Negative active material, negative electrode comprising same, secondary battery comprising same, and method for preparing negative active material

Abstract

The present invention relates to a negative electrode active material comprising silicon-based particles and a coating layer formed on at least a portion of the silicon-based particles, in which the silicon-based particles comprise SiOx (0lt; xlt; 2) and a Li compound, and a carbon layer is formed on at least a part of the surface thereof, the coating layer comprising an amphiphilic polymer.

Description

Technical Field

[0001] The present invention relates to a negative electrode active material, a negative electrode including the same, a secondary battery including the negative electrode, and a method for preparing the negative electrode active material.

[0002] This application claims the priority and benefit of Korean Patent Application No. 10-2022-0172768, filed with the Korean Intellectual Property Office on December 12, 2022, the entire contents of which are incorporated herein by reference. Background Art

[0003] In recent years, with the rapid popularization of electronic devices using batteries, such as mobile phones, laptop computers, and electric vehicles, the demand for small, lightweight, and relatively high-capacity secondary batteries has been rapidly increasing. In particular, lithium secondary batteries have attracted much attention as a driving power source for portable devices due to their light weight and high energy density. Therefore, research and development efforts to improve the performance of lithium secondary batteries are being actively carried out.

[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, for the positive electrode and the negative electrode, active material layers respectively including a positive electrode active material and a negative electrode active material may be formed on a current collector. Generally, for the positive electrode, lithium-containing metal oxides such as LiCoO2 and LiMn2O4 are used as the positive electrode active material, and for the negative electrode, a carbon-based active material or a silicon-based active material不含锂 is used as the negative electrode active material.

[0005] Among the negative electrode active materials, silicon-based active materials have attracted attention because they have a higher capacity and excellent high-speed charging characteristics compared to carbon-based active materials. However, the silicon-based active materials have the disadvantages that the degree of volume expansion / shrinkage during charge and discharge is large, and the irreversible capacity is large, so the initial efficiency is low.

[0006] On the other hand, among the silicon-based active materials, silicon-based oxides, specifically silicon-based oxides represented by SiO x (0 < x < 2) have the advantage that the degree of volume expansion / shrinkage during charge and discharge is lower than that of other silicon-based active materials such as silicon (Si). However, the silicon-based oxides still have the following disadvantages: the initial efficiency is reduced due to the presence of an irreversible capacity.

[0007] In this regard, research has been conducted to reduce the irreversible capacity and improve the initial efficiency by doping or embedding metals such as Li, Al, and Mg into silicon-based oxides. However, the negative electrode paste containing silicon-based oxides doped with metals as the negative electrode active material has the following problems: the metal oxides formed by doping metals react with moisture, thereby increasing the pH value of the negative electrode paste and changing the viscosity, and the negative electrode active material agglomerates in the paste, resulting in reduced dispersibility. Therefore, the prepared negative electrode has a poor state, and the charge-discharge efficiency of the negative electrode is reduced.

[0008] Therefore, there is a need to develop a negative electrode active material that can improve the phase stability of the negative electrode paste containing silicon-based oxides and improve the charge-discharge efficiency of the negative electrode prepared from the paste.

[0009] Citation List

[0010] Patent Literature

[0011] Patent Document 1: Korean Patent No. 10-0794192 Summary of the Invention

[0012] Technical Problem

[0013] The present invention relates to a negative electrode active material, a negative electrode containing the same, a secondary battery containing the negative electrode, and a method for preparing the negative electrode active material.

[0014] Technical Solution

[0015] An exemplary embodiment of the present invention provides a negative electrode active material, which includes: silicon-based particles, the silicon-based particles containing SiO x (0 < x < 2) and a Li compound, and having a carbon layer provided on at least a part of the surface; and a coating containing an amphiphilic polymer provided on at least a part of the silicon-based particles.

[0016] Another exemplary embodiment of the present invention provides a negative electrode containing the negative electrode active material.

[0017] Still another exemplary embodiment of the present invention provides a secondary battery containing the negative electrode.

[0018] An exemplary embodiment of the present invention provides a method for manufacturing a negative electrode active material, the method including: forming silicon-based particles, the silicon-based particles containing SiO x (0 < x < 2) and a Li compound, and having a carbon layer provided on at least a part of the surface; and reacting the silicon-based particles with an amphiphilic polymer precursor.

[0019] Advantageous Effects

[0020] The negative electrode active material according to the exemplary embodiment of the present invention includes a coating containing an amphiphilic polymer disposed on the outermost surface of the silicon-based particles containing the Li compound, and thus has the effect of improving the aqueous processability of the slurry. Specifically, since the amphiphilic polymer includes a hydrophilic group and a hydrophobic group, the amphiphilic polymer reduces the reactivity between the active material and water due to the hydrophobic group, and prevents moisture from penetrating from the aqueous slurry into the negative electrode active material, thereby effectively passivating the silicon-based particles. In addition, since the side reaction between the silicon-based particles or lithium byproducts and water is prevented to suppress gas generation, it has the effect of improving the aqueous processability of the slurry.

[0021] At the same time, due to the hydrophilic group contained in the amphiphilic polymer, it has the effect of improving the dispersibility of the negative electrode active material in the aqueous slurry.

[0022] Therefore, the negative electrode including the negative electrode active material according to the exemplary embodiment of the present invention and the secondary battery including the negative electrode have the effect of improving the discharge capacity, initial efficiency, resistance properties and / or life characteristics of the battery. DETAILED DESCRIPTION

[0023] Hereinafter, the present specification will be described in more detail.

[0024] In the present specification, when a portion is referred to as “comprising” specific constituent elements, unless explicitly described otherwise, this does not mean to exclude other constituent elements but means that the portion may further include other constituent elements.

[0025] In this specification, when a member is referred to as being disposed 'on' another member, the member may be in direct contact with the other member, or an intervening member may also be present.

[0026] It should be understood that the terms or words used throughout the specification should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted with meanings and concepts consistent with the technical spirit of the present invention based on the principle that the inventor can appropriately define the concepts of the words or terms to best interpret the present invention.

[0027] As used herein, the singular expressions “a”, “an” and “the” are intended to include the plural expressions as well, unless the context clearly indicates otherwise.

[0028] In the present specification, the crystallinity of the structure contained in the negative electrode active material can be confirmed by X-ray diffraction analysis, and the X-ray diffraction analysis can be performed using an X-ray diffraction (XRD) analyzer (trade name: D4-endeavor, manufacturer: Bruker), or in addition to the above-mentioned device, a device used in the field can also be appropriately adopted.

