Anode active material, anode slurry containing the same, anode containing the same, secondary battery containing the same, and method for manufacturing anode active material

Abstract

The present invention relates to a negative electrode active material, a negative electrode slurry containing the same, a negative electrode containing the same, a secondary battery containing 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. 10-2021-0176769, filed with the Korean Intellectual Property Office on December 10, 2021, the entire contents of which are incorporated herein by reference.

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

[0003] In recent years, with the rapid spread of battery-powered electronic devices such as mobile phones, laptops, and electric vehicles, the demand for secondary batteries that are small, lightweight, and have relatively high capacity has been rapidly increasing. In particular, lithium secondary batteries, which are lightweight and have high energy density, have attracted attention as power sources for portable devices. For this reason, active research and development efforts are being made to improve the performance of lithium secondary batteries.

[0004] Generally, 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. The positive electrode and the negative electrode may have active material layers formed on current collectors, each containing a positive electrode active material and a negative electrode active material. Generally, the positive electrode uses a lithium-containing metal oxide such as LiCoO2 or LiMn2O4 as the positive electrode active material, and the negative electrode uses a lithium-free carbon-based active material or a silicon-based active material as the negative electrode active material.

[0005] Silicon-based negative electrode active materials have been attracting attention due to their higher capacity and superior fast charging characteristics compared to carbon-based active materials. However, silicon-based active materials have the disadvantage of low initial efficiency due to their large irreversible capacity caused by large volume expansion / contraction during charging / discharging.

[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), it has an advantage in that the degree of volume expansion / contraction due to charge and discharge is smaller compared to other silicon-based active materials such as silicon (Si). However, there is still a disadvantage in that the initial efficiency decreases due to the presence of irreversible capacity in silicon-based oxides as well.

[0007] In relation to 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, silicon-based oxides doped with metals by a general method have a damaged carbon layer coated on the silicon-based oxide and are likely to form lithium by-products. Therefore, in the case of a negative electrode slurry containing a generally 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 problem that the charge and discharge efficiency of the negative electrode decreases. [[ID=​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​ One embodiment of the present invention provides an anode active material comprising: silicon-based particles containing a Li compound; and a carbon layer provided on at least a portion of the silicon-based particles, wherein, in X-ray diffraction analysis, the ratio (p2 / p1) of the peak intensity (p2) appearing at 18.8° to 19.0° to the peak intensity (p1) appearing at 24.7° to 24.9° is 0.7 or more; and the pH of the anode active material when 1 g of the anode active material is dispersed in 100 mL of water at 25°C is 7 to 10.

[0012] One embodiment of the present invention provides a method for producing a negative electrode active material, the method including the steps of: preparing a Si source and a Li source; vaporizing the Si source and the Li source by heat treatment; cooling the vaporized mixed gas of the Si source and the Li source to form silicon-based particles containing a Li compound; and forming a carbon layer on the silicon-based particles.

[0013] One embodiment of the present invention provides a negative electrode slurry containing the negative electrode active material.

[0014] One embodiment of the present invention provides a negative electrode comprising the negative electrode slurry.

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

[0016] The negative electrode active material according to one embodiment of the present invention has a lower pH, closer to neutral than conventional materials, during slurry formation, improving the processability of the slurry. Furthermore, since the crystalline Li2SiO3 and crystalline Li2SiO5 satisfy an appropriate ratio (p2 / p1) or more, a secondary battery including a negative electrode manufactured from the negative electrode active material has improved battery discharge capacity, initial efficiency, resistance performance, and / or life characteristics. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present specification will be explained in more detail below.

[0018] In this specification, when a part "comprises" a certain component, this means that it may further include other components, rather than excluding other components, unless otherwise specified.

[0019] 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.

[0020] The terms and words used in this specification should not be interpreted in a limited way to their ordinary or dictionary meanings, but should be interpreted in a way 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 explain their inventions.

[0021] As used herein, the singular expression of a term includes the plural expression unless the context clearly indicates otherwise.

[0022] In this 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-Endeavor, manufacturer: Bruker), and in addition to the above device, any device commonly used in the art may be appropriately adopted.

[0023] In this specification, the presence or absence of elements in the negative electrode active material and the content of the elements can be confirmed by ICP analysis, which can be performed using an inductively coupled plasma optical emission spectrometer (ICPAES, Perkin-Elmer 7300).

[0024] In this specification, the average particle size (D 50 The average particle size (D) can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve (graph curve of particle size distribution diagram). 50) can be measured, for example, by using a laser diffraction method. The laser diffraction method generally enables measurement of particle sizes from the submicron range to several mm, and can provide results with high reproducibility and high resolution.

[0025] 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.

[0026] <Negative electrode active material> One embodiment of the present invention provides an anode active material comprising: silicon-based particles containing a Li compound; and a carbon layer provided on at least a portion of the silicon-based particles, wherein, in X-ray diffraction analysis, the ratio (p2 / p1) of the peak intensity (p2) appearing at 18.8° to 19.0° to the peak intensity (p1) appearing at 24.7° to 24.9° is 0.7 or more; and the pH of the anode active material when 1 g of the anode active material is dispersed in 100 mL of water at 25°C is 7 to 10.

[0027] Generally, when doping silicon-based particles with Li, the silicon-based particles are coated with a carbon layer and then heat-treated (generally below 1200°C) with lithium powder before doping, or the silicon-based particles and lithium powder are heat-treated (generally below 1200°C) together and then coated with a carbon layer. When doped with Li using these methods, Li compounds (such as lithium silicate) are formed within the silicon-based particles, but the Li compound content is higher toward the outside of the particles. That is, the Li compounds are not formed uniformly inside and outside the silicon-based particles.

