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 including a lithium nickel-manganese-aluminum-based composite oxide.SOLUTION: The present invention relates to a positive electrode active material, a preparation method thereof, a positive electrode including the positive electrode active material, and a lithium secondary battery. The positive electrode active material includes a core particle containing a lithium nickel-manganese-aluminum-based composite oxide, and a coating layer disposed on a surface of the core particle and containing aluminium. A nickel content of the core particle is 60 mol% to 80 mol% and an aluminum content of the core particle is 1 mol% to 3 mol%, each based on 100 mol% of a total metal excluding lithium, and an aluminum content of the coating layer is 0.1 mol% to 2 mol% based on 100 mol% of the total metal excluding lithium.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, there is provided a positive electrode active material comprising core particles containing a lithium nickel-manganese-aluminum composite oxide, and a coating layer located on the surface of the core particles and containing aluminum, wherein the nickel content of the core particles is 60 mol % to 80 mol %, the aluminum content of the core particles is 1 mol % to 3 mol %, and the aluminum content of the coating layer is 0.1 mol % to 2 mol %, relative to 100 mol % of all metals excluding lithium.

[0006] In another embodiment of the present invention, there is provided a method for producing a positive electrode active material, comprising: mixing a nickel-manganese-aluminum composite hydroxide and a lithium raw material; performing a first heat treatment to obtain a lithium nickel-manganese-aluminum composite oxide; adding and mixing the obtained lithium nickel-manganese-aluminum composite oxide into a solution in which an aluminum raw material is mixed in an aqueous solvent; drying the resulting mixture; and performing a second heat treatment to obtain a positive electrode active material, wherein the nickel content in the nickel-manganese-aluminum composite hydroxide is 60 mol % to 80 mol % and the aluminum content is 1 mol % to 3 mol % relative to 100 mol % of all metals, and the aluminum content in the aluminum raw material is 0.1 mol % to 2 mol % relative to 100 mol % of all metals in the positive electrode active material excluding lithium.

[0007] In yet another embodiment of the present invention, there is provided a positive electrode including 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 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]

[0009] The positive electrode active material according to an 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 exhibits high initial charge / discharge capacity and efficiency even under high voltage driving conditions, thereby achieving long life characteristics. [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 scanning electron microscopy (SEM) image of the positive electrode active material of Comparative Example 1. [Figure 3] 10 is an SEM image of the positive electrode active material of Comparative Example 2. [Figure 4] 1 is a scanning electron microscopy-electron dispersive X-ray spectroscopy (SEM-EDS) image of a cross section of the positive electrode active material of Example 1. [Figure 5] 1 is a SEM-EDS image of a cross section of the positive electrode active material of Example 2. [Figure 6] 1 is a SEM-EDS image of a cross section of the positive electrode active material of Example 3. [Figure 7] 1 is an SEM-EDS image of a cross section of the positive electrode active material of Example 4. [Figure 8] 10 is an SEM-EDS image of a cross section of the positive electrode active material of Comparative Example 3. [Figure 9] 10 is an SEM-EDS image of a cross section of the positive electrode active material of Comparative Example 5. [Figure 10] 10 is an SEM image of the surface of the positive electrode active material of Comparative Example 5. [Figure 11] 1 is a depth profile of TOF-SIMS (Time-of-Flight Secondary Ion Mass Spectrometry) for the positive electrode active material of Example 1. [Figure 12]1 is a transmission electron microscopy (TEM) image of a cross section of a positive electrode active material of Example 1. [Figure 13] This is an enlarged TEM image of the area indicated by the square in Figure 12. [Figure 14] This is an image obtained by EDS analysis of the TEM image in Figure 13, highlighting O, Al, Mn, and Ni from left to right. [Figure 15] 15 is an EDS line profile showing the change in the content of O, Al, Mn, and Ni in the direction of the arrows shown in FIGS. 13 and 14. [Figure 16] 1 shows a TEM image and a TEM-EDS analysis image of a cross section of the positive electrode active material of Example 1. [Figure 17] 17 is an EDS line profile showing the change in the content of O, Al, Mn, and Ni in the direction of the arrow shown in FIG. 16. [Figure 18] 1 is a TEM image of a cross section of the positive electrode active material of Example 1. [Figure 19] This is an enlarged photograph (left) of Area 1 in Figure 18, and an image (right) highlighting aluminum in EDS analysis. [Figure 20] An enlarged photograph (left) and an EDS analysis image (right) of Area 2 in Figure 18. [Figure 21] An enlarged photograph (left) and an EDS analysis image (right) of Area 3 in Figure 18 are shown. [Figure 22] 1 is a TEM-EDS image obtained by enlarging and analyzing a primary particle located at the outermost shell of a secondary particle in a cross section of the positive electrode active material of Example 1. [Figure 23] The TEM images are of the areas indicated by the arrows (1) to (6) in FIG. 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] 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.