[0029] In this specification, the presence or absence of elements and the content of elements in the negative electrode active material can be confirmed by ICP analysis, and the ICP analysis can be performed using an inductively coupled plasma atomic emission spectrometer (ICP AES, Perkin-Elmer 7300).

[0030] In this specification, the average particle diameter (D 50 ) can be defined as the particle diameter corresponding to 50% of the cumulative volume in the particle size distribution curve (the curve of the particle size distribution diagram). The average particle diameter (D 50 ) can be measured using, for example, the laser diffraction method. In the laser diffraction method, the particle diameter in the range from the submicron region to several millimeters can generally be measured, and results with high reproducibility and high resolution can be obtained.

[0031] Hereinafter, preferred embodiments of the present invention will be described in detail. However, it should be understood that the embodiments of the present invention can be modified into various other forms, and the scope of the present invention is not limited to the embodiments described hereinafter.

[0032] <Negative electrode active material>

[0033] An exemplary embodiment of the present invention provides a negative electrode active material, which includes: silicon-based particles, the silicon-based particles containing SiO x (0 < x < 2) and a Li compound, and having a carbon layer provided on at least a part of the surface; and a coating containing an amphiphilic polymer provided on at least a part of the silicon-based particles.

[0034] The negative electrode active material according to an exemplary embodiment of the present invention includes silicon-based particles. The silicon-based particles contain SiO x (0 < x < 2) and a Li compound.

[0035] The SiO x (0 < x < 2) can correspond to the matrix in the silicon-based particles. The SiO x (0 < x < 2) can be in a form containing Si and / or SiO2, and Si can form a phase. That is, x corresponds to the ratio of the number of O contained in the SiO x (0 < x < 2) to Si. When the silicon-based particles contain the SiO x (0 < x < 2), the discharge capacity of the secondary battery can be improved.

[0036] The Li compound may correspond to a dopant in the silicon-based particles. The Li compound may exist in the silicon-based particles in the form of at least one of lithium atoms, lithium silicates, lithium silicides, and lithium oxides. When the silicon-based particles contain the Li compound, the initial efficiency is improved.

[0037] The Li compound may be distributed on the surface and / or inside of the silicon-based particles in a form that dopes the silicon-based particles. The Li compound may be distributed on the surface and / or inside of the silicon-based particles, serving to control the volume expansion / contraction of the silicon-based particles at an appropriate level and prevent damage to the active material. In addition, the Li compound may be included in terms of reducing the proportion of the irreversible phase (such as SiO2) of the silicon-based oxide particles to improve the efficiency of the active material.

[0038] In an exemplary embodiment of the present invention, the Li compound may exist in the form of a lithium silicate. The lithium silicate is represented by Li a Si b O c (2 ≤ a ≤ 4, 0 < b ≤ 2, 2 ≤ c ≤ 5), and can be classified into crystalline lithium silicate and amorphous lithium silicate. The crystalline lithium silicate may exist in the silicon-based particles in the form of at least one lithium silicate selected from the group consisting of Li2SiO3, Li4SiO4, and Li2Si2O5, and the amorphous lithium silicate may have a complex form of Li a Si b O c (2 ≤ a ≤ 4, 0 < b ≤ 2, 2 ≤ c ≤ 5). However, the present invention is not limited thereto.

[0039] In an exemplary embodiment of the present invention, based on a total of 100 parts by weight of the negative electrode active material, the content of Li may be 0.1 part by weight to 40 parts by weight or 0.1 part by weight to 25 parts by weight. Specifically, the content of Li may be 1 part by weight to 25 parts by weight, and more specifically 2 parts by weight to 20 parts by weight. As the Li content increases, the initial efficiency increases, but the discharge capacity decreases. Therefore, when the content satisfies the above range, an appropriate discharge capacity and initial efficiency can be achieved.

[0040] The content of Li element can be confirmed by ICP analysis. Specifically, after accurately weighing a predetermined amount (about 0.01 g) of the negative electrode active material, it is transferred to a platinum crucible, and the negative electrode active material is completely decomposed on a hot plate by adding nitric acid, hydrofluoric acid or sulfuric acid thereto. Thereafter, a reference calibration curve is prepared by measuring the intensity of a standard solution prepared using a standard solution (5 mg / kg) at the inherent wavelength of the element to be analyzed using an inductively coupled plasma atomic emission spectrometer (ICPAES, Perkin-Elmer 7300). Thereafter, the pretreated sample solution and the blank sample are introduced into the spectrometer, the actual intensity is calculated by measuring the respective intensities, the concentration of each component is calculated relative to the prepared calibration curve, and the conversion is performed so that the sum of the calculated concentrations of the components is equal to the theoretical value, and the element content of the prepared negative electrode active material can be analyzed.

[0041] In an exemplary embodiment of the present invention, the silicon-based particles may contain additional metal atoms. The metal atoms may be present in the silicon-based particles in the form of at least one of metal atoms, metal silicates, metal silicides, and metal oxides. The metal atoms may contain at least one selected from the group consisting of Mg, Li, Al, and Ca. Thus, the initial efficiency of the negative electrode active material can be improved.

[0042] In an exemplary embodiment of the present invention, the silicon-based particles are provided with a carbon layer on at least a portion of their surface. In this case, the carbon layer may be coated on at least a portion of the surface, that is, may be partially coated on the particle surface or may be coated on the entire particle surface. Through the carbon layer, conductivity is imparted to the negative electrode active material, thereby being able to improve the initial efficiency, service life characteristics, and battery capacity characteristics of the secondary battery.

[0043] In an exemplary embodiment of the present invention, the carbon layer includes amorphous carbon.

[0044] Furthermore, the carbon layer may further include crystalline carbon.

[0045] 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.

[0046] The amorphous carbon can appropriately maintain the strength of the carbon layer to suppress the expansion of the silicon-based particles. The amorphous carbon can be a carbide of at least one substance selected from the group consisting of tar, pitch, and other organic materials, or can be a carbon-based material formed by using hydrocarbons as a source for chemical vapor deposition.

[0047] The carbide of the other organic material may be a carbide of an organic substance selected from sucrose, glucose, galactose, fructose, lactose, mannose, ribose, aldohexose or ketohexose, and a combination thereof.

[0048] 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, etc. 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, etc.

[0049] In an exemplary embodiment of the present invention, the carbon layer may be an amorphous carbon layer.

