Anode composition, anode, and lithium secondary battery

Abstract

The present invention provides an anode active material including a silicon-based active material containing at least one of a silicon carbon composite and a silicon oxide, and a carbon-based active material, wherein the carbon-based active material includes natural graphite and artificial graphite, and has a resistance to 800 kgf / cm 2 The present invention relates to a negative electrode composition in which, when measuring powder resistance at a pressure of 1000 kJ / cm², the rolling density decreases in the order of natural graphite > artificial graphite > silicon-based active material, and the electrical conductivity decreases in the order of natural graphite > artificial graphite > silicon-based active material, as well as a negative electrode, a lithium secondary battery, a battery module, and a battery pack each containing the same.

Description

[Technical Field]

[0001] The present application relates to a negative electrode composition, a negative electrode, and a lithium secondary battery.

[0002] This application claims the benefit of the filing date of Korean Patent Application No. 10-2023-0099452 filed with the Korean Intellectual Property Office on July 31, 2023, and Korean Patent Application No. 10-2024-0100913 filed with the Korean Intellectual Property Office on July 30, 2024, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference. [Background technology]

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

[0004] Generally, a lithium secondary battery includes a positive electrode, a negative electrode, a separator between the positive electrode and the negative electrode, an electrolyte, an organic solvent, etc. The positive electrode and the negative electrode may each have an active material layer formed on a current collector, the active material layer including a positive electrode active material and a negative electrode active material. Generally, the positive electrode uses a lithium-containing metal oxide such as LiCoO2 or LiMn2O4 as the positive electrode active material, and the negative electrode uses a lithium-free carbon-based active material or a silicon-based active material as the negative electrode active material.

[0005] Among negative electrode active materials, silicon-based active materials have attracted attention due to their higher capacity and superior fast charging characteristics compared to carbon-based active materials. However, silicon-based active materials have the disadvantage of low initial efficiency due to their large volume expansion / contraction during charging / discharging and their large irreversible capacity. Therefore, silicon-based active materials have the disadvantage of degrading battery performance compared to carbon-based active materials.

[0006] Therefore, there is a need to develop negative electrode materials that can improve the performance of lithium secondary batteries. Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention relates to a negative electrode composition capable of improving the performance of a lithium secondary battery, a negative electrode including the negative electrode composition, and a secondary battery including the same. [Means for solving the problem]

[0008] One embodiment of the present invention provides an anode active material including a silicon-based active material including at least one of a silicon carbon composite and a silicon oxide, and a carbon-based active material, wherein the carbon-based active material includes natural graphite and artificial graphite, and has a resistance of 800 kgf / cm 2 When measuring powder resistance at a pressure of 1000 kJ / cm, the rolling density decreases in the order of natural graphite > artificial graphite > silicon-based active material, and the electrical conductivity decreases in the order of natural graphite > artificial graphite > silicon-based active material.

[0009] According to one embodiment of the present invention, the negative electrode composition of the above-described embodiment also includes single-walled carbon nanotubes as the conductive material.

[0010] One embodiment of the present invention provides a negative electrode comprising a negative electrode composition according to the above-described embodiment.

[0011] One embodiment of the present invention provides a lithium secondary battery comprising a negative electrode, a positive electrode, and a separator according to the above-described embodiment.

[0012] One embodiment of the present invention provides a battery module including the lithium secondary battery according to the above-described embodiment.

[0013] One embodiment of the present invention provides a battery pack including the lithium secondary battery according to the above-described embodiment.

[0014] One embodiment of the present invention provides a battery pack including a battery module according to the above-described embodiment. [Effects of the Invention]

[0015] According to an embodiment of the present invention, the performance of a lithium secondary battery can be improved by using a mixture of a silicon-based active material and a carbon-based active material having different rolling densities and electrical conductivities as an anode active material. In particular, the mixture of two carbon-based active materials having different rolling densities and electrical conductivities, which have higher rolling densities and electrical conductivities at the same pressure than a silicon-based active material, can improve the cycle characteristics and resistance of a lithium secondary battery. DETAILED DESCRIPTION OF THE INVENTION

[0016] The present invention will be described in more detail below to facilitate understanding of the present invention. The present invention may be realized in various different forms and is not limited to the embodiments described herein. In this regard, the terms and words used in the specification and claims should not be interpreted in a limited manner to their ordinary or dictionary meanings, but should be interpreted in a manner 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 describe their invention.

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

[0018] Furthermore, when a part such as a layer exists "on" or "above" another part, it does not only mean that it is "directly above" that part, but also includes the case where there is another part between them. In contrast, when a part exists "directly above" another part, it means that there is no other part between them. Furthermore, when a part exists "on" or "above" a reference part, it does not necessarily mean that it is located above or below the reference part, and is not necessarily located "above" or "above" the direction opposite to gravity.

[0019] The terms and words used in this specification should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as meanings and concepts that are 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.

[0020] As used herein, the singular expression of a term includes the plural expression unless the context clearly indicates otherwise.

[0021] In this specification, the rolling density refers to the degree of deformation and compression of particles that occurs when a certain pressure is applied to the negative electrode active material, and can be expressed in g / cc. The rolling density can be derived by measuring the powder resistivity. For example, a certain amount of the negative electrode active material is placed in a cylindrical load cell, and a pressure of 400 kgf / cm is applied. 2 ~2,000kgf / cm 2 The thickness of the negative electrode active material can be measured by applying any one of the pressures.

[0022] In this specification, the electrical conductivity means the inherent electrical conductivity of the negative electrode active material powder. The electrical conductivity can be calculated by measuring the powder resistance, and is, for example, 400 kgf / cm 2 ~2,000kgf / cm 2 While applying any one of the pressures, the surface resistance due to the pressure change is measured, and at the same time, the surface resistance and specific resistance are measured based on the measured volume and mass, and the value can be derived from the measured surface resistance and specific resistance values.

[0023] When measuring powder resistance, excessively high force, e.g., 2000 kgf / cm 2 Considering the influence of particle deformation that may occur when the pressure exceeds 800 kgf / cm 2 It is preferred to use rolled density and electrical conductivity values ​​derived by measuring powder resistivity under an applied pressure of 1000 kJ / cm.

[0024] Preferred embodiments of the present invention will be described in detail below. However, the embodiments of the present invention may be modified in various ways, and the scope of the present invention is not limited to the embodiments described below.

