Anode composition, anode for lithium secondary battery including the same, and lithium secondary battery including the anode

Abstract

The present application relates to a negative electrode composition, a negative electrode for a lithium secondary battery including the same, and a lithium secondary battery including the negative electrode.

Description

[Technical Field]

[0001] This application claims the benefit of the filing date of Korean Patent Application No. 10-2023-0100220, filed with the Korean Intellectual Property Office on August 1, 2023, the entire contents of which are incorporated herein by reference.

[0002] The present application relates to a negative electrode composition, a negative electrode for a lithium secondary battery including the same, and a lithium secondary battery including the negative electrode. [Background technology]

[0003] The rapid increase in fossil fuel use has led to an increasing demand for alternative and clean energy, and one of the most actively researched areas as part of this is the field of power generation and storage using electrochemical reactions.

[0004] Currently, a typical example of an electrochemical element that uses such electrochemical energy is a secondary battery, and the range of its use is tending to expand more and more.

[0005] As technological development and demand for mobile devices increase, the demand for secondary batteries as energy sources is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which have high energy density and voltage, long cycle life, and low self-discharge rate, have been commercialized and widely used. In addition, active research is being conducted on methods for manufacturing high-density electrodes with higher energy density per unit volume as electrodes for such high-capacity lithium secondary batteries.

[0006] Generally, a secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode contains a negative electrode active material that inserts and extracts lithium ions from the positive electrode. Silicon-based particles with a large discharge capacity can be used as the negative electrode active material.

[0007] In particular, with the recent demand for high-density energy batteries, Si / C and SiO, which have capacities 10 times larger than graphite-based materials, are being used as negative electrode active materials. x However, while silicon-based compounds, which are high-capacity materials, have a higher capacity than conventional graphite, they suffer from a problem of rapid volume expansion during charging, which can disrupt the conductive path and reduce battery performance.

[0008] Therefore, in order to solve the problems when using silicon-based compounds as negative electrode active materials, various methods have been discussed, such as methods for controlling the driving potential, methods for additionally coating a thin film on the active material layer, methods for suppressing volume expansion itself, such as methods for controlling the particle size of the silicon-based compound, or methods for preventing the conductive path from being broken. However, these methods have limitations in their application because they may actually degrade battery performance, and there are still limitations in the commercialization of negative electrode batteries with a high content of silicon-based compounds.

[0009] Furthermore, research into the above-mentioned problem has revealed that the smaller the crystal grain size of a silicon-based active material, the more micron-sized the particle size, and the better its lifespan performance. However, when the crystal grain size of a silicon-based active material is reduced or micron-sized in order to improve lifespan performance, there are problems in that the coating state on the electrode is poor and relatively uniform dispersion becomes difficult due to particle aggregation of the silicon-based active material.

[0010] Due to the above problems, the coating state of the electrode is poor, which reduces the electrode adhesion, and causes detachment from the current collector during repeated cycles, resulting in a rapid decrease in lifespan or difficulty in use due to the detachment.

[0011] Therefore, when using a silicon-based active material as a negative electrode active material to improve capacity performance, research is needed to find a method to solve the above-mentioned problems. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-080971 Summary of the Invention [Problem to be solved by the invention]

[0013] As a result of research into methods for improving the lifespan performance of negative electrodes containing silicon-based active materials, it was found that the above-mentioned problems can be solved by using silicon-based active materials of a few microns in size and, instead of the conventionally used point-like conductive materials of several tens of nanometers, by using point-like conductive materials with a central particle size that is a certain ratio to the particle size of the silicon-based active material.

[0014] In other words, when using conventional dot-shaped conductive materials on the order of several tens of nanometers, linear conductive materials such as carbon nanotubes, or a combination of linear and sheet-shaped conductive materials, it becomes difficult to ensure voids within the electrode, and as charging / discharging progresses, side reactions cause the pores within the electrode to become clogged, blocking the path of Li-ion movement, increasing resistance and leading to a decrease in cell performance.

[0015] However, it has been found that silicon-based active materials have the best electrode life when they have a particle size of several microns. Therefore, it has been found that adjusting the central particle size of the dot-like conductive material used together can improve the quality of the electrode by improving dispersibility and improve life performance by ensuring a void structure.

[0016] Therefore, the present application relates to a negative electrode composition that can solve the above-mentioned problems, a negative electrode for a lithium secondary battery including the same, and a lithium secondary battery including the negative electrode. [Means for solving the problem]

[0017] One embodiment of the present specification is a negative electrode composition including a silicon-based active material; a negative electrode conductive material; and a negative electrode binder; wherein the silicon-based active material includes one or more selected from the group consisting of Si, SiO x (0 < x ≤ 2), and metal impurities, and includes 90 parts by weight or more of Si based on 100 parts by weight of the silicon-based active material, the negative electrode conductive material includes a dot-shaped conductive material, and the center particle size of the negative electrode conductive material is 30% or more and 60% or less of the center particle size of the silicon-based active material, and provides a negative electrode composition.

[0018] Another embodiment includes 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, and the negative electrode active material layer includes the negative electrode composition according to the present application or a cured product thereof, and provides a negative electrode for a lithium secondary battery.

[0019] Finally, a lithium secondary battery is provided, which includes 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.

Advantages of the Invention

[0020] In the case of the negative electrode composition according to one embodiment of the present invention, while maintaining the center particle size of the silicon-based active material at a micro size, a dot-shaped conductive material is included as the negative electrode conductive material in order to solve the problems of uniform dispersion and the coating state of the electrode, and the center particle size of the dot-shaped conductive material is optimized with respect to the center particle size of the silicon-based active material.

[0021] That is, the negative electrode conductive material includes a dot-shaped conductive material, and the center particle size of the negative electrode conductive material satisfies 30% or more and 60% or less of the center particle size of the silicon-based active material, so that it has the characteristics of improving the quality of the electrode by improving the dispersibility and improving the life performance by ensuring the void structure.