[0028] The negative electrode active material formed by the above method has the advantage of increasing initial efficiency due to the formation of Li compounds (such as lithium silicate) within the silicon-based particles. However, the formation of Li compounds within conventional silicon-based particles destroys the particle structure, and the resulting stress causes the Si phase within the silicon-based particles to aggregate, making them vulnerable to volume expansion / contraction.

[0029] In addition, when lithium doping is performed after coating the carbon layer, damage to the carbon layer occurs, and lithium by-products that have not reacted with the silicon-based particles are present on the surface of the active material. Therefore, the lithium by-products present on the surface of the active material exhibit basicity during the preparation of the aqueous slurry, and the Si of the negative electrode active material and the base (OH) of the slurry are mixed. - ) reacts to generate gas, which changes the rheological properties.

[0030] If lithium doping is performed before coating the carbon layer, the thermal energy received during the carbon layer coating process causes the Li compounds in the silicon-based particles to penetrate into the core, changing the internal structure of the particles and resulting in a deterioration in lifespan.In addition, the carbon layer coating is performed while lithium by-products that did not react with the silicon-based particles remain, which reduces the passivation properties of the carbon layer.

[0031] To solve this problem, the present invention provides a negative electrode active material formed by a method in which a Si source and a Li source are each heat-treated to vaporize them, and lithium is doped into silicon-based particles.

[0032] The negative electrode active material manufactured as described above is one in which carbon layers are formed after uniformly doping Li into silicon-based particles. Since the carbon layers are not damaged, the passivation ability by the carbon layers is high. Also, since the source is vaporized to dope Li, there are no lithium by-products in the negative electrode active material, and it shows a lower pH closer to neutrality than in the conventional case during the production of the aqueous slurry, thus suppressing side reactions of the slurry and having the effect of improving processability. Therefore, a secondary battery including a negative electrode manufactured from the negative electrode active material has the effect of improving the discharge capacity, initial efficiency, resistance performance, and / or life characteristics of the battery.

[0033] The negative electrode active material according to an embodiment of the present invention includes silicon-based particles, and the silicon-based particles contain a Li compound. Specifically, the silicon-based particles may contain Si and a Li compound.

[0034] The Li compound may correspond to a matrix within the silicon-based composite 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.

[0035] Specifically, the silicon-based particles may be in a form containing Si and / or SiO2, and the Si may form a phase. The silicon-based particles may have a structure containing SiO x (0 < x < 2) and a Li compound.

[0036] The SiO x (0 < x < 2) may be in a form containing Si and / or SiO2, and the Si may form a phase. For example, the SiO x (0 < x < 2) may be a composite containing amorphous SiO₂ and Si crystals. That is, the x in the SiO xIt corresponds to the number ratio of O to Si contained in (0 < x < 2). The silicon-based particles are the SiO x When (0 < x < 2) is included, the discharge capacity of the secondary battery can be improved. Specifically, the SiO x (0 < x < 2) may be a compound represented by SiO x (0.5 ≦ x ≦ 1.5) in terms of the structural stability of the active material.

[0037] The Li compound may be formed by heating and vaporizing a Li source containing Li2SiO3, Li2Si2O5, Li4SiO4, and Li metal (Li metal), etc., and then reacting with Si vapor or SiO vapor heated and vaporized and then cooling.

[0038] That is, the Li may be distributed on the surface and / or inside of the silicon-based particles in a form doped into the silicon-based particles. The Li 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. Also, the Li may be included in terms of reducing the ratio of the irreversible phase (e.g., SiO2) of the silicon-based oxide particles and increasing the efficiency of the active material.

[0039] The Li compound may be lithium silicate, and the lithium silicate is Li a Si b O c (2 ≦ a ≦ 4, 0 < b ≦ 2, 2 ≦ c ≦ 5), and can be classified into crystalline lithium silicate and amorphous lithium silicate. The crystalline lithium silicate may exist in the form of at least one lithium silicate selected from the group consisting of Li2SiO3, Li4SiO4, and Li2Si2O5 in the silicon-based particles, and the amorphous lithium silicate may consist of a complex (complex) of Li a Si b O c (2 ≦ a ≦ 4, 0 < b ≦ 2, 2 ≦ c ≦ 5), and is not limited to the above form.

[0040] In one embodiment of the invention, the silicon-based particles comprise Li2SiO3 and Li2Si2O5.

[0041] In one embodiment of the present invention, the Li compounds include Li2SiO3 and Li2Si2O5.

[0042] In conventional Li doping methods, silicon-based particles are coated with carbon and then doped with lithium powder by heat treatment, resulting in a high Li concentration at the particle surface and almost no Li at the center of the silicon-based particles.In contrast, in the case of the anode active material according to the present invention, Li is uniformly doped from the center to the surface of the silicon-based particles.

[0043] In one embodiment of the present invention, the Li concentration may not have a concentration gradient from the center to the surface of the silicon-based particle, i.e., the Li concentration may be constant from the center to the surface of the silicon-based particle.

[0044] In one embodiment of the present invention, the concentration of Si may not have a concentration gradient from the center to the surface of the silicon-based particle, that is, the concentration of Si may be constant from the center to the surface of the silicon-based particle.

[0045] The absence of a concentration gradient from the center to the surface of the silicon-based particle means that the concentration of the element does not show a continuous increase / decrease.For example, when the distance Ra from the center to the surface of the silicon-based particle is taken as a reference, the concentration of the element in each region from the center to 0.25Ra, the region from 0.25Ra to 0.5Ra, the region from 0.5Ra to 0.75Ra, and the region from 0.75Ra to the surface may mean that there is no concentration gradient.The distance Ra from the center to the surface of the silicon-based particle can be assumed to be the radius when the silicon-based particle is converted into a sphere with the same cross-sectional area, and the center of the silicon-based particle may mean the center of gravity.

