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

Abstract

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

Description

TECHNICAL FIELD

[0001] This application claims priority to and the benefit of Korean Patent Application No. 10-2023-0141157, filed on October 20, 2023, in the Korean Intellectual Property Office, the entire contents of which are incorporated herein by reference.

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

[0003] Due to the rapid increase in the use of fossil fuels, the demand for the use of alternative or clean energy is increasing, and as part of this trend, the most active research field is the field of power generation and power storage using electrochemical reactions.

[0004] Currently, a secondary battery is a representative example of an electrochemical device using such electrochemical energy, and the specific use field thereof tends to gradually expand.

[0005] As technology development and demand for mobile devices increase, the demand for secondary batteries as energy sources is rapidly increasing. Among such secondary batteries, lithium secondary batteries having high energy density and voltage, long cycle life, and low self-discharge rate have been commercialized and are widely used. In addition, research is actively being conducted on a manufacturing method for a high-density electrode having higher energy density per unit volume as an electrode for such high-capacity lithium secondary batteries.

[0006] In general, a secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode includes a negative active material for intercalating and deintercalating lithium ions from the positive electrode, and a silicon-based particle having high discharge capacity can be used as the negative active material.

[0007] In particular, due to the demand for high-density energy batteries in recent years, research is being actively conducted on a method of increasing capacity by simultaneously using a silicon-based compound such as Si / C and SiOx having a capacity of 10 times or more than that of a graphite-based material as a negative active material. However, compared to graphite, which is commonly used, a silicon-based compound as a high-capacity material has a large capacity, but undergoes rapid volume expansion during charging, thereby causing the conductive path to be disconnected, thereby deteriorating the battery characteristics.

[0008] Therefore, in order to solve the problems that occur when a silicon-based compound is used as a negative electrode active material, methods of suppressing the volume expansion itself, such as a method of adjusting the driving potential, a method of additionally further coating a thin film on the active material layer, and a method of adjusting the particle diameter of the silicon-based compound, or various methods for preventing the disconnection of the conductive path, have been discussed. However, such methods can deteriorate the battery performance, whereby its application is limited, and thus there are still limitations in the commercialization of the manufacture of a battery including a negative electrode having a high content of a silicon-based compound.

[0009] Further, when a negative electrode is manufactured using a silicon-based active material, it is important that the negative electrode hole structure is simple, and it is known that increasing the particle size of the silicon-based active material contained is advantageous for this purpose. However, the silicon-based active material undergoes significant swelling during charge and discharge due to its characteristics, and it has been confirmed through research that, as the particle size increases, the displacement caused by the volume change becomes greater, and the contact surface with the negative electrode current collector layer decreases, thereby causing the electrode to be detached.

[0010] In order to overcome the above problems, when a silicon-based active material of a small particle size is applied, it has been confirmed that the problem of electrode detachment can be solved, but since the particle size is small, the reaction is concentrated on the electrode surface, thereby causing a problem of long-term life.

[0011] Therefore, there is a need to research a silicon-based active material layer that can simplify the negative electrode hole structure, prevent the volume expansion of the silicon-based compound from causing damage to the conductive path, and maximize the life characteristics even when the silicon-based compound is used as an active material to improve the capacity performance.

[0012] Prior Art Documents

[0013] Japanese Patent Application Publication No. 2009-080971 SUMMARY

[0014] TECHNICAL PROBLEM

[0015] As described above, a silicon-based active material has excellent capacity characteristics, and thus its application as a negative electrode is being discussed. However, the use thereof is limited due to the complex negative electrode hole structure caused by the size of the silicon-based active material itself and problems such as volume expansion during charge and discharge. However, it has been confirmed that, even when the silicon-based active material is applied to the negative electrode, by adjusting the median particle size (D50) of the silicon-based active material and mixing the silicon-based active material after the adjustment of the median particle size at a specific ratio, it is possible to simplify the negative electrode hole structure, to prevent the electrode from being detached due to charge and discharge, and to ensure the life characteristics.

[0016] Therefore, the present application is directed to providing a negative electrode active material having the above-described characteristics, a negative electrode for a lithium secondary battery, and a lithium secondary battery including the negative electrode.

[0017] Technical Solution

[0018] One example embodiment of the present specification provides a negative electrode active material including a silicon-based active material, wherein the silicon-based active material includes a first silicon-based active material having an average particle diameter (D50) of 2 μm or more and 5 μm or less and a second silicon-based active material having an average particle diameter (D50) of 10 μm or more and 20 μm or less, and a weight ratio of the first silicon-based active material to the second silicon-based active material is 20:80 to 80:20.

[0019] Another example embodiment provides a negative electrode for a lithium secondary battery, the negative electrode for a lithium secondary battery including: a negative electrode current collector layer; and a negative electrode active material layer disposed on one surface or both surfaces of the negative electrode current collector layer, wherein the negative electrode active material layer includes a negative electrode active material layer composition including a negative electrode active material according to the present application, a negative electrode conductive material, and a negative electrode binder.

[0020] Another example embodiment 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.

[0021] Advantageous Effects

[0022] The negative electrode active material according to one example embodiment of the present application uses a silicon-based active material as a high-capacity material to manufacture a high-capacity battery. In this case, the silicon-based active material is configured to have an adjusted average particle diameter (D50), wherein the silicon-based active material includes a first silicon-based active material having an average particle diameter (D50) of 2 μm or more and 5 μm or less and a second silicon-based active material having an average particle diameter (D50) of 10 μm or more and 20 μm or less, and a weight ratio of the first silicon-based active material to the second silicon-based active material is 20:80 to 80:20.

[0023] That is, the first silicon-based active material having a smaller average particle diameter and the second silicon-based active material having a larger average particle diameter are mixed in a specific ratio, and in particular, the ratio between the active materials having different average particle diameters is adjusted to 20% or more. When the adjustment is made as described above, the volume expansion of the active material can be reduced even during charge and discharge, thereby preventing the electrode from being detached, simplifying the pore structure of the electrode, and thus reducing the negative electrode resistance.

[0024] Accordingly, the present application adjusts the proportion in the negative active material layer according to the average particle diameter of the silicon-based active material. With the above-described feature, the present application can maintain high capacity characteristics, which are advantages of a negative electrode containing a silicon-based active material, while preventing electrode detachment and an increase in resistance, thereby enhancing life characteristics. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is a view showing a stack structure of a negative electrode for a lithium secondary battery according to one example embodiment of the present application.

