Negative electrode active material, method for manufacturing negative electrode active material, negative electrode containing negative electrode active material, and secondary battery containing the same

Abstract

The present invention relates to silicon-based composite particles containing SiO x (0 < x < 2) and a Li compound; a carbon layer; and SiO y (1 < y ≤ 2), which is a negative electrode active material, wherein the carbon layer is provided in a form covering at least a part of the surface of the silicon-based composite particles, and the SiO y (1

Description

[Technical Field]

[0001] This application claims the benefits as of the filing date of Korean Patent Application No. 10-2021-0107522, filed with the Korean Intellectual Property Office on 13 August 2021, and Korean Patent Application No. 10-2022-0014132, filed with the Korean Intellectual Property Office on 3 February 2022, all of which are incorporated herein by reference.

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

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

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

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

[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)), there is an advantage in that the degree of volume expansion / contraction in response to charge and discharge is lower compared to other silicon-based active materials such as silicon (Si). However, there is still a disadvantage in that the initial efficiency decreases due to the presence of irreversible capacity in silicon-based oxides as well.

[0007] In relation to 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 in that the metal oxide formed by doping reacts with moisture to increase the pH of the negative electrode slurry and change its viscosity. As a result, the state of the manufactured negative electrode becomes poor, and there is a problem in 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 there are 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 method for manufacturing the negative electrode active material, a negative electrode including the negative electrode active material, and a secondary battery including the same.

Means for Solving the Problems

[0012] One embodiment of the present invention is a silicon-based composite particle including SiO x (0 < x < 2) and a Li compound; a carbon layer; and a negative electrode active material including SiO y (1 < y ≤ 2), wherein the carbon layer is provided in a form covering at least a part of the surface of the silicon-based composite particle, and the SiO y (1 < y ≤ 2) is provided in a form covering at least a part of the surface of the silicon-based composite particle or at least a part of the surface of the carbon layer, and provides a negative electrode active material.

[0013] One embodiment of the present invention is a step of manufacturing a silicon-based composite particle including SiO x (0 < x < 2) and a Li compound; and a step of subjecting the silicon-based composite particle to an acid treatment to coat at least a part of the surface of the silicon-based composite particle with SiO y (1 < y ≤ 2), and provides a method for manufacturing the negative electrode active material.

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

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

Advantages of the Invention

[0016] In the present invention, by subjecting the silicon-based composite particle doped with Li to an acid treatment, lithium by-products generated during the Li doping process can be effectively removed, and SiO y (1 < y ≤ 2) is formed on the silicon-based composite particle during the acid treatment process and serves to passivate the particle. The SiO y(1 < y ≤ 2) may be provided in a form covering at least a part of the surface of the carbon layer or may be provided in a form covering at least a part of the surface of the silicon-based composite particles. Specifically, the SiO y (1 < y ≤ 2) may be provided in a form covering at least a part of the surface of the silicon-based composite particles between the surface of the silicon-based composite particles and the carbon layer, may be provided in a form covering at least a part of the region where the carbon layer is not provided in the surface of the silicon-based composite particles, or may be provided in a form covering at least a part of the surface of the carbon layer.

[0017] Also, since the silicon-based composite particles contain a carbon layer, it is possible to prevent unreacted lithium by-products from eluting during the acid treatment process and minimize the reaction between the negative electrode active material and water in the aqueous slurry.

[0018] Therefore, the negative electrode containing the negative electrode active material 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.

Brief Description of the Drawings

[0019] [Figure 1] It schematically shows the structure of the negative electrode active material according to an embodiment of the present invention. [Figure 2] It schematically shows the structure of the negative electrode active material according to an embodiment of the present invention. [Figure 3] It shows the XPS analysis results of the negative electrode active material of Example 1. [Figure 4] It shows the XPS analysis results of the negative electrode active material of Example 1.

Modes for Carrying Out the Invention

[0020] Hereinafter, this specification will be described in more detail.

[0021] In this specification, when a part "includes" a component, this means that, unless otherwise stated, it may include other components rather than excluding them.

[0022] In this specification, when a member is said to be located "on" another member, this includes not only cases where the member is in contact with another member, but also cases where another member exists between the two members.

[0023] The terms and words used herein should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather should be interpreted in a manner consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may appropriately define the concepts of terms in order to best explain their invention.

[0024] In this specification, singular expressions of terms include plural expressions unless the context clearly indicates otherwise.

[0025] 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 can be performed using an XRD (X-ray diffraction) analyzer (product name: D4-endavor, manufacturer: bruker), and other instruments used in this industry may be used as appropriate.

[0026] In this specification, the presence and content of elements in the negative electrode active material can be confirmed by ICP analysis, which can be performed using an inductively coupled plasma atomic emission spectrometer (ICPAES, Perkin-Elmer 7300).

[0027] In this specification, the specific surface area can be measured by using a BET measuring device (BEL-SORP-MAX, Nippon Bell) to degass the sample at 130°C for 2 hours, followed by N2 adsorption / desorption at 77K.

[0028] In this specification, the average particle size (D 50 ) can be defined as the particle size corresponding to 50% of the volume cumulative amount in the particle size distribution curve (graph curve of the particle size distribution diagram) of the particles. 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 ranging from the submicron region to about several millimeters, and can obtain results with high reproducibility and high resolution.

[0029] 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.

[0030] <Negative electrode active material> One embodiment of the present invention is a silicon-based composite particle containing SiO x (0 < x < 2) and a Li compound; a carbon layer; and a negative electrode active material containing SiO y (1 < y ≤ 2), wherein the carbon layer is provided in a form covering at least a part of the surface of the silicon-based composite particle, and the SiO y (1 < y ≤ 2) is provided in a form covering at least a part of the surface of the silicon-based composite particle or at least a part of the surface of the carbon layer, providing a negative electrode active material.

[0031] Generally, lithium by-products formed by unreacted lithium exist on the particles during the process of doping silicon-based particles with Li, and will show basicity when forming a slurry. Therefore, there is a problem that the rheological properties of the slurry change, and the Si of the silicon-based particles reacts with the base to generate gas.

[0032] Therefore, in the present invention, by acid-treating the lithium-doped silicon-based composite particles, the lithium by-products formed during the Li doping process can be effectively removed, and SiO y(1 < y ≤ 2) is formed on the surface of the silicon-based composite particles and will serve to passivate the particles. The SiO formed at this time y (1 < y ≤ 2) may be provided in a form that covers at least a part of the surface of the silicon-based composite particles between the surface of the silicon-based composite particles and the carbon layer, or in a form that covers at least a part of the region where the carbon layer is not provided in the surface of the silicon-based composite particles, or in a form that covers at least a part of the surface of the carbon layer.

