Negative electrode active material for lithium secondary battery, method for preparing same, 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 C / SiC peak intensity ratio of the composite particle measured by X-ray diffraction analysis after heat treatment of the composite particle at 900 DEG C to 1200 DEG C for 6 to 9 hours is 1.0 to 4.5.

Description

Technical Field

[0001] The present invention relates to a negative electrode active material for a lithium secondary battery, a preparation method thereof 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 capacity characteristics, power characteristics, and life characteristics can be provided.

[0008] According to another aspect of the present invention, a method for preparing a negative electrode active material for a lithium secondary battery having improved capacity characteristics, power characteristics, and life characteristics can be provided.

[0009] According to another aspect of the present invention, a lithium secondary battery having improved capacity characteristics, power characteristics, and lifespan characteristics can be provided.

[0010] (2) Technical solution

[0011] A negative electrode active material for a lithium secondary battery according to an exemplary 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 heat-treating the composite particles at 900° C. to 1200° C. for 6 to 9 hours, the composite particles exhibit a C / SiC peak intensity ratio, as defined by the following formula 1, of 1.0 to 4.5.

[0012] [Formula 1]

[0013] C / SiC peak intensity ratio = I(C) / I(SiC)

[0014] In Formula 1, I(C) is the maximum peak intensity within a 2θ range of 20° to 23° measured by X-ray diffraction (XRD) analysis, I(SiC) is the maximum peak intensity within a 2θ range of 34° to 37° measured by XRD analysis, and 2θ is a diffraction angle (°).

[0015] In some embodiments, the C / SiC peak intensity ratio may be 2.9 to 4.1.

[0016] In some embodiments, the heat treatment may be performed on 1 g to 5 g of the composite particles in an inert atmosphere.

[0017] In some embodiments, the pores of the carbon-based particles may have a size of 0.1 nm to 10 nm.

[0018] In some embodiments, the composite particles may further include a carbon coating formed on the silicon-containing coating.

[0019] 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.

[0020] In some embodiments, the crystallite size of silicon contained in the silicon-containing coating layer after heat-treating the composite particles at 900° C. to 1200° C. for 6 to 9 hours as measured by XRD analysis may be 10 nm or less.

[0021] In some embodiments, the grain size of silicon contained in the silicon-containing coating layer may be measured by the following Formula 2.

[0022] [Formula 2]

[0023]

[0024] In Formula 2, L is the crystallite size (nm), λ is the X-ray wavelength (nm), β is 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 is the diffraction angle (radians).

[0025] 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.

[0026] In some embodiments, the silicon contained in the silicon-containing coating after the heat treatment may include an amorphous structure.

[0027] A lithium secondary battery according to an exemplary embodiment of the present invention includes: a negative electrode including the negative electrode active material for a lithium secondary battery; 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 exemplary embodiment of the present invention, primary carbon-based particles containing pores are prepared. The primary carbon-based particles and a hydrogen-containing gas are subjected to a first calcination to form carbon-based particles. The carbon-based particles and a silicon-containing gas are subjected to a second calcination to form composite particles, the composite particles comprising 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 C / SiC peak intensity ratio of the composite particles defined by the following formula 1 is 1.0 to 4.5.

[0029] [Formula 1]

[0030] C / SiC peak intensity ratio = I(C) / I(SiC)

[0031] In Formula 1, I(C) is the maximum peak intensity within the 2θ range of 20° to 23° measured by X-ray diffraction (XRD) analysis, I(SiC) is the maximum peak intensity within the 2θ range of 34° to 37° measured by XRD analysis, and 2θ is the diffraction angle (°).

[0032] In some embodiments, the first calcination may be performed at a temperature of 300°C to 700°C.

[0033] In some embodiments, the second calcination may be performed at a temperature of 400°C to 600°C.

[0034] (3) Beneficial effects

[0035] According to one embodiment of the present invention, generation of gas due to a side reaction of a negative electrode active material with an electrolyte solution can be suppressed, and life characteristics of a secondary battery can be improved.

