Negative active material, method for preparing negative active material, negative electrode composition, lithium secondary battery negative electrode comprising same, and lithium secondary battery comprising negative electrode

Abstract

The present invention relates to a negative active material, a method for preparing the negative active material, a negative electrode composition, a lithium secondary battery negative electrode comprising same, and a lithium secondary battery comprising the negative electrode.

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. 10-2024-0154216 filed with the Korean Intellectual Property Office on November 4, 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. However, silicon-carbon composites, which have high capacity and lifespan, are causing problems with slurry processability, and accordingly, improvements in processability are also necessary in the development of high-energy-density lithium secondary batteries.

[0010] Therefore, research on the silicon carbon composite itself is necessary to improve the processability of the slurry even when using the silicon carbon composite as a negative electrode active material to enhance capacity, efficiency, and lifespan performance.

[0011] <Prior Art Literature>

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

[0013] Through research, it was confirmed that in the process of depositing SiH4 on porous carbon during the manufacturing process of silicon carbon composites, if the properties of porous carbon are controlled and the silicon deposition conditions are changed, the silicon crystallinity of the silicon carbon composite can be lowered and defects in the porous carbon being composited can be controlled. Accordingly, it was found that the silicon carbon composite manufactured in this way has excellent capacity, efficiency, and lifespan performance, and the slurry processability is also improved.

[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 comprising porous carbon and silicon deposited on the porous carbon, wherein the silicon carbon composite has a time constant (T1) of 150 to 1000 when fitting an etching time (x-axis) vs. C / Si ratio (y-axis) graph to an exponential decay function using XPS depth analysis.

[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, in the step of forming the silicon-carbon composite by depositing silicon on porous carbon, the deposition temperature is 500°C or higher and 800°C or lower, the silicon flow rate is 50 ml / min to 250 ml / min, and the silicon-carbon composite has a time constant (T1) of 150 to 1000 when fitting an etching time (x-axis) vs C / Si ratio (y-axis) graph using an exponential decay function by XPS depth analysis.

[0017] In another embodiment, the present application aims to provide a cathode composition comprising a cathode active material.

[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 particularly by a silicon-carbon composite 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 densely deposited on the porous carbon during the silicon deposition process and has a uniform surface.

[0021] In particular, the cathode undergoes a process of applying a cathode slurry to the top of the cathode current collector layer and rolling it during manufacturing, and at this time, there is an issue of stability due to the reaction of the silicon carbon composite with moisture in the water-based cathode slurry.

[0022] However, in the case of the silicon carbon composite according to the present application, when the physical properties of the porous carbon precursor are controlled and the deposition conditions of silicon are controlled during the manufacture of the silicon carbon composite, the deposition can be made more uniform and dense. The silicon carbon composite manufactured in this way has improved processability when included in an aqueous cathode slurry, and has the characteristics of improved battery capacity characteristics and enhanced lifespan characteristics.

[0023] In particular, by using a silicon carbon composite that satisfies the time constant range of the present invention, when included in the range, silicon within the silicon carbon composite is evenly deposited inside rather than on the surface, making it difficult to come into contact with water in an aqueous slurry, thus having the characteristic of excellent processability.

[0024] That is, having the above-mentioned 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 cathode active material, and improving the lifespan issue 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] FIG. 3 is a graph showing the process of deriving the time constant for Example 2 according to the present application.

[0028] Figure 4 is an SEM image of a negative electrode active material layer containing a silicon carbon composite according to Example 1.

[0029] Figure 5 is a figure showing an SEM image of a negative electrode active material layer containing a silicon carbon composite according to Comparative Example 1.

[0030] Before describing the present invention, we will first define some terms.

[0031] In this specification, when a part is described as "comprising" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0032] In this specification, 'p to q' means a range of 'p or more and q or less'.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] In this specification, the term "polymer" is understood to be used in a broad sense including copolymers unless specified as "homopolymer."

[0038] 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, molecular weight refers to the weight-average molecular weight unless otherwise specified.

[0039] 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.

[0040] One embodiment of the present specification provides a negative electrode active material comprising a silicon carbon composite comprising porous carbon and silicon deposited on the porous carbon, wherein the silicon carbon composite has a time constant (T1) of 150 to 1000 when fitting an etching time (x-axis) vs. C / Si ratio (y-axis) graph to an exponential decay function using XPS depth analysis.

