Anode active material, anode including the same, secondary battery including the same, and method for producing anode 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 of the filing dates 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, the entire contents of which are incorporated herein by reference.

[0002] 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. [Background technology]

[0003] In recent years, with the rapid spread of electronic devices using batteries, such as mobile phones, notebook computers, and electric vehicles, the demand for secondary batteries that are small, lightweight, and have a relatively high capacity is rapidly increasing. In particular, lithium secondary batteries are lightweight and have high energy density, and are in the spotlight as a driving power source for portable devices. As a result, research and development efforts are being actively made to improve the performance of lithium secondary batteries.

[0004] In general, a lithium secondary battery includes a positive electrode, a negative electrode, a separator between the positive electrode and the negative electrode, an electrolyte, an organic solvent, etc. In addition, the positive electrode and the negative electrode may have active material layers formed on current collectors, each of which includes a positive electrode active material and a negative electrode active material. In general, the positive electrode includes LiCoO 2 , LiMn 2 O 4 In the negative electrode, a lithium-containing metal oxide such as the above is used as the positive electrode active material, and a lithium-free carbon-based active material or silicon-based active material is used as the negative electrode active material.

[0005] Among negative electrode active materials, silicon-based active materials have been attracting attention because they have higher capacity and excellent high-speed charging characteristics compared to carbon-based active materials. However, silicon-based active materials have the disadvantage of low initial efficiency due to large volume expansion / contraction during charging / discharging and 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 even 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, the state of the manufactured negative electrode becomes poor, and there is a problem that 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 the negative electrode slurry containing the 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 SiOx (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, 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.

Advantages of the Invention

[0014] The negative electrode active material according to 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 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 water-based slurry, and there is an effect that highly conductive carbon exists on the outermost layer, which is advantageous for realizing capacity / efficiency.

[0016] In addition, the lithium by-products contained in the silicon-based particles can be effectively removed during the formation of the first coating layer, and the formed first coating layer effectively covers unreacted lithium by-products, thereby preventing the lithium by-products or silicate in the silicon-based particles from reacting with the moisture in the slurry to degrade the physical properties of the slurry. In addition, since the first coating layer contains Li, the lithium diffusion resistance on the surface of the negative active material is reduced, resulting in excellent discharge rate capability.

[0017] Therefore, a negative electrode including the negative electrode active material according to one embodiment of the present invention and a secondary battery including the negative electrode have the effect of improving the discharge capacity, initial efficiency, resistance performance, and / or life characteristics of the battery. [Brief description of the drawings]

[0018] [Figure 1] 1 is a schematic diagram showing the structure of a negative electrode active material according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] This specification will be explained in more detail below.

[0020] In this specification, when a part is said to "comprise" a certain component, this means that it may further include other components, not excluding other components, unless specifically stated to the contrary.

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

[0022] The terms and words used in this specification should not be interpreted in a limited manner to their ordinary or dictionary meanings, but should be interpreted in a manner that is consistent with the technical idea of ​​the present invention, based on the principle that the inventors can appropriately define the concepts of terms in order to best describe their invention.

[0023] As used herein, the singular expression of a term includes the plural expression unless the context clearly indicates otherwise.

[0024] In the present specification, the crystallinity of the structure contained in the negative electrode active material may be confirmed by X-ray diffraction analysis. The X-ray diffraction analysis may be performed using an XRD (X-ray diffraction) analysis device (product name: D4-endavor, manufacturer: Bruker), and in addition to the above device, any device used in the industry may be appropriately adopted.

[0025] In this specification, the presence or absence of an element in the negative electrode active material and the content of the element can be confirmed by ICP analysis, and the ICP analysis can be performed using an inductively coupled plasma optical 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 ) can be measured, for example, by using a laser diffraction method. The laser diffraction method generally allows measurement of particle sizes from the submicron range to about several mm, and can provide results with high reproducibility and high resolution.

[0027] Preferred embodiments of the present invention will be described in detail below. However, the embodiments of the present invention may be modified in various ways, 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 silicon oxide (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, to provide 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 SiO 2 , and the Si may form a phase. For example, the SiO x (0 < x < 2)) may be a composite containing amorphous SiO 2 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 of improving the initial efficiency.

[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 ratio of the irreversible phase (for example, SiO 2 ) of the silicon 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 represented by Li a Si b O c (2 ≤ a ≤ 4, 0 < b ≤ 2, 2 ≤ c ≤ 5), and can be classified into crystalline lithium silicate and amorphous lithium silicate. The crystalline lithium silicate may exist in the form of at least one lithium silicate selected from the group consisting of Li 2 SiO 3 , Li 4 SiO 4 , and Li 2 Si 2 O 5 , and the amorphous lithium silicate may consist of a composite 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.

