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 including the same, a secondary battery including the same, and a method for producing the negative electrode active material.

Description

Technical Field

[0001] 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 manufacturing a negative electrode active material.

[0002] This application claims the benefit of the filing date of Korean Patent Application No. 10-2022-0131448, filed with the Korean Intellectual Property Office on October 13, 2022, and all of its content is incorporated herein.

Background Art

[0003] Recently, with the rapid spread of electronic devices using batteries, such as mobile phones, notebook computers, and electric vehicles, the demand for secondary batteries that are small, light, and relatively high in capacity has been rapidly increasing. In particular, lithium secondary batteries have attracted attention as a driving power source for portable devices because they are lightweight and have a high energy density. As a result, research and development efforts to improve the performance of lithium secondary batteries have been actively promoted.

[0004] Generally, a lithium secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, an electrolyte solution, and an organic solvent. In addition, an active material layer containing a positive electrode active material and a negative electrode active material can be formed on a current collector for the positive electrode and the negative electrode. Generally, lithium-containing metal oxides such as LiCoO2 and LiMn2O4 are used as the positive electrode active material for the positive electrode, and carbon-based active materials and silicon-based active materials that do not contain lithium are used as the negative electrode active material for the negative electrode.

[0005] In the case of a silicon-based active material in the negative electrode active material, it is noted for having a higher capacity and excellent high-speed charging characteristics compared to a carbon-based active material. However, the silicon-based active material has a disadvantage in that the degree of volume expansion / contraction due to charge / discharge is large and the irreversible capacity is large, resulting in low initial efficiency.

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

[0007] Regarding 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 decrease in the charge / 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 silicon-based oxides and improve the charge / discharge efficiency of the negative electrode manufactured therefrom.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0010] 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 manufacturing the negative electrode active material.

Means for Solving the Problems

[0011] One embodiment of the present invention is SiO xSilicon-based particles containing (0 < x < 2) and a Li compound; a carbon layer provided on at least a part of the surface of the silicon-based particles; LiF; and CF a Provided is a negative electrode active material containing (0 < a < 4).

[0012] One embodiment of the present invention provides a negative electrode containing the negative electrode active material. One embodiment of the present invention provides a secondary battery containing the negative electrode.

[0013] One embodiment of the present invention is SiO x Forming silicon-based particles containing (0 < x < 2) and a Li compound and having a carbon layer provided on at least a part of the surface; and performing a fluorine plasma treatment on the silicon-based particles; provided is a method for manufacturing the negative electrode active material.

Effects of the Invention

[0014] The negative electrode active material according to one embodiment of the present invention is SiO x Silicon-based particles containing (0 < x < 2) and a Li compound; a carbon layer provided on at least a part of the surface of the silicon-based particles; LiF; and CF a Containing (0 < a < 4), when using the negative electrode active material, it has the effect of significantly improving the water-based processability of the slurry. Specifically, LiF is poorly soluble in water and can efficiently passivate the silicon-based particles in the water-based slurry, acting as an artificial SEI film during battery operation and having the effect of improving the life performance of the battery. CF a (0 < a < 4) can increase the hydrophobicity of the carbon layer, suppress the reaction between moisture and the negative electrode active material in the water-based slurry, and can effectively passivate the particles.

[0015] Therefore, the negative electrode containing the negative electrode active material according to one embodiment of the present invention and the secondary battery containing the negative electrode have the effect of improving the discharge capacity, initial efficiency, resistance performance, and / or life characteristics of the battery. [Modes for carrying out the invention]

[0016] The following provides a more detailed explanation 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.

[0017] 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.

[0018] 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 describe their invention.

[0019] In this specification, singular expressions of terms include plural expressions unless the context clearly indicates otherwise.

[0020] In this specification, the crystallinity of the structure contained in the negative electrode active material can be confirmed by X-ray diffraction analysis. X-ray diffraction analysis may be performed using an X-ray diffraction (XRD) analyzer (product name: D4-endeavor, manufacturer: bruker), or other instruments used in this industry may be appropriately employed.

[0021] 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 emission spectrometer (ICPAES, Perkin-Elmer 7300).

[0022] In this specification, the average particle size (D 50) can be defined as the particle size at the 50% volume accumulation standard in the particle size distribution curve (graph curve of the particle size distribution diagram). The average particle size (D 50 ) can be measured, for example, using the laser diffraction method. The laser diffraction method can generally measure particle sizes from the submicron region to about several millimeters, and can obtain highly reproducible and highly resolvable results.

[0023] Hereinafter, preferred embodiments of the present invention will be described in detail. However, the embodiments of the present invention may be deformed into various forms, and the scope of the present invention is not limited to the embodiments described below.

[0024] <Negative electrode active material> One embodiment of the present invention is a silicon-based particle containing SiO x (0 < x < 2) and a Li compound; a carbon layer provided on at least a part of the surface of the silicon-based particle; LiF; and CF a (0 < a < 4), providing a negative electrode active material.

[0025] The negative electrode active material according to one embodiment of the present invention contains silicon-based particles. The silicon-based particles contain SiO x (0 < x < 2) and a Li compound.

[0026] The SiO x (0 < x < 2) may correspond to a matrix in the silicon-based particle. 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 x (0 < x < 2). When the silicon-based particle contains the SiO x (0 < x < 2), the discharge capacity of the secondary battery can be improved. Specifically, the SiOx (0 < x < 2) may be SiO in terms of the structural stability of the active material. x It may be a compound represented by (0.5 ≤ x ≤ 1.5).

[0027] The Li compound can correspond to a matrix within the silicon-based composite particles. The Li compound can exist in at least one form of lithium atom, lithium silicate, silicide, and lithium oxide within the silicon-based particles. When the silicon-based particles contain the Li compound, it has the effect of improving the initial efficiency.

[0028] The Li compound can be distributed on the surface and / or inside of the silicon-based particles in a doped form. The Li compound is distributed on the surface and / or inside of the silicon-based particles, can control the volume expansion / contraction of the silicon-based particles to an appropriate level, and can play a role in preventing damage to the active material. Also, the Li compound can be contained in terms of reducing the ratio of the irreversible phase (e.g., SiO2) of the silicon-based oxide particles and increasing the efficiency of the active material.

