A negative electrode active material, a negative electrode containing the same, a secondary battery containing the same, and a method for manufacturing the negative electrode active material.

Abstract

The present invention relates to a negative electrode active material, a negative electrode containing the same, a secondary battery containing the same, and a method for producing the negative electrode active material.

Description

[Technical Field]

[0001] This application claims the benefit as of the filing date of Korean Patent Application No. 10-2022-0113645, filed with the Korean Intellectual Property Office on 7 September 2022, and Korean Patent Application No. 10-2023-0117434, filed with the Korean Intellectual Property Office on 5 September 2023, and all of its contents are incorporated herein by reference.

[0002] The present invention relates to a negative electrode active material, a negative electrode containing the same, a secondary battery containing the same, and a method for producing a negative electrode active material. [Background technology]

[0003] In recent years, with the rapid proliferation of electronic devices that use batteries, such as mobile phones, laptops, and electric vehicles, the demand for rechargeable batteries that are small, lightweight, and yet relatively high-capacity has been rapidly increasing. In particular, lithium-ion batteries are attracting attention as a power source for portable devices due to their light weight and high energy density. For this reason, research and development efforts to improve the performance of lithium-ion batteries are being actively pursued.

[0004] Generally, lithium secondary batteries include a positive electrode, a negative electrode, a separator interposed between the positive and negative electrodes, an electrolyte, an organic solvent, and the like. Furthermore, active material layers containing positive electrode active material and negative electrode active material can be formed on the current collector of the positive and negative electrodes, respectively. Generally, lithium-containing metal oxides such as LiCoO2 and LiMn2O4 are used as the positive electrode active material, while lithium-free carbon-based active materials and silicon-based active materials are used as the negative electrode active material.

[0005] Among negative electrode active materials, silicon-based active materials are attracting attention because they have a higher capacity and superior fast charging characteristics compared to carbon-based active materials. However, silicon-based active materials have the disadvantage of low initial efficiency due to a large degree of volume expansion / contraction during charging and discharging, resulting in a large irreversible capacity.

[0006] On the one hand, among silicon-based active materials, silicon-based oxides, specifically SiO In the case of silicon-based oxides represented by (0 < x < 2), there is an advantage in that the degree of volume expansion / contraction due to charge and discharge is lower compared to other silicon-based active materials such as silicon (Si). However, there is still a drawback that the initial efficiency decreases due to the presence of irreversible capacity in silicon-based oxides.

[0007] In connection with this, research has been continuously conducted to reduce the irreversible capacity and improve the initial efficiency by doping or inserting metals such as Li, Al, and Mg into silicon-based oxides. However, in the case of a negative electrode slurry containing a metal-doped silicon-based oxide as a negative electrode active material, there is a problem that the metal oxide formed by doping reacts with moisture to increase the pH of the negative electrode slurry and change the viscosity, resulting in a poor state of the manufactured negative electrode and a problem of reduced charge and discharge efficiency of the negative electrode.

[0008] Therefore, there is a need to develop a negative electrode active material that can improve the phase stability of a negative electrode slurry containing a silicon-based oxide and thereby improve the charge and discharge efficiency of the manufactured negative electrode.

[0009] Korean Registered Patent No. 10-0794192 relates to a method for manufacturing a carbon-coated silicon-graphite composite negative electrode material for a lithium secondary battery and a method for manufacturing a secondary battery including the same, but there are limitations in solving the above-mentioned problems.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0011] The present invention relates to a negative electrode active material, a negative electrode containing the same, a secondary battery containing the same, and a method for producing the negative electrode active material.

Means for Solving the Problems

[0012] One embodiment of the present invention is a negative electrode active material containing silicon-based particles containing SiO x (0 < x < 2) and a Li compound, wherein the Li compound contains at least one crystalline phase lithium silicate selected from the group consisting of crystalline phase Li2SiO3, crystalline phase Li4SiO4, and crystalline phase Li2Si2O5, and the content of the crystalline phase Li2SiO3 is more than the total of the content of the crystalline phase Li2Si2O5 and the content of the crystalline phase Li4SiO4, and the content of the crystalline phase Li2SiO3 is contained at 60 parts by weight or more based on 100 parts by weight in total of the crystalline phase lithium silicate, and the total content of the crystalline phases present in the silicon-based particles is more than the total content of the amorphous phases, and provides a negative electrode active material.

[0013] One embodiment of the present invention is a step of forming particles containing a silicon-based oxide represented by SiO x (0 < x < 2); and a step of heat-treating after mixing the particles containing the silicon-based oxide and a lithium precursor, and provides a method for producing a negative electrode active material according to one embodiment of the present invention.

[0014] One embodiment of the present invention provides a negative electrode containing the negative electrode active material according to one embodiment of the present invention. One embodiment of the present invention provides a secondary battery containing the negative electrode according to one embodiment of the present invention.

Effects of the Invention

[0015] The negative electrode active material of the present invention has a predominantly crystalline Li2SiO3 content in the crystalline lithium silicate, resulting in less loss of discharge capacity per unit weight due to increased Li content in the negative electrode active material. During Li doping, SiO2, which acts as an irreversible capacity, reacts extensively with Li, forming an electrochemically stable Li2SiO3 lithium silicate structure, thereby significantly increasing the initial efficiency. Furthermore, in the case of crystalline Li2SiO3, the structure remains stable during charging and discharging, resulting in excellent lifetime characteristics.

[0016] Furthermore, because the negative electrode active material of the present invention has a larger total content of crystalline phase compared to the total content of amorphous phase, it has a lower content of lithium oxide and lithium silicate that react with moisture, which prevents gas generation and viscosity changes in the negative electrode slurry, and improves the phase stability of the slurry containing the negative electrode active material. As a result, the negative electrode containing the negative electrode active material and the secondary battery containing the negative electrode have improved quality, and have the effect of improving charge / discharge capacity, initial efficiency, and / or life characteristics. [Modes for carrying out the invention]

[0017] The following provides a more detailed description of this specification. In this specification, when a part "includes" a component, this means that, unless otherwise stated, it may include other components rather than excluding them.

[0018] In this specification, when one member is said to be "on top of" another member, this includes not only cases where one member is in contact with another member, but also cases where another member exists between the two members.

[0019] The terms and words used herein should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather should be interpreted in a manner consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may appropriately define the concepts of terms in order to best explain their invention.

[0020] In this specification, singular expressions of terms include plural expressions unless the context clearly indicates otherwise.

[0021] In this specification, the crystallinity of the structure contained in the negative electrode active material can be confirmed by X-ray diffraction analysis, and X-ray diffraction analysis can be performed using an XRD (X-ray diffraction) analyzer (product name: D4-endeavor, manufacturer: bruker), and other instruments used in this industry may be used as appropriate.

[0022] In this specification, the presence and content of elements in the negative electrode active material can be confirmed by ICP analysis, which can be performed using an inductively coupled plasma atomic emission spectrometer (ICPAES, Perkin-Elmer 7300).

[0023] In this specification, the average particle size (D 50 The average particle size (D) can be defined as the particle size that corresponds to 50% of the cumulative volume in the particle size distribution curve (graph curve of the particle size distribution diagram). 50 The particle size can be measured, for example, using the laser diffraction method. This laser diffraction method can generally measure particle sizes from the submicron region to several millimeters in size, and can obtain highly reproducible and high-resolution results.

[0024] Preferred embodiments of the present invention will be described in detail below. However, embodiments of the present invention may be modified in various forms, and the scope of the present invention is not limited to the embodiments described below.

[0025] <Negative electrode active material> The negative electrode active material will be explained in detail below. This invention relates to a negative electrode active material, and more specifically, to a negative electrode active material for lithium secondary batteries.

[0026] One embodiment of the present invention is SiO xA negative electrode active material comprising silicon-based particles containing (0 < x < 2) and a Li compound, wherein the Li compound contains at least one crystalline lithium silicate selected from the group consisting of crystalline phase Li2SiO3, crystalline phase Li4SiO4, and crystalline phase Li2Si2O5, the content of the crystalline phase Li2SiO3 is more than the total of the content of the crystalline phase Li2Si2O5 and the content of the crystalline phase Li4SiO4, the content of the crystalline phase Li2SiO3 is contained at 60 parts by weight or more based on 100 parts by weight in total of the crystalline lithium silicate, and the total content of the crystalline phases present in the silicon-based particles is more than the total content of the amorphous phases, provides a negative electrode active material.

[0027] Conventionally, in a negative electrode active material containing a silicon-based oxide, research has been conducted to dope or distribute lithium or the like in the negative electrode active material to remove the irreversible capacity of the silicon-based oxide and improve the initial efficiency. However, such a negative electrode active material has a high content of an amorphous phase, so that during the production of a negative electrode slurry, specifically an aqueous negative electrode slurry, gas generation increases due to the reaction of moisture with a lithium oxide and / or a lithium silicate, the pH of the negative electrode slurry is increased, and the phase stability is decreased. There are problems that the quality of the produced negative electrode is poor and the charge-discharge efficiency is decreased.

[0028] In order to solve such problems, the negative electrode active material according to one embodiment of the present invention is SiO x The silicon-based particles containing (0 < x < 2) and a Li compound contain a Li compound in the form of at least one crystalline lithium silicate or amorphous lithium silicate selected from the group consisting of crystalline phase Li2SiO3, crystalline phase Li4SiO4, and crystalline phase Li2Si2O5, among which the content of the crystalline phase Li2SiO3 is more than the total of the content of the crystalline phase Li2Si2O5 and the content of the crystalline phase Li4SiO4, and the total content of the crystalline phases present in the silicon-based particles is more than the total content of the amorphous phases.

[0029] According to the negative electrode active material of the present invention, the content of the crystal phase Li2SiO3 in the crystalline lithium silicate is predominantly present, and there is little loss of discharge capacity per weight due to an increase in the content of Li in the negative electrode active material. A large amount of SiO2 and Li that act as irreversible capacity during Li doping react with each other to form a lithium silicate structure of electrochemically stable Li2SiO3, so that the initial efficiency can be significantly increased. Further, in the case of the crystal phase Li2SiO3, the structure is stable during charge and discharge, and the life characteristics are excellent.

[0030] Further, according to the negative electrode active material of the present invention, since the total content of the crystal phase is larger than the total content of the amorphous phase, the content of lithium oxide and lithium silicate that react with moisture is small, and gas generation and viscosity change of the negative electrode slurry can be prevented. Since the phase stability of the slurry containing the negative electrode active material can be improved, the negative electrode containing the negative electrode active material and the secondary battery containing the negative electrode have the effects that the quality is improved and the charge-discharge capacity, initial efficiency, and / or life characteristics are improved.

