Negative electrode active material, negative electrode containing the same, secondary battery containing the same, and method for producing 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 of the filing date of Korean Patent Application No. 10-2021-0165299, filed with the Korean Intellectual Property Office on November 26, 2021, and all of its content is 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 manufacturing the negative electrode active material.

Background Art

[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 and lightweight but relatively high in capacity has been rapidly increasing. In particular, lithium secondary batteries are lightweight and have a high energy density, and have been in the spotlight as a driving power source for portable devices. For this reason, research and development efforts to improve the performance of lithium secondary batteries are actively underway.

[0004] Generally, a lithium secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, an electrolyte, an organic solvent, and the like. In addition, an active material layer including a positive electrode active material and a negative electrode active material can be formed on a current collector for the positive electrode and the negative electrode. Generally, lithium-containing metal oxides such as LiCoO2 and LiMn2O4 are used as the positive electrode active material for the positive electrode, and carbon-based active materials and silicon-based active materials that do not contain lithium are used as the negative electrode active material for the negative electrode.

[0005] In the case of silicon-based active materials among negative electrode active materials, they are attracting attention in that they have a higher capacity than carbon-based active materials and excellent fast charging characteristics. However, silicon-based active materials have the disadvantage of low initial efficiency because the degree of volume expansion / contraction due to charge and discharge is large and the irreversible capacity is large.

[0006] On the other hand, among silicon-based active materials, silicon-based oxides, specifically SiO xIn the case of silicon-based oxides represented by (0 < x < 2), there is an advantage in that the degree of volume expansion / contraction due to charge and discharge is lower compared to other silicon-based active materials such as silicon (Si). However, there is still a disadvantage in that the initial efficiency of silicon-based oxides decreases due to the presence of irreversible capacity.

[0007] In connection with this, research has continued to reduce the irreversible capacity and improve the initial efficiency by doping or inserting metals such as Li, Al, and Mg into silicon-based oxides. 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, resulting in a poor state of the manufactured negative electrode and a decrease in the charge / discharge efficiency of the negative electrode.

[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 thereby improve the charge / discharge efficiency of the manufactured negative electrode.

[0009] Korean Registered Patent No. 10-0794192 relates to a method for manufacturing a carbon-coated silicon-graphite composite negative electrode material for a lithium secondary battery and a method for manufacturing a secondary battery including the same, but there are limitations in solving the above-described problems.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0011] 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 manufacturing the negative electrode active material.

Means for Solving the Problems

[0012] One embodiment of the present invention relates to silicon-based particles containing SiO x (0 < x < 2) and Li, with a first carbon layer provided on at least a part of the surface; a composite layer provided on at least a part of the silicon-based particles; and a second carbon layer provided on at least a part of the composite layer, the negative electrode active material containing Li, M, P, and O elements, where M is Al, B, or Zn, and the ratio of the peak intensity of the D band to the peak intensity of the G band (D / G band ratio) is 1.0 or more when analyzed by Raman spectroscopy, and provides a negative electrode active material.

[0013] One embodiment of the present invention relates to SiO x (0 < x < 2) and Li, and includes steps of forming silicon-based particles with a first carbon layer provided on at least a part of the surface; reacting the silicon-based particles with a phosphate solution to form a composite layer on at least a part of the silicon-based particles; and forming a second carbon layer on at least a part of the composite layer, and provides a method for manufacturing a negative electrode active material.

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

Effects of the Invention

[0015] A negative electrode containing a negative electrode active material according to one embodiment of the present invention and a secondary battery containing the negative electrode have the effect of improving the discharge capacity, initial efficiency, resistance performance, and / or life characteristics of the battery.

Modes for Carrying Out the Invention

[0016] Hereinafter, the present specification will be described in more detail. In this specification, when a certain part "includes" a certain component, this means that, unless otherwise stated to the contrary, it does not exclude other components, but may further include other components.

[0017] In this specification, when a certain member is located "above" another member, this includes not only the case where a certain member is in contact with another member, but also the case where there are other members between the two members.

[0018] The terms and words used in this specification should not be construed as being limited to their ordinary or dictionary meanings. In accordance with the principle that the inventors can appropriately define the concepts of the terms in order to explain their inventions in the best way, they should be construed in meanings and concepts consistent with the technical idea of the present invention.

[0019] The singular expressions of the terms used in this specification include plural expressions unless otherwise clearly indicated in the context.

[0020] In this specification, the crystallinity of the structure contained in the negative electrode active material can be confirmed by TEM or X-ray diffraction analysis. The X-ray diffraction analysis can be performed using an XRD (X-ray diffraction) analyzer (product name: D4-endavor, manufacturer: bruker), and other devices used in the industry can also be appropriately adopted in addition to the said device.

[0021] In this specification, the presence and content of elements in the negative electrode active material can be confirmed by ICP analysis. The ICP analysis can be performed using an inductively coupled plasma optical emission spectrometer (ICPAES, Perkin-Elmer 7300).

[0022] In this specification, the average particle size (D 50 ) can be defined as the particle size corresponding to 50% of the volume cumulative amount in the particle size distribution curve (graph curve of the particle size distribution diagram) of the particles. The said average particle size (D 50) can be measured, for example, using the laser diffraction method. The laser diffraction method can generally measure particle sizes in the range from the submicron region to about several millimeters, and can obtain highly reproducible and highly resolved results.

[0023] Hereinafter, preferred embodiments of the present invention will be described in detail. However, the embodiments of the present invention may be modified in various forms, and the scope of the present invention is not limited to the embodiments described below.

[0024] <Negative electrode active material> One embodiment of the present invention is SiO x (0 < x < 2) and silicon-based particles containing Li and having a first carbon layer provided on at least a part of the surface; a composite layer provided on at least a part of the silicon-based particles; and a negative electrode active material including a second carbon layer provided on at least a part of the composite layer, wherein the negative electrode active material contains Li, M, P, and O elements, the M is Al, B, or Zn, and when analyzed by Raman spectroscopy, the ratio of the peak intensity of the D band to the peak intensity of the G band (D / G band ratio) is 1.0 or more.

[0025] The negative electrode active material according to one embodiment of the present invention contains silicon-based particles. The silicon-based particles may contain SiO x (0 < x < 2) and Li and may have a first carbon layer provided on at least a part of the surface.