[0046] In one embodiment of the present invention, in an X-ray diffraction analysis of the negative electrode active material, a ratio (p2 / p1) of a peak intensity (p2) appearing at 18.8° to 19.0° to a peak intensity (p1) appearing at 24.7° to 24.9° may be 0.7 or more.

[0047] Specifically, p2 / p1 may be 0.75 or greater, and more specifically, 1 or greater, 10 or greater, 30 or greater, or 50 or greater.

[0048] When the negative electrode active material is subjected to X-ray diffraction analysis, if a peak appears at 24.7° to 24.9°, the upper limit of p2 / p1 may be 300, 200, or 150.

[0049] In the X-ray diffraction analysis of the negative electrode active material, a peak (p1) appearing at 24.7° to 24.9° may be a peak due to crystalline Li2Si2O5.

[0050] In the X-ray diffraction analysis of the negative electrode active material, a peak (p2) appearing at 18.8° to 19.0° may be a peak due to crystalline Li2SiO3.

[0051] The crystalline Li2Si2O5 is stable in the negative electrode active material, and there is little side reaction with water, especially in the negative electrode slurry, specifically in the aqueous negative electrode slurry. However, when the negative electrode active material contains a large amount of crystalline Li2Si2O5, there is a large loss of discharge capacity per weight of the active material, and the crystalline Li2Si2O5 has an unstable structure during charge and discharge, which leads to problems such as a deterioration in life characteristics.

[0052] When a battery contains a large amount of crystalline Li2SiO3, it can reduce the loss of discharge capacity per weight of the active material, and because the crystalline Li2SiO3 has an electrochemically stable structure, it can significantly increase initial efficiency and maintain a stable structure during charge and discharge, effectively improving life characteristics. However, while Li2SiO3 has a higher battery capacity at the same efficiency level than Li2SiO5, it has the problem of undergoing a side reaction with water in the anode slurry, which can result in intense gas generation, and by-products formed by the side reaction with water can increase the pH of the anode slurry, destabilizing the slurry phase and changing its viscosity.

[0053] In this regard, the negative electrode active material of the present invention has a ratio (p2 / p1) of the peak intensity (p2) appearing at 18.8° to 19.0° to the peak intensity (p1) appearing at 24.7° to 24.9° in X-ray diffraction analysis of 0.7 or more, and the content of the crystalline Li2SiO3 and the content of the crystalline Li2Si2O5 satisfy a suitable relationship, so that the irreversible capacity of the negative electrode active material can be smoothly eliminated, the initial efficiency and charge / discharge efficiency can be improved, and improved capacity can be secured compared to the same efficiency.

[0054] In addition, while conventional negative electrode active materials have a problem in that the inclusion of a certain amount of crystalline Li2SiO3 causes side reactions in the negative electrode slurry, the negative electrode active material of the present invention can ensure the phase stability of the negative electrode slurry and prevent the problem of low viscosity even when the material contains a certain amount of crystalline Li2SiO3, thereby improving the quality of the negative electrode and achieving excellent charge / discharge efficiency and capacity.

[0055] On the other hand, if p2 / p1 is less than 0.7, it is not possible to ensure suitable capacity and efficiency, and it is difficult to stably maintain the internal structure of the particles with respect to volume expansion / contraction during charge / discharge.

[0056] In one embodiment of the present invention, the Li compounds include crystalline Li2SiO3 and crystalline Li2Si2O5.

[0057] In one embodiment of the present invention, the content of said crystalline Li2SiO3 is greater than the content of said crystalline Li2Si2O5.

[0058] In one embodiment of the present invention, the crystalline Li2SiO3 may be included in an amount of 20 to 70 parts by weight, specifically 30 to 55 parts by weight, and more specifically 30 to 40 parts by weight, based on 100 parts by weight of the total negative electrode active material. When the content of crystalline Li2SiO3 satisfies the above range, high capacity and high efficiency can be ensured, and Si is uniformly distributed inside the particles, which has the effect of preventing deterioration of the internal structure of the particles due to volume expansion / contraction during charge / discharge.

[0059] In one embodiment of the present invention, the crystalline Li2Si2O5 may be included in an amount of 0.1 to 10 parts by weight, specifically 0.1 to 5 parts by weight, more specifically 0.1 to 4.5 parts by weight, based on 100 parts by weight of the total negative electrode active material. When the content of crystalline Li2Si2O5 satisfies the above range, it has the effect of stably maintaining the internal structure of the particles with respect to volume expansion / contraction during charge / discharge.

[0060] The content of crystalline Li2SiO3 and crystalline Li2Si2O5 present in the negative electrode active material can be determined by Rietveld refinement after obtaining an X-ray diffraction profile by X-ray diffraction analysis (D4 endeavor / x-ray diffraction).

[0061] In one embodiment of the present invention, the Li contained in the silicon-based particles may be 5 to 20 parts by weight, 5 to 10 parts by weight, or 6 to 9 parts by weight, based on 100 parts by weight of the total negative electrode active material. Specifically, it may be 6 to 8 parts by weight, and more specifically, it may be 7 to 8 parts by weight. As the Li content increases, the initial efficiency increases but the discharge capacity decreases. Therefore, when the Li content is within the above range, suitable discharge capacity and initial efficiency can be achieved.

[0062] The Li element content can be confirmed by ICP analysis. Specifically, a certain amount (approximately 0.01 g) of the negative electrode active material is taken and transferred to a platinum crucible. Nitric acid, hydrofluoric acid, and sulfuric acid are added and the material is completely decomposed on a hot plate. Then, an inductively coupled plasma optical emission spectrometer (ICPAES, Perkin-Elmer 7300) is used to measure the intensity of a standard solution (5 mg / kg) prepared at the characteristic wavelength of the element to be analyzed, and a reference calibration curve is created. The pretreated sample solution and a blank sample are then introduced into the instrument, and their respective intensities are measured to calculate the actual intensities. The concentrations of each component are calculated by comparing them with the created calibration curve, and the total is converted to a theoretical value, allowing the element content of the manufactured negative electrode active material to be analyzed.

