Negative electrode composition, negative electrode, and lithium secondary battery

Abstract

The present invention relates to a negative electrode composition, a negative electrode comprising the same, a lithium secondary battery, a battery module, and a battery pack, the negative electrode composition comprising a negative electrode active material, the negative electrode active material comprising a carbon-based active material and a silicon-based active material, the silicon-based active material comprising at least one of a silicon-carbon composite and a silicon oxide, wherein the carbon-based active material contains natural graphite and artificial graphite, and when powder resistance is measured at a pressure of 800 kgf / cm2, the rolling density decreases in the order of natural graphite > artificial graphite > silicon-based active material, and the conductivity decreases in the order of natural graphite > artificial graphite > silicon-based active material.

Description

Technical Field

[0001] This application claims priority to and the benefit of Korean Patent Application No. 10-2023-0099452 filed on July 31, 2023, in the Korean Intellectual Property Office, and Korean Patent Application No. 10-2024-0100913 filed on July 30, 2024, in the Korean Intellectual Property Office, the entire contents of which are incorporated herein by reference.

[0002] The present application relates to a negative electrode composition, a negative electrode and a lithium secondary battery. Background Art

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

[0004] Typically, a lithium secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive and negative electrodes, an electrolyte, an organic solvent, and the like. Furthermore, the positive and negative electrodes may each form an active material layer containing a positive electrode active material and a negative electrode active material on a current collector. Typically, lithium-containing metal oxides such as LiCoO2 and LiMn2O4 are used as the positive electrode active material, and lithium-free carbon-based active materials or silicon-based active materials are used as the negative electrode active material for the negative electrode.

[0005] Among negative electrode active materials, silicon-based active materials have attracted considerable attention due to their higher capacity than carbon-based active materials and excellent fast-charging characteristics. However, silicon-based active materials suffer from significant volume expansion and contraction during charge and discharge, resulting in high irreversible capacity and, consequently, low initial efficiency. Consequently, compared to carbon-based active materials, silicon-based active materials have the disadvantage of degrading battery performance.

[0006] Therefore, there is a need to develop a negative electrode material that can improve the performance of lithium secondary batteries. Summary of the Invention

[0007] Technical issues

[0008] The present invention relates to a negative electrode composition capable of improving the performance of a lithium secondary battery, a negative electrode comprising the negative electrode composition, and a secondary battery comprising the negative electrode.

[0009] Technical Solution

[0010] An exemplary embodiment of the present invention provides a negative electrode composition, the negative electrode composition comprising a negative electrode active material, the negative electrode active material comprising a silicon-based active material and a carbon-based active material, the silicon-based active material comprising at least one of a silicon-carbon composite and a silicon oxide, wherein the carbon-based active material comprises natural graphite and artificial graphite, and when subjected to a pressure of 800 kgf / cm 2 When the powder resistance is measured under a pressure of , the calendering 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.

[0011] Furthermore, according to an exemplary embodiment of the present invention, the negative electrode composition of the exemplary embodiment described above includes single-walled carbon nanotubes as a conductive material.

[0012] An exemplary embodiment of the present invention provides a negative electrode including the negative electrode composition according to the above exemplary embodiment.

[0013] An exemplary embodiment of the present invention provides a lithium secondary battery including the negative electrode according to the above exemplary embodiment, a positive electrode, and a separator.

[0014] An exemplary embodiment of the present invention provides a battery module including the lithium secondary battery according to the above exemplary embodiment.

[0015] An exemplary embodiment of the present invention provides a battery pack including the lithium secondary battery according to the above exemplary embodiment.

[0016] An exemplary embodiment of the present invention provides a battery pack including the battery module according to the above exemplary embodiment.

[0017] Beneficial effects

[0018] According to an exemplary embodiment of the present invention, a silicon-based active material and a carbon-based active material having different rolling densities and different electrical conductivities are mixed and used as negative electrode active materials, thereby improving the performance of a lithium secondary battery. In particular, mixing two types of carbon-based active materials, each having a higher rolling density and electrical conductivity than the silicon-based active material at the same pressure, and having different rolling densities and electrical conductivities, improves the cycle characteristics and resistance of the lithium secondary battery. DETAILED DESCRIPTION

[0019] Hereinafter, in order to better understand the present invention, the present invention will be described in more detail. The present invention can be implemented in various ways and is not limited to the following embodiments. The terms or words used throughout the specification and claims should not be interpreted as limited to their ordinary or dictionary meanings, but should be interpreted as having meanings and concepts corresponding to the technical concept of the present invention based on the concept that the inventor can appropriately define the words or terms to best explain the principles of the present invention.

[0020] It should also be understood that when used in this specification, the terms "comprises", "includes" or "has" indicate the presence of stated features, numbers, steps, constituent elements and / or combinations thereof, but do not exclude the presence or addition of one or more other features, numbers, steps, constituent elements and / or combinations thereof.

[0021] Furthermore, it should be understood that when an element, such as a layer, is referred to as being "on" another element, the element can be "directly on" the other element, or intervening elements may be present. In contrast, when an element is referred to as being "directly on" another element, there are no intervening elements. Furthermore, when an element is referred to as being "above" or "on" a reference portion, the element is above or below the reference portion, and does not necessarily mean that the element is "above" or "on" in a direction opposite to gravity.

[0022] It should be understood that the terms or words used throughout the specification should not be interpreted as limited to their ordinary or dictionary meanings, but should be interpreted as having meanings and concepts corresponding to the technical concepts of the present invention based on the principle that the inventor can appropriately define the concepts of the words or terms to best explain the present invention.

[0023] As used herein, the singular forms "a," "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0024] In this specification, the calendering density refers to the degree of deformation and compression of particles when a certain level of pressure is applied to the negative electrode active material, and can be expressed in g / cc. The calendering density can be obtained by measuring the powder resistance. For example, by placing a certain amount of negative electrode active material in a cylindrical load cell and applying a pressure of 400 kgf / cm 2 Up to 2,000kgf / cm 2 The rolled density can be measured by applying any pressure within a certain range to cause a change in the thickness of the placed negative electrode active material.

[0025] In this specification, conductivity refers to the conductivity specific to the negative electrode active material powder. The conductivity can be obtained by measuring the powder resistance. For example, the conductivity can be obtained by measuring the surface resistance and specific resistance values, which can be obtained by the following method: 2 Up to 2,000kgf / cm 2 The Surface Resistivity (SR) can be measured simultaneously at any pressure within the specified pressure range. The Surface Resistivity (SR) and Specific Resistivity (SR) can be measured simultaneously using the measured volume and mass.

[0026] Considering that when measuring the powder resistance, an excessively large force, for example, more than 2000 kgf / cm 2 The particle deformation that may occur during the pressing is preferably caused by using a pressure within the above range, preferably 800 kgf / cm 2 Calendered density and conductivity values are obtained from powder resistance measurements performed under pressure.

[0027] Hereinafter, preferred embodiments of the present invention will be described in detail. However, it should be understood that the exemplary embodiments of the present invention can be modified in various forms, and the scope of the present invention is not limited to the exemplary embodiments described below.

