Negative electrode for lithium secondarty battery, lithium secondarty battery, battery module and battery pack

Abstract

The present application relates to a negative electrode for a lithium secondary battery, a lithium secondary battery, a battery module, and a battery pack.

Description

Technology Field

[0001] The present application relates to a negative electrode for a lithium secondary battery, a lithium secondary battery, a battery module, and a battery pack. Background Technology

[0002] Due to the rapid increase in the use of fossil fuels, there is a growing demand for alternative or clean energy. As part of this effort, the fields of power generation and energy storage utilizing electrochemical reactions are the most actively researched.

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

[0004] In a lithium secondary battery, electrical energy is produced by oxidation and reduction reactions when lithium ions are inserted into or removed from the anode and cathode while the anode and cathode are filled with an organic or polymer electrolyte between an anode and a cathode made of active materials capable of lithium ion intercalation and deintercalation.

[0005] Metal oxides such as LiCoO2, LiMnO2, LiMn2O4, or LiNiO2 are used as the positive active material constituting the positive electrode of a lithium secondary battery, and carbon-based materials such as metal lithium, graphite, or activated carbon, or silicon oxide (SiO2) are used as the negative active material constituting the negative electrode. xMaterials such as ) are being used. Among the above negative electrode active materials, metallic lithium was primarily used in the beginning, but as the charge and discharge cycles progressed, lithium atoms grew on the surface of the metallic lithium, damaging the separator and causing the battery to fail. Consequently, carbon-based materials are primarily being used recently.

[0006] Although graphite is mainly used as the negative electrode active material for lithium secondary batteries, it is difficult to increase the capacity of lithium secondary batteries because graphite has a low capacity per unit mass of 372 mAh / g. Accordingly, to increase the capacity of lithium secondary batteries, negative electrode materials such as silicon, tin, and their oxides are being developed as non-carbon negative electrode materials that have a higher energy density than graphite. However, in the case of these non-carbon negative electrode materials, although the capacity is high, there is a problem in that the initial efficiency is low, resulting in high lithium consumption during the initial charge and discharge cycles and large irreversible capacity loss.

[0007] Accordingly, methods to increase capacity and improve energy density by applying carbon-based active materials are being studied, or research is underway to secure energy density and capacity along with lifespan performance by appropriately combining silicon-based and carbon-based active materials; however, a lithium secondary battery anode capable of solving the aforementioned problems has not yet been developed.

[0008] In particular, research on silicon-carbon composites is underway as next-generation silicon-based active materials, and these materials are known to be suitable for high-energy-density lithium secondary batteries due to their high capacity and efficiency. However, the aforementioned silicon-carbon composites also continue to face issues regarding lifespan characteristics, aqueous processability when used in combination with water-based binders, and gas generation.

[0009] Accordingly, there is a need to develop a cathode that can effectively improve battery life characteristics while using silicon-based and / or carbon-based active materials, and achieve rapid charging performance and high energy density. Prior art literature

[0010] Japanese Patent Publication No. 2009-080971 The problem to be solved

[0011] The present application relates to a negative electrode for a lithium secondary battery, and resolves issues regarding lifespan characteristics, water-based processability due to the use of water-based binders, and gas generation, which are problems of existing silicon-based active materials. In particular, it was found that the above problems can be resolved when the dQ / dV spectrum of the discharge profile of a negative electrode containing a silicon-carbon composite used as a silicon-based active material satisfies a specific range. Accordingly, the present application relates to a negative electrode for a lithium secondary battery, a lithium secondary battery, a battery module, and a battery pack capable of securing high energy density and high capacity along with lifespan characteristics. means of solving the problem

[0012] One embodiment of the present specification provides a negative electrode for a lithium secondary battery comprising: a negative current collector layer; and a negative active material layer provided on one or both sides of the negative current collector layer, wherein the negative active material layer comprises a negative active material layer composition including a negative active material, and the negative active material comprises a silicon carbon composite, and the negative electrode comprises a first peak in the range of 0.25V or more and 0.35V or less and a second peak in the range of 0.42V or more and 0.48V or less in the dQ / dV spectrum of the discharge profile, wherein lithium metal is used as the counter electrode of the negative electrode for the lithium secondary battery, and after repeating a charge and discharge cycle N times, with respect to the first peak (N times) and the second peak (N times), the second peak (N times) satisfies the following Equation 1.

[0013] [Equation 1]

[0014] [ (2nd Peak (1st) - 2nd Peak (2nd)) / 2nd Peak (1st)] x 100% ≤ 10

[0015] In one embodiment of the present application, a lithium secondary battery is provided comprising: a positive electrode; a negative electrode for a lithium secondary battery according to the present application; a separator provided between the positive electrode and the negative electrode; and an electrolyte.

[0016] In one embodiment of the present application, a battery module including the lithium secondary battery is provided.

[0017] Finally, a battery pack comprising the above lithium secondary battery or the above battery module is provided. Effects of the invention

[0018] In the development of automotive batteries, high energy density and high capacity are essential to improve driving performance. To satisfy these performance requirements, silicon-carbon composites must be used as negative electrode active materials; however, this leads to issues with lifespan performance due to volume expansion and problems with negative electrode slurry stability.

[0019] In the case of a negative electrode for a lithium secondary battery according to the present application, the negative electrode active material comprises a silicon carbon composite, and the dQ / dV spectrum of the discharge profile of the negative electrode includes a first peak in the range of 0.25V or more and 0.35V or less and a second peak in the range of 0.42V or more and 0.48V or less, and lithium metal is used as the counter electrode of the negative electrode for the lithium secondary battery, and after repeating the charge and discharge cycle N times, the second peak (N times) satisfies Equation 1 with respect to the first peak (N times) and the second peak (N times).

[0020] That is, when the total volume of porous carbon, SiH4 deposition conditions, and coating conditions are controlled during the manufacture of the silicon carbon composite, the dQ / dV spectrum of the cathode discharge profile can be satisfied within the range of Equation 1 as described above, and in particular, the silicon carbon composite is characterized by a small decrease in the intensity of the second peak in the second cycle after the first cycle.

[0021] When using a silicon carbon composite having the above characteristics, high energy density and high capacity characteristics can be achieved, and volume expansion can be controlled to improve lifespan performance. In particular, it has the characteristics of controlling the water-based processability and gas generation of the cathode slurry, thereby ensuring lifespan performance.

[0022] The silicon carbon composite satisfying Equation 1 above can secure lifespan performance by generating a relatively stable SEI during the charging and discharging process and reducing the electrical short circuit phenomenon of the particles. It is the result of silicon being uniformly deposited inside the pores of the porous carbon while minimizing the silicon deposited on the surface of the porous carbon. Brief explanation of the drawing

[0023] FIG. 1 is a diagram showing a stacked structure of a negative electrode for a lithium secondary battery according to one embodiment of the present application. FIG. 2 is a diagram showing a stacked structure of a lithium secondary battery according to one embodiment of the present application. Figure 3 is a figure showing the dQ / dV peak according to Example 1 of the present application. Figure 4 is a graph showing the process of deriving the dQ / dV peak according to Example 1 of the present application. Figure 5 is a figure showing the dQ / dV peak according to Comparative Example 1 of the present application. Specific details for implementing the invention

[0024] Before describing the present invention, some terms are defined first.