[0036] According to one embodiment of the present invention, the formation of the SiC phase after heat treatment can be suppressed, thereby improving capacity characteristics, power characteristics, and life characteristics in a high-temperature environment or during repeated charge and discharge.

[0037] 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

[0038] Figure 1 is a schematic cross-sectional view illustrating a composite particle according to an exemplary embodiment.

[0039] Figure 2 is a process flow chart for explaining a method for preparing a negative electrode active material for a lithium secondary battery according to an exemplary embodiment.

[0040] Figure 3 and Figure 4 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.

[0041] Figure 5 is an X-ray diffraction (XRD) analysis chart of the composite particles before heat treatment.

[0042] Figure 6 is the XRD analysis diagram of the composite particles after heat treatment.

[0043] Description of reference numerals:

[0044] 50: composite particles; 60: carbon-based particles

[0045] 62: outer surface of carbon-based particles; 65: pores

[0046] 67: Inner surface of the hole; 70: Silicone coating

[0047] 100: positive electrode; 105: positive electrode current collector

[0048] 107: positive electrode lead; 110: positive electrode active material layer

[0049] 120: negative electrode active material layer; 125: negative electrode current collector

[0050] 127: negative lead; 130: negative electrode

[0051] 140: diaphragm; 150: electrode assembly

[0052] 160: Shell DETAILED DESCRIPTION

[0053] Embodiments of the present invention provide a negative electrode active material for a lithium secondary battery (hereinafter referred to as a "negative electrode active material") comprising composite particles. Furthermore, a method for preparing the negative electrode active material is provided. Furthermore, a lithium secondary battery (hereinafter referred to as a "secondary battery") comprising the negative electrode active material is provided.

[0054] Hereinafter, embodiments of the present invention will be described in detail. However, these are merely exemplary embodiments, and the present invention is not limited to the specific embodiments described exemplarily.

[0055] Figure 1 is a schematic cross-sectional view illustrating a composite particle according to an exemplary embodiment.

[0056] For ease of explanation, Figure 1 The shape of the composite particles is schematically shown in FIG. 1 , but the structure / shape of the composite particles of the present invention is not limited to Figure 1 The structure / shape shown in FIG. For example, the cross-section of the carbon-based particles can be randomly changed from a circular shape. In addition, the silicon-containing coating can be partially formed on the pores and surface of the carbon-based particles, and can also be formed into a discontinuous plurality of islands or patterns.

[0057] Reference Figure 1 The composite particles 50 may include carbon (C)-based particles 60 and a silicon (Si)-containing coating layer 70. For example, the negative active material may include a plurality of composite particles 50.

[0058] 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.

[0059] 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.

[0060] In some embodiments, the carbon-based particles 60 may include an amorphous structure or a crystalline structure.

[0061] According to one embodiment, the carbon-based particles 60 may include an amorphous structure. In this case, the durability of the negative electrode active material can be increased, thereby suppressing cracks during charge and discharge or external impact. Therefore, the life characteristics of the secondary battery can be improved.

[0062] In some embodiments, 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 that are open to the outside of the carbon-based particles 60 (open pores).

[0063] 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.

[0064] According to one embodiment, the size of the pores 65 can be measured using a surface area analyzer (ASAP-2420) manufactured by Micromeritics, Inc. For example, the size of the pores 65 can be measured by measuring the maximum peak position of a Barrett-Joyner-Halenda (BJH) pore size distribution curve obtained from a nitrogen gas sorption isotherm of the carbon-based particle 60 sample.

[0065] A silicon-containing coating 70 may be formed on the surface of the carbon-based particles 60 comprising pores 65. For example, the volume expansion of the silicon contained in the silicon-containing coating 70 may be alleviated by the pores 65. Thus, the relatively high capacity characteristics of silicon may be utilized while preventing cracks caused by the difference in the volume expansion rate of carbon (e.g., about 150% by volume or less) and the volume expansion rate of silicon (e.g., about 400% by volume or more) during charge and discharge of the battery. Thus, the generation of gas caused by the side reaction of the negative electrode active material with the electrolyte may be suppressed, and the life characteristics of the secondary battery may be improved.

[0066] 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 .

[0067] 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 .