[0026] The SiO x (0 < x < 2) corresponds to the matrix in the silicon-based particles. The SiO x (0 < x < 2) may be in a form containing Si and SiO2, and the Si may form a phase. That is, the x corresponds to the number ratio of O to Si contained in the SiO x (0 < x < 2). When the silicon-based particles contain the SiO x (0 < x < 2), the discharge capacity of the secondary battery is improved.

[0027] In one embodiment of the present invention, the silicon-based particles may contain Li. The Li may be present in at least one form of lithium atoms, lithium silicate, lithium silicide, and lithium oxide within the silicon-based particles, and preferably may be present in the form of lithium silicate. When the Li is present in the form of a Li compound, the Li compound may correspond to a matrix within the silicon-based particles. When the silicon-based particles contain Li, there is an effect that the initial efficiency is improved.

[0028] The Li may be distributed on the surface and / or inside of the silicon-based particles in a doped form. The Li is distributed on the surface and / or inside of the silicon-based particles, and 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 may be included in terms of reducing the ratio of the irreversible phase (for example, SiO2) of the silicon-based oxide particles and increasing the efficiency of the active material.

[0029] In one embodiment of the present invention, Li may be present 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 be present in the form of at least one lithium silicate selected from the group consisting of Li2SiO3, Li4SiO4, and Li2Si2O5 within the silicon-based particles, and the amorphous lithium silicate is Li a Si b O c (2 ≤ a ≤ 4, 0 < b ≤ 2, 2 ≤ c ≤ 5) may consist of a complex structure, and is not limited to the above form.

[0030] In one embodiment of the present invention, Li contained in the silicon-based particles may be contained in an amount of 0.01 parts by weight to 10 parts by weight, 0.01 parts by weight to 5 parts by weight, 0.01 parts by weight to 1 part by weight, or 0.02 parts by weight to 0.8 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 0.05 parts by weight to 0.8 parts by weight, and more specifically, it may be contained in an amount of 0.1 parts by weight to 0.5 parts by weight. As the content of Li increases, although the initial efficiency increases, there is a problem that the discharge capacity decreases. Therefore, when the above range is satisfied, appropriate discharge capacity and initial efficiency can be realized.

[0031] In one embodiment of the present invention, Li may be contained in an amount of 0.1 parts by weight to 40 parts by weight, or 0.1 parts by weight to 25 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 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, appropriate discharge capacity and initial efficiency can be realized.

[0032] The content of the Li element can be confirmed by ICP analysis. Specifically, after collecting a certain amount (about 0.01 g) of the sample, it is transferred to a platinum crucible, nitric acid, hydrofluoric acid, and sulfuric acid are added, and it is completely decomposed on a hot plate. Then, using an inductively coupled plasma atomic emission spectrometer (ICPAES, Perkin-Elmer 7300), at the characteristic wavelength of the element to be analyzed, the intensity of the standard solution prepared using the standard solution (5 mg / kg) is measured to create a reference calibration curve. Then, the pretreated sample solution and the blank sample are introduced into the instrument, the intensities of each are measured to calculate the actual intensity, and after calculating the concentration of each component by comparing with the above-prepared calibration curve, the content of the elements of the sample can be analyzed by converting so that the sum of the whole becomes the theoretical value.

[0033] According to one embodiment of the present invention, a silicon-based particle has a first carbon layer on at least a part of its surface. In this case, the first carbon layer may be partially coated on at least a part of the surface, i.e., the surface of the particle, or may be coated on the entire surface of the particle. The carbon layer imparts electrical conductivity to the negative electrode active material, improving the initial efficiency, life characteristics, and capacity characteristics of the secondary battery.

[0034] In particular, the first carbon layer may include crystalline carbon or amorphous carbon. 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.

[0035] The amorphous carbon can appropriately maintain the strength of the first 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.

[0036] 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.

[0037] 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.

[0038] In one embodiment of the present invention, the first carbon layer may be contained in an amount of 1 to 5 parts by weight, 2 to 4 parts by weight, or 2 to 3.5 parts by weight based on 100 parts by weight of the total negative electrode active material. More specifically, it may be contained in an amount of 2.5 to 3 parts by weight. When the above range is satisfied, a decrease in the capacity and efficiency of the negative electrode active material can be prevented.

[0039] In one embodiment of the present invention, the thickness of the first carbon layer may be 1 nm to 500 nm, and specifically may be 5 nm to 300 nm. When the above range is satisfied, there is an effect that the conductivity of the negative electrode active material is improved, the volume change of the negative electrode active material is easily suppressed, the side reaction between the electrolyte and the negative electrode active material is suppressed, and the initial efficiency and / or life of the battery are improved.

[0040] Specifically, the first carbon layer may be formed by chemical vapor deposition (CVD) using at least one hydrocarbon gas selected from the group consisting of methane, ethane, and acetylene.

[0041] The negative electrode active material according to one embodiment of the present invention includes a composite layer provided on at least a part of the silicon-based particles.

[0042] The composite layer may cover at least a part of the surface of the silicon-based particles, that is, it may partially cover the surface of the particles or cover the entire surface of the particles. Examples of the shape of the composite layer include an island type or a thin film type, but the shape of the composite layer is not limited thereto.

[0043] The composite layer may be provided on at least a part of the first carbon layer. That is, the composite layer may partially cover at least a part of the first carbon layer, that is, the surface of the first carbon layer, or may cover the entire surface of the first carbon layer.

[0044] In one embodiment of the present invention, the negative electrode active material contains Li, M, P, and O elements. The M may be Al, B, or Zn.

[0045] The Li element and the M element can be confirmed by ICP-OES analysis using an inductively coupled plasma optical emission spectrometer (ICP-OES manufactured by Perkin-Elmer 7300, AVIO 500).

[0046] The P element and the O element can be detected by analysis using X-ray photoelectron spectroscopy (XPS). Further, the M element can be detected. Specifically, it can be confirmed by XPS (Nexsa ESCA System, Thermo Fisher Scientific (NEXSA 1)).

[0047] Generally, in the process of doping silicon-based particles with Li, lithium by-products formed by unreacted lithium exist on the surface of the silicon-based particles, which will show basicity during the formation of the slurry, and the lithium compound reacts with moisture to generate gas, resulting in a problem that the rheological properties of the slurry change.

