Anode active material, anode including the same, secondary battery including the same, and method for manufacturing anode 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] This application claims the benefit of the filing date of Korean Patent Application No. 10-2021-0107525 filed with the Korean Intellectual Property Office on August 13, 2021, and Korean Patent Application No. 10-2022-0008564 filed with the Korean Intellectual Property Office on January 20, 2022, the entire contents of which are incorporated herein by reference.

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

[0003] In recent years, with the rapid spread of battery-powered electronic devices such as mobile phones, laptop computers, and electric vehicles, the demand for secondary batteries that are small, lightweight, and have relatively high capacity has been rapidly increasing. In particular, lithium secondary batteries, which are lightweight and have high energy density, have attracted attention as power sources for portable devices. For this reason, active research and development efforts are being made to improve the performance of lithium secondary batteries.

[0004] Generally, a lithium secondary battery includes a positive electrode, a negative electrode, a separator between the positive electrode and the negative electrode, an electrolyte, an organic solvent, etc. The positive electrode and the negative electrode may have active material layers formed on current collectors, each containing a positive electrode active material and a negative electrode active material. Generally, the positive electrode uses a lithium-containing metal oxide such as LiCoO2 or LiMn2O4 as the positive electrode active material, and the negative electrode uses a lithium-free carbon-based active material or a silicon-based active material as the negative electrode active material.

[0005] Silicon-based negative electrode active materials have been attracting attention due to their 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 their large irreversible capacity caused by large volume expansion / contraction during charging / discharging.

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

[0007] In connection with this, research has been continuously carried out 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 the metal reacts with moisture to increase the pH of the negative electrode slurry and change its viscosity. For this reason, the state of the manufactured negative electrode becomes poor, and there is a problem that the charge-discharge efficiency of the negative electrode decreases.

[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, thereby improving the charge-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 it has limitations in solving the above-described 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 includes silicon-based particles containing SiO x (0 < x < 2) and a Li compound, and having a carbon layer provided on at least a part of the surface; and a layer containing LiF provided on at least a part of the silicon-based particles, and when analyzed by X-ray photoelectron spectroscopy (XPS), the atomic ratio of O to F (F / O ratio) is 0.45 or more, and the atomic ratio of C to F (F / C ratio) is 0.5 or less, and provides a negative electrode active material.

[0013] One embodiment of the present invention includes steps of forming silicon-based particles containing SiO x (0 < x < 2) and a Li compound, and having a carbon layer provided on at least a part of the surface; and reacting the silicon-based particles with an HF solution to form a layer containing LiF on at least a part of the silicon-based particles, and provides a method for producing the negative electrode active material described above.

[0014] One embodiment of the present invention provides a negative electrode containing the negative electrode active material.

[0015] One embodiment of the present invention provides a secondary battery containing the negative electrode.

Effects of the Invention

[0016] The negative electrode active material according to one embodiment of the present invention can effectively remove lithium by-products formed during Li doping in silicon-based particles to improve water-based processability, and can improve the life performance by providing a layer containing LiF on the silicon-based particles to act as an artificial SEI film (Artificial SEI layer). Further, by satisfying that the atomic ratio of O to F (F / O ratio) on the particle surface is 0.45 or more and the atomic ratio of C to F (F / C ratio) is 0.5 or less, the water-based processability can be significantly improved.

[0017] Therefore, a negative electrode including the negative electrode active material according to an embodiment of the present invention and a secondary battery including the negative electrode have the effect of improving the discharge capacity, initial efficiency, resistance performance, and / or life characteristics of the battery. DETAILED DESCRIPTION OF THE INVENTION

[0018] The present specification will be explained in more detail below.

[0019] In this specification, when a part "comprises" a certain component, this means that it may further include other components, rather than excluding other components, unless otherwise specified.

[0020] In this specification, when a member is said to be located "on" another member, this includes not only when the member is in contact with the other member, but also when another member is present between the two members.

[0021] The terms and words used in this specification should not be interpreted in a limited way to their ordinary or dictionary meanings, but should be interpreted in a way that is consistent with the technical idea of ​​the present invention, based on the principle that the inventors can appropriately define the concepts of terms in order to best explain their inventions.

[0022] As used herein, the singular expression of a term includes the plural expression unless the context clearly indicates otherwise.

[0023] In this specification, the crystallinity of the structure contained in the negative electrode active material may be confirmed by X-ray diffraction analysis. The X-ray diffraction analysis may be performed using an XRD (X-ray diffraction) analysis device (product name: D4-endavor, manufacturer: Bruker), and in addition to the above device, any device commonly used in the art may be appropriately adopted.

[0024] In this specification, the presence or absence and the content of elements in the negative electrode active material can be confirmed by ICP analysis, and the ICP analysis can be performed using an inductively coupled plasma atomic emission spectrometer (ICPAES, Perkin-Elmer 7300).

[0025] In this specification, the average particle diameter (D 50 ) can be defined as the particle diameter corresponding to 50% of the volume cumulative amount in the particle size distribution curve (graph curve of the particle size distribution diagram). The average particle diameter (D 50 ) can be measured, for example, using the laser diffraction method. The laser diffraction method can generally measure particle diameters from the submicron region to about several millimeters, and high reproducibility and highly resolved results can be obtained.

