CN116762188A - Negative electrode active material, method for producing negative electrode active material, negative electrode comprising negative electrode active material, and secondary battery comprising same - Google Patents

Abstract

The present invention relates to a negative active material, a preparation method thereof, a negative electrode including the negative active material, and a secondary battery including the negative electrode, wherein the negative active material includes: SiO _x (0<x<2) and Silicon-based composite particles of a Li compound; a carbon layer; and SiO _y (1<y≤2), wherein the carbon layer covers at least part of the surface of the silicon-based composite particles, and the SiO _y (1<y≤ 2) Covering at least part of the surface of the silicon-based composite particles or at least part of the surface of the carbon layer.

Description

Negative active material, manufacturing method of negative active material, including negative active material The negative electrode and the secondary battery containing the same

Technical field

This application claims priority and interest in Korean Patent Application Nos. 10-2021-0107522 and 10-2022-0014132, which were submitted to the Korean Intellectual Property Office on August 13, 2021 and February 3, 2022, respectively. The entire content of the application is approved by Incorporated into this article by reference.

The present invention relates to a negative electrode active material, a preparation method of the negative electrode active material, a negative electrode including the negative electrode active material, and a secondary battery including the same.

Background technique

Recently, with the rapid spread of electronic devices using batteries such as mobile phones, notebook computers, and electric vehicles, demand for small and lightweight secondary batteries with relatively high capacity is rapidly increasing. In particular, lithium secondary batteries are lightweight and have high energy density, and therefore are attracting attention as driving power sources for mobile devices. Therefore, research and development efforts have been actively conducted to improve the performance of lithium secondary batteries.

Generally, a lithium secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, an electrolyte, an organic solvent, and the like. Furthermore, for the positive electrode and the negative electrode, active material layers each containing the positive electrode active material and the negative electrode active material may be formed on the current collector. Generally, lithium-containing metal oxides such as LiCoO ₂ and LiMn ₂ O ₄ have been used as positive electrode active materials for the positive electrode, and lithium-free carbon-based active materials and silicon-based active materials have been used as negative electrode active materials for the negative electrode.

Among negative electrode active materials, silicon-based active materials have attracted much attention because they have high capacity and excellent high-speed charging characteristics compared to carbon-based active materials. However, silicon-based active materials suffer from a large degree of volume expansion/shrinkage due to charge/discharge and a large irreversible capacity, so they have the disadvantage of low initial efficiency.

On the other hand, among silicon-based active materials, silicon-based oxides, specifically silicon-based oxides represented by _SiO The advantage is that the volume expansion/shrinkage caused by charging/discharging is small. However, silicon-based oxides still have the disadvantage of reduced initial efficiency due to the presence of irreversible capacity.

In this regard, research has been continuously conducted to reduce the irreversible capacity and improve the initial efficiency by doping or embedding metals such as Li, Al, and Mg into silicon-based oxides. However, in the case where the negative electrode slurry contains a metal-doped silicon-based oxide as the 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. , therefore, there is a problem that the state of the prepared negative electrode deteriorates and the charge/discharge efficiency of the negative electrode decreases.

Therefore, there is a need to develop a negative electrode active material that can improve the phase stability of a negative electrode slurry containing a silicon-based oxide and improve the charge/discharge efficiency of a negative electrode prepared therefrom.

Korean Patent No. 10-0794192 relates to a method for preparing carbon-coated silicon-graphite composite negative electrode materials for lithium secondary batteries and a method for preparing secondary batteries containing the same, but there are limitations in solving the above problems.

existing technical documents

(Patent Document 1) Korean Patent No. 10-0794192

Contents of the invention

technical problem

The present invention relates to a negative electrode active material, a preparation method of the negative electrode active material, a negative electrode including the negative electrode active material, and a secondary battery including the same.

Technical solutions

An exemplary embodiment of the present invention provides a negative active material, including: silicon-based composite particles containing SiO _x (0<x<2) and a Li compound; a carbon layer; and SiO _y (1<y≤2), wherein the carbon layer is configured to coat at least a portion of the surface of the silicon-based composite particles, and SiO _y (1<y≤2) is configured to coat at least a portion of the surface of the silicon-based composite particles or to coat At least part of the surface of the carbon coating is in the form.

An exemplary embodiment of the present invention provides a method for preparing a negative active material, which method includes: preparing silicon-based composite particles containing SiO _x (0<x<2) and a Li compound; and by adding the silicon-based composite particles The composite particles are subjected to acid treatment to coat at least part of the surface of the silicon-based composite particles with SiO _y (1<y≤2).

An exemplary embodiment of the present invention provides a negative electrode including the negative active material.

An exemplary embodiment of the present invention provides a secondary battery including the negative electrode.

beneficial effects

In the present invention, by acid-treating Li-doped silicon-based composite particles, lithium by-products generated during the process of doping silicon-based composite particles with Li can be effectively removed, and in the acid treatment process, SiO _y (1<y≤2) is formed on the silicon-based composite particles, thereby passivating the particles. The SiO _y (1<y≤2) formed in this case may be provided in a form that coats at least a portion of the surface of the carbon layer or in a form that coats at least a portion of the surface of the silicon-based composite particles. Specifically, the SiO _y (1<y≤2) may be configured to coat 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 may be configured to coat the silicon-based composite particles. The particle may be in the form of at least a part of a region on the surface of which a carbon layer is not provided, or in the form of at least part of a surface coated with a carbon layer.

In addition, the silicon-based composite particles may include the carbon layer to prevent the elution of unreacted lithium by-products in the acid treatment process and minimize the reaction between the negative electrode active material and water in the aqueous slurry.

Therefore, the negative electrode including the negative electrode active material and the secondary battery including the negative electrode have the effect of improving the discharge capacity, initial efficiency, resistance performance and/or service life characteristics of the battery.

Description of the drawings

1 and 2 respectively schematically illustrate the structure of a negative active material according to an exemplary embodiment of the present invention.

Figures 3 and 4 relate to the XPS analysis results of the negative active material of Example 1 and Comparative Example 1, respectively.

Symbol Description

1: Silicon composite particles

2: Carbon layer

3:SiO _y

4: Lithium by-product

Detailed ways

In the following, this specification will be described in more detail.

In this specification, when a part "includes" a constituent element, unless otherwise specified, this does not mean that other constituent elements are excluded, but that other constituent elements may be further included.

In this specification, when one member is arranged "on" another member, this includes not only the case where one member is in contact with the other member, but also the case where the other member is present between the two members.

The terms or words used in this specification should not be construed to be limited to conventional or dictionary meanings, but should be based on the principle that the inventor can appropriately define the concepts of the terms to describe his/her own invention in the best possible way, using Explain the meaning and concepts consistent with the technical gist of the present invention.

As used in this specification, singular expressions of terms include plural expressions unless the context clearly indicates a contrary meaning.

In this specification, the crystalline form of the structure contained in the negative electrode active material can be confirmed by X-ray diffraction analysis using an X-ray diffraction (XRD) analyzer (trade name: D4-endavor, manufacturer : Bruker Co., Ltd.), in addition to this equipment, equipment used in this field can also be appropriately used.

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

In this specification, the specific surface area can be calculated by using BET measurement equipment (BEL-SORP-MAX, Bell Company, Japan), degassing the object to be measured at 130°C for 2 hours, and performing N ₂ adsorption/desorption at 77K Measurement.