[0041] When using a silicon-carbon composite satisfying the above range, the issue of cathode aqueous processability can be resolved, and it has the characteristic of providing a cathode with excellent capacity and efficiency.

[0042] 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.

[0043] 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.

[0044] In the present application, the silicon-based active material may be a silicon carbon (Si / C) composite comprising porous carbon; and silicon deposited on the porous carbon.

[0045] The above Si / C 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] In the present application, the XPS depth analysis refers to an analysis method that etches an analysis target over time and derives the elemental content in the chemical state of the zeolite target for each etching time.

[0047] The analysis conditions for the above XPS depth analysis are identical to the analysis conditions used in the industry, and specifically, the analysis can be performed under the following conditions.

[0048] <Analysis Conditions>

[0049] - X-Ray source: Monochromated Al K α (1486.6 eV)

[0050] - X-ray spot size: 400μm

[0051] - Sputtering gun: Monatomic Ar (energy: 1000 eV, current: low, raster width: 2mm)

[0052] - Etching rate: 0.09 nm / s for Ta 205

[0053] - Operation Mode: CAE (Constant Analyzer Energy) mode

[0054] - Survey scan: pass energy 200 eV, energy step 1 eV

[0055] - Narrow scan: scanned mode, pass energy 50 eV, energy stem 0.1 Ev

[0056] - Charge compensation: 0.1 V 150Μa

[0057] - SF: Al THERMO1

[0058] - ECF: TPP2M

[0059] - BG subtraction: Smart

[0060] In the present application, the silicon carbon composite can derive the time constant as described above through XPS depth analysis, and the silicon carbon composite powder can be sampled and measured alone.

[0061] In the present application, the silicon carbon composite may have a time constant (T1) of 150 to 1000 when fitting the graph of etching time (x-axis) vs. C / Si ratio (y-axis) with an exponential decay function using XPS depth analysis.

[0062] In another embodiment, the silicon carbon composite may have a time constant (T1) derived by fitting the etching time (x-axis) vs. C / Si ratio (y-axis) graph to an exponential decay function using XPS depth analysis, which is 150 to 1000, specifically 170 to 950, and more specifically 175 to 900.

[0063] In the present application, a large time constant means that the time for the C / Si ratio to saturate is longer. A larger time constant implies that silicon within the silicon-carbon composite is better deposited on the interior side of the active material than on the surface, while a smaller time constant implies that silicon is deposited relatively on the surface rather than on the interior of the active material.

[0064] In this case, the present invention uses a silicon carbon composite that satisfies the time constant range. When included in the range, the silicon in the silicon carbon composite is deposited more evenly inside than on the surface, making it difficult to come into contact with water in an aqueous slurry, thus having the characteristic of excellent processability.

[0065] In particular, a large time constant indicates that the active material is well deposited inside, but if the time constant exceeds the above range, silicon penetrates and is deposited excessively deep into the interior of the porous carbon substrate, causing internal stress concentration due to the volume expansion of silicon during charging and discharging. This results in cracking of the electrode structure or disruption of the conductive network, leading to reduced efficiency of the electrochemical reaction and problems such as decreased long-term cycle life and capacity retention rate. Additionally, if silicon is excessively present inside, the contact area with the electrolyte is relatively reduced, which may limit the initial capacity development.

[0066] On the other hand, when the time constant is below the above range, silicon is deposited shallowly mainly on the particle surface, and since volume changes during charging and discharging act directly on the outer surface, delamination or cracking of the silicon film can easily occur. As a result, the bonding strength between silicon and carbon is reduced, the electrical contact resistance of the electrode increases, and undesirable results occur, such as a rapid decrease in capacity and a decline in initial efficiency during repeated charging and discharging processes.

[0067] In one embodiment of the present application, the time constant can be derived by inputting data into a graph with the C / Si elemental content ratio of the silicon-carbon composite as the x-axis and y-axis according to the etching time, and then fitting the input data according to the following equation. At this time, the following equation can be expressed as an exponential decay function, and t1 may represent the time constant.

[0068] [ceremony]

[0069]

[0070] In the present application, the time constant may be expressed as follows, specifically meaning the time taken to reach a final value, and e -1 The faster it reaches, the shorter the time constant may be.