[0068] 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 .

[0069] 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 .

[0070] 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 .

[0071] In some embodiments, the silicon-containing coating 70 may comprise silicon, and may optionally further comprise SiO x (0 <x<2)。

[0072] 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, after the negative electrode active material is prepared and before the negative electrode is formed, a decrease in the discharge capacity and capacity efficiency of the secondary battery can be suppressed.

[0073] 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.

[0074] 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.

[0075] According to an exemplary embodiment of the present invention, the C / SiC peak intensity ratio defined by the following formula 1 after heat treating the composite particles 50 at 900° C. to 1200° C. for 6 to 9 hours may be 1.0 to 4.5. In some embodiments, the C / SiC peak intensity ratio may be 2.9 to 4.1.

[0076] [Formula 1]

[0077] C / SiC peak intensity ratio = I(C) / I(SiC)

[0078] In Formula 1, I(C) is the maximum peak intensity within the 2θ range of 20° to 23° measured by X-ray diffraction (XRD) analysis. I(SiC) is the maximum peak intensity within the 2θ range of 34° to 37° measured by XRD analysis. 2θ is the diffraction angle (°).

[0079] For example, I(C) of Formula 1 may represent the peak intensity of carbon contained in the composite particles 50. I(SiC) may represent the peak intensity of silicon carbide (SiC) contained in the composite particles 50 after the heat treatment.

[0080] Within the above-mentioned C / SiC peak intensity ratio range, the formation and growth of the SiC phase after heat treatment can be suppressed, thereby improving capacity characteristics, power characteristics, and life characteristics in a high-temperature environment or during repeated charge and discharge.

[0081] In some embodiments, the heat treatment may be performed in an inert atmosphere on 1 g to 5 g of the composite particles 50. Therefore, the heat treatment conditions may be uniformly maintained, thereby improving the reliability and reproducibility of the measurement results.

[0082] The heat treatment is not included in the preparation process of the composite particles 50 and can 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.

[0083] 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.

[0084] Hereinafter, the term "the heat treatment" in this specification may refer to a heat treatment performed under the above-mentioned conditions (at 900° C. to 1200° C. for 6 hours to 9 hours).

[0085] For example, the term “inert atmosphere” used in this specification may refer to a state in which an inert gas (eg, nitrogen (N 2 ) or argon (Ar)) is continuously purged into a chamber containing the composite particles 50 .

[0086] 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.

[0087] In an exemplary embodiment, the C / SiC peak intensity ratio can be controlled by the hydrogen reduction temperature of the carbon-based particles 60 (first calcination temperature), the hydrogen content in the hydrogen-containing gas, the silicon source content in the silicon-containing gas, the silicon deposition temperature (second calcination temperature), the calcination time, etc.

[0088] In some embodiments, the grain size of silicon contained in the silicon-containing coating 70 after heat treating the composite particles 50 at 900° C. to 1200° C. for 6 to 9 hours as measured by 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.

[0089] In some embodiments, the heat treatment may be performed by substantially the same method as the measurement of the C / SiC peak intensity ratio.

[0090] For example, even with silicon particles having a relatively small grain size or an amorphous structure, domains inside the silicon may aggregate or crystallize due to repeated charge and discharge of the secondary battery or a temperature increase caused by external heat.

[0091] Within the above-mentioned grain size range of the present invention, the grain size of the heat-treated silicon can be controlled, thereby improving the life characteristics under high temperature environment or repeated charge and discharge. For example, the grain size of the heat-treated silicon can be proportional to the size of the internal domain of the silicon.

[0092] 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 2 in an XRD analysis method.

[0093] [Formula 2]

[0094]

[0095] In Formula 2, 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 based on the peak of the (111) plane of silicon contained in the silicon-containing coating.

[0096] In some embodiments, in the above formula 2, β can use the half-width at half maximum corrected for the value derived from the device. In one embodiment, Si can be used as a standard substance reflecting the value derived 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 derived from the device can be expressed as a function of 2θ. Thereafter, the value obtained from the full-width at half-maximum value derived from the device at the corresponding 2θ obtained from the function is subtracted and corrected, and can be used as β.