[0017] The average particle size can be measured by methods well known to those skilled in the art, such as using a particle size analyzer or a transmission electron microscope image or a scanning electron microscope image. Alternatively, the average particle size can be calculated by measuring using dynamic light scattering, counting the number of particles in each particle size range, and then calculating the average particle size. Unless otherwise defined, the average particle size refers to the diameter (D50) of particles that make up 50% of the cumulative volume in a particle size distribution. Unless otherwise defined, the average particle size can be determined by measuring the size (diameter or major axis length) of 20 or more particles randomly selected from a scanning electron microscope image to obtain a particle size distribution, and then taking the diameter (D50) of particles that make up 50% of the cumulative volume in the particle size distribution as the average particle size.

[0018] Here, "or" is not to be construed in an exclusive sense, for example, "A and / or B" is to be construed as including A, B, A+B, etc.

[0019] The term "metal" is understood to include general metals, transition metals, and metalloids (semimetals).

[0020] positive electrode active material In one embodiment of the present invention, there is provided a cathode active material comprising core particles containing a lithium nickel-manganese-aluminum composite oxide, and a coating layer containing aluminum located on the surface of the core particles, wherein the nickel content of the core particles is 60 mol % to 80 mol %, the aluminum content of the core particles is 1 mol % to 3 mol %, and the aluminum content of the coating layer is 0.1 mol % to 2 mol %, relative to 100 mol % of all metals excluding lithium.

[0021] 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 reduce its content. 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 limited capacity due to their limited lithium storage capacity. Layered nickel-manganese cathode active materials offer excellent capacity and efficiency due to their high lithium storage capacity, 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] In one embodiment, aluminum is introduced as a base material and a lithium nickel-manganese-aluminum composite oxide is applied to the core particles, thereby improving structural stability and minimizing production costs. Furthermore, a certain amount of aluminum is coated using a specific method to form a uniform coating layer, thereby maximizing capacity and efficiency. The cathode active material can also reduce gas generation even under high voltage and high temperature conditions, thereby achieving long-life characteristics.

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

[0024] The nickel content is 60 mol% to 80 mol% based on 100 mol% of all metals excluding lithium in the positive electrode active material. Nickel is contained in the core particles, but a portion may migrate to the coating layer during the coating process. Therefore, the nickel content refers to the nickel content in the entire positive electrode active material. The nickel content 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% based on 100 mol% of all metals excluding lithium in the positive electrode active material. When the nickel content is within the above range, high capacity can be achieved, and structural safety can be improved even when the cobalt content is reduced.

[0025] Such composite oxides are distinguished from high-nickel composite oxides having a nickel content of more than 80 mol%. According to one embodiment, a positive electrode active material having a nickel content of 60 mol% to 80 mol% differs from a high-nickel positive electrode active material in terms of the residual lithium content on the surface, the pH condition on the surface, the surface shape, etc., and therefore the same coating method cannot be applied, resulting in different performance and application fields.

[0026] The manganese content may be, for example, 10 mol% to 39 mol%, 10 mol% to 35 mol%, 10 mol% to 30 mol%, 10 mol% to 29 mol%, 15 mol% to 39 mol%, 20 mol% to 39 mol%, or 20 mol% to 30%, relative to 100 mol% of all metals in the positive electrode active material (excluding lithium). Manganese is contained in the core particles, but a portion of it can migrate to the coating layer during the coating process. Therefore, the manganese content refers to the manganese content in the entire positive electrode active material. When the manganese content satisfies the above range, the positive electrode active material can achieve high capacity while improving structural stability.

[0027] The aluminum content in the core particles is 1 mol % to 3 mol % relative to 100 mol % of all metals in the positive electrode active material excluding lithium, and can be, for example, 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 of the core particles satisfies the above range, a stable layered structure can be maintained even if cobalt is removed from the core particles, preventing the problem of structural collapse due to charge and discharge, and achieving long-life characteristics of the positive electrode active material.

[0028] 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, nor is the aluminum concentration higher or 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 further doping with aluminum during the synthesis of the core particle and using an aluminum raw material during 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.

[0029] The lithium nickel-manganese-aluminum composite oxide is represented by, for example, the following chemical formula 1. [Chemical formula 1] Li a1 Ni x1 Mn y1 Al z1 M 1 w1 O 2-b1 X b1 In Chemical Formula 1, 0.9 ≦ a1 ≦ 1.8, 0.6 ≦ x1 ≦ 0.8, 0.1 ≦ y1 ≦ 0.39, 0.01 < z1 ≦ 0.03, 0 ≦ w1 ≦ 0.29, 0.9 ≦ x1 + y1 + z1 + w1 ≦ 1.1, and 0 ≦ b1 ≦ 0.1, and 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 Zr, and X is one or more elements selected from F, P, and S.