In this specification, the average particle diameter (D ₅₀ ) can be defined as the particle diameter corresponding to 50% of the cumulative volume in the particle size distribution curve (curve of the particle size distribution diagram) of the particles. The average particle diameter (D ₅₀ ) can be measured using, for example, laser diffraction. The laser diffraction method is generally capable of measuring particle sizes from the submicron region to several millimeters, and can obtain results with high reproducibility and high resolution.

Hereinafter, preferred exemplary embodiments of the present invention will be described in detail. However, the exemplary embodiments of the present invention may be changed into various other forms, and the scope of the present invention is not limited to the exemplary embodiments to be described below.

<Negative active material>

An exemplary embodiment of the present invention provides a negative active material, including: silicon-based composite particles containing SiO _x (0<x<2) and a Li compound; a carbon layer; and SiO _y (1<y≤2), wherein the carbon layer is configured to coat at least a portion of the surface of the silicon-based composite particles, and the SiO _y (1<y≤2) is configured to coat at least a portion of the surface of the silicon-based composite particles Or in the form of coating at least a part of the surface of the carbon layer.

Generally, in the step of doping silicon-based particles with Li, lithium by-products formed from unreacted lithium are present on the particles, thereby making the slurry alkaline. Therefore, there are problems such as changes in the rheological properties of the slurry and the reaction of Si in the silicon-based particles with alkali to generate gas.

Therefore, in the present invention, by subjecting Li-doped silicon-based composite particles to acid treatment, lithium by-products formed during the process of doping silicon-based composite particles with Li can be effectively removed, and in the acid treatment process , SiO _y (1<y≤2) is formed on the surface of the silicon-based composite particles, thereby passivating the particles. The SiO _y (1<y≤2) formed in this case may be provided in a form in which at least a part of the surface of the silicon-based composite particle is coated between the surface of the silicon-based composite particle and the carbon layer, and is configured to be coated with silicon. It is in the form of at least a part of the area on the surface of the composite particle where no carbon layer is provided, or in the form of at least part of the surface of the composite particle coated with the carbon layer.

In addition, the silicon-based composite particles may include the carbon layer to prevent the elution of unreacted lithium by-products in the acid treatment process and minimize the reaction between the negative electrode active material and water in the aqueous slurry.

A negative active material according to an exemplary embodiment of the present invention contains silicon-based composite particles. The silicon-based composite particles include SiO _x (0<x<2) and a Li compound.

The SiO _x (0<x<2) may correspond to the matrix in the silicon-based composite particles. The SiO _x (0<x<2) may be in a form including Si and SiO ₂ , and Si may also form a phase. That is, x corresponds to the number ratio of O to Si contained in 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.

In an exemplary embodiment of the present invention, the silicon-based composite particles may include a Li compound. The Li compound may correspond to the matrix in the silicon-based composite particles. The Li compound may exist in the silicon-based composite particles in the form of at least one of lithium atoms, lithium silicate, lithium silicide, and lithium oxide. When the silicon-based composite particles contain a Li compound, there is an effect of improving initial efficiency.

The Li compound is in a form in which silicon-based composite particles are doped with the compound, and may be distributed on the surface and/or inside the silicon-based composite particles. The Li compound is distributed on the surface and/or inside the silicon-based composite particles, so that the volume expansion/shrinkage of the silicon-based composite particles can be controlled to an appropriate level, and can be used to prevent damage to active materials. In addition, the Li compound may be contained in order to reduce the ratio of the irreversible phase (for example, SiO ₂ ) of the silicon-based oxide particles and thereby improve the efficiency of the active material.

In an exemplary 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 be present in the silicon-based particles in the form of at least one lithium silicate selected from the group consisting of Li ₂ SiO ₃ , Li ₄ SiO ₄ and Li ₂ Si ₂ O ₅ , And the amorphous lithium silicate may be composed of a composite structure in the form of Li _a Si _b O _c (2≤a≤4, 0<b≤2, 2≤c≤5), and is not limited to this form.

In an exemplary embodiment of the present invention, the content of Li may be 0.1 to 40 parts by weight or 0.1 to 25 parts by weight relative to a total of 100 parts by weight of the negative active material. Specifically, the content of Li may be 1 to 25 parts by weight, more specifically 2 to 20 parts by weight. There is a problem that as the content of Li increases, the initial efficiency increases but the discharge capacity decreases, so that when the content satisfies the above range, appropriate discharge capacity and initial efficiency can be achieved.

The content of Li element can be confirmed by ICP analysis. Specifically, after weighing a predetermined amount (about 0.01 g) of the negative active material, the negative active material was completely decomposed on a hot plate by transferring the sample to a platinum crucible and adding nitric acid, hydrofluoric acid, or sulfuric acid thereto. Thereafter, a reference calibration curve was prepared by measuring the intensity of a standard solution prepared using a standard solution (5 mg/kg) at the intrinsic wavelength of the element to be analyzed using an inductively coupled plasma atomic emission spectrometer (ICPAES, Perkin-Elmer 7300 Company). Thereafter, the pretreated sample solution and blank sample are each introduced into the device, the actual intensity is calculated by measuring each intensity, the concentration of each component is calculated relative to the prepared calibration curve, and then the sum can be converted to a theoretical value. The element content of the prepared negative active material was analyzed.

In an exemplary embodiment of the present invention, the silicon-based composite particles may include additional metal atoms. The metal atoms may be present in the silicon-based composite particles in the form of at least one of metal atoms, metal silicates, metal silicides, and metal oxides. The metal atom may include at least one selected from the group consisting of Mg, Li, Al, and Ca. Thereby, the initial efficiency of the negative electrode active material can be improved.

In an exemplary embodiment of the present invention, the negative active material includes a carbon layer. Specifically, the carbon layer is provided to coat at least part of the surface of the silicon-based composite particles.

Specifically, the negative active material is imparted with electrical conductivity through the carbon layer, and the initial efficiency, service life characteristics, and battery capacity characteristics of the secondary battery can be improved.

In an exemplary embodiment of the present invention, the carbon layer may include at least one of amorphous carbon and crystalline carbon.

In an exemplary embodiment of the present invention, the carbon layer may be an amorphous carbon layer. The amorphous carbon can suppress expansion of the silicon-based composite particles by appropriately maintaining the strength of the carbon layer.

Furthermore, the carbon layer may or may not contain additional crystalline carbon.

The crystallized carbon can further improve the conductivity of the negative active material. The crystalline carbon may include at least one selected from the group consisting of fullerene, carbon nanotube, and graphene.

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

The carbide of the other organic material may be a carbide of sucrose, glucose, galactose, fructose, lactose, mannose, ribose, aldohexose or ketohexose, as well as carbides of organic materials selected from combinations thereof.

The hydrocarbon may be a substituted or unsubstituted aliphatic or cycloaliphatic 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 wait. Examples of the aromatic hydrocarbons of the substituted or unsubstituted aromatic hydrocarbons include benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, Benzofuran, pyridine, anthracene, phenanthrene, etc.

In an exemplary embodiment of the present invention, the content of the carbon layer may be 0.1 to 50 parts by weight, 0.1 to 30 parts by weight, or 0.1 parts by weight relative to a total of 100 parts by weight of the negative active material. parts to 20 parts by weight. More specifically, the content of the carbon layer may be 0.5 to 15 parts by weight or 1 to 10 parts by weight. When the above range is satisfied, it is possible to prevent the capacity and efficiency of the negative electrode active material from being reduced while improving the conductivity.