[0028] The negative electrode composition according to an exemplary embodiment of the present invention includes a negative electrode active material, the negative electrode active material including a silicon-based active material and a carbon-based active material, the silicon-based active material including at least one of a silicon-carbon composite and a silicon oxide, and the carbon-based active material including natural graphite and artificial graphite. Here, the negative electrode composition is characterized in that when subjected to 800 kgf / cm 2 When the powder resistance is measured under a pressure of , the calendering 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.

[0029] According to the exemplary embodiment, the silicon-based active material and the carbon-based active material are contained together, and when the silicon-based active material and the carbon-based active material are contained together, the silicon-based active material and the carbon-based active material are contained together. 2 When the powder resistance is measured under a pressure of 800 kgf / cm, the carbon-based active material has a higher rolling density and conductivity than the silicon-based active material, so that the cycle characteristics and resistance of the lithium secondary battery can be improved. In addition, as the carbon-based active material, artificial graphite is mixed with natural graphite. When the powder resistance is measured under a pressure of 800 kgf / cm 2When the powder resistance is measured under a pressure of , the natural graphite has a relatively high calendering density and conductivity, which makes it possible to improve the performance of lithium secondary batteries. By mixing and using a negative electrode active material with a relatively high conductivity, even if surface peeling occurs between the negative electrode active material and the conductive material due to volume changes during charge and discharge, lithium charging and discharging can be more easily performed due to the high conductivity. This makes it possible to achieve the characteristics of a long-life battery. It should be noted that in the case of an active material with a relatively high calendering density, the volume change during charge and discharge can be physically controlled, which can have a beneficial effect on the cycle performance.

[0030] In the negative electrode composition according to an exemplary embodiment of the present invention, even when the condition that the rolled density of each material decreases in the order of natural graphite > artificial graphite > silicon-based active material is satisfied, if the conductivity of each material does not satisfy the order of natural graphite > artificial graphite > silicon-based active material, a phenomenon of conductivity reversal may occur due to the exposure of the inner surface with low conductivity as the particles break. For example, this corresponds to a case where the conductivity is in the order of artificial graphite > natural graphite > silicon-based active material.

[0031] Specifically, as the calendering density increases, the contact area between particles generally increases, which increases conductivity. However, if the particles break, it may have an adverse effect on conductivity. Therefore, the calendering density and conductivity need to have the same trend.

[0032] If the calendering density and the conductivity have different trends, particle breakage may occur, which may adversely affect battery performance.

[0033] Furthermore, if the rolled density and electrical conductivity of artificial graphite are higher than those of natural graphite, the degree of graphitization of the artificial graphite may increase, which may deteriorate battery performance.

[0034] Unless otherwise specified, the conductivity in this specification refers to the conductivity of various materials in a particle state, for example, before the particles are broken, rather than the conductivity after the particles are broken.

[0035] According to an exemplary embodiment, when the 2 When the powder resistance is measured under a pressure of , the pressed density of the artificial graphite is 1.1 times or more of the pressed density of the silicon-based active material, and the pressed density of the natural graphite is 1.01 times or more of the pressed density of the artificial graphite.

[0036] For example, when the pressure is 800kgf / cm 2When measuring the powder resistance under a pressure of 800 kgf / cm2, the natural graphite may have a calendering density of 1.4 to 2.5 g / cc (e.g., 1.6 to 1.7 g / cc), the artificial graphite may have a calendering density of 1.0 to 2.2 g / cc (e.g., 1.5 to 1.6 g / cc), and the silicon-based active material may have a calendering density of 0.5 to 1.8 g / cc. Specifically, when the powder resistance is measured under a pressure of 800 kgf / cm2, the natural graphite may have a calendering density of 1.4 to 2.5 g / cc (e.g., 1.6 to 1.7 g / cc), the artificial graphite may have a calendering density of 1.0 to 2.2 g / cc (e.g., 1.5 to 1.6 g / cc), and the silicon-based active material may have 2 When measuring powder resistance under pressure of , the calendering 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 calendering density of the silicon oxide may be 0.8 to 1.8 g / cc, for example, 1.4 to 1.5 g / cc.

[0037] According to an exemplary embodiment, when the 2 When the powder resistance is measured under a pressure of , the conductivity of the artificial graphite is more than 100 times that of the silicon-based active material, and the conductivity of the natural graphite is more than 2 times that of the artificial graphite.

[0038] For example, when the pressure is 800kgf / cm 2 When measuring powder resistance under a pressure of 800 kgf / cm, the conductivity of the silicon-based active material may be 0.0001 to 2 S / cm, the conductivity of the artificial graphite may be 15 to 2,000 S / cm (e.g., 15 to 100 S / cm), and the conductivity of the natural graphite may be 50 to 10,000 S / cm (e.g., 100 to 1,000 S / cm, or 100 to 500 S / cm). 2 When measuring powder resistance under a pressure of , 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.

[0039] According to one exemplary embodiment, based on 100 parts by weight of the negative electrode composition, the content of the silicon-based active material may be 0.5 to 52 parts by weight, the content of the carbon-based active material may be 45 to 99 parts by weight, and the content of the single-walled carbon nanotube may be 0.01 to 3 parts by weight, and based on 100 parts by weight of the carbon-based active material, the content of the natural graphite may be 10 to 70 parts by weight, and the content of the artificial graphite may be 30 to 90 parts by weight.

[0040] According to an exemplary embodiment, the silicon-based active material may be contained in an amount of 0.5 to 50 parts by weight, or 1 to 40 parts by weight, for example 1 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.

[0041] According to one exemplary embodiment, the carbon-based active material may be present 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 the negative electrode active material contained 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 present in an amount of 10 to 70 parts by weight, for example, 10 to 30 parts by weight, and the artificial graphite may be present in an amount of 30 to 90 parts by weight, for example, 70 to 90 parts by weight.

[0042] According to an exemplary embodiment, the silicon-based active material may include a silicon-carbon composite, a silicon oxide, or both.

[0043] According to an exemplary embodiment, the silicon-carbon composite may be a Si / C-based active material.

[0044] In this specification, the silicon-carbon composite is a composite of Si and C and is distinguished from silicon carbide represented as SiC. Silicon carbide does not electrochemically react with lithium, so all properties including lifespan may be measured as zero.

[0045] 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 in which carbon is composited with a porous silicon structure. The silicon-carbon composite may be a composite of silicon and graphite, etc. In the silicon-carbon composite, the silicon may be nano-silicon.

[0046] According to an exemplary embodiment, the silicon-carbon composite includes porous carbon-based particles and a silicon coating layer present on the surface or in internal pores of the porous carbon-based particles.

[0047] According to an exemplary embodiment, the silicon carbon composite may have a carbon monoxide content of 0.5 to 10 m / s as measured by a BET method. 2 / g specific surface area, 0.005 to 0.03 cm 3 The silicon-carbon composite may have a pore volume of 0.005 to 0.03 cm as measured by mercury penetration method (Hg porosimeter). 3 / g pore volume.

[0048] According to an exemplary embodiment, the silicon-carbon composite may have a D of 11 μm to 20 μm 90 particle size, a D of 3 μm to 10 μm 50 particle size, and a D of 0.1 μm to 3 μm 10 particle size.

