Negative electrode composition, negative electrode, 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] This 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 proliferation of battery-powered electronic devices such as mobile phones, laptops, electric vehicles, power tools, and vacuum cleaners, the demand for small, lightweight, and relatively high-capacity and / or high-power rechargeable batteries has been rapidly increasing. In particular, lithium-ion batteries, being lightweight and possessing high energy density, have attracted considerable attention as a power source for electronic devices. As a result, research and development efforts to improve the performance of lithium-ion batteries are being actively pursued.

[0004] Generally, 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, active material layers containing positive electrode active material and negative electrode active material can be formed on a current collector at both the positive and negative electrodes. Generally, lithium-containing metal oxides such as LiCoO2 and LiMn2O4 are used as the positive electrode active material, while lithium-free carbon-based active materials and silicon-based active materials are used as the negative electrode active material.

[0005] Among negative electrode active materials, silicon-based active materials are attracting attention because they have a 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 a large degree of volume expansion / contraction during charging and discharging and a 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-ion secondary batteries. [Overview of the project] [Problems that the invention aims to solve]

[0007] The present invention relates to a negative electrode composition that can improve the performance of a lithium secondary battery, a negative electrode containing the negative electrode composition, and a secondary battery containing the same. [Means for solving the problem]

[0008] One embodiment of the present invention includes a silicon-based active material comprising at least one of silicon-carbon composites and silicon oxides, and a negative electrode active material comprising a carbon-based active material, wherein the carbon-based active material comprises natural graphite and artificial graphite, and has a load of 800 kgf / cm². 2 The present invention provides a negative electrode composition in which, when measuring powder resistance at a given pressure, the rolled 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] Furthermore, according to one embodiment of the present invention, the negative electrode composition of the above-described embodiment includes single-walled carbon nanotubes as a conductive material.

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

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

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

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

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

[0015] According to embodiments of the present invention, the performance of a lithium secondary battery can be improved by using a mixture of silicon-based active material and carbon-based active material having different rolling densities and electrical conductivity as the negative electrode active material. In particular, carbon-based active materials have higher rolling densities and electrical conductivity at the same pressure compared to silicon-based active material, and by mixing two types of carbon-based active materials with different rolling densities and electrical conductivity, the cycle characteristics and resistance of the lithium secondary battery can be improved. [Modes for carrying out the invention]

[0016] The present invention will be described in more detail below to aid in understanding the invention. The present invention may be realized in various different forms and is not limited to the embodiments described herein. In this regard, terms and words used herein and in the claims should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather should be interpreted in a manner consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may appropriately define the concepts of terms in order to best describe their invention.

[0017] In this specification, terms such as “include,” “provide,” or “have” indicate the presence of implemented features, figures, stages, components, or combinations thereof, and should be understood not to preemptively exclude the possibility of the presence or addition of one or more other features, figures, stages, components, or combinations thereof.

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

[0019] The terms and words used herein should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather should be interpreted in a manner consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may appropriately define the concepts of terms in order to best explain their invention.

[0020] In this specification, singular expressions of terms include plural expressions unless the context clearly indicates otherwise.

[0021] In this specification, rolling density refers to the degree of particle deformation and compression that occurs when a certain pressure is applied to the negative electrode active material, and can be expressed in g / cc. Rolling density can be derived by measuring powder resistance, for example, by putting a certain amount of negative electrode active material into a cylinder-type load cell and applying 400 kgf / cm². 2 ~2,000 kgf / cm² 2 The pressure can be applied and measured by the change in the thickness of the inserted negative electrode active material.

[0022] In this specification, the electrical conductivity means the intrinsic electrical conductivity of the negative electrode active material powder. The electrical conductivity can be derived by measuring the powder resistance. For example, while applying any pressure from 400 kgf / cm 2 to 2,000 kgf / cm 2 , 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 can be derived from the measured surface resistance value and specific resistance value.

[0023] When measuring the powder resistance, considering the influence of particle deformation that may occur when pressed with an excessively high force, for example, a pressure exceeding 2,000 kgf / cm 2 , it is preferable to use the rolling density value and electrical conductivity value derived from the measurement of the powder resistance with a pressure applied within the above range, preferably 800 kgf / cm 2 .

[0024] Hereinafter, preferred embodiments of the present invention will be described in detail. However, the embodiments of the present invention may be deformed into various forms, and the scope of the present invention is not limited to the embodiments described below.

