Negative electrode active material, negative electrode containing the same, secondary battery containing the same, and method for producing negative electrode active material

Abstract

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

Description

Technical Field

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

[0002] This application claims the benefit of the filing date of Korean Patent Application No. 10-2022-0172768, filed with the Korean Intellectual Property Office on December 12, 2022, and all of its contents are incorporated herein by reference.

Background Art

[0003] In recent years, with the rapid spread of electronic devices using batteries, such as mobile phones, notebook computers, and electric vehicles, the demand for secondary batteries that are small, lightweight, and relatively high in capacity has been rapidly increasing. In particular, lithium secondary batteries are lightweight and have a high energy density, and have been in the spotlight as a driving power source for portable devices. Accordingly, research and development efforts to improve the performance of lithium secondary batteries have been 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 solution, an organic solvent, and the like. In addition, an active material layer containing a positive electrode active material and a negative electrode active material can be formed on a current collector for the positive electrode and the negative electrode. Generally, lithium-containing metal oxides such as LiCoO2 and LiMn2O4 are used as the positive electrode active material for the positive electrode, and carbon-based active materials and silicon-based active materials that do not contain lithium are used as the negative electrode active material for the negative electrode.

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

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

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

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

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0010] The present invention relates to a negative electrode active material, a negative electrode containing the same, a secondary battery containing the same, and a method for manufacturing the negative electrode active material.

Means for Solving the Problems

[0011] One embodiment of the present invention is SiO xSilicon-based particles containing (0 < x < 2) and a Li compound, with a carbon layer provided on at least a part of the surface; and a coating layer containing an amphiphilic polymer provided on at least a part of the silicon-based particles are provided as a negative electrode active material.

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

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

[0014] One embodiment of the present invention is SiO x A method for manufacturing a negative electrode active material is provided, including the steps of forming silicon-based particles containing (0 < x < 2) and a Li compound, with a carbon layer provided on at least a part of the surface; and reacting the silicon-based particles with an amphiphilic polymer precursor.

Effects of the Invention

[0015] The negative electrode active material according to one embodiment of the present invention includes a coating layer containing an amphiphilic polymer provided on the outermost surface of silicon-based particles containing a Li compound, and thus has the effect of improving the water-based processability of the slurry. Specifically, since the amphiphilic polymer contains a hydrophilic group and a hydrophobic group, the hydrophobic group reduces the reactivity between the active material and water, and prevents moisture from penetrating into the negative electrode active material in the water-based slurry, so that the silicon-based particles can be efficiently passivated. In addition, it has the effect of improving the water-based processability of the slurry by preventing side reactions between the silicon-based particles or lithium by-products and water and suppressing gas generation.

[0016] At the same time, the hydrophilic group contained in the amphiphilic polymer has the effect of improving the dispersibility of the negative electrode active material in the water-based slurry.

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

Mode for Carrying Out the Invention

[0018] Hereinafter, the present specification will be described in more detail.

[0019] In this specification, when a certain part “includes” a certain component, this means that, unless otherwise stated to the contrary, it does not exclude other components, but may further include other components.

[0020] In this specification, when a certain member is “on” another member, this includes not only the case where a certain member is in contact with another member, but also the case where there is another member between the two members.

[0021] The terms and words used in this specification should not be construed as being limited to their ordinary or dictionary meanings. The inventors should interpret them in accordance with the meaning and concept consistent with the technical idea of the present invention, in accordance with the principle that they can appropriately define the concept of the terms in order to explain their invention in the best way.

[0022] The singular expressions of the terms used in this specification include plural expressions unless the context clearly indicates otherwise.

[0023] In this specification, the crystallinity of the structure contained in the negative electrode active material can be confirmed by X-ray diffraction analysis. The X-ray diffraction analysis can be performed using an XRD (X-ray diffraction) analyzer (product name: D4-endeavor, manufacturer: bruker). In addition to this device, devices used in the industry can also be appropriately adopted.

[0024] In this specification, the presence or absence of elements and the element content in the negative electrode active material can be confirmed by ICP analysis, and the ICP analysis can be performed using an inductively coupled plasma optical emission spectrometer (ICPAES, Perkin-Elmer 7300).

[0025] In this specification, the average particle size (D 50 ) can be defined as the particle size corresponding to 50% of the volume cumulative amount in the particle size distribution curve (graph curve of the particle size distribution diagram). The average particle size (D 50 ) can be measured, for example, using the laser diffraction method. The laser diffraction method can generally measure particle sizes in the range from the submicron region to about several millimeters, and high reproducibility and high resolution results can be obtained.

[0026] Hereinafter, preferred embodiments of the present invention will be described in detail. However, the embodiments of the present invention may be modified in various forms, and the scope of the present invention is not limited to the embodiments described below.

[0027] <Negative electrode active material> One embodiment of the present invention provides a negative electrode active material including 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 provided on at least a part of the silicon-based particles.

[0028] The negative electrode active material according to one embodiment of the present invention includes silicon-based particles. The silicon-based particles contain SiO x (0 < x < 2) and a Li compound.

[0029] The SiO x (0 < x < 2) may correspond to a matrix in the silicon-based particles. The SiO x(0 < x < 2) may be in a form containing Si and / or SiO2, and the Si may form a phase. That is, the x corresponds to the number ratio of O to Si contained in the SiO x (0 < x < 2). When the silicon-based particles contain the SiO x (0 < x < 2), the discharge capacity of the secondary battery can be improved.