[0097] 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.

[0098] The term “amorphous structure” used in this specification may refer to a case where the shape of individual silicon contained in the silicon-containing coating layer 70 is amorphous or a case where particles are so fine that the size is difficult to measure by the Scherrer equation represented by Formula 2.

[0099] In an exemplary embodiment, the grain size of the heat-treated silicon can be controlled by 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.

[0100] Figure 2 is a process flow chart for explaining a method for preparing a negative electrode active material for a lithium secondary battery according to an exemplary embodiment.

[0101] Reference Figure 2 , a primary carbon-based particle containing pores 65 may be prepared (eg, step S10). The primary carbon-based particle may refer to a carbon-based particle that has not been subjected to hydrogen reduction treatment.

[0102] In some embodiments, the carbon-based particle source and additives may be mixed, pre-calcined, and washed to form primary carbon-based particles.

[0103] In one embodiment, the carbon-based particle source may include at least one selected from the group consisting of glucose, sucrose, cellulose, petroleum-based pitch, coal-based pitch, biomass, and resol oligomer.

[0104] In some embodiments, the additive may be provided as a chemical etchant or a hard template.

[0105] 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 of the carbon-based particle source and the additive can be carried out by a chemical activation method. In particular, the chemical etchant can act as an activating agent and can react with the carbon-based particle source to form a porous structure and release gases such as CO, CO2, CH4 or H2. For example, potassium hydroxide (KOH) can react with the carbon-based particle source to form potassium oxide or potassium carbonate.

[0106] 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.

[0107] In one embodiment, the pre-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.

[0108] 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.

[0109] In an exemplary embodiment, the primary carbon-based particles and the hydrogen-containing gas may be subjected to a first calcination to form carbon-based particles 60 (e.g., step S20). Thus, oxygen-containing functional groups on the surface of the primary carbon-based particles may be removed / reduced, thereby suppressing the formation of SiC caused by high temperatures or repeated charge and discharge. Thus, the power characteristics, capacity characteristics, and life characteristics of the lithium secondary battery may be improved.

[0110] For example, the first calcination may be performed while the hydrogen-containing gas is added to a chamber in which the primary carbon-based particles are disposed.

[0111] In some embodiments, the hydrogen-containing gas may include hydrogen (H2) and an inert gas. For example, the inert gas may include argon (Ar).

[0112] In some embodiments, the content of hydrogen gas in the total volume of the hydrogen-containing gas may be 1% to 50% by volume, 3% to 30% by volume, 5% to 20% by volume, or 10% to 15% by volume. Within the above range, the SiC phase contained in the composite particles before the heat treatment can be fully removed. Therefore, the growth of the SiC phase at high temperatures can be suppressed, thereby suppressing the degradation of life characteristics due to high temperatures or repeated charge and discharge.

[0113] In some embodiments, the first calcination can be performed at a temperature of 300°C to 700°C. In one embodiment, the first calcination can be performed at a temperature of 500°C to 700°C. Within this range, the SiC phase contained in the composite particles before the heat treatment can be sufficiently removed. As a result, the growth of the SiC phase at high temperatures can be suppressed, thereby suppressing the degradation of life characteristics caused by high temperature environments or repeated charge and discharge.

[0114] In an exemplary embodiment, the carbon-based particles 60 and the silicon-containing gas may be secondarily calcined to form composite particles 50 including the silicon-containing coating layer 70 formed on the surface of the carbon-based particles 60 (eg, step S30 ).

[0115] For example, the second calcination may be performed while the silicon-containing gas is added to the chamber where the carbon-based particles 60 are disposed.

[0116] In some embodiments, the silicon-containing gas may include silane gas and an inert gas. For example, the inert gas may include argon (Ar).

[0117] 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.

[0118] In some embodiments, the second calcination may be performed at a temperature of 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 the rolling process or repeated charge and discharge of the secondary battery may be improved.

[0119] The C / SiC peak intensity ratio of the composite particles 50 formed by the above method may be 1.0 to 4.5 after the heat treatment is performed on the composite particles 50 .