[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 Li element can be confirmed by ICP analysis. Specifically, a certain amount (about 0.01 g) of the negative electrode active material is taken and transferred to a platinum crucible, and nitric acid, hydrofluoric acid, and sulfuric acid are added to completely decompose it on a hot plate. Then, using an inductively coupled plasma optical emission spectrometer (ICPAES, Perkin-Elmer 7300), the intensity of a standard solution prepared using a standard solution (5 mg / kg) is measured at a wavelength specific to the element to be analyzed, and a reference calibration curve is created. Then, the pretreated sample solution and a blank sample are introduced into the instrument, and the intensity of each is measured to calculate the actual intensity, and the concentration of each component is calculated based on the created calibration curve, and the total is converted to a theoretical value, so that the content of the elements in the manufactured negative electrode active material can be analyzed.

[0036] In one embodiment of the present invention, the silicon-based particles may include additional metal atoms. The metal atoms may be present in the silicon-based particles in at least one form 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, the first coating layer comprising Li, Al, P, and O.

[0038] As described above, the first coating layer containing Li, Al, P, and O is provided on the silicon-based particles, which reduces the reactivity of silicate, which is highly reactive with bases, and can easily block contact between the silicon-based particles and the outside, thereby 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 be in a form that partially covers the surface of the particles, or entirely covers the surface of the particles. The shape of the first coating layer may be an island type or a thin film type, but is not limited thereto.

[0040] The first coating layer may be provided adjacent to the silicon-based particles. That is, the first coating layer may be coated 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 to 1 parts by weight based on a total of 100 parts by weight of the negative electrode active material. Specifically, the Al may be included in an amount of 0.02 to 0.9 parts by weight, 0.03 to 0.85 parts by weight, or 0.05 to 0.8 parts by weight. 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, the P may be included in an amount of 0.05 parts by weight to 2.5 parts by weight based on a total of 100 parts by weight of the negative active material. Specifically, the P may be included in an amount of 0.1 parts by weight to 2 parts by weight, 0.15 parts by weight to 1.9 parts by weight, or 0.18 parts by weight to 1.8 parts by weight. The lower limit of the P content 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 0.05 parts by weight or more and 2 parts by weight or less based on 100 parts by weight of the total of the negative active material. Specifically, the Li may be 0.1 parts by weight or more and 1.5 parts by weight or less, or 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 O content in the first coating layer may be 0.5 to 2 parts by weight based on a total of 100 parts by weight of the negative active material. Specifically, the O content in the first coating layer may be 0.6 to 1.9 parts by weight, or 0.7 to 1.8 parts by weight. The lower limit of the O 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 include 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.

[0048] In one embodiment of the present invention, the first coating layer may include 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, Li y Al z P w O v phase included in the first coating layer may include a mixture or compound formed from Li 3 PO 4 , AlPO 4 , Al(PO 3 ) 3 , or LiAlO 2 etc., but is not limited thereto.

[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 include 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 contains Li 2 O, LiOH, and Li 2 CO 3It may further contain one or more selected from the group consisting of. Generally, the substances remaining in the process of doping silicon-based particles with lithium are exposed to moisture and air, and Li 2 O, LiOH, and Li 2 CO 3 and the like can form lithium by-products. Therefore, the first coating layer may be in a form further containing one or more selected from the group consisting of Li 2 O, LiOH, and Li 2 CO 3 .

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

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

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

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

[0056] The first coating layer may be formed by dry-mixing and heat-treating 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, or by reacting while vaporizing the solvent after mixing in a 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, and 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 part by weight, 0.3 part by weight, 0.4 part by weight, 0.5 part by weight, 0.8 part by weight, 1 part by weight, 1.2 parts by weight, 1.4 parts by weight, or 1.5 part 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, partially covers or completely covers the surface of the first coating layer. Examples of the shape of the second coating layer include an island type or a 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 on 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] The second coating layer may be further provided on the area of ​​the silicon-based particle surface where the first coating layer is not provided, i.e., the second coating layer may be provided adjacent to the surface of the silicon-based particle surface where the first coating layer is not provided, in the form of silicon-based particle-second coating layer.

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

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

[0066] The crystalline carbon may further improve the electrical conductivity of the negative electrode active material. The crystalline carbon may include at least one selected from the group consisting of fullerene, carbon nanotube, 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 substances as a source of a chemical vapor deposition process.

[0068] The other carbonized organic matter may be a carbonized organic matter 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 (0 < y ≤ 10, 0 < z ≤ 10, 0 < w ≤ 10, 0 < v ≤ 10) and may further contain a phase in such a form.

[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 That is, in the process of coating the silicon-based particles with a carbon layer, the components of the first coating layer may be mixed and coated together, or the first coating layer may be formed, and then the components of the first coating layer (e.g., Li y Al z P w O v phase) and Li inside the carbon layer. y Al z P w O v A second coating layer may be formed that includes the phase.

[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, components of the first coating layer may be included during the process of forming the second coating layer, and a small amount of components of the first coating layer may be included inside the second coating layer.