[0031] The negative electrode active material according to one embodiment of the present invention includes silicon-based particles. The silicon-based particles include SiO x (0 < x < 2) and a Li compound.

[0032] The SiO x (0 < x < 2) may correspond to a matrix within the silicon-based particles. The SiO x (0 < x < 2) may be in a form containing Si and / or SiO2, and the Si may form a phase. For example, the SiO x (0 < x < 2) may be a composite containing amorphous SiO2 and Si crystals. That is, the x corresponds to the number ratio of O to Si contained in the SiO [[ID=2I]] x (0 < x < 2). When the silicon-based particles contain the SiO x (0 < x < 2), the discharge capacity of the secondary battery can be improved. Specifically, the SiO x (0 < x < 2) is SiO xThe compound may also be one represented by (0.5 ≤ x ≤ 1.5).

[0033] The Li compound may constitute a matrix within the silicon-based composite particles. The Li compound may exist within the silicon-based particles in the form of at least one of lithium atoms, lithium silicate, lithium silicide, or lithium oxide. When the silicon-based particles contain the Li compound, there is an effect of improving the initial efficiency.

[0034] The Li compound may be distributed on the surface and / or inside the silicon-based particles in a doped form. The Li compound, distributed on the surface and / or inside the silicon-based particles, can control the expansion / contraction of the silicon-based particles to an appropriate level and can play a role in preventing damage to the active material. The Li compound may also be included in a way that it lowers the proportion of the irreversible phase (e.g., SiO2) of the silicon oxide particles and increases the efficiency of the active material.

[0035] Specifically, the lithium may be distributed on the surface, inside, or both the surface and inside of the silicon-based particles. Furthermore, the lithium may be doped into the silicon-based particles.

[0036] In one embodiment of the present invention, the element Li may be included in an amount exceeding 7 parts by weight and not exceeding 10 parts by weight, based on a total of 100 parts by weight of the negative electrode active material.

[0037] Preferably, the element Li may be included in amounts of 7.2 to 9.8 parts by weight, 7.5 to 9.7 parts by weight, 8 to 9.5 parts by weight, 8.2 to 9.5 parts by weight, or 8.5 to 9.2 parts by weight, based on 100 parts by weight of the total negative electrode active material. When lithium is included within the above ranges, it is preferable because the initial efficiency and charge / discharge efficiency characteristics of the negative electrode active material can be improved. On the other hand, when Li is included in amounts less than the above, there is a problem that the Li content in the silicon-based particles is insufficient, resulting in a significant decrease in discharge capacity and efficiency. When the content exceeds the above, Li that has not reacted with the silicon-based particles remains as a byproduct, causing the aqueous slurry to exhibit strong basicity, which can adversely affect the processability of the slurry.

[0038] The upper limit of the Li content may be 10 parts by weight, 9.8 parts by weight, 9.7 parts by weight, 9.6 parts by weight, 9.5 parts by weight, 9.4 parts by weight, 9.3 parts by weight, 9.2 parts by weight, 9.1 parts by weight, or 9 parts by weight, based on 100 parts by weight of the total negative electrode active material, and the lower limit may be 7.2 parts by weight, 7.5 parts by weight, 7.8 parts by weight, 8 parts by weight, 8.2 parts by weight, or 8.5 parts by weight.

[0039] The content of the aforementioned Li element can be confirmed by ICP analysis. Specifically, a certain amount (approximately 0.01 g) of the negative electrode active material is separated, transferred to a platinum crucible, and completely decomposed on a hot plate with the addition of nitric acid, hydrofluoric acid, and sulfuric acid. Then, using an inductively coupled plasma atomic emission spectrometer (ICPAES, Perkin-Elmer 7300), the intensity of a standard solution prepared using a standard solution (5 mg / kg) is measured at the wavelength specific to the element to be analyzed to create a reference calibration curve. Subsequently, the pre-treated sample solution and a blank sample are introduced into the instrument, their respective intensities are measured to calculate the actual intensities, and the concentrations of each component are calculated against the calibration curve created above. After this, the total is converted to a theoretical value, and the elemental content of the manufactured negative electrode active material can be analyzed.

[0040] In one embodiment of the present invention, the Li compound may be distributed in the form of lithium silicate on the silicon-based particles, thereby removing the irreversible capacity of the particles and playing a role in improving the initial efficiency and charge-discharge efficiency of the negative electrode active material. At this time, silicate means a compound containing silicon, oxygen, and one or more metals.

[0041] Specifically, the Li compound may be distributed on the surface, inside, or both the surface and inside of the silicon-based particles in the form of lithium silicate, and the lithium silicate may correspond to a matrix within the particles. The lithium silicate is represented by Li a Si b O c (2 ≤ a ≤ 4, 0 < b ≤ 2, 2 ≤ c ≤ 5) and can be classified into crystalline lithium silicate and amorphous lithium silicate. The crystalline lithium silicate may exist in the form of at least one lithium silicate selected from the group consisting of Li2SiO3, Li4SiO4, and Li2Si2O5 within the silicon-based particles, and the amorphous lithium silicate may have a complex structure of the form Li a Si b O c (2 ≤ a ≤ 4, 0 < b ≤ 2, 2 ≤ c ≤ 5) and is not limited to the above form.

[0042] In one embodiment of the present invention, the Li compound may include at least one crystalline-phase lithium silicate selected from the group consisting of crystalline-phase Li2SiO3, crystalline-phase Li4SiO4, and crystalline-phase Li2Si2O5. Further, the Li compound may further include an amorphous-phase lithium silicate.

[0043] Specifically, the Li compound contained in the silicon-based particles includes crystalline-phase Li2SiO3 and crystalline-phase Li2Si2O5, and may selectively further include crystalline-phase Li4SiO4 or amorphous-phase lithium silicate.

[0044] When the negative electrode active material contains a large amount of crystalline Li2SiO3, the loss of discharge capacity per unit weight of the active material can be reduced. In the case of the crystalline Li2SiO3, the electrochemically stable structure can significantly increase the initial efficiency, and the structure remains stable during charging and discharging, effectively improving the lifespan characteristics.

[0045] In the case of the crystalline phase Li2Si2O5, it is stable in the negative electrode active material, and in particular, side reactions with water occur in negative electrode slurries, specifically aqueous negative electrode slurries. However, when the negative electrode active material contains a large amount of crystalline phase Li2Si2O5, the loss of discharge capacity per unit weight of the active material is large, and the crystalline phase Li2Si2O5 has the problem of structural instability during charging and discharging, which degrades its lifespan characteristics.

[0046] In the case of the crystalline phase Li4SiO4, there is a problem in that it undergoes a side reaction with water in the negative electrode slurry. As a result, gas generation becomes vigorous, and by-products such as Li2O formed by the side reaction with water can raise the pH of the negative electrode slurry, destabilize the slurry phase, and potentially change the viscosity.

[0047] In connection with this, the negative electrode active material of the present invention has a higher content of crystalline phase Li2SiO3 than the content of crystalline phase Li2Si2O5 and crystalline phase Li4SiO4. Therefore, it is possible to smoothly remove irreversible capacity from the negative electrode active material and improve initial efficiency and charge / discharge efficiency. This improves the phase stability of the negative electrode slurry containing the negative electrode active material, prevents problems of low viscosity, improves the quality of the negative electrode, allows for excellent levels of charge / discharge capacity, and improves charge / discharge efficiency. Furthermore, as will be described later, the negative electrode active material of the present invention, along with an increased content of crystalline phase Li2SiO3, reduces the total content of the amorphous phase. This makes it possible to improve the phase stability of the negative electrode slurry, prevent defects in the negative electrode, and significantly improve charge / discharge capacity and efficiency.

[0048] Furthermore, the negative electrode active material of the present invention may contain more than 7 parts by weight but less than or equal to 10 parts by weight of element Li. Within this range, if the content of crystalline phase Li2SiO3 is greater than the content of crystalline phase Li2Si2O5, the loss of discharge capacity per unit weight due to the increase in Li content in the negative electrode active material is small, and it has an electrochemically stable lithium silicate structure. As a result, the structure remains stable during charging and discharging, and a high discharge capacity can be achieved when the same initial efficiency is achieved, resulting in excellent lifespan characteristics. In addition, as will be described later, reducing the total content of amorphous phase in the negative electrode active material has the effect of preventing side reactions with moisture.

[0049] In contrast, when the content of crystalline phase Li2Si2O5 is greater than that of crystalline phase Li2SiO3, although side reactions with water occur less frequently, the increased Li content in the negative electrode active material leads to a significant loss of discharge capacity per unit weight. Furthermore, the structure becomes unstable during charging and discharging, which can result in lower discharge capacity and poorer lifetime characteristics when achieving the same initial efficiency.

[0050] In one embodiment of the present invention, the content of the crystalline phase Li2SiO3 is greater than the sum of the content of the crystalline phase Li2Si2O5 and the content of the crystalline phase Li4SiO4. In another embodiment, the content of the crystalline phase Li2SiO3 may be greater than the content of the crystalline phase Li2Si2O5.

[0051] In one embodiment of the present invention, the content of the crystalline phase Li2SiO3 may be 60 parts by weight or more based on 100 parts by weight of the total crystalline phase lithium silicate. In another embodiment, the content of the crystalline phase Li2SiO3 may be 65 parts by weight or more, 70 parts by weight or more, or 74 parts by weight or more.

[0052] In one embodiment of the present invention, the crystalline phase Li2SiO3 may be present in an amount of 15 to 50 parts by weight based on 100 parts by weight of the total silicon-based particles. In another embodiment, the crystalline phase Li2SiO3 may be present in an amount of 17 to 48 parts by weight, 20 to 48 parts by weight, 20 to 45 parts by weight, 25 to 45 parts by weight, 30 to 45 parts by weight, or 35 to 42 parts by weight. When the content of the crystalline phase Li2SiO3 satisfies the above ranges, it is preferable in that it is advantageous in realizing capacity per gram and that it is excellent in realizing capacity / efficiency and life characteristics because Li2SiO3 is stable during charging and discharging. If the amount exceeds the aforementioned range, the high reactivity of Li2SiO3 with water negatively affects the processability of the aqueous slurry. If the amount is below the aforementioned range, it is disadvantageous in achieving the desired capacity per gram, and the lack of stable Li2SiO3 during charging and discharging results in poor capacity / efficiency and inferior lifespan characteristics.

[0053] The upper limit of the content of the crystalline phase Li2SiO3 may be 50 parts by weight, 48 parts by weight, 45 parts by weight, 42 parts by weight, or 40 parts by weight based on a total of 100 parts by weight of the silicon-based particles, and the lower limit may be 15 parts by weight, 17 parts by weight, 20 parts by weight, 25 parts by weight, 30 parts by weight, 33 parts by weight, 35 parts by weight, or 38 parts by weight.

