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

Abstract

A negative electrode active material for a lithium secondary battery, according an embodiment of the present invention, comprises a silicon carbon (Si / C) composite having a modulus value (A) of 15-25 GPa and a hardness value (B) of 2500-5000 MPa.

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 is based on Korean Patent Application No. 10-2024-0144998, the contents of which are incorporated in whole into this application by reference herein, and claims priority thereof.

[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] Meanwhile, as technological development and demand for mobile devices increase, 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] In this application, a silicon carbon composite was manufactured by controlling the physical properties and composition of porous carbon and changing the deposition conditions during the process of depositing SiH4 on porous carbon in the manufacturing process of the silicon carbon composite, thereby improving the internal pore density of the silicon and controlling the resistance value to plastic deformation. Accordingly, the silicon carbon composite manufactured has improved characteristics, such as low plastic deformation even under external pressure.

[0007] Accordingly, the present application relates to a negative electrode active material according to the above-described technology, 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.

[0008] One embodiment of the present specification provides a negative electrode active material for a lithium secondary battery comprising a silicon carbon composite having a modulus value (A) of 15 GPa to 25 GPa and a hardness value (B) of 2500 MPa to 5000 MPa.

[0009] In another embodiment, a method for manufacturing a negative electrode active material for a lithium secondary battery is provided, comprising: a step of preparing porous carbon; and a step of depositing silicon on the porous carbon to form a silicon carbon composite; wherein, in the step of depositing silicon on the porous carbon to form a silicon carbon composite, 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, the modulus value (A) of the silicon carbon composite is 15 GPa to 25 GPa, and the hardness value (B) of the silicon carbon composite is 2500 MPa to 5000 MPa.

[0010] In another embodiment, the present application aims to provide a negative electrode composition for a lithium secondary battery comprising a negative electrode active material; a negative electrode conductive material; and a negative electrode binder.

[0011] 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.

[0012] In another embodiment, a lithium secondary battery is provided comprising: a positive electrode; a negative electrode for a lithium secondary battery according to the present application; a separator provided between the positive electrode and the negative electrode; and an electrolyte.

[0013] A negative electrode active material for a lithium secondary battery according to one embodiment of the present invention comprises a silicon-carbon composite comprising silicon deposited on porous carbon. In the case of the silicon-carbon composite according to one embodiment of the present invention, silicon is densely deposited on porous carbon during the silicon deposition process and has a uniform surface.

[0014] When manufacturing a negative electrode for a lithium secondary battery, a negative electrode slurry is applied to the top of the negative electrode current collector layer and rolled. During this process, the negative electrode active material in the form of a composite may be broken due to the rolling pressure, and a problem may occur where silicon is exposed on the surface.

[0015] In the case of the silicon carbon composite according to the present application, by controlling the physical properties of the porous carbon precursor and controlling the amount of silicon deposited when manufacturing the silicon carbon composite, a more uniform and dense deposition is achieved, and the silicon carbon composite manufactured thereby has improved particle strength, thereby improving the capacity characteristics of the battery and simultaneously enhancing the lifespan characteristics.

[0016] The negative electrode for a lithium secondary battery comprising a silicon carbon composite according to the present application can secure capacity characteristics, improve resistance by minimizing side reactions on the surface of the active material, and also improve lifespan issues caused by volume expansion.

[0017] The following drawings attached to this specification illustrate preferred embodiments of the present invention and serve to further enhance understanding of the technical concept of the present invention together with the detailed description of the invention provided below; therefore, the present invention should not be interpreted as being limited only to the matters described in such drawings.

[0018] FIG. 1 is a flowchart illustrating the manufacturing process of a silicon carbon composite according to one embodiment of the present application.

[0019] Figure 2 is a diagram showing a method for measuring physical properties according to the present application using a nano indenter (Top).

[0020] FIG. 3 is a diagram showing a stacked structure of a negative electrode for a lithium secondary battery according to one embodiment of the present application.

[0021] FIG. 4 is a diagram showing a stacked structure of a lithium secondary battery according to one embodiment of the present application.

[0022] In parts of the attached drawings, corresponding components are given the same reference numerals. Those skilled in the art understand that the drawings are intended to illustrate elements simply and clearly and are not necessarily drawn to scale. For example, to aid in understanding various embodiments, the dimensions of some elements depicted in the drawings may be exaggerated compared to others. Additionally, elements of known technology that are useful or essential in commercially viable embodiments may often be omitted so as not to hinder the spirit of the various embodiments of the present invention.

[0023] Before describing the present invention, we will first define some terms.

[0024] 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.

[0025] In this specification, 'p to q' means a range of 'p or more and q or less'.

[0026] 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.

[0027] 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.

[0028] 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.

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

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

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

[0032] As used herein, “about,” “approximately,” and “substantially” are used to mean a range of values ​​or degrees or approximations thereof, taking into account inherent manufacturing and material tolerances (e.g., ±5%).

[0033] 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.

[0034] Recently, due to the 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.

[0035] 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.

[0036] 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 in a composite state, 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.

[0037] Considering these points, the present invention provides a technology that can prevent the conduction path from being damaged due to volume expansion of the silicon carbon composite, even when the silicon carbon composite is used as a negative electrode active material.

[0038] 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.

[0039] FIG. 1 is a flowchart illustrating a process for manufacturing a silicon carbon composite according to one embodiment of the present specification.

[0040] Referring to FIG. 1, a process for manufacturing a silicon carbon (Si / C) composite according to one embodiment of the present invention comprises a carbonization process (S10) in which a resin-based raw material is heat-treated under appropriate conditions to carbonize it, a process (S20) in which the powder that has undergone the carbonization process is crushed and classified, a process (S30) in which pores are formed and expanded through the oxidation of the crushed and classified carbon, and a process (S40) in which silicon is deposited on the porous carbon in which the pores are formed.