[0026] Hereinafter, preferred embodiments of the present invention will be described in detail. However, the embodiments of the present invention may be modified into various forms, and the scope of the present invention is not limited to the embodiments described below.

[0027] <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, and having a carbon layer on at least a part of the surface; and a layer containing LiF provided on at least a part of the silicon-based particle, and when analyzed by X-ray photoelectron spectroscopy (XPS), the atomic ratio of O to F (F / O ratio) is 0.45 or more, and the atomic ratio of C to F (F / C ratio) is 0.5 or less, to provide a negative electrode active material.

[0028] The negative electrode active material according to one embodiment of the present invention contains silicon-based particles. The silicon-based particles may contain SiO<​​​​​​(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 SiO2, and the Si may form a phase. 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 particles contain the SiO x (0 < x < 2), the discharge capacity of the secondary battery can be improved.

[0030] In one embodiment of the present invention, the silicon-based particles may contain a Li compound.

[0031] The Li compound may correspond to a matrix within the silicon-based particles. The Li compound may exist in at least one form of lithium atoms, lithium silicate, lithium silicide, and lithium oxide within the silicon-based particles. When the silicon-based particles contain a Li compound, there is an effect of improving the initial efficiency.

[0032] The Li compound may be in a form doped into the silicon-based particles and distributed on the surface and / or inside of the silicon-based particles. The Li compound is distributed on the surface and / or inside of the silicon-based particles, can control the expansion / contraction of the volume of the silicon-based particles to a suitable level, and can play a role in preventing damage to the active material. Further, the Li compound may be included 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.

[0033] 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 classified into crystalline lithium silicate and amorphous lithium silicate. The crystalline lithium silicate may be present 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 is Li a Si b O c It may have a complex structure of the form (2 ≤ a ≤ 4, 0 < b ≤ 2, 2 ≤ c ≤ 5), and is not limited to the above form.

[0034] In one embodiment of the present invention, based on 100 parts by weight of the total negative electrode active material, Li may be contained in an amount of 0.1 part by weight to 40 parts by weight, or 0.1 part by weight to 25 parts by weight. Specifically, it may be contained in an amount of 1 part by weight to 25 parts by weight, and more specifically, it may be contained in an amount of 2 parts by weight to 20 parts by weight. As the content of Li increases, although the initial efficiency increases, there is a problem that the discharge capacity decreases. Therefore, when the above range is satisfied, appropriate discharge capacity and initial efficiency can be realized.

[0035] The content of the Li element can be confirmed by ICP analysis. Specifically, after taking a certain amount (about 0.01 g) of the negative electrode active material, transfer it to a platinum crucible, add nitric acid, hydrofluoric acid, and sulfuric acid, and completely decompose it on a hot plate. Then, using an inductively coupled plasma atomic emission spectrometer (ICPAES, Perkin-Elmer 7300), measure the intensity of the standard solution prepared with a standard solution (5 mg / kg) at the specific wavelength of the element to be analyzed to create a standard calibration curve. Then, introduce the pretreated sample solution and blank sample into the instrument, measure their respective intensities to calculate the actual intensity, compare with the created calibration curve to calculate the concentration of each component, and then convert it so that the sum of the whole becomes the theoretical value, and the content of the elements of the manufactured negative electrode active material can be analyzed.

[0036] 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, and metal oxides. The metal atoms may include at least one selected from the group consisting of Mg, Li, Al, and Ca. This may improve the initial efficiency of the negative electrode active material.

[0037] According to one embodiment of the present invention, a silicon-based particle has a carbon layer on at least a portion of its surface. The carbon layer may be formed on at least a portion of the surface, i.e., on the surface of the particle, or on the entire surface of the particle. The carbon layer provides conductivity to the negative electrode active material, thereby improving the initial efficiency, lifespan characteristics, and capacity characteristics of the secondary battery.

[0038] In one embodiment of the present invention, the carbon layer includes an amorphous phase.

[0039] In one embodiment of the present invention, the carbon layer comprises amorphous carbon.

[0040] The carbon layer may further include crystalline carbon.

[0041] The crystalline carbon may 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 nanotube, and graphene.

[0042] 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 a chemical vapor deposition process.

[0043] The carbonized organic material may be a carbonized organic material selected from carbonized sucrose, glucose, galactose, fructose, lactose, mannose, ribose, aldohexose, or ketohexose, and combinations thereof.

[0044] 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, hexane, or the like. The aromatic hydrocarbon of the substituted or unsubstituted aromatic hydrocarbon may be benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, coumarone, pyridine, anthracene, phenanthrene, or the like.

[0045] In one embodiment of the present invention, the carbon layer may be included in an amount 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, the carbon layer may be included in an amount of 0.5 to 15 parts by weight, 1 to 10 parts by weight, or 1 to 5 parts by weight. When the amount is within this range, a decrease in the capacity and efficiency of the negative electrode active material can be prevented.

