Anode and lithium secondary battery comprising same

Abstract

The present invention relates to an anode comprising an anode active material layer containing an anode active material, a binder, a first conductive material, and a second conductive material, wherein the number average length of the first conductive material as measured using atomic force microscopy (AFM) is 0.7㎛ to 6.0㎛; ACA as defined by, as factors, the BET specific surface area and weight% of each of the anode active material, the first conductive material, and the second conductive material is 0.5 to 5.0; and CA as defined by, as factors, the BET specific surface area and weight% of each of the first conductive material and the second conductive material is 0.1 to 8.0.

Description

Anode and lithium secondary battery containing the same Cross-citation with related applications This application claims the benefit of priority to Korean Patent Application No. 10-2023-0180064, dated December 12, 2023, the entire contents of which are incorporated herein by reference. Technical field The present invention relates to a negative electrode and a lithium secondary battery including the same. Lithium secondary batteries are generally composed of a positive electrode, a negative electrode, a separator, and an electrolyte, and the positive electrode and negative electrode include an active material capable of intercalation and deintercalation of lithium ions. Lithium secondary batteries are generally manufactured by forming an electrode assembly by interposing a separator between a positive electrode including a positive electrode active material made of a transition metal oxide containing lithium and an anode including an anode active material capable of storing lithium ions, inserting the electrode assembly into a battery case, injecting a non-aqueous electrolyte that serves as a medium for transferring lithium ions, and then sealing the electrode assembly. The non-aqueous electrolyte is generally composed of a lithium salt and an organic solvent capable of dissolving the lithium salt. Meanwhile, various studies have been conducted to utilize silicon-based active materials with large discharge capacity as cathode active materials in order to increase the capacity of the above-mentioned cathode. However, silicon-based active materials with large discharge capacity have a problem in that the conductivity inside the electrode deteriorates due to volume expansion according to charging and discharging of the secondary battery. On the other hand, research on binder polymers with strong stress has also been conducted to solve the problem of volume expansion that occurs during charging / discharging, but it was difficult to solve the problem of deterioration of conductivity due to expansion / contraction of the negative electrode active material with the binder polymer alone. To solve these problems, carbon nanotubes (CNTs) were applied as a conductive material, but since carbon nanotubes were applied without considering the specific surface area and weight between the negative active material and other conductive materials, problems of clogging occurred during the dispersion process and the transport process, and problems of short-circuiting of the conductive network occurred due to shrinkage and expansion of the active material inside the electrode during charge and discharge, resulting in problems of reduced battery life characteristics. Therefore, there is a need for research on a cathode that has no problems in the electrode manufacturing process and has excellent battery life characteristics. The present invention is intended to solve the above problems, and to provide a cathode having excellent fairness and life characteristics, characterized in that the number average length of the first conductive material, ACA expressed by Equation 1 below, and CA expressed by Equation 2 below satisfy the scope of the present invention. In addition, the present invention seeks to provide a lithium secondary battery having improved life characteristics by including the negative electrode. [1] The present invention provides an anode including a negative active material layer including a negative active material, a binder, a first conductive material, and a second conductive material, wherein the number average length of the first conductive material measured using an atomic force microscope (AFM) is 0.7 ㎛ to 6.0 ㎛, ACA expressed by the following formula 1 is 0.5 to 5.0, and CA expressed by the following formula 2 is 0.1 to 8.0. [Formula 1] In the above equation 1, the S A is the BET surface area (m) of the first challenge material 2 / g), and the above W A is the weight % of the first conductive material based on the total weight of the negative active material layer, and S B is the BET surface area (m) of the second challenge material 2 / g), and the above W Bis the weight % of the second conductive material based on the total weight of the negative active material layer, and S C is the BET surface area (m) of the above negative active material. 2 / g), and the above W C is the weight percentage of the negative electrode active material based on the total weight of the negative electrode active material layer, [Formula 2] In the above equation 2, the S A is the BET surface area (m) of the first challenge material 2 / g), and the above W A is the weight % of the first conductive material based on the total weight of the negative active material layer, and S B is the BET surface area (m) of the second challenge material 2 / g), and the above W B is the weight percentage of the second conductive material based on the total weight of the negative active material layer. [2] In the present invention, in the above [1], the average length of the first challenging material measured using an atomic force microscope (AFM) can be 0.8 ㎛ to 4.0 ㎛. [3] In the present invention, in the above [1] or [2], the ACA may be 0.9 to 2.5. [4] In at least one of the above [1] to [3], the CA may be 0.1 to 6.0. [5] In at least one of the above [1] to [4], the negative active material may include a silicon-based active material. [6] The present invention is characterized in that in at least one of the above [1] to [5], the BET specific surface area of ​​the negative active material is 0.2 m 2 / g to 20m 2 / g could be. [7] The present invention is characterized in that in at least one of the above [1] to [6], the BET surface area of ​​the first challenging material is 800 m 2 / g to 1500m 2 / g could be. [8] In at least one of the above [1] to [7], the first challenging material may include a single-walled carbon nanotube. [9] The present invention is characterized in that in at least one of the above [1] to [8], the BET surface area of ​​the second challenging material is 25 m 2 / g to 200m 2 It could be / g.

