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

Abstract

To provide a positive electrode active material that can achieve high density, high capacity, and a long life characteristic, and can reduce the high-temperature preserved gas generation quantity, and a positive electrode and a lithium secondary battery including this positive electrode active material.SOLUTION: A positive electrode active material according to an embodiment includes a core particle including layered lithium nickel manganese composite oxide and being in a secondary particle mode in which a plurality of primary particles are aggregated, an aluminum coating layer existing on a surface of the core particle, and a grain boundary coating part existing on a surface of the primary particle and containing cobalt.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a positive electrode active material, 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, or high-energy density lithium secondary batteries has recently increased rapidly, the supply of positive electrode active materials containing the rare metal cobalt is expected to be in short supply. That is, because cobalt is expensive and its remaining reserves are limited, there is a need to develop positive electrode active materials that are free of cobalt or have a reduced cobalt content. Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention provides a positive electrode active material that achieves high density, high capacity, and long life characteristics and can reduce the amount of gas generated during high-temperature storage, and a positive electrode and a lithium secondary battery using the same. [Means for solving the problem]

[0005] In one embodiment, a cathode active material is provided, the cathode active material including: a core particle in the form of a secondary particle formed by aggregating a plurality of primary particles, the core particle including a layered lithium nickel-manganese composite oxide; an aluminum coating layer located on the surface of the core particle; and a grain boundary coating portion containing cobalt located on the surface of the primary particle.

[0006] In another embodiment, the present invention provides a method for manufacturing a cathode active material, including: (i) preparing core particles, which include a layered lithium nickel-manganese composite oxide and are in the form of secondary particles formed by agglomeration of a plurality of primary particles; (ii) preparing an aluminum coating solution containing an aqueous solvent and an aluminum raw material; (iii) adding the core particles to the aluminum coating solution, mixing, and then drying to produce a coated product; and (iv) dry-mixing the coated product and a cobalt raw material, followed by heat treatment, to obtain a cathode active material.

[0007] In another embodiment, a lithium secondary battery is provided that includes the positive electrode, the negative electrode, and an electrolyte. [Effects of the Invention]

[0008] The positive electrode active material according to one embodiment can achieve high density, high capacity, and long life characteristics, and can reduce the amount of gas generation during high-temperature storage. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic diagram of a lithium secondary battery according to an embodiment; [Figure 2] 1 is a schematic diagram of a lithium secondary battery according to an embodiment; [Figure 3] 1 is a schematic diagram of a lithium secondary battery according to an embodiment; [Figure 4] 1 is a schematic diagram of a lithium secondary battery according to an embodiment; [Figure 5] 1 is a SEM-EDS image of a cross section of the positive electrode active material prepared in Example 1. [Figure 6]1 is a SEM-EDS image of a cross section of the positive electrode active material prepared in Example 1. [Figure 7] 1 is a SEM-EDS analysis image of the mapping of cobalt element in a cross section of the positive electrode active material produced in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0010] Although the present invention may be embodied in many different forms, it is not limited to the embodiments set forth herein.

[0011] 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.

[0012] As used herein, "combinations thereof" refers to mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0013] 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.

[0014] In the drawings, the thickness of various layers and regions is 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.

[0015] 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.

[0016] 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 image or a scanning electron microscope image. 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, 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 ) unless otherwise defined, the average particle size is the diameter (D) of the particle that makes up 50% of the cumulative volume in the particle size distribution obtained by measuring the size (diameter or length of the major axis) of 20 or more particles randomly selected in a scanning electron microscope image. 50 ) may be taken as the average particle size.

[0017] 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.

[0018] The term "metal" is understood to include general metals, transition metals, and metalloids.

[0019] positive electrode active material In one embodiment, a cathode active material is provided, comprising: a core particle in the form of a secondary particle formed by aggregating a plurality of primary particles, the core particle including a layered lithium nickel-manganese composite oxide; an aluminum coating layer located on the surface of the core particle; and a grain boundary coating portion containing cobalt located on the surface of the primary particle.

[0020] The recent surge in the price of the rare metal cobalt has prompted 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 lithium nickel-manganese 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.

[0021] Therefore, in one embodiment, an aluminum coating layer is introduced onto the surface of a core particle containing a layered lithium nickel-manganese composite oxide, and a cobalt-containing grain boundary coating portion is introduced onto the surface of the primary particle that constitutes the core particle in the form of a secondary particle. This strengthens the particle surface and simultaneously forms a robust internal structure, thereby improving not only the high voltage and high temperature life characteristics but also the initial charge / discharge efficiency and the amount of gas generated during high temperature storage.

