Anode composition, anode, lithium secondary battery, battery module, and battery pack

Abstract

The present invention relates to a negative electrode composition, a negative electrode, a lithium secondary battery, a battery module, and a battery pack. The negative electrode composition includes a negative electrode active material containing a silicon-carbon composite and graphite, and the tab density of the graphite is the same as or greater than the tab density of the silicon-carbon composite.

Description

[Technical Field]

[0001] The present invention claims the benefit of the filing date of Korean Patent Application No. 10-2022-0177137 filed with the Korean Intellectual Property Office on December 16, 2022, and Korean Patent Application No. 10-2023-0178444 filed with the Korean Intellectual Property Office on December 11, 2023, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a negative electrode composition, a negative electrode, a lithium secondary battery, a battery module, and a battery pack. [Background technology]

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

[0004] Lithium secondary batteries have an organic or polymer electrolyte solution filled between a positive electrode and a negative electrode, which are made of active materials that allow for the intercalation and deintercalation of lithium ions. Electrical energy is produced through oxidation and reduction reactions that occur when lithium ions are inserted into and extracted from the positive and negative electrodes.

[0005] Positive electrode active materials used in lithium secondary batteries include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2 or LiMn2O4, etc.), and lithium iron phosphate compound (LiFePO4). Among these, lithium cobalt oxide (LiCoO2) is widely used as a positive electrode active material for high voltage applications due to its advantages of high operating voltage and excellent capacity characteristics. However, rising cobalt (Co) prices and unstable supply have limited its mass use as a power source in fields such as electric vehicles, creating a need for the development of alternative positive electrode active materials.

[0006] As a result, nickel-cobalt-manganese-based lithium transition metal composite compounds (hereinafter simply referred to as "NCM-based lithium transition metal composite compounds") have been developed, in which some of the cobalt (Co) is replaced with nickel (Ni) and manganese (Mn). In recent years, research has been conducted to increase the Ni content in NCM-based lithium transition metal composite compounds to increase capacity. However, high-nickel (Ni-rich) positive electrode active materials with a high nickel content have drawbacks, such as reduced thermal stability and increased side reactions during electrochemical reactions, resulting in increased resistance and gas generation.

[0007] On the other hand, graphite is commonly used as the negative electrode active material for lithium secondary batteries. However, its low capacity per unit mass (372 mAh / g) makes it difficult to increase the capacity of lithium secondary batteries. Therefore, to increase the capacity of lithium secondary batteries, non-carbon-based negative electrode materials such as silicon, tin, and their oxides have been developed as materials with higher energy densities than graphite. However, while these non-carbon-based negative electrode materials have high capacity, they suffer from low initial efficiency, high lithium consumption during initial charging and discharging, and large irreversible capacity loss.

[0008] In addition, lithium secondary batteries have a required size depending on the application, and must be designed accordingly within a limited space. While consumer demands for increased energy density and high output performance are increasing, the use of high-capacity cathode materials requires an increased content of anode materials to match, limiting the efficiency of the battery within a limited space. Therefore, there is a need to develop batteries with improved performance, such as efficiency and lifespan, within a limited space. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Korean Patent Publication No. 10-2011-0112215 Summary of the Invention [Problem to be solved by the invention]

[0010] The present inventors have discovered that in lithium secondary batteries designed within a limited space, optimal battery performance can be achieved in a negative electrode having a specific combination by adjusting the tap density of the negative electrode active material, and have completed the present invention.

[0011] The present invention relates to a negative electrode composition, a negative electrode, a lithium secondary battery, a battery module, and a battery pack. [Means for solving the problem]

[0012] One embodiment of the present invention provides an anode composition comprising an anode active material comprising a silicon carbon composite and graphite, wherein the tap density of the graphite is equal to or greater than the tap density of the silicon carbon composite.

[0013] One embodiment of the present invention provides a negative electrode comprising: a negative electrode current collector; and a negative electrode active material layer provided on one or both sides of the negative electrode current collector and including the negative electrode composition according to the above-described embodiment.

[0014] One embodiment of the present invention provides a lithium secondary battery comprising: a positive electrode; a negative electrode according to the above-described embodiment; a separator disposed between the positive electrode and the negative electrode; and an electrolyte.

[0015] In the above-described embodiment, the positive electrode includes a lithium transition metal composite compound including nickel (Ni), cobalt (Co), and manganese (Mn) as a positive electrode active material, and the lithium transition metal composite compound may include single particles.

[0016] One embodiment of the present invention provides a battery module including the lithium secondary battery.

[0017] One embodiment of the present invention provides a battery pack including the battery module. [Effects of the Invention]

[0018] In an anode composition according to an embodiment of the present invention, the tap density of the graphite in the anode active material is equal to or greater than the tap density of the silicon carbon composite, allowing the graphite to be densely dispersed throughout the electrode, thereby ensuring uninterrupted current flow within the anode and facilitating control of the degree of orientation of the graphite within the anode. Therefore, by controlling the degree of orientation of the graphite, ion transport paths within the electrode can be uniformly designed, and lithium diffusion can occur efficiently, resulting in excellent performance during fast charging of the battery.

[0019] In addition, by controlling the degree of graphite orientation to a certain level, it is possible to prevent particle cracking during rolling, which is advantageous for dispersing the electrode slurry and facilitating rolling, thereby reducing the thickness of the electrode and increasing the mass per unit volume, thereby exhibiting more dense characteristics.

[0020] Therefore, by using a negative electrode in which the tap density between the negative electrode active materials is adjusted as described above, it is possible to easily improve the fast charging performance, efficiency, lifespan, and / or energy density of a lithium secondary battery designed in a limited space. DETAILED DESCRIPTION OF THE INVENTION

[0021] The present specification will be explained in more detail below.

[0022] In this specification, when a part is said to "comprise" a certain component, this means that it may further include other components, rather than excluding other components, unless otherwise specified.

[0023] In this specification, when a member is said to be located "on" another member, this includes not only the case where the member is in contact with the other member, but also the case where another member is present between the two members.

[0024] The terms and words used in this specification should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as meanings and concepts that are consistent with the technical idea of ​​the present invention, based on the principle that the inventors can appropriately define the concepts of terms in order to best explain their inventions.

[0025] As used herein, the singular expression of a term includes the plural expression unless the context clearly indicates otherwise.

[0026] In this specification, the term "single particle" is used to distinguish it from conventional secondary particle-like positive electrode active material particles formed by agglomeration of tens to hundreds of primary particles, and refers to both a single particle consisting of one primary particle and a similar-single particle that is an agglomeration of 30 or less primary particles.

[0027] In this specification, the average particle size (D 50The average particle size can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve (a graph curve of a particle size distribution diagram). The average particle size can be measured, for example, using a laser diffraction method. The laser diffraction method is generally capable of measuring particle sizes from the submicron range to several mm, and can provide results with high reproducibility and high resolution.

[0028] The average particle size can be measured using a Microtrac instrument (manufacturer: Microtrac, model name: S3500) with water and Triton-X100 dispersant. Specifically, the average particle size of the positive electrode active material can be measured at a refractive index of 1.5 to 1.7, and the average particle size of the negative electrode active material can be measured at a refractive index of 1.97 or 2.42. For example, the particles can be dispersed in a dispersion medium, introduced into a commercially available laser diffraction particle size analyzer, and irradiated with ultrasonic waves of approximately 28 kHz at an output of 60 W. A volume cumulative particle size distribution graph can then be obtained, and the particle size corresponding to 50% of the cumulative volume can be determined.

[0029] Preferred embodiments of the present invention will be described in detail below. However, the embodiments of the present invention may be modified in various ways, and the scope of the present invention is not limited to the embodiments described below.

