Negative electrode composition, negative electrode and lithium secondary battery

Abstract

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

Description

Technology Field

[0001] The present application relates to a cathode composition, a cathode, 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 all contents disclosed in the document of said Korean patent application are incorporated into this specification. Background Technology

[0003] Recently, accompanied by the rapid proliferation of battery-powered electronic devices such as mobile phones, laptop computers, electric vehicles, power tools, and vacuum cleaners, the demand for rechargeable batteries that are small and lightweight yet possess relatively high capacity and / or high output is rapidly increasing. In particular, lithium-ion batteries are gaining prominence as power sources for electronic devices due to their lightweight nature and high energy density. Accordingly, active research and development efforts are underway to improve the performance of lithium-ion batteries.

[0004] Generally, a lithium secondary battery comprises a positive electrode, a negative electrode, a separator interposed between the positive and negative electrodes, an electrolyte, an organic solvent, etc. Additionally, an active material layer comprising a positive active material and a negative active material, respectively, may be formed on a current collector at the positive and negative electrodes. Generally, lithium-containing metal oxides such as LiCoO2 and LiMn2O4 are used as the positive active material for the positive electrode, and carbon-based or silicon-based active materials that do not contain lithium are used as the negative active material for the negative electrode.

[0005] Among negative electrode active materials, silicon-based active materials are attracting attention for possessing higher capacity and excellent fast charging characteristics compared to carbon-based active materials. However, silicon-based active materials have the disadvantage of low initial efficiency due to significant volume expansion / contraction during charging and discharging, as well as large irreversible capacity. Consequently, silicon-based active materials have the disadvantage of degrading battery performance compared to carbon-based active materials.

[0006] Accordingly, the development of anode materials capable of improving the performance of lithium-ion batteries is required. The problem to be solved

[0007] 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 same. means of solving the problem

[0008] One embodiment of the present invention comprises a negative electrode active material comprising a silicon-based active material comprising at least one of a silicon-carbon composite and silicon oxide, and a carbon-based active material, wherein the carbon-based active material comprises natural graphite and artificial graphite, and a pressure of 800 kgf / cm² 2 When measuring powder resistance, 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. A cathode composition is provided.

[0009] In addition, according to one embodiment of the present invention, the cathode composition of the above embodiment comprises single-walled carbon nanotubes as a conductive material.

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

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

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

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

[0014] One embodiment of the present invention provides a battery pack comprising a battery module according to the above embodiment. 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 a silicon-based active material and a carbon-based active material having different rolling densities and different electrical conductivity as a negative electrode active material. In particular, the cycle characteristics and resistance of a lithium secondary battery can be improved by mixing two types of carbon-based active materials that have different rolling densities and electrical conductivity and have higher rolling density and electrical conductivity at the same pressure compared to the silicon-based active material. Specific details for implementing the invention

[0016] Hereinafter, the present invention will be described in more detail to aid in understanding the invention. The present invention may be embodied in various different forms and is not limited to the embodiments described herein. In this case, terms or words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the present invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0017] In this specification, terms such as “comprising,” “comprising,” or “having” are intended to specify the existence of the implemented features, numbers, steps, components, or combinations thereof, and should be understood as not excluding in advance the existence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0018] Furthermore, when it is said that a part, such as a layer, is "above" or "on" another part, this includes not only the case where it is "directly above" the other part, but also the case where there is another part in between. Conversely, when it is said that a part is "directly above" another part, it means that there is no other part in between. Also, saying that a part is "above" or "on" a reference part means that it is located above or below the reference part, and it does not necessarily mean that it is located "above" or "on" facing the opposite direction of gravity.

[0019] Terms or words used in this specification should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0020] The singular expressions of terms used in this specification include the plural expressions unless the context clearly indicates otherwise.

[0021] In this specification, rolling density refers to the degree of deformation and compression of particles that occurs when a certain pressure is applied to a negative electrode active material, and may be expressed in g / cc. Rolling density can be derived by measuring powder resistance; for example, by introducing a certain amount of negative electrode active material into a cylinder-type load cell and 400 kgf / cm² 2 Up to 2,000 kgf / cm² 2 It can be measured through the change in thickness of the cathode active material introduced by applying pressure of any one of the following.

[0022] In this specification, electrical conductivity refers to the intrinsic electrical conductivity of the negative electrode active material powder. Electrical conductivity can be derived by measuring powder resistance, for example, 400 kgf / cm² 2 Up to 2,000 kgf / cm² 2By applying pressure to either one, the surface resistance according to the pressure change is measured, and simultaneously, the surface resistance and resistivity are measured through the measured volume and mass, and can be derived through the measured surface resistance and resistivity values.

[0023] Excessively high force when measuring powder resistance, e.g., 2000 kgf / cm² 2 Considering the impact of particle deformation that may occur when pressed with excessive pressure, the above range, preferably 800 kgf / cm² 2 It is desirable to use the rolling density value and electrical conductivity value derived by measuring the resistance of the powder with applied pressure.

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

[0025] A cathode composition according to one embodiment of the present invention comprises a silicon-based active material comprising at least one of a silicon-carbon composite and silicon oxide, and a cathode active material comprising a carbon-based active material, wherein the carbon-based active material comprises natural graphite and artificial graphite. Here, the cathode composition is subjected to a pressure of 800 kgf / cm² 2 When measuring powder resistance, 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, together with a silicon-based active material, a pressure of 800 kgf / cm² compared to the silicon-based active material 2 When measuring powder resistance, the cycle characteristics and resistance of lithium-ion batteries can be improved by including carbon-based active materials with high rolling density and electrical conductivity. In addition, as a carbon-based active material, artificial graphite at a pressure of 800 kgf / cm² 2When measuring powder resistance, the performance of lithium secondary batteries can be improved by using a mixture of natural graphite, which has relatively high rolling density and electrical conductivity. By mixing and using a negative electrode active material with relatively high electrical conductivity, charging and discharging can be easier than with lithium due to the high electrical conductivity, even though surface delamination between the negative electrode active material and the conductive material occurs due to volume changes during charging and discharging. Consequently, the characteristics of a long-life battery can be realized. Meanwhile, in the case of an active material with a relatively high rolling density, volume changes during charging and discharging can be physically controlled, which can be advantageous for cycle performance.

