Negative electrode composition, negative electrode, and lithium secondary battery

Abstract

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

Description

Negative electrode composition, negative electrode, and lithium secondary battery

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

[0002] This application claims the benefit of the filing dates 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, the entire contents of which are incorporated herein by reference.

[0003] The recent rapid proliferation of battery-powered electronic devices, including mobile phones, laptops, electric vehicles, power tools, and vacuum cleaners, has led to a rapid increase in demand for compact, lightweight, and relatively high-capacity and / or high-output secondary batteries. In particular, lithium secondary batteries, with their lightweight design and high energy density, are attracting significant attention as power sources for electronic devices. Accordingly, active research and development efforts are underway to improve the performance of lithium secondary batteries.

[0004] In general, a lithium secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, an electrolyte, an organic solvent, etc. In addition, an active material layer including a positive electrode active material and a negative electrode active material may be formed on a current collector on the positive electrode and the negative electrode, respectively. In general, a lithium-containing metal oxide such as LiCoO2 or LiMn2O4 is used as a positive electrode active material for the positive electrode, and a carbon-based active material or a silicon-based active material that does not contain lithium is used as an negative electrode active material for the negative electrode.

[0005] Among negative active materials, silicon-based materials are attracting attention for their higher capacity and superior fast-charge characteristics compared to carbon-based materials. However, silicon-based materials exhibit significant volumetric expansion and contraction during charge and discharge, and their high irreversible capacity leads to low initial efficiency. Consequently, silicon-based materials have the disadvantage of degrading battery performance compared to carbon-based materials.

[0006] Accordingly, the development of negative electrode materials that can improve the performance of lithium secondary batteries is required.

[0007] The present invention relates to an anode composition capable of improving the performance of a lithium secondary battery, an anode comprising the anode composition, and a secondary battery comprising the same.

[0008] One embodiment of the present invention includes a negative 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, wherein the carbon-based active material includes natural graphite and artificial graphite, and a pressure of 800 kgf / cm 2 When measuring powder resistance, a negative electrode composition is provided in which the rolling density decreases in the order of natural graphite > artificial graphite > silicon-based active material, and the electrical conductivity decreases in the order of natural graphite > artificial graphite > silicon-based active material.

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

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

[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 above-described embodiment.

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

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

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

[0015] According to embodiments of the present invention, the performance of a lithium secondary battery can be improved by mixing and using a silicon-based active material and a carbon-based active material having different rolling densities and electrical conductivities 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 having higher rolling densities and electrical conductivities at the same pressure than the silicon-based active material, and having different rolling densities and electrical conductivities.

[0016] Hereinafter, the present invention will be described in more detail to facilitate understanding. The present invention may be embodied in various different forms and is not limited to the embodiments described herein. In this regard, terms and words used in this specification and claims should not be construed as limited to their conventional or dictionary meanings. Rather, they should be interpreted in the sense and concept that aligns with the technical spirit of the present invention, based on the principle that the inventor can appropriately define the concept of a term to best explain his or her invention.

[0017] It should be understood that the terms “include,” “comprising,” or “having” used in this specification are intended to specify the presence of a feature, number, step, component, or combination thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0018] Furthermore, when we say that a part of a layer or the like is "above" or "on" another part, this includes not only cases where it is "directly above" that part, but also cases where there is another part in between. Conversely, when we say that a part is "directly above" another part, it means that there is no other part in between. Furthermore, when we say that a part is "above" or "on" a reference part, it means that it is located above or below that reference part, and does not necessarily mean that it is located "above" or "on" in the direction opposite to gravity.

[0019] The terms and words used in this specification should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

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

[0021] In this specification, the rolling density refers to the degree of deformation and compression of particles that occur when a certain pressure is applied to the negative electrode active material, and can be expressed in g / cc. The rolling density can be derived by measuring powder resistance, and for example, a certain amount of negative electrode active material is injected into a cylinder-type load cell and 400 kgf / cm 2 Up to 2,000 kgf / cm 2 It can be measured by applying pressure to one of the negative electrode active materials and measuring the change in thickness.

[0022] In this specification, electrical conductivity refers to the inherent electrical conductivity of the negative electrode active material powder. The electrical conductivity can be derived by measuring powder resistance, and is, for example, 400 kgf / cm. 2 Up to 2,000 kgf / cm 2By applying pressure to one of the surfaces, the surface resistance according to the pressure change is measured, and the surface resistance and resistivity are measured through the measured volume and mass at the same time, and the measured surface resistance and resistivity values ​​can be derived.