[0048] In the present invention, by reacting the lithium by-product with a phosphate solution to form an inorganic composite layer containing Li, M, P, and O, the unreacted lithium by-product contained in the silicon-based particles can be effectively removed, and the phenomenon that the lithium by-product reacts with the moisture of the slurry to reduce the viscosity of the slurry can be prevented. In addition, the generated composite layer effectively passivates the silicon-based particles from moisture, thereby having the effect of improving the stability of the state of the electrode and / or the charge-discharge capacity.

[0049] Further, when the composite layer further contains Li, the lithium diffusion resistance on the surface of the negative electrode active material is reduced, and there is an effect that the discharge rate capability is excellent.

[0050] In one embodiment of the present invention, the molar ratio of the M element and the P element may be 1:0.5 to 1:3, 1:0.8 to 1:3, or 1:1 to 1:3, specifically 1:1 to 1:2, and more specifically 1:1. When the molar ratio of the M element and the P element does not satisfy the above range, the formed composite layer aggregates outside the surface of the active material, and it is difficult to uniformly coat the surface of the composite layer. However, when the molar ratio of the M element and the P element satisfies the above range, the composite layer formed by reacting with Li has the effect of more uniformly coating the surface of the active material.

[0051] In one embodiment of the present invention, the composite layer contains Li, M, P, and O elements. In one embodiment of the present invention, the composite layer may exist in a form containing lithium oxide, M-containing oxide, and phosphate. In one example, the composite layer may contain M-containing oxide, phosphate, lithium oxide, M-containing phosphate, lithium salt, lithium phosphate, lithium metal (M) salt, etc., and y, z, w, and v mean the atomic number ratio. In one example, when M is Al, the composite layer may contain a mixture or compound formed from Li3PO4, AlPO4, Al(PO3)3, or LiAlO2, etc., but is not limited thereto.

[0052] The contents of the Li and M elements can be confirmed by ICP-OES analysis using an inductively coupled plasma optical emission spectrometer (ICP-OES manufactured by Perkin-Elmer 7300, AVIO 500).

[0053] The contents of the M, P, and O elements can be confirmed by XPS (Nexsa ESCA System, Thermo Fisher Scientific (NEXSA 1)).

[0054] The elements contained in the composite layer are Li y M z P w O v may have a molar ratio of (0 < y ≤ 3, 0 < z ≤ 1, 0.5 ≤ w ≤ 3, 4 < v ≤ 12). Or, Li y M z P w O v may have a molar ratio of (0 < y ≤ 3, 0 < z ≤ 1, 1 ≤ w ≤ 3, 4 < v ≤ 12). By the composite layer containing elements in the molar ratio, there is an effect of more uniformly coating the surface of the active material.

[0055] In one embodiment of the present invention, the composite layer may be formed by the reaction of lithium by-products located on the silicon-based particles and a phosphate solution. Specifically, the composite layer may be formed by reacting lithium by-products remaining near the surface of the silicon-based particles due to unreacted lithium with a metal phosphate solution after manufacturing the silicon-based particles containing Li.

[0056] The phosphate solution may contain Al, B, or Zn. Specifically, the phosphate solution may be a mixed solution of a salt containing Al, B, or Zn and a phosphoric acid solution. Specifically, the phosphate solution may be a mixed solution of an Al2(SO4)3 solution and an H3PO4 solution, or a mixed solution of a B(OH)3 solution and an H3PO4 solution.

[0057] In one embodiment of the present invention, the lithium by-product may be one or more selected from the group consisting of Li2O, LiOH, and Li2CO3. That is, the composite layer may be formed by the reaction of one or more selected from the group consisting of Li2O, LiOH, and Li2CO3 with a phosphate solution.

[0058] The composite layer formed as described above is not readily soluble in water and can effectively passivate silicon-based particles in an aqueous slurry, thereby preventing the elution of Li compounds and the like contained in the silicon-based particles, and having the effect of improving the aqueous processability.

[0059] In one embodiment of the present invention, the composite layer may be contained in an amount of 0.5 parts by weight to 3 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 0.7 parts by weight to 2.9 parts by weight, or 0.8 parts by weight to 2.8 parts by weight. When the above range is satisfied, there is an effect that the lithium by-product can react sufficiently to effectively passivate the silicon-based particles. On the other hand, if the content is below the above range, the coverage rate of the composite layer may be low, and if the content is 3 parts by weight or more, the resistance may become excessively large when the battery is fabricated.

[0060] In one embodiment of the present invention, a lithium by-product may further be present between the silicon-based particles and the composite layer. Alternatively, a lithium by-product may further be present between the first carbon layer and the composite layer.

[0061] The lithium by-product may contain one or more selected from the group consisting of Li2O, LiOH, and Li2CO3. As described above, the lithium compound and the phosphate react to form a composite layer, and lithium by-products that are not completely removed during the formation of the composite layer may be present between the silicon-based particles and the composite layer or on the surface of the composite layer.

[0062] The negative electrode active material according to one embodiment of the present invention includes a composite layer provided on at least a part of the silicon-based particles, and includes a second carbon layer provided on at least a part of the composite layer.

[0063] As described above, even when forming a composite layer on silicon-based particles, not all lithium by-products need to be removed. Therefore, by providing a second carbon layer on the composite layer as described above, residual lithium by-products can be effectively coated, preventing the slurry from showing basicity during formation. Also, since the second carbon layer has hydrophobicity, it can minimize the reaction between the negative electrode active material and water in an aqueous slurry.

[0064] Therefore, a lithium compound may be present between the composite layer and the second carbon layer. The lithium compound may be the aforementioned residual lithium by-product.

[0065] Whether a lithium compound is present between the composite layer and the second carbon layer can be confirmed by X-ray diffraction analysis (XRD) or X-ray photoelectron spectroscopy (XPS).

[0066] The second carbon layer may be provided on at least a part of the surface of the silicon-based particles provided with the composite layer. That is, the second carbon layer may be present on at least a part of the composite layer, or may be present in a part of the surface of the silicon-based particles where the composite layer is not provided.

[0067] The second carbon layer may be provided on at least a part of the composite layer. That is, the second carbon layer may partially cover the surface of at least a part of the composite layer, i.e., the composite layer, or may cover the entire surface of the composite layer.