[0025] A negative electrode composition according to an embodiment of the present invention includes a negative electrode active material including a silicon-based active material and a carbon-based active material including at least one of a silicon-carbon composite and a silicon oxide, and the carbon-based active material includes natural graphite and artificial graphite. Here, when measuring the powder resistance at a pressure of 800 kgf / cm 2 , 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 above embodiment, by including a carbon-based active material having a higher rolling density and electrical conductivity than the silicon-based active material when measuring the powder resistance at a pressure of 800 kgf / cm 2 compared to the silicon-based active material, the cycle characteristics and resistance of the lithium secondary battery can be improved. Also, as the carbon-based active material, artificial graphite at 800 kgf / cm2 By mixing natural graphite, which has relatively high rolling density and electrical conductivity, with lithium-ion batteries when measuring powder resistance at pressure, the performance of lithium-ion batteries can be improved. By mixing a negative electrode active material with relatively high electrical conductivity, even if surface separation occurs between the negative electrode active material and the conductive material due to volume changes during charging and discharging, the high electrical conductivity makes it easier than charging and discharging lithium. This enables the realization of long-life battery characteristics. On the other hand, in the case of an active material with relatively high rolling density, the volume change during charging and discharging can be physically controlled, which can have a favorable effect on cycle performance.

[0027] Even if the rolling density of each material decreases in the order of natural graphite > artificial graphite > silicon-based active material in the negative electrode composition according to one embodiment of the present invention, if the electrical conductivity of each material does not satisfy the order of natural graphite > artificial graphite > silicon-based active material, the particles may break and the inner surface with low electrical conductivity will be exposed, causing a phenomenon in which the trend of electrical conductivity is reversed. For example, this occurs when the electrical conductivity is in the order of artificial graphite > natural graphite > silicon-based active material.

[0028] Specifically, while increased rolling density generally leads to a greater contact surface between particles and thus higher conductivity, particle fracture can negatively affect electrical conductivity. Therefore, rolling density and electrical conductivity should ideally exhibit a similar trend.

[0029] If the particles do not exhibit the same tendency, particle fracture may occur, which could negatively impact battery performance.

[0030] Furthermore, if artificial graphite has a higher rolling density and electrical conductivity than natural graphite, the degree of graphitization of the artificial graphite increases, which can degrade battery performance.

[0031] Unless otherwise specified, electrical conductivity as used herein refers to the electrical conductivity of each material in its particle state, for example, before cracking occurs, and not to the electrical conductivity after the particles have cracked.

[0032] According to one embodiment, the 800 kgf / cm² 2 When measuring the powder resistance at the specified pressure, 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.

[0033] For example, the aforementioned 800 kgf / cm² 2 When measuring powder resistance at this pressure, the rolling density may be 1.4-2.5 g / cc for natural graphite, for example 1.6-1.7 g / cc; 1.0-2.2 g / cc for artificial graphite, for example 1.5-1.6 g / cc; and 0.5-1.8 g / cc for silicon-based active materials. Specifically, 800 kgf / cm² 2 When measuring powder resistance at the specified pressure, the rolling 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 rolling 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 / cm² 2 When measuring the powder resistance at the specified pressure, the electrical conductivity of the artificial graphite is more than 100 times greater than that of the silicon-based active material, and the electrical conductivity of the natural graphite is more than twice as great as that of the artificial graphite.

[0035] For example, 800 kgf / cm² 2 When measuring the powder resistance at a pressure of 800 kgf / cm, the electrical conductivity may be 0.0001 to 2 S / cm for the silicon-based active material, 15 to 2,000 S / cm for the artificial graphite, for example 15 to 100 S / cm, and 50 to 10,000 S / cm for the natural graphite, for example 100 to 1,000 S / cm, or 100 to 500 S / cm. 2 When measuring the powder resistance at the specified pressure, 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, based on 100 parts by weight of the negative electrode composition, the silicon-based active material may be 0.5 to 52 parts by weight; the carbon-based active material may be 45 to 99 parts by weight; and 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 natural graphite may be 10 to 70 parts by weight; and the artificial graphite may be 30 to 90 parts by weight.

[0037] According to one embodiment, the silicon-based active material may be included in an amount of 0.5 to 50 parts by weight, 1 to 40 parts by weight, or for example, 1 to 20 parts by weight, based on 100 parts by weight of the total amount of 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 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 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, represented as SiC. The silicon carbide does not react electrochemically with lithium, and all its properties, such as lifetime, can be measured as zero.

[0042] The silicon-carbon composite may include at least one of the following: a silicon-carbon composite formed by depositing silicon onto a porous carbon structure; and a silicon-carbon composite in which carbon is compounded onto a porous silicon structure. The silicon-carbon composite may also be a composite of silicon and graphite or the like. 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 obtained by the BET method, and its surface area is 0.5 m². 2 / g~10m 2 It may be / g, and the stomatal volume is 0.005 cm³. 3 / g~0.03cm 3 The density may be / g, and the pore size measured by the BET method may be 10 nm to 20 nm. The silicon-carbon composite has a pore volume of 0.005 cm³ as measured by mercury osmosis. 3 / g~0.03cm 3 / g is also acceptable.