[0030] In Chemical Formula / , 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 ≦ 0.39, or 0.2 ≦ y1 ≦ 0.3, 0.01 < z1 ≦ 0.025, 0.01 < z1 ≦ 0.02, or 0.01 < z1 ≦ 0.019, 0 ≦ w1 ≦ 0.28, 0 ≦ w1 ≦ 0.27, 0 ≦ w1 ≦ 0.26, 0 ≦ w1 ≦ 0.25, 0 ≦ w1 ≦ 0.24, 0 ≦ w1 ≦ 0.23, 0 ≦ w1 ≦ 0.2, 0 ≦ w1 ≦ 0.15, 0 ≦ w1 ≦ 0.1, or 0 ≦ w1 ≦ 0.09 etc. may hold.

[0031] The lithium nickel - manganese - aluminum - based composite oxide of the core particles can be, for example, a cobalt - free compound that does not contain cobalt or contains a very small amount of cobalt.

[0032] The core particles can be 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.

[0033] 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 may undergo frequent side reactions with the electrolyte, 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.

[0034] Coating layer The aluminum content in the coating layer is typically 0.1 mol% to 2 mol% relative to 100 mol% of the total metals (excluding lithium) in the positive electrode active material, and may be, 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%. This refers to the aluminum content in the coating layer, separate from the aluminum contained in the core 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.

[0035] According to one embodiment, the coating layer may be in the form of a film that continuously surrounds the surface of the core particle, for example, in the form of 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.

[0036] The thickness of the coating layer is 30 nm to 200 nm, and may be, for example, 30 nm to 150 nm, 50 nm to 200 nm, 80 nm to 200 nm, or 100 nm to 200 nm. When the coating layer satisfies the above thickness range, the coating does not increase resistance or decrease capacity, improves the structural stability of the positive electrode active material, and effectively suppresses 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.

[0037] 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 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.

[0038] The coating layer may include an aluminum compound with a layered structure. That is, the coating layer may include a lithium aluminum oxide with a layered structure, such as LiAlO2. The layered coating layer is formed thinly and uniformly on the surface of the core particle, which further facilitates lithium migration, increases capacity, and protects the core particle, thereby improving life characteristics.

[0039] 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. This coating layer may be referred to as an aluminum-rich coating layer. The coating layer may be formed with a thin and uniform thickness, which may improve the high-voltage characteristics and life characteristics of the positive electrode active material.

[0040] Grain boundary coating section During the coating layer formation process, aluminum may be diffused into the core particles. Therefore, according to one embodiment, the cathode active material may further include a grain boundary coating region containing aluminum located on the surface of the primary particles within the secondary particles. Here, the term "secondary particle" refers to the core particle, and the "interior of the secondary particle" may refer to the entire interior of the secondary particle excluding the surface, or may refer to the region extending from the surface of the secondary particle toward the center of the secondary particle and 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 core particle and refers to a coating region formed on the surface of the primary particles located within the core particle. The presence of the grain boundary coating region can be confirmed by SEM-EDS analysis of a cross section of the cathode active material. The formation of the aluminum grain boundary coating region further stabilizes the structure of the cathode active material, improving its life characteristics.

[0041] 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.

[0042] The grain boundary coating portion may contain a layered aluminum compound, similar to the coating layer described above. That is, the grain boundary coating portion may contain a layered lithium aluminum oxide, such as LiAlO2. The formation of a layered grain boundary coating portion within the core particle promotes lithium migration, increasing capacity and improving structural stability, thereby improving life characteristics.

[0043] In addition, the grain boundary coating portion may further contain nickel, manganese, or a combination thereof in addition to aluminum. The grain boundary coating portion may also be referred to as an aluminum-rich coating portion.

[0044] The average particle size (D 50) is not particularly limited, and may be, for example, 10 μm to 18 μm, 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 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, and it is advantageous to form a coating layer according to an embodiment.

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

[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, a method for producing a positive electrode active material is provided, comprising: mixing a nickel-manganese-aluminum composite hydroxide and a lithium source, performing a first heat treatment to obtain a lithium nickel-manganese-aluminum composite oxide; adding the resulting lithium nickel-manganese-aluminum composite oxide to a solution prepared by mixing an aluminum source with an aqueous solvent; mixing the resulting mixture; drying; and performing a second heat treatment to obtain a positive electrode active material. In the nickel-manganese-aluminum composite hydroxide, the nickel content is 60 mol % to 80 mol % and the aluminum content is 1 mol % to 3 mol % relative to 100 mol % of all metals in the positive electrode active material, and the aluminum content in the aluminum source is 0.1 mol % to 2 mol % relative to 100 mol % of all metals in the positive electrode active material, excluding lithium. This method can produce the positive electrode active material described above.

