Positive electrode and lithium secondary battery

Abstract

To provide a positive electrode including a positive electrode active material including a layered lithium nickel-manganese-based composite oxide, which increases energy density, improves performance at high temperatures and high voltages, and improves capacity characteristics, initial charge / discharge efficiency, and high-temperature life-cycle characteristics.SOLUTION: There are provided a positive electrode and a lithium secondary battery including the same. The positive electrode includes a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material which includes: core particles including a layered lithium nickel-manganese-based composite oxide, containing 0.1 mol% to 2 mol% of cobalt based on 100 mol% of the total metal excluding lithium; and an aluminum coating layer located on the surface of the core particles. In a dQ / dV graph according to a voltage during standard charging and discharging, evaluated under conditions of 1C=200 mAh / g, 0.2 C and an applied current of 0.5 mA to 0.7 mA, a point where a tangent line drawn from a first inflection point meets a line where dQ / dV=0 appears in a voltage range of 3.68 V to 3.70 V.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a positive electrode and a lithium secondary battery. [Background technology]

[0002] Lithium secondary batteries, which have high energy density yet are easy to carry, are widely used as power sources for mobile information terminals such as mobile phones, laptops, and smartphones. Recently, active research has been conducted into using high-energy-density lithium secondary batteries as power sources for hybrid and electric vehicles or as power storage sources.

[0003] Various positive electrode active materials have been investigated to realize lithium secondary batteries suitable for these applications. Among these, lithium nickel oxide, lithium nickel manganese cobalt composite oxide, lithium nickel cobalt aluminum composite oxide, and lithium cobalt oxide are commonly used as positive electrode active materials. However, while demand for large-sized, high-capacity, and high-energy density lithium secondary batteries has rapidly increased in recent years, the supply of positive electrode active materials containing the rare metal cobalt is expected to be in short supply. In other words, because cobalt is expensive and its remaining reserves are limited, there is a need to develop positive electrode active materials that do not contain cobalt or that have a reduced cobalt content. Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention provides a positive electrode containing a positive electrode active material including a layered lithium nickel-manganese composite oxide, which increases energy density, improves performance at high temperatures and high voltages, and enhances capacity characteristics, initial charge / discharge efficiency, and high-temperature life characteristics. [Means for solving the problem]

[0005] In one embodiment of the present invention, there is provided a positive electrode comprising: a positive electrode current collector; and a positive electrode active material layer located on the positive electrode current collector, wherein the positive electrode active material layer comprises a positive electrode active material including core particles containing a layered lithium nickel-manganese composite oxide containing 0.1 mol % to 2 mol % of cobalt relative to 100 mol % of all metals excluding lithium; and an aluminum coating layer located on the surface of the core particles; and wherein, in a dQ / dV graph as a function of voltage during standard charge / discharge evaluated under conditions of 1C=200 mAh / g, 0.2C, and an applied current of 0.5 mA to 0.7 mA, the point at which a tangent drawn from the first inflection point intersects with a line at which dQ / dV=0 appears in the voltage range of 3.68 V to 3.70 V.

[0006] In yet another embodiment of the present invention, there is provided a lithium secondary battery comprising the above positive electrode, negative electrode, and electrolyte. [Effects of the Invention]

[0007] The positive electrode according to one embodiment of the present invention minimizes production costs, maximizes capacity and energy density, ensures long life characteristics, and improves high-voltage and high-temperature characteristics. A lithium secondary battery using the positive electrode can exhibit high initial charge / discharge capacity and efficiency, and achieve excellent high-temperature life characteristics and high-temperature storage characteristics. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 2] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 3] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 4] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 5] 1 is a graph showing dQ / dV during standard charge / discharge during and after formation for the half cell of Example 1. [Figure 6]1 is a graph showing dQ / dV during standard charge / discharge during and after formation for the half cell of Comparative Example 1. [Figure 7] 1 is a graph showing dQ / dV at the time of formation for half cells of Example 2 and Comparative Example 2. [Figure 8] 1 is a graph showing dQ / dV during standard charge / discharge after formation for half cells of Example 2 and Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0009] Although the present invention may be embodied in many different forms, it is not limited to the embodiments set forth herein.

[0010] The terms used herein are merely used to describe exemplary embodiments and are not intended to limit the present invention. The singular expressions include the plural expressions unless the context clearly indicates otherwise.

[0011] As used herein, "combinations thereof" refers to mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0012] It should be understood that the terms "comprise," "include," "comprise," or "have" are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, but do not preclude the possible presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0013] In the drawings, thicknesses of various layers and regions are exaggerated for clarity, and similar parts are designated by the same reference numerals throughout the specification. When a layer, film, region, plate, or other part is said to be "on" or "above" another part, this includes not only the case where it is "directly on" another part, but also the case where there is another part between them. Conversely, when a part is said to be "directly on" another part, it means that there is no other part between them.

[0014] Furthermore, the term "layer" as used herein includes not only shapes formed on the entire surface when observed in a plan view, but also shapes formed on a portion of the surface.

[0015] The average particle size can be measured by a method well known to those skilled in the art, for example, by using a particle size analyzer or by using a transmission electron microscope or a scanning electron microscope. Alternatively, the average particle size can be calculated by measuring using a dynamic light scattering method, counting the number of particles for each particle size range through data analysis, and then calculating the average particle size. Unless otherwise defined, the average particle size is the diameter (D) of particles whose cumulative volume is 50% by volume in the particle size distribution. 50 ) and, unless otherwise defined, the average particle size is determined by measuring the size (diameter or length of the major axis) of 20 or more particles randomly selected from a scanning electron microscope image to obtain a particle size distribution, and then calculating the diameter (D 50 ) can be taken as the average particle size.

[0016] Here, "or" is not to be construed in an exclusive sense; for example, "A or B" is to be construed as including A, B, A+B, etc.

[0017] The term "metal" is understood to include general metals, transition metals, and metalloids (semimetals).

[0018] positive electrode In one embodiment, a cathode includes a cathode current collector and a cathode active material layer disposed on the cathode current collector, the cathode active material layer comprising core particles including a layered lithium-nickel-manganese composite oxide containing 0.1 mol % to 2 mol % cobalt relative to 100 mol % of all metals excluding lithium, and an aluminum coating layer disposed on the core particles. The cathode active material is characterized in that, after chemical formation, a tangent line drawn from a first inflection point intersects with a line at dQ / dV = 0 in a voltage-dependent dQ / dV graph measured at 1 C = 200 mAh / g, 0.2 C, and an applied current of 0.5 mA to 0.7 mA, in a voltage range of 3.68 V to 3.70 V. A cathode with these characteristics can achieve excellent capacity, efficiency, and lifespan characteristics while reducing production costs, ensure maximized energy density, and improve performance under high-temperature and high-voltage conditions.

[0019] The formation may be the first charge / discharge process after battery fabrication. The post-formation may refer to a standard charge / discharge cycle that occurs after the formation process, e.g., the second charge / discharge cycle. The dQ / dV graph as a function of voltage is represented by a dQ / dV graph as a function of charge / discharge voltage, or simply a dQ / dV graph.

[0020] The dQ / dV graph may be obtained by, for example, charging and discharging a half-cell including a structure in which a positive electrode including the positive electrode active material, a polymer separator, and a lithium metal counter electrode are sequentially stacked, and an electrolyte solution containing a carbonate-based solvent and a lithium salt. The first inflection point represents the point at which the slope of the tangent line in the dQ / dV graph increases and then decreases, and in the case of an S-curve, it can be said to correspond to the midpoint of the S-curve. For example, the first inflection point can be said to be the point at which the slope of the tangent line in the S-curve increases and then decreases.

[0021] For example, the dQ / dV graph as a function of the post-formation voltage may have a slope of 0.02 or less, for example, 0.015 or less, or 0.01 or less, in the range of 3.60 V to 3.68 V. A positive electrode active material that satisfies these characteristics has high capacity and energy density and is excellent in performance, such as life characteristics at high temperatures and high voltages.

[0022] In a graph of dQ / dV as a function of voltage during formation, the positive electrode active material according to one embodiment may be represented by a voltage range of 3.68V to 3.72V, for example, 3.68V to 3.70V, where a tangent line drawn from the first inflection point intersects with a line where dQ / dV=0.

[0023] In addition, the point where a tangent line drawn from the first inflection point intersects with the line where dQ / dV = 0 in the dQ / dV graph according to the voltage after formation may be represented by an even lower voltage value than the point where a tangent line drawn from the first inflection point intersects with the line where dQ / dV = 0 in the dQ / dV graph according to the voltage during formation. In other words, the dQ / dV graph during standard charge / discharge is shifted to the left compared to the dQ / dV graph during formation.

[0024] Also, the dQ / dV graph during formation shows two main peaks, while the dQ / dV graph during standard charge / discharge after formation shows one main peak.

[0025] According to one embodiment, the positive electrode active material includes a core particle including a layered lithium nickel-manganese composite oxide containing 0.1 mol % to 2 mol % of cobalt relative to 100 mol % of all metals excluding lithium, and an aluminum coating layer located on the surface of the core particle.

[0026] In recent years, the price of the rare metal cobalt has skyrocketed, spurring demand for the development of cathode active materials that either eliminate cobalt or contain reduced amounts. Among these, cathode active materials with olivine crystal structures, such as lithium iron phosphate (LFP), lithium manganese phosphate (LMP), and lithium manganese iron phosphate (LMFP), or spinel crystal structures, such as lithium manganese oxide (LMO), have limitations in achieving high capacity due to the limited amount of lithium available within their structures. Layered nickel-manganese cathode active materials offer excellent capacity and efficiency characteristics due to the high amount of lithium within their structures, making them suitable for high-capacity batteries. However, the reduced cobalt content, which plays a key role in the layered structure, reduces structural stability, increases resistance, and hinders long-life performance. Furthermore, reducing the cobalt content accelerates side reactions between the cathode active material and the electrolyte under high-voltage and high-temperature conditions, increasing gas generation and reducing lifespan.