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

[0028] Specifically, while increasing rolling density generally leads to higher conductivity due to an increase in inter-grain contact surfaces, grain breakage can have a negative effect on electrical conductivity; therefore, rolling density and electrical conductivity must exhibit the same trend.

[0029] If they do not have the same tendency, effects caused by particle breakage may occur, which can adversely affect battery performance.

[0030] In addition, if artificial graphite has a higher rolling density and electrical conductivity than natural graphite, the degree of graphitization of the artificial graphite increases, which may lead to a deterioration in battery performance.

[0031] Unless otherwise noted, electrical conductivity in this specification refers to the electrical conductivity of each material in its particle state, e.g., before fracture occurs, and does not refer to the electrical conductivity after the particles have fractured.

[0032] According to one embodiment, the pressure is 800 kgf / cm² 2 When measuring powder resistance, the rolling density of the artificial graphite is at least 1.1 times greater than that of the silicon-based active material, and the natural graphite is at least 1.01 times greater than that of the artificial graphite.

[0033] For example, the above pressure of 800 kgf / cm² 2 When measuring powder resistance, the rolled density may be 1.4 to 2.5 g / cc for natural graphite, e.g. 1.6 to 1.7 g / cc; 1.0 to 2.2 g / cc for artificial graphite, e.g. 1.5 to 1.6 g / cc; and 0.5 to 1.8 g / cc for silicon-based active material. Specifically, a pressure of 800 kgf / cm² 2 When measuring powder resistance, the rolled density of the silicon carbon composite may be 0.5 to 1.2 g / cc, for example 0.8 to 1.0 g / cc, and the rolled density of the silicon oxide may be 0.8 to 1.8 g / cc, for example 1.4 to 1.5 g / cc.

[0034] According to one embodiment, the pressure is 800 kgf / cm² 2 When measuring powder resistance, the electrical conductivity of the artificial graphite is more than 100 times greater than that of the silicon-based active material, and the natural graphite is more than 2 times greater than that of the artificial graphite.

[0035] For example, a pressure of 800 kgf / cm² 2When measuring powder resistance, the electrical conductivity may be such that the silicon-based active material is 0.0001 to 2 S / cm, the artificial graphite is 15 to 2,000 S / cm, e.g., 15 to 100 S / cm, and the natural graphite is 50 to 10,000 S / cm, e.g., 100 to 1,000 S / cm, or 100 to 500 S / cm. Pressure 800 kgf / cm 2 When measuring the resistance of the powder, 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 cathode 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 is included in an amount of 0.01 to 3 parts by weight, and based on 100 parts by weight of the carbon-based active material, the natural graphite is included in an amount of 10 to 70 parts by weight; and the artificial graphite is included in an amount of 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, for example 1 to 20 parts by weight, based on a total of 100 parts by weight of the negative electrode active material included 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 cathode active material included in the cathode composition. The weight ratio of the artificial graphite and 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 denoted as SiC. Since the silicon carbide does not electrochemically react with lithium, all performance characteristics, such as lifespan, can be measured as zero.

[0042] The above 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 on a porous silicon structure. The above silicon carbon composite may be a composite of silicon and graphite, etc. In the above silicon carbon composite, the silicon may be nano-silicon.

[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 has a surface area of ​​0.5 to 10 m² by the BET method. 2 It can be / g, and the pore volume is 0.005 to 0.03 cm³ 3 It may be / g, and the pore size determined by the BET method may be 10 to 20 nm. The silicon-carbon composite has a pore volume measured by the mercury infiltration method of 0.005 to 0.03 cm³. 3 / g can be.

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

[0046] According to one embodiment, the silicon carbon composite can 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 can 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 oxygen can be controlled to 0.1 to 10 L / min.

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

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

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

[0051] The silicon nanoparticles mentioned above may be crystalline, semicrystalline, amorphous, or a combination thereof.

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

[0053] The above SiO x The active material containing (0≤x<2) is SiO x (0 <x<2) 및 기공을 포함하는 실리콘 산화물 입자일 수 있다.

[0054] The above SiO x (0 <x<2)는 상기 실리콘 산화물 입자 내에서 매트릭스(matrix)에 해당한다. 상기 SiO x (0 <x<2)는 Si 및 SiO2가 포함된 형태일 수 있으며, 상기 Si는 상(phase)을 이루고 있을 수도 있다. 즉, 상기 x는 상기 SiO x (0 <x<2) 내에 포함된 Si에 대한 O의 개수비에 해당한다. 상기 실리콘 산화물 입자가 상기 SiO x (0 <x<2)를 포함하는 경우, 이차 전지의 방전 용량이 개선될 수 있다.

[0055] The silicon oxide particles may further include at least one of an 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 above Mg compound and / or Li compound is the above SiO x(0 <x<2)의 내부 및 / 또는 표면에 존재할 수 있다. 상기 Mg 화합물 및 / 또는 Li 화합물에 의해 전지의 초기 효율이 개선될 수 있다.

[0057] The above 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.

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

[0059] The above 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.

[0060] In one embodiment of the present invention, the Li compound may include a lithium silicate form. The lithium silicate is Li a Si b O c(2≤a≤4, 0 <b≤2, 2≤c≤5)로 표시되며, 결정질 리튬 실리케이트와 비정질 리튬 실리케이트로 구분될 수 있다. 상기 결정질 리튬 실리케이트는 상기 실리콘 산화물 입자 내에서 Li2SiO3, Li4SiO4및 Li2Si2O5로 이루어진 군에서 선택된 적어도 1종의 리튬 실리케이트의 형태로 존재할 수 있으며, 비정질 리튬 실리케이트는 Li a Si b O c (2≤a≤4, 0 <b≤2, 2≤c≤5)의 형태일 수 있고, 상기 형태에 한정되지는 않는다.