[0025] In this specification, when a part is described as "comprising" a certain component, it means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0026] In this specification, 'p to q' means a range of 'p or more and q or less'.

[0027] In this specification, "specific surface area" is measured by the BET method, specifically calculated from the amount of nitrogen gas adsorbed at a liquid nitrogen temperature (77K) using BELSORP-mino II of BEL Japan. That is, in this application, the BET specific surface area may refer to the specific surface area measured by the above measurement method.

[0028] In this specification, "Dn" refers to the particle size distribution and represents the particle size at the n% point of the cumulative distribution of the number of particles according to particle size. That is, D50 is the particle size (average particle size) at the 50% point of the cumulative distribution of the number of particles according to particle size, D90 is the particle size at the 90% point of the cumulative distribution of the number of particles according to particle size, and D10 is the particle size at the 10% point of the cumulative distribution of the number of particles according to particle size. Meanwhile, the particle size distribution can be measured using the laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500) and the difference in diffraction patterns according to particle size is measured as the particles pass through the laser beam to calculate the particle size distribution.

[0029] In this specification, the meaning that a polymer contains a monomer in monomer units means that the monomer participates in a polymerization reaction and is included as a repeating unit within the polymer. In this specification, when it is stated that a polymer contains a monomer, this is interpreted as the same as the polymer containing the monomer in monomer units.

[0030] In this specification, the term "polymer" is understood to be used in a broad sense including copolymers unless "homopolymer" is specified.

[0031] In this specification, the weight-average molecular weight (Mw) and the number-average molecular weight (Mn) are polystyrene equivalent molecular weights measured by gel permeation chromatography (GPC), using commercially available monodisperse polystyrene polymers of various degrees of polymerization (standard samples) for molecular weight measurement as standard materials. In this specification, the term "molecular weight" means weight-average molecular weight unless otherwise specified.

[0032] Hereinafter, the present invention will be described in detail with reference to the drawings so that those skilled in the art can easily practice the present invention. However, the present invention may be embodied in various different forms and is not limited to the description below.

[0033] One embodiment of the present specification provides a negative electrode for a lithium secondary battery comprising: a negative current collector layer; and a negative active material layer provided on one or both sides of the negative current collector layer, wherein the negative active material layer comprises a negative active material layer composition including a negative active material, and the negative active material comprises a silicon carbon composite, and the negative electrode comprises a first peak in the range of 0.25V or more and 0.35V or less and a second peak in the range of 0.42V or more and 0.48V or less in the dQ / dV spectrum of the discharge profile, wherein lithium metal is used as the counter electrode of the negative electrode for the lithium secondary battery, and after repeating a charge and discharge cycle N times, with respect to the first peak (N times) and the second peak (N times), the second peak (N times) satisfies the following Equation 1.

[0034] [Equation 1]

[0035] [ (2nd Peak (1st) - 2nd Peak (2nd)) / 2nd Peak (1st)] x 100% ≤ 10

[0036] When using a silicon carbon composite having the above characteristics, high energy density and high capacity characteristics can be achieved, and volume expansion can be controlled to improve lifespan performance. In particular, it has the characteristics of controlling the water-based processability and gas generation of the cathode slurry, thereby ensuring lifespan performance.

[0037] FIG. 1 is a diagram showing a stacked structure of a negative electrode for a lithium secondary battery according to one embodiment of the present application. Specifically, a negative electrode (100) for a lithium secondary battery including a negative active material layer (20) on one surface of a negative current collector layer (10) can be seen, and FIG. 1 shows that the negative active material layer is formed on one surface, but it can be included on both surfaces of the negative current collector layer.

[0038] This is explained in more detail below.

[0039] In one embodiment of the present application, the negative current collector layer generally has a thickness of 1 μm to 100 μm, specifically a thickness of 8 μm to 15 μm. Such a negative current collector layer is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface treated with carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloy may be used. In addition, fine irregularities may be formed on the surface to strengthen the bonding strength of the negative active material, and it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven body, etc.

[0040] In one embodiment of the present application, the thickness of the negative current collector layer may be 1 μm or more and 100 μm or less.

[0041] However, the thickness may vary depending on the type and application of the cathode used, and is not limited thereto.

[0042] The cathode active material layer according to the present application comprises a cathode active material layer composition including a cathode active material, and the cathode active material comprises a silicon carbon composite.

[0043] In the present application, the silicon carbon composite can be represented as Si / C.

[0044] In this specification, the silicon carbon composite is a composite of Si and C and is distinguished from silicon carbide denoted as SiC. Since the silicon carbide does not electrochemically react with lithium, all performance characteristics, such as lifespan, can be measured as zero.

[0045] The above silicon carbon composite may be a composite of silicon and graphite, etc., and may form a structure in which graphene or amorphous carbon, etc. surrounds a core composed of silicon and graphite, etc. In the above silicon carbon composite, the silicon may be nano silicon. For example, the nano silicon may be silicon in the range of 1 nm to 999 nm.

[0046] The present application provides a negative electrode for a lithium secondary battery, wherein the negative electrode active material comprises 90 parts by weight or less based on 100 parts by weight of the negative electrode active material layer composition.

[0047] In another embodiment, based on 100 parts by weight of the cathode active material layer composition, the cathode active material may be 90 parts by weight or less, specifically 85 parts by weight or less, and 50 parts by weight or more, preferably 70 parts by weight or more.

[0048] The present application provides a negative electrode for a lithium secondary battery, wherein the silicon carbon composite comprises 50 parts by weight or less based on 100 parts by weight of the negative electrode active material.

[0049] In another embodiment, the silicon carbon composite based on 100 parts by weight of the cathode active material may comprise 1 part by weight or more and 50 parts by weight or less, specifically 5 parts by weight or more and 45 parts by weight or less, and more specifically 10 parts by weight or more and 35 parts by weight or less.

[0050] By including a negative electrode active material within the range described above, the negative electrode possesses the characteristic of being able to secure capacity characteristics and energy density. That is, while increasing the content of the silicon-carbon composite can improve energy density, it leads to severe volume expansion and a decrease in lifespan characteristics; conversely, if the content of the silicon-carbon composite is low, high energy density and rapid charging performance cannot be secured. Therefore, using the above-mentioned content allows for the simultaneous improvement of high energy density and rapid charging performance.

[0051] Meanwhile, the average particle size (D50 particle size) of the silicon carbon composite of the present invention is 1 μm or more and 10 μm or less, specifically 2 μm to 8 μm, and more specifically 3 μm to 8 μm. When the average particle size falls within the above range, the specific surface area of ​​the particles is within a suitable range, and the viscosity of the cathode slurry is formed within an appropriate range. Accordingly, the dispersion of the particles constituting the cathode slurry becomes smooth. In addition, since the size of the silicon carbon composite has a value greater than or equal to the lower limit range, the contact area between the silicon particles and the conductive materials is excellent due to the composite composed of the conductive material and the binder within the cathode slurry, which increases the likelihood of the conductive network continuing and thereby increases the capacity retention rate. Meanwhile, when the average particle size satisfies the above range, excessively large silicon particles are excluded, and the surface of the cathode is formed smoothly, thereby preventing current density non-uniformity during charging and discharging.

