Anode active material, preparation method for anode active material, anode composition, anode for lithium secondary battery comprising same, and lithium secondary battery comprising anode

Abstract

The present invention relates to: an anode active material; a preparation method for the anode active material; an anode composition; an anode for a lithium secondary battery, comprising same; and a lithium secondary battery comprising the anode.

Description

A negative electrode active material, a method for manufacturing a negative electrode active material, a negative electrode composition, a negative electrode for a lithium secondary battery comprising the same, and a lithium secondary battery comprising the negative electrode

[0001] This application claims the benefit of the filing date of Korean Patent Application No. 10-2024-0185772 filed with the Korean Intellectual Property Office on December 13, 2024, the entire contents of which are incorporated herein.

[0002] The present application relates to a negative electrode active material, a method for manufacturing a negative electrode active material, a negative electrode composition, a negative electrode for a lithium secondary battery comprising the same, and a lithium secondary battery comprising the negative electrode.

[0003] 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.

[0004] Currently, a representative example of an electrochemical device utilizing such electrochemical energy is the secondary battery, and its scope of application is steadily expanding.

[0005] With the increasing technological development and demand for mobile devices, the demand for secondary batteries as an energy source is rapidly rising. Among these secondary batteries, lithium-ion batteries, which possess high energy density and voltage, long cycle life, and low self-discharge rates, have been commercialized and are widely used. Furthermore, active research is being conducted on methods to manufacture high-density electrodes with higher energy density per unit volume for use in such high-capacity lithium-ion batteries.

[0006] Generally, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode includes a negative electrode active material that inserts and extracts lithium ions from the positive electrode, and a silicon-based active material with a large discharge capacity may be used as the negative electrode active material.

[0007] In particular, due to the recent demand for high-density energy batteries, research is actively being conducted on methods to increase capacity by using silicon-based compounds such as Si / C or SiOx, which have a capacity more than 10 times greater than that of graphite-based materials, as negative electrode active materials. However, while silicon-based compounds, which are high-capacity materials, have the advantage of having a large capacity compared to graphite used conventionally, they have the problem of degrading battery characteristics by rapidly expanding in volume during the charging process, thereby disrupting the conductive path.

[0008] Accordingly, various measures are being discussed to address the problems associated with using silicon-based compounds as negative electrode active materials, such as controlling the driving potential, coating additional thin films on the active material layer, controlling the particle size of silicon-based compounds to suppress volume expansion itself, or preventing the interruption of conductive paths. However, since these methods can actually degrade battery performance, their application is limited, and consequently, there are still limitations to the commercialization of negative electrode batteries with high silicon-based compound content.

[0009] Recently, among silicon-based active materials, research on silicon-carbon composites has been conducted to secure characteristics such as energy density and rapid charging. During the manufacturing process of the anode, a slurry containing the anode active material is applied onto the anode current collector layer and rolled. However, in the case of silicon-carbon composites, since silicon and carbon are combined, they easily crumble during rolling. Consequently, silicon, which is vulnerable to moisture, is exposed to moisture, leading to a problem where lifespan characteristics are degraded.

[0010] Therefore, even when using silicon-carbon composites as negative electrode active materials to improve capacity performance, research on the silicon-carbon composite itself is necessary to prevent the degradation of conductive pathways due to volume expansion of the silicon-carbon composite.

[0011] <Prior Art Literature>

[0012] Japanese Published Patent Application No. 2009-080971

[0013] Through this study, it was confirmed that controlling the properties of porous carbon and changing the deposition conditions during the process of depositing SiH4 on porous carbon in the manufacturing process of silicon-carbon composites improves the deposition uniformity and internal pore density of silicon. Consequently, it was found that the silicon-carbon composites produced in this manner can achieve a uniform silicon content.

[0014] Accordingly, the present application relates to a negative electrode active material capable of solving the aforementioned problems, a method for manufacturing a negative electrode active material, a negative electrode composition, a negative electrode for a lithium secondary battery comprising the same, and a lithium secondary battery comprising the negative electrode.

[0015] One embodiment of the present specification provides a negative electrode active material comprising a silicon carbon composite made of silicon carbon particles, wherein the silicon carbon particles comprise porous carbon; and silicon deposited on the porous carbon, wherein the silicon comprises 1 part by weight or more and 70 parts by weight or less based on 100 parts by weight of the silicon carbon particles, the standard deviation of the silicon weight in the silicon carbon composite is 30 or less, and the average of the silicon weight is 40 parts by weight or more and 70 parts by weight or less.

[0016] In another embodiment, a method for manufacturing a negative electrode active material comprises the step of forming a silicon-carbon composite by depositing silicon on porous carbon; wherein the step of forming the silicon-carbon composite by depositing silicon on porous carbon is performed for 7 hours or more and 10 hours or less at a silicon deposition flow rate of 700 SCCM or more and 1000 SCCM or less, and the silicon-carbon composite is composed of silicon-carbon particles, wherein the silicon comprises 1 part by weight or more and 70 parts by weight or less based on 100 parts by weight of the silicon-carbon particles, the standard deviation of the silicon weight in the silicon-carbon composite is 30 or less, and the average silicon weight is 40 parts by weight or more and 70 parts by weight or less.

[0017] In another embodiment, a cathode composition comprising a cathode active material according to the present application is to be provided.

[0018] In another embodiment, the present invention 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 electrode composition according to the present application or a cured product thereof.

[0019] Finally, a lithium secondary battery is provided comprising: a positive electrode; and a negative electrode for a lithium secondary battery according to the present application.

[0020] A negative electrode active material according to one embodiment of the present invention comprises a silicon-carbon composite, and is characterized in that it is composed of silicon-carbon particles comprising silicon deposited on porous carbon. In the case of the silicon-carbon composite, silicon is deposited on porous carbon, and it is important that the silicon is deposited densely on the porous carbon during the silicon deposition process, has a uniform surface, and that the amount of silicon deposited is evenly distributed on each individual particle.

