Method for producing negative electrode active material, negative electrode active material, negative electrode, and secondary battery

Abstract

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

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a negative electrode active material, a negative electrode active material, a negative electrode, and a secondary battery.

[0002] This application claims the benefit of the filing dates of Korean Patent Application No. 10-2022-0177126, filed with the Korean Intellectual Property Office on December 16, 2022, and Korean Patent Application No. 10-2023-0147653, filed with the Korean Intellectual Property Office on October 31, 2023, and all of the contents thereof are incorporated herein by reference.

Background Art

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

[0004] Generally, a lithium secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, an electrolyte, and an organic solvent. Further, an active material layer including a positive electrode active material and a negative electrode active material can be formed on a current collector for the positive electrode and the negative electrode. Generally, LiCoO 2 , LiMn 2 O 4 and the like lithium-containing metal oxides are used as the positive electrode active material, and a carbon-based active material and a silicon-based active material that do not contain lithium are used as the negative electrode active material for the negative electrode.

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

[0006] On the other hand, among silicon-based active materials, silicon-based oxides, specifically, SiO x In the case of a silicon-based oxide represented by (0 < x < 2), it has an advantage in that the degree of volume expansion / contraction due to charge / discharge compared to other silicon-based active materials such as silicon (Si) is low.

[0007] In addition, a technique of forming a carbon layer is used to improve the conductivity of the negative electrode active material. However, in a general method for manufacturing a carbon layer, there is a problem that the carbon layer is difficult to be uniformly arranged on the surface and inside of the negative electrode active material, and the improvement degree of the battery life performance is not large.

[0008] Therefore, there is a current situation where it is necessary to develop a negative electrode active material in which a carbon layer is uniformly arranged on silicon-based particles and a method for manufacturing the negative electrode active material.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0010] The present invention relates to a method for manufacturing a negative electrode active material, a negative electrode active material, a negative electrode including the same, and a secondary battery including the same.

Means for Solving the Problems

[0011] One embodiment of the present invention provides a method for manufacturing a negative electrode active material, including: heat-treating a silicon-based precursor and an ionic compound to vaporize them; co-depositing a mixed gas of the silicon-based precursor and the ionic compound in a gas phase to form silicon-based particles; and heat-treating the silicon-based particles and a carbon source.

[0012] One embodiment of the present invention provides a negative electrode active material produced by the method for producing the negative electrode active material.

[0013] One embodiment of the present invention is SiO x (0 < x < 2) and silicon-based particles containing pores; and a carbon layer provided on the surface and inside the pores of the silicon-based particles; a negative electrode active material, wherein the negative electrode active material is selected from the group consisting of Li, Na, K, Rb, and Cs. One or more alkali metal elements selected, and one or more halogen elements selected from the group consisting of F, Cl, Br, and I, and when analyzing the cross section of the negative electrode active material, the average diameter of the pores is 20 nm to 60 nm, provided is a negative electrode active material.

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

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

Effect of the Invention

[0016] In the method for producing a negative electrode active material according to one embodiment of the present invention, by vapor-depositing a silicon-based precursor and an ionic compound together to form silicon-based particles, pores are uniformly formed and the carbon layer is uniformly arranged. Therefore, the conductivity of the negative electrode active material is improved, and the discharge capacity, initial efficiency, resistance performance and / or life characteristics of the battery are improved. In addition, the ionic compound remaining without being removed further improves the conductivity of the negative electrode active material.

[0017] The negative electrode active material according to one embodiment of the present invention contains one or more alkali metal elements selected from the group consisting of Li, Na, K, Rb, and Cs, and one or more halogen elements selected from the group consisting of F, Cl, Br, and I. When performing cross-sectional analysis of the negative electrode active material, the average diameter of pores is 20 nm to 60 nm. The negative electrode active material having the above characteristics has pores uniformly formed, and a carbon layer is uniformly distributed over a wide area on the surface and inside the pores of the negative electrode active material. By including the alkali metal element and the halogen element, there is an advantage that the conductivity can be improved.

[0018] Therefore, a negative electrode containing the negative electrode active material according to one embodiment of the present invention, and a secondary battery including the negative electrode have an effect of improving the discharge capacity, initial efficiency, resistance performance, and / or life characteristics of the battery.

Mode for Carrying Out the Invention

[0019] Hereinafter, the present specification will be described in more detail.

[0020] In the present specification, when a certain part "includes" a certain component, this means that, unless otherwise stated to the contrary, it does not exclude other components, but may further include other components.

[0021] In the present specification, when a certain member is located "on" another member, this includes not only the case where a certain member is in contact with another member, but also the case where there is another member between the two members.

[0022] Terms and words used in the present specification should not be construed as being limited to their ordinary or dictionary meanings. The inventors should interpret them in accordance with the meaning and concept consistent with the technical idea of the present invention, in accordance with the principle that they can appropriately define the concept of the terms in order to explain their invention in the best way.

[0023] The singular expressions of the terms used in the present specification include plural expressions unless the context clearly indicates otherwise.

[0024] In this specification, the crystallinity of the structure contained in the negative electrode active material can be confirmed by X-ray diffraction analysis. The X-ray diffraction analysis may be performed using an X-ray diffraction (XRD) analyzer (product name: D4-endeavor, manufacturer: bruker), and devices used in the art other than the above device may also be appropriately adopted.

[0025] In this specification, the presence and content of elements in the negative electrode active material can be confirmed by ICP analysis. The ICP analysis can be performed using an inductively coupled plasma atomic emission spectrometer (ICPAES, Perkin-Elmer 7300).

[0026] In this specification, the average particle size (D 50 ) can be defined as the particle size at the 50% reference of the volume cumulative amount in the particle size distribution curve (graph curve of the particle size distribution diagram). The average particle size (D 50 ) can be measured, for example, using the laser diffraction method. The laser diffraction method can generally measure particle sizes ranging from the submicron region to about several millimeters, and results with high reproducibility and high resolution can be obtained.

[0027] In the present invention, the specific surface area of the silicon-based composite can be measured by the BET (Brunauer-Emmett-Teller; BET) method. For example, it can be measured by the BET six-point method by the nitrogen gas adsorption flow method using a porosimetry analyzer (Bell Japan Inc, Belsorp-II mini).

[0028] In the present invention, the average diameter (pore size) of the pores can be measured by a calculation formula according to the BJH (Barrett-Joyner-Halenda) method through the nitrogen adsorption method. Specifically, after deriving the pore area according to the pore size using the BELSORP-mini II model of BEL Japan, Inc., the pore size showing the largest pore area was taken as representative. The BJH method may be used, and the plot of the measured values has the diameter of the pores (Dp / nm) on the X-axis and dVp / dDp (cm 3 g -1 nm -1 ) on the Y-axis.

[0029] Hereinafter, preferred embodiments of the present invention will be described in detail. However, the embodiments of the present invention may be modified in various forms, and the scope of the present invention is not limited to the embodiments described below.