[0029] In one embodiment of the present invention, the Li compound may exist in the form of lithium silicate. The lithium silicate is Li a Si b O c (2 ≤ a ≤ 4, 0 < b ≤ 2, 2 ≤ c ≤ 5), and can be divided 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 consist of 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.

[0030] In one embodiment of the present invention, based on 100 parts by weight of the total negative electrode active material, Li may be included in an amount of 0.1 to 40 parts by weight or 0.1 to 25 parts by weight. Specifically, it may be included in an amount of 1 to 25 parts by weight, and more specifically, in an amount of 2 to 20 parts by weight. As the Li content increases, the initial efficiency increases, but the discharge capacity decreases. Therefore, when the above range is satisfied, an appropriate discharge capacity and initial efficiency can be achieved.

[0031] 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 Inductive 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 characteristic wavelength of 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 by comparing them with the calibration curve created above. Finally, the sum of the results is converted to a theoretical value, and the elemental content of the manufactured negative electrode active material can be analyzed.

[0032] In one embodiment of the present invention, the silicon-based particles may contain additional metal atoms. The metal atoms may exist in the silicon-based particles in the form of at least one of metal atoms, metal silicates, metal silicides, or 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.

[0033] In one embodiment of the present invention, the silicon-based particles are provided with a carbon layer on at least a portion of their surface. In this case, the carbon layer may be partially covering at least a portion of the surface, i.e., the particle surface, or it may be covering the entire particle surface. The carbon layer imparts conductivity to the negative electrode active material, thereby improving the initial efficiency, lifespan characteristics, and battery capacity characteristics of the secondary battery.

[0034] In one embodiment of the present invention, the carbon layer contains amorphous carbon. Furthermore, the carbon layer may further contain crystalline carbon.

[0035] 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 fluorene, carbon nanotubes, and graphene.

[0036] 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 substances as a source in chemical vapor deposition.

[0037] The aforementioned carbonized organic substances may be carbonized organic substances selected from sucrose, glucose, galactose, fructose, lactose, mannose, ribose, aldohexose or ketohexose, and combinations thereof.

[0038] 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 include methane, ethane, ethylene, acetylene, propane, butane, butene, pentane, isobutane, or hexane. The aromatic hydrocarbon of the substituted or unsubstituted aromatic hydrocarbon may include benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, coumarone, pyridine, anthracene, or phenanthrene.

[0039] 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 contained in an amount of 0.1 parts by weight to 50 parts by weight, 0.1 parts by weight to 30 parts by weight, or 0.1 parts by weight to 20 parts by weight based on 100 parts by weight of the total amount of the negative electrode active material. More specifically, it may be contained in an amount of 0.5 parts by weight to 15 parts by weight, 1 part by weight to 10 parts by weight, or 1 part by weight to 5 parts by weight. When the above range is satisfied, it is possible to prevent a decrease in the capacity and efficiency of the negative electrode active material.

[0040] In one embodiment of the present invention, the thickness of the carbon layer may be 1 nm to 500 nm, and specifically, it may be 5 nm to 300 nm. When the above range is satisfied, the conductivity of the negative electrode active material is improved, the volume change of the negative electrode active material is easily suppressed, the side reaction between the electrolyte and the negative electrode active material is suppressed, and the initial efficiency and / or lifespan of the battery is improved.

[0041] Specifically, the carbon layer can be formed by chemical vapor deposition (CVD) using at least one hydrocarbon gas selected from the group consisting of methane, ethane, and acetylene.

[0042] In one embodiment of the present invention, the negative electrode active material may include LiF; and CF a (0 < a < 4).

[0043] Specifically, during the production of the negative electrode active material, after forming silicon-based particles provided with a carbon layer on at least a part of the surface, F can be introduced to the surface of the particles through fluorine plasma treatment. In this process, F can be introduced into lithium by-products generated when doping the silicon-based particles with Li to form LiF, and F can be introduced into the carbon of the carbon layer provided on the surface of the silicon-based particles to form CF a (0 < a < 4) may exist in this form.

[0044] The LiF formed as described above is not readily soluble in water, can efficiently passivate the silicon-based particles with an aqueous slurry, prevent the elution of Li compounds contained in the silicon-based particles, prevent the slurry from becoming basic, and has the effect of improving the aqueous processability. In addition, LiF acts as an artificial SEI film during the operation of the battery, having the effect of improving the life performance of the battery. In one embodiment of the present invention, the LiF and CF a (0 < a < 4) may be provided on the silicon-based particles.

[0045] The LiF may be provided on the surface of the silicon-based particles, inside the carbon layer, or on the surface of the carbon layer. Specifically, the LiF may be provided on at least a part of the carbon layer, or on at least a part of the region of the surface of the silicon-based particles where no carbon layer is provided. Without being limited thereto, the LiF may be formed at a position where lithium by-products or lithium silicate exist in the negative electrode active material. The LiF may be partially coated on the surface or may be in a form covering the entire surface. Examples of the shape of the LiF include an island type or a thin film type, but the shape of the LiF is not limited thereto

[0046] Further, the LiF may be provided on the surface of the silicon-based particles by introducing F into the Li compound contained in the silicon-based particles.

[0047] The CF a (0 < a < 4) may be provided inside the carbon layer or on the surface of the carbon layer.

[0048] Specifically, the CF a (0 < a < 4) is formed by introducing F onto the surface of the carbon layer and has a structure containing a C-F bond. That is, the CF a (0 < a < 4) may be located inside the carbon layer or on the surface of the carbon layer. Specifically, it may be mainly located near the surface of the carbon layer.

[0049] By introducing F onto the surface of the carbon layer to form CF a (0 < a < 4), the hydrophobicity of the carbon layer increases, suppressing the reaction between moisture and the negative electrode active material in the aqueous slurry. Thus, the particles can be effectively passivated.

[0050] In one embodiment of the present invention, the negative electrode active material may further contain SiF b (0 < b < 4). When introducing F onto the surface of the silicon-based particles by fluorine plasma treatment, F can also be introduced into the silicon-based particles, forming a Si-F bond with silicon inside the particles, and existing in the form of SiF b (0 < b < 4). The SiF b (0 < b < 4) may be located inside the silicon-based particles or on the surface of the silicon-based particles. Specifically, it may be mainly located near the surface of the silicon-based particles.