[0027] According to one embodiment, the positive electrode active material may be a cobalt-less positive electrode active material containing a small or very small amount of cobalt, and may be obtained by introducing an aluminum coating layer onto the surface of layered lithium nickel-manganese composite oxide particles containing a small amount of cobalt. The positive electrode active material according to one embodiment not only has a reinforced particle surface but also a stronger internal crystalline structure, which prevents surface deterioration or crystal structure collapse even with repeated charge and discharge, thereby achieving long life characteristics, high initial discharge capacity and charge and discharge efficiency characteristics, and excellent life characteristics even under high voltage and high temperature conditions.

[0028] core particle For example, the core particle may be in the form of a secondary particle formed by agglomeration of a plurality of primary particles, and the average particle diameter (D 50 ) may be 10 μm to 18 μm, for example, 11 μm to 16 μm, or 12 μm to 15 μm. The average particle size is determined by measuring the size (diameter or length of the major axis) of 20 or more particles randomly selected in a scanning electron microscope image of the positive electrode active material to obtain a particle size distribution, and then calculating the diameter (D) of the particles whose cumulative volume is 50% by volume in the particle size distribution.50 ) may be taken as the average particle size. When the average particle size of the positive electrode active material satisfies the above range, high capacity and long life can be achieved, which is advantageous for forming a coating layer according to an embodiment.

[0029] According to one embodiment, the positive electrode active material contains 0.1 mol% to 2 mol% cobalt. The positive electrode active material can be prepared by coating a layered lithium nickel-manganese composite oxide containing no or only a small amount of cobalt with aluminum using a wet pre-addition method, followed by dry coating with cobalt, as described below. This allows cobalt to exist on the particle surface and also to flow into the interior of secondary particles, forming a structure coated on the grain boundaries. This method strengthens both the internal crystalline structure and the surface of the positive electrode active material, allowing it to exhibit excellent capacity and life characteristics even under high temperature and high voltage conditions.

[0030] A cathode active material prepared according to one embodiment may include a core particle in the form of a secondary particle formed by agglomeration of a plurality of primary particles, a coating layer containing aluminum located on the surface of the core particle, and a grain boundary coating portion containing cobalt located on the surface of the primary particles within the secondary particle. When a nickel-manganese-cobalt-based precursor is used or when a cobalt source is co-sintered during the sintering of the precursor and the lithium source to dope the cobalt, the cobalt may be uniformly present within the secondary particles. However, a cathode active material according to one embodiment may be prepared by wet-coating the surface of the core particle with aluminum and then dry-coating the cobalt. As a result, the cobalt may be present on the surface of the secondary particles, but some of the cobalt may diffuse into the interior of the secondary particles and be present at the grain boundaries, which are the surfaces of the primary particles located within the secondary particles. In other words, the cathode active material may have a structure in which the surfaces of the secondary particles are coated with aluminum in the form of a thin, uniform film, and the grain boundaries within the secondary particles are coated with cobalt. Such a positive electrode active material can maintain a structurally stable secondary particle form even after repeated charge and discharge, and can achieve excellent life characteristics even under high temperature and high voltage conditions.

[0031] The cobalt content may be 0.1 mol% to 2 mol%, for example, 0.1 mol% to 1.9 mol%, or 0.5 mol% to 1.5 mol%, based on 100 mol% of all metals excluding lithium. When the cobalt content satisfies this range, it is suitable for coating grain boundaries and strengthens the crystal structure while reducing costs, thereby improving capacity and life characteristics under high temperature and high voltage conditions.

[0032] In the layered lithium nickel-manganese composite oxide, the nickel content is 60 mol% or more relative to 100 mol% of all metals excluding lithium, and can be, for example, 60 mol% to 80 mol%, 65 mol% to 80 mol%, 70 mol% to 80 mol%, 60 mol% to 79 mol%, 60 mol% to 78 mol%, or 60 mol% to 75 mol%, etc. When the nickel content satisfies the above range, high capacity can be achieved, and structural stability can be improved even when the cobalt content is reduced.

[0033] In the layered lithium nickel-manganese composite oxide, the manganese content is 15 mol% or more relative to 100 mol% of all metals excluding lithium, and may be, for example, 15 mol% to 40 mol%, 15 mol% to 35 mol%, 15 mol% to 30 mol%, or 20 mol% to 30%, etc. When the manganese content satisfies the above range, the positive electrode active material can achieve high capacity while improving structural stability.

[0034] The lithium nickel-manganese composite oxide may be, for example, a lithium nickel-manganese-aluminum composite oxide containing aluminum in addition to nickel and manganese. When the composite oxide contains aluminum, it is advantageous for maintaining a stable layered structure even when the cobalt content is reduced. The aluminum content relative to 100 mol% of all metals excluding lithium in the lithium nickel-manganese-aluminum composite oxide may be 0.1 mol% or more, 0.5 mol% or more, or 1 mol% or more, for example, 1 mol% to 3 mol%, 1 mol% to 2.5 mol%, 1 mol% to 2 mol%, or 1.5 mol% to 2.5 mol%. Here, the aluminum content refers to the content of aluminum present in the core particles. When the aluminum content satisfies the above range, a stable layered structure can be maintained even when cobalt is excluded from the core particles, preventing structural collapse during charge and discharge, and achieving long-life cathode active materials.

[0035] According to one embodiment, the aluminum concentration within the core particle may be uniform. This means that the aluminum concentration does not have a gradient from the center to the surface within the core particle, or that the aluminum concentration is neither higher nor lower at the outside than at the inside of the core particle, but is uniformly dispersed within the core particle. This structure may be obtained by synthesizing a composite oxide using a nickel-manganese-aluminum hydroxide as a precursor, without additional aluminum doping during the core particle synthesis process, by using an aluminum raw material in the precursor preparation. The core particle may be in the form of a secondary particle formed by agglomeration of multiple primary particles, and the aluminum content within the primary particle may be the same or similar regardless of the position of the primary particle. In other words, if a primary particle is selected from any position in the cross-section of the secondary particle and the aluminum content is measured within the primary particle, rather than at the interface, the aluminum content can be expressed as the same / similar / uniform regardless of the position of the primary particle, i.e., whether the primary particle is near the center or the surface of the secondary particle. In such a structure, even if cobalt is absent or present in only a very small amount, a stable layered structure can be maintained, and no aluminum by-products or aluminum agglomerates are generated, thereby simultaneously improving the capacity, efficiency, and life characteristics of the positive electrode active material.

[0036] The layered lithium nickel-manganese composite oxide is specifically represented by the following chemical formula 1. [Chemical formula 1] Li a1 Ni x1 Mn y1 Co z1 Al v1 M 1 w1 O 2-b1 X b1

[0037] In chemical formula 1, 0.9≦a1≦1.8, 0.6≦x1≦0.8, 0.15≦y1≦0.399, 0.001≦z1≦0.02, 0≦v1≦0.03, 0≦w1≦0.3, 0.9≦x1+y1+z1+v1+w1≦1.1, and 0≦b1≦0.1; M 1is one or more elements selected from B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X is one or more elements selected from F, P, and S.

[0038] In the chemical formula 1, 0.9 ≦ a1 ≦ 1.5, or 0.9 ≦ a1 ≦ 1.2 may hold. Further, the chemical formula 1 contains aluminum, and in this case, 0.6 ≦ x1 ≦ 0.8, 0.15 ≦ y1 ≦ 0.299, 0.001 ≦ z1 ≦ 0.02, 0 < v1 ≦ 0.03 (for example, 0.001 ≦ v1 ≦ 0.03), 0 ≦ w1 ≦ 0.3 may hold.

[0039] In the chemical formula 1, for example, 0.6 ≦ x1 ≦ 0.79, 0.6 ≦ x1 ≦ 0.78, 0.6 ≦ x1 ≦ 0.75, 0.65 ≦ x1 ≦ 0.8, or 0.7 ≦ x1 ≦ 0.79, and 0.15 ≦ y1 ≦ 0.35, 0.15 ≦ y1 ≦ 0.30, 0.15 ≦ y1 ≦ 0.29, or 0.2 ≦ y1 ≦ 0.3 may hold. Further, 0.005 ≦ z1 ≦ 0.02, or 0.01 ≦ z1 ≦ 0.02, 0.01 ≦ v1 ≦ 0.025, 0.01 < v1 ≦ 0.02, or 0.01 < v1 ≦ 0.019, and 0 ≦ w1 ≦ 0.28, 0 ≦ w1 ≦​​​​​The positive electrode active material includes an aluminum coating layer located on the surface of the secondary particles. The aluminum-rich layer on the surface of the positive electrode active material effectively suppresses side reactions with the electrolyte at high voltages, improving capacity and lifespan characteristics at high voltages. Layered lithium nickel-manganese composite oxides are susceptible to chemical attack from components in the electrolyte when the battery is operated under high voltage or high temperature conditions, potentially causing frequent side reactions with the electrolyte, resulting in increased gas generation and reduced battery life and safety. However, the introduction of a coating layer according to one embodiment can alleviate these issues.

[0041] The aluminum coating layer can include, for example, aluminum oxide, lithium aluminum oxide, or a combination thereof, and can include, for example, LiAlO2.

[0042] The aluminum content of the coating layer, relative to 100 mol% of the total metals excluding lithium in the positive electrode active material, may be 0.1 mol% to 3 mol%, for example, 0.1 mol% to 2 mol%, 0.2 mol% to 1.9 mol%, 0.3 mol% to 1.8 mol%, 0.5 mol% to 1.5 mol%, or 0.8 mol% to 1.3 mol%. The content of aluminum or other components in the coating layer can be measured, for example, by SEM-EDS analysis of the surface or cross-section of the positive electrode active material. When the aluminum content in the coating layer satisfies the above range, a uniform and thin coating layer can be formed, the resistance of the positive electrode active material does not increase, side reactions with the electrolyte are effectively suppressed, and the life characteristics of lithium secondary batteries at high voltages can be improved.

