Positive electrode active material, method for producing the same, positive electrode including the same, and lithium secondary battery

Abstract

To provide a positive electrode active material having improved high voltage characteristics and high temperature characteristics while ensuring economic efficiency, high capacity, and long life characteristics, a method for producing the same, and a positive electrode and a lithium secondary battery including the same.SOLUTION: In a positive electrode active material, a core particle containing a layered lithium nickel-manganese-aluminum-based composite oxide doped with zirconium is contained, the core particle has a secondary particle formed by aggregating a plurality of primary particles. An average particle diameter (D50) of the secondary particle is 10 μm to 25 μm, and a content of zirconium is 0.2 mol% to 0.8 mol% with respect to 100 mol% of the entire metal excluding lithium in the layered lithium nickel-manganese-aluminum-based composite oxide doped with zirconium.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a positive electrode active material, a method for producing the same, a positive electrode containing the same, 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 cathode active material containing a lithium nickel-manganese-aluminum composite oxide, which is economical, has high capacity, and has long life characteristics, and has improved high voltage characteristics and high temperature characteristics; a method for producing the cathode active material; and a cathode and a lithium secondary battery including the cathode active material. [Means for solving the problem]

[0005] In one embodiment of the present invention, a cathode active material includes core particles containing a layered lithium nickel-manganese-aluminum composite oxide doped with zirconium, wherein the core particles are in the form of secondary particles formed by agglomeration of a plurality of primary particles, and the average particle diameter (D 50 ) is 10 μm to 25 μm, and the zirconium content in the zirconium-doped layered lithium nickel-manganese-aluminum composite oxide relative to 100 mol % of all metals excluding lithium is 0.2 mol % to 0.8 mol %.

[0006] In another embodiment of the present invention, there is provided a method for producing a positive electrode active material, the method comprising: mixing a nickel-manganese-aluminum-based composite hydroxide, a zirconium raw material, and a lithium raw material; and heat-treating the mixture; wherein the zirconium content of the zirconium raw material is 0.2 mol % to 0.8 mol % relative to a total of 100 mol % of all metals in the nickel-manganese-aluminum-based composite hydroxide and zirconium in the zirconium raw material.

[0007] In another embodiment of the present invention, a positive electrode is provided, comprising: 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 including the above-described positive electrode active material.

[0008] In another embodiment of the present invention, there is provided a lithium secondary battery comprising the positive electrode, the negative electrode, and an electrolyte. [Effects of the Invention]

[0009] The positive electrode active material according to one embodiment of the present invention minimizes production costs, maximizes capacity, ensures long life characteristics, and improves high voltage and high temperature characteristics. A lithium secondary battery using the positive electrode active material can exhibit high initial charge / discharge capacity and efficiency even under high voltage driving conditions, and can achieve long life characteristics under high voltage and high temperature conditions. [Brief explanation of the drawings]

[0010] [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 SEM-EDS image of the surface of the final positive electrode active material prepared in Example 1. [Figure 6] 1 is a SEM image of the surface of the positive electrode active material coated product prepared in Example 1. [Figure 7] 1 is a SEM image of the surface of the positive electrode active material coated product prepared in Example 1. [Figure 8] 1 is a SEM image of the surface of the positive electrode active material coated product prepared in Example 2. [Figure 9] 1 is a SEM image of the surface of the positive electrode active material coated product prepared in Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0011] Although the present invention may be embodied in many different forms, it is not limited to the embodiments set forth herein.

[0012] 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.

[0013] As used herein, "combinations thereof" refers to mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0014] 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.

[0015] 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.

[0016] Here, the term "layer" includes not only a shape formed on the entire surface when observed in a plan view, but also a shape formed on a part of the surface.

[0017] 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.

[0018] 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.

[0019] Here, the term "metal" is interpreted as a concept including general metals, transition metals, and metalloids (semimetals).

[0020] positive electrode active material In one embodiment, the cathode active material includes core particles containing a layered lithium nickel-manganese-aluminum composite oxide doped with zirconium, and the core particles are in the form of secondary particles formed by agglomeration of a plurality of primary particles, and the average particle diameter (D 50 ) is 10 μm to 25 μm, and the zirconium content in the zirconium-doped layered lithium nickel-manganese-aluminum composite oxide relative to 100 mol % of all metals excluding lithium is 0.2 mol % to 0.8 mol %.

[0021] The recent surge in the price of the rare metal cobalt has spurred demand for the development of cobalt-free or reduced-content cathode active materials. Among these, cathode active materials with olivine-based crystal structures, such as lithium iron phosphate (LFP), lithium manganese phosphate (LMP), and lithium manganese iron phosphate (LMFP), or spinel-based 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-aluminum cathode active materials offer excellent capacity and efficiency characteristics due to their ability to increase the amount of lithium within their structures, making them suitable for high-capacity batteries. However, the removal of cobalt, which plays a key role in the layered structure, reduces structural stability, increases resistance, and hinders long-life performance. Furthermore, the removal of cobalt accelerates side reactions between the cathode active material and electrolyte under high-voltage and high-temperature conditions, resulting in increased gas generation and reduced lifespan.