[0021] In particular, when manufacturing the cathode, a cathode slurry is applied to the top of the cathode current collector layer and rolled. During this process, the cathode active material in the form of a composite is broken due to the rolling pressure, and a problem occurs in which silicon is exposed on the surface.

[0022] However, in the case of the silicon carbon composite according to the present application, when manufacturing the silicon carbon composite, the physical properties of the porous carbon that is the precursor and the flow rate of silicon are controlled so that the deposition of silicon is more uniform and the amount of silicon deposited is evenly distributed on each individual particle, and the silicon carbon composite manufactured thereby contains at least 1 part by weight and at least 70 parts by weight of silicon based on 100 parts by weight of silicon carbon particles, the standard deviation of the silicon weight within the silicon carbon composite is 30 or less, and the average silicon weight is at least 40 parts by weight and at least 70 parts by weight.

[0023] In other words, the silicon is deposited densely on each individual silicon carbon particle, and the deposition amount is maintained equally among the silicon carbon particles. When a negative electrode active material containing this is used, it has high capacity characteristics and improved long-term lifespan performance.

[0024] Having the above characteristics, the cathode comprising the silicon carbon composite according to the present application has the characteristics of securing capacitance characteristics, improving resistance by minimizing side reactions on the surface of the active material, and improving lifespan issues caused by volume expansion.

[0025] 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.

[0026] FIG. 2 is a diagram showing a stacked structure of a lithium secondary battery according to one embodiment of the present application.

[0027] <Explanation of Symbols>

[0028] 10: Cathode current collector layer

[0029] 20: Cathode active material layer

[0030] 30: Separator

[0031] 40: Positive active material layer

[0032] 50: Positive current collector layer

[0033] 100: Negative electrode for lithium secondary battery

[0034] 200: Cathode for lithium secondary batteries

[0035] Before describing the present invention, we will first define some terms.

[0036] 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.

[0037] In this specification, 'p to q' means a range of 'p or more and q or less'.

[0038] 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.

[0039] 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 average particle size 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.

[0040] In one embodiment of the present application, particle size or particle diameter may refer to the average diameter or representative diameter of each individual grain constituting the metal powder.

[0041] 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.

[0042] In this specification, the term "polymer" is understood to be used in a broad sense including copolymers unless specified as "homopolymer."

[0043] 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.

[0044] 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.

[0045] One embodiment of the present specification provides a negative electrode active material comprising a silicon carbon composite made of silicon carbon particles, wherein the silicon carbon particles comprise porous carbon; and silicon deposited on the porous carbon, wherein the silicon comprises 1 part by weight or more and 70 parts by weight or less based on 100 parts by weight of the silicon carbon particles, the standard deviation of the silicon weight in the silicon carbon composite is 30 or less, and the average of the silicon weight is 40 parts by weight or more and 70 parts by weight or less.

[0046] The present invention is characterized by including a silicon-carbon composite as a negative electrode active material. That is, compared to the case where a conventional carbon-based active material is used, the inclusion of a silicon-carbon composite improves capacity characteristics, enables the achievement of high energy density, and also improves rapid charging performance.

[0047] In this specification, the silicon carbon composite is composed of silicon carbon particles, and the silicon carbon particles are a composite of Si and C, distinct 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.

[0048] In the present application, the silicon carbon composite may comprise silicon carbon particles comprising porous carbon and silicon deposited on the porous carbon.

[0049] The fact that it is composed of the above silicon carbon particles may mean that the silicon carbon particles within the silicon carbon composite clump together to form a single composite.

[0050] 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.

[0051] In the present application, the silicon may comprise at least 1 part by weight and no more than 70 parts by weight based on 100 parts by weight of the silicon carbon particles.

[0052] In another embodiment, based on 100 parts by weight of the silicon carbon particles, the silicon may comprise 1 part by weight or more and 70 parts by weight or less, specifically 10 parts by weight or more and 70 parts by weight or less, and more specifically 30 parts by weight or more and 70 parts by weight or less.

[0053] The silicon content based on 100 parts by weight of the silicon carbon particles can refer to the silicon content contained within a single silicon carbon particle when the porous carbon and the silicon deposited on the porous carbon are considered as one silicon carbon particle.

[0054] In the present application, the standard deviation of the silicon weight in the silicon carbon composite is 30 or less, and the average of the silicon weight may be 40 parts by weight or more and 60 parts by weight or less.

[0055] In another embodiment, the standard deviation of the silicon weight in the silicon carbon composite is 30 or less, specifically 28 or less, and may be 1 or more, or 10 or more.

[0056] In another embodiment, the average weight of silicon in the silicon carbon composite may be 40 parts by weight or more and 60 parts by weight or less, specifically 45 parts by weight or more and 58 parts by weight or less.

[0057] The standard deviation of silicon weight within a silicon-carbon composite refers to the standard deviation of silicon weight based on each silicon-carbon particle, given that the silicon-carbon composite is composed of silicon-carbon particles; similarly, the average of silicon weight within a silicon-carbon composite refers to the average of silicon weight based on each silicon-carbon particle.

[0058] As described above, the silicon content in the silicon carbon composite satisfies the above range, and the amount of silicon deposited on each individual silicon carbon particle forming the silicon carbon composite satisfies the above range, thereby enabling high energy density and high capacity, preventing volume expansion, and furthermore, enabling uniform deposition on the surface of the silicon carbon composite, which has the characteristic of improving lifespan characteristics.

[0059] The standard deviation of the silicon weight of the silicon carbon composite above refers to the standard deviation of the weight portion of silicon included in the silicon carbon composite when the cross-sectional EDS of the cathode active material layer containing the cathode active material is measured (AztecFeature) based on the cathode electrode containing the cathode active material, with the number of silicon carbon particles being 200 or more and the recognition rate being 90% or more.

[0060] In other words, the silicon carbon particles within the electrode are identified by cross-sectional SEM to measure the carbon and silicon content of each particle. Since the silicon is deposited onto porous carbon, there is a difference in the degree of silicon deposition among the porous carbon particles, that is, a difference in the silicon content within the particles.