[0033] Also, since the silicon-based composite particles contain a carbon layer, it is possible to prevent the elution of unreacted lithium by-products during the acid treatment process, and minimize the reaction between the negative electrode active material and water in the aqueous slurry.

[0034] The negative electrode active material according to an embodiment of the present invention includes silicon-based composite particles. The silicon-based composite particles contain SiO x (0 < x < 2) and a Li compound.

[0035] The SiO x (0 < x < 2) may correspond to a matrix within the silicon-based composite 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 composite particles contain the SiO x (0 < x < 2), the discharge capacity of the secondary battery can be improved.

[0036] In one embodiment of the present invention, the silicon-based composite particles may contain a Li compound. The Li compound may correspond to a matrix within the silicon-based composite particles. The Li compound may exist in at least one form of lithium atom, lithium silicate, lithium silicide, and lithium oxide within the silicon-based composite particles. When the silicon-based composite particles contain a Li compound, there is an effect that the initial efficiency is improved.

[0037] The Li compound may be distributed on the surface and / or inside of the silicon-based composite particles in a doped form. The Li compound is distributed on the surface and / or inside of the silicon-based composite particles, and can control the expansion / contraction of the volume of the silicon-based composite particles to an appropriate 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 (for example, SiO2) of the silicon-based oxide particles and increasing the efficiency of the active material.

[0038] In one embodiment of the present invention, the Li compound may exist in the form of lithium silicate. The lithium silicate is represented by Li a Si b O c (2 ≤ a ≤ 4, 0 < b ≤ 2, 2 ≤ c ≤ 5), and can be classified into crystalline lithium silicate and amorphous lithium silicate. The crystalline lithium silicate may exist in the form of at least one lithium silicate selected from the group consisting of Li2SiO3, Li4SiO4, and Li2Si2O5 within the silicon-based particles, and the amorphous lithium silicate may be Li a Si b O c (2 ≤ a ≤ 4, 0 < b ≤ 2, 2 ≤ c ≤ 5) and may consist of a complex structure, and is not limited to the above form.

[0039] In one embodiment of the present invention, the Li may be present in an amount of 0.1 to 40 parts by weight, or 0.1 to 25 parts by weight, based on 100 parts by weight of the total negative electrode active material. More specifically, it may be present 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, there is a problem that the initial efficiency increases but the discharge capacity decreases; therefore, when the above range is satisfied, a suitable discharge capacity and initial efficiency can be achieved.

[0040] The content of the aforementioned Li element can be confirmed by ICP analysis. Specifically, a fixed amount (approximately 0.01 g) of the negative electrode active material is taken, transferred to a platinum crucible, and completely decomposed on a hot plate with the addition of nitric acid, hydrofluoric acid, and sulfuric acid. Then, using an inductively coupled plasma atomic emission spectrometer (ICPAES, Perkin-Elmer 7300), the intensity of a standard solution prepared using a standard solution (5 mg / kg) is measured at the 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. After conversion so that the sum of the totals equals the theoretical value, the elemental content of the manufactured negative electrode active material can be analyzed.

[0041] In one embodiment of the present invention, the silicon-based composite particles may contain additional metal atoms. The metal atoms may exist within the silicon-based composite particles in the form of at least one of metal atoms, metal silicates, metal silicides, and metal oxides. The metal atoms may include at least one selected from the group consisting of Mg, Li, Al, and Ca. This can improve the initial efficiency of the negative electrode active material.

[0042] In one embodiment of the present invention, the negative electrode active material includes a carbon layer. Specifically, the carbon layer is provided in a form that covers at least a portion of the surface of the silicon-based composite particles.

[0043] Specifically, the carbon layer imparts conductivity to the negative electrode active material, thereby improving the initial efficiency, lifespan characteristics, and capacity characteristics of the secondary battery.

[0044] In one embodiment of the present invention, the carbon layer may contain at least one of amorphous carbon and crystalline carbon.

[0045] In one embodiment of the present invention, the carbon layer may be an amorphous carbon layer. The amorphous carbon can appropriately maintain the strength of the carbon layer and suppress the expansion of the silicon-based composite particles.

[0046] Furthermore, the carbon layer may or may not contain crystalline carbon.

[0047] The crystalline carbon can further improve the conductivity of the negative electrode active material. The crystalline carbon may include at least one selected from the group consisting of fullerene, carbon nanotubes, and graphene.

[0048] The amorphous carbon can appropriately maintain the strength of the carbon layer and suppress the expansion of the silicon-based composite particles. The amorphous carbon may be a carbon-based material formed by using at least one carbide or hydrocarbon selected from the group consisting of tar, pitch, and other organic materials as a source in chemical vapor deposition.

[0049] The aforementioned carbonized organic substances may be carbonized organic substances selected from carbonized sucrose, glucose, galactose, fructose, lactose, mannose, ribose, aldohexose, or ketohexose, and combinations thereof.

[0050] The hydrocarbon may be a substituted or unsubstituted aliphatic or alicyclic hydrocarbon, or a substituted or unsubstituted aromatic hydrocarbon. The aliphatic or alicyclic hydrocarbon of the substituted or unsubstituted aliphatic or alicyclic hydrocarbon may be methane, ethane, ethylene, acetylene, propane, butane, butene, pentane, isobutane, or hexane. Examples of the aromatic hydrocarbon of the substituted or unsubstituted aromatic hydrocarbon include benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, coumarone, pyridine, anthracene, or phenanthrene.

[0051] In one embodiment of the present invention, the carbon layer may be included in amounts of 0.1 to 50 parts by weight, 0.1 to 30 parts by weight, or 0.1 to 20 parts by weight, based on 100 parts by weight of the total negative electrode active material. More specifically, it may be included in amounts of 0.5 to 15 parts by weight, or 1 to 10 parts by weight. When these ranges are met, it is possible to improve conductivity while preventing a decrease in the capacity and efficiency of the negative electrode active material.

[0052] In one embodiment of the present invention, the thickness of the carbon layer may be 1 nm to 500 nm, more specifically 5 nm to 300 nm, and more specifically 5 nm to 100 nm. When this range is met, the conductivity of the negative electrode active material is improved, volume changes of the negative electrode active material are easily suppressed, side reactions between the electrolyte and the negative electrode active material are suppressed, and the initial efficiency and / or lifespan of the battery are improved.

[0053] 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.

[0054] The carbon layer may be formed before or after doping the silicon-based particles with lithium.

[0055] In one embodiment of the present invention, the negative electrode active material contains SiO y (1 < y ≤ 2). Specifically, the SiO y (1 < y ≤ 2) is provided in a form that covers at least a part of the surface of the silicon-based composite particles or at least a part of the surface of the carbon layer.

