Method for manufacturing a 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 producing a negative electrode active material, a negative electrode active material, a negative electrode, and a secondary battery.

[0002] This application claims the benefit as of the filing date 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 its contents are incorporated herein by reference. [Background technology]

[0003] Recently, with the rapid proliferation of electronic devices using batteries, such as mobile phones, laptops, and electric vehicles, the demand for rechargeable batteries that are small, lightweight, and yet relatively high-capacity has been rapidly increasing. In particular, lithium-ion batteries are attracting attention as a power source for portable devices because they are lightweight and have high energy density. As a result, research and development efforts to improve the performance of lithium-ion batteries are being actively pursued.

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

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

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

[0007] In addition, a technique for 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 disposed 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 practical situation where it is necessary to develop a negative electrode active material in which a carbon layer is uniformly disposed 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-evaporating 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.

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

[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.

Effects 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 a 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] A negative electrode active material according to one embodiment of the present invention comprises 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 the negative electrode active material is cross-sectionally analyzed, the average diameter of the pores is 20 nm to 60 nm. A negative electrode active material having the above characteristics has the advantage that the pores are uniformly formed, the carbon layer is uniformly distributed over a wide area on the surface and inside the pores of the negative electrode active material, and the conductivity can be improved by including the alkali metal elements and halogen elements.

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

[0019] The following provides a more detailed explanation of this specification.

[0020] In this specification, when a part "includes" a component, this means that, unless otherwise stated, it may include other components rather than excluding them.

[0021] In this specification, when one member is said to be "on top of" another member, this includes not only cases where one member is in contact with another member, but also cases where another member exists between the two members.

[0022] The terms and words used herein should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather should be interpreted in a manner consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may appropriately define the concepts of terms in order to best explain their invention.

[0023] In this specification, singular expressions of terms 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. X-ray diffraction analysis may be performed using an X-ray diffraction (XRD) analyzer (product name: D4-endeavor, manufacturer: bruker), or other instruments used in this industry may be appropriately employed.

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

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

[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 using a porosimetry analyzer (Bell Japan Inc., Belsorp-II mini) with a nitrogen gas adsorption flow method using the BET 6-point method.

[0028] In this invention, the average diameter of pores (pore size) can be measured by a calculation formula using the BJH (Barrett-Joyner-Halenda) method via nitrogen adsorption. Specifically, using the BELSORP-mini II model from BEL Japan, the pore area was derived based on the pore size, and the pore size showing the largest pore area was used as representative. The BJH method may also be used, and the plot of the measured values ​​shows the pore diameter (Dp / nm) on the X axis and dVp / dDp (cm) on the Y axis. 3 g -1 nm -1 )

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

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

[0031] When silicon-based particles are formed by depositing a silicon-based precursor and an ionic compound together, the ionic compound becomes distributed within the silicon-based particles. As the ionic compound is removed during subsequent heat treatment, pores are uniformly formed within the silicon-based particles, and a carbon layer is uniformly distributed over a wide area on the surface and / or inside the pores of the silicon-based particles. This improves the conductivity of the negative electrode active material, resulting in improved battery discharge capacity, initial efficiency, resistance performance, and / or life characteristics. Furthermore, the remaining ionic compound further enhances the conductivity of the negative electrode active material.

[0032] The silicon-based precursor may be one or more selected from the group consisting of Si powder, SiO powder, and SiO2 powder, and preferably a mixed powder of Si powder, SiO powder, and SiO2 powder.

[0033] After the silicon-based precursor and the ionic compound are heat-treated under vacuum to vaporize them, 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 vaporized by heat treatment at a temperature of 1800°C to 2500°C in an inert gas atmosphere. More specifically, they can be vaporized by heat treatment at a temperature of 2200°C to 2400°C. In this process, the silicon-based precursor and the ionic compound can be vaporized separately in different sources and then mixed, or they can be vaporized in the same source to form a mixed gas of the silicon-based precursor and the ionic compound.