[0120] Figure 3 and Figure 4 are respectively a schematic plan view and a schematic cross-sectional view showing a lithium secondary battery according to an exemplary embodiment. Figure 4 It is along Figure 3 A cross-sectional view taken along the thickness direction along the II' line.

[0121] The lithium secondary battery may include a negative electrode 130 including the negative electrode active material and a positive electrode 100 disposed opposite to the negative electrode 130 .

[0122] 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 .

[0123] 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.

[0124] 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.

[0125] 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).

[0126] 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.

[0127] [Chemical Formula 1]

[0128] Li x Ni a M b O 2+z

[0129] In Chemical Formula 1, 0.9≤x≤1.2, 0.6≤a≤0.99, 0.01≤b≤0.4, and −0.5≤z≤0.1 may be satisfied. As described above, M may include Co, Mn, and / or Al.

[0130] 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.

[0131] 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.

[0132] 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.

[0133] 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.

[0134] [Chemical Formula 1-1]

[0135] Li x Ni a M1 b1 M2 b2 O 2+z

[0136] 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, 0.6≤a≤0.99, 0.01≤b1+b2≤0.4, and -0.5≤z≤0.1 may be present.

[0137] 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.

[0138] 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.

[0139] 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.

[0140] 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.

[0141] However, as the Ni content increases, the long-term storage stability and life stability of the positive electrode or secondary battery may decrease relatively, and the side reactions with the electrolyte may also increase. However, according to an exemplary embodiment, the conductivity can be maintained by including Co, and the life stability and capacity retention characteristics can be improved by Mn.

[0142] The content of Ni in the NCM-based lithium oxide (e.g., the mole fraction of Ni in the total moles of nickel, cobalt, and manganese) can be 0.5 or more, 0.6 or more, 0.7 or more, or 0.8 or more. In some embodiments, the content of Ni can 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.

[0143] 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 (e.g., LiFePO4).

[0144] 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, a manganese-rich (Mn-rich)-based active material, a cobalt-less (Co-less)-based active material, etc., having a chemical structure or crystal structure represented by Chemical Formula 2. These can be used alone or in combination of two or more.

[0145] [Chemical Formula 2]

[0146] p[Li2MnO3]·(1-p)[Li q JO2]

[0147] 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.

[0148] The positive electrode active material may be mixed in a solvent to prepare a positive electrode slurry. The positive electrode slurry may be coated on at least one side of the positive electrode current collector 105 and then dried and rolled to prepare a positive electrode active material layer 110. The coating may include gravure coating, slot die coating, multi-layer simultaneous die coating, stamping, doctor blade coating, dip coating, bar coating, casting, and the like. The positive electrode active material layer 110 may further include a binder and may optionally further include a conductive material, a thickener, and the like.

[0149] As the solvent, N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc. can be used.

[0150] The binder may include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (poly(vinylidene fluoride-co-hexafluoropropylene)), polyacrylonitrile, polymethyl methacrylate, acrylonitrile-butadiene rubber (NBR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), etc. These may be used alone or in combination of two or more.

[0151] 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.

[0152] 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 (CNTs), vapor-grown carbon fibers (VGCFs), and carbon fibers, and / or metal-based conductive materials such as perovskites such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3. These materials may be used alone or in combination of two or more.

[0153] 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).

[0154] 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 .

[0155] 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.

[0156] 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 .

[0157] 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.

[0158] The graphite-based active material may refer to an active material containing graphite and not containing silicon.

[0159] 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 1 weight%, 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%.

[0160] 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.

[0161] In one embodiment, the negative active material may consist essentially of the composite particles 50 and the graphite-based active material.

[0162] 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.

[0163] 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.

[0164] 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.

[0165] 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.

[0166] In an exemplary embodiment, the 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 thickness of the separator may be 10 μm to 20 μm.

[0167] For example, the separator 140 may include a porous polymer film or a porous non-woven fabric.

[0168] 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.

[0169] The porous non-woven fabric may include high-melting-point glass fiber, polyethylene terephthalate fiber, or the like.

[0170] 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.

[0171] The separator 140 may have a single-layer structure or a multi-layer structure including the above-mentioned polymer film and / or non-woven fabric.