[0052] In addition, in one embodiment of the present application, the silicon carbon composite may not include particles having a particle size of less than 1 μm. Specifically, the silicon carbon composite may include particles having a particle size of 1 μm or more and 10 μm or less, and the particles having a particle size of less than 1 μm may be included in an amount of 1 part by weight or less, specifically 0.1 part by weight or less, based on 100 parts by weight of the silicon carbon composite particles. That is, the silicon carbon composite according to the present application is characterized by not including fine particles.

[0053] In one embodiment of the present application, the silicon-carbon composite generally has a characteristic BET surface area. The BET surface area of ​​the silicon-based active material is preferably 0.1 to 5 m² 2 / g, more preferably 0.1 to 4.5 m 2 / g, particularly preferably 0.2 to 4 m 2 / g, most preferably 0.2 to 3.5 m 2 / g. The BET surface area is measured according to DIN 66131 (using nitrogen).

[0054] In one embodiment of the present application, the silicon carbon composite may exist, for example, in a crystalline or amorphous form and is preferably not porous. The silicon particles are preferably spherical or fragmentary particles. Alternatively, but less preferably, the silicon particles may also have a fibrous structure or exist in the form of a silicon-containing film or coating.

[0055] In one embodiment of the present application, the silicon carbon composite may have a non-spherical shape, and the sphericity is, for example, 0.9 or less, for example, 0.7 to 0.9, for example, 0.8 to 0.9, for example, 0.85 to 0.9.

[0056] In the present application, the circularity is determined by the following formula 1-A, where A is the area and P is the boundary line.

[0057] [Equation 1-A]

[0058] 4πA / P 2

[0059] The present application provides a negative electrode for a lithium secondary battery, wherein the negative electrode active material further comprises a carbon-based active material.

[0060] In one embodiment of the present invention, the carbon-based active material may include artificial graphite and natural graphite.

[0061] In the present application, a negative electrode active material is provided in which the weight ratio of natural graphite to artificial graphite based on the carbon-based active material is 5:95 or higher and 50:50 or lower.

[0062] In another embodiment, the weight ratio of natural graphite to artificial graphite based on the carbon-based standard may satisfy 5:95 or more and 50:50 or less, preferably 7:93 to 45:55, and more preferably 10:90 to 40:60.

[0063] In the present application, the carbon-based active material includes graphite, and the graphite may include artificial graphite and natural graphite. Since it has been confirmed that artificial graphite has superior cell characteristics compared to natural graphite, the use of natural graphite is being reduced and the amount of artificial graphite used is being increased. However, from a cost perspective, artificial graphite requires the calcination and graphitization of coke, which poses a problem due to high processing costs. Accordingly, if the above range is satisfied, it has the characteristic of being able to improve cell characteristics along with addressing cost issues.

[0064] In the present application, the natural graphite is characterized by satisfying the range of Formula 1.

[0065] In the present application, the average particle size (D50) of the natural graphite is 10 μm or more and 30 μm or less, the tap density of the natural graphite is 0.5 g / cc or more and 2.0 g / cc or less, and the specific surface area of ​​the natural graphite is 1 m² 2 / g or more than 5m 2 It may be less than / g.

[0066] In another embodiment, the average particle size (D50) of the natural graphite may be 10 μm or more and 30 μm or less, specifically 12 μm or more and 27 μm or less, and more specifically 15 μm or more and 20 μm or less.

[0067] In another embodiment, the tap density of the natural graphite may be 0.5 / cc or more and 2.0g / cc or less, specifically 0.7 / cc or more and 1.5g / cc or less, and more specifically 0.9 / cc or more and 1.2g / cc or less.

[0068] In another embodiment, the specific surface area of ​​the natural graphite is 1 m² 2 / g or more than 5m 2 / g or less, specifically 1m 2 / g or more than 4m 2 / g or less, more specifically 1m 2 / g or more than 3m 2 It may be less than / g.

[0069] In the present application, the average particle size (D50) of the artificial graphite is 10 μm or more and 25 μm or less, the tap density of the artificial graphite is 0.5 g / cc or more and 1.5 g / cc or less, and the specific surface area of ​​the artificial graphite is 0.1 m² 2 / g or more 3.0m 2 It can be less than / g.

[0070] In another embodiment, the average particle size (D50) of the artificial graphite may be 10 μm or more and 25 μm or less, specifically 12 μm or more and 24 μm or less, and more specifically 14 μm or more and 23 μm or less.

[0071] In another embodiment, the tap density of the artificial graphite may be 0.5 / cc or more and 1.5g / cc or less, specifically 0.7 / cc or more and 1.3g / cc or less, and more specifically 0.9 / cc or more and 1.1g / cc or less.

[0072] In another embodiment, the specific surface area of ​​the artificial graphite is 0.1 m² 2 / g or more 3.0m 2 / g or less, specifically 0.2m 2 / g or more than 2.5m 2 / g or less, more specifically 0.2m 2 / g or more than 2.5m 2 It may be less than / g.

[0073] Conventionally, it was common practice to use only graphite-based compounds as negative electrode active materials; however, with the recent rise in demand for high-capacity batteries, there have been increasing attempts to mix in silicon-based compounds to increase capacity. Nevertheless, silicon-based compounds have a limitation in that their volume expands rapidly during the charging and discharging process, damaging the conductive pathways formed within the negative electrode active material layer and actually degrading battery performance.

[0074] Accordingly, in one embodiment of the present application, a negative electrode for a lithium secondary battery is provided, wherein the negative electrode active material layer composition further comprises a negative electrode conductive material; and a negative electrode binder.

[0075] In one embodiment of the present application, the cathode conductive material may be any material that is generally used in the art without limitation, and specifically may include one or more selected from the group consisting of point conductive materials; planar conductive materials; and linear conductive materials.

[0076] In one embodiment of the present application, the dot-shaped conductive material can be used to improve conductivity of the cathode and refers to a conductive material having a dot shape or a sphere that is conductive without causing chemical changes. Specifically, the dot-shaped conductive material may be at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, channel black, Farnes black, lamp black, thermal black, conductive fiber, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and preferably may include carbon black in terms of achieving high conductivity and excellent dispersibility.

[0077] In one embodiment of the present application, the point-shaped conductive material has a BET specific surface area of ​​40 m² 2 / g or more 70m 2 It may be less than / g, preferably 45m 2 / g or more 65m2 / g or less, more preferably 50m 2 / g or more 60m 2 It may be less than / g.

[0078] In one embodiment of the present application, the particle size of the dot-shaped conductive material may be 10 nm to 100 nm, preferably 20 nm to 90 nm, and more preferably 20 nm to 60 nm.

[0079] In one embodiment of the present application, the cathode conductive material may include a planar conductive material.

[0080] The above-mentioned planar conductive material can be described as a plate-shaped conductive material or a bulk-shaped conductive material, as it can improve conductivity by increasing surface contact between silicon particles within the cathode and simultaneously suppress the interruption of conductive pathways due to volume expansion.

[0081] In one embodiment of the present application, the planar conductive material may comprise at least one selected from the group consisting of plate-shaped graphite, graphene, graphene oxide, and graphite flakes, and preferably may be plate-shaped graphite.

[0082] In one embodiment of the present application, the average particle size (D50) of the planar conductive material may be 2 μm to 7 μm, specifically 3 μm to 6 μm, and more specifically 4 μm to 5 μm. When the above range is satisfied, dispersion is easy without causing an excessive increase in the viscosity of the cathode slurry due to the sufficient particle size. Therefore, when dispersion is performed using the same equipment and time, the dispersion effect is excellent.