In an exemplary embodiment of the present invention, the thickness of the carbon layer may be 1 nm to 500 nm, specifically 5 nm to 300 nm, more specifically 5 nm to 100 nm. When the above range is satisfied, the conductivity of the negative active material is improved, the volume change of the negative active material is easily suppressed, and the side reaction between the electrolyte and the negative active material is suppressed, thereby improving the initial efficiency of the battery. and/or longevity effects.

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

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

In an exemplary embodiment of the present invention, the negative active material includes SiO _y (1<y≤2). Specifically, the SiO _y (1<y≤2) is provided to coat at least a portion of the surface of the silicon-based composite particles or to coat at least a portion of the surface of the carbon layer.

Specifically, in the present invention, by subjecting Li-doped silicon-based composite particles to acid treatment, lithium by-products formed during the process of doping silicon-based composite particles with Li can be effectively removed, and in the acid treatment process , SiO _y (1<y≤2) is formed on the silicon-based composite particles, thereby passivating the particles.

In addition, the silicon-based composite particles may include the carbon layer to prevent the elution of unreacted lithium by-products in the acid treatment process and minimize the reaction between the negative electrode active material and water in the aqueous slurry.

The y in SiO _y (1<y≤2) corresponds to the number ratio of O to Si contained in SiO _y (1<y≤2).

The SiO _y (1<y≤2) is formed during the process of preparing silicon-based composite particles and then subjecting lithium compounds, that is, lithium by-products, remaining near the surfaces of the silicon-based composite particles or the carbon layer to acid treatment. Specifically, lithium byproducts are removed by acid treatment, lithium is deintercalated from lithium silicate near the surface of the silicon-based composite particles, and materials with various oxidation numbers are mixed to form a SiO _y (1<y≤2) phase .

The SiO _y (1<y≤2) may exist as an island-type or thin-film type layer, and may exist in various forms without being limited thereto.

In this case, SiO _y (1<y≤2) generated in the step of acid-treating the silicon-based particles may be present in each portion of the silicon-based composite particles. Specifically, the SiO _y (1<y≤2) may be configured to coat 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, and is configured to coat the silicon-based composite particles. The particle may be in the form of at least a part of a region on which a carbon layer is not provided, or may be in the form of at least a part of a surface coated with a carbon layer.

In one example, the SiO _y (1<y≤2) may be provided in a form in which at least a portion of the surface of the silicon-based composite particle is coated between the surface of the silicon-based composite particle and the carbon layer. That is, the SiO _y (1<y≤2) may be in a form in which at least part of the surface of the silicon-based composite particle is coated, and the SiO _y is further coated with a carbon layer. That is, the SiO _y (1<y≤2) may be provided adjacent to the surface of the silicon-based composite particle, 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 in which the surface of the silicon-based composite particles is partially coated or the entire surface is coated. Examples of the shape of SiO _y (1<y≤2) include island type, film type, etc., but are not limited thereto.

In one example, the carbon layer may be in the form of partially coating the surface of SiO _y (1<y≤2), or coating the entire surface. Examples of the shape of the carbon layer include island type, film type, etc., but are not limited thereto.

In one example, the SiO _y (1<y≤2) may be provided to coat at least a part of a region on the surface of the silicon-based composite particle where no carbon layer is provided. That is, the SiO _y (1<y≤2) may be provided adjacent to the surface of the silicon-based composite particle. The SiO _y (1<y≤2) may be in a form in which the surface of the silicon-based composite particles is partially coated or the entire surface is coated. Examples of the shape of SiO _y (1<y≤2) include island type, film type, etc., but are not limited thereto.

Specifically, while the silicon-based composite particles are doped with lithium, the particles generally expand, so that there may be a region where the carbon layer cannot completely coat the silicon-based composite particles. In this case, SiO _y (1<y≤2) formed during the acid treatment process of the silicon-based composite particles is formed on the region, and therefore can be disposed adjacent to the surface of the silicon-based composite particles, so that It is easier to achieve passivation of silicon-based composite particles.

In one example, the SiO _y (1<y≤2) may be configured to coat at least a portion of the surface of the carbon layer. That is, the SiO _y (1<y≤2) may be disposed adjacent to the surface of the carbon layer. The SiO _y (1<y≤2) may be in the form of a surface partially coated with a carbon layer or an entire surface coated with a carbon layer. Examples of the shape of SiO _y (1<y≤2) include island type, film type, etc., but are not limited thereto.

That is, the negative electrode active material may have a structure in which silicon-based composite particles/carbon layer/SiO _y (1<y≤2) are sequentially coated, or in which silicon-based composite particles/SiO _y (1<y≤2)/ The carbon layers are sequentially coated, or the silicon-based composite particles/SiO _y (1<y≤2) are sequentially coated, but the order is not limited to this.

As described above, when the lithium by-product remaining near the surface of the silicon-based composite particles or the carbon layer is acid-treated, it is possible to prevent the slurry from becoming alkaline due to the lithium by-product, and there is a problem due to the presence of lithium by-products. The passivation effect of SiO _y (1<y≤2) produced as a by-product prevents the Li compound contained in the silicon-based composite particles from eluting, thereby improving the aqueous processability of the slurry.

In an exemplary embodiment of the present invention, the negative active material has a peak existing between 101 eV and 104 eV when analyzed by X-ray photoelectron spectroscopy. It can be called the first peak. Specifically, the first peak appears around 102 eV to 103 eV, and may be a peak caused by SiO _y (1<y≤2).

In an exemplary embodiment of the present invention, the negative active material has a second peak existing between 99 eV and 101 eV when analyzed by X-ray photoelectron spectroscopy. Specifically, the second peak may appear around 99 eV to 100 eV, and may be a peak caused by Si.

In an exemplary embodiment of the present invention, the negative active material has a third peak existing between 102 eV and 105 eV when analyzed by X-ray photoelectron spectroscopy. Specifically, the third peak may appear near 103eV to 104eV, and may be a peak caused by _SiO2 .

In an exemplary 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 caused by Si (oxidation number = 0) and the third peak caused by SiO ₂ (oxidation number = +4), and the negative electrode active material of the present invention is on the surface Contains Si with an oxidation number between 0 and +4.

In an exemplary embodiment of the present invention, the negative active material has a fourth peak existing between 282eV and 286eV when analyzed by X-ray photoelectron spectroscopy. Specifically, the peak appears around 283 eV to 285 eV, and may be a peak caused by carbon (C) of the carbon layer.

In the present invention, X-ray photoelectron spectroscopy analysis of the negative active material can be performed by a Nexsa ESCA system, Thermo Fisher Scientific (ESCA-02).

Specifically, after acquiring a full scan spectrum (survey scan spectrum) and a narrow scan spectrum (narrow scan spectrum) for each sample, the full scan spectrum and the narrow scan spectrum can be acquired while performing a depth profile. Depth profiles up to 3000 s can be performed using single-atom Ar ions with the following measurement and data processing conditions.

