Negative electrode active material, method for producing negative electrode active material, negative electrode slurry, negative electrode, and secondary battery

Abstract

An object of the present invention is to provide a negative electrode active material, a method of preparing a negative electrode active material, a negative electrode slurry and a negative electrode including the negative electrode active material, and a secondary battery including the negative electrode, in which when the negative electrode active material is applied to a secondary battery, initial efficiency may be improved, a decrease in discharge capacity may be minimized, and viscosity of a slurry may be lowered to improve a gas generation problem.SOLUTION: According to an aspect of the present invention, there is provided a negative electrode active material including silicon-based oxides, wherein the silicon-based oxides include Li, and the negative electrode active material includes a first coating layer and a second coating layer provided on surfaces of the silicon-based oxides, wherein each of the first coating layer and the second coating layer is a carbon-based layer, and wherein a non-reversible material formed by silicon-based oxides and Li is not included between the first coating layer and the second coating layer, or LiOH and Li2CO3 are included in an amount of 100 wt% based on a total weight of the negative electrode active material, less than 1 wt%, a negative electrode including the negative electrode active material, a secondary battery including the negative electrode, and a method of preparing the negative electrode active material.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This application claims the benefit of the filing date of Korean Patent Application No. 10-2021-0164669 filed with the Korean Intellectual Property Office on November 25, 2021, and all of the contents disclosed in the Korean patent application document are incorporated herein by reference.

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

[0003] The rapid increase in fossil fuel use has led to an increasing demand for alternative and clean energy, and one of the most actively researched fields in this area is the field of power generation and storage using electrochemical reactions.

[0004] Currently, secondary batteries are a typical example of electrochemical elements that use electrochemical energy, and their range of use is expanding. In recent years, with the increasing technological development and demand for portable devices such as portable computers, mobile phones, and cameras, the demand for secondary batteries as energy sources has rapidly increased. Among these secondary batteries, much research has been conducted on high-energy density, i.e., high-capacity lithium secondary batteries, which have been commercialized and are widely used.

[0005] Generally, a secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode includes a negative electrode active material that inserts and extracts lithium ions from the positive electrode. The negative electrode active material can be silicon-containing particles with a high discharge capacity. However, as the performance requirements for lithium secondary batteries continue to increase, continuous improvements are also required for battery materials, including the negative electrode active material. Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention provides a negative electrode active material, a method for manufacturing the negative electrode active material, a negative electrode slurry including the negative electrode active material, a negative electrode, and a secondary battery including the negative electrode, which, when applied to a secondary battery, can improve initial efficiency, minimize a decrease in discharge capacity, and reduce the viscosity of the slurry, thereby alleviating the problem of gas generation. [Means for solving the problem]

[0007] One embodiment of the present invention provides an anode active material comprising silicon-based oxide particles, the silicon-based oxide particles containing Li and including a first coating layer and a second coating layer formed on the surface of the silicon-based oxide particles, the first coating layer and the second coating layer each being a carbon layer, and wherein an irreversible substance formed by the silicon-based oxide and Li is not contained between the first coating layer and the second coating layer, or LiOH and Li2CO3 are contained in an amount of less than 1 wt% each, based on 100 wt% of the total anode active material.

[0008] One embodiment of the present invention provides a method for producing an anode active material containing silicon-based oxide particles, the method comprising the steps of: forming a first coating layer, which is a carbon layer, on the silicon-based oxide particles; doping the silicon-based oxide particles on which the first coating layer is formed with Li; removing, by etching, an irreversible substance formed of the silicon-based oxide and Li on the silicon-based oxide particles on which the first coating layer is formed; and forming a second coating layer, which is a carbon layer, on the etched silicon-based oxide particles on which the first coating layer is formed.

[0009] One embodiment of the present invention provides a negative electrode slurry containing the negative electrode active material.

[0010] One embodiment of the present invention provides a negative electrode comprising the negative electrode active material.

[0011] One embodiment of the present invention provides a secondary battery including the negative electrode. [Effects of the Invention]

[0012] The anode active material according to an embodiment of the present invention includes silicon-based oxide particles containing Li, and therefore can be used as a highly efficient material. Specifically, the inclusion of lithium can improve the initial efficiency of a battery. In particular, because lithium is a lighter substance than other materials, an increase in lithium content has the advantage of minimizing the decrease in discharge capacity. Furthermore, in the Li incorporation process, lithium is doped while the carbon layer is still formed, and irreversible materials present on the carbon layer are removed by etching, thereby alleviating the problems of low viscosity of the anode slurry and gas generation.

[0013] Furthermore, by further coating a carbon layer after the etching, the reaction between the surface of the active material and the slurry solvent (water) can be blocked, thereby improving the problems of low viscosity of the negative electrode slurry and gas generation. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will now be described in more detail to aid in understanding the invention.

[0015] The terms and words used in this specification and claims should not be interpreted in a limited way to their ordinary or dictionary meanings, but should be interpreted in a way that is consistent with the technical idea of ​​the present invention, based on the principle that the inventors can appropriately define the concepts of terms in order to best explain their inventions.

[0016] The terms used in this specification are merely used to describe exemplary embodiments and are not intended to limit the present invention. The singular expressions include the plural expressions unless otherwise clearly indicated in the context.

