CN118661285A

CN118661285A - Negative electrode active material, negative electrode including the same, secondary battery including the negative electrode, and method of manufacturing negative electrode active material

Info

Publication number: CN118661285A
Application number: CN202380017034.9A
Authority: CN
Inventors: 朴熙娟; 崔静贤; 申善英; 李龙珠
Original assignee: Lg Energy Solution
Current assignee: Lg Energy Solution
Priority date: 2022-07-22
Filing date: 2023-07-14
Publication date: 2024-09-17

Abstract

The present invention relates to a negative electrode active material comprising: silicon-based particles which contain SiOx (0 < x < 2) and a Li compound and which have a carbon layer on at least a part of the surface; and an inorganic layer containing Ca provided on at least a part of the silicon-based particles.

Description

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

Technical Field

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

The present application claims priority and rights from korean patent application No. 10-2022-0091036 filed on the korean intellectual property office at 22 nd of 2022 and korean patent application No. 10-2023-0090935 filed on the korean intellectual property office at 13 nd of 2023, the entire contents of which are incorporated herein by reference.

Background

Recently, with the rapid spread of electronic devices using batteries, such as mobile phones, laptop computers, and electric vehicles, the demand for secondary batteries having small size, light weight, and relatively high capacity has been rapidly increasing. In particular, lithium secondary batteries have been in the spotlight as driving power sources for portable devices because of their light weight and high energy density. Accordingly, research and development efforts to improve the performance of lithium secondary batteries are actively underway.

Generally, a lithium secondary battery includes a positive electrode, a negative electrode, a separator provided between the positive electrode and the negative electrode, an electrolyte, an organic solvent, and the like. Further, the positive electrode and the negative electrode may be formed with active material layers each including a positive electrode active material and a negative electrode active material on the current collector. In general, for the positive electrode, lithium-containing metal oxides such as LiCoO ₂ and LiMn ₂O₄ are used as positive electrode active materials, and for the negative electrode, a carbon-based active material or a silicon-based active material that does not contain lithium is used as a negative electrode active material.

Among the negative electrode active materials, silicon-based active materials are attracting attention because of having higher capacity than carbon-based active materials and having excellent rapid charge characteristics. However, the silicon-based active material has a disadvantage in that the degree of volume expansion/contraction during charge and discharge is high, and the irreversible capacity is high, so that the initial efficiency is low.

On the other hand, among silicon-based active materials, silicon-based oxides, specifically, silicon-based oxides represented by SiO _x (0 < x < 2), have an advantage in that the degree of volume expansion/contraction during charge and discharge is lower, as compared with other silicon-based active materials such as silicon (Si). However, silicon-based oxides still have drawbacks that result in reduced initial efficiency due to the presence of irreversible capacity.

In this regard, studies have been made to reduce the irreversible capacity and to improve the initial efficiency by doping or embedding metals such as Li, al and Mg in silicon-based oxides. However, the anode slurry including a metal-doped silicon-based oxide as an anode active material has a problem in that a metal oxide formed by doping a metal reacts with moisture to raise the pH of the anode slurry and change the viscosity. Therefore, the state of the manufactured anode is poor and the charge-discharge efficiency of the anode is lowered.

Accordingly, there is a need to develop a negative electrode active material capable of improving the phase stability of a negative electrode slurry containing a silicon-based oxide and improving the charge-discharge efficiency of a negative electrode manufactured from the slurry.

Korean patent No. 10-0794192 relates to a method of manufacturing a carbon-coated silicon-graphite composite anode material for a lithium secondary battery and a method of manufacturing a secondary battery including the same, but has limitations in solving the above-described problems.

Disclosure of Invention

Technical problem

Technical proposal

An exemplary embodiment of the present invention provides a negative active material including: silicon-based particles that contain SiO _x (0 < x < 2) and a Li compound and that have a carbon layer provided on at least a part of the surface thereof; and a Ca-containing inorganic layer provided on at least a part of the silicon-based particles.

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

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

Yet another exemplary embodiment of the present invention provides a method of manufacturing a negative active material, the method including: forming a silicon-based particle that contains SiO _x (0 < x < 2) and a Li compound and has a carbon layer provided on at least a part of its surface; and reacting the silicon-based particles with a Ca precursor.

Advantageous effects

Since the anode active material according to one exemplary embodiment of the present invention contains the Ca-containing inorganic layer, there is an effect of improving the aqueous workability of the slurry. Specifically, since the Ca-containing inorganic layer has low reactivity with water, the inorganic layer does not react with water in the aqueous slurry and remains good to prevent water from penetrating into the anode active material, thereby effectively passivating the silicon-based particles. In addition, since side reactions between silicon-based particles or lithium by-products and water are prevented to suppress the generation of gas, there is an effect of improving the aqueous workability of the slurry.

Accordingly, the anode including the anode active material according to one exemplary embodiment of the present invention and the secondary battery including the anode have the effect of improving the discharge capacity, initial efficiency, resistance performance, and/or life characteristics of the battery.

Drawings

Fig. 1 shows the XRD analysis result of the anode active material of example 1.

Fig. 2 shows the XRD analysis result of the negative electrode active material of comparative example 1.

Detailed Description

Hereinafter, the present specification will be described in more detail.

In this specification, when a portion is referred to as "comprising" a particular component, it means that the portion may further comprise another component without excluding the other component, unless expressly stated to the contrary.