[0054] In one embodiment of the present invention, the crystalline phase Li2Si2O5 may be included in an amount of 0.5 parts by weight or more and 20 parts by weight or less, based on a total of 100 parts by weight of the silicon-based particles. In another embodiment, the crystalline phase Li2Si2O5 may be included in an amount of 1 part by weight or more and 18 parts by weight or less, 3 parts by weight or more and 18 parts by weight or less, 3 parts by weight or more and 15 parts by weight or less, or 3 parts by weight or more and 12 parts by weight or less.

[0055] The upper limit of the content of the crystalline phase Li2Si2O5 may be 20 parts by weight, 18 parts by weight, 15 parts by weight, or 12 parts by weight based on a total of 100 parts by weight of the silicon-based particles, and the lower limit may be 0.5 parts by weight, 1 part by weight, 3 parts by weight, or 5 parts by weight.

[0056] If the content of crystalline phase Li2Si2O5 exceeds the aforementioned range, there is a problem of poor lifetime characteristics due to excessively large capacity loss per unit weight and unstable structure of Li2Si2O5. If the content of crystalline phase Li2Si2O5 is below the aforementioned range, the processability of the aqueous slurry may decrease because there is an excessively small amount of Li2Si2O5, which has low reactivity with water. Therefore, it is preferable to satisfy the aforementioned range for the content of crystalline phase Li2Si2O5 to minimize capacity loss per unit weight, avoid excessively reducing lifetime characteristics, ensure appropriate processability of the aqueous slurry, and achieve suitable discharge capacity, initial efficiency, and lifetime characteristics when the battery is in operation.

[0057] In one embodiment of the present invention, the crystalline phase Li4SiO4 may be included in an amount of 5 parts by weight or less, specifically 3 parts by weight or less, 1 part by weight or less, or less than 0.1 parts by weight, based on 100 parts by weight of the total silicon-based particles, and more specifically, the crystalline phase Li4SiO4 may not be present in the negative electrode active material. When the content of the crystalline phase Li4SiO4 satisfies the above range, it is preferable in terms of preventing the generation of by-products such as Li2O due to the reaction of the negative electrode active material with water during the production of the negative electrode slurry, specifically an aqueous negative electrode slurry, preventing an increase in the pH of the negative electrode slurry and deterioration of the negative electrode quality.

[0058] In one embodiment of the present invention, the difference between the content of the crystalline phase Li2SiO3 and the content of the crystalline phase Li2Si2O5 may be 1 to 50 parts by weight based on 100 parts by weight of the total silicon-based particles. Specifically, the difference between the content of the crystalline phase Li2Si2O5 and the content of the crystalline phase Li2SiO3 may be 5 to 45 parts by weight, 8 to 45 parts by weight, 10 to 40 parts by weight, 20 to 40 parts by weight, or 20 to 35 parts by weight.

[0059] The upper limit of the difference between the content of the crystalline phase Li2SiO3 and the content of the crystalline phase Li2Si2O5 may be 50 parts by weight, 45 parts by weight, 40 parts by weight, or 38 parts by weight based on a total of 100 parts by weight of the silicon-based particles, and the lower limit may be 1 part by weight, 5 parts by weight, 8 parts by weight, 10 parts by weight, 15 parts by weight, or 20 parts by weight.

[0060] When the difference between the content of the crystalline phase Li2Si2O5 and the content of the crystalline phase Li2SiO3 satisfies the aforementioned range, it is possible to improve the phase stability of the negative electrode slurry, prevent defects in the negative electrode, and significantly improve the charge / discharge capacity and efficiency.

[0061] The confirmation and measurement of the crystalline lithium silicate in the crystalline phase Li2SiO3, crystalline phase Li4SiO4, or crystalline phase Li2Si2O5 is performed by X-ray diffraction analysis using an X-ray diffraction profile or 29 Si-MAS-NMR ( 29 Si-Magic Angle Spinning-Nuclear Magnetic Resonance, 29 This can be measured by analysis via Si-magic angle spinning (nuclear magnetic resonance).

[0062] Eventually, 29 Si-MAS-NMR analysis is a type of solid-phase NMR analysis technique in which the rotor containing the sample is placed at a magic angle B relative to a magnetic field B0. M This is an NMR analysis performed by rapidly spinning at a temperature (for example, 54.74°). This allows for the measurement of the presence and content of crystalline phases Li2SiO3, Li4SiO4, Li2Si2O5, Si, and SiO2 contained in the negative electrode active material of the present invention.

[0063] One embodiment of the present invention, the negative electrode active material 29During Si-MAS-NMR analysis, the height of the Li2SiO3 peak p1 appearing in the -70ppm to -80ppm chemical shift peak may be greater than the height of the Li2Si2O5 peak p2 appearing in the -90ppm to -100ppm chemical shift peak.

[0064] One embodiment of the present invention, the negative electrode active material 29 During Si-MAS-NMR analysis, the ratio p2 / p1 of the height of the Li2SiO3 peak p1 appearing at the -90ppm to -100ppm chemical shift peak to the height of the Li2Si2O5 peak p2 appearing at the -70ppm to -80ppm chemical shift peak may be 1 or less. Specifically, it may be between 0.01 and 0.8, between 0.05 and 0.7, or between 0.1 and 0.6. When it is within the above range, there is a sufficient amount of crystalline Li2SiO3 in the negative electrode active material, which allows for improved phase stability of the negative electrode slurry, prevention of negative electrode defects, and significant improvements in charge / discharge capacity and efficiency.

[0065] The upper limit of p2 / p1 may be 1, 0.8, 0.7, 0.6, 0.5, or 0.4, and the lower limit may be 0.01, 0.05, 0.1, 0.15, or 0.2.

[0066] One embodiment of the present invention, the negative electrode active material 29 During Si-MAS-NMR analysis, the Li4SiO4 peak p3, which appears in the chemical shift peak range of -60 ppm to -69 ppm, does not necessarily need to be present. This is preferable in terms of preventing the generation of by-products such as Li2O due to side reactions between Li4SiO4 and water in the negative electrode active material, the resulting increase in the pH of the negative electrode slurry, and the deterioration of the negative electrode quality.

[0067] The content of the crystalline phase Li2SiO3, crystalline phase Li4SiO4, and crystalline phase Li2Si2O5 may be achieved, but is not limited to, the methods for producing the negative electrode active material described later, by performing a heat treatment step, adjusting the heat treatment temperature, or performing an acid treatment step.

[0068] In one embodiment of the present invention, the negative electrode active material may contain less than 5 parts by weight, specifically less than 4 parts by weight, of crystalline phase SiO2 based on 100 parts by weight of the total silicon-based particles, and in another embodiment, it may contain 3 parts by weight or less. Preferably, the negative electrode active material may contain 1 part by weight or less of crystalline phase SiO2 based on 100 parts by weight of the total silicon-based particles, or may contain none at all. When the content of crystalline phase SiO2 satisfies the above range, charging and discharging of the negative electrode is easy, and the charge / discharge capacity and efficiency can be improved well.

[0069] In one embodiment of the present invention, the negative electrode active material may contain crystalline Si in amounts of 10 to 50 parts by weight, 15 to 40 parts by weight, 15 to 30 parts by weight, 20 to 30 parts by weight, or 20 to 25 parts by weight, based on 100 parts by weight of the total silicon-based particles. When the content of crystalline Si satisfies the above range, charging and discharging of the negative electrode is easy, and the charge / discharge capacity and efficiency can be improved significantly.

[0070] In one embodiment of the present invention, the total content of crystalline phases present in the silicon-based particles is greater than the total content of amorphous phases. The total content of crystalline phases refers to the total content of all crystalline phases present in the silicon-based particles, including crystalline phase Si, crystalline phase SiO2, crystalline phase Li2SiO3, crystalline phase Li4SiO4, crystalline phase Li2Si2O5, etc., while the total content of amorphous phases may refer to the content excluding the total content of crystalline phases present in the silicon-based particles. That is, the total content of amorphous phases includes amorphous phase lithium silicate as well as amorphous phase SiO2, etc., and refers to the sum of the content of all amorphous phases present in the particles.

[0071] The anode active material of the present invention is preferable in that, because the total content of the crystalline phase present in the silicon-based particles is greater than the total content of the amorphous phase, the content of amorphous lithium silicate and other elements that are highly reactive with water is reduced during the production of the anode slurry, specifically the aqueous anode slurry. This reduces the generation of by-products such as Li2O due to side reactions with water, prevents an increase in the pH of the anode slurry, and prevents defects in the quality of the anode.

[0072] In one embodiment of the present invention, the total content of the crystalline phase present in the silicon-based particles may be more than 50 parts by weight and 85 parts by weight or less, based on 100 parts by weight of the total silicon-based particles. Specifically, it may be 55 parts by weight or more and 85 parts by weight or less, 55 parts by weight or more and 80 parts by weight or less, 55 parts by weight or more and 75 parts by weight or less, 60 parts by weight or more and 70 parts by weight or less, 62 parts by weight or more and 68 parts by weight or less, 64 parts by weight or more and 68 parts by weight or less, or 64 parts by weight or more and 66 parts by weight or less.

[0073] The upper limit of the total content of the crystalline phase may be 85 parts by weight, 83 parts by weight, 80 parts by weight, 75 parts by weight, 70 parts by weight, 68 parts by weight, or 66 parts by weight, based on a total of 100 parts by weight of the silicon-based particles, and the lower limit may be 55 parts by weight, 60 parts by weight, 62 parts by weight, or 64 parts by weight.

[0074] In one embodiment of the present invention, the total content of the amorphous phase present in the silicon-based particles may be 15 parts by weight or more and less than 50 parts by weight, based on 100 parts by weight of the total silicon-based particles. Specifically, it may be 20 parts by weight or more and less than 50 parts by weight, 25 parts by weight or more and less than 50 parts by weight, 25 parts by weight or more and 45 parts by weight or less, 30 parts by weight or more and 40 parts by weight or less, 32 parts by weight or more and 36 parts by weight or less, or 34 parts by weight or more and 36 parts by weight or less.

[0075] The upper limit of the total content of the amorphous phase may be 48 parts by weight, 45 parts by weight, 40 parts by weight, 38 parts by weight, or 36 parts by weight, based on a total of 100 parts by weight of the silicon-based particles, and the lower limit may be 15 parts by weight, 20 parts by weight, 25 parts by weight, 30 parts by weight, 32 parts by weight, or 34 parts by weight.

[0076] In one embodiment of the present invention, the difference between the total content of the crystalline phase and the total content of the amorphous phase in the silicon-based particles may be 10 to 70 parts by weight, 20 to 68 parts by weight, 20 to 50 parts by weight, 25 to 40 parts by weight, 28 to 36 parts by weight, or 30 to 36 parts by weight, based on 100 parts by weight of the total silicon-based particles.