[0030] The Li compound may correspond to a matrix within the silicon-based particles. The Li compound may exist in at least one form of lithium atoms, lithium silicate, lithium silicide, and lithium oxide within the silicon-based particles. When the silicon-based particles contain a Li compound, there is an effect that the initial efficiency is improved.

[0031] The Li compound may be in a form doped into the silicon-based particles and distributed on the surface and / or inside of the silicon-based particles. The Li compound is distributed on the surface and / or inside of the silicon-based particles, can control the expansion / contraction of the volume of the silicon-based particles to an appropriate level, and can play a role in preventing damage to the active material. Also, the Li compound may be included in that it reduces the ratio of the irreversible phase (e.g., SiO2) of the silicon-based oxide particles and increases the efficiency of the active material.

[0032] In one embodiment of the present invention, the Li compound may exist in the form of lithium silicate. The lithium silicate is represented by Li a Si b O c (2 ≤ a ≤ 4, 0 < b ≤ 2, 2 ≤ c ≤ 5) and can be classified into crystalline lithium silicate and amorphous lithium silicate. The crystalline lithium silicate may exist in the form of at least one lithium silicate selected from the group consisting of Li2SiO3, Li4SiO4, and Li2Si2O5 within the silicon-based particles, and the amorphous lithium silicate is Li a Si b O cIt may be composed of a complex structure in the form of (2 ≦ a ≦ 4, 0 < b ≦ 2, 2 ≦ c ≦ 5), and is not limited to the above form.

[0033] In one embodiment of the present invention, based on 100 parts by weight of the total negative electrode active material, Li may be contained in an amount of 0.1 to 40 parts by weight, or 0.1 to 25 parts by weight. Specifically, it may be contained in an amount of 1 to 25 parts by weight, and more specifically, it may be contained in an amount of 2 to 20 parts by weight. As the content of Li increases, although the initial efficiency increases, there is a problem that the discharge capacity decreases. Therefore, when the above range is satisfied, appropriate discharge capacity and initial efficiency can be realized.

[0034] The content of the Li element can be confirmed by ICP analysis. Specifically, after separating a certain amount (about 0.01 g) of the negative electrode active material, transfer it to a platinum crucible, add nitric acid, hydrofluoric acid, and sulfuric acid, and completely decompose it on a hot plate. Then, using an inductively coupled plasma atomic emission spectrometer (ICPAES, Perkin-Elmer 7300), measure the intensity of the standard solution (5 mg / kg) prepared using a standard solution at the wavelength specific to the element to be analyzed to create a standard calibration curve. Then, introduce the pretreated sample solution and blank sample into the instrument, measure their respective intensities to calculate the actual intensity, calculate the concentration of each component with respect to the created calibration curve, and then convert it so that the total of all components becomes the theoretical value, and the content of the elements of the manufactured negative electrode active material can be analyzed.

[0035] In one embodiment of the present invention, the silicon-based particles may contain additional metal atoms. The metal atoms may exist in at least one form of metal atoms, metal silicates, metal silicides, and metal oxides within the silicon-based particles. The metal atoms may include at least one selected from the group consisting of Mg, Li, Al, and Ca. Thereby, the initial efficiency of the negative electrode active material can be improved.

[0036] In one embodiment of the present invention, a carbon layer is provided on at least a part of the surface of the silicon-based particles. At this time, the carbon layer may be in a form that partially covers at least a part of the surface, that is, the surface of the particles, or covers the entire surface of the particles. The carbon layer imparts conductivity to the negative electrode active material, and can improve the initial efficiency, life characteristics, and capacity characteristics of the secondary battery.

[0037] In one embodiment of the present invention, the carbon layer contains amorphous carbon.

[0038] Further, the carbon layer may further contain crystalline carbon.

[0039] The crystalline carbon can further improve the conductivity of the negative electrode active material. The crystalline carbon may contain at least one selected from the group consisting of fullerene, carbon nanotube, and graphene.

[0040] The amorphous carbon can appropriately maintain the strength of the carbon layer and suppress the expansion of the silicon-based particles. The amorphous carbon may be at least one carbide selected from the group consisting of tar, pitch, and other organic substances, or a carbon-based substance formed using a carbide or hydrocarbon of at least one selected from the group consisting of tar, pitch, and other organic substances as a source in a chemical vapor deposition method.

[0041] The carbide of the other organic substances may be a carbide of an organic substance selected from the group consisting of sucrose, glucose, galactose, fructose, lactose, mannose, ribose, aldohexose, or ketohexose and combinations thereof.

[0042] The hydrocarbon may be a substituted or unsubstituted aliphatic or alicyclic hydrocarbon, or a substituted or unsubstituted aromatic hydrocarbon. The aliphatic or alicyclic hydrocarbon of the substituted or unsubstituted aliphatic or alicyclic hydrocarbon may be methane, ethane, ethylene, acetylene, propane, butane, butene, pentane, isobutane, or hexane, etc. Examples of the aromatic hydrocarbon of the substituted or unsubstituted aromatic hydrocarbon include benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, coumarone, pyridine, anthracene, or phenanthrene, etc.

[0043] In one embodiment of the present invention, the carbon layer may be an amorphous carbon layer.

[0044] In one embodiment of the present invention, the carbon layer may be contained in an amount of 0.1 to 50 parts by weight, 0.1 to 30 parts by weight, or 0.1 to 20 parts by weight based on 100 parts by weight of the total negative electrode active material. More specifically, it may be contained in an amount of 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 satisfied, a decrease in the capacity and efficiency of the negative electrode active material can be prevented.