[0051] The components contained in the negative electrode active material can be confirmed by X-ray diffraction analysis (XRD) or X-ray photoelectron spectroscopy (XPS).

[0052] In the present invention, the elemental content and atomic ratio on the surface of the negative electrode active material can be confirmed by XPS (Nexsa ESCA System, Thermo Fisher Scientific (ESCA-02)). Further, the presence of LiF and CF a (0 < a < 4) can be confirmed by the XPS analysis.

[0053] Specifically, for each sample, after obtaining a survey scan spectrum and a narrow scan spectrum, a survey scan spectrum and a narrow scan spectrum can be obtained while performing a depth profile. The depth profile can be performed up to 3000 seconds using monatomic Ar ions, and the measurement and data processing conditions are as follows.

[0054] - X-ray source: Monochromated Al K α (1486.6 eV) - X-ray spot size: 400 μm - Sputtering gun: Monatomic Ar (energy: 1000 eV, current: low, raster width: 2 mm) - Etching rate: 0.09 nm / s for Ta2O5 - Operation Mode: CAE (Constant Analyzer Energy) mode - Survey scan: pass energy 200 eV, energy step 1 eV - Narrow scan: scanned mode, pass energy 50 eV, energy step 0.1 eV - Charge compensation: flood gun off -SF:Al THERMO1 -ECF:TPP-2M -BG subtraction:Shirley

[0055] In one embodiment of the present invention, the depth profile of the X-ray photoelectron spectroscopy (XPS) can be measured under a monochromated Al Kα X-ray source at 0.09 nm / s for up to 3000 seconds.

[0056] In one embodiment of the present invention, when the surface of the negative electrode active material is analyzed by X-ray photoelectron spectroscopy, Li, Si, C, N, O, or F are detected.

[0057] The elemental content calculated using X-ray photoelectron spectroscopy below is based on a 100 at% sum of all elements measured on a 100 s basis.

[0058] In one embodiment of the present invention, the F content determined by surface analysis of the negative electrode active material by X-ray photoelectron spectroscopy may be 10 at% or more. Specifically, the F content may be 10 at% to 50 at%, 12 at% to 40 at%, or 15 at% to 35 at%. The lower limit of the F content may be 10 at%, 12 at%, 14 at%, 15 at%, 16 at%, 18 at%, or 20 at%, and the upper limit may be 50 at%, 45 at%, 40 at%, 35 at%, 30 at%, or 25 at%.

[0059] When the content of element F on the surface of the negative electrode active material meets the above-mentioned requirements, sufficient F is introduced into the negative electrode active material, removing lithium by-products and effectively introducing F into the carbon layer. This prevents the negative electrode active material from reacting with water and lithium by-products from leaching out in aqueous slurries, thereby improving aqueous processability.

[0060] When the F content is above the lower limit of the range, the amount of F introduced to the surface of the negative electrode active material is appropriate, and a passivation effect appears. When the F content is below the upper limit of the range, it is possible to prevent the generation of many unstable F bonds such as CF and Si-F, thereby suppressing the generation of HF in aqueous slurries and the decomposition of components such as CMC by HF, and preventing a decrease in viscosity.

[0061] In one embodiment of the present invention, the Li content determined by surface analysis of the negative electrode active material by X-ray photoelectron spectroscopy may be 10 at% or more. Specifically, the Li content may be 10 at% to 30 at%, 15 at% to 25 at%, 18 at% to 25 at%, or 20 at% to 23 at%. The lower limit of the Li content may be 10 at%, 12 at%, 15 at%, 18 at%, or 20 at%, and the upper limit may be 30 at%, 28 at%, 25 at%, 24 at%, or 23 at%.

[0062] When the Li element content on the surface of the negative electrode active material meets the above-mentioned requirements, lithium silicate is uniformly formed inside the silicon-based particles, thereby achieving appropriate capacity and efficiency. When the Li content is above the lower limit of the above range, a sufficient amount of Li reacts with the silicon-based particles to achieve appropriate efficiency. When the Li content is below the upper limit of the above range, excessive residue of Li byproducts is suppressed, preventing an excessive rise in the pH of the slurry and minimizing gas generation due to reaction with Si.

[0063] In one embodiment of the present invention, the Si content determined by surface analysis of the negative electrode active material by X-ray photoelectron spectroscopy may be 5 at% or less. Specifically, the Si content may be 0.1 at% to 5 at%, 1 at% to 5 at%, 2 at% to 4 at%, 2.5 at% to 4 at%, or 3 at% to 3.5 at%. The lower limit of the Si content may be 0.1 at%, 1 at%, 2 at%, 2.5 at%, or 3 at%, and the upper limit may be 5 at%, 4 at%, or 3.5 at%.

[0064] When the Si element satisfies the above content on the surface of the negative electrode active material, substances such as LiF and CF that play a passivation role a (0 < a < 4) etc. exist in an appropriate amount, resulting in an excellent passivation effect and preventing gas generation in the aqueous mixing system. During the driving of the battery, the substances that play a passivation role act as resistors, and a smooth battery driving effect can be shown. When the content of Si is above the lower limit of the above range, an increase in resistance associated with excessive formation of substances that play a passivation role can be prevented. When the content of Si is below the upper limit of the above range, substances that play a passivation role can be uniformly formed to prevent the gas generation problem in the aqueous process.

[0065] In one embodiment of the present invention, the content of C by surface analysis of the negative electrode active material by X-ray photoelectron spectroscopy may be 20 at% or more. Specifically, the content of C may be 20 at% or more and 70 at% or less, 30 at% or more and 60 at% or less, or 35 at% or more and 55 at% or less. The lower limit of the content of C may be 20 at%, 25 at%, 30 at%, or 35 at%, and the upper limit may be 70 at%, 65 at%, 60 at% or 55 at%.