[0026] Figure 2 is a view showing a stack structure of a lithium secondary battery according to one example embodiment of the present application.

[0027] REFERENCE NUMERALS AND SYMBOLS

[0028] 10: negative current collector layer

[0029] 20: negative active material layer

[0030] 30: separator

[0031] 40: positive active material layer

[0032] 50: positive current collector layer

[0033] 100: negative electrode for a lithium secondary battery

[0034] 200: positive electrode for a lithium secondary battery DETAILED DESCRIPTION

[0035] Before describing the present application, some terms are defined first.

[0036] When a part of the present specification "comprises", "contains" or "has" a constituent element, unless otherwise specifically stated, this does not mean that other constituent elements are excluded, but that other constituent elements can be further included.

[0037] In the present specification, "p to q" means a range of "p or more and q or less".

[0038] In the present specification, "specific surface area" is measured by the BET method, specifically, is calculated from the amount of nitrogen adsorption at a liquid nitrogen temperature (77 K) by using a BELSORP-mini II available from BEL Japan, Inc. That is, in the present application, the BET specific surface area can mean a specific surface area measured by the above-described measurement method.

[0039] In the present specification, "Dn" means a particle size distribution, and means a particle size at an n% point in a particle number cumulative distribution according to particle size. That is, D50 is a particle size at a 50% point in a particle number cumulative distribution according to particle size (average particle size, central particle size), D90 is a particle size at a 90% point in a particle number cumulative distribution according to particle size, and D10 is a particle size at a 10% point in a particle number cumulative distribution according to particle size. Note that the particle size distribution can be determined using a laser diffraction method. Specifically, after a powder to be measured is dispersed in a dispersion medium, the resulting dispersion is introduced into a commercially available laser diffraction particle size measuring apparatus (for example, Microtrac S3500), in which a difference in diffraction pattern according to particle size is measured when a laser beam passes through a particle, and then a particle size distribution is calculated.

[0040] In the present specification, the description that "a polymer contains a certain monomer as a monomer unit" means that the monomer participates in a polymerization reaction and is contained as a repeating unit in the polymer. In the present specification, when a polymer contains a monomer, this is interpreted to be the same as when the polymer contains the monomer as a monomer unit.

[0041] In the present specification, the term "polymer" is understood in a broad sense including copolymers, unless otherwise indicated as "homopolymer".

[0042] In the present specification, weight average molecular weight (Mw) and number average molecular weight (Mn) are polystyrene converted molecular weights measured by gel permeation chromatography (GPC) while using a commercially available monodisperse polystyrene polymer having different polymerization degrees (standard sample) for measuring molecular weight as a standard material. In the present specification, unless otherwise specifically described, the molecular weight means weight average molecular weight.

[0043] Hereinafter, exemplary embodiments of the present application will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily practice the present application. However, the present application can be implemented in various different forms and is not limited to the following description.

[0044] The negative active material according to one exemplary embodiment of the present application is manufactured using a silicon-based active material as a high capacity material to manufacture a high capacity battery. In this case, the silicon-based active material is configured to have an adjusted average particle size (D50), and the silicon-based active material contains a first silicon-based active material having an average particle size (D50) of 2 μm or more and 5 μm or less and a second silicon-based active material having an average particle size (D50) of 10 μm or more and 20 μm or less, and a weight ratio of the first silicon-based active material to the second silicon-based active material is 20:80 to 80:20.

[0045] The present application adjusts the ratio in the negative active material layer according to the average particle diameter of the silicon-based active material. With the above feature, the present application aims to prevent electrode detachment while maintaining high capacity characteristics, which are advantages of a negative electrode containing the silicon-based active material, thereby enhancing the life characteristics.

[0046] Figure 1 is a view showing a stack structure of a negative electrode for a lithium secondary battery according to one example embodiment of the present application. Specifically, a negative electrode 100 for a lithium secondary battery, which includes a negative active material layer 20 on one surface of a negative current collector layer 10, can be seen. Figure 1 The negative active material layer is shown as being formed on one surface of the negative current collector layer, but can also be formed on both surfaces of the negative current collector layer.

[0047] In one example embodiment of the present application, a negative electrode for a lithium secondary battery is provided, in which the first silicon-based active material and the second silicon-based active material include one or more selected from the group consisting of SiO x (x = 0), SiO x (0 < x < 2), SiC, and Si alloy.

[0048] In one example embodiment of the present application, the first silicon-based active material can include one or more selected from the group consisting of SiO x (x = 0) and SiO x (0 < x < 2), and the content of the SiOx (x = 0) can be 70 parts by weight or more, based on 100 parts by weight of the first silicon-based active material.

[0049] In one example embodiment of the present application, the first silicon-based active material can include SiO x (x = 0), and the content of the SiO x (x = 0) can be 70 parts by weight or more, based on 100 parts by weight of the first silicon-based active material.

[0050] In another example embodiment, the content of the SiO x (x = 0) can be 70 parts by weight or more, preferably 80 parts by weight or more, more preferably 90 parts by weight or more, and can be 100 parts by weight or less, preferably 99 parts by weight or less, more preferably 95 parts by weight or less, based on 100 parts by weight of the first silicon-based active material.

[0051] In one exemplary embodiment of the present application, the first silicon-based active material can particularly use pure silicon (Si) as the silicon-based active material. Using pure silicon (Si) particles as the silicon-based active material can mean that the content of pure silicon-based particles (SiO x (x=0)) is within a certain range.

[0052] In one exemplary embodiment of the present application, the first silicon-based active material can be made of silicon-based particles having 100 parts by weight of SiO x (x=0).

[0053] In one exemplary embodiment of the present application, the second silicon-based active material can include one or more selected from the group consisting of SiO x (x=0) and SiO x (0

[0054] In one exemplary embodiment of the present application, the second silicon-based active material can include SiO x (x=0), and the content of SiO x (x=0) can be 70 parts by weight or more, based on 100 parts by weight of the second silicon-based active material.

