Negative electrode active material for lithium secondary battery, method for preparing same, and lithium secondary battery including same

Abstract

The present disclosure provides a negative electrode active material for a lithium secondary battery, a method of preparing the same, and a lithium secondary battery including the same. The negative electrode active material for a lithium secondary battery according to the present disclosure comprises a silicon-based active material. The silicon-based active material includes silicon oxide particles and a carbon coating layer formed on at least a portion of a surface of the silicon oxide particles. An O1s peak area ratio of the silicon-based active material, which is defined by a predetermined formula, is 0.025 to 0.045. The negative electrode active material for a lithium secondary battery according to the present disclosure can ensure high output and high capacity characteristics. In addition, during repeated charging and discharging, the structural stability of the silicon oxide particles at high temperature can be improved.

Description

Technical Field

[0001] This disclosure relates to a negative electrode active material for lithium secondary batteries, a method for preparing the same, and a lithium secondary battery including the same. Background Technology

[0002] Rechargeable batteries, as rechargeable and rechargeable batteries, are widely used as power sources for portable electronic communication devices such as cameras, mobile phones, and laptops, thanks to the development of the information communication and display industries. In addition, in recent years, battery packs incorporating rechargeable batteries have been developed for use as power sources in environmentally friendly vehicles such as hybrid electric vehicles.

[0003] As secondary batteries, examples include lithium secondary batteries, nickel-cadmium batteries, and nickel-metal hydride batteries. Among them, lithium secondary batteries are being actively researched and developed due to their high operating voltage, high energy density per unit weight, fast charging speed, and lightweight design.

[0004] For example, a lithium-ion secondary battery may include a positive electrode and a negative electrode. Electrodes such as the positive and negative electrodes include electrode active materials capable of reversibly absorbing and releasing lithium ions. Current can be generated through chemical reactions within the electrodes. Graphite-based or silicon-based materials can be used as active materials for the negative electrode. Silicon-based active materials offer higher energy density, but volume expansion or mechanical and chemical defects during charge and discharge can shorten the lifespan of the secondary battery. Summary of the Invention

[0005] Technical issues

[0006] One object of this disclosure is to provide a negative electrode active material for lithium secondary batteries with improved output and lifetime characteristics.

[0007] One object of this disclosure is to provide a method for preparing a negative electrode active material for lithium secondary batteries with improved output and lifespan characteristics.

[0008] One object of this disclosure is to provide a lithium secondary battery with improved output and life characteristics.

[0009] Technical solution

[0010] The negative electrode active material for lithium secondary batteries according to embodiments of this disclosure comprises a silicon-based active material. The silicon-based active material comprises silicon oxide particles and a carbon coating formed on at least a portion of the surface of the silicon oxide particles. The O1s peak area ratio, measured by X-ray photoelectron spectroscopy (XPS) analysis of the silicon-based active material and defined by Equation 1, is from 0.025 to 0.045.

[0011] [Formula 1]

[0012] O1s peak area ratio = A H / A O

[0013] In Equation 1, A H A represents the area of ​​the Si-OH peak measured by XPS on the silicon-based active material. O The area of ​​the O1s peak measured by XPS on the silicon-based active material.

[0014] According to some embodiments, the O1s peak area ratio of the silicon-based active material can be from 0.026 to 0.04.

[0015] According to some embodiments, the C1s peak area ratio, which is measured by X-ray photoelectron spectroscopy (XPS) analysis of the silicon-based active material and defined by the following formula 2, can be from 0.2 to 1.

[0016] [Equation 2]

[0017] C1s peak area ratio = A L / A C

[0018] In Equation 2, A L To determine the area of ​​the Li2CO3 peak measured by XPS on the silicon-based active material, A C The area of ​​the C1s peak measured by XPS on the silicon-based active material.

[0019] According to some embodiments, the C1s peak area ratio of the silicon-based active material can be from 0.4 to 0.8.

[0020] According to some embodiments, the silicon oxide particles may include SiO2. x (0 < x ≤ 2).

[0021] According to some embodiments, the surface arithmetic mean roughness (Ra) of the silicon-based active material measured using an atomic force microscope (AFM) can be from 0.2 nm to 5 nm.

[0022] According to some embodiments, the surface arithmetic mean roughness (Ra) of the silicon-based active material can be from 2 nm to 4.5 nm.

[0023] According to some embodiments, the surface arithmetic mean roughness (Ra) can be the arithmetic mean of the roughness values ​​other than the maximum and minimum values ​​among the surface roughness values ​​measured in 10 to 20 regions of the silicon-based active material surface with a scanning range of 0.5 μm × 0.5 μm.

[0024] According to some embodiments, the standard deviation of the measured surface roughness values, excluding the maximum and minimum values, can be from 1.5 nm to 8 nm.

[0025] According to some embodiments, the peak intensity ratio of the Raman spectrum defined by the following formula 3 can be from 0.5 to 5.5.

[0026] [Formula 3]

[0027] The peak intensity ratio of the Raman spectrum = I(520) / I(470)

[0028] In Equation 3, I(520) represents the wavelength of 520 cm⁻¹ in the Raman spectrum. -1 The peak intensity of the silicon oxide particles in the region, I(470) is the wavelength of 470 cm⁻¹ in the Raman spectrum. -1 The peak intensity of the silicon oxide particles in the region.

[0029] According to some embodiments, the crystallite size of the silicon oxide particles, as measured by X-ray diffraction (XRD) analysis and defined by the following formula 4, can be from 3 nm to 5 nm.

[0030] [Formula 4]

[0031]

[0032] In Equation 4, L is the crystallite size of the silicon oxide particle measured by XRD analysis and expressed in nanometers (nm), λ is the X-ray wavelength expressed in nanometers (nm), β is the full width at half maximum (FWHM) of the peak of the (111) plane of the silicon oxide particle expressed in radians (rad), and θ is the diffraction angle expressed in radians (rad).

[0033] According to some embodiments, the specific surface area of ​​the silicon-based active material can be 1m². 2 / g to 4m 2 / g.

[0034] According to some embodiments, the average particle size (D50) of the silicon oxide particles can be from 4 μm to 6 μm.

[0035] According to some embodiments, the negative electrode active material for lithium secondary batteries may also include carbon-based active materials.

[0036] According to some embodiments, the carbon-based active material may comprise artificial graphite, natural graphite, or mixtures thereof.

[0037] According to some embodiments, the content of the silicon-based active material in the total weight of the negative electrode active material can be greater than 0% by weight and less than 10% by weight.

[0038] A lithium secondary battery according to an embodiment of the present disclosure includes: a negative electrode comprising the aforementioned negative electrode active material for lithium secondary batteries; and a positive electrode opposite to the negative electrode.