[0066] When the C element satisfies the above content on the surface of the negative electrode active material, an appropriate amount of C-F functional groups is introduced into the carbon layer, so that the hydrophobicity of the carbon layer is increased, the reactivity with water is suppressed, and the generation of gas is also suppressed. When the content of C is above the lower limit of the above range, the carbon layer is uniformly formed, minimizing the exposed Si, thereby minimizing the gas generation problem. When the content of C is below the upper limit of the above range, the decrease in battery performance due to excessive increase in resistance during the driving of the battery can be prevented with an appropriate amount of the carbon layer.

[0067] In one embodiment of the present invention, the oxygen content of the negative electrode active material determined by surface analysis by X-ray photoelectron spectroscopy may be 15 at% or less. Specifically, the oxygen content may be 2 at% to 15 at%, 2 at% to 12 at%, or 5 at% to 10 at%. The lower limit of the oxygen content may be 2 at%, 4 at%, or 5 at%, and the upper limit may be 15 at%, 14 at%, 12 at%, or 10 at%.

[0068] When the oxygen (O) content on the surface of the negative electrode active material meets the above-mentioned requirements, hydrophilicity decreases, which reduces slurry gas and prevents efficiency degradation due to oxygen functional groups during battery operation. When the oxygen content is above the lower limit of the above range, excessive reduction to decrease the oxygen content is not performed, which suppresses the generation of HF due to the bonding of unstable fluorine (F) elements in the aqueous process. This suppresses the decomposition reaction of substances such as CMC in the slurry and prevents a rapid decrease in viscosity. When the oxygen content is below the upper limit of the above range, hydrophilicity decreases, and the material does not react easily with water, thus preventing gas generation.

[0069] By satisfying the element content range of the present invention, sufficient F is introduced into the negative electrode active material, lithium byproducts are easily removed, and LiF is formed, and F is effectively introduced into the carbon layer, forming CF a Forms LiF and CF a The appropriate amount prevents the negative electrode active material from reacting with water in the aqueous slurry and prevents lithium by-products from leaching out, thereby improving the processability in aqueous systems.

[0070] In one embodiment of the present invention, the atomic ratio of F to O (F / O ratio) of the negative electrode active material, as determined by surface analysis of the negative electrode active material by X-ray photoelectron spectroscopy, may be between 1 and 6. Specifically, it may be between 1.2 and 5 or between 1.5 and 4.5. When the above range is satisfied, F is appropriately introduced to the surface of the negative electrode active material, and LiF and CF are produced. aIt is easily formed, easily passivates silicon-based particles in the slurry, and when the battery is driven, LiF acts as an artificial SEI film, resulting in a remarkable improvement in the slurry processability and life performance. When it is above the lower limit of the above range, the introduction amount of F on the surface of the negative electrode active material is sufficient, which is advantageous for the passivation effect. When it is below the upper limit of the above range, a large number of unstable F bonds such as C-F and Si-F are prevented from occurring, the generation of HF in the aqueous slurry and the decomposition of components such as CMC in the slurry by HF are suppressed, and a significant viscosity decrease can be prevented.

[0071] In one embodiment of the present invention, the atomic ratio of Li to C (C / Li ratio) by surface analysis of the negative electrode active material using X-ray photoelectron spectroscopy may be 0.8 or more and 4 or less. Specifically, it may be 1 or more and 3.5 or less, 1.5 or more and 3 or less, or 1.7 or more and 2.5 or less. When the above range is satisfied, the contents of LiF and CF located on the surface of the negative electrode active material are appropriate, and silicon-based particles in the slurry can be easily passivated. When the battery is driven, LiF acts as an artificial SEI film, resulting in a remarkable improvement in the processability and life performance of the slurry. When it is above the lower limit of the above range, the carbon layer becomes uniform, the passivation effect increases, and it does not react with water. When it is below the upper limit of the above range, a decrease in battery performance due to an increase in resistance during battery driving can be prevented. a In one embodiment of the present invention, the content of the LiF may be more than the content of CF (0 < a < 4). Usually, after forming a carbon layer on the silicon-based particles, in the process of doping lithium into the silicon-based particles, the lithium by-products mainly exist on the carbon layer. Therefore, when the silicon-based particles are treated with fluorine plasma, F is preferentially introduced into the lithium by-products, so the content of LiF may be more than the content of CF (0 < a < 4).

[0072] In one embodiment of the present invention, the content of the LiF may be more than the content of CF a (0 < a < 4). Usually, after forming a carbon layer on the silicon-based particles, in the process of doping lithium into the silicon-based particles, the lithium by-products mainly exist on the carbon layer. Therefore, when the silicon-based particles are treated with fluorine plasma, F is preferentially introduced into the lithium by-products, so the content of LiF may be more than the content of CF a (0 < a < 4).

[0073] 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.

[0074] 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, unreacted lithium by-products may remain even after the acid treatment process.

[0075] The lithium byproduct may include one or more selected from the group consisting of Li2O, LiOH, and Li2CO3. As in the reaction described above, LiF may be formed on the lithium byproduct during fluorine plasma treatment, and unreacted lithium byproduct may be present on silicon-based particles.

[0076] The presence or absence of the aforementioned lithium by-product can be confirmed by X-ray diffraction analysis (XRD) or X-ray photoelectron spectroscopy (XPS).

[0077] 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 decreased, and aqueous processability characteristics can be improved. When it is below the upper limit of the above range, it is possible to prevent the slurry from becoming basic during formation, minimizing the occurrence of side reactions or aqueous processability issues due to viscosity changes.

[0078] 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 of the aqueous solution containing the negative electrode active material with HCl solution using a titrator, and then calculating the amount of lithium by-product.

[0079] The average particle size (D 50 ) of the negative electrode active material may be 0.1 μm to 30 μm, specifically, it may be 1 μm to 20 μm, and more specifically, it may be 1 μm to 10 μm. When the above range is satisfied, the structural stability of the active material during charge and discharge can be achieved, and problems such as excessive increase in particle size and large volume expansion / shrinkage level can be prevented, and problems such as excessive decrease in particle size and reduction in initial efficiency can be prevented.

[0080] The BET specific surface area of the negative electrode active material is 1 m 2 / g to 100 m 2 / g, specifically, it may be 1 m 2 / g to 70 m 2 / g, and more specifically, it may be 1 m 2 / g to 50 m 2 / g, for example, 2 m 2 / g to 30 m 2 / g. When the above range is satisfied, during charging and discharging of the battery, side reactions with the electrolyte can be reduced, and the life characteristics of the battery can be improved.

