A negative electrode active material, a negative electrode containing the same, a secondary battery containing the same, and a method for manufacturing the negative electrode active material.

Abstract

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

Description

[Technical Field]

[0001] This application claims the benefit as of the filing date of Korean Patent Application No. 10-2022-0150557, filed with the Korean Intellectual Property Office on November 11, 2022, and Korean Patent Application No. 10-2023-0154177, filed with the Korean Intellectual Property Office on November 9, 2023, and all of its contents are incorporated herein by reference.

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

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

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

[0005] Among negative electrode active materials, silicon-based active materials are attracting attention because they have a higher capacity and superior fast charging characteristics compared to carbon-based active materials. However, silicon-based active materials have the disadvantage of low initial efficiency due to a large degree of volume expansion / contraction 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 (0 < x < 2) The silicon-based oxide represented by has an advantage in that the degree of volume expansion / contraction due to charge and discharge is lower than that of other silicon-based active materials such as silicon (Si). However, there is still a drawback that the initial efficiency decreases due to the presence of irreversible capacity in the silicon-based oxide.

[0007] In connection with this, research has been continuously conducted to reduce the irreversible capacity and improve the initial efficiency by doping or inserting metals such as Li, Al, and Mg into the silicon-based oxide. However, in the case of a negative electrode slurry containing a metal-doped silicon-based oxide as a negative electrode active material, there is a problem that the metal oxide formed by doping reacts with moisture to increase the pH of the negative electrode slurry and change the viscosity. For this reason, there is a problem that the state of the manufactured negative electrode becomes poor and the charge and discharge efficiency of the negative electrode decreases.

[0008] Therefore, there is a need to develop a negative electrode active material that can improve the phase stability of a negative electrode slurry containing a silicon-based oxide and improve the charge and discharge efficiency of the negative electrode manufactured therefrom.

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

Means for Solving the Problems

[0011] One embodiment of the present invention is SiO xSilicon-based particles containing (0 < x < 2) and a Li compound; a first coating layer provided on at least a part of the silicon-based particles; and a second coating layer provided on at least a part of the first coating layer, wherein the first coating layer contains Li, Al, P, and O, and the second coating layer contains carbon, to provide a negative electrode active material.

[0012] One embodiment of the present invention provides a negative electrode containing the negative electrode active material.

[0013] One embodiment of the present invention provides a secondary battery containing the negative electrode.

Effects of the Invention

[0014] The negative electrode active material according to one embodiment of the present invention is SiO x Silicon-based particles containing (0 < x < 2) and a Li compound; a first coating layer provided on at least a part of the silicon-based particles; and a second coating layer provided on at least a part of the first coating layer, wherein the first coating layer contains Li, Al, P, and O, and the second coating layer contains carbon, and a first coating layer containing Li, Al, P, and O is provided between the silicon-based particles and the second coating layer containing carbon, thereby reducing the reactivity of silicate having a high reactivity with a base and easily blocking the contact between the silicon-based particles and the outside, so that there is an effect of improving the water-based processability of the slurry.

[0015] In addition, compared with a negative electrode active material in which a coating layer containing Li, Al, P, and O is provided on a carbon layer as in the prior art, a carbon layer showing hydrophobicity exists on the outermost layer, so that the contact between the negative electrode active material and water can be further blocked to improve the processability of the aqueous slurry, and there is an effect that highly conductive carbon exists on the outermost layer, which is advantageous for realizing capacity / efficiency.

[0016] Furthermore, lithium by-products contained in silicon-based particles can be effectively removed during the process of forming the first coating layer. The formed first coating layer effectively covers any unreacted lithium by-products, preventing the phenomenon in which lithium by-products or silicates in silicon-based particles react with moisture in the slurry, thereby degrading the slurry's properties. Additionally, the first coating layer contains Li, resulting in lower lithium diffusion resistance on the surface of the negative electrode active material and improved discharge rate characteristics (rate capability).

[0017] 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. [Brief explanation of the drawing]

[0018] [Figure 1] This diagram schematically shows the structure of the negative electrode active material according to one embodiment of the present invention. [Modes for carrying out the invention]

[0019] The following provides a more detailed description 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 can be performed using an XRD (X-ray diffraction) analyzer (product name: D4-endavor, manufacturer: bruker), and other instruments used in this industry may be used as appropriate.

[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 atomic 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 that corresponds to 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. This 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] Preferred embodiments of the present invention will be described in detail below. However, 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.

[0028] <Negative electrode active material> One embodiment of the present invention is SiO x (0 < x < 2) and silicon-based particles containing a Li compound; a first coating layer provided on at least a part of the silicon-based particles; and a second coating layer provided on at least a part of the first coating layer, wherein the first coating layer contains Li, Al, P, and O, and the second coating layer contains carbon, and provides a negative electrode active material.

[0029] The negative electrode active material according to one embodiment of the present invention contains silicon-based particles. The silicon-based particles contain SiO x (0 < x < 2) and a Li compound.

[0030] The SiO x (0 < x < 2) may correspond to a matrix within the silicon-based particles. The SiO x (0 < x < 2) may be in a form containing Si and / or SiO2, and the Si may form a phase. For example, the SiO x (0 < x < 2) may be a composite containing amorphous SiO2 and Si crystals. 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 particles contain the SiO x (0 < x < 2), the discharge capacity of the secondary battery can be improved.

[0031] 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, lithium silicide, and lithium oxide within the silicon-based particles. When the silicon-based particles contain a Li compound, there is an effect that the initial efficiency is improved.

[0032] The Li compound may be in a form doped into the silicon-based particles and distributed on the surface and / or inside of the silicon-based particles. The Li compound is distributed on the surface and / or inside of the silicon-based particles, can control the expansion / contraction of the volume of the silicon-based particles to an appropriate level, and can play a role in preventing damage to the active material. Further, the Li compound may be contained in terms of reducing the proportion of the irreversible phase (for example, SiO2) of the silicon-based oxide particles and increasing the efficiency of the active material.

[0033] In one embodiment of the present invention, the Li compound may exist in the form of lithium silicate. The lithium silicate is Li a Si b O c (2 ≤ a ≤ 4, 0 < b ≤ 2, 2 ≤ c ≤ 5), and can be classified into crystalline lithium silicate and amorphous lithium silicate. The crystalline lithium silicate may exist in the form of at least one lithium silicate selected from the group consisting of Li2SiO3, Li4SiO4, and Li2Si2O5 in the silicon-based particles, and the amorphous lithium silicate is Li a Si b O c (2 ≤ a ≤ 4, 0 < b ≤ 2, 2 ≤ c ≤ 5) may consist of a composite structure, and is not limited to the above form.

[0034] In one embodiment of the present invention, based on 100 parts by weight in total of the 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. 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, an appropriate discharge capacity and initial efficiency can be realized.

[0035] The content of the aforementioned Li element can be confirmed by 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 inductively coupled plasma atomic emission spectrometer (ICPAES, Perkin-Elmer 7300), the intensity of a standard solution prepared using a standard solution (5 mg / kg) is measured at the wavelength specific to 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 against the calibration curve created above. The total is then converted so that it equals the theoretical value, and the elemental content of the manufactured negative electrode active material can be analyzed.