[0056] Specifically, in the present invention, by acid-treating the silicon-based composite particles doped with Li, lithium by-products formed during the Li doping process can be effectively removed, and SiO y (1 < y ≤ 2) is formed on the silicon-based composite particles and will play a role in passivating the particles.

[0057] In addition, since the silicon-based composite particles contain a carbon layer, elution of unreacted lithium by-products during the acid-treatment process can be prevented, and the reaction between the negative electrode active material and water in the aqueous slurry can be minimized.

[0058] In the SiO y (1 < y ≤ 2), the y corresponds to the number ratio of O to Si contained in the SiO y (1 < y ≤ 2).

[0059] The SiO y (1 < y ≤ 2) is formed during the process of acid-treating lithium compounds remaining near the surface of the silicon-based composite particles or the carbon layer, that is, lithium by-products, after manufacturing the silicon-based composite particles. Specifically, the lithium by-products are removed by acid-treatment, lithium desorbs from lithium silicate near the surface of the silicon-based composite particles, substances having various oxidation numbers are mixed, and a phase of SiO y (1 < y ≤ 2) is formed.

[0060] The SiO y (1 < y ≤ 2) may exist in the form of an island type or a thin film type layer, and is not limited thereto, and may exist in various forms.

[0061] At this time, SiO y (1 < y ≤ 2) may be present in various parts of the silicon-based composite particles. Specifically, it may be provided in a form that covers at least a part of the surface of the silicon-based composite particles between the surface of the silicon-based composite particles and the carbon layer, or in a form that covers at least a part of the region where the carbon layer is not provided in the surface of the silicon-based composite particles, or in a form that covers at least a part of the surface of the carbon layer.

[0062] In one example, the SiO y (1 < y ≤ 2) may be provided in a form that covers at least a part of the surface of the silicon-based composite particles between the surface of the silicon-based composite particles and the carbon layer. That is, the SiO y (1 < y ≤ 2) may be in a form that covers at least a part of the surface of the silicon-based composite particles and has a carbon layer covered thereon. That is, the SiO y (1 < y ≤ 2) may be provided adjacent to the surface of the silicon-based composite particles, and the carbon layer may be provided adjacent to the SiO y (1 < y ≤ 2). The SiO y (1 < y ≤ 2) may be in a form that partially covers the surface of the silicon-based composite particles or covers the entire surface. Examples of the shape of the SiO y (1 < y ≤ 2) include, but are not limited to, island type or thin film type.

[0063] In one example, the carbon layer may be in a form that partially covers the surface of the SiO y (1 < y ≤ 2) or covers the entire surface. Examples of the shape of the carbon layer include, but are not limited to, island type or thin film type.

[0064] In one example, the SiO y(1 < y ≤ 2) may be provided in a form that covers at least a part of the region on the surface of the silicon-based composite particles where the carbon layer is not provided. That is, the SiO y (1 < y ≤ 2) may be provided adjacent to the surface of the silicon-based composite particles. The SiO y (1 < y ≤ 2) may be in a form that partially covers the surface of the silicon-based composite particles or covers the entire surface. The SiO y (1 < y ≤ 2) may have a shape such as an island type or a thin film type, but is not limited thereto.

[0065] Specifically, when the silicon-based composite particles are doped with lithium, the particles expand generally, and there may be a region where the carbon layer cannot cover the entire silicon-based composite particles. At this time, the SiO y (1 < y ≤ 2) formed in the process of acid-treating the silicon-based composite particles can be formed on the region and provided adjacent to the surface of the silicon-based composite particles, so that the silicon-based composite particles can be more easily passivated.

[0066] In one example, the SiO y (1 < y ≤ 2) may be provided in a form that covers at least a part of the surface of the carbon layer. That is, the SiO y (1 < y ≤ 2) may be provided adjacent to the surface of the carbon layer. The SiO y (1 < y ≤ 2) may be in a form that partially covers the surface of the carbon layer or covers the entire surface of the carbon layer. The SiO y (1 < y ≤ 2) may have a shape such as an island type or a thin film type, but is not limited thereto.

[0067] That is, the negative electrode active material has a structure coated in the order of silicon-based composite particles / carbon layer / SiO y (1 < y ≤ 2), or has a structure coated in the order of silicon-based composite particles / SiO y (1 < y ≤ 2) / carbon layer, or silicon-based composite particles / SiOy It may have a structure coated in the order of (1 < y ≤ 2), but is not limited thereto.

[0068] When acid-treating lithium by-products remaining near the surface of the silicon-based composite particles or carbon layer as described above, it is possible to prevent the slurry from being basic due to the lithium by-products, and SiO generated from the lithium by-products y Due to the passivation effect of (1 < y ≤ 2), elution of the Li compound contained in the silicon-based composite particles is prevented, and there is an effect that the water-based processability of the slurry is improved.

[0069] In one embodiment of the present invention, when analyzing the negative electrode active material by X-ray photoelectron spectroscopy, it has a peak existing at 101 eV to 104 eV. This can be regarded as the first peak. Specifically, the first peak appears in the vicinity of 102 eV to 103 eV, which may be a peak due to SiO y It may be a peak due to (1 < y ≤ 2).

[0070] In one embodiment of the present invention, the negative electrode active material has a second peak existing at 99 eV to 101 eV when analyzed by X-ray photoelectron spectroscopy. Specifically, the second peak may appear in the vicinity of 99 eV to 100 eV, which may be a peak due to Si.

[0071] In one embodiment of the present invention, the negative electrode active material has a third peak existing at 102 eV to 105 eV when analyzed by X-ray photoelectron spectroscopy. Specifically, the third peak may appear in the vicinity of 103 eV to 104 eV, which may be a peak due to SiO2.

[0072] In one embodiment of the present invention, the first peak exists between the second peak and the third peak. That is, the first peak exists between the second peak due to Si (oxidation number = 0) and the third peak due to SiO2 (oxidation number = +4), and the negative electrode active material of the present invention contains Si having an oxidation number between 0 and +4 on the surface.

[0073] In one embodiment of the present invention, when the negative electrode active material is analyzed by X-ray photoelectron spectroscopy, it has a fourth peak located at 282 eV to 286 eV. Specifically, a peak appears around 283 eV to 285 eV, which may be a peak due to carbon (C) in the carbon layer.

[0074] In the present invention, the analysis of the negative electrode active material by X-ray photoelectron spectroscopy may be performed using the Nexsa ESCA System, Thermo Fisher Scientific (ESCA-02).