[0081] <Method for manufacturing negative electrode active material> One embodiment of the present invention includes the steps of forming silicon-based particles containing SiO x (0 < x < 2) and a Li compound, and having a carbon layer on at least a part of the surface; and subjecting the silicon-based particles to fluorine plasma treatment; to provide a method for manufacturing the negative electrode active material.

[0082] The silicon-based particles can be formed by the steps of heating and vaporizing Si powder and SiO2 powder in a vacuum, then depositing the vaporized mixed gas to form preliminary particles; forming a carbon layer on the surface of the formed preliminary particles; and heat-treating after mixing the preliminary particles with a carbon layer formed thereon and Li powder.

[0083] Specifically, the mixed powder of Si powder and SiO2 powder can be heat-treated under vacuum at 1300°C to 1800°C, 1400°C to 1800°C, or 1400°C to 1600°C.

[0084] The formed preliminary particles may have the form of SiO. The carbon layer can be formed by using chemical vapor deposition (CVD) with hydrocarbon gas, or by carbonizing a substance that will serve as the carbon source.

[0085] Specifically, the formed preliminary particles can be introduced into a reactor and then formed by chemical vapor deposition (CVD) of hydrocarbon gas at 600°C to 1200°C. The hydrocarbon gas may be at least one hydrocarbon gas selected from the group including methane, ethane, propane, and acetylene, and can be heat-treated at 900°C to 1000°C.

[0086] The step of heat-treating the mixture of pre-particles with a carbon layer formed on them and Li powder may be carried out at 700°C to 900°C for 4 to 6 hours, or more specifically, at 800°C for 5 hours.

[0087] The silicon-based particles may include the Li compound described above, such as Li silicate, Li silicide, or Li oxide.

[0088] The particle size of the silicon-based particles can be adjusted by methods such as a ball mill, jet mill, or airflow classification, but is not limited to these methods.

[0089] As described above, at least a portion of the surface of the silicon-based particles having a carbon layer is provided with a lithium compound (lithium by-product). Specifically, the SiO xPreliminary particles including (0 < x < 2) are formed, and after forming a carbon layer on the preliminary particles and then doping with Li to produce the silicon-based particles, lithium compounds, that is, lithium by-products formed by unreacted lithium, remain near the surface of the silicon-based particles.

[0090] In one embodiment of the present invention, the method for manufacturing the negative electrode active material includes a step of subjecting the silicon-based particles to fluorine plasma treatment.

[0091] The fluorine plasma treatment step includes: after putting the silicon-based particles into a plasma chamber, injecting CF4 gas; increasing the pressure inside the chamber; and forming plasma in the chamber.

[0092] The plasma treatment may be performed using RF plasma. Specifically, the pressure inside the chamber before injecting CF4 gas into the chamber may be adjusted to 0.01 torr to 0.1 torr. Preferably, the pressure may be adjusted to 0.05 torr to 0.09 torr or 0.07 torr.

[0093] After that, in the step of increasing the pressure inside the chamber, the pressure inside the chamber may be adjusted to 0.1 torr to 0.5 torr. Specifically, the pressure may be adjusted to 0.15 torr to 0.3 torr or 0.2 torr.

[0094] The step of forming plasma in the chamber may be performed by applying power to the chamber. Specifically, the power may be 50 W to 300 W, 80 W to 250 W, or 100 W to 200 W.

[0095] The plasma may be held for 1 minute to 10 minutes. Preferably, it may be held for 3 minutes to 8 minutes, 5 minutes to 7 minutes, or 6 minutes. <​When plasma treatment is performed while satisfying the above range, F can be introduced into the silicon-based particles provided with the carbon layer at an appropriate content.

[0097] After forming plasma in the chamber and introducing F into the silicon-based particles provided with the carbon layer, the vacuum can be released at normal pressure and then the sample can be recovered.

[0098] The fluorine plasma treatment step may be repeated one or more times. Preferably, it may be repeated two or more times, and more preferably, it may be performed two or three times.

[0099] When F is introduced into the negative electrode active material by a dry method using plasma as in the present invention, lithium inside the silicon-based particles containing the Li compound does not dissolve, and the passivation characteristics are further improved. On the other hand, when F is introduced by a method such as hydrothermal synthesis or solvothermal synthesis, the surface of the silicon-based particles becomes porous and the passivation effect is reduced.

[0100] As described above, by fluorine plasma treatment, F is introduced into the lithium by-products formed when doping lithium into silicon-based particles to form LiF. The formed LiF easily blocks the reaction between water and the lithium compound or silicon-based particles, and acts as an artificial SEI film during the driving of the battery, resulting in the effect of improving the life performance.

[0101] Also, when F is introduced onto the surface of the carbon layer to form CF a (0 < a < 4), the hydrophobicity of the carbon layer increases, and the reaction between moisture and the negative electrode active material in the aqueous slurry is suppressed, so that the particles can be effectively passivated.

[0102] <Negative electrode> The negative electrode according to an embodiment of the present invention may include the above 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. Furthermore, the negative electrode active material layer may further include a binder, a thickener, and / or a conductive material.

[0103] The negative electrode active material layer can 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 surface of a current collector, followed by drying and rolling. The negative electrode slurry may further contain additional negative electrode active material.

[0104] As the additional negative electrode active material, a compound capable of reversibly inserting and removing lithium can 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. βExamples include metallic oxides that can be doped and dedoped with lithium, 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, and one or more of these mixtures may be used. A metallic lithium thin film may also be used as the negative electrode active material. In addition, either low-crystallinity carbon or high-crystallinity carbon may be used as the carbon material. Examples of low-crystalline carbon include soft carbon and hard carbon, while examples of high-crystalline carbon include amorphous, plate-like, flake-like, 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.

[0105] 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.

[0106] 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.

[0107] 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. By satisfying the pH range of the negative electrode slurry, the rheological properties of the slurry are stabilized. When the pH of the negative electrode slurry is within this range, the decomposition of carboxymethylcellulose (CMC) used as a thickening agent is suppressed, preventing a decrease in the viscosity of the slurry and maintaining the dispersion of the active material contained in the slurry.