Brief Description of the Drawings

[0022] [Figure 1] It is a diagram showing a laminated structure of a negative electrode for a lithium secondary battery according to one embodiment of the present application. [Figure 2] FIG. 1 is a diagram showing a stack structure of a lithium secondary battery according to an embodiment of the present application. [Figure 3] FIG. 1 illustrates the concept of sphericity. [Figure 4] FIG. 1 is a diagram showing lithium ion paths when the point-like conductive material of the present application is used. [Figure 5] FIG. 1 is a diagram showing lithium ion paths when a linear and / or sheet-shaped conductive material is used. DETAILED DESCRIPTION OF THE INVENTION

[0023] Before describing the present invention, some terms will first be defined.

[0024] In this specification, unless otherwise specified, when a part "comprises" a certain component, it does not mean that it may further include other components, but does not exclude other components.

[0025] In this specification, "p to q" means a range of "not less than p and not more than q."

[0026] In this specification, the "specific surface area" is measured by the BET method, and specifically, is calculated from the amount of nitrogen gas adsorption at liquid nitrogen temperature (77 K) using a BELSORP-mini II manufactured by BEL Japan Co., Ltd. That is, in the present application, the BET specific surface area may mean the specific surface area measured by the above-mentioned measurement method.

[0027] In this specification, "Dn" refers to particle size distribution, and refers to the particle size at the n% point in the cumulative particle number distribution according to particle size. That is, D50 is the particle size (average particle size, median particle size) at the 50% point in the cumulative particle number distribution according to particle size, D90 is the particle size at the 90% point in the cumulative particle number distribution according to particle size, and D10 is the particle size at the 10% point in the cumulative particle number distribution according to particle size. Meanwhile, the average particle size can be measured using the laser diffraction method. Specifically, the powder to be measured is dispersed in a dispersion medium and then introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500). The particle size distribution is calculated by measuring the difference in the diffraction pattern according to particle size when the particles pass through a laser beam.

[0028] In one embodiment of the present application, the particle size or particle size may refer to the average diameter or typical diameter of the individual particles that make up the metal powder.

[0029] As used herein, when a polymer contains a certain monomer as a monomer unit, it means that the monomer participates in a polymerization reaction and is contained as a repeating unit in the polymer. As used herein, when a polymer contains a monomer, it is interpreted in the same way as when a polymer contains the monomer as a monomer unit.

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

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

[0032] Hereinafter, a detailed description will be given with reference to the drawings so that those having ordinary knowledge in the technical field to which the present invention pertains can easily implement the present invention. However, the present invention may be realized in various different forms and is not limited to the following description.

[0033] One embodiment of the present specification is a negative electrode composition including a silicon-based active material; a negative electrode conductive material; and a negative electrode binder, wherein the silicon-based active material includes one or more selected from the group consisting of Si, SiO x (0 < x ≤ 2), and metal impurities, and contains 90 parts by weight or more of the Si based on 100 parts by weight of the silicon-based active material, the negative electrode conductive material includes a dot-shaped conductive material, and the central particle size of the negative electrode conductive material is 30% or more and 60% or less with respect to the central particle size of the silicon-based active material, and provides a negative electrode composition.

[0034] The negative electrode conductive material includes a dot-shaped conductive material, and by satisfying that the central particle size of the negative electrode conductive material is 30% or more and 60% or less with respect to the central particle size of the silicon-based active material, it has the characteristics of improving the quality of the electrode by improving dispersibility and improving the life performance by ensuring the void structure.

[0035] In one embodiment of the present application, the silicon-based active material includes one or more selected from the group consisting of Si, SiO x (0 < x ≤ 2), and metal impurities, and may contain 90 parts by weight or more of the Si based on 100 parts by weight of the silicon-based active material.

[0036] In one embodiment of the present application, the silicon-based active material includes Si, and may contain 95 parts by weight or more of the Si based on 100 parts by weight of the silicon-based active material.

[0037] In another embodiment, it may contain 95 parts by weight or more, preferably 96 parts by weight or more, more preferably 98 parts by weight or more of the Si based on 100 parts by weight of the silicon-based active material, and may contain 100 parts by weight or less, preferably 99 parts by weight or less, more preferably 98 parts by weight or less.

[0038] In one embodiment of the present application, pure silicon (Si) particles may be used as the silicon-based active material. The use of pure silicon (Si) particles as the silicon-based active material may mean that pure Si particles (Si) that are not bonded to other particles or elements are included in the above range, based on 100 parts by weight of the total silicon-based active material.

[0039] In one embodiment of the present application, the silicon-based active material may be composed of silicon-based particles having 100 parts by weight of Si based on 100 parts by weight of the silicon-based active material.

[0040] In one embodiment of the present application, the silicon-based active material may contain metal impurities. In this case, the impurities may be metals that may be generally contained in silicon-based active materials, and specifically, may be contained in an amount of 0.1 parts by weight or less based on 100 parts by weight of the silicon-based active material.

[0041] Meanwhile, the median particle size of the silicon-based active material of the present invention may be 1.5 μm or more and 15 μm or less. In this case, the median particle size of the silicon-based active material means the average particle size, which can be expressed as D50.

[0042] In the present application, the median particle size of the silicon-based active material may be specifically 2 μm to 8 μm, more specifically 3 μm to 6 μm. If the average particle size is below this range, the specific surface area of ​​the particles will be excessively increased, resulting in an excessively high viscosity of the negative electrode slurry. As a result, the particles constituting the negative electrode slurry will not be dispersed smoothly. Furthermore, if the size of the silicon-based active material is excessively small, the contact area between the silicon particles and the conductive material will be reduced due to the complex of the conductive material and the binder in the negative electrode slurry, increasing the possibility of the conductive network being broken, resulting in a decrease in capacity retention. On the other hand, if the average particle size exceeds this range, excessively large silicon particles will be present, resulting in an uneven negative electrode surface, which will cause non-uniform current density during charge and discharge. Furthermore, if the silicon particles are excessively large, the phase stability of the negative electrode slurry will be unstable, resulting in a decrease in processability. This will result in a decrease in the capacity retention of the battery.