[0022] Therefore, in order to maintain a stable layered structure and improve surface stability in a high-voltage region even when the cobalt element is removed from the layered nickel-manganese-aluminum-based positive electrode active material, one embodiment proposes a method of further doping the layered nickel-manganese-aluminum-based positive electrode active material with zirconium, a hetero element, thereby improving not only the high-voltage and high-temperature life characteristics but also the initial charge-discharge efficiency.

[0023] core particle The core particle contains a layered lithium nickel-manganese-aluminum composite oxide doped with zirconium.

[0024] The nickel content relative to 100 mol% of all metals excluding lithium in the positive electrode active material is 60 mol% or more, 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. Nickel is contained in the core particles but can migrate to some of the coating layers during the coating process. Therefore, the nickel content refers to the nickel content contained in the entire positive electrode active material.

[0025] The manganese content relative to 100 mol% of all metals (excluding lithium) in the positive electrode active material is 10 mol% or more, for example, 10 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. Manganese is contained in the core particles, but can migrate to some of the coating layers during the coating process. Therefore, the manganese content refers to the manganese content contained in the entire positive electrode active material.

[0026] The aluminum content relative to 100 mol% of all metals excluding lithium in the positive electrode active material is 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%. 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 if cobalt is excluded from the core particles, preventing the problem of structural collapse during charge and discharge, and achieving long-life characteristics of the positive electrode active material.

[0027] 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 can be achieved by synthesizing a composite oxide using a nickel-manganese-aluminum hydroxide as a precursor, without additional aluminum doping during the core particle synthesis process, and by using an aluminum raw material during precursor preparation. The core particle is characterized by a secondary particle form formed by the aggregation 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.

[0028] The zirconium content, relative to 100 mol% of all metals excluding lithium in the positive electrode active material, is characterized by being 0.2 mol% to 0.8 mol%, and may be, for example, 0.2 mol% to 0.7 mol%, 0.2 mol% to 0.6 mol%, or 0.2 mol% to 0.5 mol%. When the zirconium content satisfies this range, a stable layered structure can be maintained even without cobalt, preventing the problem of structural collapse during charge and discharge. This allows the positive electrode active material to achieve long-life characteristics, and in particular, improves initial discharge capacity and initial charge and discharge efficiency under high-voltage driving conditions, and improves high-temperature life characteristics.

[0029] The lithium nickel-manganese-aluminum composite oxide is specifically represented by the following chemical formula 1. [Chemical formula 1] Li a1 Ni x1 Mn y1 Al z1 Zr v1 M 1 w1 O 2-b1 X b1

[0030] In the above Chemical Formula 1, 0.9≦a1≦1.8, 0.6≦x1≦0.8, 0.1≦y1≦0.38, 0.01≦z1≦0.03, 0.002≦v1≦0.008, 0≦w1≦0.2, 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, and Zn, and X is one or more elements selected from F, P, and S.

[0031] In the above Chemical Formula 1, 0.9 ≦ a1 ≦ 1.5 or 0.9 ≦ a1 ≦ 1.2 may hold. Also, 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, 0.1 ≦ y1 ≦ 0.35, 0.1 ≦ y1 ≦ 0.30, 0.1 ≦ y1 ≦ 0.29, 0.15 ≦ y1 ≦ 0.29, or 0.2 ≦ y1 ≦ 0.3, 0.01 ≦ z1 ≦ 0.025, 0.01 < z1 ≦ 0.02, or 0.01 < z1 ≦ 0.019, 0.002 ≦ v1 ≦ 0.007, 0.002 ≦ v1 ≦ 0.006, or 0.002 ≦ v1 ≦ 0.005, 0 ≦ w1 ≦ 0.15, 0 ≦ w1 ≦ 0.1, or 0 ≦ w1 ≦ 0.09, etc. may hold.

[0032] The lithium nickel-manganese-aluminum composite oxide is a cobalt-free compound that does not contain cobalt or contains a very small amount of cobalt, and the content of cobalt relative to 100 mol% of the total metal excluding lithium may be 0 mol% to 0.01 mol%.

[0033] The core particles are characterized by being in the form of secondary particles formed by aggregation of a plurality of primary particles. The secondary particles can be spherical, ellipsoidal, polyhedral, or irregular in shape, and the primary particles can be spherical, ellipsoidal, plate-shaped, or a combination thereof. At this time, the average particle diameter (D 50 ) of the secondary particles is characterized by being 10 μm to 25 μm, and can be, for example, 11 μm to 20 μm, or 12 μm to 18 μm. The average particle diameter is obtained by measuring the sizes (diameter or major axis length) of more than 20 particles randomly from a scanning electron microscope image of the positive electrode active material to obtain a particle size distribution, and the diameter (D 50 ) of the particle with a cumulative volume of 50% by volume in the particle size distribution can be taken as the average particle diameter. When the average particle diameter of the core particles satisfies the above range, high capacity and long life can be realized, and it is advantageous to form a coating layer according to one embodiment.