[0043] Layered lithium nickel-manganese composite oxides differ significantly from oxides of other compositions, such as lithium nickel-cobalt-manganese composite oxides, lithium nickel-cobalt-aluminum composite oxides, and lithium cobalt-based oxides, in terms of the residual lithium content on the particle surface and in many other surface characteristics. Therefore, existing coating methods cannot form a uniform, well-formed coating layer. Therefore, in one embodiment, a uniform coating layer can be formed by (i) first preparing a coating solution in which the salt is completely dissolved by adding and mixing coating materials into an aqueous solvent using a salt-dissolution method, (ii) adding and mixing core particles into this coating solution to coat them, and (iii) subsequently removing the solvent, drying, and heat-treating the resulting mixture. This is a salt-dissolution wet coating method, and may be a pre-addition method in which the salt, the coating material, is first completely dissolved and then the active material particles are added. This method successfully forms a uniform, thin coating layer on the surface of the layered lithium nickel-manganese composite oxide.

[0044] This coating method can further increase the content of coating elements on the active material surface compared to conventional dry methods or post-addition wet methods. For example, the coating content on the surface of the positive electrode active material measured by EP-EDS analysis can be 5 at% to 35 at% relative to 100 at% of the total metals on the surface excluding lithium, e.g., 5 at% to 30 at%, 5 at% to 25 at%, 5 at% to 20 at%, or 10 at% to 20 at%. Within this content range, the coating layer can effectively improve high-voltage characteristics without increasing the resistance of the positive electrode active material.

[0045] The aluminum coating layer may be in the form of a film that continuously surrounds the surface of the secondary particles, for example, in the form of a shell that surrounds the entire surface of the secondary particles. This is distinct from a structure in which only a portion of the surface of the secondary particles is partially coated. According to one embodiment, the coating layer may be formed to completely surround the surface of the secondary particles, but with a very thin and uniform thickness. As a result, the cathode active material does not increase in resistance or decrease in capacity, improves structural stability, effectively suppresses side reactions with the electrolyte, reduces gas generation under high voltage and high temperature conditions, and achieves long-life characteristics.

[0046] The thickness of the aluminum coating layer may be 5 nm to 500 nm, for example, 10 nm to 500 nm, 5 nm to 450 nm, 5 nm to 400 nm, 5 nm to 350 nm, 5 nm to 300 nm, 5 nm to 250 nm, 5 nm to 200 nm, 5 nm to 150 nm, 5 nm to 100 nm, 5 nm to 80 nm, 10 nm to 50 nm, 20 nm to 500 nm, 30 nm to 500 nm, or 40 nm to 500 nm. For example, the thickness of the coating layer may be 40 nm or less. When the coating layer satisfies the above thickness range, the coating does not increase resistance or decrease capacity, but improves the structural stability of the positive electrode active material and effectively suppresses side reactions with the electrolyte. The thickness of the coating layer may be measured, for example, by SEM, TEM, TOF-SIMS, XPS, or EDS analysis, and the thickness range of the coating layer may be measured by TEM-EDS line profile.

[0047] The aluminum coating layer is characterized by its thin and uniform thickness, ranging from several tens to several hundreds of nanometers. For example, the thickness deviation of the coating layer within a single cathode active material particle may be 20% or less, 18% or less, or 15% or less. Here, the coating thickness deviation refers to the thickness of the coating layer within a single cathode active material particle. For example, the coating thickness deviation is calculated by measuring the thickness at approximately 10 points in an electron microscope image of the cross section of a single cathode active material particle, calculating the arithmetic mean, dividing the absolute value of the difference between one data point and the arithmetic mean value by the arithmetic mean value, and multiplying by 100. A coating thickness deviation or standard deviation within the above range indicates that a uniformly thick coating layer is well formed in the form of a film on the surface of the cathode active material particle, thereby improving the structural stability of the cathode active material, effectively suppressing side reactions with the electrolyte, and minimizing increases in resistance and decreases in capacity due to the coating.

[0048] The aluminum coating layer may further contain nickel, manganese, or a combination thereof in addition to aluminum. Nickel and manganese are originally contained in the core particles and are introduced during the formation of the aluminum coating layer, and their contents are not particularly limited. According to one embodiment, the aluminum coating layer necessarily contains aluminum and selectively contains nickel and manganese. The aluminum coating layer is formed to a thin and uniform thickness, which can improve the high-voltage characteristics and life characteristics of the positive electrode active material.

[0049] In addition, the aluminum coating layer may further contain sulfur in addition to aluminum. The sulfur is introduced during the process of adding aluminum sulfate to the aluminum raw material used to form the aluminum coating layer, and the content of sulfur is not particularly limited. According to an embodiment, the aluminum coating layer necessarily contains aluminum and optionally contains sulfur, thereby improving the high-voltage characteristics and life characteristics of the positive electrode active material.

[0050] The positive electrode active material may further include a coating layer containing B, Mg, Ti, V, W, Y, Zr, or a combination thereof in addition to the aluminum coating layer, and in this case, structural stability and life characteristics may be improved.

[0051] For example, the positive electrode active material may further include a zirconium coating layer disposed on the aluminum coating layer. The zirconium content in the coating layer may be 0.05 mol% to 1 mol%, for example, 0.1 mol% to 1 mol%, 0.1 mol% to 0.9 mol%, 0.1 mol% to 0.8 mol%, or 0.1 mol% to 0.6 mol%, based on 100 mol% of the total metals (excluding lithium) in the positive electrode active material. When the zirconium content satisfies the above range, the positive electrode active material does not experience a decrease in capacity or an increase in resistance, and a good coating layer is formed, effectively suppressing side reactions with the electrolyte, thereby further improving capacity and life characteristics under high-voltage driving conditions.

[0052] The positive electrode active material may further include an yttrium coating layer, and in this case, the content of yttrium may be 0.1 mol % to 1 mol % based on 100 mol % of all metals excluding lithium in the positive electrode active material.

[0053] Meanwhile, aluminum may be diffused into the secondary particles during the coating layer formation process. Therefore, according to an embodiment, the positive electrode active material may further include a grain boundary coating region containing aluminum located on the surface of the primary particles within the secondary particles. The "interior of the secondary particles" may refer to the entire interior of the secondary particles excluding the surface, or may refer to the region extending from the surface of the secondary particles toward the center of the secondary particles, extending up to approximately 60% of the radius. The grain boundary coating region is a concept distinct from the coating layer on the surface of the secondary particles, and refers to a coating region formed on the surface of the primary particles located within the secondary particles. The presence of the grain boundary coating region can be confirmed by SEM-EDS analysis of a cross section of the positive electrode active material. The formation of the aluminum grain boundary coating region further stabilizes the structure of the positive electrode active material, improving its life characteristics.

[0054] The aluminum content in the grain boundary coating portion is not particularly limited, and as an example, the aluminum content in the grain boundary coating portion may be less than the aluminum content in the coating layer.

[0055] Bimodal In one embodiment, a first positive electrode active material includes a layered lithium nickel-manganese composite oxide containing 0.1 mol % to 2 mol % of cobalt relative to 100 mol % of all metals excluding lithium, the first positive electrode active material including a core particle formed by agglomeration of a plurality of primary particles, and an aluminum coating layer located on the surface of the core particle, and a layered lithium nickel-manganese composite oxide having a single particle form and an average particle size (D 50 The present invention provides a positive electrode active material comprising a second positive electrode active material having a

[0056] The first positive electrode active material corresponds to the positive electrode active material described above, and can be expressed as large particles in this specification, and the second positive electrode active material can be expressed as small particles.

[0057] By appropriately mixing large particles in the form of secondary particles and small particles in the form of single particles, the capacity and energy density of the lithium nickel-manganese positive electrode can be maximized, and the high-temperature life characteristics and high-voltage characteristics can be improved. Here, the average particle size is determined by measuring the size (diameter or length of the major axis) of 20 or more random particles in a scanning electron microscope image of the positive electrode active material to obtain a particle size distribution, and then determining the diameter (D) of the particles that make up 50% of the cumulative volume in the particle size distribution. 50 ) can be taken as the average particle size.

[0058] The average particle size (D 50 The average particle diameter (D ) of the single particles of the second positive electrode active material may be, for example, 10 μm to 18 μm, or 12 μm to 16 μm. 50) may be, for example, 1 μm to 8 μm, 1 μm to 7 μm, 1.5 μm to 6 μm, or 2 μm to 5 μm. When the average particle size of each positive electrode active material falls within the above range, a high energy density can be achieved and excellent life characteristics can be exhibited.

[0059] The first positive electrode active material may be included in an amount of 60% to 95% by weight, for example, 70% to 90% by weight, based on a total of 100% by weight of the first positive electrode active material and the second positive electrode active material. The second positive electrode active material may be included in an amount of 5% to 40% by weight, for example, 10% to 30% by weight, based on a total of 100% by weight of the first positive electrode active material and the second positive electrode active material. When the mixing ratio of the first positive electrode active material to the second positive electrode active material satisfies the above range, it is possible to increase the energy density while maximizing the capacity.

[0060] The first positive electrode active material has been described above, and therefore a detailed description thereof will be omitted.

[0061] The term "single particle" of the second positive electrode active material means a particle that exists independently without a grain boundary within the particle and is composed of a single particle. The term may refer to a single particle, a monolith structure, a single body structure, or a non-aggregated particle in which the particles are morphologically present in an independent phase without aggregation, and may be, for example, a single crystal.

[0062] For example, the second positive electrode active material may be a cobalt-free positive electrode active material containing 0 mol% to less than 0.1 mol% of cobalt relative to 100 mol% of all metals excluding lithium, where the cobalt content may be 0.09 mol% or less, 0.05 mol% or less, 0.01 mol% or less, or 0.001 mol% or less.

[0063] The nickel content in the layered lithium nickel-manganese composite oxide that is the second positive electrode active material may be 60 mol% or more relative to 100 mol% of all metals in the lithium nickel-manganese composite oxide excluding lithium, and may be, for example, 60 mol% to 80 mol%, 65 mol% to 80 mol%, 70 mol% to 80 mol%, 60 mol% to 79 mol%, 60 mol% to 78 mol%, or 60 mol% to 75 mol%, etc. When the nickel content satisfies the above range, high capacity can be achieved, and structural stability can be improved even when the cobalt content is reduced.