[0025] According to one embodiment of the present invention, the negative electrode composition includes a silicon-based active material including at least one of a silicon carbon composite and a silicon oxide, and a carbon-based active material, and the carbon-based active material includes natural graphite and artificial graphite. 2 When measuring the powder resistance at a pressure of 1000 kJ / cm, the rolling density decreases in the order of natural graphite > artificial graphite > silicon-based active material, and the electrical conductivity decreases in the order of natural graphite > artificial graphite > silicon-based active material.

[0026] According to the embodiment, together with the silicon-based active material, the resistance is 800 kgf / cm compared to the silicon-based active material. 2 By including a carbon-based active material that has a high rolling density and electrical conductivity when measuring powder resistance at a pressure of 800 kgf / cm, the cycle characteristics and resistance of a lithium secondary battery can be improved.2 When powder resistivity is measured at a pressure of 1000 kJ / cm², the performance of lithium secondary batteries can be improved by mixing natural graphite, which has a relatively high rolling density and electrical conductivity. By mixing a negative electrode active material with a relatively high electrical conductivity, even if surface separation occurs between the negative electrode active material and the conductive material due to volume change during charging and discharging, the high electrical conductivity makes charging and discharging easier than with lithium. This allows for long-life battery characteristics to be achieved. Meanwhile, active materials with a relatively high rolling density can physically control volume change during charging and discharging, which can have a beneficial effect on cycle performance.

[0027] In an anode composition according to an embodiment of the present invention, even if the rolling density of each material satisfies the condition that it decreases in the order of natural graphite > artificial graphite > silicon-based active material, if the electrical conductivity of each material does not satisfy the order of natural graphite > artificial graphite > silicon-based active material, particles may crack, exposing inner surfaces with low electrical conductivity, resulting in a phenomenon in which the electrical conductivity trend is reversed. For example, this corresponds to the case where the electrical conductivity order is artificial graphite > natural graphite > silicon-based active material.

[0028] Specifically, as the rolling density increases, the contact surface between particles generally increases, resulting in higher electrical conductivity. However, if particles crack, this can have a negative effect on electrical conductivity. Therefore, the rolling density and electrical conductivity should have the same tendency.

[0029] If they do not have the same tendency, particle cracking may occur, which may adversely affect battery performance.

[0030] Furthermore, if the artificial graphite has a higher rolling density and electrical conductivity than natural graphite, the degree of graphitization of the artificial graphite will be high, which may result in a decrease in battery performance.

[0031] Unless otherwise specified, the electrical conductivity in this specification refers to the electrical conductivity of the particles of each material, for example, the state before cracks occur, and does not refer to the electrical conductivity after the particles have cracked.

[0032] According to one embodiment, the 800 kgf / cm 2 When measuring the powder resistance at a pressure of 1.01 times, the rolling density of the artificial graphite is 1.1 times or more larger than that of the silicon-based active material, and the rolling density of the natural graphite is 1.01 times or more larger than that of the artificial graphite.

[0033] For example, the above 800 kgf / cm 2 When measuring the powder resistivity at a pressure of 800 kgf / cm, the rolling density may be 1.4 to 2.5 g / cc, for example, 1.6 to 1.7 g / cc for natural graphite, 1.0 to 2.2 g / cc, for example, 1.5 to 1.6 g / cc for artificial graphite, and 0.5 to 1.8 g / cc for silicon-based active materials. 2 When measuring the powder resistivity at a pressure of 0.5 to 1.2 g / cc, the rolled density of the silicon carbon composite may be 0.5 to 1.2 g / cc, for example, 0.8 to 1.0 g / cc, and the rolled density of the silicon oxide may be 0.8 to 1.8 g / cc, for example, 1.4 to 1.5 g / cc.

[0034] According to one embodiment, the 800 kgf / cm 2 When measuring the powder resistance at a pressure of 100 times, the electrical conductivity of the artificial graphite is 100 times or more higher than that of the silicon-based active material, and the electrical conductivity of the natural graphite is 2 times or more higher than that of the artificial graphite.

[0035] For example, 800 kgf / cm 2 When measuring the powder resistance at a pressure of 800 kgf / cm, the electrical conductivity of the silicon-based active material may be 0.0001 to 2 S / cm, the electrical conductivity of the artificial graphite may be 15 to 2,000 S / cm, for example, 15 to 100 S / cm, and the electrical conductivity of the natural graphite may be 50 to 10,000 S / cm, for example, 100 to 1,000 S / cm, or 100 to 500 S / cm. 2 When measuring the powder resistance at a pressure of 0.0001 to 2 S / cm, the electrical conductivity of the silicon carbon composite may be 0.0001 to 2 S / cm, for example, 0.0001 to 0.5 S / cm, and the electrical conductivity of the silicon oxide may be 0.001 to 1 S / cm, for example, 0.01 to 0.5 S / cm.

[0036] According to one embodiment, the silicon-based active material may be contained in an amount of 0.5 to 52 parts by weight; the carbon-based active material may be contained in an amount of 45 to 99 parts by weight; and the single-walled carbon nanotubes may be contained in an amount of 0.01 to 3 parts by weight, based on 100 parts by weight of the carbon-based active material. The natural graphite may be contained in an amount of 10 to 70 parts by weight; and the artificial graphite may be contained in an amount of 30 to 90 parts by weight, based on 100 parts by weight of the carbon-based active material.

[0037] According to one embodiment, the silicon-based active material may be contained in an amount of 0.5 parts by weight to 50 parts by weight, 1 part by weight to 40 parts by weight, for example, 1 part by weight to 20 parts by weight, based on 100 parts by weight of the total amount of the negative electrode active material contained in the negative electrode composition.

[0038] According to one embodiment, the carbon-based active material may be included in an amount of 60 to 99 parts by weight, for example, 80 to 99 parts by weight, based on 100 parts by weight of the total amount of negative electrode active material included in the negative electrode composition. The weight ratio of the artificial graphite to the natural graphite may be 1:9 to 9:1, for example, 1:9 to 3:7. For example, based on 100 parts by weight of the carbon-based active material, the natural graphite may be 10 to 70 parts by weight, for example, 10 to 30 parts by weight; and the artificial graphite may be 30 to 90 parts by weight, for example, 70 to 90 parts by weight.

[0039] According to one embodiment, the silicon-based active material may include a silicon carbon composite, a silicon oxide, or both.

[0040] According to one embodiment, the silicon carbon composite may be a Si / C based active material.

[0041] In this specification, the silicon carbon composite is a composite of Si and C and is distinguished from silicon carbide, which is represented as SiC. Silicon carbide does not electrochemically react with lithium, and all performances, including lifespan, can be measured as zero.