[0039] The method for preparing a negative electrode active material for lithium secondary batteries according to embodiments of this disclosure involves mixing multiple silicon sources and performing heat treatment to obtain silicon oxide particles. The silicon oxide particles are then reacted with a carbon gas source to form a carbon coating, thereby obtaining a silicon-based active material. The O1s peak area ratio, as defined by Equation 1, is measured by X-ray photoelectron spectroscopy (XPS) analysis of the silicon-based active material and is between 0.025 and 0.045.

[0040] [Formula 1]

[0041] O1s peak area ratio = A H / A O

[0042] In Equation 1, A H A represents the area of ​​the Si-OH peak measured by XPS on the silicon-based active material. O The area of ​​the O1s peak measured by XPS on the silicon-based active material.

[0043] According to some embodiments, the heat treatment temperature can be from 800°C to 1200°C.

[0044] According to some embodiments, the silicon source may include silicon particles and silicon dioxide (SiO2) particles.

[0045] The effects of the invention

[0046] The negative electrode active material for lithium-ion secondary batteries according to embodiments of this disclosure comprises silicon oxide particles having a predetermined crystallinity. Therefore, high output and high capacity characteristics can be ensured. Furthermore, the structural stability of the silicon oxide particles at high temperatures can be improved during repeated charge-discharge cycles.

[0047] The negative electrode active material for lithium secondary batteries according to embodiments of this disclosure includes a carbon coating formed on at least a portion of the surface of the silicon oxide particles. Therefore, it can prevent the silicon oxide particles from deteriorating and also facilitate lithium-ion conduction. Consequently, the output characteristics, capacity characteristics, and mechanical stability of the negative electrode active material can be improved, and its lifetime characteristics and capacity retention at high temperatures can be further enhanced.

[0048] The negative electrode active material and lithium secondary battery according to embodiments of this disclosure can be widely used in green technology fields such as electric vehicles, battery charging stations, and other battery-powered solar and wind power generation. Furthermore, the negative electrode active material and lithium secondary battery according to embodiments of this disclosure can be used in eco-friendly electric vehicles, hybrid vehicles, and the like to prevent climate change by suppressing air pollution and greenhouse gas emissions. Attached Figure Description

[0049] Figure 1 and Figure 2 These are schematic top views and cross-sectional views of a lithium secondary battery according to exemplary embodiments. Detailed Implementation

[0050] According to embodiments of this disclosure, a negative electrode active material for lithium secondary batteries comprising silicon-based active materials is provided.

[0051] According to embodiments of this disclosure, a negative electrode comprising the negative electrode active material and a lithium secondary battery are provided.

[0052] The embodiments of this disclosure will be described in detail below. However, these are merely examples, and this disclosure is not limited to the specific implementations illustrated herein.

[0053] The negative electrode active material for lithium secondary batteries (hereinafter referred to as "negative electrode active material") according to embodiments of this disclosure comprises a silicon-based active material. The silicon-based active material comprises silicon oxide particles.

[0054] Silicon oxide particles possess high energy density, thus improving the initial efficiency and charge / discharge capacity of negative electrode active materials. However, silicon oxide particles can react with the electrolyte to form a solid electrolyte interphase (SEI). Due to the irreversible decomposition of the electrolyte, gas can be generated and resistance increased, leading to a decrease in capacity and lifetime characteristics.

[0055] According to exemplary embodiments of the present disclosure, silicon oxide may at least partially comprise a crystal structure.

[0056] According to one embodiment, the silicon oxide may comprise a crystalline structure and an amorphous structure. For example, a crystalline structure can suppress the volume expansion of the negative electrode active material and side reactions with the electrolyte. Moreover, an amorphous structure can maintain the crystallite size of the silicon oxide particles and the ratio of crystalline to amorphous regions within a suitable range. Thus, a secondary battery with improved capacity and lifetime characteristics can be provided.

[0057] According to an exemplary embodiment, the O1s peak area ratio, measured by X-ray photoelectron spectroscopy (XPS) analysis and defined by Equation 1, is 0.025 to 0.045.

[0058] [Formula 1]

[0059] O1s peak area ratio = A H / A O

[0060] In Equation 1, A H A represents the area of ​​the Si-OH peak measured by XPS on the silicon-based active material. O The area of ​​the O1s peak measured by XPS on the silicon-based active material.

[0061] For example, the O1s spectrum of the silicon oxide particles, as analyzed by XPS, may include Si-OH peaks in the region with a binding energy of 530.8 eV and Si-O peaks in the region with a binding energy of 532.5 eV. X The peak and the Si-O-Si peak in the region with a binding energy of 533.7 eV.

[0062] For example, an increase in the O1s peak area ratio indicates an increase in -OH bonding in the silicon oxide particles and a decrease in the crystallinity of the silicon oxide particles. Conversely, a decrease in the O1s peak area ratio indicates a decrease in -OH bonding in the silicon oxide particles and an increase in the crystallinity of the silicon oxide particles.

[0063] For example, if the O1s peak area ratio is greater than 0.045, the -OH binding in the silicon oxide particles will increase excessively. This reduces the lithium-ion conductivity in the silicon oxide particles, potentially leading to a decrease in output and capacity characteristics.

[0064] For example, if the O1s peak area ratio is less than 0.025, the -OH binding in the silicon oxide particles will be excessively reduced. This can lead to a decrease in the structural stability of the silicon oxide.

[0065] According to some embodiments, the O1s peak area ratio of the silicon oxide particles can be from 0.026 to 0.04 or from 0.025 to 0.03. Within this range, the capacity characteristics of the silicon oxide particles can be sufficiently ensured while improving structural stability. Therefore, not only can high capacity and high output characteristics be ensured, but capacity retention at high temperatures can also be improved.

[0066] For example, the O1s peak area ratio of the silicon oxide particles can be measured by XPS analysis. For example, the silicon oxide particles can be prepared as a powder sample. For this sample, an Al X-ray source can be used to obtain the O1s spectrum and perform deconvolution to measure the peak area. For example, the size of the Al X-ray source can be 500 μm, and XPS analysis can be performed by repeating the measurement 20 times in CAE mode.

[0067] According to some embodiments, the peak intensity ratio of the Raman spectrum defined by the following formula 3 can be from 0.5 to 5.5.

[0068] [Formula 3]

[0069] The peak intensity ratio of the Raman spectrum = I(520) / I(470)

[0070] In Equation 3, I(520) represents a wavelength of 520 cm⁻¹ in the Raman spectrum. -1 The peak intensity of the silicon oxide particles in the region, I(470) is the wavelength of 470 cm⁻¹ in the Raman spectrum. -1 The peak intensity of the silicon oxide particles in the region.