[0030] One embodiment of the present invention provides an anode composition comprising an anode active material comprising a silicon carbon composite and graphite, wherein the tap density of the graphite is equal to or greater than the tap density of the silicon carbon composite.

[0031] In one embodiment of the present invention, the negative electrode active material includes a silicon carbon composite and graphite, and the tap density of the graphite may be equal to or higher than the tap density of the silicon carbon composite.

[0032] Generally, lithium secondary batteries have a size required depending on the application, and must be designed accordingly within a limited space. While consumer demands for increased energy density and high-power performance are increasing, the use of high-capacity cathode materials requires an increased content of anode materials to match, limiting the efficiency of the battery within a limited space. Furthermore, depending on the type of anode material, it is necessary to design a cathode material with efficiency that matches the efficiency of the anode material.

[0033] Because the tap density of the graphite in the negative electrode active material in the negative electrode composition according to the present invention is equal to or greater than the tap density of the silicon carbon composite, the graphite can be densely dispersed throughout the electrode, thereby ensuring uninterrupted current flow within the negative electrode and making it easy to control the degree of orientation of the graphite within the negative electrode. Therefore, by controlling the degree of orientation of the graphite consistently, ion transport paths within the electrode can be uniformly designed, and lithium diffusion can occur efficiently, resulting in excellent performance during fast charging of the battery.

[0034] In addition, by controlling the degree of graphite orientation to a certain level, it is possible to prevent particle cracking during rolling, which is advantageous for dispersing the electrode slurry and facilitating rolling, thereby reducing the thickness of the electrode and increasing the mass per unit volume, thereby exhibiting more dense characteristics.

[0035] Therefore, by using a negative electrode in which the tap density between the negative electrode active materials is adjusted as described above, it is possible to easily improve the fast charging performance, efficiency, lifespan, and / or energy density of a lithium secondary battery designed in a limited space.

[0036] On the other hand, if the tap density of the graphite is lower than the tap density of the silicon carbon composite, the graphite will not be dispersed in the electrode but will aggregate, reducing the dispersibility of the slurry and making it unfavorable for rolling, increasing the thickness of the electrode, and forming void regions in the electrode, which is unfavorable in terms of electrode uniformity.

[0037] Herein, the silicon carbon composite is a composite of Si and C, and contains both Si and C (e.g., graphite). For example, peaks of Si and C can be observed by elemental analysis such as XRD or NMR. Herein, the silicon carbon composite can be expressed as Si / C. The silicon carbon composite may consist of unbonded Si and C, but may contain additional components as needed. For example, the silicon carbon composite may or may not contain silicon carbide, represented by SiC. When the silicon carbon composite contains silicon carbide, its content is 3 wt % or less. The silicon carbon composite may exist in a crystalline state, an amorphous state, or a mixture thereof. For example, C in the silicon carbon composite may exist in an amorphous state. The silicon carbon composite may be a physical or chemical composite of the carbon and silicon material, and is not limited as long as the carbon and silicon material form a composite.

[0038] Specifically, the silicon carbon composite may have a structure in which carbon is bonded to silicon or silicon oxide particles and then fired to form a carbon material on the surface of the particles, or a structure in which carbon is dispersed in an atomic state inside silicon particles, or a structure in which a core of silicon and carbon is surrounded by graphite, graphene, amorphous carbon, or the like.

[0039] According to one embodiment, the silicon carbon composite comprises porous carbon-based particles and silicon located on the surface or in the internal pores of the porous carbon-based particles.

[0040] According to one embodiment, the silicon carbon composite can be produced by a method including the step of forming silicon on the surface and in the internal pores of porous carbon particles.

[0041] The porous carbon-based particles can be prepared by a method known in the art, for example, by carbonizing organic materials such as petroleum-based materials, polymers, etc., or by chemically treating and then carbonizing naturally occurring materials such as palm bark, etc. As another example, the porous carbon-based particles can be prepared by a method including the step of etching carbon-based particles having internal pores to expand the internal pores of the carbon-based particles.

[0042] The step of expanding the internal pores of the carbon-based particles may be performed in a nitrogen (N2), oxygen (O2), or air atmosphere, and the flow rate of the oxygen (O2) or oxygen-containing air may be controlled to 0.1 L / min to 10 L / min.

[0043] The step of expanding the internal pores of the carbon-based particles may be performed at a temperature ranging from 400° C. to 1200° C. for 30 minutes to 4 hours.

[0044] The pore characteristics of the resulting porous carbon-based particles may vary depending on the conditions for expanding the internal pores of the carbon-based particles.

[0045] The step of forming the silicon may be performed using a chemical vapor deposition method, in which silicon nanoparticles are deposited on the surfaces and / or in the pores of the carbon-based particles with expanded pores, thereby forming silicon in the form of a film, islands, or a mixture thereof.

[0046] The silicon nanoparticles may be crystalline, semi-crystalline, amorphous, or a combination thereof.

[0047] In one embodiment of the present invention, the tap density of the graphite may be 0.9 g / cc or more and 1.2 g / cc or less, specifically 1 g / cc or more and 1.2 g / cc or less, 1.03 g / cc or more and 1.15 g / cc or less, or 1.05 g / cc or more and 1.12 g / cc or less.

[0048] When the graphite tap density is within this range, the graphite can be uniformly dispersed within the electrode without agglomeration. On the other hand, when the graphite tap density is below this range, the graphite agglomerates rather than being dispersed within the electrode, or void regions form within the electrode, which is detrimental to the uniformity of the electrode. When the graphite tap density is above this range, the density of the graphite within the electrode becomes too high, which can cause particle cracking during rolling and is detrimental to lithium diffusion.

[0049] In one embodiment of the present invention, the tap density of the silicon carbon composite may be 0.5 g / cc or more and 1.15 g / cc or less, specifically 0.55 g / cc or more and 1.1 g / cc or less, or 0.58 g / cc or more and 1.08 g / cc or less.

[0050] When the tap density of the silicon carbon composite satisfies the above range, the silicon carbon composite can be uniformly dispersed within the electrode without agglomeration. On the other hand, when the tap density of the silicon carbon composite is below the above range, the silicon carbon composite may agglomerate rather than be dispersed within the electrode, or void regions may form within the electrode, resulting in poor electrode uniformity. When the tap density of the silicon carbon composite exceeds the above range, the density of the silicon carbon composite within the electrode becomes too high, which can cause particle cracking during rolling and result in poor lithium diffusion.

[0051] In one embodiment of the present invention, the tap density of the graphite may have the same value as the tap density of the silicon carbon composite.

[0052] In one embodiment of the present invention, the graphite may have a tap density greater than the tap density of the silicon carbon composite.

[0053] In this specification, the tap density can be measured using a conventional tap density measuring device, specifically, a TAP-2S manufactured by LOGAN Corp. For example, the tap density may be the density calculated by placing 40 g of a sample in a container and tapping it 1000 times.

[0054] The graphite may be natural graphite or artificial graphite, or may be a mixture of natural graphite and artificial graphite.

[0055] When the graphite is a mixture of natural graphite and artificial graphite, the weight ratio of the natural graphite to the artificial graphite may be 50:50 to 90:10, specifically 60:40 to 80:20, or 65:35 to 75:25.

[0056] In one embodiment of the present invention, the average particle size (D 50 ) may be 1 μm or more. The average particle size of the silicon carbon composite may be 15 μm or less. For example, the average particle size (D 50 ) may be 1 μm or more and 15 μm or less, more than 1 μm and less than 15 μm, 2 μm or more and 14 μm or less, 3 μm or more and 13 μm or less, 3 μm to 10 μm, 4 μm to 8 μm, or 5 μm to 8 μm.