[0068] In one embodiment of the present invention, the second carbon layer contains amorphous carbon. The second carbon layer may further contain crystalline carbon.

[0069] 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 nanotube, and graphene.

[0070] The amorphous carbon can appropriately maintain the strength of the second carbon layer and suppress the expansion of the silicon-based particles. The amorphous carbon may be at least one carbide selected from the group consisting of tar, pitch, and other organic substances, or a carbon-based substance formed using a hydrocarbon as a source in a chemical vapor deposition method.

[0071] The carbide of the other organic substances may be a carbide of an organic substance selected from the group consisting of sucrose, glucose, galactose, fructose, lactose, mannose, ribose, aldohexose, or ketohexose and combinations thereof.

[0072] 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.

[0073] In one embodiment of the present invention, the second carbon layer may be included in an amount of 0.5 parts by weight to 5 parts by weight, specifically 0.5 parts by weight to 4 parts by weight, more specifically 0.7 parts by weight to 4 parts by weight, based on 100 parts by weight in total of the negative electrode active material. When the above range is satisfied, a decrease in the capacity and efficiency of the negative electrode active material can be prevented.

[0074] In one embodiment of the present invention, the thickness of the second carbon layer may be from 1 nm to 500 nm, specifically, it may be from 5 nm to 300 nm. When the above range is satisfied, the conductivity of the negative electrode active material is improved, the volume change of the negative electrode active material is easily suppressed, the side reaction between the electrolyte and the negative electrode active material is suppressed, and the initial efficiency and / or life of the battery are improved.

[0075] The second carbon layer may be formed by chemical vapor deposition (CVD) using at least one hydrocarbon gas selected from the group consisting of methane, ethane, propane, and acetylene under temperature conditions of less than 800 °C.

[0076] In the present invention, the Raman spectroscopy is a method for analyzing the structure of the carbon layer. The peak existing in the region around the wavenumber of 1,580 cm -1 in the Raman spectrum of the carbon layer is called the G band, which is a peak indicating the sp2 bond of the carbon layer and represents a carbon crystal without structural defects. On the other hand, the peak existing in the region around the wavenumber of 1,360 cm -1 in the Raman spectrum is called the D band, which is a peak indicating the sp3 bond of the carbon layer and will increase when the atomic bond composed of sp2 bonds is broken and becomes sp3 bonds. Such a D band will increase when disorder or defects are generated in the carbon layer. The G band of the Raman spectrum for the carbon layer may be a peak existing in the region of 1,550 cm -1 ~1,620 cm -1 and the D band may be a peak existing in the region of 1,330 cm -1 ~1,370 cm -1 . The wavenumber ranges for the G band and the D band correspond to the range that can be shifted according to the laser light source used in the Raman spectroscopy.

[0077] In the present invention, the crystallinity of the carbon 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 a 532 nm laser excitation, with a low laser output density and an exposure time of 30 seconds to avoid the thermal effect of the laser, and using a 100-fold optical lens. To reduce the deviation by position, a total of 25 points are measured for a 5 μm × 5 μm region, and after fitting using a Lorentzian function, the average values of the D band and the G band can be calculated and used for the calculation.

[0078] In one embodiment of the present invention, when analyzing the negative electrode active material by Raman spectroscopy, the ratio of the peak intensity of the D band to the peak intensity of the G band (D / G band ratio) may be 1.0 or more. Specifically, the D / G band ratio may be 1.01 or more, 1.02 or more, 1.03 or more, 1.04 or more, or 1.05 or more. The upper limit of the D / G band ratio may be 3 or less, 2.5 or less, 2 or less, or 1.5 or less.

[0079] When the D / G band ratio satisfies 1.0 or more, the degree of amorphization of all the carbon contained in the first carbon layer and the second carbon layer contained in the negative electrode active material increases. That is, since the carbon layer contained in the negative electrode active material contains a large amount of amorphous carbon and can effectively coat the residual lithium by-products, there is an effect of minimizing the side reaction with moisture, and there is an effect of improving the rapid charging performance. On the other hand, when the D / G band ratio is less than 1.0, the degree of amorphization of all the carbon contained in the first carbon layer and the second carbon layer decreases, and the crystallinity of the carbon layer increases. As described above, the carbon layer with high crystallinity is formed at a relatively high temperature, and conversely, there is a disadvantage that the grain size of silicon (Si) crystal grains increases and the life performance deteriorates.

[0080] In one embodiment of the present invention, the total weight of the first carbon layer and the second carbon layer may be 1.5 parts by weight to 10 parts by weight, specifically 2 parts by weight to 8 parts by weight, more specifically 3 parts by weight to 7 parts by weight, based on 100 parts by weight of the total negative electrode active material. When the above range is satisfied, a decrease in the capacity and efficiency of the negative electrode active material can be prevented.

[0081] The weight part of all Li contained in the negative electrode active material may be 1 part by weight to 10 parts by weight, specifically 5 parts by weight to 10 parts by weight, based on 100 parts by weight of the total negative electrode active material.

[0082] The BET specific surface area of the negative electrode active material is 1 m 2 / g to 10 m 2 / g, specifically 1 m 2 / g to 5 m 2 / g. When the above range is satisfied, the side reaction between the electrolyte and the negative electrode active material during charging and discharging of the battery can be reduced, so the life characteristics of the battery are improved.

[0083] The average particle diameter (D 50 ) of the negative electrode active material may be 0.1 μm to 30 μm, specifically 1 μm to 20 μm, more specifically 1 μm to 15 μm. When the above range is satisfied, the structural stability of the active material during charge and discharge can be achieved, preventing the problem that the volume expansion / contraction level increases due to the excessively large particle diameter, and preventing the problem that the initial efficiency decreases due to the excessively low particle diameter.

[0084] <Method for manufacturing negative electrode active material> One embodiment of the present invention provides a method for manufacturing a negative electrode active material, including the steps of forming silicon-based particles containing SiO x (0 < x < 2) and Li, and having a first carbon layer provided on at least a part of the surface; reacting the silicon-based particles with a phosphate solution to form a composite layer on at least a part of the silicon-based particles; and forming a second carbon layer on at least a part of the composite layer.