[0046] In one embodiment of the present invention, the thickness of the carbon layer may be 1 nm to 500 nm, specifically 5 nm to 300 nm. When the thickness is within this range, the conductivity of the negative electrode active material is improved, volume change of the negative electrode active material is easily suppressed, and side reactions between the electrolyte and the negative electrode active material are suppressed, resulting in improved initial efficiency and / or lifespan of the battery.

[0047] 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.

[0048] The negative electrode active material according to one embodiment of the present invention includes a layer containing LiF provided on at least a part of the silicon-based particles.

[0049] The layer containing LiF may be in a form coated on at least a part of the silicon-based particles having a carbon layer on the surface. That is, the layer containing LiF may be partially coated on the surface of the particles or may be in a form coated on the entire surface of the particles. Examples of the shape of the layer containing LiF include an island type or a thin film type, but the shape of the layer containing LiF is not limited thereto.

[0050] The layer containing LiF may be provided on at least a part of the carbon layer. That is, the layer containing LiF is coated adjacent to the carbon layer and may be in a form of particles - carbon layer - layer containing LiF including SiO x (0 < x < 2) and a Li compound.

[0051] The layer containing LiF may be provided on a region where the carbon layer is not provided in the surface of the particles including SiO x (0 < x < 2) and a Li compound. That is, the layer containing LiF is coated adjacent to the particles including SiO x (0 < x < 2) and a Li compound and may be in a form of particles including SiO x (0 < x < 2) and a Li compound - layer containing LiF.

[0052] The layer containing LiF may be a LiF layer composed of LiF. Alternatively, the layer containing LiF may mainly contain LiF and may contain a small amount of impurities such as lithium compounds in addition to LiF.

[0053] Whether LiF is contained in the negative electrode active material or not can be confirmed by X-ray diffraction analysis (XRD) or X-ray photoelectron spectroscopy (XPS).

[0054] In one embodiment of the present invention, the LiF-containing layer may be formed by reacting HF with one or more lithium compounds selected from the group consisting of Li2O, LiOH, and Li2CO3. The LiF formed is uniformly formed on the surface of the particles and preferentially forms a layer on the surface (top) of the lithium by-product, easily blocking the reaction between water and the lithium compound and acting as an artificial SEI layer during battery operation, thereby improving life performance.

[0055] Specifically, the LiF-containing layer may be formed by acid treating lithium compounds, i.e., lithium by-products, remaining near the surface of the silicon-based particles or carbon layer with HF after producing the silicon-based particles.

[0056] In one embodiment of the present invention, the lithium compound may be one or more selected from the group consisting of Li2O, LiOH, and Li2CO3.

[0057] When the lithium compound reacts with HF, a layer containing LiF may be produced by one or more reactions of the following formulas (1) to (3). (1) LiOH + HF → LiF + HO (2) Li2O + 2HF → 2LiF + HO (3) Li2CO3 + 2HF → 2LiF + H2CO3

[0058] The LiF-containing layer formed as described above is not easily soluble in water, and therefore can effectively passivate silicon-based particles in aqueous slurry, preventing the elution of Li compounds contained in the silicon-based particles and improving aqueous processability.In addition, the LiF-containing layer acts as an artificial SEI layer during battery operation, thereby improving the battery's lifespan performance.

[0059] In the present invention, the content and atomic ratio of elements on the surface of the negative electrode active material can be confirmed by XPS (Nexsa ESCA System, Thermo Fisher Scientific (ESCA-02)).

[0060] Specifically, after obtaining a survey scan spectrum and a narrow scan spectrum for each sample, a depth profile can be performed to obtain the survey scan spectrum and the narrow scan spectrum. The depth profile can be performed for up to 3000 seconds using monatomic Ar ions, and the measurement and data processing conditions are as follows:

[0061] -X-ray source: Monochromated Al K α(1486.6eV) -X-ray spot size: 400 μm -Sputtering gun: Monatomic Ar (energy: 1000 eV, current: low, raster width: 2 mm) -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

[0062] In one embodiment of the present invention, the X-ray photoelectron spectroscopy (XPS) depth profile can be measured under a monochromated Al K α X-ray source at 0.09 nm / s for up to 3000 seconds.

[0063] In one embodiment of the present invention, the negative electrode active material has an atomic ratio of F to O (F / O ratio) of 0.45 or more when analyzed by X-ray photoelectron spectroscopy (XPS). Specifically, the F / O ratio may be 0.48 or more, 0.55 or more, 0.6 or more, or 0.7 or more, and may be 20 or less, 15 or less, 10 or less, 5 or less, 3 or less, 2 or less, 1.5 or less, or 1.2 or less.

[0064] In one embodiment of the present invention, the negative active material has an atomic ratio of F to C (F / C ratio) of 0.5 or less when analyzed by X-ray photoelectron spectroscopy (XPS). Specifically, the F / C ratio may be 0.4 or less, 0.3 or less, 0.25 or less, or 0.22 or less, or may be greater than 0, 0.05 or more, 0.08 or more, or 0.1 or more.

[0065] When the F / O ratio and F / C ratio are satisfied, LiF is uniformly coated on the silicon-based particles, the particle coverage rate is high, and the passivation effect is enhanced. As a result, lithium by-products can be easily removed and the exposure of lithium by-products can be easily prevented. This effectively improves aqueous processability, resulting in improved battery capacity, efficiency, and / or lifespan.