[0172] According to an exemplary embodiment, a battery cell may be 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.

[0173] The electrode assembly 150 may be 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.

[0174] 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 - wait.

[0175] 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.

[0176] 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, and borate-based compounds. These additives may be used alone or in combination of two or more.

[0177] The cyclic carbonate-based compound may include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and the like.

[0178] The fluorine-substituted carbonate-based compound may include fluoroethylene carbonate (FEC) and the like.

[0179] The sultone-based compound may include 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, and the like.

[0180] The cyclic sulfate-based compound may include 1,2-ethylene sulfate, 1,2-propylene sulfate, and the like.

[0181] The cyclic sulfite-based compound may include ethylene sulfite, butylene sulfite, and the like.

[0182] The phosphate-based compound may include lithium difluoro bis-oxalato phosphate, lithium difluoro phosphate, and the like.

[0183] The borate-based compound may include lithium bis(oxalate) borate, and the like.

[0184] 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.

[0185] 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 S n (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.

[0186] 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.

[0187] like Figure 3 and Figure 4 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.

[0188] 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.

[0189] 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.

[0190] Example 1

[0191] Preparation of primary carbon-based particles (step S10)

[0192] The coconut shell was dried to remove moisture and purged with argon while being pre-calcined (carbonized) at 700°C for 6 hours. Water vapor was added to the pre-calcined particles while being activated at 500°C to prepare a particle with a specific surface area of ​​1500 m 2 / g and a pore volume of 0.7 cm 3 / g of activated carbon as primary carbon-based particles.

[0193] Formation of carbon-based particles (step S20)

[0194] A hydrogen-containing gas including hydrogen and argon at a volume ratio of 1:9 was added to the chamber where the primary carbon-based particles were placed, and a first calcination was performed at 600° C. to form carbon-based particles.

[0195] Formation of silicon-containing coating (step S30)

[0196] The carbon-based particles were placed in a CVD coater, and a silicon-containing gas comprising silane (SiH 4 ) gas and argon gas in a volume ratio of 1:9 was injected into the CVD coater at a flow rate of 50 mL / min to 100 mL / min.

[0197] The temperature of the CVD coater was increased to 400° C. at a temperature increase rate of 5° C. / min to 20° C. / min and then maintained at 400° C. for about 120 minutes (second calcination) to prepare composite particles including a silicon-containing coating layer.

[0198] Formation of the negative electrode

[0199] A negative electrode slurry was obtained by mixing 95.5 wt % of a negative electrode active material prepared by mixing 15 wt % of the 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.

[0200] The negative electrode slurry is coated on a copper substrate and dried and rolled to manufacture a negative electrode.

[0201] Lithium half-cell manufacturing

[0202] A lithium half-cell is manufactured, which includes the negative electrode and uses lithium metal (Li metal) as a counter electrode (positive electrode).

[0203] 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).

[0204] The lithium metal / separator / negative electrode assembly was placed in a coin cell plate and injected with electrolyte, then covered with a cap and clamped. The electrolyte used was a 1M LiPF6 solution prepared by using a mixed solvent of EC / EMC (3:7; volume ratio) with 2.0% by volume of fluoroethylene carbonate (FEC) 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 3 cycles (charge conditions: CC-CV 0.1C 0.01V 0.01C cut-off (CUT-OFF), discharge conditions: CC 0.1C 1.5V cut-off).

[0205] Examples 2 to 12 and Comparative Examples 2 to 4

[0206] Composite particles and lithium half-cells were prepared by the same method as in Example 1, except that the temperature of the first calcination, the content of hydrogen in the total volume of the hydrogen-containing gas, and the temperature of the second calcination were changed as shown in Table 2.

[0207] Comparative Example 1

[0208] Composite particles and a lithium half-cell were prepared by the same method as in Example 1, except that no hydrogen-containing gas was added and the primary carbon-based particles were used as carbon-based particles.