[0049] According to an exemplary embodiment, the silicon-carbon composite may be manufactured by a method including the following steps: etching carbon-based particles including internal pores to expand the internal pores of the carbon-based particles; and forming a silicon coating on the surface and in the internal pores of the carbon-based particles having the expanded internal pores.

[0050] 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 oxygen (O2) or oxygen-containing air may be controlled to 0.1 L / min to 10 L / min.

[0051] The step of expanding the internal pores of the carbon-based particles may be performed at a temperature in the range of 400 °C to 1200 °C for 30 minutes to 4 hours.

[0052] The pore characteristics of the obtained porous carbon-based particles may vary depending on the conditions used to expand the internal pores of the carbon-based particles.

[0053] The step of forming the silicon coating may be performed using chemical vapor deposition. In this case, silicon nanoparticles are deposited on the surface and / or in the internal pores of the carbon-based particles having the expanded internal pores, thereby forming a silicon coating in the form of a film, islands, or a combination thereof.

[0054] The silicon nanoparticles may be crystalline, quasi-crystalline, amorphous, or a combination thereof.

[0055] According to an exemplary embodiment, the silicon oxide may contain SiO x (0 ≤ x < 2).

[0056] The active material containing SiO x (0 ≤ x < 2) may be silicon oxide particles containing SiO x (0 < x < 2) and pores.

[0057] The SiO x (0 < x < 2) corresponds to the matrix in the silicon oxide particles. The SiO x (0 < x < 2) may be in the form of 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 SiO x (0 < x < 2). When the silicon oxide particles contain the SiOx When (0 < x < 2), it can improve the discharge capacity of the secondary battery.

[0058] 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 dopants in the silicon oxide particles.

[0059] The Mg compound and / or the Li compound may be present in the SiO x within (0 < x < 2) 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.

[0060] The Mg compound may include at least one selected from the group consisting of Mg silicate, Mg silicide, and Mg oxide. The Mg silicate may include at least one of Mg2SiO4 and MgSiO3. The Mg silicide may include Mg2Si. The Mg oxide may include MgO.

[0061] In an exemplary embodiment of the present specification, based on the total amount of the silicon oxide particles being 100% by weight, the content of the Mg element may be 0.1% to 20% by weight or 0.1% to 10% by weight. Specifically, the content of the Mg element may be 0.5% to 8% by weight or 0.8% to 4% by weight. When the above range is satisfied, the Mg compound can be included in the silicon oxide particles in an appropriate content, so that it can easily inhibit the volume change of the silicon oxide particles during the charge and discharge of the battery, and can improve the discharge capacity and initial efficiency of the battery.

[0062] The Li compound may include at least one selected from the group consisting of Li silicate, Li silicide, and Li oxide. The Li silicate may include at least one of Li2SiO3, Li4SiO4, and Li2Si2O5. The Li silicide may include Li7Si2. The Li oxide may include Li2O.

[0063] In an exemplary embodiment of the present invention, the Li compound may be in the form of lithium silicate. The lithium silicate is composed of Li a Si b O c(2≤a≤4, 0<b≤2, 2≤c≤5), and can be classified as crystalline lithium silicate and amorphous lithium silicate. The crystalline lithium silicate can be present in the silicon oxide particles in the form of at least one lithium silicate selected from the group consisting of Li2SiO3, Li4SiO4 and Li2Si2O5, and the amorphous lithium silicate can be Li a Si b O c (2≤a≤4, 0<b≤2, 2≤c≤5) However, such limitation is not intended.

[0064] In an exemplary embodiment of the present specification, the content of the Li element may be 0.1 to 20% by weight or 0.1 to 10% by weight, based on 100% by weight of the total amount of the silicon oxide particles. Specifically, the content of the Li element may be 0.5 to 8% by weight, more specifically 0.5 to 4% by weight. When the above range is met, the Li compound can be contained in the silicon oxide particles at an appropriate content, thereby easily suppressing the volume change of the negative electrode active material during charge and discharge of the battery, and improving the discharge capacity and initial efficiency of the battery.

[0065] The content of the Mg element or the Li element can be confirmed by ICP analysis. For the ICP analysis, a predetermined amount (about 0.01 g) of the negative electrode active material is accurately weighed, transferred to a platinum crucible, and nitric acid, hydrofluoric acid and sulfuric acid are added thereto to completely decompose it on a hot plate. Then, by using an inductively coupled plasma atomic emission spectrometer (ICP-AES, Perkin-Elmer 7300), the intensity of the standard liquid prepared using a standard solution (5 mg / kg) is measured at the inherent wavelength of the Mg element or the Li element to obtain a reference calibration curve. Subsequently, the pretreated sample solution and the blank sample are introduced into the spectrometer, and the actual intensity is calculated by measuring the intensity of each component, and the concentration of each component is calculated based on the obtained calibration curve, and then converted so that the sum of the calculated concentrations of the components is equal to the theoretical value, and the Mg element or Li element content in the prepared silicon oxide particles can be analyzed.

[0066] In one exemplary embodiment of the present specification, a carbon layer may be provided on the surface and / or in the pores of the silicon oxide particles. The carbon layer imparts conductivity to the silicon oxide particles, thereby improving the initial efficiency, lifespan, and battery capacity characteristics of a secondary battery containing the negative electrode active material containing the silicon oxide particles. The total amount of the carbon layer may be 5% to 40% by weight, based on 100% by weight of the total amount of the silicon oxide particles.

[0067] In an exemplary embodiment of the present specification, the carbon layer may include at least one of amorphous carbon or crystalline carbon.

[0068] The average particle size of the silicon-based active material (D 50 ) may be 0.1 μm to 30 μm, specifically 1 μm to 20 μm, and more specifically 1 μm to 10 μm. When the above range is met, the structural stability of the active material is ensured during charge and discharge, and the problem of increasing the level of volume expansion / contraction as the particle size becomes too large can be prevented, and the problem of decreasing the initial efficiency when the particle size is too small can also be prevented.

[0069] In this specification, the average particle size (D 50 ) can be defined as the particle size corresponding to 50% cumulative volume in the particle size distribution curve. 50 ) can be measured using, for example, laser diffraction. In the laser diffraction method, generally, particle sizes ranging from the submicron region to the several millimeter range can be measured, and results with high reproducibility and high resolution can be obtained. The specific surface area of the silicon-based active material can be 2 to 10 m 2 In this specification, the specific surface area is measured by the BET method.

[0070] According to an exemplary embodiment, the carbon-based active material includes natural graphite and artificial graphite. The natural graphite and the artificial graphite may each have an average particle size (D 50 ) and 0.5 to 2m 2 / g BET specific surface area. The natural graphite refers to naturally occurring graphite, and examples thereof include flake graphite, scale graphite, or soil graphite. The natural graphite has the advantages of being abundant, inexpensive, having a high theoretical capacity and compacted density, and being able to achieve high production.

[0071] In one example, the natural graphite may have a sphericity of 0.9 or greater.