[0071]

[0072] In the present application, the C / Si element content ratio can be calculated using the following formula.

[0073] [ceremony]

[0074]

[0075] In the above formula, i represents the type of element to be found, and j represents all types of elements measured via XPS. Also, C i represents the ratio of the elemental content, and A i represents the area modified by considering the inelastic mean free path within the solid, and RSF i represents the Relative Sensitive Factor. For example, if peaks of elements A and B are detected via XPS with peak areas of 1000 and 500, respectively, and RSFs of 0.8 and 1.2, respectively, then the content ratio of A is It can be calculated as follows.

[0076] In one embodiment of the present application, the above j may be silicon or carbon.

[0077] For reference, the relative sensitivity factors of Si and C used in XPS depth analysis are as follows.

[0078] RSF si =0.9

[0079] RSF c =1.0

[0080] In the present application, the Rsquare value may be 0.95 or higher when fitting with the exponential decay function.

[0081] The shape of the graph of etching time (x-axis) vs. C / Si ratio (y-axis) is similar to the exponential decay function, and if the R-square value does not satisfy the above range, the reliability of the time constant decreases, so the above value must be satisfied.

[0082] The present application provides a negative electrode active material comprising a carbon coating layer on the surface of the silicon carbon composite.

[0083] In the present application, the silicon may be 40 parts by weight or more and 60 parts by weight or less based on 100 parts by weight of the silicon carbon composite.

[0084] In another embodiment, based on 100 parts by weight of the silicon carbon composite, the silicon may be 40 parts by weight or more and 60 parts by weight or less, specifically 43 parts by weight or more and 55 parts by weight or less, and more specifically 45 parts by weight or more and 55 parts by weight or less.

[0085] As described above, by satisfying the silicon deposition amount on porous carbon to have the range described above, and simultaneously controlling the physical properties of the porous carbon described below, the aforementioned time constant is satisfied, thereby improving the capacitance characteristics and securing the lifespan characteristics.

[0086] In the present application, the negative electrode active material may further include a carbon-based active material.

[0087] In the present application, the carbon-based active material may include graphite, and the graphite may include natural graphite and artificial graphite.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] In the present application, a negative electrode active material is provided in which the silicon carbon composite comprises 80 parts by weight or less based on 100 parts by weight of the negative electrode active material.

[0095] In another embodiment, based on 100 parts by weight of the cathode active material, the silicon carbon composite may contain 80 parts by weight or less, specifically 75 parts by weight or less, more specifically 70 parts by weight or less, and may contain 1 part by weight or more, 5 parts by weight or more, more specifically 10 parts by weight or more.

[0096] 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.

[0097] Meanwhile, the average particle size (D50 particle size) of the silicon carbon composite of the present invention is 5 μm or more and 20 μm or less, specifically 5 μm to 18 μm, and more specifically 5 μm to 15 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.

[0098] 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).

[0099] 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.

[0100] 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.

[0101] In the present application, the circularity is determined by the following formula 1-B, where A is the area and P is the boundary line.

[0102] [Equation 1-B]

[0103] 4πA / P 2

[0104] In one embodiment of the present application, a cathode composition comprising the cathode active material is provided.

[0105] In the present application, the cathode composition may further include a cathode conductive material and a cathode binder as needed.

[0106] 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.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] 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.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] 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.

[0117] In one embodiment of the present application, the conductive material may include a planar conductive material.

[0118] 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.

[0119] 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.

[0120] 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.

[0121] In one embodiment of the present application, the planar conductive material may be a planar conductive material with a high specific surface area and a high BET specific surface area; or a planar conductive material with a low specific surface area.

[0122] 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.

[0123] 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.

[0124] 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.

[0125] 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.

[0126] 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.

[0127] 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.

[0128] 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.

[0129] 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.

[0130] 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.

[0131] 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.

[0132] 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.

[0133] 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.

[0134] 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.

[0135] 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.

[0136] 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.

[0137] 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.

[0138] 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.

[0139] 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.

[0140] 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 3 parts by weight or more.

[0141] One embodiment of the present application provides 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, in the step of forming the silicon-carbon composite by depositing silicon on porous carbon, the deposition temperature is 500°C or higher and 800°C or lower, the silicon flow rate is 50 ml / min to 250 ml / min, and the silicon-carbon composite has a time constant (T1) of 150 to 1000 when fitting the etching time (x-axis) vs C / Si ratio (y-axis) graph by XPS depth analysis to an exponential decay function.