[0085] The silicon-based particles provided with the first carbon layer may be formed by heating and vaporizing a mixed powder of Si powder and SiO2 powder, and then depositing the vaporized mixed gas to form preliminary particles; forming a first carbon layer on the preliminary particles; and heat-treating after mixing the preliminary particles with the first carbon layer formed and Li powder.

[0086] Specifically, the mixed powder of the Si powder and the SiO2 powder may be heat-treated at 1400°C to 1800°C, or 1400°C to 1600°C under vacuum.

[0087] The first carbon layer may be formed by using chemical vapor deposition (CVD) using a hydrocarbon gas or by a method of carbonizing a substance serving as a carbon source.

[0088] Specifically, after charging the formed preliminary particles into a reactor, chemical vapor deposition (CVD) may be performed at 600 to 1200°C using a hydrocarbon gas. The hydrocarbon gas may be at least one hydrocarbon gas selected from the group consisting of methane, ethane, propane, and acetylene, and may be heat-treated at 900°C to 1000°C.

[0089] The step of heat-treating after mixing the preliminary particles with the first carbon layer formed and Li powder may be performed at 700°C to 900°C for 4 to 6 hours, and specifically may be performed at 800°C for 5 hours.

[0090] The silicon-based particles may contain the aforementioned lithium silicate. The particle size of the particles can be adjusted by methods such as a ball mill, a jet mill, or air classification, but is not limited thereto.

[0091] The step of reacting the silicon-based particles with a phosphate solution includes reacting a lithium by-product provided on at least a part of the silicon-based particles with the phosphate solution.

[0092] The lithium by-products provided on at least a part of the silicon-based particles may be lithium by-products due to unreacted lithium during lithium doping.

[0093] The phosphate solution may contain Al, B, or Zn. Specifically, the phosphate solution may be a mixed solution of a salt containing Al, B, or Zn and a phosphoric acid solution. Specifically, the phosphate solution may be a mixed solution of an Al2(SO4)3 solution and an H3PO4 solution, or a mixed solution of a B(OH)3 solution and an H3PO4 solution. At this time, the solutions may be mixed at a weight ratio of 1:2 to 1:6 (M-containing solution: P-containing solution).

[0094] The silicon-based particles and the phosphate solution may be mixed at a weight ratio of 1:2 to 1:10, and specifically, may be mixed at a weight ratio of 1:5.

[0095] The step of reacting the silicon-based particles with the phosphate solution may be performed within 3 hours, and specifically, may be performed for 1 hour.

[0096] By the reaction, a composite layer containing Li element, M element, P element, and O element is formed. The above-described content can be applied to the composite layer.

[0097] At this time, unreacted lithium compounds may still be present between the composite layer formed with the silicon-based particles or on the surface of the composite layer.

[0098] In order to suppress side reactions caused by the unreacted lithium compounds, a step of forming a second carbon layer on at least a part of the composite layer may be performed.

[0099] The second carbon layer provided on at least a part of the composite layer may be formed by using a chemical vapor deposition (CVD) method using a hydrocarbon gas or by a method of carbonizing a substance serving as a carbon source.

[0100] 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 a temperature lower than 800°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 a temperature of 600 to less than 800°C. For example, it may be performed under heat treatment conditions of 700°C for 4 hours in an atmosphere of acetylene or propane gas.

[0101] By heat-treating at a temperature lower than 800°C as described above, the degree of amorphousness of the carbon layer can be increased and formed. By increasing the degree of amorphousness of the carbon layer, residual lithium by-products can be effectively coated, so there is an effect of minimizing side reactions with moisture and an effect of improving rapid charging performance. On the other hand, when the degree of amorphousness of the carbon layer is low, that is, when the crystallinity is high, since the carbon coating is performed at a relatively high temperature, there is a disadvantage that the size of the Si crystal grains increases and the life performance deteriorates.

[0102] When analyzing the negative electrode active material manufactured as described above by Raman spectroscopy, the ratio of the peak intensity of the D band to the peak intensity of the G band (D / G band ratio) may be 1.0 or more.

[0103] <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. Further, the negative electrode active material layer may further include a binder and / or a conductive material.

[0104] 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. The negative electrode slurry may further contain an additional negative electrode active material.

[0105] 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 alloys, Sn alloys, or Al alloys; SiO β (0 < β < 2), metal oxides capable of doping and undoping lithium such as SnO2, vanadium oxides, lithium titanate oxides, and lithium vanadate oxides; or composites containing the metallic compound and the carbonaceous material such as Si-C composites or Sn-C composites, and mixtures of any one or two or more of these may be used. Further, a thin film of metallic lithium may be used as the negative electrode active material. Also, as the carbon material, either low-crystalline carbon or high-crystalline carbon may be used. Representative examples of low-crystalline carbon are soft carbon and hard carbon, and representative examples of high-crystalline carbon are amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite, kish graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch derived cokes.

[0106] The additional negative electrode active material may be a carbon-based negative electrode active material. In one embodiment of the present invention, the weight ratio of the negative electrode active material contained in the negative electrode slurry and the additional negative electrode active material may be from 10:90 to 90:10, specifically, it may be from 10:90 to 50:50.

[0107] The negative electrode slurry may contain a solvent for forming the negative electrode slurry. Specifically, the solvent for forming the negative electrode slurry is at least one selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol in terms of facilitating the dispersion of components, and specifically, it may contain distilled water.

[0108] The negative electrode current collector may be any material that does not induce a chemical change in the battery and has conductivity, and is not particularly limited. For example, as the current collector, copper, stainless steel, aluminum, nickel, titanium, fired carbon, or a material obtained by surface treatment with carbon, nickel, titanium, silver, etc. on the surface of aluminum or stainless steel may be used. Specifically, a transition metal that adsorbs carbon well, such as copper or nickel, may be used as the current collector. The thickness of the current collector may be 6 μm to 20 μm, but the thickness of the current collector is not limited thereto.

[0109] 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, poly acrylic acid, and substances in which hydrogen thereof is substituted with Li, Na, Ca, etc., and may also include these various copolymers.

[0110] The conductive material is not particularly limited as long as it does not induce a chemical change in the battery and has conductivity. For example, graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbons, aluminum, nickel powder; conductive whiskers such as zinc oxide, potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives may be used. The thickener may be carboxymethyl cellulose (CMC), but is not limited thereto, and thickeners used in the technical field may be appropriately employed.