[0042] The silicon carbon composite may include at least one of a silicon carbon composite formed by depositing silicon on a porous carbon structure and a silicon carbon composite formed by compositing carbon on a porous silicon structure. The silicon carbon composite may be a composite of silicon and graphite. The silicon in the silicon carbon composite may be nanosilicon.

[0043] According to one embodiment, the silicon carbon composite comprises porous carbon-based particles and a silicon coating layer located on the surface or in the internal pores of the porous carbon-based particles.

[0044] According to one embodiment, the silicon carbon composite is produced by the BET method to a surface area of ​​0.5 m 2 / g~10m 2 / g, with a pore volume of 0.005 cm 3 / g~0.03cm 3 The silicon carbon composite may have a pore volume of 0.005 cm3 measured by mercury penetration spectroscopy, and the pore size measured by BET method may be 10 nm to 20 nm. 3 / g~0.03cm 3 / g.

[0045] According to one embodiment, the silicon carbon composite is 90 The particle size may be 11 μm to 20 μm, and D 50 The particle size may be 3 μm to 10 μm, and D 10 The particle size may be 0.1 μm to 3 μm.

[0046] According to one embodiment, the silicon carbon composite may be prepared by a method including the steps of: etching carbon-based particles having internal pores to expand the internal pores of the carbon-based particles; and forming a silicon coating layer on the surfaces and internal pores of the carbon-based particles whose internal pores have been expanded.

[0047] The step of expanding the internal pores of the carbon-based particles may be performed in a nitrogen (N2) atmosphere, an oxygen (O2) atmosphere, or an air atmosphere. Specifically, the flow rate of the oxygen (O2) or the air containing the oxygen may be controlled to 0.1 to 10 L / min.

[0048] The step of expanding the internal pores of the carbon-based particles may be performed at a temperature range of 400 to 1200 °C for 30 minutes to 4 hours.

[0049] Depending on the conditions for expanding the internal pores of the carbon-based particles, the pore characteristics of the obtained porous carbon-based particles may vary.

[0050] The step of forming the silicon coating layer may be performed using a chemical vapor deposition method. At this time, silicon nanoparticles may be deposited on the surface and / or internal pores of the carbon-based particles with expanded internal pores, and a silicon coating layer in the form of a film, an island, or a mixture thereof may be formed.

[0051] The silicon nanoparticles may be crystalline, quasi-crystalline, amorphous, or a combination thereof.

[0052] According to one embodiment, the silicon oxide may include SiO x (0 ≤ x < 2).

[0053] The SiO x ((0≦x<2) containing active material may be silicon oxide particles containing SiO x (0 < x < 2) and pores.

[0054] The SiO x (0 < x < 2) corresponds to the matrix in the silicon oxide particles. The SiO x (0 < x < 2) may be in a form containing Si and SiO2, and the Si may form a phase. That is, the x in the SiO xIt corresponds to the number ratio of O to Si contained in (0 < x < 2). The silicon oxide particles are the SiO x When (0 < x < 2) is included, the discharge capacity of the secondary battery can be improved.

[0055] The silicon oxide particles may further contain at least one of a Mg compound and a Li compound. The Mg compound and the Li compound may correspond to a matrix within the silicon oxide particles.

[0056] The Mg compound and / or the Li compound may be present inside and / or on the surface of the SiO x (0 < x < 2). The initial efficiency of the battery can be improved by the Mg compound and / or the Li compound.

[0057] The Mg compound may include at least any one selected from the group consisting of Mg silicate, Mg silicide, and Mg oxide. The Mg silicate may include at least any one of Mg2SiO4 and MgSiO3. The Mg silicide may include Mg2Si. The Mg oxide may include MgO.

[0058] In one embodiment of the present specification, the Mg element may be contained at 0.1 wt% to 20 wt%, or may be contained at 0.1 wt% to 10 wt% based on 100 wt% of the total silicon oxide particles. Specifically, the Mg element may be contained at 0.5 wt% to 8 wt%, or 0.8 wt% to 4 wt%. When the above range is satisfied, the Mg compound can be contained at an appropriate content within the silicon oxide particles, so that the volume change of the silicon oxide particles during charging and discharging of the battery can be easily suppressed, and the discharge capacity and initial efficiency of the battery can be improved.

[0059] The Li compound may contain at least any one selected from the group consisting of Li silicate, Li silicide, and Li oxide. The Li silicate may contain at least any one of Li2SiO3, Li4SiO4, and Li2Si2O5. The Li silicide may contain Li7Si2. The Li oxide may contain Li2O.

[0060] In one embodiment of the present invention, the Li compound may contain a form of lithium silicate. The lithium silicate is Li a Si b O c (2 ≤ a ≤ 4, 0 < b ≤ 2, 2 ≤ c ≤ 5), and can be classified into crystalline lithium silicate and amorphous lithium silicate. The crystalline lithium silicate may exist in the form of at least one lithium silicate selected from the group consisting of Li2SiO3, Li4SiO4, and Li2Si2O5 within the silicon oxide particles, and the amorphous lithium silicate may be in the form of Li a Si b O c (2 ≤ a ≤ 4, 0 < b ≤ 2, 2 ≤ c ≤ 5), and is not limited to this form.

[0061] In one embodiment of the present specification, the Li element may be contained at 0.1 wt% to 20 wt%, or may be contained at 0.1 wt% to 10 wt% based on the total 100 wt% of the silicon oxide particles. Specifically, the Li element may be contained at 0.5 wt% to 8 wt%, and more specifically, may be contained at 0.5 wt% to 4 wt%. When the above range is satisfied, the Li compound can be contained in an appropriate content within the silicon oxide particles, so that the volume change of the negative electrode active material during charging and discharging of the battery can be easily suppressed, and the discharge capacity and initial efficiency of the battery can be improved.

[0062] The Mg or Li element content can be confirmed by ICP analysis. For the ICP analysis, a certain amount (approximately 0.01 g) of the negative electrode active material is accurately separated and transferred to a platinum crucible. Nitric acid, hydrofluoric acid, and sulfuric acid are added and the mixture is completely decomposed on a hot plate. Then, an inductively coupled plasma optical emission spectrometer (ICPAES, Perkin-Elmer 7300) is used to measure the intensity of a standard solution (5 mg / kg) prepared at a wavelength specific to Mg or Li, creating a reference calibration curve. 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 using the created calibration curve, and the total is converted to a theoretical value. The Mg or Li element content of the silicon oxide particles can then be analyzed.

[0063] In one embodiment of the present specification, a carbon layer may be provided on the surface and / or inside the pores of the silicon oxide particles. The carbon layer imparts electrical conductivity to the silicon oxide particles, thereby improving the initial efficiency, life characteristics, and capacity characteristics of a secondary battery including a negative electrode active material containing the silicon oxide particles. The total weight of the carbon layer may be 5 wt % to 40 wt % based on 100 wt % of the total weight of the silicon oxide particles.