[0142] In the case of the silicon carbon composite according to the present application, when depositing silicon on porous carbon, the time constant value can be controlled by adjusting the temperature range as described above and adjusting the deposition flow rate to the above range.

[0143] Specifically, the time constant tends to decrease when the deposition flow rate and deposition time increase, while it tends to increase as the deposition temperature increases. Additionally, the time constant tends to increase when the coating time and temperature increase, and it may also show an increasing trend when the activation temperature of porous carbon increases.

[0144] In the present application, in the step of forming a silicon carbon composite by depositing silicon on the porous carbon, the silicon may be SiH4 / N2 gas, and specifically, a mixed gas in a ratio of 90 / 10 to 98 / 2 may be used.

[0145] In the present application, after depositing silicon on the porous carbon, the method may further include the step of forming a carbon layer on the surface of the silicon-carbon composite on which the silicon is deposited.

[0146] At this time, the step of forming the carbon layer can be formed by coating with acetylene, and specifically, the coating temperature of acetylene can satisfy between 500°C and 700°C.

[0147] In the present application, the pore volume of the porous carbon in the silicon-carbon composite is 0.75 g / cm³ 3 Up to 1.2 g / cm² 3 It could be.

[0148] The present application provides a method for manufacturing a negative electrode active material, wherein the deposition pressure in the step of forming a silicon-carbon composite by depositing silicon on the porous carbon is 0.1 Torr or more and 15 Torr or less.

[0149] In the present application, the deposition pressure in the step of forming a silicon carbon composite by depositing silicon on the porous carbon may be 0.1 Torr or more and 15 Torr or less, specifically 0.5 Torr or more and 10 Torr or less.

[0150] In the present application, the average particle size (D50) of the porous carbon may be 8 μm or more and 20 μm or less, specifically 9 μm or more and 15 μm or less.

[0151] 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 80% 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 20% or less.

[0152] 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.

[0153] [Equation 1]

[0154] 4πA / P 2

[0155] In the above Equation 1, A is the area and P is the boundary line.

[0156] 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.

[0157] 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.

[0158] 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.

[0159] 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.

[0160] At this time, the cathode slurry may include the aforementioned cathode composition; and a slurry solvent.

[0161] In one embodiment of the present application, the solid content of the cathode slurry may satisfy 5% or more and 40% or less.

[0162] 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.

[0163] 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.

[0164] 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.

[0165] 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.

[0166] 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.

[0167] 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.

[0168] However, the thickness may vary depending on the type and application of the cathode used, and is not limited thereto.

[0169] 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.

[0170] 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 25% or more and 45% or less.

[0171] 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.

[0172] 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.

[0173] Additionally, it may further include a separator provided between the anode and the cathode; and may further include an electrolyte as needed.

[0174] 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.

[0175] 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.

[0176] 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.

[0177] 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.

[0178] 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.

[0179] 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.

[0180] 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.

[0181] 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.

[0182] 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.

[0183] 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.

[0184] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0185] 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.

[0186] 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.

[0187] 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.

[0188] 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.

[0189] 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.

[0190] 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.

[0191] <Preparation Example>

[0192] <Example 1>

[0193] - Manufacturing of silicon carbon composites

[0194] Porous carbon raw materials were carbonized by heat treatment at 900°C under an inert gas atmosphere. After grinding and classifying the carbonized raw materials, porous carbon was produced by physical activation using steam at 800°C. The produced porous carbon was ground and classified to obtain an average particle size D50 of 9 μm. The pore volume of the obtained porous carbon was 0.80 g / cm³. 3 Up to 0.9g / cm² 3 It was.

[0195] Afterwards, a silicon carbon composite was formed by flowing a mixed gas with a ratio of SiH4 / N2=95 / 5 at a flow rate of 75 ml / min for 2 hours under conditions of 3 torr pressure and 650℃ through the porous carbon formed by washing and drying the porous carbon.

[0196] Subsequently, the above silicon carbon composite was placed in an electric furnace and acetylene gas was flowed at 600°C to produce a silicon carbon composite containing a carbon layer on the outermost surface.