[0043] In one embodiment of the present application, the silicon-based active material generally has a characteristic BET specific surface area. The BET specific surface area of ​​the silicon-based active material is preferably 0.01 m 2 / g~150.0m 2 / g, more preferably 0.1m 2 / g~100.0m 2 / g, particularly preferably 0.2m 2 / g~80.0m 2 / g, most preferably 0.2m 2 / g~18.0m 2 / g. The BET specific surface area is determined in accordance with DIN 66131 (using nitrogen).

[0044] In one embodiment of the present application, the silicon-based active material may be, for example, in a crystalline or amorphous form, and is preferably non-porous. The silicon particles are preferably spherical or shard-like particles. Alternatively, but less advantageously, the silicon particles may have a fibrous structure or be in the form of a silicon-containing film or coating.

[0045] In one embodiment of the present application, the silicon-based active material 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.

[0046] In this application, the circularity is determined by the following formula 1-1, where A is the area and P is the perimeter.

[0047] [Formula 1-1] 4πA / P 2

[0048] Silicon-based active materials have significantly higher capacities than conventionally used graphite-based active materials, and attempts to use them are increasing. However, because of their high volume expansion during the charge / discharge process, their use is limited to mixing small amounts with graphite-based active materials.

[0049] Therefore, in the case of the present invention, in order to improve capacity performance, only a silicon-based active material is used as the negative electrode active material, and in order to solve the above-mentioned problems, the particle size ratio with the negative electrode conductive material described below is optimized.

[0050] In one embodiment of the present application, there is provided a negative electrode composition, wherein the silicon-based active material is 40 parts by weight or more based on 100 parts by weight of the negative electrode composition.

[0051] In another embodiment, the amount of the silicon-based active material may be 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 negative electrode composition, and may be 95 parts by weight or less, preferably 90 parts by weight or less, and more preferably 85 parts by weight or less.

[0052] The negative electrode composition according to the present application uses a negative electrode active material that satisfies a specific size that can suppress the volume expansion rate during charge and discharge, even when a silicon-based active material with extremely high capacity is used within the above range, and by using both a negative electrode conductive material and a negative electrode binder, which will be described later, the negative electrode composition according to the present application has the characteristic of not deteriorating the performance of the negative electrode and having excellent output characteristics during charge and discharge, even when the silicon-based active material has an extremely high capacity within the above range.

[0053] While graphite-based compounds have traditionally been used exclusively as negative electrode active materials, attempts to incorporate silicon-based active materials into batteries to increase capacity have been increasing in recent years as demand for high-capacity batteries has grown. However, even if the properties of silicon-based active materials are adjusted as described above, their volume can rapidly expand during charge / discharge processes, potentially damaging the conductive paths formed in the negative electrode active material layer.

[0054] Previously, linear or sheet-shaped conductive materials were primarily used in anodes using silicon-based active materials. However, with linear conductive materials, the pores in the anode tended to become clogged as the amount of conductive material increased, leading to performance issues due to increased pore resistance. While sheet-shaped conductive materials themselves can form surface contact, rolling the anode can impair ion migration paths. In other words, the role of anode conductive materials is to create contact points between particles, enabling conductivity. However, if they clog the pore structure within the electrode, impeding the ion migration path in the electrolyte, resistance increases.

[0055] This can be seen in detail in Figure 5. Compared to Figure 4, Figure 5 uses linear and / or sheet-shaped conductive materials, which makes it difficult to ensure voids within the electrode, and side reactions during charge / discharge cause the pores within the electrode to become clogged, blocking the migration path of lithium ions, increasing resistance and leading to a decrease in cell performance.

[0056] Therefore, in one embodiment of the present application, the negative electrode conductive material may include dot-like conductive material. When dot-like conductive material is used as described above, it is easy to ensure ion migration paths, and this is more effective than using linear or sheet-like conductive material. Specifically, as can be seen from FIG. 4, by using dot-like conductive material having the characteristics described below, the pores of the negative electrode are enlarged, thereby ensuring lithium ion migration paths and reducing the rate of increase in resistance.

[0057] In one embodiment of the present application, there is provided a negative electrode composition in which the sphericity of the dot-like conductive material is represented by the following formula 1:

[0058] [Formula 1] 0.7≦X1 / Y1≦0.96 In the formula 1, X1 is the area of ​​the orthogonal projection of the point-like conductive material, Y1 means the area of ​​a circle having the same perimeter as the orthogonal projection of the point-like conductive material.

[0059] The formula 1 can be measured using a particle shape analyzer. Specifically, the dot-like conductive material according to the present application is scattered onto a glass plate by air injection, and then the scattered dot-like conductive material particles are orthogonally projected in a photograph, and the particle shapes of 10,000 dot-like conductive material particles in the photograph can be measured. In this case, the formula 1 is a value showing the average for 10,000 particles. The formula 1 according to the present application can be measured from the image, and the formula 1 can be expressed as the sphericity of the dot-like conductive material. The concept of sphericity is shown in Figure 3. Sphericity is calculated using the formula [4π * area of ​​orthogonal projection of silicon-based active material / (perimeter of orthogonal projection of silicon-based active material)]. 2 ] may also be expressed as

[0060] In other words, X1 is the actual area of ​​the point-like conductive material, and Y1 can mean the area of ​​a spherical particle with the same perimeter as the point-like conductive material.

[0061] In one embodiment of the present application, the sphericity of the conductive material particles may be, for example, 0.960 or less, for example, 0.957 or less, and the sphericity of the conductive material particles may be 0.7 or more, for example, 0.85 or more, specifically 0.9 or more, more specifically 0.91 or more, for example, 0.92 or more.

[0062] As described above, the dot-shaped conductive material satisfies the sphericity of the formula 1, and differs from sheet-shaped or linear conductive material in the range of the formula 1.

[0063] In one embodiment of the present application, the dot-like conductive material may have an ID / IG ratio of 0.01 or more and 1.5 or less when measured by Raman spectroscopy.