[0045] In one embodiment of the present invention, the thickness of the carbon layer may be 1 nm to 500 nm, and specifically may be 5 nm to 300 nm. When the above range is satisfied, there is an effect that the conductivity of the negative electrode active material is improved, the volume change of the negative electrode active material is easily suppressed, the side reaction between the electrolyte and the negative electrode active material is suppressed, and the initial efficiency and / or life of the battery are improved.

[0046] 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.

[0047] In one embodiment of the present invention, a coating layer containing an amphiphilic polymer is provided on at least a part of the silicon-based particles.

[0048] The amphiphilic polymer is a substance having both a hydrophilic group and a hydrophobic group. The amphiphilic polymer may include one or more selected from the group consisting of PEG-PPO (Polyethylene glycol-Polypropylene oxide), PEG-PS (Polyethylene glycol-Polystyrene), PS-PBA (Polystyrene-Poly(butyl acrylate)), polylysine-PPO (Polylysine-Polypropylene oxide), and polylysine-PS (Polylysine-Polystyrene), and preferably may include PEG-PS.

[0049] Specifically, during the production of the anode active material, silicon-based particles having a carbon layer provided on at least a part of the surface are formed, doped with Li, and then coated with an amphiphilic polymer, whereby a coating layer containing an amphiphilic polymer can be introduced on at least a part of the silicon-based particles.

[0050] The weight average molecular weight of the amphiphilic polymer may be 100 g / mol to 50,000 g / mol, specifically 1,000 g / mol to 30,000 g / mol, or 5,000 g / mol to 20,000 g / mol.

[0051] In the present invention, the weight average molecular weight (Mw) of the amphiphilic polymer can be measured by gel permeation chromatography (GPC) using a polystyrene standard with an Agilent 1200 series. Specifically, it can be measured using an Agilent 1200 series instrument with a Polymer Laboratories PLgel MIX - B column 300 mm in length. At this time, the measurement temperature is 40°C, the solvent used is tetrahydrofuran (THF), and the flow rate is 1 mL / min. The samples are each prepared at a concentration of 10 mg / 10 mL and then supplied in an amount of 10 μL, and the Mw value is derived using a calibration curve formed with a polystyrene standard. At this time, nine types of polystyrene standard products with molecular weights (g / mol) of 2,000 / 10,000 / 30,000 / 70,000 / 200,000 / 700,000 / 2,000,000 / 4,000,000 / 10,000,000 are used.

[0052] The amphiphilic polymer may include a unit containing a hydrophilic group and a unit containing a hydrophobic group.

[0053] The unit containing a hydrophilic group 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), or the like. It is not limited thereto, and units containing hydrophilic groups well - known in the art can be appropriately employed in the amphiphilic polymer.

[0054] The unit containing the hydrophilic group may be disposed near the outermost surface of the negative electrode active material. By introducing a hydrophilic group into the negative electrode active material, aggregation between the negative electrode active materials in the aqueous slurry can be effectively suppressed, and the dispersibility can be improved.

[0055] The unit containing the hydrophilic group may be contained in an amount of 20 parts by weight to 80 parts by weight, specifically 30 parts by weight to 70 parts by weight, or 40 parts by weight to 60 parts by weight, based on 100 parts by weight in total of the amphiphilic polymer. When the above range is satisfied, there is an effect of improving the dispersibility in the slurry. When the above range is not satisfied, there is a problem that aggregation between particles occurs in the slurry.

[0056] The unit containing the hydrophobic group may be a unit derived from polystyrene (PS), polypropylene oxide (PPO), polylactic acid (PLA, Poly(lactic acid)), polysebacic acid (PSA, Poly(sebacic acid)), poly(lactic-co-glycolic acid) (PLGA), or polyaspartic acid (PASP, Poly(aspartic acid)), etc. It is not limited thereto, and units containing hydrophobic groups well-known in the art can be appropriately adopted for the amphiphilic polymer. By introducing the hydrophobic group into the negative electrode active material, the reactivity between the negative electrode active material and water is reduced, penetration of moisture into the interior of the negative electrode active material in the aqueous slurry is prevented, and side reactions between the silicon-based particles or lithium by-products and water are prevented to suppress gas generation, so that there is an effect of improving the aqueous processability of the slurry.

[0057] The unit containing the hydrophobic group may be contained in an amount of 20 parts by weight to 80 parts by weight, specifically 30 parts by weight to 70 parts by weight, or 40 parts by weight to 60 parts by weight, based on 100 parts by weight in total of the amphiphilic polymer. When the above range is satisfied, there is an effect of preventing moisture from reacting with the active material. When the above range is not satisfied, there is a problem that moisture penetrates into the active material and the processability deteriorates.

[0058] That is, by coating the surface of the negative electrode active material with an amphiphilic polymer containing both a hydrophilic group and a hydrophobic group, a hydrophobic group that increases the water resistance of the negative electrode active material and a hydrophilic group that increases the dispersibility are simultaneously introduced, and the aqueous processability of the slurry can be effectively improved.

[0059] The weight ratio of the unit containing the hydrophilic group to the unit containing the hydrophobic group may be 20:80 to 80:20, specifically 30:70 to 70:30, or 40:60 to 60:40. When the above range is satisfied, it has the effect of excellent dispersibility in the slurry and preventing moisture from penetrating into the inside of the particles. When the above range is not satisfied, there are problems such as a decrease in dispersibility in the slurry and aggregation between particles, or moisture penetrating into the inside of the particles and causing a reaction.

[0060] The negative electrode active material according to one embodiment of the present invention, after ultrasonic treatment of a mixture of 20 g of the negative electrode active material and 80 g of distilled water, when the mixture is passed through a mesh having a diameter corresponding to D max of the negative electrode active material, the dispersibility according to the following formula 1 may be 70% or more.