-X-ray source: Monochromatic Al Kα (1486.6eV)

-X-ray spot size: 400μm

-Sputtering Gun: Monoatomic Ar (Energy: 1000eV, Flow: Low, Grating Width: 2mm)

-Etch rate: 0.09nm/s for Ta ₂ O ₅

-Operating mode: CAE (Constant Analyzer Energy) mode

-Full scan: pass energy 200eV, energy level 1eV

-Narrow scan: scan mode, pass energy 50eV, energy level 0.1eV

-Charge Compensation: Flood Gun Off

-SF:Al THERMO1

-ECF:TPP-2M

-Background Subtraction: Shirley

In an exemplary embodiment of the present invention, the depth distribution of X-ray photoelectron spectroscopy (XPS) can be measured under a monochromatic Al Kα X-ray source performing spectroscopy at 0.09 nm/s for up to 3000 seconds.

1 and 2 respectively schematically illustrate the structure of a negative active material according to an exemplary embodiment of the present invention. Specifically, at least a part of the silicon-based composite particles 1 is coated with SiO _y (1<y≤2)3, and at least a part of the SiO _y (1<y≤2)3 may be coated with the carbon layer 2. Alternatively, at least part of the silicon-based composite particles 1 is coated with the carbon layer 2, and at least part of the carbon layer 2 may be coated with SiO _y (1<y≤2)3. In addition, although not shown in FIGS. 1 and 2 , areas on the silicon-based composite particles where no carbon layer is formed may be coated with SiO _y (1<y≤2).

In FIGS. 1 and 2 , SiO _y (1<y≤2) is shown as an island shape in which the surface of the particle is partially coated, but other shapes may be shown without being limited thereto.

The negative active material according to an exemplary 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. surface layer.

The first surface layer may be in a form of coating at least part of the silicon-based composite particles, that is, partially coating the surface of the particles, or coating the entire surface of the particles. Examples of the shape of the first surface layer include island type, film type, etc., but are not limited thereto.

The second surface layer may be in the form of coating at least part of the first surface layer, that is, partially coating the surface of the first surface layer, or coating the entire surface of the first surface layer. Examples of the shape of the second surface layer include island type, film type, etc., but are not limited thereto.

The second surface layer may be additionally provided on at least a part of the silicon-based composite particles. That is, the second surface layer may exist in a form in which a portion of the silicon-based composite particle not provided with the first surface layer is coated in addition to the first surface layer. 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 the carbon layer Areas where the silicon-based composite particles cannot be completely coated.

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

In an exemplary 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 active material includes a layer including SiO y (1<y≤2) provided on at least a part of the silicon-based composite particles, and may include a layer including _{SiO y (} 1<y≤2) provided on ) layer on at least a portion of the carbon layer.

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

In addition, while the silicon-based composite particles are doped with lithium, the particles generally expand so that there may be a region in which the carbon layer cannot completely coat the silicon-based composite particles, and the SiO _y (1<y≤2) It is formed on the said area, and can be arrange|positioned adjacent to the surface of a silicon-based composite particle.

In an exemplary embodiment of the present invention, the carbon layer and SiO _y (1<y≤2) may be disposed adjacent to each other.

In an exemplary embodiment of the present invention, the first surface layer and the second surface layer may be disposed adjacent to each other. That is, no additional layer may be provided between the first surface layer and the second surface layer.

In an exemplary embodiment of the present invention, the SiO _y (1<y≤2) may be set to an amount of 0.01 to 50 parts by weight based on a total of 100 parts by weight of the negative active material. Preferably, the SiO _y (1<y≤2) can be set to an amount of 0.1 to 30 parts by weight or 1 to 20 parts by weight. When the above range is satisfied, water-based processability is improved, so that the capacity and efficiency of the negative electrode active material can be prevented from being reduced. When the content is lower than the above range, there is a problem that the passivation effect cannot be appropriately performed, and when the content is higher than the above range, there is a problem that the electrical conductivity is deteriorated, and the capacity and efficiency are reduced.

The negative active material according to an exemplary embodiment of the present invention contains SiO _y (1<y≤2), and the SiO _y (1<y≤2) may contain SiO ₂ .

In an exemplary embodiment of the present invention, the SiO _y (1<y≤2) may include an amorphous phase. In one example, during X-ray diffraction analysis of the negative active material, no crystallization peak originating from SiO _y (1<y≤2) was detected.

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

In an exemplary embodiment of the present invention, in NMR measurement of the negative active material, the ratio (p1:p2) of the peak intensity of Si (p1) and the peak intensity (p2) representing the Si-O bond may be 88: 12 to 60:40. The ratio may be specifically 85:15 to 65:35, more specifically 80:20 to 70:30. When the above range is satisfied, the _SiOy coated silicon-based composite particles in the negative electrode active material can more effectively coat the particles to prevent side reactions during the formation of the slurry.

The NMR peak intensity or weight ratio of Si and silicon-based oxides (SiO _x and SiO _y ) can be confirmed by a nuclear magnetic resonance spectrometer (Advance III HD 600MHz NMR Spectrometer from Bruker) under the condition of MAS rate = 10 kHz.

In this case, the peak of Si can be measured in the chemical shift value range of -80 ppm to -90 ppm, and the peak of the Si-O bond can be measured in the chemical shift value range of -100 ppm to -120 ppm.

In an exemplary embodiment of the present invention, the weight ratio of the carbon layer and SiO _y (1<y≤2) (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 appropriate conductivity, and when the above range is not satisfied, there is a problem of conductivity deterioration.

In an exemplary embodiment of the present invention, the negative active material may further include lithium by-products disposed on at least a part of the silicon-based composite particles. The lithium by-product may include at least one selected from the group consisting of Li ₂ O, LiOH, and Li ₂ CO ₃ .

Specifically, the lithium by-product may refer to a lithium compound remaining near the surface of the silicon-based composite particle or the carbon layer after the silicon-based composite particle is prepared. As described above, even after the acid treatment process, lithium by-products that have not reacted with the acid may remain.

1 and 2 each schematically illustrate a structure of a negative active material according to an exemplary embodiment of the present invention, and the negative active material according to an exemplary embodiment of the present invention may be one in which the lithium byproduct 4 is provided At least a part of the silicon-based composite particles 1 and the carbon layer 2 are coated with lithium by-products 4 . However, although Figures 1 and 2 show that lithium by-product is present, lithium by-product may not be present.

The content of the lithium by-product may be 5 parts by weight or less relative to a total of 100 parts by weight of the negative active material. Specifically, the content of the lithium by-product may be more than 0 parts by weight and less than 5 parts by weight, more than 0 parts by weight and less than 5 parts by weight, more than 0.01 parts by weight and less than 5 parts by weight, more than 0.05 parts by weight and less than 2 parts by weight. or less than 0.1 part by weight and less than 1 part by weight. More specifically, the content of the lithium by-product may be 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 or less. The lower limit of the content of the lithium by-product may be 0 parts by weight (exclusive), 0.01 parts by weight, or 0.1 parts by weight, and the upper limit thereof 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, and aqueous processability can be improved by reducing viscosity changes. On the contrary, when the content of the lithium by-product is higher than the above range, there is a problem that the slurry becomes alkaline during slurry formation, which causes side reactions or viscosity changes, and problems with aqueous processability.

The content of the lithium by-product can be calculated by measuring the amount of the HCl solution in a specific interval of pH change during the titration of the aqueous solution containing the negative active material with the HCl solution using a titrator, and then calculating the amount of the lithium by-product. .

