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 includes composite particles including carbon-based particles and silicon-containing particles, the silicon-containing particles being provided on a surface of the carbon-based particles and including silicon and hydrogen, the composite particles having an H / Si ratio, as defined by Formula 2, of 0.5% to 5.3%.

Description

Technical Field

[0001] This invention relates to a negative electrode active material for lithium secondary batteries, its preparation method, and a lithium secondary battery containing the same. Background Technology

[0002] Rechargeable batteries are batteries that can be repeatedly charged and discharged. With the development of the information communication and display industries, rechargeable batteries are widely used as power sources for portable electronic communication devices such as portable cameras, mobile phones, and laptops. In addition, in recent years, battery packs including rechargeable batteries have been developed for use as power sources for environmentally friendly vehicles such as electric vehicles.

[0003] Secondary batteries can be categorized into, for example, 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 for charging speed and lightweight design, so they are being actively developed and applied.

[0004] In recent years, with the expansion of applications for lithium-ion batteries, lithium-ion batteries with higher capacity and power are being developed. For example, high-capacity silicon and carbon can be combined and used as negative electrode active materials.

[0005] However, due to the large difference in volume expansion rate of silicon-carbon composite anode active materials, repeated charging / discharging may cause cracks in the anode active materials and expose them to the electrolyte. Summary of the Invention

[0006] (a) Technical problems to be solved

[0007] One technical problem of the present invention is to provide a negative electrode active material for lithium secondary batteries with improved lifespan characteristics and a method for preparing the negative electrode active material for lithium secondary batteries.

[0008] One technical problem of the present invention is to provide a lithium secondary battery with improved lifespan characteristics.

[0009] (II) Technical Solution

[0010] According to an exemplary embodiment of the present invention, the negative electrode active material for a lithium secondary battery may comprise composite particles, said composite particles comprising: carbon-based particles; and silicon-containing particles disposed on the surface of said carbon-based particles, said silicon-containing particles comprising silicon and hydrogen. The H / Si ratio of said composite particles, as defined by the following formula 2, may be from 0.5% to 5.3%.

[0011] [Equation 2]

[0012]

[0013] In Equation 2, RH R represents the hydrogen content (by weight %) in the total weight of the composite particles. Si This indicates the silicon content (by weight %) in the total weight of the composite particles.

[0014] In some implementations, the H / Si ratio can be from 1.2% to 4.9%.

[0015] In some embodiments, the silicon content in the total weight of the composite particles can be from 41% to 55% by weight.

[0016] In some embodiments, the hydrogen content in the total weight of the composite particles can be from 0.3% by weight to 2.7% by weight.

[0017] In some embodiments, the silicon-containing particles may contain SiH x (0 <x≤4)。

[0018] In some embodiments, the silicon-containing particles may comprise amorphous silicon-based materials, and the carbon-based particles may comprise amorphous structures.

[0019] In some embodiments, the carbon-based particles may contain pores.

[0020] In some embodiments, the pores of the carbon-based particles may include a shape that bends inward from the outermost part of the carbon-based particles toward the interior of the carbon-based particles.

[0021] In some embodiments, the surface of the carbon-based particles may include the outer surface and / or the inner surface of the carbon-based particles.

[0022] In some embodiments, the composite particles may further comprise a carbon coating disposed on the carbon-based particles and / or the silicon-containing particles.

[0023] A lithium secondary battery according to an exemplary embodiment may include: a negative electrode comprising the aforementioned negative electrode active material for a lithium secondary battery; and a positive electrode disposed opposite to the negative electrode.

[0024] In a method for preparing a negative electrode active material for a lithium secondary battery according to an exemplary embodiment, a carbon source may be subjected to a first heat treatment to prepare carbon-based particles. The carbon-based particles and a silicon-based source containing silicon and hydrogen may be calcined at 400°C to 550°C for 8 to 16 hours to form composite particles.

[0025] In some embodiments, the silicon-based source may comprise a compound represented by the following chemical formula 1.

[0026] [Chemical Formula 1]

[0027] SiHw X 1-w

[0028] In chemical formula 1, X can be a halogen element and can be 0. <w≤4。

[0029] In some embodiments, the silicon-based source may comprise at least one of silane (SiH4) and trichlorosilane (SiHCl3).

[0030] In some embodiments, the step of forming composite particles may further include a dehydrogenation reaction after calcination.

[0031] In some embodiments, the dehydrogenation reaction may include a second heat treatment within the reactor, wherein the hydrogen content in the total volume of the reactor is less than 0.1% by volume.

[0032] (III) Beneficial Effects

[0033] The lithium secondary battery according to an exemplary embodiment of the present invention can suppress the reduction in lifespan characteristics caused by the expansion of silicon-based materials.

[0034] The negative electrode active material according to the exemplary embodiment can suppress side reactions with the electrolyte during charging / discharging. Therefore, the lifespan and high-temperature characteristics of the lithium secondary battery containing the negative electrode active material can be improved simultaneously.

[0035] The negative electrode active material for lithium secondary batteries, the method for preparing the negative electrode active material, and the lithium secondary battery containing the negative electrode active material of the present invention can be widely used in green technology fields such as electric vehicles, battery charging stations, and other battery-based solar power generation and wind power generation. The negative electrode active material for lithium secondary batteries, the method for preparing the negative electrode active material, and the lithium secondary battery containing the negative electrode active material of the present invention can be used in eco-friendly electric vehicles, hybrid vehicles, etc., to prevent climate change by suppressing air pollution and greenhouse gas emissions. Attached Figure Description

[0036] Figure 1 This is a schematic cross-sectional view showing composite particles according to an exemplary embodiment.

[0037] Figure 2 and Figure 3 This is a schematic process flow diagram illustrating a method for preparing a negative electrode active material for lithium secondary batteries according to an exemplary embodiment.