[0111] <Secondary battery> The secondary battery according to an embodiment of the present invention may include the negative electrode according to the above-described embodiment. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and the negative electrode is the same as the above-described negative electrode. Since the negative electrode has been described above, a specific description thereof will be omitted.

[0112] 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.

[0113] In the positive electrode, the positive electrode current collector is not particularly limited as long as it does not induce a chemical change in the battery and has conductivity. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or a material obtained by surface-treating the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. may be used. Further, the positive electrode current collector may usually have a thickness of 3 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, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric body, etc.

[0114] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material is a layered compound such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe3O4; chemical formula Li 1+c1 Mn 2-c1 O4 (0 ≦ c1 ≦ 0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7; chemical formula LiNi 1-c2 M c2 O2 (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01 ≦ c2 ≦ 0.5) represented by Ni-site type lithium nickel oxide; chemical formula LiMn 2-c3 Mc3 O2 (where 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 a lithium manganese composite oxide represented by 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 Li in the chemical formula is substituted with an alkaline earth metal ion, etc., but is not limited thereto. The positive electrode may be a lithium metal (Li-metal).

[0115] The positive electrode active material layer may include a positive electrode conductive material and a positive electrode binder together with the above-described positive electrode active material.

[0116] At this time, the positive electrode conductive material is used to impart conductivity to the electrode, and in the configured battery, it can be used without particular limitation as long as it has electron conductivity without causing a chemical change. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based substances such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One kind alone or a mixture of two or more kinds thereof may be used.

[0117] In addition, the positive electrode binder serves to improve the adhesion between the positive electrode active material particles and the adhesive force between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, etc. One kind alone or a mixture of two or more kinds thereof may be used.

[0118] The separator separates the negative electrode and the positive electrode and provides a migration path for lithium ions. Usually, it can be used without particular limitation as long as it is normally used as a separator in a secondary battery. In particular, it is preferably low in resistance to the ion migration of the electrolyte and excellent in the ability to hold the electrolyte solution. Specifically, a porous polymer film, for example, a porous polymer film made of polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. Also, a normal porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fibers, polyethylene terephthalate fibers, etc. may be used. In addition, in order to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer substance may be used, and it may be selectively used as a single-layer or multilayer structure.

[0119] 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. Specifically, the electrolyte may contain a non-aqueous organic solvent and a metal salt.

[0120] Examples of the non-aqueous organic solvent include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate ester, trimethoxymethane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, ethyl propionate, etc.

[0121] In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates among the carbonate-based organic solvents, can be preferably used as high-viscosity organic solvents because they have a high dielectric constant and can dissociate lithium salts well. When such cyclic carbonates are mixed with linear carbonates having low viscosity and low dielectric constant such as dimethyl carbonate and diethyl carbonate in an appropriate ratio, an electrolyte having high electrical conductivity can be produced, so it can be more preferably used.

[0122] A lithium salt may be used as the metal salt. The lithium salt is a substance that is easily dissolved in the non-aqueous electrolyte solution. For example, as an 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 - One or more selected from the group consisting of may be used.

[0123] In addition to the constituent components of the electrolyte, the electrolyte may further contain one or more additives such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexamethylphosphoric 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 for the purpose of improving the life characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery.

[0124] According to another embodiment of the present invention, a battery module including the secondary battery as a unit cell and a battery pack including the same are provided. Since the battery module and the battery pack include the secondary battery having a high capacity, high rate characteristics, and cycle characteristics, they can be used as a power source for medium and large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

Examples

[0125] Hereinafter, preferred embodiments are presented to assist in understanding the present invention. However, it should be obvious to those skilled in the art that the said embodiments are merely illustrative of this description, and various changes and modifications are possible within the scope of this description and the scope of the technical idea. Needless to say, such variations and modifications belong to the scope of the appended claims. <Examples and Comparative Examples> Example 1 94 g of a powder obtained by mixing Si and SiO2 at a molar ratio of 1:1 was mixed in a reactor and then vacuum-heated at a sublimation temperature of 1,400°C. Thereafter, the mixed gas of vaporized Si and SiO2 was reacted in a vacuum cooling zone having a cooling temperature of 800°C and condensed into a solid phase. The preliminary silicon-based negative electrode active material was pulverized for 3 hours using a ball mill to produce silicon-based particles with a size of 6 μm. Thereafter, while flowing Ar gas to maintain an inert atmosphere, the silicon-based negative electrode active material was placed in the hot zone of a CVD apparatus, and using Ar as a carrier gas, the methane was blown into the hot zone at 900°C for 10 -1 torr and reacted for 5 hours to form a first carbon layer on the surface of the silicon-based negative electrode active material. Then, 6 g of Li metal powder was added, and additional heat treatment was performed at a temperature of 800°C in an inert atmosphere to produce silicon-based particles.

[0126] A mixed solution of a 0.1 M Al2(SO4)3 solution and a 0.1 M H3PO4 solution was mixed with the silicon-based particles at a weight ratio of 5:1. After stirring for 1 hour, it was filtered and dried to form a composite layer.

[0127] After the silicon-based particle powder formed with the composite layer was put into a reactor, propane was used as a hydrocarbon gas for chemical vapor deposition (CVD) at 700°C for 4 hours to form a second carbon layer to produce a negative electrode active material. The second carbon layer was formed at 2.4% by weight based on the total weight.

[0128] Li and Al were detected during ICP-OES analysis of the negative electrode active material, and Al, P, and O were detected during XPS analysis.

[0129] Example 2 The negative electrode active material was produced in the same manner as in Example 1, except that the weight ratio of the mixed solution to the silicon-based particles was 3:1.

[0130] Li and Al were detected during the ICP-OES analysis of the negative electrode active material, and Al, P, and O were detected during the XPS analysis.

[0131] Example 3 The negative electrode active material was produced in the same manner as in Example 1, except that the weight ratio of the mixed solution to the silicon-based particles was 7:1.

[0132] Li and Al were detected during the ICP-OES analysis of the negative electrode active material, and Al, P, and O were detected during the XPS analysis.