[0064] In one embodiment of the present specification, the carbon layer may include at least one of amorphous carbon and crystalline carbon.

[0065] The average particle size (D 50 ) may be 0.1 μm to 30 μm, specifically 1 μm to 20 μm, and more specifically 1 μm to 10 μm. When the particle size satisfies this range, the active material is structurally stable during charge and discharge, the problem of an excessively large particle size resulting in an increased level of volume expansion / contraction is prevented, and the problem of an excessively small particle size resulting in a decrease in initial efficiency is prevented.

[0066] In this specification, the average particle size (D50 The average particle size (D) can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve. 50 ) can be measured, for example, by using a laser diffraction method. The laser diffraction method is generally capable of measuring particle sizes from the submicron range to several mm, and can provide results with high reproducibility and high resolution. The specific surface area of ​​the silicon-based active material is 2 to 10 m 2 / g. In this specification, the specific surface area is measured by the BET method.

[0067] According to one embodiment, the carbon-based active material includes natural graphite and artificial graphite. Each of the natural graphite and the artificial graphite has an average particle size (D 50 ) is 10 to 30 μm, and the BET specific surface area is 0.5 to 2 m 2 / g. The natural graphite refers to graphite that is naturally produced, and examples thereof include flake graphite, scaly graphite, and soil graphite. The natural graphite has the advantages of being abundant, inexpensive, having a high theoretical capacity and a high compressed density, and being able to achieve high output.

[0068] According to one example, the natural graphite may have a sphericity of 0.9 or more.

[0069] In this specification, sphericity may be the value obtained by dividing the circumference of a circle having the same area as the projected image when a particle is projected by the perimeter of the projected image, and can be specifically expressed by the following formula 1. The sphericity can be determined from an SEM image or can be measured using a particle shape analyzer such as a Sysmex FPIA3000 manufactured by Malvern. Crystal size can also be confirmed by XRD analysis.

[0070] [Formula 1] Sphericity = Circumference of a circle with the same area as the projected image of a particle / Perimeter of the projected image

[0071] The natural graphite may be selected to satisfy the above-mentioned sphericity by checking the particle shape using an SEM and then checking it using a particle shape analyzer.

[0072] According to one example, the artificial graphite may have a sphericity of 0.9 or less.

[0073] The artificial graphite may be selected to satisfy the above sphericity by checking the particle shape using an SEM and then checking it using a particle shape analyzer.

[0074] According to one embodiment of the present invention, the negative electrode composition includes single-walled carbon nanotubes (SWCNTs) as a conductive material.

[0075] The single-walled carbon nanotubes (SWCNTs) refer to tubular carbon structures consisting of a single carbon layer. When the conductive material in the negative electrode composition contains the single-walled carbon nanotubes (SWCNTs), the charge / discharge capacity and / or lifespan of the battery can be improved. Specifically, the single-walled carbon nanotubes (SWCNTs) effectively connect the conductive paths between particles, thereby preventing the loss of the conductive paths due to swelling of the silicon-based active material. As a result, when the single-walled carbon nanotubes (SWCNTs) are contained, the lifespan of the battery can be improved.

[0076] In this specification, the length of a carbon nanotube refers to the length of the major axis passing through the center of a carbon nanotube unit, and the diameter of a carbon nanotube refers to the length of the minor axis passing through the center of the unit and perpendicular to the major axis.

[0077] The average length of the single-walled carbon nanotubes (SWCNTs) may be 0.1 μm to 50 μm, specifically 0.5 μm to 25 μm, or 0.5 μm to 20 μm. More specifically, it may be 5 μm to 15 μm. The average length of the single-walled carbon nanotubes (SWCNTs) can be calculated as the average value of the results observed by SEM.

[0078] When single-walled carbon nanotubes (SWCNTs) are used together with the silicon-based active material and carbon-based active material, the length of the carbon nanotubes is sufficient to match the distance between particles of the negative electrode active material, which makes it easier to connect conductive paths between the particles, thereby improving the electrical conductivity and strength of the negative electrode and / or the storage stability of the electrolyte.

[0079] The average diameter of the single-walled carbon nanotubes (SWCNTs) may be 1 nm to 20 nm, specifically 1.5 nm to 15 nm, or more specifically 1.5 nm to 5 nm. Because the single-walled carbon nanotubes (SWCNTs) having such an average diameter are flexible, they have the advantage that the contact between the negative electrode active material particles is not easily broken even when physically damaged. The average diameter of the single-walled carbon nanotubes (SWCNTs) can be calculated as the average value observed by TEM.

[0080] The BET specific surface area of ​​the single-walled carbon nanotubes is 200m 2 / g~2,000m 2 / g, specifically 250m 2 / g~1,500m 2 When single-walled carbon nanotubes (SWCNTs) that satisfy the above range are used, even if a small amount of conductive material is used, dispersion is easy and particles can be effectively connected.

[0081] The single-walled carbon nanotubes (SWCNTs) may be included in an amount of 0.01 to 3 parts by weight, specifically 0.01 to 2 parts by weight, 0.01 to 1 part by weight, or 0.05 to 0.5 parts by weight, based on 100 parts by weight of the negative electrode composition. When the amount is within this range, it is possible to facilitate the connection of conductive paths between active material particles and minimize side reactions in the electrolyte due to the high specific surface area.

[0082] In this specification, the specific surface area is measured by the BET method. Specifically, the specific surface area can be measured by degassing the object to be measured at 130°C for 2 hours using a BET measurement device (BEL-SORP-mini, Nippon Bell) and then performing N2 absorption / desorption at 77K.

[0083] According to one embodiment, the negative electrode composition further comprises a binder.

[0084] 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.

[0085] One embodiment of the present invention provides a negative electrode comprising a negative electrode composition according to the above-described embodiment.

[0086] 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 includes the negative electrode composition according to the above-described embodiment.

[0087] The negative electrode active material layer may be formed by applying a negative electrode slurry containing the above-described negative electrode composition to at least one surface of a negative electrode current collector, followed by drying and rolling.

[0088] The negative electrode current collector is not particularly limited as long as it does not cause 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 to this.

[0089] If necessary, an additional conductive material other than the single-walled carbon nanotubes may be included. The additional conductive material is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity, and examples thereof include graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0090] The negative electrode slurry may include a solvent for forming a negative electrode slurry. Specifically, the solvent for forming a negative electrode slurry may include at least one solvent selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol, specifically distilled water, in order to facilitate dispersion of components.