[0017] It should be understood that in this specification, the terms "comprises," "includes," or "has" are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, but do not preclude the presence or possible addition of one or more other features, numbers, steps, components, or combinations thereof.

[0018] In this specification, the average particle size (D 50 The average particle size (D) can be defined as the particle size at 50% of the cumulative volume in the particle size distribution curve. 50 ) can be measured, for example, by using a laser diffraction method. The laser diffraction method generally enables measurement of particle sizes from the submicron range to several mm, and can provide results with high reproducibility and high resolution.

[0019] In this specification, the specific surface area of ​​the silicon-based oxide particles can be measured by the Brunauer-Emmett-Teller (BET) method. For example, it can be measured by the BET 6-point method using a porosimetry analyzer (Belsorp-II mini, Bell Japan Inc.) by nitrogen gas adsorption and flow.

[0020] Herein, the Li content in each silicon-based oxide particle as a whole can be confirmed by ICP analysis. For example, for the ICP analysis, a certain amount (approximately 0.01 g) of silicon-based oxide particles is accurately separated and transferred to a platinum crucible. Nitric acid, hydrofluoric acid, and sulfuric acid are added and the particles are completely decomposed on a hot plate. Then, an inductively coupled plasma optical emission spectrometer (ICPAES, Perkin-Elmer 7300) is used to measure the intensity of a standard solution prepared using a standard solution (5 mg / kg) at a wavelength specific to Li element, and a reference calibration curve is created. The pretreated sample solution and a blank sample are then introduced into the instrument, and their respective intensities are measured to calculate the actual intensities. The concentrations of each component are calculated by comparing them with the created calibration curve, and the total is converted to a theoretical value, allowing the Li concentration in the particles to be analyzed.

[0021] Herein, the content of Li by-products (LiOH, Li2CO3) on the surfaces of the first and second coating layers after etching can be measured using pH titration. For example, 20% SiO (solvent: water) can be washed with water (stirrer) for 10 minutes, filtered for 30 minutes to extract the solution, and then pH titration can be performed to analyze the content of Li by-products (LiOH, Li2CO3).

[0022] <Negative electrode active material> According to one embodiment of the present invention, there is provided an anode active material comprising silicon-based oxide particles, the silicon-based oxide particles containing Li, and a first coating layer and a second coating layer formed on the surface of the silicon-based oxide particles, the first coating layer and the second coating layer being carbon layers, respectively, and wherein an irreversible substance formed of the silicon-based oxide and Li is not present between the first coating layer and the second coating layer, or LiOH and Li2CO3 are each present in an amount of less than 1 wt% based on 100 wt% of the total anode active material.

[0023] In the above embodiment, a first coating layer and a second coating layer are provided on the surface of the silicon-based oxide particles containing Li, which can be achieved by doping Li after forming the first coating layer using the manufacturing method described below, and then removing irreversible substances formed by the silicon-based oxide and Li between the first coating layer and the second coating layer by etching such as acid treatment before forming the second coating layer.

[0024] If silicon-based oxide particles are directly doped with Li and etched without forming a first coating layer, the physical properties of the anode material may be impaired, potentially resulting in poor battery performance. Specifically, Li-doped silicon-based oxide materials are highly susceptible to moisture and oxidation, so if Li is directly doped and etched without forming a first coating layer, the physical properties of the material will inevitably deteriorate. Furthermore, if Li is doped and etched without forming a first coating layer, not only the irreversible material to be removed but also the Li-SiO structure present inside the particles may be etched, resulting in excessive etching.

[0025] In the above-described embodiment of the present invention, after forming a first coating layer, which is a carbon layer, doping with Li and etching can remove irreversible substances from the first coating layer without impairing the physical properties of the material, contributing to surface stabilization. Furthermore, forming a second coating layer on the first coating layer can contribute to stabilization inside the particles. As described above, the removal of irreversible substances reduces the amount of irreversible substances in the first and second coating layers, and anode slurries containing such particles can improve the problems of low viscosity and gas generation.

[0026] According to one embodiment, the content of Li may be 1% by weight or more and 15% by weight or less, more preferably 1.5% by weight or more and 13% by weight or less, for example, 3% by weight or more and 12% by weight or less, based on 100% by weight of the total negative electrode active material. When the Li content is 1% by weight or more, it is advantageous for increasing the initial efficiency of the battery. When the Li content is 1% by weight or more, it is advantageous for increasing the initial efficiency of the battery, and when the Li content is 15% by weight or less, it is advantageous in terms of slurry processability.

[0027] According to one embodiment, the silicon-based oxide particles may contain SiOx (0 < x < 2) as a silicon-based oxide component. The SiOx (0 < x < 2) can correspond to a matrix within the silicon-based oxide particles. The SiOx (0 < x < 2) may be in a form containing Si and SiO2, and the Si may form a phase. That is, x corresponds to the number ratio of O to Si contained in the SiOx (0 < x < 2). When the silicon-based oxide particles contain the SiOx (0 < x < 2), the discharge capacity of the secondary battery can be improved.

[0028] According to another embodiment of the present invention, the Li may exist as a Li compound phase. The Li compound phase may exist in at least one form of lithium silicate, lithium silicide, and lithium oxide. The Li compound phase may be lithium silicate (Li-silicate), for example, Li a Si b O c (2 ≤ a ≤ 4, 0 < b ≤ 2, 2 ≤ c ≤ 5), and more specifically, it may contain one or more selected from the group consisting of Li2SiO3, Li2Si2O5, Li3SiO3, Li4SiO4, LiOH, and Li2CO3.