[0041] Meanwhile, a negative electrode active material for a secondary battery is manufactured using a silicon carbon composite produced through the above-described process, and a negative electrode is manufactured by forming a negative electrode active material layer on a negative electrode current collector using the above-described negative electrode active material.

[0042] Meanwhile, the physical properties of the silicon-carbon composite manufactured through the above process are evaluated by measuring the material's modulus and hardness values. Modulus is a value representing the material's stiffness, signifying the degree of the material's resistance to deformation under external forces, while hardness is a property indicating how well the material's surface resists external scratches or indentations. For example, modulus represents the material's overall resistance to deformation, while hardness represents the material's resistance to scratches or dents on its surface.

[0043] Referring to FIG. 2, according to one embodiment of the present specification, the modulus value and hardness value can be measured by manufacturing an epoxy mold (7) containing a silicon carbon composite and using a nano indenter (3). The nano indenter (3) is a device that measures mechanical properties such as hardness, elastic modulus, and viscoelasticity of a material by applying a fine force to the material using a nanometer-scale micro indenter (tip) (5) and measuring the load and depth change that occur at that time. The manufacturing of the epoxy mold (7) is described in more detail below.

[0044] One embodiment of the present specification provides a negative electrode active material comprising a silicon carbon composite having a modulus value (A) of about 15 GPa to 25 GPa and a hardness value (B) of about 2500 MPa to 5000 MPa.

[0045] The present invention, by including a silicon-carbon composite as a negative electrode active material, can improve capacity characteristics compared to using only conventional carbon-based active materials, achieve high energy density, and also improve rapid charging performance.

[0046] In this specification, the silicon carbon composite is a composite of Si and C and is distinguished from silicon carbide denoted as SiC.

[0047] In the present application, silicon carbon composites may be used without limitation as silicon carbon composites manufactured through general manufacturing processes used in the art, and may include, for example, silicon carbon composites of deposition or grinding types.

[0048] In the present application, the silicon-based active material may be a silicon-carbon composite comprising porous carbon; and silicon deposited on the porous carbon.

[0049] 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 with a size in the range of about 1 nm to 999 nm.

[0050] In this application, the modulus can be measured by preparing a molded specimen using epoxy to increase the analytical accuracy of the silicon-carbon composite in powder form.

[0051] For example, an epoxy resin and an epoxy curing agent are mixed in a 1:1 ratio, placed into a mold to form a first layer, and cured for 24 hours. Afterward, an epoxy resin and an epoxy curing agent are mixed in a 1:1 ratio, 1g of a silicon carbon composite is added and mixed uniformly, and then poured onto the first layer and cured to produce an epoxy mold sample. Then, 1g of the silicon carbon composite to be measured is sampled onto a polished mold, and the measurement can be performed using a nano-indenter in the depth direction from the cross-section.

[0052] In the present application, the hardness value can be expressed as indentation hardness, and, similar to the modulus, an epoxy mold sample is prepared and 1g of the silicon-carbon composite to be measured is sampled and measured using a nano-indenter in the depth direction from the cross-section, and the indentation hardness can be measured by the following formula 1-A.

[0053] [Equation 1-A]

[0054] Hardness = Pmax / A

[0055] In the above Equation 1-A,

[0056] Pmax means maximum load, and

[0057] A represents the projected contact area.

[0058] In this case, when particles are indented by a nano-indenter, perfect contact with the surface of the material is not achieved, and since certain parts do not make contact, a difference occurs between the actual rolling depth and the actual contact depth, and the hardness value can be derived by correcting for this.

[0059] In one embodiment of the present application, the modulus value (A) of the silicon carbon composite may be about 15 GPa to 25 GPa.

[0060] In another embodiment, the modulus value (A) of the silicon carbon composite may be about 15 GPa to 25 GPa, for example, about 16 GPa to 24 GPa, or about 17 GPa to 23 GPa.

[0061] In the present application, the hardness value (B) of the silicon carbon composite may be about 2500 MPa to 5000 MPa, for example, about 3000 MPa to 4900 MPa, or about 3500 MPa to 4700 MPa.

[0062] In the present application, the modulus value (A) and hardness value (B) may satisfy the following Equation 1.

[0063] [Equation 1]

[0064] 0.1 ≤ B 3 / A 2

[0065] In the present application, the above Formula 1 is 0.1 ≤ B 3 / A 2 , for example, 0.15 ≤ B 3 / A 2 , or 0.16 ≤ B 3 / A 2 It could be, B 3 / A 2 ≤ 0.45, or B 3 / A 2 ≤ 0.44, or B 3 / A 2 It can be ≤ 0.43.

[0066] In the present application, the above-mentioned Formula 1 is an indicator representing the magnitude of resistance to particle breakage (plastic deformation) of a silicon-carbon composite, and corresponds to an indicator used in interpreting analysis results in nanoindenti analysis.

[0067] The above range is B of the epoxy itself. 3 / A 2 The value is approximately 0.00046, and B of porous carbon, which is a raw material for silicon carbon composites. 3 / A 2The silicon carbon composite, in which silicon is deposited on porous carbon, has a value greater than that of the value of approximately 0.01 to 0.03 and satisfies the range of Equation 1 above, so that the change in the calcination of the cathode active material is small during the rolling process of the slurry, thereby having the characteristic of being able to control problems caused by reduced lifespan and silicon exposure.

[0068] In the case of the silicon carbon composite according to the present application, the modulus and hardness values ​​satisfy the aforementioned ranges and simultaneously have the range of Equation 1. Accordingly, the strength of the silicon carbon composite is suitable, so particle breakage can be prevented during rolling. Furthermore, although a problem may arise in securing a conductive path if the strength is too high, the problem of the conductive path can also be improved by satisfying the scope of the present invention.