[0061]

Equation

[0062] In the above formula 1, W t means the total weight of the negative electrode active material contained in the mixture, W r means the weight of the negative electrode active material that could not pass through the mesh when the mixture was passed through the mesh.

[0063] The dispersibility according to the above 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 also be 100% or less.

[0064] Specifically, the ultrasonic treatment may be performed for 1 minute to 10 minutes, preferably, it may also be performed for 5 minutes.

[0065] The dispersibility may be measured after leaving the mixture to stand for 10 minutes after subjecting the mixture to ultrasonic treatment before passing the mixture through a mesh.

[0066] The mesh may have a diameter corresponding to D max of the negative electrode active material, and a mesh of a material commonly used in the present technical field may be appropriately adopted to measure the dispersibility.

[0067] Generally, when mixing the negative electrode active material with distilled water, aggregation of the negative electrode active material occurs, and the aggregated negative electrode active material cannot pass through the mesh. As a result, there is a problem of poor dispersibility. However, since the negative electrode active material according to the present invention includes an amphiphilic polymer coating layer on the surface, aggregation between the negative electrode active materials in the aqueous slurry is effectively suppressed, and the dispersibility is improved.

[0068] In one embodiment of the present invention, the coating layer containing the amphiphilic polymer may be provided on at least a part of the carbon layer, or may be provided on at least a part of a region of the surface of the silicon-based particles where the carbon layer is not provided.

[0069] The coating layer containing the amphiphilic polymer may be in a form where it partially covers or entirely covers the surface of the silicon-based particles or the carbon layer. Examples of the shape of the coating layer containing the amphiphilic polymer include an island type or a thin film type, and specifically, it may have an island type.

[0070] In the present invention, the content of the amphiphilic polymer on the surface of the negative electrode active material can be analyzed through a combustion analyzer. Specifically, using G4 ICARUS HF manufactured by Bruker, about 0.5 g of the sample can be burned under oxygen gas with a purity of 99.95% to analyze the carbon content.

[0071] In one embodiment of the present invention, the coating layer containing the amphiphilic polymer may be included in an amount of 0.005 parts by weight to 20 parts by weight based on 100 parts by weight in total of the negative electrode active material. Specifically, it may be included in an amount of 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 layer 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 layer 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.

[0072] 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 contrary, when the amphiphilic polymer is included below the above range, the contents of the hydrophilic group and the hydrophobic group are low, and sufficient water resistance and dispersibility cannot be ensured. When the amphiphilic polymer is included exceeding the above range, the coating layer is not uniformly distributed, the dispersibility and passivation effect are reduced, and since the amphiphilic coating layer does not participate in the electrochemical reaction, there is a problem that the capacity and efficiency of the negative electrode active material are reduced.

[0073] In one 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, and specifically may be 5:95 to 60:40, or 10:90 to 50:50.

[0074] In one embodiment of the present invention, lithium by-products may be present on the silicon-based particles. Specifically, the lithium by-products may be present on the surface of the silicon-based particles or on the surface of the carbon layer. Further, the lithium by-products may be present between the coating layer containing the amphiphilic polymer and the silicon-based particles.

[0075] Specifically, the lithium by-products may mean lithium compounds remaining near the surface of the silicon-based particles or the carbon layer after the production of the silicon-based particles. As described above, even after the acid treatment step, lithium by-products that did not react with the acid may remain.

[0076] The lithium by-products may include one or more selected from the group consisting of Li2O, LiOH, and Li2CO3.

[0077] Whether the lithium by-products are present or not can be confirmed by X-ray diffraction (XRD) or X-ray photoelectron spectroscopy (XPS).

[0078] The lithium by-products may be contained in an amount of 5 parts by weight or less based on 100 parts by weight in total of the negative electrode active material. Specifically, it may be contained in an amount of 0.001 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, it may be contained in an amount of 0.1 to 0.8 parts by weight, or 0.1 to 0.5 parts by weight. When the content of the lithium by-products satisfies the above range, side reactions in the slurry can be reduced, the viscosity change can be lowered, and the aqueous system processability characteristics can be improved. On the contrary, when the content of the lithium by-products is higher than the above range, the slurry shows basicity during formation, which may cause side reactions or viscosity changes, resulting in problems with aqueous system processability.

[0079] The content of the lithium by-products can be calculated by measuring the amount of the HCl solution in a specific section where the pH changes during the process of titrating an aqueous solution containing the negative electrode active material with an HCl solution using a titrator.

[0080] The average particle size (D 50 ) of the negative electrode active material may be 0.1 μm to 30 μm, specifically may be 1 μm to 20 μm, and more specifically may be 1 μm to 10 μm. When the above range is satisfied, the structural stability of the active material during charge and discharge can be achieved, the problem that the volume expansion / shrinkage level also increases due to the excessive increase in the particle size can be prevented, and the problem that the initial efficiency decreases due to the excessive decrease in the particle size can be prevented.

[0081] <Method for manufacturing negative electrode active material> One embodiment of the present invention forms 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, and provides a method for manufacturing a negative electrode active material.

[0082] The silicon-based particles may be formed by heating and vaporizing Si powder and SiO2 powder in a vacuum, and then depositing the vaporized mixed gas to form preliminary particles; forming a carbon layer on the surface of the formed preliminary particles; and heat-treating after mixing the preliminary particles having the carbon layer formed thereon with Li powder.