Throughout this specification, when an element is referred to as being "on" another element, it can be directly contacting the other element or intervening elements may also be present.

It should be understood that the terms or words used throughout the specification should not be construed as limited to their ordinary or dictionary meanings, but should be construed as having meanings and concepts consistent with technical ideas of the present invention on the basis of the principle that the inventor can properly define the words or concepts of the terms to best explain the present invention.

As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

In this specification, crystallinity of a structure included in the anode active material can be confirmed by X-ray diffraction analysis, and the X-ray diffraction analysis can be performed using an X-ray diffraction (XRD) analyzer (product name: D4-endavor, manufacturer: bruker), or an apparatus used in the art can be appropriately employed in addition to the above-described apparatus.

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

In the present specification, the average particle diameter (D ₅₀) may be defined as a 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, a laser diffraction method. In the laser diffraction method, the particle diameter in the submicron range to several millimeters range can be measured in general, and the result of high reproducibility and high resolution can be obtained.

Hereinafter, preferred embodiments of the present invention will be described in detail. However, it should be understood that the embodiments of the present invention may be modified in various forms, and the scope of the present invention is not limited to the following embodiments.

< Negative electrode active Material >

The anode active material according to an exemplary embodiment of the present invention includes silicon-based particles. The silicon-based particles contain SiO _x (0 < x < 2) and a Li compound.

The SiO _x (0 < x < 2) may correspond to a matrix in the silicon-based particles. The SiO _x (0 < x < 2) may be in a form comprising Si and/or SiO ₂, and Si may 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 particles contain SiO _x (0 < x < 2), the discharge capacity of the secondary battery can be improved.

The lithium compound may correspond to a dopant in the silicon-based composite particles. The lithium compound may be present in the silicon-based particles in the form of at least one of a lithium atom, a lithium silicate, a lithium silicide, or a lithium oxide. When the silicon-based particles contain Li compounds, the initial efficiency improves.

The Li compound may be distributed on the surface and/or inside of the silicon-based particles in a form doped to the silicon-based particles. The Li compound may be distributed on the surface and/or inside of the silicon-based particles for controlling the volume expansion/contraction of the silicon-based particles to an appropriate level and preventing damage to the active material. Further, 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 to improve the efficiency of the active material.

In one exemplary embodiment of the present invention, the Li compound may exist in the form of lithium silicate. The lithium silicate is represented by Li _aSi_bO_c (2.ltoreq.a.ltoreq.4, 0.ltoreq.b.ltoreq.2, 2.ltoreq.c.ltoreq.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 ₂SiO₃、Li₄SiO₄ and Li ₂Si₂O₅, and the amorphous lithium silicate may have a composite form of Li _aSi_bO_c (2.ltoreq.a.ltoreq.4, 0.ltoreq.b.ltoreq.2, 2.ltoreq.c.ltoreq.5). However, the present invention is not limited thereto.

In one 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 based on 100 parts by weight of the total negative electrode active material. Specifically, the content of Li may be 1 to 25 parts by weight, more specifically 2 to 20 parts by weight. As the Li content increases, the initial efficiency increases, but the discharge capacity decreases. Therefore, when the above range is satisfied, an appropriate discharge capacity and initial efficiency can be achieved.

The content of Li element can be determined by ICP analysis. Specifically, a predetermined amount (about 0.01 g) of the anode active material was precisely divided, transferred to a platinum crucible, and completely decomposed on a hot plate by adding nitric acid, hydrofluoric acid, and sulfuric acid. Then, by using an inductively coupled plasma atomic emission spectrometer (ICP-AES, perkin-Elmer 7300), a reference calibration curve was obtained 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. Subsequently, the pretreated sample solution and the blank sample are introduced into a spectrometer, and the elemental content of the prepared anode active material can be analyzed by measuring the intensities of the respective components to calculate the actual intensities, calculating the concentrations of the respective components based on the obtained calibration curve, and performing conversion so that the sum of the calculated concentrations of the components is equal to a theoretical value.

In one exemplary embodiment of the present invention, the silicon-based particles may contain other metal atoms. The metal atoms may be present in the silicon-based 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. Accordingly, the initial efficiency of the anode active material can be improved.

In one exemplary embodiment of the present invention, the silicon-based particles have a carbon layer on at least a portion of the surface thereof. In this case, the carbon layer may be coated on at least a part of the surface, that is, may be partially coated on the surface of the particles, or may be coated on the entire surface of the particles. The carbon layer imparts conductivity to the negative electrode active material, so that initial efficiency, life characteristics, and battery capacity characteristics of the secondary battery can be improved.

In an exemplary embodiment of the present invention, the carbon layer comprises amorphous carbon.

In addition, the carbon layer may further include crystalline carbon.

The crystalline carbon may further improve the conductivity of the anode active material. The crystalline carbon may include at least one selected from the group consisting of fullerenes, carbon nanotubes, and graphene.

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

The carbide of the other organic material may be an organic carbide selected from the group consisting of carbides of sucrose, glucose, galactose, fructose, lactose, mannose, ribose, aldose, or ketohexose, and combinations thereof.

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

In one exemplary embodiment of the present invention, the carbon layer may be an amorphous carbon layer.