[0076] In one embodiment of the present specification, the second coating layer may be provided on the outermost layer of the negative active material. Specifically, the carbon component of the second coating layer may be provided on the outermost layer of the negative active material. When carbon is present on the outermost layer of the negative active material as described above, the hydrophobicity of carbon acts more effectively than when carbon is not present on the outermost layer of the negative active material, so that the contact between the negative active material and water can be further blocked, 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 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. Specifically, the second coating layer may be included 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 amount is within the above range, 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 0.1 parts by weight to 50 parts by weight, 0.1 parts by weight to 30 parts by weight, or 0.1 parts by weight to 20 parts by weight based on 100 parts by weight of the total of the negative electrode active material. More specifically, the carbon may be 0.5 parts by weight to 15 parts by weight, 1 parts by weight to 10 parts by weight, 1 parts by weight to 8 parts by weight, or 1 parts by weight to 5 parts by weight. When the above range is satisfied, the capacity and efficiency of the negative electrode active material can be prevented from decreasing. 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 parts 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, specifically, 5 nm to 300 nm. When the thickness satisfies the above range, the conductivity of the negative electrode active material is improved, the volume change of the negative electrode active material is easily suppressed, and the side reaction between the electrolyte and the negative electrode active material is suppressed, thereby improving the initial efficiency and / or life of the battery.

[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 part 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 part by weight or more and 20 parts by weight or less, 0.2 part by weight or more and 15 parts by weight or less, 0.3 part by weight or more and 10 parts by weight or less, or 0.4 part 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 part by weight, 0.2 part by weight, 0.3 part by weight, 0.4 part by weight, or 0.5 part 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 with high reactivity with a base can be reduced, 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, it has an adverse effect on electrical conductivity, and there is a problem that it is difficult to realize capacity / efficiency during charge and discharge. When it is contained less than the above range, the reactivity of the silicate cannot be reduced, and there is a problem that it is difficult to improve the water-based processability of the slurry.

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

[0084] FIG. 1 is a schematic diagram showing the structure of an anode active material according to one embodiment of the present invention, illustrating a configuration in which a silicon-based particle 1, a first coating layer 2, and a second coating layer 5 are provided. Specifically, a first coating layer 2 may be provided on the silicon-based particle 1, and a second coating layer 5 may be provided on the first coating layer 2. In this case, the second coating layer 5 may include carbon 4 and may have Li y Al z P w O v Phase 3 may further 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 100 parts by weight of the total of the first coating layer and the second coating layer. 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 carbon content is 45 parts by weight or more in the total coating layer as described above, the hydrophobic carbon layer is present in the outermost layer, which further blocks contact with water, thereby improving the processability of the aqueous slurry, and the carbon with high conductivity is present in the outermost layer, which is advantageous in achieving capacity / efficiency. On the other hand, if the carbon content is less than the above range, the negative electrode active material cannot be effectively prevented from contacting water, making it difficult to improve the processability of the aqueous slurry. If the carbon content exceeds the above range, the material is excessively hydrophobic, resulting in poor dispersibility during preparation 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 the above ranges, the first coating layer and the second coating layer can effectively cover the silicon-based particles, and side reactions in the slurry can be efficiently suppressed, and capacity and / or efficiency can be stably achieved. On the other hand, if the content of the first coating layer is excessively higher than that of the second coating layer, it is difficult to achieve capacity or efficiency, and if the content of the second coating layer is excessively higher than that of the first coating layer, it is 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 parts by weight or more and 150 parts by weight or less 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. In addition, 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 range, the second coating layer and the first coating layer can effectively cover the silicon-based particles, thereby efficiently suppressing side reactions in the slurry, and the capacity and / or efficiency can be stably achieved.

[0088] In one embodiment of the present invention, a lithium by-product may be present on the silicon-based particle. Specifically, the lithium by-product may be present between the silicon-based particle and the first coating layer, within the first coating layer, or on the first coating layer. The lithium by-product may also be present between the silicon-based particle and the second coating layer.

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

[0090] The lithium by-product is Li 2 O, LiOH, and Li 2 CO 3 The composition may include one or more selected from the group consisting of:

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

[0092] The lithium by-product may be included in an amount of 5 parts by weight or less based on 100 parts by weight of the total negative electrode active material. Specifically, the lithium by-product may be included in an amount 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, the lithium by-product may be included in an amount of 0.1 to 0.8 parts by weight, or 0.1 to 0.5 parts by weight. When the content of the lithium by-product satisfies the above range, the side reaction in the slurry can be reduced, and the viscosity change can be reduced to improve the aqueous processability. On the other hand, when the content of the lithium by-product is higher than the above range, the slurry shows basicity during formation, which causes side reactions and changes in viscosity, resulting in problems in aqueous processability.

[0093] The content of the lithium by-product may be calculated by measuring the amount of the HCl solution in a specific range where the pH changes during titration of the aqueous solution containing the negative active material with the HCl solution using a titrator.

[0094] The average particle size (D 50 ) may be 0.1 μm to 30 μm, specifically 1 μm to 20 μm, and more specifically 1 μm to 10 μm. When the above range is satisfied, the structure of the active material during charging and discharging can be stabilized, the problem of the volume expansion / contraction level increasing due to the particle size being too large can be prevented, and the problem of the initial efficiency decreasing due to the particle size being too small can be prevented.