[0010] In at least one of the above [1] to [9], the second conductive material may include a dot-shaped conductive material.

[0011] The present invention provides a lithium secondary battery including at least one negative electrode among the above [1] to

[0010] . The negative electrode according to the present invention is characterized in that the number average length of the first conductive agent, the ACA expressed by the following formula 1, and the CA expressed by the following formula 2 satisfy the scope of the present invention. The negative electrode satisfying the above conditions has an advantage in that, when manufacturing the negative electrode, the negative electrode slurry has an appropriate viscosity and excellent dispersibility, so that there is no clogging or coating defects in the electrode manufacturing process and uniform electrode manufacturing is possible. In addition, even if shrinkage and expansion of the active material occur during charge and discharge, the conductive network can be appropriately maintained, so that the life characteristics of the battery are improved. The terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as having meanings and concepts that conform to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term in order to explain his or her own invention in the best manner. It should be understood that the terms “comprise,” “include,” or “have,” as used herein, are intended to specify the presence of a feature, number, step, component, or combination thereof, but do not exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof. In the present invention, “specific surface area (m 2 / g)” is measured by the BET method, and can be specifically calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77K) using BELSORP-mino II from BEL Japan. In the present invention, the "average particle diameter (D 50 )" means the particle size based on 50% of the volume cumulative particle size distribution of the particles. The average particle diameter D 50 can be measured using a laser diffraction method. The laser diffraction method can generally measure particle diameters from the submicron range to several mm, and can obtain results with high reproducibility and high resolution. In the present invention, the number average length (㎛) of the first conductive material can be derived by obtaining a number cumulative length distribution by obtaining the lengths of 400 or more first conductive materials through images measured at a magnification of 20 ㎛ x 20 ㎛, 15 ㎛ x 15, and / or 10 ㎛ x 10 ㎛ under the conditions of set point 0.4 V and scan rate 1.5 Hz in AC Air Topography mode (Tapping mode) using an atomic force microscope (AFM) (Asylum Research, Cypher ES AFM System) for the first conductive material. cathode Hereinafter, the cathode according to the present invention will be described. Previously, carbon nanotubes (CNTs) were applied as a conductive material for the negative electrode. However, since carbon nanotubes were applied without considering the specific surface area and weight between the negative active material and other conductive materials, problems of blockage occurred during the dispersion process and the transport process, and short circuits occurred in the conductive network due to shrinkage and expansion of the active material in the electrode during charging and discharging, resulting in problems of reduced battery life characteristics. The inventors of the present invention have conducted continuous research to solve such problems and, as a result, have found that when the average length measured using an atomic force microscope of the first conductive material is controlled while the area ratio between the negative active material and the conductive materials and the area ratio between the conductive materials are controlled within a certain range, the electrode manufacturing process can be excellent and the life characteristics of the battery can be improved, thereby completing the present invention. The negative electrode according to the present invention comprises a negative electrode active material layer including a negative electrode active material, a binder, a first conductive material, and a second conductive material, wherein the number average length of the first conductive material measured using an atomic force microscope (AFM) is 0.7 µm to 6.0 µm, ACA expressed by the following formula 1 is 0.5 to 5.0, and CA expressed by the following formula 2 is 0.1 to 8.0. [Formula 1] In the above equation 1, the S A is the BET surface area (m) of the first challenge material 2 / g), and the above W A is the weight % of the first conductive material based on the total weight of the negative active material layer, and S B is the BET surface area (m) of the second challenge material 2 / g), and the above W B is the weight % of the second conductive material based on the total weight of the negative active material layer, and S C is the BET surface area (m) of the above negative active material. 2 / g), and the above W Cis the weight percentage of the negative electrode active material based on the total weight of the negative electrode active material layer. [Formula 2] In the above equation 2, the S A is the BET surface area (m) of the first challenge material 2 / g), and the above W A is the weight % of the first conductive material based on the total weight of the negative active material layer, and S B is the BET surface area (m) of the second challenge material 2 / g), and the above W B is the weight percentage of the second conductive material based on the total weight of the negative active material layer. The number average length of the first conductive material measured using an atomic force microscope (AFM) is 0.7 µm to 6.0 µm, and specifically, the number average length of the first conductive material measured using an atomic force microscope (AFM) may be 0.7 µm or more, 0.75 µm or more, or 0.8 µm or more, and may be 6.0 µm or less, 5.5 µm or less, 5.0 µm or less, 4.5 µm or less, or 4.0 µm or less. The number average length may be measured through the above-described atomic force microscope measurement, and in this case, since the length characteristics can be accurately measured, it is preferable in that the excellent effect intended by the present invention can be exhibited. In detail, when measuring the average length of the conductive material, the volume cumulative average particle diameter (D) of the dispersion containing the conductive material is used to predict the formation of a conductive path and uniform distribution at the electrode. 