[0071] For example, in a Raman spectrum obtained by Raman spectroscopy, I(520) can be the peak intensity corresponding to the crystalline region of the silicon oxide particles (e.g., the region having a crystalline silicon (Si) structure). I(470) can be the peak intensity corresponding to the amorphous region of the silicon oxide particles (e.g., the region having an amorphous silicon (Si) structure).

[0072] For example, a higher peak intensity ratio in the Raman spectrum indicates that the growth of crystalline silicon (hereinafter referred to as c-Si) in the silicon oxide particles is more promoted than the growth of amorphous silicon (hereinafter referred to as a-Si). Conversely, a lower peak intensity ratio in the Raman spectrum indicates that the growth of c-Si is more passivated than that of a-Si.

[0073] As the c-Si content increases, the volume change of the negative electrode active material during charging and discharging can increase, and the life characteristics of the secondary battery can decrease.

[0074] According to some embodiments, the peak intensity ratio of the Raman spectrum can be from 1.5 to 3. Within this range, the a-Si content increases, thus both suppressing the volume expansion of the negative electrode active material during charging and discharging and increasing the energy density.

[0075] For example, the Raman spectroscopy analysis can be performed by selecting a predetermined region on the surface of the silicon oxide particles and using Raman mapping of the region with a Raman spectrometer.

[0076] For example, the Raman spectroscopy analysis can be performed by arbitrarily designating 100 to 5000 regions on the surface of the silicon oxide particles. The area of ​​each region can be (30 μm to 50 μm) × (30 μm to 75 μm).

[0077] In one embodiment, the mapping interval for the Raman mapping may be set to approximately 1 μm to approximately 10 μm for the x-axis and approximately 1 μm to approximately 5 μm for the y-axis.

[0078] The laser wavelength of the Raman spectrometer can be, for example, from about 532 nm to about 785 nm, the laser output can be from about 5 mW to about 90 mW, the laser exposure time can be from about 3 seconds to about 20 seconds, and the number of scans can be from 1 to 5.

[0079] According to some embodiments, the crystallite size of the silicon oxide particles, measured by X-ray diffraction (XRD) analysis, can be 3 nm to 5 nm, or 3.5 nm to 4.5 nm. Within these ranges, initial output characteristics can be improved, and crack formation in the negative electrode active material can be suppressed. This further enhances the output and lifetime characteristics of the secondary battery.

[0080] For example, the crystallite size of the silicon oxide particles can be calculated using the Scherrer equation as defined in Equation 4.

[0081] [Formula 4]

[0082]

[0083] In Equation 4, L is the crystallite size of the silicon oxide particle measured by XRD analysis and expressed in nanometers (nm), λ is the X-ray wavelength expressed in nanometers (nm), β is the full width at half maximum (FWHM) of the peak of the (111) plane of the silicon oxide particle expressed in radians (rad), and θ is the diffraction angle expressed in radians (rad).

[0084] In some embodiments, β in Equation 4 can be the full width at half maximum (FWHM) obtained by correcting the value from the source device. In one embodiment, Si can be used as a standard substance to reflect the value from the source device. In this case, the FWHM of the source device can be expressed as a function of 2θ by fitting a FWHM curve of Si over the entire 2θ range. The correction value obtained by subtracting the FWHM value of the source device at the corresponding 2θ position from the above function can be used as β.

[0085] In some embodiments, the silicon oxide particles may comprise silicon oxide. For example, the silicon oxide may include SiO₂. x (0 < x ≤ 2).

[0086] In one embodiment, the silicon oxide (SiO) x This can include lithium compounds or magnesium compounds. For example, SiO2 containing lithium compounds or magnesium compounds. x It can be SiO2 pretreated with lithium or magnesium. x For example, SiO2 containing lithium compounds or magnesium compounds. x It can include lithium silicate or magnesium silicate, etc.

[0087] The silicon oxide particles can serve as the main particles that substantially provide negative electrode activity. For example, in terms of the energy density and charge / discharge capacity of a secondary battery, the silicon oxide particles can function as the main compounds providing negative electrode activity.

[0088] According to an exemplary embodiment, the silicon-based active material includes a carbon coating formed on at least a portion of the surface of the silicon oxide particles. The carbon coating can inhibit the silicon oxide particles from being exposed to the electrolyte, thereby maintaining the activity of the negative electrode.

[0089] For example, during repeated charging and discharging of a secondary battery, the surface of the silicon oxide particles can be subjected to mechanical and chemical damage. Furthermore, side reactions can occur when the surface of the silicon oxide particles comes into contact with the electrolyte, generating gas.

[0090] The carbon coating can suppress the swelling of the silicon oxide particles caused by repeated charge and discharge, and can suppress side reactions with the electrolyte. This improves the lifespan and capacity retention of the secondary battery.

[0091] According to some embodiments, the carbon coating may comprise amorphous carbon such as hard carbon, soft carbon, calcined coke, and mesophase pitch carbides, and / or crystalline carbon such as natural graphite and artificial graphite. These can be used alone or in combination of two or more.

[0092] According to one embodiment, the carbon coating may comprise amorphous carbon. For example, it may comprise hard carbon and / or soft carbon. For example, the amorphous carbon may have enhanced structural stability. This prevents the degradation of the silicon oxide particles caused by charging and discharging at the low state of charge (SOC), where the silicon-based active material primarily reacts.

[0093] In one embodiment, the carbon coating may be formed discontinuously on the surface of the silicon oxide particles. For example, the amorphous carbon may be formed in the form of islands in localized areas of the silicon oxide particles.

[0094] In one embodiment, the carbon coating may be formed continuously and uniformly on the surface of the silicon oxide particles. For example, the amorphous carbon may exist in the form of a film covering at least a portion of the surface of the silicon oxide particles.

[0095] In some embodiments, the thickness of the carbon coating can be from 0.001 μm to 0.5 μm, 0.001 μm to 0.3 μm, or 0.001 μm to 0.1 μm. Within these ranges, the capacity and output characteristics of the secondary battery can be ensured, while preventing physical damage to the silicon oxide particles.

[0096] According to some embodiments, the carbon coating content can be from 0.1% to 10% by weight, or from 1% to 5% by weight, of the total weight of the silicon-based active material. Within the above range, the carbon coating can be uniformly formed on the surface of the silicon oxide particles. This ensures the negative electrode activity based on the silicon oxide particles while suppressing side reactions with the electrolyte.

[0097] The carbon coating content can be measured using thermogravimetric analysis (TGA). For example, the carbon coating content can be calculated by measuring the weight change after heat treatment and injection of nitrogen (N2) gas.

[0098] According to some embodiments, the C1s peak area ratio, which is measured by X-ray photoelectron spectroscopy (XPS) analysis of the silicon-based active material and defined by the following formula 2, can be from 0.2 to 1.