[0095] The BET specific surface area of ​​the negative electrode active material is 1 m 2 / g~100m 2 / g, specifically 1m 2 / g~70m 2 / g, more specifically 1m 2 / g~50m 2 / g, for example 2m 2 / g~30m 2 When the content of the electrolyte is within this range, side reactions with the electrolyte during charging and discharging of the battery can be reduced, thereby improving the life characteristics of the battery.

[0096] <Method for manufacturing negative electrode active material> One embodiment of the present invention provides a method for manufacturing a negative electrode active material, comprising: manufacturing preliminary silicon-based particles containing SiO x (0 < x < 2); manufacturing silicon-based particles by heat-treating the mixture of the preliminary silicon-based particles and a Li precursor; 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.

[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 SiO 2 powder under vacuum and then depositing the vaporized mixed gas.

[0099] The Si powder and SiO 2 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 SiO 2 powder may be heat-treated under vacuum at 1300°C to 1800°C, 1400°C to 1800°C, or 1400°C to 1600°C.

[0101] The vaporized mixed gas by the heat treatment can be cooled under vacuum and deposited into 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 (Li-doped) 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 ball mill, jet mill, or air classification, but 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 a 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 a 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 part by weight 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 part by weight to 4 parts by weight, or may be contained in an amount of 1 part by weight to 3 parts by weight.

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

[0114] Specifically, i) a step of dry-mixing the silicon-based particles and aluminum phosphate and then heat-treating them, or ii) a step of mixing the silicon-based particles and aluminum phosphate in a solvent, followed by heat-treating to vaporize the solvent while reacting the silicon-based particles and aluminum phosphate, 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 lithium by-products formed or remaining in the manufacturing process of the silicon-based particles can be reacted 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, Al(PO 3 ) 3 Or AlPO 4It may be so, but not limited thereto, and salts used in the art to form the first coating layer may be appropriately employed.

[0116] In another embodiment, the step of providing a 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, a precursor containing Al (aluminum precursor), and a precursor containing P (phosphorus precursor).

[0117] Specifically, iii) a step of dry-mixing and heat-treating the silicon-based particles, the aluminum precursor, and the phosphorus precursor, or iv) a 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 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, 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 (0 < a ≤ 10, 0 < b ≤ 10) aluminum oxide in the form may be used, specifically, Al 2 O 3 may be used.

[0119] Alternatively, the aluminum precursor may be aluminum hydroxide, aluminum nitrate, or aluminum sulfate, etc., specifically, Al(OH) 3 , Al(NO 3 ) 3 ·9H 2 O, or Al 2 (SO 4 ) 3 may be used, and not limited thereto, and aluminum precursors used in the art to form the first coating layer may be appropriately employed.

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

[0121] Alternatively, the phosphorus precursor may be ammonium phosphate, diammonium phosphate, phosphoric acid, etc. Specifically, (NH 4 ) 3 PO 4 , (NH 4 ) 2 HPO 4 , H 3 PO 4 , or NH 4 H 2 PO 4 and is not limited thereto. Phosphorus precursors used in the art for forming the first coating layer may be appropriately employed.

[0122] In yet another embodiment, the step of providing the first coating layer on at least a portion of the silicon-based particles may include 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) dry-mixing and heat-treating the silicon-based particles and the Li-Al-P-O-based precursor, or vi) mixing the silicon-based particles and the Li-Al-P-O-based precursor in a solvent and then heat-treating to vaporize the solvent while reacting the silicon-based particles and the Li-Al-P-O-based precursor may form the first coating layer on at least a portion 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 vIt may be in the form of (0 < y ≤ 10, 0 < z ≤ 10, 0 < w ≤ 10, 0 < v ≤ 10). Specifically, Li 3 PO 4 , AlPO 4 , Al(PO 3 ) 3 , or a mixture or compound formed complexly from LiAlO 2 etc., and is not limited thereto. You may appropriately adopt a configuration used in the industry to form the first coating layer.

[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 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, and it becomes difficult for Li ions to enter and exit through the first coating layer. Therefore, there are problems such as a decrease in resistance and life characteristics, and 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. As a result, 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 that the discharge rate characteristic is excellent.

[0126] In the step of providing the first coating layer on at least a part of the silicon-based particles, the heat treatment temperature is preferably 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. You may appropriately adopt a solvent used in the industry.

[0128] The first coating layer formed on the silicon-based particles preferably contains Li y Al z P wO v (0 < y ≤ 10, 0 < z ≤ 10, 0 < w ≤ 10, 0 < v ≤ 10) phase, including Li y Al z P w O v The 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 introducing the formed preliminary particles into a reactor, chemical vapor deposition (CVD) may be performed with 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 also be heat-treated at 500°C to 900°C.

[0133] The heat treatment temperature during the chemical vapor deposition is preferably 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 method for manufacturing a negative electrode active material, including the steps of: manufacturing preliminary silicon-based particles containing SiO x (0 < x < 2); heat-treating after mixing the preliminary silicon-based particles and a Li precursor to manufacture silicon-based particles; and 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.

