amorphous structure or a crystalline structure.

[0047] According to one embodiment, the carbon-based particles may include an amorphous structure. In this case, the durability of the negative electrode active material can be increased, thereby suppressing cracking during charge and discharge or external impact. As a result, the lifespan characteristics of the secondary battery can be improved.

[0048] The silicon-containing coating 70 can be formed on the surface of the carbon-based particles 60 containing pores 65. For example, the volume expansion of the silicon contained in the silicon-containing coating 70 can be alleviated by the pores 65. Therefore, the relatively high capacity characteristics of silicon can be utilized, and at the same time, cracks caused by the difference in the volume expansion rate of carbon (e.g., about 150 volume % or less) and the volume expansion rate of silicon (e.g., about 400 volume % or more) during charging and discharging of the battery can be prevented. Therefore, the generation of gas caused by the side reaction of the negative active material and the electrolyte can be suppressed, and the life characteristics of the secondary battery can be improved.

[0049] The pores 65 of the carbon-based particles 60 may include a shape that curves from the outermost portion of the carbon-based particles 60 toward the inner portion of the carbon-based particles 60. For example, the pores 65 may include pores open to the outside of the carbon-based particles 60 (open pores).

[0050] The terms “surface of the carbon-based particle” and / or “surface of the carbon-based particle 60 ” used in this specification may refer to the outer surface 62 of the carbon-based particle 60 , the inner surface 67 of the pore 65 , or the outer surface 62 of the carbon-based particle 60 and the inner surface 67 of the pore 65 .

[0051] For example, the silicon-containing coating 70 may be formed on at least a portion of the outer surface 62 of the carbon-based particle 60 .

[0052] For example, the silicon-containing coating 70 may be formed on at least a portion of the inner surface 67 of the pores 65 of the carbon-based particles 60 .

[0053] For example, the silicon-containing coating 70 may be formed on at least a portion of the outer surface 62 of the carbon-based particle 60 and on at least a portion of the inner surface 67 of the pore 65 .

[0054] According to an exemplary embodiment of the present invention, after the composite particles 50 are heat-treated at 900° C. to 1200° C. for 6 to 9 hours, the grain size of silicon contained in the silicon-containing coating 70 measured by X-ray diffraction (XRD) analysis may be 10 nm or less, and in some embodiments, the grain size may be 9 nm or less or 8 nm or less.

[0055] In some embodiments, the heat treatment may be performed in an inert atmosphere on 1 g to 5 g of the composite particles 50. Thus, uniform heat treatment conditions may be maintained, thereby improving the reliability and reproducibility of measurement results.

[0056] For example, the term “inert atmosphere” used in this specification may refer to a state in which a chamber containing the composite particles 50 is continuously purged with an inert gas (eg, nitrogen (N 2 ) or argon (Ar) gas).

[0057] For example, even silicon particles with a relatively small grain size or an amorphous structure may aggregate or crystallize domains within the silicon as the secondary battery is repeatedly charged and discharged or the temperature rises due to external heat.

[0058] Within the above-mentioned grain size range of the present invention, the grain size of the silicon after heat treatment can be controlled, thereby improving the life characteristics under high temperature environment or repeated charge and discharge. For example, the grain size of the silicon after heat treatment can be proportional to the internal domain size of the silicon.

[0059] Hereinafter, the term "the heat treatment" in this specification may refer to the heat treatment performed under the above conditions (at 900° C. to 1200° C. for 6 hours to 9 hours).

[0060] In some embodiments, the grain size of silicon contained in the silicon-containing coating layer 70 may be measured by a Scherrer equation represented by the following Formula 1 in an XRD analysis method.

[0061] [Formula 1]

[0062]

[0063] In Formula 1, L represents the crystallite size (nm), λ represents the X-ray wavelength (nm), β represents the full width at half maximum of the corresponding peak (radians), and θ represents the diffraction angle (radians). According to an exemplary embodiment, the full width at half maximum in the XRD analysis for measuring the crystallite size can be measured from the peak of the (111) plane of silicon contained in the silicon-containing coating.

[0064] In some embodiments, in the above formula 2, β can use the half-maximum full width corrected for the value from the device. In one embodiment, Si can be used as a standard substance reflecting the value from the device. In this case, by fitting the full-width at half-maximum curve over the entire 2θ range of Si, the full-width at half-maximum from the device can be expressed as a function of 2θ. Thereafter, the value of the full-width at half-maximum from the device at the corresponding 2θ obtained from the function is subtracted and corrected, and can be used as β.

[0065] The heat treatment may not be included in the preparation process of the composite particles 50, and the heat treatment may be performed on the finished composite particles 50. Therefore, the accuracy of the evaluation of the high-temperature life characteristics and cycle characteristics of the negative electrode active material can be improved.

[0066] For example, the composite particles 50 that have undergone the heat treatment may be naturally cooled to room temperature and then subjected to XRD analysis.

[0067] In some embodiments, the silicon contained in the heat-treated silicon-containing coating 70 may have an amorphous structure, thereby improving lifespan characteristics in a high-temperature environment or during repeated charge and discharge.

[0068] The term “amorphous structure” used in this specification may refer to a case where individual silicon contained in the silicon-containing coating layer 70 is amorphous in shape or is a particle so small that the size cannot be measured by the Scherrer equation represented by Formula 1.