[0197] <Example 2>

[0198] - Manufacturing of silicon carbon composites

[0199] In the above Example 1, porous carbon was prepared by performing a physical activation reaction at 900°C, and the pore volume of the porous carbon was 0.90 g / cm³ 3 Up to 1.0 g / cm² 3 It was manufactured in the same manner as Example 1 above, except for the fact that...

[0200] <Example 3>

[0201] - Manufacturing of silicon carbon composites

[0202] The above-mentioned Example 1 was prepared in the same manner as the above, except that a mixed gas with a ratio of SiH4 / N2=95 / 5 was flowed through porous carbon at a flow rate of 75 ml / min for 2 hours under conditions of 1 torr pressure and 650°C.

[0203] <Example 4>

[0204] - Manufacturing of silicon carbon composites

[0205] A mixture of gas with a ratio of SiH4 / N2=98 / 2 was flowed through porous carbon at a flow rate of 50 ml / min for 2 hours under conditions of 700°C, and then acetylene gas was flowed at 650°C; otherwise, it was prepared in the same manner as Example 1 above.

[0206] <Comparative Example 1>

[0207] - Manufacturing of silicon carbon composites

[0208] The above-mentioned Example 1 was prepared in the same manner as the above, except that a mixed gas with a ratio of SiH4 / N2=95 / 5 was flowed through porous carbon at a flow rate of 300 ml / min for 2 hours under conditions of 3 torr pressure and 650℃.

[0209] <Comparative Example 2>

[0210] - Manufacturing of silicon carbon composites

[0211] Porous carbon was prepared by a physical activation reaction at 600℃, and the pore volume of the porous carbon was 0.65 g / cm³ 3 Up to 0.75 g / cm² 3 It was manufactured in the same manner as Example 1 above, except for the fact that...

[0212] <Comparative Example 3>

[0213] - Manufacturing of silicon carbon composites

[0214] The above-mentioned Example 1 was prepared in the same manner as the above, except that a mixed gas with a ratio of SiH4 / N2=95 / 5 was flowed through porous carbon at a flow rate of 75 ml / min under conditions of 100 torr pressure and 650°C for 2 hours.

[0215] <Comparative Example 4>

[0216] - Manufacturing of silicon carbon composites

[0217] The above silicon carbon composite was prepared in the same manner as Example 1, except that it was placed in an electric furnace and acetylene gas was flowed at 450°C.

[0218] <Comparative Example 5>

[0219] - Manufacturing of silicon carbon composites

[0220] The above-mentioned Example 1 was prepared in the same manner as the above, except that a mixed gas with a ratio of SiH4 / N2=95 / 5 was flowed through porous carbon at a flow rate of 75 ml / min for 2 hours under conditions of 3 torr pressure and 950°C.

[0221] <Comparative Example 6>

[0222] - Manufacturing of silicon carbon composites

[0223] The porous carbon was ground without classification, and the D50 was prepared in the same manner as Example 1 above, except that the D50 was made to 7 μm.

[0224] <Comparative Example 7>

[0225] - Manufacturing of silicon carbon composites

[0226] It was prepared in the same manner as Example 1, except that a mixed gas with a ratio of SiH4 / N2=95 / 5 was deposited on porous carbon at a flow rate of 250 ml / min at 400°C, and then coated with acetylene gas at 800°C.

[0227] <Reference Example 1>

[0228] - Manufacturing of silicon carbon composites

[0229] It was manufactured in the same manner as Example 1 above, except that the average particle size D50 of the porous carbon was 5 μm.

[0230] XPS Depth analysis was performed on the silicon carbon composite powders for the above examples and comparative examples, specifically under the analysis conditions as follows, and the results are listed in Table 1.