[0135] When producing the negative electrode active material by the above-mentioned method, the precursor 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) are mixed and then carbonized by heat treatment, whereby the first coating layer and the second coating layer can be simultaneously formed on the silicon-based particles.

[0136] The silicon-based particles, the Al precursor, the P precursor, the precursor containing Al and P, and the carbon source may be the same as those described above.

[0137] In the step of mixing one or more selected from the group consisting of an Al precursor, a P precursor, and a precursor containing Al and P with a carbon source and heat-treating the mixture, the heat-treatment temperature is preferably lower than the temperature at which the preliminary silicon-based particles and the Li precursor are mixed and then heat-treated.

[0138] Specifically, the heat treatment may be performed at 500°C to 700°C, and more specifically, 550°C to 650°C. However, the heat treatment temperature is not limited thereto and may vary depending on the salt or precursor used. If 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, which may result in a decrease in resistance and life characteristics, and a decrease in capacity and / or efficiency.

[0139] <Negative electrode> The negative electrode according to an embodiment of the present invention may include the negative electrode active material described above. 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.

[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 surface of a current collector, followed by drying and rolling.

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

[0142] The additional negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, and Al alloys; SiO β (0<β<2), SnO 2 Examples of the negative electrode active material include metal oxides capable of doping and dedoping lithium, such as vanadium oxide, lithium titanium oxide, and lithium vanadium oxide; or composites containing the metallic compounds and carbonaceous materials, such as Si-C composites and Sn-C composites, and any one or a mixture of two or more of these may be used. In addition, a thin film of metallic lithium may be used as the negative electrode active material. In addition, the carbon material may be either low-crystalline carbon or high-crystalline carbon. Typical low-crystalline carbons are soft carbon and hard carbon, and typical high-crystalline carbons are amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch based carbon fiber, mesocarbon microbeads, mesophase pitches, and high-temperature fired carbons such as petroleum or coal tar pitch derived cokes.

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

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

[0145] The negative electrode slurry may include a solvent for forming a negative electrode slurry. Specifically, the solvent for forming a negative electrode slurry may include at least one selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol, specifically, distilled water, in order to facilitate dispersion of components.

[0146] The negative electrode slurry containing the negative electrode active material according to one embodiment of the present invention may have a pH of 7 to 11 at 25° C. When the pH of the negative electrode slurry satisfies the above range, the rheological properties of the slurry are stabilized. On the other hand, when the pH of the negative electrode slurry is less than 7 or exceeds 11, there is a problem that decomposition of carboxymethyl cellulose (CMC) used as a thickener occurs, the viscosity of the slurry decreases, and the degree of dispersion of the active material contained in the slurry decreases.

[0147] The negative electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and has electrical conductivity. For example, the current collector may be made of copper, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel whose surface is treated with carbon, nickel, titanium, silver, or the like. Specifically, a transition metal that easily adsorbs carbon, such as copper or nickel, may be used as the current collector. The thickness of the current collector may be 6 μm to 20 μm, but is not limited thereto.

[0148] The binder may include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, polyacrylic acid, and substances in which hydrogen is substituted with Li, Na, Ca, or the like, or may include 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, and examples of the conductive material that may be used include graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; metal powders such as 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.

[0150] The thickener may be carboxymethyl cellulose (CMC), but is not limited thereto, and any thickener used in the present technical field may be appropriately adopted.

[0151] In an embodiment of the present invention, the weight ratio of the negative electrode active material to the additional negative electrode active material contained in the negative electrode slurry may be 1:99 to 30:70, specifically, 5:95 to 30:70, or 10:90 to 20:80.

[0152] In an embodiment of the present invention, the total amount of the negative electrode active material contained in the negative electrode slurry may be 60 parts by weight to 99 parts by weight, specifically 70 parts by weight to 98 parts by weight, based on 100 parts by weight of a 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 thickener may be included in an amount of 0.5 parts by weight to 25 parts by weight, specifically 0.5 parts by weight to 20 parts by weight, and more specifically 1 part by weight to 20 parts by weight, based on 100 parts by weight of the total solid content of the negative electrode slurry.

[0156] The negative electrode slurry according to an embodiment of the present invention may further include a solvent for forming a negative electrode slurry. Specifically, the solvent for forming a negative electrode slurry may include at least one selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol, specifically, distilled water, in order to facilitate dispersion of components.

[0157] In one embodiment of the present invention, the solid content weight of the negative electrode slurry may be 20 parts by weight to 75 parts by weight, specifically 30 parts by weight to 70 parts by weight, based on 100 parts by weight of the total of the negative electrode slurry.