[0072] In this specification, sphericity can be a value obtained by dividing the circumference of a circle having the same area as the projected image by the circumference of the projected image when the particle is projected, and specifically, can be expressed by the following mathematical formula 1. Sphericity can be obtained from an SEM image, or alternatively, can be measured using a particle shape analyzer such as the Sysmex FPIA3000 available from Malvern. In addition, the crystal size can be confirmed by XRD analysis.

[0073] [Mathematical formula 1]

[0074] Sphericity = circumference of a circle with the same area as the projected image of the particle / circumference of the projected image

[0075] The particle shape of the natural graphite can be confirmed by SEM and by using a particle shape analyzer, so that natural graphite satisfying the sphericity can be selected and used.

[0076] In one example, the artificial graphite may have a sphericity of 0.9 or less.

[0077] The artificial graphite can be selected and used by confirming the particle shape by SEM and using a particle shape analyzer, thereby selecting artificial graphite that satisfies the sphericity.

[0078] According to an exemplary embodiment of the present invention, the negative electrode composition includes single-walled carbon nanotubes (SWCNTs) as a conductive material.

[0079] The single-walled carbon nanotube (SWCNT) refers to a tubular carbon structure composed of a single carbon layer. When the conductive material in the negative electrode composition includes the single-walled carbon nanotube (SWCNT), the charge and discharge capacity and / or life performance of the battery can be improved. Specifically, the single-walled carbon nanotube (SWCNT) connects the conductive paths between the particles well, thereby preventing the loss of the conductive path due to the expansion of the above-mentioned silicon-based active material. As a result, when the single-walled carbon nanotube (SWCNT) is included, the life performance of the battery can be improved.

[0080] In this specification, the length of a carbon nanotube refers to the length of a major axis passing through the center of the carbon nanotube unit, and the diameter of a carbon nanotube refers to the length of a minor axis passing through the center of the unit and perpendicular to the major axis.

[0081] 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, the average length of the single-walled carbon nanotubes (SWCNTs) may be 5 μm to 15 μm. The average length of the single-walled carbon nanotubes (SWCNTs) may be calculated as the average of results observed using SEM.

[0082] When single-walled carbon nanotubes (SWCNTs) are used together with the above-mentioned silicon-based active materials and carbon-based active materials, it is ensured that the length of the carbon nanotubes is equal to the distance between the particles of the negative electrode active material, which facilitates the connection of the conductive paths between the particles, thereby improving the conductivity, strength and / or electrolyte storage retention of the negative electrode.

[0083] The average diameter of the single-walled carbon nanotube (SWCNT) may be 1 nm to 20 nm, specifically 1.5 nm to 15 nm. More specifically, the average diameter of the single-walled carbon nanotube (SWCNT) may be 1.5 nm to 5 nm. The single-walled carbon nanotube (SWCNT) having such an average diameter has a flexible property, so that even when physically damaged, the contact between the negative electrode active material particles is not easily disconnected. The average diameter of the single-walled carbon nanotube (SWCNT) can be calculated as the average value observed by TEM.

[0084] The BET specific surface area of the single-walled carbon nanotubes can be 200 m 2 / g to 2,000m 2 / g, specifically 250m 2 / g to 1,500m 2 When single-walled carbon nanotubes (SWCNTs) satisfying the above range are used, even a small amount of conductive material can be easily dispersed and effectively connect particles.

[0085] The single-walled carbon nanotube (SWCNT) content may be 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 total amount of the negative electrode composition. When the above range is met, the connection of the conductive path between the active material particles is promoted while minimizing the electrolyte side reaction caused by the high specific surface area.

[0086] In this specification, the specific surface area is measured by the BET method, specifically, it can be measured by degassing the measurement object at 130° C. for 2 hours using a BET measurement device (BEL-SORP-mini, Nippon Bell Co., Ltd.) and performing N 2 adsorption / desorption at 77K.

[0087] According to an exemplary embodiment, the negative electrode composition further includes a binder.

[0088] The adhesive may include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene propylene diene monomer rubber (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, polyacrylic acid, and the above materials in which hydrogen is replaced by Li, Na, Ca, etc., and may also include various copolymers thereof.

[0089] An exemplary embodiment of the present invention provides a negative electrode including the negative electrode composition according to the above exemplary embodiment.

[0090] 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 exemplary embodiment.

[0091] The negative electrode active material layer may be formed by applying a negative electrode slurry including the above-described negative electrode composition to at least one surface of a negative electrode collector, and drying and roll-pressing it.

[0092] The negative electrode current collector is not particularly limited as long as it has conductivity and does not cause chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. can be used for the current collector. Specifically, transition metals that adsorb carbon well, such as copper and nickel, can be used for the current collector. The thickness of the current collector can be 6 μm to 20 μm. However, the thickness of the current collector is not limited thereto.

[0093] If desired, in addition to the single-walled carbon nanotubes described above, additional conductive materials may be included. The additional conductive material is not particularly limited, as long as it is conductive and does not cause chemical changes in the battery. Examples include graphite, such as natural graphite or artificial graphite; carbon black, such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers, such as carbon fibers and metal fibers; conductive tubes, such as carbon nanotubes; fluorocarbon powder; metal powder, such as aluminum powder 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.

[0094] The negative electrode slurry may include a solvent for forming the negative electrode slurry. Specifically, in terms of promoting dispersion of components, the solvent for forming the negative electrode slurry may include at least one selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol, specifically distilled water.

[0095] An exemplary embodiment of the present invention provides a lithium secondary battery including the negative electrode according to the above exemplary embodiment, a positive electrode, and a separator.

[0096] 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 a positive electrode active material.

[0097] In the positive electrode, the positive electrode current collector is not particularly limited as long as it has conductivity and does not cause chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, fired carbon, aluminum or stainless steel each surface-treated with carbon, nickel, titanium, silver, etc., etc. can be used. In addition, the positive electrode current collector can generally have a thickness of 3 to 500 μm, and the surface of the current collector can be formed with fine concave and convex to enhance the adhesion of the positive electrode active material. For example, the positive electrode current collector can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and non-woven fabrics.

[0098] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), or a compound substituted by one or more transition metals; lithium iron oxide such as LiFe3O4; lithium manganese oxide such as Li 1+c1 Mn 2-c1 O4 (0≤c1≤0.33), LiMnO3, LiMn2O3 and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5 and Cu2V2O7; Ni-site lithium nickel oxide, with the chemical formula LiNi 1-c2 M c2 O2 (wherein M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B and Ga, and satisfies 0.01≤c2≤0.3); lithium manganese composite oxide, represented by the chemical formula LiMn 2-c3 M c3 O2 (wherein M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01≤c3≤0.1) or Li2Mn3MO8 (wherein M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); LiMn2O4, wherein a portion of Li in the chemical formula is replaced by an alkaline earth metal ion; etc., but is not limited thereto. The positive electrode may be Li metal.

[0099] The positive electrode active material layer may further include a positive electrode conductive material and a positive electrode binder in addition to the positive electrode active material.