[0029] According to one embodiment, the irreversible substance formed between the first coating layer and the second coating layer by silicon-based oxide and Li may be lithium silicate, and specifically may include one or more selected from the group consisting of Li2SiO3, Li2Si2O5, Li3SiO3, Li4SiO4, LiOH, and Li2CO3, for example, LiOH or Li2CO3.

[0030] The lithium silicate (Li-silicate) may be produced in different phases depending on the Li content, and Li2SiO3 or Li2Si2O5 may be mainly produced.

[0031] In an embodiment of the present invention, the LiOH and Li2CO3 may be generated by a reaction between the Li, HO, and CO2 after the first coating layer, which is a carbon layer, is formed and before the Li is doped and etching is performed. These may be removed by the etching, and the LiOH and Li2CO3 may be contained in a small amount, i.e., less than 1 wt% each, based on 100 wt% of the total negative electrode active material.

[0032] The Li compound may be doped into the silicon-based oxide particles and distributed on the surface and / or inside the silicon-based compound particles. The Li compound, distributed on the surface and / or inside the silicon-based oxide particles, can control the volumetric expansion / contraction of the silicon-based oxide particles to an appropriate level and prevent damage to the active material. The Li compound may also be included to reduce the proportion of irreversible phases (e.g., SiO2) in the silicon-based oxide particles and increase the efficiency of the active material.

[0033] According to one embodiment, the first coating layer may cover the entire surface of the silicon-based oxide particle, or may cover only a portion of the surface. The second coating layer may be provided on at least a portion of the surface of the silicon-based oxide particle provided with the first coating layer.

[0034] According to one embodiment, a portion of the second coating layer may be provided in direct contact with the surface of the silicon-based oxide particles, but a portion or all of the second coating layer may be provided on and in contact with the first coating layer.

[0035] According to one embodiment, the first coating layer and the second coating layer may each be a carbon layer.

[0036] The carbon layer of the first coating layer and the carbon layer of the second coating layer impart electrical conductivity to the silicon-based oxide particles, effectively suppressing volumetric changes in the negative electrode active material containing the silicon-based oxide particles, thereby improving the life characteristics of the battery.

[0037] In one embodiment of the present specification, the carbon layer may contain at least one of amorphous carbon and crystalline carbon.

[0038] The crystalline carbon can further improve the conductivity of the silicon-based oxide particles. The crystalline carbon may include at least one selected from the group consisting of fullerene, carbon nanotube, and graphene.

[0039] The amorphous carbon may be a carbon-based material formed by using at least one carbide or hydrocarbon selected from the group consisting of tar, pitch, and other organic materials as a source in a chemical vapor deposition process.

[0040] The carbonized organic material may be a carbonized organic material selected from the group consisting of sucrose, glucose, galactose, fructose, lactose, mannose, ribose, aldohexose, and ketohexose, and combinations thereof.

[0041] The hydrocarbon may be a substituted or unsubstituted aliphatic or alicyclic hydrocarbon, or a substituted or unsubstituted aromatic hydrocarbon. Examples of the aliphatic or alicyclic hydrocarbon include methane, ethane, ethylene, acetylene, propane, butane, butene, pentane, isobutane, and hexane. Examples of the substituted or unsubstituted aromatic hydrocarbon include benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, coumarone, pyridine, anthracene, and phenanthrene.

[0042] In one embodiment, the carbon layer may be included in an amount of 1 wt % to 50 wt % based on 100 wt % of the total negative electrode active material, specifically 1 wt % to 40 wt %, 1 wt % to 30 wt %, or 1 wt % to 20 wt %, more specifically 1 wt % to 15 wt %. For example, when the first and second coating layers are both carbon layers, the carbon layer may be included in an amount of 1 wt % to 7 wt % based on 100 wt % of the total negative electrode active material when measured after coating only the first coating layer, and may be included in an amount of 1 wt % to 15 wt % based on 100 wt % of the total negative electrode active material when measured after coating up to the second coating layer.

[0043] When the above range is satisfied, the conductivity of the negative electrode active material is improved, and the volume change of the negative electrode active material during charging and discharging of the battery is easily suppressed, thereby improving the life characteristics of the battery.

[0044] In one embodiment, the thickness of each of the carbon layers may be 1 nm to 500 nm, specifically, 5 nm to 300 nm. When the thickness satisfies the above range, the volume change of the negative electrode active material is easily suppressed, and side reactions between the electrolyte and the negative electrode active material are suppressed, thereby improving the life characteristics of the battery.

[0045] In one embodiment, the carbon layer may contain any one of the elements Li, F, and O. The element may be an additional component element contained in the carbon layer depending on the composition of the electrolyte solution.

[0046] According to another embodiment of the present invention, the silicon-based oxide particles may include a phosphate layer including at least one of aluminum phosphate and lithium phosphate provided on the surface thereof, and the phosphate layer may be an aluminum phosphate layer, a lithium phosphate layer, or an aluminum lithium phosphate layer.