[0030] <Method for manufacturing negative electrode active material> One embodiment of the present invention provides a method for manufacturing a negative electrode active material, including: heat-treating and vaporizing a silicon-based precursor and an ionic compound; co-depositing the mixed gas of the silicon-based precursor and the ionic compound in the gas phase to form silicon-based particles; and heat-treating the silicon-based particles and a carbon source.

[0031] When the silicon-based precursor and the ionic compound are co-deposited to form silicon-based particles, the ionic compound is distributed within the silicon-based particles, and the ionic compound is removed in the subsequent heat treatment process, so that pores are uniformly formed within the silicon-based particles, and a carbon layer is uniformly arranged over a large area on the surface and / or inside the pores of the silicon-based particles. As a result, the conductivity of the negative electrode active material is improved, and the discharge capacity, initial efficiency, resistance performance, and / or life characteristics of the battery are improved. In addition, the remaining ionic compound that is not removed further improves the conductivity of the negative electrode active material.

[0032] The silicon-based precursor includes Si powder, SiO powder, and SiO 2It may be one or more selected from the group consisting of powders, preferably Si powder, SiO powder, and SiO 2 It may also be a mixed powder of powders.

[0033] After heat-treating and vaporizing the silicon-based precursor and the ionic compound in a vacuum, the vaporized mixed gas can be deposited together to form silicon-based particles containing the ionic compound.

[0034] Specifically, the silicon-based precursor and the ionic compound can be heat-treated and vaporized at a temperature of 1800 °C or higher and 2500 °C or lower in an inert gas atmosphere. Specifically, it can be heat-treated and vaporized at a temperature of 2200 °C or higher and 2400 °C or lower. At this time, the silicon-based precursor and the ionic compound can be mixed after being vaporized by other sources respectively, or vaporized by the same source to form a mixed gas of the silicon-based precursor and the ionic compound.

[0035] The deposition may be performed in an inert gas atmosphere and at a temperature of 500 °C or higher and 1000 °C or lower. Specifically, it may be performed by heat treatment (cooling) under conditions of 600 °C or higher and 800 °C or lower.

[0036] During the production of the negative electrode active material, the silicon-based precursor and the ionic compound are deposited together to produce silicon-based particles. At this time, pores can be uniformly formed in the silicon-based particles by the ionic compound.

[0037] The ionic compound contains one or more alkali metal elements selected from the group consisting of Li, Na, K, Rb, and Cs, and one or more halogen elements selected from the group consisting of F, Cl, Br, and I. Specifically, the ionic compound may exist with the alkali metal element in the form of a cation and the halogen element in the form of an anion bonded by ionic bonds. Preferably, the halogen element is Cl, Br, or I, and more preferably Cl.

[0038] In one embodiment of the present invention, the ionic compound may be one or more selected from the group consisting of LiF, LiCl, NaF, and NaCl.

[0039] The ionic compound may have a melting point of 600°C to 800°C and a boiling point of 1300°C to 1700°C.

[0040] At this time, the ionic compound is removed during the heat treatment of the silicon-based particles to form pores, and a part of the ionic compound that is not removed remains in the negative electrode active material.

[0041] The weight ratio of the silicon-based precursor and the ionic compound may be 90:10 to 99.9:0.1 or 95:5 to 99:1.

[0042] When the negative electrode active material is manufactured by introducing the ionic compound in the above content, an appropriate content of the ionic compound is introduced into the silicon-based particles, and pores can be uniformly formed later.

[0043] In one embodiment of the present invention, additional heat treatment may be performed on the silicon-based particles containing the ionic compound formed in the vapor deposition step at a temperature of 800°C to 1100°C.

[0044] During the additional heat treatment process, the ionic compound contained in the silicon-based particles is appropriately removed, and a large number of pores can be uniformly formed in the silicon-based particles. In addition, the ionic compound that is not removed is partially contained in the silicon-based particles, which has the effect of further improving the conductivity of the material.

[0045] The silicon-based particles formed as described above may contain SiO x (0 < x < 2), an alkali metal element, and a halogen element. The alkali metal element and the halogen element are derived from the remaining ionic compound that is not removed and may be distributed on the surface and / or inside of the silicon-based particles.

[0046] In one embodiment of the present invention, in order to dope the silicon-based particles with a metal (for example, Li or Mg), the step of heat-treating and vaporizing the silicon-based precursor and the ionic compound may include the process of heat-treating and vaporizing the metal precursor. Specifically, the metal precursor may be vaporized from different sources from the silicon-based precursor and the ionic compound and then mixed, or may be vaporized from the same source to form a mixed gas.

[0047] The metal precursor may be heat-treated and vaporized under conditions of 1000 °C or higher and 1400 °C or lower.

[0048] The metal precursor may be a Li precursor or a Mg precursor.

[0049] The Li precursor may be, for example, Li powder, LiOH, Li 2 O, etc., and is not limited thereto.

[0050] The Mg precursor may be, for example, Mg powder, and is not limited thereto.

[0051] After further heat-treating by including a Li precursor or a Mg precursor, the silicon-based particles formed by vapor-phase deposition of the mixed gas may further contain one or more of Li compounds and Mg compounds, and the Li or Mg may be distributed on the surface and / or inside of the silicon-based particles in a doped form.

[0052] In another embodiment, in order to dope the silicon-based particles with a metal (for example, Li or Mg), after the step of heat-treating the silicon-based particles and the carbon source, a step of heat-treating after mixing the silicon-based particles and the metal precursor may be performed. If necessary, the step may be performed under heat treatment or by using an electrochemical method.

[0053] The step of heat-treating after mixing the silicon-based particles and the metal precursor may be performed in an inert atmosphere.

[0054] The step of heat-treating after mixing the formed silicon-based oxide and the metal precursor may be performed in an inert atmosphere at 400°C to 1400°C, 500°C to 1000°C, or 700°C to 900°C. Also, after the heat treatment, additional heat treatment may be performed, and the additional heat treatment may be performed at 700°C to 1100°C or 800°C to 1000°C.

[0055] In one embodiment of the present invention, in order to form a carbon layer on the silicon-based particles, a step of heat-treating the silicon-based particles and a carbon source may be performed.

[0056] The carbon source may be a hydrocarbon gas, but is not limited thereto, and substances known in the art may be appropriately employed.

[0057] In the step of heat-treating the silicon-based particles and the carbon source, a chemical vapor deposition method (CVD) or a method of carbonizing a substance serving as a carbon source may be utilized to form a carbon layer on the silicon-based particles.

[0058] The step of heat-treating the silicon-based particles and the carbon source may be performed at 800°C to 1200°C.

[0059] Specifically, after the formed silicon-based particles are introduced into a reactor, a carbon source, for example, a hydrocarbon gas, may be subjected to chemical vapor deposition (CVD) at 800°C to 1200°C to form a carbon layer. The hydrocarbon gas may be at least one hydrocarbon gas selected from the group including methane, ethane, propane, and acetylene, and preferably, heat treatment may be performed at 800°C to 1000°C.