[0133] Example 4 The negative electrode active material was produced in the same manner as in Example 1, except that B(OH)3 was used instead of Al2(SO4)3.

[0134] Li and B were detected during the ICP-OES analysis of the negative electrode active material, and B, P, and O were detected during the XPS analysis.

[0135] Example 5 The negative electrode active material was produced in the same manner as in Example 1, except that the CVD reaction time was set to 2 hours during the introduction process of the second carbon layer.

[0136] Li and Al were detected during the ICP-OES analysis of the negative electrode active material, and Al, P, and O were detected during the XPS analysis.

[0137] Example 6 The negative electrode active material was produced in the same manner as in Example 1, except that the CVD reaction time was set to 10 hours during the introduction process of the second carbon layer.

[0138] Li and Al were detected during the ICP-OES analysis of the negative electrode active material, and Al, P, and O were detected during the XPS analysis.

[0139] Comparative Example 1 A negative electrode active material was produced in the same manner as in Example 1, except that the second carbon layer was not formed.

[0140] Li and Al were detected during the ICP-OES analysis of the negative electrode active material, and Al, P, and O were detected during the XPS analysis.

[0141] Comparative Example 2 A negative electrode active material was produced in the same manner as in Example 1, except that the composite layer and the second carbon layer were not formed.

[0142] Al was not detected during the ICP-OES analysis of the negative electrode active material, and Al and P were not detected during the XPS analysis.

[0143] Comparative Example 3 A negative electrode active material was produced in the same manner as in Example 1, except that the heat treatment temperature of the second carbon layer was set to 900 °C.

[0144] Li and Al were detected during the ICP-OES analysis of the negative electrode active material, and Al, P, and O were detected during the XPS analysis.

[0145] Comparative Example 4 A negative electrode active material was produced in the same manner as in Example 1, except that Al2(SO4)3 was not used in the production process of the composite layer and only H3PO4 was used.

[0146] Al was not detected during the ICP-OES analysis of the negative electrode active material, and P and O were detected during the XPS analysis.

[0147] Comparative Example 5 The negative electrode active material was manufactured in the same manner as in Example 1, except that only Al2(SO4)3 was used without using H3PO4 in the manufacturing process of the composite layer.

[0148] Li and Al were detected during the ICP-OES analysis of the negative electrode active material, and P was not detected during the XPS analysis.

[0149] The compositions of the negative electrode active materials manufactured in the above Examples and Comparative Examples are as shown in Tables 1 and 2 below.

[0150]

Table 1

[0151] <Measurement of the content of the carbon layer> The contents of the first carbon layer and the second carbon layer were analyzed using a CS-analyzer (CS-800, Eltra), and the content of the second carbon layer was confirmed by calculating "the content of the total carbon layer - the content of the first carbon layer".

[0152] <Elemental analysis by ICP and XPS analysis> The content of the composite layer was calculated based on the contents of Li and M obtained by ICP analysis and the content ratios of M, P, and O obtained from the XPS depth profile.

[0153] The contents of the Li and M elements were confirmed by ICP-OES analysis using an inductively coupled plasma optical emission spectrometer (ICP-OES manufactured by Perkin-Elmer 7300, AVIO 500).

[0154] The contents of the M, P, and O elements were confirmed by XPS (Nexsa ESCA System, Thermo Fisher Scientific (NEXSA 1)).

[0155] XPS was measured by the following method. First, for each sample, a survey scan spectrum and a narrow scan spectrum were obtained in the as-received state. Next, while performing a depth profile, a survey scan spectrum and a narrow scan spectrum were obtained. The depth profile was performed up to 3000 seconds using monatomic Ar (low current). The contents of elements M, P, and O were confirmed from the above results.

[0156] The measurement and data processing conditions are as follows. -X-ray source: Monochromated Al K α (1486.6 eV) -X-ray spot size: 400 μm -Sputtering gun: Monatomic Ar (energy: 1000 eV, current: low, raster width: 2 mm) -Etching rate: 0.09 nm / s for Ta2O5 -Operation Mode: CAE (Constant Analyzer Energy) mode -Survey scan: pass energy 200 eV, energy step 1 eV -Narrow scan: scanned mode, pass energy 50 eV, energy step 0.1 eV -Charge compensation: flood gun off -SF: Al THERMO1 -ECF: TPP-2M -BG subtraction: Shirley

[0157] <Measurement of D / G band ratio by Raman spectroscopy> Specifically, measurements were carried out using a Renishaw 2000 Raman microscope system and laser excitation at 532 nm. To avoid the thermal effect of the laser, measurements were taken with a low laser output density and an exposure time of 30 seconds using a 100x optical lens. To reduce the deviation by position, a total of 25 points were measured for a 5 μm × 5 μm region, and after fitting using a Lorentzian function, the average values of the D band and G band were calculated to compute the D / G band ratio.

[0158]

Table 2

[0159] The average particle size (D 50 ) of the negative electrode active material was measured by the laser scattering method of Microtrac.

[0160] The BET specific surface area of the negative electrode active material was measured using a BET measuring device (BEL-SORP-MAX, Nippon Bell). The gas was removed at 200 °C for 8 hours, and N2 adsorption / desorption was carried out at 77 K.

[0161] The content of the Li atoms was confirmed by ICP analysis using an inductively coupled plasma optical emission spectrometer (ICP-OES, Perkin-Elmer 7300, AVIO 500).

[0162] <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.

[0163] Manufacture of negative electrode As the negative electrode material, the negative electrode active material produced in Example 1 and graphite as a carbon-based active material (average particle size (D 50): 20 μm) were used, which were mixed at a weight ratio of 15:85.

[0164] The negative electrode material, styrene-butadiene rubber (SBR) as a binder, Super C65 as a conductive material, and carboxymethyl cellulose (CMC) as a thickener were mixed at a weight ratio of 96:2:1:1, and this was added to distilled water as a solvent for forming a negative electrode slurry to produce a negative electrode slurry.

[0165] The negative electrode slurry was coated on one side of a copper current collector (thickness: 15 μm) as a negative electrode current collector at a loading amount of 3.6 mAh / cm 2 and rolled (roll press), and dried in a vacuum oven at 130 °C for 10 hours to form a negative electrode active material layer (thickness: 50 μm), which was used as the negative electrode in Example 1A (negative electrode thickness: 65 μm).