[0100] In this case, the positive electrode conductive material is used to impart conductivity to the electrode and can be used without particular limitation, as long as the positive electrode conductive material has electronic conductivity without causing chemical changes in the constituted battery. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and any one of these or a mixture of two or more thereof can be used.

[0101] In addition, the positive electrode binder is used to improve the bonding between the positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples may include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer rubber (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber or various copolymers thereof, and any one thereof or a mixture of two or more thereof may be used.

[0102] The separator is used to separate the negative electrode from the positive electrode and provide a migration path for lithium ions, wherein any separator can be used as the separator without particular limitation, as long as it is generally used for secondary batteries, in particular, a separator having high moisturizing ability for the electrolyte and low resistance to the movement of electrolyte ions can be preferably used. Specifically, a porous polymer film can be used, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer and an ethylene / methacrylate copolymer; or a laminated structure of two or more layers thereof. In addition, a common porous non-woven fabric can be used, for example, a non-woven fabric formed of a high melting point glass fiber, polyethylene terephthalate fiber, etc. In addition, in order to ensure heat resistance or mechanical strength, a coated separator comprising a ceramic component or a polymer material can be used, and a separator having a single-layer or multi-layer structure can be selectively used.

[0103] The lithium secondary battery may further include an electrolyte. Examples of the electrolyte may include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, or molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries, but are not limited thereto.

[0104] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0105] As the non-aqueous organic solvent, for example, an aprotic organic solvent such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate or ethyl propionate can be used.

[0106] Especially, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate as cyclic carbonates are high-viscosity organic solvents, and can be preferably used because they have a high dielectric constant to dissociate lithium salts well. When the cyclic carbonate is mixed with a linear carbonate with low viscosity and low dielectric constant such as dimethyl carbonate or diethyl carbonate in a suitable ratio and used, an electrolyte with high electrical conductivity can be prepared, so such a combination can be more preferred.

[0107] As the metal salt, a lithium salt can be used, and the lithium salt is a material that is easily soluble in the non-aqueous electrolyte. As the anion of the lithium salt, for example, one or more selected from the group consisting of: F - 、Cl - , I - 、NO3 - 、N(CN)2 - 、BF4 - 、ClO4 - PF6 - 、(CF3)2PF4 - 、(CF3)3PF3 - 、(CF3)4PF2 - 、(CF3)5PF - 、(CF3)6P - CF3SO3 - CF3CF2SO3 - 、(CF3SO2)2N - 、(FSO2)2N - CF3CF2(CF3)2CO - 、(CF3SO2)2CH - 、(SF5)3C - 、(CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - 、CH3CO2- 、SCN - and (CF3CF2SO2)2N - .

[0108] In order to improve the life characteristics of the battery, inhibit the reduction of the battery capacity, improve the discharge capacity of the battery, etc., the electrolyte may further include, in addition to the above-mentioned electrolyte components, one or more additives such as the following: halogenated alkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme dimethyl ether, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol or aluminum trichloride.

[0109] Another exemplary embodiment of the present invention provides a battery module including the secondary battery as a unit cell and a battery pack including the battery module.

[0110] Another exemplary embodiment of the present invention provides a battery pack including the secondary battery. Since the battery module and the battery pack include secondary batteries having high capacity, high rate performance, and high cycle characteristics, the battery module and the battery pack 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.

[0111] Hereinafter, the embodiments will be described in detail to specifically describe this specification. However, the embodiments according to this specification can be modified in other forms, and the scope of this application should not be interpreted as being limited to the following embodiments. The embodiments of the present application are provided to more fully explain this specification to those skilled in the art.

[0112] Invention Mode

[0113] Example 1 (Silicon-carbon composite 1, artificial graphite 2, natural graphite 2)

[0114] [Preparation of Silicon-Carbon Composite 1]

[0115] The cellulose powder was placed in a tubular electric furnace, and then, after the temperature was raised to 400°C at a rate of 4°C / min, heated under a nitrogen atmosphere for 2 hours. Thereafter, after the temperature of the electric furnace was raised to 900°C at a rate of 4°C / min, the cellulose powder was heated under a nitrogen atmosphere for 2 hours. After mixing the above powder with sulfuric acid and nitric acid in a volume ratio of 3:1, the mixture was stirred at 60°C for 2 hours and centrifuged to obtain a precipitate. The obtained powder was washed five times with a solvent in which ethanol and distilled water were mixed in a volume ratio of 1:3, and then dried at 120°C for 12 hours. The carbon-based particles were placed in a KOH solvent and then 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 more than 12 hours. The porous carbon structure was placed in a horizontal electric furnace and treated by flowing SiH4 / He (= 5 / 95) gas at 700°C at a flow rate of 50 ml / min for 1 hour to prepare a silicon-carbon composite. Thereafter, the silicon-carbon composite was placed in an electric furnace and reacted by flowing methane at 700°C for 2 hours to prepare a silicon-carbon composite 1 including a carbon layer on the surface.

[0116] [Preparation of artificial graphite 2]

[0117] Raw coke particles, calcined coke particles and a petroleum-based asphalt binder are placed in a reactor. The raw coke particles and the calcined coke particles are mixed in a weight ratio of 30:70. Based on the total weight of the raw coke particles, the calcined coke particles and the petroleum-based asphalt, the mixing amount of the asphalt binder is 7 wt%. The mixture of the raw coke particles, the calcined coke particles and the petroleum-based asphalt is graphitized by heat treatment at 3000°C for 50 hours, thereby preparing artificial graphite particles in the form of secondary particles in which primary particles are combined. The artificial graphite particles in the form of secondary particles are mixed with the petroleum-based asphalt and heat treated at 1250°C in a roller hearth kiln to form an amorphous carbon coating on the surface of the artificial graphite particles, thereby preparing artificial graphite 2. The final D of artificial graphite 2 50 Controlled to the level of 16μm.

[0118] [Preparation of natural graphite 2]

[0119] Natural graphite raw materials are extracted from graphite ore by flotation. The natural graphite raw materials are treated with acid or alkali to remove impurities from the natural graphite raw materials, and washed and dried to prepare flaky natural graphite. The obtained flaky natural graphite is spheroidized using a vortex mill, treated with sulfuric acid to remove impurities, and dried to prepare spherical natural graphite. The spherical natural graphite is filled into a mold, pressurized by cold isostatic pressing (CIP), and then crushed. During the pressurization, the pressurization pressure is 90 MPa and the pressurization time is 15 minutes. The pressurized spherical natural graphite and asphalt are mixed, and the mixture is dry-heat-treated at 1,300°C for 24 hours under an inert atmosphere to form an amorphous carbon coating on the spherical natural graphite, thereby preparing natural graphite 2. The carbon coating is formed at 5% by weight of the total weight of the natural graphite active material.