[0034] The core particles are susceptible to chemical attack from components in the electrolyte when the battery is operated under high voltage or high temperature conditions, and side reactions with the electrolyte may occur frequently, resulting in a large amount of gas generation and reduced battery life and safety. However, these problems can be solved by introducing a coating layer according to one embodiment described below.

[0035] Coating layer According to one embodiment, the cathode active material includes: a core particle containing a layered lithium nickel-manganese-aluminum composite oxide doped with zirconium; and a coating layer containing aluminum located on the surface of the core particle; wherein the core particle is in the form of a secondary particle formed by agglomeration of a plurality of primary particles, and the average particle diameter (D 50 ) is 10 μm to 25 μm, and the zirconium content in the zirconium-doped layered lithium nickel-manganese-aluminum composite oxide relative to 100 mol % of all metals excluding lithium may be 0.2 mol % to 0.8 mol %. The core particle has been described above, so it will be omitted here, and only the coating layer will be described.

[0036] The aluminum content in the coating layer relative to 100 mol % of all metals, excluding lithium, in the entire positive electrode active material is 0.5 mol % to 1.5 mol %, for example, 0.5 mol % to 1.3 mol %, 0.6 mol % to 1.1 mol %, or 0.7 mol % to 0.9 mol %. The aluminum content in the coating layer refers to only the content of aluminum contained in the coating layer, separate from the aluminum contained in the core particles. The aluminum content in the coating layer of the entire positive electrode active material 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 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.

[0037] According to one embodiment, the coating layer may be, for example, a film that continuously surrounds the surface of the core particle, e.g., a shell that surrounds the entire surface of the core particle. This is distinct from a structure in which only a portion of the surface of the core particle is partially coated. According to one embodiment, the coating layer may be formed to completely surround the surface of the core particle, but with a very thin and uniform thickness. As a result, the cathode active material does not increase in resistance or decrease in capacity, has improved structural stability, effectively suppresses side reactions with the electrolyte, reduces gas generation under high voltage and high temperature conditions, and achieves long-life characteristics.

[0038] For example, the coating layer may have a fibrous shape, e.g., a mesh-like or spider web-like shape. The mesh-like coating layer is formed over the entire surface of the core particle, and thus can be described as surrounding the entire surface of the core particle. This is distinct from a structure in which only a portion of the surface of the core particle is coated locally. The coating layer may be formed with a very thin and uniform thickness while having a fibrous shape. This prevents an increase in resistance or a decrease in capacity of the positive electrode active material, 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.

[0039] According to one embodiment, the thickness of the coating layer is 30 nm to 500 nm, for example, 30 nm to 450 nm, 30 nm to 400 nm, 30 nm to 350 nm, 30 nm to 300 nm, 30 nm to 250 nm, 30 nm to 200 nm, 30 nm to 150 nm, 50 nm to 500 nm, 80 nm to 500 nm, or 100 nm to 500 nm. When the coating layer satisfies the above thickness range, the coating does not increase resistance or decrease capacity, but can improve the structural stability of the positive electrode active material and effectively suppress side reactions with the electrolyte. The thickness of the coating layer can be measured, for example, by TOF-SIMS, XPS, or EDS analysis, and the thickness range of the coating layer can be measured by TEM-EDS line profile analysis.

[0040] According to one embodiment, the coating layer has a thin, 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 may be calculated by measuring the thickness at approximately 10 points on an electron microscope image of a 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 the result by 100. Having the coating thickness deviation within the above range means that a uniformly thick coating layer is formed on the surface of the cathode active material particle in a good shape, 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.

[0041] The coating layer can include, for example, a layered aluminum compound, such as aluminum oxide, lithium aluminum oxide, or a combination thereof, such as LiAlO 2 .

[0042] Meanwhile, the coating layer may further contain nickel, manganese, or a combination thereof in addition to aluminum. The nickel and manganese are originally contained in the core particles and are introduced during the coating layer formation process, and their contents are not particularly limited. According to one embodiment, the coating layer necessarily contains aluminum and selectively contains nickel and manganese. The 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.

[0043] According to one embodiment, the surface of the positive electrode active material has an Al content of 45 wt% to 55 wt% relative to 100 wt% of the total metals excluding lithium. The high Al content can further improve the structural stability of the positive electrode active material. The Al content on the surface of the positive electrode active material can be measured, for example, by energy dispersive spectroscopy (EDS).