[0038] Figure 4 and Figure 5 These are schematic plan views and schematic cross-sectional views of a lithium secondary battery according to an exemplary embodiment. Detailed Implementation

[0039] An embodiment of the present invention provides a negative electrode active material for a lithium secondary battery (hereinafter, simply referred to as "negative electrode active material") comprising composite particles, wherein the composite particles comprise silicon (Si), hydrogen (H), and carbon (C). Furthermore, a lithium secondary battery (hereinafter, simply referred to as "secondary battery") comprising the negative electrode active material is provided.

[0040] The present invention will now be described in detail with reference to the accompanying drawings. However, these are merely exemplary embodiments, and the present invention is not limited to the specific embodiments described herein.

[0041] Figure 1 This is a schematic cross-sectional view showing composite particles according to an exemplary embodiment.

[0042] For ease of explanation, Figure 1 The shape of the composite particles is schematically shown, but the structure / shape of the composite particles of the present invention is not limited thereto. Figure 1 The structure / shape shown is as follows. For example, the cross-section of the carbon-based particles can be randomly varied from a circle. Furthermore, silicon-containing particles can be partially disposed in the pores and surfaces of the carbon-based particles, and can also be configured as multiple discontinuous islands or patterns.

[0043] Reference Figure 1 The composite particles 50 may include: carbon-based particles 60 containing carbon (C); and silicon-containing particles 70 containing silicon (Si) and hydrogen (H).

[0044] The carbon-based particles 60 may contain pores 65. For example, the carbon-based particles 60 may be porous particles containing a plurality of pores 65.

[0045] In some embodiments, the carbon-based particles 60 may include activated carbon, carbon nanotubes (CNTs), carbon nano-wires, graphene, carbon fibers, carbon black, graphite, porous carbons including microporous carbon, mesoporous carbon, and macroporous carbon, cryogels, xerogels, and aerogels. For example, the carbon-based particles 60 may further include carbon-based materials derived from biomass. These may be used alone or in combination of two or more.

[0046] In some embodiments, the carbon-based particles 60 may be amorphous carbon. Examples of the amorphous carbon may include hard carbon, soft carbon, coke, mesocarbon microbeads (MCMBs), mesophase pitch-based carbon fibers (MPCFs), etc. Thus, the durability of the composite particles 50 can be increased, and the generation of cracks due to charging / discharging or external impact can be suppressed. Therefore, the life characteristics of the secondary battery can be improved.

[0047] According to an exemplary embodiment, the silicon-containing particles 70 may contain silicon (Si) and hydrogen (H).

[0048] In some embodiments, the silicon-containing particles 70 may contain SiH x (0 < x ≤ 4). For example, the content of the SiH x (0 < x ≤ 4) may be lower than the content of the carbon-based particles 60. Thus, the silicon-containing particles 70 can be densely filled inside the carbon-based particles 60 even at low temperatures, and the reduction of the life characteristics due to the increase in the content of the SiH x (0 < x ≤ 4) can be suppressed.

[0049] In some embodiments, the silicon-containing particles 70 may contain amorphous silicon-based materials. For example, the silicon-containing particles 70 may contain amorphous silicon-based compounds. For example, the silicon-containing particles 70 may be amorphous silicon. Thus, the life characteristics at high-temperature environments or during repeated charging / discharging can be improved.

[0050] As used in this specification, the terms "amorphous silicon-based material", "amorphous silicon-based compound" or "amorphous silicon" may refer to a situation where the shape of individual silicon particles located inside the particles is amorphous or the particles are too small to be measured using, for example, the Scherrer equation represented by Equation 1 below.

[0051] [Formula 1]

[0052]

[0053] In Equation 1, L represents the grain size (nm), λ represents the X-ray wavelength (nm), β represents the full width at half maximum (FWHM) of the corresponding peak (radians (rad)), and θ represents the diffraction angle (radians). According to an exemplary embodiment, the FWHM in XRD analysis used to measure grain size can be measured based on the peaks of the (111) plane of silicon contained in the silicon-containing particles.

[0054] In some embodiments, in the spectrum of the silicon-containing particles 70 obtained by Raman spectroscopy, the ratio of the intensity of amorphous silicon (a-Si) to the intensity of crystalline silicon (c-Si) can be greater than 0 and less than 1, 0.35 to 0.7, 0.45 to 0.7, or 0.45 to 0.65. Within the above ranges, the silicon-containing particles 70 can be an amorphous silicon-based compound, and lifetime characteristics under high-temperature conditions or repeated charge / discharge cycles can be further improved.

[0055] In some embodiments, silicon-containing particles 70 may be disposed on the surface of the carbon-based particles 60 containing pores 65. The pores 65 mitigate the volume expansion of the silicon contained in the silicon-containing particles 70. Therefore, the relatively high capacity characteristics of silicon can be utilized, while preventing cracking during battery charging / discharging due to the difference in the volume expansion rate of carbon (e.g., less than about 150 vol%) and silicon (e.g., more than about 400 vol%). Thus, gas generation due to side reactions between the negative electrode active material and the electrolyte can be suppressed, and the lifespan characteristics of the secondary battery can be improved.

[0056] In some embodiments, the pore 65 of the carbon-based particle 60 may include a shape that bends inward from the outermost part of the carbon-based particle 60 into the interior of the carbon-based particle 60. For example, the pore 65 may include an opening (pore) that opens outward from the carbon-based particle 60.

[0057] The terms “surface of carbon-based particles” and / or “surface of carbon-based particles 60” as used in this specification may include the outer and / or inner surfaces of the carbon-based particles.

[0058] In some implementations, "the surface of the carbon-based particles" and / or "the surface of the carbon-based particles 60" may refer to the outer surface 62 of the carbon-based particles 60, the inner surface 67 of the pores 65, or the outer surface 62 of the carbon-based particles 60 and the inner surface 67 of the pores 65.

[0059] For example, silicon-containing particles 70 can be disposed on at least a portion of the outer surface 62 of carbon-based particles 60.

[0060] For example, silicon-containing particles 70 can be disposed on at least a portion of the inner surface 67 of the pores 65 of the carbon-based particles 60.