[0120] [Preparation of slurry]

[0121] As the negative electrode active material, silicon carbon composite 1, natural graphite 2 and artificial graphite 2 having the rolled density and conductivity shown in Table 1 below were used in a weight ratio of 15:15:70. Specifically, when the pressure was 800 kgf / cm 2 When the powder resistance was measured under a pressure of 1000 rpm, the silicon-carbon composite 1 had a calendering density of 0.859 g / cc and a conductivity of 0.664 S / cm, the natural graphite 2 had a calendering density of 1.6 g / cc and a conductivity of 337 S / cm, and the artificial graphite 2 had a calendering density of 1.58 g / cc and a conductivity of 96.6 S / cm. The negative electrode slurry was prepared by mixing the negative electrode active material, the conductive agent (carbon black, single-walled carbon nanotubes (SWCNTs)) and the binder (CMC (carboxymethyl cellulose), SBR (styrene-butadiene rubber)) in a weight ratio of 95.3:1:3.7.

[0122] [Preparation of negative electrode]

[0123] The negative electrode slurry was applied to a Cu metal film having a thickness of about 20 μm and then dried at a circulating air temperature of 60° C. The film was then rolled, dried in a vacuum oven at 130° C. for about one day, and punched into 1.4875 cm 2 to prepare the negative electrode.

[0124] [Preparation of Secondary Battery]

[0125] As the positive electrode, a 1.7671 cm 2A Li metal thin film was prepared. A Li coin-type half-cell was prepared by inserting a porous polyethylene separator between the positive and negative electrodes and injecting an electrolyte in which 1M LiPF6 was dissolved in a mixed solution prepared by mixing EC (ethylene carbonate) and EMC (ethyl methyl carbonate) at a mixing ratio of 3:7 and containing a haloalkylene carbonate-based additive compound.

[0126] Example 2 (Silicon Oxide 1, Artificial Graphite 2, Natural Graphite 2)

[0127] [Manufacturing of Silicon Oxide 1]

[0128] SiO formed by mixing Si and SiO2 in a molar ratio of 1:1 is placed in crucible No. 1, heated to a sublimation temperature of 1,400°C, and evaporated. Metallic magnesium is placed in crucible No. 2, heated separately at 800°C, and evaporated. All crucibles are depressurized to a level of 0.1 torr, and then the raw materials are evaporated. The Mg-containing vapor mixture is reacted for 6 hours and then condensed into a solid phase in a vacuum zone at 800°C. The silicon-based active material prepared by the above method is pulverized using a ball mill for about 3 to 4 hours. Then, the pulverized silicon-based active material is reacted with methane (CH4) at 1 L / min at 0.1 torr for about 5 hours using a CVD device under an inert gas Ar atmosphere to form a carbon layer on the surface of the silicon-based active material to prepare a magnesium silicon oxide active material coated with a carbon layer thereon. The D of the final active material is 50 Controlled to the level of 6μm.

[0129] [Preparation of slurry]

[0130] A slurry was prepared in the same manner as in Example 1 except that silicon oxide 1, natural graphite 2 (see the preparation method of Example 1), and artificial graphite 2 (see the preparation method of Example 1) having the rolled density and conductivity shown in Table 1 below were used as negative electrode active materials in a weight ratio of 20:10:70. Specifically, when the pressure was 800 kgf / cm 2 When the powder resistance was measured under a pressure of , silicon oxide 1 had a calendering density of 1.42 g / cc and a conductivity of 0.122 S / cm, natural graphite 2 had a calendering density of 1.6 g / cc and a conductivity of 337 S / cm, and artificial graphite 2 had a calendering density of 1.58 g / cc and a conductivity of 96.6 S / cm.

[0131] [Preparation of negative electrode and secondary battery]

[0132] A negative electrode and a secondary battery were prepared in the same manner as in Example 1 using the above slurry.

[0133] Example 3 (Silicon-carbon composite 2, artificial graphite 1, natural graphite 1)

[0134] [Preparation of Silicon Carbon Composite 2]

[0135] The silicon-carbon composite was heat-treated at 700° C. for 2 hours in an atmosphere of O2 / Ar (= 5 / 95) to form an oxide layer. Silicon-carbon composite 2 was prepared in the same manner as in Example 1, except that the silicon-carbon composite was placed in an electric furnace and reacted by flowing methane at 700° C. for 2 hours to form a carbon layer on the surface.

[0136] [Preparation of Artificial Graphite 1]

[0137] The mixing amount of the asphalt binder was 4.5 wt% based on the total weight of the raw coke particles, the calcined coke particles, and the petroleum-based asphalt. An artificial graphite active material was prepared in the same manner as in Artificial Graphite 2 of Example 1, except that the artificial graphite particles in the form of secondary particles and the petroleum-based asphalt were mixed and heat-treated in a roller kiln at 1150° C. to form an amorphous carbon coating on the surfaces of the artificial graphite particles.

[0138] [Preparation of natural graphite 1]

[0139] A natural graphite active material was prepared in the same manner as in Natural Graphite 2 of Example 1, except that pressurized spherical natural graphite and pitch were mixed and the mixture was dry-heat-treated in an inert atmosphere at 1,100° C. for 24 hours to form an amorphous carbon coating.

[0140] [Preparation of slurry]

[0141] A slurry was prepared in the same manner as in Example 1 except that silicon-carbon composite 2, natural graphite 1, and artificial graphite 1 having the rolled density and conductivity shown in Table 1 below were used as negative electrode active materials at a weight ratio of 15:15:70. Specifically, the slurry was a composition wherein when subjected to 800 kgf / cm 2 When the powder resistance was measured under a pressure of 100 Å, the silicon-carbon composite 2 had a calendering density of 0.914 g / cc and a conductivity of 0.00025 S / cm, the natural graphite 1 had a calendering density of 1.61 g / cc and a conductivity of 149 S / cm, and the artificial graphite 1 had a calendering density of 1.54 g / cc and a conductivity of 30.1 S / cm.

[0142] [Preparation of negative electrode and secondary battery]

[0143] A negative electrode and a secondary battery were prepared in the same manner as in Example 1 using the above slurry.

[0144] Example 4 (Silicon-carbon composite 1, artificial graphite 1, natural graphite 2)

[0145] [Preparation of slurry]

[0146] A slurry was prepared in the same manner as in Example 1 except that silicon-carbon composite 1 (see the preparation method of Example 1), natural graphite 2 (see the preparation method of Example 1), and artificial graphite 1 (see the preparation method of Example 3) having the rolled density and conductivity shown in Table 1 below were used as negative electrode active materials at a weight ratio of 15:15:70. Specifically, the slurry was a composition wherein when subjected to a pressure of 800 kgf / cm 2 When the powder resistance was measured under a pressure of 100 Å, the silicon-carbon composite 1 had a rolled density of 0.859 g / cc and a conductivity of 0.664 S / cm, the natural graphite 2 had a rolled density of 1.6 g / cc and a conductivity of 337 S / cm, and the artificial graphite 1 had a rolled density of 1.54 g / cc and a conductivity of 30.1 S / cm.

[0147] [Preparation of negative electrode and secondary battery]

[0148] Using the above slurry, a negative electrode and a secondary battery were prepared.