[0075] Specifically, after obtaining survey scan spectra and narrow scan spectra for each sample, depth profiling can be performed while obtaining survey scan spectra and narrow scan spectra again. Depth profiling can be performed for up to 3000 seconds using monatomic Ar ions, and the measurement and data processing conditions are as follows. -X-ray source: Monochromated Al K α(1486.6eV) - X-ray spot size: 400 μm - Sputtering gun: Monatomic Ar (energy: 1000eV, current: low, raster width: 2mm) - Etching rate: 0.09 nm / s for Ta2O5 -Operation Mode: CAE (Constant Analyzer Energy) mode - Survey scan: pass energy 200eV, energy step 1eV - 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

[0076] In one embodiment of the present invention, the depth profile of the X-ray photoelectron spectroscopy (XPS) can be measured by performing it at 0.09 nm / s up to 3000 seconds under a monochromated Al Kα X-ray source.

[0077] FIG. 1 and FIG. 2 schematically show the structure of the negative electrode active material according to one embodiment of the present invention. Specifically, SiO y (1 < y ≦ 2)3 is coated on at least a part of the silicon-based composite particles 1, and a carbon layer 2 may be coated on at least a part of the SiO y (1 < y ≦ 2)3. Alternatively, a carbon layer 2 may be coated on at least a part of the silicon-based composite particles 1, and SiO y (1 < y ≦ 2)3 may be coated on at least a part of the carbon layer 2. Further, although not shown in FIGS. 1 and 2, SiO y (1 < y ≦ 2) may be coated on a region where no carbon layer is formed on the silicon-based composite particles.

[0078] In FIGS. 1 and 2, SiO y (1 < y ≦ 2) is shown as an island-type shape that partially covers the surface of the particles, but is not limited thereto, and other shapes may be shown.

[0079] The negative electrode active material according to one embodiment of the present invention may include a first surface layer provided on at least a part of the silicon-based composite particles; and a second surface layer provided on at least a part of the first surface layer.

[0080] The first surface layer may be at least partially on the silicon-based composite particles, that is, it may be partially coated on the surface of the particles or may be in a form that coats the entire surface of the particles. Examples of the shape of the first surface layer include, but are not limited to, island type or thin film type.

[0081] The second surface layer may be at least partially on the first surface layer, that is, it may be partially coated on the surface of the first surface layer or may be in a form that coats the entire surface of the first surface layer. Examples of the shape of the second surface layer include, but are not limited to, island type or thin film type.

[0082] The second surface layer may be further provided on at least a part of the silicon-based composite particles. That is, in addition to the first surface layer, it may also exist in a form that is further coated on a portion of the silicon-based composite particles where the first surface layer is not provided. For example, when the first surface layer is a carbon layer and the second surface layer is a layer containing SiO y (1 < y ≤ 2), the layer containing SiO y (1 < y ≤ 2) may be formed on a region where the carbon layer cannot completely cover the silicon-based composite particles.

[0083] In one embodiment of the present invention, the first surface layer is a carbon layer, and the second surface layer may be a layer containing SiO y (1 < y ≤ 2). Specifically, the negative electrode active material includes a carbon layer provided on at least a part of the silicon-based composite particles, and may include a layer containing SiO y (1 < y ≤ 2) provided on at least a part of the carbon layer.

[0084] In one embodiment of the present invention, the first surface layer is a layer containing SiO y (1 < y ≤ 2), and the second surface layer may be a carbon layer. Specifically, the negative electrode active material includes a layer containing SiO yIt includes a layer containing (1 < y ≤ 2), and the SiO y It may include a carbon layer provided on at least a part of the layer containing (1 < y ≤ 2).

[0085] That is, SiO formed by acid treatment y (1 < y ≤ 2) may be provided on the surface of the carbon layer in the form of the second surface layer, or may be provided between the carbon layer and the surface of the silicon-based composite particles.

[0086] Also, when the silicon-based composite particles are doped with lithium, the particles expand generally, and there may be a region where the carbon layer cannot completely cover the silicon-based composite particles. The SiO y (1 < y ≤ 2) may be formed on the region and provided adjacent to the surface of the silicon-based composite particles.

[0087] In one embodiment of the present invention, the carbon layer and SiO y (1 < y ≤ 2) may be provided adjacent to each other.

[0088] In one embodiment of the present invention, the first surface layer and the second surface layer may be provided adjacent to each other. That is, an additional layer may not be provided between the first surface layer and the second surface layer.

[0089] In one embodiment of the present invention, the SiO y (1 < y ≤ 2) may be contained in an amount of 0.01 to 50 parts by weight based on 100 parts by weight of the total negative electrode active material. Preferably, it may be contained in an amount of 0.1 to 30 parts by weight, or may be contained in an amount of 1 to 20 parts by weight. When the above range is satisfied, the water-based processability is improved, and a decrease in the capacity and efficiency of the negative electrode active material can be prevented. When the content is lower than the above range, the passivation role cannot be performed well, and when the content is higher than the above range, there is a problem that the electrical conductivity decreases and the capacity and efficiency decrease.

[0090] The negative electrode active material according to one embodiment of the present invention is SiO y(1 < y ≤ 2) is included, and the SiO y (1 < y ≤ 2) may contain SiO2.

[0091] In one embodiment of the present invention, the SiO y (1 < y ≤ 2) may contain an amorphous phase. In one example, when performing X-ray diffraction analysis on the negative electrode active material, no crystalline peak derived from SiO y (1 < y ≤ 2) is detected.

[0092] In one embodiment of the present invention, the weight ratio of Si:(SiO x (0 < x < 2) + SiO y (1 < y ≤ 2)) in the negative electrode active material may be 88:12 to 60:40. Specifically, it may be 85:15 to 65:35, and more specifically, it may be 80:20 to 70:30. When the above range is satisfied, SiO y coating the silicon-based composite particles in the negative electrode active material can further effectively coat the particles and prevent side reactions during the formation of the slurry.

[0093] In one embodiment of the present invention, when performing NMR measurement on the negative electrode active material, the ratio (p1:p2) of the peak intensity (p1) of Si to the peak intensity (p2) indicating the Si-O bond may be 88:12 to 60:40. Specifically, it may be 85:15 to 65:35, and more specifically, it may be 80:20 to 70:30. When the above range is satisfied, SiO y coating the silicon-based composite particles in the negative electrode active material can further effectively coat the particles and prevent side reactions during the formation of the slurry.

[0094] The NMR peak intensity or weight ratio of the Si and the silicon-based oxide (SiO x and SiO y ) can be confirmed by nuclear magnetic resonance spectroscopy (Bruker's Advance III HD 600MHz NMR Spectrometer) under the condition of MAS rate = 10kHz.

[0095] At this time, the peak of Si may be measured within a chemical shift value range of -80 ppm to -90 ppm, and the peak of the Si-O bond may be measured within a chemical shift value range of -100 ppm to -120 ppm.

[0096] In one embodiment of the present invention, the carbon layer and SiO y (1 < y ≤ 2) weight ratio (carbon layer: SiO y (1 < y ≤ 2)) may be 1:10 to 1:2. When the above range is satisfied, there is a passivation effect while maintaining suitable conductivity. When the above range is not satisfied, there is a problem that the conductivity decreases.