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

[0046] According to one embodiment, the silicon-carbon composite may be manufactured by a method comprising the steps of: etching carbon-based particles containing internal pores to expand the internal pores of the carbon-based particles; and forming a silicon coating layer on the surface and internal pores of the carbon-based particles with expanded internal pores.

[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 in 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, islands, or a mixed form 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% based on 100 wt% of the total silicon oxide particles, or may be contained at 0.1 wt% to 10 wt%. 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 content of the aforementioned Mg or Li element can be confirmed by ICP analysis. For the ICP analysis, a fixed amount (approximately 0.01 g) of the negative electrode active material is accurately separated, transferred to a platinum crucible, and completely decomposed on a hot plate with the addition of nitric acid, hydrofluoric acid, and sulfuric acid. Subsequently, using an inductively coupled plasma atomic emission spectrometer (ICPAES, Perkin-Elmer 7300), the intensity of a standard solution prepared using a standard solution (5 mg / kg) is measured at wavelengths specific to the Mg or Li element to create a reference calibration curve. Then, the pre-treated sample solution and a blank sample are introduced into the instrument, their respective intensities are measured to calculate the actual intensities, and the concentrations of each component are calculated against the created calibration curve. After conversion, the total sum is converted to a theoretical value, and the content of the Mg or Li element in the manufactured silicon oxide particles can be analyzed.

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

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

[0065] The average particle size (D) of the silicon-based active material 50 The particle size may be 0.1 μm to 30 μm, more specifically 1 μm to 20 μm, and more specifically 1 μm to 10 μm. When the above range is met, the structural stability of the active material during charging and discharging can be ensured, the problem of volume expansion / contraction levels increasing due to excessively large particle size can be prevented, and the problem of initial efficiency decreasing due to excessively small particle size can be 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 The particle size can be measured, for example, using the laser diffraction method. This laser diffraction method can generally measure particle sizes from the submicron region to several millimeters, and can obtain highly reproducible and high-resolution results. The specific surface area of ​​the silicon-based active material is 2 to 10 m². 2 It may also be / 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 artificial graphite has an average particle size (D 50 The surface area is 10-30 μm, and the BET specific surface area is 0.5-2 m². 2 It may also be / g. The term "natural graphite" refers to graphite that occurs naturally, and examples include flake graphite, scaly graphite, or soil graphite. The advantages of natural graphite are that it is abundant, inexpensive, has high theoretical capacity and compressible density, and can achieve high output.

[0068] For example, the natural graphite may have a sphericity of 0.9 or higher.

[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 by the perimeter of the projected image, and can specifically be expressed by the following formula 1. The sphericity can be determined from an SEM image, or it can be measured using a particle shape analyzer, such as the sysmex FPIA3000 manufactured by Malvern. Furthermore, the crystal size can be confirmed by XRD analysis.

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

[0071] The aforementioned natural graphite may be selected and applied after confirming the particle shape using a scanning electron microscope (SEM) and then confirming it using a particle shape analyzer, thereby satisfying the sphericity requirement.

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

[0073] The aforementioned artificial graphite may be selected and applied after confirming the particle shape using a scanning electron microscope (SEM) and then confirming it using a particle shape analyzer, thereby satisfying the sphericity requirement.

[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 term "single-walled carbon nanotube (SWCNT)" refers to a tubular carbon structure consisting of a single layer of carbon. When the conductive material in the negative electrode composition includes the single-walled carbon nanotube (SWCNT), the charge / discharge capacity and / or lifespan of the battery can be improved. Specifically, the single-walled carbon nanotube (SWCNT) effectively connects the conductive paths between particles, thereby preventing the loss of conductive paths due to the swelling of the silicon-based active material mentioned above. As a result, when the single-walled carbon nanotube (SWCNT) is included, the lifespan of the battery can be improved.

[0076] In this specification, the length of a carbon nanotube means the length of the major axis passing through the center of the carbon nanotube unit, and the diameter of a carbon nanotube means 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, more 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 aforementioned silicon-based and carbon-based active materials, the length of the carbon nanotubes is ensured to be equal to the distance between the negative electrode active material particles. This further facilitates the connection of conductive paths between particles, improving the electrical conductivity, strength, and / or storage and maintenance properties of the electrolyte of the negative electrode.

[0079] The average diameter of the single-walled carbon nanotubes (SWCNTs) may be 1 nm to 20 nm, and more specifically, 1.5 nm to 15 nm. More specifically, it may be 1.5 nm to 5 nm. Single-walled carbon nanotubes (SWCNTs) with such an average diameter have flexible properties, and therefore, even if they are physically damaged, the connections (contacts) between the negative electrode active material particles are not easily broken. 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 aforementioned single-walled carbon nanotube is 200 m². 2 / g~2,000m 2 It can also be / g, specifically 250m 2 / g~1,500m 2 It may also be per g. When using single-walled carbon nanotubes (SWCNTs) that satisfy the above range, dispersion is easy even with a small amount of conductive material, and the particles can be effectively linked together.