[0061] The main feature of the present invention is that, in this application, data for each particle is provided when a large number of such particles are measured, and the average and standard deviation of the silicon weight of these values ​​(silicon carbon composite) are derived.

[0062] For reference, the mean and standard deviation may be calculated using methods known in the industry, specifically using the following formulas.

[0063] [ceremony]

[0064]

[0065] In the above formula, δ represents the standard deviation, x represents the displacement (data value), μ represents the mean of the data, and N represents the total number of data.

[0066] In other words, as described above, the silicon content deposited between the silicon-carbon composite particles is uniformly deposited. When a negative electrode active material containing a uniformly deposited silicon-carbon composite is utilized, side reactions can be minimized through a uniform electrochemical reaction, thereby providing the characteristic of improving the lifespan performance of the cell.

[0067] The present application provides a negative electrode active material having a silicon / carbon content ratio of 0.7 or more and 2.5 or less within the silicon carbon particles.

[0068] In another embodiment, the silicon / carbon content ratio in the silicon carbon particles may be 0.7 or more and 2.5 or less, specifically 0.75 or more and 2.45 or less, and more specifically 0.8 or more and 2.4 or less.

[0069] Each silicon carbon particle has the weight ratio described above, and the ratio of porous carbon to silicon to control volume expansion is suitable, thereby enabling the production of a battery with excellent high energy density and lifespan performance.

[0070] In the present application, the negative electrode active material may further include a carbon-based active material.

[0071] In the present application, the carbon-based active material may include graphite, and the graphite may include natural graphite and artificial graphite.

[0072] In the present application, the average particle size (D50) of the natural graphite is 5㎛ or more and 20㎛ or less, and the average particle size (D50) of the artificial graphite may be 5㎛ or more and 20㎛ or less.

[0073] In another embodiment, the average particle size (D50) of the natural graphite may be 5㎛ or more and 20㎛ or less, preferably 7㎛ or more and 18㎛ or less, and more preferably 9㎛ or more and 15㎛ or less.

[0074] In another embodiment, the average particle size (D50) of the artificial graphite may be 5㎛ or more and 20㎛ or less, preferably 8㎛ or more and 18㎛ or less, and more preferably 10㎛ or more and 16㎛ or less.

[0075] In the present application, the weight ratio of artificial graphite to natural graphite based on 100 parts by weight of the carbon-based active material may be 60:40 to 80:20.

[0076] In another embodiment, the weight ratio of artificial graphite to natural graphite based on 100 parts by weight of the carbon-based active material may satisfy 60:40 to 80:20, preferably 65:35 to 78:22, and more preferably 70:30 to 75:25.

[0077] Graphite may include both synthetic and natural graphite; as it has been confirmed that synthetic graphite exhibits superior cell characteristics compared to natural graphite, the use of natural graphite is being reduced while the amount of synthetic graphite is being increased. However, from a cost perspective, synthetic graphite poses a problem due to high processing costs resulting from the calcination and graphitization of coke. Consequently, satisfying the aforementioned range provides the characteristic of improving cell characteristics while addressing cost issues.

[0078] In the present application, a negative electrode active material is provided in which the silicon carbon composite comprises 60 parts by weight or less based on 100 parts by weight of the negative electrode active material.

[0079] In another embodiment, based on 100 parts by weight of the cathode active material, the silicon carbon composite may contain 60 parts by weight or less, specifically 55 parts by weight or less, more specifically 50 parts by weight or less, and may contain 1 part by weight or more, 3 parts by weight or more, more specifically 5 parts by weight or more.

[0080] 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.

[0081] Meanwhile, the average particle size (D50 particle size) of the silicon carbon composite of the present invention is 1 μm or more and 15 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 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 carbon composite 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.

[0082] 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-carbon composite is preferably 0.01 to 150 m² 2 / g, more preferably 0.1 to 100m 2 / g, particularly preferably 0.2 to 80 m 2 / g, most preferably 0.2 to 18 m 2 / g. The BET surface area is measured according to DIN 66131 (using nitrogen).

[0083] In one embodiment of the present application, the silicon of the silicon-carbon composite may exist, for example, in a crystalline or amorphous form, and the silicon is preferably spherical or fragmentary particles. Alternatively, but less preferably, the silicon may also have a fibrous structure or exist in the form of a silicon-containing film or coating.

[0084] 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.

[0085] 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.

[0086] [Equation 1-A]

[0087] 4πA / P 2

[0088] In one embodiment of the present application, a cathode composition comprising the cathode active material is provided.

[0089] The above cathode composition may include a cathode conductive material and / or a cathode binder as needed.

[0090] In one embodiment of the present application, the cathode active material is provided in an amount of 40 parts by weight or more based on 100 parts by weight of the cathode composition.

[0091] In another embodiment, the cathode active material may comprise 40 parts by weight or more, preferably 60 parts by weight or more, more preferably 65 parts by weight or more, and even more preferably 70 parts by weight or more, based on 100 parts by weight of the cathode composition, and may be 99 parts by weight or less, preferably 98 parts by weight or less, and even more preferably 96 parts by weight or less.

[0092] The cathode composition according to the present application uses a cathode active material that satisfies a specific pore distribution capable of controlling volume expansion and side reactions during the charging and discharging process, even when using a silicon carbon composite with significantly high capacity within the above range, thereby having the characteristic of not degrading the performance of the cathode even when including the above range and having excellent output characteristics during charging and discharging.

[0093] Conventionally, it was common practice to use only graphite-based compounds as negative electrode active materials. However, with the recent increase in demand for high-capacity batteries, there have been increasing attempts to mix and use silicon-based active materials to increase capacity. However, in the case of silicon-based active materials, even if the characteristics of the silicon-based active material itself are controlled as described above, the volume expands rapidly during the charging and discharging process, which can cause some problems that damage the conductive paths formed within the negative electrode active material layer.