[0063] According to an embodiment of the present invention, a carbon layer may be provided on at least a portion of the surface of the silicon-based particle. In this case, the carbon layer may be provided on at least a portion of the surface, i.e., the surface of the particle, or may be provided on the entire surface of the particle. The carbon layer may impart conductivity to the anode active material, thereby improving the initial efficiency, life characteristics, and capacity characteristics of the secondary battery.

[0064] Specifically, the carbon layer may include crystalline carbon or amorphous carbon, and preferably includes amorphous carbon.

[0065] The crystalline carbon may 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.

[0066] The amorphous carbon may be a carbon-based material formed by using at least one carbide or hydrocarbon selected from the group consisting of tar, pitch, and other organic substances as a source in a chemical vapor deposition process.

[0067] The carbonized organic material may be a carbonized organic material selected from carbonized sucrose, glucose, galactose, fructose, lactose, mannose, ribose, aldohexose, or ketohexose, and combinations thereof.

[0068] 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, hexane, or the like. The aromatic hydrocarbon of the substituted or unsubstituted aromatic hydrocarbon may be benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, coumarone, pyridine, anthracene, phenanthrene, or the like.

[0069] Specifically, the carbon layer may be formed by disposing a carbonaceous precursor on silicon-based particles and then heat-treating the resulting material. The carbonaceous precursor may be graphene or graphite for producing crystalline carbon, or may be a carbonaceous material formed by using at least one carbide selected from the group consisting of tar, pitch, and other organic substances for producing amorphous carbon, or a hydrocarbon such as methane, ethane, or acetylene as a source in a chemical vapor deposition process.

[0070] In one embodiment of the present invention, the carbon layer does not contain Li.

[0071] In one embodiment of the present invention, no Li is detected on the surface of the negative electrode active material.

[0072] In one embodiment of the present invention, in an XPS analysis of the surface of the negative electrode active material, the molar ratio of Li to C (Li / C molar ratio) may be 1 or less. Specifically, the molar ratio of Li to C (Li / C molar ratio) may be 0.5 or less, 0.3 or less, 0.1 or less, 0.05 or less, or 0.03 or less. The molar ratio of Li to C (Li / C molar ratio) may be 0 or more or greater than 0.

[0073] When the molar ratio of Li to C on the surface of the negative electrode active material (Li / C molar ratio) satisfies the above range, the Li content on the surface of the negative electrode active material is almost zero, and the pH value when dispersed in water is low, preventing changes in rheological properties during slurry formation. In contrast, in the case of silicon-based particles doped with Li using a conventional Li-doping method, the molar ratio of Li to C on the surface of the negative electrode active material (Li / C molar ratio) exceeds the above range, which causes the slurry to become a strong base during slurry formation, resulting in changes in the rheological properties of the slurry and side reactions.

[0074] This can be confirmed by measuring the Li content on the surface of the negative electrode active material using an XPS (Nexsa ESCA System, Thermo Fisher Scientific (NEXSA 1)) depth profile.

[0075] The carbon layer effectively prevents the elution of Li2SiO3 from the silicon-based particles. In addition, by minimizing lithium by-products on the surface of the negative electrode active material, the carbon layer improves passivation ability, and when preparing an aqueous slurry, it can adjust the pH of the slurry, reducing side reactions and improving rheological properties.

[0076] In one embodiment of the present invention, when 1 g of the negative electrode active material is dispersed in 100 mL of water at 25° C., the pH may be 7 to 10. Specifically, it may be 8 to 10, and more specifically, it may be 9 to 9.5.

[0077] In an anode active material according to one embodiment of the present invention, Li is uniformly doped into silicon-based particles without generating lithium by-products during the doping process. Furthermore, by subsequently coating the silicon-based particles with a carbon layer, the silicon-based particles are covered with the carbon layer, resulting in a low pH when dispersed in water and preventing changes in rheological properties during slurry formation. In contrast, in the case of silicon-based particles doped with Li using conventional Li-doping methods, the carbon layer is damaged or lithium by-products are present, resulting in a strongly basic slurry with a pH exceeding 9 when dispersed in water, which can cause changes in the rheological properties of the slurry and side reactions.

[0078] In one embodiment of the present invention, the surface of the negative electrode active material is free of lithium by-products, including at least one selected from the group consisting of lithium silicate, LiO, LiOH, and LiCO. This can be confirmed by measuring the Li content on the surface of the negative electrode active material using an XPS (Nexsa ESCA System, Thermo Fisher Scientific (NEXSA 1)) depth profile.

[0079] In the conventional Li doping method, silicon-based particles are coated with carbon and then doped with lithium powder by heat treatment, which damages the carbon layer and results in the presence of Li compounds in the carbon layer.In addition, unreacted lithium forms lithium by-products and may exist on the surface of the negative electrode active material.

[0080] In contrast, in the case of the anode active material according to the present invention, the carbon layer is formed after doping lithium into silicon-based particles, so the carbon layer is not damaged, the carbon layer does not contain Li compounds, and the passivation ability of the carbon layer in the aqueous slurry is improved. Furthermore, even if unreacted Li exists, the carbon layer is formed on it, so no lithium by-products are present on the surface of the anode active material.

[0081] In one embodiment of the present invention, the carbon layer may be included in an amount of 0.1 to 10 parts by weight, or 1 to 10 parts by weight, specifically 1 to 5 parts by weight, more specifically 2 to 4 parts by weight, based on a total of 100 parts by weight of the negative electrode active material. When the amount is within the above range, a decrease in the capacity and efficiency of the negative electrode active material can be prevented.