[0044] In addition, the 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 added to form the aluminum coating layer, and the sulfur content is not particularly limited. According to one embodiment, the coating layer selectively contains sulfur while containing aluminum, thereby improving the high-voltage characteristics and life characteristics of the positive electrode active material.

[0045] In an embodiment of the positive electrode active material, the cobalt content may be, for example, 0.01 mol% or less, 0.005 mol% or less, or 0.001 mol% or less, relative to 100 mol% of all metals excluding lithium, for example, 0 mol% to 0.01 mol%, 0 mol% to 0.005 mol%, or 0 mol% to 0.001 mol%.

[0046] In addition, the cathode 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 cathode active material, the manufacturing method described below allows core particles with a stable structure and a coating layer with a uniform thickness to be formed without using sodium ions.

[0047] Method for producing positive electrode active material In one embodiment, there is provided a method for producing a positive electrode active material, the method comprising: mixing a nickel-manganese-aluminum-based composite hydroxide, a zirconium source material, and a lithium source material, and heat-treating the mixture; wherein the zirconium content of the zirconium source material is 0.2 mol % to 0.8 mol %, relative to a total of 100 mol % of all metals in the nickel-manganese-aluminum-based composite hydroxide and zirconium in the zirconium source material.

[0048] The nickel-manganese-aluminum composite hydroxide is a precursor of core particles and may be in the form of secondary particles formed by aggregation of a plurality of primary particles. It may contain no cobalt or a very small amount of cobalt, for example, a cobalt-free nickel-manganese-aluminum composite hydroxide. The nickel-manganese-aluminum composite hydroxide can be prepared by a conventional coprecipitation method.

[0049] In the nickel-manganese-aluminum composite hydroxide, the nickel content relative to 100 mol% of the total metals is 60 mol% to 80 mol%, and may be, 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 safety can be improved even when the cobalt content is reduced.

[0050] In the nickel-manganese-aluminum composite hydroxide, the manganese content relative to 100 mol% of the total metals is 10 mol% or more, and may be, for example, 10 mol% to 40 mol%, 15 mol% to 35 mol%, 15 mol% to 30 mol%, or 20 mol% to 30%, etc. When the manganese content in the composite hydroxide satisfies the above range, high capacity can be achieved, the structural safety of the positive electrode active material can be improved, and production costs can be reduced, resulting in increased economic efficiency.

[0051] In the nickel-manganese-aluminum composite hydroxide, the aluminum content relative to 100 mol% of all metals is 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, high capacity can be achieved, the structural safety of the positive electrode active material can be improved, and production costs can be reduced, resulting in improved economic efficiency.

[0052] In one embodiment, a method for manufacturing a positive electrode active material uses a nickel-manganese-aluminum composite hydroxide as a precursor, in which aluminum is uniformly dispersed within the structure, without further doping aluminum during the preparation of core particles. The use of such a precursor allows for the manufacture of a positive electrode active material that stably maintains its layered structure even during repeated charge and discharge cycles, even without cobalt. Furthermore, aluminum by-products and aluminum aggregates are not formed, thereby improving the capacity, efficiency, and lifespan of the positive electrode active material.

[0053] In the nickel-manganese-aluminum 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. Such a nickel-manganese-aluminum composite hydroxide can avoid an increase in unit price due to cobalt, making it economical, and can maximize capacity and improve structural stability.

[0054] The nickel-manganese-aluminum composite hydroxide is, for example, represented by the following chemical formula 2. [Chemical formula 2] Ni x2 Mn y2 Al z2 M 2 w2 (OH)2

[0055] In chemical formula 2, 0.6≦x2≦0.8, 0.1≦y2≦0.4, 0 <z2≦0.03、0≦w2≦0.3、および0.9≦x2+y2+z2+w2≦1.1であり、M 2 is one or more elements selected from Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr.

[0056] In Chemical Formula 2, for example, 6≦x2≦0.8, 0.1≦y2≦0.39, 0.01≦z2≦0.03, and 0≦w2≦0.29.

[0057] The nickel-manganese-aluminum composite hydroxide is in the form of particles, and the average particle size (D 50 ) can be 10 μm to 25 μm, 11 μm to 20 μm, or 12 μm to 18 μm.

[0058] The zirconium source may be, for example, zirconium oxide.

[0059] The nickel-manganese-aluminum composite hydroxide and the zirconium raw material can be mixed at a molar ratio of 1:0.001 to 1:0.1, for example, at a molar ratio of 1:0.001 to 1:0.01.