[0036] In one embodiment of the present invention, the silicon-based particles may contain additional metal atoms. The metal atoms may exist within the silicon-based particles in the form of at least one of metal atoms, metal silicates, metal silicides, and metal oxides. The metal atoms may include at least one selected from the group consisting of Mg, Li, Al, and Ca. This can improve the initial efficiency of the negative electrode active material.

[0037] In one embodiment of the present invention, a first coating layer is provided on at least a portion of the silicon-based particles, and the first coating layer contains Li, Al, P, and O.

[0038] As described above, by providing a first coating layer containing Li, Al, P, and O on the silicon-based particles, the reactivity of silicates, which are highly reactive with bases, is reduced, and contact between the silicon-based particles and the outside can be easily blocked, thus improving the aqueous processability of the slurry.

[0039] Specifically, the first coating layer may be in a form that covers at least a portion of the silicon-based particles. That is, the first coating layer may partially cover the surface of the particles or cover the entire surface of the particles. Examples of the shape of the first coating layer include island type or thin film type, but the shape of the first coating layer is not limited to these.

[0040] The first coating layer may be provided adjacent to the silicon-based particles. That is, the first coating layer may be applied adjacent to the silicon-based particles. The first coating layer may completely or partially cover the silicon-based particles.

[0041] In one embodiment of the present invention, the first coating layer may contain Li, Al, P, and O.

[0042] In one embodiment of the present invention, the Al may be included in an amount of 0.01 parts by weight or more and 1 part by weight or less based on 100 parts by weight of the total negative electrode active material. Specifically, it may be included in an amount of 0.02 parts by weight or more and 0.9 parts by weight or less, in an amount of 0.03 parts by weight or more and 0.85 parts by weight or less, or in an amount of 0.05 parts by weight or more and 0.8 parts by weight or less. The lower limit of the Al content is 0.01 parts by weight, 0.03 parts by weight, 0.05 parts by weight, 0.08 parts by weight, 0.1 parts by weight, 0.12 parts by weight, or 0.15 parts by weight, and the upper limit is 1 part by weight, 0.9 parts by weight, 0.85 parts by weight, 0.8 parts by weight, 0.7 parts by weight, 0.6 parts by weight, or 0.5 parts by weight.

[0043] In one embodiment of the present invention, P may be present in an amount of 0.05 parts by weight or more and 2.5 parts by weight or less based on 100 parts by weight of the total negative electrode active material. Specifically, it may be present in an amount of 0.1 parts by weight or more and 2 parts by weight or less, 0.15 parts by weight or more and 1.9 parts by weight or less, or 0.18 parts by weight or more and 1.8 parts by weight or less. The lower limit of the content of P is 0.05 parts by weight, 0.1 parts by weight, 0.15 parts by weight, 0.18 parts by weight, 0.2 parts by weight, 0.25 parts by weight, 0.3 parts by weight, 0.35 parts by weight, 0.4 parts by weight, 0.45 parts by weight or 0.5 parts by weight, and the upper limit is 2.5 parts by weight, 2 parts by weight, 1.8 parts by weight, 1.5 parts by weight, 1.2 parts by weight or 1 part by weight.

[0044] In one embodiment of the present invention, the Li contained in the first coating layer may be present in an amount of 0.05 parts by weight or more and 2 parts by weight or less, based on 100 parts by weight of the total negative electrode active material. Specifically, it may be present in an amount of 0.1 parts by weight or more and 1.5 parts by weight or less, or in an amount of 0.15 parts by weight or more and 1 part by weight or less. The lower limit of the Li content in the first coating layer is 0.05 parts by weight, 0.1 parts by weight, 0.15 parts by weight, 0.2 parts by weight, 0.25 parts by weight, 0.3 parts by weight, 0.35 parts by weight, 0.4 parts by weight, 0.45 parts by weight, or 0.5 parts by weight, and the upper limit is 2 parts by weight, 1.5 parts by weight, 1.2 parts by weight, or 1 part by weight.

[0045] In one embodiment of the present invention, the amount of oxygen contained in the first coating layer may be 0.5 parts by weight or more and 2 parts by weight or less based on 100 parts by weight of the total negative electrode active material. Specifically, it may be 0.6 parts by weight or more and 1.9 parts by weight or less, or 0.7 parts by weight or more and 1.8 parts by weight or less. The lower limit of the oxygen content in the first coating layer is 0.5 parts by weight, 0.6 parts by weight, or 0.7 parts by weight, and the upper limit is 2 parts by weight, 1.9 parts by weight, or 1.8 parts by weight.

[0046] In one embodiment of the present invention, the first coating layer may contain a phase containing Li, Al, P, and O.

[0047] In one embodiment of the present invention, the first coating layer contains Li y Al z P w O v (0 < y ≤ 10, 0 < z ≤ 10, 0 < w ≤ 10, 0 < v ≤ 10) phase may be included. The y, z, w, and v represent the atomic number ratios of each atom.

[0048] In one embodiment of the present invention, the first coating layer may contain one or more selected from the group consisting of aluminum oxide, phosphorus oxide, lithium oxide, aluminum phosphate, lithium salt, lithium phosphate, and lithium aluminate. As an example, the Li y Al z P w O v phase contained in the first coating layer may include, but is not limited to, a mixture or compound formed from Li3PO4, AlPO4, Al(PO3)3, or LiAlO2, etc.

[0049] When the first coating layer containing the above components is provided, it is possible to prevent the phenomenon that the Li compound contained in the silicon-based particles reacts with the moisture in the slurry to lower the viscosity of the slurry, thereby having the effect of improving the stability of the electrode state and / or the charge-discharge capacity.

[0050] In one embodiment of the present invention, the first coating layer may contain an amorphous phase. As an example, the first coating layer may be an amorphous phase. As an example, when performing X-ray diffraction analysis of the negative electrode active material according to one embodiment of the present invention, crystalline peaks derived from the first coating layer may not appear.

[0051] In one embodiment of the present invention, the first coating layer may further contain one or more selected from the group consisting of Li2O, LiOH, and Li2CO3. Generally, in the process of doping silicon-based particles with lithium, the remaining substances are exposed to moisture and air, and lithium by-products such as Li2O, LiOH, and Li2CO3 can be formed. Therefore, the first coating layer may be in a form further containing one or more selected from the group consisting of Li2O, LiOH, and Li2CO3.

[0052] In one embodiment of the present invention, y may satisfy 0 < y ≤ 3.

[0053] In one embodiment of the present invention, z may satisfy 0 < z ≤ 1.

[0054] In one embodiment of the present invention, w may satisfy 0.5 ≤ w ≤ 3.

[0055] In one embodiment of the present invention, v may satisfy 4 < v ≤ 12.

[0056] The first coating layer may be formed by dry-mixing i) silicon-based particles and aluminum phosphate, ii) silicon-based particles, an aluminum precursor, and a phosphorus precursor, or iii) silicon-based particles and a Li-Al-P-O-based precursor followed by heat treatment, or by reacting after mixing in a solvent while vaporizing the solvent.