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

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

[0025] An anode composition according to one embodiment of the present invention comprises an anode active material comprising a silicon-based active material and a carbon-based active material including at least one of a silicon-carbon composite and a silicon oxide, wherein the carbon-based active material comprises natural graphite and artificial graphite. Here, the anode composition is heated to a pressure of 800 kgf / cm. 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 implementation, together with the silicon-based active material, the pressure is 800 kgf / cm compared to the silicon-based active material. 2 By including carbon-based active materials with high rolling density and electrical conductivity in powder resistance measurement, the cycle characteristics and resistance of lithium secondary batteries can be improved. In addition, as a carbon-based active material, artificial graphite was used at a pressure of 800 kgf / cm. 2When measuring powder resistance in , the performance of lithium secondary batteries can be improved by mixing and using natural graphite, which has relatively high rolling density and electrical conductivity. By mixing and using an anode active material with relatively high electrical conductivity, even if surface detachment between the anode active material and the conductive material occurs due to volume change during charge and discharge, the high electrical conductivity makes charging and discharging easier than lithium. As a result, the characteristics of a long-life battery can be realized. Meanwhile, in the case of an active material with relatively high rolling density, the volume change during charge and discharge can be physically controlled, which can have a beneficial effect on cycle performance.

[0027] According to an embodiment of the present invention, even if the negative electrode composition satisfies the condition that the rolling density of each material 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, and for example, this applies when the electrical conductivity is in the order of artificial graphite > natural graphite > silicon-based active material.

[0028] Specifically, as the rolling density increases, the contact surface between particles generally increases, which increases the conductivity. However, if the particles break, this can have a negative effect on the electrical conductivity. Therefore, the rolling density and electrical conductivity should have the same trend.

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

[0030] Additionally, if the rolled density and electrical conductivity of artificial graphite are higher than those of natural graphite, the graphitization degree of the artificial graphite may increase, which may deteriorate battery performance.

[0031] Unless otherwise stated, the electrical conductivity in this specification refers to the electrical conductivity of the particle state of each material, for example, the electrical conductivity before breakage, and does not refer to the electrical conductivity after the particle is broken.

[0032] According to one implementation state, the above pressure is 800 kgf / cm 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 rolling density of the natural graphite is at least 1.01 times greater than that of the artificial graphite.

[0033] For example, the pressure is 800 kgf / cm 2 When measuring the powder resistance, the rolling density may be 1.4 to 2.5 g / cc for natural graphite, for example, 1.6 to 1.7 g / cc, 1.0 to 2.2 g / cc for artificial graphite, for example, 1.5 to 1.6 g / cc, and 0.5 to 1.8 g / cc for silicon-based active materials. Specifically, the pressure may be 800 kgf / cm 2 When measuring the 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 implementation state, the above pressure is 800 kgf / cm 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 electrical conductivity of the natural graphite is more than twice greater than that of the artificial graphite.

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

[0036] According to one embodiment, the silicon-based active material may be 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, based on 100 parts by weight of the negative electrode composition, and the natural graphite may be included in an amount of 10 to 70 parts by weight, and the artificial graphite may be included in an amount of 30 to 90 parts by weight, based on 100 parts by weight of the carbon-based active material.

[0037] According to one embodiment, the silicon-based active material may be 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 100 parts by weight of the total negative 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 negative active material included in the negative electrode 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 included in an amount of 10 to 70 parts by weight, for example, 10 to 30 parts by weight; and the artificial graphite may be included in an amount of 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 distinct from silicon carbide, denoted as SiC. Since the silicon carbide does not electrochemically react with lithium, all performances, including lifespan, may be measured as 0.

[0042] The above silicon-carbon composite may include at least one of a silicon-carbon composite formed by depositing silicon into a porous carbon structure; and a silicon-carbon composite in which carbon is composited into a porous silicon structure. The silicon-carbon composite may be a composite of silicon and graphite, etc. The silicon in the silicon-carbon composite may be nano silicon.

[0043] According to one embodiment, the silicon carbon composite includes porous carbon particles and a silicon coating layer positioned on the surface or internal pores of the porous carbon particles.

[0044] According to one embodiment, the silicon carbon composite has a surface area of ​​0.5 to 10 m by the BET method. 2 / g, and the pore volume can be 0.005 to 0.03 cm 3 / g, and the pore size by the BET method may be 10 to 20 nm. The silicon carbon composite has a pore volume of 0.005 to 0.03 cm as measured by the mercury penetration method. 3 / g could be.