A carbon layer may additionally be provided on at least a portion of the surface of the lithium by-product. The carbon layer may be configured to coat the lithium byproduct. Specifically, the carbon layer may be formed during preparation of the silicon-based composite particles, and the lithium byproduct that has not reacted with the acid may exist in a lower part of the carbon layer or in an upper part of the carbon layer.

In an exemplary embodiment of the present invention, the ratio of the amorphous phase may be 32% or more relative to the total weight of silicon-based composite particles and SiO _y (1<y≤2) in the negative active material. Specifically, the ratio may be 32% to 70%, 35% to 60%, or 35% to 55%.

As described above, since SiO _y (1<y≤2) generated by acid treatment of lithium by-products remaining near the surface of silicon-based composite particles or carbon layers contains an amorphous phase, the negative electrode active material after acid treatment The ratio of the amorphous phase in the medium increases. Therefore, when the weight ratio of the silicon-based composite particles and the amorphous phase (based on the total weight) of SiO _y (1<y≤2) in the negative electrode active material satisfies the above range, an amorphous phase containing SiO _y (1< y≤2) layer has the effect of improving passivation characteristics.

The ratio of the amorphous phase in the negative active material can be measured using quantitative analysis by X-ray diffraction analysis (D4 Endeavor from Bruker Corporation).

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

The average particle size (D ₅₀ ) of the negative active material may be 0.1 μm to 30 μm, specifically 1 μm to 20 μm, more specifically 1 μm to 10 μm. When the above range is met, the structural stability of the active material during charge and discharge is ensured, and the problem of volume expansion/contraction levels becoming larger as the particle size increases excessively can be prevented, as well as the reduction in initial efficiency due to too small particle size. The problem.

<Preparation method of negative active material>

An exemplary embodiment of the present invention provides a method for preparing a negative active material, which method includes: preparing silicon-based composite particles containing SiO _x (0<x<2) and a Li compound; and by combining the silicon-based composite particles The composite particles are acid-treated to form SiO _y (1<y≤2).

The silicon-based composite particles can be formed by heating and vaporizing Si powder and SiO ₂ powder under vacuum, and then depositing the vaporized mixed gas to form preliminary particles; mixing the preliminary particles with Li powder, The resulting mixture is then heat treated.

In this case, the step may include forming a carbon layer. The carbon layer may be formed after forming the preliminary particles and before mixing the preliminary particles and Li powder, or may be performed after mixing the preliminary particles and Li powder and then heat-treating the resulting mixture.

Alternatively, the silicon-based composite particles can be formed by heating and vaporizing Si powder and SiO ₂ powder under vacuum, and then depositing the vaporized mixed gas to form preliminary particles; and combining the preliminary particles with Li powder Mix and then heat treat the resulting mixture.

Specifically, the mixed powder of Si powder and SiO ₂ powder can be heat treated under vacuum at 1400°C to 1800°C or 1400°C to 1600°C.

The formed preliminary particles may exist in the form of SiO _x (x=1).

The silicon-based composite particles may contain the above-mentioned Li silicate, Li silicide, Li oxide, etc.

The particle size of the silicon-based composite particles can be adjusted by methods such as ball milling, jet milling, or jet classification, and the method is not limited thereto.

In the formation of the carbon layer, the carbon layer may be prepared by utilizing a chemical vapor deposition (CVD) method using hydrocarbon gas, or by carbonizing a material used as a carbon source.

Specifically, the carbon layer can be formed by introducing the formed preliminary particles into a reaction furnace, and then performing chemical vapor deposition (CVD) on 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°C to 1000°C.

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

In order to remove lithium by-products remaining in the step of forming the silicon-based composite particles, the silicon-based composite particles may be subjected to acid treatment.

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

As the acid during the acid treatment, phosphoric acid (H ₃ PO ₄ ), sulfuric acid (H ₂ SO ₄ ), boric acid (H ₃ BO ₃ ), citric acid, protonated aniline, etc. can be used. Specifically, phosphoric acid (H _{3 PO4} ). However, the acid is not limited thereto, and may appropriately adopt any configuration known in the art.

As the solvent during the acid treatment, distilled water, alcohol, N-methylpyrrolidone (NMP), etc. can be used, and for example, ethanol can be used. However, the solvent is not limited thereto, and any composition known in the art may be appropriately adopted depending on the type of acid.

The acid treatment may be carried out in the range of 50°C to 200°C, but the temperature 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 lower or 70°C to 90°C or lower.

The unreacted lithium compound, that is, the lithium by-product remains during the preparation of the silicon-based composite particles and remains near the surface of the silicon-based composite particles or the carbon layer. Therefore, when the silicon-based composite particles are treated with an acid, the remaining lithium by-product reacts with the acid and is removed, and Li is deintercalated from the lithium silicate near the surface of the silicon-based composite particles, thereby forming SiO _y (1<y ≤2).

The formed SiO _y (1<y≤2) may be provided to coat at least part of the surface of the silicon-based composite particles, or may be provided to coat at least part of a region where no carbon layer is provided on the surface of the silicon-based composite particles. form, or is disposed in the form of at least a portion of the surface coated with the carbon layer.

As described above, the lithium by-product formed during the Li doping process can be effectively removed by acid-treating the silicon-based composite particles, and in the acid treatment process, SiO _y (1<y≤2) is formed in the silicon-based composite particles. on the particles, thus playing a passivating effect on the particles.

SiO _y (1<y≤2) formed by the acid treatment step may exist as an island-type or thin-film type layer, and may exist in various forms without being limited thereto. In addition, the formed SiO _y (1<y≤2) may be present in each part on the silicon-based composite particles.

That is, the negative active material formed by the above preparation method may have a composition in which silicon-based composite particles/carbon layer/SiO _y (1<y≤2) are sequentially coated, or in which silicon-based composite particles/SiO _y (1<y ≤2)/carbon layer are coated in sequence, or silicon-based composite particles/SiO _y (1<y≤2) are coated in sequence, but the order is not limited to this.

By forming a layer containing SiO _y (1<y≤2) as described above, lithium by-products remaining in the silicon-based composite particles can be effectively removed and the particles can be effectively passivated. Therefore, there is a possibility of preventing the silicon-based composite particles from The Li compound contained in it dissolves and improves the effect of water-based processability.

In addition, the silicon-based composite particles may include a carbon layer to prevent the elution of unreacted lithium by-products in the acid treatment process and to minimize the reaction between the negative electrode active material and water in the aqueous slurry.

<Negative>

The negative electrode according to an exemplary embodiment of the present invention may include the above-mentioned negative electrode active material.

Specifically, the negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The negative active material layer may include the negative active material. In addition, the negative active material layer may further include a binder and/or a conductive material.

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

The negative electrode slurry includes the negative active material, a binder and/or a conductive material.

The negative electrode slurry may further include additional negative electrode active materials.