[0082] 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 15 μm. When the above range is satisfied, the active material is structurally stable during charge and discharge, the problem of an excessively large particle size resulting in an increased level of volume expansion / contraction is prevented, and the problem of an excessively small particle size resulting in a decrease in initial efficiency is prevented.

[0083] The particle size of the negative active material may be adjusted by methods such as, but not limited to, a ball mill, a jet mill, or air classification.

[0084] <Method of manufacturing negative electrode active material> One embodiment of the present invention provides a method for producing a negative electrode active material, the method including the steps of: preparing a Si source and a Li source; vaporizing the Si source and the Li source by heat treatment; cooling the vaporized mixed gas of the Si source and the Li source to form silicon-based particles containing a Li compound; and forming a carbon layer on the silicon-based particles.

[0085] One embodiment of the present invention provides a method for producing a negative electrode active material, including the steps of preparing a Si source and a Li source; vaporizing the Si source and the Li source by heat treatment, respectively; mixing the vaporized Si source and the Li source, and then cooling the mixed gas to form silicon-based particles containing a Li compound; and forming a carbon layer on the silicon-based particles.

[0086] A method for producing a negative electrode active material according to one embodiment of the present invention includes the steps of providing a Si source and a Li source.

[0087] In one embodiment of the present invention, the Si source may include one or more selected from the group consisting of Si powder and SiO powder. Preferably, the Si source may include Si powder and may further include SiO powder. By vaporizing Si as described above, the present invention allows for vaporization at a lower temperature, making process control easier. In contrast, when vaporizing Si and SiO or vaporizing only SiO, the temperature conditions are not moderate, making process control difficult.

[0088] In one embodiment of the present invention, the Li source may include one or more selected from the group consisting of Li2SiO3 powder, Li2Si2O5 powder, Li4SiO4 powder, and Li powder.

[0089] In particular, when lithium silicate powder is used, the composition can be easily controlled, and the internal structure of the silicon-based particles can be synthesized more uniformly.

[0090] The Li source may include Li2SiO3 powder in an amount of 30 parts by weight or more, 40 parts by weight or more, 50 parts by weight or more, 70 parts by weight or more, 80 parts by weight or more, or 90 parts by weight or more based on the total Li source.

[0091] The weight ratio of the Si source to the Li source may be 5:1 to 1:5, 3:1 to 1:3, or 2:1 to 1:2. It may be preferably 1.2:1 to 1:1.2, and more preferably 1:1. When the ratio is within the above range, it is effective to form particles in which Si and Li compounds (lithium silicate) are uniformly distributed.

[0092] According to an embodiment of the present invention, a method for preparing an anode active material includes a step of vaporizing the Si source and the Li source by heat treatment. Specifically, the Si source and the Li source may be mixed and then heat treated together, or the Si source and the Li source may be heat treated separately.

[0093] The heat treatment may be carried out at a temperature of 1200° C. to 1600° C., preferably 1200° C. to 1500° C., 1300° C. to 1500° C., or 1300° C. to 1400° C., for 1 hour to 10 hours.

[0094] The heat treatment may be carried out in a vacuum or at a pressure of 0.01 torr to 0.1 torr, preferably 0.01 torr to 0.05 torr.

[0095] A method for producing a negative electrode active material according to one embodiment of the present invention includes a step of cooling a mixed gas of vaporized Si source and Li source to form silicon-based particles containing a Li compound.

[0096] The mixed gas may be formed by heat-treating the Si source and the Li source together after mixing them, or by mixing them after heat-treating the Si source and the Li source respectively.

[0097] The cooling may be performed at 500°C to 900°C, preferably 600°C to 850°C, or 600°C to 800°C for 1 hour to 10 hours.

[0098] The cooling may be performed in a vacuum state or at 0.01 torr to 0.1 torr, preferably 0.01 torr to 0.05 torr.

[0099] The silicon-based particles formed by the above process contain a Li compound, and the Li compound may exist in at least one form of lithium atom, lithium silicate, lithium silicide, and lithium oxide within the silicon-based particles, and preferably may exist in the form of lithium silicate.

[0100] The silicon-based particles may be in a form containing Si and SiO2, and the Si may form a phase. The Si and SiO2 may be represented by SiO x (0 < x < 2), and the silicon-based particles may have a structure containing SiO x (0 < x < 2) and Li. [[ID=​​​​​​​​​​Specifically, the silicon-based particles may be introduced into a reactor, and then a hydrocarbon gas may be subjected to chemical vapor deposition (CVD) at a temperature of 1000° C. or less. The hydrocarbon gas may be methane, ethane, propane, or acetylene, and the carbon source may be graphene or graphite for producing crystalline carbon, or at least one carbide selected from the group consisting of tar, pitch, and other organic substances for producing amorphous carbon, or a carbon-based material formed using a hydrocarbon such as methane, ethane, or acetylene as a source for chemical vapor deposition.

[0104] The hydrocarbon gas may be heat-treated at a temperature of 600° C. to 1000° C., preferably 600° C. to 900° C., for 1 hour to 5 hours.

[0105] <Negative electrode slurry> One embodiment of the present invention provides a negative electrode slurry containing the negative electrode active material.

[0106] The negative electrode slurry may include the negative electrode active material, a binder, and a conductive material.

[0107] The negative electrode active material may be a negative electrode active material according to an embodiment of the present invention.

[0108] In the case of conventional Li doping methods, when forming an aqueous slurry, Li compounds are eluted from the damaged carbon layer of the negative electrode active material, and lithium by-products from unreacted lithium cause the pH of the aqueous slurry to exceed 11, making it basic. As a result, the base contained in the negative electrode slurry reacts with Si present in the negative electrode active material to generate gas, which changes the rheological properties of the slurry.