In one exemplary embodiment of the present invention, the carbon layer may be contained in an amount of 0.1 to 50 parts by weight, 0.1 to 30 parts by weight, or 0.1 to 20 parts by weight, based on a total of 100 parts by weight of the anode active material. More specifically, the carbon layer may be contained in an amount of 0.5 to 15 parts by weight, 1 to 10 parts by weight, or 1 to 5 parts by weight. When the above range is satisfied, a decrease in capacity and efficiency of the anode active material can be prevented.

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

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.

In one exemplary embodiment of the present invention, a Ca-containing inorganic layer is disposed on at least a portion of the silicon-based particles. Specifically, during the production of the anode active material, silicon-based particles having a carbon layer provided on at least a portion of the surface thereof are formed, li is doped, and then a Ca precursor is used to introduce a Ca-containing inorganic layer onto at least a portion of the silicon-based particles.

The Ca-containing inorganic layer may include a Ca-containing inorganic material. In addition, the inorganic layer may further contain other materials, for example, that are present during the reaction of the Ca precursor with the silicon-based particles.

Since the Ca-containing inorganic layer formed as described above is not well soluble in water and has low reactivity with water, the inorganic layer does not react with water in the aqueous slurry and remains well, thereby preventing water from penetrating into the anode active material to effectively passivate the silicon-based particles. Further, elution of Li compound contained in the silicon-based particles is prevented to prevent the slurry from becoming alkaline, thereby improving the aqueous workability. Further, since the Ca precursor for forming the Ca-containing inorganic layer is easily synthesized into salts and relatively easily obtained, the above-mentioned effects can be more advantageously achieved.

In one exemplary embodiment of the present invention, the Ca-containing inorganic layer may be disposed on at least a portion of the carbon layer, or may be disposed on at least a portion of the region of the surface of the silicon-based particle where the carbon layer is not disposed.

The Ca-containing inorganic layer may be partially coated on the surface of the silicon-based particles or the carbon layer, or may be coated on the entire surface. The Ca-containing inorganic layer may be island-type or film-type in shape, and specifically may be provided as island-type.

The Ca-containing inorganic layer may contain at least one selected from the group consisting of CaCO ₃, caO, and Ca (OH) ₂. Specifically, the Ca-containing inorganic layer may include CaCO ₃ or Ca (OH) ₂. The composition of the Ca-containing inorganic layer is not limited thereto, and may include, for example, a Ca-containing inorganic material formed using a Ca precursor known in the art.

The components contained in the anode active material can be determined by X-ray diffraction analysis (XRD) or SEM-EDX.

In one exemplary embodiment of the present invention, during X-ray diffraction analysis (XRD) of the anode active material, a peak may exist at 29 ° or more and 30 ° or less. The peak appearing at 29 ° or more and 30 ° or less may be a peak caused by Ca, and may exist in the form of a shoulder peak.

In one exemplary embodiment of the present invention, other peaks may exist at 28 ° or more and less than 29 ° during X-ray diffraction (XRD) analysis of the anode active material. The peak appearing at 28 ° or more and less than 29 ° may be a peak caused by Si, and the peak caused by Ca may exist in the form of a shoulder peak on the right side of the peak caused by Si.

In the example, fig. 1 shows an XRD analysis pattern of the anode active material manufactured in example 1 described below, in which it can be confirmed that a peak caused by Si occurs at 28 ° to less than 29 °, and a peak caused by Ca in the form of a shoulder peak is detected at 29 ° to 30 °.

In the present invention, the content of Ca on the surface of the anode active material can be analyzed by scanning electron microscope energy dispersive X-ray spectroscopy (SEM-EDX). In particular, hitachi S-4800 can be used to analyze the content under conditions of an accelerating voltage of 15 kV and a working distance of 15 mm.

In one exemplary embodiment of the present invention, the content of Ca may be 0.05 to 10 parts by weight when the anode active material is analyzed by scanning electron microscope energy dispersive X-ray spectroscopy (SEM-EDX). Specifically, the content of Ca may be 0.1 to 5 parts by weight or 0.5 to 4 parts by weight. The upper limit of the content of Ca may be 10 parts by weight, 8 parts by weight, 5 parts by weight, or 4 parts by weight, and the lower limit may be 0.05 parts by weight, 0.1 parts by weight, 0.3 parts by weight, 0.5 parts by weight, 0.7 parts by weight, or 0.8 parts by weight. The Ca content can be obtained based on the region on the surface of the anode active material analyzed by SEM-EDX under the conditions that the acceleration voltage is 15 kV and the working distance is 15 mm.

In one exemplary embodiment of the present invention, the content of Ca may be 0.005 to 5 parts by weight based on 100 parts by weight of the total negative electrode active material. Specifically, the content of Ca may be 0.01 to 3 parts by weight or 0.1 to 2 parts by weight. The upper limit of the content of Ca may be 5 parts by weight, 4 parts by weight, 3 parts by weight, or 2 parts by weight, and the lower limit may be 0.005 parts by weight, 0.01 parts by weight, 0.1 parts by weight, 0.2 parts by weight, or 0.3 parts by weight.

In one exemplary embodiment of the present invention, the content of the Ca-containing inorganic layer may be 0.01 to 10 parts by weight based on 100 parts by weight of the total negative electrode active material. Specifically, the content of the Ca-containing inorganic layer may be 0.1 to 5 parts by weight, 0.4 to 5 parts by weight, or 0.5 to 4 parts by weight. The upper limit of the content of the Ca-containing inorganic layer may be 10 parts by weight, 8 parts by weight, 6 parts by weight, 5 parts by weight, 4 parts by weight, or 3.5 parts by weight, and the lower limit may be 0.01 parts by weight, 0.05 parts by weight, 0.1 parts by weight, 0.2 parts by weight, 0.3 parts by weight, 0.4 parts by weight, 0.5 parts by weight, 0.6 parts by weight, or 0.7 parts by weight.