50 and / or D 90) were often measured and utilized. However, the particle size distribution in such a dispersed state does not accurately reflect the length of the actual conductive material, so there is a problem that the performance of the electrode may appear differently even when applying one having the same particle size distribution. The length characteristics obtained from the number-cumulative length distribution through an atomic force microscope image according to one embodiment of the present invention can be said to be a more effective feature for improving the performance of the electrode because the dispersed state and the electrode state appear substantially the same. When the above average length is less than 0.7 ㎛, it may not be easy to maintain the conductive network connection path due to the volume change of the electrode due to charge and discharge. In addition, when the above average length exceeds 6.0 ㎛, the number of first conductive materials per unit weight may decrease, but the distribution of the first conductive material within the electrode may not be uniform, which may cause a problem. In addition, the viscosity of the slurry may increase, which may lower the dispersibility, or there may be a problem of clogging or coating failure during slurry transport. Therefore, when the above range is satisfied, the conductive network connection path may be appropriately maintained while maintaining the distribution of the first conductive material within the electrode uniformly, so that the life characteristics may be improved. The ACA expressed by the above formula 1 is the ratio of the area of ​​the negative active material to the area of ​​the first conductive material and the second conductive material, and the ACA can be obtained by multiplying the specific surface area and the weight % of each material. In order to achieve the excellent effect intended by the present invention, an appropriate combination of the specific surface area and the weight % of each of the first conductive material, the second conductive material, and the negative active material is required. Specifically, the total area of ​​the conductive materials can be obtained by adding the product of the specific surface area of ​​the first conductive material and the weight% of the first conductive material in the denominator and the product of the specific surface area of ​​the second conductive material and the weight% of the second conductive material. In addition, the total area of ​​the negative active material can be obtained by multiplying the specific surface area of ​​the negative active material and the weight of the negative active material in the numerator. This ACA is a ratio representing the total area of ​​the negative active material to the total area of ​​the conductive material, and the ratio of the total area of ​​the conductive materials to the total area of ​​the negative active material must be controlled within a certain range so as to exhibit excellent processability and excellent life characteristics. For example, a large total area of ​​the negative electrode active material means that the loading amount or the specific surface area of ​​the negative electrode active material is relatively high, or the average particle size (D) of the negative electrode active material is 50 ) is small, and when the loading amount is high, an improvement in the capacity characteristics can be expected, but it can be counter-evidence that the conductive path is not formed normally relatively. In addition, a large total area of ​​the conductive material can mean that the conductive path is well formed in a network structure, but in that it means that the loading amount of the active material is low, the ratio of these areas can be seen as having a trade-off relationship. In addition, it can be difficult to conclude that the conductive path is well formed just because the total area occupied by the conductive material is large with respect to the formation of the conductive path, so it is simply considered that the content or specific surface area of ​​the conductive material, the content of the negative active material, and the average particle diameter (D 50 ) or surface area, it may not be easy to identify the relationship for improving battery performance. However, according to one embodiment of the present invention, by mixing the first conductive material and the second conductive material in the negative electrode active material layer, a conductive path between the negative electrode active materials, a conductive path within the negative electrode active material, and a conductive path on the pores of the negative electrode active material can be formed simultaneously, thereby controlling the area occupied by the conductive material and the degree of formation of the conductive path to be in a maximally proportional relationship, and thus controlling the ratio with respect to the area of ​​the negative electrode active material can be a factor capable of improving the performance of the battery. The ACA expressed by the above formula 1 is 0.5 to 5.0, and specifically, the ACA expressed by the above formula 1 may be 0.5 or more, 0.6 or more, 0.7 or more, 0.8 or more, or 0.9 or more, and may be 5.0 or less, 4.5 or less, 4.0 or less, 3.5 or less, 3.0 or less, or 2.5 or less. When the ACA is less than 0.5, the initial conductive path of the electrode may be sufficiently formed, but the content of the negative active material may decrease and the viscosity of the slurry may increase, thereby resulting in poor fairness. Accordingly, there may occur a problem in which the life characteristics of the battery deteriorate. In addition, when the ACA exceeds 5.0, the initial conductive path of the electrode may not be sufficiently formed, and there may be a problem in which the life characteristics of the battery deteriorate during charge and discharge. Therefore, when the above range is satisfied, the process for manufacturing the electrode is excellent without any problems, and the initial conductive path of the electrode is sufficiently formed while the conductive path can be continuously maintained during charging and discharging, so that the life characteristics of the battery can be excellent. The CA expressed by the above formula 2 is the ratio of the area of ​​the second conductive material to the area of ​​the first conductive material, and the CA can be obtained by multiplying the specific surface area and the weight % of each material. In order to achieve the excellent effect intended by the present invention, an appropriate combination of the specific surface area and the weight % of each of the first and second conductive materials is also required. Specifically, the total area of ​​the first conductive materials can be obtained by multiplying the specific surface area of ​​the first conductive material in the denominator by the weight% of the first conductive material. In addition, the total area of ​​the second conductive materials can be obtained by multiplying the specific surface area of ​​the second conductive material in the numerator by the weight% of the second conductive material. This CA is a ratio representing the total area of ​​the second conductive materials to the total area of ​​the first conductive materials, and the ratio of the total area of ​​the first conductive materials to the total area of ​​the second conductive materials must be controlled within a certain range so as to exhibit excellent processability and excellent life characteristics. The CA expressed by the above formula 2 is 0.1 to 8.0. Specifically, the CA expressed by the above formula 2 may be 0.1 to 7.5, more specifically 0.1 to 7.0, even more specifically 0.1 to 6.5, and even more specifically 0.1 to 6.0. When the CA expressed by the above formula 2 is less than 0.1 or exceeds 8.0, a problem may occur in which the conductive path cannot properly form a network structure or the fairness during electrode manufacturing is poor. Therefore, when the above range is satisfied, the ratio of the area of ​​the first conductive material to the area of ​​the second conductive material can be appropriately controlled, so that the electrode fairness is excellent and the conductive path can be continuously maintained during charge and discharge, so that the life characteristics of the battery can be improved. Meanwhile, the negative electrode may include a negative electrode current collector; and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The above negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. Specifically, the negative electrode current collector may be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., an aluminum-cadmium alloy, etc. The above negative electrode collector may typically have a thickness of 3 to 500 μm. The above negative electrode current collector may form fine irregularities on the surface to strengthen the bonding strength of the negative electrode active material. For example, the above negative electrode current collector may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc. The negative electrode active material layer is disposed on at least one surface of the negative electrode current collector. Specifically, the negative electrode active material layer may be disposed on one surface or both surfaces of the negative electrode current collector. The above negative active material is a material capable of reversibly inserting / deleting lithium ions, and may include at least one selected from the group consisting of a carbon-based active material, a silicon-based active material, and lithium metal, and specifically may include at least one selected from a carbon-based active material and a silicon-based active material. The above carbon-based active material may include at least one selected from the group consisting of graphite, hard carbon, soft carbon, carbon black, graphene, and fibrous carbon, and may specifically include graphite. The graphite may include, for example, at least one selected from the group consisting of artificial graphite and natural graphite. The average particle diameter (D) of the above carbon-based active material 50 ) may be 10 ㎛ to 30 ㎛, preferably 15 ㎛ to 25 ㎛, in order to ensure structural stability during charging and discharging and reduce side reactions with the electrolyte. The above silicon-based active material is SiO x (0≤x<2), Si / C composite, metal-doped SiO x (0≤x<2) and at least one selected from the group consisting of Si alloy (Si-alloy), preferably SiO x(0≤x<2) and a Si / C composite. In the case of SiO2, since it does not react with lithium ions and thus cannot store lithium, it is preferable that x is within the above range. In addition, the Si / C composite means a form in which carbon is physically mixed with silicon or silicon oxide, and for example, a Si / C composite can be formed by mixing silane gas into porous carbon and thermally decomposing it, a Si / C composite can be formed by physically mixing carbon and silicon particles, a Si / C composite can be formed by heat-treating and coating carbon on the surface of silicon particles, and a Si / C composite can be formed by etching a silicon-based material and then additionally coating carbon, but is not limited thereto. The BET surface area of ​​the above negative active material is 0.2 m 2 / g to 20m 2 / g can be, specifically 1m 2 / g to 15m 2 / g can be, more specifically, 1m 2 / g to 10m 2 / g. When the BET surface area range of the above negative active material is satisfied, it can be an appropriate surface area to satisfy the ACA range, and it is preferable in that the conductive connectivity of the negative active material particles is smooth and particle breakage due to volume expansion can be reduced. The average particle diameter (D) of the above silicon-based active material 50 ) may be 1 ㎛ to 30 ㎛, preferably 3 ㎛ to 20 ㎛, and more preferably 5 ㎛ to 10 ㎛ in order to reduce side reactions with the electrolyte while ensuring structural stability during charge and discharge. The above negative active material may be included in an amount of 60 wt% to 99 wt%, preferably 75 wt% to 95 wt%, based on the total weight of the negative active material layer. The above binder is used to improve the performance of the battery by improving the adhesion between the negative electrode active material layer and the negative electrode current collector, and may include, for example, at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, polyacrylamide, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, and materials in which hydrogen of these is substituted with Li, Na, Ca, or the like. and may also include various copolymers thereof. The above binder may be included in the negative electrode active material layer in an amount of 0.5 wt% to 10 wt%, preferably 1 wt% to 5 wt%. The BET surface area of ​​the first challenge material is 800 m 2 / g to 1500m 2 / g, specifically 900m 2 / g to 1200m 2 / g, more specifically 1000m 2 / g to 1200m 2 / g. When