[0069] In an exemplary embodiment, the grain size of the heat-treated silicon can be controlled according to the size of the pores 65 of the carbon-based particles 60, the content of the silicon source in the deposition gas (e.g., silicon-containing gas) used in the preparation process, the calcination temperature, the calcination time, etc.

[0070] In some embodiments, the size of the pores 65 of the carbon-based particles 60 may be 0.1 nm to 10 nm, 0.5 nm to 8 nm, or 1 nm to 5 nm. Within the above range, excessive deposition of silicon can be prevented, thereby further suppressing the generation of cracks in the negative electrode active material during charge and discharge of the secondary battery.

[0071] The size of the pore 65 may refer to a diameter of an entrance of the pore 65 formed at a surface portion of the carbon-based particle 60 .

[0072] In some embodiments, the silicon-containing coating 70 may comprise silicon, and may optionally further comprise SiO x (0 <x<2)。

[0073] In some embodiments, the heat-treated composite particles 50 may further contain silicon carbide (SiC). For example, through the heat treatment, a SiC phase may grow on the composite particles 50 and / or the silicon-containing coating 70. As a result, the durability and stability of the negative electrode active material in a high temperature environment or during repeated charge and discharge can be improved.

[0074] For example, when heat treatment is performed in the step of forming composite particles 50 and the finished composite particles 50 are not heat treated, SiC may not be sufficiently formed.

[0075] In some embodiments, the heat-treated composite particles 50 may satisfy the following Formula 2.

[0076] [Formula 2]

[0077] I(Si(220)) / I(SiC)<1.0

[0078] In Formula 2, I(Si(220)) is the maximum peak intensity within the 2θ range of 46° to 48° measured by XRD analysis, and I(SiC) is the maximum peak intensity within the 2θ range of 34° to 36° measured by XRD analysis, where 2θ represents a diffraction angle (°).

[0079] For example, I(Si(220)) may represent the peak intensity of the (220) plane of silicon contained in the silicon-containing coating layer 70. I(SiC) may represent the peak intensity of SiC formed on the composite particle 50 and / or the silicon-containing coating layer 70 according to the heat treatment.

[0080] The term "peak intensity" in the present specification may refer to a peak height in an XRD analysis chart in which the horizontal axis is 2θ and the vertical axis is peak intensity.

[0081] When the above-mentioned formula 2 is satisfied, the SiC phase can be formed in the composite particles 50 at an appropriate ratio, thereby further improving the driving stability of the negative electrode active material.

[0082] In some embodiments, the composite particles 50 may further include a carbon coating (not shown) formed on the silicon-containing coating 70. Thus, the silicon in the negative electrode active material can be prevented from coming into contact with water. Consequently, the reduction in discharge capacity and capacity efficiency of the secondary battery can be suppressed from the time the negative electrode active material is prepared until the negative electrode is formed.

[0083] In some embodiments, a carbon coating layer may also be formed on portions of the surface of the carbon-based particles 60 where the silicon-containing coating layer 70 is not formed. For example, the carbon coating layer may entirely cover the carbon-based particles 60 and the silicon-containing coating layer 70. Thus, the mechanical and chemical stability of the negative active material may be improved.

[0084] In one embodiment, the carbon coating may include at least one of carbon and a conductive polymer. For example, the conductive polymer may include polyacetylene, polyaniline, polypyrrole, polythiophene, and the like.

[0085] Hereinafter, a method for preparing the negative electrode active material for a lithium secondary battery according to an exemplary embodiment is provided.

[0086] In an exemplary embodiment, carbon-based particles 60 including pores 65 may be prepared.

[0087] In some embodiments, the primary carbon-based particles and additives may be mixed, first calcined, and washed to form the carbon-based particles 60 .

[0088] In one embodiment, the primary carbon-based particles may comprise at least one selected from the group consisting of glucose, sucrose, cellulose, petroleum-based pitch, coal-based pitch, biomass, and resol oligomer.

[0089] In some embodiments, the additive may be provided as a chemical etchant or a hard template.

[0090] In one embodiment, the chemical etchant may include alkaline chemicals and / or acidic chemicals such as potassium hydroxide (KOH), potassium acetate, potassium carbonate (K2CO3), sodium hydroxide (NaOH), sodium carbonate (Na2CO3), ammonia (NH4OH), sulfuric acid (H2SO4). These can be used alone or in combination of two or more. For example, the reaction between the primary carbon-based particles and the additive can be carried out by chemical activation.

[0091] In one embodiment, the hard template may include silica, polystyrene, etc. These may be used alone or in combination of two or more. The hard template may be provided, for example, as an additive for forming pores. For example, the size of the pores 65 may be adjusted according to the particle size of the hard template.

[0092] In one embodiment, the first calcination may be performed at 600° C. to 900° C. Within the above range, the size and / or volume of the pores 65 may be appropriately controlled.

[0093] In one embodiment, the washing can be performed by adding an acidic solution or an alkaline solution to the mixture. For example, the acidic solution can include a hydrochloric acid (HCl) solution, a sulfuric acid (H2SO4) solution, etc. For example, the alkaline solution can include a NaOH solution, etc.