[0097] In one embodiment of the present invention, the negative electrode active material may further include lithium by-products provided on at least a part of the silicon-based composite particles. The lithium by-products may include at least one selected from the group consisting of Li2O, LiOH, and Li2CO3.

[0098] Specifically, the lithium by-products may mean lithium compounds remaining near the surface of the silicon-based composite particles or the carbon layer after manufacturing the silicon-based composite particles. As described above, even after the acid treatment step, lithium by-products that did not react with the acid may remain.

[0099] FIG. 1 and FIG. 2 schematically show the structure of the negative electrode active material according to one embodiment of the present invention. The negative electrode active material according to one embodiment of the present invention may be in a form in which the lithium by-products 4 are provided on at least a part of the silicon-based composite particles 1 and are covered with the carbon layer 2. However, although FIG. 1 and FIG. 2 are shown as having lithium by-products, the lithium by-products may not exist.

[0100] The lithium by-product may be contained in an amount of 5 parts by weight or less based on 100 parts by weight in total of the negative electrode active material. Specifically, it may be contained in an amount of 0 parts by weight or more and less than 5 parts by weight, more than 0 parts by weight and 5 parts by weight or less, 0.01 parts by weight or more and 5 parts by weight or less, 0.05 parts by weight or more and less than 2 parts by weight, or 0.1 parts by weight or more and 1 part by weight or less. More specifically, it may be contained in an amount of 0.1 parts by weight or more and 0.8 parts by weight or less, or 0.1 parts by weight or more and 0.5 parts by weight. The lower limit of the content of the lithium by-product may be 0 parts by weight (not included), 0.01 parts by weight, or 0.1 parts by weight, and the upper limit may be 5 parts by weight, 1 part by weight, 0.8 parts by weight, or 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, the viscosity change can be lowered, and the aqueous system processability characteristics can be improved. On the contrary, when the content of the lithium by-product is higher than the above range, it shows basicity during the formation of the slurry, which may cause side reactions or viscosity changes, resulting in problems of aqueous system processability problems.

[0101] The content of the lithium by-product can be calculated by measuring the amount of the HCl solution in a specific section where the pH changes during the process of titrating an aqueous solution containing the negative electrode active material with an HCl solution using a titrator.

[0102] At least a part of the surface of the lithium by-product may further be provided with a carbon layer. The carbon layer may be provided in a form covering the lithium by-product. Specifically, the carbon layer may be formed during the production of the silicon-based composite particles, and the lithium by-product that did not react with the acid may be present below or above the carbon layer. <(

[0103] In one embodiment of the present invention, based on the total weight of the silicon-based composite particles and SiO y (1 < y ≤ 2), the proportion of the amorphous phase may be 32% or more. Specifically, it may be 32% - 70%, 35% - 60%, or 35% - 55%.

[0104] SiO produced by acid-treating lithium by-products remaining near the surface of the silicon-based composite particles or carbon layer as described above y (1 < y ≤ 2) contains an amorphous phase, and the proportion of the amorphous phase in the negative electrode active material will increase after the acid treatment. Therefore, when the weight ratio of the amorphous phases of the silicon-based composite particles and SiO y (1 < y ≤ 2) in the negative electrode active material satisfies the above range, a layer containing SiO y (1 < y ≤ 2) is appropriately formed, and there is an effect that the passivation characteristics are improved.

[0105] The proportion of the amorphous phase in the negative electrode active material can be measured by quantitative analysis using X-ray diffraction analysis method (D4 Endeavor of Bruker).

[0106] The BET specific surface area of the negative electrode active material may be 1 m 2 / g or more and 20 m 2 / g or less, may be 1 m 2 / g or more and 15 m 2 / g or less, may be more than 2 m 2 and less than 10 m 2 / g, may be 2.5 m 2 / g or more and 8 m 2 / g or less. The upper limit of the BET specific surface area may be 20 m 2 / g, 18 m 2 / g, 15 m 2 / g, 10 m 2 / g, 8 m 2 / g, 5 m 2 / g, or 4 m 2 / g, and the lower limit may be 1 m 2 / g, 1.5 m 2 / g, 2 m 2 / g, or 2.5 m 2 / g.

[0107] The average particle size (D 50It 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, preventing the problem that the volume expansion / shrinkage 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.

[0108] <Method for manufacturing negative electrode active material> One embodiment of the present invention is SiO x (0 < x < 2) and a step of manufacturing silicon-based composite particles containing a Li compound; and a step of acid-treating the silicon-based composite particles to form SiO y (1 < y ≤ 2), and provides a method for manufacturing a negative electrode active material.

[0109] The silicon-based composite 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; and a step of heat-treating after mixing the preliminary particles and Li powder.

[0110] At this time, the step may include a step of forming a carbon layer. The step of forming the carbon layer may be performed before forming the preliminary particles and mixing the Li powder, or may be performed after the step of heat-treating after mixing the Li powder.

[0111] Alternatively, the silicon-based composite 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; and a step of heat-treating after mixing the preliminary particles and Li powder.

[0112] Specifically, the mixed powder of the Si powder and the SiO2 powder may be heat-treated at 1400 °C to 1800 °C or 1400 °C to 1600 °C under vacuum.

[0113] The formed preliminary particles are SiO xIt may also exist in the form (x=1).

[0114] The silicon-based composite particles may also include the aforementioned Li silicate, Li silicide, Li oxide, etc.

[0115] The particle size of the silicon-based composite particles can be adjusted by methods such as a ball mill, jet mill, or air classification, but is not limited to these methods.

[0116] In the step of forming the carbon layer, a chemical vapor deposition (CVD) method using hydrocarbon gas may be used, or a carbon layer may be produced by carbonizing a substance that will serve as a carbon source.

[0117] Specifically, the formed preliminary particles may be introduced into a reactor and then formed by chemical vapor deposition (CVD) of a hydrocarbon gas 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 to 1000°C.

[0118] In this case, if the manufacturing step of the silicon-based composite particles does not include a step of forming a carbon layer, it may further include a step of forming a carbon layer on the acid-treated particles after the acid treatment step.

[0119] In order to remove lithium by-products remaining during the process of forming the silicon-based composite particles, the silicon-based composite particles may be subjected to an acid treatment step.

[0120] In the aforementioned acid treatment process, silicon-based composite particles and acid may be mixed in a weight ratio of 80:20 to 99.9:0.01. Specifically, they may be mixed in weight ratios of 85:15 to 99.5:0.5, 90:10 to 99.5:0.5, or 95:5 to 99:1.