[0047] The phosphate layer may be formed by dry-mixing the silicon-based oxide particles with a phosphate, followed by heat treatment and coating; mixing the phosphate with a solvent, the silicon-based oxide particles with the phosphate, and then evaporating the solvent to allow the reaction to occur and then coating; dry-mixing an aluminum or lithium precursor, e.g., aluminum oxide or lithium oxide, with a phosphorus precursor, e.g., phosphorus oxide, followed by heat treatment and then coating; or mixing an aluminum or lithium precursor, e.g., aluminum oxide or lithium oxide with a phosphorus precursor, e.g., phosphorus oxide, in a solvent, followed by evaporating the solvent to allow the reaction to occur and then coating.

[0048] For example, the following methods can be used: dry-mixing the silicon-based oxide particles with AlyPzOw (aluminum phosphate-based) and then heat-treating the mixture to form a coating; mixing AlyPzOw and silicon-based oxide particles in a solvent and then evaporating the solvent to allow the mixture to react and form a coating; dry-mixing AlxOy (aluminum precursor) and PzOw (P precursor) and then heat-treating the mixture to form a coating; or mixing AlxOy (aluminum precursor) and PzOw (P precursor) in a solvent and then evaporating the solvent to allow the mixture to react and form a coating.

[0049] As another example, a method of dry-mixing the above silicon-based oxide particles and LixAlyPzOw (Li-Al-P-O system) and performing a heat treatment for coating, or a method of mixing LixAlyPzOw and silicon-based oxide particles in a solvent and then reacting them while evaporating the solvent for coating can be used.

[0050] Here, x, y, z, and w may satisfy 0 < x ≦ 10, 0 < y ≦ 10, 0 < z ≦ 10, and 0 < w ≦ 10, and they represent the atomic number ratios.

[0051] According to one embodiment of the present invention, x may satisfy 0 < x ≦ 3.

[0052] According to one embodiment of the present invention, y may satisfy 0 < y ≦ 1.

[0053] According to one embodiment of the present invention, z may satisfy 0.5 ≦ z ≦ 3.

[0054] According to one embodiment of the present invention, w may satisfy 4 < w ≦ 12.

[0055] As an example, AlPO4 or Al(PO3)3 may be used as the surface treatment substance for forming the phosphate layer, and the substances formed on the particle surface may be Li3PO4 or AlPO4.

[0056] In the phosphate layer, Al may be contained in an amount of 0.01 wt% to 0.5 wt% based on 100 wt% of the negative electrode active material, and P may be contained in an amount of 0.01 wt% to 1.5 wt% based on 100 wt% of the total silicon-based oxide particles. When the above range is satisfied, there is an advantage that the reaction between the silicon-based oxide particles and water in the aqueous mixing step is suppressed, and the slurry processability is improved.

[0057] According to another embodiment of the present invention, the silicon-based oxide particles may have an average particle size (D50) of 1 μm to 30 μm. Specifically, the silicon-based oxide particles may have an average particle size (D50) of 3 μm to 20 μm, more specifically, 5 μm to 10 μm. When the average particle size (D50) satisfies the above range, side reactions between the negative electrode active material and the electrolyte are controlled, and the discharge capacity and initial efficiency of the battery can be effectively achieved.

[0058] According to another embodiment of the present invention, the BET specific surface area of ​​the silicon-based oxide particles is 0.5 m 2 / g~60m 2 The BET specific surface area of ​​the silicon-based oxide particles may be 0.6 m / g. 2 / g~20m 2 / g, more specifically, 0.8m 2 / g~12m 2 When the above range is satisfied, side reactions between the electrolyte and the negative electrode active material may be reduced during charging and discharging of the battery, thereby improving the life characteristics of the battery.

[0059] According to another embodiment of the present invention, the silicon-based oxide particles may further include Si crystal grains. The Si crystal grains may have a grain size of 1 nm to 15 nm. For example, the grain size of the Si crystal grains may be 1 nm to 14 nm, or 1 nm to 13 nm. The grain size of the Si crystal grains can be calculated by XRD analysis.

[0060] <Method of manufacturing negative electrode active material> According to one embodiment, a method for producing an anode active material containing silicon-based oxide particles includes the steps of: forming a first coating layer, which is a carbon layer, on silicon-based oxide particles; doping the silicon-based oxide particles on which the first coating layer is formed with Li; removing an irreversible substance formed of the silicon-based oxide and Li on the silicon-based oxide particles on which the first coating layer is formed by etching; and forming a second coating layer, which is a carbon layer, on the etched silicon-based oxide particles on which the first coating layer is formed.

[0061] Before or after forming the first coating layer, which is the carbon layer, the silicon-based oxide particles may be pulverized by a mechanical milling method, if necessary, to adjust the particle size.

[0062] The step of forming the first coating layer, which is a carbon layer, on the surface of the silicon-based oxide particles may be performed by, for example, injecting a carbon-based source gas such as methane gas and performing a heat treatment in a rotary tubular furnace. Specifically, the silicon-based oxide particles are placed in a rotary tubular furnace, and the temperature is increased to 800°C to 1,150°C, 900°C to 1,050°C, or 950°C to 1,000°C at a rate of 3 to 10°C / min or about 5°C / min. Argon gas and a carbon-based material source gas are then introduced into the rotary tubular furnace while the furnace is rotating, and the heat treatment is performed for 30 minutes to 8 hours, thereby forming the carbon layer.