[0094] In an exemplary embodiment, the carbon-based particles 60 and the silicon-containing gas may be calcined together (e.g., a second calcination) to form composite particles 50, which include a silicon-containing coating 70 formed on the surface of the carbon-based particles 60. For example, the silicon-containing gas may include silane gas and an inert gas. For example, the inert gas may include argon (Ar) gas.

[0095] In some embodiments, the volume of the silane gas relative to the total volume of the silicon-containing gas may be 10% to 70% by volume, 20% to 70% by volume, 20% to 50% by volume, or 30% to 50% by volume. Within these ranges, the domain size of silicon contained in the silicon-containing coating 70 before heat treatment can be reduced. Therefore, the grain size of the silicon after heat treatment can be reduced.

[0096] In some embodiments, the second calcination may be performed at 400° C. to 600° C. Within this range, the grain size of silicon contained in the silicon-containing coating layer 70 before the heat treatment may be reduced. Therefore, the mechanical stability of the negative electrode active material during a rolling process or repeated charge and discharge of a secondary battery may be improved.

[0097] After the composite particles 50 formed by the above method are subjected to the heat treatment, the crystallite size of silicon contained in the silicon-containing coating layer 70 measured by XRD analysis may be 10 nm or less.

[0098] Figure 2 and Figure 3 are respectively a schematic plan view and a schematic cross-sectional view showing a lithium secondary battery according to an exemplary embodiment. Figure 3 It is along Figure 2 A cross-sectional view taken along the thickness direction along the II' line.

[0099] The lithium secondary battery may include a negative electrode 130 and a positive electrode 100 . The negative electrode 130 includes the above-mentioned negative electrode active material. The positive electrode 100 is disposed opposite to the negative electrode 130 .

[0100] The positive electrode 100 may include a positive electrode current collector 105 and a positive electrode active material layer 110 formed on at least one side of the positive electrode current collector 105 .

[0101] The positive electrode current collector 105 may include stainless steel, nickel, aluminum, titanium, or alloys thereof. The positive electrode current collector 105 may also include aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver. For example, the thickness of the positive electrode current collector 105 may be 10 μm to 50 μm.

[0102] The positive electrode active material layer 110 may include a positive electrode active material. The positive electrode active material may include a compound that can reversibly intercalate and deintercalate lithium ions.

[0103] According to an exemplary embodiment, the positive active material may include lithium-nickel metal oxide. The lithium-nickel metal oxide may further include at least one of cobalt (Co), manganese (Mn), and aluminum (Al).

[0104] In some embodiments, the positive active material or the lithium-nickel metal oxide may include a layered structure or a crystal structure represented by the following Chemical Formula 1.

[0105] [Chemical Formula 1]

[0106] Li x Ni a M b O 2+z

[0107] In Chemical Formula 1, 0.9≤x≤1.2, 0.5≤a≤0.99, 0.01≤b≤0.5, and -0.5≤z≤0.1 may be satisfied. As described above, M may include Co, Mn, and / or Al.

[0108] The chemical structure represented by Chemical Formula 1 represents the bonding relationship contained in the layered structure or crystal structure of the positive active material, and does not exclude other additional elements. For example, M may include Co and / or Mn, and Co and / or Mn may be provided together with Ni as the main active element (main active element) of the positive active material. Chemical Formula 1 is provided to represent the bonding relationship of the main active elements, and it should be understood that Chemical Formula 1 is a formula including the introduction and substitution of additional elements.

[0109] In one embodiment, in addition to the main active element, an auxiliary element for enhancing the chemical stability of the positive electrode active material or the layered structure / crystal structure may be further included. The auxiliary element may be mixed into the layered structure / crystal structure to form a bond, and it should be understood that this case is also included in the chemical structure represented by Chemical Formula 1.

[0110] The auxiliary element may include, for example, at least one selected from the group consisting of Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra, P, and Zr. The auxiliary element, such as Al, may function as an auxiliary active element that contributes to the capacity / power activity of the positive electrode active material together with Co or Mn.

[0111] For example, the positive active material or the lithium-nickel metal oxide may include a layered structure or a crystal structure represented by the following Chemical Formula 1-1.

[0112] [Chemical Formula 1-1]

[0113] Li x Ni a M1 b1 M2 b2 O 2+z

[0114] In Chemical Formula 1-1, M1 may include Co, Mn, and / or Al. M2 may include the auxiliary elements described above. In Chemical Formula 1-1, 0.9≤x≤1.2, 0.5≤a≤0.99, 0.01≤b1+b2≤0.5, and -0.5≤z≤0.1 may be present.

[0115] The positive electrode active material may further include a coating element or a doping element. For example, an element substantially identical to or similar to the auxiliary element may be used as the coating element or the doping element. For example, one or a combination of two or more of the above elements may be used as the coating element or the doping element.

[0116] The coating element or the doping element may be present on the surface of the lithium-nickel metal oxide particle or permeate through the surface of the lithium-nickel metal oxide particle and be included in the bonding structure represented by Chemical Formula 1 or Chemical Formula 1-1.

[0117] The positive active material may include nickel-cobalt-manganese (NCM)-based lithium oxide. In this case, an NCM-based lithium oxide with an increased nickel content may be used.