[0158] <Secondary battery> A secondary battery according to an embodiment of the present invention may include the 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, and the negative electrode is the same as the negative electrode described above. The negative electrode has been described above, so a detailed description thereof 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 including 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 has conductivity, and for example, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector may usually have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase the adhesive force of the positive electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0161] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material may be lithium cobalt oxide (LiCoO 2 ), lithium nickel oxide (LiNiO 2 ), or compounds substituted with one or more transition metals; LiFe 3 O 4 Lithium iron oxide, etc.; chemical formula Li 1+c1 Mn 2-c1 O 4 (0≦c1≦0.33), LiMnO 3 , LiMn 2 O 3 , LiMnO 2 Lithium manganese oxides such as lithium copper oxide (Li 2 CuO 2 );LiV 3 O 8 , V 2 O5 , Cu 2 V 2 O 7 Vanadium oxides such as LiNi 1-c2 M c2 O 2 (wherein M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and 0.01≦c2≦0.5 is satisfied); 2-c3 M c3 O 2 (wherein M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01≦c3≦0.1), or Li 2 Mn 3 MO 8 (wherein M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); or LiMn 2 O 4 The positive electrode may be, but is not limited to, Li metal.

[0162] The positive electrode active material layer may contain a positive electrode conductive material and a positive electrode binder in addition to 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 any particular limitation as long as it has electronic conductivity without causing chemical changes in the battery that is constructed.Specific examples include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fibers; 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; and conductive polymers such as polyphenylene derivatives, and the like, and one or more of these may be used alone or in mixture.

[0164] The positive electrode binder plays a role of improving the adhesion between the positive electrode active material particles and the adhesive strength 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, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof, and one or more of these may be used alone or in combination.

[0165] The separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator that is normally used as a separator in a secondary battery can be used without any particular limitation. In particular, it is preferable that the separator has low resistance to ion movement of the electrolyte and has excellent electrolyte moisture absorption ability. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a normal porous nonwoven fabric, for example, a nonwoven fabric made of high-melting glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, in order to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymeric substance may be used, and may be selectively used as a single layer or multilayer structure.

[0166] Examples of the electrolytic solution include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

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

[0168] Examples of the non-aqueous organic solvent that can be used include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[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 a high dielectric constant and dissociate lithium salts well. When such cyclic carbonates are mixed in an appropriate ratio with linear carbonates having low viscosity and low dielectric constant, such as dimethyl carbonate and diethyl carbonate, an electrolyte solution having high electrical conductivity can be prepared, and therefore such a mixture can be used even more preferably.

[0170] The metal salt may be a lithium salt, which is a substance that is easily dissolved in the non-aqueous electrolyte. For example, the anion of the lithium salt may be F - , Cl - , I - , NO 3 - , N(CN) 2 - , B.F. 4 - , ClO 4 - , P.F.6 - 、(CF 3 ) 2 PF 4 - 、(CF 3 ) 3 PF 3 - 、(CF 3 ) 4 PF 2 - 、(CF 3 ) 5 PF - 、(CF 3 ) 6 P - 、CF 3 SO 3 - 、CF 3 CF 2 SO 3 - 、(CF 3 SO 2 ) 2 N - 、(FSO 2 ) 2 N - 、CF 3 CF 2 (CF 3 ) 2 CO - 、(CF 3 SO 2 ) 2 CH - 、(SF 5 ) 3 C - 、(CF 3 SO 2 ) 3 C - 、CF 3 (CF 2 ) 7 SO 3 - 、CF 3 CO 2 - 、CH 3 CO 2 - 、SCN - 、および(CF 3 CF 2 SO 2 ) 2 N -One or more selected from the group consisting of may be used.

[0171] In addition to the components of the electrolyte, the electrolyte may further include one or more additives such as a haloalkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, in order to improve the life characteristics of the battery, suppress a decrease in battery capacity, and improve the discharge capacity of the battery.

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

[0173] Below, preferred examples are presented to aid in understanding the present invention. However, the following examples are merely for the purpose of illustrating the present description, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope and technical spirit of the present description, and it is natural that such changes and modifications fall within the scope of the appended claims.

[0174] <Examples and Comparative Examples> Example 1 Si and SiO 2 100 g of powder made by mixing these in a 1:1 molar ratio was heated in a vacuum reactor at a sublimation temperature of 1,400°C. After that, the vaporized Si, SiO 2The gas mixture was reacted in a vacuum cooling zone with a cooling temperature of 800°C and condensed into a solid phase. Then, heat treatment was performed in an inert atmosphere at a temperature of 800°C to produce preliminary silicon-based particles. Then, the preliminary silicon-based particles were put into a ball mill, and 15 SUS ball media were put into the ball mill, and the ball mill was pulverized for 3 hours to obtain a particle size of 6 μm (D 50 ) size silicon-based particles were produced.

[0175] 10 g of Li metal powder was added to 90 g of the silicon-based particles, and heat-treated at 800° C. in an inert atmosphere to produce Li-doped silicon-based particles.

[0176] The Li-doped silicon-based particles (98.5 g) were doped with Al(PO 3 ) 3 After mixing 1.5 g of the above, the mixture was heat-treated at 600° C. to produce silicon-based particles having a first coating layer containing Li, Al, and P formed on the surface of the silicon-based particles.