[0083] In one embodiment of the present application, the planar conductive material provides a cathode composition in which D10 is 0.5 μm or more and 1.5 μm or less, D50 is 2.5 μm or more and 3.5 μm or less, and D90 is 7.0 μm or more and 15.0 μm or less.

[0084] In one embodiment of the present application, the planar conductive material may be a high specific surface area planar conductive material having a high BET specific surface area; or a low specific surface area planar conductive material.

[0085] In one embodiment of the present application, a planar conductive material with a high specific surface area or a planar conductive material with a low specific surface area may be used without limitation as the planar conductive material; however, since the planar conductive material according to the present application may be affected to some extent by dispersion in electrode performance, it may be particularly preferable to use a planar conductive material with a low specific surface area that does not cause problems with dispersion.

[0086] In one embodiment of the present application, the planar conductive material has a BET specific surface area of ​​5 m² 2 It can be more than / g.

[0087] In another embodiment, the planar conductive material has a BET specific surface area of ​​5m² 2 / g or more than 500m 2 It may be less than / g, preferably 5m 2 / g or more than 300m 2 / g or less, more preferably 5m 2 / g or more 250m 2 It may be less than / g.

[0088] In another embodiment, the planar conductive material is a high specific surface area planar conductive material, and has a BET specific surface area of ​​50 m² 2 / g or more than 500m 2 / g or less, preferably 80m 2 / g or more than 300m 2 / g or less, more preferably 100m 2 / g or more than 300m 2 It can satisfy a range of / g or less.

[0089] In another embodiment, the planar conductive material is a low specific surface area planar conductive material, and the BET specific surface area is 5m² 2 / g or more 40m 2 / g or less, preferably 5m 2 / g or more 30m 2 / g or less, more preferably 5m 2 / g or more 25m 2 It can satisfy a range of / g or less.

[0090] Other conductive materials may include linear conductive materials such as carbon nanotubes. The carbon nanotubes may be bundled carbon nanotubes. The bundled carbon nanotubes may comprise a plurality of carbon nanotube units. Specifically, "bundle type" here refers to a secondary shape in the form of a bundle or rope in which a plurality of carbon nanotube units are arranged in parallel or intertwined with the axes along the length direction of the carbon nanotube units in substantially the same orientation, unless otherwise noted. The carbon nanotube units have a graphite sheet having a cylindrical shape with a nano-sized diameter and an sp2 bonding structure. Depending on the angle and structure in which the graphite sheet is rolled, it may exhibit conductive or semiconductor properties. Compared to entangled type carbon nanotubes, the bundled carbon nanotubes described above can be uniformly dispersed during cathode manufacturing and smoothly form a conductive network within the cathode, thereby improving the conductivity of the cathode.

[0091] In particular, the linear conductive material according to one embodiment of the present application may be a single-walled carbon nanotube (SWCNT).

[0092] The above single-walled carbon nanotube is a material in which carbon atoms arranged in a hexagonal shape form a tube. Depending on its unique chirality, it exhibits insulating, conductive, or semiconductor properties. Since the carbon atoms are connected by strong covalent bonds, it has a tensile strength approximately 100 times greater than that of steel, excellent flexibility and elasticity, and is chemically stable.

[0093] The average diameter of the single-walled carbon nanotubes is 0.5 nm to 15 nm. According to one embodiment of the present invention, the average diameter of the single-walled carbon nanotubes may be 1 to 10 nm, or 1 nm to 5 nm, or 1 nm to 2 nm. When the average diameter of the single-walled carbon nanotubes satisfies these ranges, the electrical conductivity of the cathode can be maintained even when the single-walled carbon nanotubes are included in a very small amount, and desirable viscosity and solid content can be obtained when preparing a conductive material dispersion. In the conductive material dispersion, the single-walled carbon nanotubes may clump together and exist in an entangled state (aggregate). Accordingly, the above average diameter can be derived by confirming the diameter of any entangled single-walled carbon nanotube aggregate extracted from the above conductive material dispersion using SEM or TEM, and then dividing the diameter of the aggregate by the number of single-walled carbon nanotubes constituting the aggregate.

[0094] The BET specific surface area of ​​the above single-walled carbon nanotube is 500 m² 2 / g to 1,500 m 2 / g, or 900 m 2 / g to 1,200 m 2 It can be / g, specifically 250 m 2 / g to 330 m 2 It may be / g. If the above range is satisfied, a conductive material dispersion with a desirable solid content is obtained, and the viscosity of the cathode slurry is prevented from rising excessively. The above BET specific surface area can be measured through the nitrogen adsorption BET method.

[0095] The aspect ratio of the single-walled carbon nanotube may be 50 to 20,000, or the length of the single-walled carbon nanotube may be 5 to 100 μm or 5 to 50 μm. When the aspect ratio or length satisfies these ranges, the specific surface area is high, so the single-walled carbon nanotube can be adsorbed to the active material particles within the cathode with a strong attractive force. Accordingly, the conductive network can be smoothly maintained even with the volume expansion of the cathode active material. The aspect ratio can be confirmed by calculating the average of the aspect ratios of 15 single-walled carbon nanotubes with a large aspect ratio and 15 single-walled carbon nanotubes with a small aspect ratio when observing the single-walled carbon nanotube powder through SEM.

[0096] Compared to multi-walled or double-walled carbon nanotubes, single-walled carbon nanotubes have a large aspect ratio, making them long and bulky; therefore, they are advantageous in that they can construct electrical networks using only a small amount.

[0097] In one embodiment of the present application, the cathode conductive material may satisfy an amount of 1 part by weight or more and 30 parts by weight or less based on 100 parts by weight of the cathode active material layer composition.

[0098] In another embodiment, the cathode conductive material may be 1 part by weight or more and 30 parts by weight or less, preferably 5 parts by weight or more and 25 parts by weight or less, based on 100 parts by weight of the cathode active material layer composition, more preferably 10 parts by weight or more and 15 parts by weight or less.

[0099] In one embodiment of the present application, the cathode conductive material comprises a point conductive material; a planar conductive material; and a linear conductive material, wherein the ratio of the point conductive material:planar conductive material:linear conductive material may satisfy a ratio of 1:1:0.01 to 1:1:1.

[0100] In one embodiment of the present application, the point-shaped conductive material may satisfy a range of 1 part by weight or more and 60 parts by weight or less, preferably 5 parts by weight or more and 50 parts by weight or less, based on 100 parts by weight of the cathode conductive material.

[0101] In one embodiment of the present application, the planar conductive material may satisfy a range of 1 part by weight or more and 60 parts by weight or less, preferably 5 parts by weight or more and 50 parts by weight or less, based on 100 parts by weight of the cathode conductive material.

[0102] In one embodiment of the present application, the linear conductive material may satisfy a range of 0.01 parts by weight or more and 10 parts by weight or less, preferably 0.05 parts by weight or more and 8 parts by weight or less, and more preferably 0.1 parts by weight or more and 5 parts by weight or less, based on 100 parts by weight of the cathode conductive material.

[0103] In one embodiment of the present application, the cathode conductive material may include a linear conductive material and a planar conductive material.

[0104] In one embodiment of the present application, the cathode conductive material comprises a linear conductive material and a planar conductive material, and the ratio of the linear conductive material to the planar conductive material may satisfy 0.01:1 to 0.1:1.