[0118] Ni can be provided as a transition metal related to the power and capacity of lithium secondary batteries. Therefore, as described above, by using a high-content (high-nickel (High-Ni)) composition for the positive electrode active material, a high-capacity positive electrode and a high-capacity lithium secondary battery can be provided.

[0119] However, as the Ni content increases, the long-term storage stability and lifespan stability of the positive electrode or secondary battery may be relatively reduced, and side reactions with the electrolyte may also increase. However, according to exemplary embodiments, the inclusion of Co can maintain conductivity while the inclusion of Mn can improve lifespan stability and capacity retention characteristics.

[0120] The Ni content in the NCM-based lithium oxide (e.g., the mole fraction of nickel in the total moles of nickel, cobalt, and manganese) may be greater than 0.5, greater than 0.6, greater than 0.7, or greater than 0.8. In some embodiments, the Ni content may be 0.8 to 0.95, 0.82 to 0.95, 0.83 to 0.95, 0.84 to 0.95, 0.85 to 0.95, or 0.88 to 0.95.

[0121] In some embodiments, the positive electrode active material may further include a lithium cobalt oxide-based active material, a lithium manganese oxide-based active material, a lithium nickel oxide-based active material, or a lithium iron phosphate (LFP)-based active material (eg, LiFePO 4 ).

[0122] In some embodiments, the positive electrode active material may include, for example, a lithium-rich layered oxide (LLO) / over-lithiated oxide (OLO)-based active material having a chemical structure or crystal structure represented by Chemical Formula 2, a manganese-rich (Mn-rich) based active material, a cobalt-less (Co-less) based active material, etc. These may be used alone or in combination of two or more.

[0123] [Chemical Formula 2]

[0124] p[Li2MnO3]·(1-p)[Li q JO2]

[0125] In Chemical Formula 2, 0 < p < 1, 0.9 ≤ q ≤ 1.2, and J may include at least one element selected from Mn, Ni, Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, and B.

[0126] The positive electrode active material may be mixed in a solvent to prepare a positive electrode paste. The positive electrode paste may be coated on at least one surface of the positive electrode current collector 105 and then dried and calendered to prepare the positive electrode active material layer 110. The coating may include methods such as gravure coating, slot die coating, multilayer simultaneous die coating, imprinting, doctor blade coating, dip coating, bar coating, casting, etc. The positive electrode active material layer 110 may further include a binder and may optionally further include a conductive material, a thickener, etc.

[0127] The solvent may be N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc.

[0128] The binder may include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (poly(vinylidene fluoride-co-hexafluoropropylene)), polyacrylonitrile, polymethyl methacrylate, nitrile rubber (NBR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), etc. These may be used alone or in combination of two or more.

[0129] In one embodiment, a PVDF-based binder can be used as a positive electrode binder. In this case, the amount of binder used to form the positive electrode active material layer 110 can be reduced, and the amount of positive electrode active material can be relatively increased. Therefore, the power characteristics and capacity characteristics of the secondary battery can be improved.

[0130] The conductive material may be added to enhance the conductivity and / or mobility of lithium ions or electrons of the positive electrode active material layer 110. For example, the conductive material may include carbon-based conductive materials such as graphite, carbon black, acetylene black, Ketjen black, graphene, carbon nanotubes, vapor-grown carbon fiber (VGCF), and carbon fiber, and / or metal-based conductive materials such as perovskite materials such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3. These materials may be used alone or in combination of two or more.

[0131] The positive electrode slurry may further include a thickener and / or a dispersant, etc. In one embodiment, the positive electrode slurry may include a thickener such as carboxymethyl cellulose (CMC).

[0132] The negative electrode 130 may include a negative electrode current collector 125 and a negative electrode active material layer 120 formed on at least one side of the negative electrode current collector 125 .

[0133] For example, the negative electrode current collector 125 may include copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, etc. These may be used alone or in combination of two or more. For example, the thickness of the negative electrode current collector 125 may be 10 μm to 50 μm.

[0134] The negative electrode active material layer 120 may include a negative electrode active material, and the negative electrode active material may include the composite particles 50 . For example, the negative electrode active material may include a plurality of composite particles 50 .

[0135] In some embodiments, the negative electrode active material may include composite particles 50 and a graphite-based active material. For example, the graphite-based active material may include artificial graphite and / or natural graphite.

[0136] In the total weight of the negative electrode active material (for example, the total weight of multiple composite particles 50 and the graphite-based active material), the content of the composite particles 50 can be greater than 3 weight%, greater than 5 weight%, greater than 10 weight%, greater than 15 weight%, greater than 20 weight%, greater than 25 weight%, greater than 30 weight%, greater than 35 weight%, greater than 40 weight% or greater than 45 weight%.

[0137] The content of the composite particles in the total weight of the negative electrode active material may be 90 wt % or less, 85 wt % or less, 80 wt % or less, 75 wt % or less, 70 wt % or less, 65 wt % or less, 60 wt % or less, 55 wt % or less, or 50 wt % or less.

[0138] In one embodiment, the negative electrode active material may consist essentially of the composite particles 50 and the graphite-based active material.