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

[0036] In the production of the negative electrode active material, silicon-based particles are produced by depositing a silicon-based precursor and an ionic compound together, and in this process, pores can be uniformly formed within the silicon-based particles by the ionic compound.

[0037] The ionic compound comprises 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 contain the alkali metal elements in the form of cations and the halogen elements in the form of anions, ionically bonded together. 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 manufacturing the negative electrode active material 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, the step of heat-treating and vaporizing the silicon-based precursor and the ionic compound in order to dope the silicon-based particles with a metal (e.g., Li or Mg) may include a step of heat-treating and vaporizing the metal precursor. Specifically, the metal precursor may be vaporized separately from the silicon-based precursor and the ionic compound in different sources and then mixed, or they may be vaporized in the same source to form a mixed gas.

[0047] The metal precursor may be vaporized by heat treatment under conditions of 1000°C to 1400°C.

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

[0049] The Li precursor may be, for example, Li powder, LiOH, Li2O, etc., and is not limited thereto.

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

[0051] The silicon-based particles formed by vapor deposition of the mixed gas after heat treatment with a further Li precursor or Mg precursor may further contain one or more of the Li compound and Mg compound, and the Li or Mg may be distributed on the surface and / or inside the silicon-based particles in a doped form.

[0052] In another embodiment, in order to dope the silicon-based particles with a metal (e.g., Li or Mg), a step may be performed in which the silicon-based particles are mixed with a metal precursor and then heat-treated, after the step of heat-treating the silicon-based particles and the carbon source. If necessary, this step may be performed under heat treatment or by electrochemical methods.

[0053] The step of heat-treating the mixture of silicon-based particles and metal precursor may be carried out in an inert atmosphere.

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

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

[0056] The carbon source may be, but is not limited to, a hydrocarbon gas, and any substance known in the industry may be appropriately used.

[0057] In the step of heat-treating the silicon-based particles and the carbon source, a carbon layer may be formed on the silicon-based particles by using chemical vapor deposition (CVD) or a method that carbonizes the substance that will become the carbon source.

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

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

[0060] In this process, the carbon layer is uniformly distributed over a wide area on the surface and / or inside the pores of the silicon-based particles during the heat treatment of the carbon source, thereby improving the conductivity of the negative electrode active material.

[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 produced by the method for producing 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 one or more selected from the group consisting of Li, Na, K, Rb, and Cs An alkali metal element, 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, provided a negative electrode active material.

[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 fully exhibited and the battery characteristics are deteriorated.

[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, excluding the pores of the silicon-based particles, the carbon layer is disposed on the external 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 containing 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 SiO2, and the Si may form a phase. That is, the x corresponds to the number ratio of O to Si contained in the SiO x (0 < x < 2). When the silicon-based composite particles contain the SiO x (0 < x < 2), the discharge capacity of the secondary battery can be improved.

[0071] In one embodiment of the present invention, when performing 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 this invention, 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 copper foil (Cu Foil) is milled using a Hitachi IM4000 apparatus. Specifically, an ion beam is irradiated at a voltage of 1.5 kV and processed for about 3 to 4 hours per sample, after which 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 pore diameter obtained by the aforementioned cross-sectional analysis relates to the diameter of pores located inside the negative electrode active material, and differs from the diameter of pores near the surface of the negative electrode active material measured by the nitrogen adsorption method.

[0074] If the average diameter of the pores is less than 20 nm, the pores have difficulty accommodating excessive changes in the volume of the silicon-based particles, and particle cracking and other issues are observed during long-term cycle behavior, resulting in a problem of a rapid decrease in battery capacity. If the average diameter of the pores exceeds 60 nm, the amount of carbon layer coating is insufficient, increasing the resistance of the cell, and increasing side reactions between the electrolyte and the silicon-based particles, thus reducing the battery's lifespan characteristics.