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

[0062] The content of the Mg or Li elements can be confirmed through ICP analysis. For the ICP analysis, a specific amount (approx. 0.01 g) of the cathode active material is accurately aliquoted, transferred to a platinum crucible, and completely decomposed on a hot plate by adding nitric acid, hydrofluoric acid, and sulfuric acid. Subsequently, a reference calibration curve is constructed by measuring the intensity of a standard solution (5 mg / kg) prepared using an inductively

[0063] In one embodiment of the present specification, a carbon layer may be provided on the surface and / or inside the pores of the silicon oxide particles. By the carbon layer, conductivity is imparted to the silicon oxide particles, and the initial efficiency, lifespan characteristics, and battery capacity characteristics of a secondary battery including a negative electrode active material containing the silicon oxide particles may be improved. The total weight of the carbon layer may be included in an amount of 5% to 40% by weight based on 100% by weight of the total silicon oxide particles.

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

[0065] Average particle size (D) of the above silicon-based active material 50The particle size 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 satisfied, structural stability of the active material during charging and discharging is ensured, the problem of volume expansion / contraction increasing as the particle size becomes excessively large is prevented, and the problem of initial efficiency decreasing due to the particle size becoming excessively low is prevented.

[0066] In this specification, the average particle size (D 50 ) can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve. The above average particle size (D 50 ) can be measured, for example, using the laser diffraction method. The laser diffraction method generally enables the measurement of particle sizes ranging from the submicron range to several millimeters, and can obtain results with high reproducibility and high resolution. The specific surface area of ​​the silicon-based active material is 2 to 10 m² 2 It may 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 comprises natural graphite and artificial graphite. Natural graphite and artificial graphite each have an average particle size (D 50 ) is 10 to 30 µm, and the BET specific surface area is 0.5 to 2 m 2 It may be / g. The above natural graphite refers to graphite that occurs naturally, and examples include scaled graphite, scalely graphite, or soil graphite. The above natural graphite has the advantages of being abundant, having a low price, high theoretical capacity and compaction density, and the ability to realize high output.

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

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

[0070] [Mathematical Formula 1]

[0071] Sphericity = Circumference of a circle with the same area as the projected image / Perimeter of the projected image

[0072] The above natural graphite can be applied by selecting those that satisfy the degree of sphericity through a method of confirming the particle shape using SEM and confirming it using a particle shape analyzer.

[0073] According to one example, the artificial graphite may have a degree of sphericity of 0.9 or less.

[0074] The above artificial graphite can be applied by selecting one that satisfies the degree of sphericity through a method of confirming the particle shape using SEM and confirming it using a particle shape analyzer.

[0075] According to one embodiment of the present invention, the cathode composition comprises single-walled carbon nanotubes (SWCNT) as a conductive material.

[0076] The above single-walled carbon nanotube (SWCNT) refers to a tube-shaped carbon structure composed of a single layer of carbon. When the conductive material in the above-mentioned cathode composition includes the above-mentioned single-walled carbon nanotube (SWCNT), the charge / discharge capacity and / or lifespan performance of the battery may be improved. Specifically, since the above-mentioned single-walled carbon nanotube (SWCNT) effectively connects the conductive paths between particles, it can prevent the loss of conductive paths due to swelling of the aforementioned silicon-based active material. Consequently, when the above-mentioned single-walled carbon nanotube (SWCNT) is included, the lifespan performance of the battery may be improved.

[0077] In this specification, the length of a carbon nanotube refers to the length of the major axis passing through the center of the carbon nanotube unit, and the diameter of a carbon nanotube refers to the length of the minor axis passing through the center of the unit and perpendicular to the major axis.

[0078] The average length of the single-walled carbon nanotube (SWCNT) may be 0.1 μm to 50 μm, specifically 0.5 μm to 25 μm or 0.5 μm to 20 μm. More specifically, it may be 5 μm to 15 μm. The average length of the single-walled carbon nanotube (SWCNT) can be calculated as the average value of the results observed with an SEM.

[0079] When single-walled carbon nanotubes (SWCNTs) are used together with the aforementioned silicon-based active material and carbon-based active material, the length of the carbon nanotubes is secured to be equal to the distance between the anode active material particles, thereby facilitating the connection of conductive paths between particles and improving the electrical conductivity, strength, and / or electrolyte retention of the anode.

[0080] 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, it may be 1.5 nm to 5 nm. Since the single-walled carbon nanotube (SWCNT) having such an average diameter has flexible characteristics, it has the effect of preventing the contact between the cathode active material particles from easily breaking even when physically damaged. The average diameter of the single-walled carbon nanotube (SWCNT) can be calculated as an average value observed by TEM.

[0081] The BET specific surface area of ​​the above single-walled carbon nanotube is 200 m² 2 / g to 2,000 m 2 It can be / g, specifically 250 m 2 / g to 1,500 m 2 It can be / g. When using single-walled carbon nanotubes (SWCNTs) satisfying the above range, dispersion is easy even with a small amount of conductive material, which has the effect of effectively connecting the particles.

[0082] The above 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 cathode composition, specifically in an amount 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 while minimizing side reactions in the electrolyte due to the high specific surface area.

[0083] 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 instrument (BEL-SORP-mini, Nippon Bell) on the subject to measurement, degassing at 130°C for 2 hours, and performing N2 absorption / desorption at 77K.

[0084] According to one embodiment, the cathode composition further comprises a binder.

[0085] The binder may comprise at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, 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 materials in which the hydrogens thereof are substituted with Li, Na, or Ca, etc., and may also comprise various copolymers thereof.

[0086] One embodiment of the present invention provides a cathode comprising a cathode composition according to the embodiments described above.

[0087] Specifically, the cathode may include a cathode current collector and a cathode active material layer disposed on the cathode current collector. The cathode active material layer comprises a cathode composition according to the aforementioned embodiment.

[0088] The above-described cathode active material layer can be formed by applying a cathode slurry containing the aforementioned cathode composition to at least one surface of a cathode current collector, and then drying and rolling it.

[0089] The above-mentioned negative current collector may be conductive without causing chemical changes in the battery, and is not particularly limited. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used as the current collector. Specifically, transition metals that adsorb carbon well, such as copper and nickel, may be used as the current collector. The thickness of the above-mentioned current collector may be 6 μm to 20 μm, but the thickness of the above-mentioned current collector is not limited thereto.