[0061] For example, silicon-containing particles 70 may be disposed on at least a portion of the outer surface 62 of the carbon-based particles 60 and at least a portion of the inner surface 67 of the pores 65.

[0062] According to an exemplary embodiment, the H / Si ratio of the composite particles 50, as defined by the following formula 2, can be from 0.5% to 5.3%.

[0063] [Equation 2]

[0064]

[0065] In Equation 2, R H This can be the hydrogen content (weight %) in the total weight of the composite particles 50. For example, R H The hydrogen content (wt%) in the total weight of composite particles 50 can be measured by the Oxygen / Nitrogen / Hydrogen analysis (ONH analysis).

[0066] In Equation 2, R Si This can be the silicon content (weight %) in the total weight of the composite particles 50. For example, R Si The content (wt%) of silicon in the total weight of composite particles 50, as measured by inductively coupled plasma-optical emission spectrometry (ICP-OES).

[0067] When the H / Si ratio of the composite particles 50 is less than 0.5%, the silicon-containing particles 70 may be set at a high temperature. For example, when silicon-containing particles are set on carbon-based particles 60 at a high temperature, the H / Si ratio may decrease. When silicon-containing particles are set at a high temperature, the crystallinity of silicon may increase. Therefore, when the H / Si ratio is less than 0.5%, the charge / discharge life characteristics of the secondary battery may decrease.

[0068] When the H / Si ratio of the composite particles 50 exceeds 5.3%, side reactions between hydrogen and the electrolyte may occur due to the high hydrogen content. These side reactions, occurring during charging / discharging of the secondary battery or at high temperatures, may cause damage such as cracks in the composite particles 50. Therefore, when the H / Si ratio exceeds 5.3%, the charge / discharge lifespan and high-temperature characteristics of the secondary battery may decrease.

[0069] In some embodiments, the H / Si ratio of the composite particles 50, as expressed by Formula 2, can be 0.6% to 5.1%, 0.6% to 5%, 1.2% to 4.9%, or 2% to 4.9%. Within these ranges, the silicon and hydrogen content of the composite particles 50 can be appropriately maintained. Therefore, lifetime characteristics and high-temperature characteristics can be further improved.

[0070] In some embodiments, the silicon content in the total weight of the composite particles 50 can be 41% to 55% by weight, 48% to 53% by weight, 49% to 53% by weight, 50% to 53% by weight, or 51% to 53% by weight. Within the above content range, the high energy density of silicon can improve the electrical characteristics of the secondary battery, such as charge / discharge capacity, while the carbon-based particles 60 can appropriately suppress volume expansion, thus improving lifetime and high-temperature characteristics.

[0071] In some embodiments, the hydrogen content in the total weight of the composite particles 50 can be from 0.3 wt% to 2.7 wt%, 0.3 wt% to 2.6 wt%, 0.5 wt% to 2.6 wt%, 0.8 wt% to 2.6 wt%, or 1.1 wt% to 2.6 wt%. Within the above content range, the silicon-containing particles 70 can be stably disposed on the surface of the carbon-based particles 60 and can densely fill the pores of the carbon-based particles 60. Furthermore, the silicon-containing particles 70 can be disposed on the surface of the carbon-based particles 60 at a relatively low temperature, thus reducing the crystallinity of silicon. Therefore, the lifespan and high-temperature characteristics of the secondary battery can be improved.

[0072] In some embodiments, the content of carbon-based particles 60 in the total weight of composite particles 50 can be from 42.3% to 58.7% by weight, 44.4% to 51.7% by weight, 44.4% to 50.5% by weight, 44.4% to 49.2% by weight, or 44.4% to 47.9% by weight. Within the above content range, silicon-containing particles 70 can be sufficiently disposed on the surface of carbon-based particles 60, and the volume expansion of silicon-containing particles 70 can be suppressed. Therefore, the structural stability of composite particles 50 can be improved, and the life characteristics and high-temperature characteristics of secondary batteries can be improved.

[0073] In some embodiments, the composite particles 50 may further comprise a carbon coating disposed on the carbon-based particles 60 and / or the silicon-containing particles 70.

[0074] In some embodiments, the composite particles 50 may further include a carbon coating (not shown) disposed on the silicon-containing particles 70. This prevents contact between the silicon of the negative electrode active material and water or electrolyte. Therefore, the reduction in discharge capacity and capacity efficiency of the secondary battery can be suppressed after the preparation of the negative electrode active material and before the formation of the negative electrode.

[0075] In some embodiments, the carbon coating may also be applied to the portion of the carbon-based particle 60 where the silicon-containing particle 70 is not located. For example, the carbon coating may completely cover both the carbon-based particle 60 and the silicon-containing particle 70. Therefore, the mechanical and chemical stability of the negative electrode active material can be improved.

[0076] In one embodiment, the carbon coating may comprise at least one of carbon and a conductive polymer. For example, the conductive polymer may include polyacetylene, polyaniline, polypyrrole, polythiophene, etc.

[0077] The following provides an exemplary embodiment of a method for preparing the above-mentioned negative electrode active material for lithium secondary batteries. Figure 2 and Figure 3 This is a schematic process flow diagram illustrating a method for preparing a negative electrode active material for lithium secondary batteries according to an exemplary embodiment. Specifically, Figure 3 It is used for step-by-step explanation Figure 2 A schematic process flow diagram of the S20 process.

[0078] Reference Figure 2 The carbon source can be subjected to a first heat treatment to prepare carbon-based particles (e.g., S10 process). For example, the carbon source can be subjected to a first heat treatment to prepare porous carbon-based particles.

[0079] In some embodiments, subjecting the carbon source to a first heat treatment may involve carbonizing or activating the carbon source to remove moisture and impurities. Therefore, when the silicon-based source is placed within the carbon structure, side reactions can be suppressed, and moisture and impurities can be removed, thereby allowing for stable movement and placement of the silicon-based source.

[0080] The carbon source may include, for example, biomass such as glucose, sucrose, cellulose, petroleum-based pitch, coal-based pitch, palm, and rice bran, as well as resol oligomers. These can be used alone or in combination of two or more.