[0108] The negative electrode current collector is not particularly limited as long as it does not induce 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.

[0109] 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, polytetrafluoroethylene, 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 a variety of copolymers thereof.

[0110] The conductive material is not particularly limited as long as it does not induce 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; fluorocarbons; metal powders such as 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.

[0111] The conductive material may be included in an amount of 0.01% to 30% by weight, based on 100% by weight of the negative electrode active material layer, and preferably in an amount of 0.1% to 20% by weight.

[0112] 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 appropriately adopted.

[0113] 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, and more specifically, it may be 5:95 to 30:70 or 10:90 to 20:80.

[0114] In one embodiment of the present invention, the total negative electrode active material contained in the negative electrode slurry may be present 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.

[0115] 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.

[0116] 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.

[0117] 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.

[0118] 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.

[0119] 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.

[0120] <Secondary battery> A secondary battery according to one embodiment of the present invention may include a negative electrode according to the embodiment described above. 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, wherein the negative electrode is the same as the negative electrode described above. Since the negative electrode has been described above, a detailed explanation will be omitted.

[0121] 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.

[0122] In the positive electrode, the positive electrode current collector is not particularly limited as long as it does not induce a chemical change in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector may also have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase adhesion to the positive electrode active material. For example, it may be used in various forms such as film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0123] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe3O4; or a compound with the chemical formula Li 1+c1 Mn 2-c1 Lithium manganese oxides such as O4 (0 ≤ c1 ≤ 0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7; chemical formula LiNi 1-c2 M c2 Ni-site type lithium nickel oxide represented as O2 (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, satisfying 0.01 ≤ c2 ≤ 0.3); chemical formula LiMn 2-c3 M c3 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); examples include, but are not limited to, LiMn2O4 in which part of the Li in the chemical formula is substituted with alkaline earth metal ions. The positive electrode may also be metallic lithium (Li-metal).

[0124] 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.

[0125] In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and can be used without particular limitations as long as it has electronic conductivity in the battery without causing a chemical change. Specific examples include graphite such as natural graphite or artificial graphite; carbon-containing 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.

[0126] 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, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one or more of these may be used.

[0127] The separator separates the negative and positive electrodes and provides a passage for lithium ions to move. Generally, any separator used in secondary batteries is acceptable 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 ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof may be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made of 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 these may be selectively used as single-layer or multi-layer structures.

[0128] Examples of the electrolyte 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.

[0129] Specifically, the electrolyte may contain a non-aqueous organic solvent and a metal salt. 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.

[0130] 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 conductivity can be produced, and therefore they can be used even more preferably.

[0131] 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:

[0132] 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, hexaphosphate 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.

[0133] Another embodiment of the present invention provides a battery module and a battery pack containing the secondary battery as a unit cell. Since the battery module and battery pack include 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]

[0134] <Examples and Comparative Examples> Example 1 94g of a powder mixture of Si and SiO2 in a 1:1 molar ratio was mixed in a reaction furnace and then vacuum-heated at a sublimation temperature of 1400°C. The vaporized Si-SiO2 mixture was then reacted in a vacuum-controlled cooling zone with a cooling temperature of 800°C to condense into a solid phase. Next, the condensed particles were crushed in a ball mill for 3 hours to produce particles with a size of 6 μm. Then, while maintaining an inert atmosphere by flowing Ar gas, the particles were placed in the hot zone of a CVD apparatus, and methane was blown into the 900°C hot zone using Ar as a carrier gas for 5 hours. -1 The particles were reacted with Torr to form a carbon layer on their surface. Then, 6 g of Li metal powder was added to the particles with the carbon layer and mixed, followed by an additional heat treatment in an inert atmosphere at a temperature of 800°C to produce silicon-based particles containing a Li compound.

[0135] Ten grams of the silicon-based particles were spread thinly to a thickness of 3 mm or less in an RF plasma chamber. Then, CF4 gas was injected under a pressure of 0.07 torr to increase the pressure inside the chamber to 0.2 torr. Subsequently, 150 W of power was applied to the chamber to form a plasma, which was held for 6 minutes. After releasing the vacuum at atmospheric pressure, the sample was collected. The above process was repeated two more times (a total of three times) to obtain the negative electrode active material of Example 1.

[0136] Example 2 The negative electrode active material for Example 2 was obtained by manufacturing in the same manner as in Example 1, except that the power intensity applied when forming the plasma was set to 200W.

[0137] Example 3 The negative electrode active material of Example 3 was obtained by manufacturing in the same manner as in Example 1, except that the power intensity applied when forming the plasma was set to 100W.

[0138] Comparative Example 1 The negative electrode active material of Comparative Example 1 was obtained by manufacturing in the same manner as in Example 1, except that plasma treatment was omitted.

[0139] Comparative Example 2 Silicon-based particles containing a Li compound were obtained by the same method as in Example 1, except that plasma treatment was omitted. A mixture of 0.1M Al2(SO4)3 solution and 0.1M H3PO4 solution was mixed with the silicon-based particles in a weight ratio of 5:1, stirred for 1 hour, and then filtered and dried to form an inorganic coating layer containing aluminum phosphate on the silicon-based particles.

[0140] Comparative Example 3 Silicon-based particles containing a Li compound were obtained by the same method as in Example 1, except that plasma treatment was omitted. After introducing the silicon-based particles into the reactor, propane was vapor-deposited (CVD) at 700°C for 4 hours as a hydrocarbon gas to form an additional carbon layer on the silicon-based particles, thereby producing the negative electrode active material.

[0141] Comparative Example 4 Silicon-based particles containing a Li compound were obtained by the same method as in Example 1, except that plasma treatment was omitted. The silicon-based particles and a 0.1 M HF solution were mixed in a 1:7 weight ratio, stirred for 1 hour, then filtered and dried, and finally heat-treated at 300°C to produce a negative electrode active material with a LiF layer introduced on its surface.

[0142] <Measurement of carbon layer content> The carbon content of the aforementioned layer was analyzed using a CS-analyzer (CS-800, Eltra).