[0064] The manganese content in the second positive electrode active material may be, for example, 15 mol % or more relative to 100 mol % of all metals excluding lithium in the layered lithium nickel-manganese composite oxide, and may be, for example, 15 mol % to 40 mol %, 15 mol % to 35 mol %, 15 mol % to 30 mol %, or 20 mol % to 30 mol %, etc. When the manganese content satisfies the above range, the positive electrode active material can achieve high capacity while improving structural stability.

[0065] The lithium nickel-manganese-based composite oxide of the second positive electrode active material may be a lithium nickel-manganese-aluminum-based composite oxide containing aluminum in addition to nickel and manganese. When the composite oxide contains aluminum, it is advantageous for maintaining a stable layered structure even when cobalt is excluded from the structure. The aluminum content relative to 100 mol% of the lithium nickel-manganese-aluminum-based composite oxide may be 0.1 mol% or more, 0.5 mol% or more, or 1 mol% or more, for example, 1 mol% to 3 mol%, 1 mol% to 2.5 mol%, 1 mol% to 2 mol%, or 1 mol% to 1.9 mol%. When the aluminum content is within the above range, a stable layered structure can be maintained even when cobalt is excluded, preventing the problem of structural collapse during charge and discharge, and achieving long-life characteristics for the positive electrode active material.

[0066] The lithium nickel-manganese composite oxide of the second positive electrode active material is represented by the following chemical formula 2. [Chemical Formula 2] Li a2 Ni x2 Mn y2 Al z2 M 2 w2 O 2-b2 X b2

[0067] In Chemical Formula 2, 0.9 ≦ a2 ≦ 1.8, 0.6 ≦ x2 ≦ 0.8, 0.15 ≦ y2 ≦ 0.4, 0 ≦ z2 ≦ 0.03, 0 ≦ w2 ≦ 0.3, 0.9 ≦ x2 + y2 + z2 + w2 ≦ 1.1, and 0 ≦ b2 ≦ 0.1, and M 2 is one or more elements selected from B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, and Zr, and X is one or more elements selected from F, P, and S.

[0068] In Chemical Formula 2, 0.9 ≦ a2 ≦ 1.5, or 0.9 ≦ a2 ≦ 1.2 may hold. Additionally, Chemical Formula 2 contains aluminum, and in this case, it can satisfy 0.6 ≦ x2 ≦ 0.8, 0.15 ≦ y2 ≦ 0.39, 0.01 ≦ z2 ≦ 0.03, and 0 ≦ w2 ≦ 0.29. For example, it can satisfy 0.6 ≦ x2 ≦ 0.8, 0.15 ≦ y2 ≦ 0.39, 0.01 < z2 ≦ 0.03, and 0 ≦ w2 ≦ 0.29.

[0069] In Chemical Formula 2, for example, 0.6 ≦ x2 ≦ 0.79, 0.6 ≦ x2 ≦ 0.78, 0.6 ≦ x2 ≦ 0.75, 0.65 ≦ x2 ≦ 0.8, or 0.7 ≦ x2 ≦ 0.79 may be satisfied, 0.15 ≦ y2 ≦ 0.35, 0.15 ≦ y2 ≦ 0.30, 0.15 ≦ y2 ≦ 0.29, 0.15 ≦ y2 ≦ 0.39, or 0.2 ≦ y2 ≦ 0.3 may be satisfied, 0.01 ≦ z2 ≦ 0.025, 0.01 < z2 ≦ 0.02, or 0.01 < z2 ≦ 0.019 may be satisfied, and 0 ≦ w2 ≦ 0.28, 0 ≦ w

[0070] The second positive electrode active material may further include a coating layer located on the surface of the single particles and containing Al, B, Mg, Ti, V, W, Y, Zr, or a combination thereof. The content of the coating material may be 0.1 mol % to 5 mol % relative to 100 mol % of all metals excluding lithium in the second positive electrode active material, for example, 0.1 mol % to 3 mol %, 0.3 mol % to 2 mol %, or 0.5 mol % to 1.5 mol %. When such a coating layer is included, the second positive electrode active material may achieve even better life characteristics.

[0071] For example, the second positive electrode active material may include an aluminum coating layer located on the surface of the single particle. By including an aluminum-rich layer on the surface of the second positive electrode active material, side reactions with the electrolyte at high voltages may be effectively suppressed, thereby improving capacity and lifespan characteristics at high voltages.

[0072] The aluminum content in the coating layer of the second positive electrode active material may be 0.1 mol% to 2 mol%, for example, 0.2 mol% to 1.9 mol%, 0.3 mol% to 1.8 mol%, 0.5 mol% to 1.5 mol%, or 0.8 mol% to 1.3 mol%, based on 100 mol% of all metals (excluding lithium) in the second positive electrode active material. This refers to the content of aluminum contained in the coating layer separately from the aluminum contained within the individual particles. The aluminum content in the coating layer can be measured, for example, by SEM-EDS analysis of the surface or cross-section of the positive electrode active material. When the aluminum content in the coating layer satisfies the above range, a uniform and thin coating layer can be formed, the resistance of the positive electrode active material is not increased, side reactions with the electrolyte are effectively suppressed, and the life characteristics of lithium secondary batteries under high-voltage and high-temperature conditions can be improved. For example, if the aluminum content of the coating layer is too high, a uniform coating layer may not be formed or the resistance may increase, resulting in reduced charge / discharge efficiency and life characteristics. If the aluminum content of the coating layer is too low, a coating layer of appropriate thickness may not be formed, resulting in reduced effectiveness in suppressing side reactions with the electrolyte.

[0073] For example, the coating layer of the second positive electrode active material may further include yttrium. The yttrium content in the coating layer of the second positive electrode active material may be 0.1 mol % to 1 mol %, relative to 100 mol % of all metals excluding lithium in the second positive electrode active material, for example, 0.1 mol % to 0.9 mol %, 0.1 mol % to 0.8 mol %, 0.1 mol % to 0.6 mol %, 0.1 mol % to 0.4 mol %, or 0.1 mol % to 0.3 mol %. When the yttrium content satisfies the above range, a good coating layer is formed without a decrease in capacity or an increase in resistance of the positive electrode active material, and side reactions with the electrolyte are effectively suppressed, thereby effectively reducing the amount of gas generation under high voltage and high temperature conditions.

[0074] The coating layer of the second positive electrode active material may be in the form of a film that continuously surrounds the surface of the single particle, or may be in the form of a shell that surrounds the entire surface of the single particle. This is distinct from a structure in which only a portion of the particle surface is partially coated. According to one embodiment, the coating layer may be formed to a very thin and uniform thickness while completely surrounding the surface of the single particle. This improves the structural stability of the positive electrode active material without increasing resistance or decreasing capacity, and effectively suppresses side reactions with the electrolyte, thereby achieving long-life characteristics at high voltages.

[0075] The thickness of the coating layer of the second positive electrode active material may be 5 nm to 500 nm, for example, 5 nm to 450 nm, 5 nm to 400 nm, 5 nm to 350 nm, 5 nm to 300 nm, 5 nm to 250 nm, 5 nm to 200 nm, 5 nm to 150 nm, 5 nm to 100 nm, 5 nm to 80 nm, 10 nm to 50 nm, 20 nm to 500 nm, 30 nm to 500 nm, or 40 nm to 500 nm. For example, the thickness of the coating layer may be 40 nm or less. When the coating layer satisfies the above thickness range, the coating may improve the structural stability of the positive electrode active material and effectively suppress side reactions with the electrolyte, even without increasing resistance or decreasing capacity. The thickness of the coating layer may be measured, for example, by SEM, TEM, TOF-SIMS, XPS, or EDS analysis, and the thickness range of the coating layer may be measured by TEM-EDS line profile.

[0076] In the coating layer of the second positive electrode active material, aluminum may exist in the form of a continuous film, and yttrium may exist in the form of islands, depending on the properties of each element.

[0077] In one embodiment, aluminum and yttrium may be mixed in one coating layer, and in this case, aluminum may be present in the form of a continuous film, and yttrium may be present in the form of islands, but the forms are not limited thereto.

[0078] In another embodiment, aluminum and yttrium may form separate layers. For example, the second positive electrode active material may include a first coating layer containing aluminum located on the surface of the single particle, and a second coating layer containing yttrium located on the first coating layer. Aluminum may first adhere to or be absorbed onto the surface of the single particle to form a thin first coating layer, and then yttrium may be coated on top of the first coating layer to form the second coating layer. While the first and second coating layers may contain both aluminum and yttrium, the first coating layer may be an aluminum-rich coating layer primarily composed of aluminum, and the second coating layer may be an yttrium-rich coating layer primarily composed of yttrium. In this case, yttrium may also exist in the second coating layer in the form of islands, but this is not limited thereto.

[0079] The thicknesses of the first coating layer and the second coating layer are not particularly limited, but the thickness of the first coating layer may be 5 nm to 200 nm, for example, 5 nm to 100 nm, 5 nm to 80 nm, or 10 nm to 50 nm. The thickness of the second coating layer may be 5 nm to 300 nm, for example, 5 nm to 200 nm, 5 nm to 100 nm, 5 nm to 80 nm, or 10 nm to 50 nm. When each thickness falls within the above range, the coating does not increase resistance or decrease capacity, but the structural stability of the positive electrode active material is improved, and side reactions with the electrolyte are effectively suppressed, thereby improving life characteristics at high voltages.

[0080] The positive electrode active material according to one embodiment may be characterized by being sodium-free. Although sodium ions are generally used in the manufacturing process of a positive electrode active material, the manufacturing method described below may allow positive electrode active material particles with a stable structure and a coating layer with a uniform thickness to be formed without using sodium ions.

[0081] According to an embodiment, the positive electrode active material may contain sulfur (S) components on the surface, which may be due to the aluminum coating material.