[0121] As the acid during the acid treatment, phosphoric acid (H3PO4), sulfuric acid (H2SO4), boric acid (H3BO3), citric acid, protonated aniline, etc. may be used. Specifically, phosphoric acid (H3PO4) may be used. However, it is not limited thereto, and configurations well-known in the technical field may be appropriately adopted.

[0122] As the solvent during the acid treatment, distilled water, alcohol, N-methylpyrrolidone (NMP), etc. may be used. For example, ethanol may be used. However, it is not limited thereto, and configurations well-known in the technical field may be appropriately adopted according to the type of acid.

[0123] The acid treatment may be performed in the range of 50°C to 200°C, but it is not limited thereto, and the acid treatment temperature may vary according to the types of acid and solvent. For example, when ethanol is used as the solvent, the acid treatment may be performed at 60°C to 100°C or below or 70°C to 90°C or below.

[0124] During the production of the silicon-based composite particles, unreacted lithium compounds, that is, lithium by-products will remain, and these will remain near the surface of the silicon-based composite particles or the carbon layer. Therefore, when the silicon-based composite particles are acid-treated, the remaining lithium by-products react with the acid and are removed, and Li desorbs from the lithium silicate near the surface of the silicon-based composite particles, and SiO y (1 < y ≤ 2) is formed.

[0125] The formed SiO y (1 < y ≤ 2) may be provided in a form covering at least a part of the surface of the silicon-based composite particles, or in a form covering at least a part of the region where the carbon layer in the surface of the silicon-based composite particles is not provided, or in a form covering at least a part of the surface of the carbon layer.

[0126] By acid-treating the silicon-based composite particles as described above, lithium by-products formed during the Li doping process can be effectively removed, and SiO y (1 < y ≤ 2) is formed on the silicon-based composite particles and will serve to passivate the particles.

[0127] SiO formed by the acid treatment process y (1 < y ≤ 2) may exist in the form of an island type or a thin film type layer, and is not limited thereto, and may exist in various forms. Also, the formed SiO y (1 < y ≤ 2) may exist in various parts on the silicon-based composite particles.

[0128] That is, the negative electrode active material formed by the manufacturing method as described above has a structure coated in the order of silicon-based composite particles / carbon layer / SiO y (1 < y ≤ 2), or has a structure coated in the order of silicon-based composite particles / SiO y (1 < y ≤ 2) / carbon layer, or may have a structure coated in the order of silicon-based composite particles / SiO y (1 < y ≤ 2), but is not limited thereto.

[0129] As described above, by forming a layer containing SiO y (1 < y ≤ 2), lithium by-products remaining in the silicon-based composite particles can be effectively removed, and the particles can be effectively passivated, so that the Li compounds contained in the silicon-based composite particles are prevented from eluting and the aqueous processability is improved.

[0130] Also, since the silicon-based composite particles contain a carbon layer, unreacted lithium by-products during the acid treatment process can be prevented from eluting, and the reaction between the negative electrode active material and water in the aqueous slurry can be minimized.

[0131] <Negative electrode> The negative electrode according to one embodiment of the present invention may include the negative electrode active material described above.

[0132] 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 contain the negative electrode active material. Furthermore, the negative electrode active material layer may further include a binder and / or a conductive material.

[0133] The negative electrode active material layer may be formed by applying a negative electrode slurry containing a negative electrode active material, a binder, and / or a conductive material to at least one surface of a negative electrode current collector, drying, and rolling.

[0134] The negative electrode slurry comprises the negative electrode active material, a binder, and / or a conductive material.

[0135] The negative electrode slurry may further contain additional negative electrode active material.

[0136] As the additional negative electrode active material, compounds capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and SiO2. βExamples include lithium-doped and dedoped metal oxides such as (0<β<2), SnO2, vanadium oxide, lithium titanium oxide, and lithium vanadium oxide; or composites containing the metallic compound and carbonaceous material, such as Si-C composites or Sn-C composites. One or more of these mixtures may be used. A metallic lithium thin film may also be used as the negative electrode active material. As for the carbon material, either low-crystallinity carbon or high-crystallinity carbon may be used. Examples of low-crystalline carbon include soft carbon and hard carbon, while examples of high-crystalline carbon include amorphous, plate-like, flaky, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0137] The additional negative electrode active material may be a carbon-based negative electrode active material.

[0138] 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, 10:90 to 50:50.

[0139] 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.

[0140] The binder may contain at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and substances in which the hydrogen atoms of these substances are substituted with Li, Na, or Ca, and may also contain a variety of copolymers thereof.

[0141] 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; metal powders such as fluorocarbon, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives may be used.

[0142] 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 terms of facilitating the dispersion of components.

[0143] <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, and 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.

[0144] 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.

[0145] 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 to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase the adhesion strength of the positive electrode active material. For example, it may be used in various forms such as film, sheet, foil, mesh, porous material, foam, nonwoven fabric.

[0146] 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 Li-metal.

[0147] 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.

[0148] 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 does not cause chemical changes and has electronic conductivity in the battery that is constructed. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more may be used.

[0149] 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.

[0150] 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.

[0151] 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.

[0152] Specifically, the electrolyte may contain a non-aqueous organic solvent and a metal salt.

[0153] 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.

[0154] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, can be preferably used because they are high-viscosity organic solvents with high dielectric constants that readily dissociate lithium salts. Furthermore, when such cyclic carbonates are mixed with linear carbonates with low viscosity and low dielectric constant, such as dimethyl carbonate and diethyl carbonate, in appropriate proportions, an electrolyte with high electrical conductivity can be produced, making them even more preferable.

[0155] As the metal salt, a lithium salt may be used, and the lithium salt is a substance that dissolves easily 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:

[0156] In addition to the components of the electrolyte, the electrolyte may further contain one or more additives for the purpose of improving the battery's lifespan, suppressing the decrease in battery capacity, and improving the battery's discharge capacity, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexalic acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride.

[0157] According to another embodiment of the present invention, a battery module and a battery pack including the secondary battery as a unit cell are provided. 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]

[0158] Hereinafter, examples will be given to specifically describe this specification in detail. However, the examples according to this specification may be deformed into various other forms, and it should not be construed that the scope of this application is limited to the examples described below. The examples of this application are provided to more fully explain this specification to those with average knowledge in the industry.