[0077] The upper limit of the difference between the total content of the crystalline phase and the total content of the amorphous phase present in the silicon-based particles is 70 parts by weight, 68 parts by weight, 66 parts by weight, 60 parts by weight, 50 parts by weight, 40 parts by weight, or 36 parts by weight, based on 100 parts by weight of the total silicon-based particles, and the lower limit may be 10 parts by weight, 15 parts by weight, 20 parts by weight, 25 parts by weight, 28 parts by weight, or 30 parts by weight.

[0078] In one embodiment of the present invention, the ratio of the total weight of the crystalline phase to the total weight of the amorphous phase present in the silicon-based particles (total weight of crystalline phase: total weight of amorphous phase) may be 55:45 to 85:15, 60:40 to 80:20, or 60:40 to 75:25.

[0079] When the relationship between the content of crystalline and amorphous phases present in the silicon-based particles satisfies the aforementioned range, the content of crystalline and amorphous phases present in the negative electrode active material is appropriately adjusted, which is preferable in that, during the production of the negative electrode slurry (specifically, the aqueous negative electrode slurry), the content of amorphous phase lithium silicate and other elements that are highly reactive with water is reduced, the generation of by-products such as Li2O due to side reactions with water, the resulting increase in pH of the negative electrode slurry, and changes in viscosity are prevented, and the content of crystalline phase SiO2, which would hinder the development of charge / discharge capacity and efficiency, is not excessively increased.

[0080] Even if the content of the crystalline phase Li2SiO3 in lithium silicate is the highest, if the total content of the crystalline phase present in the negative electrode active material exceeds the aforementioned range, there is a problem that the crystalline phase is excessively present in the negative electrode active material, making charging and discharging difficult, making it difficult to achieve capacity / efficiency, and reducing lifetime characteristics. If the content is below the aforementioned range, there is a problem that the crystalline phase is not sufficiently present, making it difficult to effectively control side reactions with water.

[0081] The total content of the crystalline phase and the total content of the amorphous phase present in the silicon-based particles can be measured by a quantitative analysis method using X-ray diffraction (XRD).

[0082] In one embodiment of the present invention, the silicon-based particles may contain additional metal atoms. The metal atoms may exist within the silicon-based particles in the form of at least one of metal atoms, metal silicates, metal silicides, and metal oxides. The metal atoms may include at least one selected from the group consisting of Mg, Li, Al, and Ca. This can improve the initial efficiency of the negative electrode active material.

[0083] In one embodiment of the present invention, the silicon-based particles have a carbon layer provided on at least a portion of their surface. In this case, the carbon layer may be in a form that partially covers at least a portion of the surface, i.e., the surface of the particles, or it may cover the entire surface of the particles. The carbon layer imparts conductivity to the negative electrode active material, thereby improving the initial efficiency, life characteristics, and capacity characteristics of the secondary battery.

[0084] In one embodiment of the present invention, the carbon layer contains amorphous carbon. The carbon layer may further contain crystalline carbon.

[0085] The crystalline carbon can further improve the conductivity of the negative electrode active material. The crystalline carbon may include at least one selected from the group consisting of fullerene, carbon nanotubes, and graphene.

[0086] The amorphous carbon can appropriately maintain the strength of the carbon layer and suppress the expansion of the silicon-based particles. The amorphous carbon may be a carbon-based material formed by using at least one carbide or hydrocarbon selected from the group consisting of tar, pitch, and other organic materials as a source in chemical vapor deposition.

[0087] The aforementioned carbonized organic substances may be carbonized organic substances selected from carbonized sucrose, glucose, galactose, fructose, lactose, mannose, ribose, aldohexose, or ketohexose, and combinations thereof.

[0088] The hydrocarbon may be a substituted or unsubstituted aliphatic or alicyclic hydrocarbon, or a substituted or unsubstituted aromatic hydrocarbon. The aliphatic or alicyclic hydrocarbon of the substituted or unsubstituted aliphatic or alicyclic hydrocarbon may be methane, ethane, ethylene, acetylene, propane, butane, butene, pentane, isobutane, or hexane. Examples of the aromatic hydrocarbon of the substituted or unsubstituted aromatic hydrocarbon include benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, coumarone, pyridine, anthracene, or phenanthrene.

[0089] In one embodiment of the present invention, the carbon layer may be an amorphous carbon layer. In one embodiment of the present invention, the carbon layer may be included in amounts of 0.1 to 50 parts by weight, 0.1 to 30 parts by weight, or 0.1 to 20 parts by weight, based on 100 parts by weight of the total negative electrode active material. More specifically, it may be included in amounts of 0.5 to 15 parts by weight, 1 to 10 parts by weight, or 1 to 5 parts by weight. When these ranges are met, a decrease in the capacity and efficiency of the negative electrode active material can be prevented.

[0090] In one embodiment of the present invention, the thickness of the carbon layer may be 1 nm to 500 nm, and more specifically, 5 nm to 300 nm. When this range is met, the conductivity of the negative electrode active material is improved, volume changes of the negative electrode active material are easily suppressed, side reactions between the electrolyte and the negative electrode active material are suppressed, and the initial efficiency and / or lifespan of the battery are improved.

[0091] Specifically, the carbon layer may be formed by chemical vapor deposition (CVD) using at least one hydrocarbon gas selected from the group consisting of methane, ethane, and acetylene.

[0092] In this invention, the crystallinity of the carbon layer can be confirmed by calculating the D / G band ratio using Raman spectroscopy. Specifically, a Renishaw 2000 Raman microscope system and 532 nm laser excitation are used, and measurements can be taken with a low laser power density and a 30-second exposure time, using a 100x optical lens, to avoid the thermal effect of the laser. To reduce positional deviations, a total of 25 points are measured in a 5 μm × 5 μm area, and after fitting using a Lorentzian function, the average values ​​of the D and G bands can be calculated.

[0093] In one embodiment of the present invention, lithium byproducts may be present on the silicon-based particles. Specifically, the lithium byproducts may be present on the surface of the silicon-based particles or on the surface of the carbon layer. Alternatively, the lithium byproducts may be present between the surface layer (described later) and the silicon-based particles.

[0094] Specifically, the lithium by-product may refer to lithium compounds remaining near the surface of silicon-based particles or carbon layers after the production of silicon-based particles. As mentioned above, lithium by-products that have not reacted with the acid may remain even after the acid treatment process.

[0095] The lithium by-product may include one or more selected from the group consisting of Li2O, LiOH, and Li2CO3.

[0096] The presence or absence of the aforementioned lithium by-products can be confirmed by X-ray diffraction analysis (XRD) or X-ray photoelectron analysis (XPS).

[0097] The lithium by-product may be present in an amount of 5 parts by weight or less, based on 100 parts by weight of the total negative electrode active material. Specifically, it may be present in amounts of 0.01 to 5 parts by weight, 0.05 to 2 parts by weight, or 0.1 to 1 part by weight. More specifically, it may be present in amounts of 0.1 to 0.8 parts by weight, or 0.1 to 0.5 parts by weight. When the lithium by-product content satisfies the above range, side reactions in the slurry can be reduced, viscosity changes can be lowered, and aqueous processability characteristics can be improved. On the other hand, when the lithium by-product content is higher than the above range, the slurry exhibits basicity during formation, which leads to the occurrence of side reactions, changes in viscosity, and problems with aqueous processability.

[0098] The content of the lithium by-product can be calculated by measuring the amount of HCl solution in a specific interval where the pH changes during the titration process of an aqueous solution containing the negative electrode active material with an HCl solution using a titrator, and then calculating the amount of lithium by-product.

[0099] In one embodiment of the present invention, lithium by-products selected from the group consisting of crystalline lithium silicate, Li2O, LiOH, and Li2CO3 may be substantially absent or not present at all on the surface of the negative electrode active material. These lithium by-products can increase the pH of the negative electrode slurry, decrease its viscosity, and worsen the electrode condition of the negative electrode. By performing an acid treatment process on the negative electrode active material to remove by-products such as lithium silicate and Li2O present on the surface of the negative electrode active material, it is possible to achieve a desirable level of improvement in the quality of the negative electrode and the charge / discharge efficiency.

[0100] A silicon-based particle according to one embodiment of the present invention includes a surface layer provided on at least a portion of the silicon-based particle, the surface layer may contain Al, P, and O. In one embodiment of the present invention, the surface layer may further contain the element Li.

[0101] The surface layer may be in a form that coats at least a part of the silicon-based particles having a carbon layer provided on the surface. That is, the surface layer may be in a form that partially coats the surface of the particles or coats the entire surface of the particles. Examples of the shape of the surface layer include an island type or a thin film type, but the shape of the surface layer is not limited thereto.

[0102] The surface layer may be provided on at least a part of the outer surface of the carbon layer. That is, the surface layer is coated adjacent to the carbon layer, and SiO x (0 < x < 2) and may be provided in the form of a silicon-based particle-carbon layer-surface layer containing a Li compound. The surface layer may substantially or completely cover the carbon layer or may partially cover the carbon layer.

[0103] The surface layer is the SiO x (0 < x < 2) and may be provided on a region where no carbon layer is provided on the surface of the silicon-based particle containing a Li compound. That is, the surface layer is coated adjacent to the silicon-based particle containing SiO x [[ID=I4]](0 < x < 2) and a Li compound, and may be provided in the form of a silicon-based particle-surface layer containing SiO x (0 < x < 2) and a Li compound.

[0104] In one embodiment of the present invention, the Al may be contained in an amount of 0.05 parts by weight to 0.4 parts by weight based on 100 parts by weight in total of the negative electrode active material. Specifically, it may be contained in an amount of 0.1 parts by weight to 0.4 parts by weight, may be contained in an amount of 0.12 parts by weight to 0.35 parts by weight, or may be contained in an amount of 0.15 parts by weight to 0.3 parts by weight. [[ID=ZI]]

[0105] In one embodiment of the present invention, the P may be contained in an amount of 0.05 parts by weight to 2 parts by weight based on 100 parts by weight in total of the negative electrode active material. Specifically, it may be contained in an amount of 0.1 parts by weight to 1.5 parts by weight, or may be contained in an amount of 0.15 parts by weight to 1 part by weight.

[0106] The surface layer is Alz P w O v (0 < z ≤ 10, 0 < w ≤ 10, 0 < v ≤ 10) may include a phase. The Al z P w O v phase may include aluminum oxide, phosphorus oxide, aluminum phosphate, etc. z, y, and v represent the atomic number ratios. As an example, the Al z P w O v phase may include a mixture or compound formed from AlPO4 or Al(PO3)3, etc., but is not limited thereto.