[0139] The negative electrode active material may be mixed in a solvent to prepare a negative electrode slurry. The negative electrode slurry may be coated / deposited on the negative electrode current collector 125, dried, and rolled to prepare the negative electrode active material layer 120. The coating may include gravure coating, slot die coating, multi-layer simultaneous die coating, stamping, blade coating, dip coating, rod coating, casting, and other methods. The negative electrode active material layer 120 may further include a binder and may optionally further include a conductive material, a thickener, and the like.

[0140] The solvent contained in the negative electrode slurry may include water, pure water, deionized water, distilled water, ethanol, isopropyl alcohol, methanol, acetone, n-propyl alcohol, tert-butyl alcohol, etc. These may be used alone or in combination of two or more.

[0141] As the binder, the conductive material, and the thickener, the above-mentioned substances that can be used when manufacturing the positive electrode 100 can be used.

[0142] In some embodiments, the negative electrode binder may use styrene-butadiene-rubber (SBR)-based binders, carboxymethyl cellulose (CMC), polyacrylic acid-based binders, polyethylenedioxythiophene (poly(3,4-ethylenedioxythiophene)), PEDOT-based binders, etc. These may be used alone or in combination of two or more.

[0143] In an exemplary embodiment, a separator 140 may be provided between the positive electrode 100 and the negative electrode 130. The separator 140 may be provided to prevent a short circuit between the positive electrode 100 and the negative electrode 130 and to generate a flow of ions. For example, the separator may have a thickness of 10 μm to 20 μm.

[0144] For example, the separator 140 may include a porous polymer film or a porous non-woven fabric.

[0145] The porous polymer film may include polyolefin-based polymers such as ethylene polymer, propylene polymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, which may be used alone or in combination of two or more.

[0146] The porous non-woven fabric may include high melting point glass fiber, polyethylene terephthalate fiber, and the like.

[0147] The separator 140 may also include a ceramic-based material. For example, inorganic particles may be coated on or dispersed in the polymer film to improve heat resistance.

[0148] The separator 140 may have a single-layer or multi-layer structure including the above-mentioned polymer film and / or non-woven fabric.

[0149] According to an exemplary embodiment, a battery cell is defined by a positive electrode 100, a negative electrode 130, and a separator 140, and a plurality of battery cells may be stacked to form, for example, an electrode assembly 150 in the form of a jelly roll. For example, the electrode assembly 150 may be formed by winding, stacking, z-folding, stack-folding, or the like, the separator 140.

[0150] The electrode assembly 150 is housed in the case 160 together with an electrolyte, thereby defining a lithium secondary battery. According to an exemplary embodiment, the electrolyte may use a non-aqueous electrolyte.

[0151] The non-aqueous electrolyte may contain a lithium salt as an electrolyte and an organic solvent. The lithium salt may be, for example, Li + X - Indicates that, as the anion of the lithium salt (X - ), we can exemplify F - 、Cl - Br - , I - 、NO3 - 、N(CN)2 - 、BF4 - 、ClO4 - PF6 - 、(CF3)2PF4 - 、(CF3)3PF3 - 、(CF3)4PF2 -, (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - etc.

[0152] The organic solvent may be propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate, diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methylpropyl carbonate, ethylpropyl carbonate, dipropyl carbonate, vinylene carbonate, methyl acetate (MA), ethyl acetate (EA), n-propyl acetate (n-PA), 1,1-dimethylethyl acetate (DMEA), methyl propionate (MP), ethyl propionate (EP), ethyl fluoroacetate (FEA), ethyl difluoroacetate (DFEA), ethyl trifluoroacetate (TFEA), dibutyl ether, tetraethylene glycol dimethyl ether (TEGDME), diethylene glycol dimethyl ether (DME), and the like. ether (DEGDME), dimethoxyethane, tetrahydrofuran (THF), 2-methyltetrahydrofuran, ethanol, isopropyl alcohol, dimethyl sulfoxide, acetonitrile, diethoxyethane, sulfolane, γ-butyrolactone and propylene sulfite. These can be used alone or in combination of two or more.

[0153] The non-aqueous electrolyte may further include additives. The additives may include, for example, cyclic carbonate-based compounds, fluorine-substituted carbonate-based compounds, sultone-based compounds, cyclic sulfate-based compounds, cyclic sulfite-based compounds, phosphate-based compounds, borate-based compounds, etc. These additives may be used alone or in combination of two or more.

[0154] The cyclic carbonate-based compound may include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and the like.

[0155] The fluorine-substituted carbonate-based compound may include fluoroethylene carbonate (FEC) and the like.

[0156] The sultone-based compound may include 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, and the like.

[0157] The cyclic sulfate-based compound may include 1,2-ethylene sulfate, 1,2-propylene sulfate, and the like.

[0158] The cyclic sulfite-based compound may include ethylene sulfite, butylene sulfite, and the like.

[0159] The phosphate-based compound may include lithium difluoro bis-oxalato phosphate, lithium difluoro phosphate, and the like.

[0160] The borate-based compound may include lithium bis(oxalate) borate and the like.

[0161] In some embodiments, a solid electrolyte can be used instead of the non-aqueous electrolyte. In this case, the lithium secondary battery can be made into an all-solid-state battery. In addition, a solid electrolyte layer can be provided between the positive electrode 100 and the negative electrode 130 instead of the separator 140.