[0045] According to one embodiment, the silicon carbon composite is D 90 The particle size can be 11 to 20 ㎛, D 50 The particle size can be 3 to 10 ㎛, 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 including the steps of etching carbon particles containing internal pores to expand the internal pores of the carbon particles; and the steps of forming a silicon coating layer on the surface and internal pores of the carbon particles having expanded internal pores.

[0047] The step of expanding the internal pores of the above carbon 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 the oxygen can be controlled to 0.1 to 10 L / min.

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

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

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

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

[0052] According to one embodiment, the silicon oxide is SiO x (0≤x<2) can be included.

[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 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 above Mg compound and / or Li compound is 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 wt% to 20 wt%, or 0.1 wt% to 10 wt%, based on 100 wt% of the total silicon oxide particles. Specifically, the Mg element may be included in an amount of 0.5 wt% to 8 wt% or 0.8 wt% to 4 wt%. When the above range is satisfied, the Mg compound can be included in an appropriate amount in the silicon oxide particles, so that volume changes of the silicon oxide particles can be easily suppressed during charging and discharging of the battery, and the discharge capacity and initial efficiency of the battery can be improved.

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

[0060] In one embodiment of the present invention, the Li compound may include a lithium silicate form. The lithium silicate may include 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 wt% to 20 wt%, or 0.1 wt% to 10 wt%, based on 100 wt% of the total silicon oxide particles. Specifically, the Li element may be included in an amount of 0.5 wt% to 8 wt%, and more specifically, may be included in an amount of 0.5 wt% to 4 wt%. When the above range is satisfied, the Li compound can be included in an appropriate amount in 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 above Mg element or Li element can be confirmed through ICP analysis. For the ICP analysis, a certain amount (approximately 0.01 g) of the negative electrode active material is precisely aliquoted, transferred to a platinum crucible, and completely decomposed on a hot plate by adding nitric acid, hydrofluoric acid, and sulfuric acid. Thereafter, an inductively coupled plasma electroluminescence spectrometer (ICPAES, Perkin-Elmer 7300) is used to measure the intensity of the standard solution prepared using a standard solution (5 mg / kg) at the wavelength unique to the Mg element or Li element, thereby creating a reference calibration curve. Thereafter, the pretreated sample solution and blank sample are introduced into the device, and the respective intensities are measured to calculate the actual intensity, and the concentration of each component is calculated against the created calibration curve, and then the content of the Mg element or Li element of the manufactured silicon oxide particles can be analyzed by converting so that the sum of the entire values ​​becomes the theoretical value.

[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 provided to the silicon oxide particles, and the initial efficiency, life characteristics, and battery capacity characteristics of a secondary battery including a negative electrode active material including the silicon oxide particles may be improved. The total weight of the carbon layer may be comprised in an amount of 5 wt% to 40 wt% based on 100 wt% of the total weight of the silicon oxide particles.

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

[0065] The average particle diameter (D) of the above silicon-based active material 50) may be 0.1 ㎛ to 30 ㎛, specifically 1 ㎛ to 20 ㎛, and more specifically 1 ㎛ to 10 ㎛. When the above range is satisfied, the structural stability of the active material during charge and discharge can be ensured, the problem of the volume expansion / contraction level increasing as the particle size becomes excessively large can be prevented, and the problem of the initial efficiency decreasing as the particle size becomes excessively low can be prevented.

[0066] In this specification, the average particle diameter (D 50 ) can be defined as the particle size corresponding to 50% of the volume accumulation in the particle size distribution curve. The average particle size (D 50 ) can be measured, for example, using a laser diffraction method. The laser diffraction method can generally measure particle diameters 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 m 2 / g may be. 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. Natural graphite and artificial graphite each have an average particle diameter (D 50 ) is 10 to 30㎛, and the BET specific surface area is 0.5 to 2 m 2 / g may be. The above natural graphite refers to graphite that is produced naturally, and examples thereof include scaled graphite, scaley graphite, or soil graphite. The above natural graphite has the advantages of being abundant, low in price, having high theoretical capacity and compaction density, and being able to realize high output.

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

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

[0070] [Mathematical Formula 1]

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

[0072] The above natural graphite can be applied by selecting those that satisfy the sphericity by checking the particle shape through SEM and checking through a particle shape analyzer.