[0057] In one embodiment of the present invention, the first coating layer may be contained in an amount exceeding 0 parts by weight and not exceeding 10 parts by weight based on 100 parts by weight in total of the negative electrode active material. Specifically, it may be contained in an amount of 0.1 parts by weight or more and 10 parts by weight or less, 0.3 parts by weight or more and 8 parts by weight or less, or 0.4 parts by weight or more and 5 parts by weight or less. When the content of the first coating layer is less than the above range, it is difficult to prevent gas generation in the slurry. When it is more than the above range, there is a problem that it is difficult to achieve capacity or efficiency.

[0058] The upper limit of the content of the first coating layer may be 10 parts by weight, 8 parts by weight, 6 parts by weight, 5 parts by weight, 4 parts by weight, 3.5 parts by weight, 3 parts by weight, or 2 parts by weight, and the lower limit may be 0.1 parts by weight, 0.3 parts by weight, 0.4 parts by weight, 0.5 parts by weight, 0.8 parts by weight, 1 part by weight, 1.2 parts by weight, 1.4 parts by weight, or 1.5 parts by weight.

[0059] In one embodiment of the present invention, a second coating layer may be provided on at least a part of the first coating layer, and the second coating layer contains carbon.

[0060] Specifically, the second coating layer may be in a form that at least partially covers the surface of the first coating layer, that is, it partially covers or completely covers the surface of the first coating layer. Examples of the shape of the second coating layer include island type or thin film type, but the shape of the second coating layer is not limited thereto.

[0061] The second coating layer containing carbon imparts conductivity to the negative electrode active material, and can improve the initial efficiency, life characteristics, and battery capacity characteristics of the secondary battery.

[0062] The second coating layer may be provided adjacent to the first coating layer. That is, the second coating layer is coated adjacent to the first coating layer, and SiO x (0 < x < 2) and particles containing a Li compound - first coating layer - second coating layer may be provided. The second coating layer may be in a form that completely covers or partially covers the first coating layer.

[0063] Furthermore, the second coating layer may be provided on the silicon-based particle surface in a region where the first coating layer is not provided. That is, the second coating layer may be provided adjacent to the surface of the silicon-based particle that is not covered by the first coating layer, in the form of a silicon-based particle-second coating layer.

[0064] The second coating layer may be in a form that covers at least a portion of the silicon-based particles. That is, the second coating layer may partially cover the surface of the silicon-based particles.

[0065] In one embodiment of the present invention, the second coating layer may contain amorphous carbon. The second coating layer may further contain crystalline carbon.

[0066] The crystalline carbon can further improve the conductivity of the negative electrode active material. The crystalline carbon may include at least one selected from the group consisting of fullerene, carbon nanotubes, and graphene.

[0067] 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 materials as a source in chemical vapor deposition.

[0068] The aforementioned carbonized organic substances may be carbonized organic substances selected from carbonized sucrose, glucose, galactose, fructose, lactose, mannose, ribose, aldohexose, or ketohexose, and combinations thereof.

[0069] The hydrocarbon may be a substituted or unsubstituted aliphatic or alicyclic hydrocarbon, or a substituted or unsubstituted aromatic hydrocarbon. The aliphatic or alicyclic hydrocarbon of the substituted or unsubstituted aliphatic or alicyclic hydrocarbon may be methane, ethane, ethylene, acetylene, propane, butane, butene, pentane, isobutane, or hexane, etc. Examples of the aromatic hydrocarbon of the substituted or unsubstituted aromatic hydrocarbon include benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, coumarone, pyridine, anthracene, or phenanthrene, etc.

[0070] In one embodiment of the present invention, the second coating layer may be an amorphous carbon layer.

[0071] In one embodiment of the present invention, the second coating layer may further contain Li, Al, P, and O. Specifically, the second coating layer may be a carbon layer further containing Li, Al, P, and O.

[0072] In one embodiment of the present invention, the second coating layer may further contain a phase containing Li, Al, P, and O. That is, the second coating layer may be a carbon layer, and may have a structure further containing a phase containing Li, Al, P, and O inside the carbon layer.

[0073] Specifically, the second coating layer contains Li y Al z P w O v and may further have a form containing a phase (0 < y ≤ 10, 0 < z ≤ 10, 0 < w ≤ 10, 0 < v ≤  10).

[0074] The Li y Al z P w ] O v phase contained in the second coating layer is the Li y Alz P w O v It may be the same as the phase. That is, the components of the first coating layer may be mixed together and coated during the process of coating the silicon-based particles with a carbon layer, or the first coating layer may be formed and then the components of the first coating layer (e.g., Li) may be added to the carbon layer during the carbon coating process. y Al z P w O v (phase) is included, and Li is inside the carbon layer y Al z P w O v A second coating layer containing the phase may be formed.

[0075] In one embodiment of the present invention, the carbon content may be 70 parts by weight or more based on 100 parts by weight of the second coating layer. Specifically, the carbon content may be 80 parts by weight or more, 90 parts by weight or more, 95 parts by weight or more, or 98 parts by weight or more. As described above, the components of the first coating layer may be included in the process of forming the second coating layer, and a small amount of the components of the first coating layer may be included inside the second coating layer.

[0076] In one embodiment of this specification, the second coating layer may be provided on the outermost surface of the anode active material. Specifically, the carbon component in the second coating layer may be provided on the outermost surface of the anode active material. When carbon is present on the outermost surface of the anode active material as described above, the hydrophobicity of the carbon acts more effectively than when carbon is not present on the outermost surface of the anode active material, further blocking contact between the anode active material and water, thereby further improving the processability of the aqueous slurry, and the conductivity of carbon is advantageous in achieving capacity / efficiency.

[0077] In one embodiment of the present invention, the second coating layer may be present in an amount of 0.1 to 50 parts by weight based on 100 parts by weight of the total negative electrode active material. Specifically, it may be present in an amount of 1 to 30 parts by weight, 2 to 20 parts by weight, 3 to 10 parts by weight, or 3 to 8 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.

[0078] The upper limit of the content of the second coating layer may be 50 parts by weight, 40 parts by weight, 30 parts by weight, 20 parts by weight, 15 parts by weight, 10 parts by weight, 8 parts by weight, 7 parts by weight, 6 parts by weight, or 5 parts by weight, and the lower limit may be 0.1 parts by weight, 1 part by weight, 2 parts by weight, 3 parts by weight, or 4 parts by weight.

[0079] In one embodiment of the present invention, the carbon contained in the negative electrode active material may be present 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 present in amounts of 0.5 to 15 parts by weight, 1 to 10 parts by weight, 1 to 8 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. The upper limit of the carbon content in the negative electrode active material may be 50 parts by weight, 40 parts by weight, 30 parts by weight, 20 parts by weight, 10 parts by weight, 8 parts by weight, 6 parts by weight, or 5 parts by weight, and the lower limit may be 0.1 parts by weight, 1 part by weight, 2 parts by weight, 3 parts by weight, or 4 parts by weight.

[0080] In one embodiment of the present invention, the thickness of the second coating 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, side reactions between the electrolyte and the negative electrode active material are suppressed, and the initial efficiency and / or lifespan of the battery are improved.

[0081] Specifically, the second coating layer may be formed by chemical vapor deposition (CVD) using at least one hydrocarbon gas selected from the group consisting of methane, ethane, and acetylene.