[0107] The surface layer may include Li y Al z P w O v (0 < y ≤ 10, 0 < z ≤ 10, 0 < w ≤ 10, 0 < v ≤ 10) may include a phase. The Li y Al z P w O v phase may include aluminum oxide, phosphorus oxide, lithium oxide, aluminum phosphate, lithium salt, lithium phosphate, lithium aluminate, etc. y, z, w, and v represent the atomic number ratios. As an example, the Li y Al z P w O v phase may include a mixture or compound formed from Li3PO4, AlPO4, Al(PO3)3, or LiAlO2, etc., but is not limited thereto.

[0108] The y may satisfy 0 < y ≤ 3. The z may satisfy 0 < z ≤ 1. The w may satisfy 0.5 ≤ w ≤ 3. The v may satisfy 4 < v ≤ 10.

[0109] When an inorganic surface layer containing the aforementioned phase is provided, it is possible to prevent the phenomenon in which Li compounds contained in silicon-based particles react with the water in the slurry, thereby lowering the viscosity of the slurry. This has the effect of improving the stability of the electrode state and / or the charge / discharge capacity.

[0110] In one embodiment of the present invention, the surface layer may include an amorphous phase. Specifically, the surface layer may be an amorphous phase.

[0111] When the surface layer contains the amorphous phase described above, the movement of Li ions becomes easier than when it does not contain the amorphous phase. This effectively reduces side reactions in the slurry and allows for stable volume and / or efficiency.

[0112] In one embodiment of the present invention, the surface layer may further contain one or more substances selected from the group consisting of Li2O, LiOH, and Li2CO3. Generally, when a substance remains after doping silicon-based particles with lithium, it can be exposed to moisture and air, forming lithium byproducts such as Li2O, LiOH, and Li2CO3. Therefore, the surface layer may be in a form that contains one or more substances selected from the group consisting of Li2O, LiOH, and Li2CO3.

[0113] In one embodiment of the present invention, when the negative electrode active material is subjected to X-ray diffraction analysis, crystalline peaks originating from the surface layer do not necessarily appear. Specifically, Li contained in the surface layer y Al z P w O v(0 < y ≤ 10, 0 < z ≤ 10, 0 < w ≤ 10, 0 < v ≤ 10) crystalline peaks derived from the phase may not be detected. When crystalline peaks derived from the surface layer appear, there is a problem that the surface layer contains an excessive amount of crystalline substances, resulting in a decrease in capacity and / or efficiency. As an example, in the case of crystalline peaks derived from the surface layer, it can be known through the changes before and after the surface layer coating. Specifically, in the case of XRD, crystalline peaks are detected. When there is no difference in the XRD graphs of the negative electrode active material before and after the surface layer coating, it means that crystalline peaks derived from the surface layer do not appear, and it can be confirmed that the surface layer is formed in an amorphous phase.

[0114] In one embodiment of the present invention, the amorphous phase contained in the surface layer may be contained in an amount exceeding 50 parts by weight based on 100 parts by weight in total of the surface layer. Specifically, the amorphous phase may be contained in an amount of 60 parts by weight or more, 70 parts by weight or more, 80 parts by weight or more, 90 parts by weight or more, 95 parts by weight or more, or 99 parts by weight or more based on 100 parts by weight in total of the surface layer, and may also be contained in an amount of 100 parts by weight or less, or less than 100 parts by weight. By satisfying the above range, side reactions in the slurry can be effectively suppressed, and there is an effect that capacity and / or efficiency can be stably realized.

[0115] In one embodiment of the present invention, the surface layer may be contained in an amount of 10 parts by weight or less based on 100 parts by weight in total of the negative electrode active material. Specifically, it may be contained in an amount of 8 parts by weight or less, 6 parts by weight or less, or 5 parts by weight or less, and may also be contained in an amount of 0.1 parts by weight or more, or 0.5 parts by weight or more. More specifically, it may be contained in an amount of 1 part by weight or more and 5 parts by weight or less, or 1.5 parts by weight or more and 3 parts by weight or less. When the content of the surface layer is less than the above range, it is difficult to prevent gas generation in the slurry. When it is excessive compared to the above range, there is a problem that it is difficult to realize capacity or efficiency.

[0116] In one embodiment of the present invention, the weight ratio of the surface layer to the carbon layer may be 1:0.1 to 1:30. Specifically, it may be 1:0.5 to 1:5, 1:1 to 1:4, or 1:1 to 1:3. By satisfying such a range, the carbon layer and the surface layer can effectively coat the silicon-based composite particles, efficiently suppressing side reactions in the slurry, and stably achieving capacity and / or efficiency. On the other hand, if the content of the surface layer is excessively high compared to the carbon layer, it becomes difficult to achieve capacity or efficiency, and if the content of the carbon layer is excessively high compared to the surface layer, it becomes difficult to prevent gas generation in the slurry.

[0117] In one embodiment of the present invention, the surface layer may be included in an amount of 90 parts by weight or less based on 100 parts by weight of the carbon layer. Specifically, the surface layer may be included in an amount of 80 parts by weight or less, 70 parts by weight or less, 60 parts by weight or less, or 50 parts by weight or less based on 100 parts by weight of the carbon layer. Alternatively, the surface layer may be included in an amount of 0.1 parts by weight or more, 1 part by weight or more, 5 parts by weight or more, or 10 parts by weight or more based on 100 parts by weight of the carbon layer. By satisfying the above ranges, the carbon layer and the surface layer can effectively coat the silicon-based composite particles, efficiently suppressing side reactions in the slurry, and achieving stable capacity and / or efficiency.

[0118] The average particle size (D) of the negative electrode active material 50 The particle size may be 0.1 μm to 14 μm, more specifically 1 μm to 12 μm, and more specifically 1 μm to 10 μm. When the above range is met, the structural stability of the active material during charging and discharging can be ensured, the problem of volume expansion / contraction levels becoming large due to excessively large particle size can be prevented, and the problem of initial efficiency decreasing due to excessively small particle size can be prevented.

[0119] The BET specific surface area of ​​the negative electrode active material is 1 m². 2 / g~100m 2 It can also be expressed as / g, specifically 1m 2 / g~70m 2It may be / g, more specifically 1 m 2 / g to 50 m 2 / g, for example 2 m 2 / g to 30 m 2 It may be / g. When the above range is satisfied, side reactions with the electrolyte during charging and discharging of the battery can be reduced, so that the life characteristics of the battery can be improved.

[0120] <Method for manufacturing negative electrode active material> The present invention provides a method for manufacturing a negative electrode active material, specifically, the method for manufacturing the negative electrode active material described above.

[0121] One embodiment of the present invention is SiO x A step of forming particles containing a silicon-based oxide represented by (0 < x < 2); and a step of heat-treating after mixing the particles containing the silicon-based oxide and a lithium precursor are included, and a method for manufacturing a negative electrode active material of the present invention is provided.

[0122] The step of forming the particles containing the silicon-based oxide represented by the above SiO x (0 < x < 2) may include a step of heating and vaporizing Si powder and SiO2 powder in a vacuum and then depositing the vaporized mixed gas.

[0123] Specifically, the mixed powder of the Si powder and the SiO2 powder may be heat-treated at 1300°C to 1800°C, 1400°C to 1800°C, or 1400°C to 1600°C under vacuum.

[0124] The particles formed by the above method are represented by SiO x (0 < x < 2), and the silicon-based oxide is preferably a compound represented by SiO x (0.5 ≤ x ≤ 1.5) in terms of the structural stability of the active material. The formed silicon-based oxide may have the form of SiO.

[0125] In the method for manufacturing a negative electrode active material according to one embodiment of the present invention, before mixing the lithium precursor, SiO xA step of forming a carbon layer on the surface of particles containing a silicon-based oxide represented by (0 < x < 2) may be further included.

[0126] The carbon layer is disposed or formed on the particles and can function as a protective layer that appropriately controls the volume expansion due to charge and discharge of the negative electrode active material and prevents side reactions with the electrolyte. On the other hand, the carbon layer formation step may be performed before the mixing step of the particles and the lithium precursor in terms of preventing changes in the crystalline phase and amorphous phase of the negative electrode active material.

[0127] The carbon layer may be formed by using a chemical vapor deposition (CVD) method using a hydrocarbon gas or a method of carbonizing a substance serving as a carbon source.

[0128] Specifically, after the formed particles are introduced into a reactor, chemical vapor deposition (CVD) may be performed at 600°C to 1200°C using a hydrocarbon gas so as to prevent changes in the crystalline phase and amorphous phase. The hydrocarbon gas may be at least one hydrocarbon gas selected from the group consisting of methane, ethane, propane, and acetylene, and may be heat-treated at 900°C to 1000°C.

[0129] The particle size of the particles containing the silicon-based oxide may be adjusted by a method such as a ball mill, a jet mill, or air classification, and is not limited thereto.

[0130] The method for manufacturing a negative electrode active material according to an embodiment of the present invention may include a step of heat-treating after mixing the particles containing the silicon-based oxide and a lithium precursor.

[0131] By the step of heat-treating after mixing the particles containing the silicon-based oxide and the lithium precursor, SiO x(0 < x < 2) and silicon-based particles containing a Li compound can be produced. In the silicon-based particles, the content of the crystalline phase Li2SiO3 in the particles is higher than the content of the crystalline phase Li2Si2O5 and the content of the crystalline phase Li4SiO4, and the total content of the crystalline phases present in the particles may be higher than the total content of the amorphous phase.

[0132] The lithium precursor can be made to contain a Li compound in the particles containing the silicon-based oxide by a heat treatment step described later. Specifically, the lithium precursor may contain at least one selected from the group consisting of lithium metal, LiOH, LiH, and Li2CO3. Specifically, it may contain lithium metal in terms of preventing additional oxidation during the reaction between the particles containing the silicon-based oxide and the lithium precursor. The lithium precursor may be in particulate form, specifically, it may be lithium metal powder.

[0133] Specifically, the lithium precursor may contain lithium metal powder (SLMP, stabilized lithium metal powder).

[0134] In one embodiment of the present invention, the particles containing the silicon-based oxide and the lithium precursor may be solid mixed. Specifically, during the mixing, the particles containing the silicon-based oxide and the lithium precursor may be in a solid state. In this case, since the porosity and specific surface area in the negative electrode active material can be controlled to appropriate levels during the formation of the negative electrode active material by heat treatment described later, volume expansion control of the negative electrode active material during charge and discharge can be preferably performed.

[0135] In one embodiment of the present invention, the weight ratio of the particles containing the silicon-based oxide to the lithium precursor may be 80:20 to 94:6. Specifically, it may be 85:15 to 93:7, 88:12 to 93:7, or 90:10 to 92:8.