[0082] Method for producing positive electrode active material According to one embodiment, a cathode active material can be manufactured by (i) preparing core particles, which include a layered lithium nickel-manganese composite oxide and are in the form of secondary particles formed by agglomeration of a plurality of primary particles; (ii) preparing an aluminum coating solution containing an aqueous solvent and an aluminum raw material; (iii) adding the core particles to the aluminum coating solution, mixing, and drying to prepare a coated product; and (iv) dry-mixing the coated product with a cobalt raw material and heat-treating the mixture.

[0083] In step (i), the core particles can be obtained by, for example, mixing a nickel-manganese composite hydroxide and a lithium source and subjecting the mixture to a first heat treatment. The nickel-manganese composite hydroxide, which is a precursor of the core particles, can contain no or a very small amount of cobalt, and can be, for example, a cobalt-free nickel-manganese composite hydroxide. The nickel-manganese composite hydroxide can be prepared by a common coprecipitation method.

[0084] In the nickel-manganese composite hydroxide, the nickel content relative to 100 mol% of the total metals may be 60 mol% to 80 mol%, for example, 65 mol% to 80 mol%, 70 mol% to 80 mol%, 60 mol% to 79 mol%, 60 mol% to 78 mol%, or 60 mol% to 75 mol%, etc. When the nickel content satisfies the above range, high capacity can be achieved, and structural stability can be improved even when the cobalt content is reduced.

[0085] In the nickel-manganese composite hydroxide, the manganese content relative to 100 mol% of the total metals may be 15 mol% or more, for example, 15 mol% to 40 mol%, 15 mol% to 35 mol%, 15 mol% to 30 mol%, or 20 mol% to 30%, etc. When the manganese content satisfies the above range, it is possible to improve the structural stability of the positive electrode active material while realizing high capacity, and it is possible to reduce production costs and improve economic efficiency.

[0086] Furthermore, when the nickel-manganese composite hydroxide further contains aluminum, the aluminum content relative to 100 mol% of the total metals may be 0.1 mol% or more, 0.5 mol% or more, or 1 mol% or more, for example, 1 mol% to 3 mol%, 1 mol% to 2.5 mol%, 1 mol% to 2 mol%, or 1 mol% to 1.9 mol%. When the aluminum content in the composite hydroxide satisfies the above range, it is possible to improve the structural stability of the positive electrode active material while achieving high capacity, and it is possible to reduce production costs and improve economic efficiency.

[0087] According to one embodiment, a method for manufacturing a cathode active material may involve using an aluminum precursor to manufacture a precursor without further doping with aluminum, thereby using a nickel-manganese-aluminum composite hydroxide as a precursor, in which aluminum is uniformly dispersed within the structure. Using such a precursor may allow for the manufacture of a cathode active material that stably maintains its layered structure even during repeated charge and discharge cycles, even without cobalt, and may prevent the formation of aluminum by-products or aluminum aggregates, thereby improving the capacity, efficiency, and lifespan of the cathode active material.

[0088] In the nickel-manganese composite hydroxide, the cobalt content relative to 100 mol% of the total metals may be 0.01 mol% or less, 0.005 mol% or less, or 0.001 mol% or less, for example, 0 mol% to 0.01 mol%, 0 mol% to 0.005 mol%, or 0 mol% to 0.001 mol%. Such a nickel-manganese composite hydroxide can avoid the increase in unit price due to cobalt, is economical, maximizes capacity, and improves structural stability.

[0089] The nickel-manganese composite hydroxide is in the form of particles, and the average particle size (D 50 ) may be 10 μm to 18 μm, for example, 11 μm to 18 μm, or 12 μm to 16 μm.

[0090] The nickel-manganese composite hydroxide and the lithium raw material may be mixed at a molar ratio of 1:0.9 to 1:1.8, for example, at a molar ratio of 1:0.9 to 1:1.5 or 1:1 to 1:1.2.

[0091] The first heat treatment can be performed in an oxygen atmosphere, for example, at a temperature range of 750°C to 950°C, or 780°C to 900°C, or 810°C to 890°C, for 2 hours to 20 hours, or 4 hours to 12 hours.

[0092] The first heat treatment can produce a lithium nickel-manganese composite oxide. In the resulting lithium nickel-manganese composite oxide, the nickel content can be 60 mol% to 80 mol%, the manganese content can be 15 mol% or more, the aluminum content can be 0 mol% to 3 mol%, and the cobalt content can be a very small amount of 0 mol% to 0.01 mol%, based on 100 mol% of all metals excluding lithium. This composite oxide differs significantly from oxides of other compositions, such as lithium nickel-cobalt-manganese composite oxide, lithium nickel-cobalt-aluminum composite oxide, and lithium cobalt oxide, in the amount of residual lithium on the particle surface and in many of its surface properties. Therefore, it is impossible to form a uniform, well-formed coating layer using existing coating methods.

[0093] Therefore, in the method for manufacturing a positive electrode active material according to one embodiment, steps (ii) and (iii) include preparing an aluminum coating solution in which salt is completely dissolved by a salt-dissolution method by adding and mixing an aqueous solvent and an aluminum raw material, adding and mixing core particles into the aluminum coating solution, and then drying and coating the aluminum coating solution, thereby forming a uniform coating layer on the positive electrode active material.

[0094] This is a salt-dissolution wet coating method, and can be a pre-addition method in which the coating raw material salt is first completely dissolved and then the active material particles are added. This method can successfully form a uniform, thin coating layer on the surface of the layered lithium nickel-manganese composite oxide. This coating method can further increase the content of coating elements on the active material surface compared to conventional dry methods or post-addition wet methods.

[0095] The aqueous solvent may include distilled water, an alcoholic solvent, or a combination thereof. The aluminum source may be, for example, aluminum sulfate. Aluminum sulfate may be an optimal source for forming a uniform aluminum coating layer on the layered lithium nickel-manganese composite oxide.

[0096] The aluminum content in the aluminum raw material is 0.1 mol% to 3.0 mol%, for example, 0.1 mol% to 2.0 mol%, 0.5 mol% to 1.5 mol%, or 0.7 mol% to 1.3 mol%, based on a total of 100 mol% consisting of all metals (excluding lithium) in the core particles and the aluminum in the aluminum raw material. By designing the aluminum coating content within this range, a coating layer having a thin and uniform thickness of tens to hundreds of nanometers can be formed, reducing the amount of gas generation in the lithium secondary battery under high-voltage or high-temperature operating conditions and improving its high capacity and long-life characteristics.

[0097] The aluminum source material is added to the aqueous solvent and mixed for approximately 1 to 60 minutes, e.g., 3 to 30 minutes, or 5 to 10 minutes. The mixing speed is 100 to 800 rpm, e.g., 200 to 600 rpm, or 250 to 500 rpm. Under these mixing conditions, the aluminum source material is completely dissolved in the aqueous solvent to produce a colorless and transparent coating solution. A uniform coating layer according to one embodiment can be effectively formed using this coating solution. The pH of the coating solution after mixing is, for example, 1.5 to 4, e.g., 2.0 to 3.5, 2.5 to 3.3, 2.7 to 3.3, or 2.9 to 3.2.

[0098] The core particles are added to the prepared coating solution, and at this time, the quality of the coating can be improved by adding the core particles while the coating solution is being stirred.

[0099] Furthermore, the time required to add the core particles to the coating solution may be 30 seconds / 500g to 2 minutes / 500g, for example, 30 seconds / 500g to 1.5 minutes / 500g. By appropriately adjusting the rate at which the core particles are added, the pH of the supernatant can be appropriately adjusted after coating is complete, thereby effectively forming a uniform coating layer according to one embodiment. If the rate at which the core particles are added is too slow, the reaction rate per particle may vary, and a uniform coating layer may not be formed. If the rate at which the core particles are added is too fast, the rate of change in pH may be too rapid, and a uniform coating layer may not be formed.

[0100] The time for stirring after all the core particles are added to the coating solution is approximately 15 to 60 minutes, for example, 20 to 50 minutes, or 30 to 45 minutes. The time from the start of adding the core particles to the coating solution to the completion of stirring, i.e., the coating reaction time, can be appropriately adjusted to approximately 1 hour or less.

[0101] In one embodiment, when the core particles are added to the coating solution and mixing is stopped, that is, when mixing or coating is completed, the pH of the supernatant may be in the range of 5.5 to 8.5. If the pH of the supernatant is less than 5.5, it becomes too acidic and a uniform coating layer may not be formed, and if the pH is more than 8.5, it becomes too basic and it may also be difficult to form a uniform aluminum coating layer.

[0102] After removing the aqueous solvent from the mixed solution, the resulting product can be dried, for example, at 40°C to 240°C, 100°C to 220°C, or 150°C to 200°C, and as an example, can be dried under vacuum conditions. Under such conditions, a good coated product can be obtained.

[0103] After removing the aqueous solvent from the mixed solution, the resulting product is dried and can be considered a coated product. The coated product includes core particles and an aluminum-containing coating layer located on the surface of the core particles. For example, the coating layer can have a fibrous shape, such as a mesh or spider web shape. Such a mesh shape can be formed continuously across the entire surface of the core particles. The mesh-like coating layer can surround the core particles with a very thin and uniform thickness, thereby strengthening the surface of the positive electrode active material, improving structural stability, and improving high-temperature and high-voltage characteristics.

[0104] In step (iv), the coating material and a cobalt raw material are dry-mixed and heat-treated to obtain a cathode active material, where an aluminum coating layer containing LiAlO2 or the like is formed on the surface of the secondary particles, and a cobalt coating is formed on the surface of the secondary particles and on the grain boundaries, which are the surfaces of the primary particles inside the secondary particles. As a result, the surfaces of the primary particles are coated with cobalt, and the surfaces of the secondary particles are coated with aluminum and cobalt, modifying the surfaces, improving capacity and lifespan characteristics and reducing gas generation during high-temperature storage.

[0105] The cobalt source material may be, for example, cobalt hydroxide (Co(OH)2), cobalt oxide, or a combination thereof. A lithium source material may be further mixed during the dry mixing of the coating material and the cobalt source material. In this case, the lithium source material may be lithium hydroxide (LiOH), for example, anhydrous lithium hydroxide.