[0050] In an exemplary embodiment of the present invention, the content of the carbon layer may be 0.1 to 50 parts by weight, 0.1 to 30 parts by weight, or 0.1 to 20 parts by weight, based on a total of 100 parts by weight of the negative electrode active material. More specifically, the content of the carbon layer may be 0.5 to 15 parts by weight, 1 to 10 parts by weight, or 1 to 5 parts by weight. When the above range is met, the capacity and efficiency of the negative electrode active material can be prevented from being reduced.

[0051] In an exemplary embodiment of the present invention, the thickness of the carbon layer may be 1 nm to 500 nm, specifically 5 nm to 300 nm. When the above range is met, the conductivity of the negative electrode active material is improved, the volume change of the negative electrode active material is easily suppressed, and the side reaction between the electrolyte and the negative electrode active material is suppressed, thereby improving the initial efficiency and / or service life of the battery.

[0052] Specifically, the 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.

[0053] In an exemplary embodiment of the present invention, a coating layer containing an amphiphilic polymer is provided on at least a portion of the silicon-based particles.

[0054] The amphiphilic polymer is a material having both a hydrophilic group and a hydrophobic group. The amphiphilic polymer may include one or more selected from the group consisting of polyethylene glycol-polypropylene oxide (PEG-PPO), polyethylene glycol-polystyrene (PEG-PS), polystyrene-poly (butyl acrylate) (PS-PBA), polylysine-polypropylene oxide (Polylysine-PPO), and polylysine-polystyrene (Polylysine-PS), and preferably may include PEG-PS.

[0055] Specifically, in the manufacturing process of the negative electrode active material, silicon-based particles (wherein the silicon-based particles are provided with a carbon layer on at least a portion of the surface) are formed, doped with Li, and then coated with an amphiphilic polymer to introduce a coating containing an amphiphilic polymer on at least a portion of the silicon-based particles.

[0056] The weight average molecular weight of the amphiphilic polymer may be 100 g / mol to 50,000 g / mol, and specifically may be 1,000 g / mol to 30,000 g / mol or 5,000 g / mol to 20,000 g / mol.

[0057] In the present invention, the weight average molecular weight (Mw) of the amphiphilic polymer can be measured using an Agilent 1200 series, by gel permeation chromatography (GPC), using a polystyrene (PS) standard. Specifically, the weight average molecular weight can be measured using an Agilent 1200 series device, using a Polymer Laboratories PLgel MIX-B 300 mm long column. In this case, the measurement temperature is 40 ° C, the solvent used is tetrahydrofuran (THF), and the flow rate is 1 mL / min. Prepare each sample with a concentration of 10 mg / 10 mL, then supply it in an amount of 10 μL, and use a calibration curve formed with a polystyrene standard to derive the weight average molecular weight (Mw) value. In this case, nine polystyrene standards were used, whose molecular weights (g / mol) were 2,000 / 10,000 / 30,000 / 70,000 / 200,000 / 700,000 / 2,000,000 / 4,000,000 / 10,000,000, respectively.

[0058] The amphiphilic polymer may include a hydrophilic group-containing unit and a hydrophobic group-containing unit.

[0059] The hydrophilic group-containing unit may be a unit derived from polyethylene glycol (PEG), polylysine, poly[oligo(ethylene glycol) methyl ether methacrylate] (POEGMA), polyvinyl alcohol (PVA), polyglutamic acid (PGA), polyvinyl pyrrolidone (PVP), polyacrylamide (PAM), etc. However, it is not limited thereto, and the hydrophilic group-containing unit known in the art may be appropriately used for the amphiphilic polymer.

[0060] The hydrophilic group-containing unit may be arranged near the outermost surface of the negative electrode active material. By introducing the hydrophilic group into the negative electrode active material, the agglomeration between the negative electrode active materials in the aqueous slurry may be effectively suppressed, thereby improving the dispersibility.

[0061] Based on 100 parts by weight of the amphiphilic polymer in total, the content of the unit containing the hydrophilic group may be 20 to 80 parts by weight, specifically 30 to 70 parts by weight or 40 to 60 parts by weight. When the above range is met, the dispersibility in the slurry is improved, and when the above range is not met, there is a problem of agglomeration between particles in the slurry.

[0062] The unit containing the hydrophobic group may be a unit derived from polystyrene (PS), polypropylene oxide (PPO), polylactic acid (PLA), polysebacic acid (PSA), polylactic acid-co-glycolic acid (PLGA), polyaspartic acid (PASP), etc. However, it is not limited thereto, and units containing hydrophobic groups known in the art may be appropriately used for the amphiphilic polymer. By introducing a hydrophobic group into the negative electrode active material, the reactivity between the negative electrode active material and water can be reduced, thereby preventing moisture in the aqueous slurry from penetrating into the negative electrode active material, and preventing the side reaction between the silicon-based particles or lithium byproducts and water, thereby inhibiting the generation of gas, which has the effect of improving the water-based processability of the slurry.

[0063] The content of the hydrophobic group-containing unit may be 20 to 80 parts by weight, specifically 30 to 70 parts by weight or 40 to 60 parts by weight, based on 100 parts by weight of the amphiphilic polymer in total. When the above range is met, there is an effect of preventing moisture from reacting with the active material, while when the above range is not met, there is a problem of moisture penetrating into the active material and reducing processability.

[0064] That is, the surface of the negative electrode active material is coated with the amphiphilic polymer containing both hydrophilic groups and hydrophobic groups, thereby simultaneously introducing hydrophobic groups that improve the water resistance of the negative electrode active material and hydrophilic groups that improve the dispersibility, effectively improving the water-based processability of the slurry.

[0065] The weight ratio of the hydrophilic group-containing unit to the hydrophobic group-containing unit may be 20:80 to 80:20, specifically 30:70 to 70:30 or 40:60 to 60:40. When the above range is met, the dispersibility of the slurry is excellent, and it has the effect of preventing water from penetrating into the particles. When the above range is not met, the dispersibility in the slurry is deteriorated, resulting in agglomeration between particles or water penetrating into particles to cause a reaction.

[0066] After ultrasonic treatment of a mixture of 20 g of the negative electrode active material and 80 g of distilled water, the mixture was passed through a max The negative active material according to an exemplary embodiment of the present invention may have a dispersibility according to the following Formula 1 of 70% or more when the mesh size corresponds to 0.1 μm.