As the additional negative electrode active material, a compound capable of reversibly intercalating and deintercalating lithium can be used. Specific examples thereof include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber and amorphous carbon; metal compounds that can be alloyed with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; metal oxides that can be doped and dedoped with lithium such as SiO _β (0<β<2), SnO ₂ , vanadium oxide, lithium titanium oxide, and lithium vanadium oxide or a composite containing a metal compound and a carbonaceous material such as a Si-C composite or a Sn-C composite, and any one thereof or a mixture of two or more thereof can be used. In addition, a metallic lithium film can be used as the negative electrode active material. Alternatively, both low-crystalline carbon and high-crystalline carbon, etc. may be used as the carbon material. Typical examples of low crystalline carbon include soft carbon and hard carbon, and typical examples of high crystalline carbon include irregular, plate-like, flake, spherical or fibrous natural graphite or artificial graphite, floating graphite, pyrolytic carbon, mesophase pitch It is carbon fiber, mesocarbon microbeads, mesophase pitch and high temperature fired carbon such as coke derived from petroleum or coal tar pitch.

The additional negative active material may be a carbon-based negative active material.

In an exemplary embodiment of the present invention, the weight ratio of the negative active material and the additional negative active material contained in the negative slurry may be 10:90 to 90:10, specifically 10: 90 to 50:50.

It is sufficient that the negative electrode current collector has conductivity without causing chemical changes to the battery, and is not particularly limited. For example, as the current collector, copper, stainless steel, aluminum, nickel, titanium, fired carbon, or aluminum or stainless steel materials whose surfaces are treated with carbon, nickel, titanium, silver, etc. can be used. Specifically, a transition metal that adsorbs carbon well such as copper or nickel can be used as the current collector. Although the thickness of the current collector may be 6 μm to 20 μm, the thickness of the current collector is not limited thereto.

The adhesive may include at least one selected from the group consisting of: polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethacrylate Methyl acrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, tris Ethylene propylene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluorine rubber, polyacrylic acid and materials whose hydrogen is replaced by Li, Na, Ca, etc., and may also include various copolymers thereof.

The conductive material is not particularly limited as long as the conductive material has conductivity and does not cause chemical changes to the battery. For example, graphite such as natural graphite or artificial graphite can be used; carbon black such as acetylene black, Ketjen black, channel black , furnace black, lamp black and thermal carbon black; conductive fibers such as carbon fiber or metal fiber; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon powder, aluminum powder and nickel powder; conductive whiskers such as zinc oxide and titanium Potassium acid; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives, etc.

The negative electrode slurry may further contain a solvent for forming the negative electrode slurry. Specifically, in terms of promoting the dispersion of components, the negative electrode slurry forming solvent may include at least one selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol, specifically distilled water.

<Second battery>

A secondary battery according to an exemplary embodiment of the present invention may include the above-mentioned negative electrode according to the exemplary embodiment. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and the negative electrode is the same as the negative electrode described above. Since the negative electrode has been described previously, its detailed description will be omitted.

The cathode may include a cathode current collector and a cathode active material layer formed on the cathode current collector and containing the cathode active material.

In the positive electrode, the positive current collector is not particularly limited as long as the positive current collector has conductivity without causing chemical changes to the battery. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or Aluminum or stainless steel materials whose surface has been treated with carbon, nickel, titanium, silver, etc. In addition, the thickness of the positive electrode current collector may generally be 3 μm to 500 μm, and the adhesion of the positive electrode active material may also be enhanced by forming fine unevenness on the surface of the current collector. For example, the positive electrode current collector may be used in various forms such as films, sheets, foils, meshes, porous bodies, foam bodies, and nonwoven fabric bodies.

The positive active material may be a commonly used positive active material. Specifically, the positive active material includes: layered compounds such as lithium cobalt oxide (LiCoO ₂ ) and lithium nickel oxide (LiNiO ₂ ) or compounds substituted with more than one transition metal; lithium iron oxide such as LiFe ₃ O ₄ ; Lithium manganese oxides such as chemical formula Li _1+c1 Mn _2-c1 O ₄ (0≤c1≤0.33), LiMnO ₃ , LiMn ₂ O ₃ and LiMnO ₂ ; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxidation Materials such as LiV ₃ O ₈ , V ₂ O ₅ and Cu ₂ V ₂ O ₇ ; Ni site type lithium nickel oxide, composed of the chemical formula LiNi _1-c2 M _c2 O ₂ (here, M is selected from Co, Mn, At least one of the group consisting of Al, Cu, Fe, Mg, B and Ga, and c2 satisfies 0.01≤c2≤0.3); lithium manganese composite oxide is represented by the chemical formula LiMn _2-c3 M _c3 O ₂ (here , M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn and Ta, and c3 satisfies 0.01≤c3≤0.1) or Li ₂ Mn ₃ MO ₈ (here, M is selected from At least any one of the group consisting of Fe, Co, Ni, Cu and Zn) represents; LiMn ₂ O ₄ , in which Li in the chemical formula is partially replaced by alkaline earth metal ions or the like, but is not limited thereto. The positive electrode may be Li metal.

On the basis of containing the above-mentioned cathode active material, the cathode active material layer may also contain a cathode conductive material and a cathode binder.

In this case, the positive conductive material is used to impart conductivity to the electrode and can be used without particular limitation as long as the positive conductive material has electron conductivity without causing chemical changes in the constituted battery. Specific examples thereof 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 powder or metal fiber For example, 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 any one thereof or its A mixture of two or more.

Alternatively, the positive electrode binder is used to improve the bonding between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples thereof may include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), Starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluorine rubber or various copolymers thereof, and any one thereof or a mixture of two or more thereof may be used.

The separator separates the negative electrode and the positive electrode and provides a channel for movement of lithium ions, and can be used without particular limitation as long as the separator is commonly used as a separator in secondary batteries, particularly, A separator that has excellent electrolyte moisturizing ability and low resistance to ion movement in the electrolyte is preferred. Specifically, porous polymer films may be used, for example, made of polyolefin-based polymers such as ethylene homopolymers, propylene homopolymers, ethylene/butylene copolymers, ethylene/hexene copolymers, and ethylene/methacrylate copolymers. A porous polymer film formed from a material, or a laminated structure of two or more layers thereof. In addition, conventional porous non-woven fabrics, such as non-woven fabrics made of high melting point glass fiber, polyethylene terephthalate fiber, etc., can also be used. In addition, coated membranes containing ceramic components or polymeric materials can be used to ensure thermal resistance or mechanical strength, and can optionally be used as single-layer or multi-layer structures.

Examples of the electrolyte include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc. that can be used in the preparation of lithium secondary batteries, but not Limited to this.

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

As the non-aqueous organic solvent, for example, aprotic organic solvents such as N-methyl-2-pyrrolidone, 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, dimethylformamide Oxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2- Imidazolinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate and ethyl propionate.

In particular, among carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, can be preferably used because cyclic carbonates have a high dielectric constant as a high-viscosity organic solvent and thus dissociate well. Lithium salt, and when cyclic carbonate is mixed with low viscosity and low dielectric constant linear carbonate such as dimethyl carbonate and diethyl carbonate in an appropriate ratio, an electrolyte with high conductivity can be prepared, so this The combined use is more preferred.