[0060] At this time, since the carbon layer is uniformly arranged over a large area on the surface and / or inside the pores of the silicon-based particles during the process of heat-treating the carbon source, the conductivity of the negative electrode active material is improved.

[0061] The particle size of the silicon-based particles can be adjusted by methods such as a ball mill, a jet mill, or air classification, but is not limited thereto.

[0062] In one embodiment of the present invention, the average diameter of the pores contained in the silicon-based particles may be 20 nm or more and 60 nm or less.

[0063] <Negative electrode active material> One embodiment of the present invention provides a negative electrode active material manufactured by the method for manufacturing a negative electrode active material described above.

[0064] One embodiment of the present invention is SiO x (0 < x < 2) and silicon-based particles containing pores; and a carbon layer provided on the surface and inside the pores of the silicon-based particles; a negative electrode active material, wherein the negative electrode active material is selected from the group consisting of Li, Na, K, Rb, and Cs. One or more alkali metal elements selected, and one or more halogen elements selected from the group consisting of F, Cl, Br, and I, and when performing cross-sectional analysis of the negative electrode active material, the average diameter of the pores is 20 nm to 60 nm. A negative electrode active material is provided.

[0065] Generally, when forming a carbon layer to improve the conductivity of a negative electrode active material, there is a problem that the carbon layer is concentrated and coated only on the surface of the negative electrode active material, so that the conductivity of the negative electrode active material is not sufficiently exhibited and the battery characteristics deteriorate.

[0066] On the other hand, the negative electrode active material according to the present invention uses an ionic compound during the production of the negative electrode active material to form a large number of pores having a specific size in the silicon-based particles so that the carbon layer is effectively arranged in the pores of the silicon-based particles. Thus, the carbon coating area can be increased, and the conductivity of the material can be improved by the elements derived from the ionic compound remaining inside the negative electrode active material.

[0067] In this specification, the statement that a carbon layer is provided on the surface of silicon-based particles means that, except for the pores of the silicon-based particles, the carbon layer is disposed on the outer surface of the particles.

[0068] In this specification, the statement that a carbon layer is provided in the pores of silicon-based particles means that the carbon layer is disposed on the surface and / or the internal space of the pores contained in the silicon-based particles.

[0069] The negative electrode active material according to one embodiment of the present invention contains silicon-based particles including SiO x (0 < x < 2) and pores.

[0070] The SiO x (0 < x < 2) corresponds to a matrix within the silicon-based composite particles. The SiO x (0 < x < 2) may be in a form containing Si and / or SiO 2 , and the Si may form a phase. That is, the x corresponds to the number ratio of O to Si contained in the SiO x (0 < x < 2). When the silicon-based composite particles contain the SiO x (0 < x < 2), the discharge capacity of the secondary battery can be improved.

[0071] In one embodiment of the present invention, when performing a cross-sectional analysis of the negative electrode active material, the average diameter of the pores may be 20 nm to 60 nm, specifically, 22 nm to 58 nm, 24 nm to 55 nm, or 30 nm to 50 nm.

[0072] In the present invention, the cross-sectional analysis of the negative electrode active material may be performed using an Ion Milling apparatus. Specifically, an electrode sample prepared by coating the negative electrode active material on a copper foil (Cu Foil) is milled using a Hitachi IM4000 apparatus. Specifically, after irradiating an ion beam at a voltage of 1.5 kV and treating for about 3 to 4 hours per sample, a cross-sectional image can be measured with a Hitachi S-4800 SEM. Based on the measured SEM cross-sectional image, the average diameter of the pores appearing in the cross-section of the negative electrode active material can be determined.

[0073] The diameter of the pores obtained by the above-described cross-sectional analysis relates to the diameter of the pores located inside the negative electrode active material, and is different from the diameter of the pores near the surface of the negative electrode active material measured by the nitrogen adsorption method.

[0074] When the average diameter of the pores is less than 20 nm, it is difficult for the pores to accommodate an excessive change in the volume of the silicon-based particles, and particle cracking etc. are observed during long-term cycle behavior, so there is a problem that a rapid capacity decrease of the battery appears. When the average diameter of the pores exceeds 60 nm, the coating amount of the carbon layer is small, the resistance of the cell increases, the side reaction between the electrolyte and the silicon-based particles increases, and the life characteristics of the battery are degraded.

[0075] When a carbon layer is formed inside the pores, the average diameter of the pores can be calculated from the diameter of the pores including the carbon layer.

[0076] In one embodiment of the present invention, the silicon-based particles may contain one or more of a Li compound and a Mg compound.

[0077] In one embodiment of the present invention, the silicon-based particles may further contain a Li compound.

[0078] The Li compound may correspond to a matrix within the silicon-based particles. The Li compound may exist in at least one form of lithium atoms, lithium silicate, silicide, and lithium oxide within the silicon-based particles. When the silicon-based particles contain the Li compound, it has the effect of improving the initial efficiency.

[0079] The Li compound may be distributed on the surface and / or inside of the silicon-based particles in a doped form. The Li compound is distributed on the surface and / or inside of the silicon-based particles, and can control the volume expansion / contraction of the silicon-based particles to an appropriate level, and can play a role in preventing damage to the active material. Also, the Li compound can be contained in terms of reducing the ratio of the irreversible phase (e.g., SiO 2 ) of the silicon-based particles and increasing the efficiency of the negative electrode active material.

[0080] In one embodiment of the present invention, the Li compound may exist in the form of lithium silicate. The lithium silicate is represented by Li a Si b O c (2 ≤ a ≤ 4, 0 < b ≤ 2, 2 ≤ c ≤ 5), and can be divided into crystalline lithium silicate and amorphous lithium silicate. The crystalline lithium silicate may exist in the form of at least one lithium silicate selected from the group consisting of Li 2 SiO 3 , Li 4 SiO 4 and Li 2 Si 2 O 5 within the silicon-based particles, and the amorphous lithium silicate may consist of a complex structure of the form Li a Si b O c (2 ≤ a ≤ 4, 0 < b ≤ 2, 2 ≤ c ≤ 5), and is not limited to the above form.

[0081] In another embodiment, the Li silicide is Li 7 Si2 may be included, and the Li oxide may contain Li 2 O.

[0082] In one embodiment of the present invention, based on 100 parts by weight of the total negative electrode active material, Li may be contained in an amount of 0.1 part by weight to 40 parts by weight or 0.1 part by weight to 25 parts by weight. Specifically, it may be contained in an amount of 1 part by weight to 25 parts by weight, and more specifically, it may be contained in an amount of 2 parts by weight to 20 parts by weight or 2 parts by weight to 10 parts by weight. As the content of Li increases, although the initial efficiency increases, there is a problem that the discharge capacity decreases. Therefore, when the above range is satisfied, appropriate discharge capacity and initial efficiency can be realized.