[0109] In contrast, the anode slurry of the present invention uses an anode active material in which lithium is uniformly doped into silicon-based particles and then a carbon layer is formed, so that passivation by the carbon layer in the aqueous slurry prevents elution of lithium compounds, and the aqueous slurry exhibits a lower, near-neutral pH than conventional slurry because there is almost no unreacted lithium by-product. Therefore, the low base content in the slurry suppresses side reactions and improves rheological properties.

[0110] In one embodiment of the present specification, the negative electrode slurry may have a pH of 7 to 9 at 25°C, specifically 7.5 to 8.5, and more specifically 7.5 to 8. 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 9, decomposition of carboxymethyl cellulose (CMC), which is used as a thickener, occurs, causing a decrease in the viscosity of the slurry, and resulting in a decrease in the degree of dispersion of the active material contained in the slurry.

[0111] In one embodiment of the present invention, 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, 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.

[0112] In one embodiment of the present invention, the conductive material is not particularly limited as long as it does not induce a chemical change in the battery and is conductive, and examples thereof 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.

[0113] In one embodiment of the present invention, the negative electrode slurry may further include a thickener. The thickener may be, but is not limited to, carboxymethyl cellulose (CMC), and any thickener used in the art may be used.

[0114] The negative electrode slurry may further include an additional negative electrode active material.

[0115] 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; and SiO. βExamples of the negative electrode active material include metal oxides capable of doping and dedoping lithium, such as SnO2, vanadium oxide, lithium titanium oxide, and lithium vanadium oxide (0<β<2); or composites containing the metallic compounds and carbonaceous materials, such as Si-C composites and Sn-C composites. A mixture of two or more of these may be used. A thin film of metallic lithium may also be used as the negative electrode active material. The carbon material may be either low-crystalline carbon or high-crystalline carbon. Typical low-crystalline carbons are soft carbon and hard carbon, while 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-calcined carbons such as petroleum or coal tar pitch-derived cokes.

[0116] The additional negative electrode active material may be a carbon-based negative electrode active material, for example, graphite.

[0117] In one 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.

[0118] In one 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 the total solid content of the negative electrode slurry.

[0119] 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.

[0120] 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.

[0121] 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, 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.

[0122] The negative electrode slurry according to an embodiment of the present invention may further include a solvent for forming the negative electrode slurry. Specifically, the solvent for forming the negative electrode slurry may 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.

[0123] 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 negative electrode slurry.

[0124] <Negative electrode> An anode according to one embodiment of the present invention may include the anode slurry described above.

[0125] The negative electrode according to an embodiment of the present invention may include the negative electrode active material described above.

[0126] 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 and / or a conductive material.

[0127] The negative electrode may be manufactured by the steps of: preparing a negative electrode slurry including the above-described negative electrode active material; applying the negative electrode slurry onto a negative electrode current collector; and drying and rolling the applied negative electrode slurry.

[0128] The negative electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and is conductive. For example, the current collector may be made of copper, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel whose surface has been 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.

[0129] The negative electrode active material, the binder, and the conductive material are as described above.

[0130] <Secondary battery> A secondary battery according to an embodiment of the present invention may include the anode according to the embodiment described above. Specifically, the secondary battery may include an anode, a cathode, a separator interposed between the cathode and the anode, and an electrolyte, and the anode is the same as the anode described above. Since the anode has been described above, detailed description thereof will be omitted.

[0131] 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.

[0132] The positive electrode current collector in the positive electrode is not particularly limited as long as it does not induce chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like may be used. The positive electrode current collector may typically have a thickness of 3 μm to 500 μm, and the surface of the current collector may be formed with fine irregularities to enhance the adhesive strength of the positive electrode active material. The positive electrode current collector may be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0133] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; a lithium iron oxide such as LiFe3O4; or a compound having the chemical formula Li 1+c1 Mn 2-c1 O4 (0≦c1≦0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, and 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 0.01≦c2≦0.5 is satisfied); 2-c3 M c3 Examples of the lithium manganese composite oxide include, but are not limited to, lithium manganese composite oxides represented by Li2Mn3MO8 (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 Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); or LiMn2O4 in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion. The positive electrode may be lithium metal.

[0134] The positive electrode active material layer may contain a positive electrode conductive material and a positive electrode binder in addition to the above-described positive electrode active material.

[0135] 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 does not cause chemical changes in the battery that is constructed and has electronic conductivity. 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 fiber; metal powder or metal fiber 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 combination.

[0136] The positive electrode binder improves adhesion between positive electrode active material particles and between the positive electrode active material and the positive electrode current collector. Specific examples of the positive electrode binder 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. One or more of these may be used alone or in combination.

[0137] The separator separates the negative electrode and positive electrode and provides a path for lithium ion migration. Any separator typically used in secondary batteries can be used without particular limitations. It is particularly preferable that the separator exhibits low resistance to electrolyte ion migration and has excellent electrolyte humidification capacity. Specifically, porous polymer films, such as those made from polyolefin polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminate structures of two or more layers thereof, may be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. To ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymeric material may be used, and it may be selectively used as a single-layer or multi-layer structure.

[0138] 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 manufacturing lithium secondary batteries.

[0139] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0140] 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, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0141] In particular, among the carbonate organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are preferably used as high-viscosity organic solvents, have a high dielectric constant, and dissociate lithium salts well. When such cyclic carbonates are mixed with linear carbonates having low viscosity and low dielectric constants, such as dimethyl carbonate and diethyl carbonate, in an appropriate ratio, an electrolyte having high electrical conductivity can be prepared, and therefore such cyclic carbonates are even more preferably used.

[0142] 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 - , 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:

[0143] In addition to the constituent 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 dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing a decrease in battery capacity, and improving the discharge capacity of the battery.