[0055] In another exemplary embodiment, the content of SiO x (x=0) can be 70 parts by weight or more, preferably 80 parts by weight or more, more preferably 90 parts by weight or more, and can be 100 parts by weight or less, preferably 99 parts by weight or less, more preferably 95 parts by weight or less, based on 100 parts by weight of the second silicon-based active material.

[0056] In one exemplary embodiment of the present application, the second silicon-based active material can particularly use pure silicon (Si) as the silicon-based active material. Using pure silicon (Si) particles as the silicon-based active material can mean that the content of pure silicon-based particles (SiO x (x=0) is within a certain range.

[0057] In one exemplary embodiment of the present application, the second silicon-based active material can be made of silicon-based particles having 100 parts by weight of SiO x (x=0).

[0058] The capacity of silicon-based active materials is significantly higher than that of graphite-based active materials, which are commonly used, and thus attempts have been made to apply them. However, silicon-based active materials have a high volume expansion rate during charge and discharge, and thus, for example, only a small amount of them is mixed with graphite-based active materials and used.

[0059] Accordingly, the present application solves the above problems by adjusting the ratio according to the average particle diameter of the silicon-based active material itself, rather than adjusting the composition of the conductive material and the binder, while improving the capacity performance using only silicon-based active materials as the negative electrode active material, thereby solving the existing problems.

[0060] In one exemplary embodiment of the present application, the silicon-based active material includes silicon-based particles having a particle size distribution of 0.01 μm or more and 30 μm or less.

[0061] The fact that the silicon-based active material includes silicon-based particles having a particle size distribution of 0.01 μm or more and 30 μm or less means that it includes a plurality of individual silicon-based particles having a particle size within a specific range, and in this case, the number of silicon-based particles included is not limited.

[0062] The silicon-based active material includes silicon-based particles having a particle size distribution of 0.01 μm or more and 30 μm or less, and the silicon-based active material includes a first silicon-based active material having an average particle diameter (D50) of 2 μm or more and 5 μm or less and a second silicon-based active material having an average particle diameter (D50) of 10 μm or more and 20 μm or less.

[0063] That is, the silicon-based active material can include various silicon-based particles having a particle size distribution of 0.01 μm or more and 30 μm or less, and in this case, the first silicon-based active material can include silicon-based particles having an average particle diameter (D50) of 2 μm or more and 5 μm or less, and the second silicon-based active material can include silicon-based particles having an average particle diameter (D50) of 10 μm or more and 20 μm or less.

[0064] When the particles are spherical, the particle size of the silicon-based active material can be represented by the diameter thereof. Even if the shape of the particles is not a spherical shape, the particle size can be measured in comparison with the case of a spherical shape. In general, the particle sizes of individual silicon-based particles can each be measured by a method commonly used in the art.

[0065] The present application provides the negative electrode active material, in which the silicon-based active material includes silicon-based particles having a particle size distribution of 0.01 μm or more and 30 μm or less, and the content of particles having a particle size of less than 2 μm is 5 parts by weight or less based on 100 parts by weight of the silicon-based active material.

[0066] Specifically, the content of particles having a particle size of less than 2 μm can be 5 parts by weight or less, 3 parts by weight or less, and specifically 1 part by weight or less, and can be 0 parts by weight or more, or 0.1 parts by weight or more, based on 100 parts by weight of the silicon-based active material.

[0067] As described above, the silicon-based active material according to the present application does not contain fine particles. If fine particles are contained, the simplification of the negative electrode pore structure cannot be achieved, which becomes a factor contributing to an increase in resistance. Therefore, the silicon-based active material satisfies the above range.

[0068] In an exemplary 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 to 150.0 m 2 / g, more preferably 0.1 to 100.0 m 2 / g, particularly preferably 0.2 to 80.0 m 2 / g, most preferably 0.2 to 18.0 m 2 / g. The BET specific surface area is measured according to DIN 66131 (using nitrogen).

[0069] In one exemplary embodiment of the present application, the silicon-based active material can exist, for example, in a crystalline form or an amorphous form, and is preferably non-porous. The silicon-based active material is preferably a spherical or flaky particle. Alternatively, but not preferably, the silicon-based active material can also have a fibrous structure or exist in the form of a silicon-containing film or coating.

[0070] In one exemplary embodiment of the present application, the content of the negative active material can be 60 parts by weight or more, based on 100 parts by weight of the negative electrode composition.

[0071] In another exemplary embodiment, the content of the negative active material can be 60 parts by weight or more, preferably 65 parts by weight or more, more preferably 70 parts by weight or more, and the content thereof can be 95 parts by weight or less, preferably 90 parts by weight or less, more preferably 85 parts by weight or less, based on 100 parts by weight of the negative electrode composition.

[0072] The negative electrode for lithium secondary batteries according to the present application distributes a silicon-based active material having a specific average particle diameter, which is capable of controlling the volume expansion rate during charge and discharge even when a silicon-based active material having a significantly high capacity is used within a specified range, in the negative electrode. Therefore, the negative electrode has excellent output characteristics when charged and discharged without reducing the performance of the negative electrode even when the content of the silicon-based active material is within the specified range.

[0073] In one exemplary embodiment of the present application, the silicon-based active material can have a non-spherical shape, and its sphericity (circularity) 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.

[0074] In the present application, the sphericity (circularity) is determined by the following Formula 1, in which A is an area, and P is a boundary line.

[0075] [Formula 1]

[0076] 4πA / P 2

[0077] In one exemplary embodiment of the present application, the negative active material is provided, in which the weight ratio of the first silicon-based active material to the second silicon-based active material is 20:80 to 80:20.

[0078] In another exemplary embodiment, the weight ratio of the first silicon-based active material to the second silicon-based active material can be 20 to 80:80 to 20, preferably 30 to 70:70 to 30, and more preferably 35 to 65:65 to 35.

[0079] The silicon-based active material described in the present application includes the first silicon-based active material having an average particle diameter (D50) of 2 μm or more and 5 μm or less, and the second silicon-based active material having an average particle diameter (D50) of 10 μm or more and 20 μm or less, and can satisfy the above weight ratio.

[0080] That is, based on 100 parts by weight of the silicon-based active material, when the content of the first silicon-based active material is 40 parts by weight, the content of the second silicon-based active material can be 60 parts by weight.