[0082] In one embodiment of the present invention, the Li y Al z P w O v (0 < y ≤ 10, 0 < z ≤ 10, 0 < w ≤ 10, 0 < v ≤ 10) phase may be contained in an amount of 0.1 parts by weight or more and 30 parts by weight or less based on 100 parts by weight in total of the negative electrode active material. Specifically, it may be contained in an amount of 0.1 parts by weight or more and 20 parts by weight or less, 0.2 parts by weight or more and 15 parts by weight or less, 0.3 parts by weight or more and 10 parts by weight or less, or 0.4 parts by weight or more and 8 parts by weight or less. The Li y Al z P w O v phase may have a lower limit of the content of 0.1 parts by weight, 0.2 parts by weight, 0.3 parts by weight, 0.4 parts by weight, or 0.5 parts by weight, and an upper limit of 30 parts by weight, 20 parts by weight, 15 parts by weight, 10 parts by weight, 8 parts by weight, 7 parts by weight, 6 parts by weight, 5 parts by weight, 4 parts by weight, 3 parts by weight, or 2 parts by weight. As described above, when the content of the Li y Al z P w O v phase satisfies the above range, the reactivity of the silicate having a large reactivity with a base can be lowered, and the contact between the silicon-based particles and the outside can be easily blocked, so that there is an effect of improving the water-based processability of the slurry. On the contrary, when it exceeds the above range, there is a problem that it has an adverse effect on electrical conductivity and it is difficult to achieve capacity / efficiency during charge and discharge. When it is contained less than the above range, there is a problem that the reactivity of the silicate cannot be lowered and it is difficult to improve the water-based processability of the slurry.

[0083] In this invention, the crystallinity of the carbon in the second coating layer can be confirmed by calculating the D / G band ratio using Raman spectroscopy. Specifically, measurements can be taken using a Renishaw 2000 Raman microscope system and 532 nm laser excitation, with a low laser power density and a 30-second exposure time, and a 100x optical lens to avoid the thermal effect of the laser. To reduce positional deviations, a total of 25 points are measured in a 5 μm × 5 μm area, and after fitting using a Lorentzian function, the average values ​​of the D and G bands can be calculated.

[0084] Figure 1 schematically shows the structure of a negative electrode active material according to one embodiment of the present invention, and shows a configuration comprising silicon-based particles 1, a first coating layer 2, and a second coating layer 5. Specifically, the first coating layer 2 may be provided on the silicon-based particles 1, and the second coating layer 5 may be provided on the first coating layer 2. In this case, the second coating layer 5 contains carbon 4 and has Li inside. y Al z P w O v Phase 3 may also be included.

[0085] In one embodiment of the present invention, the carbon content may be 45 parts by weight or more and 95 parts by weight or less based on a total of 100 parts by weight of the first and second coating layers. Specifically, the carbon content may be 48 parts by weight or more and 93 parts by weight or less, 49 parts by weight or more and 92 parts by weight or less, 50 parts by weight or more and 91 parts by weight or less, more than 50 parts by weight and 90 parts by weight or less, 60 parts by weight or more and 85 parts by weight or less, or 70 parts by weight or more and 80 parts by weight or less. When the total coating layer contains 45 parts by weight or more of carbon as described above, the hydrophobic carbon layer is located on the outermost layer, further blocking contact with water and improving the processability of the aqueous slurry, and the presence of highly conductive carbon on the outermost layer is advantageous for achieving capacity / efficiency. In contrast, if the carbon content is below the aforementioned range, it is not possible to effectively block contact between the negative electrode active material and water, making it difficult to improve the processability of the aqueous slurry. If the carbon content exceeds the aforementioned range, the material becomes excessively hydrophobic, resulting in poor dispersibility during the production of the aqueous slurry.

[0086] In one embodiment of the present invention, the weight ratio of the first coating layer to the second coating layer may be 1:0.5 to 1:30. Specifically, it may be 1:0.5 to 1:20, 1:0.5 to 1:15, 1:1 to 1:15, 1:2 to 1:10, or 1:3 to 1:5. By satisfying such a range, the first and second coating layers can effectively coat the silicon-based particles, efficiently suppressing side reactions in the slurry, and stably achieving capacity and / or efficiency. On the other hand, if the content of the first coating layer is excessively high compared to the second coating layer, it becomes difficult to achieve capacity or efficiency, and if the content of the second coating layer is excessively high compared to the first coating layer, it becomes difficult to prevent gas generation in the slurry.

[0087] In one embodiment of the present invention, the first coating layer may be included in an amount of 5 to 150 parts by weight based on 100 parts by weight of the second coating layer. Specifically, the first coating layer may be included in an amount of 120 parts by weight or less, 110 parts by weight or less, 100 parts by weight or less, 90 parts by weight or less, 80 parts by weight or less, 70 parts by weight or less, 60 parts by weight or less, or 50 parts by weight or less, based on 100 parts by weight of the second coating layer. Alternatively, the first coating layer may be included in an amount of 5 parts by weight or more, 8 parts by weight or more, 10 parts by weight or more, or 20 parts by weight or more, based on 100 parts by weight of the second coating layer. By satisfying the above ranges, the second coating layer and the first coating layer can effectively coat the silicon-based particles and efficiently suppress side reactions in the slurry, thereby achieving stable capacity and / or efficiency.

[0088] In one embodiment of the present invention, lithium byproducts may be present on the silicon-based particles. Specifically, the lithium byproducts may be present between the silicon-based particles and the first coating layer, inside the first coating layer, or on the first coating layer. Alternatively, the lithium byproducts may be present between the silicon-based particles and the second coating layer.

[0089] Specifically, the lithium by-product may refer to lithium compounds remaining near the surface of silicon-based particles or carbon layers after the production of silicon-based particles.

[0090] The lithium by-product may include one or more selected from the group consisting of Li2O, LiOH, and Li2CO3.

[0091] The presence or absence of the aforementioned lithium by-product can be confirmed by X-ray diffraction (XRD) or X-ray photoelectron spectroscopy (XPS).

[0092] The lithium by-product may be present in an amount of 5 parts by weight or less, based on 100 parts by weight of the total negative electrode active material. Specifically, it may be present in amounts of 0.01 to 5 parts by weight, 0.05 to 2 parts by weight, or 0.1 to 1 part by weight. More specifically, it may be present in amounts of 0.1 to 0.8 parts by weight, or 0.1 to 0.5 parts by weight. When the lithium by-product content satisfies the above range, side reactions in the slurry can be reduced, viscosity changes can be lowered, and aqueous processability characteristics can be improved. On the other hand, when the lithium by-product content is higher than the above range, the slurry exhibits basicity during formation, which leads to the occurrence of side reactions and viscosity changes, resulting in problems with aqueous processability.

[0093] The content of the lithium by-product can be calculated by measuring the amount of HCl solution in a specific interval where the pH changes during the titration process of an aqueous solution containing the negative electrode active material with an HCl solution using a titrator, and then calculating the amount of lithium by-product.

[0094] 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. When the above range is met, the structural stability of the active material during charging and discharging can be ensured, the problem of volume expansion / contraction levels increasing due to excessively large particle size can be prevented, and the problem of initial efficiency decreasing due to excessively small particle size can be prevented.

[0095] The BET specific surface area of ​​the negative electrode active material is 1 m². 2 / g~100m 2 It can also be expressed as / g, specifically 1m 2 / g~70m 2 It can also be / g, or more specifically 1m 2 / g~50m 2 It may also be / 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, thereby improving the battery's lifespan characteristics.