When the content range as described above is satisfied, the aqueous processability is improved by preventing the reaction of the anode active material with moisture or the elution of lithium by-products in the aqueous slurry. On the other hand, when the content exceeds the above range, the capacity and efficiency of the anode active material decrease because the Ca-containing inorganic layer does not participate in the electrochemical reaction. When the content is less than the above range, there is a problem that the Ca-containing inorganic layer cannot properly exert its passivation effect.

In one exemplary embodiment of the present invention, lithium by-products disposed on at least a portion of the silicon-based particles may also be included. In particular, lithium by-products may be present on the surface of the silicon-based particles or on the surface of the carbon layer. In addition, lithium by-products may exist between the Ca-containing inorganic layer and the silicon-based particles.

In particular, the lithium by-product may refer to a lithium compound that remains near the surface of the silicon-based particles or the carbon layer after the silicon-based particles are manufactured. As described above, even after the acid treatment process, lithium by-products unreacted with the acid may remain.

The lithium by-product may include one or more selected from the group consisting of Li ₂ O, liOH and Li ₂CO₃.

The presence or absence of lithium by-products can be determined by X-ray diffraction analysis (XRD) or X-ray photoelectron spectroscopy analysis (XPS).

The content of the lithium by-product may be 5 parts by weight or less based on 100 parts by weight of the total negative electrode active material. Specifically, the content of the lithium by-product may be 0.001 to 5 parts by weight, 0.01 to 5 parts by weight, 0.05 to 2 parts by weight, or 0.1 to 1 part by weight. More specifically, the content of the lithium by-product may be 0.1 to 0.8 parts by weight or 0.1 to 0.5 parts by weight. When the content of the lithium by-product satisfies the above range, side reactions in the slurry can be reduced and the change in viscosity can be reduced, thereby improving the aqueous processing characteristics. On the other hand, when the content of the lithium by-product is higher than the above range, the slurry becomes alkaline upon formation, which causes side reactions or viscosity changes and causes problems in terms of aqueous processability.

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

The average particle diameter (D ₅₀) of the anode 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 satisfied, structural stability of the active material is ensured during charge and discharge, a problem that the volume expansion/contraction level increases as the particle diameter becomes excessively large can be prevented, and a problem that the initial efficiency decreases as the particle diameter becomes excessively small can also be prevented.

< Method for producing negative electrode active Material >

An exemplary embodiment of the present invention provides a method of manufacturing a negative active material, the method including: forming a silicon-based particle that contains SiO _x (0 < x < 2) and a Li compound and has a carbon layer provided on at least a part of its surface; and reacting the silicon-based particles with a Ca precursor.

The silicon-based particles may be formed by:

a step of heating and gasifying the Si powder and the SiO ₂ powder under vacuum,

A step of depositing the gasified mixed gas to form preliminary particles;

a step of forming a carbon layer on the surface of the formed preliminary particles, and

And a step of mixing and heat-treating the preliminary particles having the carbon layer formed thereon with the Li powder.

Specifically, the mixed powder of the silicon powder and the SiO ₂ powder may be heat-treated under vacuum at 1300 to 1800 ℃, 1400 to 1800 ℃, or 1400 to 1600 ℃.

The formed preliminary particles may have the form of SiO.

The carbon layer may be formed by using Chemical Vapor Deposition (CVD) using a hydrocarbon gas or by carbonizing a material used as a carbon source.

Specifically, the carbon layer may be formed by placing the formed preliminary particles into a reactor, and then depositing a hydrocarbon gas at 600 to 1200 ℃ by Chemical Vapor Deposition (CVD). 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 ℃.

The heat treatment step after mixing the preliminary particles having the carbon layer formed thereon and the Li powder may be performed at 700 to 900 ℃ for 4 to 6 hours, specifically, at 800 ℃ for 5 hours.

The silicon-based particles may contain a silicate of Li, a silicide of Li, an oxide of Li, or the like as the Li compound.

The particle size of the silicon-based particles may be adjusted by a method such as a ball mill, a jet mill, or air classification, but the present invention is not limited thereto.

The Li compound (lithium by-product) is provided on at least a part of the surface of the silicon-based particles having the carbon layer. Specifically, in the process of forming preliminary particles containing SiO _x (0 < x < 2), forming a carbon layer on the preliminary particles, and then doping Li to manufacture the above silicon-based particles, lithium compounds, i.e., lithium by-products generated due to unreacted lithium remain near the surfaces of the silicon-based particles.

In one exemplary embodiment of the present invention, a method of manufacturing a negative electrode active material includes a step of reacting silicon-based particles with a Ca precursor.

Specifically, the step of reacting the silicon-based particles with the Ca precursor may be performed by mixing the silicon-based particles and the Ca precursor, and then heat-treating the mixture.

The mixture of the silicon-based particles and the Ca precursor may be heat-treated at a temperature of 500 to 1200 ℃ under an Ar atmosphere. Specifically, the mixture may be heat treated at 550 ℃ to 1000 ℃ or 600 ℃ to 800 ℃ for 1 hour to 5 hours or 2 hours to 4 hours. Through the heat treatment step, a Ca-containing inorganic layer is formed on the surface of the silicon-based particles.