[0069] 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, for example, about 43 parts by weight or more and 60 parts by weight or less, or about 45 parts by weight or more and 55 parts by weight or less.

[0070] 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 modulus and hardness values ​​are satisfied, thereby improving capacitance characteristics and securing lifespan characteristics.

[0071] In the present application, the silicon carbon composite may further comprise a carbon coating layer. The composition and manufacturing method of the carbon coating layer may use compositions and manufacturing methods known in the art.

[0072] In the present application, the negative electrode active material may further include a carbon-based active material.

[0073] In the present application, the carbon-based active material may include graphite, and the graphite may include natural graphite and artificial graphite.

[0074] In the present application, the average particle size (D50) of the natural graphite is about 5㎛ or more and 20㎛ or less, and the average particle size (D50) of the artificial graphite may be about 5㎛ or more and 20㎛ or less.

[0075] In another embodiment, the average particle size (D50) of the natural graphite may be about 5㎛ or more and 20㎛ or less, for example, about 7㎛ or more and 18㎛ or less, or about 9㎛ or more and 15㎛ or less.

[0076] In another embodiment, the average particle size (D50) of the artificial graphite may be about 5㎛ or more and 20㎛ or less, for example, about 8㎛ or more and 18㎛ or less, or about 10㎛ or more and 16㎛ or less.

[0077] 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 about 60:40 to 80:20.

[0078] 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 about 60:40 to 80:20, for example, 65:35 to 78:22, or about 70:30 to 75:25.

[0079] 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 requires the calcination and graphitization of coke, resulting in relatively high processing costs. Consequently, satisfying the aforementioned range offers the advantage of improved cell characteristics along with cost savings.

[0080] In the present application, a negative electrode active material is provided in which the silicon carbon composite comprises about 80 parts by weight or less based on 100 parts by weight of the negative electrode active material.

[0081] In another embodiment, based on 100 parts by weight of the cathode active material, the silicon carbon composite may contain about 80 parts by weight or less, for example, about 75 parts by weight or less, or about 70 parts by weight or less, and may contain about 1 part by weight or more, 5 parts by weight or more, or about 10 parts by weight or more.

[0082] 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.

[0083] Meanwhile, the average particle size (D50 particle size) of the silicon carbon composite of the present invention is approximately 1 μm or more and 10 μm or less, and may be, for example, approximately 2 μm to 8 μm, or approximately 3 μm to 8 μm. When the average particle size falls within the above range, the specific surface area of ​​the particles is within a suitable range, and the viscosity of the cathode slurry is formed within an appropriate range. Accordingly, the dispersion of the particles constituting the cathode slurry becomes smooth. In addition, since the size of the silicon carbon composite has a value greater than or equal to the lower limit range, the contact area between the silicon 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.

[0084] 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 about 0.01 m² according to one embodiment. 2 / g to 150 m 2 / g, or about 0.1 m 2 / g to 100m 2 / g, or about 0.2 m 2 / g to 80 m 2 / g, or about 0.2 m 2 / g to 18 m 2 / g. The BET surface area is measured according to DIN 66131 (using nitrogen).

[0085] 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 may be, for example, spherical or fragmentary particles. Alternatively, the silicon may also have a fibrous structure or exist in the form of a silicon-containing film or coating.

[0086] In one embodiment of the present application, the silicon carbon composite may have a non-spherical shape, and the sphericity is, for example, about 0.9 or less, for example, about 0.7 to 0.9, or about 0.8 to 0.9, or about 0.85 to 0.9.

[0087] 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.

[0088] [Equation 1-B]

[0089] 4πA / P 2

[0090] In one embodiment of the present application, a negative electrode composition for a lithium secondary battery is provided, comprising: a negative electrode active material for a lithium secondary battery; a negative electrode conductive material; and a negative electrode binder.

[0091] In one embodiment of the present application, the cathode active material provides a cathode composition having at least about 40 parts by weight based on 100 parts by weight of the cathode composition.

[0092] In another embodiment, the cathode active material may comprise about 40 parts by weight or more, for example, about 60 parts by weight or more, or about 65 parts by weight or more, or about 70 parts by weight or more, based on 100 parts by weight of the cathode composition, or about 99 parts by weight or less, for example, about 98 parts by weight or less, or about 96 parts by weight or less.

[0093] 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.

[0094] 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.

[0095] Accordingly, in one embodiment of the present application, the cathode conductive material may include one or more selected from point conductive materials, planar conductive materials, and linear conductive materials.

[0096] In one embodiment of the present application, the point-shaped conductive material may be used to improve conductivity of the cathode and refers to a point-shaped or spherical conductive material having conductivity without causing chemical changes. For example, the point-shaped conductive material may be at least one selected from 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 may include carbon black in terms of achieving high conductivity and excellent dispersibility.

[0097] In one embodiment of the present application, the point-shaped conductive material has a BET specific surface area of ​​approximately 40 m² 2 / g or more 70m2 It may be less than / g, for example, about 45m 2 / g or more 65m 2 / g or less, or about 50m 2 / g or more 60m 2 It may be less than / g.

[0098] In one embodiment of the present application, the point-shaped conductive material may satisfy a volatile matter content of about 0.01% or more and 1% or less, for example, about 0.01% or more and 0.3% or less, or about 0.01% or more and 0.1% or less.

[0099] 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 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.

[0100] 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.

[0101] In one embodiment of the present application, the particle size of the dot-shaped conductive material may be about 10 nm to 100 nm, for example, about 20 nm to 90 nm, or about 20 nm to 60 nm.

[0102] In one embodiment of the present application, the conductive material may include a planar conductive material.

[0103] 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.

[0104] In one embodiment of the present application, the planar conductive material may comprise at least one selected from plate-shaped graphite, graphene, graphene oxide, and graphite flakes, and may be plate-shaped graphite according to one embodiment.