[0099] [Equation 2]

[0100] C1s peak area ratio = A L / A C

[0101] In Equation 2, A L To determine the area of ​​the Li2CO3 peak measured by XPS on the silicon-based active material, A C The area of ​​the C1s peak measured by XPS on the silicon-based active material.

[0102] According to one embodiment, a lithium compound can be formed on the surface of the silicon-based active material. For example, pretreatment of the carbon coating with lithium can form a Li2CO3 compound on the surface of the silicon-based active material.

[0103] For example, the C1s spectrum obtained by XPS analysis of the silicon-based active material may include a Li2CO3 peak in the region with a binding energy of 280 eV to 294 eV. The spectrum can be obtained, for example, by deconvolution of the 280 eV to 294 eV region. The area of ​​the Li2CO3 peak relative to the area of ​​the C1s peak in the spectrum can be measured.

[0104] For example, if the C1s peak area ratio is greater than 1, the Li2CO3 binding in the carbon coating will be excessively increased. This reduces the lithium-ion conduction pathways on the surface of the silicon oxide particles, potentially leading to a decrease in output and capacity characteristics.

[0105] For example, if the C1s peak area ratio is less than 0.02, the Li2CO3 binding in the carbon coating will be excessively reduced. Consequently, the structural stability of the silicon oxide will decrease.

[0106] According to some embodiments, the C1s peak area ratio of the silicon-based active material can be 0.4 to 0.8, 0.5 to 0.75, or 0.6 to 0.7. Within these ranges, the smooth conduction of lithium ions in the silicon-based active material can be sufficiently ensured, while also improving structural stability. This not only ensures the high capacity and high output characteristics of the secondary battery but also improves capacity retention at high temperatures.

[0107] According to some embodiments, the surface arithmetic mean roughness (Ra) of the silicon-based active material measured using an atomic force microscope (AFM) can be from 0.2 nm to 5 nm.

[0108] When the surface arithmetic mean roughness (Ra) of the silicon-based active material is within the aforementioned range, the surface area of ​​the active material particles exposed to the electrolyte is reduced, thus further suppressing side reactions in the electrolyte. Consequently, the degradation of silicon oxide particles can be suppressed or prevented, thereby further improving the capacity retention rate of the secondary battery.

[0109] For example, if the electrode active material and / or the surface roughness of the electrode active material is high, the uneven structure will increase the surface area exposed to the electrolyte. Therefore, side reactions between the electrolyte and the electrode active material will increase, and repeated charge-discharge cycles can lead to structural collapse of the electrode active material and depletion of the electrolyte.

[0110] According to some embodiments, the surface arithmetic mean roughness (Ra) of the silicon-based active material can be from 2 nm to 4.5 nm. Within this range, side reactions between the silicon-based active material and the electrolyte can be further suppressed, and a carbon coating can be uniformly formed.

[0111] According to some embodiments, the surface arithmetic mean roughness (Ra) can be the arithmetic mean of the roughness values ​​other than the maximum and minimum values ​​among the surface roughness values ​​measured in 10 to 20 regions of the silicon-based active material surface with a scanning range of 0.5 μm × 0.5 μm.

[0112] The 0.5μm × 0.5μm scanning range can be interpreted as the range of a portion of the surface of an electrode or electrode active material particle for a lithium secondary battery, specified in the surface direction of the electrode active material layer when observed by an atomic force microscope (AFM).

[0113] In one embodiment, the surface roughness value of each measurement area can be obtained by measuring the roughness value of the measurement area multiple times for each measurement area with a scanning range of 0.5μm×0.5μm, and then arithmetically averaging the measured roughness values.

[0114] For example, the roughness value can be obtained from the electrode active material particles present in each measurement area, and can represent the center line average roughness in the direction perpendicular to the measurement surface.

[0115] The roughness values ​​of each measurement area can be measured from multiple directions for each measurement area. For example, the roughness values ​​can be measured from more than 15 directions for each measurement area, and these values ​​can be arithmetically averaged to calculate the surface roughness value of the measurement area. For example, the roughness values ​​of each measurement area can be measured more than 15 times, more than 30 times, or 50 to 200 times. The measurement directions for the measurement areas can be randomly selected.

[0116] According to some embodiments, the standard deviation of the measured surface roughness values, excluding the maximum and minimum values, can be between 1.5 nm and 8 nm. Within this range, the surface roughness of the silicon-based active material is uniformly formed, thereby suppressing side reactions with the electrolyte and facilitating smooth lithium-ion conduction. Thus, a secondary battery that ensures both high output and high capacity characteristics while improving mechanical stability can be provided.

[0117] For example, the standard deviation can be an indicator of the uniformity of the surface roughness of the electrode for lithium secondary batteries. For example, if the surface roughness values ​​measured in any region of the electrode surface for lithium secondary batteries have a low standard deviation or a narrow distribution, the roughness deviation in local areas can be reduced.

[0118] For example, as the standard deviation increases, certain areas of the electrode surface may exhibit relatively high roughness. Consequently, the reaction between the electrode active material and the electrolyte may concentrate in these areas, thereby reducing the structural stability of the electrode and the lifetime characteristics of the electrode active material.

[0119] According to some embodiments, the specific surface area of ​​the silicon-based active material can be 1m². 2 / g to 4m 2 / g, or 2m 2 / g to 3.5m 2 / g. For example, the specific surface area can be measured using a specific surface area measuring device using the BET (Brunauer-Emmett-Teller) method based on nitrogen adsorption.

[0120] Within the aforementioned range, the capacity retention rate of secondary batteries can be improved, and the charge-discharge capacity characteristics based on lithium-ion insertion and extraction can be further enhanced.

[0121] According to some embodiments, the average particle size (D50) of the silicon oxide particles can be from 4 μm to 6 μm.

[0122] According to one embodiment, the D10 of the silicon oxide particles can be from 1 μm to 4 μm.

[0123] According to one embodiment, the D90 of the silicon oxide particles can be 6 μm to 9 μm.

[0124] For example, D10, D50, and D90 can represent the particle size when the volume fraction in the volume-weighted particle size distribution measured from the silicon oxide particles is 10%, 50%, and 90%, respectively.

[0125] Within the aforementioned range, the uniformity of the silicon oxide particles and the packing density of the negative electrode active material can be improved, mitigating particle degradation. Consequently, the volume change of the negative electrode containing the negative electrode active material can be reduced.

[0126] In some embodiments, the negative electrode active material may further comprise a carbon-based active material. For example, the negative electrode active material may comprise a mixture of the silicon oxide particles and the carbon-based active material.

[0127] In some embodiments, the carbon-based active material may comprise amorphous carbon such as calcined coke, mesophase pitch carbides, hard carbon, and soft carbon, and / or crystalline carbon such as natural graphite and artificial graphite. These can be used alone or in combination of two or more.