[0159] <Examples and Comparative Examples> Example 1 94 g of a powder obtained by mixing Si and SiO2 at a molar ratio of 1:1 was mixed in a reactor and then vacuum-heated at a sublimation temperature of 1,400°C. Thereafter, the vaporized Si and SiO2 mixed gas was reacted in a cooling zone under vacuum having a cooling temperature of 800°C and condensed into a solid phase. Next, the condensed particles were pulverized using a ball mill for 3 hours to produce silicon-based particles having a size of 6 μm. Thereafter, while flowing Ar gas to maintain an inert atmosphere, the silicon-based particles were positioned in the hot zone of a CVD apparatus, and using Ar as a carrier gas, the methane was blown into the hot zone at 900°C and reacted at 10 -1 torr for 20 minutes to form a carbon layer on the surface. Thereafter, 6 g of Li metal powder was added, and after additional heat treatment was performed at a temperature of 800°C in an inert atmosphere, acid treatment was performed at a temperature of 80°C using ethanol as a solvent at a weight ratio of silicon-based particles: phosphoric acid = 99:1, and SiO y (1 < y ≤ 2) was formed to produce a negative electrode active material.

[0160] As a result of XPS analysis of the negative electrode active material, as shown in Figure 3, a first peak around 102 eV to 103 eV, a second peak around 99 eV to 100 eV, a third peak around 103 eV to 104 eV, and a fourth peak around 283 eV to 285 eV were obtained.

[0161] Example 2 A negative electrode active material was produced in the same manner as in Example 1, except that the process of introducing methane and performing heat treatment was carried out for 1 hour.

[0162] XPS analysis of the aforementioned negative electrode active material yielded a first peak around 102 eV to 103 eV, a second peak around 99 eV to 100 eV, a third peak around 103 eV to 104 eV, and a fourth peak around 283 eV to 285 eV.

[0163] Example 3 The negative electrode active material was manufactured in the same manner as in Example 1, except that the process of adding methane and heat treatment was changed to occur after the acid treatment.

[0164] XPS analysis of the aforementioned negative electrode active material yielded a first peak around 102 eV to 103 eV, a second peak around 99 eV to 100 eV, a third peak around 103 eV to 104 eV, and a fourth peak around 283 eV to 285 eV.

[0165] Example 4 The negative electrode active material was manufactured in the same manner as in Example 1, except that the temperature at which methane was added and heat-treated was changed to 1,100°C.

[0166] XPS analysis of the aforementioned negative electrode active material yielded a first peak around 102 eV to 103 eV, a second peak around 99 eV to 100 eV, a third peak around 103 eV to 104 eV, and a fourth peak around 283 eV to 285 eV.

[0167] Example 5 The negative electrode active material was manufactured in the same manner as in Example 1, except that it was acid-treated with silicon-based composite particles in a weight ratio of 90:10 phosphoric acid.

[0168] XPS analysis of the aforementioned negative electrode active material yielded a first peak around 102 eV to 103 eV, a second peak around 99 eV to 100 eV, a third peak around 103 eV to 104 eV, and a fourth peak around 283 eV to 285 eV.

[0169] Comparative Example 1 The negative electrode active material was produced in the same manner as in Example 1, except for the acid treatment process. The formed negative electrode active material did not contain SiO y (1 < y ≤ 2).

[0170] As a result of XPS analysis of the negative electrode active material, as shown in FIG. 4, a second peak around 99 eV to 100 eV, a third peak around 103 eV to 104 eV, and a fourth peak around 283 eV to 285 eV were obtained.

[0171] Comparative Example 2 The negative electrode active material was produced in the same manner as in Example 1, except for the process of introducing methane and performing heat treatment.

[0172] As a result of XPS analysis of the negative electrode active material, a first peak around 102 eV to 103 eV, a second peak around 99 eV to 100 eV, and a third peak around 103 eV to 104 eV were obtained.

[0173] The compositions of the negative electrode active materials produced in the above Examples and Comparative Examples are as shown in Table 1 below.

[0174]

Table 1

[0175] The analysis of the negative electrode active material by X-ray photoelectron spectroscopy was performed using a Nexsa ESCA System, Thermo Fisher Scientific (ESCA-02). Specifically, after obtaining a survey scan spectrum and a narrow scan spectrum for each sample, a depth profile was performed while obtaining the survey scan spectrum and the narrow scan spectrum. The depth profile was performed up to 3000 seconds using monatomic Ar ions, and the measurement and data processing conditions are as follows. -X-ray source: Monochromated Al K α(1486.6eV) - X-ray spot size: 400 μm - Sputtering gun: Monatomic Ar (energy: 1000eV, current: low, raster width: 2mm) - Etching rate: 0.09 nm / 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

[0176] The particle size analysis of the negative electrode active material was performed using a Microtrac S3500 instrument by laser diffraction particle size analysis.

[0177] The Li atom content was confirmed by ICP analysis using an inductively coupled plasma emission spectrometer (ICP-OES, AVIO 500, Perkin-Elmer 7300).

[0178] The presence and content of the aforementioned carbon layer were confirmed under oxygen conditions by elemental analysis via combustion (Bruker's G4 ICARUS).

[0179] The aforementioned Si and silicon-based oxide (SiO xand SiO y The NMR peak intensity or weight ratio of ) was confirmed by nuclear magnetic resonance spectroscopy (Bruker Advance III HD 600 MHz NMR Spectrometer) under conditions of MAS rate = 10 kHz.

[0180] The content of the aforementioned lithium by-product was measured by Karl Fischer titration (Mettler Toledo's Titrator Excellence T5) by placing the sample in distilled water, filtering it, and titrating the eluted components with HCl solution.

[0181] The proportion of the total amorphous phase in the negative electrode active material was measured by quantitative analysis using X-ray diffraction (Bruker's D4 Endeavor).

[0182] <Experimental Example: Evaluation of Discharge Capacity, Initial Efficiency, and Lifetime (Capacity Retention Rate) Characteristics> A negative electrode and a battery were manufactured using the negative electrode active materials of the examples and comparative examples, respectively.

[0183] A mixture was prepared by mixing carbon black as the negative electrode active material and conductive material, and PAA (polyacrylic acid) as a binder in a weight ratio of 80:10:10. Then, 7.8g of distilled water was added to 5g of the mixture and stirred to produce a negative electrode slurry. The negative electrode slurry was applied to a copper (Cu) metal thin film, which was a negative electrode current collector with a thickness of 20μm, and dried. During this process, the temperature of the circulating air was 60°C. Next, the film was rolled (rolled in a roll press) and dried in a vacuum oven at 130°C for 12 hours to produce a negative electrode.

[0184] The manufactured negative electrode was 1.7671 cm 2A circularly cut lithium (Li) metal thin film was used as the positive electrode. A porous polyethylene separator was interposed between the positive and negative electrodes. A lithium coin half-cell was manufactured by dissolving vinylene carbonate in a mixed solution of methyl ethyl carbonate (EMC) and ethylene carbonate (EC) in a volume ratio of 7:3, dissolving 0.5 parts by weight of vinylene carbonate, and injecting an electrolyte solution containing 1M LiPF6.

[0185] The manufactured batteries were subjected to charging and discharging tests to evaluate their discharge capacity, initial efficiency, and capacity retention rate, and these results are shown in Table 2 below.