[0105] In one embodiment of the present application, the average particle size (D50) of the planar conductive material may be about 2 μm to 7 μm, for example, about 3 μm to 6 μm, or about 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.

[0106] 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.

[0107] 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, a planar conductive material with a low specific surface area that does not cause a problem with dispersion may be used.

[0108] In one embodiment of the present application, the planar conductive material has a BET specific surface area of ​​about 1 m² 2 It can be more than / g.

[0109] In another embodiment, the planar conductive material has a BET specific surface area of ​​approximately 1 m²2 / g or more than 500m 2 It may be less than / g, for example, about 5m 2 / g or more than 300m 2 / g or less, or about 5m 2 / g or more 250m 2 It may be less than / g.

[0110] 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.

[0111] In another embodiment, the planar conductive material is a high specific surface area planar conductive material, with a BET specific surface area of ​​approximately 50 m² 2 / g or more than 500m 2 / g or less, for example, about 80m 2 / g or more than 300m 2 / g or less, or about 100m 2 / g or more than 300m 2 It can satisfy a range of / g or less.

[0112] In another embodiment, the planar conductive material is a low specific surface area planar conductive material, with a BET specific surface area of ​​approximately 1 m² 2 / g or more 40m 2 / g or less, e.g., about 5m 2 / g or more 30m 2 / g or less, or about 5m 2 / g or more 25m 2 It can satisfy a range of / g or less.

[0113] 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. Here, "bundle type" 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.

[0114] In the present application, a cathode composition is provided in which the cathode conductive material is about 20 parts by weight or less based on 100 parts by weight of the cathode composition.

[0115] In another embodiment, the cathode conductive material may be about 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 about 0.01 parts by weight or more, or 0.02 parts by weight or more.

[0116] The cathode conductive material according to the present application has a composition distinct from the anode conductive material applied to the anode. For example, 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. The anode conductive material, on the other hand, acts as a buffer during rolling and provides partial conductivity; thus, their composition and roles differ from those of the cathode conductive material of the present invention.

[0117] Furthermore, the cathode conductive material according to the present application is applied to silicon-based active materials and has a different composition from that of a conductive material applied to a graphite-based active material. For example, a conductive material used in an electrode having a graphite-based active material simply has particles smaller than those of the active material, thereby providing improved output characteristics and some conductivity; thus, its composition and role differ from that of a cathode conductive material applied together with a silicon-based active material as in the present invention.

[0118] In one embodiment of the present application, the planar conductive material used as the aforementioned negative electrode conductive material has a structure and function different from that of a carbon-based active material generally used as a negative electrode active material. For example, 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.

[0119] Meanwhile, planar conductive materials used as cathode conductive materials are materials having a planar or plate-like form, which can be described as plate-like graphite. For example, it refers to a material included to maintain conductive pathways within the cathode active material layer; rather than serving the role of lithium storage and release, it signifies a material intended to secure conductive pathways in a planar form within the cathode active material layer.

[0120] 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.

[0121] Furthermore, in this 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.

[0122] In one embodiment of the present application, the carbon-based active material, artificial graphite or natural graphite, is in a point-like form and has a BET specific surface area of ​​about 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 ​​approximately 5 m². 2 It can be more than / g.

[0123] In one embodiment of the present application, the cathode binder may comprise at least one selected from polyvinylidenefluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidenefluoride, 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.

[0124] 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 may be applied, for example, a water-based binder or a PAM-based binder may be used.

[0125] In one embodiment of the present application, the cathode binder may be about 30 parts by weight or less, for example, about 25 parts by weight or less, or 20 parts by weight or less, based on 100 parts by weight of the cathode composition, and may be 5 parts by weight or more, or 10 parts by weight or more.

[0126] One embodiment of the present application provides a method for manufacturing a negative electrode active material comprising: a step of preparing porous carbon; and a step of depositing silicon on the porous carbon to form a silicon-carbon composite; wherein, in the step of depositing silicon on the porous carbon to form a silicon-carbon composite, the silicon is about 40 parts by weight or more and 60 parts by weight or less based on 100 parts by weight of the silicon-carbon composite, the modulus value (A) of the silicon-carbon composite is about 15 GPa to 25 GPa, and the hardness value (B) of the silicon-carbon composite is about 2500 MPa to 5000 MPa.

[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 about 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 about 10% or less.

[0128] The present application possesses the aforementioned physical properties when the conditions of the porous carbon as described above are appropriately selected. For example, in the manufacture of a silicon carbon composite, when a porous carbon made of resin rather than biomass is used, in which the micropore volume of the porous carbon is approximately 90% or more, the rigidity of the formed silicon carbon composite is increased, and accordingly, the physical properties described above are satisfied, thereby providing a feature that can enhance the lifespan performance of a secondary battery.

[0129] The porous carbon of the present application can be manufactured from resin-based porous carbon raw materials.

[0130] In addition, the above porous carbon provides a method for manufacturing a cathode active material having a degree of sphericity of about 0.7 to 0.9 as defined by Formula 1 below.

[0131] [Equation 1]

[0132] 4πA / P 2

[0133] In the above Equation 1, A is the area and P is the boundary line.

[0134] As described above, when the properties of porous carbon are controlled, 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.

[0135] 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.

[0136] FIG. 3 is a diagram showing a stacked structure of a negative electrode for a lithium secondary battery according to one embodiment of the present application.

[0137] Referring to FIG. 3, a negative electrode (100) for a lithium secondary battery including a negative active material layer (20) on one side of a negative current collector layer (10) can be seen. FIG. 3 shows that the negative active material layer (20) is formed on one side of the negative current collector layer (10), but the negative active material layer (20) can be formed on both sides of the negative current collector layer (10).