the above range is satisfied, the specific surface area of ​​the first conductive material may be appropriate so as to satisfy the ACA and / or CA range, and may greatly contribute to the formation of a conductive network between negative active materials or on the surface of the negative active material, thereby improving the cycle characteristics of the battery. The above first challenge material may be a carbon nanotube. The graphite sheet of the carbon nanotube has a cylinder shape with a nano-sized diameter, and sp 2 It has a bonding structure. At this time, depending on the angle and structure at which the graphite plane is rolled, it can exhibit the characteristics of a conductor or a semiconductor. The carbon nanotube can be classified into a single-walled carbon nanotube (SWCNT, single-walled carbon nanotube), a double-walled carbon nanotube (DWCNT, double-walled carbon nanotube), and a multi-walled carbon nanotube (MWCNT, multi-walled carbon nanotube) depending on the number of bonds forming the wall. The above first conductive material may be a single-walled carbon nanotube. When the above first conductive material is a single-walled carbon nanotube, it is preferable in that even if only a small amount is added, sufficient conductivity can be secured, thereby reducing electrode resistance. The above single-walled carbon nanotube may have an average diameter of 0.5 nm to 10 nm, specifically 0.5 nm to 5.0 nm, more specifically 0.5 nm to 3 nm, and even more specifically 0.5 nm to 2 nm. When the above range is satisfied, it is preferable in that the single-walled carbon nanotube can form an appropriate conductive network with the negative electrode active material. The above average diameter may be derived by observing the diameters of 100 single-walled carbon nanotubes included in the negative electrode active material layer using TEM or AFM and then calculating an average value. The above first conductive agent may be included in an amount of 0.01 wt% to 0.5 wt%, specifically 0.05 wt% to 0.5 wt%, and more specifically 0.05 wt% to 0.2 wt%, based on the total weight of the negative electrode active material layer. When the above range is satisfied, it is preferable in that the conductivity of the negative electrode active material layer can be easily secured even with a low content. The BET surface area of ​​the above second challenge material is 25 m2 / g to 200m 2 / g, specifically 35m 2 / g to 200m 2 / g, more specifically 35m 2 / g to 150m 2 / g. When the above range is satisfied, the specific surface area of ​​the second conductive material can be appropriate to satisfy the ACA and / or CA range, the processability during electrode manufacturing can be excellent, and conductivity on the surface of the negative electrode active material can be easily secured, which is preferable. The above second conductive agent may be a dot-shaped conductive agent. The dot-shaped conductive agent may be carbon black, specifically, at least one selected from acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black. More specifically, the dot-shaped conductive agent may be at least one selected from acetylene black and Ketjen black. Such dot-shaped conductive agent may generally be arranged in a gap between negative active materials in the negative active material layer, and may contribute to the formation of a conductive path in a different manner from the linear first conductive agent. Accordingly, when the second conductive agent, which is the dot-shaped conductive agent, is introduced with a specific surface area in the above-described range, there is an advantage in that the battery performance can be controlled more effectively through the above-described relationship. The above second conductive agent may be present in an amount of 0.1 wt% to 5.0 wt%, specifically 0.1 wt% to 4.0 wt%, and more specifically 0.1 wt% to 3.0 wt%, based on the total weight of the negative electrode active material layer. When the above range is satisfied, the slurry may have an appropriate viscosity, thereby improving the processability during electrode manufacturing, and is preferable in that the surface conductivity of the negative electrode active material and the conductivity between the negative electrode active materials may be excellent. The average particle diameter (D) of the second challenge material 50) may be 5 ㎛ to 70 ㎛, specifically 10 ㎛ to 60 ㎛, and more specifically 15 ㎛ to 50 ㎛. The thickness of the above negative active material layer may be 10 µm to 100 µm, preferably 50 µm to 80 µm. The above negative electrode can be manufactured by coating a negative electrode slurry composition including a negative electrode active material, a binder, a first conductive agent, a second conductive agent, and / or a solvent for forming a negative electrode slurry on at least one surface of a negative electrode current collector, and then drying and rolling. The solvent for forming the negative electrode slurry may include at least one selected from the group consisting of distilled water, NMP (N-methyl-2-pyrrolidone), ethanol, methanol, and isopropyl alcohol, preferably distilled water, in order to facilitate dispersion of the negative electrode active material, binder, and / or conductive agent, for example. The solid content of the negative electrode slurry may be 30 wt% to 80 wt%, specifically 40 wt% to 70 wt%. Lithium secondary battery Next, a lithium secondary battery according to the present invention will be described. The lithium secondary battery according to the present invention includes the negative electrode of the present invention described above, and more specifically, it may be a lithium secondary battery including the negative electrode of the present invention. The above lithium secondary battery specifically includes a positive electrode, a negative electrode positioned opposite the positive electrode, and a separator and an electrolyte interposed between the positive electrode and the negative electrode. Since the negative electrode is the same as described above, a detailed description is omitted, and only the remaining components are specifically described below. In addition, the lithium secondary battery may optionally further include a battery container that accommodates the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container. In the above lithium secondary battery, the positive electrode may include a positive electrode current collector and a positive electrode active material layer positioned on the positive electrode current collector. The positive