[0128] In one embodiment, the carbon-based active material may comprise artificial graphite, natural graphite, or mixtures thereof. This allows for improved high-temperature storage characteristics and high-temperature lifespan characteristics without reducing the energy density and capacity of the lithium-ion secondary battery.

[0129] According to some embodiments, the content of silicon oxide particles in the total weight of the negative electrode active material can be greater than 0% by weight and less than 10% by weight. Within this range, the expansion of the negative electrode active material and internal short circuits in the electrode can be suppressed, thereby improving lifetime and capacity retention.

[0130] According to embodiments of this disclosure, a method for preparing the above-described negative electrode active material for lithium secondary batteries according to exemplary embodiments is provided.

[0131] According to an exemplary embodiment, multiple silicon sources can be mixed and subjected to heat treatment to obtain silicon oxide particles.

[0132] According to some embodiments, the temperature of the heat treatment can be from 800°C to 1200°C.

[0133] According to some embodiments, the silicon source may include silicon particles and silicon dioxide (SiO2) particles. For example, the silicon source may include at least one selected from the group consisting of silicon and silicon dioxide (SiO2). According to one embodiment, the silicon source may use a mixture of silicon and silicon dioxide. For example, the silicon source may be a mixture of silicon (Si) and silicon dioxide (SiO2) in a weight ratio of 1:1 to 1:3, for example, 1:2. For example, the silicon source may be mixed and placed in a reactor, and heat-treated under a vacuum atmosphere at temperatures of about 800°C to 1200°C, 850°C to 1000°C, 900°C to 1000°C, or 930°C to 980°C. In some embodiments, the heat treatment time may be 4 hours to 6 hours, and the heating rate may be 3°C / min to 7°C / min.

[0134] For example, the silicon source can be placed in a reactor and heat-treated by mixing at 300 rpm to 700 rpm.

[0135] In an exemplary embodiment, a mixture of heat-treated silicon sources can be deposited onto a cooling plate for cooling. The temperature of the cooling plate can be approximately 700°C to 900°C.

[0136] The cooled mixture of silicon sources can be pulverized and graded to form silicon oxide particles.

[0137] For example, the O1s peak area ratio of silicon oxide particles can be adjusted by regulating the heat treatment temperature, heat treatment time, heating rate, mixing rate and / or the temperature of the cooling plate of the reactor.

[0138] For example, multiple silicon oxide particles are formed by changing the heat treatment temperature of the reactor and the temperature of the cooling plate, and particles with an O1s peak area ratio of 0.025 to 0.045 among the formed silicon oxide particles are selected as negative electrode active materials.

[0139] In some embodiments, the prepared silicon oxide particles and carbon source gas can be mixed and calcined to form a carbon coating on at least a portion of the surface of the silicon oxide particles.

[0140] For example, the carbon source gas can be a mixture of methane and argon.

[0141] In some embodiments, the methane gas may be replaced by ethylene gas, propylene gas, or acetylene gas, or may be used together with ethylene gas, propylene gas, or acetylene gas.

[0142] In some embodiments, the carbon coating can be formed by chemical vapor deposition (CVD). For example, the carbon coating can be formed by adding a carbon source gas to silicon oxide particles and firing at a temperature of about 400°C to 1200°C. For example, during the firing process, the heating rate can be from 5°C / min to 20°C / min, and the firing time can be from 60 minutes to 360 minutes.

[0143] Figure 1 and Figure 2 These are schematic top views and cross-sectional views illustrating a secondary battery according to an exemplary embodiment, respectively. For example, Figure 2 For along Figure 1 The cross-sectional view of the I-I' line cutting is shown.

[0144] Reference Figure 1 and Figure 2 The lithium secondary battery may include a positive electrode 100 and a negative electrode 130 opposite to the positive electrode 100.

[0145] 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.

[0146] According to an exemplary embodiment, the positive electrode active material layer 110 may be formed on both sides (e.g., the top and bottom) of the positive electrode current collector 105. For example, the positive electrode active material layer 110 may be formed on the top and bottom surfaces of the positive electrode current collector 105, respectively.

[0147] The positive current collector 105 may contain stainless steel, nickel, aluminum, titanium, or alloys thereof. The positive current collector 105 may also contain aluminum or stainless steel that has undergone carbon, nickel, titanium, or silver surface treatment.

[0148] The positive electrode active material layer 110 may comprise a positive electrode active material, a binder, and / or a conductive material. For example, the positive electrode active material can be mixed with the binder and / or conductive material in a solvent and stirred to prepare a positive electrode slurry. The positive electrode slurry can be coated onto the positive electrode current collector 105, and then compressed and dried to form the positive electrode active material layer 110.

[0149] The positive electrode active material may contain compounds capable of reversibly inserting and deintercalating lithium ions.

[0150] 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).

[0151] The positive electrode active material may contain lithium transition metal oxide represented by chemical formula 1.

[0152] [Chemical Formula 1]

[0153] Li a Ni b M 1-b O2

[0154] In chemical formula 1, 0.95≤a≤1.05, b≥0.5, and M can be at least one element selected from Na, Mg, Ca, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Ba, and Sr.

[0155] In one embodiment, the lithium transition metal oxide comprises nickel (Ni) and may also comprise at least one of cobalt (Co) and manganese (Mn). For example, the lithium transition metal oxide may comprise a nickel-cobalt-manganese (NCM) based lithium oxide.

[0156] Nickel (Ni) can be provided as a metal relevant to the capacity of lithium-ion batteries. While higher nickel content generally results in higher capacity and output for lithium-ion batteries, excessive nickel content can negatively impact mechanical and electrical stability.

[0157] Cobalt (Co) can improve the conductivity or resistance of lithium secondary batteries, while manganese (Mn) can improve their mechanical and electrical stability.

[0158] The chemical structure represented by Formula 1 indicates the lattice structure or bonding relationships contained within the crystal structure of the cathode active material, and does not exclude other additional elements. For example, M can be the main active element of the cathode active material. Formula 1 is used to express the bonding relationships of the main active element and should be understood as including the introduction and substitution of additional elements.

[0159] In one embodiment, auxiliary elements may also be included, which are added to the main active element to increase the chemical stability of the positive electrode active material or the crystal structure. These auxiliary elements may be mixed into the crystal structure to form bonds, and it should be understood that this is also included within the scope of the chemical structure represented by Formula 1.

[0160] The adhesive may include vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, etc.

[0161] The conductive material may include carbon-based conductive materials such as graphite, carbon black, graphene, and carbon nanotubes, and / or metal-based conductive materials such as perovskite materials such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3.

[0162] In some embodiments, the electrode density of the positive electrode 100 can be from 3.0 g / cc to 3.9 g / cc, or from 3.2 g / cc to 3.8 g / cc.

[0163] 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. The negative electrode active material layer 120 may be coated on the top and bottom surfaces of the negative electrode current collector 125, respectively.