[0138] In one embodiment of the present application, the negative electrode (100) 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 (10).

[0139] At this time, the cathode slurry may include the aforementioned cathode composition; and a slurry solvent.

[0140] In one embodiment of the present application, the solid content of the cathode slurry may satisfy about 5% or more and 40% or less.

[0141] In another embodiment, the solid content of the cathode slurry may satisfy a range of about 5% or more and 40% or less, for example, about 7% or more and 35% or less, or about 10% or more and 30% or less.

[0142] 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.

[0143] 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.

[0144] 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 for example, water or NMP (N-Methyl-2-Pyrrolidone) may be used.

[0145] In one embodiment of the present application, the negative current collector layer (10) generally has a thickness of about 1 μm to 100 μm. The negative current collector layer (10) 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, a surface treated with carbon, nickel, titanium, silver, etc. on the surface of copper or stainless steel, an aluminum-cadmium alloy, etc. 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.

[0146] In one embodiment of the present application, a negative electrode (100) for a lithium secondary battery is provided, wherein the thickness of the negative electrode current collector layer (10) is 1 μm or more and 100 μm or less, and the thickness of the negative electrode active material layer (20) is about 5 μm or more and 500 μm or less.

[0147] However, the thickness can be varied depending on the type and use of the cathode (100) used and is not limited thereto.

[0148] In one embodiment of the present application, the porosity of the negative electrode active material layer (20) may satisfy a range of about 10% or more and 60% or less.

[0149] In another embodiment, the porosity of the cathode active material layer (20) may satisfy a range of about 10% or more and 60% or less, for example, about 20% or more and 50% or less, or about 25% or more and 45% or less.

[0150] The above porosity varies according to the composition and content of the silicon-based active material; conductive material; and binder included in the negative electrode active material layer (20), and 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, and accordingly, the electrical conductivity and resistance of the electrode have an appropriate range.

[0151] In one embodiment of the present application, a lithium secondary battery is provided comprising: a positive electrode; a negative electrode (100) for a lithium secondary battery according to the present application; a separator provided between the positive electrode and the negative electrode (100); and an electrolyte.

[0152] FIG. 4 is a diagram showing a stacked structure of a lithium secondary battery (300) according to one embodiment of the present application. For example, a negative electrode (100) for a lithium secondary battery including a negative active material layer (20) on one side 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 side 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.

[0153] A lithium secondary battery (300) according to one embodiment of the present specification may include a negative electrode (100) for a lithium secondary battery as described above. The lithium secondary battery (300) may include a negative electrode (100), a positive electrode (200), a separator (30) interposed between the positive electrode (200) and the negative electrode (100), and an electrolyte (not shown), wherein the negative electrode (100) is identical to the negative electrode (100) described above. Since the negative electrode (100) has been described above, further explanation is omitted.

[0154] The above positive electrode (200) may include a positive electrode current collector (50) and a positive electrode active material layer (40) formed on the positive electrode current collector (50) and including the positive electrode active material.

[0155] In the above positive electrode (200), the positive electrode current collector (50) 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. The above positive electrode current collector (50) may typically have a thickness of about 3 μm to 500 μm, and fine irregularities may be formed on the surface of the above positive electrode current collector (50) 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 body, etc.

[0156] The above-mentioned positive electrode active material may be a commonly used positive electrode active material. For example, 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 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 Co, Ni, Fe, Cr, Zn and Ta, satisfying 0.01≤c3≤0.1) or Li2Mn3MO8 (where M is at least one selected from 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.

[0157] The above positive active material layer (40) may include a positive conductive material and a positive binder together with the positive active material described above.

[0158] The above-mentioned positive electrode conductive material is used to impart conductivity to the electrode, and in the battery being constructed, any material that possesses electronic conductivity without causing chemical changes can be used without any special limitations. 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 fibers; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more may be used.

[0159] The above-mentioned anode binder serves to improve adhesion between anode active material particles and adhesion between the anode active material and the anode current collector. 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.

[0160] The above separator (30) separates the negative electrode (100) and the positive electrode (200) and provides a passage for the movement of lithium ions. Any separator typically used in secondary batteries can be used without special limitations, and one that has low resistance to the movement of electrolyte ions and excellent electrolyte moisture retention capacity may be selected. For example, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used as the above separator (30). In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used as the above separator (30). In addition, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

[0161] Examples of the above electrolytes that can be used when manufacturing a lithium secondary battery (300) 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.

[0162] The above electrolyte may include a non-aqueous organic solvent and a metal salt.

[0163] 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.

[0164] Among the above carbonate-based organic solvents, cyclic carbonates such as ethylene carbonate and propylene carbonate are high-viscosity organic solvents with high dielectric constants that effectively dissociate lithium salts. By mixing these cyclic carbonates with low-viscosity, low-dielectric-constant linear carbonates such as dimethyl carbonate and diethyl carbonate in appropriate proportions, an electrolyte with high electrical conductivity can be produced.

[0165] 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 can be used.

[0166] 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.

[0167] One embodiment of the present invention provides a battery module including the lithium secondary battery (300) 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.

[0168] Hereinafter, examples are presented to aid in understanding the present invention; however, the above examples 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.

[0169] <Preparation Example>

[0170] <Example 1>

[0171] The resin-based raw material was placed in a tubular furnace, and the atmosphere inside the furnace was replaced with an inert gas for 2 hours under an Ar atmosphere of 50-200 ml / min under conditions of no temperature increase. The temperature was raised to 400°C at a rate of 5°C / min and then heated under an argon atmosphere for 2 hours. Afterward, the carbonization process was carried out by raising the temperature of the furnace to 900°C at a rate of 5°C / min and then heating under an argon atmosphere for 2 hours.

[0172] The powder obtained after the reaction was washed with ethanol 2 to 3 times.