[0209] Experimental example

[0210] (1) Measurement of C / SiC peak intensity ratio before heat treatment

[0211] The composite particles prepared according to the above-described Examples and Comparative Examples were subjected to XRD analysis without undergoing a separate heat treatment, thereby obtaining a graph having peak intensity on the vertical axis and 2θ (diffraction angle) on the horizontal axis.

[0212] In the figure, the maximum peak intensity within the 2θ range of 20° to 23° measured by XRD analysis is defined as I(C), and the maximum peak intensity within the 2θ range of 34° to 37° measured by XRD analysis is defined as I(SiC).

[0213] Substituting I(C) and I(SiC) into Formula 1, the C / SiC peak intensity ratio before heat treatment was measured.

[0214] Figure 5 : is the XRD analysis diagram of Example 1 and Comparative Example 1 before heat treatment. Figure 5 In the graph, the vertical axis represents peak intensity, the horizontal axis represents 2θ (diffraction angle), and I(SiC) and I(C) are measured.

[0215] (2) Measurement of C / SiC peak intensity ratio after heat treatment

[0216] 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). Thereafter, the C / SiC peak intensity ratio of the composite particles was measured by the same method as in Experimental Example (1).

[0217] Figure 6 : is the XRD analysis diagram of Example 1 and Comparative Example 1 after the heat treatment. Figure 6 In the graph, the vertical axis represents peak intensity, the horizontal axis represents 2θ (diffraction angle), and I(SiC) and I(C) are measured.

[0218] Reference Figure 5 and Figure 6 In Example 1, the SiC peak intensity was small even after the heat treatment, but in Comparative Example 1, the SiC peak intensity increased significantly after the heat treatment.

[0219] In addition, specific XRD analysis equipment / conditions are shown in Table 1 below.

[0220] [Table 1]

[0221]

[0222] (3) Whether the silicon after heat treatment is amorphous and measurement of grain size

[0223] 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.) Afterwards, the composite particles were subjected to XRD analysis, and the grain size was calculated using Formula 2.

[0224] When the crystallite size of silicon is so small that it is difficult to measure by XRD analysis, it is said to be amorphous.

[0225] (4) Measurement of initial discharge capacity and initial efficiency

[0226] The lithium half-cells of Examples and Comparative Examples were charged (CC-CV 0.1C 0.01V 0.01C cut-off) and discharged (CC 0.1C 1.5V cut-off) once at room temperature (25°C), and the initial charge capacity and initial discharge capacity were measured.

[0227] The initial efficiency was evaluated by dividing the initial discharge capacity by the initial charge capacity and multiplying by 100.

[0228] (5) Evaluation of capacity retention (50 cycles)

[0229] The lithium half-cells of Examples and Comparative Examples were charged (CC-CV 0.1C 0.01V 0.01C cutoff) and discharged (CC 0.1C 1.5V cutoff) 50 times at room temperature (25°C). The capacity retention was evaluated by dividing the 50th discharge capacity by the 1st discharge capacity and multiplying the result by 100.

[0230] The measurement results and evaluation results are shown in Tables 2 and 3 below.

[0231] The temperature of the first calcination, the hydrogen content in the total volume of the hydrogen-containing gas, the temperature of the second calcination, the C / SiC peak intensity ratio before heat treatment, the C / SiC peak intensity ratio after heat treatment, and the silicon grain size after heat treatment are shown in Table 2. The initial discharge capacity, initial efficiency, and capacity retention are shown in Table 3.

[0232] [Table 2]

[0233]

[0234] [Table 3]

[0235]

[0236] Referring to Table 2 and Table 3, in the examples where the C / SiC peak intensity ratio after the heat treatment is 1.0 to 4.5, the initial discharge capacity, initial efficiency, and capacity retention rate are generally improved compared to the comparative examples.

[0237] In Examples and Comparative Examples, the C / SiC peak intensity ratio before the heat treatment was similar, but in Examples, the formation and growth of SiC were suppressed even after the heat treatment, as compared with Comparative Examples.

[0238] In Example 6, in which the temperature of the first calcination was lower than 300° C., the initial discharge capacity and the capacity retention ratio were relatively lower than those of the other examples.

[0239] In Example 7, in which the temperature of the first calcination exceeded 700° C., the initial efficiency was relatively lowered compared to the other examples.