[0057] The silicon carbon composite can improve the battery's lifespan even when formed with a small average particle size of 1 μm to 15 μm. For example, when the average particle size of the silicon carbon composite is in the range of 1 μm to 15 μm, the volume expansion and contraction rate during charge and discharge is reduced, improving the battery's lifespan. In addition, the specific surface area is prevented from increasing excessively, and side reactions with the electrolyte during cycling are prevented, improving the battery's lifespan.

[0058] In one embodiment of the present invention, the average particle size (D 50) may be 10 μm to 20 μm. Specifically, it may be 15 μm to 20 μm. When the average particle size of the graphite falls within the above range, the influence of particle aggregation is reduced, and the dispersibility of the slurry can be improved.

[0059] According to one embodiment of the present invention, the average particle size of the silicon carbon composite is smaller than the average particle size of the graphite.

[0060] According to one embodiment of the present invention, the sphericity (aspect ratio) of the graphite is 0.8 to 0.9, and the sphericity of the silicon carbon composite is 0.3 to 0.7. When the sphericity of the graphite and the silicon carbon composite is within the above ranges, advantages are obtained in terms of production yield and rolling density. When the sphericity is below the upper limit, the material yield is excellent and production costs are reduced. When the sphericity is above the lower limit, the rolling density of the electrode is high and the possibility of phenomena such as particle depressions is reduced.

[0061] According to one embodiment of the present invention, the sphericity of the graphite may be 0.8 to 0.9, or 0.83 to 0.90, and the sphericity of the silicon carbon composite may be 0.3 to 0.7, or 0.42 to 0.70.

[0062] In this specification, sphericity may be calculated by dividing the circumference of a circle having the same area as the projected image by the perimeter of the projected image when a particle is projected, and can be specifically expressed by the following Equation 1. The sphericity can be determined from an SEM image. Cross-sectional analysis of the negative electrode active material can be performed using an ion milling device. Specifically, an electrode sample prepared by coating the negative electrode active material on copper foil is milled using a Hitachi IM4000 device. Specifically, the sample is irradiated with an ion beam at a voltage of 1.5 kV for approximately 3 to 4 hours, and then a cross-sectional image can be measured using a Hitachi S-4800 SEM. The sphericity of the negative electrode active material can be measured based on the measured SEM cross-sectional image.

[0063] [Formula 1] Sphericity = Circumference of a circle with the same area as the projected image of a particle / Perimeter of the projected image

[0064] According to one embodiment of the present invention, the graphite has a true density of 2 g / cc to 3 g / cc, and the silicon carbon composite has a true density of 1.8 g / cc to 2.2 g / cc. When the graphite and silicon carbon composite have a true density of 2.2 g / cc or less, dispersion in the slurry is relatively easy, preventing positional deviation after coating of the negative electrode active material layer. When the true density is 1.8 g / cc or more, phenomena such as particle scattering are prevented, and adjustment of the solid content of the slurry is easy. According to one embodiment of the present invention, the graphite may have a true density of 2 g / cc to 3 g / cc, 2 g / cc to 2.24 g / cc, or 2.23 g / cc to 2.24 g / cc, and the silicon carbon composite may have a true density of 1.8 g / cc to 2.2 g / cc, or 1.9 g / cc to 2.2 g / cc.

[0065] The true density can be calculated by calculating the volume of the sample from the difference in volume between before and after the sample is placed in a container of known volume and after filling it with He gas, and then dividing the weight of the sample by the volume.

[0066] According to one embodiment of the present invention, the BET specific surface area of ​​the graphite is 1 m 2 / g~3m 2 / g, and the BET specific surface area of ​​the silicon carbon composite is 1 m 2 / g~10m 2 / g. The BET specific surface area of ​​the graphite is 1 m 2 / g~3m 2 / g, 1.0m 2 / g~2.2m 2 / g, 1.0m 2 / g~2.1m 2 / g, 1.7m 2 / g~3.0m 2 / g, 1.7m 2 / g~2.2m 2 / g, or 1.7m 2 / g~2.1m2 / g, and the BET specific surface area of ​​the silicon carbon composite may be 1 m 2 / g~10m 2 / g, 1.0m 2 / g~7.1m 2 / g, 1.0m 2 / g~6.7m 2 / g, 3.1m 2 / g~10m 2 / g, 3.1m 2 / g~7.1m 2 / g, or 3.1m 2 / g~6.7m 2 / g.

[0067] Generally, the smaller the BET of a material, the easier it is to disperse the material in the slurry during mixing, which is advantageous for increasing electrode density. When the BET specific surface area of ​​the graphite and silicon carbon composite is within the above range, it is possible to prevent the acceleration of side reactions in the electrolyte, thereby preventing deterioration of cycle life and the acceleration of side reactions during high-temperature storage. In one example, the specific surface area is measured by the BET method. Specifically, the measurement object is degassed at 300°C for 1 hour using a BET measurement device (BEL-SORP-mini, Nippon Bell) and subjected to N2 adsorption / desorption at 77K. That is, in this specification, the BET specific surface area refers to the specific surface area of ​​the particles themselves measured by the above-mentioned measurement method.

[0068] According to one embodiment of the present invention, the negative electrode composition contains 3 to 30 parts by weight of a silicon carbon composite per 100 parts by weight of the total negative electrode active material. For example, the silicon carbon composite may be contained in an amount of 3 to 20 parts by weight, or 3 to 13 parts by weight, or preferably 5 to 10 parts by weight, per 100 parts by weight of the negative electrode active material. By using a silicon carbon composite in this range, excellent battery characteristics can be achieved in combination with the above-mentioned positive electrode material. In particular, when the silicon carbon composite is contained in an amount of 3 parts by weight or more, the effects of using the silicon carbon composite can be fully demonstrated. Furthermore, since silicon carbon composites have a higher capacity than SiOx-based active materials, it is difficult to balance the capacity with the positive electrode active material when used in excess. In particular, when the silicon carbon composite is contained in an amount of 30 parts by weight or less, expansion during charge and discharge can be prevented, improving cycle characteristics.

[0069] The silicon carbon composite is a material that has higher capacity and higher efficiency than silicon-based oxides, and even when it does not contain a conductive material, it can exhibit superior resistance effects compared to anodes that contain silicon-based oxides and conductive materials. Furthermore, since the silicon carbon composite exhibits higher Si crystallinity than silicon-based oxides, it can exhibit superior effects during high-power evaluation.

[0070] In one embodiment of the present invention, the graphite may be natural graphite, artificial graphite, or a mixture thereof. The graphite may be included in an amount of 70 parts by weight to 97 parts by weight based on 100 parts by weight of the total negative electrode active material included in the negative electrode active material layer.

[0071] The graphite may be included in an amount of 75 parts by weight or more, 80 parts by weight or more, or 85 parts by weight or more, based on 100 parts by weight of the total negative electrode active material. The graphite may be included in an amount of 95 parts by weight or less, 93 parts by weight or less, or 90 parts by weight or less, based on 100 parts by weight of the total negative electrode active material. When the graphite is a mixture of artificial graphite and natural graphite, the artificial graphite and natural graphite may be included in an amount of 90:10 parts by weight to 50:50 parts by weight, 85:15 parts by weight to 60:40 parts by weight, 80:20 parts by weight to 60:40 parts by weight, 80:20 parts by weight to 65:35 parts by weight, or 75:25 parts by weight to 65:35 parts by weight, based on 100 parts by weight of the graphite.