[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] According to one embodiment, a method for producing a positive electrode active material uses a nickel-manganese-aluminum composite hydroxide precursor in which aluminum is uniformly dispersed within the structure, without further doping aluminum during the production of core particles. The use of such a precursor allows for the production of a positive electrode active material that stably maintains its layered structure even after repeated charge and discharge cycles, even without the need for cobalt. Furthermore, the capacity, efficiency, and lifespan of the positive electrode active material can be improved without the formation of aluminum by-products or aluminum aggregates.

[0050] The nickel content in the nickel-manganese-aluminum composite hydroxide is 60 mol% to 80 mol%, based on 100 mol% of the total metals, 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%. 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. Such composite hydroxides are distinguished from high-nickel composite hydroxides with a nickel content of more than 80 mol%. The composite hydroxide according to one embodiment has different surface properties from high-nickel composite hydroxides, such as the residual lithium content on the surface, pH, and shape, making it difficult to apply the same coating method to both.

[0051] The manganese content in the nickel-manganese-aluminum composite hydroxide may be 10 mol% to 39 mol%, such as 10 mol% to 35 mol%, 10 mol% to 30 mol%, 10 mol% to 29 mol%, 15 mol% to 39 mol%, 20 mol% to 39 mol%, or 20 mol% to 30 mol%, based on 100 mol% of the total metals. The aluminum content in the nickel-manganese-aluminum composite hydroxide may be 1 mol% to 3 mol%, such as 1 mol% to 2.5 mol%, 1 mol% to 2 mol%, or 1 mol% to 1.9 mol%, based on 100 mol% of the total metals. When the manganese and aluminum contents in the composite hydroxide satisfy the above ranges, high capacity can be achieved, the structural stability of the positive electrode active material can be improved, and production costs can be reduced, resulting in improved economic efficiency.

[0052] The cobalt content in the nickel-manganese-aluminum composite hydroxide may be 0.01 mol% or less, 0.005 mol% or less, or 0.001 mol% or less, based on 100 mol% of the total metals. Such nickel-manganese-aluminum composite hydroxide is economical as it can avoid the increase in unit price due to cobalt, and it can be said that it maximizes capacity and has improved structural stability.

[0053] An example of the nickel-manganese-aluminum composite hydroxide is represented by the following chemical formula 2. [Chemical formula 2] Ni x2 Mn y2 Al z2 M 2 w2 (OH)2 In chemical formula 2, 0.6≦x2≦0.8, 0.1≦y2≦0.39, 0.01 <z2≦0.03、0≦w2≦0.29、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.

[0054] The nickel-manganese-aluminum composite hydroxide is in the form of particles, and the average particle size (D 50 ) can be 10 μm to 18 μm, 11 μm to 16 μm, or 12 μm to 15 μm.

[0055] The nickel-manganese-aluminum composite hydroxide and the lithium raw material can 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 1:0.9 to 1:1.2.

[0056] 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.

[0057] The first heat treatment can produce a lithium nickel-manganese-aluminum composite oxide. The resulting composite oxide contains at least 60 mol% of nickel, for example, 60 mol% to 80 mol%, based on 100 mol% of all metals excluding lithium. It 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 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. In one embodiment, a method is provided for forming a very thin, uniform coating layer on the surface of a lithium nickel-manganese-aluminum composite oxide with a very small amount of cobalt and a nickel content of 60 mol% to 80 mol%, thereby improving high-voltage and high-temperature properties.

[0058] In one embodiment, the lithium nickel-manganese-aluminum composite oxide obtained by the first heat treatment is mixed with an aqueous solvent containing an aluminum raw material, and then dried and subjected to a second heat treatment to form a coating layer according to one embodiment. This can be considered a type of wet coating method.

[0059] The aqueous solvent may include distilled water, an alcohol-based solvent, or a combination thereof.

[0060] The aluminum source may include, for example, aluminum nitrate, aluminum sulfate, aluminum carbonate, aluminum hydroxide, or a combination thereof. For example, the aluminum source may include aluminum sulfate, which is advantageous for forming a coating layer with a uniform thickness on the surface of the lithium nickel-manganese-aluminum composite oxide particles.

[0061] The aluminum raw material is a raw material for forming the coating layer, and the aluminum content in the aluminum raw material can be designed to be 0.1 mol% to 2 mol% relative to 100 mol% of all metals excluding lithium in the final cathode active material, 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%. By designing the content of the coating raw material within this range, a coating layer with a thin and uniform thickness on the order 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 high-capacity and long-life characteristics.

[0062] The solution obtained by mixing the aluminum raw material with the aqueous solvent has a pH of 1.5 to 3.5, for example, 2.0 to 3.4, 2.5 to 3.3, 2.7 to 3.3, or 2.9 to 3.2. The lithium nickel-manganese-aluminum composite oxide is added to the aqueous solvent containing the aluminum raw material and mixed for approximately 5 to 80 minutes, 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. Satisfying these conditions is advantageous for forming a coating layer of uniform thickness.

[0063] 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.