[0144] 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 high cycle characteristics, and 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.

[0145] Below, preferred examples are presented to help understand the present invention. However, the above examples are merely illustrative of 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. It goes without saying that such changes and modifications fall within the scope of the appended claims.

[0146] <Examples and Comparative Examples> Example 1 94 g of powders of Si and Li2SiO3 mixed in a molar ratio of 2:1 were mixed in a reactor and then vacuum heated at a sublimation temperature of 1,400°C. The vaporized Si and Li2SiO3 mixed gas was then reacted in a vacuum cooling zone with a cooling temperature of 800°C and solidified to produce silicon-based particles. The silicon-based particles were pulverized using a ball mill for 3 hours to obtain an average particle size (D 50 Then, while maintaining an inert atmosphere by flowing Ar gas, the silicon-based particles were placed in the hot zone of a CVD apparatus, and methane was blown into the hot zone at 900°C using Ar as a carrier gas to form a 10 -1 The reaction was carried out at torr for 5 hours to produce a negative electrode active material in which a carbon layer was formed on the surface of the silicon-based particles.

[0147] Example 2 A negative electrode active material was prepared in the same manner as in Example 1, except that Si, Li2SiO3, and Li2Si2O5 powders were mixed in a ratio of 2:0.4:0.6, respectively.

[0148] Example 3 A negative electrode active material was prepared in the same manner as in Example 1, except that Si, Li2SiO3, and Li4SiO4 powders were mixed in a ratio of 2:0.95:0.05, respectively.

[0149] Comparative Example 1 94 g of powders of Si and SiO2 mixed in a 1:1 molar ratio were mixed in a reactor and then vacuum heated at a sublimation temperature of 1,400°C. The vaporized Si and SiO2 mixed gas was then reacted in a vacuum cooling zone with a cooling temperature of 800°C, and solidified to form silicon-based particles. The silicon-based particles were pulverized using a ball mill for 3 hours, and D 50 Then, while maintaining an inert atmosphere by flowing Ar gas, the silicon-based particles were placed in the hot zone of a CVD apparatus, and methane was blown into the hot zone at 900°C using Ar as a carrier gas to form a 10 -1 The silicon-based particles were reacted at torr for 5 hours to form a carbon layer on the surface of the silicon-based particles.The particles were then mixed with 8 g of Li metal powder and further heat-treated at 800°C in an inert atmosphere to prepare a negative electrode active material.

[0150] Comparative Example 2 A negative electrode active material was prepared in the same manner as in Comparative Example 1, except that the content of Li metal powder was 5 g.

[0151] Comparative Example 3 An AlPO4 layer was coated on the negative active material prepared in Comparative Example 1 to prepare a negative active material.

[0152] Specifically, a solution obtained by mixing 0.1M Al2(SO4)3 solution and 0.1M H3PO4 solution in a ratio of 1:2 to 1:6 was mixed with the negative active material prepared in Comparative Example 1 in a weight ratio of 1:5, and the mixture was stirred for 1 hour, filtered, and dried to prepare a negative active material coated with an AlPO4 layer in a weight ratio of 1%.

[0153] Comparative Example 4 A negative electrode active material was prepared in the same manner as in Example 1, except that Si, Li2SiO3, and Li2Si2O5 powders were mixed in a ratio of 2:0.2:0.8, respectively.

[0154] The composition of the negative electrode active materials produced in the above Examples and Comparative Examples was measured as follows and shown in Table 1.

[0155] <X-ray Diffraction Analysis> The X-ray diffraction analysis was performed using an XRD (X-ray diffraction) instrument (product name: D4-endeavor, manufacturer: bruker). A powdered sample was sampled into a holder and irradiated with Cu K alpha X-ray.

[0156] <Measurement of Carbon Layer Content> The content of the carbon layer was measured using a CS-analyzer (CS-800, ELTRA).

[0157] <Analysis by X-ray Photoelectron Spectroscopy (XPS)> The molar ratio of Li to C (Li / C mol ratio) on the surface of the negative electrode active material was confirmed by the depth profile of XPS (Nexsa ESCA System, Thermo Fisher Scientific (NEXSA 1)). Specifically, the depth profile was performed using monatomic Ar (low current) up to 3,000 seconds, and the elemental content was confirmed from the results at 100 seconds of the depth profile.

[0158] The measurement and data processing conditions are as follows.

[0159] -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 200eV, energy step 1eV -Narrow scan: scanned mode, pass energy 50eV, energy step 0.1eV -Charge compensation: flood gun off -SF: Al THERMO1 -ECF: TPP-2M -BG subtraction: Shirley Under the above conditions, the molar ratio of Li to C (Li / C mol ratio) was calculated based on the total content of the elements measured per 100 seconds as a reference.

[0160] <Measurement of pH> After dispersing 1 g of the negative electrode active material in 100 g of Di water at 25°C, the pH was measured using a pH meter.

[0161]

Table 1

[0162] <Experimental Example: Evaluation of Discharge Capacity, Initial Efficiency, and Life (Capacity Retention) Characteristics> As the negative electrode material, a mixture of the negative electrode active material produced in Example 1 and graphite (average particle size (D 50 ): 20 μm) with a weight ratio of 15:85 was used.

[0163] The above 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.

[0164] The negative electrode slurry was applied to one side of a copper current collector (thickness: 15 μm) as a negative electrode current collector at 3.6 mAh / cm 2The coated layer was rolled 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 of Example 1 (thickness of negative electrode: 65 μm).

[0165] 1.7671cm 2 The lithium (Li) metal thin film cut into a circular shape was used as the positive electrode. A porous polyethylene separator was placed between the positive electrode and the negative electrode, and an electrolyte solution prepared by dissolving 0.5 parts by weight of vinylene carbonate in a mixed solution of ethyl methyl carbonate (EMC) and ethylene carbonate (EC) in a volume ratio of 7:3 and dissolving LiPF6 at a concentration of 1M was injected to fabricate a lithium coin half-cell.