[0072] In one embodiment of the present invention, the weight ratio of the graphite to the silicon carbon composite may be 0.1:99.9 to 30:70, 1:99 to 20:80, 5:95 to 20:80, 5:95 to 15:85, 8:92 to 12:88, or 10:90 to 12:88.

[0073] In one embodiment of the present invention, the negative electrode active material may be contained in an amount of 80 parts by weight or more and 99.9 parts by weight or less, preferably 90 parts by weight or more and 99.9 parts by weight or less, more preferably 95 parts by weight or more and 99.9 parts by weight or less, and even more preferably 97 parts by weight or more and 99.9 parts by weight or less, relative to 100 parts by weight of the solid content of the negative electrode composition.

[0074] In one embodiment of the present invention, the negative electrode composition may further include a negative electrode binder in addition to the silicon carbon composite and graphite.

[0075] The negative electrode binder may improve adhesion between negative electrode active material particles and between the negative electrode active material particles and the negative electrode current collector. Any material known in the art may be used as the negative electrode binder. Non-limiting examples of the negative electrode binder include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and substances in which hydrogen is substituted with Li, Na, Ca, or the like, or various copolymers thereof.

[0076] The negative electrode binder may be included in an amount of 0.1 parts by weight to 50 parts by weight, for example, preferably 0.3 parts by weight to 35 parts by weight, more preferably 0.5 parts by weight to 10 parts by weight, based on 100 parts by weight of the solid content of the negative electrode composition.

[0077] The negative electrode composition may not contain a conductive material, but may further contain a conductive material as needed. The conductive material contained in the negative electrode composition is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, or 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 may be used. The content of the conductive material in the negative electrode active material layer may be 0.01 to 30 parts by weight, preferably 0.03 to 25 parts by weight, per 100 parts by weight of the negative electrode active material layer.

[0078] One embodiment of the present invention provides a negative electrode comprising: a negative electrode current collector; and a negative electrode active material layer provided on one or both sides of the negative electrode current collector and including the negative electrode composition according to the above-described embodiment.

[0079] According to one embodiment of the present invention, the porosity of the negative electrode active material layer is 23% to 28%, for example, 24% to 27%, or 25% to 26%. When the porosity is below the upper limit of the range, a decrease in electrode density can be prevented, thereby preventing a decrease in cell energy density. When the porosity is above the lower limit of the range, cracking of active material particles in the electrode can be prevented. The porosity can be measured as follows. The porosity of the electrode active material layer can be calculated from the true density of the material constituting the electrode active material layer, the weight and thickness of the active material, etc. Specifically, the porosity is a value calculated using the following formula: Porosity of electrode active material layer (%) = {1 - (electrode active material layer Dense degree / electrode active material layer true density)}×100

[0080] The true density of the electrode active material layer is 3*4 (cm 2 The density of the electrode active material layer is measured when an electrode of the same size is pressed in a press device until the thickness of the negative electrode does not change, and the density of the electrode active material layer is measured when an electrode of the same size is taken before pressing.

[0081] One embodiment of the present invention provides a lithium secondary battery comprising: a positive electrode; a negative electrode according to the above-described embodiment; a separator disposed between the positive electrode and the negative electrode; and an electrolyte.

[0082] The positive electrode may include a positive electrode current collector and a positive electrode active material layer provided on one or both surfaces of the positive electrode current collector.

[0083] The positive electrode active material layer may have a porosity of 18% to 21%, for example, 20% to 21%.

[0084] According to one embodiment, the positive electrode includes a lithium complex transition metal compound including nickel (Ni), cobalt (Co), and manganese (Mn) as a positive electrode active material.

[0085] In one embodiment of the present invention, the positive electrode active material contains nickel, cobalt, and manganese, and may further contain aluminum.

[0086] In this specification, the positive electrode active material contains 80 mol % or more, or 80 mol % or more and less than 100 mol % of nickel among metals excluding lithium, and the lithium transition metal composite compound containing 80 mol % or more and less than 100 mol % of nickel among metals excluding lithium may include one or a mixture of two or more types represented by the following Chemical Formula 1:

[0087] [Chemical formula 1] Li a Ni 1-b-c-d Co b Mn c Q d O 2+δ In the above formula, Q is any one or more elements selected from the group consisting of Na, K, Mg, Ca, Sr, Ni, Co, Ti, Al, Si, Sn, Mn, Cr, Fe, V, and Zr, where 1 ≦ a ≦ 1.5, 0 < b ≦ 0.5, 0 < c ≦ 0.5, 0 ≦ d ≦ 0.1, 0 < b + c + d ≦ 20, and -0.1 ≦ δ ≦ 1.0.

[0088] In the lithium composite transition metal compound of Chemical Formula 1, Li may be contained in a content corresponding to a, that is, 1 ≦ a ≦ 1.5. If a is less than 1, the capacity may decrease. If it exceeds 1.5, the particles may sinter in the firing process, making it difficult to manufacture the positive electrode active material. Considering the improvement effect of the capacity characteristics of the positive electrode active material by controlling the content of Li and the balance of the sinterability during the manufacture of the active material, the Li may more preferably be contained in a content of 1.1 ≦ a ≦ 1.2.

[0089] In the lithium composite transition metal compound of Chemical Formula, Ni may be contained in a content corresponding to 1-(b + c + d), for example, 0.8 ≦ 1-(b + c + d) < 1. If the content of Ni in the lithium composite transition metal compound of Chemical Formula 1 is a composition of 0.8 or more, a sufficient amount of Ni contributing to charge and discharge can be ensured, and high capacity can be achieved. Preferably, 1-(b + c + d), which is the content of Ni, may be 0.88, preferably 0.9 or more, and more preferably 0.93 or more. Preferably, 1-(b + c + d), which is the content of Ni, may be 0.99 or less, 0.95 or less.

[0090] In the lithium composite transition metal compound of Chemical Formula 1, Co may be contained in a content corresponding to b, that is, 0 < b ≦ 0.5. If the content of Co in the lithium composite transition metal compound of Chemical Formula 1 exceeds 0.5, there is a risk of cost increase. Considering the significance of the improvement effect of the capacity characteristics by containing Co, more specifically, the Co may be contained in a content of 0.03 ≦ b ≦ 0.2.

[0091] In the lithium composite transition metal compound of Chemical Formula 1, Mn may be contained in a content corresponding to c, that is, a content of 0 < c ≤ 0.5. When c in the lithium composite transition metal compound of Chemical Formula 1 exceeds 0.5, the output characteristics and capacity characteristics of the battery may rather deteriorate. More specifically, Mn may be contained in a content of 0.01 ≤ c ≤ 0.2.

[0092] In the lithium composite transition metal compound of Chemical Formula 1, Q may be a doping element contained in the crystal structure of the lithium composite transition metal compound, and Q may be contained in a content corresponding to d, that is, 0 ≤ d ≤ 0.1. Q may be one or more selected from Na, K, Mg, Ca, Sr, Ni, Co, Ti, Al, Si, Sn, Mn, Cr, Fe, V, and Zr. For example, Q may be Al.

[0093] In one embodiment of the present invention, the lithium composite transition metal compound may contain single particles.

[0094] In one embodiment of the present invention, the lithium composite transition metal compound may further contain secondary particles.

[0095] The single particles can be produced by mixing and firing a transition metal precursor and a lithium raw material substance. The secondary particles may be produced by a method different from that of the single particles, and their composition may be the same as or different from the composition of the single particles.