[0105] In one embodiment of the present application, the negative electrode conductive material specifically comprises a linear conductive material and a planar conductive material, each satisfying the composition and ratio, so that the lifespan characteristics of the existing lithium secondary battery are not significantly affected, and the number of charge and discharge points increases, resulting in excellent output characteristics at a high C-rate.

[0106] In one embodiment of the present application, the cathode conductive material may be made of a linear conductive material.

[0107] At this time, the linear conductive material may be 0.01 to 2 parts by weight, or 0.02 to 0.7 parts by weight, or 0.02 to 0.3 parts by weight, based on 100 parts by weight of the cathode active material layer composition. When the content of the linear conductive material satisfies these ranges, an electrical network can be sufficiently established within the cathode active material layer, and it is advantageous in terms of mixing and coating processability during electrode manufacturing.

[0108] The cathode conductive material according to the present application has a completely separate composition from the anode conductive material applied to the anode. That is, the second cathode conductive material according to the present application serves to hold the contact points between silicon-based active materials, which undergo significant volume expansion of the electrodes due to charging and discharging. The anode conductive material, on the other hand, acts as a buffer during rolling and provides partial conductivity; thus, its composition and role are completely different from those of the cathode conductive material of the present invention.

[0109] In one embodiment of the present application, the cathode binder may comprise at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, polyacrylic acid, and materials in which hydrogens thereof are substituted with Li, Na, or Ca, etc., and may also comprise various copolymers thereof.

[0110] The cathode binder according to one embodiment of the present application serves to hold the active material and the conductive material to prevent distortion and structural deformation of the cathode structure during volume expansion and relaxation of the cathode active material. Any general binder that satisfies the above role can be applied, specifically a water-based binder can be used, and more specifically, a PAM-based binder can be used.

[0111] In one embodiment of the present application, the cathode binder is 30 parts by weight or less, preferably 25 parts by weight or less, more preferably 20 parts by weight or less, based on 100 parts by weight of the cathode active material layer composition, and may be 5 parts by weight or more, or 10 parts by weight or more.

[0112] In one embodiment of the present application, a cathode slurry comprising the cathode active material layer composition and a cathode slurry solvent is provided.

[0113] In the present application, the solid content of the cathode slurry may satisfy a range of 10% to 40%.

[0114] The above slurry solvent can be used without limitation as used in the industry, and specifically, water can be used.

[0115] In the present application, the cathode slurry can be coated on one or both sides of the cathode current collector layer to form a cathode active material layer. At this time, the coating method may use any method known in the art without limitation.

[0116] In the present application, the cathode comprises a first peak in the range of 0.25V or more and 0.35V or less and a second peak in the range of 0.42V or more and 0.48V or less in the dQ / dV spectrum of the discharge profile, and lithium metal is used as the counter electrode of the cathode for the lithium secondary battery, and after repeating the charge and discharge cycle N times, the second peak (N times) satisfies the aforementioned Equation 1 with respect to the first peak (N times) and the second peak (N times).

[0117] In the present application, the above Equation 1 may satisfy [ (2nd peak (1 time) - 2nd peak (2 times)) / 2nd peak (1 time)] x 100% ≤ 10, specifically [ (2nd peak (1 time) - 2nd peak (2 times)) / 2nd peak (1 time)] x 100% ≤ 9, [ (2nd peak (1 time) - 2nd peak (2 times)) / 2nd peak (1 time)] x 100% ≤ 7, and 0.1 ≤ [ (2nd peak (1 time) - 2nd peak (2 times)) / 2nd peak (1 time)] x 100%, specifically 1 ≤ [ (2nd peak (1 time) - 2nd peak (2 times)) / 2nd peak (1 time)] x 100%, more specifically 3 ≤ [ (2nd peak (1 time) - 2nd peak (2 times)) / 2nd peak (1 time)] x A range of 100% can be satisfied, and the upper and lower limits can be used in combination without restriction.

[0118] In the present application, the first and second peaks are Li as lithium is inserted into the silicon of the silicon carbon composite. x Si y It corresponds to a peak that appears during the discharge process after phase generation. Generally, in silicon carbon composites, the first peak is a peak that necessarily exists as a material characteristic, but is characterized by controlling the intensity of the first and second peaks according to the present application.

[0119] That is, when manufacturing a silicon carbon composite, if the total volume of porous carbon, SiH4 deposition conditions, and coating conditions are controlled, the dQ / dV spectrum of the cathode discharge profile can be controlled to the range of Equation 1 as described above, and accordingly, the effect of improving lifespan performance can be confirmed.

[0120] In the present application, the first and second peaks can be derived by evaluating a coin half cell using lithium metal as the counter electrode for a negative electrode for a lithium secondary battery according to the present application. Specifically, charging and discharging are performed at a C-rate of 0.1C, and charging is done in CC / CV mode, CV 5MV, 0.0005C, while discharging is done in CC mode, discharging to 1.5V, and profile data is extracted where the x-axis is capacity (mAh) and the y-axis is voltage (V). Subsequently, only the data in the 0 to 1.0V range is selected from the discharge profile, and the derivative value of dQ / dV can be obtained using the ORIGIN program in the following way.

[0121] 1. Extract raw data from an average of 5,000 to 6,000 data rows depending on the recording conditions.

[0122] 2. Selectively extract X and Y axis data for 500 rows in the Y-axis range of 0 to 1.0V from the discharge raw data using the Interpolate function.

[0123] 3. Derivative the dQ / dV value by taking the first derivative with Voltage on the X-axis and Capacity (mAh) on the Y-axis of the extracted data.

[0124] 4. Refine the data by normalizing it so that the first peak in the range of 0.25 to 0.35V becomes 100%.

[0125] The present application provides a negative electrode for a lithium secondary battery in which the peak intensity fraction of the second peak (1 time) / first peak (1 time) is 0.5 or more and 0.8 or less.

[0126] In another embodiment, the peak intensity fraction of the second peak (1 time) / first peak (1 time) may be 0.5 or more and 0.8 or less, specifically 0.55 or more and 0.75 or less, and more specifically 0.55 or more and 0.7 or less.

[0127] The present application provides a negative electrode for a lithium secondary battery in which the peak intensity fraction of the second peak (2 times) / first peak (2 times) is 0.55 or higher and 0.70 or lower.

[0128] In the present application, when the peak intensity fraction of the second peak (1 time) / first peak (1 time) is defined as the peak intensity fraction (1 time), and the peak intensity fraction of the second peak (2 times) / first peak (2 times) is defined as the peak intensity fraction (2 times), a negative electrode for a lithium secondary battery is provided that satisfies the following Equation 2.

[0129] [Equation 2]

[0130] 10 ≤ [ Peak intensity fraction (2 times) / ( Peak intensity fraction (1 time) - Peak intensity fraction (2 times)) ] x 100%

[0131] In another embodiment, the above Equation 2 may satisfy 10 ≤ [ peak intensity fraction (2 times) / (peak intensity fraction (1 time) - peak intensity fraction (2 times)) ] x 100%, specifically 11 ≤ [ peak intensity fraction (2 times) / (peak intensity fraction (1 time) - peak intensity fraction (2 times)) ] x 100%, 12 ≤ [ peak intensity fraction (2 times) / (peak intensity fraction (1 time) - peak intensity fraction (2 times)) ] x 100%, and [ peak intensity fraction (2 times) / (peak intensity fraction (1 time) - peak intensity fraction (2 times)) ] x 100% ≤ 80, specifically [ peak intensity fraction (2 times) / (peak intensity fraction (1 time) - peak intensity fraction (2 times)) ] x 100% ≤ 70, more specifically [ peak intensity The range of Fraction (2 times) / (Peak intensity Fraction (1 time) - Peak intensity Fraction (2 times)) ] x 100% ≤ 60 can be satisfied, and the upper and lower limits can be used in combination without restriction.