[0166] In addition, the batteries of Examples 2, 3, and Comparative Examples 1 to 4 were each manufactured in the same manner as Example 1, except that the negative electrode active material of Example 1 was replaced with the negative electrode active material of Example 2, Example 3, and Comparative Examples 1 to 4, respectively.

[0167] The manufactured batteries were charged and discharged to evaluate the discharge capacity, initial efficiency, and capacity retention rate, and the results are shown in Table 2 below.

[0168] The first and second cycles were charged and discharged at 0.1 C, and from the third cycle onwards, the charge and discharge rate was 0.5 C. The 300th cycle ended in a charged state (with lithium in the negative electrode).

[0169] Charging conditions: CC (constant current) / CV (constant voltage) (5mV / 0.005C current cut-off) Discharge condition: CC (constant current) condition 1.5V The discharge capacity (mAh / g) and initial efficiency (%) were calculated from the results of one charge / discharge. Specifically, the initial efficiency (%) was calculated as follows:

[0170] Initial efficiency (%) = (discharge capacity after one discharge / one charge capacity) x 100 The capacity retention rate was calculated as follows.

[0171] Capacity retention rate (%) = (299 discharge capacity / 1 discharge capacity) × 100

[0172] [Table 2]

[0173] The negative electrode active material according to one embodiment of the present invention is manufactured by uniformly doping Li to minimize lithium by-products on the particle surface, and then coating the particles with a carbon layer to stabilize side reactions and rheological properties during slurry formation. Furthermore, the ratio of crystalline Li2SiO3 and crystalline Li2SiO5 is at or above an appropriate ratio (p2 / p1), resulting in excellent battery discharge capacity, initial efficiency, and capacity retention.

[0174] In Table 2, Examples 1 to 3 have a peak intensity p2 / p1 of 0.7 or more, a very low Li / C molar ratio on the surface of the negative electrode active material, and a low pH when dispersed in water. Therefore, it was confirmed that the rheological properties of the slurry are stable, side reactions are minimized, and the battery discharge capacity, initial efficiency, and capacity retention rate are all excellent.

[0175] In contrast, in Comparative Examples 1 to 3, the raw materials were heat-treated without vaporization during the preparation of the negative electrode active material, resulting in the generation of unreacted lithium by-products during the lithium doping process. As a result, the Li / C molar ratio near the surface of the negative electrode active material was very high, and the pH when dispersed in water was 12 or higher, indicating strong basicity. Even when an additional inorganic coating was performed as in Comparative Example 3, the lithium by-products made it difficult for the negative electrode active material to be completely coated, indicating strong basicity. Therefore, it was confirmed that side reactions with the negative electrode active material occurred, deteriorating the physical properties of the slurry and decreasing the initial efficiency and capacity retention rate.

[0176] In the case of Comparative Example 4, it was confirmed that the p2 / p1 ratio was less than 0.7, the content of crystalline Li2Si2O5 was high, the loss of discharge capacity per weight of active material was large, the structure was unstable, and the life characteristics were deteriorated, resulting in a decrease in initial efficiency and capacity retention rate.

Claims

1. A negative electrode active material comprising silicon-based particles containing a Li compound and a carbon layer provided on at least a portion of the silicon-based particles, In X-ray diffraction analysis, the ratio (p2 / p1) of the peak intensity (p2) appearing at 18.8° to 19.0° to the peak intensity (p1) appearing at 24.7° to 24.9° is 50 or more; The negative electrode active material has a pH of 9 to 10 when 1 g of the negative electrode active material is dispersed in 100 mL of water at 25°C.

2. The silicon-based particles include Li ２ SiO ３ and Li ２ Si ２ O ５ The negative electrode active material according to claim 1 , comprising:

3. The negative electrode active material according to claim 1 , wherein the concentration of Li does not have a concentration gradient from the center to the surface of the silicon-based particle.

4. The negative electrode active material according to claim 1 , wherein a molar ratio of Li to C is 1 or less when the surface of the negative electrode active material is analyzed by XPS.

5. 2. The negative electrode active material of claim 1, wherein the silicon-based particles contain 5 to 10 parts by weight of Li based on a total of 100 parts by weight of the negative electrode active material.

6. The negative electrode active material of claim 1 , wherein the carbon layer is included in an amount of 0.1 to 10 parts by weight based on a total of 100 parts by weight of the negative electrode active material.

7. providing a Si source and a Li source; a step of vaporizing the Si source and the Li source by heat treatment; cooling the vaporized mixed gas of the Si source and the Li source to form silicon-based particles containing a Li compound; and forming a carbon layer on the silicon-based particles; Including, The Li source is Li ２ SiO ３ Contains powder, The Li ２ SiO ３ The method for producing a negative electrode active material, wherein the powder is contained in an amount of 30 parts by weight or more based on the total Li source.

8. The method for producing a negative electrode active material according to claim 7 , wherein the Si source comprises at least one selected from the group consisting of Si powder and SiO powder.

9. The Li source is Li ４ SiO ４ Powder, Li ２ Si ２ O ５ The method for producing a negative electrode active material according to claim 7 , further comprising at least one selected from the group consisting of a Li powder and a Li powder.

10. The method for producing a negative electrode active material according to claim 7, wherein the heat treatment is carried out at 1200°C to 1600°C.

11. The method for producing a negative electrode active material according to claim 7, wherein the mixed gas is cooled at 500°C to 900°C.

12. A negative electrode slurry comprising the negative electrode active material according to any one of claims 1 to 6.

13. An anode comprising the anode slurry of claim 12.

14. A secondary battery comprising the negative electrode according to claim 13.

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