[0083] Specifically, the mixed powder of the Si powder and the SiO2 powder may be heat-treated at 1300 °C to 1800 °C, 1400 °C to 1800 °C, or 1400 °C to 1600 °C under vacuum.

[0084] The formed preliminary particles may have the form of SiO.

[0085] The carbon layer may be formed by using chemical vapor deposition (CVD) using a hydrocarbon gas or by a method of carbonizing a substance serving as a carbon source.

[0086] Specifically, after introducing the formed preliminary particles into the reactor, hydrocarbon gas may be used for chemical vapor deposition (CVD) at 600°C to 1200°C to form them. The hydrocarbon gas may be at least one hydrocarbon gas selected from the group consisting of methane, ethane, propane, and acetylene, and may be heat-treated at 900°C to 1000°C.

[0087] The step of heat-treating after mixing the preliminary particles with carbon layer formed thereon and Li powder may be carried out at 700°C to 900°C for 4 to 6 hours, specifically, it may be carried out at 800°C for 5 hours.

[0088] The silicon-based particles may contain, as the aforementioned Li compound, Li silicate, Li silicide, or Li oxide, etc.

[0089] The particle size of the silicon-based particles may be adjusted by methods such as ball mill, jet mill, or air classification, and is not limited thereto.

[0090] On at least a part of the surface of the silicon-based particles provided with a carbon layer as described above, a lithium compound (lithium by-product) is provided. Specifically, in the process of forming preliminary particles containing SiO x (0 < x < 2), forming a carbon layer on the preliminary particles, and then doping with Li to produce the aforementioned silicon-based particles, a lithium compound, that is, a lithium by-product formed by unreacted lithium, remains near the surface of the silicon-based particles.

[0091] In one embodiment of the present invention, the method for manufacturing the negative electrode active material includes reacting the silicon-based particles with an amphiphilic polymer precursor and coating at least a part of the silicon-based particles with an amphiphilic polymer.

[0092] The amphiphilic polymer precursor may be a precursor capable of forming the aforementioned PEG-PPO, PEG-PS, PS-PBA, polylysine-PPO, or polylysine-PS. As an example, as the amphiphilic polymer precursor, PS-b-PEO (Polystyrene-block-Polyethylene oxide) or PS-b-PBA (Polystyrene-b-poly(butyl acrylate)) may be used.

[0093] The step of reacting the silicon-based particles with the amphiphilic polymer precursor may include a step of activating the surface of the silicon-based particles; and a step of mixing the silicon-based particles and the amphiphilic polymer in a solvent.

[0094] Specifically, the activation step may be performed 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.

[0095] The weight ratio of the silicon-based particles to the amphiphilic polymer may be 99.9:0.1 to 80:20. Specifically, it may be 99.5:0.5 to 85:15, or 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 contrary, when the amphiphilic polymer is contained in excess, the coating layer is not uniformly distributed, resulting in a decrease in dispersibility and passivation effect, and the amphiphilic coating layer does not participate in the electrochemical reaction, leading to problems such as a decrease in the capacity and efficiency of the negative electrode active material.

[0096] After mixing the silicon-based particles and the amphiphilic polymer in a solvent, stirring can be carried out to provide the amphiphilic polymer on the surface of the silicon-based particles.

[0097] The solvent may preferably be dimethyl sulfoxide (DMSO), but is not limited thereto, and solvents used in the technical field can be appropriately adopted.

[0098] The stirring may be performed for 30 minutes to 6 hours, preferably for 1 hour to 5 hours, or 2 hours to 4 hours.

[0099] The negative electrode active material containing the amphiphilic polymer introduced by the method described above can improve the water-based processability of the slurry and the dispersibility of the negative electrode active material in the slurry, so that the negative electrode can be stably formed. Thereby, the negative electrode containing the negative electrode active material according to the present invention and the secondary battery containing the negative electrode can improve the discharge capacity, initial efficiency, resistance performance, and / or life characteristics of the battery.

[0100] <Negative electrode> The negative electrode according to an embodiment of the present invention may contain the negative electrode active material described above.

[0101] 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 contain the negative electrode active material. Further, the negative electrode active material layer may further contain a binder, a thickener, and / or a conductive material.

[0102] The negative electrode active material layer may be formed by applying a negative electrode slurry containing a negative electrode active material, a binder, a thickener, and / or a conductive material to at least one side of the current collector, followed by drying and rolling.

[0103] The negative electrode slurry may further contain an additional negative electrode active material.

[0104] As the additional negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; SiO β (0 < β < 2), metal oxides such as SnO2, vanadium oxides, lithium titanate oxides, and lithium vanadate oxides that can be doped and undoped with lithium; or composites containing the metallic compound and the carbonaceous material such as Si-C composites or Sn-C composites, etc. may be mentioned, and any one or a mixture of two or more of these may be used. Further, a thin film of metallic lithium may be used as the negative electrode active material. Also, as the carbon material, either low-crystalline carbon or high-crystalline carbon may be used. Representative examples of low-crystalline carbon are soft carbon and hard carbon, and representative examples of high-crystalline carbon are amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite, kish graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch derived cokes.

[0105] The additional negative electrode active material may be a carbon-based negative electrode active material.

[0106] The negative electrode slurry may contain a solvent for forming the negative electrode slurry. Specifically, the solvent for forming the negative electrode slurry is at least one selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol in terms of facilitating the dispersion of components, and specifically, may contain distilled water.

[0107] The negative electrode slurry containing a negative electrode active material according to an 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, there is an effect that the rheological properties of the slurry are stabilized. On the contrary, when the pH of the negative electrode slurry is less than 7 or the pH of the negative electrode slurry exceeds 11, decomposition of carboxymethyl cellulose (CMC) used as a thickener occurs, resulting in a decrease in the viscosity of the slurry and a problem that the degree of dispersion of the active material contained in the slurry decreases.