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

[0074] The above artificial graphite can be applied by selecting those that satisfy the sphericity by checking the particle shape through SEM and checking through a particle shape analyzer.

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

[0076] The single-walled carbon nanotube (SWCNT) refers to a tube-shaped carbon structure composed of a single carbon layer. When the conductive material in the negative electrode composition includes the single-walled carbon nanotube (SWCNT), the charge / discharge capacity and / or life performance of the battery can be improved. Specifically, the single-walled carbon nanotube (SWCNT) effectively connects the conductive path between particles, thereby preventing the loss of the conductive path due to swelling of the silicon-based active material described above. Consequently, when the single-walled carbon nanotube (SWCNT) is included, the life performance of the battery can be improved.

[0077] In this specification, the length of a carbon nanotube means the length of the major axis passing through the center of a unit of the carbon nanotube, 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.

[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) may be calculated as an average value of the results observed using 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 equivalent to the distance between the particles of the negative electrode active material, so that the connection of the conductive path between the particles becomes easier, thereby improving the electrical conductivity, strength, and / or electrolyte storage capacity of the negative electrode.

[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 a flexible characteristic, even when physically damaged, the contact between the negative electrode active material particles is not easily broken. The average diameter of the single-walled carbon nanotube (SWCNT) can be calculated as an average value observed by TEM.

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

[0082] The above single-walled carbon nanotube (SWCNT) 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, and specifically, may be included 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, there is an effect of facilitating the connection of conductive paths between active material particles while minimizing electrolyte side reactions due to a high specific surface area.

[0083] In this specification, the specific surface area is measured by the BET method, and specifically, the surface area can be measured by removing gas from the measurement target at 130°C for 2 hours using a BET measurement device (BEL-SORP-mini, Nippon Bell) and performing N2 absorption / desorption at 77K.

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

[0085] The above binder may include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluoroelastomer, polyacrylic acid, and materials in which hydrogens thereof are substituted with Li, Na, Ca, etc., and may also include various copolymers thereof.

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

[0087] 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.

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

[0089] The negative current collector may be any conductive material that does not cause chemical changes in the battery, and is not particularly limited thereto. For example, the current collector may be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like. Specifically, a transition metal that readily absorbs carbon, such as copper or nickel, may be used as the current collector. The current collector may have a thickness of 6 μm to 20 μm, but the thickness of the current collector is not limited thereto.

[0090] If necessary, an additional conductive material other than the single-walled carbon nanotubes described above may be included. The additional conductive material is not particularly limited as long as it has conductivity and does not cause a chemical change in the battery, and examples thereof include graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, paneth black, lamp black, thermal black, etc.; conductive fibers such as carbon fiber or metal fiber; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, and 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-described 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 dispersion of the components.

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

[0094] In the above positive electrode, the positive electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change 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 positive electrode current collector may typically have a thickness of 3 to 500 ㎛, and fine unevenness may be formed on the surface of the current collector to increase the adhesive strength 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, or non-woven fabric.

[0095] The above 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), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe3O4; or a compound having 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 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, and satisfies 0.01≤c2≤0.3); chemical formula LiMn 2-c3 M c3Lithium manganese composite oxide represented by O2 (wherein M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01≤c3≤0.1) or Li2Mn3MO8 (wherein M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); LiMn2O4, etc., in which a part of Li in the chemical formula is replaced with an alkaline earth metal ion, but is not limited thereto. The positive electrode may be Li-metal.

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

[0097] At this time, the positive electrode conductive material is used to provide conductivity to the electrode, and in the battery to be constructed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any special restrictions. 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, summer black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like, and one of these may be used alone or a mixture of two or more may be used.

[0098] In addition, the positive electrode binder plays a role of improving the adhesion between positive electrode active material particles and the adhesiveness 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, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluoroelastomer, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof.

[0099] The separator separates the negative and positive electrodes and provides a passage for lithium ions to move. Any separator commonly used in secondary batteries can be used without any particular restrictions, and in particular, one that has low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, can be used. In addition, a conventional porous non-woven fabric, for example, a non-woven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. can also be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength can be used, and can 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 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.