[0132] That is, the negative electrode comprising the silicon-carbon composite according to the present application is characterized by a low rate of change in the fraction of the second peak according to two or more cycles relative to the fraction of the second peak in the first cycle. In other words, by satisfying the above range, the lithium secondary battery can achieve high capacity and high energy density while simultaneously ensuring lifespan performance. This is achieved by satisfying the above range by changing the particle size, SiH4 deposition, and coating conditions during the manufacturing process of the silicon-carbon composite; specifically, fine particles of porous carbon (particles smaller than 1 μm) are removed, and the total volume of porous carbon is 0.6 cm 3 / g to 0.9cm 3 When controlling the deposition conditions by adjusting the amount of silicon deposition to 45% to 51% while controlling the amount of silicon deposition in / g, silicon is uniformly deposited within the pores of the porous carbon, and the intensity of the second peak can be controlled, and accordingly, the range of the aforementioned Equations 1 and 2 can be controlled.

[0133] The present application provides a lithium secondary battery in which the rolled density of the negative electrode active material layer is 0.9 g / cc or more and 1.3 g / cc or less.

[0134] In one embodiment of the present application, a lithium secondary battery is provided comprising: a positive electrode; a negative electrode for a lithium secondary battery according to the present application; a separator provided between the positive electrode and the negative electrode; and an electrolyte.

[0135] FIG. 2 is a diagram showing a stacked structure of a lithium secondary battery according to one embodiment of the present application. Specifically, a negative electrode (100) for a lithium secondary battery including a negative active material layer (20) on one surface of a negative current collector layer (10) can be seen, and a positive electrode (200) for a lithium secondary battery including a positive active material layer (40) on one surface of a positive current collector layer (50) can be seen, and the structure is formed such that the negative electrode (100) for a lithium secondary battery and the positive electrode (200) for a lithium secondary battery are stacked with a separator (30) in between.

[0136] A secondary battery according to one embodiment of the present specification may particularly include a negative electrode for a lithium secondary battery as described above. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the negative electrode is identical to the negative electrode described above. Since the negative electrode has been described above, a detailed description thereof is omitted.

[0137] The above positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and comprising the positive electrode active material.

[0138] In the above-mentioned positive electrode, the positive electrode current collector is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the above-mentioned positive electrode current collector may typically have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase the adhesion of the positive electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0139] The above-mentioned positive electrode active material may be a commonly used positive electrode active material. Specifically, the above-mentioned positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe3O4; or a compound with the chemical formula Li 1+c1 Mn 2-c1 Lithium manganese oxides such as O4 (0≤c1≤0.33), LiMnO3, LiMn2O3, LiMnO2, etc.; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7, etc.; chemical formula LiNi 1-c2 M c2 Ni-site type lithium nickel oxide represented by O2 (wherein M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, satisfying 0.01≤c2≤0.3); chemical formula LiMn 2-c3 M c3Examples include lithium manganese composite oxides represented by O2 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn and Ta, satisfying 0.01≤c3≤0.1) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu and Zn); and LiMn2O4 in which a portion of the Li in the chemical formula is substituted with alkaline earth metal ions, but are not limited thereto. The anode may also be Li-metal.

[0140] The above-described positive active material layer may include a positive conductive material and a positive binder together with the positive active material described above.

[0141] At this time, the positive electrode conductive material is used to impart conductivity to the electrode, and in the battery being constructed, any material that has electronic conductivity without causing chemical changes can be used without special limitations. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, or silver; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxide such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more may be used.

[0142] In addition, the anode binder serves to improve adhesion between anode active material particles and adhesion between the anode active material and the anode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more may be used.

[0143] As a separator, it separates the negative and positive electrodes and provides a pathway for the movement of lithium ions. Any separator typically used in secondary batteries can be used without special restrictions, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte wettability. Specifically, a porous polymer film, such as a porous polymer film made from a polyolefin-based polymer like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and it may optionally be used in a single-layer or multi-layer structure.

[0144] Examples of the above electrolytes that can be used in the manufacture of lithium secondary batteries include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., but are not limited to these.

[0145] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0146] As the above-mentioned non-aqueous organic solvent, for example, aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyl lactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolone, formamide, dimethylformamide, dioxolone, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolone derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, ethyl propionate, etc. may be used.

[0147] In particular, among the above carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents with high dielectric constants that effectively dissociate lithium salts, so they can be used preferably. Furthermore, if low-viscosity, low-dielectric constant linear carbonates such as dimethyl carbonate and diethyl carbonate are mixed with these cyclic carbonates in appropriate proportions, an electrolyte with high electrical conductivity can be produced, making it even more preferable to use.

[0148] The metal salt mentioned above may be a lithium salt, and the lithium salt is a substance that dissolves well in the non-aqueous electrolyte; for example, as the anion of the lithium salt, F - , Cl - , I - , NO3 -, N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - One or more types selected from the group consisting of can be used.

[0149] In addition to the above electrolyte components, the above electrolyte may further include one or more additives for the purpose of improving the lifespan characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery, such as, for example, a haloalkylene carbonate-based compound such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, triamide hexaphosphate, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride.

[0150] One embodiment of the present invention provides a battery module including the secondary battery as a unit cell and a battery pack including the same. Since the battery module and the battery pack include the secondary battery having high capacity, high rate capability and cycle capability, they can be used as a power source for a medium-to-large device selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles and power storage systems.

[0151] Hereinafter, preferred embodiments are presented to aid in understanding the present invention; however, the above embodiments are merely illustrative of the description, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and spirit of the description, and that such variations and modifications fall within the scope of the appended claims.

[0152] <Preparation Example>

[0153] <Example 1>

[0154] Manufacture of Silicon Carbon Composites

[0155] Biomass-based raw materials, such as cellulose powder and coconut shells, were placed in a turbular furnace, and the atmosphere inside the furnace was replaced with an inert gas for 2 hours under an Ar atmosphere at a flow rate of 50–200 ml / min, without increasing the temperature. Subsequently, the temperature was raised to 400°C at a rate of 5°C / min and heated under an argon atmosphere for 2 hours. The carbonization process was then carried out by raising the temperature to 900°C at a rate of 5°C / min and heating under an argon atmosphere for 2 hours; the powder obtained after the reaction was washed 2–3 times with ethanol. Carbon-based particles dried at 100°C for more than 12 hours were heated at 700°C for 3 hours under an argon atmosphere using CO2 as a 10–20% balance gas to expand pores. Afterward, they were washed with distilled water and dried at 100°C for more than 12 hours. As an activation process, 1,800 m 2After obtaining porous carbon with a specific surface area of ​​the level of / g, fine particles smaller than 1μm are removed through classification.