[0060] The heat treatment can be carried out in an oxygen atmosphere, for example, at temperatures ranging from 750°C to 950°C, 780°C to 900°C, or 810°C to 890°C, for 2 to 20 hours, or 4 to 12 hours. This heat treatment can produce a zirconium-doped layered lithium nickel-manganese-aluminum composite oxide. The resulting composite oxide can contain 0.2 mol% to 0.8 mol% zirconium and 60 mol% to 80 mol% nickel, based on 100 mol% of the total metals, and can contain zero or a very small amount of cobalt of 0.01 mol% or less. This composite oxide differs significantly from existing nickel-based oxides of other compositions, such as lithium nickel-cobalt-manganese composite oxide and lithium nickel-cobalt-aluminum composite oxide, in terms of the residual lithium content on the particle surface and many other surface properties. Therefore, it is impossible to form a uniform, well-formed coating layer using existing coating methods. In one embodiment, a method is provided for improving high voltage and high temperature characteristics by forming a very thin and uniform coating layer on the surface of a lithium nickel-manganese-aluminum composite oxide having an extremely small cobalt content and a nickel content of 60 mol % or more.

[0061] In one embodiment, a coating layer according to one embodiment can be formed by first preparing a coating solution by adding and mixing an aluminum raw material into an aqueous solvent, then adding and mixing the resulting cathode active material containing a lithium nickel-manganese-aluminum composite oxide thereto, followed by drying and a second heat treatment. This is a salt-dissolution wet coating method, and may be a pre-addition method in which the salt, which is the coating raw material, is first completely dissolved and then the active material particles are added.

[0062] The aqueous solvent may include distilled water, an alcohol-based solvent, or a combination thereof. The aluminum source may be, for example, aluminum sulfate. Aluminum sulfate is an optimal source for forming a uniform aluminum coating layer on a layered lithium nickel-manganese-aluminum composite oxide. The aluminum source is a source for forming the coating layer, and the aluminum content in the aluminum source may be designed to be 0.5 mol% to 1.5 mol% relative to 100 mol% of the total metals excluding lithium in the final cathode active material, for example, 0.5 mol% to 1.3 mol%, 0.6 mol% to 1.1 mol%, or 0.7 mol% to 0.9 mol%. Designing the content of the coating source within the above range allows for the formation of a thin and uniform coating layer on the order of tens to hundreds of nanometers, thereby reducing the amount of gas generation from the lithium secondary battery under high-voltage or high-temperature operating conditions and improving its high capacity and long-life characteristics.

[0063] The coating solution obtained by adding and mixing the aluminum raw material into the aqueous solvent has a pH of 1.5 to 3.5, and can be, for example, 2.0 to 3.4, 2.5 to 3.3, 2.7 to 3.3, or 2.9 to 3.2.

[0064] The positive electrode active material is added to the coating solution and mixed for about 5 to 80 minutes, or 5 to 60 minutes, or 5 to 40 minutes. The pH of the mixed solution after stirring is 4.5 to 8.5, for example, 5.0 to 8.0, 5.5 to 7.5, or 6.0 to 7.0. Meeting these conditions is advantageous for forming a coating layer of uniform thickness.

[0065] Drying after the mixing step can be understood as a step of removing the solvent, and can be carried out at, for example, 40°C to 240°C, 100°C to 220°C, or 150°C to 200°C.

[0066] The first heat treatment is the process of mixing and heat-treating the nickel-manganese-aluminum composite hydroxide, the zirconium raw material, and the lithium raw material, and the second heat treatment is the process of drying the resulting mixture after removing the solvent from the mixed solution. The second heat treatment can be understood as a process of forming a coating layer, and can be performed, 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. The second heat treatment temperature can be lower than the first heat treatment temperature, and the second heat treatment time can be the same as or even shorter than the first heat treatment time. By performing the second heat treatment under these conditions, a desired coating layer can be obtained.

[0067] 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.

[0068] 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 / cm2 ~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 3.3 g / cc to 3.7 g / cc, for example, 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] The positive electrode current collector may be made of Al, but is not limited to this.

[0073] 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.

[0074] 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 lithium secondary batteries according to an embodiment, with FIG. 1 illustrating a cylindrical battery, FIG. 2 illustrating a prismatic battery, and FIGS. 3 and 4 illustrating pouch battery types. 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 housing the electrode assembly 40. The positive electrode 10, the negative electrode 20, and the separator 30 may be immersed in an electrolyte (not shown). The lithium secondary battery 100 may include a sealing member 60 that seals the case 50, as shown in FIG. 1. 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.

[0075] 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.

[0076] 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.

[0077] negative electrode active material The negative electrode active material includes a material capable of reversibly inserting / extracting lithium ions, lithium metal, a lithium metal alloy, a material capable of being doped with and dedoped from lithium, or a transition metal oxide.

[0078] The material capable of reversibly inserting / extracting lithium ions may be a carbon-based negative electrode active material, such as crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite, such as amorphous, plate-like, flake-like, spherical, or fibrous natural graphite or artificial graphite. Examples of the amorphous carbon include soft carbon, hard carbon, mesophase pitch carbide, and calcined coke.

[0079] As the lithium metal alloy, 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.

[0080] As the substance capable of doping and undoping lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used. As the Si-based negative electrode active material, 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 can be used. As the Sn-based negative electrode active material, Sn, SnO2, a Sn alloy, or a combination thereof can be used.