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

[0102] As the above non-aqueous organic solvent, for example, an aprotic organic solvent such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyl tetrahydrofuran, dimethylsulfoxide, 1,3-dioxolan, formamide, dimethylformamide, dioxolan, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxy methane, dioxolan derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl pyrropionate, ethyl propionate, etc. can 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 and thus can be preferably used because they easily dissociate lithium salts. In addition, when low-viscosity, low-dielectric constant linear carbonates such as dimethyl carbonate and diethyl carbonate are mixed and used in an appropriate ratio with these cyclic carbonates, an electrolyte with high electrical conductivity can be produced, so that they can be used even more preferably.

[0104] The metal salt may be a lithium salt, and the lithium salt is a substance that is easily dissolved in the non-aqueous electrolyte, for example, the anion of the lithium salt is F - , Cl - , I- , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - One or more selected from the group consisting of can be used.

[0105] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as, for example, a haloalkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, a cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery.

[0106] 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.

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

[0108] Hereinafter, examples will be provided to specifically explain the present specification. However, the embodiments described herein may be modified in various ways, and the scope of the present application is not limited to the embodiments described below. The embodiments of the present application are provided to more fully explain the present specification to those of ordinary skill in the art.

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

[0110] [Manufacture of Silicon Carbon Composite 1]

[0111] Cellulose powder was placed in a tubular furnace, heated to 400°C at a rate of 4°C / min, and heated for 2 hours under a nitrogen atmosphere. Thereafter, the furnace was heated to 900°C at a rate of 4°C / min, and heated for 2 hours under a nitrogen atmosphere. The powder was mixed with sulfuric acid and nitric acid 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 mixed with ethanol and distilled water in a volume ratio of 1:3, and dried at 120°C for 12 hours. The carbon particles were placed in a KOH solvent, heated at 800°C in a nitrogen atmosphere 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 more than 12 hours. The porous carbon structure was placed in a horizontal furnace, and SiH4 / He = 5 / 95 gas was flowed at a flow rate of 50 ml / min at 700°C for 1 hour to produce a silicon carbon composite. Thereafter, the silicon carbon composite was placed in the furnace, and methane was flowed at 700°C to react for 2 hours to produce a silicon carbon composite 1 including a carbon layer on the surface.

[0112] [Manufacturing of Artificial Graphite 2]

[0113] Green coke particles, calcined coke particles, and a petroleum-based pitch binder were introduced into a reactor. The green coke and the calcined coke particles were mixed in a weight ratio of 30:70. The pitch binder was mixed in an amount of 7 wt% based on the total weight of the green coke particles, the calcined coke particles, and the petroleum pitch. The mixture of the green coke particles, the calcined coke particles, and the petroleum pitch was heat-treated at 3000°C for 50 hours to graphitize the mixture, thereby producing artificial graphite particles in the form of secondary particles in which primary particles are bound. The artificial graphite in the form of secondary particles and the petroleum pitch were mixed and heat-treated at 1250°C in a roller hearth kiln to form an amorphous carbon coating layer on the surface of the artificial graphite particles, thereby producing artificial graphite 2. The D50 of the final artificial graphite 2 was controlled to the level of 16 μm.

[0114] [Manufacturing of Natural Graphite 2]

[0115] Natural graphite raw material was extracted from graphite ore through flotation. The natural graphite was treated with acid or base to remove impurities, and washed and dried to produce flaky natural graphite. The flaky natural graphite obtained above was spheroidized using a vortex flow pulverizer, impurities were removed with sulfuric acid, and the spherical natural graphite was produced by drying. The spherical natural graphite was filled into a mold, pressurized using cold isostatic pressing (CIP), and then crushed. The pressurization pressure was 90 MPa and the pressurization time was 15 minutes. The pressed spherical natural graphite and pitch were mixed, and the mixture was dry heat-treated 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 above carbon coating layer was formed at 5 wt% of the total weight of the natural graphite active material.

[0116] [Slurry production]

[0117] As a 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 was used at a pressure of 800 kgf / cm. 2 When measuring the powder resistance, the rolling density was 0.859 g / cc, and the electrical conductivity was 0.664 S / cm, 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. The negative electrode slurry was prepared by mixing the negative electrode active material, conductive agent (carbon black, single-walled carbon nanotube (SWCNT)), and 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 film with a thickness of 20 μm and dried at a circulating air temperature of 60°C. Then, 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 punching out a circular shape.