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

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

[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 form doped into the silicon-based particles. 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., SiO2) 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 Li2SiO3, Li4SiO4, and Li2Si2O5 within the silicon-based particles, and the amorphous lithium silicate may have 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 may contain Li7Si2, and the Li oxide may contain Li2O.

[0082] In one embodiment of the present invention, based on 100 parts by weight of the total negative electrode active material, Li may be included in amounts of 0.1 to 40 parts by weight or 0.1 to 25 parts by weight. Specifically, it may be included in amounts of 1 to 25 parts by weight, and more specifically, in amounts of 2 to 20 parts by weight or 2 to 10 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.

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

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

[0085] The Mg compound may be distributed on the surface and / or inside the silicon-based particles in a doping form. The Mg compound, when distributed on the surface and / or inside the silicon-based particles, 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. The Mg compound may also be included in a way that reduces the proportion of the irreversible phase (e.g., SiO2) of the silicon-based particles and increases 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 Mg2SiO4 and MgSiO3.

[0087] In another embodiment, the magnesium silicide may contain Mg2Si, and the magnesium oxide may contain MgO.

[0088] The Li and Mg content can be confirmed by inductively coupled plasma (ICP) analysis. Specifically, a certain amount (approximately 0.01 g) of the negative electrode active material is separated, transferred to a platinum crucible, and completely decomposed on a hot plate with the addition of nitric acid, hydrofluoric acid, and sulfuric acid. Then, using an inductive plasma emission spectrometer (ICPAES, Perkin-Elmer 7300), the intensity of a standard solution prepared using a standard solution (5 mg / kg) is measured at the characteristic wavelength of the element to be analyzed to create a reference calibration curve. Subsequently, the pre-treated sample solution and a blank sample are introduced into the instrument, their respective intensities are measured to calculate the actual intensities, and the concentrations of each component are calculated by comparing them with the calibration curve created above. Finally, the sum of the concentrations is converted to a theoretical value, and the elemental 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 the silicon-based particles in the form of at least one of metal atoms, metal silicates, metal silicides, or metal oxides. The metal atoms may include at least one selected from the group consisting of Mg, Li, Al, and Ca. This can improve the initial efficiency of the negative electrode active material.

[0090] In one embodiment of the present invention, the carbon layer may be provided on the surface and within the pores of the silicon-based particles. This imparts conductivity to the silicon-based particles, effectively suppresses volume changes in the negative electrode active material containing the silicon-based particles, and improves the battery's lifespan characteristics.

[0091] In this case, the carbon layer may be in a form that partially covers the surface and at least a portion of the pores of the silicon-based particles, i.e., partially covers the surface and the inside of the pores of the particles, or it may be in a form that covers the entire surface and the inside of the pores of the particles.

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

[0093] Furthermore, 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 include 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 a carbon-based material formed by using at least one carbide or hydrocarbon selected from the group consisting of tar, pitch, and other organic substances as a source in chemical vapor deposition.

[0096] The aforementioned carbonized organic substances may be carbonized organic substances 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. Examples of the substituted or unsubstituted aliphatic or alicyclic hydrocarbon include methane, ethane, ethylene, acetylene, propane, butane, butene, pentane, isobutane, or hexane. Examples of the substituted or unsubstituted aromatic hydrocarbon include benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, coumarone, pyridine, anthracene, or phenanthrene.

[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 amounts of 0.1 to 50 parts by weight, 0.1 to 30 parts by weight, or 0.1 to 20 parts by weight, based on 100 parts by weight of the total negative electrode active material. More specifically, it may be included in amounts of 0.5 to 15 parts by weight, 1 to 10 parts by weight, or 1 to 5 parts by weight. When the above ranges are met, a decrease in the capacity and efficiency of the negative electrode active material can be prevented.