As the metal salt, a lithium salt can be used. The lithium salt is a material that is easily soluble in a non-aqueous electrolyte. For example, as the anion of the lithium salt, one or more types selected from the group consisting of: F ^- , Cl ^- , I ^- , NO ₃ ^- , N(CN) ₂ ^- , BF ₄ ^- , ClO ₄ ^- , PF ₆ ^- , (CF ₃ ) ₂ PF ₄ ^- , (CF ₃ ) ₃ PF ₃ ^- , ( CF ₃ ) ₄ PF ₂ ^- , (CF ₃ ) ₅ PF ^- , (CF ₃ ) ₆ P ^- , CF ₃ SO ₃ ^- , CF ₃ CF ₂ SO ₃ ^- , (CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- , CF ₃ CF ₂ (CF ₃ ) ₂ CO ^- , (CF ₃ SO ₂ ) ₂ CH ^- , (SF ₅ ) ₃ C ^- , (CF ₃ SO ₂ ) ₃ C ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- , CF ₃ CO ₂ ^- , CH ₃ CO ₂ ^- , SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- .

In the electrolyte, in order to improve the service life characteristics of the battery, suppress the decrease in battery capacity, and improve the discharge capacity of the battery, in addition to the above-mentioned electrolyte components, one or more additives may be further included, such as halide carbonate. Alkylene ester compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexamethylphosphoric triamide, Nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted Azolidinones, N,N-substituted imidazolidines, glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol or aluminum trichloride.

According to yet another exemplary embodiment of the present invention, a battery module including a secondary battery as a unit cell and a battery pack including the same are provided. The battery modules and battery packs contain secondary batteries with high capacity, high rate characteristics, and cycle characteristics, and thus can be used as a vehicle selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems. Power supply for medium and large installations in the group.

Mode for use in the invention

Hereinafter, the present specification will be described in detail with reference to Examples for specifically describing the present specification. However, the embodiments according to the present specification may be changed in various forms, and the scope of the application should not be construed as being limited to the embodiments described in detail below. The examples of the present application are provided to more fully explain this specification to those of ordinary skill in the art.

<Examples and Comparative Examples>

Example 1

After mixing 94 g of powder in which Si and _SiO2 were mixed at a molar ratio of 1:1 in a reaction furnace, the resulting mixture was heated under vacuum at a sublimation temperature of 1400°C. Thereafter, the mixed gas of vaporized Si and _SiO reacts and condenses into a solid phase in a cooling zone in a vacuum state with a cooling temperature of 800°C. Next, silicon-based particles having a size of 6 μm were prepared by pulverizing the aggregated particles using a ball mill for 3 hours. Thereafter, the silicon-based particles were placed in the hot zone of the CVD equipment while maintaining an inert atmosphere by flowing Ar gas, and methane was blown into the hot zone at 900°C using Ar as a carrier gas and heated at 10 ^-1 Torr React for 20 minutes to form a carbon layer on the surface. Thereafter, 6 g of Li metal powder was added, and additional heat treatment was performed at a temperature of 800° C. in an inert atmosphere, and then ethanol was used as a solvent at a temperature of 80° C. at a weight ratio of silicon-based particles: phosphoric acid = 99:1. Acid treatment is performed to prepare a negative active material in which SiO _y (1<y≤2) is formed on the surface of the particles.

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

Example 2

A negative electrode active material was prepared in the same manner as in Example 1, except that the heat treatment process by introducing methane was performed for 1 hour.

As a result of the XPS analysis of the negative electrode active material, a first peak near 102 eV to 103 eV, a second peak near 99 eV to 100 eV, a third peak near 103 eV to 104 eV, and a fourth peak near 283 eV to 285 eV were obtained.

Example 3

A negative electrode active material was prepared in the same manner as in Example 1, except that the process of heat treatment by introducing methane was changed to be after acid treatment.

As a result of the XPS analysis of the negative electrode active material, a first peak near 102 eV to 103 eV, a second peak near 99 eV to 100 eV, a third peak near 103 eV to 104 eV, and a fourth peak near 283 eV to 285 eV were obtained.

Example 4

A negative electrode active material was prepared in the same manner as in Example 1, except that the temperature for heat treatment by introducing methane was changed to 1100°C.

As a result of the XPS analysis of the negative electrode active material, a first peak near 102 eV to 103 eV, a second peak near 99 eV to 100 eV, a third peak near 103 eV to 104 eV, and a fourth peak near 283 eV to 285 eV were obtained.

Example 5

A negative electrode active material was prepared in the same manner as in Example 1, except that acid treatment was performed at a weight ratio of silicon-based composite particles:phosphoric acid=90:10.

As a result of the XPS analysis of the negative electrode active material, a first peak near 102 eV to 103 eV, a second peak near 99 eV to 100 eV, a third peak near 103 eV to 104 eV, and a fourth peak near 283 eV to 285 eV were obtained.

Comparative example 1

A negative active material was prepared in the same manner as in Example 1 except for the acid treatment process. The formed negative electrode active material does not contain SiO _y (1<y≤2).

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

Comparative example 2

A negative electrode active material was prepared in the same manner as in Example 1 except for the steps of introducing methane and performing heat treatment.

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

The compositions of the negative active materials prepared in the Examples and Comparative Examples are shown in Table 1 below.

[Table 1]

X-ray photoelectron spectroscopy analysis of the negative active material was performed using a Nexsa ESCA system, Thermo Fisher Scientific (ESCA-02). Specifically, after acquiring a full scan spectrum and a narrow scan spectrum for each sample, the full scan spectrum and the narrow scan spectrum can be acquired while performing depth distribution. Depth profiles up to 3000 s were performed using single-atom Ar ions, and the measurement and data processing conditions were as follows.

-X-ray source: Monochromatic Al Kα (1486.6eV)

-X-ray spot size: 400μm

-Sputtering Gun: Monoatomic Ar (Energy: 1000eV, Flow: Low, Grating Width: 2mm)

-Etch rate: 0.09nm/s for Ta ₂ O ₅

-Operating mode: CAE (Constant Analyzer Energy) mode

-Full scan: pass energy 200eV, energy level 1eV

-Narrow scan: scan mode, pass energy 50eV, energy level 0.1eV

-Charge Compensation: Flood Gun Off

-SF: Al THERMO1

-ECF:TPP-2M

-Background Subtraction: Shirley

The particle size of the negative active material was analyzed by laser diffraction particle size analysis using a Microtrac S3500 device.

The content of Li atoms was confirmed by ICP analysis using an inductively coupled plasma atomic emission spectrometer (ICP-OES, AVIO 500 from Perkin-Elmer 7300 Company).

The presence and content of the carbon layer was confirmed by combustion using elemental analysis (G4 ICARUS from Bruker) under oxygen conditions.

The NMR peak intensity or weight ratio of Si and silicon-based oxides (SiO _x and SiO _y ) was confirmed by a nuclear magnetic resonance spectrometer (Advance III HD 600MHz NMR Spectrometer from Bruker) under the condition of MAS rate = 10 kHz.

The content of lithium by-products was measured using Karl Fischer titration (Titrator Excellence T5 from Mettler Toledo) by adding the sample to distilled water, then filtering the resulting product, and titrating the dissolved components with HCl solution.

The ratio of the total amorphous phase in the negative electrode active material was measured by quantitative analysis using X-ray diffraction analysis (D4 Endeavor from Bruker Corporation).

<Experimental example: Evaluation of discharge capacity, initial efficiency, and service life (capacity retention rate) characteristics>

The negative electrode active materials in Examples and Comparative Examples were used to prepare negative electrodes and batteries, respectively.