[0120] [Manufacturing of secondary batteries]

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

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

[0123] [Manufacture of silicon oxide 1]

[0124] SiO, a mixture of Si and SiO2 in a 1:1 molar ratio, was placed in crucible 1 and heated to a sublimation temperature of 1400℃ to evaporate. Metallic magnesium was placed in crucible 2 and separately heated to 800℃ to evaporate. All crucibles were decompressed to 0.1 torr and the raw materials were evaporated. The vaporous mixture containing Mg was reacted for 6 hours and then solidified into a solid state in a vacuum area at 800℃. The silicon-based active material manufactured by the above method was pulverized using a ball mill for 3 to 4 hours. Thereafter, a CVD device was used under an inert gas Ar atmosphere to react methane (CH4) at 0.1 torr at a rate of 1 L / min for about 5 hours to form a carbon layer on the surface of the silicon-based active material, thereby manufacturing a magnesium silicon oxide active material coated with a carbon layer. The D50 of the final active material was controlled to be 6 μm.

[0125] [Slurry production]

[0126] As a negative electrode active material, a slurry was prepared in the same manner as in Example 1, except that silicon oxide 1, natural graphite 2 (see the manufacturing method of Example 1), and artificial graphite 2 (see the manufacturing method of Example 1) having the rolling density and electrical conductivity of Table 1 below were used in a weight ratio of 20:10:70. Specifically, the silicon oxide 1 was prepared under a pressure of 800 kgf / cm 2 When measuring the powder resistance, the rolling 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] [Manufacture of Silicon Carbon Composite 2]

[0131] An oxide layer was formed on the silicon carbon composite by heat treatment in an O2 / Ar = 5 / 95 atmosphere at 700°C for 2 hours. A silicon carbon composite 2 was manufactured in the same manner as in Example 1, except that the silicon carbon composite was placed in an electric furnace, methane was flowed in at 700°C, and the reaction was performed for 2 hours to form a carbon layer on the surface.

[0132] [Manufacturing of artificial graphite 1]

[0133] The pitch binder was mixed at 4.5 wt% based on the total weight of green coke particles, calcined coke particles, and petroleum pitch. An artificial graphite active material was manufactured in the same manner as artificial graphite 2 of Example 1, except that the artificial graphite in the form of secondary particles and the petroleum 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] [Manufacturing 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 the pressurized spherical natural graphite and pitch were mixed, and the mixture was heat-treated in a dry manner in an inert atmosphere at 1,100°C for 24 hours to form an amorphous carbon coating layer.

[0136] [Slurry production]

[0137] As a negative electrode active material, 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 in a weight ratio of 15:15:70. Specifically, the silicon carbon composite 2 was prepared under a pressure of 800 kgf / cm. 2 When measuring the powder resistance, the natural graphite 1 has a rolling density of 0.914 g / cc and an electrical conductivity of 0.00025 S / cm, and the artificial graphite 1 has values ​​of 1.54 g / cc and 30.1 S / cm, respectively.

[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] [Slurry production]

[0142] As a negative electrode active material, a slurry was prepared in the same manner as in Example 1, except that silicon carbon composite 1 (see the manufacturing method of Example 1), natural graphite 2 (see the manufacturing method of Example 1), and artificial graphite 1 (see the manufacturing 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. Specifically, the silicon carbon composite 1 was prepared under a pressure of 800 kgf / cm 2 When measuring the powder resistance, the natural graphite 2 has a rolling density of 0.859 g / cc and an electrical conductivity of 0.664 S / cm, and the artificial graphite 1 has a composition having values ​​of 1.54 g / cc and 30.1 S / cm, respectively.

[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, artificial graphite 1, natural graphite 2)

[0146] [Slurry production]

[0147] As a negative electrode active material, a slurry was prepared in the same manner as in Example 1, except that silicon oxide 1 (see the manufacturing method of Example 2), natural graphite 2 (see the manufacturing method of Example 1), and artificial graphite 1 (see the manufacturing 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. Specifically, the silicon oxide active material was prepared under a pressure of 800 kgf / cm 2 When measuring the powder resistance, the natural graphite 2 has a rolling density of 1.42 g / cc and an electrical conductivity of 0.122 S / cm, and the artificial graphite 1 has a composition having values ​​of 1.54 g / cc and 30.1 S / cm, respectively.