[0090] If necessary, additional conductive materials other than the aforementioned single-walled carbon nanotubes may be included. The additional conductive materials are not particularly limited as long as they are conductive without causing chemical changes in the battery, and examples may be used, such as graphite, such as natural graphite or artificial graphite; carbon black, such as acetylene black, ketjen black, channel black, Farnes black, lamp black, thermal black; conductive fibers, such as carbon fibers or metal fibers; conductive tubes, such as carbon nanotubes; metal powders, such as fluorocarbon, aluminum, or nickel powder; conductive whiskers, such as zinc oxide or potassium titanate; conductive metal oxides, such as titanium oxide; and conductive materials, such as polyphenylene derivatives.

[0091] The above cathode slurry may include a solvent for forming the cathode slurry. Specifically, the solvent for forming the cathode slurry may include 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.

[0092] One embodiment of the present invention provides a lithium secondary battery comprising a negative electrode, a positive electrode, and a separator according to the above embodiment.

[0093] The above positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and comprising the positive electrode active material.

[0094] In the above-mentioned positive electrode, the positive electrode current collector is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the above-mentioned positive electrode current collector may typically have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase the adhesion of the positive electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0095] The above-mentioned positive electrode active material may be a commonly used positive electrode active material. Specifically, the above-mentioned 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, etc.; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7, etc.; chemical formula LiNi 1-c2 M c2 Ni-site type lithium nickel oxide represented by O2 (wherein 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 c3Examples include lithium manganese composite oxides represented by O2 (wherein 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 (wherein M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); and LiMn2O4 in which part of the Li of the chemical formula is substituted with alkaline earth metal ions, but are not limited thereto. The anode may also be Li-metal.

[0096] The above-described positive active material layer may include a positive conductive material and a positive binder together with the positive active material described above.

[0097] At this time, the positive electrode conductive material is used to impart conductivity to the electrode, and in the battery being constructed, any material that has electronic conductivity without causing chemical changes can be used without special limitations. 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 powder or metal fiber such as copper, nickel, aluminum, or silver; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxide such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more may be used.

[0098] In addition, the anode binder serves to improve adhesion between anode active material particles and adhesion between the anode active material and the anode 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.

[0099] As a separator, it separates the negative and positive electrodes and provides a pathway for the movement of lithium ions. Any separator typically used in secondary batteries can be used without special restrictions, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte wettability. Specifically, a porous polymer film, such as a porous polymer film made from a polyolefin-based polymer like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and it may optionally be used in a single-layer or multi-layer structure.

[0100] The above lithium secondary battery may additionally include an electrolyte. Examples of the above electrolytes that can be used in the manufacture of lithium secondary batteries include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., but are not limited to these.

[0101] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0102] As the above-mentioned 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, gamma-butyl lactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolone, formamide, dimethylformamide, dioxolone, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolone derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, ethyl propionate, etc. may be used.

[0103] In particular, among the above carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents with high dielectric constants that effectively dissociate lithium salts, so they can be used preferably. Furthermore, if low-viscosity, low-dielectric constant linear carbonates such as dimethyl carbonate and diethyl carbonate are mixed with these cyclic carbonates in appropriate proportions, an electrolyte with high electrical conductivity can be produced, making it even more preferable to use.

[0104] The metal salt mentioned above may be a lithium salt, and the lithium salt is a substance that dissolves well 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 - One or more types selected from the group consisting of can be used.

[0105] In addition to the above electrolyte components, the above electrolyte may further include one or more additives for the purpose of improving the lifespan characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery, such as, for example, a haloalkylene carbonate-based compound such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, triamide hexaphosphate, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride.

[0106] According to another embodiment of the present invention, a battery module comprising the secondary battery as a unit cell and a battery pack comprising the same are provided.

[0107] According to another embodiment of the present invention, a battery pack comprising the secondary battery is provided. Since the battery module and the battery pack include the secondary battery having high capacity, high rate capability and cycle capability, they can be used as a power source for a medium-to-large device selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles and power storage systems.

[0108] Hereinafter, to specifically explain this specification, examples will be described in detail. However, the embodiments according to this specification may be modified in various different forms, and the scope of this application is not to be interpreted as being limited to the embodiments described below. The embodiments of this application are provided to more completely explain this specification to those with average knowledge in the art.

[0109] Example 1 (Silicon carbon composite 1, artificial graphite 2, natural graphite 2)

[0110] [Manufacturing of Silicon Carbon Composite 1]

[0111] Cellulose powder was placed in a tubular furnace and heated to 400°C at a rate of 4°C / min, then heated under a nitrogen atmosphere for 2 hours. Subsequently, the furnace was heated to 900°C at a rate of 4°C / min, then heated under a nitrogen atmosphere for 2 hours. The powder was mixed with sulfuric acid and nitric acid in a 3:1 volume ratio, stirred at 60°C for 2 hours, and then centrifuged to obtain a precipitate. The obtained powder was washed 5 times in a solvent mixed with ethanol and distilled water in a 1:3 volume ratio, and then dried at 120°C for 12 hours. The carbon-based particles were placed in a KOH solvent and heated at 800°C under a nitrogen atmosphere for 2 hours to obtain a porous carbon structure. The porous carbon structure was washed 3 times with distilled water and then dried at 120°C for at least 12 hours. The above porous carbon structure was placed in a horizontal furnace, and a silicon carbon composite was prepared by flowing SiH4 / He = 5 / 95 gas at a flow rate of 50 ml / min at 700°C for 1 hour. Subsequently, the silicon carbon composite was placed in a furnace, and methane was flowed at 700°C for 2 hours to produce a silicon carbon composite 1 containing a carbon layer on its surface.