[0083] In one embodiment of the present invention, the silicon-based particles may further contain an Mg compound.

[0084] The Mg compound may correspond to a matrix within the silicon-based particles. The Mg compound may exist in at least one form of magnesium atoms, magnesium silicate, magnesium silicide, and magnesium oxide within the silicon-based particles. When the silicon-based particles contain an Mg compound, there is an effect that the initial efficiency is improved.

[0085] The Mg compound may be distributed on the surface and / or inside of the silicon-based particles in a form doped into the silicon-based particles. The Mg compound is distributed on the surface and / or inside of the silicon-based particles, and can control the volume expansion / contraction of the silicon-based particles to an appropriate level, and can play a role in preventing damage to the active material. Further, the Mg compound can be contained in terms of reducing the ratio of the irreversible phase (for example, SiO 2 ) of the silicon-based particles to increase the efficiency of the negative electrode active material.

[0086] In one embodiment of the present invention, the Mg compound may exist in the form of magnesium silicate. The magnesium silicate can be divided into crystalline magnesium silicate and amorphous magnesium silicate. The magnesium silicate may contain at least one of Mg 2 SiO 4 and MgSiO 3 .

[0087] In another embodiment, the magnesium silicide may contain Mg 2 Si, and the magnesium oxide may contain MgO.

[0088] The contents of the Li element and the Mg element can be confirmed by inductively coupled plasma (ICP) analysis. Specifically, after separating a certain amount (about 0.01 g) of the negative electrode active material, it is transferred to a platinum crucible, nitric acid, hydrofluoric acid, and sulfuric acid are added, and it is completely decomposed on a hot plate. Then, using an inductively coupled plasma optical emission spectrometer (ICPAES, Perkin-Elmer 7300), at the characteristic wavelength of the element to be analyzed, the intensity of the standard solution prepared using a standard solution (5 mg / kg) is measured to create a standard calibration curve. Then, the pretreated sample solution and the blank sample are introduced into the instrument, the intensities of each are measured to calculate the actual intensity, and after calculating the concentration of each component by comparing with the created calibration curve, it is converted so that the total sum becomes the theoretical value, and the element content of the manufactured negative electrode active material can be analyzed.

[0089] In one embodiment of the present invention, the silicon-based particles may contain additional metal atoms. The metal atoms may exist in at least one form of metal atoms, metal silicates, metal silicides, and metal oxides within the silicon-based particles. The metal atoms may contain 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.

[0090] In one embodiment of the present invention, the carbon layer may be provided on the surface of and within the pores of the silicon-based particles. Thereby, conductivity is imparted to the silicon-based particles, the volume change of the negative electrode active material including the silicon-based particles is effectively suppressed, and the life characteristics of the battery can be improved.

[0091] At this time, the carbon layer may be in a form that partially covers at least a part of the surface of and within the pores of the silicon-based particles, that is, the surface of the particles and the inside of the pores, or covers the entire surface of the particles and the inside of the pores.

[0092] In one embodiment of the present invention, the carbon layer contains amorphous carbon.

[0093] Further, the carbon layer may further contain crystalline carbon.

[0094] The crystalline carbon can further improve the conductivity of the negative electrode active material. The crystalline carbon may contain at least one selected from the group consisting of fluorene, carbon nanotubes, and graphene.

[0095] The amorphous carbon can appropriately maintain the strength of the carbon layer and suppress the expansion of the silicon-based particles. The amorphous carbon may be at least one carbide selected from the group consisting of tar, pitch, and other organic substances, or a carbon-based substance formed using a hydrocarbon as a source in chemical vapor deposition.

[0096] The carbide of the other organic substances may be a carbide of an organic substance selected from sucrose, glucose, galactose, fructose, lactose, mannose, ribose, aldohexose or ketohexose, and combinations thereof.

[0097] The hydrocarbon may be a substituted or unsubstituted aliphatic or alicyclic hydrocarbon, or a substituted or unsubstituted aromatic hydrocarbon. The aliphatic or alicyclic hydrocarbon of the substituted or unsubstituted aliphatic or alicyclic hydrocarbon may include methane, ethane, ethylene, acetylene, propane, butane, butene, pentane, isobutane, or hexane. The aromatic hydrocarbon of the substituted or unsubstituted aromatic hydrocarbon may include benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, coumarone, pyridine, anthracene, or phenanthrene.

[0098] In one embodiment of the present invention, the carbon layer may be an amorphous carbon layer.

[0099] In one embodiment of the present invention, the carbon layer may be included in an amount of 0.1 parts by weight to 50 parts by weight, 0.1 parts by weight to 30 parts by weight, or 0.1 parts by weight to 20 parts by weight based on 100 parts by weight in total of the negative electrode active material. More specifically, it may be included in an amount of 0.5 parts by weight to 15 parts by weight, 1 part by weight to 10 parts by weight, or 1 part by weight to 5 parts by weight. When the above range is satisfied, it is possible to prevent a decrease in the capacity and efficiency of the negative electrode active material.

[0100] In one embodiment of the present invention, the thickness of the carbon layer may be 1 nm to 500 nm, and specifically, it may be 5 nm to 300 nm. When the above range is satisfied, the conductivity of the negative electrode active material is improved, the volume change of the negative electrode active material is easily suppressed, the side reaction between the electrolyte and the negative electrode active material is suppressed, and the initial efficiency and / or life of the battery is improved.

[0101] Specifically, the carbon layer can be formed by chemical vapor deposition (CVD) using at least one hydrocarbon gas selected from the group consisting of methane, ethane, and acetylene.

[0102] In one embodiment of the present invention, the negative electrode active material contains one or more alkali metal elements selected from the group consisting of Li, Na, K, Rb, and Cs, and one or more halogen elements selected from the group consisting of F, Cl, Br, and I. Specifically, during the production of the negative electrode active material, a silicon-based precursor and an ionic compound containing the alkali metal element and the halogen element are co-evaporated to produce silicon-based particles. At this time, pores are uniformly formed in the silicon-based particles by the ionic compound, and the silicon-based particles may contain the alkali metal element and the halogen element.

[0103] In one example, the alkali metal element and the halogen element may be located inside the pores of the negative electrode active material.

[0104] In one embodiment of the present invention, the content of the alkali metal element may be 0.01 parts by weight or more and less than 10 parts by weight based on 100 parts by weight of the negative electrode active material. Specifically, the content of the alkali metal element may be more than 0.01 parts by weight and less than 10 parts by weight, 0.01 parts by weight or more and 5 parts by weight or less, 0.05 parts by weight or more and 5 parts by weight or less, 0.05 parts by weight or more and 2.5 parts by weight or less, 0.05 parts by weight or more and 2 parts by weight or less, or 0.1 parts by weight or more and 1.5 parts by weight or less based on 100 parts by weight of the negative electrode active material. At this time, the content of the alkali metal element may mean the content of the alkali metal element derived from the ionic compound.