[0106] The cobalt content in the cobalt raw material is 0.1 mol% to 2.0 mol%, for example, 0.5 mol% to 2.0 mol%, or 1.0 mol% to 2.0 mol%, relative to 100 mol% of the total metals excluding lithium in the positive electrode active material. By designing the cobalt content within this range, cobalt can be diffused not only on the surface of the core particles but also inside the core particles, coating the grain boundaries of the primary particles. This improves the life characteristics under high-voltage or high-temperature operating conditions and the initial charge / discharge efficiency.

[0107] In step (iv), the coating material and the cobalt raw material are dry-mixed together to form a zirconium coating. The zirconium raw material may be, for example, zirconium oxide.

[0108] The zirconium content in the zirconium raw material is 0.01 mol% to 1.5 mol% based on 100 mol% of all metals excluding lithium in the positive electrode active material, and can be designed to be, for example, 0.05 mol% to 1.0 mol%, 0.1 mol% to 1.0 mol%, 0.1 mol% to 0.5 mol%, or 0.1 mol% to 0.4 mol%. By designing the zirconium coating content within this range, a coating layer with a thin and uniform thickness of tens to hundreds of nanometers can be formed, thereby improving life characteristics under high voltage or high temperature operating conditions and initial charge / discharge efficiency.

[0109] The first heat treatment refers to the mixing of the nickel-manganese composite hydroxide and the lithium raw material followed by heat treatment, and the second heat treatment refers to the heat treatment of the coated product. The second heat treatment can be understood as a process for forming a coating layer, and can be carried out, for example, in an oxygen atmosphere at a temperature range of 700°C to 850°C, 750°C to 840°C, or 800°C to 830°C for 2 to 20 hours or 3 to 10 hours. When the second heat treatment temperature is set within the above range, the tendency of aluminum to diffuse into the interior of the secondary particles is reduced, and aluminum remains mainly on the surface of the secondary particles. At the same time, the surface of the secondary particles can be coated with a very thin, uniformly thick shell, and zinc can also be well coated on the surface of the secondary particles.

[0110] positive electrode In one embodiment, the positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, the positive electrode active material layer including the positive electrode active material described above. The positive electrode active material layer may further include other positive electrode active materials in addition to the positive electrode active material described above. The positive electrode active material layer may also optionally further include a binder, a conductive material, or a combination thereof.

[0111] According to one embodiment, the loading level of the positive electrode active material layer is 10 mg / cm 2 ~40mg / cm 2 For example, 10 mg / cm 2 ~30mg / cm 2 or 10 mg / cm 2 ~20mg / cm 2 In addition, the density of the positive electrode active material layer in the final rolled positive electrode may be 3.0 g / cc to 3.7 g / cc, for example, 3.1 g / cc to 3.7 g / cc, 3.3 g / cc to 3.6 g / cc, or 3.4 g / cc to 3.58 g / cc. When using a positive electrode active material according to an embodiment, it is advantageous to achieve such a loading level and positive electrode density, and a positive electrode satisfying the above-mentioned ranges of loading level and positive electrode density is suitable for realizing a high-capacity, high-energy-density lithium secondary battery.

[0112] binder The binder serves to firmly adhere the positive electrode active material particles to each other and to firmly adhere the positive electrode active material to the current collector. Representative examples of binders include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and nylon.

[0113] Conductive material The conductive material is used to impart electrical conductivity to the electrode, and any material that is electron-conductive and does not cause chemical changes in the battery that is constructed can be used. Examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0114] The content of the binder and the conductive material may be 0.5% by weight to 5% by weight, respectively, relative to 100% by weight of the positive electrode active material layer.

[0115] The positive electrode current collector may be made of Al, but is not limited to this.

[0116] Lithium secondary battery In one embodiment, a lithium secondary battery is provided that includes the positive electrode, the negative electrode, and the electrolyte described above. For example, the lithium secondary battery may include a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte.

[0117] Lithium secondary batteries can be classified into cylindrical, prismatic, pouch, and coin types depending on their shape. FIGS. 1 to 4 are schematic diagrams showing a lithium secondary battery according to an embodiment, where FIG. 1 shows a circular battery, FIG. 2 shows a prismatic battery, and FIGS. 3 and 4 show pouch-type battery shapes. Referring to FIGS. 1 to 4, a lithium secondary battery 100 may include an electrode assembly 40 having a positive electrode 10 and a negative electrode 20 with a separator 30 interposed therebetween, and a case 50 in which the electrode assembly 40 is housed. The positive electrode 10, the negative electrode 20, and the separator 30 may be immersed in an electrolyte (not shown). As shown in FIG. 1, the lithium secondary battery 100 may include a sealing member 60 that seals the case 50. Also, in FIG. 2, the lithium secondary battery 100 may include a positive electrode lead tab 11, a positive electrode terminal 12, a negative electrode lead tab 21, and a negative electrode terminal 22. As shown in FIGS. 3 and 4, the lithium secondary battery 100 may include electrode tabs 70, i.e., a positive electrode tab 71 and a negative electrode tab 72, which serve as electrical paths for conducting the current generated in the electrode assembly 40 to the outside.

[0118] A lithium secondary battery according to an embodiment may be capable of being charged at a high voltage or may be suitable for being driven at a high voltage. For example, the charging voltage of the lithium secondary battery may be 4.45 V or higher, such as 4.45 V to 4.7 V, 4.45 V to 4.6 V, or 4.45 V to 4.55 V. By using a positive electrode active material according to an embodiment, the lithium secondary battery can significantly reduce gas generation even when charged at a high voltage, thereby achieving high capacity and long life characteristics.

[0119] negative electrode The negative electrode may include a current collector and a negative electrode active material layer located on the current collector. The negative electrode active material layer includes a negative electrode active material and may further include a binder, a conductive material, or a combination thereof.

[0120] negative electrode active material The negative electrode active material includes a material capable of reversibly inserting / desorbing lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and undoping lithium, or a transition metal oxide.

[0121] As the material capable of reversibly inserting / desorbing the lithium ions, a carbon-based negative electrode active material can be used, which can include, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical or fibrous natural graphite, or artificial graphite, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0122] As the alloy of the lithium metal, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0123] As the material capable of doping and undoping lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used. The Si-based negative electrode active material can be silicon, a silicon-carbon composite, SiOx (0 < x < 2), a Si-Q alloy (where Q is an element selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements (excluding Si), group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof, for example, Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof), or a combination thereof. The Sn-based negative electrode active material can be Sn, SnO2, a Sn alloy, or a combination thereof.

[0124] The silicon-carbon composite may be a composite of silicon and amorphous carbon. 50 ) may be, for example, 0.5 μm to 20 μm. According to one embodiment, the silicon-carbon composite may be in the form of silicon particles, and the surfaces of the silicon particles may be coated with amorphous carbon. For example, it may include secondary particles (cores) formed by granulating primary silicon particles, and an amorphous carbon coating layer (shell) located on the surfaces of the secondary particles. The amorphous carbon may also be located between the primary silicon particles, for example, the primary silicon particles may be coated with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0125] The silicon-carbon composite may further include crystalline carbon. For example, the silicon-carbon composite may include a core including crystalline carbon and silicon particles, and an amorphous carbon coating layer located on the core surface. The crystalline carbon may be artificial graphite, natural graphite, or a combination thereof. Examples of the amorphous carbon include soft carbon, hard carbon, mesophase pitch carbide, and calcined coke.

[0126] When the silicon-carbon composite contains silicon and amorphous carbon, the silicon content may be 10 to 50% by weight and the amorphous carbon content may be 50 to 90% by weight, based on 100% by weight of the silicon-carbon composite.Alternatively, when the composite contains silicon, amorphous carbon, and crystalline carbon, the silicon content may be 10 to 50% by weight, the crystalline carbon content may be 10 to 70% by weight, and the amorphous carbon content may be 20 to 40% by weight, based on 100% by weight of the silicon-carbon composite.

[0127] The thickness of the amorphous carbon coating layer may be 5 nm to 100 nm. 50) can be 10 nm to 1 μm, or 10 nm to 200 nm. The silicon particles may exist alone as silicon, or in the form of a silicon alloy, or in an oxidized form. The oxidized form of silicon may be SiO x (0 < x < 2). At this time, the atomic content ratio of Si:O indicating the degree of oxidation can be 99:1 to 33:67. In this specification, unless otherwise defined, the average particle size (D 50 ) means the diameter of the particle with a cumulative volume of 50% by volume in the particle size distribution.

[0128] The Si-based negative electrode active material or the Sn-based negative electrode active material can be used by mixing with a carbon-based negative electrode active material. When the Si-based negative electrode active material or the Sn-based negative electrode active material and the carbon-based negative electrode active material are used in combination, the mixing ratio can be 1:99 to 90:10 by weight ratio.

[0129] Binder The binder serves to well adhere the negative electrode active material particles to each other and also to well adhere the negative electrode active material to the current collector. As the binder, a non-aqueous binder, an aqueous binder, a dry binder or a combination thereof can be used.

[0130] Examples of the non-aqueous binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene-propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide or a combination thereof.

[0131] The water-based binder may be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0132] When an aqueous binder is used as the negative electrode binder, a cellulose-based compound that can impart viscosity may be further included. The cellulose-based compound may be a mixture of one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or alkali metal salts thereof. The alkali metal may be sodium, potassium, or lithium.

[0133] The dry binder is a fiberizable polymeric material, such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0134] Conductive material The conductive material is used to impart conductivity to the electrode and can be any material that is electronically conductive and does not cause chemical changes in the battery. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0135] The content of the negative electrode active material may be 95% to 99.5% by weight, and the content of the binder may be 0.5% to 5% by weight, relative to 100% by weight of the negative electrode active material layer. For example, the negative electrode active material layer may contain 90% to 99% by weight of the negative electrode active material, 0.5% to 5% by weight of the binder, and 0.5% to 5% by weight of the conductive material.

[0136] current collector The negative electrode current collector may contain, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or an alloy thereof, and may be in the form of a foil, sheet, or foam. The thickness of the negative electrode current collector may be, for example, 1 μm to 20 μm, 5 μm to 15 μm, or 7 μm to 10 μm.