[0096] For example, the calcination is performed at a temperature that allows the formation of single particles. To achieve this, the calcination must be performed at a temperature higher than that used for the production of secondary particles. For example, when the precursor composition is the same, the calcination must be performed at a temperature about 30°C to 100°C higher than that used for the production of secondary particles. The calcination temperature for forming the single particles may vary depending on the metal composition of the precursor. For example, when a high-nickel (Ni) NCM-based lithium transition metal oxide having a nickel (Ni) content of 80 mol% or more is to be formed into single particles, the calcination temperature may be about 700°C to 1000°C, preferably about 800°C to 950°C. When the calcination temperature satisfies the above range, a positive electrode active material containing single particles with excellent electrochemical properties can be produced. When the calcination temperature is lower than 790°C, a positive electrode active material containing a lithium transition metal compound in the form of secondary particles is produced. When the calcination temperature exceeds 950°C, excessive calcination may occur, resulting in an inadequate formation of a layered crystal structure and reduced electrochemical properties.

[0097] In this specification, the term "single particle" is used to distinguish it from conventional secondary particles formed by agglomeration of tens to hundreds of primary particles, and is a concept that includes a single particle consisting of one primary particle and a similar-single particle that is an agglomeration of 30 or less primary particles.

[0098] Specifically, in the present invention, a single particle may be a single particle consisting of one primary particle or a similar-single particle which is an aggregate of 30 or less primary particles, and a secondary particle may be in the form of an aggregate of several hundred primary particles.

[0099] In one embodiment of the present invention, the tap density of the secondary particles may be greater than the tap density of the single particles.

[0100] In one embodiment of the present invention, the tap density of the secondary particles may be 2 g / cc or more and 3.2 g / cc or less, specifically 2.1 g / cc or more and 3 g / cc or less, 2.2 g / cc or more and 2.9 g / cc or less, or 2.3 g / cc or more and 2.8 g / cc or less.

[0101] When the tap density of the secondary particles of the positive electrode active material satisfies the above range, the secondary particles of the positive electrode active material may be uniformly dispersed in the electrode without agglomeration.

[0102] In one embodiment of the present invention, the tap density of the single particle may be 1.3 g / cc or more and 2.3 g / cc or less, specifically 1.4 g / cc or more and 2.3 g / cc or less, 1.5 g / cc or more and 2.3 g / cc or less, or 1.6 g / cc or more and 2.25 g / cc or less.

[0103] When the tap density of the single particles of the positive electrode active material satisfies the above range, the single particles of the positive electrode active material may be uniformly dispersed in the electrode without agglomeration.

[0104] In one embodiment of the present invention, the tap density of the single particle may be greater than the tap density of the graphite.

[0105] In one embodiment of the present invention, the average particle diameter (D 50 ) may be 1 μm or more. The average particle size of the single particles may be 12 μm or less. For example, the average particle size of the single particles may be 1 μm or more and 12 μm or less, 1 μm or more and 8 μm or less, 1 μm or more and 6 μm or less, more than 1 μm and 6 μm or less, 2 μm or more and 6 μm or less, or 3 μm or more and 5 μm or less.

[0106] The single particles can have excellent particle strength even when formed into a small particle size of 1 μm to 12 μm, thereby reducing the increase in fine particles in the electrode due to particle cracking, thereby improving the lifespan of the battery. For example, the single particles can have a resistance of 650 kgf / cm 2 The particle strength may be 100 MPa to 300 MPa when the particle is rolled with a force of 650 kgf / cm. 2 Even if the electrode is rolled with a strong force, the phenomenon of increasing fine particles in the electrode due to cracking of particles is alleviated, thereby improving the life characteristics of the battery.

[0107] The method for forming the single particles is not particularly limited, but may generally be formed by over-firing at an elevated firing temperature, or may be prepared by using an additive such as a grain growth promoter that is useful for over-firing, or by changing the starting material.

[0108] The single particles have high rigidity and exhibit relatively low degradation in battery performance even when the electrode density is high. Therefore, the energy density can be increased by adjusting the average particle size range of the single particles and the silicon carbon composite.

[0109] In one embodiment of the present invention, the average particle size of the single particle may be smaller than the average particle size of the silicon carbon composite.

[0110] When the average particle size of the single particles is smaller than the average particle size of the silicon carbon composite, the diffusion resistance of the single particles is relatively reduced, thereby improving the lifespan performance. That is, as the average particle size of the single particles increases, the diffusion resistance increases. When the average particle size of the single particles is larger than the average particle size of the silicon carbon composite, the diffusion resistance increases relatively, which may cause lithium deposition, resulting in a decrease in battery performance and a decrease in lifespan performance.

[0111] Furthermore, when the average particle size of the single particles is smaller than the average particle size of the silicon carbon composite, side reactions with the electrolyte due to an increase in specific surface area can be prevented, thereby improving the lifespan.

[0112] According to one embodiment of the present invention, the average particle size of the single particles may be 1 μm to 12 μm smaller than the average particle size of the silicon carbon composite, specifically 1.5 μm to 11.5 μm, or 2 μm to 11 μm smaller.

[0113] When the average particle size of the single particles is smaller than the average particle size of the silicon carbon composite, for example, when the above range is satisfied, the diffusion resistance of the single particles is relatively reduced, and the life performance can be improved. That is, as the average particle size of the single particles increases, the diffusion resistance increases. When the average particle size of the single particles is larger than the average particle size of the silicon carbon composite, the diffusion resistance increases relatively, and lithium deposition can occur, resulting in a decrease in battery performance and a decrease in life performance.

[0114] Furthermore, when the average particle size of the single particle is smaller than the average particle size of the silicon carbon composite, for example, when the average particle size satisfies the above range, side reactions with the electrolyte due to an increase in specific surface area can be prevented, thereby improving the lifespan.

[0115] According to one embodiment of the present invention, the ratio of the average particle size of the single particle to the average particle size of the silicon carbon composite may be 1.5:2 to 1.5:20.

[0116] When the above range is satisfied, the diffusion resistance of the single particles is relatively reduced, and the lifespan performance can be improved. That is, as the average particle size of the single particles increases, the diffusion resistance increases. When the average particle size of the single particles is larger than the average particle size of the silicon carbon composite, the diffusion resistance increases relatively, which can cause lithium precipitation, resulting in a decrease in battery performance and a decrease in lifespan performance.

[0117] Furthermore, when the average particle size of the single particle is smaller than the average particle size of the silicon carbon composite, for example, when the average particle size satisfies the above range, side reactions with the electrolyte due to an increase in specific surface area can be prevented, thereby improving the lifespan.

[0118] In one embodiment of the present invention, the lithium transition metal composite compound further includes secondary particles, and the average particle size of the single particles is smaller than the average particle size of the secondary particles.

[0119] In the present invention, the single particle may be a single particle consisting of one primary particle or a similar-single particle which is an aggregate of 30 or less primary particles, and the secondary particle may be in the form of an aggregate of several hundred primary particles.

[0120] The lithium transition metal composite compound may further include secondary particles. The secondary particles refer to a form formed by agglomeration of primary particles, and can be distinguished from the concept of single particles, which includes one primary particle, one single particle, or a similar-single particle that is an agglomeration of 30 or less primary particles.

[0121] The average particle size of the secondary particles (D 50 ) may be 1 μm to 20 μm. Specifically, it may be 2 μm to 17 μm, 3 μm to 15 μm, 5 μm to 15 μm, 7 μm to 15 μm, or 9 μm to 15 μm.

[0122] The specific surface area (BET) of the secondary particles is 0.05 m 2 / g~10m 2 / g, preferably 0.1m 2 / g~1m 2 / g, more preferably 0.3m 2 / g~0.8m 2 / g.

[0123] In one embodiment of the present invention, the secondary particles are aggregates of primary particles, and the average particle size of the primary particles is 0.5 μm to 3 μm. Specifically, the secondary particles may be in the form of aggregates of several hundred primary particles, and the average particle size of the primary particles may be 0.6 μm to 2.8 μm, 0.8 μm to 2.5 μm, or 0.8 μm to 1.5 μm.