[0081] When a silicon-based active material is used to manufacture a negative electrode, it is important that the negative electrode hole structure is simple, and it is known that increasing the particle size of the silicon-based active material contained is advantageous for this purpose. However, the silicon-based active material undergoes significant swelling during charge and discharge due to its characteristics, and it has been confirmed that as the particle size increases, the displacement caused by the volume change becomes greater, and the contact surface with the negative electrode current collector layer decreases, thereby causing electrode detachment. In order to overcome the above problems, when a small particle size silicon-based active material is applied, it has been confirmed that the electrode detachment problem can be solved, but since the particle size is small, the reaction is concentrated on the surface of the electrode, thereby causing a long-term life problem.

[0082] To further solve the above problems, the arrangement of silicon-based active materials having different average particle diameters (D50) is adjusted by arranging a silicon-based active material having a smaller average particle size on the negative electrode current collector layer side and a silicon-based active material having a larger average particle size on the surface. This method aims to enhance the life characteristics while ensuring the capacity characteristics.

[0083] However, even with such a method, it is difficult to coat by the arrangement due to the limitations of the load, and problems such as delamination at the boundary between silicon-based active materials having different average particle diameters also occur.

[0084] Therefore, the present application contains the first silicon-based active material having an average particle diameter (D50) of 2 μm or more and 5 μm or less and the second silicon-based active material having an average particle diameter (D50) of 10 μm or more and 20 μm or less, and the proportion thereof is adjusted to ensure the life characteristics and improve the occlusion phenomenon of the surface particles.

[0085] That is, the first silicon-based active material and the second silicon-based active material having different particle diameters are mixed and applied, and in particular, when the proportion of silicon-based active materials having different particle sizes is adjusted to 20% or more based on the entire silicon-based active material, the life characteristics can be ensured and the occlusion phenomenon of the surface particles can also be improved.

[0086] In one exemplary embodiment of the present application, the negative electrode for a lithium secondary battery is provided, in which the first silicon-based active material has an average particle diameter (D50) of 2 μm or more and 5 μm or less, and the second silicon-based active material has an average particle diameter (D50) of 10 μm or more and 20 μm or less.

[0087] In the present application, the first silicon-based active material can have an average particle diameter (D50) of 2 μm or more and 5 μm or less, preferably 2 μm or more and 4.5 μm or less, more preferably 2.5 μm or more and 4 μm or less.

[0088] In the present application, the second silicon-based active material can have an average particle diameter (D50) of 10 μm or more and 20 μm or less, preferably 10 μm or more and 19 μm or less, more preferably 12 μm or more and 18 μm or less.

[0089] The present application provides a negative electrode for a lithium secondary battery, the negative electrode for a lithium secondary battery comprising: a negative electrode current collector layer; and a negative electrode active material layer disposed on one surface or both surfaces of the negative electrode current collector layer, wherein the negative electrode active material layer comprises a negative electrode active material layer composition comprising a negative electrode active material according to the present application, a negative electrode conductive material, and a negative electrode binder.

[0090] In the related art, generally only a graphite-based compound is used as a negative electrode active material. However, in recent years, as the demand for high-capacity batteries has increased, attempts to mix and use a silicon-based compound in order to increase capacity have increased. However, with a silicon-based compound, even if the properties of the silicon-based active material itself are adjusted as described above, the volume rapidly expands during charge and discharge, thereby destroying the conductive path formed in the negative electrode active material layer.

[0091] Therefore, in one exemplary embodiment of the present application, the negative electrode conductive material can include one or more selected from the group consisting of a point-shaped conductive material, a planar conductive material, and a linear conductive material.

[0092] In one exemplary embodiment of the present application, the point-shaped conductive material refers to a spherical or point-shaped conductive material that can be used to improve the conductivity of the negative electrode, has conductivity without causing a chemical change. Specifically, the point-shaped conductive material can be at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal crack black, conductive fiber, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivative, and in terms of high conductivity and excellent dispersibility, preferably can include carbon black.

[0093] In one exemplary embodiment of the present application, the BET specific surface area of the point-shaped conductive material can be 40 m 2 / g or more and 70 m 2 / g or less, preferably 45 m 2 / g or more and 65 m 2 / g or less, more preferably 50 m 2 / g or more and 60 m 2 / g or less.

[0094] In one exemplary embodiment of the present application, the content of the functional group (volatile matter) of the point-shaped conductive material can fall within a range of 0.01% or more and 1% or less, preferably 0.01% or more and 0.3% or less, more preferably 0.01% or more and 0.1% or less.

[0095] In particular, when the content of the functional group of the point-shaped conductive material falls within the specified range, the functional group is present on the surface of the point-shaped conductive material, so that the point-shaped conductive material can be smoothly dispersed in a solvent when water is used as the solvent.

[0096] In the manufacturing of the point-shaped conductive material, a high functional group content can mean that a large amount of foreign matter is present, a low functional group content can mean that further heat treatment has been performed, and the point-shaped conductive material according to the present application can satisfy the functional group content range by partially heat-treating the point-shaped conductive material so as to satisfy the functional group content within the specified range.

[0097] In one exemplary embodiment of the present application, the particle diameter of the point-shaped conductive material can be 10 nm to 100 nm, preferably 20 nm to 90 nm, and more preferably 20 nm to 60 nm.

[0098] In one exemplary embodiment of the present application, the negative electrode conductive material can include a planar conductive material.

[0099] The planar conductive material refers to a conductive material for improving the conductivity by increasing the surface contact between silicon particles in the negative electrode, while serving to suppress the disconnection of the conductive path due to volume expansion. The planar conductive material can be expressed as a plate-shaped conductive material or a bulk-shaped conductive material.

[0100] In one exemplary embodiment of the present application, the planar conductive material can include at least one selected from the group consisting of plate-shaped graphite, graphene, graphene oxide, and graphite flake, and can be preferably plate-shaped graphite.

[0101] In one exemplary embodiment of the present application, the planar conductive material can have an average particle diameter (D50) of 2 to 7 μm, specifically 3 to 6 μm, and more specifically 4 to 5 μm. When the specified range is satisfied, sufficient particle size results in easy dispersion without causing excessive increase in the viscosity of the negative electrode slurry. Accordingly, the dispersion effect is excellent when dispersion is performed using the same equipment and time.