[0136] In one embodiment of the present invention, the silicon oxide-containing particles and the lithium precursor may be mixed while undergoing heat treatment under an inert gas atmosphere.

[0137] The heat treatment temperature of the silicon oxide-containing particles and lithium precursor mixture may be 650°C to 950°C, specifically 670°C to 900°C, or 700°C to 850°C. Mixing while heat treatment under the above conditions is preferable because it facilitates the development of the crystalline phase lithium silicate of Li2SiO3.

[0138] The heat treatment process within the aforementioned temperature range allows the manufactured silicon-based particles to contain Li compounds at appropriate levels. Specifically, the Li compounds can be distributed on the surface, inside, or both the surface and inside of the silicon-based particles. The silicon-based particles may contain lithium silicate as the aforementioned Li compound, and may further contain lithium silicide or lithium oxide, etc.

[0139] The aforementioned anode active material can be manufactured by the heat treatment process within the temperature range described above. Specifically, the lithium can be distributed in the particles in the form of lithium silicate by the heat treatment process within the temperature range described above, thereby removing the irreversible capacity of the silicon oxide-containing particles and improving the initial efficiency and charge / discharge efficiency of the anode active material. Specifically, the lithium may exist in the form of at least one crystalline lithium silicate or amorphous lithium silicate selected from the group consisting of crystalline Li2SiO3, crystalline Li4SiO4, and crystalline Li2Si2O5. In this case, in the anode active material manufactured by the method for manufacturing the anode active material of the present invention, the content of crystalline Li2SiO3 may be greater than the sum of the content of crystalline Li2Si2O5 and crystalline Li4SiO4, and the content of crystalline Li2SiO3 may be 60 parts by weight or more based on 100 parts by weight of the total crystalline lithium silicate.

[0140] Furthermore, the heat treatment process within the aforementioned temperature range allows the total content of the crystalline phase present in the silicon-based particles to be greater than the total content of the amorphous phase. This reduces the content of lithium oxide and lithium silicate that react with moisture, preventing gas generation and viscosity changes in the negative electrode slurry, and improving the phase stability of the slurry containing the negative electrode active material. As a result, the negative electrode containing the negative electrode active material and the secondary battery containing the negative electrode can be improved in quality and charge / discharge efficiency.

[0141] If the heat treatment process is carried out at a temperature below 650°C, the amorphous phase content of the negative electrode active material produced by the above manufacturing method will increase, which may cause problems with the processability of the aqueous slurry. If the heat treatment process is carried out at a temperature exceeding 950°C, the crystalline phase SiO2 content will increase, and the crystalline phase SiO2 will act as a resistor during charging and discharging, making charging and discharging difficult, which is undesirable because it will result in a decrease in charge / discharge capacity and efficiency.

[0142] Furthermore, the heat treatment may be performed for 1 to 12 hours, specifically 2 to 8 hours. When the treatment is performed within this range, the lithium silicate can be uniformly distributed within the silicon-based particles, thereby further improving the aforementioned effect of improving charge and discharge efficiency.

[0143] Furthermore, the heat treatment may be carried out in an inert atmosphere in order to prevent further oxidation of the silicon oxide-containing particles and the lithium precursor. Specifically, the heat treatment may be carried out in an inert atmosphere consisting of at least one gas selected from the group consisting of nitrogen gas, argon gas, and helium gas.

[0144] The method for producing the negative electrode active material of the present invention may further include a step of performing an acid treatment after the heat treatment step.

[0145] After the heat treatment step, at least a portion of the surface of the formed silicon-based particles is coated with a lithium compound (lithium by-product). Specifically, the SiO xIn the process of doping particles containing (0 < x < 2) with a Li compound, lithium compounds, that is, lithium by-products formed by unreacted lithium, remain near the surface of the silicon-based particles. The lithium by-products may be lithium silicate, Li2O, etc., which can increase the pH of the negative electrode slurry containing the negative electrode active material, lower the viscosity, and cause deterioration of the electrode state of the negative electrode. Accordingly, an acid treatment step is performed after the heat treatment step to remove by-products such as lithium silicate and Li2O present on the surface of the negative electrode active material, thereby realizing the improvement of the quality of the negative electrode and the improvement of the charge-discharge efficiency at a preferable level.

[0146] Specifically, the acid treatment may be performed for 0.3 hours to 6 hours, specifically 0.5 hours to 4 hours, with an acid aqueous solution containing at least one acid selected from the group consisting of hydrochloric acid (HCl), sulfuric acid (H2SO4), nitric acid (HNO3), and phosphoric acid (H3PO4), specifically at least one acid selected from the group consisting of hydrochloric acid (HCl), sulfuric acid (H2SO4), and nitric acid (HNO3). This is preferable in that by-products present on the surface of the negative electrode active material can be easily removed by this step.

[0147] The pH of the acid aqueous solution at 23°C may be 3 or less, specifically 2 or less, more specifically 1 or less, in terms of easily removing by-products present on the surface of the negative electrode active material.

[0148] The method for manufacturing the negative electrode active material of the present invention may further include a step of providing a surface layer on at least a part of the silicon-based particles formed after the heat treatment step. As an example, when the acid treatment step is performed after the heat treatment step, it may further include a step of providing the surface layer after the acid treatment step.

[0149] The surface layer may be provided by mixing the silicon-based particles and aluminum phosphate. Specifically, i) a step of dry-mixing the silicon-based particles and aluminum phosphate and then performing heat treatment, or ii) a step of mixing the silicon-based particles and aluminum phosphate in a solvent, followed by heat treatment to vaporize the solvent while reacting the silicon-based particles and aluminum phosphate, may be used to form a surface layer on at least a part of the silicon-based particles. When forming the surface layer by the above method, a surface layer can be easily formed by reacting lithium by-products formed or remaining in the manufacturing process of the silicon-based particles with aluminum phosphate.

[0150] The aluminum phosphate may be in the form of Al b P c O d (0 < b ≤ 10, 0 < c ≤ 10, 0 < d ≤ 10). Specifically, it may be Al(PO3)3 or AlPO4, and is not limited thereto. Salts used in the industry for forming the surface layer may be appropriately employed.

[0151] Alternatively, iii) a step of dry-mixing the silicon-based particles, an aluminum precursor, and a phosphorus precursor and then performing heat treatment, or iv) a step of mixing the silicon-based particles, an aluminum precursor, and a phosphorus precursor in a solvent, followed by heat treatment to vaporize the solvent while reacting the silicon-based composite particles, the aluminum precursor, and the phosphorus precursor, may be used to form a surface layer on at least a part of the silicon-based particles. When forming the surface layer by the above method, a surface layer can be easily formed by reacting lithium by-products, an aluminum precursor, and a phosphorus precursor formed in the manufacturing process of the silicon-based composite particles.

[0152] The aluminum precursor may be aluminum oxide in the form of Al a O b (0 < a ≤ 10, 0 < b ≤ 10), and specifically, it may be Al2O3.

[0153] Alternatively, the aluminum precursor may be aluminum hydroxide, aluminum nitrate, aluminum sulfate, etc. Specifically, it may be Al(OH)3, Al(NO3)3·9H20, or Al2(SO4)3, but is not limited thereto, and an aluminum precursor used in the art to form the surface layer may be appropriately adopted.

[0154] The phosphorus precursor is P c O d It may be phosphorus oxide in the form of (0 < c ≦ 10, 0 < d ≦ 10).

[0155] Alternatively, the phosphorus precursor may be ammonium phosphate, diammonium phosphate, phosphoric acid, etc. Specifically, it may be (NH4)3PO4, (NH4)2HPO4, H3PO4, or NH4H2PO4, but is not limited thereto, and a phosphorus precursor used in the art to form the surface layer may be appropriately adopted.

[0156] Alternatively, in step v), the silicon-based particles and the Li-Al-P-O-based precursor are dry-mixed and heat-treated, or in step vi), the silicon-based composite particles and the Li-Al-P-O-based precursor are mixed in a solvent and then heat-treated to vaporize the solvent while reacting the silicon-based composite particles and the Li-Al-P-O-based precursor, so that a surface layer may be formed on at least a part of the silicon-based particles. When forming the surface layer by the above method, the Li-Al-P-O-based precursor can be directly introduced to form the surface layer.

[0157] The Li-Al-P-O-based precursor is Li y Al z P w O v It may be in the form of (0 < y ≦ 10, 0 < z ≦ 10, 0 < w ≦ 10, 0 < v ≦ 10). Specifically, it may be a mixture or compound formed complexly from Li3PO4, AlPO4, Al(PO3)3, LiAlO2, etc., but is not limited thereto, and a configuration used in the art to form the surface layer may be appropriately adopted.

[0158] In the step of providing a surface layer on at least a part of the silicon-based particles, the heat treatment may be performed at 500 °C to 700 °C, specifically, it may also be performed at 550 °C to 650 °C. However, it is not limited thereto and may vary depending on the salt or precursor used, etc.

[0159] When the heat treatment temperature satisfies the above range, the reaction between the salt or precursor and the Li by-product occurs well, and since the surface layer contains Li, the durability of the formed negative electrode active material against moisture increases, the entry and exit of Li ions by the surface layer becomes easy, the lithium diffusion resistance on the surface of the negative electrode active material decreases, and there is an effect that the discharge rate characteristic (rate capability) is excellent.

[0160] The solvent may be water or ethanol, and is not limited thereto, and solvents used in the industry may be appropriately adopted.

[0161] The surface layer formed on the silicon-based particles preferably contains Li y Al z P w O v (0 < y ≤ 10, 0 < z ≤ 10, 0 < w ≤ 10, 0 < v ≤ 10) phase, and the Li y Al z P w O v phase may be an amorphous phase.

[0162] <Negative electrode> The negative electrode according to an embodiment of the present invention may include the above-described negative electrode active material. Specifically, the negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The negative electrode active material layer may include the negative electrode active material. Further, the negative electrode active material layer may further include a binder, a thickener, and / or a conductive material.

[0163] The negative electrode active material layer may be formed by applying a negative electrode slurry containing a negative electrode active material, a binder, a thickener, and / or a conductive material to at least one side of a current collector, drying, and rolling. The negative electrode slurry may further contain additional negative electrode active material.

[0164] As the additional negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and SiO2. β Examples include lithium-doped and dedoped metal oxides such as (0<β<2), SnO2, vanadium oxide, lithium titanium oxide, and lithium vanadium oxide; or composites containing the metallic compound and carbonaceous material, such as Si-C composites or Sn-C composites. One or more of these mixtures may be used. A metallic lithium thin film may also be used as the negative electrode active material. As for the carbon material, either low-crystallinity carbon or high-crystallinity carbon may be used. Examples of low-crystalline carbon include soft carbon and hard carbon, while examples of high-crystalline carbon include amorphous, plate-like, flaky, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0165] The additional negative electrode active material may be a carbon-based negative electrode active material. In one embodiment of the present invention, the weight ratio of the negative electrode active material contained in the negative electrode slurry to the additional negative electrode active material may be 10:90 to 90:10, and more specifically, it may be 10:90 to 50:50.