[0124] When the average particle size of the primary particles satisfies the above range, a single-particle positive electrode active material with excellent electrochemical properties can be formed. If the average particle size of the primary particles is too small, the number of agglomerates of the primary particles forming the lithium nickel-based oxide particles increases, reducing the effect of suppressing particle cracking during rolling. If the average particle size of the primary particles is too large, the lithium diffusion path within the primary particles becomes longer, increasing resistance and reducing output characteristics.

[0125] In one embodiment of the present invention, the average particle size of the single particles may be smaller than the average particle size of the secondary particles, thereby allowing the single particles to have excellent particle strength even when formed to have a small particle size, thereby mitigating the phenomenon of an increase in fine particles in the electrode due to particle cracking, and thereby improving the life characteristics of the battery.

[0126] In one embodiment of the present invention, the average particle size of the single particles is 1 μm to 18 μm smaller than the average particle size of the secondary particles.

[0127] For example, the average particle size of the single particles may be 1 μm to 16 μm smaller, 1.5 μm to 15 μm smaller, or 2 μm to 14 μm smaller than the average particle size of the secondary particles.

[0128] When the average particle size of the single particles is smaller than the average particle size of the secondary particles, for example, when the above range is satisfied, the single particles can have excellent particle strength even when formed to have a small particle size, thereby mitigating the phenomenon of an increase in fine particles in the electrode due to particle cracking, and improving the life characteristics and energy density of the battery.

[0129] In one embodiment of the present invention, the average particle size of the silicon carbon composite may be smaller than that of the graphite. When the average particle size of the silicon carbon composite is smaller than that of the graphite, the volume expansion / contraction rate during charge / discharge is reduced, thereby reducing particle cracking and improving the battery life.

[0130] In the lithium secondary battery according to the above-described embodiment, the negative electrode active material may further contain a carbon-based active material. Specifically, the carbon-based active material may be graphite. The graphite may be natural graphite, artificial graphite, or a mixture thereof.

[0131] According to an embodiment of the present invention, the average particle diameter of the silicon-carbon composite may be 1 μm to 25 μm smaller than the average particle diameter of the graphite. For example, the average particle diameter of the silicon-carbon composite may be 2 μm to 24 μm smaller than the average particle diameter of the graphite, 3 μm to 23 μm smaller, or 4 μm to 22 μm smaller.

[0132] When the average particle diameter of the silicon-carbon composite is smaller than the average particle diameter of the graphite, for example, when the above range is satisfied, there is an effect that the life performance of the battery is further improved. <​​​​​​​​​​​​​​​​​​​

[0138] When the average particle sizes of the secondary particles, the single particles, and the graphite are A, B, and C, respectively, B <A<Cであってもよい。

[0139] When the average particle sizes of the secondary particles, the graphite, and the silicon carbon composite are A, C, and D, respectively, D≦A <Cであってもよい。

[0140] When the above range is satisfied, the battery life performance is improved.

[0141] In one embodiment of the present invention, in the lithium secondary battery according to the above-described embodiment, the single particles are included in an amount of 15 parts by weight to 100 parts by weight based on 100 parts by weight of the positive electrode active material, and the silicon carbon composite is included in an amount of 3 parts by weight to 30 parts by weight based on 100 parts by weight of the negative electrode active material.

[0142] In one embodiment of the present invention, the single particles are contained in an amount of 15 to 100 parts by weight relative to 100 parts by weight of the positive electrode active material, or 20 to 100 parts by weight, or 30 to 100 parts by weight relative to 100 parts by weight of the positive electrode active material.

[0143] For example, the single particles may be included in an amount of 15 parts by weight or more, 20 parts by weight or more, 25 parts by weight or more, 30 parts by weight or more, 35 parts by weight or more, 40 parts by weight or more, or 45 parts by weight or more, relative to 100 parts by weight of the positive electrode active material. For example, the single particles may be included in an amount of 100 parts by weight or less, 90 parts by weight or less, 80 parts by weight or less, 70 parts by weight or less, or 60 parts by weight or less, relative to 100 parts by weight of the positive electrode active material.

[0144] When the single particles are contained in the above range, excellent battery characteristics can be exhibited in combination with the above-mentioned negative electrode material. In particular, when the single particles are contained in an amount of 15 parts by weight or more, the phenomenon of an increase in fine particles in the electrode due to particle cracking during the rolling process after electrode fabrication is mitigated, thereby improving the battery life characteristics.

[0145] In one embodiment of the present invention, the lithium composite transition metal compound may further include secondary particles, and the amount of the secondary particles may be 85 parts by weight or less relative to 100 parts by weight of the positive electrode active material. The amount of the secondary particles may be 80 parts by weight or less, 75 parts by weight or less, 70 parts by weight or less, or 60 parts by weight or less relative to 100 parts by weight of the positive electrode active material. The amount of the secondary particles may be 10 parts by weight or more, 20 parts by weight or more, 30 parts by weight or more, or 40 parts by weight or more relative to 100 parts by weight of the positive electrode active material.

[0146] In one embodiment of the present invention, the weight ratio of the single particles to the secondary particles may be 1:9 to 9:1, 2:8 to 8:2, 3:7 to 7:3, or 4:6 to 6:4.

[0147] When the above range is satisfied, the above-described effects due to the presence of the single particle positive electrode active material can be maximized. When the secondary particle positive electrode active material is included, the components thereof may be the same as those exemplified as the single particle positive electrode active material described above, or may be other components, and may refer to an aggregated form of single particles.

[0148] In one embodiment of the present invention, the positive electrode active material may be contained in an amount of 80 parts by weight or more and 99.9 parts by weight or less, preferably 90 parts by weight or more and 99.9 parts by weight or less, more preferably 95 parts by weight or more and 99.9 parts by weight or less, and even more preferably 98 parts by weight or more and 99.9 parts by weight or less, relative to 100 parts by weight of the positive electrode active material layer.

[0149] According to one embodiment of the present invention, the positive electrode active material layer further includes a positive electrode binder and a conductive material.

[0150] The positive electrode binder may serve to improve adhesion between positive electrode active material particles and between the positive electrode active material particles and the positive electrode current collector. Any positive electrode binder known in the art may be used, and non-limiting examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These binders may be used alone or in combination.

[0151] The positive electrode binder may be included in an amount of 0.1 parts by weight to 50 parts by weight, for example, preferably 0.3 parts by weight to 35 parts by weight, more preferably 0.5 parts by weight to 20 parts by weight, based on 100 parts by weight of the positive electrode active material layer.

[0152] The conductive material contained in the positive electrode active material layer is used to impart conductivity to the electrode, and can be any material that has electronic conductivity without causing chemical changes in the battery. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. These may be used alone or in combination.

[0153] Specifically, in one embodiment, the conductive material may include one or more of single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). The conductive material may be included in an amount of 0.1 to 2 parts by weight, preferably 0.3 to 1.5 parts by weight, more preferably 0.5 to 1.2 parts by weight, based on 100 parts by weight of the composition for a positive electrode active material layer.

[0154] The positive electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like may be used. The positive electrode current collector may typically have a thickness of 1 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesive strength of the positive electrode active material. The positive electrode current collector may be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0155] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, the current collector may be made of copper, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, or the like. Specifically, a transition metal that easily adsorbs carbon, such as copper or nickel, may be used as the current collector. The thickness of the current collector may be 1 μm to 500 μm, but is not limited thereto.