The Ca precursor may be, for example, ca (OAc) ₂、CaCl₂, caO, or Ca (NO ₃)₂, however, the present invention is not limited thereto, and Ca precursors known in the art may be suitably employed and used.

The content of the Ca precursor may be 0.01 to 20 parts by weight, specifically 0.1 to 15 parts by weight or 1 to 12 parts by weight based on 100 parts by weight of the total of the mixture of the silicon-based particles and the Ca precursor. The lower limit of the content of the Ca precursor may be 0.01 part by weight, 0.1 part by weight, 1 part by weight, 2 parts by weight, 3 parts by weight, 4 parts by weight, 5 parts by weight, 6 parts by weight, 7 parts by weight, or 8 parts by weight, and the upper limit may be 20 parts by weight, 18 parts by weight, 16 parts by weight, 14 parts by weight, 12 parts by weight, or 10 parts by weight.

Specifically, a Ca-containing inorganic layer is formed from a Ca precursor on the silicon-based particles, and the formed inorganic layer easily blocks the reaction between water and the lithium compound or the silicon-based particles, thereby suppressing gas generation of the slurry to improve aqueous workability.

In addition, in the case of using a Ca precursor, a method of synthesizing a Ca-containing inorganic layer is simple, thereby facilitating a manufacturing process of the anode active material.

< Cathode >

The anode according to an exemplary embodiment of the present invention may include the anode active material described above.

Specifically, the anode may include an anode current collector and an anode active material layer disposed on the anode current collector. The anode active material layer may contain an anode active material. In addition, the anode active material layer may further include a binder, a thickener, and/or a conductive material.

The anode active material layer may be formed by applying an anode slurry including an anode active material, a binder, a thickener, and/or a conductive material to at least one surface of a current collector and drying and calendaring it.

The anode slurry may further contain other anode active materials.

As the other anode active material, a compound capable of reversibly intercalating and deintercalating lithium may be used. Specific examples include: carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber and amorphous carbon; a metal species capable of forming an alloy with lithium such as Si, al, sn, pb, zn, bi, in, mg, ga, cd, si alloy, sn alloy, or Al alloy; metal oxides capable of doping and undoped lithium such as SiO _β(0<β<2)、SnO₂, vanadium oxide, lithium titanium oxide and lithium vanadium oxide; a composite material containing a metal-based substance and a carbonaceous material, such as a Si-C composite material or a Sn-C composite material, and any one or a mixture of two or more thereof may be used. In addition, a metallic lithium thin film may be used as the anode active material. In addition, as the carbon material, both low crystalline carbon and high crystalline carbon may be used. Representative examples of low crystalline carbon include soft carbon and hard carbon, and representative examples of high crystalline carbon include irregular, plate-type, scaly, spherical or fibrous natural or artificial graphite, coagulated graphite, pyrolytic carbon, mesophase pitch-based carbon fibers, mesophase carbon microbeads, mesophase pitch, and high temperature fired carbon such as petroleum or coal tar pitch-derived coke.

The other anode active material may be a carbon-based anode active material.

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

The anode slurry including the anode active material according to an exemplary embodiment of the present invention may have a pH of 7 to 11 at 25 ℃. When the pH of the negative electrode slurry satisfies the above range, the rheological properties of the slurry are stable. On the other hand, when the pH of the anode slurry is less than 7 or the pH of the anode slurry exceeds 11, carboxymethyl cellulose (CMC) used as a thickener is decomposed, resulting in a decrease in viscosity of the slurry and a decrease in dispersibility of an active material contained in the slurry.

The negative electrode current collector is not particularly limited as long as it has conductivity without causing chemical changes in the battery. For example, as the current collector, it is possible to use: copper, stainless steel, aluminum, nickel, titanium, and fired carbon; aluminum or stainless steel each surface-treated with carbon, nickel, titanium, silver, or the like. In particular, a transition metal such as copper or nickel, which readily adsorbs carbon, may be used as the current collector. The thickness of the current collector may be 6 μm to 20 μm. However, 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, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene Propylene Diene Monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and the above materials whose hydrogen is substituted with Li, na, ca, or the like, and may also include various copolymers thereof.

The conductive material is not particularly limited as long as it has conductivity without causing chemical changes in the battery, and for example, may be used: graphite such as natural graphite or artificial graphite; carbon blacks 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; a fluorocarbon compound; metal powders such as aluminum and nickel powders; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives and the like.

The thickener may be carboxymethyl cellulose (CMC), but is not limited thereto, and a thickener used in the art may be suitably used.

In one exemplary embodiment of the present invention, the weight ratio of the anode active material and the other anode active materials included in the anode slurry may be 1:99 to 30:70, specifically 5:95 to 30:70 or 10:90 to 20:80.

In one exemplary embodiment of the present invention, the total content of the anode active material contained in the anode slurry may be 60 to 99 parts by weight, specifically 70 to 98 parts by weight, based on 100 parts by weight total of solids in the anode slurry.

In one exemplary embodiment of the present invention, the binder may be contained in an amount of 0.5 to 30 parts by weight, specifically 1 to 20 parts by weight, based on 100 parts by weight total of solids in the negative electrode slurry.