[0067] [Formula 1]

[0068]

[0069] In the above formula 1, W t represents the total weight of the negative electrode active material contained in the mixture, W r It represents the weight of the negative electrode active material that has not passed through the mesh when the mixture has passed through the mesh.

[0070] The dispersibility according to Formula 1 may be 70% or more, 73% or more, 75% or more, 80% or more, 85% or more, or 88% or more, and may be 100% or less.

[0071] Specifically, the ultrasonic treatment may be performed for 1 to 10 minutes, preferably 5 minutes.

[0072] The dispersibility may be measured after the mixture is ultrasonically treated and allowed to stand for 10 minutes before passing the mixture through the screen.

[0073] The mesh may have a D max The corresponding diameter size can be appropriately measured by using a sieve made of a material commonly used in the technical field to measure the dispersibility.

[0074] Generally, when the negative electrode active material is mixed with distilled water, agglomeration of the negative electrode active material occurs, and the agglomerated negative electrode active material cannot pass through the sieve, resulting in poor dispersibility. However, since the negative electrode active material according to the present invention includes an amphiphilic polymer coating on its surface, agglomeration between the negative electrode active materials in the aqueous slurry is effectively suppressed, thereby improving dispersibility.

[0075] In an exemplary embodiment of the present invention, the coating layer containing an amphiphilic polymer may be provided on at least a portion of the carbon layer, or may be provided on at least a portion of a region on the surface of the silicon-based particle where the carbon layer is not provided.

[0076] The coating containing the amphiphilic polymer may be coated on a portion of the surface of the silicon-based particles or the carbon layer, or may be coated on the entire surface of the silicon-based particles or the carbon layer. The coating containing the amphiphilic polymer may be in an island shape or a film shape, specifically in an island shape.

[0077] In the present invention, the content of the amphiphilic polymer on the surface of the negative electrode active material can be analyzed by a combustion analyzer. Specifically, the carbon content can be analyzed by burning about 0.5 g of a sample in 99.95% pure oxygen using a G4 ICARUS HF manufactured by Bruker.

[0078] In an exemplary embodiment of the present invention, based on a total of 100 parts by weight of the negative electrode active material, the content of the coating containing the amphiphilic polymer may be 0.005 parts by weight to 20 parts by weight. Specifically, the content of the coating containing the amphiphilic polymer may be 0.01 parts by weight to 10 parts by weight, 0.05 parts by weight to 5 parts by weight, 0.1 parts by weight to 5 parts by weight, or 0.5 parts by weight to 5 parts by weight. The upper limit of the content of the coating may be 20 parts by weight, 15 parts by weight, 10 parts by weight, 7 parts by weight, 5 parts by weight, 4.5 parts by weight, 4 parts by weight, 3 parts by weight, 2 parts by weight, or 1 part by weight, and the lower limit of the content of the coating may be 0.005 parts by weight, 0.01 parts by weight, 0.05 parts by weight, 0.1 parts by weight, 0.3 parts by weight, 0.5 parts by weight, 0.6 parts by weight, or 0.7 parts by weight.

[0079] When the amphiphilic polymer is introduced within the above range, the water resistance and dispersibility of the negative electrode active material can be effectively improved. On the other hand, if the content of the amphiphilic polymer is lower than the above range, sufficient water resistance and dispersibility cannot be ensured due to the low content of the hydrophilic group and the hydrophobic group. If the content of the amphiphilic polymer is higher than the above range, the dispersion and passivation effects are reduced due to the uneven distribution of the coating, and the capacity and efficiency of the negative electrode active material are reduced because the amphiphilic coating does not participate in the electrochemical reaction.

[0080] In an exemplary embodiment of the present invention, the weight ratio of the coating layer containing the amphiphilic polymer to the carbon layer may be 1:99 to 70:30, specifically 5:95 to 60:40 or 10:90 to 50:50.

[0081] In an exemplary embodiment of the present invention, the lithium byproduct may be present on the silicon-based particles. Specifically, the lithium byproduct may be present on the surface of the silicon-based particles or on the surface of the carbon layer. In addition, the lithium byproduct may be present between the coating layer containing the amphiphilic polymer and the silicon-based particles.

[0082] Specifically, the lithium byproduct may mean a lithium compound remaining near the surface of the silicon-based particle or the carbon layer after preparing the silicon-based particle. As described above, even after the acid treatment process, lithium byproducts that have not reacted with the acid may remain.

[0083] The lithium by-product may include one or more selected from the group consisting of Li2O, LiOH, and Li2CO3.

[0084] The presence or absence of the lithium by-product may be confirmed by X-ray diffraction analysis (XRD) or X-ray photoelectron analysis (XPS).

[0085] Based on a total of 100 parts by weight of the negative electrode active material, the content of the lithium by-product may be 5 parts by weight or less. Specifically, the content of the lithium by-product may be 0.001 to 5 parts by weight, 0.01 to 5 parts by weight, 0.05 to 2 parts by weight, or 0.1 to 1 part by weight. More specifically, the content of the lithium by-product may be 0.1 to 0.8 parts by weight or 0.1 to 0.5 parts by weight. When the content of the lithium by-product meets the above range, the side reactions in the slurry can be reduced, and the change in viscosity can be reduced, thereby improving the water-based processability characteristics. On the other hand, when the content of the lithium by-product is higher than the above range, the slurry becomes alkaline when formed, which may cause side reactions or viscosity changes and water-based processability problems.

[0086] Regarding the content of the lithium by-product, the amount of the HCl solution in a specific interval of pH change may be measured using a titrator during titration of the aqueous solution containing the negative electrode active material with the HCl solution, and then the amount of the lithium by-product may be calculated.

[0087] The average particle size of the negative electrode active material (D 50 ) may be 0.1 μm to 30 μm, specifically 1 μm to 20 μm, and more specifically 1 μm to 10 μm. When the above range is met, the structural stability of the active material during charge and discharge is ensured, and the problem of increasing the volume expansion / contraction level due to the particle size becoming too large can be prevented, and the problem of reducing the initial efficiency due to the particle size becoming too small can also be prevented.

[0088] <Method for preparing negative electrode active material>

[0089] An exemplary embodiment of the present invention provides a method for preparing a negative electrode active material, the method comprising: forming silicon-based particles comprising SiO x (0 < x < 2) and a Li compound, and having a carbon layer provided on at least a part of the surface; and reacting the silicon-based particles with an amphiphilic polymer precursor.