[0143] <Measurement of Li content in the negative electrode active material> The Li atom content was confirmed by ICP analysis using an inductively coupled plasma emission spectrometer (ICP-OES, AVIO 500, Perkin-Elmer 7300).

[0144] <Element content and atomic ratio measurement by X-ray photoelectron spectroscopy (XPS)> The element content (at%) on the surface of the negative electrode active material was confirmed by XPS (Nexsa ESCA System, Thermo Fisher Scientific (ESCA-02)).

[0145] Specifically, for each sample, a survey scan spectrum and a narrow scan spectrum were obtained, and then a survey scan spectrum and a narrow scan spectrum were obtained while performing a depth profile. The depth profile was performed up to 3000 seconds using monatomic Ar ions. The measurement and data processing conditions are as follows.

[0146] -X-ray source:Monochromated Al Kα(1486.6eV) -X-ray spot size:400μm -Sputtering gun:Monatomic Ar(energy:1000eV, current:low, raster width:2mm) -Etching rate:0.09nm / s for Ta2O5 -Operation Mode:CAE(Constant Analyzer Energy)mode -Survey scan:pass energy 200eV, energy step 1eV -Narrow scan:scanned mode, pass energy 50eV, energy step 0.1eV -Charge compensation:flood gun off -SF:Al THERMO1 -ECF:TPP-2M -BG subtraction:Shirley

[0147] Under the aforementioned conditions, the content of each element was calculated based on the total elemental content of 100 at%, measured on a 100s basis. The composition of the negative electrode active material produced in the above examples and comparative examples is shown in Table 1 below.

[0148] [Table 1]

[0149] <Experimental Example 1: Evaluation of discharge capacity, initial efficiency, and lifespan (capacity retention rate) characteristics> Manufacturing of negative electrodes As the negative electrode material, a mixture of the negative electrode active material produced in Example 1 and graphite (average particle size (D50): 20 μm) as a carbon-based active material was used in a weight ratio of 10:90. The anode material, styrene-butadiene rubber (SBR) as a binder, Super C65 as a conductive material, and carboxymethylcellulose (CMC) as a thickener were mixed in a weight ratio of 96:2:1:1, and this mixture was added to distilled water as a solvent for forming the anode slurry to produce the anode slurry.

[0150] As the negative electrode current collector, a copper current collector (thickness: 15 μm) is used, with the negative electrode slurry applied to one surface at a rate of 3.6 mAh / cm². 2 The material was coated with the specified loading amount, rolled (roll press), and dried in a vacuum oven at 130°C for 10 hours to form a negative electrode active material layer (thickness: 50 μm), which was used as the negative electrode according to Example 1 (negative electrode thickness: 65 μm). Furthermore, the negative electrodes of Examples 2, 3, and Comparative Examples 1-4 were manufactured in the same manner as in Example 1, except that the negative electrode active materials of Examples 2, 3, and Comparative Examples 1-4 were used instead of the negative electrode active material of Example 1.

[0151] Manufacturing of rechargeable batteries A lithium metal foil was prepared as the positive electrode. A porous polyethylene separator was interposed between the negative electrode and positive electrode of Examples 1-3 and Comparative Examples 1-4, which were manufactured as described above, and an electrolyte solution was injected to produce coin-shaped half-cells of Examples 1-3 and Comparative Examples 1-4, respectively.

[0152] As the electrolyte, a solution was used in which ethyl methyl carbonate (EMC) and ethylene carbonate (EC) were mixed in a volume ratio of 7:3, vinylene carbonate (VC) was dissolved at a concentration of 0.5% by weight, and LiPF6 was dissolved at a concentration of 1M.

[0153] Discharge capacity, initial efficiency, and lifespan (capacity retention rate) characteristic evaluation The discharge capacity, initial efficiency, and cycle capacity retention rate of the secondary batteries produced in Examples 1-3 and Comparative Examples 1-4 were evaluated using an electrochemical charger / discharger. Cycle capacity retention was tested at a temperature of 25°C, with the first and second cycles performed at 0.1C for charging and discharging, and from the third cycle onward at 0.5C (charging conditions: CC / CV, 5mV / 0.005 cut-off; discharging conditions: CC, 1.5V cut-off). The discharge capacity (mAh / g) and initial efficiency (%) were derived from the results of the first charge-discharge cycle.

[0154] The capacity retention rate was calculated as follows: Capacity retention rate (%) = {(Discharge capacity in cycle N) / (Discharge capacity in cycle 1)} × 100 (In the above formula, N is an integer greater than or equal to 1.) The capacity retention rate (%) after 50 cycles is shown in Table 2 below.

[0155] <Experimental Example 2: Evaluation of Processability (Slurry Gas Generation Amount) Characteristics> As the negative electrode material, a mixture of the negative electrode active material produced in the above examples and comparative examples and graphite (average particle size (D50): 20 μm) as a carbon-based active material was used in a weight ratio of 10:90.

[0156] As the negative electrode material, styrene-butadiene rubber (SBR) as the binder, Super C65 as the conductive material, and carboxymethyl cellulose (CMC) as the thickener were mixed at a weight ratio of 96:2:1:1, and this was added to distilled water as a solvent for forming the negative electrode slurry to prepare a negative electrode slurry.

[0157] The negative electrode slurry was put into an aluminum pouch with a volume of 7 mL and sealed. The difference between the weight of the aluminum pouch containing the negative electrode slurry in the atmosphere and the weight in water at 23 °C was determined, and this was divided by the density of water at 23 °C to measure the volume of the gas immediately after manufacturing the negative electrode slurry.

[0158] Next, after storing the aluminum pouch containing the negative electrode slurry at 60 °C for 3 days, the difference between the weight of the aluminum pouch containing the negative electrode slurry in the atmosphere and the weight in water at 60 °C was determined, and this was divided by the density of water at 60 °C to measure the volume of the gas after storing the negative electrode slurry for 3 days.

[0159] The difference between the volume of the gas measured after storing the negative electrode slurry for 3 days and the volume of the gas measured immediately after manufacturing the negative electrode slurry was defined as the gas generation amount, as shown in Table 2 below.