[0064] In another embodiment, the dot-like conductive material may have an ID / IG ratio of 0.01 or more and 1.5 or less, 0.02 or more and 1.3 or less, more specifically 0.03 or more and 1.05 or less, when measured by Raman spectroscopy.

[0065] The ID / IG refers to an index for identifying defects within the structure, and the degree of defects present in the point-like conductive material can be confirmed by measurement using Raman spectroscopy. By including point-like conductive material that satisfies the range of Raman spectroscopy, the battery will have the characteristic of having excellent life performance when driven by a battery in the future.

[0066] In one embodiment of the present application, the dot-like conductive material refers to a dot-like or spherical conductive material that can be used to improve the conductivity of a negative electrode, does not cause chemical changes, and has conductivity. Specifically, the dot-like conductive material may be one selected from the group consisting of carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and preferably includes carbon black, which achieves high conductivity and excellent dispersibility.

[0067] In one embodiment of the present application, the point-like conductive material has a BET specific surface area of ​​40 m 2 / g or more 70m 2 / g or less, preferably 45m 2 / g or more 65m 2 / g or less, more preferably 50m 2 / g or more 60m 2 / g or less.

[0068] In one embodiment of the present application, the dot-like conductive material may have 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.

[0069] In particular, when the content of functional groups in the dot-like conductive material satisfies the above range, the functional groups are present on the surface of the dot-like conductive material, and when water is used as a solvent, the dot-like conductive material can be smoothly dispersed in the solvent. In particular, by using a specific silicon-based active material, the present invention can reduce the content of functional groups in the dot-like conductive material, thereby achieving an excellent effect of improving dispersibility.

[0070] In one embodiment of the present application, the silicon-based active material is characterized by including a dot-like conductive material having a functional group content within the above range, and the content of the functional group can be adjusted depending on the degree of heat treatment of the dot-like conductive material.

[0071] In an embodiment of the present application, the median particle size of the negative electrode conductive material may be 0.45 μm or more and 9 μm or less, preferably 0.6 μm or more and 3 μm or less, and more preferably 0.90 μm or more and 1.8 μm or less.

[0072] In an embodiment of the present application, the central particle size of the dot-like conductive material may be 0.45 μm or more and 9 μm or less, preferably 0.6 μm or more and 3 μm or less, and more preferably 0.90 μm or more and 1.8 μm or less.

[0073] In the present application, the negative electrode conductive material having a median particle size of 1 μm or less may be included in an amount of 5 parts by weight or less based on 100 parts by weight of the negative electrode conductive material.

[0074] The present application is characterized by the use of a negative electrode conductive material having a median particle size within the above range, rather than the dot-like conductive material of several tens of nanometers that was used in the production of conventional pure silicon (Pure Si) electrodes.

[0075] In the case of point-shaped conductive materials, unlike linear conductive materials and sheet-shaped conductive materials, the problems mentioned above can be solved as they are conductive materials having a spherical shape, and when point-shaped conductive materials are used, it is easy to ensure a path for ion movement, and the effect is superior to when using linear conductive materials or sheet-shaped conductive materials.

[0076] That is, the negative electrode conductive material includes dot-like conductive material, and the median particle size of the negative electrode conductive material satisfies the above range relative to the median particle size of the silicon-based active material, thereby achieving the characteristics of improved electrode quality due to improved dispersibility and improved life performance due to the ensured void structure.

[0077] In one embodiment of the present application, the dot-like conductive material may be included in an amount of 95 parts by weight or more, 96 parts by weight to 98 parts by weight or more, or 100 parts by weight or less, based on 100 parts by weight of the negative electrode conductive material.

[0078] In one embodiment of the present application, the negative electrode conductive material may be made of dot-like conductive material.

[0079] In one embodiment of the present application, there is provided a negative electrode composition, wherein the median particle size of the negative electrode conductive material is 30% to 60% of the median particle size of the silicon-based active material.

[0080] In one embodiment of the present application, the negative electrode conductive material may further include one or more selected from the group consisting of sheet-shaped conductive materials and linear conductive materials.

[0081] The sheet-like conductive material can improve conductivity by increasing surface contact between silicon particles in the negative electrode and can also prevent the conductive path from being broken due to volume expansion. The sheet-like conductive material can be referred to as a plate-like conductive material or a bulk-like conductive material.

[0082] In one embodiment of the present application, the sheet-like conductive material may include at least one selected from the group consisting of platelet graphite, graphene, graphene oxide, and graphite flakes, and may preferably be platelet graphite.

[0083] In one embodiment of the present application, the average particle size (D50) of the sheet-like 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, the sufficient particle size does not cause an excessive increase in viscosity of the negative electrode slurry and dispersion is easy. Therefore, when dispersion is performed using the same device and for the same time, the dispersion effect is excellent.

[0084] In one embodiment of the present application, the sheet-shaped conductive material provides a negative electrode composition having a D10 of 0.5 μm or more and 2.0 μm or less, a D50 of 2.5 μm or more and 3.5 μm or less, and a D90 of 6.5 μm or more and 15.0 μm or less.

[0085] In one embodiment of the present application, the sheet-shaped conductive material may be a sheet-shaped conductive material having a high BET specific surface area; or a sheet-shaped conductive material having a low specific surface area.

[0086] In one embodiment of the present application, the sheet-like conductive material can be a sheet-like conductive material with a high specific surface area or a sheet-like conductive material with a low specific surface area, without any restrictions. However, since dispersion can have some effect on electrode performance, it is particularly preferable to use a sheet-like conductive material with a low specific surface area in which dispersion does not cause problems.

[0087] In one embodiment of the present application, the sheet-shaped conductive material has a BET specific surface area of ​​0.25 m 2 / g or more.

[0088] In another embodiment, the sheet-shaped conductive material has a BET specific surface area of ​​1 m 2 / g or more 500m 2 / g or less, preferably 5m 2 / g or more 300m 2 / g or less, more preferably 5m 2 / g or more 250m 2 / g or less.

[0089] The sheet-shaped conductive material according to the present application may be a sheet-shaped conductive material with a high specific surface area or a sheet-shaped conductive material with a low specific surface area.