[0173] Carbon-based particles dried at 100°C for at least 12 hours were mixed with KOH in a 1:4 weight ratio, and heated at 700°C for 4 hours under an argon atmosphere to expand the pores. Subsequently, the mixture was washed with distilled water and dried at 100°C for at least 12 hours. The porous carbon produced by the activation process exhibited a 97% proportion of primary pores with a diameter of less than 2 nm when measured by the nitrogen adsorption method, and a total pore volume of 0.87 m 3 / g, 1800-2000m 2 It corresponded to porous carbon characterized by a specific surface area at the level of / g.

[0174] The above porous carbon includes a spheroidization step during the manufacturing process, and the method can be selected from spray drying, rotary atomizer, or sol-gel. Subsequently, fine particles smaller than 1 µm are removed through a classification process.

[0175] The porous carbon, having completed classification, was placed in the hot zone of a CVD apparatus, and a silicon / carbon composite was prepared by flowing SiH4 / H2=5 / 95 gas at a flow rate of 50-210 ml / min at 600°C for 6 hours under a low-pressure environment of 1 to 10 Torr. Without removing it from the furnace, the furnace temperature was changed to 650°C at a rate of 5°C / min while flowing only Ar gas. The mixture was reacted for 3 hours while flowing C2H2 / H2 / Ar=10 / 50 / 40 gas at a rate of 200 ml / min for 1 hour to form a carbon layer on the surface, thereby preparing a silicon carbon composite containing a carbon layer on the surface of the silicon carbon composite.

[0176] <Example 2>

[0177] It was manufactured in the same manner as Example 1, except that the degree of sphericity of the porous carbon was low due to a process without spheric treatment.

[0178] <Example 3>

[0179] In the above Example 1, the raw material used was a biomass-based raw material such as cellulose powder or coconut shell instead of a resin-based raw material, and the activation process was prepared in the same manner as Example 1, except that a physical activation method was used in which carbon-based particles dried at 100°C for 12 hours or more were heated at 700°C for 3 hours in an argon atmosphere with CO2 as a balance gas of 10% to 20% to expand the pores.

[0180] <Comparative Example 1>

[0181] Biomass-based raw materials, such as cellulose powder and coconut shells rather than resin-based materials, were carbonized by heat treatment at 500°C to 1000°C under an inert gas atmosphere. After grinding and classifying the carbonized porous carbon, pores were formed through physical activation using an oxidizing gas (steam, CO2, O2, etc.) to oxidize the porous carbon. The resulting porous carbon is a non-spherical porous carbon in which, when measured by the nitrogen adsorption method, the proportion of first pores with a diameter of less than 2 nm is 92% and the proportion of second pores with a diameter of 2 nm or more is 8%, with a total pore volume of 0.75 m 3 / g, 1600 m 2 It had a specific surface area of ​​the level of / g.

[0182] Without undergoing a separate classification process to remove fine particles, the porous carbon was placed in the hot zone of a CVD apparatus, and a silicon-carbon composite was prepared by flowing SiH4 / H2=5 / 95 gas at a flow rate of 50 to 210 ml / min at 600°C for 3 hours under a low-pressure environment of 1 to 10 Torr.

[0183] Afterward, without removing it from the furnace, only Ar gas was flowed while changing the furnace temperature to 650℃ at a rate of 5℃ / min. A carbon layer was formed on the surface of the silicon carbon composite by reacting for 1 hour while flowing C2H2 / H2 / Ar=10 / 50 / 40 gas at a rate of 200ml / min for 1 hour.

[0184] <Comparative Example 2>

[0185] In the activation process of porous carbon, carbon-based particles dried at 100°C for more than 12 hours were heated at 700°C for 5 hours in an argon atmosphere using CO2 as a 10–20% balance gas to expand the pores. The specific surface area of ​​the porous carbon prepared by the above method was 1800 m². 2 It is characterized by being at the / g level.

[0186] Afterwards, the process was carried out for 5 hours in the SiH4CVD process, and it was manufactured in the same manner as Comparative Example 1, except that a carbon layer was not formed on the surface.

[0187] <Comparative Example 3>

[0188] The SiH4CVD process was manufactured using the same method as Comparative Example 1, except that the process time was 1 hour and the process of forming a carbon layer on the surface was carried out for 7 hours.

[0189] <Comparative Example 4>

[0190] The SiH4CVD process was manufactured using the same method as Comparative Example 1, except that the process time was 1 hour and the temperature of the process for forming a carbon layer on the surface was 580℃ for 4 hours.

[0191] <Comparative Example 5>

[0192] In Example 2 above, carbon-based particles and KOH are mixed in a weight ratio of 1:5, and the stirring time is increased by 30 minutes. Activation is carried out by heating at 700°C for 7 hours. Afterward, the mixture is washed with distilled water and dried at 100°C for at least 12 hours.

[0193] The porous carbon generated by the activation process has a proportion of first pores with a diameter of less than 2 nm as measured by the nitrogen adsorption method of 97%, and a total pore volume of 1.1 m³ 3 / g, 2000~2200m 2 It corresponded to porous carbon characterized by a specific surface area at the level of / g.

[0194] The process of depositing Si was carried out for 5 hours, and the product was manufactured in the same manner as Example 2 above, except that a carbon layer was not formed on the surface.

[0195] <Comparative Example 6>

[0196] A product prepared by the same method as in Example 1 above, except that the carbon-based particles and KOH were used in a weight ratio of 1:3, with a total pore volume of 0.75 m 3 / g, 1600~1800m 2 Porous carbon characterized by a specific surface area of ​​the level of / g was prepared.