[0112] [Manufacture of Artificial Graphite 2]

[0113] A petroleum-based pitch binder was introduced into a reactor with green coke particles and calcined coke particles. The green coke and calcined coke particles were mixed in a weight ratio of 30:70. The pitch binder was mixed at 7% by weight based on the total weight of the green coke particles, calcined coke particles, and petroleum-based pitch. Artificial graphite particles in the form of secondary particles, in which primary particles are bonded, were manufactured by graphitizing the mixture of the green coke particles, calcined coke particles, and petroleum-based pitch through heat treatment at 3000°C for 50 hours. Artificial graphite 2 was manufactured by mixing the artificial graphite in the form of secondary particles with petroleum-based pitch and heat-treating it at 1250°C in a roller hearth kiln to form an amorphous carbon coating layer on the surface of the artificial graphite particles. The D50 of the final synthetic graphite 2 was controlled to the 16μm level.

[0114] [Manufacture of Natural Graphite 2]

[0115] Natural graphite raw material was extracted from graphite ore through flotation. To remove impurities from the natural graphite, it was treated with an acid or a base, and then 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, pressed using the cold isostatic pressing (CIP) method, and then crushed. During the pressing process, the pressing pressure was 90 MPa and the pressing time was 15 minutes. The pressed spherical natural graphite was mixed with pitch, and the mixture was heat-treated in a dry manner at 1,300°C for 24 hours in an inert atmosphere 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 relative to the total weight of the natural graphite active material.

[0116] [Manufacturing of Slurry]

[0117] As the negative electrode active material, silicon carbon composite 1, natural graphite 2, and artificial graphite 2, having the rolled density and electrical conductivity of Table 1 below, were used in a weight ratio of 15:15:70. Specifically, silicon carbon composite 1 was used at a pressure of 800 kgf / cm² 2 When measuring powder resistance, the rolled density was 0.859 g / cc and the electrical conductivity was 0.664 S / cm, respectively, and the natural graphite 2 had values ​​of 1.6 g / cc and 337 S / cm, respectively, and the artificial graphite 2 had values ​​of 1.58 g / cc and 96.6 S / cm, respectively. A cathode slurry was prepared by mixing a cathode active material, a conductive material (carbon black, single-walled carbon nanotube (SWCNT)), and a binder (CMC (Carboxymethyl cellulose), SBR (Styrene-Butadiene Rubber)) in a weight ratio of 95.3:1:3.7.

[0118] [Manufacturing of the cathode]

[0119] The above cathode slurry was applied to a Cu metal thin film with a thickness of approximately 20 μm and dried at a circulating air temperature of 60°C. Subsequently, after rolling, it was dried in a vacuum oven at 130°C for about a day, and then 1.4875 cm 2 The cathode was manufactured by stamping it into a circular shape.

[0120] [Manufacturing of secondary batteries]

[0121] 1.7671cm 2 A Li metal thin film formed by stamping was used as the anode. A porous polyethylene separator was placed between the anode and the cathode, and an electrolyte containing 1M concentration of dissolved LiPF6 containing an additive of a mixed solution with a mixing ratio of EC (ethylene carbonate) and EMC (methyl ethyl carbonate) of 3:7 was injected to manufacture a Li coin half-cell.

[0122] Example 2 (silicon oxide 1, synthetic graphite 2, natural graphite 2)

[0123] [Preparation of Silicon Oxide 1]

[0124] SiO mixed with 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 evaporated separately by applying heat at 800°C. The crucibles were all depressurized to a level of 0.1 torr, after which the raw materials were evaporated. The mixture in a vapor state containing Mg was reacted for 6 hours and then condensed into a solid state in a vacuum region at 800°C. The silicon-based active material prepared by the above method was ground using a ball mill for about 3 to 4 hours. Subsequently, methane (CH4) was reacted at a rate of 1 L / min at 0.1 torr for about 5 hours using a CVD device under an Ar inert gas atmosphere 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 D50 of the final active material was controlled to a level of 6 μm.

[0125] [Manufacturing of Slurry]

[0126] A slurry was prepared in the same manner as in Example 1, except that silicon oxide 1, natural graphite 2 (refer to the manufacturing method of Example 1), and artificial graphite 2 (refer to the manufacturing method of Example 1), having the rolling density and electrical conductivity of Table 1 below, were used as the negative electrode active material in a weight ratio of 20:10:70. Specifically, the silicon oxide 1 was subjected to a pressure of 800 kgf / cm² 2 When measuring powder resistance, the rolled density is 1.42 g / cc and the electrical conductivity is 0.122 S / cm, the natural graphite 2 has values ​​of 1.6 g / cc and 337 S / cm, respectively, and the artificial graphite 2 has values ​​of 1.58 g / cc and 96.6 S / cm, respectively.

[0127] [Manufacturing of Cathodes and Secondary Batteries]

[0128] Using the above slurry, a negative electrode and a secondary battery were manufactured in the same manner as in Example 1.

[0129] Example 3 (silicon carbon composite 2, artificial graphite 1, natural graphite 1)

[0130] [Manufacturing of Silicon Carbon Composite 2]

[0131] An oxide layer was formed on the silicon carbon composite by heat treating it at 700°C for 2 hours under an O2 / Ar = 5 / 95 atmosphere. 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 with methane flowing at 700°C for 2 hours to form a carbon layer on the surface.

[0132] [Manufacture of Artificial Graphite 1]

[0133] The pitch binder was mixed at 4.5% by weight based on the total weight of green coke particles, calcined coke particles, and petroleum-based pitch. An artificial graphite active material was prepared in the same manner as artificial graphite 2 of Example 1, except that artificial graphite in the form of secondary particles 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.

[0134] [Manufacture of Natural Graphite 1]

[0135] A natural graphite active material was prepared in the same manner as natural graphite 2 of Example 1, except that pressurized spherical natural graphite and pitch were mixed, and the mixture was heat-treated in a dry manner at 1,100°C for 24 hours in an inert atmosphere to form an amorphous carbon coating layer.

[0136] [Manufacturing of Slurry]

[0137] 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 of 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 was subjected to a pressure of 800 kgf / cm² 2 When measuring powder resistance, the composition has a rolled density of 0.914 g / cc and an electrical conductivity of 0.00025 S / cm, and the natural graphite 1 has values ​​of 1.61 g / cc and 149 S / cm, and the artificial graphite 1 has values ​​of 1.54 g / cc and 30.1 S / cm.