[0090] The silicon-based particles can be formed by the steps of: heating and vaporizing Si powder and SiO2 powder under vacuum, depositing the vaporized mixed gas to form precursor particles; forming a carbon layer on the surface of the formed precursor particles; and mixing the precursor particles having the carbon layer formed thereon with Li powder and performing heat treatment. Specifically, the mixed powder of the Si powder and the SiO2 powder can be heat-treated under vacuum at 1300 °C to 1800 °C, 1400 °C to 1800 °C, or 1400 °C to 1600 °C.

[0091] The formed precursor particles can have the form of SiO.

[0092] The carbon layer can be formed by chemical vapor deposition (CVD) using a hydrocarbon gas or by carbonizing a material as a carbon source.

[0093] Specifically, the carbon layer can be formed by the following method: introducing the formed precursor particles into a reaction furnace, and then depositing a hydrocarbon gas by chemical vapor deposition (CVD) at 600 to 1200 °C. The hydrocarbon gas can be at least one hydrocarbon gas selected from the group consisting of methane, ethane, propane, and acetylene, and heat treatment can be performed at 900 °C to 1000 °C.

[0094] The step of mixing the precursor particles having the carbon layer formed thereon with Li powder and performing heat treatment can be carried out at 700 °C to 900 °C for 4 to 6 hours, specifically at 800 °C for 5 hours.

[0095] The silicon-based particles can contain Li silicate, Li silicide, Li oxide, etc. as the above Li compound.

[0096] The particle size of the silicon-based particles can be adjusted by methods such as a ball mill, a jet mill, or air classification, but the present invention is not limited thereto.

[0097] As described above, a lithium compound (lithium by-product) is provided on at least a part of the surface of the silicon-based particles having the carbon layer. Specifically, in the formation of the inclusion of SiO xDuring the process of preparing the above-mentioned silicon-based particles by using precursor particles where (0 < x < 2), forming a carbon layer on the precursor particles, and then doping with Li, a Li compound, i.e., a lithium by-product formed from unreacted lithium, remains near the surface of the silicon-based particles.

[0098] In an exemplary embodiment of the present invention, a method for manufacturing a negative electrode active material includes reacting the silicon-based particles with an amphiphilic polymer precursor to coat at least a part of the silicon-based particles with the amphiphilic polymer.

[0099] The amphiphilic polymer precursor can be a precursor capable of forming the aforementioned PEG-PPO, PEG-PS, PS-PBA, polylysine-PPO, or polylysine-PS. In one example, polystyrene-block-polyethylene oxide (PS-b-PEO) or polystyrene-block-poly(butyl acrylate) (PS-b-PBA) can be used as the amphiphilic polymer precursor.

[0100] The step of reacting the silicon-based particles with the amphiphilic polymer precursor may include: activating the surface of the silicon-based particles; and mixing the silicon-based particles and the amphiphilic polymer in a solvent.

[0101] The activation step can specifically be carried out by exposing the silicon-based particles to ultraviolet light. By activating the surface of the silicon-based particles, the amphiphilic polymer can be easily coated on the silicon-based particles.

[0102] The weight ratio of the silicon-based particles to the amphiphilic polymer can be from 99.9:0.1 to 80:20. Specifically, the weight ratio can be from 99.5:0.5 to 85:15 or from 99:1 to 90:10. By reacting the silicon-based particles and the amphiphilic polymer within the above range, the water resistance and dispersibility of the negative electrode active material can be effectively improved. On the other hand, if an excessive amount of the amphiphilic polymer is included, due to uneven coating distribution, the dispersibility and passivation effect are reduced, and since the amphiphilic coating does not participate in the electrochemical reaction, the capacity and efficiency of the negative electrode active material will decrease.

[0103] The silicon-based particles and the amphiphilic polymer can be mixed in a solvent and then stirred to dispose the amphiphilic polymer on the surface of the silicon-based particles.

[0104] The solvent can preferably be dimethyl sulfoxide (DMSO), but is not limited thereto, and solvents used in the technical field can be appropriately adopted.

[0105] The stirring can be carried out for 30 minutes to 6 hours, preferably 1 hour to 5 hours or 2 hours to 4 hours.

[0106] The negative electrode active material containing an amphiphilic polymer introduced by the above method can improve the aqueous processability of the slurry and improve the dispersibility of the negative electrode active material in the slurry, so that the negative electrode can be stably formed. Therefore, the negative electrode containing the negative electrode active material according to the present invention and the secondary battery containing the negative electrode can have improved discharge capacity, initial efficiency, resistance performance and / or life characteristics of the battery.

[0107] <Negative electrode>

[0108] A negative electrode according to an exemplary embodiment of the present invention may include the above-mentioned negative electrode active material.

[0109] Specifically, the negative electrode may include a negative electrode current collector and the 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. In addition, the negative electrode active material layer may further include a binder, a thickener and / or a conductive material.

[0110] The negative electrode active material layer may be formed by applying a negative electrode slurry including the negative electrode active material, a binder, a thickener and / or a conductive material to at least one surface of a current collector, and drying and rolling it.

[0111] The negative electrode slurry may further include additional negative electrode active materials.

[0112] As the additional negative electrode active material, a compound capable of reversibly intercalating and deintercalating lithium can be used. Specific examples include: carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metal compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; metal oxides capable of doping and dedoping lithium, such as SiO β (0<β<2), SnO2, vanadium oxide, lithium titanium oxide and lithium vanadium oxide; or a composite comprising a metal compound and a carbonaceous material, such as a Si-C composite or a Sn-C composite, and any one thereof or a mixture of two or more thereof can be used. In addition, a metallic lithium film can be used as the negative electrode active material. In addition, both low-crystalline carbon and high-crystalline carbon can be used as the carbon material. Representative examples of the low-crystalline carbon include soft carbon and hard carbon, and representative examples of the high-crystalline carbon include amorphous, plate-like, flaky, spherical or fibrous natural graphite or artificial graphite, floating graphite, pyrolytic carbon, mesophase pitch-based carbon fibers, mesophase carbon microbeads, mesophase pitch, and high-temperature fired carbon (e.g., coke from petroleum or coal tar pitch).

[0113] The additional negative electrode active material may be a carbon-based negative electrode active material.

[0114] The negative electrode slurry may include a solvent for forming the negative electrode slurry. Specifically, from the perspective of facilitating the dispersion of components, the negative electrode slurry may include at least one selected from the group consisting of distilled water, ethanol, methanol, and isopropanol, specifically distilled water.