[0164] In some embodiments, the negative electrode active material according to the above embodiments can be mixed with a binder, conductive material and / or dispersant in a solvent and stirred to prepare a negative electrode slurry. The negative electrode slurry can be coated on at least one side of the negative electrode current collector 125, and then dried and calendered to prepare the negative electrode 130.

[0165] For example, the negative current collector 125 may contain gold, stainless steel, nickel, aluminum, titanium, copper or alloys thereof, for example, it may contain copper or copper alloys.

[0166] The adhesive and conductive material may be substances substantially the same as or similar to the substances described above. In some embodiments, the adhesive used to form the negative electrode may include, for example, an aqueous adhesive such as styrene-butadiene rubber (SBR) to be compatible with the carbon-based active material, and may be used with a thickener such as carboxymethyl cellulose (CMC).

[0167] In an exemplary embodiment, the electrode density of the negative electrode 130 can be from 1.0 g / cc to 1.9 g / cc.

[0168] In some embodiments, a diaphragm 140 may also be provided between the positive electrode 100 and the negative electrode 130.

[0169] The diaphragm 140 may include a porous polymer film made of a polyolefin polymer (e.g., ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, ethylene / methacrylate copolymer, etc.). The diaphragm may also include a nonwoven fabric formed of high-melting-point glass fiber, polyethylene terephthalate fiber, etc.

[0170] According to an exemplary embodiment, an electrode unit is defined by a positive electrode 100, a negative electrode 130, and a separator 140, and an electrode assembly 150 can be formed by repeatedly arranging multiple said electrode units. For example, the electrode assembly 150 can be a winding type, a stacking type, a z-folding type, or a stack-folding type.

[0171] The lithium secondary battery can be defined by housing the electrode assembly 150 within the casing.

[0172] In one embodiment, the electrolyte may be housed together with the electrode assembly 150 within the housing 160.

[0173] According to an exemplary embodiment, a non-aqueous electrolyte can be used as the electrolyte.

[0174] The non-aqueous electrolyte comprises a lithium salt as the electrolyte and an organic solvent, wherein the lithium salt is, for example, represented by Li. + X - As the anion of the lithium salt (X - ), 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 - wait.

[0175] As the organic solvents mentioned above, for example, propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, γ-butyrolactone, propylene sulfite, and tetrahydrofuran can be used. These can be used alone or in combination of two or more.

[0176] like Figure 1 As shown, the positive current collector 105 and negative current collector 125 belonging to each electrode unit have protruding electrode tabs (positive electrode tab and negative electrode tab), which can extend to one side of the housing 160. The electrode tabs can be fused to the side of the housing 160 to connect with electrode leads (positive electrode lead 107 and negative electrode lead 127) extending or exposed outside the housing 160.

[0177] Figure 1 The diagram shows that the positive electrode lead 107 and the negative electrode lead 127 are formed on the same side of the lithium secondary battery or the housing 160, but they can also be formed on opposite sides. For example, the positive electrode lead 107 can be formed at one end of the housing 160, and the negative electrode lead 127 can be formed at the other end of the housing 160.

[0178] For example, the lithium secondary battery can be manufactured in the shape of a cylindrical can, prismatic can, pouch, or coin.

[0179] The embodiments of this disclosure will be further illustrated below with specific experimental examples. The embodiments and comparative examples included in the experimental examples are for illustrative purposes only and do not limit the scope of the appended claims. Those skilled in the art will understand that various changes and modifications can be made to the embodiments within the scope of this disclosure and the technical concept, and these changes and modifications naturally fall within the scope of the appended claims.

[0180] Examples and Comparative Examples

[0181] 1. Preparation of negative electrode active materials (A-1 to A-13)

[0182] Si and SiO2, used as silicon sources, are mixed in a 1:2 weight ratio and then heat-treated to obtain silicon oxide (SiO2). x ) particles.

[0183] Specifically, 1000g of silicon source was added to the reactor, and heat treatment was carried out simultaneously with mixing at approximately 500rpm over approximately 4 to 6 hours. The heating rate of the heat treatment was approximately 5°C / min, and the heat treatment temperature and time of the silicon source were adjusted as shown in Table 1.

[0184] Silicon oxide particles with a carbon coating were prepared by depositing methane gas on the silicon oxide particles using chemical vapor deposition (CVD).

[0185] Then, the physical properties of the silicon-based active material containing silicon oxide particles with carbon coating were analyzed.

[0186] Then, the silicon-based active materials that meet the physical properties in Table 2 below are mixed with artificial graphite at a weight ratio of 5:95 to prepare negative electrode active materials A-1 to A-13.

[0187] 2. Measure the O1s peak area ratio

[0188] The silicon-based active materials mixed in the negative electrode active materials (A-1 to A-13) of the examples and comparative examples were attached to carbon belts for sampling, and XPS analysis was performed to measure the O1s peak area ratio in the silicon oxide particles.

[0189] Specifically, the peak areas in the regions with binding energies of 530.8 eV, 532.5 eV, and 533.7 eV were measured by deconvolution of the O1s spectrum obtained through XPS analysis of the surface of the silicon oxide particles. The ratio of the Si-OH area to the O1s peak area in the region with a binding energy of 530.8 eV was measured using Equation 1 to obtain the O1s peak area ratio.

[0190] [XPS Analysis Conditions]

[0191] i) X-ray type: Al kα (alpha), 1486.68 eV, 900 μm beam size

[0192] ii) Analyzer: CAE (constant analyzer energy) mode

[0193] iii) Number of scans: 50

[0194] iv) Pass energy: 20 eV

[0195] v) Dwell Time: 100ms

[0196] 3. Measure the C1s peak area ratio

[0197] The silicon-based active material mixed in the negative electrode active materials (A-1 to A-13) of the examples and comparative examples was attached to a carbon strip for sampling, and XPS analysis was performed to measure the C1s peak area ratio in the carbon coating.

[0198] Specifically, the peak area in the region with a binding energy of 280 eV to 294 eV is measured by deconvolution of the C1s spectrum obtained by XPS analysis of the surface of the silicon-based active material. The ratio of the Li2CO3 area to the C1s peak area in the region with a binding energy of 280 eV to 294 eV is measured using Equation 2 to obtain the C1s peak area ratio.

[0199] Adjust the XPS analysis conditions to the same conditions as those for the O1s peak area ratio measurement.

[0200] 4. Measuring surface roughness

[0201] For the silicon-based active materials mixed in the negative electrode active materials (A-1 to A-13) of the Examples and Comparative Examples, the surface roughness was measured using atomic force microscopy (AFM).