[0081] In one embodiment, an additive may be added during the first heat treatment. For example, the additive may be provided as a chemical etchant or a hard template. For instance, the reaction between the carbon source and the additive can be carried out by chemical activation or physical etching. Thus, impurities and moisture in the carbon source can be removed. Furthermore, porous carbon-based particles can be prepared.

[0082] In one embodiment, the first heat treatment can be performed at 500°C to 1100°C, 600°C to 1000°C, or 650°C to 900°C. Within these temperature ranges, moisture and impurities can be sufficiently removed, and the carbon source can be carbonized or activated.

[0083] In an exemplary embodiment, the carbon-based particles and a hydrogen-containing silicon-based source can be calcined together to form composite particles (e.g., S20-1 process).

[0084] In some embodiments, the silicon-based source may comprise a compound represented by the following chemical formula 1. Therefore, the silicon-based source can be disposed at relatively low temperatures on the surface (e.g., the outer and / or inner surfaces) and internal pores of the carbon structure, thereby suppressing side reactions caused by high-temperature reactions. Thus, the lifetime and high-temperature characteristics of the secondary battery can be improved.

[0085] [Chemical Formula 1]

[0086] SiH w X 1-w

[0087] In chemical formula 1, X can be a halogen element and can be 0. <w≤4。

[0088] In one embodiment, the silicon-based source may comprise at least one of silane (SiH4) and trichlorosilane (SiHCl3). Therefore, the silicon-based source can be more stably disposed on the surface (e.g., outer and / or inner surface) and internal pores of the carbon structure.

[0089] In some embodiments, the calcination can be carried out in an inert gas atmosphere. In one embodiment, the calcination can be performed simultaneously by injecting a silicon-based source and an inert gas together into the carbon structure. For example, after adding the carbon structure inside the calcination reactor, the silicon-based source and the inert gas can be injected into the calcination reactor simultaneously for calcination. For example, the inert gas can be used as a carrier gas.

[0090] For example, the inert gas may include argon (Ar), nitrogen (N2), etc. For example, the inert gas may be 1% to 15% of the total volume of the silicon-based source and the inert gas, 1% to 10% of the total volume, or 2% to 10% of the total volume. Within the above range, the silicon-based source can be delivered together with the inert gas to the outer surface of the carbon structure and the inner surface of the pores of the carbon structure.

[0091] According to an exemplary embodiment, the calcination can be carried out at a temperature of 400°C to 550°C.

[0092] When the calcination is carried out at a temperature below 400°C, the silicon-based source cannot be adequately disposed on the carbon-based particles, thus the specific surface area of ​​the silicon-containing particles may increase excessively. Consequently, due to the expansion of the silicon-containing particles, cracks may form in the negative electrode active material, and the lifespan and high-temperature characteristics of the secondary battery may decrease.

[0093] When the calcination is carried out at a temperature exceeding 550°C, the crystallinity of the silicon-containing particles may increase. Due to the increased crystallinity of the silicon-containing particles, the volume expansion rate of the secondary battery according to charge / discharge may increase. Therefore, the life characteristics of the secondary battery may decrease.

[0094] In some embodiments, the calcination can be carried out at temperatures of 450°C to 550°C, 450°C to 530°C, or 450°C to 500°C. Within these temperature ranges, the lifespan and high-temperature characteristics of the secondary battery can be further improved.

[0095] In one embodiment, the calcination can be performed at a heating rate of 1°C / min to 10°C / min, 3°C / min to 7°C / min, or 4°C / min to 6°C / min, and at the aforementioned calcination temperatures. Within these temperature ranges, abrupt temperature changes can be prevented, thereby suppressing excessive crystallinity of the silicon contained in the silicon-based source. Therefore, the lifespan and high-temperature characteristics of the secondary battery can be improved.

[0096] According to an exemplary implementation, the calcination can be carried out for 8 to 16 hours.

[0097] When the calcination time is less than 8 hours, the silicon-based source cannot be adequately deposited on the carbon structure, thus the specific surface area of ​​the silicon-containing particles may increase excessively. Consequently, side reactions between the composite particles and the electrolyte may occur, and the lifespan and high-temperature characteristics of the secondary battery may be reduced.

[0098] When the calcination time exceeds 16 hours, excessive silicon-based sources may be deposited on the carbon structure. Therefore, the silicon-induced volume expansion rate during charging / discharging of the secondary battery may increase, and the battery's lifetime characteristics may decrease.

[0099] In some embodiments, the calcination can be carried out for 8 to 14 hours, 9 to 14 hours, or 10 to 14 hours. Within these ranges, the lifespan and high-temperature characteristics of the secondary battery can be further improved.

[0100] Reference Figure 3 Composite particles can be formed by calcining a carbon structure and a silicon-based source (e.g., the S20-1 process) followed by a dehydrogenation reaction (e.g., the S20-2 process).

[0101] In some embodiments, the dehydrogenation reaction may include a second heat treatment in a reactor of carbon-based particles provided with a silicon-based source through calcination.

[0102] In some embodiments, the dehydrogenation reaction can be carried out at the above-mentioned calcination temperature.

[0103] In some embodiments, the dehydrogenation reaction can be carried out for 2 to 6 hours, 3 to 6 hours, or 3 to 5 hours. Within these time ranges, the crystallinity of the silicon-containing particles does not increase excessively, while the hydrogen content can be adjusted. Therefore, the volume expansion rate of the composite particles can be reduced, and the lifespan and high-temperature characteristics of the secondary battery can be improved.

[0104] In some embodiments, the dehydrogenation reaction (e.g., a second heat treatment) can be carried out under conditions where the hydrogen content in the total volume inside the reactor is less than 0.1 vol%, more than 0 vol% but less than 0.1 vol%, or between 0.01 vol% and 0.1 vol%. For example, after the above-described calcination process, it can be carried out under inert gas conditions. Therefore, hydrogen contained in the carbon structure along with silicon can be sufficiently removed.

[0105] The above method can be used to prepare a negative electrode active material for lithium secondary batteries containing composite particles with an adjusted H / Si ratio.