In one exemplary embodiment of the present invention, the content of the conductive material may be 0.5 to 25 parts by weight, specifically 1 to 20 parts by weight, based on 100 parts by weight total of solids in the negative electrode slurry.

In one exemplary embodiment of the present invention, the content of the thickener may be 0.5 to 25 parts by weight, specifically 0.5 to 20 parts by weight, more specifically 1 to 20 parts by weight, based on 100 parts by weight of total solids in the negative electrode slurry.

The anode slurry according to an exemplary embodiment of the present invention may further include an anode slurry-forming solvent. Specifically, in terms of promoting the dispersion of the components, the negative electrode slurry-forming solvent may include at least one selected from the group consisting of distilled water, ethanol, methanol, and isopropanol, specifically distilled water.

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

< Secondary Battery >

The secondary battery according to an exemplary embodiment of the present invention may include the above-described negative electrode according to an exemplary embodiment of the present invention. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte, and the negative electrode is identical to the above-described negative electrode. Since the negative electrode has been described above, a detailed description thereof is omitted.

The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and including a positive electrode active material.

In the positive electrode, the positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical changes in the battery. For example, it is possible to use: stainless steel, aluminum, nickel, titanium, and fired carbon; aluminum or stainless steel each surface-treated with carbon, nickel, titanium, silver, or the like. Further, the positive electrode current collector may generally have a thickness of 3 μm to 500 μm, and the surface of the current collector may be formed with fine irregularities to enhance the adhesion of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric body.

The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material may be the following: layered compounds such as lithium cobalt oxide (LiCoO ₂) and lithium nickel oxide (LiNiO ₂) or compounds substituted with one or more transition metals; lithium iron oxides such as LiFe ₃O₄; lithium manganese oxides such as the chemical formulas Li _1+c1Mn_2-c1O₄ (0≤c1≤0.33)、LiMnO₃、LiMn₂O₃ and LiMnO ₂; lithium copper oxide (Li ₂CuO₂); vanadium oxides such as LiV ₃O₈、V₂O₅ and Cu ₂V₂O₇; a Ni-site lithium nickel oxide represented by the chemical formula LiNi _1-c2M_c2O₂ (wherein M is at least one selected from Co, mn, al, cu, fe, mg, B and Ga, and satisfies 0.01.ltoreq.c2.ltoreq.0.3); a lithium manganese composite oxide represented by the chemical formula LiMn _2-c3M_c3O₂ (wherein M is at least one selected from Co, ni, fe, cr, zn and Ta, and 0.01.ltoreq.c3.ltoreq.0.1 is satisfied) or Li ₂Mn₃MO₈ (wherein M is at least one selected from Fe, co, ni, cu and Zn); liMn ₂O₄ in which a part of Li in the chemical formula is substituted with an alkaline earth metal ion, etc., but is not limited thereto. The positive electrode may be Li metal.

The positive electrode active material layer may include a positive electrode conductive material and a positive electrode binder, and the positive electrode active materials described above.

In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and can be used without particular limitation as long as the positive electrode conductive material has electron conductivity without causing chemical changes in the battery. Specific examples may include: graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal 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 a conductive polymer such as a polyphenylene derivative or the like, and any one or a mixture of two or more thereof may be used.

In addition, the positive electrode binder serves to improve the bonding between the positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples may include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene Propylene Diene Monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and the like, and any one or a mixture of two or more thereof may be used.

The separator is used to separate the anode and the cathode and provide a moving path of lithium ions, wherein as the separator, any separator may be used without any particular limitation as long as it is generally used in a secondary battery, and in particular, a separator having a high moisture retention ability to an electrolyte and a low resistance to migration of electrolyte ions may be preferably used. Specifically, it is possible to use: porous polymer films, for example, porous polymer films made from polyolefin-based polymers such as ethylene homopolymers, propylene homopolymers, ethylene/butene copolymers, ethylene/hexene copolymers, and ethylene/methacrylate copolymers; or a laminate structure having two or more layers thereof. In addition, a general porous nonwoven fabric, for example, a nonwoven fabric formed of high-melting glass fibers, polyethylene terephthalate fibers, or the like may be used. Further, in order to secure heat resistance or mechanical strength, a coated separator including a ceramic component or a polymer material may be used, and a separator having a single-layer or multi-layer structure may be selectively used.

Examples of the electrolyte may include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, etc., which may be used to manufacture a lithium secondary battery, but are not limited thereto.

In particular, the electrolyte may comprise a non-aqueous organic solvent and a metal salt.

As the nonaqueous organic solvent, for example, an aprotic organic solvent 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, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphotriester, trimethoxymethane, dioxolane derivative, sulfolane, methyl sulfolane, 1, 3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, or ethyl propionate can be used.

In particular, among carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents, since they have a high dielectric constant to dissociate lithium salts well and can be preferably used. When the cyclic carbonate is mixed with a linear carbonate having a low viscosity and a low dielectric constant, such as dimethyl carbonate or diethyl carbonate, in an appropriate ratio and used, an electrolyte having high conductivity can be prepared, and thus can be more preferably used.

As the metal salt, a lithium salt may be used, and the lithium salt is a material that is easily soluble in a nonaqueous electrolytic solution, wherein as an anion of the lithium salt, one or more species ：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 (CF ₃CF₂SO₂)₂N^-) selected from the following may be used.