[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, artificial graphite 2, natural graphite 1)

[0151] [Slurry production]

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

[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, artificial graphite 2, natural graphite 2)

[0156] [Slurry production]

[0157] As a negative electrode active material, a slurry was prepared in the same manner as in Example 1, except that silicon oxide 1 (see the manufacturing method of Example 2), natural graphite 2 (see the manufacturing method of Example 1), and artificial graphite 2 (see the manufacturing method of Example 1) having the rolling density and electrical conductivity of Table 1 below were used in a weight ratio of 20:10:70. The silicon oxide active material was prepared under a pressure of 800 kgf / cm 2 When measuring the powder resistance, the rolling density was 1.42 g / cc and the electrical conductivity was 0.122 S / cm, and the natural graphite 1 had values ​​of 1.61 g / cc and 149 S / cm, respectively, and 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 agent (carbon black), and 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] [Manufacture of Silicon Carbon Composite 3]

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

[0163] [Manufacturing 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 the artificial graphite particles were partially oxidized by heat treatment in a hot zone in an O2 / Ar = 5 / 95 atmosphere at 800°C for 2 hours, thereby preparing artificial graphite 3 in the same manner as the method for preparing artificial graphite 2 of Example 1.

[0165] [Slurry production]

[0166] As a negative electrode active material, a slurry was prepared in the same manner as in Example 1, except that silicon carbon composite 3, natural graphite 2 (refer to the manufacturing method of Example 1), and artificial graphite 3, each having a rolling density and electrical conductivity as shown in Table 1 below, were used in a weight ratio of 20:10:70. Specifically, the silicon carbon composite 3 was prepared under a pressure of 800 kgf / cm. 2When measuring the powder resistance, the natural graphite 2 has a rolling density of 1.32 g / cc and an electrical conductivity of 8.1 S / cm, and the artificial graphite 3 has a composition having values ​​of 1.56 g / cc and 5.8 S / cm, respectively.

[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] [Manufacture of silicon oxide 2]

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

[0172] [Manufacturing of artificial graphite 4]

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

[0174] [Slurry production]

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

[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] [Manufacturing of Natural Graphite 3]

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

[0181] [Slurry production]

[0182] As a negative electrode active material, a slurry was prepared in the same manner as in Example 1, except that silicon oxide 1 (see the preparation method of Example 2), natural graphite 3, and artificial graphite 1 (see the preparation method of Example 3) having the rolling density and electrical conductivity shown in Table 1 below were used in a weight ratio of 20:10:70. Specifically, the silicon oxide 1 was prepared under a pressure of 800 kgf / cm. 2 When measuring the powder resistance, the natural graphite 3 has a rolling density of 1.42 g / cc and an electrical conductivity of 0.122 S / cm, and the artificial graphite 1 has values ​​of 1.54 g / cc and 30.1 S / cm, respectively.

[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] Rolled density (g / cc) Electrical conductivity (S / cm) Natural graphite 11.61149 Natural graphite 21.6337 Natural graphite 31.624.5 Artificial graphite 11.5430.1 Artificial graphite 21.5896.6 Artificial graphite 31.565.8 Artificial graphite 41.4580.2 Silicon oxide 11.420.122 Silicon oxide 21.520.178 Silicon carbon composite 10.8590.664 Silicon carbon composite 20.9140.00025 Silicon carbon composite 31.328.1

[0186] 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.

[0187] Active material type Rolled 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 20.8591.581.60.66496.6337 Example 2 Silicon oxide 1 Artificial graphite 2 Natural graphite 21.421.581.60.12296.6337 Example 3 Silicon-carbon composite 2 Artificial graphite 1 Natural graphite 10.9141.541.610.0002530.1149 Example 4 Silicon-carbon composite 1 Artificial graphite 1 Natural graphite 20.8591.541.60.66430.1337Example 5Silicon oxide 1Artificial graphite 1Natural graphite 21.421.541.60.12230.1337Example 6Silicon oxide 1Artificial graphite 2Natural graphite 11.421.581.610.12296.6149Example 7Silicon oxide 1Artificial graphite 2Natural graphite 21.421.581.60.12296.6337Comparative example 1Silicon-carbon composite 3Artificial graphite 3Natural graphite 21.321.561.68.15.8337Comparative example 2Silicon oxide 2Artificial graphite 4Natural graphite 11.521.451.610.17880.2149Comparative Example 3Silicon Oxide 1Artificial Graphite 1Natural Graphite 31.421.541.60.12230.124.5

[0188] Rolling density ratioElectrical conductivity ratioArtificial graphite / silicon-based active materialNatural graphite / artificial graphiteArtificial graphite / silicon-based active materialNatural graphite / artificial graphiteExample 11.841.01145.483.49Example 21.111.01791.803.49Example 31.681.05120,400.004.95Example 41.791.0445.3311.20Example 51.081.04246.7211.20Example 61.111.02791.801.54Comparative example 11.181.030.7258.10Comparative example 20.951.11450.561.86Comparative example 31.081.04246.720.81

[0189] <Experimental Example: Evaluation of discharge capacity, initial efficiency, and lifespan (capacity retention rate) characteristics>

[0190] Batteries were manufactured using the negative electrodes of the examples and comparative examples, respectively.