[0231] <Analysis Conditions>

[0232] - X-Ray source: Monochromated Al K α (1486.6 eV)

[0233] - X-ray spot size: 400μm

[0234] - Sputtering gun: Monatomic Ar (energy: 1000 eV, current: low, raster width: 2mm)

[0235] - Etching rate: 0.09 nm / s for Ta 205

[0236] - Operation Mode: CAE (Constant Analyzer Energy) mode

[0237] - Survey scan: pass energy 200 eV, energy step 1 eV

[0238] - Narrow scan: scanned mode, pass energy 50 eV, energy stem 0.1 Ev

[0239] - Charge compensation: 0.1 V 150Μa

[0240] - SF: Al THERMO1

[0241] - ECF: TPP2M

[0242] - BG subtraction: Smart

[0243] Time constant (T1) R square Example 1 268 0.9758 Example 2 220 0.9940 Example 3 455 0.9965 Example 4 86 10.9582 Comparative Example 1 114 0.9632 Comparative Example 2 131 0.9975 Comparative Example 3 120 1.0000 Comparative Example 4 133 0.9764 Comparative Example 5 65 0.9985 Comparative Example 6 148 0.9638 Comparative Example 7 1157 0.9687 Reference Example 1 228 0.9638

[0244] For reference, FIG. 4 is an SEM image of a negative electrode active material layer containing a silicon carbon composite according to Example 1, and FIG. 5 is an SEM image of a negative electrode active material layer containing a silicon carbon composite according to Comparative Example 1. Specifically, FIG. 4 and FIG. 5 are SEM images of a negative electrode containing only a silicon carbon composite, a conductive material (carbon black, single-walled carbon nanotube), and a binder (CMC, SBR).

[0245] In Figure 4, it was confirmed that the silicon deposition uniformity was superior compared to the case of Figure 5, as the time constant satisfied the range of the present application.

[0246] Specifically, in the case of high uniformity (Fig. 4), the difference in brightness between silicon-carbon composite particles is small (i.e., the more silicon is deposited, the brighter it appears), indicating that the silicon deposition is uniform. In addition, silicon is formed with a relatively uniform thickness throughout the porous carbon particles and is evenly distributed both inside the pores and on the particle surfaces. Accordingly, it can be seen that the boundaries between the silicon layers are smooth, and the overall electrode structure is maintained in a dense yet uniform manner.

[0247] On the other hand, in the case of low uniformity (Fig. 5), it was observed that silicon was deposited unevenly, as there was a significant difference in brightness between the silicon-carbon composite particles (i.e., the less silicon is deposited, the darker it appears). Additionally, it was observed that silicon grew with an uneven thickness, concentrated in specific areas, particularly near the particle surface or pore entrance, and in some areas, almost no silicon was deposited.

[0248] At this time, the derivation of the time constants in the above examples, comparative examples, and reference examples was carried out as follows.

[0249] 1) Silicon carbon composite powder is sampled to determine the elemental content (atm%) in the chemical state (C, Si) of the active material for each etching time (0s, 10s, 30s, 50s, 100s, 200s, 300s, 500s, 1000s, 1500s, 2000s, 3000s, 4000s, 5000s, 7000s).

[0250] 2) The ratio of the derived C and Si element content is represented as the C / Si ratio, with this on the y-axis and the etching time on the x-axis, and the data is input into a graph.

[0251] 3) Based on the input data, derive the time constant by fitting it to the equation below.

[0252]

[0253] FIG. 3 is a graph showing the process of deriving the time constant for Example 2 according to the present application. Specifically, the graph fitted with the exponential decay function based on the raw data (black line) can be represented by the red line.

[0254] <Manufacturing of the Cathode>

[0255] As the negative electrode active material, the silicon carbon composite, natural graphite, and artificial graphite of Table 1 were used in a weight ratio of 10:15:75, and distilled water was used as the solvent.

[0256] Specifically, the cathode composition was prepared by mixing a cathode active material, a conductive material (carbon black, single-walled carbon nanotube (SWCNT)), and a binder (CMC (Carboxymethyl cellulose), SBR (Styrene-Butadiene Rubber)) in a weight ratio of 95.3:1:3.7 to prepare a cathode slurry.

[0257] The above cathode slurry was applied to a Cu metal thin film with a thickness of approximately 15 μm and dried at a circulating air temperature of 60°C. Subsequently, after rolling, it was dried in a vacuum oven at 130°C for about a day, and then 1.7671 cm 2 A cathode was manufactured by stamping into a circular shape (rolled density 1.5 g / cc, porosity 28%).

[0258] Manufacturing of secondary batteries

[0259] An anode slurry was prepared by adding LiNi0.6Co0.2Mn0.2O2 (average particle size (D50): 15㎛) as the anode active material, carbon black (product name: Super C65, manufacturer: Timcal) as the conductive material, and polyvinylidene fluoride (PVdF) as the binder to N-methyl-2-pyrrolidone (NMP) as a solvent for forming the anode slurry in a weight ratio of 97:1.5:1.5.