[0066] On the other hand, if the negative electrode active material does not satisfy the F / O ratio and / or F / C ratio, the particle coverage rate is low and LiF is partially formed thickly, making particle passivation difficult and easily exposing lithium by-products, resulting in poor aqueous processability and resulting in reduced battery performance.

[0067] Therefore, when the F / O ratio and F / C ratio of the negative electrode active material satisfy the above-mentioned ranges, optimal battery characteristics can be exhibited.

[0068] In one embodiment of the present invention, when the negative electrode active material is analyzed by X-ray photoelectron spectroscopy (XPS), F may be 0.1 at % to 0.3 at % based on 100 at % of all elements.

[0069] In one embodiment of the present invention, when the negative electrode active material is analyzed by X-ray photoelectron spectroscopy (XPS), O may be 5 at % to 14 at % or 8 at % to 13.5 at % based on 100 at % of all elements.

[0070] In one embodiment of the present invention, when the negative electrode active material is analyzed by X-ray photoelectron spectroscopy (XPS), C may be 50 at % to 65 at % or 55 at % to 61 at % based on 100 at % of all elements.

[0071] In one embodiment of the present invention, when the negative electrode active material is analyzed by X-ray photoelectron spectroscopy (XPS), Si may be 6 at % to 8 at % or 7 at % to 8 at % based on 100 at % of all elements.

[0072] In one embodiment of the present invention, when the negative electrode active material is analyzed by X-ray photoelectron spectroscopy (XPS), Li may be 10 at % to 25 at % or 10 at % to 20 at % based on 100 at % of all elements.

[0073] In one embodiment of the present invention, the layer containing LiF may be included in an amount of 0.5 to 5 parts by weight, specifically, 0.7 to 0.8 parts by weight, or 4 to 3 parts by weight, or 2.5 to 100 parts by weight of the total negative electrode active material.

[0074] In one embodiment of the present invention, LiF may be included in an amount of 0.5 to 5 parts by weight, specifically, 0.7 to 0.8 parts by weight, or 4 to 3 parts by weight, or 2.5 to 100 parts by weight of the total negative electrode active material.

[0075] When the content of LiF satisfies the above range, a sufficient layer is formed on the surface (top) of the lithium by-product, which easily blocks the reaction between water and lithium compounds, and acts as an artificial SEI layer during battery operation, thereby improving the life performance.

[0076] On the other hand, when LiF is contained in an amount less than 0.5 parts by weight, the content of LiF is too low, so that the particles cannot be properly passivated, and lithium by-products react with water, resulting in poor aqueous processability.

[0077] In one embodiment of the present invention, a lithium compound (lithium by-product) may be present between the silicon-based particles and the layer containing LiF.

[0078] Specifically, the lithium compound (by-product) may refer to a lithium compound remaining near the surface of the silicon-based particles or the carbon layer after the silicon-based particles are prepared. As described above, even after the acid treatment process, lithium by-products that have not reacted with the acid may remain.

[0079] The lithium compound may include one or more selected from the group consisting of Li2O, LiOH, and Li2CO3. As in the above-mentioned reaction, the lithium compound reacts with HF to form a layer containing LiF, and a lithium compound (lithium by-product) generated by the remaining lithium that does not react with HF may be present between the silicon-based particles and the layer containing LiF.

[0080] Whether or not a lithium compound is present between the silicon-based particles and the layer containing LiF can be confirmed by X-ray diffraction analysis (XRD) or X-ray photoelectron spectroscopy (XPS).

[0081] The lithium compound (by-product) may be included 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 included in an amount 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 included in an amount of 0.1 to 0.8 parts by weight, or 0.1 to 0.5 parts by weight. When the content of the lithium by-product satisfies the above range, side reactions in the slurry can be reduced, viscosity changes can be reduced, and aqueous processability can be improved. On the other hand, when the content of the lithium by-product is higher than the above range, the slurry exhibits basicity during formation, which can cause side reactions or viscosity changes, resulting in aqueous processability issues.

[0082] The content of the lithium compound (by-product) can be calculated by measuring the amount of HCl solution at a specific pH range during titration of the aqueous solution containing the negative active material with an HCl solution using a titrator.

[0083] The average particle size (D 50) may be from 0.1 μm to 30 μm, specifically may be from 1 μm to 20 μm, and more specifically may be from 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, preventing the problem that the volume expansion / contraction level also increases due to the excessive increase in the particle size, and preventing the problem that the initial efficiency decreases due to the excessive decrease in the particle size.

[0084] <Method for manufacturing negative electrode active material> One embodiment of the present invention is SiO x (0 < x < 2) and a step of forming silicon-based particles including a Li compound and having a carbon layer on at least a part of the surface; and a step of reacting the silicon-based particles with an HF solution to form a layer containing LiF on at least a part of the silicon-based particles, to provide the method for manufacturing the negative electrode active material.