[0090] In another embodiment, the sheet-shaped conductive material is a sheet-shaped conductive material having a high specific surface area, and a BET specific surface area of ​​50 m 2 / g or more 500m 2 / g or less, preferably 80m 2 / g or more 300m 2 / g or less, more preferably 100m 2 / g or more 300m 2 / g or less.

[0091] In another embodiment, the sheet-shaped conductive material is a sheet-shaped conductive material having a low specific surface area, and a BET specific surface area of ​​1 m 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 / g or less.

[0092] Another example of a linear conductive material is carbon nanotubes. The carbon nanotubes may be bundled carbon nanotubes. The bundled carbon nanotubes may include multiple carbon nanotube units. Specifically, unless otherwise specified, the term "bundle type" refers to a secondary shape in which multiple carbon nanotube units are arranged side by side or entangled with each other, in a bundle or rope-like configuration. The carbon nanotube units each have a cylindrical graphite sheet with a nanometer-sized diameter and an sp2 bonding structure. Depending on the curved angle and structure of the graphite sheet, the bundled carbon nanotubes can exhibit conductive or semiconductive properties. Compared to entangled carbon nanotubes, the bundled carbon nanotubes can be more uniformly dispersed during negative electrode fabrication, smoothly forming a conductive network within the negative electrode and improving the conductivity of the negative electrode.

[0093] In one embodiment of the present application, there is provided a negative electrode composition, wherein the negative electrode conductive material is contained in an amount of 1 part by weight or more and 20 parts by weight or less, based on 100 parts by weight of the negative electrode composition.

[0094] In another embodiment, the negative electrode conductive material may be 1 part by weight or more and 20 parts by weight or less, preferably 3 parts by weight or more and 15 parts by weight or less, more preferably 5 parts by weight or more and 15 parts by weight or less, and most preferably 8 parts by weight or more and 13 parts by weight or less, based on 100 parts by weight of the negative electrode composition.

[0095] The negative electrode conductive material according to the present application has a structure that is completely different from the positive electrode conductive material used in the positive electrode. That is, the negative electrode conductive material according to the present application serves to form a contact between the silicon-based active materials, which undergo a very large volume expansion of the electrode upon charge and discharge, while the positive electrode conductive material serves to act as a buffer during rolling and to impart some conductivity, and therefore has a structure and role that are completely different from the negative electrode conductive material of the present invention.

[0096] Furthermore, the negative electrode conductive material according to the present application is applied to a silicon-based active material and has a completely different structure from conductive materials applied to graphite-based active materials. That is, conductive materials used in electrodes having graphite-based active materials simply have smaller particles than the active material, and therefore have the properties of improving output characteristics and imparting some conductivity, and are completely different in structure and role from negative electrode conductive materials applied together with silicon-based active materials as in the present invention.

[0097] In one embodiment of the present application, the sheet-like conductive material used as the 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. Specifically, the carbon-based active material used as the negative electrode active material may be artificial graphite or natural graphite, and refers to a material that is processed into a spherical or dotted shape to facilitate the storage and release of lithium ions.

[0098] In contrast, the sheet-like conductive material used as the negative electrode conductive material is a material having a sheet or plate shape and can be expressed as plate-like graphite. That is, it is a material contained in the negative electrode active material layer to maintain a conductive path, and does not play a role in storing and releasing lithium, but refers to a material that ensures a conductive path in a sheet shape inside the negative electrode active material layer.

[0099] That is, in this application, the term "platy graphite is used as a conductive material" means that it is processed into a sheet or plate shape and used as a material to ensure a conductive path rather than to store or release lithium. In this case, the negative electrode active material contained therein has high capacity characteristics for storing and releasing lithium, and serves to store and release all lithium ions transferred from the positive electrode.

[0100] In contrast, in the present application, the term "carbon-based active material is used as an active material" means that the carbon-based active material is processed into a dotted or spherical shape and used as a material that stores or releases lithium.

[0101] That is, in one embodiment of the present application, the carbon-based active material, artificial graphite or natural graphite, is dot-shaped and has a BET specific surface area of ​​0.1 m 2 / g or more 4.5m 2 The sheet-shaped conductive material, plate-shaped graphite, may be in the form of a sheet and have a BET specific surface area of ​​5 m 2 / g or more.

[0102] In one embodiment of the present application, the negative electrode binder may include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and substances in which hydrogen is substituted with Li, Na, Ca, or the like, or may include various copolymers thereof.

[0103] In one embodiment of the present application, there is provided a negative electrode composition, wherein the negative electrode binder includes a water-based binder, and the water-based binder includes one or more selected from the group consisting of polyacrylic acid (PAA) and polyacrylamide (PAM).

[0104] The negative electrode binder according to one embodiment of the present application plays a role in holding the active material and the conductive material together to prevent distortion and structural deformation of the negative electrode structure when the volume of the silicon-based active material expands and relaxes. As long as the binder fulfills the above role, any common binder can be used. Specifically, a water-based binder may be used, and more specifically, a PAM-based binder may be used.

[0105] In one embodiment of the present application, the amount of the negative electrode binder may be 30 parts by weight or less, preferably 25 parts by weight or less, and more preferably 20 parts by weight or less, based on 100 parts by weight of the negative electrode composition, or may be 5 parts by weight or more, or 10 parts by weight or more.

[0106] One embodiment of the present application provides a negative electrode for a lithium secondary battery, comprising: a negative electrode current collector layer; and a negative electrode active material layer formed on one or both surfaces of the negative electrode current collector layer, the negative electrode composition according to the present application or a cured product thereof.

[0107] 1 is a diagram showing the laminated structure of a negative electrode for a lithium secondary battery according to one embodiment of the present application. Specifically, a negative electrode for a lithium secondary battery 100 can be seen, which includes a negative electrode active material layer 20 on one side of a negative electrode current collector layer 10. While FIG. 1 shows the negative electrode active material layer formed on one side, it may be formed on both sides of the negative electrode current collector layer.