[0106] Figure 4 and Figure 5 These are schematic plan views and schematic cross-sectional views illustrating a lithium secondary battery according to an exemplary embodiment. For example, Figure 5 It is along Figure 4 A cross-sectional view taken along the thickness direction of the I-I' line.

[0107] A lithium secondary battery may include a negative electrode 130 containing the aforementioned negative electrode active material and a positive electrode 100 disposed opposite to the negative electrode 130.

[0108] The positive electrode 100 may include a positive electrode current collector 105 and a positive electrode active material layer 110, wherein the positive electrode active material layer 110 is formed on at least one side of the positive electrode current collector 105.

[0109] The positive electrode current collector 105 may comprise stainless steel, nickel, aluminum, titanium, or alloys thereof. The positive electrode current collector 105 may also comprise 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 from 10 μm to 50 μm.

[0110] The positive electrode active material layer 110 may contain a positive electrode active material. The positive electrode active material may contain compounds that enable reversible insertion and extraction of lithium ions.

[0111] According to an exemplary embodiment, the positive electrode active material may comprise a lithium-nickel metal oxide. The lithium-nickel metal oxide may further comprise at least one of cobalt (Co), manganese (Mn), and aluminum (Al).

[0112] In some embodiments, the positive electrode active material or the lithium-nickel metal oxide may comprise a layered structure or a crystal structure represented by the following chemical formula 2.

[0113] [Chemical Formula 2]

[0114] Li x Ni a M b O 2+z

[0115] In chemical formula 2, the values ​​can be 0.9≤x≤1.2, 0.6≤a≤0.99, 0.01≤b≤0.4, or -0.5≤z≤0.1. As mentioned above, M can contain Co, Mn, and / or Al.

[0116] The chemical structure represented by Formula 2 indicates the bonding relationships contained in the layered or crystalline structure of the positive electrode active material, and does not exclude other additional elements. For example, M may contain Co and / or Mn, and Co and / or Mn may be provided together with Ni as the main active element of the positive electrode active material. Formula 2 is provided to represent the bonding relationships of the main active elements, and it should be understood that Formula 2 includes the introduction and substitution of additional elements.

[0117] In one embodiment, in addition to the primary active element, auxiliary elements may be further included to enhance the chemical stability of the positive electrode active material or the layered / crystal structure. These auxiliary elements may be incorporated into the layered / crystal structure to form a bond, and this should be understood to also include the chemical structures represented by Formula 2.

[0118] The auxiliary element may include at least one of, for example, 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, or Zr. The auxiliary element may function as an auxiliary active element, together with Co or Mn, to contribute to the capacity / power activity of the positive electrode active material; for example, Al.

[0119] For example, the positive electrode active material or the lithium-nickel metal oxide may contain a layered structure or a crystal structure represented by the following chemical formula 2-1.

[0120] [Chemical Formula 2-1]

[0121] Li x Ni a M1 b1 M2 b2 O 2+z

[0122] In chemical formula 2-1, M1 may contain Co, Mn, and / or Al. M2 may contain the aforementioned auxiliary elements. In chemical formula 2-1, the values ​​can be 0.9≤x≤1.2, 0.6≤a≤0.99, 0.01≤b1+b2≤0.4, and -0.5≤z≤0.1.

[0123] The positive electrode active material may further include coating elements or doping elements. For example, elements that are substantially the same as or similar to the auxiliary elements described above can be used as coating elements or doping elements. For example, one or more combinations of the elements described above can be used as coating elements or doping elements.

[0124] The coating element or dopant element may exist on the surface of the lithium-nickel metal oxide particles or penetrate through the surface of the lithium-nickel metal oxide particles and be contained in the bonding structure represented by chemical formula 2 or chemical formula 2-1.

[0125] The positive electrode active material may contain nickel-cobalt-manganese (NCM)-based lithium oxide. In this case, NCM-based lithium oxide with increased nickel content can be used.

[0126] 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-Ni) composition for the positive electrode active material, a high-capacity positive electrode and a high-capacity lithium secondary battery can be provided.

[0127] However, as the Ni content increases, the long-term storage stability and life stability of the positive electrode or secondary battery may be relatively reduced, and side reactions with the electrolyte may also increase. However, according to an exemplary embodiment, conductivity can be maintained by including Co, and life stability and capacity retention characteristics can be improved by Mn.

[0128] The content of Ni in the NCM-based lithium oxide (for example, the mole fraction of Ni in the total moles of nickel, cobalt, and manganese) can be 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.

[0129] 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 (for example, LiFePO4).

[0130] 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.

[0131] [Chemical Formula 3]

[0132] p[Li2MnO3]·(1-p)[Li q JO2]

[0133] In Chemical Formula 3, 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.

[0134] The positive electrode active material can be mixed in a solvent to prepare a positive electrode slurry. The positive electrode slurry can be coated onto at least one side of the positive electrode current collector 105, then dried and calendered to prepare a positive electrode active material layer 110. The coating process can include gravure coating, slot die coating, multilayer simultaneous die coating, embossing, doctor blade coating, dip coating, bar coating, casting, and other methods. The positive electrode active material layer 110 may further contain a binder and optionally further contain conductive materials, thickeners, etc.

[0135] The solvent can be N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc.

[0136] The adhesive may include polyvinylidene fluoride (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) copolymer, polyacrylonitrile, polymethyl methacrylate, nitrile rubber (NBR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), etc. These can be used alone or in combination of two or more.

[0137] In one embodiment, a PVDF-based binder can be used as the 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.

[0138] The conductive material can be added to enhance the conductivity and / or the mobility of lithium ions or electrons in 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 fibers, and / or metal-based conductive materials including perovskite materials such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3. These can be used alone or in combination of two or more.

[0139] The cathode slurry may further contain thickeners and / or dispersants. In one embodiment, the cathode slurry may contain thickeners such as carboxymethyl cellulose (CMC).