[0102] In one exemplary embodiment of the present application, the negative electrode composition is provided, in which the planar conductive material has a D10 of 0.5 μm or more and 1.5 μm or less, a D50 of 4.0 μm or more and 5.0 μm or less, and a D90 of 7.0 μm or more and 15.0 μm or less.

[0103] In one exemplary embodiment of the present application, for the planar conductive material, a high specific surface area planar conductive material having a high BET specific surface area, or a low specific surface area planar conductive material can be used.

[0104] In one exemplary embodiment of the present application, for the planar conductive material, a high specific surface area planar conductive material or a low specific surface area planar conductive material can be used without any limitation. However, particularly, the planar conductive material according to the present application can be affected to some extent by the dispersing effect in terms of electrode performance, and therefore it is particularly preferable to use a low specific surface area planar conductive material which does not cause a dispersing problem.

[0105] In one exemplary embodiment of the present application, the BET specific surface area of the planar conductive material can be 5 m 2 / g or more.

[0106] In another exemplary embodiment, the BET specific surface area of the planar conductive material can be 5 m 2 / g or more and 500 m 2 / g or less, preferably 5 m 2 / g or more and 300 m 2 / g or less, more preferably 5 m 2 / g or more and 250 m 2 / g or less.

[0107] In another exemplary embodiment, the planar conductive material is a high specific surface area planar conductive material, and the BET specific surface area can fall within a range of 50 m 2 / g or more and 500 m 2 / g or less, preferably 80 m 2 / g or more and 300 m 2 / g or less, more preferably 100 m 2 / g or more and 300 m 2 / g or less.

[0108] In another exemplary embodiment, the planar conductive material is a low specific surface area planar conductive material, and the BET specific surface area can fall within a range of 5 m 2 / g or more and 40 m 2 / g or less, preferably 5 m 2 / g or more and 30 m 2 / g or less, more preferably 5 m 2 / g or more and 25 m 2 / g or less.

[0109] The other conductive material can include a linear conductive material such as a carbon nanotube. The carbon nanotube can be a bundled carbon nanotube. The bundled carbon nanotube can include a plurality of carbon nanotube units. Specifically, unless otherwise specified, the term "bundled" refers herein to a secondary shape in which a plurality of carbon nanotube units are aligned side by side with substantially the same orientation of longitudinal axes of the carbon nanotube units, or are tangled. The carbon nanotube unit has a cylindrical graphite sheet with a nanoscale diameter, and has an sp2 bonding structure. In this case, depending on the curling angle and structure of the graphite sheet, a conductive material or a semiconductive material can be exhibited. Compared to a tangled carbon nanotube, the bundled carbon nanotube can be more uniformly dispersed during the manufacture of the negative electrode, and can more smoothly form a conductive network in the negative electrode to improve the conductivity of the negative electrode.

[0110] In one exemplary embodiment of the present application, the negative electrode composition is provided, in which the negative electrode conductive material includes a linear conductive material, and the linear conductive material is a carbon nanotube.

[0111] In one exemplary embodiment of the present application, the negative electrode conductive material can include a planar conductive material and a linear conductive material.

[0112] In one exemplary embodiment of the present application, the negative electrode conductive material can include a planar conductive material and a linear conductive material, and the ratio of the planar conductive material to the linear conductive material can satisfy 1:0.01 to 1:0.1.

[0113] In one exemplary embodiment of the present application, the negative electrode composition is provided, in which the content of the negative electrode conductive material is 5 parts by weight or more and 40 parts by weight or less, based on 100 parts by weight of the negative electrode composition.

[0114] In another exemplary embodiment, the content of the negative electrode conductive material can be 5 parts by weight or more and 40 parts by weight or less, preferably 10 parts by weight or more and 30 parts by weight or less, and more preferably 15 parts by weight or more and 25 parts by weight or less, based on 100 parts by weight of the negative electrode composition.

[0115] In one exemplary embodiment of the present application, when the negative electrode conductive material includes the planar conductive material and the linear conductive material and satisfies the above composition and ratio, respectively, the service life characteristics of the existing lithium secondary battery are not significantly affected, and the number of sites at which the battery can be charged and discharged is increased, so that the output characteristics at a high C rate are excellent.

[0116] The negative electrode conductive material according to the present application has a completely different constitution from the conductive material applied to the positive electrode. That is, the negative electrode conductive material according to the present application is used to maintain contact between the silicon-based active material, which has a very large volume expansion due to charge and discharge, and the positive electrode conductive material is used to serve as a buffer at the time of calendering while imparting a certain degree of conductivity, and is completely different in constitution and function from the negative electrode conductive material according to the present application.

[0117] In addition, the negative electrode conductive material according to the present application is applied to a silicon-based active material and has a completely different constitution from the conductive material applied to a graphite-based active material. That is, since the conductive material for an electrode having a graphite-based active material simply has smaller particles than the active material, the conductive material has the characteristics of improving output characteristics and imparting a certain degree of conductivity, and is completely different in constitution and function from the negative electrode conductive material applied with the silicon-based active material in the present application.

[0118] In one exemplary embodiment of the present application, the planar conductive material used as the above-described negative electrode conductive material has a different structure and function from a carbon-based active material generally used as a conventional negative electrode active material. Specifically, the carbon-based active material used as a negative electrode active material can be artificial graphite or natural graphite, and refers to a material processed into a spherical or point-like shape and used to facilitate storage and release of lithium ions.

[0119] On the other hand, the planar conductive material used as the negative electrode conductive material is a material having a planar or plate-like shape, and can be expressed as plate-like graphite. That is, the planar conductive material is a material included to maintain a conductive path in a negative electrode active material layer, and is not a material that functions to store and release lithium, but refers to a material used in a planar shape to secure a conductive path inside the negative electrode active material layer.

[0120] That is, in the present application, the use of plate-like graphite as a conductive material refers to processing graphite into a planar or plate-like shape and using it as a material to secure a conductive path rather than functioning to store or release lithium. In this case, the negative electrode active material included together has a high capacity characteristic in terms of storing and releasing lithium, and functions to store and release all lithium ions transferred from the positive electrode.

[0121] On the other hand, in the present application, the use of a carbon-based active material as an active material refers to processing the carbon-based active material into a point-like or spherical shape and using it as a material to store or release lithium.