[0156] In one embodiment of the present invention, the thickness of the positive electrode active material layer and the negative electrode active material layer is 10 μm or more and 500 μm or less. The thickness of the positive electrode active material layer may be 90% to 110%, for example 95% to 105%, of the thickness of the negative electrode active material layer, or these thicknesses may be the same. Specifically, the thickness of the positive electrode and the negative electrode active material layer may be 15 μm or more and 400 μm or less, 20 μm or more and 300 μm or less, 25 μm or more and 200 μm or less, or 30 μm or more and 100 μm or less.

[0157] In one embodiment of the present invention, the loading amount per unit volume of the positive electrode active material layer is 250 mg / 25 cm 2 ~900mg / 25cm 2 The loading amount per unit volume of the negative electrode active material layer is 100 mg / 25 cm 2 ~600mg / 25cm 2 Specifically, the loading amount per unit volume of the positive electrode active material layer is 270 mg / 25 cm 2 ~800mg / 25cm 2 , 285mg / 25cm 2 ~700mg / 25cm 2 , or 300 mg / 25 cm 2 ~600mg / 25cm 2 The loading amount per unit volume of the negative electrode active material layer may be 120 mg / 25 cm 2 ~500mg / 25cm 2 , 135mg / 25cm 2 ~400mg / 25cm 2 , 150mg / 25cm 2 ~300mg / 25cm 2 may be.

[0158] The positive and negative electrodes can be fabricated by a conventional method for fabricating positive and negative electrodes, except for using the above-described positive and negative active materials. Specifically, the active material layer can be fabricated by coating a current collector with a composition for forming an active material layer, including the above-described active materials and, optionally, a binder and a conductive material, followed by drying and rolling. The types and contents of the positive and negative active materials, binder, and conductive material are as described above. The solvent may be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. One or a mixture of two or more of these solvents may be used. The amount of solvent used should be sufficient to dissolve or disperse the active material, conductive material, and binder, while maintaining a viscosity that allows excellent thickness uniformity during subsequent coating for fabricating positive and negative electrodes, taking into account the coating thickness and manufacturing yield of the slurry. Alternatively, the positive electrode and the negative electrode can be produced by casting the active material layer-forming composition on a separate support, peeling the composition from the support, and laminating the resulting film on a current collector.

[0159] The separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator typically used in secondary batteries can be used without particular limitation. It is particularly preferred that the separator exhibits low resistance to electrolyte ion migration and excellent electrolyte humidification. Specifically, porous polymer films, such as those made from polyolefin polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminate structures of two or more layers thereof, may be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. To ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymeric material may be used, and it may be selectively used as a single-layer or multi-layer structure.

[0160] 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 manufacturing lithium secondary batteries.

[0161] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0162] Examples of the non-aqueous organic solvent that can be used include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0163] In particular, among the carbonate organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, can be preferably used as high-viscosity organic solvents, because they have a high dielectric constant and dissociate lithium salts well. When such cyclic carbonates are mixed in an appropriate ratio with linear carbonates having low viscosity and low dielectric constants, such as dimethyl carbonate and diethyl carbonate, an electrolyte having high electrical conductivity can be prepared, and therefore such cyclic carbonates can be used more preferably.

[0164] The metal salt may be a lithium salt, which is a substance that is easily dissolved in the non-aqueous electrolyte solution. For example, the anion of the lithium salt may be F - , Cl - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3- , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - , and (CF3CF2SO2)2N - One or more selected from the group consisting of:

[0165] In addition to the constituent components of the electrolyte, the electrolyte may further include one or more additives, such as a haloalkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinoneimine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride, in order to improve the life characteristics of the battery, suppress a decrease in battery capacity, and improve the discharge capacity of the battery.

[0166] The energy density of the lithium secondary battery according to one embodiment of the present invention may be 400 Wh / L to 900 Wh / L. Specifically, the energy density of the lithium secondary battery may be 425 Wh / L to 875 Wh / L, 450 Wh / L to 850 Wh / L, 475 Wh / L to 825 Wh / L, or 500 Wh / L to 800 Wh / L. When the above range is satisfied, the energy density of the lithium secondary battery designed in a limited space can be increased, and high-power performance and cycle performance of the battery can also be improved.

[0167] The lithium secondary battery according to an embodiment of the present invention may be a cylindrical battery. The cylindrical battery may refer to a battery having a cylindrical shape, including an assembly including a positive electrode, a negative electrode, a separator, and an electrolyte. Specifically, the battery may be composed of a cylindrical can, a battery assembly disposed inside the cylindrical can, and a top cap. However, the lithium secondary battery is not limited thereto and may be a prismatic battery or a pouch-type battery.

[0168] One embodiment of the present invention provides a battery module including the cylindrical battery as a unit cell, and a battery pack including the battery module. The battery module and the battery pack include the secondary battery having high capacity, high rate characteristics, and high cycle characteristics, and can be used as a power source for medium- to large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0169] The lithium secondary battery according to the present invention stably exhibits excellent discharge capacity, output characteristics, and cycle performance, and 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, as well as portable devices such as mobile phones, laptops, and digital cameras. For example, the battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, such as power tools; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems. [Example]

[0170] Below, preferred examples are presented to help understand the present invention, but these examples are merely illustrative of the present description, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope and technical spirit of the present description, and it goes without saying that such changes and modifications fall within the scope of the appended claims.

[0171] <Examples and Comparative Examples> Example 1 (1) Manufacturing of the negative electrode A negative electrode active material layer-forming composition was prepared containing 97.7 parts by weight of graphite (artificial graphite:natural graphite = 70:30 weight ratio, 90 parts by weight based on 100 parts by weight of negative electrode active material) and silicon carbon composite (10 parts by weight based on 100 parts by weight of negative electrode active material) as negative electrode active materials, 1.15 parts by weight of SBR (styrene butadiene rubber) and 1 part by weight of CMC (carboxymethyl cellulose) as binders, 0.09 parts by weight of dispersant, and 0.06 parts by weight of single-walled CNTs. The negative electrode active material layer-forming composition was coated onto a 15 μm-thick copper foil to a dry thickness of 86 μm and then dried to prepare a negative electrode.

[0172] In this case, the graphite has a tap density of 1.1 g / cc and D 50 The silicon carbon composite has a tap density of 0.65 g / cc and a D 50 The diameter was 5.1 μm.

[0173] (2) Manufacturing of the positive electrode A positive electrode active material layer-forming composition was prepared, containing 98.04 parts by weight of a lithium composite transition metal compound containing single particles and secondary particles (single particles:secondary particles = 80:20 weight ratio) with 93.3 mol% Ni, 4.9 mol% Co, and 1.8 mol% Mn (excluding lithium) as the positive electrode active material (based on 100 parts by weight of the positive electrode active material layer), 1 part by weight of PVDF as a binder, and a CNT pre-dispersion containing 0.8 parts by weight of CNTs and 0.16 parts by weight of a dispersant as a conductive material. The positive electrode active material layer-forming composition was coated onto a 30 μm-thick aluminum foil to a dry thickness of 103 μm and then dried to prepare a positive electrode.

[0174] At this time, the lithium composite transition metal compound has a tap density of 1.8 g / cc as a single particle, and D 50 The secondary particles of the lithium composite transition metal compound have a tap density of 2.4 g / cc and a D 50 The diameter was 9.5 μm.

[0175] (3) Manufacture of lithium secondary batteries The positive electrode and the negative electrode were stacked with a separator interposed therebetween, and an electrolyte (1.0 M LiPF6, EC (ethylene carbonate) / EMC (ethyl methyl carbonate) = 30 / 70 (Vol%), VC (vinylene carbonate) 1.5%) was injected to fabricate a lithium secondary battery.