[0085] The silicon-based particles may be formed by a step of heating and vaporizing Si powder and SiO2 powder in a vacuum and then depositing the vaporized mixed gas to form preliminary particles; a step of forming a carbon layer on the surface of the formed preliminary particles; and a step of heat-treating after mixing the preliminary particles with the carbon layer formed and Li powder.

[0086] 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. <00​​​​​​​​​Specifically, after the formed preliminary particles are introduced into the reactor, hydrocarbon gas may be formed by chemical vapor deposition (CVD) at 600 to 1200 °C. 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.

[0090] The step of heat-treating after mixing the preliminary particles with carbon layer formed and Li powder may be carried out at 700 °C to 900 °C for 4 to 6 hours, specifically, it may be carried out at 800 °C for 5 hours.

[0091] The silicon-based particles may contain, as the aforementioned Li compound, Li silicate, Li silicide, or Li oxide.

[0092] The particle size of the silicon-based particles can be adjusted by methods such as ball mill, jet mill, or air classification, but is not limited thereto.

[0093] At least a part of the surface of the silicon-based particles provided with a carbon layer as described above is provided with a lithium compound (lithium by-product). Specifically, in the process of forming preliminary particles containing SiO x (0 < x < 2), forming a carbon layer on the preliminary particles, and then doping with Li to produce the aforementioned silicon-based particles, a lithium compound, that is, a lithium by-product formed by unreacted lithium, remains near the surface of the silicon-based particles.

[0094] [[ID=2D]]

[0095] Specifically, in order to suppress side reactions caused by the unreacted lithium compound, a step of forming a layer containing LiF on at least a part of the silicon-based particles may be performed.

[0096] The formed LiF preferentially forms a layer on the surface (top) of the lithium by-products, easily blocking the reaction between water and lithium compounds, and acts as an artificial SEI layer when the battery is in operation, improving the battery life.

[0097] In one embodiment of the present invention, the step of reacting the silicon-based particles with an HF solution to form a layer containing LiF on at least a portion of the silicon-based particles includes the step of reacting a lithium compound provided on at least a portion of the silicon-based particles with an HF solution.

[0098] Specifically, the layer containing LiF may be formed by reacting a lithium compound provided on at least a portion of the silicon-based particles with an HF solution.

[0099] The layer containing LiF may be formed by a reaction between HF and lithium compounds (Li2O, LiOH, and Li2CO3) of lithium that did not react with the preliminary particles (SiO) during the formation of the silicon-based particles described above.

[0100] When the lithium compound reacts with the HF solution, a layer containing LiF may be produced by one or more reactions of the following formulas (1) to (3). (1) LiOH + HF → LiF + HO (2) Li2O + 2HF → 2LiF + HO (3) Li2CO3 + 2HF → 2LiF + H2CO3

[0101] The HF solution may be 0.03M to 0.3M, specifically 0.05M to 0.2M.

[0102] The silicon-based particles and the HF solution may be mixed at a weight ratio of 1:1 to 1:10, specifically at a weight ratio of 1:5 to 1:10.

[0103] After mixing the silicon particles with the HF solution, the mixture may be heat-treated at 200°C to 500°C, specifically at 250°C to 350°C.

[0104] When a layer containing LiF is formed by the chemical reaction between a lithium compound and HF as described above, LiF is uniformly formed on the surface of the particles, and the formed LiF preferentially forms a layer on the surface (top) of the lithium by-product, easily blocking the reaction between water and the lithium compound, and acts as an artificial SEI layer during battery operation, resulting in improved life performance.

[0105] <Negative electrode> The negative electrode according to an embodiment of the present invention may include the negative electrode active material described above.

[0106] 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.

[0107] 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 surface of a current collector, followed by drying and rolling.

[0108] The negative electrode slurry may further include an additional negative electrode active material.

[0109] The additional negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. Specific examples thereof 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, and Al alloys; and SiO. βExamples of the negative electrode active material include metal oxides capable of doping and dedoping lithium, such as SnO2, vanadium oxide, lithium titanium oxide, and lithium vanadium oxide (0<β<2); or composites containing the metallic compounds and carbonaceous materials, such as Si-C composites and Sn-C composites. A mixture of two or more of these may be used. A thin film of metallic lithium may also be used as the negative electrode active material. The carbon material may be either low-crystalline carbon or high-crystalline carbon. Typical low-crystalline carbons are soft carbon and hard carbon, while typical high-crystalline carbons are amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitches, and high-temperature-calcined carbons such as petroleum or coal tar pitch-derived cokes.

[0110] The additional negative electrode active material may be a carbon-based negative electrode active material.

[0111] In one embodiment of the present invention, the weight ratio of the negative electrode active material and the additional negative electrode active material contained in the negative electrode slurry may be 10:90 to 90:10, specifically 10:90 to 50:50.

[0112] The negative electrode slurry may include a solvent for forming a negative electrode slurry. Specifically, the solvent for forming a negative electrode slurry may include at least one solvent selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol, specifically distilled water, in order to facilitate dispersion of components.

[0113] The negative electrode current collector is not particularly limited as long as it does not induce chemical changes 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 whose surface has been treated with carbon, nickel, titanium, silver, or the like. Specifically, a transition metal that easily adsorbs carbon, such as copper or 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.