[0115] The negative electrode slurry including the negative electrode active material according to an exemplary embodiment of the present invention may have a pH of 7 to 11 at 25° C. When the pH of the negative electrode slurry satisfies the above range, the rheological properties of the slurry are stabilized. On the other hand, when the pH of the negative electrode slurry is less than 7 or the pH of the negative electrode slurry exceeds 11, carboxymethyl cellulose (CMC) used as a thickener decomposes, resulting in a decrease in the viscosity of the slurry and a decrease in the dispersion of the active material contained in the slurry.

[0116] The negative electrode current collector is not particularly limited as long as it has conductivity and does not cause chemical changes in the battery. For example, as the current collector, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel each surface-treated with carbon, nickel, titanium, silver, etc. can be used. Specifically, transition metals such as copper and nickel that adsorb carbon well can be used as current collectors. The current collector may have a thickness of 6 μm to 20 μm. However, the thickness of the current collector is not limited thereto.

[0117] The binder may include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene propylene diene monomer rubber (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, polyacrylic acid and the above materials in which hydrogen is replaced by Li, Na, Ca, etc., and may also include various copolymers thereof.

[0118] There is no particular limitation on the conductive material as long as it has conductivity without causing chemical changes in the battery. For example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black and thermal black; conductive fibers such as carbon fibers or metal fibers; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon powders, aluminum powders and nickel powders; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives, etc. can be used.

[0119] The thickener may be carboxymethyl cellulose (CMC), but is not limited thereto, and thickeners used in the art may be appropriately used.

[0120] In an exemplary embodiment of the present invention, a weight ratio of the negative electrode active material and the additional negative electrode active material included in the negative electrode slurry may be 1:99 to 30:70, specifically 5:95 to 30:70 or 10:90 to 20:80.

[0121] In an exemplary embodiment of the present invention, the content of all negative electrode active materials in the negative electrode slurry may be 60 to 99 parts by weight, specifically 70 to 98 parts by weight, based on a total of 100 parts by weight of solid components of the negative electrode slurry.

[0122] In an exemplary embodiment of the present invention, the binder may be included in an amount of 0.5 to 30 parts by weight, for example 1 to 20 parts by weight, based on a total of 100 parts by weight of solid content of the negative electrode slurry.

[0123] In an exemplary embodiment of the present invention, the content of the conductive material may be 0.5 to 25 parts by weight, specifically 1 to 20 parts by weight, based on a total of 100 parts by weight of the solid content of the negative electrode slurry.

[0124] In an exemplary embodiment of the present invention, the thickener may be included in an amount of 0.5 to 25 parts by weight, specifically 0.5 to 20 parts by weight, more specifically 1 to 20 parts by weight, based on a total of 100 parts by weight of the solid content of the negative electrode slurry.

[0125] The negative electrode slurry according to an exemplary embodiment of the present invention may further include a solvent for forming the negative electrode slurry. Specifically, from the perspective of facilitating the dispersion of components, the negative electrode slurry forming solvent may include at least one selected from the group consisting of distilled water, ethanol, methanol and isopropanol, specifically distilled water.

[0126] In an exemplary embodiment of the present invention, the solid content of the negative electrode slurry may be 20 to 75 parts by weight, specifically 30 to 70 parts by weight, based on a total of 100 parts by weight of the negative electrode slurry.

[0127] <Secondary Battery>

[0128] A secondary battery according to an exemplary embodiment of the present invention may include the negative electrode according to the exemplary embodiment described above. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and the negative electrode is the same as the negative electrode described above. Since the negative electrode has been described above, its specific description is omitted.

[0129] The positive electrode may include a positive electrode collector and a positive electrode active material layer formed on the positive electrode collector and including a positive electrode active material.

[0130] In the positive electrode, there is no particular restriction on the positive electrode collector, as long as the positive electrode collector has conductivity and does not cause chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, fired carbon, aluminum or stainless steel each surface-treated with carbon, nickel, titanium, silver, etc., etc. can be used. In addition, the positive electrode collector can generally have a thickness of 3 to 500 μm, and fine concavoconvexities can be formed on the surface of the collector to enhance the adhesion of the positive electrode active material. For example, the positive electrode collector can be used in various forms, such as films, sheets, foils, nets, porous bodies, foams, and non-woven fabrics.

[0131] 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) and lithium nickel oxide (LiNiO2), or a compound replaced by one or more transition metals; a lithium iron oxide such as LiFe3O4; a lithium manganese oxide such as Li 1+c1 Mn 2-c1 O4 (0≤c1≤0.33), LiMnO3, LiMn2O3 and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5 and Cu2V2O7; Ni-site lithium nickel oxide, with the chemical formula LiNi 1-c2 M c2 O2 (wherein 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≤0.3); lithium manganese composite oxide, represented by the chemical formula LiMn 2-c3 M c3 O2 (wherein M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn and Ta, and satisfies 0.01≤c3≤0.1) or Li2Mn3MO8 (wherein M is at least one selected from the group consisting of Fe, Co, Ni, Cu and Zn); LiMn2O4, in which a portion of the Li in the chemical formula is replaced by an alkaline earth metal ion, etc., but is not limited thereto. The positive electrode may be Li metal.

[0132] The positive electrode active material layer may further include a positive electrode conductive material and a positive electrode binder in addition to the positive electrode active material.

[0133] In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and can be used without particular limitation, as long as the positive electrode conductive material has electronic conductivity without causing chemical changes in the constituted battery. Specific examples may 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; or conductive polymers, such as polyphenylene derivatives, etc., and any one thereof or a mixture of two or more thereof may be used.

[0134] In addition, the positive electrode binder is used to improve the bonding between the positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode collector. Specific examples may include: polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer rubber (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber or various copolymers thereof, and any one thereof or a mixture of two or more thereof may be used.

[0135] The diaphragm is used to separate the negative electrode and the positive electrode, and provides a mobile channel for lithium ions, wherein any diaphragm can be used as a diaphragm without particular limitation, as long as the diaphragm is generally used as a secondary battery, in particular, it is preferred to use a diaphragm with high electrolyte moisture retention ability and low resistance to the movement of electrolyte ions. Specifically, a porous polymer film can be used, for example, a porous polymer film manufactured by a polyolefin-based polymer (such as, ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer), or a laminated structure of more than two layers thereof. In addition, conventional porous nonwoven fabrics can be used, such as nonwoven fabrics formed by high melting point glass fiber, polyethylene terephthalate fiber, etc. In addition, a coated diaphragm comprising a ceramic component or a polymer material can be used to ensure heat resistance or mechanical strength, and a diaphragm with a monolayer or multilayer structure can be selectively used.