[0094] Accordingly, in one embodiment of the present application, the cathode conductive material may include one or more selected from the group consisting of point conductive materials, planar conductive materials, and linear conductive materials.

[0095] In one embodiment of the present application, the point-shaped conductive material can be used to improve conductivity of the cathode and refers to a point-shaped or spherical conductive material having conductivity without causing chemical changes. Specifically, the point-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.

[0096] 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 65m 2 / g or less, more preferably 50m 2 / g or more 60m 2 It may be less than / g.

[0097] In one embodiment of the present application, the point-shaped conductive material may satisfy a volatile matter content of 0.01% or more and 1% or less, preferably 0.01% or more and 0.3% or less, and more preferably 0.01% or more and 0.1% or less.

[0098] In particular, when the functional group content of the point-shaped conductive material satisfies the above range, the functional groups present on the surface of the point-shaped conductive material allow the point-shaped conductive material to be smoothly dispersed within the solvent when water is used as the solvent. In particular, in the present invention, the functional group content of the point-shaped conductive material can be lowered by using a specific silicon-based active material, thereby providing an excellent effect in improving dispersibility.

[0099] In one embodiment of the present application, the invention is characterized by including a point-shaped conductive material having a functional group content within the above range together with a silicon-based active material, wherein the control of the functional group content can be controlled according to the degree of heat treatment of the point-shaped conductive material.

[0100] 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.

[0101] In one embodiment of the present application, the conductive material may include a planar conductive material.

[0102] The above-described planar conductive material can improve conductivity by increasing surface contact between silicon particles within the cathode, while simultaneously suppressing the disruption of conductive pathways due to volume expansion. The above-described planar conductive material may be described as a plate-shaped conductive material or a bulk-shaped conductive material.

[0103] 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.

[0104] 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 3.5 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.

[0105] 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.

[0106] 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.

[0107] In one embodiment of the present application, the planar conductive material has a BET specific surface area of ​​1 m² 2 It can be more than / g.

[0108] In another embodiment, the planar conductive material has a BET specific surface area of ​​1 m² 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 2It may be less than / g.

[0109] The planar conductive material according to the present application may use a planar conductive material with a high specific surface area; or a planar conductive material with a low specific surface area.

[0110] 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.

[0111] In another embodiment, the planar conductive material is a low specific surface area planar conductive material, and has a BET specific surface area of ​​1 m² 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.

[0112] 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.

[0113] In the present application, the cathode composition is provided in which the cathode conductive material is 20 parts by weight or less based on 100 parts by weight of the cathode composition.

[0114] In another embodiment, the cathode conductive material may be 20 parts by weight or less, 17 parts by weight or less, or 15 parts by weight or less based on 100 parts by weight of the cathode composition, and may be 0.01 parts by weight or more, or 0.02 parts by weight or more.

[0115] 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 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, whereas the anode conductive material serves as a buffer during rolling and provides partial conductivity; thus, their composition and roles are completely different from those of the cathode conductive material of the present invention.

[0116] Furthermore, the cathode conductive material according to the present application is applied to silicon-based active materials and has a completely different composition from that of a conductive material applied to graphite-based active materials. That is, a conductive material used in an electrode having a graphite-based active material simply has particles smaller than the active material, thereby providing improved output characteristics and some conductivity; thus, its composition and role are completely different from that of a cathode conductive material applied together with a silicon-based active material as in the present invention.

[0117] In one embodiment of the present application, the planar conductive material used as the aforementioned negative electrode conductive material has a structure and role different from that of a carbon-based active material generally used as a negative electrode active material. Specifically, the carbon-based active material used as a negative electrode active material may be artificial graphite or natural graphite, and refers to a material processed into a spherical or dot shape to facilitate the storage and release of lithium ions.

[0118] On the other hand, planar conductive materials used as cathode conductive materials are substances having a planar or plate-like form, which can be described as plate-like graphite. In other words, they refer to materials included to maintain conductive pathways within the cathode active material layer; they do not serve the role of lithium storage or release, but rather are materials intended to secure conductive pathways in a planar form within the cathode active material layer.

[0119] In other words, in the present application, the fact that plate-shaped graphite is used as a conductive material means that it is processed into a planar or plate-shaped form and used as a material that secures a conductive pathway rather than serving the role of storing or releasing lithium. At this time, the negative electrode active material included together has high capacity characteristics for lithium storage and release and plays a role in storing and releasing all lithium ions delivered from the positive electrode.

[0120] On the other hand, in the present application, the fact that a carbon-based active material is used as an active material means that it is processed into a point or spherical shape and used as a material that serves the role of storing or releasing lithium.

[0121] That is, in one embodiment of the present application, the carbon-based active material, artificial graphite or natural graphite, is in a point-like form, with a BET specific surface area of ​​0.1 m² 2 / g or more than 4.5 m 2 It can satisfy a range of / g or less. In addition, plate-shaped graphite, a planar conductive material, has a planar form with a BET specific surface area of ​​5m² 2 It can be more than / g.

[0122] 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.

[0123] 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 silicon-based 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.

[0124] In one embodiment of the present application, the cathode binder may be 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 composition, and may be 1 part by weight or more, or 2 parts by weight or more.

[0125] One embodiment of the present application provides a method for manufacturing a silicon negative electrode active material comprising the step of forming a silicon carbon composite by depositing silicon on porous carbon; wherein the step of forming the silicon carbon composite by depositing silicon on porous carbon is performed for 7 hours or more and 10 hours or less at a silicon deposition flow rate of 700 SCCM or more and 1000 SCCM or less, and the silicon carbon composite is composed of silicon carbon particles, wherein the silicon comprises 1 part by weight or more and 70 parts by weight or less based on 100 parts by weight of the silicon carbon particles, the standard deviation of the silicon weight in the silicon carbon composite is 30 or less, and the average silicon weight is 40 parts by weight or more and 70 parts by weight or less.