[0114] The binder may include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, 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 hydrogen is substituted with Li, Na, Ca, or the like, or may include various copolymers thereof.

[0115] The conductive material is not particularly limited as long as it does not induce chemical changes in the battery and is conductive, and examples thereof include graphite such as natural graphite and 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.

[0116] The thickener may be carboxymethyl cellulose (CMC), but is not limited thereto, and any thickener used in the technical field may be appropriately adopted.

[0117] <Secondary battery> A secondary battery according to an embodiment of the present invention may include the anode according to the embodiment described above. Specifically, the secondary battery may include an anode, a cathode, a separator interposed between the cathode and the anode, and an electrolyte, and the anode is the same as the anode described above. Since the anode has been described above, detailed description thereof will be omitted.

[0118] 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 including the positive electrode active material.

[0119] The positive electrode current collector in the positive electrode is not particularly limited as long as it does not induce chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like may be used. The positive electrode current collector may typically have a thickness of 3 to 500 μm, and the surface of the current collector may be provided with fine irregularities to enhance adhesion of the positive electrode active material. The positive electrode current collector may be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0120] 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; a lithium iron oxide such as LiFe3O4; or a compound having the chemical formula Li 1+c1 Mn 2-c1 O4 (0≦c1≦0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, and Cu2V2O7; chemical formula LiNi 1-c2 M c2 Ni-site type lithium nickel oxide represented by the chemical formula LiMnO2 (wherein M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and 0.01≦c2≦0.3 is satisfied); 2-c3 M c3 Examples of the lithium manganese composite oxide include, but are not limited to, lithium manganese composite oxides represented by Li2Mn3MO8 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01≦c3≦0.1), 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. The positive electrode may be Li-metal.

[0121] The positive electrode active material layer may contain a positive electrode conductive material and a positive electrode binder in addition to the above-described positive electrode active material.

[0122] In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and can be used without any particular limitation as long as it does not cause chemical changes in the battery that is constructed and has electronic conductivity. Specific examples include graphite such as natural graphite and 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 powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives, and the like, and one or more of these may be used alone or in combination.

[0123] The positive electrode binder improves adhesion between positive electrode active material particles and between the positive electrode active material and the positive electrode current collector. Specific examples of the positive electrode binder include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. One or more of these may be used alone or in combination.

[0124] The separator separates the negative electrode and positive electrode and provides a path for lithium ions to move. Any separator typically used in secondary batteries can be used without particular limitations. It is particularly preferable that the separator exhibits low resistance to ion migration in the electrolyte and has excellent electrolyte humidification capacity. Specifically, porous polymer films, such as those made from polyolefin polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminate structures of two or more layers thereof, may be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. To ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymeric material may be used, and it may be selectively used as a single-layer or multi-layer structure.

[0125] Examples of the electrolyte solution 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 manufacturing lithium secondary batteries.

[0126] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0127] Examples of the non-aqueous organic solvent that can be used include 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, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0128] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are preferably used because they are high-viscosity organic solvents with high dielectric constants that effectively dissociate lithium salts. When such cyclic carbonates are mixed with linear carbonates having low viscosity and low dielectric constants, such as dimethyl carbonate and diethyl carbonate, in an appropriate ratio, an electrolyte solution having high electrical conductivity can be prepared, and therefore these cyclic carbonates are even more preferably used.

[0129] The metal salt may be a lithium salt, which is a substance that is easily dissolved in the non-aqueous electrolyte solution. For example, the anion of the lithium salt may be 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 - One or more selected from the group consisting of:

[0130] In addition to the components of the electrolyte, the electrolyte may further include one or more additives, such as a haloalkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing a decrease in battery capacity, and improving the discharge capacity of the battery.

[0131] According to another embodiment of the present invention, there is provided a battery module including the secondary battery as a unit cell, and a battery pack including the same. The battery module and the battery pack include the secondary battery having high capacity, high rate characteristics, and high cycle characteristics, and 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. [Example]

[0132] Hereinafter, the present specification will be described in detail with reference to examples. However, the examples of the present specification may be modified into various other forms, and the scope of the present application should not be construed as being limited to the examples described below. The examples of the present application are provided to more completely explain the present specification to those skilled in the art.

[0133] <Examples and Comparative Examples> Example 1 94 g of powders of Si and SiO2 mixed at a 1:1 molar ratio were mixed in a reactor and then vacuum heated at a sublimation temperature of 1,400°C. The vaporized Si and SiO2 mixed gas was then reacted in a vacuum cooling zone with a cooling temperature of 800°C to solidify. The solidified particles were then pulverized using a ball mill for 3 hours to produce particles of 6 μm in size. The particles were then placed in the hot zone of a CVD device while maintaining an inert atmosphere by flowing Ar gas, and the methane was blown into the hot zone at 900°C using Ar as a carrier gas for 5 hours and 10 minutes. -1 The particles were reacted under torr to form a carbon layer on the surface of the particles, and then 6 g of Li metal powder was added and mixed with the particles with the carbon layer formed, followed by additional heat treatment at 800°C in an inert atmosphere to produce Li-containing silicon-based particles.