In order to improve the life characteristics of the battery, suppress the decrease in the capacity of the battery, improve the discharge capacity of the battery, etc., the electrolyte may further contain one or more additives such as: halogenated alkylene carbonates such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, (formal) glyme, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substitutedOxazolidinone, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol or aluminum trichloride.

Another embodiment of the present invention provides a battery module including the secondary battery as a unit cell and a battery pack including the battery module. Since the battery module and the battery pack include secondary batteries having high capacity, high rate performance, and high cycle characteristics, the battery module and the battery pack can be used as a power source for a medium-to-large-sized device selected from the group consisting of: electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and electric power storage systems.

Best mode

< Examples and comparative examples >

Example 1

Si and SiO ₂ powders 94: 94 g mixed in a 1:1 molar ratio were mixed in a reactor and heated in vacuo to a sublimation temperature of 1400 ℃. Then, the mixed gas of vaporized Si and SiO ₂ was reacted in a cooling zone in a vacuum state at a cooling temperature of 800 ℃ and condensed into a solid phase. Then, the condensed particles were pulverized for 3 hours using a ball mill to produce silicon-based particles having a size of 6 μm. Thereafter, the silicon-based particles were placed in a hot zone of a CVD apparatus while an inert atmosphere was maintained by flowing Ar gas, and reacted at 10 ^-1 torr for 20 minutes while methane was blown into the hot zone of 900 ℃ using Ar as a carrier gas, thereby forming a carbon layer on the surface of the silicon-based particles. Then, after adding 6 g Li metal powder and performing further heat treatment under an inert atmosphere and a temperature of 800 ℃, ca (OAc) ₂ and silicon-based particles were mixed and introduced at a weight ratio of 2:98, and heated in an argon atmosphere at 650 ℃ for 3 hours to manufacture a negative electrode active material forming a Ca-containing inorganic layer on the particle surface.

Example 2

A negative electrode active material was produced in the same manner as in example 1 except that the weight ratio of Ca (OAc) ₂ to silicon-based particles was 10:90.

Example 3

A negative electrode active material was produced in the same manner as in example 1, except that the heat treatment temperature after mixing the silicon-based particles with Ca (OAc) ₂ was changed to 1000 ℃.

Comparative example 1

A negative electrode active material was produced in the same manner as in example 1, except that the process of mixing and heat-treating Ca (OAc) ₂ was not performed.

Comparative example 2

A negative electrode active material was produced in the same manner as in example 1, except that the step of introducing and heat-treating Li metal powder was not performed.

< X-ray diffraction (XRD) analysis of negative electrode active Material >

Fig. 1 shows an XRD analysis pattern of the anode active material manufactured in example 1, in which it was confirmed that the peak caused by Si appeared at 28 ° to less than 29 °, and the peak caused by Ca was detected in the form of shoulder peak at 29 ° to 30 °. On the other hand, fig. 2 shows an XRD analysis pattern of the anode active material manufactured in comparative example 1, in which a peak caused by Si appears at 28 ° to less than 29 °, but a shoulder-shaped peak caused by Ca is not detected.

< Analysis of carbon layer content >

The content of the carbon layer was analyzed using a CS analyzer (CS-800, ELTRA).

< Analysis of Li content in negative electrode active Material >

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

< SEM-EDX analysis of the surface of negative electrode active Material >

The surface of the negative electrode active material was analyzed by scanning electron microscope energy dispersive X-ray spectroscopy (SEM-EDX). Specifically, the surface was analyzed using Hitachi S-4800 under an acceleration voltage of 15 kV and a working distance of 15 mm.

< Analysis of Ca content and inorganic layer content contained in negative electrode active Material >

The content of Ca was confirmed by ICP analysis using an inductively coupled plasma atomic emission spectrometer (ICP-OES, AVIO 500, perkin-Elmer 7300), and the content of Ca contained in the anode active material and the content of the inorganic layer were analyzed accordingly.

< Analysis of D ₅₀ and specific surface area of negative electrode active Material >

D ₅₀ of the anode active material was analyzed by a laser diffraction particle size analysis method using a Microtrac S3500 instrument, and the BET specific surface area of the anode active material was measured using a BET measuring instrument (BEL-SORP-MAX, nippon Bell).

The analysis results of the anode active materials manufactured in the above examples and comparative examples are shown in table 1 below.

< Experimental example: evaluation of discharge capacity, initial efficiency and Life (Capacity Retention Rate) Properties ]

Negative electrodes and batteries were manufactured using the negative electrode active materials of examples and comparative examples, respectively.

The mixture was manufactured by mixing a negative electrode active material, carbon black as a conductive material, and polyacrylic acid (PAA) as a binder at a weight ratio of 80:10:10. Thereafter, 7.8: 7.8 g distilled water was added to the 5g mixture, which was then stirred to manufacture a negative electrode slurry. The negative electrode slurry was applied to a copper (Cu) metal thin film having a thickness of 20 μm as a negative electrode current collector, and dried. In this case, the temperature of the circulated air was 60 ℃. Then, the film was calendered and dried in a vacuum oven at 130 ℃ for 12 hours to fabricate a negative electrode.