[0091] One embodiment of the present invention provides a lithium secondary battery comprising a negative electrode, a positive electrode, and a separator according to the above-described embodiment.

[0092] 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.

[0093] The positive electrode current collector in the positive electrode is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel whose surface has been 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 fine irregularities may be formed on the surface of the current collector 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.

[0094] 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 c2Ni-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 oxides 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 satisfying 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.

[0095] 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.

[0096] In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and can be any material that 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-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. These may be used alone or in combination of two or more.

[0097] 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. These binders may be used singly or in combination.

[0098] The separator separates the negative electrode and positive electrode and provides a path for lithium ions to move. Any separator typically used in secondary batteries can be used without particular limitation. It is particularly preferable that the separator exhibits low resistance to 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 laminated 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.

[0099] The lithium secondary battery may further include an electrolyte, which may be used in manufacturing a lithium secondary battery, such as, but not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, or a molten inorganic electrolyte.

[0100] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0101] 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.

[0102] In particular, among the carbonate organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, can be preferably used as high-viscosity organic solvents, because they have a high dielectric constant and dissociate lithium salts well. When such cyclic carbonates are mixed with linear carbonates having low viscosity and low dielectric constants, such as dimethyl carbonate and diethyl carbonate, in an appropriate ratio, an electrolyte having high electrical conductivity can be prepared, and therefore such cyclic carbonates can be more preferably used.

[0103] 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:

[0104] 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 derivative, sulfur, quinoneimine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride, in order to improve the life characteristics of the battery, suppress a decrease in battery capacity, and improve the discharge capacity of the battery.

[0105] 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.

[0106] According to another embodiment of the present invention, there is provided a battery pack including the secondary battery. The battery module and battery pack include the secondary battery having high capacity, high rate characteristics, and high cycle characteristics, and can be used as a power source for medium to large devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0107] Hereinafter, the present specification will be described in detail with reference to examples. However, the examples according to the present specification may be modified into various other forms, and the scope of the present application should not be interpreted as being limited to the examples described below. The examples of the present application are provided to more completely explain the present specification to those skilled in the art. [Example]

[0108] Example 1 (Silicon Carbon Composite 1, Artificial Graphite 2, Natural Graphite 2) [Production of silicon carbon composite 1] The cellulose powder was placed in a tubular furnace, heated to 400°C at a rate of 4°C / min, and then heated under a nitrogen atmosphere for 2 hours. The furnace was then heated to 900°C at a rate of 4°C / min and then heated under a nitrogen atmosphere for 2 hours. The powder was mixed with sulfuric acid and nitric acid in a 3:1 volume ratio, stirred at 60°C for 2 hours, and centrifuged to obtain a precipitate. The resulting powder was washed five times with a 1:3 volume ratio mixture of ethanol and distilled water and then dried at 120°C for 12 hours. The carbonaceous particles were placed in a KOH solvent and heated at 800°C for 2 hours under a nitrogen atmosphere to obtain a porous carbon structure. The porous carbon structure was washed three times with distilled water and then dried at 120°C for at least 12 hours. The porous carbon structure was placed in a horizontal furnace and a SiH4 / He=5 / 95 gas mixture was passed through at a flow rate of 50 ml / min at 700°C for 1 hour to produce a silicon carbon composite. The silicon carbon composite was then placed in the furnace and reacted with methane at 700°C for 2 hours to produce silicon carbon composite 1 having a carbon layer on the surface.

[0109] [Manufacturing of artificial graphite 2] Green coke particles, calcined coke particles, and a petroleum-based pitch binder were added to a reactor. The green coke and calcined coke particles were mixed in a weight ratio of 30:70. The pitch binder was mixed at 7 wt% based on the total weight of the green coke particles, calcined coke particles, and petroleum-based pitch. The mixture of the green coke particles, calcined coke particles, and petroleum-based pitch was heat-treated at 3000°C for 50 hours to be graphitized, thereby producing secondary particles of artificial graphite particles in the form of primary particles bonded together. The secondary particles of artificial graphite and petroleum-based pitch were mixed and heat-treated in a roller hearth kiln at 1250°C to form an amorphous carbon coating layer on the surface of the artificial graphite particles, thereby producing artificial graphite 2. The final D of artificial graphite 2 50 was controlled at the 16 μm level.

[0110] [Production of natural graphite 2] Natural graphite raw material was extracted from graphite ore by floatation. The natural graphite was treated with acid or base to remove impurities, washed, and dried to produce flake natural graphite. The obtained flake natural graphite was spheroidized using a vortex flow pulverizer, and impurities were removed with sulfuric acid. The resulting spherical natural graphite was then dried to produce spherical natural graphite. The spherical natural graphite was packed into a mold, pressed using cold isostatic pressing (CIP), and crushed. The pressing pressure was 90 MPa, and the pressing time was 15 minutes. The pressed spherical natural graphite was mixed with pitch, and the mixture was heat-treated at 1,300°C in an inert atmosphere for 24 hours using a dry method to form an amorphous carbon coating layer on the spherical natural graphite, producing natural graphite 2. The carbon coating layer was formed in an amount of 5 wt% based on the total weight of the natural graphite active material.

[0111] [Slurry production] As the negative electrode active material, silicon carbon composite 1, natural graphite 2, and artificial graphite 2 having the rolling density and electrical conductivity shown in Table 1 below were used in a weight ratio of 15:15:70. Specifically, silicon carbon composite 1 had a rolling density of 800 kgf / cm 2 When the powder resistivity was measured at a pressure of 1.000, the powder had a rolled density of 0.859 g / cc and an electrical conductivity of 0.664 S / cm, while the natural graphite 2 had values ​​of 1.6 g / cc and 337 S / cm, and the artificial graphite 2 had values ​​of 1.58 g / cc and 96.6 S / cm. The negative electrode active material, conductive materials (carbon black, single-walled carbon nanotubes (SWCNTs)), and binders (carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR)) were mixed in a weight ratio of 95.3:1:3.7 to prepare a negative electrode slurry.

[0112] [Manufacturing of negative electrodes] The negative electrode slurry was applied to a Cu metal thin film with a thickness of 20 μm, and then dried in circulating air at 60° C. After rolling, it was dried in a vacuum oven at 130° C. for 1 day, and then cut into 1.4875 cm 2 The negative electrode was then manufactured by punching out a circular piece.