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

[0109] The binder may include at least one selected from the group consisting of polyvinylidene fluoride - hexafluoropropylene copolymer (PVDF - co - HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene - propylene - diene monomer (EPDM), sulfonated EPDM, styrene - butadiene rubber (SBR), fluororubber, poly acrylic acid, and substances in which hydrogen thereof is substituted with Li, Na, Ca, etc., and may also include various copolymers thereof.

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

[0111] The thickener may be carboxymethyl cellulose (CMC), but is not limited thereto, and thickeners used in the technical field may be appropriately employed.

[0112] In one embodiment of the present invention, the weight ratio of the negative electrode active material contained in the negative electrode slurry to the additional negative electrode active material may be 1:99 to 30:70, specifically 5:95 to 30:70, or 10:90 to 20:80.

[0113] In one embodiment of the present invention, all the negative electrode active materials contained in the negative electrode slurry may be contained in an amount of 60 to 99 parts by weight, specifically 70 to 98 parts by weight, based on 100 parts by weight of the total solid content of the negative electrode slurry.

[0114] In one embodiment of the present invention, the binder may be contained 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.

[0115] In one embodiment of the present invention, the conductive material may be contained 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.

[0116] In one embodiment of the present invention, the thickener may be contained 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 100 parts by weight of the total solid content of the negative electrode slurry.

[0117] The negative electrode slurry according to one embodiment of the present invention may further contain a solvent for forming the negative electrode slurry. Specifically, the solvent for forming the negative electrode slurry may be at least one selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol, specifically, it may contain distilled water, in terms of facilitating the dispersion of components.

[0118] In one embodiment of the present invention, the solid content weight of the negative electrode slurry may be 20 to 75 parts by weight, specifically 30 to 70 parts by weight, based on 100 parts by weight of the total negative electrode slurry.

[0119] <Secondary battery> The secondary battery according to an embodiment of the present invention may include the negative electrode according to the above-described embodiment. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolytic solution, and the negative electrode is the same as the negative electrode described above. Since the negative electrode has been described above, a specific description thereof will be omitted.

[0120] The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and containing the positive electrode active material.

[0121] In the positive electrode, the positive electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or a material obtained by surface-treating the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. may be used. Further, the positive electrode current collector may usually have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase the adhesive force of the positive electrode active material. For example, it may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric body, etc.

[0122] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material is a layered compound such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe3O4; chemical formula Li 1+c1 Mn 2-c1 O4 (0 ≦ c1 ≦ 0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7; chemical formula LiNi 1-c2 M c2 O2 (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01 ≦ c2 ≦ 0.3) represented by Ni-site type lithium nickel oxide; chemical formula LiMn 2-c3 Mc3 O2 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01 ≦ c3 ≦ 0.1), or a lithium manganese composite oxide represented by Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); or LiMn2O4 in which part of Li in the chemical formula is substituted with an alkaline earth metal ion, etc., but is not limited thereto. The positive electrode may be a lithium metal (Li-metal).

[0123] The positive electrode active material layer may contain a positive electrode conductive material and a positive electrode binder together with the positive electrode active material described above.

[0124] At this time, the positive electrode conductive material is used to impart conductivity to the electrode, and in the configured battery, it can be used without particular limitation as long as it has electron conductivity without causing a chemical change. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based substances such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. Among these, one kind alone or a mixture of two or more kinds may be used.

[0125] In addition, the positive electrode binder serves to improve the adhesion between the positive electrode active material particles and the adhesive force between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, etc. One of these alone or a mixture of two or more may be used.

[0126] The separator separates the negative electrode and the positive electrode and provides a migration path for lithium ions. Usually, any material that can be used as a separator in a secondary battery can be used without particular limitation. In particular, it is preferably low in resistance to the ion migration of the electrolyte solution and excellent in the ability to hold the electrolyte solution. Specifically, a porous polymer film, for example, a porous polymer film made from polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. Also, a normal porous non-woven fabric, for example, a non-woven fabric made of high-melting-point glass fibers, polyethylene terephthalate fibers, etc. may be used. Further, in order to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer substance may be used, and it may be selectively used as a single-layer or multi-layer structure.

[0127] Examples of the electrolyte solution include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used during the manufacture of lithium secondary batteries.

[0128] Specifically, the electrolytic solution may contain a non-aqueous organic solvent and a metal salt.

[0129] Examples of the non-aqueous organic solvent include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate ester, trimethoxymethane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, ethyl propionate, etc.

[0130] In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates among the carbonate-based organic solvents, can be preferably used as high-viscosity organic solvents because they have a high dielectric constant and can well dissociate lithium salts. When such cyclic carbonates are mixed with linear carbonates having low viscosity and low dielectric constant, such as dimethyl carbonate and diethyl carbonate, at an appropriate ratio and used, an electrolytic solution having high electrical conductivity can be prepared, so it can be more preferably used.

[0131] As the metal salt, a lithium salt may be used. The lithium salt is a substance that is easily dissolved in the non-aqueous electrolytic solution. For example, as the anion of the lithium salt, F - , Cl - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2- , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - , and (CF3CF2SO2)2N - One or more selected from the group consisting of may be used.

[0132] In addition to the constituent components of the electrolytic solution, the electrolytic solution may further contain one or more additives such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride in order to improve the life characteristics of the battery, suppress the decrease in battery capacity, and improve the discharge capacity of the battery.