[0064] The second heat treatment can be understood as a step of 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. The second heat treatment temperature can be lower than the first heat treatment temperature, and the second heat treatment time is preferably the same as or shorter than the first heat treatment time. By carrying out the second heat treatment under these conditions, a desired coating layer can be obtained.

[0065] 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.

[0066] 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 3.3 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] The positive electrode current collector may be made of Al, but is not limited to this.

[0071] Lithium secondary battery In one embodiment, a lithium secondary battery is provided that includes the positive electrode, negative electrode, and electrolyte described above.

[0072] Lithium secondary batteries can be classified into cylindrical, prismatic, pouch, coin, and other types depending on their shape. FIG. 1 is a schematic diagram showing a lithium secondary battery according to one embodiment. Referring to FIG. 1, 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 impregnated with an electrolyte (not shown).

[0073] 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 may significantly reduce gas generation even when charged at a high voltage, thereby achieving high capacity and long life.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] The silicon-carbon composite can be a composite of silicon and amorphous carbon. The average particle size (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 in an amorphous carbon matrix.

[0080] 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.

[0081] 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.

[0082] 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% by volume in the particle size distribution.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] The dry binder can be a fiberizable polymeric material such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] The electrolyte may further contain vinyl ethyl carbonate, vinylene carbonate or ethylene carbonate based compounds to improve the battery life.

[0099] 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.

[0100] 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(oxalate)phosphate (LiDFBOP), lithium difluorooxalateborate (LiDFOB), and lithium bis(oxalate)borate (LiBOB).

[0101] 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.

[0102] 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.

[0103] 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.

[0104] 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, and polytetrafluoroethylene, or a copolymer or mixture of two or more of these polymers.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] 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.

[0111] 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 and subjected to a first heat treatment at 850°C for 8 hours in an oxygen atmosphere to obtain a compound with a composition of LiNi 0.75 Mn 0.23 Al 0.02 O2 and the average particle size (D 50 A composite oxide in the form of secondary particles with a particle size of about 14 μm was produced.

[0112] After mixing aluminum sulfate with distilled water as a solvent, the composite oxide was added and mixed for 20 to 60 minutes. The aluminum content in the aluminum sulfate was designed to be 1.0 mol% relative to 100% by weight of the total metals (excluding lithium) in the final cathode active material. After removing the solvent from the mixed solution, the mixture was dried at 190°C and then subjected to a second heat treatment at 825°C for 8 hours in an oxygen atmosphere to produce the final cathode active material.

[0113] 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 10 mg / cm.2 The density of the final rolled positive electrode was about 3.4 g / cc.

[0114] 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.

[0115] 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.

[0116] 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 the aluminum sulfate was designed and mixed to be 0.5 mol % relative to 100 wt % of the total metals excluding lithium in the final cathode active material.

[0117] Example 3 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 the aluminum sulfate was designed and mixed to be 1.5 mol % relative to 100 wt % of the total metals excluding lithium in the final cathode active material.

[0118] Example 4 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 the aluminum sulfate was designed and mixed to be 2.0 mol % relative to 100 wt % of the total metals excluding lithium in the final cathode active material.

[0119] Comparative Example 1 Ni 0.75 Mn 0.25(OH)2, LiOH and Al2O3 were mixed in a molar ratio of 1:1:0.02 and heat-treated in an oxygen atmosphere at 850°C for 8 hours to obtain a composition of LiNi 0.75 Mn 0.23 Al 0.02 O2 and the average particle size (D 50 A lithium secondary battery was fabricated in substantially the same manner as in Example 1, except that an aluminum-doped composite oxide in the form of secondary particles having a particle size of about 14 μm was used as a positive electrode active material.

[0120] Comparative Example 2 Ni 0.75 Mn 0.25 Al 0.02 (OH)2 and LiOH were mixed in a 1:1 molar ratio and heat-treated in an oxygen atmosphere at 850°C for 8 hours to form a LiNi 0.75 Mn 0.23 Al 0.02 O2 and the average particle size (D 50 A lithium secondary battery was fabricated in substantially the same manner as in Example 1, except that an aluminum-doped composite oxide in the form of secondary particles having a particle size of about 14 μm was used as a positive electrode active material.

[0121] Comparative Example 3 A positive electrode active material was prepared in substantially the same manner as in Example 1, except that the aluminum coating was performed in a dry manner. 0.75 Mn 0.23 Al 0.02 A composite oxide in the form of secondary particles (O2) and aluminum oxide powder were mixed and heat-treated in an oxygen atmosphere at 825°C for 8 hours to prepare an Al-coated cathode active material. A lithium secondary battery was fabricated in substantially the same manner as in Example 1, except that the cathode active material was used.

[0122] Comparative Example 4 The composition is LiNi 0.94 Co 0.03 Al 0.03 O2 and the average particle size (D 50A lithium secondary battery was manufactured in substantially the same manner as in Example 1, except that a composite oxide in the form of secondary particles having a particle size of about 14 μm was used as the positive electrode active material.