[0081] The single-walled carbon nanotubes (SWCNTs) may be included in an amount of 0.01 to 3 parts by weight based on 100 parts by weight of the negative electrode composition, specifically in amounts of 0.01 to 2 parts by weight, 0.01 to 1 part by weight, or 0.05 to 0.5 parts by weight. When the above range is satisfied, it has the effect of facilitating the connection of conductive paths between active material particles and minimizing side reactions of 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 using a BET measuring device (BEL-SORP-mini, Nippon Bell) to remove gas at 130°C for 2 hours, followed by N2 adsorption / desorption at 77K.

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

[0084] The binder may contain at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, 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 the hydrogen atoms of these substances are substituted with Li, Na, or Ca, and may also contain various copolymers thereof.

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

[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 embodiment described above.

[0087] The negative electrode active material layer may be formed by applying a negative electrode slurry containing the aforementioned negative electrode composition to at least one side of a negative electrode current collector, drying it, and rolling it.

[0088] The negative electrode current collector is not particularly limited, as long as it does not cause a chemical change in the battery and is conductive. For example, the current collector may be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. Specifically, transition metals that readily adsorb carbon, such as copper and nickel, may be used as the current collector. The thickness of the current collector may be 6 μm to 20 μm, but is not limited thereto.

[0089] If necessary, additional conductive materials other than the single-walled carbon nanotubes mentioned above may be included. The additional conductive materials are not particularly limited as long as they do not cause chemical changes in the battery and are conductive, and may include, for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers 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 contain a solvent for forming the negative electrode slurry. Specifically, the solvent for forming the negative electrode slurry may contain at least one selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol, specifically distilled water, in order to facilitate the dispersion of the components.

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

[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 containing the positive electrode active material.

[0093] In the positive electrode, the positive electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector may also have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase the adhesion strength of the positive electrode active material. For example, it may be used in various forms such as 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; lithium iron oxide such as LiFe3O4; or a compound with the chemical formula Li 1+c1 Mn 2-c1 Lithium manganese oxides such as O4 (0 ≤ c1 ≤ 0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7; chemical formula LiNi 1-c2 M c2Ni-site type lithium nickel oxide represented as O2 (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, satisfying 0.01 ≤ c2 ≤ 0.3); chemical formula LiMn 2-c3 M c3 Lithium manganese composite oxides represented as O2 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, 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); LiMn2O4 in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion, etc., are examples, but are not limited thereto. The positive electrode may be Li metal.

[0095] The positive electrode active material layer may also include a positive electrode conductive material and a positive electrode binder, along with the positive electrode active material described above.

[0096] 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 it has electronic conductivity without causing a chemical change in the battery that is constructed. Specific examples include graphite such as natural graphite or 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 powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these alone or a mixture of two or more may be used.

[0097] Furthermore, the positive electrode binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more may be used.

[0098] The separator separates the negative and positive electrodes and provides a pathway for lithium ions to move. Generally, any separator commonly used in secondary batteries can be used without particular limitations, but it is especially preferable that it has low resistance to ion movement in the electrolyte and excellent electrolyte moisture absorption capacity. Specifically, porous polymer films, such as porous polymer films made from polyolefin polymers like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or laminated structures of two or more layers thereof may be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, to ensure heat resistance or mechanical strength, coated separators containing ceramic components or polymeric substances may be used, and they may be selectively used as single-layer or multi-layer structures.

[0099] The lithium secondary battery may further contain an electrolyte. Examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

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

[0101] As the non-aqueous organic solvent, for example, 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, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate, and ethyl propionate may be used.

[0102] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, can be preferably used as high-viscosity organic solvents because they have high dielectric constants and dissociate lithium salts well. Furthermore, when such cyclic carbonates are mixed with linear carbonates with low viscosity and low dielectric constant, such as dimethyl carbonate and diethyl carbonate, in appropriate proportions, an electrolyte with high electrical conductivity can be produced, making them even more preferable.

[0103] As the metal salt, a lithium salt may be used, and the lithium salt is a substance that is easily soluble in the non-aqueous electrolyte, for example, as the anion of the lithium salt, F - Cl - , I - NO3 - , N(CN)2 - BF4 - ClO4 - PF6 - (CF3)2PF4 - (CF3)3PF3- (CF3)4PF2 - (CF3)5PF - (CF3)6P - CF3SO3 - CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2) 2CH - (SF5)3C - , (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - , and (CF3CF2SO2)2N - You may use one or more selected from the group consisting of the following:

[0104] In addition to the components of the electrolyte, the electrolyte may further contain one or more additives for purposes such as improving the battery's lifespan, suppressing the decrease in battery capacity, and improving the battery's discharge capacity, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexalic acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride.