[0105] In one embodiment of the present invention, the content of the halogen element may be 0.01 parts by weight or more and less than 10 parts by weight based on 100 parts by weight of the negative electrode active material. Specifically, the content of the halogen element may be more than 0.01 parts by weight and less than 10 parts by weight, 0.01 parts by weight or more and 5 parts by weight or less, 0.05 parts by weight or more and 5 parts by weight or less, 0.05 parts by weight or more and 2.5 parts by weight or less, 0.05 parts by weight or more and 2 parts by weight or less, or 0.1 parts by weight or more and 1.5 parts by weight or less based on 100 parts by weight of the negative electrode active material. At this time, the content of the halogen element may mean the content of the halogen element derived from the ionic compound.

[0106] When the alkali metal element and the halogen element are present in the negative electrode active material in the above contents, a large number of pores are formed in the silicon-based particles, and the carbon layer is effectively arranged in the pores of the silicon-based particles, resulting in an increase in the carbon coating area.

[0107] On the other hand, when the alkali metal element and the halogen element are not present in the negative electrode active material, that is, when an ionic compound is not added during the production of the silicon-based particles, no pores are formed in the silicon-based particles, the carbon coating area is reduced, and carbon is concentrated and coated only on the surface of the silicon-based particles, resulting in a problem that the conductivity of the negative electrode active material is reduced and the battery characteristics are degraded.

[0108] In addition, when the alkali metal element and the halogen element are present in an amount greater than the above content range, the number of pores is small, the average particle size is small, and the carbon layer is not properly arranged, resulting in a problem that the energy density of the battery is reduced and the discharge capacity, efficiency, and / or life characteristics of the battery are degraded during the cycle behavior.

[0109] In one embodiment of the present invention, when the alkali metal element and the halogen element are present in the negative electrode active material in the above contents, the conductivity of the negative electrode active material can be further improved.

[0110] In one embodiment of the present invention, the negative electrode active material may contain Li, Na, or K. Specifically, the negative electrode active material may contain at least one alkali metal element of Li and Na.

[0111] In one embodiment of the present invention, the negative electrode active material may contain F or Cl. Specifically, the negative electrode active material may contain at least one halogen element of F and Cl. More specifically, the negative electrode active material may contain Cl.

[0112] In one embodiment of the present invention, the negative electrode active material contains an ionic compound. When manufacturing the negative electrode active material, a silicon-based precursor and an ionic compound are vapor-deposited together to produce silicon-based particles. At this time, pores can be uniformly formed in the silicon-based particles by the ionic compound.

[0113] In one example, the ionic compound may be located inside the pores of the negative electrode active material.

[0114] The ionic compound contains one or more alkali metal elements selected from the group consisting of Li, Na, K, Rb, and Cs, and one or more halogen elements selected from the group consisting of F, Cl, Br, and I. Specifically, the ionic compound may exist with the alkali metal element in the form of a cation and the halogen element in the form of an anion bonded by an ionic bond.

[0115] In one embodiment of the present invention, the ionic compound may be one or more selected from the group consisting of LiF, LiCl, NaF, and NaCl.

[0116] The ionic compound may have a melting point of 600°C to 800°C and a boiling point of 1300°C to 1700°C.

[0117] At this time, the ionic compound is removed during the heat treatment of the silicon-based particles to form pores, and a part of the ionic compound that is not removed remains in the negative electrode active material.

[0118] The content of the ionic compound may be more than 0 parts by weight and less than 10 parts by weight based on 100 parts by weight of the negative electrode active material. Specifically, it may be more than 0 parts by weight and 5 parts by weight or less, 0.1 parts by weight or more and 4 parts by weight or less, or 0.1 parts by weight or more and 3 parts by weight or less.

[0119] When the ionic compound is present in the negative electrode active material in the above content, a large number of pores are formed in the silicon-based particles, and the carbon layer is effectively arranged in the pores of the silicon-based particles, resulting in an increase in the carbon coating area.

[0120] On the other hand, when the ionic compound is not present, that is, when the ionic compound is not added during the production of the silicon-based particles, no pores are formed in the silicon-based particles, the carbon coating area is reduced, and carbon is concentrated and coated only on the surface of the silicon-based particles, resulting in a problem that the conductivity of the negative electrode active material is reduced and the battery characteristics are deteriorated. When the ionic compound is present in an amount above the above content range, the number of pores is small, the average particle size is small, and the carbon layer is not properly arranged, resulting in a problem that the energy density of the battery is reduced.

[0121] In addition, when the ionic compound is present in the negative electrode active material in the above content, the conductivity of the negative electrode active material can be further improved.

[0122] The average particle size (D 50 ) of the negative electrode active material may be 0.1 μm to 30 μm, specifically, it may be 1 μm to 20 μm, and more specifically, it may be 1 μm to 10 μm or more. When the above range is satisfied, the structural stability of the active material during charge and discharge is ensured, and the problem that the volume expansion / shrinkage level also increases due to the excessive increase in the particle size is prevented, and the problem that the initial efficiency decreases due to the excessive decrease in the particle size can be prevented.

[0123] The BET specific surface area of the negative electrode active material may be 1 m 2 / g to 100 m 2 / g, specifically, it may be 1 m 2 / g to 70 m 2 / g, more specifically, it may be 1 m 2 / g to 50 m 2 / g, for example, 2 m 2 / g to 30 m 2It may also be / g. When the above range is satisfied, during charging and discharging of the battery, side reactions with the electrolyte can be reduced, and the life characteristics of the battery can be improved.

[0124] <Negative electrode> The negative electrode according to an embodiment of the present invention may contain the above-mentioned negative electrode active material.

[0125] Specifically, the negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The negative electrode active material layer may contain the negative electrode active material. Further, the negative electrode active material layer may further contain a binder, a thickener, and / or a conductive material.

[0126] The negative electrode active material layer can be formed by applying a negative electrode slurry containing a negative electrode active material, a binder, a thickener, and / or a conductive material to at least one surface of the current collector, followed by drying and rolling.

[0127] The negative electrode slurry may further contain an additional negative electrode active material.

[0128] As the additional negative electrode active material, a compound capable of reversible insertion and desorption of lithium can be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; SiO β (0 < β < 2), SnO 2, metal oxides such as vanadium oxide, lithium titanate, and lithium vanadate that can be doped and undoped with lithium; or composites containing the metallic compound and a carbonaceous material, such as Si-C composites or Sn-C composites, etc. may be mentioned, and a mixture of any one or two or more of these may be used. Further, a thin film of metallic lithium may be used as the negative electrode active material. Further, as the carbon material, any of low-crystalline carbon and highly crystalline carbon may be used. Representative examples of low-crystalline carbon are soft carbon and hard carbon, and representative examples of highly crystalline carbon are amorphous, plate-like, flaky, spherical or fibrous natural graphite or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleμm or coal tar pitch derived cokes.