electrode current collector may be any conductive material that does not cause a chemical change in the battery, and is not particularly limited. For example, the positive electrode current collector may be made of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. The positive electrode current collector may have a thickness of 3 μm to 500 μm, and fine unevenness may be formed on the surface of the positive electrode current collector to increase adhesion to the positive electrode active material layer. For example, it may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a non-woven fabric. The cathode active material layer may include a cathode active material, and may further include a conductive material, a binder, etc., as needed. The above cathode active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically may include a lithium metal oxide containing lithium and one or more metals such as cobalt, manganese, nickel or aluminum. More specifically, the lithium metal oxide may be a lithium-manganese oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt oxide (e.g., LiCoO2, etc.), a lithium-nickel oxide (e.g., LiNiO2, etc.), a lithium-nickel-manganese oxide (e.g., LiNi 1-Y Mn Y O2(here, 0 <Y<1), LiMn 2-Z Ni Z O4 (wherein, 0<Z<2) etc.), lithium-nickel-cobalt oxides (e.g., LiNi 1-Y1 Co Y1 O2(here, 0 <Y1<1) 등), 리튬-망간-코발트계 산화물(예를 들면, LiCo 1-Y2 Mn Y2 O2(here, 0 <Y2<1), LiMn 2-Z1 Co Z1O4 (wherein, 0<Z1<2) etc.), lithium-nickel-manganese-cobalt oxides (e.g., Li(Ni p Co q Mn r )O2(where, 0<p<1, 0<q<1, 0<r<1, p+q+r=1) or Li(Ni p1 Co q1 Mn r1 )O4 (wherein, 0<p1<2, 0<q1<2, 0<r1<2, p1+q1+r1=2) etc.), or lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r2 M s2 )O2 (wherein, M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, and p2, q2, r2 and s2 are atomic fractions of independent elements, respectively, 0<p2<1, 0<q2<1, 0<r2<1, 0<s2<1, p2+q2+r2+s2=1), etc.), lithium iron phosphate (e.g., Li 1+a Fe 1-x M x (PO 4-b )X b (Here, M is at least one selected from Al, Mg, and Ti, X is at least one selected from F, S, and N, and -0.5≤a≤0.5, 0≤x≤0.5, 0≤b≤0.1) and the like, and one or more compounds among these may be included. Among these, the lithium metal oxides are LiCoO2, LiMnO2, LiNiO2, lithium nickel manganese cobalt oxide (e.g., Li(Ni)) in that they can improve the capacity characteristics and stability of the battery. 1 / 3 Mn 1 / 3 Co 1 / 3 )O2, Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni) 0.5 Mn 0.3 Co 0.2)O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2 and Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, etc.), lithium nickel cobalt aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05 )O2, etc.), or lithium nickel manganese cobalt aluminum oxide (e.g. Li(Ni 0.86 Co 0.05 Mn 0.07 Al 0.02 )O2), lithium iron phosphate (e.g., LiFePO4), etc., and one or a mixture of two or more of these may be used. The above positive electrode active material may be included in an amount of 60 wt% to 99 wt%, preferably 70 wt% to 99 wt%, and more preferably 80 wt% to 98 wt%, based on the total weight of the positive electrode active material layer. The cathode conductive agent is a component for further improving the conductivity of the cathode active material. The conductive agent is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, carbon powder such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powder such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; conductive fibers such as carbon fibers or metal fibers; fluorinated carbon powder; conductive powder such as aluminum powder or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives, etc. can be used. Typically, the positive electrode conductive material may be included in an amount of 1 wt% to 20 wt%, preferably 1 wt% to 15 wt%, and more preferably 1 wt% to 10 wt%, based on the total weight of the positive electrode active material layer. The positive binder is a component that assists in the bonding of active materials and conductive materials and bonding to the current collector. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polyethylene (PE), polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluororubber, and various copolymers. Typically, the positive electrode binder may be included in an amount of 1 wt% to 20 wt%, preferably 1 wt% to 15 wt%, and more preferably 1 wt% to 10 wt% based on the total weight of the positive electrode active material layer. Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. If it is a separator that is usually used in lithium secondary batteries, it can be used without any special restrictions, and in particular, it is preferable that it has low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, can be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fibers, polyethylene terephthalate fibers, etc. can be used. In addition, a coated separator containing a ceramic component or a polymer material can be used to secure heat resistance or mechanical strength, and can be selectively used in a single-layer or multi-layer structure. In addition, the electrolyte used in the present invention may include, but is not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, etc. that can be used in the manufacture of a lithium secondary battery. Specifically, the electrolyte may include an organic solvent and a lithium salt. As the organic solvent, any solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move may be used without particular limitation. Specifically, the organic solvent may include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; Examples of solvents that can be used include carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (wherein R represents a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; and sulfolanes. Among these, a carbonate solvent is preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable. The above lithium salt can be used without any special limitation as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the anion of the above lithium salt is F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - The lithium salt may be at least one selected from the group consisting of LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. It is preferable to use the concentration of the lithium salt within the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively. In addition to the electrolyte components, the electrolyte may further contain one or more additives, such as, for example, haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxy ethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. In this case, the additives may be contained in an amount of 0.1 to 5 wt% with respect to the total weight of the electrolyte. Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the present invention. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein. Example 1: Preparation of cathode Si / C composite (specific surface area: 2.53 m 2 / g) and natural graphite (specific surface area: 0.93 m 2 / g) mixed in a weight ratio of 90:10 with a negative electrode active material (specific surface area: 2.37 m 2 / g), aqueous binder, first conductive material (SWCNT, specific surface area: 1000 m 2 / g) and the second challenge material (carbon black, specific surface area: 65 m 2 / g) was mixed in water as a solvent to prepare a cathode slurry composition. At this time, the content of each material was set to 90 wt% of negative active material, 8.96 wt% of binder, 0.04 wt% of first conductive material, and 1 wt% of second conductive material based on solid content. At this time, the water-based binder is a polymer in which acrylamide and acrylic acid are used in a molar ratio of 60:40 and polymerized (ammonium persulfate polymerization initiator, 80°C, polymerization reaction for 6 hours). Thereafter, the negative electrode slurry composition was applied to one surface of a copper current collector having a thickness of 18 μm to a thickness of 50 μm, and then dried and rolled at 120°C to manufacture a negative electrode. Examples 2 to 3 and Comparative Examples 1 to 3: Preparation of cathode As described in Table 1 below, the negative electrodes of Examples 2 to 3 and Comparative Examples 1 to 3 were manufactured in the same manner as in Example 1, except that the specific surface areas and weight ratios of the negative active material, the first conductive agent, and the second conductive agent were applied. At this time, based on the solid content of each material, the weight % of the negative active material, the first conductive material, and the second conductive material are listed in Table 1 below, and the binder content is appropriately adjusted so that the sum of the weight % of the negative active material, the binder, the first conductive material, and the second conductive material becomes 100 weight %. The above manufacturing method, the average length (㎛) of the first challenge material, the ACA expressed by the above [Formula 1], and the CA expressed by the above [Formula 2] are summarized and shown in Table 1 below. Negative active material 1 Conductive agent 2 Conductive agent 1 Number of conductive agents Average length (㎛) ACACA Specific surface area (m 2 / g) weight % specific surface area (m 2 / g) weight % specific surface area (m 2 / g) weight % Example 12.379010000.046510.902.031.63 Example 21.279012000.08250.52.301.050.13 Example 33.89908000.0410024.001.516.25 Comparative Example 12.37908000.0086514.002.9910.16 Comparative Example 22.379010000.012510.966.092.50 Comparative Example 30.839015000.0215010.900.425.00 At this time, the average length (㎛) of the first challenge material was measured using an atomic force microscope (AFM). Specifically, the first challenge agent of the above examples and comparative examples was diluted in water, and 50 ㎕ of the diluted solution was dropped onto the surface of freshly cleaved mica, and then vacuum dried to prepare a sample. The prepared sample was photographed using an atomic force microscope (AFM) (Asylum Research, Cypher ES AFM System) under the following conditions. - Measurement mode: AC Air Topography mode (Tapping mode) - Measurement conditions: Set point 0.4 V, Scan rate 1.5 Hz - Measurement image size: Measured at magnifications of 20 ㎛ x 20 ㎛, 15 ㎛ x 15 and 10 ㎛ x 10 ㎛ - Probe: AC160TS (n-type doped Si, reflective Al coating, f0 300 kHz, k 26 N / m) The lengths of more than 400 first challenge materials were measured (using an image processing program) using AFM images obtained by measuring under the above conditions, and then the length distribution was obtained and the average length (㎛) was measured. Experimental Example 1: Evaluation of Lifetime Characteristics and Coating Fairness (Life characteristics) Coin half cells were manufactured using the cathodes of the above examples and comparative examples. In detail, the above-mentioned negative electrode was punched into a circle with a diameter of 14 mm to produce a test negative electrode, 0.3 mm thick lithium metal was used as the positive electrode, 0.1 mm thick porous polyethylene was used as the separator, and an electrolyte containing 1 M LiPF6 dissolved in a 50:50 mixed solution of ethyl carbonate (EC) and methyl ethyl carbonate (EMC) was injected to produce a coin half-cell with a diameter of 32 mm. The above coin half-cell was charged at a constant current of 0.05 C until the voltage reached 0.01 V, and discharged at a constant current of 0.05 C until the voltage reached 1.5 V, which was considered one cycle. A total of 30 charge-discharge cycles were performed to calculate the capacity retention rate. Specifically, the capacity retention rate was derived by the following calculation. Capacity retention rate (%) = (30 discharge capacity / 1 discharge capacity). (Coating fairness) In the cathode manufacturing process of the above examples and comparative examples, when coating the cathode slurry composition on the copper foil, whether or not stains occurred on the electrode surface, whether or not pinholes occurred, and whether or not the filter in the slurry circulation pump became clogged were determined. If any of the problems occurred, they were evaluated as X, and if no problems occurred, they were evaluated as O. Capacity retention rate (%)Coating processabilityExample 186OExample 285OExample 383OComparative example 166OComparative example 265OComparative example 377X Referring to the above [Table 2], in the case of Examples 1 to 3, no problems occurred in the coating process, and it can be confirmed that the capacity retention rate is also superior compared to the comparative examples. In the case of Comparative Example 1, since the CA exceeds the scope of the present invention, it can be confirmed that the conductive network is not sufficiently formed, resulting in a significant decrease in the capacity retention rate. In the case of Comparative Examples 2 and 3, since the ACA is below or exceeds the range of the present invention, it can be confirmed that an abnormality occurs in the coating process and the conductive network is not properly formed, resulting in a significant decrease in the capacity retention rate.