[0123] Comparative Example 5 A positive electrode active material was prepared by wet-coating Al using the composite oxide of Comparative Example 4 in the same manner as in Example 1. A lithium secondary battery was prepared in substantially the same manner as in Example 1, except that the positive electrode active material was used.

[0124] Comparative Example 6 A cathode active material and a lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that the aluminum content in the aluminum sulfate was designed to be 3.0 mol % relative to 100 wt % of the total metals excluding lithium in the final cathode active material.

[0125] The design details of the positive electrode active materials of Examples 1 to 4 and Comparative Examples 1 to 6 are briefly shown in Table 1 below.

[0126] Evaluation Example 1: Comparison of Comparative Example 1 and Comparative Example 2 FIG. 2 shows an SEM image of the cathode active material of Comparative Example 1, and FIG. 3 shows an SEM image of the cathode active material of Comparative Example 2. In Comparative Example 1, lithium nickel-manganese-aluminum oxide was prepared by synthesizing lithium nickel-manganese oxide and then doping it with aluminum. Referring to FIG. 2, it was found that the surfaces of the secondary particles of the cathode active material were not uniform, and aluminum by-products were formed, as indicated by the circles. In Comparative Example 2, nickel-manganese-aluminum hydroxide was used as a precursor to prepare lithium nickel-manganese-aluminum oxide in which aluminum was distributed at a uniform concentration within the secondary particles. Referring to FIG. 3, it was found that spherical cathode active material with very uniform surfaces was successfully synthesized, and no aluminum by-products were formed. The examples can be understood to use Comparative Example 2 as a base material.

[0127] Evaluation example 2: Coating layer comparison SEM-EDS images of the cross sections of the positive electrode active materials of Examples 1 to 4, Comparative Example 3, and Comparative Example 5 are shown in Figures 4 to 9, respectively. In the figures, the highlighted areas indicate aluminum. An SEM image of the surface of the positive electrode active material of Comparative Example 5 is shown in Figure 10.

[0128] As shown in Figures 4 to 7, the positive electrode active materials of Examples 1 to 4 successfully formed a very thin, uniformly thick aluminum coating layer on the surface of the secondary particles, forming a core-shell structure. Meanwhile, Figure 8 shows that in Comparative Example 3, which used a dry coating method, aluminum aggregated irregularly on the surface of the secondary particles, and no coating layer surrounding the secondary particles was formed. Also, Figures 9 and 10 show that in Comparative Example 5, which used a nickel-cobalt-aluminum oxide with a nickel content of 94 mol% as the base material and applied the same coating method as the Examples, aluminum aggregated unevenly on the surface of the secondary particles, and no coating layer surrounding the secondary particles was formed. The positive electrode active material of Comparative Example 5 differed from the Examples in composition, residual lithium content on the composite oxide surface, and pH conditions, and therefore, it is understood that a uniform coating layer was not formed even when the coating method of the Examples was applied.

[0129] Evaluation Example 3: Analysis of the coating layer and grain boundary coating part of the example FIG. 11 is a graph showing the TOF-SIMS depth profile of the positive electrode active material of Example 1, illustrating how the ratio of the aluminum content to the nickel content changes from the surface to the interior of the secondary particles.

[0130] FIG. 12 is a TEM image of a cross section of the positive electrode active material of Example 1, and FIG. 13 is an enlarged image of the area indicated by a square in FIG. 12. FIG. 14 is an image obtained by EDS analysis of the TEM image of FIG. 13, highlighting oxygen, aluminum, manganese, and nickel, from left to right. FIG. 15 is an EDS line profile showing the change in oxygen, aluminum, manganese, and nickel content in the direction of the arrows shown in FIGS. 13 and 14.

[0131] 11 to 15, it can be seen that the positive electrode active material according to Example 1 has a thin and uniform Al coating layer having a thickness of about 30 nm to 200 nm formed on the surface of the core particle.

[0132] The leftmost image in Figure 16 is a TEM image of a cross section of the cathode active material of Example 1, showing a magnified view of a primary particle located at the outermost shell of a secondary particle. The four images on the right of Figure 16 are TEM-EDS images, highlighting O, Al, Mn, and Ni from left to right. Figure 17 is an EDS line profile showing the change in the O, Al, Mn, and Ni content in the direction of the arrow in Figure 16. Referring to Figures 16 and 17, it can be seen that Al is also coated at the interfaces of the primary particles located at the outermost shell of the secondary particles, i.e., grain boundary coatings are formed.