[0177] Thereafter, the silicon-based particles on which the first coating layer was formed were placed in a hot zone of a CVD apparatus while maintaining an inert atmosphere by flowing Ar gas, and the methane was blown into the hot zone at 700° C. using Ar as a carrier gas for 10 minutes. -1 The reaction was carried out at torr for 20 minutes to form a second coating layer (carbon layer) on the surface of the silicon-based particles.

[0178] D of the negative electrode active material 50 The BET specific surface area is 2.5m 2 / g.

[0179] The negative electrode active material had a first coating layer containing Li, Al, P, and O between silicon-based particles and a second coating layer containing carbon. Inductively Coupled Plasma (ICP) analysis of the negative electrode active material revealed that the contents of Li, Al, and P were 9.5 wt%, 0.15 wt%, and 0.5 wt%, respectively, based on a total of 100 wt% of the negative electrode active material.

[0180] Example 2 95g of Li-doped silicon-based particles were doped with Al(PO 3 ) 3 The same procedure as in Example 1 was followed, except that 5 g of each of the above was mixed and heat-treated.

[0181] When the negative active material was subjected to ICP analysis, the contents of Li, Al, and P were 9.0 wt%, 0.5 wt%, and 1.8 wt%, respectively, based on a total of 100 wt% of the negative active material.

[0182] Example 3 99.5g of Li-doped silicon-based particles were doped with Al(PO 3 ) 3 The same procedure as in Example 1 was followed, except that 0.5 g of each of the above was mixed and heat-treated.

[0183] When the negative active material was subjected to ICP analysis, the contents of Li, Al, and P were 9.5 wt%, 0.05 wt%, and 0.18 wt%, respectively, based on a total of 100 wt% of the negative active material.

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

[0185] In the negative electrode active material of Comparative Example 1, a coating layer containing Li, Al, P, and O was formed after the formation of a carbon layer, so that the coating layers were formed in the reverse order to those in Examples 1 to 3.

[0186] When the negative active material was subjected to ICP analysis, the contents of Li, Al, and P were 9.5 wt%, 0.15 wt%, and 0.5 wt%, respectively, based on a total of 100 wt% of the negative active material.

[0187] Comparative Example 2 90g of Li-doped silicon-based particles were doped with Al(PO 3 ) 3 The same procedure as in Comparative Example 1 was followed, except that 10 g of each of the above ingredients was mixed and heat-treated.

[0188] When the negative active material was subjected to ICP analysis, the contents of Li, Al, and P were 9.0 wt%, 1.0 wt%, and 3.0 wt%, respectively, based on a total of 100 wt% of the negative active material.

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

[0190] Comparative Example 4 The same procedure as in Example 1 was repeated up to the process of adding 10 g of Li metal powder to 90 g of the silicon-based particles and performing heat treatment at a temperature of 800° C. in an inert atmosphere to produce Li-doped silicon-based particles.

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

[0192] Thereafter, a heat treatment was performed at 700° C. for 20 minutes in an argon gas atmosphere to prepare a negative electrode active material.

[0193] [Table 1]

[0194] The contents of the above elements were confirmed by ICP analysis using an inductively coupled plasma optical emission spectrometer (ICP-OES, AVIO 500, manufactured by Perkin-Elmer 7300).

[0195] D of the negative electrode active material 50 was analyzed by PSD measurement method using a microtrac instrument.

[0196] The specific surface area was measured by degassing at 200° C. for 8 hours using a BET measuring device (BEL-SORP-MAX, Nippon Bell) and measuring the specific surface area at 77 K with N 2 Adsorption / desorption was carried out and measured.

[0197] <Experimental example: Evaluation of discharge capacity, initial efficiency, and life (capacity retention rate) characteristics> Negative electrodes and batteries were manufactured using the negative electrode active materials of the examples and comparative examples, respectively.

[0198] The negative electrode active material, carbon black as a conductive material, and PAA (polyacrylic acid) as a binder were mixed in a weight ratio of 80:10:10 to prepare a mixture. Then, 7.8g of distilled water was added to 5g of the mixture and stirred to prepare a negative electrode slurry. The negative electrode slurry was applied to a copper (Cu) metal thin film as a negative electrode current collector having a thickness of 20μm and dried. At this time, the temperature of the circulating air was 60°C. Next, the mixture was rolled and dried in a vacuum oven at 130°C for 12 hours to prepare a negative electrode.

[0199] The manufactured negative electrode and 1.7671 cm 2 The lithium (Li) metal thin film cut into a circular shape was used as a positive electrode, and a porous polyethylene separator was placed between the positive electrode and the negative electrode. 0.5 parts by weight of vinylene carbonate was dissolved in a mixed solution of ethyl methyl carbonate (EMC) and ethylene carbonate (EC) in a volume ratio of 7:3 to prepare a 1M concentration LiPF 6A lithium coin half-cell was fabricated by injecting an electrolyte containing the above dissolved carbon nanotubes.