[0063] The step of doping the silicon-based oxide particles having the first coating layer with Li may be performed by mixing the silicon-based oxide particles having the carbon layer with lithium metal powder or a lithium precursor, for example, lithium metal powder, LiOH, or Li2O, and, if necessary, heat treating the mixture at 400°C to 1200°C. Alternatively, the step may be performed using an electrochemical method.

[0064] The step of removing the irreversible material formed of the silicon-based oxide and Li on the silicon-based oxide particles on which the first coating layer is formed may be performed by etching.

[0065] In this case, the etching may be performed using an acid or a base. The acid may be at least one of hydrofluoric acid (HF), nitric acid (HNO), sulfuric acid (HSO), and hydrochloric acid (HCl), and the base may be at least one of sodium hydroxide (NaOH) and potassium hydroxide (KOH). Specifically, a mixed solution of hydrofluoric acid and ethanol may be used during the etching. The etching may be performed for 1 to 3 hours, specifically, for 1 to 2.5 hours.

[0066] In one embodiment, the etching may be performed using NaOH, HF or KOH.

[0067] The above-described etching removes the irreversible material on the first coating layer, which may be, for example, LiOH, Li2CO3, lithium silicate, or the like.

[0068] A step of forming a second coating layer, which is at least one of an aluminum phosphate layer and a carbon layer, on the silicon-based oxide particles on which the first coating layer has been formed by etching as described above is carried out. The second coating layer may be a carbon layer, and the method exemplified as the method for forming the first coating layer may be used.

[0069] According to one embodiment, the second coating layer may further comprise an aluminum phosphate layer, which may be formed by the same method as the phosphate layer formation method described above.

[0070] The step of doping the silicon-based oxide particles having the first coating layer with Li may be performed by mixing the silicon-based oxide particles having the carbon layer with lithium metal powder or a lithium precursor, for example, lithium metal powder, LiOH, or LiO, and, if necessary, heat treating the mixture at 400° C. to 1200° C. Alternatively, the step may be performed using an electrochemical method.

[0071] <Negative electrode> A negative electrode according to another embodiment of the present invention may include a negative electrode active material, wherein the negative electrode active material is the same as the negative electrode active material of the above embodiment. Specifically, the negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The negative electrode active material layer may include the negative electrode active material. Furthermore, the negative electrode active material layer may further include a binder and / or a conductive material.

[0072] One embodiment of the present invention provides a negative electrode slurry containing the above-described negative electrode active material.

[0073] According to one embodiment, the negative electrode slurry may further include a solvent in addition to the materials for the negative electrode active material layer. For example, the viscosity of the negative electrode slurry may be measured using a graphite mixture composition, such as 80% artificial graphite and 20% silicon-based oxide, with a total negative electrode active material of 96.5%, 1% conductive material, 1.5% binder, and 1% thickener. The viscosity of the negative electrode slurry may be 10,000 cps to 25,000 cps when measured at room temperature.

[0074] According to one embodiment, 20 g of the negative electrode slurry is placed in a pouch, sealed, and then stored in a chamber at 40°C. The gas generation level measured by measuring the volume change may be 10 mL to 200 mL after storage in the chamber at 40°C for 7 days. The volume change may be determined by placing the sealed pouch in water and measuring the volume change of the water. Specifically, the gas generation level may be 10 mL to 150 mL, 10 mL to 100 mL, or 10 mL to 70 mL.

[0075] The negative electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and is conductive. For example, the current collector may be made of copper, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, or the like. Specifically, a transition metal that easily adsorbs carbon, such as copper or nickel, may be used as the current collector. The thickness of the current collector may be 6 μm to 20 μm, but is not limited thereto.

[0076] 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, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and substances in which hydrogen is substituted with Li, Na, Ca, or the like, or may include various copolymers thereof.

[0077] The conductive material is not particularly limited as long as it does not induce chemical changes in the battery and is conductive. For example, graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; fluorocarbons; metal powders such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives may be used.

[0078] <Secondary battery> A secondary battery according to another embodiment of the present invention may include the negative electrode of the above-described embodiment. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and the negative electrode is the same as the negative electrode described above.

[0079] The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and including the positive electrode active material.

[0080] The positive electrode current collector in the positive electrode is not particularly limited as long as it does not induce chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like may be used. The positive electrode current collector may typically have a thickness of 3 μm to 500 μm, and the surface of the current collector may be formed with fine irregularities to enhance the adhesive strength of the positive electrode active material. The positive electrode current collector may be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0081] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; a lithium iron oxide such as LiFe3O4; 1+c1 Mn 2-c1 O4 (0≦c1≦0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, and Cu2V2O7; chemical formula LiNi 1-c2 M c2 Ni-site type lithium nickel oxide represented by the chemical formula LiMnO2 (wherein M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and 0.01≦c2≦0.3 is satisfied); 2-c3 M c3 Examples of the lithium manganese composite oxide include, but are not limited to, lithium manganese composite oxides represented by Li2Mn3MO8 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01≦c3≦0.1) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); and LiMn2O4, in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion. The positive electrode may be Li-metal.

[0082] The positive electrode active material layer may contain a positive electrode conductive material and a positive electrode binder in addition to the above-described positive electrode active material.

[0083] In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and can be used without any particular limitation as long as it has electronic conductivity without causing chemical changes in the battery that is constructed. Specific examples include graphite such as natural graphite and artificial graphite; carbon-containing materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives, and the like, and one or more of these may be used alone or in combination.