A lithium (Li) metal thin film obtained by cutting a lithium (Li) metal foil into a circular shape of 1.7671 cm ² was used as the positive electrode. A porous polyethylene separator was interposed between the positive electrode and the negative electrode, and an electrolyte obtained by dissolving 0.5 wt% of vinylene carbonate in a mixed solution of methyl carbonate (EMC) and Ethylene Carbonate (EC) in a mixed volume ratio of 7:3 and dissolving LiPF ₆ to a concentration of 1M was injected to manufacture a lithium coin half-cell.

The prepared battery was charged and discharged to evaluate the discharge capacity, initial efficiency and capacity retention rate, which are shown in table 2 below.

For the first cycle and the second cycle, charging and discharging were performed at 0.1C, and from the third cycle to the 49 th cycle, charging and discharging were performed at 0.5C. At the 50 th cycle, the charge and discharge were terminated in a charged state (lithium is contained in the anode).

Charging conditions: CC (constant current)/CV (constant voltage) (5 mV/0.005C current cut-off)

Discharge conditions: CC (constant current) Condition 1.5V

From the results after one charge and discharge, the discharge capacity (mAh/g) and the initial efficiency (%) were obtained. Specifically, the initial efficiency (%) is calculated as follows.

Initial efficiency (%) = (discharge capacity of first time/charge capacity of first time) ×100

The capacity retention was calculated as follows.

Capacity retention (%) = (49 th discharge capacity/first discharge capacity) ×100

< Experimental example: evaluation of Property of processability (gas Generation)

As part of the processability evaluation, a slurry of 20 g made from graphite, anode active material, carbon black, CMC, and PAA mixed in a weight ratio of 77:20:1:1:1 was placed in a bag of about 10 cm x 15 cm, then vacuum sealed, placed in an oven at 40 ℃, and the volume change was measured.

The time point (hours) of gas generation was measured on the basis of "the time point when the volume of the bag was increased by 2 mL or more compared to the volume measured immediately after vacuum sealing of the bag". The results are shown in table 2 below.

The negative electrode active material according to the present invention is characterized in that a Ca-containing inorganic layer is provided on silicon-based particles containing a Li compound. Since the inorganic layer has low reactivity with water, the inorganic layer does not react with water in the aqueous slurry and remains good, thereby preventing water from penetrating into the anode active material to effectively passivate the silicon-based particles. In addition, since side reactions between silicon-based particles or lithium by-products and water are prevented to suppress the generation of gas, there is an effect of improving the aqueous workability of the slurry.

In table 2 above, in the case of examples 1 to 3, it was confirmed that the overall discharge capacity, initial efficiency and capacity retention rate were superior to those of comparative example 1, since the silicon-based particles could be effectively passivated by forming the Ca-containing inorganic layer on the silicon-based particles through the Ca precursor. In addition, side reactions in the aqueous slurry can be prevented to delay the time point of gas generation, thereby ensuring excellent aqueous workability.

In the case of comparative example 2, since the silicon-based particles were not doped with Li, the discharge capacity was high, and since no lithium by-product was generated, no gas was generated. However, it was confirmed that the initial efficiency and the capacity retention rate were significantly reduced as compared with examples 1 to 3, since the particles were not doped with Li.

Accordingly, in the present invention, by providing a negative electrode active material having a Ca-containing inorganic layer provided on silicon-based particles containing a Li compound, the overall aqueous processability, discharge capacity, efficiency, and capacity retention can be easily improved by the passivation effect.

Claims

1. A negative electrode active material, the negative electrode active material comprising:

Silicon-based particles that contain SiO _x (0 < x < 2) and a Li compound and that have a carbon layer provided on at least a part of the surface thereof; and

And a Ca-containing inorganic layer provided on at least a part of the silicon-based particles.

2. The anode active material according to claim 1, wherein in X-ray diffraction analysis, a peak exists at 29 ° or more and 30 ° or less.

3. The negative electrode active material according to claim 1, wherein the Ca-containing inorganic layer is provided in islands on at least a part of the silicon-based particles.

4. The anode active material according to claim 1, wherein the Ca-containing inorganic layer contains at least one selected from the group consisting of CaCO ₃, caO, and Ca (OH) ₂.

5. The anode active material according to claim 2, wherein in X-ray diffraction analysis, other peaks exist at 28 ° or more and less than 29 °.

6. The anode active material according to claim 1, wherein an element content of Ca is 0.05 to 10 parts by weight when analyzed by scanning electron microscope energy dispersive X-ray spectroscopy (SEM-EDX).

7. The anode active material according to claim 1, wherein the content of Ca is 0.005 to 5 parts by weight based on 100 parts by weight of the anode active material in total.

8. The anode active material according to claim 1, wherein the content of the Ca-containing inorganic layer is 0.01 to 10 parts by weight based on 100 parts by weight of the anode active material in total.

9. The anode active material according to claim 1, further comprising a lithium by-product disposed on at least a portion of the silicon-based particles.

10. The anode active material according to claim 9, wherein the content of the lithium by-product is 5 parts by weight or less based on 100 parts by weight of the anode active material in total.

11. The anode active material according to claim 1, wherein the content of Li is 0.1 to 40 parts by weight based on 100 parts by weight of the anode active material in total.

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

13. A method of manufacturing the anode active material according to any one of claims 1 to 12, the method comprising:

forming a silicon-based particle that contains SiO _x (0 < x < 2) and a Li compound and has a carbon layer provided on at least a part of its surface; and

The silicon-based particles are reacted with a Ca precursor.

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

15. A secondary battery comprising the negative electrode of claim 14.