[0240] In Example 10, in which the temperature of the second calcination was lower than 400° C., the initial discharge capacity and the capacity retention ratio were relatively lower than those of the other examples.

[0241] In Example 11, in which the temperature of the second calcination exceeded 600° C., the initial efficiency was relatively lowered compared to the other examples.

[0242] In Examples 10 to 12 in which the grain size of silicon exceeded 10 nm, the initial discharge capacity, initial efficiency, and / or capacity retention ratio were relatively lowered compared to the other examples.

Claims

1. A negative electrode active material for a lithium secondary battery, comprising composite particles, wherein the composite particles comprise: carbon-based particles comprising pores; and a silicon-containing coating formed on the surface of the carbon-based particles, in, The C / SiC peak intensity ratio of the composite particles defined by the following formula 1 after heat-treating the composite particles at 900° C. to 1200° C. for 6 to 9 hours is 1.0 to 4.5, [Formula 1] C / SiC peak intensity ratio = I(C) / I(SiC) In Formula 1, I(C) is the maximum peak intensity within a 2θ range of 20° to 23° measured by X-ray diffraction (XRD) analysis, I(SiC) is the maximum peak intensity within a 2θ range of 34° to 37° measured by XRD analysis, and 2θ is a diffraction angle and the unit is °.

2. The negative electrode active material for lithium secondary batteries according to claim 1, wherein The C / SiC peak intensity ratio is 2.9 to 4.

1.

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

5. The negative electrode active material for lithium secondary batteries according to claim 1, wherein The composite particles further include a carbon coating formed on the silicon-containing coating.

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

7. The negative electrode active material for lithium secondary batteries according to claim 1, wherein The crystallite size of silicon contained in the silicon-containing coating layer after heat-treating the composite particles at 900° C. to 1200° C. for 6 to 9 hours, as measured by XRD analysis, is 10 nm or less.

8. The negative electrode active material for lithium secondary batteries according to claim 7, wherein The grain size of silicon contained in the silicon-containing coating layer is measured by the following formula 2, [Formula 2] In Formula 2, L is the grain size and the unit is nm, λ is the X-ray wavelength and the unit is nm, β is the half-maximum full width of the peak of the (111) plane of silicon contained in the silicon-containing coating and the unit is radian, and θ is the diffraction angle and the unit is radian.

9. The negative electrode active material for lithium secondary batteries according to claim 7, wherein The crystallite size of silicon contained in the silicon-containing coating layer after the heat treatment, as measured by XRD analysis, is 8 nm or less.

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

11. A lithium secondary battery comprising: A negative electrode comprising the negative electrode active material for a lithium secondary battery according to any one of claims 1 to 10; as well as A positive electrode is arranged opposite to the negative electrode.

12. A method for preparing a negative electrode active material for a lithium secondary battery, comprising the following steps: preparing primary carbon-based particles comprising pores; subjecting the primary carbon-based particles and hydrogen-containing gas to a first calcination to form carbon-based particles; as well as subjecting the carbon-based particles and the silicon-containing gas to a second calcination to form composite particles, the composite particles comprising a silicon-containing coating formed on surfaces of the carbon-based particles, wherein the composite particles after heat-treating the composite particles at 900° C. to 1200° C. for 6 to 9 hours have a C / SiC peak intensity ratio defined by the following formula 1 of 1.0 to 4.5, [Formula 1] C / SiC peak intensity ratio = I(C) / I(SiC) In Formula 1, I(C) is the maximum peak intensity within a 2θ range of 20° to 23° measured by X-ray diffraction (XRD) analysis, I(SiC) is the maximum peak intensity within a 2θ range of 34° to 37° measured by XRD analysis, and 2θ is a diffraction angle and the unit is °.

13. The method for preparing a negative electrode active material for a lithium secondary battery according to claim 12, wherein: The first calcination is performed at a temperature of 300°C to 700°C.

14. The method for preparing a negative electrode active material for a lithium secondary battery according to claim 12, wherein: The second calcination is performed at a temperature of 400°C to 600°C.

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