[0137] electrolyte The electrolyte for a lithium secondary battery can be, for example, an electrolytic solution, which can include a non-aqueous organic solvent and a lithium salt.

[0138] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reactions of the battery can migrate, and can be a carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based solvent, an aprotic solvent, or a combination thereof.

[0139] Examples of carbonate solvents that can be used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. Examples of ester solvents that can be used include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, caprolactone, etc. Examples of ether solvents that can be used include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran. Examples of ketone solvents that can be used include cyclohexanone. Examples of alcohol solvents that can be used include ethyl alcohol and isopropyl alcohol. Examples of aprotic solvents that can be used include nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, which may contain a double bond, an aromatic ring, or an ether group); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane and 1,4-dioxolane; and sulfolanes.

[0140] The non-aqueous organic solvent may be used alone or in combination of two or more kinds. When a mixture of two or more kinds is used, the mixing ratio may be appropriately adjusted depending on the desired battery performance, which is widely understood by those skilled in the art.

[0141] When a carbonate-based solvent is used, a cyclic carbonate and a chain carbonate can be mixed and used, and the cyclic carbonate and the chain carbonate can be mixed in a volume ratio of 1:1 to 1:9.

[0142] The non-aqueous organic solvent may further include an aromatic hydrocarbon organic solvent. For example, a carbonate solvent and an aromatic hydrocarbon organic solvent may be mixed in a volume ratio of 1:1 to 30:1.

[0143] The electrolyte may further contain vinyl ethyl carbonate, vinylene carbonate or ethylene carbonate based compounds to improve the battery life.

[0144] Representative examples of the ethylene carbonate compounds include fluoroethylene carbonate, difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, and cyanoethylene carbonate.

[0145] Lithium salts are substances that dissolve in organic solvents and act as a source of lithium ions within the battery, enabling basic lithium secondary battery operation and facilitating the movement of lithium ions between the positive and negative electrodes. Representative examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide; LiFSI), LiC4F9SO3, and LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (x and y are integers of 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFOB), and lithium bis(oxalato)borate (LiBOB).

[0146] The lithium salt concentration is preferably within the range of 0.1 M to 2.0 M. When the lithium salt concentration is within this range, the electrolyte has appropriate ion conductivity and viscosity, thereby exhibiting excellent performance and allowing lithium ions to migrate effectively.

[0147] Separator Depending on the type of lithium secondary battery, a separator may be present between the positive and negative electrodes. Such separators may be made of polyethylene, polypropylene, polyvinylidene fluoride, or multilayer films of two or more of these. Of course, mixed multilayer films such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may also be used.

[0148] The separator may include a porous substrate and a coating layer including an organic material, an inorganic material, or a combination thereof located on one or both sides of the porous substrate.

[0149] The porous substrate may be a polymer membrane formed of any one polymer selected from polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyether ketone, polyaryl ether ketone, polyetherimide, polyamide imide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon (registered trademark), and polytetrafluoroethylene, or a copolymer or mixture of two or more of these polymers.

[0150] The porous substrate can have a thickness of about 1 μm to 40 μm, for example, 1 μm to 30 μm, 1 μm to 20 μm, 5 μm to 15 μm, or 10 μm to 15 μm.

[0151] The organic material may include a (meth)acrylic copolymer including a first structural unit derived from (meth)acrylamide and a second structural unit including at least one of a structural unit derived from (meth)acrylic acid or a (meth)acrylate and a structural unit derived from (meth)acrylamidosulfonic acid or a salt thereof.

[0152] The inorganic material may include, but is not limited to, inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof. The average particle size (D 50 ) is 1 nm to 2000 nm, and can be, for example, 100 nm to 1000 nm, or 100 nm to 700 nm.

[0153] The organic material and the inorganic material may be mixed in one coating layer, or may be stacked in a coating layer containing an organic material and a coating layer containing an inorganic material.

[0154] The thickness of each of the coating layers may be 0.5 μm to 20 μm, for example, 1 μm to 10 μm, or 1 μm to 5 μm.

[0155] Examples of the present invention and comparative examples are described below. The following examples are merely illustrative of the present invention, and the present invention is not limited to the following examples.

[0156] Example 1 1. Production of positive electrode active material Ni 0.75 Mn 0.23 Al 0.02 (OH)2 and LiOH were mixed in a molar ratio of 1:1.05 and subjected to a first heat treatment at 845°C for 8 hours in an oxygen atmosphere to obtain a composition of Li 1.05 Ni 0.75 Mn 0.23 Al 0.02O2 and the average particle size (D 50 ) was about 14 μm in size.

[0157] Aluminum sulfate was added to a distilled water solvent and stirred at 350 rpm for approximately 5 minutes to prepare a coating solution. The salt was confirmed to have completely dissolved in the coating solution, making it colorless and transparent. 500 g of the prepared lithium nickel-manganese composite oxide was added to the continuously stirred coating solution for 1.5 minutes and stirred for approximately 25 minutes. The aluminum content in the aluminum sulfate was designed to be 1.0 mol% relative to 100 wt% of the total metals in the positive electrode active material, excluding lithium. The pH of the supernatant after stirring was confirmed to be 5.5. The solvent was removed from the mixed solution using an aspirator and filter press, and the mixture was dried in vacuum at 190°C to obtain a coated product.

[0158] The coated material was dry-mixed with cobalt hydroxide (Co(OH)2) and LiOH, and then subjected to a second heat treatment in an oxygen atmosphere at 825°C for 8 hours to prepare a cathode active material. The cobalt content in the cobalt hydroxide was designed to be 2.0 mol% relative to 100 mol% of the total metals (excluding lithium) in the cathode active material.

[0159] 2. Fabrication of Half-cells 98.5 wt% of the prepared positive electrode active material, 1.0 wt% of polyvinylidene fluoride binder, and 0.5 wt% of carbon nanotube conductive material were mixed to prepare a positive electrode active material layer slurry, which was then coated on an aluminum foil current collector, dried, and rolled to prepare a positive electrode. At this time, the loading level of the positive electrode active material layer was 10 mg / cm. 2 And so.

[0160] A polytetrafluoroethylene separator was placed between the positive electrode and the lithium metal counter electrode, and the cell was inserted into a case. An electrolyte solution of 1M LiPF6 dissolved in a solvent of ethylene carbonate and dimethyl carbonate in a volume ratio of 3:7 was then poured into the case to prepare a half-cell.

[0161] Example 2 Using the cathode active material prepared in Example 1 as the first cathode active material, a second cathode active material was prepared by the following method, and the first cathode active material and the second cathode active material were mixed in a weight ratio of 7:3 to prepare a cathode active material according to Example 2 having a pellet density of 3.56 g / cc. A half cell was prepared in substantially the same manner as in Example 1.

[0162] Manufacture of second positive electrode active material Ni 0.75 Mn 0.25 (OH)2, LiOH and Al2O3 were mixed in a molar ratio of 1:1:0.05 and heat-treated in an oxygen atmosphere at 900°C for 8 hours to obtain a composition of Li 1.05 Ni 0.75 Mn 0.23 Al 0.02 O2 and the average particle size (D 50 ) was about 3 μm in size.

[0163] The lithium nickel-manganese composite oxide, Al2O3, and Y2O3 were dry mixed and heat-treated in an oxygen atmosphere at 825°C for 8 hours to prepare a second positive electrode active material. At this time, the final second positive electrode active material was mixed so that the coating aluminum was 0.4 mol% and the yttrium was 0.05 mol% relative to 100 wt% of the total metals excluding lithium.

[0164] Comparative Example 1 A half cell was fabricated in substantially the same manner as in Example 1, except that the second positive electrode active material of Example 2 was used alone as the positive electrode active material.

[0165] Comparative Example 2 A third positive electrode active material was prepared by wet-coating aluminum as in Example 1, and then heat-treating the aluminum-coated product in an oxygen atmosphere at 825°C for 8 hours without performing a cobalt dry-coating process using cobalt hydroxide and LiOH. The third positive electrode active material was mixed with the second positive electrode active material of Example 2 in a weight ratio of 7:3 to prepare a positive electrode active material according to Comparative Example 2. A half-cell was prepared in substantially the same manner as in Example 1.

[0166] Comparative Example 3 In Example 1, Ni 0.75 Mn 0.23 Al 0.02 A cathode active material and half cell were prepared in substantially the same manner as in Example 1, except that (OH)2 and LiOH were mixed together with cobalt hydroxide (Co(OH)2), and the mixture was subjected to a first heat treatment at 845°C for 8 hours, followed by aluminum oxide coating to obtain a coated product. After that, a second heat treatment was performed at 825°C for 8 hours without performing cobalt dry coating. The cobalt content of the cobalt hydroxide was designed to be 2.0 mol%, and the aluminum content of the aluminum oxide was designed to be 1.0 mol%, relative to 100 mol% of the total metals excluding lithium.

[0167] Evaluation example 1: dQ / dV evaluation The half-cells prepared in Examples 1 and 2 and Comparative Examples 1 to 3 were charged at 25°C at a constant current of 0.2 C to an upper limit voltage of 4.45 V, then at a constant voltage of 0.05 C, and then discharged at 0.2 C to a cut-off voltage of 3.0 V, to carry out a chemical formation process (first charge / discharge). Next, one cycle of standard charge / discharge (second charge / discharge) was carried out under the same conditions as the chemical formation process. 1 C = 200 mAh / g, and the applied current was in the range of 0.5 mA to 0.7 mA.

[0168] FIG. 5 shows graphs of dQ / dV as a function of voltage during formation and standard charge / discharge for the half-cell of Example 1. Referring to FIG. 5, it can be seen that the point where a tangent line drawn from the first inflection point intersects with the line where dQ / dV = 0 in the graph during standard charge / discharge after formation is located within a voltage range of 3.68 V to 3.70 V. Also, in the graph during formation, the point where a tangent line drawn from the first inflection point intersects with the line where dQ / dV = 0 is located within a voltage range of 3.68 V to 3.70 V, but is located further to the right of the voltage during standard charge / discharge. In other words, it can be seen that the graph during standard charge / discharge after formation is shifted to the left compared to the graph during formation. Furthermore, referring to FIG. 5, it can be seen that the graph during formation shows two main peaks, while the graph after formation shows one main peak.