[0129] The additional negative electrode active material may be a carbon-based negative electrode active material.

[0130] The negative electrode slurry may contain a solvent for forming the negative electrode slurry. Specifically, the solvent for forming the negative electrode slurry is at least one selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol in terms of facilitating the dispersion of components, and specifically, may contain distilled water.

[0131] The negative electrode slurry containing the negative electrode active material according to one embodiment of the present invention may have a pH of 7 to 11 at 25°C. By the pH of the negative electrode slurry satisfying the above range, there is an effect that the rheological properties of the slurry are stabilized. On the other hand, when the pH of the negative electrode slurry is less than 7 or the pH of the negative electrode slurry exceeds 11, decomposition of carboxymethyl cellulose (CMC) used as a thickener occurs, resulting in a decrease in the viscosity of the slurry and a decrease in the dispersibility of the active material contained in the slurry.

[0132] The negative electrode current collector may be any material that does not induce a chemical change in the battery and has conductivity, and is not particularly limited. For example, as the current collector, copper, stainless steel, aluminum, nickel, titanium, fired carbon, or a material obtained by surface-treating the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. may be used. Specifically, a transition metal that adsorbs carbon well, such as copper or nickel, may be used as the current collector. The thickness of the current collector may be 6 μm to 20 μm, but the thickness of the current collector is not limited thereto.

[0133] The binder 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, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and substances obtained by substituting hydrogen thereof with Li, Na, or Ca, etc., and may also include various copolymers thereof.

[0134] The conductive material is not particularly limited as long as it does not induce a chemical change in the battery and has conductivity. For example, graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbons, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives may be used.

[0135] The thickener may be carboxymethyl cellulose (CMC), but is not limited thereto, and a thickener used in the technical field may be appropriately adopted.

[0136] In one embodiment of the present invention, the weight ratio of the negative electrode active material and the additional negative electrode active material contained in the negative electrode slurry may be 1:99 to 30:70, specifically, 5:95 to 30:70 or 10:90 to 20:80.

[0137] In one embodiment of the present invention, the total negative electrode active material contained in the negative electrode slurry may be contained in an amount of 60 parts by weight to 99 parts by weight, specifically, 70 parts by weight to 98 parts by weight, based on 100 parts by weight of the total solid content of the negative electrode slurry.

[0138] In one embodiment of the present invention, the binder may be contained in an amount of 0.5 part by weight to 30 parts by weight, specifically, 1 part by weight to 20 parts by weight, based on 100 parts by weight of the total solid content of the negative electrode slurry.

[0139] In one embodiment of the present invention, the conductive material may be contained in an amount of 0.5 part by weight to 25 parts by weight, specifically, 1 part by weight to 20 parts by weight, based on 100 parts by weight of the total solid content of the negative electrode slurry.

[0140] In one embodiment of the present invention, the thickener may be included in an amount of 0.5 parts by weight to 25 parts by weight, specifically 0.5 parts by weight to 20 parts by weight, and more specifically 1 part by weight to 20 parts by weight, based on 100 parts by weight of the total solid content of the negative electrode slurry.

[0141] The negative electrode slurry according to one embodiment of the present invention may further include a solvent for forming the negative electrode slurry. Specifically, the solvent for forming the negative electrode slurry may be at least one selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol, specifically, it may include distilled water, in terms of facilitating the dispersion of components.

[0142] In one embodiment of the present invention, the weight of the solid content of the negative electrode slurry may be 20 parts by weight to 75 parts by weight, specifically 30 parts by weight to 70 parts by weight, based on 100 parts by weight of the total negative electrode slurry.

[0143] <Secondary battery> The secondary battery according to one embodiment of the present invention may include a negative electrode according to the above-described one 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 electrolytic solution, and the negative electrode is the same as the above-described negative electrode. Since the negative electrode has been described above, specific description thereof is omitted.

[0144] The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and containing the positive electrode active material.

[0145] In the positive electrode, the positive electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and has conductivity. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or those obtained by surface treatment of the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. may be used. Further, the positive electrode current collector may usually have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesive force of the positive electrode active material. For example, it may be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, non-woven fabric bodies, etc.

[0146] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material is a layered compound such as lithium cobalt oxide (LiCoO 2 ), lithium nickel oxide (LiNiO 2 ), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe 3 O 4 ; lithium manganese oxides represented by the chemical formula Li 1+c1 Mn 2-c1 O 4 (0 ≦ c1 ≦ 0.33), LiMnO 3 , LiMn 2 O 3 , LiMnO 2 ; lithium copper oxide (Li 2 CuO 2 ); vanadium oxides such as LiV 3 O 8 , V 2 O 5 , Cu 2 V 2 O 7 ; Ni-site type lithium nickel oxides represented by the chemical formula LiNi 1-c2 M c2 O 2 (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01 ≦ c2 ≦ 0.3); lithium manganese oxides 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 satisfies 0.01 ≦ c3 ≦ 0.1), or Li 2 Mn 3 MO 8 (Here, M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn) lithium manganese composite oxide represented by; a part of Li in the chemical formula is replaced by an alkaline earth metal ion LiMn 2 O 4 and the like, but not limited thereto. The positive electrode may be Li metal (Li-metal).

[0147] The positive electrode active material layer may include a positive electrode conductive material and a positive electrode binder together with the above-described positive electrode active material.

[0148] At this time, the positive electrode conductive material is used to impart conductivity to the electrode, and in the configured battery, it can be used without particular limitation as long as it has conductivity without causing a chemical change. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based substances such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one kind alone or a mixture of two or more kinds thereof may be used.

[0149] In addition, the positive electrode binder plays a role in improving the adhesion between the positive electrode active material particles and the adhesive force between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, etc. One kind alone or a mixture of two or more kinds thereof may be used.

[0150] The separator separates the negative electrode and the positive electrode and provides a migration path for lithium ions. Usually, any material that can be used as a separator in a secondary battery can be used without particular limitation. In particular, it is preferably low in resistance to the ion migration of the electrolytic solution and excellent in the ability to hold the electrolytic solution. Specifically, a porous polymer film, for example, a porous polymer film made of polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. Also, a normal porous non-woven fabric, for example, a non-woven fabric made of high-melting glass fibers, polyethylene terephthalate fibers, etc. may be used. Further, in order to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer substance may be used, and it may be selectively used as a single-layer or multi-layer structure.

[0151] Examples of the electrolytic solution include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

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

[0153] Examples of the non-aqueous organic solvent include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate ester, trimethoxymethane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, ethyl propionate, etc. may be used.