[0081] The silicon-carbon composite can be a composite of silicon and amorphous carbon. The average particle diameter (D 50 ) of the silicon-carbon composite particles can be, for example, 0.5 μm to 20 μm. According to one embodiment, the silicon-carbon composite can be in a form in which silicon particles and amorphous carbon are coated on the surface of the silicon particles. For example, it can include secondary particles (cores) formed by granulating primary silicon particles and an amorphous carbon coating layer (shell) located on the surface of the secondary particles. The amorphous carbon can also be located between the primary silicon particles, and for example, the primary silicon particles can be coated with amorphous carbon. The secondary particles may be dispersed and present in an amorphous carbon matrix.

[0082] The silicon-carbon composite may further contain crystalline carbon. For example, the silicon-carbon composite may include a core containing crystalline carbon and silicon particles, and an amorphous carbon coating layer located on the surface of the core. 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.

[0083] When the silicon-carbon composite contains silicon and amorphous carbon, the content of silicon may be 10% to 50% by weight based on 100% by weight of the silicon-carbon composite, and the content of amorphous carbon may be 50% to 90% by weight. When the composite contains silicon, amorphous carbon, and crystalline carbon, based on 100% by weight of the silicon-carbon composite, the content of silicon may be 10% to 50% by weight, the content of crystalline carbon may be 10% to 70% by weight, and the content of amorphous carbon may be 20% to 40% by weight.

[0084] Also, the thickness of the amorphous carbon coating layer may be 5 nm to 100 nm. The average particle diameter (D 50 ) of the silicon particles (primary particles) may 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 represented by SiO x (0 < x < 2). At this time, the atomic content ratio of Si:O indicating the degree of oxidation may be 99:1 to 33:67. In this specification, unless otherwise defined, the average particle diameter (D 50 ) means the diameter of the particle with a cumulative volume of 50% in the particle size distribution.

[0085] 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 is mixed with the carbon-based negative electrode active material, the mixing ratio may be 1:99 to 90:10 by weight.

[0086] binder The binder serves to firmly adhere the negative electrode active material particles to each other and to the current collector. The binder may be a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0087] Non-aqueous binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

[0088] 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.

[0089] 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.

[0090] The dry binder can be a fiberizable polymeric material such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0091] Conductive material The conductive material is used to impart conductivity to the electrode and can be any material that is electron-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.

[0092] 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.

[0093] current collector The negative electrode current collector can include, 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 can be in the form of a foil, sheet, or foam. The thickness of the negative electrode current collector can be, for example, 1 μm to 20 μm, 5 μm to 15 μm, or 7 μm to 10 μm.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] The electrolyte may further contain vinyl ethyl carbonate, vinylene carbonate or ethylene carbonate based compounds to improve the battery life.

[0101] 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.

[0102] 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 F2y+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).

[0103] The concentration of the lithium salt is preferably within the range of 0.1 M to 2.0 M. When the concentration of the lithium salt is within this range, the electrolyte has appropriate ion conductivity and viscosity, thereby exhibiting excellent performance and allowing lithium ions to migrate effectively.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] The organic material may include a (meth)acrylic copolymer including a first structural unit derived from (meth)acrylamide, a structural unit derived from (meth)acrylic acid or (meth)acrylate, and a second structural unit including at least one of a structural unit derived from (meth)acrylamidosulfonic acid or a salt thereof.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] 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.

[0113] Example 1 1. Production of positive electrode active material Ni 0.75 Mn 0.24 Al 0.01 (OH)2, LiOH, and ZrO2 were mixed in a molar ratio of 1:1.05:0.002 and subjected to a first heat treatment at 845°C for 8 hours in an oxygen atmosphere to obtain a composition of LiNi 0.748 Mn 0.24 Al 0.01 Zr 0.002 O2 and the average particle size (D 50 The lithium nickel-manganese-aluminum composite oxide was produced in the form of secondary particles with a particle size of approximately 14 μm, and the lithium nickel-manganese-aluminum composite oxide was designed so that the zirconium content was 0.2 mol% relative to 100 mol% of all metals excluding lithium.

[0114] A coating solution was prepared by adding 600g of distilled water and aluminum sulfate to a 1L reactor and stirring at 350 rpm for 5 minutes to dissolve the salt. The coating solution was confirmed to be colorless and transparent, with the salt completely dissolved. 500g of the lithium nickel-manganese-aluminum composite oxide prepared was added to the continuously stirred coating solution for 1.5 minutes and stirred for approximately 30 minutes. The aluminum content in the aluminum sulfate was designed to be 0.8 mol% based on 100% by weight of the total metals (excluding lithium) in the final positive electrode active material.

[0115] The solvent was removed from the mixed solution using an aspirator and a filter press, and the mixture was dried in vacuum at 190°C to obtain a coated product.