[0126] In the present application, the total pore volume of the porous carbon is 0.7 cm 3 / g or more than 1.0 cm 3 A method for manufacturing a negative electrode active material having a g or less is provided.

[0127] In the present application, the porous carbon may have a ratio of first pores having a diameter of less than 2 nm when measured by nitrogen adsorption method of 90% or more, and the porous carbon may have a ratio of second pores having a diameter of 2 nm or more and 50 nm or less when measured by nitrogen adsorption method of 10% or less.

[0128] The present application achieves the aforementioned properties of uniformly deposited silicon when the conditions of the porous carbon and the silicon deposition flow rate are changed as described above. That is, in the manufacture of a silicon-carbon composite, by controlling the silicon deposition flow rate and the pore volume of the porous carbon, the deposition amount and uniformity of silicon deposited on each individual particle are improved, thereby satisfying the aforementioned average value and standard deviation of silicon weight.

[0129] In addition, the above porous carbon provides a method for manufacturing a cathode active material having a degree of sphericity of 0.7 to 0.9 as defined by Formula 1 below.

[0130] [Equation 1]

[0131] 4πA / P 2

[0132] In the above Equation 1, A is the area and P is the boundary line.

[0133] In other words, when the properties of porous carbon are controlled as described above, mechanical strength can be increased, and when silicon is deposited using porous carbon satisfying the above properties, it has the characteristic of improving density and deposition uniformity.

[0134] In one embodiment of the present application, a negative electrode for a lithium secondary battery is provided, comprising: a negative electrode current collector layer; and a negative electrode active material layer formed on one or both sides of the negative electrode current collector layer, the negative electrode composition according to the present application or a cured product thereof.

[0135] 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. 4 shows that the negative active material layer is formed on one surface, but can be included on both surfaces of the negative current collector layer.

[0136] In one embodiment of the present application, the negative electrode for the lithium secondary battery may be formed by applying and drying a negative electrode slurry containing the negative electrode composition on one or both sides of a negative electrode current collector layer.

[0137] At this time, the cathode slurry may include the aforementioned cathode composition; and a slurry solvent.

[0138] In one embodiment of the present application, the solid content of the cathode slurry may satisfy 5% or more and 40% or less.

[0139] In another embodiment, the solid content of the cathode slurry may satisfy a range of 5% or more and 40% or less, preferably 7% or more and 35% or less, and more preferably 10% or more and 30% or less.

[0140] The solid content of the above cathode slurry may refer to the content of the cathode composition included in the above cathode slurry, and may refer to the content of the cathode composition based on 100 parts by weight of the cathode slurry.

[0141] When the solid content of the above cathode slurry satisfies the above range, the viscosity is suitable when forming the cathode active material layer, thereby minimizing particle aggregation of the cathode composition and enabling the cathode active material layer to be formed efficiently.

[0142] In one embodiment of the present application, the slurry solvent may be used without limitation as long as it can dissolve the cathode composition, and specifically, water or NMP may be used.

[0143] In one embodiment of the present application, the negative current collector layer generally has a thickness of 1 μm to 100 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.

[0144] In one embodiment of the present application, a negative electrode for a lithium secondary battery is provided, wherein the thickness of the negative electrode current collector layer is 1 μm or more and 100 μm or less, and the thickness of the negative electrode active material layer is 5 μm or more and 500 μm or less.

[0145] However, the thickness may vary depending on the type and application of the cathode used, and is not limited thereto.

[0146] In one embodiment of the present application, the porosity of the negative electrode active material layer may satisfy a range of 10% or more and 60% or less.

[0147] In another embodiment, the porosity of the negative electrode active material layer may satisfy a range of 10% or more and 60% or less, preferably 20% or more and 50% or less, and more preferably 30% or more and 45% or less.

[0148] The above porosity varies depending on the composition and content of the silicon-based active material, conductive material, and binder included in the cathode active material layer, and in particular, satisfies the above range by including the silicon-based active material and conductive material according to the present application in a specific composition and content, thereby characterized in that the electrical conductivity and resistance of the electrode have an appropriate range.

[0149] In one embodiment of the present application, a lithium secondary battery is provided comprising: a positive electrode; and a negative electrode for a lithium secondary battery according to the present application.

[0150] The above lithium secondary battery may include a separator provided between the positive electrode and the negative electrode as needed; and / or an electrolyte.

[0151] 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.

[0152] 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.

[0153] 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.

[0154] 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.

[0155] 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.

[0156] 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.

[0157] 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.

[0158] 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.

[0159] The above separator separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions. Any separator typically used in secondary batteries can be used without special limitations, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte moisture retention capacity. 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.

[0160] 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.

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

[0162] 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.

[0163] 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.

[0164] 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.

[0165] 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.

[0166] 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.

[0167] 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.

[0168] <Preparation Example>

[0169] 1. Manufacture of silicon carbon composites

[0170] <Example 1>

[0171] After carbonizing the porous carbon raw material through heat treatment at 500°C to 1000°C under an inert gas atmosphere, the carbonized porous carbon was ground and classified. Subsequently, pores were formed through physical activation by oxidizing the porous carbon using an oxidizing gas (steam, CO2, O2, etc.), and the Total Pore Volume of the resulting porous carbon, measured by the nitrogen adsorption method, was 0.9 cm⁻¹. 3 / g was.

[0172] Afterwards, silicon was deposited on the porous carbon for 8 hours while SiH4 was flowed through the porous carbon at a rate of 1000 SCCM to form a silicon carbon composite.

[0173] <Example 2>

[0174] In the above Example 1, a negative electrode active material was prepared in the same manner as in Example 1, except that the flow rate of SiH4 was 800 SCCM and deposited for 10 hours.

[0175] <Example 3>

[0176] In the above Example 1, the Total Pore Volume is 0.8 cm 3 A negative electrode active material was prepared in the same manner as in Example 1, except that porous carbon with a g content was used.

[0177] <Example 4>

[0178] In the above Example 3, a negative electrode active material was prepared in the same manner as in Example 3, except that the flow rate of SiH4 was 800 SCCM and deposited for 10 hours.