[0154] In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates among the carbonate-based organic solvents, can be preferably used as high-viscosity organic solvents because they have a high dielectric constant and can dissociate lithium salts well. When such cyclic carbonates are mixed and used in an appropriate ratio with linear carbonates such as dimethyl carbonate and diethyl carbonate having low viscosity and low dielectric constant, an electrolytic solution having high conductivity can be prepared, so it can be more preferably used.

[0155] As the metal salt, a lithium salt may be used. The lithium salt is a substance that is easily soluble in the non-aqueous electrolytic solution. For example, as an anion of the lithium salt, 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 -One or more selected from the group consisting of may be used.

[0156] In addition to the constituent components of the electrolytic solution, for the purpose of improving the life characteristics of the battery, suppressing a decrease in battery capacity, improving the discharge capacity of the battery, etc., the electrolytic solution may further contain one or more additives such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, triamide hexaline, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride.

[0157] According to still another embodiment of the present invention, there are provided a battery module including the secondary battery as a unit cell and a battery pack including the same. Since the battery module and the battery pack include the secondary battery having a high capacity, high rate characteristics, and cycle characteristics, they can be used as a power source for medium to large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

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

Examples

[0159] <Examples and Comparative Examples> Example 1 Si and SiO 2900 g of the powder mixed in a 1:1 molar ratio and 10 g of an ionic compound (NaCl) were appropriately mixed, and the resulting powder was vacuum-heated in a reactor at a sublimation temperature of 2,400 °C. Subsequently, the mixed gas of vaporized Si, SiO 2 , and the ionic compound was reacted in a vacuum cooling zone (cooling zone) having a cooling temperature of 800 °C and condensed into a solid phase. Then, heat treatment was performed at a temperature of 800 °C in an inert atmosphere to produce preliminary silicon-based particles. Then, using a ball mill, 15 SUS ball media (sus ball media) were introduced into the preliminary silicon-based particles, and then pulverized for 3 hours to produce silicon-based particles with a size of 6 μm (D 50 ). Then, while flowing Ar gas to maintain an inert atmosphere, the silicon-based particles were placed in the hot zone of a CVD apparatus, and using Ar as a carrier gas, the methane was blown into the hot zone at 900 °C, and 10 -1 torr and reacted for 5 hours to form a carbon layer on the surface of the silicon-based particles.

[0160] The silicon-based particles with the carbon layer formed and lithium metal powder as a lithium precursor were solid-phase mixed at a weight ratio of 90:10 to produce a composition for forming a negative electrode active material.

[0161] The composition for forming a negative electrode active material was heat-treated at 800 °C for 3 hours.

[0162] The heat-treated composition for forming a negative electrode active material was acid-treated with a hydrochloric acid aqueous solution having a pH of 1 at 23 °C for 1 hour to produce a negative electrode active material.

[0163] The Na content of the negative electrode active material was 1.5 wt%, and the Cl content was 1.2 wt%.

[0164] Example 2 A negative electrode active material was produced in the same manner as in Example 1, except that the heat treatment performed after condensing the mixed gas was carried out at a temperature of 860 °C.

[0165] The Na content of the negative electrode active material was 1.3 wt%, and the Cl content was 1.0 wt%.

[0166] Example 3 The negative electrode active material was produced in the same manner as in Example 1, except that the heat treatment performed after condensing the mixed gas was carried out at a temperature of 900°C.

[0167] The Na content of the negative electrode active material was 0.7 wt%, and the Cl content was 0.7 wt%.

[0168] Example 4 The negative electrode active material was produced in the same manner as in Example 1, except that the heat treatment performed after condensing the mixed gas was carried out at a temperature of 1100°C.

[0169] The Na content of the negative electrode active material was 0.1 wt%, and the Cl content was 0.1 wt%.

[0170] Example 5 The negative electrode active material was produced in the same manner as in Example 1, except that LiCl was used instead of NaCl.

[0171] The Li content of the negative electrode active material was 6.2 wt%, and the Cl content was 1.5 wt%. At this time, the Li content derived from the ionic compound was 1.2 wt%, and the Li content derived from the lithium precursor was 5 wt%.

[0172] Example 6 The negative electrode active material was produced in the same manner as in Example 1, except that Mg metal powder was used instead of lithium metal powder.

[0173] The Na content of the negative electrode active material was 1.4 wt%, and the Cl content was 1.3 wt%.

[0174] Comparative Example 1 The negative electrode active material was produced in the same manner as in Example 1, except that the ionic compound was not mixed.

[0175] Comparative Example 2 The negative electrode active material was produced in the same manner as in Example 1, except that the heat treatment performed after condensing the mixed gas was carried out at a temperature of 700°C.

[0176] Comparative Example 3 The negative electrode active material was produced in the same manner as in Example 1, except that the heat treatment performed after condensing the mixed gas was carried out at a temperature of 600°C.

[0177] Comparative Example 4 The negative electrode active material was produced in the same manner as in Example 1, except that the heat treatment performed after condensing the mixed gas was carried out at a temperature of 650°C.

[0178] Comparative Example 5 The negative electrode active material was produced in the same manner as in Example 1, except that the heat treatment performed after condensing the mixed gas was carried out at a temperature of 500°C.

[0179] Comparative Example 6 The negative electrode active material was produced in the same manner as in Comparative Example 1, except that Mg metal powder was used instead of lithium metal powder.

[0180] <Analysis of the content of the carbon layer> The content of the carbon layer was analyzed using a CS analyzer (CS-800, Eltra).

[0181] <Analysis of element content> The element content (wt%) of the negative electrode active material was confirmed by SEM-EDS (JEOL LTD; JSM-7610F).

[0182] The cross-section of the negative electrode active material was prepared using an Ion Milling device. First, an electrode sample prepared by coating the negative electrode active material on a copper foil (Cu Foil) was milled using a Hitachi IM4000 device. Specifically, after irradiating an ion beam at a voltage of 1.5 kV for about 3 to 4 hours per sample, the overall SEM cross-section image was subjected to EDS measurement to measure the elemental content inside the material.

[0183] <Cross-section analysis of negative electrode active material (measurement of average diameter)> The cross-section analysis of the negative electrode active material was performed using an Ion Milling device. First, an electrode sample prepared by coating the negative electrode active material on a copper foil (Cu Foil) was milled using a Hitachi IM4000 device. Specifically, after irradiating an ion beam at a voltage of 1.5 kV for about 3 to 4 hours per sample, the cross-section image was measured with a Hitachi S-4800 SEM. Next, based on the measured SEM cross-section image, the average diameter of the pores appearing on the cross-section of the negative electrode active material was calculated.

[0184] <D of negative electrode active material 50 and specific surface area analysis> The D of the negative electrode active material 50 was analyzed by laser diffraction particle size analysis using a Microtrac S3500 device, and the BET specific surface area of the negative electrode active material was measured using a BET measuring device (BEL-SORP-MAX, Nippon Bell).