[0149] Example 5 (Silicon Oxide 1, Artificial Graphite 1, Natural Graphite 2)

[0150] [Preparation of slurry]

[0151] A slurry was prepared in the same manner as in Example 1 except that silicon oxide 1 (see the preparation method of Example 2), natural graphite 2 (see the preparation method of Example 1), and artificial graphite 1 (see the preparation method of Example 3) having the rolled density and conductivity shown in Table 1 below were used as negative electrode active materials in a weight ratio of 20:10:70. Specifically, the slurry was a composition in which when subjected to 800 kgf / cm 2 When the powder resistance was measured under a pressure of , the silicon oxide active material had a calendering density of 1.42 g / cc and a conductivity of 0.122 S / cm, the natural graphite 2 had a calendering density of 1.6 g / cc and a conductivity of 337 S / cm, and the artificial graphite 1 had a calendering density of 1.54 g / cc and a conductivity of 30.1 S / cm.

[0152] [Preparation of negative electrode]

[0153] A negative electrode and a secondary battery were prepared in the same manner as in Example 1 using the above slurry.

[0154] Example 6 (Silicon Oxide 1, Artificial Graphite 2, Natural Graphite 1)

[0155] [Preparation of slurry]

[0156] A slurry was prepared in the same manner as in Example 1 except that silicon oxide 1 (see the preparation method of Example 2), natural graphite 1 (see the preparation method of Example 3), and artificial graphite 2 (see the preparation method of Example 1) having the rolled density and conductivity shown in Table 1 below were used as negative electrode active materials in a weight ratio of 20:10:70. The slurry was a composition in which when subjected to 800 kgf / cm 2 When the powder resistance was measured under a pressure of , the silicon oxide active material had a calendering density of 1.42 g / cc and a conductivity of 0.122 S / cm, natural graphite 1 had a calendering density of 1.61 g / cc and a conductivity of 149 S / cm, and artificial graphite 2 had a calendering density of 1.58 g / cc and a conductivity of 96.6 S / cm.

[0157] [Preparation of negative electrode and secondary battery]

[0158] A negative electrode and a secondary battery were prepared in the same manner as in Example 1 using the above slurry.

[0159] Example 7 (Silicon Oxide 1, Artificial Graphite 2, Natural Graphite 2)

[0160] [Preparation of slurry]

[0161] A slurry was prepared in the same manner as in Example 1 except that silicon oxide 1 (see the preparation method of Example 2), natural graphite 2 (see the preparation method of Example 1), and artificial graphite 2 (see the preparation method of Example 1) having the rolled density and conductivity shown in Table 1 below were used as negative electrode active materials in a weight ratio of 20:10:70. 2 When the powder resistance was measured under a pressure of 1000 rpm, the silicon oxide active material had a calendering density of 1.42 g / cc and a conductivity of 0.122 S / cm, natural graphite 1 had a calendering density of 1.61 g / cc and a conductivity of 149 S / cm, and artificial graphite 2 had a calendering density of 1.58 g / cc and a conductivity of 96.6 S / cm. A negative electrode slurry was prepared by mixing the negative electrode active material, a conductive material (carbon black), and a binder (CMC (carboxymethyl cellulose) and SBR (styrene-butadiene rubber)) in a weight ratio of 95.3:1:3.7.

[0162] [Preparation of negative electrode and secondary battery]

[0163] A negative electrode and a secondary battery were prepared in the same manner as in Example 1 using the above slurry.

[0164] Comparative Example 1 (Silicon Carbon Composite 3, Artificial Graphite 3, Natural Graphite 2)

[0165] [Preparation of Silicon Carbon Composite 3]

[0166] The carbon-based particles prepared by the method for manufacturing a silicon-carbon composite as specified in Example 1 were treated by flowing SiH4 / He (= 5 / 95) gas at 700°C at a flow rate of 50 ml / min for 1 hour to prepare a silicon-carbon composite. Then, the silicon-carbon composite was placed in a solvent in which phosphoric acid and ethanol were mixed at a volume ratio of 10:90. The silicon-carbon composite dispersed in the solvent was heated at 1000°C for 4 hours in an argon atmosphere to obtain a final P (phosphorus)-doped silicon-carbon composite. Thereafter, the P-doped silicon-carbon composite was placed in an electric furnace and reacted by flowing methane at 700°C for 2 hours to prepare a P-doped silicon-carbon composite negative electrode active material having a carbon layer on the surface.

[0167] [Preparation of artificial graphite 3]

[0168] Artificial graphite 3 was prepared in the same manner as artificial graphite 2 of Example 1, except that a mixture of raw coke particles, calcined coke particles and petroleum pitch was graphitized by heat treatment at 3000°C for 50 hours to prepare artificial graphite particles in the form of secondary particles, and then the artificial graphite particles were partially oxidized in a hot zone by heat treatment at 800°C for 2 hours in an O2 / Ar (= 5 / 95) atmosphere.

[0169] [Preparation of slurry]

[0170] A slurry was prepared in the same manner as in Example 1 except that silicon-carbon composite 3, natural graphite 2 (see the preparation method of Example 1) and artificial graphite 3 having the rolled density and conductivity shown in Table 1 below were used as negative electrode active materials in a weight ratio of 20:10:70. Specifically, the slurry was a composition in which when subjected to 800 kgf / cm 2 When the powder resistance was measured under a pressure of 100 Å, the silicon-carbon composite 3 had a rolled density of 1.32 g / cc and a conductivity of 8.1 S / cm, the natural graphite 2 had a rolled density of 1.6 g / cc and a conductivity of 337 S / cm, and the artificial graphite 3 had a rolled density of 1.56 g / cc and a conductivity of 5.8 S / cm.

[0171] [Preparation of negative electrode and secondary battery]

[0172] A negative electrode and a secondary battery were prepared in the same manner as in Example 1 using the above slurry.

[0173] Comparative Example 2 (Silicon Oxide 2, Artificial Graphite 4, Natural Graphite 1)

[0174] [Manufacturing of Silicon Oxide 2]

[0175] In addition to pulverizing the silicon-based active material using a ball mill for about 5 to 6 hours to 50 Silicon oxide 2 was prepared in the same manner as silicon oxide 1 of Example 2 except that the thickness was controlled to a level of 3 μm.

[0176] [Preparation of artificial graphite 4]

[0177] In addition to the final artificial graphite active material D 50 Artificial graphite 4 was prepared in the same manner as artificial graphite 2 of Example 1, except that the particle size was 29 μm.

[0178] [Preparation of slurry]

[0179] A slurry was prepared in the same manner as in Example 1 except that silicon oxide 2, natural graphite 1 (see the preparation method of Example 3) and artificial graphite 4 having the rolled density and conductivity shown in Table 1 below were used as negative electrode active materials in a weight ratio of 20:10:70. Specifically, the slurry was a composition in which when subjected to 800 kgf / cm 2 When the powder resistance was measured under a pressure of , silicon oxide 2 had a calendering density of 1.52 g / cc and a conductivity of 0.178 S / cm, natural graphite 1 had a calendering density of 1.61 g / cc and a conductivity of 149 S / cm, and artificial graphite 4 had a calendering density of 1.45 g / cc and a conductivity of 80.2 S / cm.

[0180] [Preparation of negative electrode and secondary battery]

[0181] A negative electrode and a secondary battery were prepared in the same manner as in Example 1 using the above slurry.