[0096] <Method for manufacturing negative electrode active material> One embodiment of the present invention includes the steps of manufacturing preliminary silicon-based particles containing SiO x (0 < x < 2); heat-treating the mixture of the preliminary silicon-based particles and a Li precursor to manufacture silicon-based particles; mixing and reacting the silicon-based particles with one or more selected from the group consisting of an Al precursor, a P precursor, and a precursor containing Al and P to provide a first coating layer; and forming a second coating layer from a carbon precursor on the silicon-based particles provided with the first coating layer, thereby providing a method for manufacturing a negative electrode active material.

[0097] When manufacturing a negative electrode active material by the method described above, after forming a first coating layer containing Li, Al, P, and O on the silicon-based particles, a second coating layer containing carbon can be formed on the silicon-based particles provided with the first coating layer by chemical vapor deposition (CVD) or the like.

[0098] The preliminary silicon-based particles can be manufactured by heating and vaporizing Si powder and SiO2 powder in a vacuum and then depositing the vaporized mixed gas.

[0099] The Si powder and SiO2 powder may be included in a weight ratio of 2:8 to 8:2, specifically, may be included in a weight ratio of 4:6 to 6:4 or 5:5.

[0100] Specifically, the mixed powder of the Si powder and SiO2 powder may be heat-treated at 1300°C to 1800°C, 1400°C to 1800°C, or 1400°C to 1600°C under vacuum.

[0101] The mixed gas vaporized by the heat treatment can be cooled under vacuum and deposited on a solid phase. Further, the deposited solid phase can be heat-treated in an inert atmosphere to manufacture preliminary silicon-based particles. The heat treatment may be performed at 500°C to 1000°C or 700°C to 900°C.

[0102] The formed preliminary silicon-based particles may exist in the form of SiO x (x = 1).

[0103] Next, after mixing the preliminary silicon-based particles and the Li precursor and then performing heat treatment, silicon-based particles containing a Li compound (doped with Li) can be produced. The Li precursor may be, for example, Li powder.

[0104] The step of heat treatment after mixing the preliminary silicon-based particles and Li powder may be performed at 700 °C to 900 °C for 4 hours to 6 hours, specifically, it may be performed at 800 °C for 5 hours.

[0105] The silicon-based particles formed by the heat treatment contain SiO x (0 < x < 2) and a Li compound.

[0106] The silicon-based particles may contain, as the aforementioned Li compound, lithium silicate, lithium silicide, or lithium oxide, etc.

[0107] The particle size of the silicon-based particles may be further adjusted by methods such as a ball mill, a jet mill, or air classification, and is not limited thereto.

[0108] As described above, at least a part of the surface of the silicon-based particles is provided with a lithium compound (lithium by-product). Specifically, in the process of forming preliminary silicon-based particles containing SiO x (0 < x < 2) and doping with Li to produce the aforementioned silicon-based particles, a lithium compound, that is, a lithium by-product formed by unreacted lithium, remains near the surface of the silicon-based particles.

[0109] Next, a first coating layer can be provided on at least a part of the silicon-based particles containing the Li compound.

[0110] The step of providing the first coating layer on at least a part of the silicon-based particles may include a step of mixing and reacting the silicon-based particles with one or more selected from the group consisting of an Al precursor, a P precursor, and a precursor containing Al and P.

[0111] In one embodiment, the step of providing the first coating layer on at least a part of the silicon-based particles may include a step of mixing and reacting the silicon-based particles with a precursor containing Al and P.

[0112] The precursor containing Al and P may be contained in an amount of 0.1 to 5 parts by weight based on 100 total parts by weight of the mixture. Specifically, it may be contained in an amount of 0.5 to 4 parts by weight, or may be contained in an amount of 1 to 3 parts by weight.

[0113] The precursor containing Al and P may be aluminum phosphate.

[0114] Specifically, i) a step of dry-mixing and heat-treating the silicon-based particles and aluminum phosphate, or ii) a step of mixing the silicon-based particles and aluminum phosphate in a solvent and then heat-treating to vaporize the solvent while reacting the silicon-based particles and aluminum phosphate may form the first coating layer on at least a part of the silicon-based particles. When forming the first coating layer by the method described above, the lithium by-products formed or remaining in the manufacturing process of the silicon-based particles can react with aluminum phosphate to easily form the first coating layer.

[0115] The aluminum phosphate is Al b P c O d It may be in the form of (0 < b ≤ 10, 0 < c ≤ 10, 0 < d ≤ 10). Specifically, it may be Al(PO3)3 or AlPO4, and is not limited thereto, and salts used in the industry for forming the first coating layer may be appropriately adopted.

[0116] In another embodiment, the step of providing the first coating layer on at least a part of the silicon-based particles may include the step of mixing and reacting the silicon-based particles, a precursor containing Al (aluminum precursor), and a precursor containing P (phosphorus precursor).

[0117] Specifically, iii) the step of dry-mixing and heat-treating the silicon-based particles, the aluminum precursor, and the phosphorus precursor, or iv) the step of mixing the silicon-based particles, the aluminum precursor, and the phosphorus precursor in a solvent and then heat-treating to vaporize the solvent while reacting the silicon-based particles, the aluminum precursor, and the phosphorus precursor may form the first coating layer on at least a part of the silicon-based particles. When forming the first coating layer by the method described above, lithium by-products, aluminum precursors, and phosphorus precursors formed in the manufacturing process of the silicon-based particles can be reacted to easily form the first coating layer.

[0118] The aluminum precursor is Al a O b aluminum oxide in the form of (0 < a ≤ 10, 0 < b ≤ 10), and specifically, it may be Al2O3.

[0119] Alternatively, the aluminum precursor may be aluminum hydroxide, aluminum nitrate, or aluminum sulfate, etc., and specifically, it may be Al(OH)3, Al(NO3)3·9H2O, or Al2(SO4)3, and is not limited thereto. Aluminum precursors used in the industry for forming the first coating layer may be appropriately adopted.

[0120] The phosphorus precursor is P c O d phosphorus oxide in the form of (0 < c ≤ 10, 0 < d ≤ 10) may be used.

[0121] Alternatively, the phosphorus precursor may be ammonium phosphate, diammonium phosphate, phosphoric acid, etc., specifically, it may be (NH4)3PO4, (NH4)2HPO4, H3PO4, or NH4H2PO4, and is not limited thereto. Any phosphorus precursor used in the art to form the first coating layer may be appropriately employed.

[0122] In another embodiment, the step of providing a first coating layer on at least a part of the silicon-based particles may include the step of mixing and reacting the silicon-based particles with a precursor containing Li, Al, P, and O (Li-Al-P-O-based precursor).

[0123] Specifically, v) the step of dry-mixing and heat-treating the silicon-based particles and the Li-Al-P-O-based precursor, or vi) the step of mixing the silicon-based particles and the Li-Al-P-O-based precursor in a solvent, followed by heat-treating to vaporize the solvent while reacting the silicon-based particles and the Li-Al-P-O-based precursor, may be used to form a first coating layer on at least a part of the silicon-based particles. When forming the first coating layer by the method described above, the Li-Al-P-O-based precursor can be directly introduced to form the first coating layer.