[0022] core particle The core particle according to one embodiment includes a layered lithium nickel-manganese composite oxide.

[0023] In the layered lithium nickel-manganese composite oxide, the nickel content may be 60 mol% or more relative to 100 mol% of all metals excluding lithium, 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 this range, high capacity can be achieved, and structural stability can be improved even when the cobalt content is reduced.

[0024] In the layered lithium nickel-manganese composite oxide, the manganese content may be 15 mol% or more relative to 100 mol% of all metals excluding lithium, for example, 15 mol% to 40 mol%, 15 mol% to 35 mol%, 15 mol% to 30 mol%, or 20 mol% to 30%, etc. When the manganese content satisfies this range, the positive electrode active material can achieve high capacity while improving structural stability.

[0025] For example, the lithium nickel-manganese composite oxide may be a lithium nickel-manganese-aluminum composite oxide containing aluminum in addition to nickel and manganese. When the composite oxide contains aluminum, it is advantageous for maintaining a stable layered structure even when cobalt is excluded from the structure. The aluminum content relative to 100 mol% of all metals (excluding lithium) in the lithium nickel-manganese-aluminum composite oxide may be 0.1 mol% or more, 0.5 mol% or more, or 1 mol% or more, for example, 1 mol% to 3 mol%, 1 mol% to 2.5 mol%, 1 mol% to 2 mol%, or 1.5 mol% to 2.5 mol%. Here, the aluminum content refers to the content of aluminum present in the core particles. When the aluminum content satisfies the above range, a stable layered structure can be maintained even when cobalt is excluded from the core particles, preventing structural collapse during charge and discharge, and achieving long-life cathode active materials.

[0026] According to one embodiment, the aluminum concentration within the core particle may be uniform. This means that the aluminum concentration is not 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 rather that the aluminum 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 by using an aluminum raw material during precursor preparation without additional doping of aluminum during the core particle synthesis process. The core particle is 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, by selecting a primary particle at any position in the cross-section of the secondary particle and measuring the aluminum content within the primary particle (not 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 this structure, a stable layered structure can be maintained even when cobalt is absent or present in only a small amount, and aluminum by-products and aluminum aggregates are not generated, thereby improving the capacity, efficiency, and life characteristics of the positive electrode active material simultaneously.

[0027] The layered lithium nickel-manganese composite oxide can be specifically represented by the following chemical formula 1. [Chemical formula 1] Li a1 Ni x1 Mn y1 Al z1 M 1 w1 O 2-b1 X b1

[0028] In the above chemical formula 1, 0.9≦a1≦1.8, 0.6≦x1≦0.8, 0.1≦y1≦0.4, 0≦z1≦0.03, 0≦w1≦0.3, 0.9≦x1+y1+z1+w1≦1.1, and 0≦b1≦0.1; M 1is one or more elements selected from B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zr, and Zn, and X is one or more elements selected from F, P, and S.

[0029] In the chemical formula 1, 0.9 ≦ a1 ≦ 1.5, or 0.9 ≦ a1 ≦ 1.2 may be satisfied. Further, the chemical formula 1 may contain aluminum. In this case, 0.6 ≦ x1 ≦ 0.8, 0.1 ≦ y1 ≦ 0.39, 0.01 ≦ z1 ≦ 0.03, and 0 ≦ w1 ≦ 0.29 can be satisfied. For example, 0.6 ≦ x1 ≦ 0.8, 0.1 ≦ y1 ≦ 0.39, 0.01 < z1 ≦ 0.03, and 0 ≦ w1 ≦ 0.29 can be satisfied.

[0030] In the chemical formula 1, for example, 0.6 ≦ x1 ≦ 0.79, 0.6 ≦ x1 ≦ 0.78, 0.6 ≦ x1 ≦ 0.75, 0.65 ≦ x1 ≦ 0.8, or 0.7 ≦ x1 ≦ 0.79 may be satisfied, 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 may be satisfied, 0.01 ≦ z1 ≦ 0.025, 0.01 < z1 ≦ 0.02, or 0.01 < z1 ≦ 0.019 may be satisfied, 0 ≦ wx1 ≦ 0.28, 0 ≦ w1 ≦ 0.27, 0 ≦ w1 ≦ 0.26, 0 ≦ w1 ≦ 0.25, 0 ≦ w1 ≦ 0.24, 0 ≦ w1 ≦ 0.23, 0 ≦ w1 ≦ 0.22, 0 ≦ w1 ≦ 0.21, 0 ≦ w1 ≦ 0.2, 0 ≦ w1 ≦ 0.15, 0 ≦ w1 ≦ 0.1, or 0 ≦ w1 ≦ 0.09 etc. may be satisfied.