[0122] That is, in one exemplary embodiment of the present application, artificial graphite or natural graphite as a carbon-based active material has a point-like shape, and the BET specific surface area thereof can fall within a range of 0.1 m 24.5 m 2 / g or less. In addition, the plate-shaped graphite as the planar conductive material has a planar shape, and its BET specific surface area can be 5 m 2 / g or more.

[0123] In one exemplary embodiment of the present application, the negative electrode binder can include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluoro rubber, polyacrylic acid, and the above materials in which hydrogen is replaced with Li, Na, Ca, etc., and can further include various copolymers thereof.

[0124] The negative electrode binder according to one exemplary embodiment of the present application is used to hold the active material and the conductive material, thereby preventing distortion and structural deformation of the negative electrode structure during volume expansion and relaxation of the silicon-based active material. When such a role is satisfied, all conventional binders can be applied. Specifically, water-based binders can be used, and more specifically, PAM-based binders can be used.

[0125] In one exemplary embodiment of the present application, the content of the negative electrode binder can 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, and can be 5 parts by weight or more or 10 parts by weight or more.

[0126] In one exemplary embodiment of the present application, the negative electrode for a lithium secondary battery is provided, in which the negative electrode active material layer is a single-layer negative electrode active material layer or a multi-layer negative electrode active material layer.

[0127] That is, the negative electrode for a lithium secondary battery according to the present application can include a single-layer negative electrode active material layer or a double-layer negative electrode active material layer, and the proportion of the silicon-based active material having different particle diameters included in the entire negative electrode active material layer can be applied in the same manner, except that the negative electrode active material layer is single-layer or multi-layer.

[0128] In one exemplary embodiment of the present application, the negative electrode for a lithium secondary battery is provided, in which 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 10 μm or more and 250 μm or less.

[0129] However, the thickness can be variously changed depending on the type and use of the negative electrode to be used, and is not limited thereto.

[0130] In one example embodiment of the present application, the thickness of the negative current collector layer is generally 1 μm to 100 μm. Such a negative current collector layer is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, baked carbon, copper or stainless steel each surface-treated with carbon, nickel, titanium, silver, or the like, aluminum-cadmium alloy, or the like can be used. In addition, the negative current collector layer can be formed with fine irregularities on the surface to enhance the adhesion of the negative active material, and can be used in various forms such as a film, a sheet, a foil, a mesh, a porous body, a foam, or a nonwoven fabric body.

[0131] In one example embodiment of the present application, the porosity of the negative active material layer can fall within a range of 10% or more and 60% or less.

[0132] In another example embodiment, the porosity of the negative active material layer can fall within a range of 10% or more and 60% or less, preferably 20% or more and 50% or less, more preferably 30% or more and 45% or less.

[0133] One example 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.

[0134] Figure 2 is a view showing the stacked structure of a lithium secondary battery according to one example embodiment of the present application. Specifically, it can be seen that the negative electrode for a lithium secondary battery 100 includes a negative active material layer 20 on one surface of a negative current collector layer 10, and it can be seen that the positive electrode for a lithium secondary battery 200 includes a positive active material layer 40 on one surface of a positive current collector layer 50, and the negative electrode for a lithium secondary battery 100 and the positive electrode for a lithium secondary battery 200 are formed in a stacked structure with the separator 30 interposed therebetween.

[0135] The secondary battery according to one example embodiment of the present application can particularly include the above-described negative electrode for a lithium secondary battery. Specifically, the secondary battery can 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 above-described negative electrode. Since the negative electrode has been described above, a detailed description thereof will be omitted.

[0136] The positive electrode can include a positive current collector and a positive active material layer formed on the positive current collector and including a positive active material.

[0137] In the positive electrode, the positive electrode current collector is not particularly limited as long as it has conductivity and does not cause chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, baked carbon, aluminum or stainless steel each surface-treated with carbon, nickel, titanium, silver, or the like, and the like can be used. In addition, the thickness of the positive electrode current collector can generally be 3 μm to 500 μm, and the surface of the current collector can be formed with fine irregularities to enhance the adhesion of the positive electrode active material. For example, the positive electrode current collector can be used in various forms such as a film, a sheet, a foil, a mesh, a porous body, a foamed body, and a nonwoven fabric body.

[0138] The positive electrode active material can be a generally used positive electrode active material. Specifically, the positive electrode active material can be a layered compound such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2) or a compound substituted with one or more transition metals; a lithium iron oxide such as LiFe3O4; a lithium manganese oxide such as Li 1+c1 Mn 2-c1 O4 (0≤c1≤0.33), LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, and Cu2V2O7; a Ni-site type lithium nickel oxide represented by the chemical formula LiNi 1-c2 M c2 O2 (wherein M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01≤c2≤0.3); a lithium manganese composite oxide represented by the chemical formula LiMn 2-c3 M c3 O2 (wherein 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 (wherein M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); LiMn2O4 in which a part of Li in the chemical formula is substituted with an alkaline earth metal ion, and the like, but is not limited thereto. The positive electrode can be a Li metal.

[0139] The positive electrode active material layer can further include a positive electrode conductive material and a positive electrode binder in addition to the above-described positive electrode active material.

[0140] In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and can be used without particular limitation as long as the positive electrode conductive material has electron conductivity without causing chemical changes in the battery as constructed. Specific examples can 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 crack 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; or conductive polymers, such as polyaniline derivatives, and the like, and any one of these or a mixture of two or more of these can be used.

[0141] Further, the positive electrode binder is used to improve the binding between the positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples can include polyvinylidene fluoride (PVDF), vinylidene-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and the like, and any one of these or a mixture of two or more of these can be used.

[0142] The separator is used to separate the negative electrode from the positive electrode and to provide a path for the movement of lithium ions, and any separator can be used as the separator without particular limitation as long as it is generally used for secondary batteries, and in particular, a separator that has high moisture retention capacity for electrolyte and low resistance to the movement of electrolyte ions can be preferably used. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or having a laminated structure of two or more layers thereof, can be used. Further, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting point glass fibers, polyethylene terephthalate fibers, or the like, can be used. Further, a coated separator containing a ceramic component or a polymeric material can be used to ensure heat resistance or mechanical strength, and a separator having a single layer or a multi-layer structure can be selectively used.