[0136] Examples of the electrolyte may include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, etc., which may be used to prepare a lithium secondary battery, but are not limited thereto.

[0137] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0138] As the nonaqueous organic solvent, for example, an aprotic organic solvent such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate or ethyl propionate can be used.

[0139] Especially, in the carbonate-based organic solvent, ethylene carbonate and propylene carbonate as cyclic carbonate have high dielectric constant as high viscosity organic solvent, thus well dissociate lithium salt, and therefore can be preferably used. When the cyclic carbonate can be mixed with low viscosity and low dielectric constant linear carbonate (such as dimethyl carbonate and diethyl carbonate) in an appropriate ratio, an electrolyte with high conductivity can be prepared, and therefore can be more preferably used.

[0140] As the metal salt, a lithium salt can be used. The lithium salt is a material that is easily dissolved in a non-aqueous electrolyte. For example, as the anion of the lithium salt, a metal salt selected from the group consisting of 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 of the groups consisting of.

[0141] In the electrolyte, in order to improve the service life characteristics of the battery, inhibit the reduction of the battery capacity and improve the discharge capacity of the battery, in addition to containing the above-mentioned electrolyte components, one or more additives may be included, for example, halogenated alkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme dimethyl ether, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted Oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol or aluminum trichloride.

[0142] Another exemplary embodiment of the present invention provides a battery module including the secondary battery as a unit cell, and a battery pack including the battery module. Since the battery module and the battery pack include the secondary battery having high capacity, high rate capability, and high cycle characteristics, the battery module and the battery pack can be used as a power source for medium and large devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0143] Mode for the Invention

[0144] <Examples and Comparative Examples>

[0145] Example 1

[0146] After mixing 94 g of Si and SiO2 powder mixed in a 1:1 molar ratio in a reaction furnace, vacuum heating was performed to a sublimation temperature of 1,400°C. Then, the mixed gas of vaporized Si and SiO2 was reacted in a cooling zone under a vacuum state at a cooling temperature of 800°C and condensed into a solid phase. Then, the condensed particles were crushed using a ball mill for 3 hours to produce silicon-based particles with a size of 6 μm. Thereafter, while argon gas was flowed to maintain an inert atmosphere, the silicon-based particles were placed in a hot zone of a CVD device, and methane was blown into the hot zone at 900°C using argon as a carrier gas at 10 -1The reaction was carried out under the support for 20 minutes to form a carbon layer on the surface of the silicon-based particles. Then, 6g of Li metal powder was added, and an additional heat treatment was performed at a temperature of 800°C in an inert atmosphere, and the particle surface was activated by exposing the particle surface to ultraviolet light. Next, polyethylene glycol-block-polystyrene (PEG-b-PS) and silicon-based particles were mixed in a dimethyl sulfoxide (DMSO) solvent at a weight ratio of 1:99, and the mixture was stirred at room temperature to react for 2 hours to prepare a negative electrode active material formed with a polymer coating.

[0147] Example 2

[0148] A negative active material was prepared in the same manner as in Example 1, except that PEG-b-PS was changed to PS-b-PBA.

[0149] Example 3

[0150] A negative electrode active material was prepared in the same manner as in Example 1 except that the weight ratio of PEG-b-PS:silicon-based particles was changed to 10:90.

[0151] Comparative Example 1

[0152] A negative electrode active material was prepared in the same manner as in Example 1, except that the step of forming the polymer coating layer was not performed.

[0153] Comparative Example 2

[0154] A negative active material was prepared in the same manner as in Example 1, except that the solvent in Example 1 was changed to water, PEG-b-PS was changed to hexamethyldisilazane (HMDS), and heat was applied to introduce trimethylsilyl groups on the surface.

[0155] <Carbon layer content analysis>

[0156] The content of the carbon layer was analyzed using a CS analyzer (CS-800, ELTRA).

[0157] <Analysis of Li content in negative electrode active materials>

[0158] The Li atom content was confirmed by ICP analysis using an inductively coupled plasma atomic emission spectrometer (ICP-OES, AVIO500, Perkin-Elmer 7300).

[0159] <Analysis of amphiphilic polymer content>

[0160] The content of the amphiphilic polymer was confirmed by carbon content analysis using a combustion analyzer (G4 ICARUS HF, from Bruker Corporation).

[0161] <Negative electrode active material D 50 And analysis of specific surface area>

[0162] The D of the negative active material was analyzed by laser diffraction particle size analysis using a Microtrac S3500 instrument. 50 The BET specific surface area of ​​the negative electrode active material was measured using a BET measuring instrument (BEL-SORP-MAX, Bell Company, Japan).

[0163] The analysis results of the negative electrode active materials produced in the above-mentioned Examples and Comparative Examples are shown in Table 1 below.

[0164]

[0165] <Experimental Example: Evaluation of Discharge Capacity, Initial Efficiency, and Life (Capacity Retention Rate) Characteristics>

[0166] A negative electrode and a battery were manufactured using the negative electrode active materials of the example and the comparative example, respectively.

[0167] The negative electrode active material, carbon black as a conductive material, and polyacrylic acid (PAA) as a binder were mixed in a weight ratio of 80:10:10 to prepare a mixture. Then, 7.8 g of distilled water was added to 5 g of the mixture, and then stirred to prepare a negative electrode slurry. The negative electrode slurry was applied on a copper (Cu) metal film having a thickness of 20 μm as a negative electrode collector and dried. In this case, the temperature of the circulating air was 60 ° C. Then, the film was rolled and dried in a vacuum oven at 130 ° C for 12 hours to prepare a negative electrode.

[0168] Cut the lithium foil into 1.7671cm 2 A lithium (Li) metal film obtained by forming a circular shape is used as a positive electrode. A porous polyethylene separator is inserted between the positive electrode and the negative electrode, and an electrolyte is injected to manufacture a lithium coin-type half-cell. The electrolyte is obtained 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 to a concentration of 1M.

[0169] The prepared battery was charged and discharged to evaluate the discharge capacity, initial efficiency and capacity retention rate, as shown in Table 2 below.

[0170] The first and second cycles were charged and discharged at 0.1 C, and the third to 49th cycles were charged and discharged at 0.5 C. At the 50th cycle, the charge and discharge were terminated in the charged state (the negative electrode contained lithium).