[0162] The solid electrolyte may include a sulfide-based electrolyte. As non-limiting examples, the sulfide-based electrolyte may include Li2S-P2S5, Li2S-P2S5-LiCl, Li2S-P2S5-LiBr, Li2S-P2S5-LiCl-LiBr, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m Sn (m and n are positive numbers, Z is Ge, Zn or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (p and q are positive numbers, M is P, Si, Ge, B, Al, Ga or In), Li7-xPS6-xCl x (0≤x≤2), Li7-xPS6-xBr x (0≤x≤2), Li7-xPS6-xI x (0≤x≤2), etc. These can be used alone or in combination of two or more.

[0163] In one embodiment, the solid electrolyte may also include an oxide-based amorphous solid electrolyte such as Li2O-B2O3-P2O5, Li2O-SiO2, Li2O-B2O3, Li2O-B2O3-ZnO, etc.

[0164] like Figure 2 and Figure 3 As shown, the tabs (positive tabs and negative tabs) may protrude from the positive current collector 105 and the negative current collector 125 belonging to each battery cell and extend to one side of the case 160. The tabs may be fused to the one side of the case 160 to form electrode leads (positive lead 107 and negative lead 127) extending to the outside of the case 160 or exposed to the outside of the case 160.

[0165] The lithium secondary battery may be manufactured in a cylindrical shape using a can, a prismatic shape, a pouch shape, a coin shape, or the like.

[0166] The following further describes the embodiments of the present invention with reference to specific experimental examples. The examples and comparative examples included in the experimental examples are intended only to illustrate the present invention and are not intended to limit the claims. Various changes and modifications to the embodiments may be made within the scope and technical concept of the present invention, which will be apparent to those skilled in the art, and such variations and modifications are naturally within the scope of the claims.

[0167] Example 1

[0168] Preparation of carbon-based particles

[0169] Asphalt and potassium acetate were dry-mixed at a weight ratio of 5:5 and subjected to a first calcination at 800°C for 2 hours. The first calcined mixture was washed with an excess of 0.5M HCl aqueous solution to prepare carbon-based particles containing pores. The specific volume of the pores of the carbon-based particles was 0.6 cm 3 / g method to prepare carbon-based particles.

[0170] Formation of silicon-containing coating

[0171] A silicon-containing gas comprising silane and argon was injected into a CVD coater at a flow rate of 50 to 100 mL / min. The silane gas content was 50% by volume relative to the total volume of the silicon-containing gas. The temperature was then raised to 550°C at a rate of 5 to 20°C / min and maintained for approximately 120 minutes to produce composite particles comprising a silicon-containing coating.

[0172] The composite particles were prepared so that the silicon content was 45% by weight relative to the total weight of the composite particles.

[0173] Formation of the negative electrode

[0174] A negative electrode slurry was obtained by mixing 95.5 wt % of a negative electrode active material prepared by mixing 15 wt % of the prepared composite particles and 80.5 wt % of artificial graphite, 1 wt % of carbon nanotubes (CNTs) as a conductive material, 2 wt % of styrene-butadiene rubber (SBR) as a binder, and 1.5 wt % of carboxymethyl cellulose (CMC) as a thickener.

[0175] The negative electrode slurry is coated on a copper substrate and dried and rolled to manufacture a negative electrode.

[0176] Lithium half-cell manufacturing

[0177] A lithium half-cell was manufactured, which included the negative electrode manufactured by the above method and used lithium metal as a counter electrode (positive electrode).

[0178] Specifically, a separator (polyethylene, 20 μm thick) was placed between the negative electrode and lithium metal (1 mm thick) to form a lithium coin half-cell of CR2016 (20 mm in diameter, 1.6 mm in thickness).

[0179] The lithium metal / separator / negative electrode assembly was placed in a coin cell plate and injected with electrolyte, then capped and clamped. The electrolyte used was a 1M LiPF6 solution formed using a mixed solvent of EC / EMC (3:7; volume ratio) and 2.0% by volume of fluoroethylene carbonate (FEC) was added relative to the total volume of the electrolyte. After clamping, the plate was immersed for 3 to 24 hours, and then charged and discharged at 0.1C for three cycles (charge conditions: CC-CV 0.1C 0.01V 0.01C cut-off (CUT-OFF), discharge conditions: CC 0.1C 1.5V cut-off).

[0180] Example 2

[0181] A negative electrode and a lithium half-cell were manufactured by the same method as in Example 1, except that an equal amount of a dispersion of silicon dioxide having an average particle size of 5 nm was added instead of potassium acetate, and 0.5 M NaOH aqueous solution was used instead of HCl aqueous solution for washing.

[0182] Example 3, Example 4, Example 7 to Example 9 and Comparative Example 4 and Comparative Example 5

[0183] A negative electrode and a lithium half-cell were manufactured by the same method as in Example 1, except that the content of the silane gas relative to the total volume of the silicon-containing gas was changed as shown in Table 2 below.

[0184] Example 5

[0185] A negative electrode and a lithium half-cell were manufactured by the same method as in Example 1, except that an equal amount of a dispersion of silicon dioxide having an average particle size of 5 nm was added instead of potassium acetate, and a 0.5 M NaOH aqueous solution was used instead of an HCl aqueous solution for washing, and the content of the silane gas relative to the total volume of the silicon-containing gas was changed as shown in Table 2 below.