[0116] The coated product was subjected to a second heat treatment at 750° C. for 8 hours in an oxygen atmosphere to prepare a final positive electrode active material.

[0117] 2. Lithium secondary battery manufacturing 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 20 mg / cm. 2 The density of the final rolled positive electrode was about 3.4 g / cc.

[0118] Anode active material layer slurry was prepared by mixing 97.5 wt% graphite anode active material, 1.5 wt% carboxymethyl cellulose, and 1 wt% styrene butadiene rubber in an aqueous solvent. The anode active material layer slurry was coated onto a copper foil current collector, dried, and rolled to prepare anodes.

[0119] A lithium secondary battery was fabricated in a conventional manner using a polytetrafluoroethylene separator and an electrolyte solution prepared by dissolving 1M LiPF6 in a solvent containing a mixture of ethylene carbonate and dimethyl carbonate in a volume ratio of 3:7.

[0120] Example 2 A cathode active material and a lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that in the preparation of the cathode active material, the aluminum content in aluminum sulfate was designed and mixed to be 1.0 mol % relative to 100 mol % of the total metals excluding lithium in the final cathode active material.

[0121] Example 3 A positive electrode active material and a lithium secondary battery were manufactured in substantially the same manner as in Example 2, except that the lithium nickel-manganese-aluminum composite oxide was designed so that the zirconium content was 0.5 mol % relative to 100 mol % of all metals excluding lithium.

[0122] Example 4 A positive electrode active material and a lithium secondary battery were manufactured in substantially the same manner as in Example 2, except that the lithium nickel-manganese-aluminum composite oxide was designed so that the zirconium content was 0.8 mol % relative to 100 mol % of all metals excluding lithium.

[0123] Comparative Example 1 A positive electrode active material and a lithium secondary battery were manufactured in substantially the same manner as in Example 2, except that ZrO2 was not added in the preparation of the positive electrode active material, i.e., the zirconium doping process was not performed.

[0124] Comparative Example 2 A positive electrode active material and a lithium secondary battery were manufactured in substantially the same manner as in Example 2, except that the lithium nickel-manganese-aluminum composite oxide was designed so that the zirconium content was 0.1 mol % relative to 100 mol % of all metals excluding lithium.

[0125] Comparative Example 3 A positive electrode active material and a lithium secondary battery were manufactured in substantially the same manner as in Example 2, except that the lithium nickel-manganese-aluminum composite oxide was designed so that the zirconium content was 1.0 mol % relative to 100 mol % of all metals excluding lithium.

[0126] Evaluation example 1: Zirconium doping analysis of positive electrode active material The zirconium doping state of the cathode active material prepared in Example 1 was confirmed by SEM-EDS mapping. Figure 5 is an SEM-EDS image showing Zr on the surface of the final cathode active material prepared in Example 1. Referring to Figure 5, it can be seen that zirconium is doped throughout the cathode active material, thereby enhancing structural stability and enabling improved electrochemical performance at high voltages.

[0127] Evaluation example 2: Positive electrode active material surface analysis The positive electrode active materials prepared in Examples 1 and 2 were photographed using a scanning electron microscope (SEM) and compared. FIG. 6 is an SEM image of the surface of the positive electrode active material coated product prepared in Example 1, and FIG. 7 is an enlarged image thereof. FIG. 8 is an SEM image of the surface of the positive electrode active material coated product prepared in Example 2, and FIG. 9 is an enlarged image thereof. The amount of aluminum coating in Example 2 was greater than that in Example 1, and referring to FIGS. 6 to 9, it was confirmed that the aluminum coating layer on the surface became thicker as the amount of aluminum coating increased.

[0128] Evaluation example 3: Initial charge / discharge capacity and efficiency evaluation The lithium secondary batteries manufactured in Examples 1 to 5 and Comparative Examples 1 to 3 were initially charged and discharged at 25° C. at a constant current of 0.2 C to an upper limit voltage of 4.45 V, at a constant voltage of 0.05 C, and then discharged at 0.2 C to an end voltage of 3.0 V. Table 1 below shows the initial charge capacity, initial discharge capacity, and the ratio of the latter to the former calculated as efficiency.

[0129] Evaluation example 4: High temperature life characteristics Following the initial charge and discharge of Evaluation Example 3, 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.

[0130] [Table 1]

[0131] Referring to Table 1 above, it was confirmed that Comparative Example 1, which was not doped with zirconium, was inferior in high-temperature life characteristics compared to the other Examples and Comparative Examples.

[0132] It was found that in Examples 1 to 4, in which the zirconium content in the lithium nickel-manganese-aluminum composite oxide was in the range of 0.2 mol % to 0.8 mol %, the high-temperature life characteristics were improved compared to Comparative Examples 2 and 3, in which the zirconium content was not in the range. In addition, it was confirmed that in Example 1, in which the aluminum coating amount was 0.8 mol %, high initial charge / discharge capacity, initial charge / discharge efficiency, and excellent high-temperature life characteristics were simultaneously achieved.