[0166] The negative electrode slurry may contain a solvent for forming the negative electrode slurry. Specifically, the solvent for forming the negative electrode slurry may contain at least one selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol, specifically distilled water, in order to facilitate the dispersion of the components.

[0167] A negative electrode slurry containing a negative electrode active material according to one embodiment of the present invention may have a pH of 7 to 11 at 25°C. A pH within this range of the negative electrode slurry has the effect of stabilizing the rheological properties of the slurry. Conversely, if the pH of the negative electrode slurry is less than 7 or greater than 11, decomposition of carboxymethylcellulose (CMC), used as a thickening agent, occurs, leading to a decrease in the viscosity of the slurry and a reduction in the dispersion of the active material contained in the slurry.

[0168] The negative electrode current collector is not particularly limited, as long as it does not cause a chemical change in the battery and is conductive. For example, the current collector may be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. Specifically, transition metals that readily adsorb carbon, such as copper and nickel, may be used as the current collector. The thickness of the current collector may be 6 μm to 20 μm, but is not limited thereto.

[0169] The binder may contain at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and substances in which the hydrogen atoms of these substances are substituted with Li, Na, or Ca, and may also contain various copolymers thereof.

[0170] The conductive material is not particularly limited as long as it does not cause a chemical change in the battery and is conductive. For example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives may be used.

[0171] The aforementioned thickening agent may be carboxymethylcellulose (CMC), but is not limited thereto, and any other thickening agent used in the present art may be used as appropriate.

[0172] In one embodiment of the present invention, the weight ratio of the negative electrode active material contained in the negative electrode slurry to the additional negative electrode active material may be 1:99 to 30:70, specifically 5:95 to 30:70, or 10:90 to 20:80.

[0173] In one embodiment of the present invention, the total negative electrode active material contained in the negative electrode slurry may be in an amount of 60 to 99 parts by weight, specifically 70 to 98 parts by weight, based on 100 parts by weight of the total solid content of the negative electrode slurry.

[0174] In one embodiment of the present invention, the binder may be included in an amount of 0.5 to 30 parts by weight, specifically 1 to 20 parts by weight, based on 100 parts by weight of the total solid content of the negative electrode slurry.

[0175] In one embodiment of the present invention, the conductive material may be included in an amount of 0.5 to 25 parts by weight, specifically 1 to 20 parts by weight, based on 100 parts by weight of the total solid content of the negative electrode slurry.

[0176] In one embodiment of the present invention, the thickening agent may be included in an amount of 0.5 to 25 parts by weight, more specifically 0.5 to 20 parts by weight, or more specifically 1 to 20 parts by weight, based on 100 parts by weight of the total solid content of the negative electrode slurry.

[0177] A negative electrode slurry according to one embodiment of the present invention may further contain a solvent for forming the negative electrode slurry. Specifically, the solvent for forming the negative electrode slurry may contain at least one selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol, specifically distilled water, in order to facilitate the dispersion of components.

[0178] In one embodiment of the present invention, the weight of the solid content of the negative electrode slurry may be 20 to 75 parts by weight, specifically 30 to 70 parts by weight, based on 100 parts by weight of the total negative electrode slurry.

[0179] <Secondary battery> The secondary battery according to an embodiment of the present invention may include the negative electrode according to the above-described embodiment. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and the negative electrode is the same as the above-described negative electrode. Since the negative electrode has been described above, a specific description thereof will be omitted.

[0180] The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and containing the positive electrode active material.

[0181] In the positive electrode, the positive electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or a material obtained by surface treatment of the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. may be used. Further, the positive electrode current collector may usually have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase the adhesion of the positive electrode active material. For example, it may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric body, etc.

[0182] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material is a layered compound such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe3O4; chemical formula Li 1+c1 Mn 2-c1 O4 (0 ≦ c1 ≦ 0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7; chemical formula LiNi 1-c2 M c2 O2 (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01 ≦ c2 ≦ 0.5) of Ni-site type lithium nickel oxide; chemical formula LiMn 2-c3 Mc3 Lithium manganese composite oxides represented as O2 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, satisfying 0.01 ≤ c3 ≤ 0.1) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); or LiMn2O4 in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion, etc., are examples, but are not limited thereto. The positive electrode may also be metallic lithium (Li-metal).

[0183] The positive electrode active material layer may also include a positive electrode conductive material and a positive electrode binder, along with the positive electrode active material described above.

[0184] In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and can be used without particular limitation as long as it has electronic conductivity without causing a chemical change in the battery that is constructed. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these alone or a mixture of two or more may be used.

[0185] Furthermore, the positive electrode binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more may be used.

[0186] A separator separates the negative and positive electrodes and provides a passage for lithium ions to move. Generally, any separator used in secondary batteries can be used without particular limitations, but it is especially preferable that it has low resistance to ion movement in the electrolyte and excellent electrolyte moisture absorption capacity. Specifically, porous polymer films, such as porous polymer films made from polyolefin polymers like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or laminated structures of two or more layers thereof may be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, to ensure heat resistance or mechanical strength, coated separators containing ceramic components or polymeric substances may be used, and they may be selectively used as single-layer or multi-layer structures.

[0187] Examples of the aforementioned electrolytes include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries. Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0188] As the non-aqueous organic solvent, for example, aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate, and ethyl propionate may be used.

[0189] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, can be preferably used as high-viscosity organic solvents because they have high dielectric constants and dissociate lithium salts well. Furthermore, when such cyclic carbonates are mixed with linear carbonates with low viscosity and low dielectric constant, such as dimethyl carbonate and diethyl carbonate, in appropriate proportions, an electrolyte with high electrical conductivity can be produced, and therefore they can be used even more preferably.

[0190] As the metal salt, a lithium salt may be used, and the lithium salt is a substance that is easily soluble in the non-aqueous electrolyte, for example, as the anion of the lithium salt, F - Cl - , 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 - You may use one or more selected from the group consisting of the following:

[0191] In addition to the components of the electrolyte, the electrolyte may further contain one or more additives for the purpose of improving the battery's lifespan, suppressing the decrease in battery capacity, and improving the battery's discharge capacity, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexalic acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride.

[0192] According to another embodiment of the present invention, a battery module and a battery pack containing the secondary battery as a unit cell are provided. Since the battery module and battery pack contain the secondary battery having high capacity, high rate characteristics and cycle characteristics, they can be used as a power source for medium to large devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems. [Examples]

[0193] <Examples and Comparative Examples> Example 1 100g of a powder mixture of Si and SiO2 in a 1:1 molar ratio was vacuum-heated in a reaction furnace at a sublimation temperature of 1,400°C. The vaporized Si-SiO2 mixture was then reacted in a vacuum cooling zone with a cooling temperature of 800°C to condense into a solid phase. Subsequently, pre-silicon particles were produced by heat treatment in an inert atmosphere at 800°C. These pre-silicon particles were then ground for 3 hours using a ball mill after adding 15 SUS ball media to the particles, resulting in a particle size of 6 μm (D 50 Silicon-based particles of size ) were manufactured. Then, while maintaining an inert atmosphere by flowing Ar gas, the silicon-based particles were positioned in the hot zone of the CVD apparatus, and methane was blown into the 900°C hot zone using Ar as the carrier gas. -1 The reaction was carried out in Torr for 20 minutes to form a carbon layer on the surface of the silicon-based particles.

[0194] A composition for forming a negative electrode active material was produced by solid-phase mixing silicon-based particles on which the carbon layer was formed with lithium metal powder as a lithium precursor in a weight ratio of 90:10. The aforementioned composition for forming the negative electrode active material was heat-treated at 800°C for 3 hours.

[0195] The heat-treated negative electrode active material forming composition was acid-treated with an aqueous hydrochloric acid solution having a pH of 1 at 23°C for 1 hour.

[0196] The substance obtained by the acid treatment described above was used as the negative electrode active material in Example 1. 50 Its diameter is 6 μm, and its specific surface area is 3 m². 2 It was / g.

[0197] Example 2 The negative electrode active material was produced in the same manner as in Example 1, except that the silicon-based particles on which the carbon layer was formed and lithium metal powder as a lithium precursor were solid-phase mixed in a weight ratio of 92:8 to produce the composition for forming the negative electrode active material.

[0198] Example 3 A composition for forming a negative electrode active material was produced by solid-phase mixing silicon-based particles on which the carbon layer is formed with lithium metal powder as a lithium precursor in a weight ratio of 90:10, and the negative electrode active material was produced in the same manner as in Example 1, except that no acid treatment was performed.

[0199] Example 4 The negative electrode active material was produced in the same manner as in Example 1, except that a composition for forming a negative electrode active material was produced by solid-phase mixing silicon-based particles on which the carbon layer was formed with lithium metal powder as a lithium precursor in a weight ratio of 90:10, and the composition for forming a negative electrode active material was heat-treated at 850°C for 3 hours.

[0200] Example 5 98.5 g of the negative electrode active material obtained in Example 1 was mixed with 31.5 g of Al(PO3), and then heat-treated at 600°C to form a surface layer containing Li, Al, P, and O on the surface. This mixture was used as the negative electrode active material for Example 5.

[0201] Example 6 The negative electrode active material obtained in Example 1 is D 50 The negative electrode active material was prepared in the same manner as in Example 1, except that it was ground to a size of 8 μm.

[0202] Comparative Example 1 The anode active material was produced in the same manner as in Example 1, except that the anode active material forming composition was heat-treated at 500°C for 3 hours and no acid treatment was performed.

[0203] Comparative Example 2 The negative electrode active material-forming composition was heat-treated at 1000°C for 3 hours, and the negative electrode active material was produced in the same manner as in Example 1, except that acid treatment was not performed.

[0204] Comparative Example 3 The negative electrode active material-forming composition was heat-treated at 1000°C for 3 hours, and the negative electrode active material was produced in the same manner as in Example 1, except that acid treatment was performed for 3 hours.

[0205] Comparative Example 4 The silicon-based oxide particles formed with the carbon layer and lithium metal powder as a lithium precursor were solid-phase mixed at a weight ratio of 94:6 to produce a negative electrode active material-forming composition. The negative electrode active material-forming composition was heat-treated at 500°C for 3 hours, and the negative electrode active material was produced in the same manner as in Example 1, except that acid treatment was not performed.