[0113] [Secondary battery manufacturing] 1.7671cm 2 A Li metal thin film punched into the shape of a square was used as the positive electrode. A porous polyethylene separator was placed between the positive and negative electrodes, and an electrolyte solution of 1M LiPF6 dissolved in a mixed solution of EC (ethylene carbonate) and EMC (ethyl methyl carbonate) in a 3:7 ratio, containing additives, was injected to fabricate a Li coin half cell.

[0114] Example 2 (Silicon oxide 1, artificial graphite 2, natural graphite 2) [Production of silicon oxide 1] SiO, a mixture of Si and SiO2 in a 1:1 molar ratio, was placed in crucible 1 and heated to a sublimation temperature of 1400°C for evaporation. Metallic magnesium was placed in crucible 2 and heated to 800°C for evaporation. The crucible was then depressurized to a 0.1 torr level, and the raw materials were evaporated. The Mg-containing vapor mixture was reacted for 6 hours and then solidified in a vacuum at 800°C. The silicon-based active material produced by this method was pulverized using a ball mill for approximately 3-4 hours. Then, methane (CH4) was reacted in a CVD apparatus under an inert Ar atmosphere at 0.1 torr for approximately 5 hours at a rate of 1 L / min to form a carbon layer on the surface of the silicon-based active material, producing a carbon-coated magnesium silicon oxide active material. The final active material D 50 was controlled to the 6 μm level.

[0115] [Slurry production] A slurry was prepared in the same manner as in Example 1, except that silicon oxide 1, natural graphite 2 (see the manufacturing method in Example 1), and artificial graphite 2 (see the manufacturing method in Example 1) having the rolling density and electrical conductivity shown in Table 1 below were used as the negative electrode active material in a weight ratio of 20:10:70. Specifically, silicon oxide 1 had a rolling density of 800 kgf / cm. 2 When the powder resistivity was measured at a pressure of 1.6 g / cc, the natural graphite 2 had a rolled density of 1.42 g / cc and an electrical conductivity of 0.122 S / cm, and the artificial graphite 2 had values ​​of 1.6 g / cc and 337 S / cm, respectively, and 1.58 g / cc and 96.6 S / cm, respectively.

[0116] [Manufacturing of anodes and secondary batteries] Using the slurry, a negative electrode and a secondary battery were produced in the same manner as in Example 1.

[0117] Example 3 (Silicon carbon composite 2, artificial graphite 1, natural graphite 1) [Production of silicon carbon composite 2] The silicon carbon composite was heat-treated in an O2 / Ar=5 / 95 atmosphere at 700°C for 2 hours to form an oxide layer. Silicon carbon composite 2 was produced in the same manner as in Example 1, except that the silicon carbon composite was placed in an electric furnace and reacted for 2 hours under a flow of methane at 700°C to form a carbon layer on the surface.

[0118] [Production of artificial graphite 1] The pitch binder was mixed at 4.5 wt % based on the total weight of the green coke particles, calcined coke particles, and petroleum-based pitch. An artificial graphite active material was prepared in the same manner as in Artificial Graphite 2 of Example 1, except that secondary particles of artificial graphite and petroleum-based pitch were mixed and heat-treated at 1,150°C in a roller hearth kiln to form an amorphous carbon coating layer on the surface of the artificial graphite particles.

[0119] [Production of natural graphite 1] A natural graphite active material was prepared in the same manner as in Natural Graphite 2 in Example 1, except that compressed spherical natural graphite and pitch were mixed, and the mixture was heat-treated at 1,100°C in an inert atmosphere for 24 hours using a dry method to form an amorphous carbon coating layer.

[0120] [Slurry production] A slurry was prepared in the same manner as in Example 1, except that a silicon carbon composite 2 having the rolling density and electrical conductivity shown in Table 1 below, natural graphite 1, and artificial graphite 1 were used in a weight ratio of 15:15:70 as the negative electrode active material. Specifically, the silicon carbon composite 2 had a rolling density of 800 kgf / cm. 2 When the powder resistivity was measured at a pressure of 1.61 g / cc, the natural graphite 1 had a rolled density of 0.914 g / cc and an electrical conductivity of 0.00025 S / cm, and the artificial graphite 1 had values ​​of 1.61 g / cc and 149 S / cm, respectively, and 1.54 g / cc and 30.1 S / cm, respectively.

[0121] [Manufacturing of anodes and secondary batteries] Using the slurry, a negative electrode and a secondary battery were produced in the same manner as in Example 1.

[0122] Example 4 (Silicon Carbon Composite 1, Artificial Graphite 1, Natural Graphite 2) [Slurry production] A slurry was prepared in the same manner as in Example 1, except that a silicon carbon composite 1 (see the manufacturing method in Example 1), natural graphite 2 (see the manufacturing method in Example 1), and artificial graphite 1 (see the manufacturing method in Example 3) having the rolling density and electrical conductivity shown in Table 1 below were used in a weight ratio of 15:15:70 as the negative electrode active material. Specifically, the silicon carbon composite 1 had a rolling density of 800 kgf / cm. 2 When the powder resistivity was measured at a pressure of 1.6 g / cc, the natural graphite 2 had a rolled density of 0.859 g / cc and an electrical conductivity of 0.664 S / cm, and the artificial graphite 1 had values ​​of 1.6 g / cc and 337 S / cm, respectively, and 1.54 g / cc and 30.1 S / cm, respectively.

[0123] [Manufacturing of anodes and secondary batteries] The slurry was used to manufacture a negative electrode and a secondary battery.

[0124] Example 5 (Silicon oxide 1, artificial graphite 1, natural graphite 2) [Slurry production] A slurry was prepared in the same manner as in Example 1, except that silicon oxide 1 (see the manufacturing method in Example 2), natural graphite 2 (see the manufacturing method in Example 1), and artificial graphite 1 (see the manufacturing method in Example 3) having the rolling density and electrical conductivity shown in Table 1 below were used as the negative electrode active material in a weight ratio of 20:10:70. Specifically, the silicon oxide active material had a pressure of 800 kgf / cm. 2 When the powder resistivity was measured at a pressure of 1.6 g / cc, the natural graphite 2 had a rolled density of 1.42 g / cc and an electrical conductivity of 0.122 S / cm, and the artificial graphite 1 had values ​​of 1.6 g / cc and 337 S / cm, respectively, and 1.54 g / cc and 30.1 S / cm, respectively.

[0125] [Manufacturing of negative electrodes] Using the slurry, a negative electrode and a secondary battery were produced in the same manner as in Example 1.