[0133] According to another embodiment of the present invention, a battery module including the secondary battery as a unit cell and a battery pack including the same are provided. Since the battery module and the battery pack include the secondary battery having high capacity, high rate characteristics, and cycle characteristics, they 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.

Example

[0134] <Examples and Comparative Examples> Example 1 94 g of a powder obtained by mixing Si and SiO₂ at a molar ratio of 1:1 was mixed in a reactor and then vacuum-heated at a sublimation temperature of 1,400 °C. Thereafter, the mixed gas of vaporized Si and SiO₂ was reacted in a vacuum cooling zone having a cooling temperature of 800 °C and condensed into a solid phase. Next, the condensed particles were pulverized using a ball mill for 3 hours to produce silicon-based particles with a size of 6 μm. Thereafter, while flowing Ar gas to maintain an inert atmosphere, the silicon-based particles were placed in the hot zone of a CVD apparatus, and using Ar as a carrier gas, the methane was blown into the hot zone at 900 °C and reacted at 10 -1 torr for 20 minutes to form a carbon layer on the surface of the silicon-based particles. Thereafter, 6 g of Li metal powder was added, and after additional heat treatment was performed at a temperature of 800 °C in an inert atmosphere, the particles were exposed to ultraviolet rays to activate the particle surface. Next, in a DMSO (dimethylsulfoxide) solvent, PEG-b-PS (Polyethylene glycol-block-Polystyrene):silicon-based particles were mixed at a weight ratio of 1:99 and reacted with stirring at room temperature for 2 hours to produce a negative electrode active material having a polymer coating layer formed thereon.

[0135] Example 2 A negative electrode active material was produced in the same manner as in Example 1, except that PEG-b-PS was changed to PS-b-PBA.

[0136] Example 3 A negative electrode active material was produced 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.

[0137] Comparative Example 1 A negative electrode active material was produced in the same manner as in Example 1, except that the process of forming the polymer coating layer was not performed.

[0138] Comparative Example 2 In Example 1, the negative electrode active material was produced in the same manner as in Example 1, except that the solvent was changed to water and PEG-b-PS was changed to HMDS (hexamethyldisilazane), and heat was applied to introduce trimethylsilyl groups onto the surface.

[0139] <Analysis of the content of the carbon layer> The content of the carbon layer was analyzed using a CS-analyzer (CS-800, Eltra).

[0140] <Analysis of the content of Li contained in the negative electrode active material> The content of the Li atoms was confirmed by ICP analysis using an inductively coupled plasma optical emission spectrometer (ICP-OES, AVIO 500, manufactured by Perkin-Elmer 7300).

[0141] <Analysis of the content of the amphiphilic polymer> The content of the amphiphilic polymer was confirmed by carbon content analysis using a combustion analyzer (G4 ICARUS HF, manufactured by Bruker).

[0142] <D of the negative electrode active material 50 and analysis of the specific surface area> The D of the negative electrode active material 50 was analyzed by laser diffraction particle size analysis using a Microtrac S3500 device, and the BET specific surface area of the negative electrode active material was measured using a BET measuring device (BEL-SORP-MAX, Nippon Bell).

[0143] The analysis results of the negative electrode active materials produced in the above Examples and Comparative Examples are shown in Table 1 below.

[0144]

Table 1

[0145] <Experimental Example: Evaluation of discharge capacity, initial efficiency, and life (capacity retention) characteristics> Anode and battery were manufactured using the anode active materials of the examples and comparative examples, respectively.

[0146] The above anode active material, carbon black as a conductive material, and PAA (poly acrylic acid) as a binder were mixed at a weight ratio of 80:10:10 to produce a mixture. Then, 7.8 g of distilled water was added to 5 g of the mixture, followed by stirring to produce an anode slurry. The anode slurry was applied to and dried on a copper (Cu) metal thin film, which was an anode current collector with a thickness of 20 μm. At this time, the temperature of the circulating air was 60°C. Next, it was roll-pressed and dried in a vacuum oven at 130°C for 12 hours to produce an anode.

[0147] The manufactured anode was cut into a circle with a diameter of 1.7671 cm 2 and a lithium (Li) metal thin film was used as the cathode. A porous polyethylene separator was interposed between the cathode and the anode, and 0.5 parts by weight of vinylene carbonate was dissolved in a mixed solution of ethyl methyl carbonate (EMC) and ethylene carbonate (EC) with a mixed volume ratio of 7:3, and an electrolyte solution in which 1 M concentration of LiPF6 was dissolved was injected to manufacture a lithium coin half-cell.

[0148] Charge and discharge were performed on the manufactured battery to evaluate the discharge capacity, initial efficiency, and capacity retention rate, which are shown in Table 2 below.

[0149] For the first cycle and the second cycle, charge and discharge were performed at 0.1C, and from the third cycle to the 49th cycle, charge and discharge were performed at 0.5C. The 50th cycle ended in a charged state (with lithium in the anode).

[0150] Charging conditions: CC (constant current) / CV (constant voltage) (5 mV / 0.005C current cut-off) Discharging conditions: CC (constant current) condition 1.5V

[0151] From the results of one charge-discharge cycle, the discharge capacity (mAh / g) and the initial efficiency (%) were derived. Specifically, the initial efficiency (%) was derived by the following calculation. Initial efficiency (%) = (discharge capacity in one cycle / charge capacity in one cycle) × 100

[0152] The capacity retention rate was derived by the following calculation respectively. Capacity retention rate (%) = (discharge capacity in 49th cycle / discharge capacity in one cycle) × 100

[0153] <Experimental Example: Evaluation of Slurry Dispersibility> The negative electrode active materials produced in Examples 1 to 3 and Comparative Examples 1 to 2 were mixed with distilled water at a weight ratio of 20:80, ultrasonic-treated for 5 minutes, left standing for 10 minutes, and then the D of each negative electrode active material max The mixture was passed through a mesh having a diameter corresponding to D. The active material remaining on the mesh was dried in an oven at 80 °C for half a day or more and then weighed.