[0100] In one embodiment of the present invention, the thickness of the carbon layer may be 1 nm to 500 nm, and more specifically, 5 nm to 300 nm. When this range is met, the conductivity of the negative electrode active material is improved, volume changes of the negative electrode active material are easily suppressed, and side reactions between the electrolyte and the negative electrode active material are suppressed, resulting in improved initial efficiency and / or lifespan of the battery.

[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 comprises 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, silicon-based particles are produced by depositing a silicon-based precursor and an ionic compound containing the alkali metal elements and halogen elements together. In this case, pores are uniformly formed within the silicon-based particles by the ionic compound, and the silicon-based particles may contain the alkali metal elements and halogen elements.

[0103] In one example, the alkali metal element and 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. In this case, the content of the alkali metal element may refer to the content of alkali metal elements derived from ionic compounds.

[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. In this case, the content of the halogen element may refer to the content of halogen elements derived from ionic compounds.

[0106] When the alkali metal element and halogen element are present in the negative electrode active material in the aforementioned amounts, numerous pores are formed within the silicon-based particles, and the carbon layer is effectively positioned within the pores of the silicon-based particles, resulting in an increased carbon coating area.

[0107] On the other hand, if the alkali metal elements and halogen elements are not present in the negative electrode active material, that is, if ionic compounds are not added during the manufacturing of silicon-based particles, pores are not formed within 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 decrease in the conductivity of the negative electrode active material and a decrease in battery performance.

[0108] Furthermore, when alkali metal elements and halogen elements are present in amounts exceeding the aforementioned content range, the number of pores is reduced, the average particle size is small, and the carbon layer is not properly arranged. This leads to a decrease in the energy density of the battery, and during cycle behavior, the discharge capacity, efficiency, and / or life characteristics of the battery are reduced.

[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 aforementioned amounts, 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 among 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 from among 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 includes an ionic compound. During the production of the negative electrode active material, silicon-based particles are produced by depositing a silicon-based precursor and the ionic compound together, and in this process, pores can be uniformly formed within 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 comprises 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 elements in the form of cations and the halogen elements in the form of anions, ionically bonded together.

[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] In this process, the ionic compound is removed during the heat treatment of the silicon-based particles, forming pores, while some of the remaining ionic compound is present in the negative electrode active material.

[0118] The content of the ionic compound may be greater 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 greater 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 aforementioned ionic compound is present in the negative electrode active material at the aforementioned content, numerous pores are formed within the silicon-based particles, and the carbon layer is effectively positioned within the pores of the silicon-based particles, resulting in an increased carbon coating area.

[0120] On the other hand, if the ionic compound is not present, that is, if the ionic compound is not added during the manufacturing of silicon-based particles, pores are not formed within the silicon-based particles, the carbon coating area is reduced, and the carbon is concentrated and coated only on the surface of the silicon-based particles, resulting in a decrease in the conductivity of the negative electrode active material and a decrease in battery performance. If the ionic compound is present in a content range or higher, the number of pores is small, the average particle size is small, and the carbon layer is not properly arranged, resulting in a decrease in the energy density of the battery.

[0121] Furthermore, when the ionic compound is present in the negative electrode active material at the aforementioned content, the conductivity of the negative electrode active material can be further improved.

[0122] The average particle size (D) of the negative electrode active material 50 The particle size may be 0.1 μm to 30 μm, more specifically 1 μm to 20 μm, and more specifically 1 μm to 10 μm or larger. When the above range is met, it is possible to ensure the structural stability of the active material during charging and discharging, prevent the problem of volume expansion / contraction levels becoming large due to excessively large particle size, and prevent the problem of initial efficiency decreasing due to excessively small particle size.

[0123] The BET specific surface area of ​​the negative electrode active material is 1 m². 2 / g~100m 2 It may also be / g, specifically 1m 2 / g~70m 2 It may also be / g, or more specifically, 1m 2 / g~50m 2 / g, for example, 2m 2 / g~30m 2 It may also be / g. When the above range is met, side reactions with the electrolyte during battery charging and discharging can be reduced, and the battery's lifespan characteristics can be improved.