[0133] 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]

[0134] 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 active material comprising: core particles containing a layered lithium nickel-manganese-aluminum composite oxide doped with zirconium; The core particle is in the form of a secondary particle formed by agglomeration of a plurality of primary particles, The average particle size of the secondary particles (D 50 ) is 10 μm to 25 μm, The zirconium-doped layered lithium nickel-manganese-aluminum composite oxide has a zirconium content of 0.2 mol % to 0.8 mol % relative to 100 mol % of all metals excluding lithium.

2. 2. The positive electrode active material according to claim 1, wherein the zirconium-doped layered lithium nickel-manganese-aluminum composite oxide has a nickel content of 60 mol% to 80 mol%, a manganese content of 10 mol% or more, and an aluminum content of 1 mol% to 3 mol%, relative to 100 mol% of all metals excluding lithium.

3. The positive electrode active material according to claim 1 , wherein the aluminum concentration is uniform within the core particle.

4. 2. The positive electrode active material according to claim 1, wherein the zirconium-doped layered lithium nickel-manganese-aluminum composite oxide has a cobalt content of 0 mol % to 0.01 mol % relative to 100 mol % of all metals excluding lithium.

5. The zirconium-doped layered lithium nickel-manganese-aluminum composite oxide is the positive electrode active material according to claim 1, represented by the following chemical formula 1: [Chemical formula 1] Li a1 N x1 Mn y1 A z1 Zhr v1 M 1 w1 O 2-b1 X b1 In the formula 1, 0.9≦a1≦1.8, 0.6≦x1≦0.8, 0.1≦y1≦0.38, 0.01≦z1≦0.03, 0.002≦v1≦0.008, 0≦w1≦0.2, 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, and Zn, and X is one or more elements selected from F, P, and S.

6. The positive electrode active material of claim 1 , further comprising a coating layer containing aluminum located on a surface of the core particle.

7. 7. The positive electrode active material according to claim 6, wherein the aluminum content in the coating layer is 0.5 mol % to 1.5 mol % relative to 100 mol % of all metals excluding lithium in the entire positive electrode active material.

8. The positive electrode active material of claim 6 , wherein the coating layer is in the form of a shell that continuously surrounds the surface of the core particle.

9. The cathode active material according to claim 6, wherein the coating layer has a thickness of 30 nm to 500 nm.

10. The positive electrode active material of claim 6 , wherein the thickness deviation of the coating layer within one positive electrode active material particle is 20% or less.

11. A step of mixing a nickel-manganese-aluminum composite hydroxide, a zirconium raw material, and a lithium raw material and heat-treating the mixture; In the method for producing a positive electrode active material, the zirconium content of the zirconium raw material is 0.2 mol % to 0.8 mol % relative to a total of 100 mol % of all metals in the nickel-manganese-aluminum composite hydroxide and zirconium in the zirconium raw material.

12. 12. The method for producing a positive electrode active material according to claim 11, wherein, in the nickel-manganese-aluminum composite hydroxide, the nickel content is 60 mol% to 80 mol%, the manganese content is 10 mol% or more, the aluminum content is 1 mol% to 3 mol%, and the cobalt content is 0 mol% to 0.01 mol%, relative to 100 mol% of all metals.

13. The method for producing a positive electrode active material according to claim 11, wherein the heat treatment is carried out at 750°C to 950°C.

14. (i) preparing a cathode active material containing a layered lithium nickel-manganese-aluminum composite oxide doped with zirconium by the method for preparing a cathode active material according to claim 11; (ii) adding an aluminum raw material to an aqueous solvent and mixing them to prepare a coating solution; (iii) adding the positive electrode active material to the coating solution and mixing them to prepare a mixed solution; and (iv) removing the aqueous solvent from the mixed solution, and then drying and heat-treating the resultant to form a coating layer on the surface of the positive electrode active material.

15. The method for producing a positive electrode active material according to claim 14, wherein the aluminum content of the coating layer is 0.5 mol % to 1.5 mol % relative to 100 mol % of all metals excluding lithium in the entire positive electrode active material.

16. a positive electrode current collector, and a positive electrode active material layer located on the positive electrode current collector Including, The positive electrode active material layer comprises the positive electrode active material according to any one of claims 1 to 10.

17. The loading level of the positive electrode active material layer is 10 mg / cm 2 ~40 mg / cm 2 17. The positive electrode of claim 16, wherein

18. 17. The positive electrode according to claim 16, wherein the density of the positive electrode active material layer is 3.3 g / cc to 3.7 g / cc.

19. The positive electrode of claim 16 ; a negative electrode; and Electrolyte; A lithium secondary battery comprising:

20. 20. The lithium secondary battery according to claim 19, wherein the lithium secondary battery has a charging voltage of 4.45 V or higher.

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