[0108] In one embodiment of the present application, the negative electrode for a lithium secondary battery may be formed by applying a negative electrode slurry containing the negative electrode composition to one or both surfaces of a negative electrode current collector layer and drying the applied slurry.

[0109] In this case, the negative electrode slurry may include the above-described negative electrode composition and a slurry solvent.

[0110] In one embodiment of the present application, the solid content of the negative electrode slurry may be 5% or more and 40% or less.

[0111] In another embodiment, the solid content of the negative electrode slurry may be in the range of 5% to 40%, preferably 7% to 35%, more preferably 10% to 30%.

[0112] The solid content of the negative electrode slurry refers to the content of the negative electrode composition contained in the negative electrode slurry, and may refer to the content of the negative electrode composition based on 100 parts by weight of the negative electrode slurry.

[0113] When the solid content of the negative electrode slurry satisfies the above range, the viscosity during the formation of the negative electrode active material layer is suitable, and particle aggregation of the negative electrode composition is minimized, thereby enabling the negative electrode active material layer to be efficiently formed.

[0114] In one embodiment of the present application, the slurry solvent can be any solvent that can dissolve the negative electrode composition, and specifically, water or NMP may be used.

[0115] In one embodiment of the present application, the negative electrode current collector layer generally has a thickness of 1 μm to 100 μm. Such a negative electrode current collector layer is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, or an aluminum-cadmium alloy may be used. Furthermore, the surface may be formed with fine irregularities to strengthen the binding force of the negative electrode active material, and the negative electrode current collector layer may be used in various forms such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0116] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, 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.

[0117] However, the thickness may vary depending on the type and application of the negative electrode used, and is not limited thereto.

[0118] In one embodiment of the present application, the porosity of the negative electrode active material layer may be in the range of 10% or more and 60% or less.

[0119] In another embodiment, the porosity of the negative electrode active material layer may be in the range of 10% or more and 60% or less, preferably 20% or more and 50% or less, and more preferably 30% or more and 45% or less.

[0120] The porosity varies depending on the composition and content of the silicon-based active material, conductive material, and binder contained in the negative electrode active material layer. In particular, the silicon-based active material and conductive material according to the present application are contained in a specific composition and content, thereby satisfying the above range, and the electrode is characterized by having an appropriate range of electrical conductivity and resistance.

[0121] One embodiment of the present application provides a lithium secondary battery including: a positive electrode; a negative electrode for a lithium secondary battery according to the present application; a separator disposed between the positive electrode and the negative electrode; and an electrolyte.

[0122] 2 is a diagram showing a laminated structure of a lithium secondary battery according to one embodiment of the present application. Specifically, a lithium secondary battery anode 100 including an anode active material layer 20 on one side of an anode current collector layer 10 can be seen, and a lithium secondary battery cathode 200 including a cathode active material layer 40 on one side of a cathode current collector layer 50 can be seen, and the lithium secondary battery anode 100 and lithium secondary battery cathode 200 are shown stacked with a separator 30 interposed therebetween.

[0123] A secondary battery according to an embodiment of the present specification may include, in particular, the negative electrode for a lithium secondary battery 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, and the negative electrode is the same as the negative electrode described above. Since the negative electrode has been described above, detailed description thereof will be omitted.

[0124] The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and including the positive electrode active material.

[0125] The positive electrode current collector in the positive electrode is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like may be used. The positive electrode current collector may typically have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesive strength of the positive electrode active material. The positive electrode current collector may be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0126] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the 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; a lithium iron oxide such as LiFe3O4; 1+c1 Mn 2-c1 O4 (0≦c1≦0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, and Cu2V2O7; chemical formula LiNi 1-c2 M c2 Ni-site type lithium nickel oxide represented by the chemical formula LiMnO2 (wherein M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and 0.01≦c2≦0.3 is satisfied); 2-c3 M c3Examples of the lithium manganese composite oxides include, but are not limited to, lithium manganese composite oxides represented by Li2Mn3MO8 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 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 part of the Li in the chemical formula is substituted with an alkaline earth metal ion. The positive electrode may be Li metal.

[0127] The positive electrode active material layer may contain a positive electrode conductive material and a positive electrode binder in addition to the above-described positive electrode active material.

[0128] In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and can be any material that has electronic conductivity without causing chemical changes in the battery that is constructed. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. These may be used alone or in combination of two or more.

[0129] The positive electrode binder improves adhesion between positive electrode active material particles and between the positive electrode active material and the positive electrode current collector. Specific examples of the positive electrode binder include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These binders may be used singly or in combination.

[0130] The separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator typically used in secondary batteries can be used without particular limitation. It is particularly preferable that the separator exhibits low resistance to electrolyte ion migration and excellent electrolyte humidification. Specifically, porous polymer films, such as those made from polyolefin polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof, may be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymeric material may be used, and may be selectively used as a single-layer or multi-layer structure.

[0131] Examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in manufacturing lithium secondary batteries.

[0132] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0133] Examples of the non-aqueous organic solvent that can be used include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0134] In particular, among the carbonate organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, can be preferably used as high-viscosity organic solvents, because they have a high dielectric constant and dissociate lithium salts well. When such cyclic carbonates are mixed with linear carbonates having low viscosity and low dielectric constants, such as dimethyl carbonate and diethyl carbonate, in an appropriate ratio, an electrolyte having high electrical conductivity can be prepared, and therefore such cyclic carbonates can be more preferably used.

[0135] The metal salt may be a lithium salt, which is a substance that is easily dissolved in the non-aqueous electrolyte. For example, the anion of the lithium salt may be F - , Cl - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2- , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - , and (CF3CF2SO2)2N - One or more selected from the group consisting of:

[0136] In addition to the constituent components of the electrolyte, the electrolyte may further include one or more additives, such as a haloalkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinoneimine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride, in order to improve the life characteristics of the battery, suppress a decrease in battery capacity, and improve the discharge capacity of the battery.