[0105] According to another embodiment of the present invention, a battery module including the secondary battery as a unit cell and a battery pack including the same are provided.

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

[0107] The following describes the Specification in detail with reference to examples. However, the examples provided herein may be modified in various other forms, and the scope of this application should not be construed as being limited to the examples described below. The examples of this application are provided to give a more complete explanation of this Specification to a person of average knowledge in the industry. [Examples]

[0108] Example 1 (Silicon-carbon composite 1, artificial graphite 2, natural graphite 2) [Manufacturing of silicon-carbon composite 1] Cellulose powder was placed in a tubular electric furnace and heated to 400°C at a rate of 4°C / min, then heated under a nitrogen atmosphere for 2 hours. After that, the electric furnace was heated to 900°C at a rate of 4°C / min, then heated under a nitrogen atmosphere for 2 hours. Sulfuric acid and nitric acid were mixed with the powder in a volume ratio of 3:1, stirred at 60°C for 2 hours, and then centrifuged to obtain a precipitate. The obtained powder was washed five times with a solvent mixture of ethanol and distilled water 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 heated under a nitrogen atmosphere at 800°C for 2 hours to obtain a porous carbon structure. The porous carbon structure was washed three times with distilled water and then dried at 120°C for 12 hours or more. The porous carbon structure was placed in a horizontal electric furnace, and SiH4 / He=5 / 95 gas was flowed through it at a flow rate of 50 ml / min at 700°C for 1 hour to produce a silicon-carbon composite. Subsequently, the silicon-carbon composite was placed in an electric furnace, and methane was flowed through it at 700°C for 2 hours to produce silicon-carbon composite 1 containing a carbon layer on its surface.

[0109] [Manufacturing of Artificial Graphite 2] Green coke particles and calcined coke particles were added to a reactor along with a petroleum-based pitch binder. The green coke and calcined coke particles were mixed in a weight ratio of 30:70. The pitch binder was mixed at a concentration of 7% by weight based on the total weight of the green coke particles, calcined coke particles, and petroleum-based pitch. The mixture of green coke particles, calcined coke particles, and petroleum-based pitch was heat-treated at 3000°C for 50 hours to graphitize it, thereby producing artificial graphite particles in the form of secondary particles with primary particles bound together. The secondary particulate artificial graphite was mixed with petroleum-based pitch 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 artificial graphite 2 D 50 It was controlled to the 16 μm level.

[0110] [Manufacturing of Natural Graphite 2] Natural graphite raw materials were extracted from graphite ore by flotation. To remove impurities from the natural graphite, it was treated with an acid or base, washed, and dried to produce flake-like natural graphite. The flake-like natural graphite obtained above was spheroidized using a vortex flow pulverizer, impurities were removed with sulfuric acid, and it was dried to produce spherical natural graphite. The spherical natural graphite was filled into a mold and pressed using the cold isostatic pressing method (CIP) to crush it. The pressing pressure was 90 MPa and the pressing time was 15 minutes. The pressed spherical natural graphite and pitch were mixed, 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, thereby producing natural graphite 2. The carbon coating layer was formed at 5% by weight of 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 / cm³. 2 When measuring the powder resistance at the specified pressure, the rolled density was 0.859 g / cc and the electrical conductivity was 0.664 S / cm. The natural graphite 2 had values ​​of 1.6 g / cc and 337 S / cm, respectively, while the artificial graphite 2 had values ​​of 1.58 g / cc and 96.6 S / cm, respectively. The negative electrode slurry was prepared by mixing the negative electrode active material, conductive material (carbon black, single-walled carbon nanotube (SWCNT)), and binder (CMC (carboxymethylcellulose), SBR (styrene-butadiene rubber)) in a weight ratio of 95.3:1:3.7.

[0112] [Manufacturing of negative electrodes] The negative electrode slurry was applied to a 20 μm thick Cu metal thin film and then dried in circulating air at 60°C. Next, after rolling, it was dried in a vacuum oven at 130°C for one day, and then rolled to 1.4875 cm². 2 The negative electrode was manufactured by punching out a circular shape.

[0113] [Manufacturing of secondary batteries] 1.7671cm 2 A die-cut Li metal thin film was used as the positive electrode. A porous polyethylene separator was interposed between the positive and negative electrodes, and an electrolyte solution containing 1M LiPF6 dissolved in a mixed solution of EC (ethylene carbonate) and EMC (ethyl methyl carbonate) in a 3:7 ratio, along with additives, was injected to produce a Li coin half-cell.