A mixture was prepared by mixing the negative active material, the conductive material carbon black, and the binder polyacrylic acid (PAA) in a weight ratio of 80:10:10. Thereafter, 7.8 g of distilled water was added to 5 g of the mixture, and the resulting mixture was stirred to prepare a negative electrode slurry. This negative electrode slurry was applied to a copper (Cu) metal film having a thickness of 20 μm as a negative electrode current collector and dried. In this case, the temperature of the circulating air is 60°C. Subsequently, a negative electrode was prepared by rolling the negative electrode current collector and drying it in a vacuum oven at 130° C. for 12 hours.

The prepared negative electrode was cut into ^1.7671cm2 circles, and a lithium (Li) metal film was used as the positive electrode. A porous polyethylene separator is inserted between the positive electrode and the negative electrode, in which vinylene carbonate is dissolved at 0.5 parts by weight. The mixing volume ratio of ethylmethyl carbonate (EMC) and ethylene carbonate (EC) is 7: 3 and an electrolyte in which LiPF ₆ was dissolved at a concentration of 1 M was injected into it to prepare a lithium coin half cell.

The discharge capacity, initial efficiency, and capacity retention rate were evaluated by charging and discharging the prepared battery, and are shown in Table 2 below.

For the 1st and 2nd cycles, the battery was charged and discharged at 0.1C, and from the 3rd to the 49th cycle, the battery was charged and discharged at 0.5C. The 50th cycle is completed in the charged state (where the negative electrode contains lithium).

Charging conditions: CC (constant current)/CV (constant voltage) (5mV/0.005C current cutoff)

Discharge conditions: CC (constant current) condition 1.5V

The discharge capacity (mAh/g) and initial efficiency (%) were derived from the results during one charge/discharge. Specifically, the initial efficiency (%) is derived from the following calculation formula.

Initial efficiency (%) = (1 discharge capacity/1 charge capacity) × 100

Each capacity retention rate is derived from the following calculation formula.

Capacity retention rate (%) = (49 times discharge capacity/1 time discharge capacity) × 100

<Experimental example: Evaluation of processability (shear viscosity) characteristics>

As part of the processability evaluation, the shear at a shear rate = 1 Hz of a slurry prepared by mixing graphite: negative active material: carbon black: CMC: PAA in a weight ratio of 77:20:1:1:1 was measured. shear viscosity changes and are shown in Table 2 below. Specifically, the shear viscosity change amount (%) is derived from the following formula.

Shear viscosity change (%) = ((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

[Table 2]

The negative active material according to the present invention is characterized by having a carbon layer and SiO _y (1<y≤2) on the silicon-based composite particles, the negative active material has a low content of lithium by-products, and since the carbon layer and SiO _y are included (1<y≤2) layer has excellent passivation effect.

In Table 2, in Examples 1 to 5, the acid-treated negative active material has a low content of lithium by-products, and the formation of SiO _y (1<y≤2) makes the ratio of the amorphous phase in the negative active material Increase. It can be confirmed that in Examples 1 to 5, the content of lithium by-products in the negative electrode active material is low, and due to the passivation effect brought by SiO _y (1<y≤2), the overall discharge capacity is lower than that of the comparative example. , initial efficiency and capacity retention are better. In addition, it was confirmed that SiO _y (1<y≤2) minimizes the influence of lithium compounds eluted from lithium by-products or silicon-based composite particles, and compared with Comparative Examples 1 and 2, it was confirmed that the shear viscosity change of the slurry significantly reduced.

In contrast, in Comparative Example 1, acid treatment was not performed and SiO _y was not formed from lithium by-product (1<y≤2). It can be confirmed that in the case of Comparative Example 1, since the lithium content is higher than that of the Example, the initial efficiency is slightly higher than that of the Example, but the discharge capacity and capacity retention rate are significantly reduced, and the shear viscosity change amount The amount of shear viscosity change is significantly greater than that in the examples because side reactions of the slurry occur due to lithium by-products and the viscosity of the slurry changes.

In the case of Comparative Example 2, since the carbon layer is not included, the expansion of the silicon-based composite particles cannot be prevented, the electrical conductivity is low, and the silicon-based composite particles cannot be effectively coated. Therefore, it was confirmed that due to the volume expansion of the negative active material during charge/discharge, it was unable to exhibit an appropriate capacity, and the lithium by-product that was not coated with the carbon layer caused a side reaction of the slurry, and the viscosity of the slurry changed, so it was not related to Compared with the examples, the discharge capacity and capacity maintenance rate are significantly reduced, and the shear viscosity change is significantly larger.

Therefore, the present invention can effectively remove lithium by-products and easily improve the overall water system by utilizing the passivation effect by providing a negative active material in which a carbon layer and SiO _y (1<y≤2) are provided on silicon-based composite particles. Processability, discharge capacity, efficiency and capacity retention.

Claims (14)

1. A negative active material, comprising: Silicon-based composite particles include SiO _x and Li compounds where 0<x<2; a carbon layer; and SiO _y where 1<y≤2, wherein the carbon layer is disposed to coat at least a portion of the surface of the silicon-based composite particles, and The SiO _y in which 1<y≤2 is provided in a form of coating at least a portion of the surface of the silicon-based composite particles or coating at least a portion of the surface of the carbon layer. 2. The negative active material according to claim 1, wherein the negative active material has a peak existing at 101 eV to 104 eV when analyzed by X-ray photoelectron spectroscopy. 3. The negative active material according to claim 1, wherein the SiO _y wherein 1<y≤2 is configured to coat the silicon-based composite between the surface of the silicon-based composite particles and the carbon layer. The form of at least a part of the surface of the particle, the form of being provided to coat at least part of the area on the surface of the silicon-based composite particle where the carbon layer is not provided, or the form being provided to coat at least part of the surface of the carbon layer. form. 4. The negative active material according to claim 1, wherein the content of _SiOy (1<y≤2) is 0.1 to 50 parts by weight relative to a total of 100 parts by weight of the negative active material. 5. The negative electrode active material according to claim 1, further comprising a lithium by-product provided on at least a part of the silicon-based composite particles. 6. The negative active material according to claim 5, wherein the content of the lithium by-product is 5 parts by weight or less relative to a total of 100 parts by weight of the negative active material. 7. The negative active material of claim 5, further comprising a carbon layer disposed on at least a portion of the lithium byproduct. 8. The negative active material according to claim 1, wherein during NMR measurement of the negative active material, a ratio of the peak intensity (p1) of Si to the peak intensity (p2) representing the Si-O bond (p1:p2 ) is 88:12 to 60:40. 9. The negative electrode active material according to claim 1, wherein a ratio of the amorphous phase is 32% or more relative to the total weight of the silicon-based composite particles and the _SiOy (1<y≤2). 10. The negative active material according to claim 1, wherein the Li content contained in the silicon-based composite particles is 0.1 to 40 parts by weight relative to a total of 100 parts by weight of the negative active material. 11. The negative active material according to claim 1, wherein the content of the carbon layer is 0.1 to 20 parts by weight relative to a total of 100 parts by weight of the negative active material. 12. A method of preparing the negative active material according to any one of claims 1 to 11, the method comprising: Preparing silicon-based composite particles comprising SiO _x and a Li compound in which 0<x<2; and SiO _y in which 1<y≤2 is formed by subjecting the silicon-based composite particles to acid treatment. 13. A negative electrode, comprising the negative electrode active material according to any one of claims 1 to 11. 14. A secondary battery including the negative electrode according to claim 13.