[0137] According to one embodiment of the present invention, there is provided a battery module including the secondary battery as a unit cell, and a battery pack including the same. The battery module and the battery pack include the secondary battery having high capacity, high rate characteristics, and high cycle characteristics, and therefore can be used as a power source for medium- to large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0138] Below, preferred examples are presented to help understand the present invention. However, the following examples are merely for the purpose of illustrating the present description, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope and technical spirit of the present description, and it is natural that such changes and modifications fall within the scope of the appended claims. [Example]

[0139] <Production example> <Production of negative electrodes> A negative electrode slurry was prepared by adding Si as a silicon-based active material, carbon black C as a dot-like conductive material, and polyacrylamide as a binder in a weight ratio of 80:10:10 to distilled water as a solvent for forming a negative electrode slurry (solid concentration 25 wt%).

[0140] As a specific mixing method, the dot-like conductive material, binder, and water were dispersed using a homomixer at 2500 rpm for 30 minutes, and then the silicon-based active material was added, followed by dispersion at 2500 rpm for 30 minutes to prepare a negative electrode slurry.

[0141] The negative electrode current collector layer was made of a copper current collector (thickness: 8 μm) and the negative electrode slurry was applied to both sides of the copper current collector at a rate of 85 mg / 25 cm. 2 The coated layer was rolled and dried in a vacuum oven at 130°C for 10 hours to form a negative electrode active material layer (thickness: 33 μm), which was used as a negative electrode (negative electrode thickness: 41 μm, negative electrode porosity: 40.0%).

[0142] In this case, the median particle size of the silicon-based active material and the median particle size of the dot-like conductive material satisfy the ranges in Table 1 below.

[0143] [Table 1]

[0144] In Table 1, the median particle size of the silicon-based active material and the median particle size of the dot-like conductive material can be adjusted to the above ranges by classification. Specifically, the median particle size in Table 1 was adjusted by adjusting the grinding time, deposition time, and temperature before classification.

[0145] <Comparative Example 6> A negative electrode was prepared in the same manner as in Example 1, except that carbon black C as the dot-like conductive material was replaced with carbon black C:carbon nanotubes as the linear conductive material in a weight ratio of 7:3.

[0146] <Comparative Example 7> A negative electrode was prepared in the same manner as in Example 1, except that carbon black C was used as the dot-like conductive material in place of carbon black C in Example 1, and carbon nanotubes were used as the linear conductive material in a weight ratio of 5:5.

[0147] <Comparative Example 8> A negative electrode was prepared in the same manner as in Example 1, except that carbon black C was used as the dot-like conductive material in place of carbon black C:carbon nanotubes as the linear conductive material in a weight ratio of 3:7.

[0148] <Comparative Example 9> A negative electrode was prepared in the same manner as in Example 1, except that carbon nanotubes were used as the linear conductive material instead of carbon black C as the dot-like conductive material.

[0149] <Secondary battery manufacturing> LiNi as the positive electrode active material 0.6 Co 0.2 Mn 0.2O2 (average particle size (D50): 15 μm), carbon black (product name: Super C65, manufacturer: Timcal) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were added in a weight ratio of 97:1.5:1.5 to N-methyl-2-pyrrolidone (NMP) as a solvent for forming a positive electrode slurry to prepare a positive electrode slurry (solid concentration: 78 wt%).

[0150] The positive electrode slurry was applied to both sides of an aluminum current collector (thickness: 12 μm) at a rate of 537 mg / 25 cm. 2 The coated layer was rolled and dried in a vacuum oven at 130°C for 10 hours to form a positive electrode active material layer (thickness: 65 μm) to prepare a positive electrode (thickness: 77 μm, porosity: 26%).

[0151] A polyethylene separator was interposed between the positive electrode and the negative electrode of each of the examples and comparative examples, and an electrolyte was injected into the separator to prepare a lithium secondary battery.

[0152] The electrolyte was an organic solvent made by mixing fluoroethylene carbonate (FEC) and diethyl carbonate (DMC) in a volume ratio of 10:90, to which 3 wt % vinylene carbonate was added based on the total weight of the electrolyte, and LiPF6 was added as a lithium salt at a concentration of 1M.

[0153] <Experimental Example> Experimental Example 1: Lifetime performance results of mono-cell The secondary batteries including the negative electrodes prepared in the Examples and Comparative Examples were subjected to a lifespan evaluation using an electrochemical charger / discharger to evaluate the capacity retention. The secondary batteries were subjected to an in-situ cycle test at 4.2-3.0 V, 1 C / 0.5 C, and the capacity retention was measured every 50 cycles by charging / discharging at 0.33 C / 0.33 C (4.2-3.0 V). The results are shown in Table 2.

[0154] Lifetime retention rate (%) = {(discharge capacity at Nth cycle) / (discharge capacity at first cycle)} × 100

[0155] [Table 2]

[0156] Experimental example 2: Resistance change of a mono cell In Experimental Example 1, the capacity retention rate was measured by charging / discharging at 0.33C / 0.33C (4.2-3.0V) every 50 cycles during the test, and then the resistance was measured by discharging at 2.5C pulse at SOC50, and the resistance increase rate was compared and analyzed.

[0157] The data at 200 cycles for each of the resistance increase rates were calculated, and the results are shown in Table 3 below.

[0158] [Table 3]

[0159] Experimental Example 3: Change in pore resistance within the electrode To analyze the Li-ion diffusion resistance of the negative electrodes of Example 1 and Comparative Examples 6 to 8 without considering the effect of charge transfer, a coin symmetry cell was fabricated using two negative electrodes and EIS measurements were performed. The frequency-dependent impedance data obtained from the measurements was fitted, and the liquid diffusion resistance was compared and analyzed. The measurement results for the Li-ion diffusion resistance in the electrodes are shown in Table 4 below.

[0160] [Table 4]

[0161] As can be seen from Tables 2 and 3, the life retention rate and resistance increase rate of the examples were confirmed to be superior to those of the comparative examples by maintaining the median particle size of the silicon-based active material at a micron size, including a dot-like conductive material as the negative electrode conductive material in order to solve the problems of uniform dispersion and the coating state of the electrode, and optimizing the median particle size of the dot-like conductive material relative to the median particle size of the silicon-based active material.