[0126] Example 6 (silicon oxide 1, artificial graphite 2, natural graphite 1) [Slurry production] A slurry was prepared in the same manner as in Example 1, except that the negative electrode active material was a mixture of silicon oxide 1 (see the manufacturing method in Example 2), natural graphite 1 (see the manufacturing method in Example 3), and artificial graphite 2 (see the manufacturing method in Example 1) in a weight ratio of 20:10:70, each having the rolling density and electrical conductivity shown in Table 1 below. The silicon oxide active material had a pressure of 800 kgf / cm. 2 When the powder resistivity was measured at a pressure of 1.61 g / cc, the natural graphite 1 had a rolled density of 1.42 g / cc and an electrical conductivity of 0.122 S / cm, and the artificial graphite 2 had values ​​of 1.61 g / cc and 149 S / cm, respectively, and 1.58 g / cc and 96.6 S / cm, respectively.

[0127] [Manufacturing of anodes and secondary batteries] Using the slurry, a negative electrode and a secondary battery were produced in the same manner as in Example 1.

[0128] Example 7 (Silicon oxide 1, artificial graphite 2, natural graphite 2) [Slurry production] A slurry was prepared in the same manner as in Example 1, except that the negative electrode active material was a mixture of silicon oxide 1 (see the manufacturing method in Example 2), natural graphite 2 (see the manufacturing method in Example 1), and artificial graphite 2 (see the manufacturing method in Example 1) in a weight ratio of 20:10:70, each having the rolling density and electrical conductivity shown in Table 1 below. The silicon oxide active material had a pressure of 800 kgf / cm. 2When the powder resistivity was measured at a pressure of 1.00, the powder had a rolled density of 1.42 g / cc and an electrical conductivity of 0.122 S / cm, while the natural graphite 2 had values ​​of 1.6 g / cc and 337 S / cm, and the artificial graphite 2 had values ​​of 1.58 g / cc and 96.6 S / cm. The negative electrode active material, conductive material (carbon black), and binders (CMC (carboxymethyl cellulose) and SBR (styrene-butadiene rubber)) were mixed in a weight ratio of 95.3:1:3.7 to prepare a negative electrode slurry.

[0129] [Manufacturing of anodes and secondary batteries] Using the slurry, a negative electrode and a secondary battery were produced in the same manner as in Example 1.

[0130] Comparative Example 1 (Silicon Carbon Composite 3, Artificial Graphite 3, Natural Graphite 2) [Production of silicon carbon composite 3] A silicon-carbon composite was prepared by flowing SiH4 / He=5 / 95 gas at a flow rate of 50 mL / min at 700°C for 1 hour through the carbon-based particles prepared by the silicon-carbon composite manufacturing method described in Example 1. The silicon-carbon composite was then placed in a solvent containing a 10:90 volumetric ratio of phosphoric acid and ethanol. The silicon-carbon composite dispersed in the solvent was heated at 1000°C for 4 hours in an argon atmosphere to finally obtain a phosphorus-doped silicon-carbon composite. The phosphorus-doped silicon-carbon composite was then placed in an electric furnace and reacted for 2 hours under methane flow at 700°C to produce a phosphorus-doped silicon-carbon composite anode active material with a surface carbon layer.

[0131] [Manufacturing of artificial graphite 3] Artificial graphite 3 was produced in the same manner as in Example 1 for producing artificial graphite 2, except that a mixture of green coke particles, calcined coke particles, and petroleum pitch was graphitized by heat-treating it at 3000°C for 50 hours, and then the artificial graphite particles were partially oxidized by heat-treating them in a hot zone at 800°C for 2 hours in an O2 / Ar=5 / 95 atmosphere.

[0132] [Slurry production] A slurry was prepared in the same manner as in Example 1, except that a silicon carbon composite 3 having the rolling density and electrical conductivity shown in Table 1 below, natural graphite 2 (see the preparation method in Example 1), and artificial graphite 3 were used in a weight ratio of 20:10:70 as the negative electrode active material. Specifically, the silicon carbon composite 3 had a rolling density of 800 kgf / cm. 2 When the powder resistivity was measured at a pressure of 1.6 g / cc, the natural graphite 2 had a rolled density of 1.32 g / cc and an electrical conductivity of 8.1 S / cm, and the artificial graphite 3 had values ​​of 1.6 g / cc and 337 S / cm, respectively, and 1.56 g / cc and 5.8 S / cm, respectively.

[0133] [Manufacturing of anodes and secondary batteries] Using the slurry, a negative electrode and a secondary battery were produced in the same manner as in Example 1.

[0134] Comparative Example 2 (Silicon oxide 2, artificial graphite 4, natural graphite 1) [Production of silicon oxide 2] The silicon-based active material was pulverized using a ball mill for about 5 to 6 hours, and then D 50 Silicon oxide 2 was produced in the same manner as silicon oxide 1 in Example 2, except that the grain size was controlled to the 3 μm level.

[0135] [Manufacturing of Artificial Graphite 4] The final artificial graphite active material D 50 Artificial graphite 4 was produced in the same manner as artificial graphite 2 in Example 1, except that the particle size was 29 μm.

[0136] [Slurry production] A slurry was prepared in the same manner as in Example 1, except that silicon oxide 2, natural graphite 1 (see the preparation method in Example 3), and artificial graphite 4, each having the rolling density and electrical conductivity shown in Table 1 below, were used in a weight ratio of 20:10:70. Specifically, silicon oxide 2 was used at a pressure of 800 kgf / cm. 2When the powder resistivity was measured at a pressure of 1.52 g / cc, the composition had a rolled density of 1.52 g / cc and an electrical conductivity of 0.178 S / cm, while the natural graphite 1 had values ​​of 1.61 g / cc and 149 S / cm, and the artificial graphite 4 had values ​​of 1.45 g / cc and 80.2 S / cm, respectively.

[0137] [Manufacturing of anodes and secondary batteries] Using the slurry, a negative electrode and a secondary battery were produced in the same manner as in Example 1.

[0138] Comparative Example 3 (Silicon Oxide 1, Artificial Graphite 1, Natural Graphite 3) [Production of natural graphite 3] The natural graphite active material was prepared in the same manner as in Example 1, except that the carbon coating layer was formed in an amount of 2 wt % based on the total weight of the natural graphite active material.

[0139] [Slurry production] A slurry was prepared in the same manner as in Example 1, except that silicon oxide 1 (see the manufacturing method in Example 2), natural graphite 3, and artificial graphite 1 (see the manufacturing method in Example 3) having the rolling density and electrical conductivity shown in Table 1 below were used as the negative electrode active material in a weight ratio of 20:10:70. Specifically, silicon oxide 1 was used at a pressure of 800 kgf / cm. 2 When the powder resistivity was measured at a pressure of 1.6 g / cc, the natural graphite 3 had a rolled density of 1.42 g / cc and an electrical conductivity of 0.122 S / cm, and the artificial graphite 1 had values ​​of 1.6 g / cc and 24.5 S / cm, respectively, and 1.54 g / cc and 30.1 S / cm, respectively.