[0200] The produced batteries were charged and discharged to evaluate the discharge capacity, initial efficiency, and capacity retention rate. The results are shown in Table 2 below.

[0201] The first and second cycles were charged and discharged at 0.1 C, and the third to 49th cycles were charged and discharged at 0.5 C. The 50th cycle was completed in a charged state (with lithium 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] From the results of one charge / discharge, the discharge capacity (mAh / g) and initial efficiency (%) were derived. Specifically, the initial efficiency (%) was derived by the following calculation. Initial efficiency (%) = (single discharge capacity / single charge capacity) x 100

[0204] The capacity retention rates were calculated as follows. Capacity retention rate (%) = (49 discharge capacity / 1 discharge capacity) × 100

[0205] <Experimental example: Evaluation of shear viscosity characteristics> As part of the processability evaluation, the amount of change in shear viscosity at a shear rate of 1 Hz of a slurry produced by mixing graphite: the negative electrode active material: carbon black: CMC: SBR in a weight ratio of 77:20:1:1:1 was measured, and the results are shown in Table 2. Specifically, the amount of change in shear viscosity (%) was calculated 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 a layer containing Li, Al, P, and O is coated on silicon-based particles so as to be closer to the carbon layer, and it was confirmed that Examples 1 to 3 using the negative electrode active material according to the present invention have excellent discharge capacity, initial efficiency, and capacity retention, and have a significantly low shear viscosity of the slurry, which is excellent in processability. This is believed to be because the layer containing Li, Al, P, and O located near the surface of the silicon-based particles can easily prevent reaction with the water in the slurry, the hydrophobic carbon layer exists in the outermost layer, which further blocks contact between the negative electrode active material and water, thereby improving the processability of the aqueous slurry, and the highly conductive carbon exists in the outermost layer, which is advantageous in achieving overall capacity / efficiency.

[0208] In contrast, in Comparative Examples 1 and 2, a carbon layer is closely coated on the silicon-based particles as a first coating layer, and a layer containing Li, Al, P, and O is coated on the carbon layer. This makes it difficult to remove lithium by-products generated during Li doping of the silicon-based particles. Also, since a carbon layer does not exist on the outermost surface, side reactions are likely to occur in the slurry, making it difficult to process the slurry and achieve the capacity / efficiency of the battery.

[0209] Comparative Example 3 corresponds to a case where a layer containing Li, Al, P, and O is coated on a silicon-based particle as a single layer without a second coating layer (carbon layer), and Comparative Example 4 corresponds to a case where a single layer (a layer containing Li, Al, P, O, and C) containing the material of the first coating layer and the material of the second coating layer is coated without distinction between the first and second coating layers. It was confirmed that Comparative Examples 3 and 4 are composed of a single layer, and are prone to contact between the negative electrode active material and water, and show inferior effects 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 comprising Li, Al, P, and O; and a second coating layer comprising 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 a silicon-based particle comprising a Li compound; a first coating layer disposed 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. Including, the first coating layer comprises Li, Al, P, and O; The negative electrode active material, wherein the second coating layer comprises carbon.

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

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

4. 2. The negative electrode active material of claim 1, wherein the first coating layer comprises at least one 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 Li ｙ A ｚ P ｗ O ｖ The negative electrode active material according to claim 1 , further comprising a (0<y≦10, 0<z≦10, 0<w≦10, 0<v≦10) phase.

6. 2 . The negative active material of claim 1 , wherein the carbon content is from 45 parts by weight to 95 parts by weight, based on a total of 100 parts by weight of the first coating layer and the second coating layer.

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

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

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

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

11. The Li ｙ A ｚ P ｗ O ｖ 4. 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 contained in an amount of 0.1 parts by weight to 30 parts by weight based on a total of 100 parts by weight of the negative electrode active material.

12. The negative active material of claim 1 , wherein the second coating layer is present in an amount of 0.1 parts by weight to 50 parts by weight based on a total of 100 parts by weight of the negative 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 to 40 parts by weight based on a total of 100 parts by weight of the negative electrode active material.

14. SiO ｘ preparing a preliminary silicon-based particle comprising (0<x<2); preparing silicon-based particles by mixing the preliminary silicon-based particles with a Li precursor and then heat-treating the mixture; forming a first coating layer by mixing and reacting the silicon-based particles with at least one selected from the group consisting of an Al precursor, a P precursor, and a precursor containing Al and P; and forming a second coating layer from a carbon precursor on the silicon-based particles having the first coating layer formed thereon; The method for producing the negative electrode active material according to any one of claims 1 to 13, comprising:

15. SiO ｘ preparing a preliminary silicon-based particle comprising (0<x<2); preparing silicon-based particles by mixing the preliminary silicon-based particles with a Li precursor and then heat-treating the resulting mixture; and mixing the silicon-based particles with at least one selected from the group consisting of an Al precursor, a P precursor, and a precursor containing Al and P, and a carbon source, and heat-treating the mixture; The method for producing the negative electrode active material according to any one of claims 1 to 13, comprising:

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

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

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