[0166] Also, except that the negative electrode active materials produced in Examples 2 to 6 and Comparative Examples 1 to 5 were used instead of the negative electrode active material of Example 1, the negative electrodes of Examples 2 to 6 and Comparative Examples 1 to 5 were produced in the same manner as in Example 1.

[0167] Manufacture of secondary battery A lithium metal foil was prepared as the positive electrode. A porous polyethylene separator was interposed between the negative electrodes and the positive electrodes of Examples 1 to 6 and Comparative Examples 1 to 5 produced above, and an electrolytic solution was injected to produce coin-type half cells of Examples 1 to 6 and Comparative Examples 1 to 5.

[0168] As the electrolyte, a solution in which ethylene methyl carbonate (EMC) and ethylene carbonate (EC) were mixed at a volume ratio of 7:3, vinylene carbonate (VC) was dissolved at 0.5 wt%, and LiPF6 was dissolved at a concentration of 1 M was used.

[0169] Evaluation of capacity retention rate For the secondary batteries produced in Examples 1 to 6 and Comparative Examples 1 to 5, the cycle capacity retention rate was evaluated using an electrochemical charge / discharge device.

[0170] The evaluation of the cycle capacity retention rate was carried out at a temperature of 25°C. For the first cycle and the second cycle, charge and discharge were performed at 0.1C, and from the third cycle onwards, charge and discharge were performed at 0.5C (charging conditions: CC / CV, 5mV / 0.005C cut-off, discharging conditions: CC, 1.5V cut off).

[0171] From the results of the first charge and discharge, the discharge capacity (mAh / g) and the initial efficiency (%) were derived. The capacity retention rate was calculated as follows. Capacity retention rate (%) = {(discharge capacity in the Nth cycle) / (discharge capacity in the first cycle)} × 100 (In the above formula, N is an integer of 1 or more.) The cycle capacity retention rate (%) at the 50th cycle is shown in Table 3 below.

[0172]

Table 3

[0173] The negative electrode active material according to the present invention includes a first carbon layer, a composite layer, and a second carbon layer, and is characterized by a high degree of amorphization of the carbon layer. When an inorganic substance surface layer such as the composite layer is provided, lithium by-products contained in the silicon-based particles can be effectively removed, and unreacted lithium by-products can be effectively coated to prevent the phenomenon that the lithium by-products react with the moisture in the slurry and deteriorate the physical properties of the slurry. In addition, it has the effect of increasing the content of amorphous carbon, effectively controlling the grain size of Si, and improving the stability of the electrode state and / or the charge and discharge capacity.

[0174] In Table 3 above, it can be confirmed that Examples 1 to 6 are excellent in all of the discharge capacity, initial efficiency, and capacity retention rate.

[0175] On the other hand, in Comparative Example 1 and Comparative Example 2, since they do not contain the second carbon layer or do not contain the composite layer, it was confirmed that side reactions with moisture occurred and the initial efficiency and capacity retention rate decreased. In Comparative Example 3, the D / G band ratio is low, the crystallinity of the carbon layer is high, and the carbon coating is performed at a relatively high temperature, so it was confirmed that the size of the Si crystal grains increased and the life performance decreased. In the case of Comparative Example 4, since only an acid is used without using a metal salt, Li inside the silicon-based particles is eluted during the reaction, so a phenomenon of decreasing efficiency and capacity retention rate occurs. In the case of Comparative Example 5, since there is no phosphate, the adsorption capacity decreases, desorption of the composite layer occurs, the passivation effect decreases, and it was confirmed that the efficiency and capacity retention rate decrease.

Claims

1. SiO ｘ (0 < x < 2) and containing Li, and silicon-based particles provided with a first carbon layer on at least a part of the surface, a composite layer provided on at least a part of the silicon-based particles, and a negative electrode active material including a second carbon layer at least partially covering the surface of the composite layer, the negative electrode active material contains Li, M, P, and O elements, the M is Al, B, or Zn, a negative electrode active material in which the D / G band ratio, which is the ratio of the peak intensity of the D band to the peak intensity of the G band during analysis by Raman spectroscopy, is 1.0 or more.

2. The negative electrode active material according to claim 1, wherein the M is Al or B.

3. The negative electrode active material according to claim 1, wherein the molar ratio of the M element and the P element is 1:0.5 to 1:

3.

4. The negative electrode active material according to claim 1, wherein the composite layer contains Li, M, P, and O elements.

5. The elements contained in the composite layer are Li ｘ M ｙ P ｚ O ｗ having a molar ratio of (0 < x ≤ 3, 0 < y ≤ 1, 0.5 ≤ z ≤ 3, 4 < w ≤ 12), the negative electrode active material according to claim 4.

6. The negative electrode active material according to claim 1, wherein a lithium compound exists between the composite layer and the second carbon layer.

7. The lithium compound is Li ２ O, LiOH, and Li ２ CO ３ containing one or more selected from the group consisting of, the negative electrode active material according to claim 6.

8. The composite layer is Li ２ O, LiOH, and Li ２ CO ３ The negative electrode active material according to claim 1, which is formed by reaction of one or more selected from the group consisting of

9. The negative electrode active material according to claim 1, wherein the first carbon layer is contained in an amount of 1 to 5 parts by weight based on 100 parts by weight in total of the negative electrode active material.

10. The negative electrode active material according to claim 1, wherein the composite layer is contained in an amount of 0.5 to 3 parts by weight based on 100 parts by weight in total of the negative electrode active material.

11. The negative electrode active material according to claim 1, wherein the second carbon layer is contained in an amount of 0.5 to 5 parts by weight based on 100 parts by weight in total of the negative electrode active material.

12. The negative electrode active material according to claim 1, wherein the total weight of the first carbon layer and the second carbon layer is 1.5 to 10 parts by weight based on 100 parts by weight in total of the negative electrode active material.

13. SiO ｘ (0 < x < 2) and Li, and forming silicon-based particles provided with a first carbon layer on at least a part of the surface Reacting the silicon-based particles with a phosphate solution to form a composite layer on at least a part of the silicon-based particles, and Forming a second carbon layer that at least partially covers the surface of the composite layer A method for manufacturing a negative electrode active material, comprising:

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

15. A secondary battery comprising the negative electrode according to claim 14.

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