[0031] The layered lithium nickel - manganese - based composite oxide may be a cobalt - free compound that does not contain cobalt or contains a very small amount of cobalt. The content of cobalt based on 100 mol% of the total metal excluding lithium may be 0.01 mol% or less, 0.005 mol% or less, 0.001 mol% or less. For example, it may be 0 mol% to 0.01 mol%, 0 mol% to 0.005 mol%, or 0 mol% to 0.001 mol%.

[0032] The core particle is a secondary particle formed by agglomeration of multiple primary particles. The secondary particles may be spherical, ellipsoidal, polyhedral, or irregular in shape, and the primary particles that make up the secondary particles may be spherical, ellipsoidal, plate-shaped, or a combination thereof.

[0033] Coating layer According to one embodiment, the positive electrode active material includes an aluminum coating layer located on the surface of the core particle, and a grain boundary coating portion located on the surface of the primary particle and containing cobalt.

[0034] The lithium nickel-manganese composite oxide is 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. This can result in a large amount of gas generation, which can reduce the battery life and safety. However, by introducing a coating layer according to one embodiment, this problem can be resolved.

[0035] The coating layer of the positive electrode active material may include aluminum, and may optionally further include a zirconium coating layer on the aluminum coating layer. In this case, the content of the coating element relative to 100 mol% of all metals excluding lithium in the entire positive electrode active material may vary depending on the type of coating element, and may be 0.01 mol% to 5 mol%, for example, 0.05 mol% to 3 mol%, or 0.1 mol% to 2 mol%.

[0036] For example, when an aluminum coating layer is used, the aluminum content of the aluminum coating layer may be 0.1 mol% to 3.0 mol%, e.g., 0.1 mol% to 2.0 mol%, 0.5 mol% to 1.5 mol%, or 0.7 mol% to 1.3 mol%, based on 100 mol% of all metals excluding lithium in the entire positive electrode active material. The aluminum content of the aluminum coating layer may refer to only the content of aluminum contained in the aluminum coating layer, regardless of the aluminum contained in the core particles. When an aluminum coating layer is used, the aluminum coating layer may include, for example, a layered aluminum compound, such as aluminum oxide, lithium-aluminum oxide, or a combination thereof, such as LiAlO.

[0037] For example, when a zirconium coating layer is formed on an aluminum coating layer, the zirconium content of the zirconium coating layer may be 0.1 mol % to 1.5 mol %, e.g., 0.1 mol % to 1.0 mol %, 0.1 mol % to 0.5 mol %, or 0.1 mol % to 0.4 mol %, relative to 100 mol % of all metals excluding lithium in the entire positive electrode active material. When the aluminum and / or zirconium content of the coating layer satisfies these ranges, the positive electrode active material does not experience a decrease in capacity or an increase in resistance, and a good coating layer is formed, effectively suppressing side reactions with the electrolyte and effectively reducing gas generation under high voltage and high temperature conditions.

[0038] According to one embodiment, the aluminum 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 aluminum coating layer may be formed to a very thin and uniform thickness while completely surrounding the surface of the core particle. 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.

[0039] According to one embodiment, the thickness of the aluminum coating layer may be 10 nm to 500 nm, e.g., 10 nm to 450 nm, 10 nm to 400 nm, 10 nm to 350 nm, 10 nm to 300 nm, 10 nm to 250 nm, 10 nm to 200 nm, 10 nm to 150 nm, 10 nm to 100 nm, 10 nm to 50 nm, 20 nm to 500 nm, 30 nm to 500 nm, or 40 nm to 500 nm. For example, the thickness of the aluminum coating layer may be approximately 40 nm or less. When the aluminum coating layer satisfies this thickness range, the coating does not increase resistance or decrease capacity, improves the structural stability of the cathode active material, and effectively suppresses side reactions with the electrolyte. The thickness of the aluminum coating layer may be measured, for example, by SEM, TEM, TOF-SIMS, XPS, or EDS analysis, and the thickness range of the aluminum coating layer may be measured by TEM-EDS line profile analysis.

[0040] According to one embodiment, the aluminum coating layer is thin, ranging in thickness from tens to hundreds of nanometers, yet uniform in thickness. For example, the thickness deviation of the aluminum coating layer within a single cathode active material particle may be 20% or less, 18% or less, or 15% or less. Here, the thickness deviation of the aluminum coating layer refers to the thickness of the coating layer within a single cathode active material particle. For example, the thickness deviation of the aluminum coating layer may be calculated by measuring the thickness at approximately 10 points on an electron microscope image of the cross section of a single cathode active material particle, calculating the arithmetic mean, and then 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 thickness deviation or standard deviation of the aluminum coating layer within the above ranges indicates that a coating layer of uniform thickness 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 resistance increase and capacity loss due to the coating.