[0171] Charging conditions: CC (constant current) / CV (constant voltage) (5mV / 0.005C current cutoff)

[0172] Discharge conditions: CC (constant current) condition 1.5V

[0173] The discharge capacity (mAh / g) and initial efficiency (%) are obtained from the results after one charge and discharge. Specifically, the initial efficiency (%) is obtained by the following calculation.

[0174] Initial efficiency (%) = (one discharge capacity / one charge capacity) × 100

[0175] The capacity retention rate was calculated as follows.

[0176] Capacity retention rate (%) = (49 discharge capacity / 1 discharge capacity) × 100

[0177] <Experimental Example: Evaluation of Slurry Dispersibility>

[0178] The negative electrode active materials prepared in each of Examples 1 to 3 and Comparative Examples 1 to 2 were mixed with distilled water at a weight ratio of 20:80, ultrasonically treated for 5 minutes, allowed to stand for 10 minutes, and then the diameter size of each negative electrode active material was compared with D max Corresponding to the sieve, the active material remaining on the sieve was dried in an oven at 80°C for at least half a day, and then its weight was measured.

[0179] The dispersion was calculated as follows.

[0180]

[0181] W t represents the total weight of the negative electrode active material contained in the mixture, W r It represents the weight of the negative electrode active material that has not passed through the mesh when the mixture has passed through the mesh.

[0182] <Experimental Example: Evaluation of Processability (Gas Generation) Characteristics>

[0183] As part of the processability evaluation, 20 g of a slurry prepared by mixing graphite, the negative electrode active material, carbon black, CMC and PAA in a weight ratio of 77:20:1:1:1 was placed in a bag of about 10 cm*15 cm, then vacuum-sealed and placed in an oven at 40°C to measure the volume change.

[0184] The gas generation time (hours) was measured based on the time when the bag volume increased by 2 mL or more relative to the volume measured immediately after the bag was vacuum-sealed. The results are shown in Table 2 below.

[0185]

[0186] The negative electrode active material according to the present invention is characterized in that a coating containing an amphiphilic polymer is provided on the silicon-based particles containing the Li compound. Since the hydrophobic groups of the amphiphilic polymers have low reactivity with water, the inorganic layer does not react with the water in the aqueous slurry and is well maintained, thereby preventing water from penetrating into the negative electrode active material to effectively passivate the silicon-based particles. In addition, since the side reaction between the silicon-based particles or lithium byproducts and water is prevented, the generation of gas is suppressed, so that the water-based processability of the slurry is improved. At the same time, since the hydrophilic groups contained in the amphiphilic polymers are located on the surface of the negative electrode active material, the dispersibility of the negative electrode active material in the aqueous slurry is improved.

[0187] On the other hand, it can be confirmed that, as in Comparative Example 1, when a polymer coating is not formed, it is difficult to form a stable electrode due to low aqueous dispersibility, and due to the side reaction between lithium by-products and water, the gas generation time point of the negative electrode slurry is advanced, resulting in deterioration of the processability of the slurry and a significant reduction in the capacity retention rate of the secondary battery using the negative electrode active material.

[0188] In Comparative Example 2, in order to make the surface of the negative electrode active material hydrophobic, trimethylsilyl groups were introduced instead of the polymer coating. It can be confirmed that although the gas generation time point of the negative electrode slurry is delayed, the hydrophilicity of the negative electrode active material is still reduced, the aqueous dispersibility is also low, and the capacity retention rate of the secondary battery using the negative electrode active material is significantly reduced.

Claims

1. A negative electrode active material comprising: Silicon-based particles, the silicon-based particles containing SiO x (0 < x < 2) and a Li compound, and having a carbon layer provided on at least a part of the surface; and A coating layer containing an amphiphilic polymer is disposed on at least a portion of the silicon-based particles. 2 . The negative electrode active material according to claim 1 , wherein the amphiphilic polymer comprises a unit containing a hydrophilic group and a unit containing a hydrophobic group. 3 . The negative electrode active material according to claim 2 , wherein the hydrophilic group-containing unit is a unit derived from one or more selected from the group consisting of polyethylene glycol, polylysine, and poly[oligo(ethylene glycol) methyl ether methacrylate]. 4 . The negative electrode active material according to claim 2 , wherein the hydrophobic group-containing unit is a unit derived from one or more selected from the group consisting of polystyrene and polypropylene oxide. 5 . The negative electrode active material according to claim 2 , wherein a weight ratio of the hydrophilic group-containing unit to the hydrophobic group-containing unit is 3:7 to 7:

3. 6 . The negative electrode active material according to claim 1 , wherein the coating layer containing the amphiphilic polymer is contained in an amount of 0.005 parts by weight to 20 parts by weight based on a total of 100 parts by weight of the negative electrode active material. 7 . The negative electrode active material according to claim 1 , wherein the amphiphilic polymer comprises one or more selected from the group consisting of PEG-PPO, PEG-PS, PS-PBA, polylysine-PPO, and polylysine-PS.

8. The negative electrode active material according to claim 1, wherein a mixture of 20 g of the negative electrode active material and 80 g of distilled water is subjected to ultrasonic treatment and then the mixture is passed through a max When the corresponding mesh is used, the negative electrode active material has a dispersibility of more than 70% according to the following formula 1, [Formula 1] In formula 1, W t represents the total weight of the negative electrode active material contained in the mixture, W r It represents the weight of the negative electrode active material that has not passed through the mesh when the mixture has passed through the mesh. 9 . The negative electrode active material according to claim 1 , further comprising a lithium byproduct provided on at least a portion of the silicon-based particles. 10 . The negative electrode active material according to claim 9 , wherein the content of the lithium by-product is 5 parts by weight or less based on 100 parts by weight of the total negative electrode active material. 11 . The negative electrode active material according to claim 1 , wherein the content of Li is 0.1 parts by weight to 40 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 carbon layer is contained in an amount of 0.1 parts by weight to 50 parts by weight based on a total of 100 parts by weight of the negative electrode active material.

13. A method for preparing a negative electrode active material according to any one of claims 1 to 12, the method comprising: Form silicon-based particles, the silicon-based particles containing SiO x (0 < x < 2) and a Li compound, and having a carbon layer provided on at least a part of the surface; and The silicon-based particles are reacted with an amphiphilic polymer precursor. 14 . A negative electrode comprising the negative electrode active material according to claim 1 . 15 . A secondary battery comprising the negative electrode according to claim 14 .

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