[0206] Comparative Example 5 The silicon-based oxide particles formed with the carbon layer and lithium metal powder as a lithium precursor were solid-phase mixed at a weight ratio of 94:6 to produce a negative electrode active material-forming composition. The negative electrode active material-forming composition was heat-treated at 1000°C for 3 hours, and the negative electrode active material was produced in the same manner as in Example 1, except that acid treatment was performed for 3 hours.

[0207] Comparative Example 6 The negative electrode active material obtained in Example 1 was 50 The negative electrode active material was produced in the same manner as in Example 1, except that it was pulverized to a size of 15 μm. The negative electrode active materials produced in Examples 1 to 6 and Comparative Examples 1 to 6 were analyzed by the following method and shown in Table 1.

[0208] <Measurement of p2 / p1> In Table 1, p2 / p1 was 29 Calculated as follows by Si MAS NMR analysis. -p2 / p1: 29The ratio of the peak height of Li2Si2O5 (p2) to the peak height of Li2SiO3 (p1) during Si MAS NMR analysis.

[0209] <Measurement of crystalline phase Li2Si2O5, crystalline phase Li2SiO3, crystalline phase Li4SiO4, crystalline phase SiO2, crystalline phase Si, total content of crystalline phase, and total content of amorphous phase> Measurements were performed using an XRD (X-ray diffraction) instrument (product name: D4-endeavor, manufacturer: bruker). The light source type and wavelength used was the X-ray wavelength generated by Cu Kα, with a light source wavelength (λ) of 0.15406 nm. After mixing the reference material MgO and the negative electrode active material in a weight ratio of 20:80, the mixture was placed in a cylindrical holder with a diameter of 2.5 cm and a height of 2.5 mm. The sample was then flattened with a glass slide to ensure a constant height within the holder, preparing the sample for XRD analysis. The scan time was set to 1 hour and 15 minutes, the measurement area was set to a 2θ range of 10° to 90°, and the step time and step size were set to scan 2θ at a rate of 0.02° per second. The measurement results were analyzed using X-ray diffraction pattern analysis software to obtain the X-ray diffraction profile obtained by Rietveld purification. Based on the above analysis, the total content of crystalline phases Li2Si2O5, Li2SiO3, Li4SiO4, SiO2, and Si, as well as the total content of amorphous phases, were measured.

[0210] [Table 1]

[0211] - The negative electrode active materials of Examples 1-6 and Comparative Examples 1-6 do not contain crystalline Li4SiO4. The D of the negative electrode active material 50 The PSD (Photon Scale Degradation) was analyzed using a microtrac device.

[0212] The specific surface area of ​​the negative electrode active material was measured using a BET measuring device (BEL-SORP-MAX, Nippon Bell) by degassing at 200°C for 8 hours and then performing N2 adsorption / desorption at 77K.

[0213] Experimental example: Evaluation of discharge capacity, initial efficiency, and lifespan (capacity retention rate) characteristics. A negative electrode and a battery were manufactured using the negative electrode active materials of the examples and comparative examples, respectively. A mixture was prepared by mixing the aforementioned negative electrode active material, carbon black as a conductive material, and PAA (polyacrylic acid) as a binder in a weight ratio of 80:10:10. Then, 7.8g of distilled water was added to 5g of the mixture and stirred to produce a negative electrode slurry. The negative electrode slurry was applied to a copper (Cu) metal thin film, which was a negative electrode current collector with a thickness of 20μm, and dried. During this process, the temperature of the circulating air was 60°C. Next, the film was rolled (rolled in a roll press) and dried in a vacuum oven at 130°C for 12 hours to produce a negative electrode.

[0214] The manufactured negative electrode and 1.7671 cm 2 A circularly cut lithium (Li) metal thin film was used as the positive electrode. A porous polyethylene separator was interposed between the positive electrode and the negative electrode, and an electrolyte solution containing 0.5 parts by weight of vinylene carbonate dissolved in a mixed solution of ethyl methyl carbonate (EMC) and ethylene carbonate (EC) in a volume ratio of 7:3, and LiPF6 at a concentration of 1M was injected to produce a lithium coin half-cell.

[0215] The manufactured batteries were subjected to charging and discharging tests to evaluate their discharge capacity, initial efficiency, and capacity retention rate, and these results are shown in Table 2 below.

[0216] The first and second cycles were charged and discharged at 0.1C, and from the third to the 49th cycle, they were charged and discharged at 0.5C. The 50th cycle ended in a charged state (lithium was in the negative electrode).

[0217] Charging conditions: CC (constant current) / CV (constant voltage) (5mV / 0.005C current cut-off) Discharge condition: CC (constant current) condition 1.5V

[0218] The discharge capacity (mAh / g) and initial efficiency (%) were derived from the results of a single charge-discharge cycle. Specifically, the initial efficiency (%) was derived by the following calculation. Initial efficiency (%) = (1st discharge capacity / 1st charge capacity) × 100 The capacity retention rates were derived using the following calculations. Capacity retention rate (%) = (49th discharge capacity / 1st discharge capacity) × 100

[0219] [Table 2]

[0220] In Table 2, Examples 1 to 6 using the negative electrode active material according to the present invention have a high content of the crystalline phase Li2SiO3, resulting in less loss of discharge capacity per unit weight due to the increased Li content in the negative electrode active material. Furthermore, because the total content of the crystalline phase in the negative electrode active material is greater than the total content of the amorphous phase, the phase stability of the slurry is improved. This confirms that the electrochemically stable lithium silicate structure of Li2SiO3 significantly increases initial efficiency and lifetime characteristics.

[0221] In Example 5, by providing a surface layer containing Li, Al, P, and O on the surface of the negative electrode active material, it is possible to prevent the phenomenon in which the Li compound contained in the silicon-based particles reacts with the moisture in the slurry and lowers the viscosity of the slurry. This confirms that the initial efficiency and lifetime characteristics are further improved.

[0222] In contrast, Comparative Examples 1 to 6 show that, based on 100 parts by weight of the total crystalline silicate, the crystalline phase Li2SiO3 is contained in less than 60 parts by weight, or the total content of the crystalline phase is low, resulting in high capacity loss per unit weight or an unstable structure of Li2Si2O5, leading to low initial efficiency and / or low lifetime characteristics. In particular, in the case of Comparative Examples 4 and 5, although the discharge capacity increases due to the low Li content, the efficiency decreases by more than 10%, and the lifetime is worse by more than 50%.

Claims

1. SiO ｘ A negative electrode active material comprising silicon-based particles containing (0 < x < 2) and Li compounds, The Li compound is a crystalline Li ２ SiO ３ And, crystalline phase Li ４ SiO ４ and crystalline phase Li ２ Si ２ O ５ The lithium silicate comprises at least one of the following, The content of the crystalline phase Li ２ SiO ３ is more than the total of the content of the crystalline phase Li ２ Si ２ O ５ and the content of the crystalline phase Li ４ SiO ４ and is The crystalline phase Li ２ SiO ３ The content of is 60 parts by weight or more, based on a total of 100 parts by weight of the crystalline lithium silicate. The total content of the crystalline phase present in the silicon-based particles is greater than the total content of the amorphous phase. The negative electrode active material wherein the total content of the crystalline phase present in the silicon-based particles is 64 parts by weight or more and 80 parts by weight or less, based on 100 parts by weight of the total silicon-based particles.

2. The negative electrode active material according to claim 1, wherein the element Li is contained in an amount of more than 7 parts by weight and no more than 10 parts by weight, based on a total of 100 parts by weight of the negative electrode active material.

3. The Li compound is a crystalline Li ２ SiO ３ and crystalline phase Li ２ Si ２ O ５ The negative electrode active material according to claim 1, comprising:

4. The crystalline phase Li ２ SiO ３ The negative electrode active material according to claim 1, wherein it is contained in an amount of 15 parts by weight or more and 50 parts by weight or less, based on a total of 100 parts by weight of the silicon-based particles.

5. The crystalline phase Li ２ SiO ３ Content and crystalline phase Li ２ Si ２ O ５ The difference in content from the above is 1 to 50 parts by weight based on a total of 100 parts by weight of the silicon-based particles, as described in claim 1.

6. The crystalline phase Li ４ SiO ４ The negative electrode active material according to claim 1, which does not contain the negative electrode active material.

7. ２９ During Si-MAS-NMR analysis, Li appears as a chemical shift peak in the -70 ppm to -80 ppm range. ２ SiO ３ The height of peak p1 is the Li that appears at the chemical shift peak between -90 ppm and -100 ppm. ２ Si ２ O ５ The negative electrode active material according to claim 1, wherein the height of the peak p2 is greater than that of the peak p2.

8. ２９ During Si-MAS-NMR analysis, Li appears as a chemical shift peak in the -70 ppm to -80 ppm range. ２ SiO ３ Li appears in the chemical shift peaks between -90 ppm and -100 ppm relative to the height of peak p1. ２ Si ２ O ５ The negative electrode active material according to claim 1, wherein the ratio of the peak heights p2 / p1 is 1 or less.

9. ２９ During Si-MAS-NMR analysis, Li appears as a chemical shift peak between -60 ppm and -69 ppm. ４ SiO ４ The negative electrode active material according to claim 1, wherein the peak p3 is absent.

10. Crystal phase SiO ２ The negative electrode active material according to claim 1, wherein the silicon-based particles are included in an amount of less than 5 parts by weight based on a total of 100 parts by weight.

11. The negative electrode active material according to claim 1, further comprising a carbon layer provided on the silicon-based particles.

12. The negative electrode active material according to claim 1, further comprising a surface layer provided on the silicon-based particles containing Al, P, and O.

13. SiO ｘ A step of forming particles containing a silicon-based oxide represented by (0 < x < 2), and A step of heat treatment after mixing the silicon oxide-containing particles with a lithium precursor, A method for producing a negative electrode active material according to any one of claims 1 to 12, including the method described in any one of claims 1 to 12.

14. The method for producing a negative electrode active material according to claim 13, further comprising the step of performing an acid treatment after the heat treatment step.

15. The method for producing a negative electrode active material according to claim 13, further comprising the step of providing a surface layer on at least a portion of the silicon-based particles formed after the heat treatment step.

16. The method for producing a negative electrode active material according to claim 13, wherein the heat treatment is performed at 650°C to 950°C.

17. The method for producing a negative electrode active material according to claim 13, wherein the heat treatment is performed for 1 to 12 hours.

18. Negative electrode current collector, and A negative electrode active material layer disposed on at least one side of the negative electrode current collector, Includes, The negative electrode comprises a negative electrode material containing the negative electrode active material described in any one of claims 1 to 12.

19. The negative electrode according to claim 18, The positive electrode opposite the negative electrode, A separator interposed between the negative electrode and the positive electrode, and electrolyte A secondary battery containing a battery.

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