[0197] Afterward, the porous carbon that had been classified was placed in the hot zone of a CVD apparatus, and a silicon / carbon composite was prepared by flowing SiH4 / H2=5 / 95 gas at a flow rate of 50-210 ml / min at 600°C for 4 hours under a low-pressure environment of 1 to 10 Torr. The furnace temperature was then changed to 650°C at a rate of 5°C / min while flowing only Ar gas without removing the composite from the furnace. The composite was prepared in the same manner as in Example 1 above, except that a carbon layer was formed on the surface by reacting for 7 hours while flowing C2H2 / H2 / Ar=10 / 50 / 40 gas at a rate of 200 ml / min for 1 hour.

[0198] <Comparative Example 7>

[0199] (1) Preparation of silicon oxide containing magnesium

[0200] Si and SiO2 were mixed in a 1:1 molar ratio in crucible No. 1 and heated to a sublimation temperature of 1400°C. In crucible No. 2, metallic magnesium was separately heated and evaporated between 600°C and 1000°C.

[0201] All of the above crucibles were under reduced pressure to a level of 0.1 torr. A vapor mixture containing Mg obtained from crucible No. 1 and crucible No. 2 was reacted for 6 hours and then condensed into a solid state in a vacuum region at 800°C.

[0202] The silicon-based active material prepared by the above method was ground using a ball mill for approximately 3 to 4 hours to produce particles with a D50 of 6 μm. Subsequently, methane (CH4) was 10 using a CVD apparatus under an inert gas atmosphere (Ar). -1 Magnesium-containing silicon oxide was prepared by forming a carbon layer on the surface of a silicon-based active material by reacting at 1 L / min for about 5 hours at torr. The Mg content in the powder was analyzed by ICP-MS and measured to be 8 wt%.

[0203] The modulus and hardness values ​​were measured for the active materials prepared in the above examples and comparative examples, respectively, and the results are shown in Table 1 below.

[0204] Silicon Carbon Composite Modulus (GPa) Silicon Carbon Composite Hardness (MPa) Silicon Carbon Composite B 3 / A 2 (Equation 1) Example 1 21.734670.510.21576 Example 2 19.914301.670.2008 Example 3 18.23766.40.1613 Comparative Example 1 12.811916.50.0429 Comparative Example 2 13.552547.20.0900 Comparative Example 3 8.351249.10.02795 Comparative Example 4 7.341243.840.03571 Comparative Example 5 192300.050.033 Comparative Example 6 23.565000.497 Comparative Example 7 30.148705.7750.726

[0205] For reference, Example 1 above used spherical porous carbon of resin, and Example 2 had a value of Equation 1 of 0.2008, which is lower than Example 1, where the value of Equation 1 was 0.21576 because no spherical treatment was performed. Additionally, Example 3 used biomass raw materials, so the strength of the porous carbon was relatively weak, resulting in a value of Equation 1 of 0.0429, which is lower than Example 1.

[0206] Comparative Example 1 used the same biomass raw material as Example 3, but because fine particles were present and the amount of SiH4 deposition was small, the internal pores of the final active material were larger, so the value of Equation 1 was measured to be relatively low. Comparative Example 2 did not undergo carbon coating on the final surface, and Comparative Example 3 had a very low amount of SiH4 deposition, so it was found that the value of Equation 1 was relatively low compared to Comparative Example 1. Finally, in the case of Comparative Example 4, the value of Equation 1 was measured to be relatively low because the outermost carbon coating temperature was low.

[0207] In addition, it was found that in Comparative Example 5, the hardness value was lowered because a carbon coating layer was not formed, similar to Comparative Example 2, and in Comparative Example 6, the hardness value of the entire composite increased because the time for the outermost carbon coating was increased. In addition, Comparative Example 7 concerns carbon-coated Mg-doped silicon oxide, and it was confirmed that in this case, the modulus value and hardness value exceeded the scope of the present application.

[0208] <Manufacturing of the Cathode>

[0209] A cathode slurry was prepared by adding a negative electrode active material containing the silicon-based active material of Table 1, a negative electrode conductive material, and polyacrylamide as a binder to distilled water as a solvent for forming a negative electrode slurry in a weight ratio of 80:10:10 (solid content concentration 25 wt%).

[0210] According to one embodiment, the cathode conductive material was carbon black (specific surface area: 45 m2 / g, diameter: 30 to 50 nm).

[0211] As a mixing method, the above-mentioned cathode conductive material, binder, and water were dispersed using a homo mixer at 2500 rpm for 30 minutes, and then the above-mentioned silicon-based active material was added and dispersed at 2500 rpm for 30 minutes to prepare a cathode slurry.

[0212] As a cathode current collector layer, the above cathode slurry is applied to both sides of a copper current collector (thickness: 8㎛) at a rate of 85 mg / 25 cm 2 A negative active material layer (thickness: 33㎛) was formed by coating with a loading amount, rolling, and drying in a vacuum oven at 130℃ for 10 hours, and this was used as the negative electrode (negative electrode thickness: 41㎛, negative electrode porosity 40.0%).

[0213] <Experimental Example>

[0214] A coin half cell was manufactured using lithium metal as the counter electrode of the negative electrode for the above lithium secondary battery, and was charged and discharged at a C-rate of 0.1C. Charging was performed in CC / CV mode with a CV of 5Mv and 0.005C, and discharging was performed in CC mode with a discharge of up to 1.0V. The results are shown in Table 2 below.