[0202] Specifically, the surface roughness of the silicon-based active material sample was measured using AFM in tapping mode over a scanning range of 0.5 μm × 0.5 μm in 10 regions. The arithmetic mean surface roughness (Ra) was obtained by arithmetically averaging the roughness values ​​excluding the maximum and minimum values. Furthermore, the standard deviation of the roughness values ​​excluding the maximum and minimum values ​​was obtained.

[0203] 5. Measuring volumetric reference particle size distribution

[0204] For the silicon-based active materials mixed in the negative electrode active materials (A-1 to A-13) of the examples and comparative examples, they were dispersed in ethanol (CH3CH2OH) as the dispersion medium. The differences in diffraction patterns at different particle sizes were measured and calculated using a laser diffraction particle size analyzer (Microtrac MT 3000). D10, D50, and D90 were measured by calculating the particle diameters at points with volume fractions of 10%, 50%, and 90% in the measured volume-based particle size distribution curve.

[0205] 6. Measuring the size of Si crystallites

[0206] For the silicon-based active materials mixed in the negative electrode active materials (A-1 to A-13) of the examples and comparative examples, peak values ​​were obtained by scanning with a Cu X-ray source at 45 kV and 40 mA, specifying 2θ values ​​from 5° to 80°. The crystallite size was calculated by deconvolution of the obtained peak values ​​with the crystal peak and the amorphous peak. The crystallite size of the (111) crystal plane was measured.

[0207] 7. Measurement of crystallinity (I(520) / I(470))

[0208] Raman spectra were obtained by performing Raman spectroscopy analysis on the silicon-based active materials mixed in the negative electrode active materials (A-1 to A-13) of the examples and comparative examples. The Raman spectra at 520 cm⁻¹ were measured respectively. -1 Peak intensity at 470 cm⁻¹ -1 The peak intensity at the center (center, 1000 cm⁻¹) is the measured value. -1 I(520) / I(470) is calculated by shifting and deconvolution.

[0209] 8. Measure the specific surface area of ​​BET.

[0210] For the silicon-based active materials mixed in the negative electrode active materials (A-1 to A-13) of the examples and comparative examples, the specific surface area was measured using the BET method based on nitrogen adsorption using a BELSORP-mino II measuring device. Specifically, the sample was heated to 200°C using a pretreatment device and then exposed to nitrogen for 60 minutes. After recording the weight of the sample including the support, only the weight of the sample to be tested was entered. After adding an appropriate amount (baseline) of liquid nitrogen, the specific surface area was measured.

[0211] Table 1

[0212]

[0213] Table 2

[0214]

[0215] 9. Manufacturing lithium secondary batteries

[0216] A negative electrode slurry was prepared by mixing the aforementioned negative electrode active material, carbon nanotubes (CNTs) as a conductive material, and styrene-butadiene rubber (SBR) as a binder in a weight ratio of 80:10:10. The negative electrode slurry was coated onto copper foil, then dried and calendered to produce a material with a density of 3 mg / cm². 2 (Based on profile) and negative electrode with a compound density of 1.42 g / cc.

[0217] A coin cell-type secondary battery was fabricated using lithium foil as the relative electrode and an electrolyte containing 1% by weight of FEC and 1.0 M LiPF6 mixed solvent (EC:EMC = 3:7, volume ratio). The secondary battery was placed at room temperature (25°C) for 12 hours, and then its performance was evaluated.

[0218] Experimental Example

[0219] (1) Evaluate the adhesion of the negative electrode

[0220] For the negative electrodes of the examples and comparative examples, a peel-off test was performed using a 90° adhesive force measuring instrument (UTM) to evaluate the adhesion (N) between the negative electrode active material layer and the negative electrode.

[0221] (2) Evaluate the negative electrode resistance

[0222] For the negative electrode of the examples and comparative examples, the resistance (mΩ·cm) of the negative electrode was measured using a Hioki XF057 Probeunit measuring device under the conditions of a current of 100μA, a voltage range of 0.5V, and 500 pin contacts.

[0223] (3) Evaluate the negative electrode expansion rate

[0224] The lithium secondary batteries of the examples and comparative examples were pre-cycled at 0.005V to 1.5V, 0.1C, and 0.01CV, and then additionally charged at 0.005V, 0.1C, and 0.01CV. The thickness of the negative electrode active material layer was measured, and the negative electrode expansion rate (%) was calculated as the rate of increase relative to the initial thickness of the negative electrode active material layer.

[0225] (4) Evaluate the initial discharge capacity and initial efficiency.

[0226] For the lithium secondary batteries of the examples and comparative examples, the initial charge capacity (mAh / g) and initial discharge capacity (mAh / g) were measured by charging (CC / CV, 0.1C, lower limit voltage 0.005V, cut-off current 0.01C) and discharging (CC, 0.1C, upper limit voltage 1.5V cut-off) at 25°C. Furthermore, the initial efficiency (%) was evaluated by measuring the percentage (%) of the initial discharge capacity (mAh / g) relative to the initial charge capacity (mAh / g).

[0227] (5) Evaluate lifespan characteristics (35℃)

[0228] For the lithium secondary batteries of the examples and comparative examples, the first cycle was performed by charging (CC / CV, 0.1C, lower limit voltage 0.005V, cutoff current 0.01C) and discharging (CC, 0.1C, upper limit voltage 1.5V cutoff) at 35°C, which constitutes one cycle. Afterwards, 1000 charge-discharge cycles were repeated at a 1C current density, and the discharge capacity was measured. The lifetime characteristics were evaluated as a percentage (%) of the discharge capacity of the 1000th cycle divided by the discharge capacity of the first cycle.

[0229] (6) Evaluate high-temperature life characteristics (45℃)

[0230] For the lithium secondary batteries of the examples and comparative examples, the first cycle was performed by charging (CC / CV, 0.1C, lower limit voltage 0.005V, cutoff current 0.01C) and discharging (CC, 0.1C, upper limit voltage 1.5V cutoff) at 45°C, which constituted one cycle. Afterwards, the charge-discharge cycle was repeated 800 times at 10-minute intervals, and the discharge capacity was measured. The high-temperature lifetime characteristics were evaluated as a percentage (%) of the value obtained by dividing the discharge capacity of the 800th cycle by the discharge capacity of the first cycle.

[0231] (7) Evaluate high-temperature storage characteristics (60℃)

[0232] For the lithium secondary batteries of the examples and comparative examples, after one charge (CC / CV, 0.5C, upper limit voltage 4.2V, cutoff current 0.05C) and discharge (CC, 0.5C, lower limit voltage 2.5V cutoff) at 25°C, they were charged to 100% SOC and stored at 60°C for 12 weeks. The high-temperature storage characteristics were evaluated by measuring the discharge capacity after 12 weeks and dividing it by the initial discharge capacity as a percentage (%).