[0176] Examples 2 to 4 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the positive and negative active materials having the tap density and particle size shown in Table 1 below were used.

[0177] Comparative Examples 1 to 6 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the positive and negative active materials having the tap density and particle size shown in Table 1 below were used.

[0178] The compositions of the negative electrode active materials prepared in the examples and comparative examples are as shown in Table 1 below.

[0179] [Table 1]

[0180] The tap densities of the positive electrode active material and the negative electrode active material were calculated by placing 40 g of a sample in a container and tapping it 1000 times using a TAP-2S device manufactured by LOGAN.

[0181] D of the positive electrode active material and the negative electrode active material 50 was analyzed by PSD measurement method using a microtrac instrument.

[0182] The porosity of the active material layers of the positive electrode and negative electrode was calculated using the following relational expression. Porosity of electrode active material layer (%) = {1 - (active material layer Dense layer / active material layer true density)}×100

[0183] The sphericity, true density, and BET specific surface area of ​​the graphite and silicon carbon composites used as negative electrode active materials in the Examples and Comparative Examples are shown in Table 2 below.

[0184] Hereinafter, the true density of the active material layer is 3*4 (cm 2 The density of the electrode active material layer is measured when an electrode of the same size is pressed in a press device until the thickness of the negative electrode does not change, and the density of the active material layer is measured when an electrode of the same size is taken before pressing.

[0185] [Table 2]

[0186] <Experimental example: Evaluation of discharge capacity, initial efficiency, and life (capacity retention rate) characteristics> The lithium secondary batteries manufactured in the examples and comparative examples were charged and discharged to evaluate the discharge capacity, initial efficiency, and capacity retention rate. The results are shown in Table 3 below.

[0187] The first and second cycles were charged and discharged at 0.1 C, and the third to 49th cycles were charged and discharged at 0.5 C. The 50th cycle was completed in a charged state (with lithium in the anode).

[0188] Charging conditions: CC (constant current) / CV (constant voltage) (5mV / 0.005C current cut-off) Discharge condition: CC (constant current) condition 1.5V

[0189] The discharge capacity (mAh / g) and initial efficiency (%) were calculated from the results of one charge / discharge. Specifically, the initial efficiency (%) was calculated as follows: Initial efficiency (%) = (single discharge capacity / single charge capacity) x 100

[0190] The capacity retention rate was calculated as follows. Capacity retention rate (%) = (49 discharge capacity / 1 discharge capacity) × 100

[0191] <Experimental example: electrode thickness evaluation> The thicknesses of the positive and negative electrodes prepared in the Examples and Comparative Examples were measured using a Micro-Hite 350 (Tesa) device and then added together. The average of approximately three measurements was calculated as the electrode thickness. The calculated electrode thickness of Example 1 was set as 100%, and the electrode thicknesses of Examples 2 to 4 and Comparative Examples 1 to 6 were calculated relative to this as shown in Table 3 below.

[0192] <Experimental example: Evaluation at the time of Li plating> The first and second cycles were charged / discharged at 0.1 C, and from the third cycle onwards, the cell resistance was measured while charging / discharging at a rate of 3 C.

[0193] Charging conditions: CC (constant current) / CV (constant voltage) (5mV / 0.005C current cut-off) Discharge condition: CC (constant current) condition 1.5V

[0194] The time when the cell resistance suddenly decreased and the current value suddenly changed was calculated as the time when Li plating occurred.

[0195] [Table 3]

[0196] As shown in Tables 1 to 3, the secondary batteries of Examples 1 to 4, which used negative electrodes in which the tap density of graphite was equal to or greater than that of the silicon carbon composite, had thinner electrodes and superior capacity retention rates than those of Comparative Examples 1 to 6. The SOC at which Li coating occurs, where lithium is deposited, was 95% or greater, resulting in significantly improved charge capacities. This is believed to be because the graphite tap density was equal to or greater than that of the silicon carbon composite, allowing the graphite to be densely dispersed throughout the electrode, thereby ensuring uninterrupted current flow within the negative electrode and facilitating adjustment of the degree of graphite orientation within the negative electrode. In contrast, in Comparative Examples 1 to 6, the graphite tap density was lower than that of the silicon carbon composite, resulting in agglomeration rather than dispersion within the electrode, reducing slurry dispersibility and making rolling difficult. This resulted in a significant increase in electrode thickness, a decrease in capacity retention, and an inferior charge capacity, where Li coating occurs at 82% to 90% SOC.

Claims

1. a negative electrode active material including a silicon carbon composite and graphite; the graphite has a tap density equal to or greater than the tap density of the silicon carbon composite; The graphite has a sphericity of 0.8 to 0.9, and the silicon carbon composite has a sphericity of 0.3 to 0.

7.

2. A negative electrode active material comprising a silicon carbon composite and graphite, the graphite has a tap density equal to or greater than the tap density of the silicon carbon composite; a negative electrode composition, wherein the graphite has a true density of 2 to 3 g / cc, and the silicon carbon composite has a true density of 1.8 to 2.2 g / cc.

3. 3. The negative electrode composition according to claim 1, wherein the graphite has a tap density of 0.9 g / cc to 1.2 g / cc.

4. 3. The negative electrode composition according to claim 1, wherein the silicon carbon composite has a tap density of 0.5 g / cc to 1.15 g / cc.

5. 3. The negative electrode composition according to claim 1, wherein the silicon carbon composite has an average particle size of 1 μm or more and 15 μm or less.

6. The negative electrode composition according to claim 1 or 2, wherein the silicon carbon composite has an average particle size smaller than the average particle size of the graphite.

7. The BET specific surface area of ​​the graphite is 1 m ２ / g to 3m ２ / g, and the BET specific surface area of ​​the silicon carbon composite is 1 m ２ / g to 10m ２ The negative electrode composition according to claim 1 or 2, wherein the Cr content is 1 / g.

8. An anode comprising: an anode current collector; and an anode active material layer provided on one or both sides of the anode current collector, the anode active material layer comprising the anode composition according to claim 1 or 2.

9. The negative electrode according to claim 8, wherein the negative electrode active material layer has a porosity of 23% to 28%.

10. A lithium secondary battery comprising: a positive electrode; the negative electrode according to claim 8; a separator provided between the positive electrode and the negative electrode; and an electrolyte.

11. The positive electrode is 11. The lithium secondary battery according to claim 10, comprising a lithium composite transition metal compound containing nickel (Ni), cobalt (Co), and manganese (Mn) as a positive electrode active material, the lithium composite transition metal compound including single particles.

12. The lithium secondary battery according to claim 11 , wherein the lithium composite transition metal compound further comprises secondary particles.

13. The lithium secondary battery according to claim 12 , wherein the tap density of the secondary particles is greater than the tap density of the single particles.

14. The lithium secondary battery according to claim 11, wherein the tap density of the single particles is greater than the tap density of the graphite.

15. 12. The lithium secondary battery according to claim 11, wherein the average particle size of the single particles is 1 μm or more and 12 μm or less.

16. The lithium secondary battery according to claim 11 , wherein the average particle size of the single particle is smaller than the average particle size of the silicon carbon composite.

17. The single particles are included in an amount of 15 parts by weight to 100 parts by weight based on 100 parts by weight of the positive electrode active material, The lithium secondary battery of claim 11, wherein the silicon carbon composite is contained in an amount of 3 to 30 parts by weight based on 100 parts by weight of the negative electrode active material.

18. 12. The lithium secondary battery according to claim 11, wherein the lithium composite transition metal compound contains 80 mol % or more of nickel among metals other than lithium.

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

20. A battery pack comprising the battery module of claim 19.

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