[0143] Examples of the electrolyte can include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, or a molten-type inorganic electrolyte that can be used to manufacture the lithium secondary battery, but are not limited thereto.

[0144] Specifically, the electrolyte can contain a non-aqueous organic solvent and a metal salt.

[0145] As the non-aqueous organic solvent, for example, an aprotic organic solvent such as N-methyl-2-pyrrolidone, 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, trimethoxy methane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate or ethyl propionate can be used.

[0146] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate as cyclic carbonates are high-viscosity organic solvents, and since they have high dielectric constants, lithium salts are well dissociated, and thus can be preferably used. When the cyclic carbonates are mixed with linear carbonates such as dimethyl carbonate and diethyl carbonate, which have low viscosity and low dielectric constants, at a suitable ratio and used, an electrolyte having high conductivity can be prepared, and thus such a combination can be more preferable.

[0147] As the metal salt, a lithium salt, which is a material that is easily dissolved in the non-aqueous electrolyte, can be used, and for example, one or more selected from the group consisting of 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 - .

[0148] For the purpose of improving the life characteristics of the battery, suppressing the decrease in the battery capacity, improving the discharge capacity of the battery, and the like, one or more additives, such as a halogenated alkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, a cyclic ether, ethylenediamine, n-glyme, hexamethylphosphoric triamide, a nitrobenzene derivative, sulfur, a quinonimine dye, an N-substituted oxazolidinone, an N,N-substituted imidazolidine, an ethylene glycol dialkyl ether, an ammonium salt, a pyrrole, 2-methoxyethanol, or aluminum trichloride, can be further contained in the electrolyte on the basis of the above-mentioned electrolyte components.

[0149] One exemplary embodiment of the present application provides a battery module including the secondary battery as a unit cell and a battery pack including the same. Since the battery module and the battery pack include the secondary battery having high capacity, high rate capability, and high cycle characteristics, the battery module and the battery pack can be used as a power source for a medium-large device selected from the group consisting of an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, and an electric power storage system.

[0150] Invention Mode

[0151] Hereinafter, preferred embodiments will be provided to better understand the present application. It will be apparent to those skilled in the art that the embodiments are provided only for the purpose of illustration of the present application, and various modifications and changes can be made within the scope and technical spirit of the present application. Such modifications and changes naturally fall within the scope of the claims contained herein.

[0152] <Preparation Example>

[0153] <Preparation Example 1> Negative electrode of SLC

[0154] A negative electrode active material layer composition was prepared using Si (first silicon-based active material, second silicon-based active material) as a silicon-based active material, a first conductive material, a second conductive material, and polyacrylamide as a binder in a weight ratio of 80:9.6:0.4:10, and was added to distilled water as a solvent for negative electrode slurry formation, thereby preparing a negative electrode slurry.

[0155] The first conductive material was plate-shaped graphite (specific surface area: 17 m 2 / g, average particle diameter (D50): 3.5 μm), and the second conductive material was SWCNT.

[0156] As a mixing method, the first conductive material, the binder, and water were dispersed using a homogenizer for 30 minutes at 1500 rpm, the silicon-based active material was added to the resulting dispersion, the resulting mixture was dispersed for 30 minutes at 2500 rpm, and then the second conductive material was added to the resulting dispersion, which was then dispersed for 10 minutes at 2500 rpm. Then, the negative electrode active material layer was coated on both surfaces of a copper current collector (thickness: 15 μm) serving as a negative electrode current collector with a slurry at a loading of 20 mg / 25 cm 2 and then dried.

[0157] In this case, the average particle diameter and the weight fraction of the first silicon-based active material and the second silicon-based active material contained in the negative electrode slurry are shown in Table 1 below.

[0158] [Table 1]

[0159] Preparation Example 2: Negative electrode of DLC

[0160] A first negative electrode active material layer composition was prepared using Si (first silicon-based active material, second silicon-based active material) as a silicon-based active material, a first conductive material, a second conductive material, and polyacrylamide as a binder at a weight ratio of 80:9.6:0.4:10, and was added to distilled water as a solvent for forming a negative electrode slurry, thereby preparing a negative electrode slurry (i.e., a first negative electrode active material layer slurry).

[0161] Then, a second negative electrode active material layer slurry was prepared in the same manner as the first negative electrode active material layer slurry, except that the weight ratio of the first silicon-based active material to the second silicon-based active material (as shown in Table 2 below) was different.

[0162] The first conductive material was plate-shaped graphite (specific surface area: 17 m 2 / g, average particle diameter (D50): 3.5 μm), and the second conductive material was SWCNT.

[0163] Then, the first negative electrode active material layer slurry was coated on both surfaces of a copper current collector (thickness: 15 μm) serving as a negative electrode current collector with a loading of 8 mg / 25 cm 2 , and the second negative electrode active material layer slurry was coated with a loading of 12 mg / 25 cm 2 , thereby preparing an electrode.

[0164] In this case, the average particle diameter and the weight fraction of the first silicon-based active material and the second silicon-based active material contained in the negative electrode slurry are shown in Table 2 below.

[0165] [Table 2]

[0166] <Preparation of secondary battery>

[0167] A positive electrode slurry was prepared by adding LiNi 0.6 Co 0.2 Mn 0.2 O2 (average particle diameter (D50): 15 μm), carbon black (product name: Super C65, manufacturer: Timcal Corporation), and polyvinylidene fluoride (PVdF) as a binder were added to N-methyl-2-pyrrolidone (NMP) as a solvent for forming a positive electrode slurry in a weight ratio of 97:1.5:1.5 to prepare a positive electrode slurry (solid concentration: 78 wt%).

[0168] The positive electrode slurry was coated on both surfaces of an aluminum current collector (thickness: 12 μm) serving as a positive electrode current collector at a loading of 537 mg / 25 cm 2 , and then calendered and dried in a vacuum oven at 130°C for 10 hours to form a positive electrode active material layer (total thickness of the positive electrode active material layer: 65 μm), thereby preparing a positive electrode (positive electrode thickness: 77 μm, porosity: 26%).

[0169] A lithium secondary battery was prepared by interposing a polyethylene separator between the above-described positive electrode and the negative electrode described in the examples and comparative examples and injecting an electrolyte.