[0124] <Negative electrode> A negative electrode according to one embodiment of the present invention may contain the aforementioned 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 include the negative electrode active material. Furthermore, the negative electrode active material layer may further include a binder, a thickener, and / or a conductive material.

[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 a current collector, followed by drying and rolling.

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

[0128] As the additional negative electrode active material, compounds that allow for reversible insertion and removal of lithium can be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds that can alloy with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and SiO2. β Examples include metallic oxides that can be doped and dedoped with lithium, such as (0<β<2), SnO2, vanadium oxide, lithium titanium oxide, and lithium vanadium oxide; or composites containing the metallic compound and carbonaceous material, such as Si-C composites or Sn-C composites, and one or more of these mixtures may be used. A metallic lithium thin film may also be used as the negative electrode active material. In addition, either low-crystalline carbon or high-crystalline carbon may be used as the carbon material. Typical examples of low-crystalline carbon include soft carbon and hard carbon, while typical examples of high-crystalline carbon include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[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 may contain at least one selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol, specifically distilled water, in order to facilitate the dispersion of the components.

[0131] A negative electrode slurry containing a negative electrode active material according to one embodiment of the present invention may have a pH of 7 to 11 at 25°C. By satisfying the above pH range, the rheological properties of the slurry are stabilized. On the other hand, if the pH of the negative electrode slurry is less than 7 or greater than 11, decomposition of carboxymethylcellulose (CMC) used as a thickening agent occurs, leading to a decrease in slurry viscosity and a reduction in the dispersion of the active material contained within the slurry.

[0132] The negative electrode current collector is not particularly limited as long as it does not induce a chemical change in the battery and is conductive. For example, the current collector may be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. Specifically, transition metals that readily adsorb carbon, such as copper and nickel, may be used as the current collector. The thickness of the current collector may be 6 μm to 20 μm, but is not limited thereto.

[0133] The binder may contain at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and substances in which the hydrogen atoms of these are substituted with Li, Na, or Ca, and may also contain a variety of copolymers thereof.

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

[0135] The aforementioned thickening agent may be carboxymethylcellulose (CMC), but is not limited thereto, and any other thickening agent used in the present art may be appropriately adopted.

[0136] In one embodiment of the present invention, the weight ratio of the negative electrode active material contained in the negative electrode slurry to the additional negative electrode active material may be 1:99 to 30:70, and more specifically, it may be 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 present in an amount of 60 to 99 parts by weight, specifically 70 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 included in an amount of 0.5 to 30 parts by weight, specifically 1 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 included in an amount of 0.5 to 25 parts by weight, specifically 1 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 thickening agent may be included in an amount of 0.5 to 25 parts by weight, more specifically 0.5 to 20 parts by weight, or more specifically 1 to 20 parts by weight, based on 100 parts by weight of the total solid content of the negative electrode slurry.

[0141] A negative electrode slurry according to one embodiment of the present invention may further contain a solvent for forming the negative electrode slurry. Specifically, the solvent for forming the negative electrode slurry may contain at least one selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol, specifically distilled water, in order to facilitate 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 to 75 parts by weight, specifically 30 to 70 parts by weight, based on 100 parts by weight of the total negative electrode slurry.

[0143] <Secondary battery> A secondary battery according to one embodiment of the present invention may include a negative electrode according to the above-described embodiment. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the negative electrode is the same as the negative electrode described above. Since the negative electrode has been described above, a detailed explanation will be omitted.

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

[0145] In the positive electrode, the positive electrode current collector is not particularly limited as long as it does not induce a chemical change in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector may also have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase the adhesion strength of the positive electrode active material. For example, it may be used in various forms such as film, sheet, foil, mesh, porous material, foam, nonwoven fabric.