[0084] The positive electrode binder improves adhesion between positive electrode active material particles and between the positive electrode active material and the positive electrode current collector. Specific examples of the positive electrode binder include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. One or more of these may be used alone or in combination.

[0085] The separator separates the negative electrode and positive electrode and provides a path for lithium ion migration. Any separator typically used in secondary batteries can be used without particular limitations. It is particularly preferable that the separator exhibits low resistance to electrolyte ion migration and has excellent electrolyte humidifying ability. Specifically, porous polymer films, such as those made from polyolefin polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminate structures of two or more layers thereof, may be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. To ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymeric material may be used, and it may be selectively used as a single-layer or multi-layer structure.

[0086] Examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in manufacturing lithium secondary batteries.

[0087] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0088] Examples of the non-aqueous organic solvent that can be used include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0089] In particular, among the carbonate organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are preferably used as high-viscosity organic solvents, have a high dielectric constant, and dissociate lithium salts well. When such cyclic carbonates are mixed in an appropriate ratio with linear carbonates having low viscosity and low dielectric constants, such as dimethyl carbonate and diethyl carbonate, an electrolyte having high conductivity can be prepared, and therefore these cyclic carbonates are even more preferably used.

[0090] The metal salt may be a lithium salt, which is a substance that is easily dissolved in the non-aqueous electrolyte solution. For example, the anion of the lithium salt may be F - , Cl - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3- , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - , and (CF3CF2SO2)2N - One or more selected from the group consisting of:

[0091] In addition to the constituent components of the electrolyte, the electrolyte may further include one or more additives, such as a haloalkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing a decrease in battery capacity, and improving the discharge capacity of the battery.

[0092] According to another embodiment of the present invention, there is provided a battery module including the secondary battery as a unit cell, and a battery pack including the same. The battery module and the battery pack include the secondary battery having high capacity, high rate characteristics, and high cycle characteristics. The secondary battery 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.

[0093] Below, preferred examples are presented to help understand the present invention, but these examples are merely illustrative of the present description, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope and technical spirit of the present description, and it goes without saying that such changes and modifications fall within the scope of the appended claims.

[0094] <Example> Example 1: Production of negative electrode active material (1) Preparation of preliminary silicon-based oxide particles (formation of first coating layer) A homogeneous mixture of Si powder and SiO2 powder in a 1:1 molar ratio was heat-treated at 1400°C in a reduced pressure atmosphere to recover the SiO2 powder. The reacted powder was cooled and precipitated, then pulverized in a jet mill to recover particles with an average particle size (D50) of approximately 6 μm.

[0095] The collected particles were placed in a tube furnace and subjected to CVD (Chemical Vapor Deposition) treatment under a mixed gas of argon (Ar) and methane (CH4) to produce preliminary silicon-based oxide particles with a carbon coating layer.

[0096] (2) Production of silicon-based oxide particles (Li doping) The preliminary silicon-based oxide powder and Li metal powder were heat-treated in an inert atmosphere at a temperature of 800° C. for 2 hours to produce particles containing Li.

[0097] (3) Preparation of spare negative electrode active material (etching process) A mixed solution of hydrofluoric acid and ethanol was used as the etching solution, and silicon oxide particles were added to the etching solution in a weight ratio of 20:1. After mixing for about 1 hour, the mixture was filtered, washed, and dried to form preliminary negative electrode active material particles.

[0098] (4) Production of negative electrode active material (formation of second coating layer) The preliminary negative electrode active material particles were placed in a tube furnace and subjected to CVD (Chemical Vapor Deposition) treatment under a mixed gas of argon (Ar) and methane (CH4) to produce negative electrode active material particles having a carbon coating layer as the second coating layer.

[0099] As a result of ICP analysis, the Li content of the prepared negative electrode active material was 4.8 wt % based on 100 wt % of the negative electrode active material particles.

[0100] As a result of CS analysis, the C content of the prepared negative electrode active material was 7 wt % based on 100 wt % of the negative electrode active material particles.

[0101] The negative electrode active material particles were mixed with the solvent water at a ratio of approximately 20% for 10 minutes, filtered, and the pH of the solution was titrated. The LiOH and Li2CO3 contents were measured to be 0.23 wt% and 0.11 wt%, respectively, based on 100 wt% of the total negative electrode active material.

[0102] Example 2: Production of negative electrode active material A negative electrode active material was prepared in the same manner as in Example 1, except that the etching time was 30 minutes when preparing the preliminary negative electrode active material.

[0103] Example 3: Production of negative electrode active material A negative active material was prepared in the same manner as in Example 1, except that the ratio of the preliminary silicon-based oxide powder and the Li metal powder was changed when preparing the silicon oxide particles.

[0104] Example 4: Production of negative electrode active material A negative electrode active material was prepared in the same manner as in Example 3, except that the etching time was 30 minutes when preparing the preliminary negative electrode active material.

[0105] Comparative Example 1: Production of negative electrode active material A negative active material was prepared in the same manner as in Example 1, except that a surface coating layer made of AlPO4 was formed instead of the carbon coating layer.

[0106] The surface coating layer made of AlPO4 is formed by mixing the prepared preliminary negative electrode active material particles with Al(PO3)3 and then heat treating the mixture at a temperature of 600°C.

[0107] As a result of ICP analysis, the Al and P contents of the prepared negative electrode active material were 0.18 wt % and 0.54 wt %, respectively, based on 100 wt % of the total negative electrode active material.