[0114] Example 2 (Silicon oxide 1, Artificial graphite 2, Natural graphite 2) [Production of silicon oxide 1] 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 to evaporate it. Metallic magnesium was placed in crucible 2 and heated to 800°C to evaporate it separately. After reducing the pressure of all crucibles to 0.1 torr, the raw materials were evaporated. The mixture in vapor state containing Mg was reacted for 6 hours, and then condensed into a solid phase in a vacuum at 800°C. The silicon-based active material produced by the above method was pulverized using a ball mill for about 3-4 hours. Subsequently, under an inert gas atmosphere of Ar, methane (CH4) was reacted with the silicon-based active material at a rate of 1 L / min at 0.1 torr for about 5 hours using a CVD apparatus to form a carbon layer on the surface of the silicon-based active material, thereby producing a magnesium silicon oxide active material coated with a carbon layer. The final active material D 50 It 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 manufacturing method of Example 1), and artificial graphite 2 (see manufacturing method of 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, the silicon oxide 1 had a rolling density of 800 kgf / cm³. 2 When measuring the powder resistance at the specified pressure, the rolled density was 1.42 g / cc and the electrical conductivity was 0.122 S / cm. The natural graphite 2 had values ​​of 1.6 g / cc and 337 S / cm, respectively, while the artificial graphite 2 had values ​​of 1.58 g / cc and 96.6 S / cm, respectively.

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

[0117] Example 3 (Silicon-carbon composite 2, artificial graphite 1, natural graphite 1) [Manufacturing of Silicon Carbon Composite 2] An oxide layer was formed by heat-treating the silicon-carbon composite in an O2 / Ar=5 / 95 atmosphere at 700°C for 2 hours. 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 methane was flowed through it at 700°C for 2 hours to form a carbon layer on the surface.

[0118] [Manufacturing of Artificial Graphite 1] The pitch binder was mixed at a concentration of 4.5% by weight, based on the total weight of green coke particles, calcined coke particles, and petroleum-based pitch. The artificial graphite active material was produced in the same manner as artificial graphite 2 of Example 1, except that the secondary particulate artificial graphite and petroleum-based pitch were mixed and heat-treated at 1150°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 produced in the same manner as natural graphite 2 of Example 1, except that pressurized spheroidal 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 silicon-carbon composite 2, natural graphite 1, and artificial graphite 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 15:15:70. Specifically, the silicon-carbon composite 2 had a rolling density of 800 kgf / cm³. 2 When measuring the powder resistance at the specified pressure, the composition has a rolling density of 0.914 g / cc and an electrical conductivity of 0.00025 S / cm. The natural graphite 1 has values ​​of 1.61 g / cc and 149 S / cm, respectively, while the artificial graphite 1 has values ​​of 1.54 g / cc and 30.1 S / cm, respectively.

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

[0122] Example 4 (Silicon Carbon Composite 1, Artificial Graphite 1, Natural Graphite 2) [Production of Slurry] As the negative electrode active material, except that Silicon Carbon Composite 1 (refer to the production method of Example 1), Natural Graphite 2 (refer to the production method of Example 1), and Artificial Graphite 1 (refer to the production method of Example 3) having the rolling density and electrical conductivity shown in Table 1 below were used in a weight ratio of 15:15:70, a slurry was produced in the same manner as in Example 1. Specifically, when measuring the powder resistance of the Silicon Carbon Composite 1 at a pressure of 800 kgf / cm 2 it has a rolling density of 0.859 g / cc and an electrical conductivity of 0.664 S / cm. The Natural Graphite 2 has values of 1.6 g / cc and 337 S / cm respectively, and the Artificial Graphite 1 has values of 1.54 g / cc and 30.1 S / cm respectively.

[0123] [Production of Negative Electrode and Secondary Battery] Using the above slurry, a negative electrode and a secondary battery were produced. <I

[0124] Example 5 (Silicon Oxide 1, Artificial Graphite 1, Natural Graphite 2) [Production of Slurry] As the negative electrode active material, except that Silicon Oxide 1 (refer to the production method of Example 2), Natural Graphite 2 (refer to the production method of Example 1), and Artificial Graphite 1 (refer to the production method of Example 3) having the rolling density and electrical conductivity shown in Table 1 below were used in a weight ratio of 20:10:70, a slurry was produced in the same manner as in Example 1. Specifically, when measuring the powder resistance of the Silicon Oxide active material at a pressure of 800 kgf / cm 2 it has a rolling density of 1.42 g / cc and an electrical conductivity of 0.122 S / cm. The Natural Graphite has values of 1.6 g / cc and 337 S / cm respectively, and the Artificial Graphite 1 has values of 1.54 g / cc and 30.1 S / cm respectively.

[0125] [Production of Negative Electrode] Using the slurry described above, a negative electrode and a secondary battery were manufactured in the same manner as in Example 1.