[0124] The Li-Al-P-O-based precursor is Li y Al z P w O v It may be in the form of (0 < y ≤ 10, 0 < z ≤ 10, 0 < w ≤ 10, 0 < v ≤ 10). Specifically, it may be a mixture or compound formed complexly from Li3PO4, AlPO4, Al(PO3)3, LiAlO2, etc., and is not limited thereto. Any configuration used in the art to form the first coating layer may be appropriately employed.

[0125] In the step of providing the first coating layer on at least a part of the silicon-based particles, the heat treatment may be performed at 500°C to 700°C, specifically, it may also be performed at 550°C to 650°C. However, it is not limited thereto and may vary depending on the salt or precursor used. When the heat treatment temperature is higher than the above range, the first coating layer is formed in a crystalline state, making it difficult for Li ions to enter and exit through the first coating layer, resulting in problems such as a decrease in resistance and life characteristics, as well as a decrease in capacity and / or efficiency. When the heat treatment temperature satisfies the above range, the reaction between the salt or precursor and the Li by-product occurs well, and the first coating layer comes to contain Li, so the durability of the formed negative electrode active material against moisture increases, the lithium diffusion resistance on the surface of the negative electrode active material decreases, and there is an effect of excellent discharge rate characteristics.

[0126] In the step of providing the first coating layer on at least a part of the silicon-based particles, it is preferable that the heat treatment temperature is lower than the temperature at which heat treatment is performed after mixing the preliminary silicon-based particles and the Li precursor.

[0127] The solvent may be water or ethanol, and is not limited thereto, and solvents used in the industry may be appropriately adopted.

[0128] The first coating layer formed on the silicon-based particles preferably contains Li y Al z P w O v (0 < y ≤ 10, 0 < z ≤ 10, 0 < w ≤ 10, 0 < v ≤ 10) phase, and the Li y Al z P w O v phase may be an amorphous phase.

[0129] The content regarding the first coating layer is as described above.

[0130] Next, a second coating layer can be provided on the surface of the silicon-based particles.

[0131] The second coating layer may be a carbon layer, and the carbon layer may be formed by using a chemical vapor deposition (CVD) method using a carbon-based substance, for example, a hydrocarbon gas, or by a method of carbonizing a substance serving as a carbon source.

[0132] Specifically, after the formed preliminary particles are introduced into a reactor, they may be formed by chemical vapor deposition (CVD) of a hydrocarbon gas at 500°C to 1200°C. The hydrocarbon gas may be at least one hydrocarbon gas selected from the group consisting of methane, ethane, propane, and acetylene, and may be heat-treated at 500°C to 900°C.

[0133] It is preferable that the heat treatment temperature during the chemical vapor deposition is lower than the temperature at which heat treatment is performed after mixing the preliminary silicon-based particles and the Li precursor.

[0134] Another embodiment of the present invention is a step of manufacturing preliminary silicon-based particles containing SiO x (0 < x < 2); a step of manufacturing silicon-based particles by heat-treating after mixing the preliminary silicon-based particles and a Li precursor; and a step of mixing and heat-treating the silicon-based particles with one or more selected from the group consisting of an Al precursor, a P precursor, and a precursor containing Al and P, and a carbon source, to provide a method for manufacturing a negative electrode active material.

[0135] When manufacturing the negative electrode active material by the method described above, by mixing the precursors of the first coating layer (Al precursor, P precursor, and precursor containing Al and P) and the precursor of the second coating layer (carbon source) and then carbonizing by heat treatment, the first coating layer and the second coating layer can be simultaneously formed on the silicon-based particles. <​​​​​​In the step of mixing at least one selected from the group consisting of the Al precursor, the P precursor, and the precursor containing Al and P with the carbon source and then performing heat treatment, it is preferable that the heat treatment temperature is lower than the temperature at which heat treatment is performed after mixing the preliminary silicon-based particles and the Li precursor.

[0138] Specifically, the heat treatment may be performed at 500 °C to 700 °C, and specifically may be performed at 550 °C to 650 °C. However, it is not limited thereto and may vary depending on the salt or precursor used. When the heat treatment temperature is higher than the above range, the first coating layer and the second coating layer are formed in a crystalline state, making it difficult for Li ions to enter and exit, resulting in a decrease in resistance and life characteristics, and a possible decrease in capacity and / or efficiency.

[0139] <Negative electrode> The negative electrode according to an embodiment of the present invention may include the above-described negative electrode active material. Specifically, the negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The negative electrode active material layer may include the negative electrode active material. Further, the negative electrode active material layer may further include a binder, a thickener, and / or a conductive material.

[0140] The negative electrode active material layer may 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 side of the current collector, followed by drying and rolling.

[0141] The negative electrode slurry may further include an additional negative electrode active material.

[0142] As the additional negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; SiO βExamples include lithium-doped and dedoped metal oxides such as (0<β<2), SnO2, vanadium oxide, lithium titanium oxide, and lithium vanadium oxide; or composites containing the metallic compound and carbonaceous material, such as Si-C composites or Sn-C composites. One or more of these mixtures may be used. A metallic lithium thin film may also be used as the negative electrode active material. As for the carbon material, either low-crystallinity carbon or high-crystallinity carbon may be used. Examples of low-crystalline carbon include soft carbon and hard carbon, while examples of high-crystalline carbon include amorphous, plate-like, flaky, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0143] The additional negative electrode active material may be a carbon-based negative electrode active material.

[0144] In one embodiment of the present invention, the weight ratio of the negative electrode active material contained in the negative electrode slurry to the additional negative electrode active material may be 10:90 to 90:10, and more specifically, it may be 10:90 to 50:50.

[0145] 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.

[0146] 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. A pH within this range of the negative electrode slurry has the effect of stabilizing the rheological properties of the slurry. Conversely, 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 in the slurry.

[0147] The negative electrode current collector is not particularly limited, as long as it does not cause 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.

[0148] 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 substances are substituted with Li, Na, or Ca, and may also contain various copolymers thereof.

[0149] The conductive material is not particularly limited as long as it does not cause 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.

[0150] 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 used as appropriate.

[0151] 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, specifically 5:95 to 30:70, or 10:90 to 20:80.

[0152] In one embodiment of the present invention, the total negative electrode active material contained in the negative electrode slurry may be 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.

[0153] 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.

[0154] 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.

[0155] 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.

[0156] 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.

[0157] In one embodiment of the present invention, the solid content weight 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.

[0158] <Secondary battery> A secondary battery according to one embodiment of the present invention may include a negative electrode according to the embodiment described above. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, 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.

[0159] 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.

[0160] In the positive electrode, the positive electrode current collector is not particularly limited as long as it does not cause 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, or nonwoven fabric.

[0161] 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 ≤ 0.5); chemical formula LiMn 2-c3 M c3 Lithium manganese composite oxides represented as O2 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, satisfying 0.01 ≤ c3 ≤ 0.1) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); or LiMn2O4 in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion, etc., are examples, but are not limited thereto. The positive electrode may be Li metal.

[0162] 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.

[0163] In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and can be used without particular limitation as long as it has electronic conductivity without causing a chemical change in the battery that is constructed. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these alone or a mixture of two or more may be used.