[0108] Comparative Example 2: Preparation of negative electrode active material A negative electrode active material was prepared in the same manner as in Comparative Example 1, except that the etching time during preparation of the preliminary negative electrode active material was 30 minutes.

[0109] Comparative Example 3: Production of negative electrode active material A negative active material was prepared in the same manner as in Comparative Example 1, except that the ratio of the preliminary silicon-based oxide powder and the Li metal powder was changed when preparing the silicon oxide particles.

[0110] Comparative Example 4: Production of negative electrode active material A negative electrode active material was prepared in the same manner as in Comparative Example 3, except that the etching time was 30 minutes.

[0111] Comparative Example 5: Production of negative electrode active material A negative active material was prepared in the same manner as in Example 1, except that the carbon coating layer was not formed during the preparation of the preliminary silicon-based oxide particles.

[0112] Comparative Example 6: Production of negative electrode active material A negative active material was prepared in the same manner as in Comparative Example 1, except that the carbon coating layer was not formed when preparing the preliminary silicon-based oxide particles.

[0113] Comparative Example 7: Production of negative electrode active material The negative electrode active material was prepared in the same manner as in Example 1, except that the carbon coating layer was not formed.

[0114] Comparative Example 8: Production of negative electrode active material A negative electrode active material was prepared in the same manner as in Example 1, except that the etching step, which is a step for preparing a preliminary negative electrode active material, was not performed.

[0115] Comparative Example 9: Production of negative electrode active material A negative electrode active material was prepared in the same manner as in Comparative Example 1, except that the etching step, which is a step for preparing a preliminary negative electrode active material, was not performed.

[0116] [Table 1]

[0117] <Slurry viscosity, gas generation rate measurement> Examples 1A to 4A The negative electrode active material prepared in Example 1 and artificial graphite were mixed in a weight ratio of 2:8 to prepare a mixed negative electrode active material, carbon black as a conductive material, carboxymethyl cellulose (CMC) as a binder, and styrene-butadiene rubber (SBR), and these were mixed together with water as a solvent in a weight ratio of mixed negative electrode active material:conductive material:binder (CMC):binder (styrene-butadiene rubber) = 96.5:1:1:1.5 to prepare a negative electrode slurry of Example 1A.

[0118] Negative electrode slurries of Examples 2A to 4A were prepared in the same manner as in Example 1A, except that the negative electrode active materials of Examples 2 to 4 were used as the negative electrode active materials.

[0119] The prepared slurry was stored at room temperature for 2 days and then measured at 23°C using a rheometer (TA, HR20). The relative viscosity is shown in Table 2 below, based on the 1 Hz viscosity value of Example 1.

[0120] Gas generation can be confirmed by placing 20 g of the above-mentioned slurry in a pouch, sealing it, storing it in a chamber at 40°C for 7 days, and measuring the volume of the pouch that has changed. The amount of gas generated can also be confirmed by placing the sealed pouch in water and measuring the volume of the water that has changed. The amount of gas generated is shown in Table 2 below.

[0121] [Comparative Examples 1A to 9A] Negative electrode slurries of Comparative Examples 1A to 9A were prepared in the same manner as in Example 1A, except that the negative electrode active materials of Comparative Examples 1 to 9 were used as the negative electrode active materials.

[0122] [Table 2]

[0123] In the case of Comparative Examples 1A to 9A, it was confirmed that the viscosity of the slurry containing Li was reduced by Li doping, resulting in the problem of gas generation.

[0124] Meanwhile, in Examples 1A to 4A, silicon-based oxide particles contained Li, and the silicon-based oxide particles were provided with a first coating layer (carbon layer) and a second coating layer (carbon layer), and either no irreversible material formed by the silicon-based oxide and Li was contained between the first coating layer and the second coating layer, or the slurries contained LiOH and Li2CO3 in amounts less than 1 wt% each based on 100 wt% of the total negative electrode active material. It was confirmed that these slurries had higher viscosities and reduced the problem of gas generation compared to Comparative Examples 1A to 9A.

[0125] <Production of anodes and lithium secondary batteries> Examples 1B to 4B The negative electrode active material prepared in Example 1 was mixed with carbon black as a conductive material and Li-PAA as a binder in a weight ratio of 80:10:10 with water (HO) as a solvent to prepare a uniform negative electrode slurry. The prepared negative electrode slurry was coated on one side of a copper current collector, dried, rolled, and then punched to a predetermined size to prepare a negative electrode.

[0126] A Li metal was used as a counter electrode, and a polyolefin separator was placed between the negative electrode and the Li metal. An electrolyte of 1M LiPF6 dissolved in a solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) mixed in a volume ratio of 30:70 was then injected to prepare the negative electrode and coin-type half cell of Example 1B.

[0127] Negative electrodes and coin-type half cells of Examples 2B to 4B were produced in the same manner as in Example 1B, except that the negative electrode active materials of Examples 2 to 4 were used as the negative electrode active materials.

[0128] [Comparative Examples 1B to 9B] Negative electrodes and coin-type half cells of Comparative Examples 1B to 9B were manufactured in the same manner as in Example 1B, except that the negative electrode active materials of Comparative Examples 1 to 9 were used as the negative electrode active materials.