[0260] An anode was manufactured by coating the above anode slurry onto an aluminum current collector (thickness: 12㎛) as an anode current collector, rolling it, drying it in a vacuum oven at 130℃ for 8 hours, and then stamping it into a circular shape of 1.4875cm2.

[0261] A lithium secondary battery was manufactured by interposing a polyethylene separator between the anode and the cathode of the above example and comparative example and injecting an electrolyte.

[0262] The above electrolyte is an electrolyte in which 1M concentration of LiPF6 is dissolved, containing an additive of a mixed solution of EC (ethylene carbonate) and EMC (methyl ethyl carbonate) with a mixing ratio of 3:7.

[0263] <Experimental Example>

[0264] Experimental Example 1: Evaluation of Coin Half Cell Capacity / Efficiency

[0265] The capacity / efficiency of the first cycle of the secondary battery containing the negative electrode prepared in the above examples and comparative examples was measured using an electrochemical charge / discharger. The test was conducted using lithium metal as the counter electrode of the negative electrode. Lithiocation was tested under CC / CV (5mV / 0.005C current cut-off), and delithiation was tested under CC conditions with a 1.5V cut-off condition.

[0266] Discharge capacity (mAh / g) = 1st cycle delithiation capacity (mAh) / weight of negative electrode active material (g)

[0267] Initial efficiency (%) = {(1st cycle delithiation capacity) / (1st cycle lithiation capacity)} × 100

[0268] Experimental Example 2: Cell Lifetime Performance Results

[0269] For the secondary batteries containing the negative electrodes prepared in the above examples and comparative examples, a lifespan evaluation was conducted using an electrochemical charge / discharger and the capacity retention rate was evaluated. The secondary batteries were subjected to in-situ cycle tests up to 300 cycles at 4.2-2.5V 1C / 1C.

[0270] Life retention rate (%) = {(Discharge capacity at the 300th cycle) / (Discharge capacity at the 1st cycle)} × 100

[0271] Experimental Example 3: Rate of change in slurry viscosity

[0272] To measure the rate of change in slurry viscosity, a slurry was prepared by mixing graphite: the above-mentioned cathode active material: carbon black: CMC: PAA in a weight ratio of 77: 20: 1: 1: 1. The shear viscosity of the prepared slurry was measured at a shear rate of 1 Hz, and the amount of change over time was measured and compared.

[0273] The percentage change in shear viscosity was derived by the following formula.

[0274] Rate of change in shear viscosity (%) = ((shear viscosity of slurry after 2 days - viscosity of slurry immediately after mixing) / viscosity of slurry immediately after mixing) × 100

[0275] Experimental Example 4: Pouch Volume Change Rate

[0276] To measure the rate of change in slurry viscosity, a slurry was prepared by mixing graphite: the above-mentioned cathode active material: carbon black: CMC: PAA in a weight ratio of 77: 20: 1: 1: 1. 20g of the prepared slurry was placed in a pouch, sealed, and then 40 o After storing in C for 2 days, the volume was measured and the rate of change was compared.

[0277] The evaluation results for the above Experimental Examples 1 to 4 are shown in Table 2 below.

[0278] Discharge Capacity (mAh / g) Initial Efficiency (%) Capacity Retention Rate (%) Slurry Viscosity Change Rate (%, after 2 days) Pouch Volume Change Rate (%, @40℃, after 2 days) Example 1 50 891.19 2.1-1.6 0.5 Example 2 50 591.39 1.9-4.2 3.8 Example 3 50 290.59 1.1-0.5 0.2 Example 4 50 090.19 0.30.1 0.0 Comparative Example 1 49 990.08 5.4-38.0 28.9 Comparative Example 2 49 590.28 0.7-56.5 35.1 Comparative Example 3 47 588.17 3.1-19.5 12.6 Comparative Example 4 49 589.68 4.4-47.6 32.6 Comparative Example 548089.078.9-40.129.4 Comparative Example 649089.382.8-22.815.5 Comparative Example 747287.579.90.30.0 Reference Example 149289.672.7-42.130.2

[0279] In the case of the silicon carbon composite of the embodiment according to the present application, a silicon carbon composite satisfying a specific time constant range is used. When included in the range, silicon within the silicon carbon composite is evenly deposited inside rather than on the surface, making it difficult to come into contact with water in an aqueous slurry, resulting in excellent processability and a low rate of change in the viscosity of the slurry.