[0140] The negative electrode 130 may include a negative electrode current collector 125 and a negative electrode active material layer 120, wherein the negative electrode active material layer 120 is formed on at least one side of the negative electrode current collector 125.

[0141] For example, the negative electrode current collector 125 may include copper foil, nickel foil, stainless steel foil, titanium foil, foam nickel, foam copper, polymer substrate coated with conductive metal, etc. These can be used alone or in combination of two or more. For example, the thickness of the negative electrode current collector 125 can be from 10 μm to 50 μm.

[0142] The negative electrode active material layer 120 may contain a negative electrode active material, which may include the aforementioned composite particles 50. For example, the negative electrode active material may contain a plurality of composite particles 50. In one embodiment, the negative electrode active material may be substantially composed of composite particles 50.

[0143] The negative electrode active material can be mixed in a solvent to prepare a negative electrode slurry. The negative electrode slurry can be coated / deposited onto the negative electrode current collector 125, followed by drying and calendering to prepare a negative electrode active material layer 120. The coating process can include gravure coating, slot die coating, multilayer simultaneous die coating, embossing, blade coating, dip coating, rod coating, casting, etc. The negative electrode active material layer 120 may further contain a binder and optionally further contain conductive materials, thickeners, etc.

[0144] The solvents contained in the negative electrode slurry may include water, pure water, deionized water, distilled water, ethanol, isopropanol, methanol, acetone, n-propanol, tert-butanol, etc. These can be used alone or in combination of two or more.

[0145] As the adhesive, conductive material and thickener, the aforementioned substances that can be used in the manufacture of the positive electrode 100 can be used.

[0146] In some implementations, the negative electrode binder can be a styrene-butadiene rubber (SBR) based binder, a carboxymethyl cellulose (CMC) based binder, a polyacrylic acid based binder, or a poly(3,4-ethylenedioxythiophene) (PEDOT) based binder. These can be used alone or in combination of two or more.

[0147] In an exemplary embodiment, a separator 140 may be disposed between the positive electrode 100 and the negative electrode 130. The separator 140 may be configured to prevent short circuits between the positive electrode 100 and the negative electrode 130 and to allow ion flow. For example, the thickness of the separator may be from 10 μm to 20 μm.

[0148] For example, diaphragm 140 may comprise a porous polymer membrane or a porous nonwoven fabric.

[0149] The porous polymer membrane may include polyolefin-based polymers such as ethylene polymers, propylene polymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers. These may be used alone or in combination of two or more.

[0150] The porous nonwoven fabric may include high-melting-point glass fibers, polyethylene terephthalate fibers, etc.

[0151] The diaphragm 140 may also include a ceramic-based material. For example, inorganic particles may be coated on or dispersed in the polymer membrane to improve heat resistance.

[0152] The diaphragm 140 may have a single-layer or multi-layer structure comprising the aforementioned polymer membrane and / or nonwoven fabric.

[0153] According to an exemplary embodiment, the battery cell can be defined by a positive electrode 100, a negative electrode 130, and a separator 140, and an electrode assembly 150 can be formed, for example, in the form of a jelly roll, by stacking multiple battery cells. For example, the electrode assembly 150 can be formed by winding, stacking, z-folding, stack-folding, etc. of the separator 140.

[0154] The electrode assembly 150 can be housed together with the electrolyte in the housing 160, thereby defining a lithium secondary battery. According to an exemplary embodiment, the electrolyte can be a non-aqueous electrolyte.

[0155] Non-aqueous electrolytes may contain a lithium salt as the electrolyte and an organic solvent, wherein the lithium salt may be, for example, Li... + X - This indicates that the anion (X) of the lithium salt is... - ), can be exemplified by 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.

[0156] The organic solvent may be, for example, propylene carbonate (PC), ethylene carbonate (EC), butene carbonate, diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, vinylene carbonate, methyl acetate (MA), ethyl acetate (EA), n-propylacetate (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), and diethylene glycol dimethyl ether. These include ether (DEGDME), dimethoxyethane, tetrahydrofuran (THF), 2-methyltetrahydrofuran, ethyl alcohol, isopropyl alcohol, dimethyl sulfoxide, acetonitrile, diethoxyethane, sulfolane, γ-butyrolactone, and propylene sulfite, among others. These can be used alone or in combination of two or more.

[0157] The non-aqueous electrolyte may further contain additives. These additives may include, for example, cyclic carbonate compounds, fluorinated carbonate compounds, sulfonyl lactone compounds, cyclic sulfate compounds, cyclic sulfite compounds, phosphate compounds, and borate compounds. These may be used alone or in combination of two or more.

[0158] The cyclic carbonate-based compound may include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), etc.

[0159] The fluorinated carbonate compounds may include fluoroethylene carbonate (FEC), etc.

[0160] The sulfonyl compounds may include 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, etc.

[0161] The cyclic sulfate-based compounds may include 1,2-ethylene sulfate, 1,2-propylene sulfate, etc.

[0162] The cyclic sulfite-based compounds may include ethylene sulfite, butylene sulfite, etc.

[0163] The phosphate-based compounds may include lithium difluorobis-oxalato phosphate, lithium difluorophosphate, etc.

[0164] The borate-based compounds may include lithium bis(oxalate) borate, etc.

[0165] like Figure 5 As shown, the tabs (positive tab and negative tab) can protrude from the positive current collector 105 and negative current collector 125 belonging to each cell and extend to one side of the housing 160. The tabs can be fused to said side of the housing 160 to form electrode leads (positive lead 107 and negative lead 127) extending to or exposed outside the housing 160.

[0166] The lithium secondary battery can be manufactured in shapes such as cylindrical, prismatic, pouch, or coin, for example, using a can.

[0167] The embodiments of the present invention will be further described below with reference to specific experimental examples. The embodiments and comparative examples included in the experimental examples are only for illustrating the present invention and are not intended to limit the claims. Various changes and modifications can be made to the embodiments within the scope and technical concept of the present invention, which will be obvious to those skilled in the art, and such variations and modifications are naturally within the scope of the claims.