[0186] The first and second cycles were charged and discharged at 0.1C, and from the third to the fortieth cycle, they were charged and discharged at 0.5C. The 50th cycle ended in a charged state (lithium was in the negative electrode). Charging conditions: CC (constant current) / CV (constant voltage) (5mV / 0.005C current cut-off) Discharge condition: CC (constant current) condition 1.5V

[0187] The discharge capacity (mAh / g) and initial efficiency (%) were derived from the results of a single charge-discharge cycle. Specifically, the initial efficiency (%) was derived by the following calculation. Initial efficiency (%) = (Discharge capacity per cycle / Charge capacity per cycle) × 100

[0188] The capacity retention rates were derived using the following calculations. Capacity retention rate (%) = (49 discharge capacity / 1 discharge capacity) × 100

[0189] <Experimental Example: Evaluation of Processability (Shear Viscosity) Characteristics> As part of the engineering evaluation, the change in shear viscosity at a shear rate of 1 Hz of the slurry produced by mixing graphite: the negative electrode active material: carbon black: CMC: PAA at a weight ratio of 77:20:1:1:1 was measured and described in Table 2 below. Specifically, the change amount (%) of the shear viscosity was derived by the following calculation formula. Change amount of shear viscosity (%) = ((Shear viscosity of the slurry after 48 hours - Shear viscosity of the slurry immediately after mixing) / Shear viscosity of the slurry immediately after mixing) × 100

[0190]

Table 2

[0191] The negative electrode active material according to the present invention is characterized in that a carbon layer and SiO y (1 < y ≤ 2) are provided, the content of lithium by-products in the negative electrode active material is low, and the layer containing the carbon layer and SiO y (1 < y ≤ 2) has an excellent passivation effect.

[0192] In Table 2 above, in Examples 1 to 5, the content of lithium by-products in the negative electrode active material is low due to acid treatment, and SiO y (1 < y ≤ 2) is formed, so that the proportion of the amorphous phase in the negative electrode active material increases. The negative electrode active materials of Examples 1 to 5 have a low content of lithium by-products in the negative electrode active material, and due to the passivation effect of SiO y (1 < y ≤ 2), it was confirmed that they are superior to the comparative examples in terms of overall discharge capacity, initial efficiency, and capacity retention rate. Also, by minimizing the influence of lithium by-products or lithium compounds eluted from silicon-based composite particles by SiO y (1 < y ≤ 2), it was confirmed that the change amount of the shear viscosity of the slurry is significantly lower than that of Comparative Examples 1 and 2.

[0193] In contrast, in the case of Comparative Example 1, acid treatment was not performed, and SiO y (1 < y ≤ 2) was not formed. In the case of Comparative Example 1, the lithium content was higher than that of the Examples, and the initial efficiency was slightly higher. However, side reactions of the slurry occurred due to lithium by-products, and the viscosity of the slurry changed. Therefore, it was confirmed that the discharge capacity and capacity retention rate were significantly lower, and the change amount of shear viscosity was significantly larger than those of the Examples.

[0194] In the case of Comparative Example 2, it does not contain a carbon layer, cannot prevent the expansion of silicon-based composite particles, has low conductivity, and cannot effectively coat the silicon-based composite particles. Therefore, it is impossible to exhibit an appropriate capacity due to the volume expansion of the negative electrode active material during charge / discharge, and side reactions of the slurry occur due to lithium by-products not coated with a carbon layer, and the viscosity of the slurry changes. Therefore, it was confirmed that the discharge capacity and capacity retention rate were significantly lower, and the change amount of shear viscosity was significantly larger than those of the Examples.

[0195] Therefore, in the present invention, by providing a negative electrode active material provided with a carbon layer and SiO)] y (1 < y ≤ 2) on the silicon-based composite particles, lithium by-products can be effectively removed, and the overall aqueous system workability, discharge capacity, efficiency, and capacity retention rate can be easily improved by using the passivation effect.

Explanation of Reference Numerals

[0196] 1 ··· Silicon-based composite particles 2 ··· Carbon layer 3 ··· SiO y 4 ··· Lithium by-product

Claims

1. SiO ｘ (0 < x < 2) and silicon-based composite particles containing Li compounds; carbon layer; and SiO ｙ A negative electrode active material containing (1 < y ≤ 2), The carbon layer is provided in a form that covers at least a portion of the surface of the silicon-based composite particles, The SiO ｙ (1 < y ≤ 2) is provided in a form that covers at least a portion of the surface of the silicon-based composite particles or at least a portion of the surface of the carbon layer, During NMR measurement, the ratio of the peak intensity of Si (p1) to the peak intensity indicating the Si-O bond (p2) (p1:p2) is 88:12 to 60:

40. A negative electrode active material in which the proportion of the amorphous phase is 32% or more, based on the total weight of the silicon-based composite particles and the SiO y (1 < y ≤ 2).

2. The negative electrode active material according to claim 1, which has a peak located at 10¹ eV to 10⁴ eV when analyzed by X-ray photoelectron spectroscopy.

3. The SiO ｙ The negative electrode active material according to claim 1, wherein (1 < y ≤ 2) is provided in a form that covers at least a portion of the surface of the silicon-based composite particle between the surface of the silicon-based composite particle and the carbon layer, or in a form that covers at least a portion of the region in the surface of the silicon-based composite particle where the carbon layer is not provided, or in a form that covers at least a portion of the surface of the carbon layer.

4. The SiO ｙ The negative electrode active material according to claim 1, wherein (1 < y ≤ 2) is included in an amount of 0.1 parts by weight to 50 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, further comprising lithium byproducts provided on at least a portion of the silicon-based composite particles.

6. The negative electrode active material according to claim 5, wherein the lithium by-product is contained in an amount of 5 parts by weight or less based on 100 parts by weight of the total negative electrode active material.

7. The negative electrode active material according to claim 5, further comprising a carbon layer provided on at least a portion of the lithium byproduct.

8. The negative electrode active material according to claim 1, wherein the Li contained in the silicon-based composite particles is present in an amount of 0.1 parts by weight to 40 parts by weight based on a total of 100 parts by weight of the negative electrode active material.

9. The anode active material according to claim 1, wherein the carbon layer is contained in an amount of 0.1 to 20 parts by weight based on a total of 100 parts by weight of the anode active material.

10. SiO ｘ A step of producing silicon-based composite particles containing (0 < x < 2) and a Li compound; and The aforementioned silicon-based composite particles are treated with acid to obtain SiO ｙ Steps to form (1 < y ≤ 2) A method for producing a negative electrode active material according to any one of claims 1 to 9, including

11. A negative electrode comprising the negative electrode active material according to any one of claims 1 to 9.

12. A secondary battery comprising the negative electrode described in claim 11.

Images