[0280] That is, through Table 2 above, it was confirmed that the negative electrode containing the silicon carbon composite according to the present application, having the above-mentioned characteristics, can secure capacitance characteristics, improve resistance by reducing side reactions on the surface of the negative electrode active material, and improve the lifespan problem due to volume expansion.

[0281] For reference, Comparative Example 1 had a high flow rate, so silicon was not deposited uniformly inside, and consequently, the time constant range was measured differently, resulting in poor battery performance and aqueous slurry processability results due to deposition on the surface. Comparative Example 2 had a small volume of pores in the porous carbon raw material, so silicon was filled into all internal pores before being deposited on the surface; consequently, the time constant range differed from that of the present application, resulting in inferior battery performance and aqueous slurry processability.

[0282] Comparative Examples 3 and 5 each showed inferior results in battery performance and water-based slurry processability because silicon was not uniformly deposited inside the porous carbon pores during the process of depositing silicon at low pressure and high temperature, respectively, and the time constant range was measured differently from the range of the present application.

[0283] Comparative Example 6 underwent the same deposition and coating processes as the example, but because the particle size was small, the silicon remaining after filling the internal pores was deposited on the surface, and the time constant range was measured differently, resulting in poor evaluation results for battery performance and water-based slurry processability.

[0284] Comparative Example 7 was a case where the thermal decomposition and surface diffusion of the vapor phase precursor did not occur sufficiently during the process of depositing silicon at a low temperature, resulting in reduced coating uniformity. At low temperatures, the decomposition rate of the precursor and the surface diffusion coefficient decreased rapidly, so the active species could not reach deep into the pores and silicon grew selectively, confined to the outer surface or near the pore entrance. Consequently, a variation in the thickness of the silicon coating layer occurred, and as a result, a phenomenon was observed where the distribution of silicon inside and outside the porous structure became non-uniform.

Claims

1. A negative electrode active material comprising a silicon carbon composite comprising porous carbon; and silicon deposited on the porous carbon, The above silicon-carbon composite is a negative electrode active material having a time constant (T1) of 150 to 1000 when fitting the graph of etching time (x-axis) vs. C / Si ratio (y-axis) using an exponential decay function via XPS depth analysis.

2. In Claim 1, A negative electrode active material comprising a carbon coating layer further comprising the surface of the above silicon carbon composite.

3. In Claim 1, A negative electrode active material in which the silicon is 40 parts by weight or more and 60 parts by weight or less, based on 100 parts by weight of the silicon carbon composite.

4. In Claim 1, The above silicon carbon composite is a negative electrode active material having an average particle size (D50) of 5 μm or more and 20 μm or less.

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 80 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 In the step of forming a silicon-carbon composite by depositing silicon on the porous carbon, the deposition temperature is 500°C or higher and 800°C or lower, and the silicon flow rate is 50 ml / min to 250 ml / min. A method for manufacturing a negative electrode active material in which the above silicon carbon composite has a time constant (T1) of 150 to 1000 when fitting the graph of etching time (x-axis) vs. C / Si ratio (y-axis) by XPS depth analysis with an exponential decay function.

8. In Claim 7, The above porous carbon has a ratio of 80% or more of first pores having a diameter of less than 2 nm when measured by the nitrogen adsorption method, and A method for manufacturing a negative electrode active material in which the above-mentioned porous carbon has a ratio of 20% or less of a second pore having a diameter of 2 nm or more and 50 nm or less when measured by nitrogen adsorption method.

9. In Claim 7, A method for manufacturing a negative electrode active material, wherein the deposition pressure in the step of forming a silicon-carbon composite by depositing silicon on the porous carbon is 0.1 Torr or more and 15 Torr or less.

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

11. In Claim 10, 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.

12. 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, The negative electrode for a lithium secondary battery, wherein the negative electrode active material layer comprises a negative electrode composition according to claim 10 or a cured product thereof.

13. In Claim 12, 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.

14. Anode; and Negative electrode for a lithium secondary battery according to claim 12; A lithium secondary battery including

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