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

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

[0193] The 1st and 2nd cycles were charged and discharged at 0.1C, and from the 3rd to the 299th cycles, the charging and discharging was performed at 0.5C. The 50th cycle was terminated in a charged state (with lithium in the negative electrode).

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

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

[0196] Based on the results of a single charge / discharge cycle, the discharge capacity (mAh / g) and initial efficiency (%) were derived. Specifically, the initial efficiency (%) was derived using the following calculation.

[0197] Initial efficiency (%) = (1-time discharge capacity / 1-time charge capacity) × 100 (%)

[0198] The capacity retention rate was derived by the following calculations.

[0199] Capacity retention rate (%) = (299 discharge capacity / 1 discharge capacity) × 100 (%)

[0200] Total discharge capacity (mAh / g) Initial efficiency (%) Capacity retention rate (%) Example 150491.388.0 Example 250488.186.5 Example 350491.087.7 ​​Example 450490.685.1 Example 550487.784.9 Example 650487.685.5 Example 750486.584.1 Comparative example 150486.180.1 Comparative example 250484.871.9 Comparative example 350485.683.6

[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 characteristics. It is known that silicon-based active materials react more severely with the electrolyte than carbon-based active materials due to their unstable surfaces. When the electrical conductivity of the silicon-based active material was higher than that of artificial graphite, the reduction reaction of the electrolyte was promoted on the surface of the silicon-based active material, forming a thick film, resulting in low efficiency and capacity retention.

[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, low initial efficiency and capacity retention characteristics were exhibited. The rolling density means how densely the carbon-based active material and the silicon-based active material exist during electrode rolling, enabling them to act as a passage for electrons and lithium. When the rolling density of the silicon-based active material was higher than that of the artificial graphite, as the cycle progressed, the silicon-based active material experienced extreme volume change, creating larger pores, and exhibited inferior capacity retention characteristics. In Comparative Example 3, the electrical conductivity of natural graphite was lower than that of the artificial graphite, and in this case, low initial efficiency and capacity retention characteristics were exhibited. On the other hand, Examples 1 to 7 showed high initial efficiency and capacity retention characteristics by using active materials that satisfied the rolling density and electrical conductivity relationship of the present invention.

[0203] In particular, examples 1 to 3 show that the electrical conductivity of artificial graphite is 10 times higher than that of silicon-based active materials. 2 The size of the artificial graphite is more than twice as large as that of the natural graphite, the rolling density of the artificial graphite is more than 1.1 times as large as that of the silicon-based active material, and the natural graphite is more than 1.01 times as large as that of the artificial graphite, showing superior initial efficiency and capacity retention.

Claims

1. A negative active material comprising a silicon-based active material and a carbon-based active material including at least one of a silicon carbon composite and a silicon oxide, The above carbon-based active material includes natural graphite and artificial graphite, Pressure 800kgf / cm 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.

2. In claim 1, the electrical conductivity of the artificial graphite is 10 times higher than that of the silicon-based active material. 2 A cathode composition having a size greater than or equal to a ship, wherein the natural graphite is at least twice as large as the artificial graphite.

3. In claim 1, the negative electrode composition 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.

4. In claim 1, the negative electrode composition has an electrical conductivity of 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. In claim 1, the rolling density is a negative electrode composition in which the natural graphite has a density of 1.4 to 2.5 g / cc, the artificial graphite has a density of 1.0 to 2.2 g / cc, the silicon carbon composite has a density of 0.5 to 1.2 g / cc, and the silicon oxide has a density of 0.8 to 1.8 g / cc.

6. In claim 1, the cathode composition comprises a single-walled carbon nanotube as a conductive material.

7. In claim 6, Based on 100 parts by weight of the negative electrode 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. An anode composition comprising 10 to 70 parts by weight of the natural graphite and 30 to 90 parts by weight of the artificial graphite based on 100 parts by weight of the carbon-based active material.

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

9. A cathode comprising a cathode composition according to any one of claims 1 to 8.

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

11. A battery module including a lithium secondary battery according to claim 10.

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

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