[0233] (8) Evaluate output characteristics

[0234] The HPPC room temperature output characteristics (W / kg) of the lithium secondary batteries of the examples and comparative examples were measured using the HPPC (Hybrid Pulse Power Characterization by FreedomCar Battery Test Manual) measurement method.

[0235] The results are shown in Table 3 below.

[0236] Table 3

[0237]

[0238] Referring to Tables 2 and 3, in the case of the embodiments, the negative electrode exhibits high adhesion and low resistance, and a low volume expansion rate even during charge and discharge. Furthermore, the lithium secondary battery demonstrates high initial efficiency and output characteristics, and its lifespan characteristics at both room temperature and high temperature are further improved compared to the comparative examples.

[0239] In the comparative example, the negative electrode exhibits lower adhesion, higher expansion rate, and higher resistance. Furthermore, compared to the example, the lithium-ion secondary battery shows lower lifespan, lower output characteristics, and lower initial efficiency.

[0240] The content described above is merely an example of applying the principles of this disclosure, and other components may be included without departing from the scope of this disclosure.

Claims

1. A negative electrode active material for lithium secondary batteries, comprising a silicon-based active material, said silicon-based active material comprising silicon oxide particles and a carbon coating formed on at least a portion of the surface of said silicon oxide particles. The O1s peak area ratio, measured by X-ray photoelectron spectroscopy analysis of the silicon-based active material and defined by Equation 1, is between 0.025 and 0.

045. [Formula 1] O1s peak area ratio = A H / A O In Equation 1, A H To measure the area of ​​the Si-OH peak by X-ray photoelectron spectroscopy analysis of the silicon-based active material, A O The area of ​​the O1s peak was measured for X-ray photoelectron spectroscopy analysis of the silicon-based active material.

2. The negative electrode active material for lithium secondary batteries according to claim 1, wherein, The area ratio of the O1s peak in the silicon-based active material is between 0.026 and 0.

04.

3. The negative electrode active material for lithium secondary batteries according to claim 1, wherein, The C1s peak area ratio, measured by X-ray photoelectron spectroscopy analysis of the silicon-based active material and defined by Equation 2, is between 0.2 and 1. [Equation 2] C1s peak area ratio = A L / A C In Equation 2, A L To measure the area of ​​the Li2CO3 peak by X-ray photoelectron spectroscopy analysis of the silicon-based active material, A C The area of ​​the C1s peak was measured for X-ray photoelectron spectroscopy analysis of the silicon-based active material.

4. The negative electrode active material for lithium secondary batteries according to claim 3, wherein, The C1s peak area ratio of the silicon-based active material is 0.4 to 0.

8.

5. The negative electrode active material for lithium secondary batteries according to claim 1, wherein, The silicon oxide particles include SiO x , 0 < x ≤ 2.

6. The negative electrode active material for lithium secondary batteries according to claim 1, wherein, The surface arithmetic mean roughness Ra of the silicon-based active material, measured using an atomic force microscope, ranges from 0.2 nm to 5 nm.

7. The negative electrode active material for lithium secondary batteries according to claim 6, wherein, The surface arithmetic mean roughness Ra of the silicon-based active material is between 2 nm and 4.5 nm.

8. The negative electrode active material for lithium secondary batteries according to claim 6, wherein, The surface arithmetic mean roughness Ra is the arithmetic mean of the roughness values, excluding the maximum and minimum values, measured in 10 to 20 regions of the surface of the silicon-based active material with a scanning range of 0.5 μm × 0.5 μm.

9. The negative electrode active material for lithium secondary batteries according to claim 8, wherein, The standard deviation of the measured surface roughness values, excluding the maximum and minimum values, is 1.5 nm to 8 nm.

10. The negative electrode active material for lithium secondary batteries according to claim 1, wherein, The peak intensity ratio of the Raman spectrum, as defined by Equation 3, is between 0.5 and 5.

5. [Formula 3] The peak intensity ratio of the Raman spectrum = I(520) / I(470) In Equation 3, I(520) represents the wavelength of 520 cm⁻¹ in the Raman spectrum. -1 The peak intensity of the silicon oxide particles in the region, I(470) is the wavelength of 470 cm⁻¹ in the Raman spectrum. -1 The peak intensity of the silicon oxide particles in the region.

11. The negative electrode active material for lithium secondary batteries according to claim 1, wherein, The crystallite size of the silicon oxide particles, as measured by X-ray diffraction analysis and defined by Equation 4 below, is 3 nm to 5 nm. [Formula 4] In Equation 4, L is the crystallite size of the silicon oxide particle measured by X-ray diffraction analysis and expressed in nanometers (nm), λ is the X-ray wavelength expressed in nanometers (nm), β is the full width at half maximum (FWHM) of the peak of the (111) plane of the silicon oxide particle expressed in radians (rad), and θ is the diffraction angle expressed in radians (rad).

12. The negative electrode active material for lithium secondary batteries according to claim 1, wherein, The specific surface area of ​​the silicon-based active material is 1m². 2 / g to 4m 2 / g.

13. The negative electrode active material for lithium secondary batteries according to claim 1, wherein, The average particle size D50 of the silicon oxide particles is 4 μm to 6 μm.

14. The negative electrode active material for lithium secondary batteries according to claim 1, wherein, It also includes carbon-based active materials.

15. The negative electrode active material for lithium secondary batteries according to claim 14, wherein, The carbon-based active material comprises artificial graphite, natural graphite, or a mixture thereof.

16. The negative electrode active material for lithium secondary batteries according to claim 1, wherein, In the total weight of the negative electrode active material, the content of the silicon-based active material is greater than 0% by weight and less than 10% by weight.

17. A lithium secondary battery, comprising: The negative electrode comprises the negative electrode active material for lithium secondary batteries according to claim 1; and The positive electrode is opposite to the negative electrode.

18. A method for preparing a negative electrode active material for lithium secondary batteries, comprising: The steps of mixing multiple silicon sources and performing heat treatment to obtain silicon oxide particles; as well as The step of reacting the silicon oxide particles with a carbon source gas to form a carbon coating to obtain a silicon-based active material. The O1s peak area ratio, measured by X-ray photoelectron spectroscopy analysis of the silicon-based active material and defined by Equation 1, is between 0.025 and 0.

045. [Formula 1] O1s peak area ratio = A H / A O In Equation 1, A H To measure the area of ​​the Si-OH peak by X-ray photoelectron spectroscopy analysis of the silicon-based active material, A O The area of ​​the O1s peak was measured for X-ray photoelectron spectroscopy analysis of the silicon-based active material.

19. The method for preparing the negative electrode active material for lithium secondary batteries according to claim 18, wherein, The heat treatment temperature is between 800°C and 1200°C.

20. The method for preparing the negative electrode active material for lithium secondary batteries according to claim 18, wherein, The silicon source includes silicon particles and silicon dioxide (SiO2) particles.

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