[0160]

Table 2

[0161] The negative electrode active material according to the present invention contains silicon-based particles, LiF, and CF a (0 < a < 4). In Examples 1 to 3 using the negative electrode active material of the present invention, it was confirmed that they were excellent in discharge capacity, initial efficiency, and capacity retention rate, and there was no or significantly low gas generation amount in the slurry. This is because LiF and CF contained in the negative electrode active material of the present invention aWhen (0 < a < 4) passivates silicon-based particles efficiently with a slurry and the surface of the negative electrode active material contains Li and F within the above range, it is considered that LiF is appropriately distributed on the particle surface, effectively suppressing side reactions in the slurry.

[0162] On the other hand, in Comparative Example 1, the negative electrode active material does not contain LiF and CF a (0 < a < 4), and it was confirmed that moisture in the slurry easily reacts with the silicon-based particles to generate gas, resulting in a decrease in discharge capacity, initial efficiency, and capacity retention rate.

[0163] In Comparative Examples 2 and 3, instead of containing LiF and CF a (0 < a < 4), an inorganic coating layer or an additional carbon layer was coated on the surface of the negative electrode active material. Although the amount of gas generation decreased slightly compared to Comparative Example 1, the amount of gas generation was still large, and it was confirmed that the discharge capacity, initial efficiency, and capacity retention rate decreased.

[0164] In Comparative Example 4, LiF was coated on the surface of the negative electrode active material. Although the silicon-based particles were passivated by LiF, the degree was low, and it was confirmed that the amount of gas generation was still large and the discharge capacity, initial efficiency, and capacity retention rate were not improved.

[0165] Therefore, in the present invention, silicon-based particles, LiF, and CF a (0

Claims

1. SiO ｘ (0 < x < 2) and silicon-based particles containing Li compounds, A carbon layer provided on at least a portion of the surface of the silicon-based particles, LiF, and CF ａ (0<a<4)、 Includes, Surface analysis of the negative electrode active material by X-ray photoelectron spectroscopy revealed that the Li content was 10 at% or more. The negative electrode active material has a F content of 10 at% or more and 50 at% or less, as determined by surface analysis of the negative electrode active material by X-ray photoelectron spectroscopy.

2. The LiF is provided on the surface of the silicon-based particles, inside the carbon layer, or on the surface of the carbon layer, and the CF ａ (0 < a < 4) is the negative electrode active material according to claim 1, provided inside the carbon layer or on the surface of the carbon layer.

3. SiO ｘ (0 < x < 2) and silicon-based particles containing Li compounds, A carbon layer provided on at least a portion of the surface of the silicon-based particles, LiF, and CF ａ (0<a<4)、 Includes, The Li content of the negative electrode active material, as determined by surface analysis using X-ray photoelectron spectroscopy, is 10 at% or more and 30 at% or less. The negative electrode active material has a F content of 10 at% or more and 50 at% or less, as determined by surface analysis of the negative electrode active material by X-ray photoelectron spectroscopy.

4. The negative electrode active material according to claim 1, wherein the oxygen content of the negative electrode active material determined by surface analysis of the negative electrode active material by X-ray photoelectron spectroscopy is 15 at% or less.

5. The negative electrode active material according to claim 1, wherein the Si content determined by surface analysis of the negative electrode active material by X-ray photoelectron spectroscopy is 5 at% or less.

6. The negative electrode active material according to claim 1, wherein the carbon content determined by surface analysis of the negative electrode active material by X-ray photoelectron spectroscopy is 20 at% or more.

7. SiO ｘ (0 < x < 2) and silicon-based particles containing Li compounds, A carbon layer provided on at least a portion of the surface of the silicon-based particles, LiF, and CF ａ (0<a<4)、 Includes, A negative electrode active material in which the atomic ratio of oxygen to fluorine (F / O ratio), determined by surface analysis of the negative electrode active material by X-ray photoelectron spectroscopy, is between 1 and 6.

8. The negative electrode active material according to claim 1, wherein the atomic ratio of C to Li (C / Li ratio) determined by surface analysis of the negative electrode active material by X-ray photoelectron spectroscopy is 0.8 or more and 4 or less.

9. SiO ｘ (0 < x < 2) and silicon-based particles containing Li compounds, A carbon layer provided on at least a portion of the surface of the silicon-based particles, LiF, and CF ａ (0<a<4)、 Includes, The content of LiF is the same as that of CF ａ The content is greater than (0 < a < 4), The negative electrode active material has a F content of 10 at% or more and 50 at% or less, as determined by surface analysis of the negative electrode active material by X-ray photoelectron spectroscopy.

10. SiO ｘ (0 < x < 2) and silicon-based particles containing Li compounds, A carbon layer provided on at least a portion of the surface of the silicon-based particles, LiF, CF ａ (0 < a < 4), and SiF ｂ A negative electrode active material containing (0 < b < 4).

11. The negative electrode active material according to claim 1, comprising 0.1 to 40 parts by weight of Li based on a total of 100 parts by weight of the negative electrode active material.

12. The anode active material according to claim 1, wherein the carbon layer is contained in an amount of 0.1 to 50 parts by weight, based on a total of 100 parts by weight of the anode active material.

13. SiO ｘ The steps include forming silicon-based particles comprising (0 < x < 2) and a Li compound, with a carbon layer provided on at least a portion of the surface, and The step of treating the silicon-based particles with fluorine plasma, A method for producing a negative electrode active material, comprising: The aforementioned negative electrode active material is Silicon-based particles containing SiO₂x (0 < x < 2) and Li compounds, A carbon layer provided on at least a portion of the surface of the silicon-based particles, LiF, and CF a (0<a<4), Includes, A method for producing a negative electrode active material, wherein the Li content of the negative electrode active material, as determined by surface analysis of the negative electrode active material by X-ray photoelectron spectroscopy, is 10 at% or more.

14. The aforementioned fluorine plasma treatment step is After the silicon-based particles are placed in the plasma chamber, CF ４ At the stage of injecting gas, The steps of increasing the pressure inside the chamber, Steps to form plasma in the chamber, A method for producing a negative electrode active material according to claim 13, including the method described in claim 13.

15. A negative electrode comprising the negative electrode active material according to any one of claims 1 to 12.

16. A secondary battery comprising the negative electrode described in claim 15.

Images