[0138] [Manufacturing of Cathodes and Secondary Batteries]

[0139] Using the above slurry, a negative electrode and a secondary battery were manufactured in the same manner as in Example 1.

[0140] Example 4 (Silicon carbon composite 1, artificial graphite 1, natural graphite 2)

[0141] [Manufacturing of Slurry]

[0142] A slurry was prepared in the same manner as in Example 1, except that silicon carbon composite 1 (refer to the manufacturing method of Example 1), natural graphite 2 (refer to the manufacturing method of Example 1), and artificial graphite 1 (refer to the manufacturing method of Example 3), having the rolling density and electrical conductivity of Table 1 below, were used as the negative electrode active material in a weight ratio of 15:15:70. Specifically, the silicon carbon composite 1 was subjected to a pressure of 800 kgf / cm² 2 When measuring powder resistance, the composition has a rolled 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, and the artificial graphite 1 has values ​​of 1.54 g / cc and 30.1 S / cm.

[0143] [Manufacturing of Cathodes and Secondary Batteries]

[0144] Using the above slurry, a negative electrode and a secondary battery were manufactured.

[0145] Example 5 (silicon oxide 1, synthetic graphite 1, natural graphite 2)

[0146] [Manufacturing of Slurry]

[0147] A slurry was prepared in the same manner as in Example 1, except that silicon oxide 1 (refer to the manufacturing method of Example 2), natural graphite 2 (refer to the manufacturing method of Example 1), and artificial graphite 1 (refer to the manufacturing method of Example 3), having the rolling density and electrical conductivity of Table 1 below, were used as the negative electrode active material in a weight ratio of 20:10:70. Specifically, the silicon oxide active material was subjected to a pressure of 800 kgf / cm² 2 When measuring powder resistance, the composition has a rolled density of 1.42 g / cc and an electrical conductivity of 0.122 S / cm, the natural graphite 2 has values ​​of 1.6 g / cc and 337 S / cm, and the artificial graphite 1 has values ​​of 1.54 g / cc and 30.1 S / cm.

[0148] [Manufacturing of the cathode]

[0149] Using the above slurry, a negative electrode and a secondary battery were manufactured in the same manner as in Example 1.

[0150] Example 6 (silicon oxide 1, synthetic graphite 2, natural graphite 1)

[0151] [Manufacturing of Slurry]

[0152] A slurry was prepared in the same manner as in Example 1, except that silicon oxide 1 (refer to the manufacturing method of Example 2), natural graphite 1 (refer to the manufacturing method of Example 3), and artificial graphite 2 (refer to the manufacturing method of Example 1), having the rolling density and electrical conductivity of Table 1 below, were used as the negative electrode active material in a weight ratio of 20:10:70. The silicon oxide active material was subjected to a pressure of 800 kgf / cm² 2When measuring powder resistance, the composition has a rolled density of 1.42 g / cc and an electrical conductivity of 0.122 S / cm, and the natural graphite 1 has values ​​of 1.61 g / cc and 149 S / cm, and the artificial graphite 2 has values ​​of 1.58 g / cc and 96.6 S / cm.

[0153] [Manufacturing of Cathodes and Secondary Batteries]

[0154] Using the above slurry, a negative electrode and a secondary battery were manufactured in the same manner as in Example 1.

[0155] Example 7 (silicon oxide 1, synthetic graphite 2, natural graphite 2)

[0156] [Manufacturing of Slurry]

[0157] A slurry was prepared in the same manner as in Example 1, except that silicon oxide 1 (refer to the manufacturing method of Example 2), natural graphite 2 (refer to the manufacturing method of Example 1), and artificial graphite 2 (refer to the manufacturing method of Example 1), having the rolling density and electrical conductivity of Table 1 below, were used as the negative electrode active material in a weight ratio of 20:10:70. The silicon oxide active material was subjected to a pressure of 800 kgf / cm² 2 When measuring powder resistance, the rolled density was 1.42 g / cc and the electrical conductivity was 0.122 S / cm. Natural graphite 1 had values ​​of 1.61 g / cc and 149 S / cm, respectively, and artificial graphite 2 had values ​​of 1.58 g / cc and 96.6 S / cm, respectively. A cathode slurry was prepared by mixing a cathode 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.

[0158] [Manufacturing of Cathodes and Secondary Batteries]

[0159] Using the above slurry, a negative electrode and a secondary battery were manufactured in the same manner as in Example 1.

[0160] Comparative Example 1 (silicon carbon composite 3, artificial graphite 3, natural graphite 2)

[0161] [Manufacturing of Silicon Carbon Composite 3]

[0162] Carbon-based particles prepared by the method for preparing a silicon carbon composite specified in Example 1 were subjected to a SiH4 / He = 5 / 95 gas flow rate of 50 ml / min at 700°C for 1 hour to prepare a silicon carbon composite, after which the silicon carbon composite was placed in a solvent mixed with phosphoric acid and ethanol in a 10:90 volume ratio. The silicon carbon composite dispersed in the solvent was heated at 1000°C for 4 hours under an argon atmosphere to obtain a final phosphorus (P)-doped silicon carbon composite. Subsequently, the phosphorus-doped silicon carbon composite was placed in an electric furnace and reacted by flowing methane at 700°C for 2 hours to prepare a phosphorus-doped silicon carbon composite negative electrode active material containing a carbon layer on its surface.

[0163] [Manufacture of Artificial Graphite 3]

[0164] Artificial graphite particles of secondary particles were prepared by graphitizing a mixture of green coke particles, calcined coke particles, and petroleum pitch through heat treatment at 3000°C for 50 hours, and then artificial graphite 3 was prepared in the same manner as the method for preparing artificial graphite 2 of Example 1, except that the artificial graphite particles were heat-treated in a hot zone under an O2 / Ar = 5 / 95 atmosphere at 800°C for 2 hours to partially oxidize them.

[0165] [Manufacturing of Slurry]

[0166] A slurry was prepared in the same manner as in Example 1, except that silicon carbon composite 3 having the rolling density and electrical conductivity of Table 1 below, natural graphite 2 (refer to the manufacturing method of Example 1), and artificial graphite 3 were used as the negative electrode active material in a weight ratio of 20:10:70. Specifically, the silicon carbon composite 3 was subjected to a pressure of 800 kgf / cm² 2When measuring powder resistance, the composition has a rolled 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, and the artificial graphite 3 has values ​​of 1.56 g / cc and 5.8 S / cm.