[0146] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe3O4; or a compound with the chemical formula Li 1+c1 Mn 2-c1 Lithium manganese oxides such as O4 (0 ≤ c1 ≤ 0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7; chemical formula LiNi 1-c2 M c2 Ni-site type lithium nickel oxide represented as O2 (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, satisfying 0.01 ≤ c2 ≤ 0.3); chemical formula LiMn 2-c3 Mc3 Lithium manganese composite oxides represented as O2 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, satisfying 0.01 ≤ c3 ≤ 0.1) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); examples include, but are not limited to, LiMn2O4 in which part of the Li in the chemical formula is substituted with alkaline earth metal ions. The positive electrode may also be Li-metal.

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

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

[0149] Furthermore, the positive electrode binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one or more of these may be used.

[0150] The separator separates the negative and positive electrodes and provides a passage for lithium ions to move. Generally, any separator used in secondary batteries is acceptable without particular limitations, but it is especially preferable that it has low resistance to ion movement in the electrolyte and excellent electrolyte moisture absorption capacity. Specifically, porous polymer films, such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof may be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, to ensure heat resistance or mechanical strength, coated separators containing ceramic components or polymeric substances may be used, and these may be selectively used as single-layer or multi-layer structures.

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

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

[0153] As the non-aqueous organic solvent, for example, aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate, and ethyl propionate may be used.

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

[0155] As the metal salt, a lithium salt may be used, and the lithium salt is a substance that is easily soluble in the non-aqueous electrolyte, for example, as the anion of the lithium salt, F - Cl - , I - NO3 - , N(CN)2 - BF4 - ClO4 - PF6 - (CF3)2PF4 - (CF3)3PF3 -(CF3)4PF2 - (CF3)5PF - (CF3)6P - CF3SO3 - CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2) 2CH - (SF5)3C - , (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - , and (CF3CF2SO2)2N - You may use one or more selected from the group consisting of the following:

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

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

[0158] The following describes the Specification in detail with reference to examples. However, the examples relating to this Specification may be modified in various forms, and the scope of this application should not be construed as being limited to the examples described below. The examples relating to this Application are provided to give a more complete explanation of this Specification to a person of average skill in the art. [Examples]

[0159] <Examples and Comparative Examples> Example 1 900 g of a powder containing Si and SiO2 in a 1:1 molar ratio and 10 g of an ionic compound (NaCl) were appropriately mixed and heated under vacuum in a reaction furnace at a sublimation temperature of 2,400°C. The vaporized mixture of Si, SiO2, and the ionic compound was then reacted in a vacuum cooling zone with a cooling temperature of 800°C to condense into a solid phase. Subsequently, the mixture was heat-treated in an inert atmosphere at 800°C to produce preliminary silicon-based particles. These preliminary silicon-based particles were then processed using a ball mill, with 15 SUS ball media added and ground for 3 hours to a particle size of 6 μm (D 50 Silicon-based particles of the size of ) were manufactured. Then, while maintaining an inert atmosphere by flowing Ar gas, the silicon-based particles were positioned in the hot zone of the CVD apparatus, and using Ar as a carrier gas, the methane was blown into the 900°C hot zone, 10 -1 The silicon-based particles were reacted in Torr for 5 hours to form a carbon layer on their surface.

[0160] A composition for forming a negative electrode active material was produced by solid-phase mixing silicon-based particles on which the carbon layer was formed with lithium metal powder as a lithium precursor in a weight ratio of 90:10.

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

[0162] The heat-treated negative electrode active material forming composition was acid-treated with an aqueous hydrochloric acid solution with 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 The negative electrode active material was manufactured in the same manner as in Example 1, except that the heat treatment performed after condensing the gas mixture 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 manufactured in the same manner as in Example 1, except that the heat treatment performed after condensing the gas mixture 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 manufactured in the same manner as in Example 1, except that the heat treatment performed after condensing the gas mixture 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 prepared 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%. In this case, 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 prepared 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 prepared in the same manner as in Example 1, except that ionic compounds were not mixed in.