[0126] Example 6 (1 silicon oxide, 2 artificial graphite, 1 natural graphite) [Slurry production] A slurry was prepared in the same manner as in Example 1, except that silicon oxide 1 (see manufacturing method in Example 2), natural graphite 1 (see manufacturing method in Example 3), and artificial graphite 2 (see 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. The silicon oxide active material had a rolling density of 800 kgf / cm³. 2 When measuring the powder resistance at the specified pressure, the composition has a rolling density of 1.42 g / cc and an electrical conductivity of 0.122 S / cm. Natural graphite 1 has values ​​of 1.61 g / cc and 149 S / cm, respectively, while artificial graphite 2 has values ​​of 1.58 g / cc and 96.6 S / cm, respectively.

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

[0128] Example 7 (1 silicon oxide, 2 artificial graphite, 2 natural graphite) [Slurry production] A slurry was prepared in the same manner as in Example 1, except that silicon oxide 1 (see manufacturing method in Example 2), natural graphite 2 (see manufacturing method in Example 1), and artificial graphite 2 (see 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. The silicon oxide active material had a rolling density of 800 kgf / cm³. 2When measuring the powder resistance at the specified pressure, the rolled density was 1.42 g / cc and the electrical conductivity was 0.122 S / cm. The natural graphite 2 had values ​​of 1.6 g / cc and 337 S / cm, respectively, while the artificial graphite 2 had values ​​of 1.58 g / cc and 96.6 S / cm, respectively. The negative electrode slurry was prepared by mixing the negative electrode active material, conductive material (carbon black), and binder (CMC (carboxymethylcellulose) and SBR (styrene-butadiene rubber)) in a weight ratio of 95.3:1:3.7.

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

[0130] Comparative Example 1 (Silicon-carbon composite 3, artificial graphite 3, natural graphite 2) [Manufacturing of silicon-carbon composite 3] In Example 1, carbon-based particles were produced by the silicon-carbon composite manufacturing method described in Example 1. SiH4 / He=5 / 95 gas was flowed through these particles 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 a solvent containing phosphoric acid and ethanol in a volume ratio of 10:90. The silicon-carbon composite dispersed in the solvent was heated at 1000°C for 4 hours under an argon atmosphere to obtain a silicon-carbon composite doped with phosphorus (P). Subsequently, the phosphorus-doped silicon-carbon composite was placed in an electric furnace and reacted with methane flowed at 700°C for 2 hours to produce a phosphorus-doped silicon-carbon composite negative electrode active material containing a carbon layer on its surface.

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

[0132] [Slurry production] A slurry was prepared in the same manner as in Example 1, except that the negative electrode active material consisted of silicon-carbon composite 3, natural graphite 2 (see manufacturing method in Example 1), and artificial graphite 3 having the rolling density and electrical conductivity shown in Table 1 below, in a weight ratio of 20:10:70. Specifically, the silicon-carbon composite 3 had a rolling density of 800 kgf / cm³. 2 When measuring the powder resistance at the specified pressure, the composition has a rolling density of 1.32 g / cc and an electrical conductivity of 8.1 S / cm. The natural graphite 2 has values ​​of 1.6 g / cc and 337 S / cm, respectively, while the artificial graphite 3 has values ​​of 1.56 g / cc and 5.8 S / cm, respectively.

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

[0134] Comparative Example 2 (Silicon oxide 2, Synthetic graphite 4, Natural graphite 1) [Manufacturing of silicon oxide 2] The silicon-based active material is pulverized using a ball mill for about 5-6 hours, D 50 Silicon oxide 2 was produced in the same manner as silicon oxide 1 in Example 2, except that the coefficient 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 its 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 manufacturing method in Example 3), and artificial graphite 4 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 2 had a rolling density of 800 kgf / cm³. 2When measuring the powder resistance at the pressure of [[ID=]], the composition has a rolled density of 1.52 g / cc and an electrical conductivity of 0.178 S / cm. The natural graphite 1 has values of 1.61 g / cc and 149 S / cm respectively, and the artificial graphite 4 has values of 1.45 g / cc and 80.2 S / cm respectively.

[0137] [Manufacture of negative electrode and secondary battery] Using the slurry, a negative electrode and a secondary battery were manufactured in the same manner as in Example 1.

[0138] Comparative Example 3 (Silicon oxide 1, Artificial graphite 1, Natural graphite 3) [Manufacture of natural graphite 3] It was manufactured in the same manner as the method for manufacturing natural graphite 2 in Example 1, except that the natural graphite active material was a natural graphite active material formed with a carbon coating layer of 2% by weight based on the total weight of the natural graphite active material.

[0139] [Manufacture of slurry] As the negative electrode active material, except that silicon oxide 1 (refer to the manufacturing method of Example 2), natural graphite 3, and artificial graphite 1 (refer to the manufacturing method of Example 3) having the rolled density and electrical conductivity shown in Table 1 below were used in a weight ratio of 20:10:70, a slurry was manufactured in the same manner as in Example 1. Specifically, when measuring the powder resistance at the pressure of 800 kgf / cm 2 the silicon oxide 1 has a rolled density of 1.42 g / cc and an electrical conductivity of 0.122 S / cm, the natural graphite 3 has values of 1.6 g / cc and 24.5 S / cm respectively, and the artificial graphite 1 has values of 1.54 g / cc and 30.1 S / cm respectively.