[0185]

Table 1

[0186] <Experimental example: Evaluation of conductivity of negative electrode active material> The conductivity of the negative electrode active material was measured using a powder resistance measuring device (HPRM-1000, manufactured by HANTECH CO., LTD.). After uniformly charging 3 g of the sample (negative electrode active material) into a cylindrical mold with a diameter of 20 mm, the resistance was measured at 400 kgf intervals from 400 kgf to 2000 kgf. Subsequently, the conductivity of the negative electrode active material was relatively evaluated with Example 1 as a reference in Table 2 below.

[0187] <Experimental Example: Evaluation of Discharge Capacity, Initial Efficiency, and Life (Capacity Retention Rate) Characteristics> Using the negative electrode active materials of the examples and comparative examples respectively, negative electrodes and batteries were manufactured.

[0188] The negative electrode active material, carbon black as a conductive material, and PAA (poly acrylic acid) as a binder were mixed at a weight ratio of 80:10:10 to produce a mixture. Subsequently, 7.8 g of distilled water was added to 5 g of the mixture and uniformly mixed to produce a negative electrode slurry. The negative electrode slurry was applied to a copper (Cu) metal thin film, which is a negative electrode current collector with a thickness of 15 μm, and dried. At this time, the temperature of the circulated air was 60°C. Then, it was roll-pressed and dried in a vacuum oven at 130°C for 12 hours to produce a negative electrode.

[0189] The manufactured electrode was cut into a negative electrode, and a circular lithium (Li) metal thin film with a diameter 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 0.5 parts by weight of vinylene carbonate was dissolved in a mixed solution of ethyl methyl carbonate (EMC) and ethylene carbonate (EC) with a mixed volume ratio of 7:3. 1 M concentration of LiPF 6 was dissolved in the electrolyte solution and injected to manufacture a lithium coin half-cell.

[0190] Charging and discharging were performed on the manufactured battery to evaluate the discharge capacity, initial efficiency, and capacity retention rate, and these were described in Table 2 below.

[0191] The first cycle and the second cycle were charged and discharged at 0.1C, and the third cycle to the forty-ninth cycle were charged and discharged at 0.5C. The last cycle ended in a charged state (with lithium in the negative electrode).

[0192] Charging condition: CC (constant current) / CV (constant voltage) (5mV / 0.005C current cut-off) Discharging condition: CC (constant current) condition 1.5V Based on the results of the first charge-discharge cycle, the discharge capacity (mAh / g) and the initial efficiency (%) were derived. Specifically, the initial efficiency (%) was derived by the following calculation.

[0193] Initial efficiency (%) = (first discharge capacity / first charge capacity) × 100 The capacity retention rate was derived by the following calculations respectively.

[0194] Capacity retention rate (%) = (forty-ninth discharge capacity / first discharge capacity) × 100

[0195]

Table 2

[0196] According to Table 2 above, the negative electrode active materials of Examples 1 to 6, which contain an alkali metal element and a halogen element and have a pore size of 20nm to 60nm, have a carbon layer effectively arranged in the pores of the silicon-based particles, a high carbon coating area, and the conductivity is improved by the ions remaining inside the negative electrode active material. Thus, it was confirmed that the discharge capacity, efficiency and / or life characteristics were improved.

[0197] On the one hand, as in Comparative Example 1 and Comparative Example 6, when the negative electrode active material does not contain an alkali metal element and a halogen element, pores are not formed and the conductivity is not improved, so it was confirmed that the efficiency and / or life characteristics deteriorate. As in Comparative Example 1 and Comparative Example 6, even if the active material particles contain an alkali metal such as lithium or an alkaline earth metal such as magnesium, when producing the preliminary silicon-based particles, if an ionic compound is not added, an appropriate pore size of the active material particles cannot be realized.

[0198] In the case of Comparative Examples 2 to 5, although the ionic compound was contained in excess in the negative electrode active material and the conductivity was improved, a decrease in the material capacity occurred due to the excessively contained ionic compound, and during the cycle behavior, it was confirmed that the discharge capacity, efficiency and / or life characteristics of the battery were greatly reduced.

Claims

1. A step of heat-treating a silicon-based precursor and an ionic compound to vaporize them; A step of co-depositing the mixed gas of the silicon-based precursor and the ionic compound in the gas phase to form silicon-based particles; and A step of heat-treating the silicon-based particles and a carbon source; A method for manufacturing a negative electrode active material, comprising the above steps.

2. The silicon-based precursor is a mixed powder of Si powder, SiO powder, and SiO ２ powder, and the method for producing the negative electrode active material according to claim 1.

3. The method for manufacturing a negative electrode active material according to claim 1, wherein the ionic compound contains one or more alkali metal elements selected from the group consisting of Li, Na, K, Rb, and Cs, and one or more halogen elements selected from the group consisting of F, Cl, Br, and I.

4. The method for manufacturing a negative electrode active material according to claim 1, wherein the ionic compound is one or more selected from the group consisting of LiF, LiCl, NaF, and NaCl.

5. The method for manufacturing a negative electrode active material according to claim 1, wherein the deposition is performed in an inert gas atmosphere at a temperature of 500°C or higher and 1000°C or lower.

6. The method for manufacturing a negative electrode active material according to claim 1, wherein the step of heat-treating the silicon-based particles and the carbon source is performed at 800°C to 1200°C.

7. A negative electrode active material manufactured by the method for manufacturing a negative electrode active material according to any one of claims 1 to 6.

8. SiO ｘ silicon-based particles containing (0 < x < 2) and pores; and A carbon layer provided on the surface and in the pores of the silicon-based particles; A negative electrode active material comprising the above, wherein the negative electrode active material contains one or more alkali metal elements selected from the group consisting of Li, Na, K, Rb, and Cs, and one or more halogen elements selected from the group consisting of F, Cl, Br, and I, when performing cross-sectional analysis of the negative electrode active material, the average diameter of the pores is 20 nm to 60 nm.

9. The negative electrode active material according to claim 8, wherein the negative electrode active material contains at least one alkali metal element of Li and Na.

10. The negative electrode active material according to claim 8, wherein the negative electrode active material contains at least one halogen element of F and Cl.

11. The alkali metal element is one or more selected from the group consisting of Na, K, Rb, and Cs, and the alkali metal element is contained in an amount of more than 0.01 part by weight and less than 10 parts by weight based on 100 parts by weight of the negative electrode active material.

12. The halogen element is one or more selected from the group consisting of Cl, Br, and I, and The negative electrode active material according to claim 8, wherein the halogen element is contained in an amount of more than 0.01 part by weight and less than 10 parts by weight based on 100 parts by weight of the negative electrode active material.

13. The negative electrode active material according to claim 8, wherein the alkali metal element and the halogen element are located inside the pores.

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

15. The negative electrode active material according to claim 8, wherein the silicon-based particles further contain an Li compound or an Mg compound.

16. A negative electrode comprising the negative electrode active material according to any one of claims 8 to 15.

17. A secondary battery comprising the negative electrode according to claim 16.

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