[0164] Furthermore, the positive electrode binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more may be used.

[0165] The separator separates the negative and positive electrodes and provides a passage for lithium ions to move. Generally, any separator commonly used in secondary batteries can be used 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 those made from polyolefin polymers like 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 those made from 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 they may be selectively used as single-layer or multi-layer structures.

[0166] 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.

[0167] Specifically, the electrolyte may contain a non-aqueous organic solvent and a metal salt.

[0168] 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.

[0169] 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 electrical conductivity can be produced, and therefore they can be used even more preferably.

[0170] 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:

[0171] In addition to the components of the electrolyte, the electrolyte may further contain one or more additives for purposes such as 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, hexaphosphate 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.

[0172] According to another embodiment of the present invention, a battery module and a battery pack including the secondary battery as a unit cell are provided. Since the battery module and battery pack include the secondary battery having high capacity, high rate characteristics and cycle characteristics, they can be used as a power source for medium to large devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems. [Examples]

[0173] The following are preferred embodiments to aid in understanding the present invention. However, these embodiments are merely illustrative examples, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope of this description and the technical concept, and such variations and modifications will naturally fall within the scope of the appended claims.

[0174] <Examples and Comparative Examples> [Example 1] 100g of a powder mixture of Si and SiO2 in a 1:1 molar ratio was vacuum-heated in a reaction furnace at a sublimation temperature of 1,400°C. The vaporized Si-SiO2 mixture was then reacted in a vacuum cooling zone with a cooling temperature of 800°C to condense into a solid phase. Subsequently, pre-silicon particles were produced by heat treatment in an inert atmosphere at 800°C. After adding these pre-silicon particles, 15 SUS ball media were added using a ball mill and ground for 3 hours to a particle size of 6 μm (D 50 We manufactured silicon-based particles of the following size.

[0175] 90 g of the aforementioned silicon-based particles were mixed with 10 g of Li metal powder, and heat-treated in an inert atmosphere at a temperature of 800°C to produce Li-doped silicon-based particles.

[0176] 98.5 g of the aforementioned Li-doped silicon-based particles were mixed with 1.5 g of Al(PO3)3, and then heat-treated at 600°C to produce silicon-based particles in which a first coating layer containing Li, Al, and P was formed on the surface of the silicon-based particles.

[0177] Subsequently, while maintaining an inert atmosphere by flowing Ar gas, the silicon-based particles on which the first coating layer has been formed are positioned in the hot zone of the CVD apparatus, and using Ar as a carrier gas, the methane is blown into the 700°C hot zone. -1 The reaction was carried out in Torr for 20 minutes to form a second coating layer (carbon layer) on the surface of the silicon-based particles.

[0178] The D of the negative electrode active material 50 The surface area is 6 μm, and the BET specific surface area is 2.5 m². 2 It was / g.

[0179] The negative electrode active material has a first coating layer containing Li, Al, P, and O between a second coating layer containing silicon-based particles and carbon. When the negative electrode active material was analyzed by ICP, the content of Li, Al, and P was 9.5 wt%, 0.15 wt%, and 0.5 wt%, respectively, based on 100 wt% of the total negative electrode active material.

[0180] [Example 2] The product was manufactured in the same manner as in Example 1, except that 5 g of Al(PO3)3 was mixed with 95 g of lithium-doped silicon-based particles and then heat-treated.

[0181] During ICP analysis of the anode active material, the content of Li, Al, and P was 9.0 wt%, 0.5 wt%, and 1.8 wt%, respectively, based on 100 wt% of the total anode active material.

[0182] [Example 3] The product was manufactured in the same manner as in Example 1, except that 99.5 g of lithium-doped silicon-based particles were mixed with 0.5 g of Al(PO3)3 and then heat-treated.

[0183] During ICP analysis of the anode active material, the content of Li, Al, and P was 9.5 wt%, 0.05 wt%, and 0.18 wt%, respectively, based on 100 wt% of the total anode active material.

[0184] [Comparative Example 1] The negative electrode active material was manufactured in the same manner as in Example 1, except that a carbon layer was first formed on the surface of the silicon-based particles before doping them with Li.

[0185] In Comparative Example 1, the negative electrode active material was formed by creating a coating layer containing Li, Al, P, and O after the formation of the carbon layer, thus forming the coating layer in the reverse order compared to Examples 1-3.

[0186] During ICP analysis of the anode active material, the content of Li, Al, and P was 9.5 wt%, 0.15 wt%, and 0.5 wt%, respectively, based on 100 wt% of the total anode active material.

[0187] [Comparative Example 2] The same method as in Comparative Example 1 was used, except that 90 g of lithium-doped silicon-based particles were mixed with 10 g of Al(PO3)3 and then heat-treated.

[0188] During ICP analysis of the anode active material, the content of Li, Al, and P was 9.0 wt%, 1.0 wt%, and 3.0 wt%, respectively, based on 100 wt% of the total anode active material.

[0189] [Comparative Example 3] The negative electrode active material was manufactured in the same manner as in Example 1, except that a second coating layer was not formed.

[0190] [Comparative Example 4] The process of producing lithium-doped silicon-based particles was carried out in the same manner as in Example 1, up to the point where 10 g of Li metal powder was added to 90 g of the aforementioned silicon-based particles and heat-treated in an inert atmosphere at a temperature of 800°C.

[0191] When 1.5 g of Al(PO3)3 was mixed with 98.5 g of the aforementioned silicon-based particles, 5 g of pitch was added, and then the mixture was heat-treated at 600°C to produce a negative electrode active material in which a first coating layer containing Li, Al, P, and C was formed on the surface of the silicon-based particles.

[0192] Subsequently, the negative electrode active material was produced by heat treatment at 700°C in an argon gas atmosphere for 20 minutes.

[0193] [Table 1]

[0194] The content of the aforementioned elements was confirmed by ICP analysis using an inductively coupled plasma atomic emission spectrometer (ICP-OES, AVIO 500, manufactured by Perkin-Elmer 7300).

[0195] The D of the negative electrode active material 50 The PSD (Photon Scale Degradation) was analyzed using a microtrac device.

[0196] The specific surface area was measured using a BET measuring device (BEL-SORP-MAX, Nippon Bell) by degassing the gas at 200°C for 8 hours and then performing N2 adsorption / desorption at 77K.

[0197] <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.

[0198] A mixture was prepared by mixing the aforementioned negative electrode active material, carbon black as a conductive material, and PAA (polyacrylic acid) as a binder in a weight ratio of 80:10:10. Then, 7.8g of distilled water was added to 5g of the mixture and stirred to produce a negative electrode slurry. The negative electrode slurry was applied to a copper (Cu) metal thin film, which was a negative electrode current collector with a thickness of 20μm, and dried. During this process, the temperature of the circulating air was 60°C. Next, the film was rolled (rolled in a roll press) and dried in a vacuum oven at 130°C for 12 hours to produce a negative electrode.

[0199] The manufactured negative electrode and 1.7671 cm 2A 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 electrode and the negative electrode, dissolving vinylene carbonate at a volume ratio of 7:3 in a mixed solution of ethyl methyl carbonate (EMC) and ethylene carbonate (EC), dissolving 0.5 parts by weight in vinylene carbonate, and injecting an electrolyte solution containing 1M LiPF6.