[0168] Examples and Comparative Examples

[0169] Example 1

[0170] Preparation of composite particles

[0171] Activated carbon, used as a carbon source, was subjected to a first heat treatment at 800°C to prepare carbon-based particles. 1.5 kg of the prepared carbon-based particles were then added to a CVD reactor.

[0172] A mixture of silane gas (as the silicon-based source) and argon gas (as the inert gas) is injected into the CVD reactor at a flow rate of 5 mL / min to 25 mL / min. The argon content is 93% by volume relative to the total volume of the mixture. The injection temperature and injection pressure of the mixture are 0 °C and 1 atm, respectively.

[0173] Then, the temperature was increased to 450°C at a rate of 5°C / min and held for 8 hours to prepare composite particles containing silicon particles.

[0174] Manufacturing of negative electrode

[0175] A negative electrode slurry is obtained by mixing 95.5% by weight of composite particles prepared as the negative electrode active material, 1% by weight of carbon nanotubes (CNTs) as the conductive material, 2% by weight of styrene-butadiene rubber (SBR) as the binder, and 1.5% by weight of carboxymethyl cellulose (CMC) as the thickener.

[0176] The negative electrode slurry is coated onto a copper substrate and then dried and rolled to manufacture the negative electrode.

[0177] Manufacturing of the positive electrode

[0178] LiNi as the active material 0.6 Co 0.2 Mn 0.2 O2, acetylene black (Denka Black) as a conductive material, and polyvinylidene fluoride (PVDF) as a binder are mixed in a weight ratio of 92:5:3 to prepare a positive electrode slurry.

[0179] The positive electrode slurry is uniformly coated onto aluminum foil and then dried and rolled to manufacture the positive electrode.

[0180] Manufacturing of lithium secondary batteries

[0181] The positive and negative electrodes manufactured as described above are cut to specified dimensions and stacked. A separator (polyethylene, 15 μm thick) is placed between the positive and negative electrodes to form a cell. The tab portions of the positive and negative electrodes are then welded together. The welded positive / separator / negative electrode assembly is placed in a soft case, and the three sides except for the electrolyte injection side are sealed. At this point, the portion with the tabs is included in the sealed area. Electrolyte is injected through the remaining sides except for the sealed area, and the remaining sides are sealed again. The mixture is then immersed for at least 12 hours to manufacture a lithium secondary battery.

[0182] The electrolyte used is a 1M LiPF6 solution prepared using a mixed solvent of EC / EMC / DEC (25 / 45 / 30: volume ratio), with the addition of 3% by weight of fluoroethylene carbonate (FEC), 1% by weight of 1,3-propenyl sulpholol (PRS), and 0.5% by weight of lithium bis(oxalato)borate (LiBOB) to the total weight of the electrolyte.

[0183] Then, pre-charge for 36 minutes at a current (2.5A) corresponding to 0.25C. After 1 hour, degassing and aging for at least 24 hours are performed, followed by formation charge-discharge (charging conditions: CC-CV 0.2C 4.2V 0.05C cut-off; discharging conditions: CC 0.2C 2.5V cut-off). Afterward, standard charge-discharge is performed (charging conditions: CC-CV 0.5C 4.2V 0.05C cut-off; discharging conditions: CC 0.5C 2.5V cut-off).

[0184] Examples 2 to 14 and Comparative Examples 1 to 10

[0185] The lithium secondary battery was manufactured using the same method as in Example 1, except that the calcination temperature, calcination time, whether or not a dehydrogenation reaction was performed, and the time for the dehydrogenation reaction were changed, as shown in Table 1 below.

[0186] Dehydrogenation reaction

[0187] In the preparation of composite particles, after the calcination process, argon and nitrogen mixed in a 1:1 ratio are injected into the CVD reactor at a flow rate of 5 mL / min to 25 mL / min at the same temperature as the calcination temperature to carry out the dehydrogenation reaction.

[0188] [Table 1]

[0189]

[0190] Evaluation example

[0191] (1) Measurement of silicon and hydrogen content in composite particles

[0192] The silicon content and hydrogen content in the total weight of the composite particles prepared according to the above embodiments and comparative examples were measured.

[0193] The silicon content was measured using a 5800 ICP-OES (Agilent Technologies), and the hydrogen content was measured using an ONH 836 (LECO Technologies).

[0194] The measured silicon and hydrogen contents are shown in Table 2 below.

[0195] (2) Calculation of H / Si ratio

[0196] Substitute the measured silicon and hydrogen contents into Equation 2 below to calculate the H / Si ratio.

[0197] [Equation 2]

[0198]

[0199] In Equation 2, R H R represents the hydrogen content (by weight %) in the total weight of the composite particles. Si The silicon content (by weight %) in the total weight of the composite particles.

[0200] The calculated H / Si ratio is shown in Table 2 below.

[0201] [Table 2]

[0202]

[0203] Referring to Table 2, in the examples where calcination was carried out at 400°C to 550°C for 8 to 16 hours, the H / Si ratio was 0.5% to 5.3%.

[0204] In Comparative Example 1, where the calcination temperature was reduced to 300°C, no silicon was deposited.

[0205] In Comparative Examples 2 to 7, which were calcined at temperatures below 400°C, the H / Si ratio was 6.8% or higher.

[0206] In Comparative Examples 8 to 10, where calcination was carried out for a long time or at a temperature exceeding 550°C, the H / Si ratio was 0.4% or less.

[0207] Experimental Example

[0208] (1) Evaluation of lifespan characteristics at room temperature (25℃)

[0209] The lithium secondary batteries manufactured according to the above embodiments and comparative examples were repeatedly charged (CC-CV 0.5C 4.2V 0.05C cutoff) and discharged (CC 0.5C 2.75V cutoff) 50 times, and then the room temperature life characteristic (%) was measured by calculating the percentage (%) of the discharge capacity of the 50th discharge relative to the discharge capacity of the 1st discharge.