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

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

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

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

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

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

[0181] <Element content analysis> The elemental 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 apparatus. First, electrode samples prepared by coating the negative electrode active material onto copper foil (Cu Foil) were milled using a Hitachi IM4000 apparatus. Specifically, an ion beam was irradiated at a voltage of 1.5kV for about 3-4 hours per sample, and then the elemental content inside the material was measured by EDS measurement of the entire SEM cross-sectional image.

[0183] <Cross-sectional analysis of negative electrode active material (average diameter measurement)> Cross-sectional analysis of the negative electrode active material was performed using an ion milling system. First, electrode samples prepared by coating the negative electrode active material onto copper foil (Cu Foil) were milled using a Hitachi IM4000 system. Specifically, an ion beam was irradiated at a voltage of 1.5 kV for approximately 3 to 4 hours per sample, after which a cross-sectional image was measured using a Hitachi S-4800 SEM. Next, the average diameter of the pores appearing in the cross-section of the negative electrode active material was calculated based on the measured SEM cross-sectional image.

[0184] <D of the negative electrode active material 50 and specific surface area analysis > The D of the negative electrode active material 50 The material was analyzed using laser diffraction particle size analysis with a Microtrac S3500 instrument, 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 meter (HPRM-1000, HANTECH CO.). After uniformly placing 3g of the sample (negative electrode active material) into a cylindrical mold with a diameter of 20mm, the resistance was measured in 400kgf increments from 400kgf to 2000kgf. The conductivity of the negative electrode active material was then relatively evaluated in Table 2 below, with Example 1 as the reference.

[0187] <Experimental Example: Evaluation of discharge capacity, initial efficiency, and lifetime (capacity retention rate) characteristics> A negative electrode and a battery were manufactured using the negative electrode active materials of the examples and comparative examples, respectively.

[0188] A mixture was prepared by mixing the aforementioned negative electrode active material, the conductive material carbon black, and the binder PAA (polyacrylic acid) in a weight ratio of 80:10:10. Then, 7.8 g of distilled water was added to 5 g of the mixture and mixed uniformly to produce a negative electrode slurry. The negative electrode slurry was applied to a copper (Cu) metal thin film, which was a negative electrode current collector with a thickness of 15 μm, and dried. During this process, the temperature of the circulating air was 60°C. Next, the film was rolled (rolled in a roll press) and dried in a vacuum oven at 130°C for 12 hours to produce a negative electrode.

[0189] The manufactured electrode is used as the negative electrode, 1.7671 cm⁻¹ 2 A lithium coin half-cell was manufactured by using a circularly cut lithium (Li) metal thin film as the positive electrode, interposing a porous polyethylene separator between the positive and negative electrodes, dissolving 0.5 parts by weight of vinylene carbonate in a mixed solution of ethyl methyl carbonate (EMC) and ethylene carbonate (EC) in a volume ratio of 7:3, and injecting an electrolyte solution containing 1M LiPF6.

[0190] The manufactured batteries were subjected to charging and discharging tests, and their discharge capacity, initial efficiency, and capacity retention rate were evaluated and are shown in Table 2 below.

[0191] The first and second cycles were charged and discharged at 0.1C, and from the third to the fortieth cycle, they were charged and discharged at 0.5C. The final cycle ended in a charged state (lithium was in the negative electrode).

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

[0193] Initial efficiency (%) = (Discharge capacity per cycle / Charge capacity per cycle) × 100 The capacity retention rates were derived using the following calculations.

[0194] Capacity retention rate (%) = (49 times discharge capacity / 1 time discharge capacity) × 100

[0195] [Table 2]

[0196] According to Table 2, the negative electrode active materials of Examples 1 to 6, which contain alkali metal elements and halogen elements and have pore sizes of 20 nm to 60 nm, have a carbon layer effectively positioned within the pores of silicon-based particles, resulting in a high carbon coating area and improved conductivity due to ions remaining inside the negative electrode active material. This was confirmed to improve discharge capacity, efficiency, and / or lifetime characteristics.