[0140] [Manufacture of negative electrode and secondary battery] Using the slurry, a negative electrode and a secondary battery were manufactured in the same manner as in Example 1.

[0141] [[ID=三十二]]

Table 1

[0142] The rolling density and electrical conductivity 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 Lifetime (Capacity Retention Rate) Characteristics> Batteries were manufactured using the negative electrodes from the examples and comparative examples, respectively. 1.7671cm 2 A circularly cut lithium (Li) metal thin film was used as the positive electrode. A porous polyethylene separator was interposed between the positive electrode and the negative electrode, and an electrolyte solution containing 0.5 parts by weight of vinylene carbonate dissolved in a mixed solution of methyl ethyl carbonate (EMC) and ethylene carbonate (EC) in a volume ratio of 7:3 was injected to produce a lithium coin half-cell.

[0146] The manufactured batteries were subjected to charging and discharging tests to evaluate their discharge capacity, initial efficiency, and capacity retention rate, which are shown in Table 4 below.

[0147] The first and second cycles were charged and discharged at 0.1C, and from the third to the 299th cycle, they were charged and discharged at 0.5C. The 50th cycle ended in a charged state (lithium was in the negative electrode). 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 derived from the results of a single charge-discharge cycle. Specifically, the initial efficiency (%) was derived by the following calculation. Initial efficiency (%) = (Discharge capacity per cycle / Charge capacity per cycle) × 100 (%)

[0149] The capacity retention rates were derived using the following calculations. 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, resulting in lower initial efficiency and capacity retention characteristics. It is known that silicon-based active materials react more vigorously with the electrolyte than carbon-based active materials due to their unstable surface. When the electrical conductivity of the silicon-based active material is higher than that of artificial graphite, the reduction reaction of the electrolyte is promoted on the surface of the silicon-based active material, forming a thick film, which resulted in lower efficiency and capacity retention.

[0152] Furthermore, in Comparative Example 2, the rolling density of the artificial graphite was lower than that of the silicon-based active material, resulting in lower initial efficiency and capacity retention characteristics. Rolling density refers to the density at which the carbon-based and silicon-based active materials exist during electrode rolling, enabling them to act as pathways for the movement of electrons and lithium. When the rolling density of the silicon-based active material was higher than that of artificial graphite, as the cycle progressed, the silicon-based active material underwent a drastic volume change, creating larger voids and resulting in inferior capacity retention characteristics. In Comparative Example 3, the electrical conductivity of the natural graphite was lower than that of artificial graphite, also resulting in lower initial efficiency and capacity retention characteristics. In contrast, Examples 1 to 7 showed high initial efficiency and capacity retention by using active materials that satisfied the relationship between rolling density and electrical conductivity of the present invention.

[0153] In particular, in Examples 1-3, the electrical conductivity of artificial graphite was 10 times that of silicon-based active materials.2 The natural graphite was more than twice as large compared to the aforementioned material, and the rolled density of the artificial graphite was more than 1.1 times greater than that of the silicon-based active material, while that of the natural graphite was more than 1.01 times greater than that of the artificial graphite, demonstrating superior initial efficiency and capacity retention.

Claims

1. The negative electrode active material includes a silicon-based active material containing 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 / cm² ２ A negative electrode composition in which, when measuring powder resistance at a given pressure, the rolled 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 that of the silicon-based active material. ２ The negative electrode composition according to claim 1, wherein the natural graphite is more than 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. The negative electrode composition according to claim 1, wherein the electrical conductivity is 50 to 10,000 S / cm for the natural graphite, 15 to 2,000 S / cm for the artificial graphite, 0.0001 to 2 S / cm for the silicon-carbon composite, and 0.001 to 1 S / cm for the silicon oxide.

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

6. The anode composition according to claim 1, wherein the anode composition comprises a single-walled carbon nanotube 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 in an amount of 45 to 99 parts by weight; and the single-walled carbon nanotube in an amount of 0.01 to 3 parts by weight. The negative electrode composition according to claim 6, wherein, based on 100 parts by weight of the carbon-based active material, 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.

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

9. The negative electrode composition according to claim 1, wherein the silicon-based active material includes a carbon layer on its surface.

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

11. A lithium secondary battery comprising the negative electrode, positive electrode, and separator described in claim 10.

12. A battery module comprising the lithium secondary battery described in claim 11.

13. A battery pack comprising the lithium secondary battery described in claim 11.

14. A battery pack comprising the battery module described in claim 12.

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