[0210] Room temperature lifetime characteristic (%) = (50th discharge capacity / 1st discharge capacity) × 100

[0211] <Evaluation Criteria>

[0212] Very poor: Room temperature lifespan characteristics <70%

[0213] Poor: 70% ≤ room temperature lifespan characteristic < 80%

[0214] Standard: 80% ≤ room temperature lifespan characteristic < 93%

[0215] Excellent: 93% or less of normal temperature lifespan characteristics

[0216] The evaluation results of the ambient temperature life characteristics are shown in Table 3 below.

[0217] (2) Evaluation of storage capacity retention rate at high temperature (60℃)

[0218] The lithium secondary batteries manufactured according to the above embodiments and comparative examples were charged (CC-CV 0.5C, 4.2V 0.1C cutoff) to a state of charge (SOC) of 100% and stored in a chamber at 60°C. After 8 weeks of storage, the discharge capacity was measured in a chamber at 25°C, and the high-temperature storage capacity retention rate (%) of this discharge capacity relative to the initial discharge capacity was measured.

[0219] <Evaluation Criteria>

[0220] Very poor: High-temperature storage capacity retention <50%

[0221] Poor: 50% ≤ High-temperature storage capacity retention rate < 80%

[0222] Standard: 80% ≤ High-temperature storage capacity retention rate < 88%

[0223] Excellent: 88% or less of high-temperature storage capacity retention

[0224] The measured high-temperature storage capacity retention rate is shown in Table 3 below.

[0225] [Table 3]

[0226]

[0227] Referring to Table 3, in the examples with an H / Si ratio of 0.5% to 5.3%, the room temperature lifetime characteristic is above 80%, and the high temperature storage capacity retention rate is above 80%.

[0228] In Example 3, which involves a dehydrogenation reaction, the room temperature lifetime characteristics and high temperature storage capacity retention are improved compared to Example 2, where all other conditions are kept the same.

[0229] In Comparative Example 1, where the calcination temperature was reduced to 300°C, no silicon was used, resulting in a room temperature lifetime characteristic of less than 70% and a high temperature storage characteristic of less than 50%.

[0230] In Comparative Examples 2 and 3, where the H / Si ratio was 6.8% to 7.1%, the room temperature lifetime characteristic was less than 80%, and the high temperature storage capacity retention was less than 50%.

[0231] In Comparative Examples 4 to 7, where the H / Si ratio was 7.2% or higher, the high-temperature storage capacity retention was less than 80%.

[0232] In Comparative Examples 8 to 10, where the H / Si ratio was less than 0.5%, the room temperature lifetime characteristic was less than 80%.

[0233] In Comparative Example 10, where the dehydrogenation reaction time was increased to 8 hours, the lifetime characteristics decreased.

Claims

1. A negative electrode active material for lithium secondary batteries, wherein the negative electrode active material for lithium secondary batteries comprises composite particles, the composite particles comprising: Carbon-based particles; and Silicon-containing particles are disposed on the surface of the carbon-based particles, and the silicon-containing particles contain silicon and hydrogen. in, The H / Si ratio of the composite particles, as defined by Formula 2, is between 0.5% and 5.3%. [Equation 2] In Equation 2, R H R represents the hydrogen content relative to the total weight of the composite particles, expressed as a percentage by weight. Si The content of silicon relative to the total weight of the composite particles is expressed in weight.

2. The negative electrode active material for lithium secondary batteries according to claim 1, wherein, The H / Si ratio is between 1.2% and 4.9%.

3. The negative electrode active material for lithium secondary batteries according to claim 1, wherein, The silicon content in the total weight of the composite particles is 41% to 55% by weight.

4. The negative electrode active material for lithium secondary batteries according to claim 1, wherein, The hydrogen content in the total weight of the composite particles is from 0.3% to 2.7% by weight.

5. The negative electrode active material for lithium secondary batteries according to claim 1, wherein, The silicon-containing particles contain SiH x 0 <x≤4。 6. The negative electrode active material for lithium secondary batteries according to claim 1, wherein, The silicon-containing particles comprise an amorphous silicon-based compound, and the carbon-based particles comprise an amorphous structure.

7. The negative electrode active material for lithium secondary batteries according to claim 1, wherein, The carbon-based particles contain pores.

8. The negative electrode active material for lithium secondary batteries according to claim 7, wherein, The pores of the carbon-based particles include a shape that bends inward from the outermost part of the carbon-based particles toward the interior of the carbon-based particles.

9. The negative electrode active material for lithium secondary batteries according to claim 1, wherein, The surface of the carbon-based particles includes the outer surface and / or inner surface of the carbon-based particles.

10. The negative electrode active material for lithium secondary batteries according to claim 1, wherein, The composite particles further comprise a carbon coating disposed on the carbon-based particles and / or the silicon-containing particles.

11. A lithium secondary battery, comprising: Negative electrode, said negative electrode comprising the negative electrode active material for lithium secondary batteries as described in claim 1; and The positive electrode is positioned opposite the negative electrode.

12. A method for preparing a negative electrode active material for lithium secondary batteries, comprising the following steps: The carbon source is subjected to a first heat treatment to prepare carbon-based particles; as well as The carbon-based particles and a silicon-based source containing silicon and hydrogen are calcined at 400°C to 550°C for 8 to 16 hours to form composite particles.

13. The method for preparing the negative electrode active material for lithium secondary batteries according to claim 12, wherein, The silicon-based source comprises a compound represented by the following chemical formula 1. [Chemical Formula 1] SiH w X 1-w In chemical formula 1, X is a halogen element, 0 <w≤4。 14. The method for preparing the negative electrode active material for lithium secondary batteries according to claim 13, wherein, The silicon-based source comprises at least one of silane (SiH4) and trichlorosilane (SiHCl3).

15. The method for preparing the negative electrode active material for lithium secondary batteries according to claim 12, wherein, The method further includes a step of performing a dehydrogenation reaction after calcination.

16. The method for preparing the negative electrode active material for lithium secondary batteries according to claim 15, wherein, The dehydrogenation reaction includes a second heat treatment in the reactor, wherein the hydrogen content in the total volume of the reactor is less than 0.1% by volume.

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