[0134] The silicon-based particles and 0.1M HF solution were mixed in a weight ratio of 1:7, stirred for 1 hour, filtered, dried, and then heat-treated at 300°C to prepare a negative electrode active material having a LiF layer introduced therein.

[0135] Example 2 A negative electrode active material was prepared in the same manner as in Example 1, except that a 0.15M HF solution was used.

[0136] Example 3 A negative electrode active material was prepared in the same manner as in Example 1, except that a 0.05M HF solution was used.

[0137] Example 4 The negative electrode active material was produced in the same manner as in Example 1, except that a 0.2 M HF solution was used.

[0138] Comparative Example 1 The negative electrode active material was produced in the same manner as in Example 1, except that the step of introducing the LiF layer was excluded.

[0139] Comparative Example 2 The negative electrode active material was produced in the same manner as in Example 1, except that when introducing the LiF layer, after mixing LiF powder and the silicon-based particles at a weight ratio of 1.5:100, the LiF layer was introduced onto the surface of the silicon-based particles by a ball mill.

[0140] Comparative Example 3 The negative electrode active material was produced in the same manner as in Example 1, except that when introducing the LiF layer, after mixing LiF powder and the silicon-based particles at a weight ratio of 0.4:100, the LiF layer was introduced onto the surface of the silicon-based particles by a ball mill.

[0141] <Measurement of the content of the carbon layer> The content of the carbon layer was analyzed using a CS-analyzer (CS-800, Eltra).

[0142] <Measurement of the elemental content and atomic ratio by X-ray photoelectron spectroscopy (XPS)> The elemental content (at%) and atomic ratio of the surface of the negative electrode active material were confirmed by XPS (Nexsa ESCA System, Thermo Fisher Scientific (ESCA-02)).

[0143] Specifically, a survey scan spectrum and a narrow scan spectrum were obtained for each sample. Then, a depth profile was performed while obtaining the survey scan spectrum and the narrow scan spectrum. The depth profile was performed for up to 3000 seconds using monatomic Ar ions. The measurement and data processing conditions were as follows:

[0144] -X-ray source: Monochromated Al K α(1486.6eV) -X-ray spot size: 400 μm -Sputtering gun: Monatomic Ar (energy: 1000 eV, current: low, raster width: 2 mm) -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

[0145] As a result of the measurement as described above, the content and atomic ratio of each element were calculated based on the total content of 100 at% of the measured elements.

[0146] <Measurement of the content of Li contained in the negative electrode active material> The content of the Li atoms was confirmed by ICP analysis using an inductively coupled plasma optical emission spectrometer (ICP-OES of Perkin-Elmer 7300, AVIO 500).

[0147] <Analysis of the content of LiF> 20 ml to 200 ml of the sample was aliquoted into a Corning tube and eluted by shaking with 30 g of ultrapure water for 24 hours. At this time, if necessary, additional dilution was performed so that the sample concentration was within the standard calibration curve (1 mg / kg). After measuring the content of F under the following analysis conditions using IC6000 (Thermo Fisher Scientific), the content of LiF was calculated based on the measured content of F.

[0148] [Analysis conditions] -Column: IonPac AS18 (4x250 mm), IonPac AG18 (4x50 mm) -Eluent type: KOH (30.5 mM), Eluent flow rate: 1 mL / min -Detector: Suppressed Conductivity Detector, SRS current: 76 mA, Injection volume: 25 uL The composition of the negative electrode active materials produced in the above Examples and Comparative Examples is as shown in Table 1 below.

[0149]

Table 1

[0150] <Experimental example: Evaluation of discharge capacity, initial efficiency, and life (capacity retention) characteristics> Manufacture of the negative electrode The composite negative electrode active material prepared in Example 1 was used as the negative electrode material, and graphite (average particle size (D 50 ):20 μm) mixed at a weight ratio of 15:85 was used.

[0151] The negative electrode material, styrene-butadiene rubber (SBR) as a binder, Super C65 as a conductive material, and carboxymethyl cellulose (CMC) as a thickener were mixed in a weight ratio of 96:2:1:1, and the mixture was added to distilled water as a solvent for forming a negative electrode slurry to prepare a negative electrode slurry.

[0152] The negative electrode slurry was applied to one surface of a copper current collector (thickness: 15 μm) as a negative electrode current collector at 3.6 mAh / cm 2 The coated layer was rolled 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 of Example 1 (thickness of negative electrode: 65 μm).

[0153] In addition, negative electrodes of Examples 2 to 4 and Comparative Examples 1 to 3 were produced in the same manner as in Example 1, except that the negative electrode active material of Example 1 was replaced with the negative electrode active material of Examples 2 to 4 and Comparative Examples 1 to 3, respectively.

[0154] Secondary battery manufacturing A lithium metal foil was prepared as the positive electrode.

[0155] A porous polyethylene separator was interposed between the negative electrode and positive electrode of Examples 1 to 4 and Comparative Examples 1 to 3 produced above, and an electrolyte solution was injected to produce coin-shaped half cells of Examples 1 to 4 and Comparative Examples 1 to 3, respectively.