[0200] The manufactured batteries were subjected to charging and discharging tests to evaluate their discharge capacity, initial efficiency, and capacity retention rate, and these results are shown in Table 2 below.

[0201] The first and second cycles were charged and discharged at 0.1C, and from the third to the 49th cycle, they were charged and discharged at 0.5C. The 50th cycle ended in a charged state (lithium was in the negative electrode).

[0202] Charging conditions: CC (constant current) / CV (constant voltage) (5mV / 0.005C current cut-off) Discharge condition: CC (constant current) condition 1.5V

[0203] The discharge capacity (mAh / g) and initial efficiency (%) were derived from the results of a single charge-discharge cycle. Specifically, the initial efficiency (%) was derived by the following calculation. Initial efficiency (%) = (Discharge capacity per cycle / Charge capacity per cycle) × 100

[0204] The capacity retention rates were derived using the following calculations. Capacity retention rate (%) = (49 discharge capacity / 1 discharge capacity) × 100

[0205] <Experimental Example: Evaluation of Shear Viscosity Characteristics> As part of the process evaluation, the change in shear viscosity at a shear rate of 1 Hz was measured for a slurry produced by mixing graphite, the aforementioned negative electrode active material, carbon black, CMC, and SBR in a weight ratio of 77:20:1:1:1, and the results are shown in Table 2 below. Specifically, the change in shear viscosity (%) was derived using the following formula. Change in shear viscosity (%) = ((Shear viscosity of slurry after 48 hours - Shear viscosity of slurry immediately after mixing) / Shear viscosity of slurry immediately after mixing) × 100

[0206] [Table 2]

[0207] The negative electrode active material according to the present invention has a structure in which layers containing Li, Al, P, and O are coated on silicon-based particles so that they are closer to the carbon layer than the silicon-based particles. Examples 1 to 3 using the negative electrode active material of the present invention demonstrated excellent discharge capacity, initial efficiency, and capacity retention, as well as remarkably low slurry shear viscosity and excellent processability. This is thought to be because the layers containing Li, Al, P, and O located close to the surface of the silicon-based particles easily prevent reaction with water in the slurry, the hydrophobic carbon layer is located on the outermost layer to further block contact between the negative electrode active material and water, improving the processability of the aqueous slurry, and the highly conductive carbon is located on the outermost layer, which is advantageous for achieving overall capacity / efficiency.

[0208] In contrast, in Comparative Examples 1 and 2, a carbon layer is coated as a first coating layer close to the silicon-based particles, and a layer containing Li, Al, P, and O is coated on top of that. Therefore, it was confirmed that it is difficult to remove lithium byproducts generated during Li doping of the silicon-based particles, and because the carbon layer is not present on the outermost layer, side reactions are likely to occur in the slurry, making it difficult to achieve the processability of the slurry and the capacity / efficiency of the battery.

[0209] Furthermore, Comparative Example 3 corresponds to a case where layers containing Li, Al, P, and O are coated as single layers on silicon-based particles without a second coating layer (carbon layer), while Comparative Example 4 corresponds to a case where, without distinguishing between the first and second coating layers, the material of the first coating layer and the material of the second coating layer are coated as a single layer (a layer containing Li, Al, P, O, and C). Comparative Examples 3 and 4 are composed of single layers, making contact between the negative electrode active material and water more likely, and it was confirmed that they exhibit inferior effects compared to Comparative Examples 1 and 2 in terms of slurry processability and battery capacity / efficiency.

[0210] Therefore, the present invention provides a negative electrode active material comprising silicon-based particles; a first coating layer containing Li, Al, P, and O; and a second coating layer containing carbon, thereby significantly improving the overall aqueous processability, discharge capacity, efficiency, and capacity retention rate. [Explanation of symbols]

[0211] 1. Silicon-based particles 2 ···First coating layer 3 ···Li y Al z P w O v phase 4 ···Carbon 5 ···Second coating layer

Claims

1. SiO ｘ (0 < x < 2) and silicon-based particles containing Li compounds; A first coating layer provided on at least a portion of the silicon-based particles; and A second coating layer provided on at least a portion of the first coating layer Includes, The first coating layer comprises Li, Al, P, and O. The anode active material wherein the second coating layer contains carbon.

2. The negative electrode active material according to claim 1, wherein the second coating layer further comprises Li, Al, P, and O.

3. The first coating layer is Li ｙ Al ｚ P ｗ O ｖ The negative electrode active material according to claim 1, comprising a phase (0 < y ≤ 10, 0 < z ≤ 10, 0 < w ≤ 10, 0 < v ≤ 10).

4. The negative electrode active material according to claim 1, wherein the first coating layer comprises one or more selected from the group consisting of aluminum oxide, phosphorus oxide, lithium oxide, aluminum phosphate, lithium salt, lithium phosphate, and lithium aluminate.

5. The second coating layer is a carbon layer, and Li ｙ Al ｚ P ｗ O ｖ (0 < y ≤ 10, 0 < z ≤ 10, 0 < w ≤ 10, 0 < v ≤ 10) phase is included. The negative electrode active material according to claim 1.

6. The negative electrode active material according to claim 1, wherein the carbon content is 45 parts by weight or more and 95 parts by weight or less, based on a total of 100 parts by weight of the first coating layer and the second coating layer.

7. The negative electrode active material according to claim 1, wherein the carbon content is 70 parts by weight or more based on 100 parts by weight of the second coating layer.

8. The negative electrode active material according to claim 1, wherein the first coating layer is provided adjacent to the silicon-based particles.

9. The negative electrode active material according to claim 1, wherein the second coating layer is provided on the outermost surface of the negative electrode active material.

10. The negative electrode active material according to claim 1, wherein the second coating layer is an amorphous carbon layer.

11. The Li ｙ Al ｚ P ｗ O ｖ The negative electrode active material according to claim 3, wherein the (0 < y ≤ 10, 0 < z ≤ 10, 0 < w ≤ 10, 0 < v ≤ 10) phase is included in an amount of 0.1 parts by weight or more and 30 parts by weight or less, based on 100 parts by weight of the total negative electrode active material.

12. The negative electrode active material according to claim 1, wherein the second coating layer is contained in an amount of 0.1 parts by weight or more and 50 parts by weight or less, based on a total of 100 parts by weight of the negative electrode active material.

13. The negative electrode active material according to claim 1, wherein Li is contained in an amount of 0.1 parts by weight or more and 40 parts by weight or less, based on a total of 100 parts by weight of the negative electrode active material.

14. SiO ｘ A step of producing preliminary silicon-based particles including (0 < x < 2); A step of producing silicon-based particles by mixing the aforementioned preliminary silicon-based particles and a Li precursor and then heat-treating them; A step of providing a first coating layer by either mixing and reacting the silicon-based particles with an Al precursor and a P precursor, or mixing and reacting the silicon-based particles with a precursor containing Al and P; and Steps to form a second coating layer from a carbon precursor on silicon-based particles on which the first coating layer is provided. A method for producing a negative electrode active material according to any one of claims 1 to 13, including the method described in any one of claims 1 to 13.

15. A negative electrode comprising the negative electrode active material according to any one of claims 1 to 13.

16. A secondary battery comprising the negative electrode described in claim 15.

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