Claims

1. A negative electrode active material layer comprising a negative electrode active material, a binder, a first conductive material, and a second conductive material, The average length of the first challenge material measured using an atomic force microscope (AFM) is 0.7 ㎛ to 6.0 ㎛, ACA expressed by the following equation 1 is 0.5 to 5.0, A cathode having a CA of 0.1 to 8.0, expressed by the following formula 2: [Formula 1] In the above equation 1, the S A is the BET surface area (m) of the first challenge material 2 / g), and the above W A is the weight % of the first conductive material based on the total weight of the negative active material layer, and S B is the BET surface area (m) of the second challenge material 2 / g), and the above W B is the weight % of the second conductive material based on the total weight of the negative active material layer, and S C is the BET surface area (m) of the above negative active material. 2 / g), and the above W C is the weight percentage of the negative electrode active material based on the total weight of the negative electrode active material layer, [Formula 2] In the above equation 2, the S A is the BET surface area (m) of the first challenge material 2 / g), and the above W A is the weight % of the first conductive material based on the total weight of the negative active material layer, and S B is the BET surface area (m) of the second challenge material 2 / g), and the above W B is the weight percentage of the second conductive material based on the total weight of the negative active material layer.

2. In paragraph 1, A cathode having an average length of 0.8 ㎛ to 4.0 ㎛ as measured using an atomic force microscope (AFM) of the first challenge material.

3. In paragraph 1, The above ACA is a cathode having a value of 0.9 to 2.

5.

4. In paragraph 1, The above CA is a cathode having a value of 0.1 to 6.

0.

5. In paragraph 1, A negative electrode wherein the above negative active material includes a silicon-based active material.

6. In paragraph 1, The BET surface area of ​​the above negative active material is 0.2 m 2 / g to 20m 2 / g is the negative pole.

7. In paragraph 1, The BET surface area of ​​the first challenge material is 800 m 2 / g to 1500m 2 / g is the negative pole.

8. In paragraph 1, The above first challenge material is a cathode comprising a single-walled carbon nanotube.

9. In paragraph 1, The BET surface area of ​​the above second challenge material is 25 m 2 / g to 200m 2 / g is the negative pole.

10. In paragraph 1, A cathode in which the second conductive material comprises a dot-shaped conductive material.

11. A lithium secondary battery comprising the negative electrode of paragraph 1.

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