[0182] Comparative Example 3 (Silicon Oxide 1, Artificial Graphite 1, Natural Graphite 3)

[0183] [Preparation of natural graphite 3]

[0184] Natural graphite was prepared in the same manner as in Natural Graphite 2 of Example 1, except that the natural graphite active material had a carbon coating layer formed at 2 wt % based on the total weight of the natural graphite active material.

[0185] [Preparation of slurry]

[0186] A slurry was prepared in the same manner as in Example 1 except that silicon oxide 1 (see the preparation method of Example 2), natural graphite 3, and artificial graphite 1 (see the preparation method of Example 3) having the rolled density and conductivity shown in Table 1 below were used as negative electrode active materials in a weight ratio of 20:10:70. Specifically, the slurry was a composition in which when subjected to 800 kgf / cm 2When the powder resistance was measured under a pressure of , silicon oxide 1 had a calendering density of 1.42 g / cc and a conductivity of 0.122 S / cm, natural graphite 3 had a calendering density of 1.6 g / cc and a conductivity of 24.5 S / cm, and artificial graphite 1 had a calendering density of 1.54 g / cc and a conductivity of 30.1 S / cm.

[0187] [Preparation of negative electrode and secondary battery]

[0188] A negative electrode and a secondary battery were prepared in the same manner as in Example 1 using the above slurry.

[0189]

[0190] The calendering density and electrical conductivity of the active materials used in Examples and Comparative Examples are shown in Tables 2 and 3 below.

[0191]

[0192]

[0193] <Experimental Example: Evaluation of Discharge Capacity, Initial Efficiency, and Life (Capacity Retention) Characteristics>

[0194] Batteries were prepared using the negative electrodes of the examples and comparative examples, respectively.

[0195] As the positive electrode, a 1.7671 cm 2 A circular lithium (Li) metal film was prepared. A porous polyethylene separator was interposed between the positive electrode and the negative electrode, and an electrolyte was injected to prepare a lithium coin half-cell. The electrolyte was obtained by dissolving 0.5 parts by weight of vinylene carbonate in a mixed solution of ethyl methyl carbonate (EMC) and ethylene carbonate (EC) with a mixing volume ratio of 7:3, and dissolving LiPF6 to a concentration of 1M.

[0196] The prepared batteries were charged and discharged to evaluate discharge capacity, initial efficiency, and capacity retention rate, and the evaluation results are shown in Table 4 below.

[0197] For the first and second cycles, charge and discharge were performed at 0.1 C, and from the third cycle to the 299th cycle, charge and discharge were performed at 0.5 C. At the 50th cycle, charge and discharge were terminated in a charged state (lithium contained in the negative electrode).

[0198] Charging conditions: CC (constant current) / CV (constant voltage) (5mV / 0.005C current cutoff)

[0199] Discharge condition: CC (constant current) condition 1.5V

[0200] The discharge capacity (mAh / g) and initial efficiency (%) were calculated from the results after one charge and discharge. Specifically, the initial efficiency (%) was calculated as follows.

[0201] Initial efficiency (%) = (first discharge capacity / first charge capacity) × 100 (%)

[0202] The capacity retention rate was calculated as follows.

[0203] Capacity retention rate (%) = (299th discharge capacity / first discharge capacity) × 100 (%)

[0204]

[0205] In Comparative Example 1, the conductivity of the silicon-based active material was higher than that of artificial graphite, resulting in low initial efficiency and capacity retention. Silicon-based active materials are known to react more violently with the electrolyte than carbon-based active materials due to their unstable surface. When the conductivity of the silicon-based active material becomes higher than that of artificial graphite, the reduction reaction of the electrolyte on the surface of the silicon-based active material is accelerated, forming a thick film and resulting in low efficiency and capacity retention.

[0206] In addition, in Comparative Example 2, the calendering density of artificial graphite is lower than the calendering density of the silicon-based active material, in which case, low initial efficiency and capacity retention characteristics are exhibited. Calendering density refers to how high the density of the carbon-based active material and the silicon-based active material is present during electrode calendering, so that the migration path of electrons and lithium can be achieved. When the calendering density of the silicon-based active material is higher than the calendering density of the artificial graphite, the silicon-based active material undergoes significant volume changes as the cycle proceeds, resulting in the formation of larger pores and poor capacity retention characteristics. In Comparative Example 3, the electrical conductivity of natural graphite is lower than that of artificial graphite, in which case, low initial efficiency and capacity retention characteristics are also exhibited. On the other hand, Examples 1 to 7 exhibit high initial efficiency and capacity retention by using active materials that satisfy the relationship between calendering density and electrical conductivity of the present invention.

[0207] In particular, Examples 1 to 3 exhibited excellent initial efficiency and capacity retention, wherein the electrical conductivity of the artificial graphite was 10 times that of the silicon-based active material. 2 times or more, and the electrical conductivity of the natural graphite is more than 2 times the electrical conductivity of the artificial graphite, the rolled density of the artificial graphite is more than 1.1 times the rolled density of the silicon-based active material, and the rolled density of the natural graphite is more than 1.01 times the rolled density of the artificial graphite.

Claims

1. A negative electrode composition comprising a negative electrode active material, wherein the negative electrode active material comprises a silicon-based active material and a carbon-based active material, wherein the silicon-based active material comprises at least one of a silicon-carbon composite and a silicon oxide. wherein the carbon-based active material comprises natural graphite and artificial graphite, and When the pressure is 800kgf / cm 2 When the powder resistance is measured under a pressure of , the calendering 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 negative electrode composition according to claim 1, wherein the electrical conductivity of the artificial graphite is 10 times that of the silicon-based active material. 2 times, and the electrical conductivity of the natural graphite is more than 2 times that of the artificial graphite. 3 . The negative electrode composition according to claim 1 , wherein the pressed density of the artificial graphite is 1.1 times or more than the pressed density of the silicon-based active material, and the pressed density of the natural graphite is 1.01 times or more than the pressed density of the artificial graphite.

4. 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. The negative electrode composition according to claim 1, wherein the natural graphite has a pressed density of 1.4 to 2.5 g / cc, the artificial graphite has a pressed density of 1.0 to 2.2 g / cc, the silicon-carbon composite has a pressed density of 0.5 to 1.2 g / cc, and the silicon oxide has a pressed density of 0.8 to 1.8 g / cc. The negative electrode composition according to claim 1 , wherein the negative electrode composition comprises single-walled carbon nanotubes as a conductive material.

7. The negative electrode composition according to claim 6, wherein the content of the silicon-based active material is 0.5 to 52 parts by weight, the content of the carbon-based active material is 45 to 99 parts by weight, and the content of the single-walled carbon nanotube is 0.01 to 3 parts by weight, based on 100 parts by weight of the negative electrode composition. The natural graphite is present in an amount of 10 to 70 parts by weight, and the artificial graphite is present in an amount of 30 to 90 parts by weight, based on 100 parts by weight of the carbon-based active material. The negative electrode composition according to claim 1 , further comprising a binder. 9 . A negative electrode comprising the negative electrode composition according to claim 1 .

10. A lithium secondary battery comprising: The negative electrode according to claim 9; positive electrode; and diaphragm. 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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