[0179] <Comparative Example 1>

[0180] In the above Example 1, a negative electrode active material was prepared in the same manner as in Example 1, except that the flow rate of SiH4 was 1200 SCCM and deposited for 8 hours.

[0181] <Comparative Example 2>

[0182] In the above Example 3, a negative electrode active material was prepared in the same manner as in Example 3, except that the flow rate of SiH4 was 1200 SCCM and deposited for 8 hours.

[0183] <Comparative Example 3>

[0184] In the above Example 1, a negative electrode active material was prepared in the same manner as in Example 1, except that the flow rate of SiH4 was 800 SCCM and deposited for 8 hours.

[0185] <Comparative Example 4>

[0186] In the above Example 1, a negative electrode active material was prepared in the same manner as in Example 1, except that the flow rate of SiH4 was 1500 SCCM and it was deposited for 10 hours.

[0187] 2. Cross-sectional analysis of cathode active material (Si, C content analysis)

[0188] Cross-sectional analysis of the cathode active materials of the above examples and comparative examples was performed using an ion milling device. First, electrode samples prepared by coating the cathode active material onto copper foil (Cu Foil) were milled using a Hitachi IM4000 device. Specifically, an ion beam was fired at a voltage of 1.5 kV and treated for about 3 to 4 hours per sample, after which cross-sectional images were measured using a Hitachi S-4800 SEM. Next, silicon-carbon composite particles were selected based on the measured SEM cross-sectional images, and the Si and Carbon content of each particle were measured through EDS mapping. The results were summarized and listed in Table 1 below.

[0189] Cathode Evaluation Standard Deviation of Silicon Content in Silicon Carbon Composite Average Silicon Content in Silicon Carbon Composite Content of Silicon Carbon Composite Based on Cathode Active Material Silicon Carbon Composite D50 (μm) Example 1: 17467~10% 9.2 Example 2: 20487~10% 7.7 Example 3: 254777~10% 8.2 Example 4: 27607~10% 7.9 Comparative Example 1: 324777~10% 9.2 Comparative Example 2: 50657~10% 8.9 Comparative Example 3: 15307~10% 9.2 Comparative Example 4: 55757~10% 9.2

[0190] For reference, the standard deviation of the silicon content and the average of the silicon content within the silicon carbon composites of Example 1 and Comparative Example 1 were specifically calculated based on the data in Table 2 below. That is, the silicon content for approximately 300 types of particles within the silicon carbon composites was listed in Table 2, from which the average and standard deviation could be calculated. In the case of Example 1, the average was calculated to be 46.30 and the standard deviation 16.67, while in the case of Comparative Example 1, the average was calculated to be 47.28 and the standard deviation 31.86, and these values ​​were rounded in Table 1.

[0191] Table 2 shows the results according to Example 1 and Comparative Example 1, but the remaining examples and comparative examples were calculated in the same way.

[0192] Particle Number Example 1 Comparative Example 1 15 1.995 146 6.430 3126 2.492 337 8.87 186 36 6.705 410.632 3245 6.797 15.86 4085 6 1.62 608 37.88 401 647.53 1248 0.2345 475 4.35 4336 7.76 21685 4.9 848878.41584936.6260778.407661065.2953260.24471148.6028579.982591242.592361.7229130.781244.003051454.9476195.446181578.6049 259.35131632.9778563.343661743.426563.918221844.5046345.910271962.6584248.991732053.9756187.229672153.085461.324872253.988 655.326982345.647253.988442452.4578252.165962540.5387659.566452652.2538645.072382763.9815776.794362838.3695988.45312943.035 5755.504443061.759396.816283155.400193.112413262.5191896.231483336.6804748.178793453.5162666.711853554.665155.241013628.97 4074.798723757.7473866.321473833.826037.819993945.3356478.641864052.1559798.775864132.2983577.366644246.114350.783824336.19 48744.679824419.0081743.908014543.584536.568824663.6552645.241844711.9479544.11254839.5114197.075344942.3461134.110565045. 6327257.86935156.302920.460325223.1218474.475415340.0021555.466145444.7393948.013835565.021652.517155649.5140753.925795743.929755.642995835.9982396.099555939.0425648.585276057.6850997.254426152.0391492.443426243.6002526.136526326.7597178.472546469.3098636.666386549.575021.331396649.525550.905886762.969623.539326856.6778546.229626944.4124168.087987060.6108782.524347157.2541846.461557212.63970.682077358.7787744.724747452.233833.713087552.6768366.492677633.9768854.396467749.961240.983797863.6604284.098467956.1900588.446978018.375666.135268119.0842951.290928248.7761656.113278359.4903755.102968450.813980.922198547.1291557.076738644.422544.193218744.6753245.66328851.5407757.852588950.1407464.821999026.2349310.10559141.5915198.537819267.0517652.193469355.70610.7179448.5869252.054029546.506448.750719650.6928944.268929757.1015784.707869857.5734945.984869969.6926781.2644110040.811151.6435510153.3388450.6149910246.0459897.032961030.791341.8096710455.3391686.7807610557.7928247.9968510642.225964.4058710767.098631.097510842.5732510.1284510911.7851236.697311031.4914360.4935211143.6883454.3215411258.769151.0899411338.3310645.821211415.661886.133541154.8127537.7161111610.2395945.9523911745.9533687.3356611848.7695264.2771811954.531222.0328412041.1503741.1678912150.4252666.1813412253.4985289.4450112360.0174857.668421241.9036488.5940412551.466231.930212649.4433210.1122312755.4878472.4173812857.2159962.9405712954.5556551.2921513046.8266680.2181913157.287541.5014213260.8432163.5254713346.7709694.3156813470.0136499.5038213558.7017197.5397413642.782864.3905113745.4969157.9590913843.7799677.7175613952.629420.6507214040.582580.8890514141.195394.1153414264.1919511.534814374.909510.9395514440.7380648.856314565.4844584.9845814652.6500954.2921214753.757731.600681485.0864945.9641114960.541690.8758615042.9854848.964515152.0925366.3982815218.8701263.7427315362.976566.7685615455.782631.1699215562.927760.5325815648.3535698.7544415750.659482.7144815874.2759996.4451115932.62280.82816051.4946355.1339316151.232931.9092416239.9990789.1654316352.878936.5760616454.222521.0634916544.8509389.1533416656.322012.4531616754.6694597.4555416848.5620737.8959416952.5080654.7468317059.5635510.0254317141.7052636.4428617249.6280989.4451317361.4691380.1341917452.6331451.4694717544.36790.484881762.16080.3214417729.2914125.0621117854.5087537.954117954.2125987.4869718071.4922558.7168218155.250382.2161718218.2534899.6700918351.866051.005418450.6559378.4456618553.7475263.141718653.655520.6670518755.391070.9241618820.1420697.11881895.8133271.1082119047.7813580.2345419158.9172854.5804319240.0507711.1405319355.6634661.9657619448.2549157.5769119552.3531689.1354619658.0495451.374519766.8809636.6578919855.6386596.1579519957.7796579.8655920052.7212794.3521520160.703186.335120254.6147925.13592031.7307811.5901420453.1806561.1541220549.5222745.612312063.017710.668072072.742410.7170920852.29260.9450620954.3111960.892632101.4560559.5720321149.738072.4098721249.3102761.323221356.177320.8747721448.8203580.2883421550.729597.0563821660.836440.9312121761.6889871.1164421849.3166960.4995421950.754444.1785822061.696691.6543122148.4511258.6508622213.869658.822832231.160390.9252222460.6326870.5176122587.3320887.2977322645.1578175.3315422734.8898864.1125322851.5289866.5534122924.335124.482423042.0807447.3624323169.2712436.4581223258.7363750.674252339. 9393896.8753223415.5032489.4452123551.997071.2063123614.672538.1550423766.6268636.661223849.3780863.2874223955.6538958.8544824055.4030275.6748924153.3370146.480692422.4835457.6297524344.8455544.7389824432.776512.23 24324545.1968655.633482461.978030.2848824716.0736912.236222482.3967654.3753724947.2887521.5112625066.7179270.5112625129.9356955.2695125249.375441.7645625347.0754315.111525464.9526663.1115725549.8322747.8692525646.2 135995.2436525755.6348499.114325847.5495252.4771625940.568277.3204826016.9513245.3096826164.2847159.5332526245.531291.553626348.2913867.5117126449.1454824.194626551.7210220.1112526655.0136769.7097626749.518390.4521.