[0154] The dispersibility was calculated as follows.

[0155]

Equation

[0156] W t means the total weight of the negative electrode active material contained in the mixture, W r means the weight of the negative electrode active material that could not pass through the mesh when the mixture was passed through the mesh.

[0157] <Experimental Example: Evaluation of Processability (Gas Generation) Characteristics> As part of the evaluation of processability, 20 g of a slurry produced by mixing graphite: the negative electrode active material: carbon black: CMC: PAA at a weight ratio of 77:20:1:1:1 was put into a pouch of about 10 cm * 15 cm, vacuum-sealed, and then placed in an oven at 40 °C to measure the volume change.

[0158] The gas generation time (hour) was measured based on the time when the volume of the pouch increased by 2 mL or more with respect to the volume measured immediately after vacuum-sealing the pouch, and it is shown in Table 2 below.

[0159]

Table 2

[0160] The negative electrode active material according to the present invention is characterized in that a coating layer containing an amphiphilic polymer is provided on silicon-based particles containing an Li compound. Since the hydrophobic group of the amphiphilic polymer has little reactivity with water, the inorganic layer is well maintained without reacting with water in the aqueous slurry, and water is prevented from penetrating into the negative electrode active material, so that the silicon-based particles can be efficiently passivated. In addition, in order to prevent side reactions between the silicon-based particles or lithium by-products and water and suppress gas generation, there is an effect of improving the aqueous processability of the slurry. At the same time, due to the hydrophilic group contained in the amphiphilic polymer, a hydrophilic group is located on the surface of the negative electrode active material, and there is an effect that the dispersibility of the negative electrode active material in the aqueous slurry can be improved.

[0161] On the other hand, when a polymer coating layer is not formed as in Comparative Example 1, the aqueous dispersibility is low, it is difficult to form a stable electrode, and the gas generation time of the negative electrode slurry becomes fast due to side reactions between lithium by-products and water, resulting in a decrease in slurry processability. It was confirmed that the capacity retention rate of the secondary battery using the negative electrode active material decreased significantly.

[0162] In the case of Comparative Example 2, a trimethylsilyl group was introduced to impart hydrophobicity to the surface of the negative electrode active material instead of the polymer coating layer. Although the gas generation time of the negative electrode slurry is delayed to some extent, it was still confirmed that the hydrophilicity of the negative electrode active material decreased and the aqueous dispersibility was slightly low, and it was confirmed that the capacity retention rate of the secondary battery using the negative electrode active material decreased significantly.

Claims

1. SiO ｘ Silicon-based particles containing SiO (0 < x < 2) and a Li compound, with a carbon layer provided on at least a part of the surface; and A coating layer containing an amphiphilic polymer provided on at least a part of the silicon-based particles comprising a negative electrode active material.

2. The negative electrode active material according to claim 1, wherein the amphiphilic polymer contains a unit containing a hydrophilic group and a unit containing a hydrophobic group.

3. The unit containing a hydrophilic group in the negative electrode active material according to claim 2 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 unit containing a hydrophobic group in the negative electrode active material according to claim 2 is a unit derived from one or more selected from the group consisting of polystyrene and polypropylene oxide.

5. In the negative electrode active material according to claim 2, the weight ratio of the unit containing a hydrophilic group to the unit containing a hydrophobic group is 3:7 to 7:

3.

6. 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 100 parts by weight in total of the negative electrode active material according to claim 1.

7. The amphiphilic polymer in the negative electrode active material according to claim 1 contains one or more selected from the group consisting of PEG-PPO, PEG-PS, PS-PBA, polylysine-PPO, and polylysine-PS.

8. When the mixture of 20 g of the negative electrode active material and 80 g of distilled water is ultrasonicated and then passed through a mesh having a diameter corresponding to D of the negative electrode active material, the dispersibility according to the following formula 1 is 70% or more. The negative electrode active material according to claim 1: ｍａｘ When the mixture is passed through a mesh having a diameter corresponding to D of the negative electrode active material, the dispersibility according to the following formula 1 is 70% or more. The negative electrode active material according to claim 1: 【Number 1】 In the above formula (1), W ｔ means the total weight of the negative electrode active material contained in the mixture, W ｒ means the weight of the negative electrode active material that could not pass through the mesh when the mixture was passed through the mesh.

9. The negative electrode active material according to claim 1, further comprising lithium by-products provided on at least a part of the silicon-based particles.

10. The negative electrode active material according to claim 9, wherein the lithium by-products are contained in an amount of 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 Li is contained in an amount of 0.1 part by weight to 40 parts by weight based on 100 parts by weight of the total negative electrode active material.

12. The negative electrode active material according to claim 1, wherein the carbon layer is contained in an amount of 0.1 part by weight to 50 parts by weight based on 100 parts by weight of the total negative electrode active material.

13. SiO ｘ (0 < x < 2) and a Li compound, and forming silicon-based particles provided with a carbon layer on at least a part of the surface; and reacting the silicon-based particles with an amphiphilic polymer precursor The method for producing a negative electrode active material according to any one of claims 1 to 12, comprising:

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

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

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