[0133] FIG. 18 is a TEM image of a cross section of the positive electrode active material of Example 1, and FIG. 19 is a magnified photograph (left) of Area 1 in FIG. 18 and an image (right) of aluminum highlighted by EDS analysis. FIG. 20 is a magnified photograph (left) and EDS analysis image (right) of Area 2 in FIG. 18, and FIG. 21 is a magnified photograph (left) and EDS analysis image (right) of Area 3 in FIG. 18. The directions toward Areas 1, 2, and 3 in FIG. 18 can be said to be directions from the interior of the core particle to the surface. Referring to FIGS. 18 to 21, it can be seen that an Al grain boundary coating is formed at the interface of the primary particles at every position, including the interior of the core particle.

[0134] Figure 22 is a TEM-EDS image of a cross section of the cathode active material of Example 1, showing a magnified analysis of a primary particle located at the outermost shell of a secondary particle. The highlighted area indicates aluminum. Figure 23 shows TEM analysis images of the areas indicated by arrows (1) through (6) in Figure 22. In Figure 23, locations (1) through (4) can be considered the surface of the secondary particle, and therefore represent the location where an aluminum coating layer can be observed. Location (5) represents the interior of the primary particle. Location (6) represents the location between primary particles, i.e., the grain boundary, where an aluminum grain boundary coating can be observed. Referring to Figure 23, a layered structure is observed at all locations, including the surface of the secondary particle, the interior of the primary particle, and the grain boundary. In other words, both the coating layer and the grain boundary coating were analyzed to have a layered structure, confirming that the coating layer and the grain boundary coating comprise layered lithium aluminum oxide, e.g., LiAlO2.

[0135] Evaluation example 4: Evaluation of electrochemical properties The lithium secondary batteries manufactured in Examples 1 to 4 and Comparative Examples 1 to 6 were initially charged and discharged at a constant current of 0.2 C at 25°C up to an upper limit voltage of 4.45 V, and at a constant voltage of 0.05 C, and then discharged at 0.2 C down to an end voltage of 3.0 V. The initial charge capacity, initial discharge capacity, and the ratio of the latter to the former were efficiently calculated and are shown in Table 1. Next, a cycle of charging at 1.0 C and discharging at 1.0 C at 45°C in the voltage range of 3.0 V to 4.45 V was repeated 25 times or more, and the ratio of the 25-cycle discharge capacity to the initial discharge capacity was calculated and shown in Table 1 below as a high-temperature life.

[0136] [Table 1]

[0137] First, comparing Comparative Example 1 and Comparative Example 2, it was confirmed that Comparative Example 2, which introduced aluminum as a precursor, had an increased initial charge / discharge capacity and improved high-temperature lifespan characteristics compared to Comparative Example 1, which additionally doped aluminum. The example shows a case in which Comparative Example 2 was used as a base material and a coating was performed using a specific method according to an embodiment to form a uniform coating layer. It was confirmed that coating with an Al content of 2 mol% or less could simultaneously improve the initial charge / discharge capacity, efficiency, and high-temperature lifespan characteristics.

[0138] Comparative Example 3 was a case where coating was performed using a dry method, and a uniform coating layer was not formed as in Evaluation Example 2, and therefore the high-temperature life characteristics were significantly reduced compared to the Examples.

[0139] Comparative Examples 4 and 5 used a lithium nickel-cobalt-aluminum oxide with a nickel content of 94 mol%. While these materials exhibited high initial charge / discharge capacity and efficiency, their high-temperature lifespan characteristics were analyzed to be inferior to those of the Examples, and the use of cobalt resulted in increased costs. Comparative Example 5 applied the same coating method as the Examples to the base material of Comparative Example 4. However, unlike Evaluation Example 2, a uniform coating layer was not formed in Comparative Example 5. Furthermore, as shown in Table 1, the initial charge / discharge capacity and efficiency were actually lower. It is understood that the failure to form a uniform coating layer in the form of a shell surrounding the core results in a decrease in the battery's charge / discharge capacity, an increase in resistance, and a decrease or no improvement in lifespan characteristics.

[0140] On the other hand, Comparative Example 6 used the same base material and coating method as in the Example, but increased the Al coating content by 3 mol%, and it was analyzed that the initial charge-discharge capacity was significantly reduced and the initial charge-discharge efficiency was also reduced.

[0141] 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]

[0142] 100 Lithium secondary battery 10 positive electrode 20 negative electrode 30 Separator 40 Electrode assembly 50 cases

Claims

1. Core particles containing a lithium nickel-manganese-aluminum composite oxide, and a coating layer containing aluminum located on the surface of the core particle, the nickel content of the core particle is 60 mol% to 80 mol%, the aluminum content of the core particle is 1 mol% to 3 mol%, and the aluminum content of the coating layer is 0.1 mol% to 2 mol%, based on 100 mol% of all metals excluding lithium; The positive electrode active material, wherein the coating layer further contains nickel, manganese, or a combination thereof.

2. 2. The cathode active material of claim 1, 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.

3. The positive electrode active material of claim 1 , wherein the coating layer is in the form of a shell that continuously surrounds the surface of the core particle.