[0156] The electrolyte used was a solution 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 0.5 wt %, and LiPF6 was dissolved at a concentration of 1M.

[0157] Evaluation of discharge capacity, initial efficiency, and life (capacity retention rate) characteristics The secondary batteries manufactured in Examples 1 to 4 and Comparative Examples 1 to 3 were evaluated for discharge capacity, initial efficiency, and cycle capacity retention rate using an electrochemical charger / discharger.

[0158] The cycle capacity retention rate was measured at 25°C. The first and second cycles were charged and discharged at 0.1C, and from the third cycle onwards, the charge and discharge was carried out at 0.5C (charge conditions: CC / CV, 5mV / 0.005C cut-off, discharge conditions: CC, 1.5V cut-off).

[0159] The discharge capacity (mAh / g) and initial efficiency (%) were derived from the results of one charge / discharge.

[0160] The capacity retention rate was calculated as follows. Capacity retention rate (%) = {(discharge capacity at Nth cycle) / (discharge capacity at 1st cycle)} × 100 (In the above formula, N is an integer of 1 or more.)

[0161] The capacity retention rate (%) at the 50th cycle is shown in Table 2 below.

[0162] [Table 2]

[0163] In Examples 1 to 4, a layer containing LiF is provided on silicon-based particles, and the F / O ratio is 0.45 or more and the F / C ratio is 0.5 or less. It has been confirmed that the surface of the silicon-based particles is uniformly coated with a layer containing LiF, which can block the reaction between lithium by-products and moisture, resulting in excellent discharge capacity, initial efficiency, and capacity retention.

[0164] In contrast, when the silicon-based particles do not have a LiF layer on their surfaces as in Comparative Example 1, the aqueous slurry processability deteriorates due to the reaction between the lithium by-products of the negative electrode active material and water, resulting in a decrease in the discharge capacity, initial efficiency, and capacity retention of the battery.

[0165] In Comparative Example 2, a layer containing LiF was formed on the silicon-based particles, but the F / C ratio was high at 0.62. This indicates that the LiF was partially thickly formed, making it difficult to passivate the particles and easily exposing lithium by-products, resulting in poor aqueous processability and resulting in reduced battery discharge capacity, initial efficiency, and capacity retention.

[0166] In Comparative Example 3, a layer containing LiF was formed on the surface of the silicon-based particles, but the LiF content was low, resulting in a low F / O ratio of 0.4. This indicates that LiF was partially formed on the particles, making particle passivation difficult and easily exposing lithium by-products, resulting in poor aqueous processability, which in turn reduced the battery's discharge capacity, initial efficiency, and capacity retention.

Claims

1. SiO ｘ (0<x<2) and a Li compound, and a silicon-based particle having a carbon layer on at least a portion of the surface thereof; and a layer containing LiF provided on at least a portion of the silicon-based particles; Including, When analyzed by X-ray photoelectron spectroscopy (XPS), the atomic ratio of F to O (F / O ratio) is 0.45 or more and 2 or less, and the atomic ratio of F to C (F / C ratio) is 0.5 or less; The negative electrode active material, wherein the layer containing LiF is provided on at least a portion of the carbon layer.

2. The negative electrode active material of claim 1 , wherein the negative electrode active material has an atomic ratio of F to O (F / O ratio) of 0.48 to 2 when analyzed by X-ray photoelectron spectroscopy (XPS).

3. The negative electrode active material of claim 1 , wherein the negative electrode active material has an atomic ratio of F to C (F / C ratio) of more than 0 and less than or equal to 0.3 when analyzed by X-ray photoelectron spectroscopy (XPS).

4. The negative electrode active material according to claim 1 , wherein the layer containing LiF is contained in an amount of 0.5 parts by weight to 5 parts by weight, based on a total of 100 parts by weight of the negative electrode active material.

5. The negative electrode active material according to claim 1 , wherein a lithium compound is present between the silicon-based particles and the layer containing LiF.

6. The lithium compound is Li ２ O, LiOH, and Li ２ CO ３ The negative electrode active material according to claim 5 , comprising one or more selected from the group consisting of:

7. The negative electrode active material of claim 1, wherein Li is contained in an amount of 0.1 to 40 parts by weight based on a total of 100 parts by weight of the negative electrode active material.

8. The negative electrode active material of claim 1, wherein the carbon layer is included in an amount of 0.1 to 50 parts by weight based on 100 parts by weight of the total negative electrode active material.

9. SiO ｘ forming silicon-based particles comprising a (0<x<2) and Li compound, the particles having a carbon layer on at least a portion of the surface thereof; and reacting the silicon-based particles with an HF solution to form a layer containing LiF on at least a portion of the silicon-based particles; The method for producing the negative electrode active material according to any one of claims 1 to 8, comprising:

10. 10. The method for producing a negative electrode active material according to claim 9, wherein the step of reacting the silicon-based particles with an HF solution to form a layer containing LiF on at least a portion of the silicon-based particles comprises the step of reacting a lithium compound provided on at least a portion of the silicon-based particles with an HF solution.

11. A negative electrode comprising the negative electrode active material according to any one of claims 1 to 8.

12. A secondary battery comprising the negative electrode according to claim 11.

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