[0156] The porous carbon that had been classified was placed in the hot zone of a CVD apparatus, and a silicon-carbon composite was prepared by flowing SiH4 / H2=5 / 95 gas at a flow rate of 50 to 210 ml / min at 600°C for 3 hours under a low-pressure environment of 1 to 10 Torr.

[0157] Afterward, without removing it from the furnace, only Ar gas was flowed while changing the furnace temperature to 650℃ at a rate of 5℃ / min. A carbon layer was formed on the surface of the silicon carbon composite by reacting for 1 hour while flowing C2H2 / H2 / Ar=10 / 50 / 40 gas at a rate of 200ml / min for 1 hour.

[0158] <Example 2>

[0159] It was manufactured using the same process as Example 1 above, except that resin-based raw materials were used and the activation process was manufactured by chemical activation.

[0160] In the activation process, carbon-based particles dried at 100°C for more than 12 hours were mixed with KOH in a 1:4 weight ratio and heated at 700°C for 4 hours under an argon atmosphere to expand the pores.

[0161] <Example 3>

[0162] The silicon-carbon composite was prepared in the same manner as in Example 2, except that the porous carbon that had been classified was placed in the hot zone of a CVD apparatus and SiH4 / H2=5 / 95 gas was flowed at a flow rate of 50 to 210 ml / min at 600°C for 6 hours under a low-pressure environment of 1 to 10 Torr.

[0163] <Example 4>

[0164] The silicon-carbon composite was prepared in the same manner as Example 1, except that there was no process for removing fine particles of less than 1 μm after manufacturing the porous carbon, and that SiH4 / H2=5 / 95 gas was flowed through the carbon-based particles at a flow rate of 50 to 210 ml / min at 600°C for 6 hours, and there was no process for forming a carbon coating layer on the surface after manufacturing the silicon-carbon composite.

[0165] <Example 5>

[0166] It was manufactured in the same manner as Example 2, except that a spheroidization step was included in the carbon composite manufacturing process. One of the spheroidization methods was selected from spray drying, rotary atomizer, and sol-gel.

[0167] <Example 6>

[0168] In the above Example 2, the above was prepared in the same manner as Example 2, except that the ratio of carbon-based particles to KOH in the activation process of porous carbon was 1:3, fine particles were not removed in the classification, and the SiH4 / H2 deposition process conditions were SiH4 / H2 = 10 / 90 at 300 ml / min at 650°C.

[0169] <Comparative Example 1>

[0170] The above-mentioned porous carbon, having completed classification, was placed in the hot zone of a CVD apparatus, and a silicon-carbon composite was prepared by flowing SiH4 / H2=5 / 95 gas at a flow rate of 50 to 210 ml / min at 600°C for 2 hours under a low-pressure environment of 1 to 10 Torr.

[0171] <Comparative Example 2>

[0172] The silicon carbon composite was prepared using the same method as in Example 1, except that after preparation, only Ar gas was flowed while reacting for 3 hours at a furnace temperature of 580℃ and C2H2 / H2 / Ar=10 / 50 / 40 gas was flowed at a rate of 220 ml / min to form a carbon layer on the surface of the silicon carbon composite.

[0173] <Comparative Example 3>

[0174] The silicon carbon composite was prepared using the same method as in Example 1, except that after preparation, only Ar gas was flowed while reacting for 3 hours at a furnace temperature of 750℃ and C2H2 / H2 / Ar=10 / 50 / 40 gas was flowed at a rate of 220 ml / min to form a carbon layer on the surface of the silicon carbon composite.

[0175] Coin half cell manufacturing

[0176] To obtain the values ​​corresponding to Table 1 below, electrodes were manufactured and evaluated using the following manufacturing method.

[0177] A negative electrode active material layer composition was prepared using the silicon-based active material prepared above (average particle size (D50): 5 μm), graphite, a first conductive material, a second conductive material, and polyacrylamide as a binder in a weight ratio of 80:9.6:0.4:10. Distilled water was added as a solvent for forming the negative electrode slurry to prepare a negative electrode slurry. (Solid content concentration 28 wt%)

[0178] The first conductive material above is plate-shaped graphite (specific surface area: 17 m² 2 / g, average particle size (D50): 3.5 μm), and the second conductive material is carbon nanotubes.

[0179] As a mixing method, the first conductive material, the second conductive material, the binder, and water were dispersed using a homo mixer at 2500 rpm for 30 minutes, and then the silicon-based active material was added and dispersed at 2500 rpm for 30 minutes to prepare a cathode slurry.

[0180] As a cathode current collector, the above cathode slurry is applied at a rate of 3.00 mg / cm² on both sides of a copper current collector (thickness: 15 μm). 2 A negative electrode active material layer (thickness: 23 μm) was formed by coating with a loading amount, rolling, and drying in a vacuum oven at 130°C for 10 hours.

[0181] A coin half cell was manufactured using lithium metal as the counter electrode of the negative electrode for the above lithium secondary battery, and charged and discharged at a C-rate of 0.1C. Charging was performed in CC / CV mode with CV 5mV and 0.005C, and discharging was performed in CC mode with the voltage at 1.5V. Profile data was extracted with the x-axis representing capacity (mAh) and the y-axis representing voltage (V). Subsequently, only the data in the 0 to 1.0V range was selected from the discharge profile, and the derivative values ​​of dQ / dV were derived using the ORIGIN program by the following method.

[0182] 1. Extract raw data from an average of 5,000 to 6,000 data rows depending on the recording conditions.

[0183] 2. Selectively extract X and Y axis data for 500 rows in the Y-axis range of 0 to 1.0V from the discharge raw data using the Interpolate function.

[0184] 3. Derivative the dQ / dV value by taking the first derivative with Voltage on the X-axis and Capacity (mAh) on the Y-axis of the extracted data.

[0185] 4. Refine the data by normalizing it so that the first peak in the range of 0.25 to 0.35V becomes 100%.

[0186] The results derived according to the above are shown in Table 1 below.

[0187] Equation 1 Equation 2 Peak intensity fraction of 2nd peak (1 time) / 1st peak (1 time) Peak intensity fraction of the 2nd peak (2 times) / 1st peak (2 times) Example 1 6.9 13.5 0.58 0.54 Example 2 1.98 49.6 0.60 0.58 Example 3 3.57 27 0.56 0.54 Example 4 3.57 27 0.64 0.59 Example 5 1.75 56 0.57 0.56 Example 6 8.62 10.6 0.58 0.53 Comparative Example 1 37.3 1.7 0.67 0.42 Comparative Example 2 11 8.3 0.65 0.58 Comparative Example 3 13 6.7 1.08 0.94

[0188] Figure 3 is a figure showing the dQ / dV peak according to Example 1 of the present application. For reference, Figure 4 is a graph that appears in the process of deriving the dQ / dV peak according to Example 1 of the present application. Specifically, Figure 4 relates to profile data in which the x-axis represents capacity (mAh) and the y-axis represents voltage (V), wherein the Coin half cell of Example 1 is charged / discharged at a C-rate of 0.1C, charging is in CC / CV mode, CV 5mV, 0.005C, and discharging is in CC mode, discharging to 1.5V. Figure 3 is a graph in which the data is normalized so that the first peak in the range of 0.25 to 0.35V becomes 100%.

[0189] For reference, Fig. 5 is a figure showing the dQ / dV peak according to Comparative Example 1 of the present application.