[0193] 3. Experimental Example

[0194] - Manufacturing of lithium secondary batteries

[0195] A composition for forming an anode active material layer was prepared by including 98.04 parts by weight of a lithium composite transition metal compound containing single particles and secondary particles, having a content of Ni 80 mol%, Co 4.9 mol%, and Mn 1.8 mol% among metals excluding lithium as an anode active material, based on 100 parts by weight of an anode active material layer, 1 part by weight of PVDF as a binder, and a CNT pre-dispersion liquid containing 0.8 parts by weight of CNT and 0.16 parts by weight of a dispersant as a conductive material.

[0196] The above composition for forming the positive electrode active material layer was coated onto an aluminum foil with a thickness of 30 μm to a dry thickness of 103 μm, and then dried to produce a positive electrode.

[0197] A composition for forming a negative electrode active material layer was prepared by including, based on 100 parts by weight of the negative electrode active material layer, 97.7 parts by weight of graphite (90 to 93 parts by weight based on 100 parts by weight of the negative electrode active material) and the silicon carbon composite of the aforementioned examples and comparative examples (7 to 10 parts by weight based on 100 parts by weight of the 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, and additionally, a CNT pre-dispersion liquid comprising 0.09 parts by weight of a dispersant and 0.06 parts by weight of single-walled CNT.

[0198] A battery was fabricated by stacking the above positive and negative electrodes with a separator in between and injecting an electrolyte (1.0M LiPF6, EC(ethylene carbonate) / EMC(ethylmethyl carbonate)=30 / 70 (Vol%), VC(vinylene carbonate) 1.5%).

[0199] - Discharge capacity

[0200] A battery was fabricated by stacking lithium metal and a negative electrode with a separator in between and injecting an electrolyte (1.0M LiPF6, EC(ethylene carbonate) / EMC(ethylmethyl carbonate)=30 / 70 (Vol%), VC(vinylene carbonate) 1.5%). Charge and discharge were performed on the fabricated lithium secondary battery to evaluate the discharge capacity, which is listed in Table 3 below.

[0201] Discharge conditions: CC (constant current) / CV (constant voltage) (5mV / 0.005C current cut-off)

[0202] Charging conditions: CC (constant current) condition, 1.0 V cut-off

[0203] - Lifespan (capacity retention rate)

[0204] A battery was fabricated by stacking the above positive and negative electrodes with a separator in between and injecting an electrolyte (1.0M LiPF6, EC(ethylene carbonate) / EMC(ethylmethyl carbonate)=30 / 70 (Vol%), VC(vinylene carbonate) 1.5%).

[0205] The lifespan of the secondary battery was evaluated using an electrochemical charge / discharger, and the capacity retention rate was evaluated. The secondary battery was subjected to a cycle test at 4.4-2.5V 1C / 1C. The lifespan retention rate was measured as the ratio of the discharge capacity at the 200th cycle to the discharge capacity at the first cycle.

[0206] Life retention rate (%) = {(Discharge capacity at the 200th cycle) / (Discharge capacity at the first cycle)} × 100

[0207] - Evaluation of cell thickness characteristics

[0208] The thickness of the secondary battery fabricated above was compared before and after performing the cycle as follows.