[0162] Specifically, as can be seen from Comparative Examples 1, 2, and 5, even if the median particle size of the silicon-based active material satisfies the range of the present application, if the median particle size of the point-like conductive material is outside the range and does not satisfy the particle size relationship, the life retention rate and resistance increase rate are inferior to those of the Examples.When the results of Comparative Examples 3 and 4 were examined, it was confirmed that even if the median particle size of the point-like conductive material is at the same level as that of the Examples, if the median particle size of the silicon-based active material is outside the range and does not satisfy the particle size relationship, the life retention rate and resistance increase rate are inferior to those of the Examples.

[0163] For reference, in the case of Example 4, the particle size relationship between the dot-like conductive material and the silicon-based active material is satisfied, but the particle size of the dot-like conductive material is partially increased, and although there is no inferiority in performance in terms of life performance and resistance increase rate compared to other Examples, there is a possibility that it may be partially inferior to other Examples in terms of design, such as energy density and electrode thickness. However, even in this case, it has the characteristic of being superior in terms of life and resistance compared to the other Comparative Examples 1 to 5.

[0164] In addition, conventionally, linear or sheet-shaped conductive materials have been used primarily in anodes using silicon-based active materials. However, with linear conductive materials, the pores in the anode tend to become clogged as the amount of conductive material increases, leading to increased pore resistance and performance issues. While sheet-shaped conductive materials themselves can form surface contact, rolling the anode can impair the ion migration path. In other words, the role of anode conductive materials is to create contact points between particles to enable conductivity, but if they clog the pore structure within the electrode and impede the ion migration path in the electrolyte, resistance increases.

[0165] To confirm this, the change in pore resistance in Experimental Example 3 was measured, and the results can be seen in Table 4. Specifically, in Comparative Examples 6 to 9, dot-like conductive materials and linear conductive materials were used. Comparing Comparative Examples 6 to 9, it was confirmed that as the amount of linear conductive materials increased, the tendency for the pores in the negative electrode to become blocked increased, resulting in an increase in pore resistance. Furthermore, when the negative electrode of Example 1 was used, it was confirmed that the pore resistance was maintained low by not including linear conductive materials but using specific dot-like conductive materials.

[0166] This can also be confirmed from Figure 5. Compared to Figure 4, Figure 5 uses linear and / or sheet-like conductive materials, which make it difficult to ensure voids within the electrode, and side reactions during charge / discharge clog pores in the electrode, blocking the lithium ion migration path, increasing resistance and leading to a decrease in cell performance. Therefore, the present application includes dot-like conductive materials as in the above examples, which, as can be seen from Figure 4, makes it easy to ensure ion migration paths and provides superior effects compared to the use of linear or sheet-like conductive materials. [Explanation of symbols]

[0167] 10 Negative electrode current collector layer 20...Negative electrode active material layer 30 Separator 40...Cathode active material layer 50 Positive electrode current collector layer 100 ···Negative electrode for lithium secondary battery 200 ···Positive electrode for lithium secondary battery 1. Silicon-based active materials 2. Conductive dots 3. Wire or sheet conductive material 4. Lithium-ion pathway

Claims

1. A negative electrode composition comprising: a silicon-based active material; a negative electrode conductive material; and a negative electrode binder, The silicon-based active material is Si, SiO ｘ (0<x≦2), and metal impurities, and the silicon-based active material contains 90 parts by weight or more of Si based on 100 parts by weight of the silicon-based active material; the negative electrode conductive material includes dot-like conductive material, a median particle size of the negative electrode conductive material is 30% to 60% of a median particle size of the silicon-based active material;

2. The negative electrode composition according to claim 1 , wherein the dot-like conductive material is included in an amount of 95 parts by weight or more based on 100 parts by weight of the negative electrode conductive material.

3. The negative electrode composition according to claim 1 , wherein the silicon-based active material has a median particle size of 1.5 μm or more and 15 μm or less.

4. The negative electrode composition according to claim 1 , wherein the median particle size of the negative electrode conductive material is 0.45 μm or more and 9 μm or less.

5. The negative electrode composition according to claim 1 , wherein the negative electrode conductive material having a median particle size of 1 μm or less is included in an amount of 5 parts by weight or less based on 100 parts by weight of the negative electrode conductive material.

6. The negative electrode composition according to claim 1, wherein the sphericity of the dot-like conductive material is represented by the following formula 1: [Formula 1] 0.7≦X1 / Y1≦0.96 In the formula 1, X1 is the area of ​​the orthogonal projection of the point-like conductive material, Y1 means the area of ​​a circle having the same perimeter as the orthogonal projection of the point-like conductive material.

7. 2. The negative electrode composition according to claim 1, wherein the dot-like conductive material comprises at least one material selected from the group consisting of carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives.

8. the negative electrode binder includes an aqueous binder, 2. The negative electrode composition of claim 1, wherein the aqueous binder comprises one or more selected from the group consisting of polyacrylic acid (PAA) and polyacrylamide (PAM).

9. The negative electrode composition according to claim 1 , wherein the silicon-based active material is present in an amount of 40 parts by weight or more based on 100 parts by weight of the negative electrode composition.

10. The negative electrode composition according to claim 1 , wherein the negative electrode conductive material is present in an amount of 1 part by weight to 20 parts by weight based on 100 parts by weight of the negative electrode composition.

11. a negative electrode current collector layer; and a negative electrode active material layer provided on one or both surfaces of the negative electrode current collector layer, The negative electrode active material layer comprises the negative electrode composition according to any one of claims 1 to 10 or a cured product thereof.

12. the negative electrode current collector layer has a thickness of 1 μm or more and 100 μm or less, 12. The negative electrode for a lithium secondary battery according to claim 11, wherein the thickness of the negative electrode active material layer is 5 μm or more and 500 μm or less.

13. positive electrode; The negative electrode for a lithium secondary battery according to claim 11; a separator disposed between the positive electrode and the negative electrode; and electrolyte A lithium secondary battery comprising:

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