[0167] [Manufacturing of Cathodes and Secondary Batteries]

[0168] Using the above slurry, a negative electrode and a secondary battery were manufactured in the same manner as in Example 1.

[0169] Comparative Example 2 (silicon oxide 2, artificial graphite 4, natural graphite 1)

[0170] [Preparation of Silicon Oxide 2]

[0171] Silicon-based active material is ground using a ball mill for about 5 to 6 hours, and D 50 Silicon oxide 2 was prepared using the same method as silicon oxide 1 of Example 2, except that the silicon oxide was controlled to a level of 3 μm.

[0172] [Manufacture of Artificial Graphite 4]

[0173] D of the final artificial graphite active material 50 Artificial graphite 4 was prepared in the same way as artificial graphite 2 of Example 1, except that it was 29 μm.

[0174] [Manufacturing of Slurry]

[0175] A slurry was prepared in the same manner as in Example 1, except that silicon oxide 2, natural graphite 1 (refer to the manufacturing method of Example 3), and artificial graphite 4, having the rolling density and electrical conductivity of Table 1 below, were used in a weight ratio of 20:10:70 as the negative electrode active material. Specifically, the silicon oxide 2 was subjected to a pressure of 800 kgf / cm² 2When measuring powder resistance, the composition has a rolled density of 1.52 g / cc and an electrical conductivity of 0.178 S / cm, and the natural graphite 1 has values ​​of 1.61 g / cc and 149 S / cm, and the artificial graphite 4 has values ​​of 1.45 g / cc and 80.2 S / cm.

[0176] [Manufacturing of Cathodes and Secondary Batteries]

[0177] Using the above slurry, a negative electrode and a secondary battery were manufactured in the same manner as in Example 1.

[0178] Comparative Example 3 (silicon oxide 1, artificial graphite 1, natural graphite 3)

[0179] [Manufacture of Natural Graphite 3]

[0180] The natural graphite active material was prepared using the same method as the natural graphite 2 of Example 1, except that the carbon coating layer formed at 2% by weight relative to the total weight of the natural graphite active material.

[0181] [Manufacturing of Slurry]

[0182] A slurry was prepared in the same manner as in Example 1, 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 rolling density and electrical conductivity of Table 1 below, were used as the negative electrode active material in a weight ratio of 20:10:70. Specifically, the silicon oxide 1 was subjected to a pressure of 800 kgf / cm² 2 When measuring powder resistance, the composition 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, and the artificial graphite 1 has values ​​of 1.54 g / cc and 30.1 S / cm.

[0183] [Manufacturing of Cathodes and Secondary Batteries]

[0184] Using the above slurry, a negative electrode and a secondary battery were manufactured in the same manner as in Example 1.

[0185] Rolling density (g / cc) Electrical conductivity (S / cm) Natural graphite 1 1.61 149 Natural graphite 2 1.6 337 Natural graphite 3 1.6 24.5 Artificial graphite 1 1.54 30.1 Artificial graphite 2 1.58 96.6 Artificial graphite 3 1.56 5.8 Artificial graphite 4 1.45 80.2 Silicon oxide 1 1.42 0.122 Silicon oxide 2 1.52 0.178 Silicon carbon composite 1 0.859 0.664 Silicon carbon composite 2 0.914 0.00025 Silicon carbon composite 3 1.32 8.1

[0186] The rolled density and electrical conductivity of the active materials used in the examples and comparative examples are shown in Tables 2 and 3 below.

[0187] Types of active substances Rolling density (g / cc) Electrical conductivity (S / cm) Silicon-based active material Artificial graphite natural graphite Silicon-based active material Artificial graphite natural graphite Silicon-based active material Artificial graphite natural graphite Example 1 Silicon carbon composite 1 Artificial graphite 2 Natural graphite 2 0.859 1.58 1.6 0.664 96.6 337 Example 2 Silicon oxide 1 Artificial graphite 2 Natural graphite 2 1.42 1.58 1.6 0.122 96.6 337 Example 3 Silicon carbon composite 2 Artificial graphite 1 Natural graphite 1 0.914 1.54 1.61 0.00025 30.1 149 Example 4 Silicon carbon composite 1 Artificial graphite 1 Natural graphite 2 0.859 1.54 1.6 0.664 30.1 337 Example 5 Silicon oxide 1 Artificial graphite 1 Natural graphite 2 1.42 1.54 1.6 0.122 30.1 337 Example 6 Silicon oxide 1 Artificial graphite 2 Natural graphite 1 1.42 1.58 1.61 0.122 96.6 149 Example 7 Silicon oxide 1 Artificial graphite 2 Natural graphite 2 1.42 1.58 1.6 0.122 96.6 337 Comparative Example 1 Silicon carbon composite 3 Artificial graphite 3 Natural graphite 2 1.32 1.56 1.6 8.1 5.8 337 Comparative Example 2 Silicon oxide 2 Artificial graphite 4 Natural graphite 1 1.52 1.45 1.61 0.178 80.2 149 Comparative Example 3 Silicon oxide 1 Artificial graphite 1 Natural graphite 3 1.42 1.54 1.6 0.122 30.1 24.5

[0188] Rolled density ratio Electrical conductivity ratio Artificial graphite / silicon-based active material Natural graphite / synthetic graphite Artificial graphite / silicon-based active material Natural graphite / synthetic graphite Example 1 1.84 1.01 145.48 3.49 Example 2 1.11 1.01 791.80 3.49 Example 3 1.68 1.05 120,400.00 4.95 Example 4 1.79 1.04 45.33 11.20 Example 5 1.08 1.04 246.72 11.20 Example 6 1.11 1.02 791.80 1.54 Comparative Example 1 1.18 1.03 0.72 58.10 Comparative Example 2 0.95 1.11 450.56 1.86 Comparative Example 3 1.08 1.04 246.72 0.81

[0189] <Experimental Example: Evaluation of Discharge Capacity, Initial Efficiency, and Lifetime (Capacity Retention Rate) Characteristics>

[0190] A battery was manufactured using the negative electrodes of the examples and comparative examples, respectively.