[0209] The thickness was calculated using the following formula, with the thickness of the cell in a fully charged state after 2 cycles as the Initial thickness and the thickness of the cell in a fully charged state after 200 cycles as the After thickness. The calculated cell thickness of Example 1 was set to 100%, and based on this, the cell thicknesses of Examples 2 to 4 and Comparative Examples 1 to 4 were calculated relatively and listed in Table 3 below.

[0210] Cell Thickness = (After Thickness - Initial Thickness) / (Initial Thickness) X 100

[0211] Discharge Capacity (mAh / g) Cycle Retention (Room Temperature 200 Cycles, %) Cell Thickness (Comparison with Example 1 as 100) (Room Temperature 200 Cycles, SOC 100) Example 1 49297 100 (Reference) Example 2 49295 103 Example 3 49293 108 Example 4 49293 107 Comparative Example 1 49285 125 Comparative Example 2 49282 128 Comparative Example 3 49289 110 Comparative Example 4 49285 132

[0212] Specifically, the Cycle Retention in Table 3 above refers to the result indicating how well the capacity measured at discharge is maintained as the battery undergoes repeated charging and discharging cycles. While capacity naturally decreases with repeated charging and discharging, the rate of decrease becomes smaller if the battery reacts stably with lithium. Conversely, if the reaction with lithium continues irreversibly due to non-uniform reactions, the portion unable to participate in the reaction increases, causing the capacity retention rate to drop.

[0213] Cell thickness is an evaluation that compares the degree of swelling of the cell, specifically the electrode, as charging and discharging proceeds. By comparing the cell thickness in the fully charged state (SOC100), it is possible to verify the stable structural maintenance of the cell over cycles. If a non-uniform reaction occurs, the swollen silicon-carbon composite may not partially return to its original size, potentially causing electrode failure.

[0214] As can be seen in Table 2 above, in the case of the embodiment according to the present application, silicon is deposited densely on each individual silicon carbon particle, and the deposition amount is maintained equally among the silicon carbon particles. Therefore, when using a negative electrode active material containing this, it can be seen that capacity is maintained well compared to the comparative example, and it can also be seen that the cell thickness is lower compared to the comparative example. In other words, it was confirmed that the embodiment in which silicon is uniformly deposited has high capacity characteristics compared to the comparative example, and at the same time, has improved long-term lifespan performance.

[0215] In the case of Comparative Examples 1 and 2, the average silicon content in the silicon-carbon composite satisfies the scope of the present application, but the standard deviation exceeds the scope of the present application. In this case, the silicon content deposited per particle included in the silicon-carbon composite varies significantly from one another, and it was confirmed that the cycle life performance and swelling characteristics deteriorated because the silicon was not deposited uniformly.

[0216] In the case of Comparative Example 3, the silicon content per particle was too low, resulting in unfavorable discharge capacity and efficiency characteristics. Consequently, it was confirmed that cycle life and swelling characteristics were degraded due to the difference in efficiency when evaluating the graphite mixture.

[0217] In the case of Comparative Example 4, it was confirmed that the silicon content per particle was too high, making it difficult to deposit silicon uniformly within the porous carbon, and that the structure of the porous carbon was unable to smoothly accommodate volume expansion, resulting in a decrease in cycle life performance and swelling characteristics.

Claims

1. Includes a silicon carbon composite composed of silicon carbon particles, The above silicon carbon particles comprise porous carbon; and silicon deposited on the porous carbon, and Based on 100 parts by weight of the above silicon carbon particles, the above silicon comprises 1 part by weight or more and 70 parts by weight or less, A negative electrode active material having a standard deviation of silicon weight in the silicon-carbon composite of 30 or less, and an average silicon weight of 40 parts by weight or more and 70 parts by weight or less.

2. In Claim 1, A negative electrode active material having an average particle size (D50) of 1 μm or more and 15 μm or less of the silicon carbon composite.

3. In Claim 1, A negative electrode active material having a silicon / carbon content ratio of 0.7 or more and 2.5 or less within the silicon carbon particles.

4. In Claim 1, The above silicon carbon particles are a negative electrode active material that further includes a carbon coating layer.

5. In Claim 1, The above-mentioned negative electrode active material is a negative electrode active material that further comprises a carbon-based active material.

6. In Claim 1, A negative electrode active material comprising 60 parts by weight or less of the silicon carbon composite based on 100 parts by weight of the above negative electrode active material.

7. A method for manufacturing a negative electrode active material comprising the step of forming a silicon-carbon composite by depositing silicon on porous carbon, wherein The step of forming a silicon-carbon composite by depositing silicon on the porous carbon is performed for 7 hours or more and 10 hours or less at a silicon deposition flow rate of 700 SCCM or more and 1000 SCCM or less, and The above silicon carbon composite is composed of silicon carbon particles, and Based on 100 parts by weight of the above silicon carbon particles, the above silicon comprises 1 part by weight or more and 70 parts by weight or less, A method for manufacturing a silicon negative electrode active material in which the standard deviation of the silicon weight in the silicon carbon composite is 30 or less, and the average of the silicon weight is 40 parts by weight or more and 70 parts by weight or less.

8. In Claim 7, The total pore volume of the above porous carbon is 0.7 cm 3 / g or more than 1.0 cm 3 A method for manufacturing a negative electrode active material having a g or less.

9. A cathode composition comprising a cathode active material according to any one of claims 1 to 6.

10. In Claim 9, The above cathode active material is a cathode composition comprising 40 parts by weight or more based on 100 parts by weight of the above cathode composition.

11. A negative current collector layer; and a negative active material layer provided on one or both sides of the negative current collector layer, comprising The above negative electrode active material layer comprises a negative electrode composition according to claim 9 or a cured product thereof, for a lithium secondary battery negative electrode.

12. In Claim 11, The thickness of the above-mentioned cathode current collector layer is 1 μm or more and 100 μm or less, and A negative electrode for a lithium secondary battery having a negative electrode active material layer thickness of 5 μm or more and 500 μm or less.

13. Anode; and negative electrode for a lithium secondary battery according to claim 11; A lithium secondary battery including

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