[0169] 6 is a graph showing dQ / dV as a function of voltage during formation and standard charge / discharge for the half cell of Comparative Example 1. Referring to FIG. 6, it can be seen that in Comparative Example 1, the points where the tangents drawn from the first inflection point intersect with the line where dQ / dV = 0 during both formation and standard charge / discharge are not within the voltage range of 3.68V to 3.70V, and both formation and standard charge / discharge show two main peaks, showing a different pattern from the graph of Example 1.

[0170] Fig. 7 is a graph showing dQ / dV during anodization for Example 2 and Comparative Example 2. Referring to the graph on the right of Fig. 7, it is confirmed that in the case of Example 2, the point where a tangent drawn from the first inflection point during anodization intersects with the line where dQ / dV = 0 is located in the voltage range of 3.70 V to 3.72 V. Referring to the graph on the left of Fig. 7, the slope of the graph between 3.6 V and 3.7 V is calculated to satisfy the condition of 0.02 or less.

[0171] 8 is a graph showing dQ / dV during standard charge / discharge after formation for Example 2 and Comparative Example 2. Referring to Fig. 8, in the case of Example 2, the point where the tangent line drawn from the first inflection point intersects with the line where dQ / dV = 0 is located in the voltage range of 3.68V to 3.70V, and it can be seen that the graph shows a different shape from that of Comparative Example 2.

[0172] Meanwhile, analysis of the dQ / dV graph for the half-cell of Comparative Example 3 confirmed that the point where the tangent line drawn from the first inflection point in the graph during standard charge / discharge intersects with the line where dQ / dV = 0 falls outside the range of 3.68 V to 3.70 V. This is understood to be due to the relatively low cobalt content on the surface of the positive electrode active material, resulting in high resistance.

[0173] Evaluation example 2: Evaluation of battery initial charge / discharge capacity and high-temperature life characteristics The discharge capacities during standard charge and discharge in Evaluation Example 1 for the half cells of Examples 1 and 2 and Comparative Examples 1 to 3 are shown as initial discharge capacities in Table 1 below. Following the standard charge and discharge, a cycle of charging at 1.0 C and discharging at 1.0 C in a voltage range of 3.0 V to 4.45 V at 45°C was repeated 50 times or more, and the ratio of the 50-cycle discharge capacity to the initial discharge capacity was calculated and shown in Table 1 below as high-temperature life.

[0174] [Table 1]

[0175] Referring to Table 1 above, it can be seen that Examples 1 and 2 exhibit high initial discharge capacity and excellent high-temperature life characteristics. In addition, it can be seen that Example 1 is superior to Comparative Examples 1 and 3 in initial discharge capacity and high-temperature life characteristics, and Example 2 is superior to Comparative Example 2 in initial discharge capacity and high-temperature life characteristics.

[0176] Although the preferred embodiments have been described in detail above, the scope of the present invention is not limited to these, and various modifications and improvements made by those skilled in the art using the basic concepts defined in the claims also fall within the scope of the present invention. [Explanation of symbols]

[0177] 100 Lithium secondary battery 10 positive electrode 11 Positive electrode lead tab 12 Positive terminal 20 negative electrode 21 Negative electrode lead tab 22 Negative terminal 30 Separator 40 Electrode assembly 50 cases 60 Sealing member 70 Electrode tab 71 Positive electrode tab 72 Negative electrode tab

Claims

1. a positive electrode current collector, and a positive electrode active material layer located on the positive electrode current collector A positive electrode comprising: The positive electrode active material layer is Core particles containing a layered lithium nickel-manganese composite oxide containing 0.1 mol % to 2 mol % of cobalt relative to 100 mol % of all metals excluding lithium; and an aluminum coating layer located on the surface of the core particle; a positive electrode active material comprising In a graph of dQ / dV as a function of voltage during standard charge / discharge, evaluated under conditions of 1C = 200 mAh / g, 0.2C, and an applied current of 0.5 mA to 0.7 mA, the point where a tangent drawn from the first inflection point intersects with the line where dQ / dV = 0 appears in the voltage range of 3.68 V to 3.70 V, positive electrode.

2. The positive electrode according to claim 1, wherein the dQ / dV graph according to the voltage during standard charge and discharge has a slope of 0.02 or less in the range of 3.60 V to 3.68 V.

3. In a graph of dQ / dV according to the voltage during formation, the point at which a tangent drawn from the first inflection point intersects with a line where dQ / dV = 0 appears in a voltage range of 3.68 V to 3.72 V. The positive electrode according to claim 1.

4. 2. The positive electrode according to claim 1, wherein the point at which a tangent line drawn from the first inflection point in a dQ / dV graph corresponding to the voltage during standard charge / discharge intersects with the line where dQ / dV = 0 appears at a voltage value lower than the point at which a tangent line drawn from the first inflection point in a dQ / dV graph corresponding to the voltage during formation intersects with the line where dQ / dV = 0.

5. The dQ / dV graph according to the voltage during the standard charge / discharge shows one main peak.

2. The positive electrode according to claim 1, wherein a graph of dQ / dV as a function of voltage during formation shows two main peaks.

6. The positive electrode active material is in the form of secondary particles formed by agglomeration of a plurality of primary particles, and the average particle diameter (D 50 2. The positive electrode according to claim 1, wherein the thickness of the first electrode is 10 μm to 18 μm.

7. 2. The positive electrode according to claim 1, wherein the layered lithium nickel-manganese composite oxide contains 60 mol % or more of nickel and 15 mol % or more of manganese, relative to 100 mol % of all metals excluding lithium.

8. 2. The positive electrode according to claim 1, wherein the layered lithium nickel-manganese composite oxide further contains aluminum, and the content of aluminum relative to 100 mol % of all metals excluding lithium is 1 mol % to 3 mol %.

9. The positive electrode active material is in the form of secondary particles formed by agglomeration of a plurality of primary particles, The positive electrode according to claim 1 , comprising a grain boundary coating portion located on a surface of a primary particle inside the secondary particle and containing cobalt.

10. The layered lithium nickel-manganese composite oxide is a positive electrode according to claim 1, represented by chemical formula 1: [Chemical formula 1] Li a1 Ni x1 Mn y1 Co z1 Al v1 M 1 w1 O 2-b1 X b1 In Chemical Formula 1, 0.9≦a1≦1.8, 0.6≦x1≦0.8, 0.15≦y1≦0.399, 0.001≦z1≦0.02, 0≦v1≦0.03, 0≦w1≦0.3, 0.9≦x1+y1+z1+v1+w1≦1.1, and 0≦b1≦0.1; M 1 is one or more elements selected from B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X is one or more elements selected from F, P, and S.

11. the aluminum coating layer is in the form of a shell that continuously surrounds the surface of the core particle, 2. The positive electrode according to claim 1, wherein the thickness of the aluminum coating layer is 5 nm to 500 nm.

12. 2. The positive electrode according to claim 1, wherein the aluminum content of the aluminum coating layer is 0.1 mol % to 3 mol % relative to 100 mol % of all metals excluding lithium in the entire positive electrode active material.

13. The positive electrode active material is a first positive electrode active material including a layered lithium nickel-manganese composite oxide containing 0.1 mol % to 2 mol % of cobalt relative to 100 mol % of all metals excluding lithium, a core particle formed by agglomeration of a plurality of primary particles, and an aluminum coating layer located on the surface of the core particle; and The layered lithium nickel-manganese composite oxide is in the form of a single particle and has an average particle size (D 50 ) a second positive electrode active material having 10. The positive electrode of claim 1, comprising:

14. 14. The positive electrode according to claim 13, wherein the first positive electrode active material is contained in an amount of 60% by weight to 95% by weight, and the second positive electrode active material is contained in an amount of 5% by weight to 40% by weight, relative to a total of 100% by weight of the first positive electrode active material and the second positive electrode active material.

15. The average particle size (D 50 ) is 10 μm to 18 μm, The average particle size (D 50 14. The positive electrode of claim 13, wherein the thickness of the first electrode is 1 μm to 8 μm.

16. The positive electrode according to claim 13, wherein the layered lithium nickel-manganese composite oxide of the second positive electrode active material contains 60 mol % or more of nickel, 15 mol % or more of manganese, and 0 mol % to 3 mol % of aluminum, relative to 100 mol % of all metals excluding lithium.

17. 14. The positive electrode of claim 13, wherein the second positive electrode active material contains 0 mol % to less than 0.1 mol % cobalt relative to 100 mol % of all metals excluding lithium.

18. The layered lithium nickel-manganese composite oxide of the second positive electrode active material is represented by the following chemical formula 2: [Chemical formula 2] Li a2 Ni x2 Mn y2 Al z2 M 2 w2 O 2-b2 X b2 In Chemical Formula 2, 0.9≦a2≦1.8, 0.6≦x2≦0.8, 0.15≦y2≦0.4, 0≦z2≦0.03, 0≦w2≦0.3, 0.9≦x2+y2+z2+w2≦1.1, and 0≦b2≦0.1; M 2 is one or more elements selected from Al, B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X is one or more elements selected from F, P, and S.

19. 14. The positive electrode of claim 13, wherein the second positive electrode active material further comprises a coating layer located on a surface of the single particle and containing Al, B, Mg, Ti, V, W, Y, Zr, or a combination thereof.

20. The loading level of the positive electrode active material layer is 10 mg / cm 2 ~40 mg / cm 2 and 2. The positive electrode according to claim 1, wherein the density of the positive electrode active material layer is 3.0 g / cc to 3.7 g / cc.

21. The positive electrode according to claim 1 . a negative electrode, and A lithium secondary battery, including an electrolyte.

22. 22. The lithium secondary battery according to claim 21, wherein the lithium secondary battery has an upper limit charging voltage of 4.45 V or higher.

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