[0041] Meanwhile, the aluminum coating layer may further contain nickel, manganese, or a combination thereof in addition to aluminum. The nickel and manganese may be contained in the core particles and introduced during the formation of the aluminum coating layer, and their contents are not particularly limited. According to one embodiment, the aluminum coating layer essentially contains aluminum and selectively contains nickel and manganese, and is formed with a thin and uniform thickness to improve the high-voltage characteristics and life characteristics of the positive electrode active material.

[0042] In addition, the aluminum coating layer may further contain sulfur in addition to aluminum. The sulfur may be introduced during the process of adding aluminum sulfate, which is one of the aluminum raw materials added to form the aluminum coating layer, and the sulfur content is not particularly limited. According to an embodiment, the aluminum coating layer essentially contains aluminum and optionally contains sulfur, thereby improving the high-voltage characteristics and life characteristics of the positive electrode active material.

[0043] Meanwhile, during the formation of the aluminum coating layer, aluminum diffuses into the secondary particles. Therefore, according to one embodiment, the positive electrode active material may further include a grain boundary coating region containing aluminum located on the surface of the primary particles within the secondary particles. The "interior of the secondary particles" may refer to the entire interior of the secondary particles excluding the surface, or may refer to the region extending from the surface of the secondary particles toward the center of the secondary particles, extending up to approximately 60% of the radius. The grain boundary coating region is distinct from the coating layer on the surface of the secondary particles and refers to a coating region formed on the surface of the primary particles located within the secondary particles. The presence of the grain boundary coating region can be confirmed by SEM-EDS analysis of a cross section of the positive electrode active material. The formation of the aluminum grain boundary coating region further stabilizes the structure of the positive electrode active material, improving its lifespan.

[0044] The aluminum content in the grain boundary coating portion is not particularly limited, and for example, the aluminum content in the grain boundary coating portion may be less than the aluminum content in the coating layer.

[0045] According to one embodiment, the cathode active material includes core particles in the form of secondary particles formed by agglomeration of a plurality of primary particles, and a grain boundary coating portion containing cobalt located on the surface of the primary particles. The cathode active material is formed by coating the surface of the core particles with aluminum and then dry-coating cobalt. In the cathode active material, cobalt is barely present on the surface of the core particles but diffused into the interior of the core particles. When doped with cobalt, cobalt is uniformly present inside the primary particles. However, the cathode active material according to one embodiment is characterized in that cobalt is coated only on the grain boundaries, not inside the primary particles. That is, LiAlO2 is formed on the surface of the core particles by aluminum coating, and cobalt is diffused inside the core particles by cobalt dry-coating, coating the grain boundaries of the primary particles. This results in a surface modification, with cobalt coating on the surfaces of the primary particles and aluminum coating on the surfaces of the secondary particles, improving capacity and life characteristics and reducing gas generation during high-temperature storage. In this case, the cobalt content of the grain boundary coating portion may be 0.1 mol% to 5.0 mol%, for example, 0.5 mol% to 4.0 mol%, 1.0 mol% to 3.0 mol%, or 2.0 mol% to 3.0 mol%, relative to 100 mol% of all metals excluding lithium in the entire positive electrode active material. When the cobalt content of the grain boundary coating portion satisfies this range, cobalt is diffused into the core particles, forming a coating portion at the grain boundaries of the primary particles, effectively suppressing side reactions with the electrolyte and effectively reducing gas generation under high voltage and high temperature conditions.

[0046] The surface of the core particle may contain no or a very small amount of cobalt, and the cobalt content relative to 100 mol% of all metals excluding lithium may be 0.01 mol% or less, 0.005 mol% or less, or 0.001 mol% or less, for example, 0 mol% to 0.01 mol%, 0 mol% to 0.005 mol%, or 0 mol% to 0.001 mol%. That is, the coating layer on the surface of the core particle may contain no or a very small amount of cobalt, and cobalt is diffused into the interior of the core particle, coating the grain boundaries of the primary particles with cobalt.

[0047] The average particle size (D-) of the positive electrode active material according to an embodiment is not particularly limited, and may be, for example, 10 μm to 25 μm, for example, 11 μm to 20 μm, or 12 μm to 18 μm. The average particle size is determined by measuring the size (diameter or major axis length) of 20 or more random particles in a scanning electron microscope image of the positive electrode active material to obtain a particle size distribution, and then calculating the diameter (D-) of the particles whose cumulative volume accounts for 50% by volume in the particle size distribution. 50 When the average particle size of the positive electrode active material satisfies this range, high capacity and long life can be achieved, which may be advantageous for forming a coating layer according to an embodiment.