[0186] Example 6

[0187] A negative electrode and a lithium half-cell were manufactured by the same method as in Example 1, except that an equal amount of a dispersion of silicon dioxide having an average particle size of 6 nm was added instead of potassium acetate, and washing was performed with a 0.5 M NaOH aqueous solution instead of the HCl aqueous solution.

[0188] Example 10

[0189] The carbon-based particles having the silicon-containing coating formed thereon are placed in a thermal chemical vapor deposition (TCVD) chamber and heat-treated at a temperature below 600° C. while supplying a mixed gas of ethylene gas and argon gas, thereby preparing composite particles having the carbon coating formed on the silicon-containing coating.

[0190] A negative electrode and a lithium half-cell were manufactured by the same method as in Example 1 except for the above contents.

[0191] Comparative Example 1

[0192] A negative electrode and a lithium half-cell were manufactured by the same method as in Example 1, except that an equal amount of a dispersion of silicon dioxide having an average particle size of 10 nm was added instead of potassium acetate, and 0.5 M NaOH aqueous solution was used instead of HCl aqueous solution for washing.

[0193] Comparative Example 2

[0194] A negative electrode and a lithium half-cell were manufactured by the same method as in Example 1, except that an equal amount of a dispersion of silicon dioxide having an average particle size of 50 nm was added instead of potassium acetate, and 0.5 M NaOH aqueous solution was used instead of HCl aqueous solution for washing.

[0195] Comparative Example 3

[0196] A negative electrode and a lithium half-cell were manufactured by the same method as in Example 1, except that an equal amount of a dispersion of silicon dioxide having an average particle size of 100 nm was added instead of potassium acetate, and 0.5 M NaOH aqueous solution was used instead of HCl aqueous solution for washing.

[0197] Experimental example

[0198] (1) Measurement of pore size of carbon-based particles

[0199] The pore size of the carbon-based particles prepared according to the above-mentioned embodiments and comparative examples was measured using a surface area analyzer (ASAP-2420) from Micromeritics. Specifically, the pore size of the carbon-based particles was measured by measuring the maximum peak position of a Barrett-Joyner-Halenda (BJH) pore size distribution curve obtained by measuring the nitrogen gas isothermal adsorption-desorption curve (nitrogen gas adsorption isotherm) of the samples obtained from the embodiments and comparative examples.

[0200] (2) Measurement of silicon content (Si content) in composite particles

[0201] Samples of the composite particles prepared according to the above examples and comparative examples were placed in a polypropylene tube. Nitric acid and a small amount of hydrofluoric acid were added to the tube and allowed to stand at room temperature overnight to dissolve. After the sample was dissolved, the tube was cooled and saturated boric acid solution was added to neutralize the hydrofluoric acid. The sample was then diluted with ultrapure water. Carbon components were removed using a 0.45 μm syringe filter.

[0202] The sample was put into an inductively coupled plasma spectrometer (ICP-OES Optima 8300, Perkin Elmer) for analysis to measure the silicon content relative to the total weight of the composite particles.

[0203] (3) Whether silicon is amorphous before heat treatment and measurement of grain size

[0204] For the composite particles prepared according to the above examples and comparative examples, the crystallite size was calculated using XRD analysis and Formula 1.

[0205] When the silicon particle size is so fine that it is difficult to measure by XRD analysis, it is considered to be amorphous.

[0206] (4) Whether the silicon after heat treatment is amorphous and measurement of grain size

[0207] The composite particles prepared according to the above examples and comparative examples were heat treated at 900° C. for 6 hours and then naturally cooled to room temperature (25° C.) Then, the crystallite size of the composite particles was calculated using XRD analysis and Formula 1.

[0208] When the silicon particle size is so fine that it is difficult to measure by XRD analysis, it is considered to be amorphous.

[0209] In addition, specific XRD analysis equipment / conditions are shown in Table 1 below.

[0210] [Table 1]

[0211]

[0212] (5) Measurement of I(Si(220)) / I(SiC)

[0213] The composite particles prepared according to the above examples and comparative examples were subjected to XRD analysis to obtain a graph in which the vertical axis represents peak intensity and the horizontal axis represents 2θ (diffraction angle).

[0214] In the figure, the maximum peak intensity within the 2θ range of 46° to 48° measured by XRD analysis is set as I(Si(220)), and the maximum peak intensity within the 2θ range of 34° to 36° measured by XRD analysis is set as I(SiC).

[0215] Substituting I(Si(220)) and I(SiC) into Formula 2, I(Si(220)) / I(SiC) was obtained.

[0216] Figure 4 : The XRD analysis diagrams of Example 1, Comparative Example 1 and Comparative Example 3. Figure 4 In the figure, I(SiC) and I(Si(220)) were measured by setting the vertical axis to peak intensity and the horizontal axis to 2θ (diffraction angle).

[0217] (6) Measurement of capacity retention

[0218] The lithium half-cells according to Examples and Comparative Examples were charged (CC / CV 0.5C 0.01V 0.01C cutoff) and discharged (CC 0.1C 3.0V cutoff) 50 times, and the capacity retention was evaluated by dividing the 50th discharge capacity by the 1st discharge capacity.