[0170] The electrolyte was obtained by adding vinylene carbonate in an amount of 3 wt% based on the total weight of the electrolyte to an organic solvent in which fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) were mixed at a volume ratio of 10:90, and adding LiPF6 as a lithium salt to a concentration of 1 M.

[0171] <Experimental example>

[0172] Experimental Example 1: Cycle life data

[0173] For the secondary battery containing the negative electrode manufactured in the examples and comparative examples, the life and capacity retention rate were evaluated using an electrochemical charge-discharge device. The secondary battery was subjected to in-situ cycle testing at 4.2-3.0 V 1C / 0.5C, and during the testing, 0.33 C / 0.33 C charge-discharge (4.2-3.0 V) was performed every 50 cycles, thereby measuring the capacity retention rate.

[0174] Capacity retention rate (%) = {(discharge capacity at the Nth cycle) / (discharge capacity at the first cycle)} x 100

[0175] [Table 3]

[0176] Experimental Example 2: Cycle resistance increase rate

[0177] In the test in Experimental Example 1, the capacity retention rate was measured by charging / discharging (4.2-3.0 V) the battery at 0.33 C / 0.33 C per 50 cycles, then the resistance was measured by discharging the battery at 2.5 C at SOC 50, and then the resistance increase rate was compared and analyzed.

[0178] For the evaluation of the resistance increase rate measurement, data at 200 cycles were each calculated, and the results are shown in Table 4 below.

[0179] [Table 4]

[0180] As can be seen in the above Tables 3 and 4, it was confirmed that when the first silicon-based active material having a smaller average particle diameter and the second silicon-based active material having a larger average particle diameter are mixed in a specific ratio, particularly, when the ratio between the active materials having different average particle diameters is adjusted as described above, the volume expansion of the active material can be reduced even during charging and discharging, thereby preventing the electrode from being detached, simplifying the pore structure of the electrode, and thus reducing the negative electrode resistance.

[0181] Comparative Example 1 corresponds to a case where only a silicon-based active material having a small particle size is included, and Comparative Example 2 corresponds to a case where only a silicon-based active material having a large particle size is included. In Comparative Example 1, it was confirmed that better cycle performance was exhibited compared to Comparative Example 2, but after a certain number of cycles, the reaction was concentrated on the surface, leading to sudden death, and in Comparative Example 2, detachment from the surface of the current collector occurred due to large volume expansion of the Si active material from the initial cycle, thereby leading to deterioration of cycle performance.

[0182] Comparative Example 3 and Comparative Example 4 correspond to cases where a silicon-based active material having a larger particle size and a silicon-based active material having a smaller particle size are applied as in the present application, but the ratio falls outside the range of the present application. Specifically, it was confirmed that when the active material having a smaller particle size is below the range of the present application (as in Comparative Example 3), similar low cycle performance to Comparative Example 2 having 100% large particle size active material was exhibited, and when the active material having a larger particle size is below the range of the present application (as in Comparative Example 4), similar performance to Comparative Example 1 was exhibited.

[0183] In Comparative Example 5 in which the weight ratio satisfies the range of the present application but the particle diameter falls outside the range of the present application, performance deterioration due to large volume expansion regardless of the ratio, in addition, when the active material of smaller particle diameter falls outside the range of the present application, there is no difference in initial life performance, but the point of sudden death is advanced.

[0184] For reference, Example 14 and Example 15 and Comparative Example 6 and Comparative Example 7 have a double-layer active material structure (DLD) having the same principle as the above-described examples and comparative examples.

Claims

1. A negative electrode active material comprising a silicon-based active material, The silicon-based active material comprises a first silicon-based active material with an average particle size (D50) of 2 μm or more and 5 μm or less, and a second silicon-based active material with an average particle size (D50) of 10 μm or more and 20 μm or less. The weight ratio of the first silicon-based active material to the second silicon-based active material is 20:80 to 80:

20.

2. The negative electrode active material according to claim 1, wherein the weight ratio of the first silicon-based active material to the second silicon-based active material is 35:65 to 65:

35.

3. The negative electrode active material according to claim 1, wherein the silicon-based active material comprises silicon particles with a particle size distribution of 0.01 μm to 30 μm, and Of the 100 parts by weight of the silicon-based active material, the content of particles with a particle size of less than 2 μm is less than 5 parts by weight.

4. The negative electrode active material according to claim 1, wherein the first silicon-based active material and the second silicon-based active material comprise one or more selected from the group consisting of SiO x (x = 0), SiO x (0 < x < 2), SiC, and Si alloys.

5. The negative electrode active material according to claim 1, wherein the first silicon-based active material comprises one or more selected from the group consisting of SiO x (x = 0) and SiO x (0 < x < 2), and based on 100 parts by weight of the first silicon-based active material, the content of SiO x (x = 0) is 70 parts by weight or more.

6. The negative electrode active material according to claim 1, wherein the second silicon-based active material comprises one or more selected from the group consisting of SiO x (x = 0) and SiO x (0 < x < 2), and based on 100 parts by weight of the second silicon-based active material, the content of SiO x (x = 0) is 70 parts by weight or more.

7. A negative electrode for a lithium secondary battery, comprising: Negative current collector layer; and A layer of negative electrode active material disposed on one or both surfaces of the negative electrode current collector layer. The negative electrode active material layer comprises a negative electrode active material layer composition, wherein the negative electrode active material layer composition comprises a negative electrode active material, a negative electrode conductive material, and a negative electrode binder according to any one of claims 1 to 6.

8. The negative electrode for a lithium secondary battery according to claim 7, wherein the content of the negative electrode active material layer composition is 60 parts by weight or more, based on 100 parts by weight of the negative electrode active material layer composition.

9. The negative electrode for a lithium secondary battery according to claim 7, wherein the conductive material of the negative electrode comprises a planar conductive material and a linear conductive material.

10. The negative electrode for a lithium secondary battery according to claim 7, wherein the negative electrode active material layer is a single-layer negative electrode active material layer or a multi-layer negative electrode active material layer.

11. The negative electrode for a lithium secondary battery according to claim 7, 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 more than 10 μm and less than 250 μm.

12. A lithium secondary battery, comprising: positive electrode; The negative electrode for a lithium secondary battery according to claim 7; A membrane disposed between the positive electrode and the negative electrode; and Electrolytes.

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