4. The cathode active material of claim 1 , wherein the coating layer has a thickness of 30 nm to 200 nm.

5. The positive electrode active material of claim 1 , wherein the thickness of the coating layer within one positive electrode active material has a deviation of 20% or less.

6. The positive electrode active material according to claim 1 , wherein the coating layer comprises an aluminum compound having a layered structure.

7. The coating layer is LiAlO 2 The positive electrode active material of claim 1 , comprising:

8. The positive electrode active material according to claim 1, wherein the lithium nickel-manganese-aluminum composite oxide of the core particle is represented by Chemical Formula 1: [Chemical formula 1] Li a1 Ni x1 Mn y1 Al z1 M 1 w1 O 2-b1 X b1 In Chemical Formula 1, 0.9≦a1≦1.8, 0.6≦x1≦0.8, 0.1≦y1≦0.39, 0.01<z1≦0.03, 0≦w1≦0.29, 0.9≦x1+y1+z1+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 Zr, and X is one or more elements selected from F, P, and S.

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

10. 2. The positive electrode active material according to claim 1, wherein the lithium nickel-manganese-aluminum composite oxide of the core particle is a cobalt-free compound.

11. 2. The positive electrode active material according to claim 1, wherein the content of cobalt is 0 mol % to 0.01 mol % relative to 100 mol % of all metals excluding lithium.

12. The cathode active material according to claim 1 , wherein the core particle is in the form of a secondary particle formed by aggregating a plurality of primary particles.

13. The positive electrode active material of claim 12 , further comprising a grain boundary coating portion located on a surface of the primary particle inside the secondary particle and containing aluminum.

14. The positive electrode active material according to claim 13 , wherein the grain boundary coating portion includes an aluminum compound having a layered structure.

15. The grain boundary coating portion is LiAlO 2 The positive electrode active material of claim 13 , comprising:

16. The positive electrode active material of claim 13 , wherein the grain boundary coating further contains nickel, manganese, or a combination thereof.

17. The positive electrode active material according to claim 13 , wherein the content of aluminum in the grain boundary coating portion is less than the content of aluminum in the coating layer.

18. The average particle size (D 50 2. The positive electrode active material according to claim 1, wherein the particle size is 10 μm to 18 μm.

19. The positive electrode active material according to claim 1 , wherein the positive electrode active material does not contain sodium.

20. A nickel-manganese-aluminum composite hydroxide and a lithium raw material are mixed and subjected to a first heat treatment to obtain a lithium nickel-manganese-aluminum composite oxide; The lithium nickel-manganese-aluminum composite oxide thus obtained is introduced into a solution in which an aluminum raw material is mixed in an aqueous solvent, and the resulting mixture is then dried and subjected to a second heat treatment to obtain a positive electrode active material; In the nickel-manganese-aluminum composite hydroxide, the nickel content is 60 mol% to 80 mol% and the aluminum content is 1 mol% to 3 mol% relative to 100 mol% of the total metals; The method for producing a positive electrode active material, wherein the content of aluminum in the aluminum raw material is 0.1 mol % to 2 mol % relative to 100 mol % of all metals in the positive electrode active material excluding lithium.

21. 21. The method for producing a positive electrode active material according to claim 20, wherein the aluminum content in the aluminum raw material is 0.5 mol% to 1.5 mol% relative to 100 mol% of all metals excluding lithium in the positive electrode active material.

22. 21. The method of claim 20, wherein the aluminum source comprises aluminum nitrate, aluminum sulfate, aluminum carbonate, aluminum hydroxide, or a combination thereof.

23. The method for producing a positive electrode active material according to claim 20, wherein the solution in which the aluminum raw material is mixed with the aqueous solvent has a pH of 1.5 to 3.

5.

24. 21. The method for producing a positive electrode active material according to claim 20, wherein the step of adding the obtained lithium nickel-manganese-aluminum composite oxide to a solution obtained by mixing an aluminum raw material in an aqueous solvent and mixing the resulting mixture is carried out for 5 minutes to 80 minutes, and the pH of the solution after mixing is 4.5 to 8.

5.

25. The method for producing a positive electrode active material according to claim 20, wherein the drying is performed at 40°C to 240°C.

26. The first heat treatment is carried out at 750°C to 950°C, The method for producing a positive electrode active material according to claim 20, wherein the second heat treatment is performed at 700°C to 850°C.

27. 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 comprises the positive electrode active material according to any one of claims 1 to 19.

28. The loading level of the positive electrode active material layer is 10 mg / cm 2 ~40 mg / cm 2 28. The positive electrode of claim 27, wherein

29. 28. The positive electrode according to claim 27, wherein the density of the positive electrode active material layer is 3.3 g / cc to 3.7 g / cc.

30. The positive electrode according to claim 27 . a negative electrode, and A lithium secondary battery, including an electrolyte.

31. 31. The lithium secondary battery according to claim 30, wherein the charging voltage is 4.45 V or higher.

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