[0129] <Evaluation of discharge capacity, initial efficiency, and cycle characteristics of secondary batteries> The secondary batteries of Examples 1B to 4B and Comparative Examples 1B to 9B were charged and discharged to evaluate the discharge capacity, initial efficiency, and cycle characteristics, which are shown in Table 3 below.

[0130] The batteries manufactured in Examples 1B to 4B and Comparative Examples 1B to 9B were charged at 25°C at a constant current (CC) of 0.1 C until the voltage reached 5 mV, and then charged at a constant voltage (CV) until the charge current reached 0.005 C (cut-off current), after which they were left for 20 minutes and then discharged at a constant current (CC) of 0.1 C until the voltage reached 1.5 V, and the initial efficiency was confirmed.

[0131] Thereafter, the charge / discharge cycle was repeated at 0.5 C up to 40 times, and the capacity retention rate was measured to evaluate the cycle characteristics.

[0132] From the results of one charge / discharge, the initial efficiency (%) was calculated using the following formula.

[0133] Initial efficiency (%) = {discharge capacity of negative electrode active material (mAh / g) / charge capacity of negative electrode active material (mAh / g)} × 100

[0134] The capacity retention rate was calculated using the following formula:

[0135] Capacity retention rate (%) = (40 times discharge capacity / 1 time discharge capacity) × 100

[0136] [Table 3]

[0137] In Examples 1B to 4B, the silicon-based oxide particles contain Li, and the silicon-based oxide particles are provided with a first coating layer (carbon layer) and a second coating layer (carbon layer). Either an irreversible material formed by the silicon-based oxide and Li is not present between the first coating layer and the second coating layer, or LiOH and Li2CO3 are each present in an amount of less than 1 wt% based on 100 wt% of the total negative electrode active material, thereby improving the initial efficiency and lifespan characteristics of the battery.

[0138] On the other hand, in the case of Comparative Examples 1B to 4B, the second coating layer contained an aluminum phosphate layer, and when compared with Examples 1B to 4B, it was confirmed that this did not contribute to stabilizing the interior of the particles, resulting in a decrease in discharge capacity, initial efficiency, and capacity retention rate.

[0139] In the case of Comparative Examples 5B and 6B, the first coating layer, a carbon layer, was not included, and Li was directly doped onto the silicon-based oxide particles and then etched. This resulted in impaired physical properties as a negative electrode material, a deterioration in battery performance, and a decrease in discharge capacity, initial efficiency, and capacity retention rate.

[0140] In the case of Comparative Example 7B, the second coating layer, a carbon layer, was not included, and it was confirmed that it was unable to contribute to stabilizing the interior of the particles, resulting in a decrease in discharge capacity, initial efficiency, and capacity retention rate.

[0141] In the case of Comparative Examples 8B and 9B, it was confirmed that the presence of an irreversible substance formed by silicon-based oxide and Li between the first coating layer and the second coating layer resulted in problems such as a decrease in the viscosity of the negative electrode slurry and gas generation, resulting in a decrease in discharge capacity, initial efficiency, and capacity retention rate.

Claims

1. An anode active material comprising silicon-based oxide particles, the silicon-based oxide particles containing Li, and a first coating layer and a second coating layer provided on the surfaces of the silicon-based oxide particles, the first coating layer and the second coating layer being carbon layers, respectively; The first coating layer and the second coating layer are not provided with an irreversible substance formed by silicon-based oxide and Li, or LiOH and Li ２ CO ３ and each of these is contained in an amount of less than 1 wt % based on 100 wt % of the total negative electrode active material.

2. The negative electrode active material of claim 1 , wherein the Li content is from 1 wt % to 15 wt % based on 100 wt % of the total negative electrode active material.

3. The Li contained in the silicon-based oxide particles is Li ２ SiO ３ , Li ２ Si ２ O ５ , Li ３ SiO ３ , Li ４ SiO ４ , LiOH and Li ２ CO ３ The negative electrode active material according to claim 1 , wherein the negative electrode active material is present as a Li compound phase containing one or more selected from the group consisting of:

4. The average particle size (D ５０ 2. The negative electrode active material according to claim 1, wherein the thickness of the first and second electrodes is 1 μm to 30 μm.

5. The BET specific surface area of ​​the silicon-based oxide particles is 0.5 m ２ / g~60m ２ The negative electrode active material according to claim 1 , wherein the SiO 2 content is 1 / g.

6. 2. The negative electrode active material according to claim 1, wherein the silicon-based oxide particles include Si crystal grains having a grain size of 1 nm to 15 nm.

7. A method for producing a negative electrode active material containing silicon-based oxide particles, comprising: forming a first coating layer, which is a carbon layer, on the silicon-based oxide particles; doping the silicon-based oxide particles on which the first coating layer is formed with Li; removing, by etching, an irreversible substance formed of the silicon-based oxide and Li on the silicon-based oxide particles on which the first coating layer is formed; and forming a second coating layer, which is a carbon layer, on the silicon-based oxide particles on which the etched first coating layer has been formed; The method for producing the negative electrode active material according to claim 1 , comprising:

8. The method for producing a negative electrode active material according to claim 7 , wherein the etching is performed using NaOH, HF or KOH.

9. A negative electrode slurry comprising the negative electrode active material according to claim 1 .

10. A negative electrode comprising the negative electrode active material according to claim 1 .

11. A secondary battery comprising the negative electrode of claim 10.

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