[0190] Experimental Example 1: Battery Performance Evaluation

[0191] A cathode slurry was prepared by adding and mixing an appropriate amount of distilled water to a mixture of a negative electrode active material comprising the above-prepared silicon carbon composite and graphite, a conductive material comprising carbon black and SWCNT, and a binder comprising carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR) in a weight ratio of 95.3:1:3.6 such that the total solid content was approximately 46% by weight.

[0192] At this time, the ratio of silicon carbon composite to graphite in the cathode active material may be a weight ratio of 8 to 12:88 to 92.

[0193] The above cathode slurry was applied to a Cu metal thin film with a thickness of approximately 20 μm and dried at a circulating air temperature of 60°C. Subsequently, after rolling, it was dried in a vacuum oven at 130°C for about a day, and then the cathode was manufactured by stamping it into a circular shape of 1.4875 cm².

[0194] Charge and discharge were performed on the battery manufactured above, and the discharge capacity, initial efficiency, and capacity retention rate were evaluated and listed in Table 2 below.

[0195] The first and second cycles were charged and discharged at 0.1C, and from the third cycle to the 300th cycle, they were charged and discharged at 0.5C. The 300th cycle was terminated in a charged state (where lithium is contained in the negative electrode).

[0196] Charging conditions: CC (constant current) / CV (constant voltage) (5mV / 0.005C current cut-off)

[0197] Discharge condition: CC (constant current) condition 1.5V

[0198] The discharge capacity (mAh / g) and initial efficiency (%) were derived from the results of a single charge-discharge cycle. Specifically, the initial efficiency (%) was derived by the following calculation.

[0199] Initial efficiency (%) = (Discharge capacity per cycle / Charge capacity per cycle) × 100

[0200] The capacity retention rates were each derived by the following calculations.

[0201] Capacity Retention Rate (%) = (299 Discharge Cycles Capacity / 1 Discharge Cycle Capacity) × 100

[0202] Discharge capacity (mAh / g) Initial efficiency (%) Lifespan characteristics (%) Example 1 495 91.2 90 Example 2 496 91.3 88.9 Example 3 495 91.4 89.5 Example 4 500 90.9 86.5 Example 5 496 89.8 89.8 Example 6 514 89.9 88.2 Comparative Example 1 509 89.0 83.5 Comparative Example 2 500 90.9 83 Comparative Example 3 503 88.65 80

[0203] As can be seen in Table 2 above, the dQ / dV spectrum of the discharge profile of the cathode of the example can satisfy the range of Equation 1, and in particular, the silicon carbon composite has a small decrease in the intensity of the second peak in the second cycle after the first cycle. When using a silicon carbon composite having such characteristics, high energy density and high capacity characteristics can be achieved, and at the same time, volume expansion can be controlled to improve lifespan performance. In particular, it was confirmed that the lifespan performance can be secured by controlling the water-based processability and gas generation of the cathode slurry.

[0204] This ensures lifespan performance by generating a relatively stable SEI during the charging and discharging process and reducing the electrical short circuit phenomenon of the particles. The silicon carbon composite satisfying the aforementioned Equation 1 is the result of silicon being uniformly deposited inside the pores of the porous carbon while minimizing the silicon deposited on the surface of the porous carbon.

[0205] It was confirmed that the comparative example exhibited inferior lifetime characteristics compared to the example due to volume expansion or a decrease in conductivity properties during the cycling process, resulting from the shape in which silicon was locally deposited on the porous carbon surface or the temperature and time conditions of the C2H2 coating process after SiH4 deposition were not optimized, thus failing to fully cover the surface pores or Si layer. Explanation of the symbols

[0206] 10: Cathode current collector layer 20: Cathode active material layer 30: Separator 40: Positive active material layer 50: Positive current collector layer 100: Negative electrode for lithium secondary battery 200: Cathode for lithium secondary batteries

Claims

Claim 1 A silicon-carbon composite satisfying the following Equation 2, wherein, in the dQ / dV spectrum of the discharge profile, the first peak in the range of 0.25V to 0.35V and the second peak in the range of 0.42V to 0.48V are included, and after repeating N charge and discharge cycles including (N-1) cycles to N cycles, for the first peak (N times) and the second peak (N times), N is an integer greater than or equal to 2, and the peak intensity fraction of the second peak (N-1 times) / first peak (N-1 times) is defined as the peak intensity fraction (N-1 times), and the peak intensity fraction of the second peak (N times) / first peak (N times) is defined as the peak intensity fraction (N times): [Equation 2] 10 ≤ [ Peak intensity fraction (N times) / ( Peak intensity fraction (N-1 times) - Peak intensity fraction (N times)) ] x 100% Claim 2 A silicon carbon composite according to claim 1, wherein the peak intensity fraction of the second peak (N-1 times) / first peak (N-1 times) is 0.5 or more and 0.8 or less. Claim 3 A silicon carbon composite according to claim 1, wherein the peak intensity fraction of the second peak (N times) / first peak (N times) is 0.55 or more and 0.7 or less. Claim 4 A silicon carbon composite according to claim 1, wherein the average particle size (D50) of the silicon carbon composite is 1 μm or more and 10 μm or less. Claim 5 A negative electrode active material comprising a silicon carbon composite according to any one of claims 1 to 4. Claim 6 The negative electrode active material of claim 5, wherein the negative electrode active material further comprises a carbon-based active material. Claim 7 A negative electrode active material according to claim 5, wherein the silicon carbon composite comprises 50 parts by weight or less based on 100 parts by weight of the negative electrode active material. Claim 8 A negative electrode for a lithium secondary battery comprising: a negative electrode current collector layer; and a negative electrode active material layer provided on one or both sides of the negative electrode current collector layer, wherein the negative electrode active material layer comprises a negative electrode active material layer composition comprising a negative electrode active material according to claim 5. Claim 9 A negative electrode for a lithium secondary battery according to claim 8, wherein the negative electrode active material layer composition further comprises a negative electrode conductive material; and a negative electrode binder. Claim 10 A negative electrode for a lithium secondary battery according to claim 8, wherein the rolled density of the negative electrode active material layer is 0.9 g / cc or more and 1.3 g / cc or less. Claim 11 A lithium secondary battery comprising: a positive electrode; a negative electrode for a lithium secondary battery according to claim 8; a separator provided between the positive electrode and the negative electrode; and an electrolyte. Claim 12 A battery module comprising a lithium secondary battery according to claim 11. Claim 13 A battery pack comprising a lithium secondary battery according to claim 11. Claim 14 Cathode current collector layer; A negative electrode for a lithium secondary battery comprising a negative electrode active material layer provided on one or both sides of the negative electrode current collector layer, wherein the negative electrode active material layer comprises a negative electrode active material comprising a silicon carbon composite, and the silicon carbon composite comprises a first peak in the range of 0.25V to 0.35V and a second peak in the range of 0.42V to 0.48V in the dQ / dV spectrum of the discharge profile, and after repeating a charge and discharge cycle including N cycles from (N-1) cycles N times, for the first peak (N times) and the second peak (N times), N is an integer greater than or equal to 2, and the second peak (N times) satisfies the following Equation 1, [Equation 1][ (second peak (N-1 times) - second peak (N times)) / second peak (N-1 times)] x 100% ≤ 10, and the negative electrode is a lithium secondary battery having a capacity retention rate of 85% or more after 300 charge-discharge cycles Negative electrode for battery.

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