[0140] [Manufacturing of anodes and secondary batteries] Using the slurry, a negative electrode and a secondary battery were produced in the same manner as in Example 1.

[0141] [Table 1]

[0142] The rolling densities and electrical conductivities of the active materials used in the examples and comparative examples are shown in Tables 2 and 3 below.

[0143] [Table 2]

[0144] [Table 3]

[0145] <Experimental example: Evaluation of discharge capacity, initial efficiency, and life (capacity retention rate) characteristics> Batteries were manufactured using the negative electrodes of the example and comparative example. 1.7671cm 2 A lithium (Li) metal thin film cut into a circular shape was used as the positive electrode. A porous polyethylene separator was placed between the positive electrode and the negative electrode, and an electrolyte solution prepared by dissolving 0.5 parts by weight of vinylene carbonate in a 7:3 volumetric ratio mixture of methyl ethyl carbonate (EMC) and ethylene carbonate (EC) and dissolving 1M LiPF6 was injected to fabricate a lithium coin half-cell.

[0146] The manufactured batteries were charged and discharged to evaluate the discharge capacity, initial efficiency, and capacity retention rate, and the results are shown in Table 4 below.

[0147] The first and second cycles were charged and discharged at 0.1 C, and from the third to the 299th cycles, they were charged and discharged at 0.5 C. The 50th cycle was completed in a charged state (with lithium in the anode). Charging conditions: CC (constant current) / CV (constant voltage) (5mV / 0.005C current cut-off) Discharge condition: CC (constant current) condition 1.5V

[0148] The discharge capacity (mAh / g) and initial efficiency (%) were calculated from the results of one charge / discharge. Specifically, the initial efficiency (%) was calculated as follows: Initial efficiency (%) = (single discharge capacity / single charge capacity) x 100 (%)

[0149] The capacity retention rate was calculated as follows. Capacity retention rate (%)=(299 discharge capacity / 1 discharge capacity)×100(%)

[0150] [Table 4]

[0151] In Comparative Example 1, the electrical conductivity of the silicon-based active material was higher than that of artificial graphite, and in this case, low initial efficiency and capacity retention characteristics were observed. Silicon-based active materials are known to react more violently with the electrolyte than carbon-based active materials due to their unstable surfaces. When the electrical conductivity of the silicon-based active material was higher than that of artificial graphite, the reduction reaction of the electrolyte was promoted on the surface of the silicon-based active material, forming a thick coating, resulting in low efficiency and capacity retention.

[0152] In Comparative Example 2, the rolling density of the artificial graphite was lower than that of the silicon-based active material, resulting in poor initial efficiency and capacity retention. The rolling density refers to the density at which the carbon-based active material and silicon-based active material are present during electrode rolling, enabling them to function as a pathway for electron and lithium migration. When the rolling density of the silicon-based active material is higher than that of artificial graphite, the silicon-based active material undergoes drastic volume changes as cycling progresses, creating larger voids and resulting in poor capacity retention. In Comparative Example 3, the electrical conductivity of natural graphite was lower than that of artificial graphite, resulting in poor initial efficiency and capacity retention. In contrast, Examples 1 to 7, using active materials satisfying the rolling density and electrical conductivity relationship of the present invention, exhibited high initial efficiency and capacity retention.

[0153] In particular, in Examples 1 to 3, the electrical conductivity of the artificial graphite was 10 times higher than that of the silicon-based active material.2 The rolling density of the artificial graphite was more than 1.1 times higher than that of the silicon-based active material, and more than 1.01 times higher than that of the natural graphite, showing better initial efficiency and capacity retention.

Claims

1. The negative electrode active material includes a silicon-based active material including at least one of a silicon carbon composite and a silicon oxide, and a carbon-based active material, The carbon-based active material includes natural graphite and artificial graphite, 800 kgf / cm ２ a negative electrode composition, wherein when measuring powder resistance at a pressure of 1000 kJ / cm, the rolling density decreases in the order of natural graphite > artificial graphite > silicon-based active material, and the electrical conductivity decreases in the order of natural graphite > artificial graphite > silicon-based active material.

2. The electrical conductivity of the artificial graphite is 10 times higher than that of the silicon-based active material. ２ 2. The negative electrode composition of claim 1, wherein the natural graphite is at least twice as large as the artificial graphite.

3. The negative electrode composition according to claim 1 , wherein the rolling density of the artificial graphite is 1.1 times or more greater than that of the silicon-based active material, and the rolling density of the natural graphite is 1.01 times or more greater than that of the artificial graphite.

4. 2. The negative electrode composition according to claim 1, wherein the electrical conductivity of the natural graphite is 50 to 10,000 S / cm, the electrical conductivity of the artificial graphite is 15 to 2,000 S / cm, the electrical conductivity of the silicon carbon composite is 0.0001 to 2 S / cm, and the electrical conductivity of the silicon oxide is 0.001 to 1 S / cm.

5. 2. The negative electrode composition according to claim 1, wherein the rolling density of the natural graphite is 1.4 to 2.5 g / cc, the rolling density of the artificial graphite is 1.0 to 2.2 g / cc, the rolling density of the silicon carbon composite is 0.5 to 1.2 g / cc, and the rolling density of the silicon oxide is 0.8 to 1.8 g / cc.

6. The negative electrode composition according to claim 1 , wherein the negative electrode composition comprises single-walled carbon nanotubes as a conductive material.

7. Based on 100 parts by weight of the negative electrode composition, the silicon-based active material is included in an amount of 0.5 to 52 parts by weight; the carbon-based active material is included in an amount of 45 to 99 parts by weight; and the single-walled carbon nanotubes are included in an amount of 0.01 to 3 parts by weight.

7. The negative electrode composition of claim 6, wherein the natural graphite is contained in an amount of 10 to 70 parts by weight; and the artificial graphite is contained in an amount of 30 to 90 parts by weight, based on 100 parts by weight of the carbon-based active material.

8. The negative electrode composition of claim 1 , further comprising a binder.

9. A negative electrode comprising the negative electrode composition according to any one of claims 1 to 8.

10. A lithium secondary battery comprising the negative electrode according to claim 9, a positive electrode, and a separator.

11. A battery module comprising the lithium secondary battery according to claim 10.

12. A battery pack comprising the lithium secondary battery according to claim 10.

13. A battery pack comprising the battery module according to claim 11.

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