[0197] On the other hand, as in Comparative Examples 1 and 6, when the negative electrode active material does not contain alkali metal elements and halogen elements, pores are not formed and conductivity is not improved, thus it was confirmed that efficiency and / or lifetime characteristics deteriorate. As in Comparative Examples 1 and 6, even if the active material particles contain alkali metals such as lithium or alkaline earth metals such as magnesium, if ionic compounds are not added when producing the preliminary silicon-based particles, it is not possible to realize the appropriate pore size of the active material particles.

[0198] In Comparative Examples 2 to 5, although conductivity was improved due to the excessive inclusion of ionic compounds in the negative electrode active material, it was confirmed that the material capacity decreased due to the excessive inclusion of ionic compounds, resulting in a significant reduction in the battery's discharge capacity, efficiency, and / or life characteristics during cycle behavior.

Claims

1. A step in which silicon-based precursors and ionic compounds are heat-treated and vaporized; A step of forming silicon-based particles by depositing a mixed gas of the silicon-based precursor and the ionic compound together in the gas phase; A step of performing an additional heat treatment at a temperature of 800°C to 1100°C on the silicon-based particles containing the ionic compound formed by the aforementioned vapor deposition, thereby forming pores within the silicon-based particles; and A step of heat-treating the silicon-based particles and the carbon source to form a carbon layer on the surface and within the pores of the silicon-based particles; A method for producing a negative electrode active material, including the material itself.

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

3. The method for producing a negative electrode active material according to claim 1, wherein the ionic compound comprises 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 producing 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 producing a negative electrode active material according to claim 1, wherein the deposition is carried out in an inert gas atmosphere and at a temperature of 500°C to 1000°C.

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

7. The negative electrode active material is SiO ｘ The silicon-based particles having (0 < x < 2) and pores; and A carbon layer provided on the surface and within the pores of the silicon-based particles; Includes, It comprises 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. The method for producing a negative electrode active material according to claim 1, wherein, when the cross-sectional analysis of the negative electrode active material is performed, the average diameter of the pores is 20 nm to 60 nm.

8. The method for producing a negative electrode active material according to claim 7, wherein the negative electrode active material comprises at least one alkali metal element selected from Li and Na.

9. The method for producing a negative electrode active material according to claim 7, wherein the negative electrode active material contains at least one halogen element selected from F and Cl.

10. The alkali metal element is one or more selected from the group consisting of Na, K, Rb, and Cs. The method for producing a negative electrode active material according to claim 7, wherein the alkali metal element is included in an amount greater than 0.01 parts by weight and less than 10 parts by weight, based on 100 parts by weight of the negative electrode active material.

11. The halogen element is one or more selected from the group consisting of Cl, Br, and I. The method for producing a negative electrode active material according to claim 7, wherein the halogen element is contained in an amount greater than 0.01 parts by weight and less than 10 parts by weight, based on 100 parts by weight of the negative electrode active material.

12. The method for producing a negative electrode active material according to claim 7, wherein the alkali metal element and the halogen element are located inside the pores.

13. The method for producing a negative electrode active material according to claim 7, wherein the carbon layer is included in an amount of 0.1 to 50 parts by weight, based on a total of 100 parts by weight of the negative electrode active material.

14. The method for producing a negative electrode active material according to claim 7, wherein the silicon-based particles further comprise a Li compound or a Mg compound.

15. The method for producing a negative electrode active material according to Claim 1, wherein the step of heat-treating the silicon-based particles and the carbon source to form a carbon layer on the surface and inside the pores of the silicon-based particles includes forming the carbon layer by chemical vapor deposition (CVD) of the carbon source onto the silicon-based particles.

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