[0219] The measurement results and evaluation results are shown in Table 2 below.

[0220] [Table 2]

[0221]

[0222] Referring to Table 2, in the examples in which the grain size of silicon contained in the silicon-containing coating after the heat treatment is 10 nm or less (including an amorphous structure), the capacity retention is improved as a whole compared to the comparative examples.

[0223] In both Examples and Comparative Examples, silicon before the heat treatment had an amorphous structure. However, in Examples, the size of silicon internal domains was smaller than in Comparative Examples, and thus aggregation or crystallization of silicon caused by the heat treatment was reduced.

[0224] In Examples and Comparative Examples, the silicon contents relative to the total weight of the composite particles were substantially similar, but the physical properties and life characteristics of the composite particles were measured differently depending on the pore size and the silane gas concentration.

[0225] In Example 6, in which the pore size of the carbon-based particles exceeded 10 nm, the capacity retention ratio decreased compared with the other examples.

[0226] In Example 7 where I(Si(220)) / I(SiC) is 1.0 or greater, the capacity retention rate is lower than that of the other examples.

[0227] In Examples 8 and 9 in which the content of the silane gas was not within the range of 10% to 70% by volume relative to the total volume of the silicon-containing gas, the capacity retention ratio decreased compared to the other examples.

[0228] In Example 10, in which a carbon coating layer was further formed on the silicon-containing coating layer, the capacity retention rate was improved compared to the other examples.

Claims

1. A negative electrode active material for a lithium secondary battery, the negative electrode active material for a lithium secondary battery comprising composite particles, the composite particles comprising: a carbon-based particle comprising pores; and a silicon-containing coating formed on the surface of the carbon-based particles, in, After the composite particles are heat-treated at 900° C. to 1200° C. for 6 to 9 hours, the crystallite size of silicon contained in the silicon-containing coating layer measured by X-ray diffraction (XRD) analysis is 10 nm or less.

2. The negative electrode active material for lithium secondary battery according to claim 1, wherein The grain size of silicon contained in the silicon-containing coating is measured by the following formula 1: [Formula 1] In Formula 1, L is the crystal size and is measured in nm, λ is the X-ray wavelength and is measured in nm, β is the half-maximum full width of the peak of the (111) plane of silicon contained in the silicon-containing coating and is measured in radians, and θ is the diffraction angle and is measured in radians.

3. The negative electrode active material for lithium secondary battery according to claim 1, wherein The heat treatment is performed on 1 g to 5 g of the composite particles in an inert atmosphere.

4. The negative electrode active material for lithium secondary battery according to claim 1, wherein The grain size of silicon contained in the silicon-containing coating layer after the heat treatment measured by XRD analysis is 8 nm or less.

5. The negative electrode active material for lithium secondary battery according to claim 1, wherein The silicon contained in the silicon-containing coating after the heat treatment has an amorphous structure.

6. The negative electrode active material for lithium secondary battery according to claim 1, wherein The pores of the carbon-based particles have a size of 0.1 nm to 10 nm.

7. The negative electrode active material for lithium secondary battery according to claim 1, wherein The pores of the carbon-based particles have a size of 1 nm to 5 nm.

8. The negative electrode active material for lithium secondary battery according to claim 1, wherein The composite particles after the heat treatment further include silicon carbide (SiC).

9. The negative electrode active material for lithium secondary battery according to claim 1, wherein The composite particles after the heat treatment satisfy the following formula 2: [Formula 2] I(Si(220)) / I(SiC)<1.0 In Formula 2, I(Si(220)) is the maximum peak intensity in the 2θ range of 46° to 48° measured by XRD analysis, I(SiC) is the maximum peak intensity in the 2θ range of 34° to 36° measured by XRD analysis, and 2θ is the diffraction angle and the unit is °.

10. The negative electrode active material for lithium secondary battery according to claim 1, wherein The composite particle further includes a carbon coating formed on the silicon-containing coating.

11. The negative electrode active material for lithium secondary battery according to claim 1, wherein The pores of the carbon-based particles include a shape bent from the outermost portion of the carbon-based particles toward the inner portion of the carbon-based particles.

12. A lithium secondary battery comprising: A negative electrode, the negative electrode comprising the negative electrode active material for a lithium secondary battery according to claim 1; and A positive electrode is arranged opposite to the negative electrode.

13. A method for preparing a negative electrode active material for a lithium secondary battery, comprising the following steps: preparing a carbon-based particle comprising pores; as well as calcining the carbon-based particles and a silicon-containing gas together to form composite particles, the composite particles comprising a silicon-containing coating formed on the surface of the carbon-based particles, Wherein, after the composite particles are heat treated at 900° C. to 1200° C. for 6 to 9 hours, the grain size of silicon contained in the silicon-containing coating layer measured by X-ray diffraction (XRD) analysis is 10 nm or less.

14. The method for preparing a negative electrode active material for a lithium secondary battery according to claim 13, wherein: The silicon-containing gas includes silane gas, and the volume of the silane gas is 10 volume % to 70 volume % relative to the total volume of the silicon-containing gas.

15. The method for preparing a negative electrode active material for a lithium secondary battery according to claim 14, wherein: The volume of the silane gas is 20 volume % to 50 volume % relative to the total volume of the silicon-containing gas.

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