[0215] Electrode Density 0.9~0.99 g / cc Electrode Density 1~1.3 g / cc Capacity (mAh / g) Initial Efficiency (%) Capacity (%) Reduction Rate Initial Efficiency Reduction Amount (%) Example 1 180 784.8 1.1 00.6 Example 2 193 287.2 1.1 90.8 Example 3 186 288.3 1.1 21 Comparative Example 1 189 087.4 3.7 00.9 Comparative Example 2 184 3881.0 31.3 Comparative Example 3 168 083 4.7 61 Comparative Example 4 188 087.4 1.7 01.6 Comparative Example 5 190 088.6 0.4 71.5 Comparative Example 6 178 084.0 3.3 70.2 Comparative Example 7 134 877.8 1.7 10.1

[0216] As can be seen in Table 2 above, the reduction rates of capacity and efficiency at electrode densities of 1 to 1.3 g / cc and 0.9 to 0.99 g / cc for the embodiments and comparative examples of the present invention are listed in Table 2, and it was confirmed that the reduction rate of the comparative example was greater than that of the embodiment. That is, the embodiment is a high-capacity cathode (1700 mAh / g or more), with a capacity reduction rate of about 1.2% or less and an initial efficiency reduction amount of about 1.0% or less, and it was confirmed that the comparative example was evaluated to have a greater phenomenon of physical property degradation due to rolling compared to the embodiment.

[0217] When comparing numerically in Table 2, it can be seen that Comparative Examples 1, 6, and 7 have a low initial efficiency reduction but a relatively large capacity reduction rate compared to the Examples, and Comparative Examples 2 and 5 have a small capacity reduction rate but a relatively large initial efficiency reduction. Similarly, it can be seen that Comparative Examples 3 and 4 show results similar to Comparative Example 1.

[0218] For reference, in the case of Comparative Example 7, SiO was used, and it was found that the capacity itself was lower than that of the example and could not be used for the intended purpose as it fell outside the hardness and modulus range of the present application.

[0219] In the case of the embodiments of the present invention, a silicon carbon composite satisfying the physical properties of Table 1 was used. By using resin-based porous carbon, the physical strength of the material is relatively excellent, and it is characterized by well-developed micropores. For this reason, the embodiments of Table 1 have a high modulus of approximately 15 GPa to 25 GPa, which represents the elastic performance of the material before plastic deformation occurs. Additionally, the expansion of the material during discharge is small, and the more spherical the material, the more uniformly the irreversible phase is generated, exhibiting excellent efficiency characteristics.

[0220] Meanwhile, the comparative example is a biomass-based material, and it can be confirmed that it is inferior in the above characteristics because the ratio of meso and macro pores, which are characteristic of biomass, is relatively high. Also, since the total pore volume differs depending on the porous carbon, there is a difference in the content of Si that can be deposited, and as a result, the modulus is less than about 15 GPa, which is lower than that of the example, so it can be confirmed that the example is superior to the comparative example.

[0221] Additionally, hardness, which refers to the resistance required to cause small local deformations on the surface of a material and is a factor that allows the material surface to withstand local deformation or intrusion, is also superior in the example compared to the comparative example, just like the modulus; this may mean that under the same indentation conditions, more particles of the material in the comparative example break compared to the example.

[0222] In the embodiment of the present invention, it is presumed that electrical short circuits will be small from the perspective of the electrode at high rolling density, in addition to the above characteristics, and it was confirmed that the reduction in efficiency in the embodiment is relatively small due to the above characteristics.

[0223] Although the foregoing has been described with reference to the embodiments of the present disclosure, a person skilled in the art or having ordinary knowledge in the art will understand that various modifications and changes can be made to the various embodiments of the present disclosure without departing from the technical scope of the various embodiments of the present disclosure as set forth in the claims below. Accordingly, the technical scope of the various embodiments of the present disclosure should not be limited to the contents described in the detailed description of the specification, but should be determined by the claims.

Claims

1. The modulus value (A) representing the stiffness of the material is 15 GPa to 25 GPa, and A negative electrode active material for a lithium secondary battery comprising a silicon carbon (Si / C) composite having a hardness value (B) indicating resistance to scratches or dents on the surface of the material of 2500 MPa to 5000 MPa.

2. In Claim 1, A negative electrode active material for a lithium secondary battery in which the above modulus value (A) and hardness value (B) satisfy the following Equation 1. [Equation 1] 0.1 ≤ B 3 / A 2 3. In Claim 1, The silicon carbon composite comprises porous carbon; and silicon deposited on the porous carbon, and A negative electrode active material for a lithium secondary battery, wherein 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 for a lithium secondary battery having an average particle size (D50) of 1 μm or more and 10 μm or less.

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

6. In Claim 1, A negative electrode active material for a lithium secondary battery 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. Step of preparing porous carbon; and A method for manufacturing a negative electrode active material comprising the step of forming a silicon-carbon composite by depositing silicon on the porous carbon above, In the step of forming a silicon carbon composite by depositing silicon on the porous carbon, 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, and A method for manufacturing a negative electrode active material for a lithium secondary battery, wherein the modulus value (A) of the silicon carbon composite is 15 GPa to 25 GPa and the hardness value (B) of the silicon carbon composite is 2500 MPa to 5000 MPa.

8. In Claim 7, The above porous carbon is a method for manufacturing a negative electrode active material for a lithium secondary battery, manufactured from a resin-based porous carbon raw material.

9. In Claim 7, The above porous carbon has a ratio of first pores having a diameter of less than 2 nm when measured by the nitrogen adsorption method of 90% or more, and A method for manufacturing a negative electrode active material for a lithium secondary battery, wherein the above-mentioned porous carbon has a ratio of 10% or less of a second pore having a diameter of 2 nm or more and 50 nm or less when measured by a nitrogen adsorption method.

10. A negative electrode composition for a lithium secondary battery comprising a negative electrode active material according to any one of claims 1 to 6; a negative electrode conductive material; and a negative electrode binder.

11. In Claim 10, The above negative electrode active material is a negative electrode composition for a lithium secondary battery comprising 40 parts by weight or more based on 100 parts by weight of the above negative electrode 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 above negative electrode active material layer is a negative electrode for a lithium secondary battery comprising 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; Negative electrode for a lithium secondary battery according to claim 12; A separator provided between the anode and the cathode; and A lithium secondary battery containing an electrolyte.

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