[0191] A lithium (Li) metal thin film cut into a circular shape of 1.7671 cm² was used as the anode. A porous polyethylene separator was interposed between the anode and the cathode, and a lithium coin half-cell was manufactured by dissolving vinylene carbonate dissolved at 0.5 parts by weight in a mixed solution of methyl ethyl carbonate (EMC) and ethylene carbonate (EC) in a mixed volume ratio of 7:3, and injecting an electrolyte solution in which LiPF6 at a concentration of 1 M was dissolved.

[0192] Charge and discharge were performed on the manufactured batteries to evaluate the discharge capacity, initial efficiency, and capacity retention rate, and these results are listed in Table 4 below.

[0193] The first and second cycles were charged and discharged at 0.1C, and from the third cycle to the 299th cycle, they were charged and discharged at 0.5C. The 50th cycle was terminated in a charged state (where lithium is contained in the negative electrode).

[0194] Charging conditions: CC (constant current) / CV (constant voltage) (5mV / 0.005C current cut-off)

[0195] Discharge condition: CC (constant current) condition 1.5V

[0196] 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.

[0197] Initial Efficiency (%) = (Discharge Capacity / Charge Capacity) × 100 (%)

[0198] The capacity retention rates were each derived by the following calculations.

[0199] Capacity Retention Rate (%) = (299 Discharge Cycles Capacity / 1 Discharge Cycle Capacity) × 100 (%)

[0200] battery Discharge capacity (mAh / g) Initial efficiency (%) Capacity retention rate (%) Example 1 504 91.3 88.0 Example 2 504 88.1 86.5 Example 3 504 91.0 87.7 Example 4 504 90.6 85.1 Example 5 504 87.7 84.9 Example 6 504 87.6 85.5 Example 7 504 86.5 84.1 Comparative Example 1 504 86.1 80.1 Comparative Example 2 504 84.8 71.9 Comparative Example 3 504 85.6 83.6

[0201] In Comparative Example 1, the electrical conductivity of the silicon-based active material was higher than that of artificial graphite, and in this case, it exhibited low initial efficiency and capacity retention rate characteristics. It is known that silicon-based active materials react more severely 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, it promotes the reduction reaction of the electrolyte on the surface of the silicon-based active material to form a thick film, resulting in low efficiency and capacity retention rate.

[0202] In addition, in Comparative Example 2, the rolling density of the artificial graphite was lower than that of the silicon-based active material, and in this case, it exhibited low initial efficiency and capacity retention characteristics. Rolling density refers to the density at which carbon-based and silicon-based active materials exist during electrode rolling, enabling them to serve as pathways for the movement of electrons and lithium. When the rolling density of the silicon-based active material is higher than that of the artificial graphite, as the cycle progresses, the silicon-based active material undergoes extreme volume changes, creating larger voids and exhibiting inferior capacity retention characteristics.

[0203] In Comparative Example 3, the electrical conductivity of natural graphite is lower than that of artificial graphite, and in this case, low initial efficiency and capacity retention rate characteristics were also exhibited. On the other hand, Examples 1 to 7 showed high initial efficiency and capacity retention rates by using an active material that satisfies the relationship between rolling density and electrical conductivity of the present invention.

[0204] In particular, Examples 1 to 3 show that the electrical conductivity of the artificial graphite is 10 compared to the silicon-based active material. 2 It was found that the rolling density of artificial graphite was more than twice as large as that of silicon-based active material, and that natural graphite was more than twice as large as that of artificial graphite, and that the rolling density of artificial graphite was more than 1.1 times larger than that of silicon-based active material, and that natural graphite was more than 1.01 times larger than that of artificial graphite, thereby exhibiting superior initial efficiency and capacity retention rate.

Claims

Claim 1 A negative electrode active material comprising a silicon-based active material comprising at least one of a silicon-carbon composite and silicon oxide, and a carbon-based active material, wherein the silicon-based active material and the carbon-based active material comprise a carbon layer provided on at least a portion of their surfaces, and the carbon-based active material comprises natural graphite and artificial graphite, and a pressure of 800 kgf / cm² 2 A cathode composition in which, when measuring powder resistance, 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. Claim 2 In claim 1, the electrical conductivity is 10 times that of the artificial graphite relative to the silicon-based active material. 2 A cathode composition in which the natural graphite is more than twice as large as the artificial graphite. Claim 3 A cathode composition according to claim 1, wherein the rolling density of the artificial graphite is at least 1.1 times greater than that of the silicon-based active material and the natural graphite is at least 1.01 times greater than that of the artificial graphite. Claim 4 A cathode composition according to claim 1, wherein the electrical conductivity of the natural graphite is 50 to 10,000 S / cm, the artificial graphite is 15 to 2,000 S / cm, the silicon carbon composite is 0.0001 to 2 S / cm, and the silicon oxide is 0.001 to 1 S / cm. Claim 5 A cathode 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. Claim 6 A cathode composition according to claim 1, wherein the cathode composition comprises single-walled carbon nanotubes as a conductive material. Claim 7 A cathode composition according to claim 6, wherein, based on 100 parts by weight of the cathode composition, the silicon-based active material comprises 0.5 to 52 parts by weight; the carbon-based active material comprises 45 to 99 parts by weight; and the single-walled carbon nanotube comprises 0.01 to 3 parts by weight; and based on 100 parts by weight of the carbon-based active material, the natural graphite comprises 10 to 70 parts by weight; and the artificial graphite comprises 30 to 90 parts by weight. Claim 8 A cathode composition according to claim 1, further comprising a binder. Claim 9 A cathode comprising a cathode composition according to any one of claims 1 to 8. Claim 10 A lithium secondary battery comprising a negative electrode, a positive electrode, and a separator according to claim 9. Claim 11 A battery module comprising a lithium secondary battery according to claim 10. Claim 12 A battery pack comprising a lithium secondary battery according to claim 10. Claim 13 A battery pack comprising a battery module according to claim 11.

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