[0048] Method for producing positive electrode active material In one embodiment, a method for manufacturing a positive electrode active material includes: (i) preparing core particles, which include a layered lithium nickel-manganese composite oxide and are in the form of secondary particles formed by agglomeration of a plurality of primary particles; (ii) preparing an aluminum coating solution containing an aqueous solvent and an aluminum raw material; (iii) adding the core particles to the aluminum coating solution, mixing, and then drying to produce a coated product; and (iv) dry-mixing the coated product and a cobalt raw material, followed by heat treatment, to obtain a positive electrode active material.

[0049] In one embodiment of the method for manufacturing a positive electrode active material, step (i) includes mixing a nickel-manganese composite hydroxide and a lithium source and performing a first heat treatment. The nickel-manganese composite hydroxide is a precursor of core particles and may contain no or only a small amount of cobalt, for example, a cobalt-free nickel-manganese composite hydroxide. The nickel-manganese composite hydroxide may be manufactured by a common coprecipitation method.

[0050] In the nickel-manganese composite hydroxide, the nickel content relative to 100 mol% of the total metals may be 60 mol% to 80 mol%, for example, 65 mol% to 80 mol%, 70 mol% to 80 mol%, 60 mol% to 79 mol%, 60 mol% to 78 mol%, or 60 mol% to 75 mol%, etc. When the nickel content satisfies the above range, high capacity can be achieved, and structural stability can be improved even when the cobalt content is reduced.

[0051] In the nickel-manganese composite hydroxide, the manganese content relative to 100 mol% of the total metals may be 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, high capacity can be achieved while improving the structural stability of the positive electrode active material, and production costs can be reduced, improving economic efficiency.

[0052] Furthermore, when the nickel-manganese composite hydroxide further contains aluminum, the aluminum content relative to 100 mol% of the total metals may be 0.1 mol% or more, 0.5 mol% or more, or 1 mol% or more, for example, 1 mol% to 3 mol%, 1 mol% to 2.5 mol%, 1 mol% to 2 mol%, or 1 mol% to 1.9 mol%. When the aluminum content in the composite hydroxide satisfies the above range, high capacity can be achieved while improving the structural stability of the positive electrode active material, and production costs can be reduced, improving economy.

[0053] According to an embodiment, a method for manufacturing a positive electrode active material may involve using a nickel-manganese-aluminum composite hydroxide as a precursor, in which aluminum is uniformly dispersed within the structure, by using an aluminum raw material in the precursor manufacturing process without additionally doping aluminum during the manufacturing of core particles. When such a precursor is used, a positive electrode active material can be manufactured that stably maintains its layered structure even during repeated charge and discharge cycles, even without cobalt, and the capacity, efficiency, and life characteristics of the positive electrode active material can be improved without the formation of aluminum by-products or aluminum aggregates.

[0054] In the nickel-manganese composite hydroxide, the cobalt content relative to 100 mol% of the total metals may be 0.01 mol% or less, 0.005 mol% or less, or 0.001 mol% or less, for example, 0 mol% to 0.01 mol%, 0 mol% to 0.005 mol%, or 0 mol% to 0.001 mol%. Such nickel-manganese composite hydroxide is economical because it can avoid the increase in unit price due to cobalt, and it can be said to maximize capacity and improve structural stability.

[0055] The nickel-manganese composite hydroxide can be represented by the following chemical formula 2, for example. [Chemical formula 2] Ni x2 Mn y2 Al z2 M 2 w2 (OH)2

[0056] In the above chemical formula 2, 0.6≦x2≦0.8, 0.1≦y2≦0.4, 0≦z2≦0.03, 0≦w2≦0.3, and 0.9≦x2+y2+z2+w2≦1.1; and M 2 is one or more elements selected from B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zr, and Zn.

[0057] In Chemical Formula 2, for example, 0.6≦x2≦0.8, 0.1≦y2≦0.39, 0.01≦z2≦0.03, and 0≦w2≦0.29 may be satisfied.

[0058] The nickel-manganese composite hydroxide is in the form of particles, and the average particle size (D 50 ) may be 10 μm to 25 μm, for example, 11 μm to 20 μm, or 12 μm to 18 μm.

[0059] The nickel-manganese composite hydroxide and the lithium raw material may be mixed at a molar ratio of 1:0.9 to 1:1.8, for example, at a molar ratio of 1:0.9 to 1:1.5 or 1:1 to 1:1.2.

[0060] 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.

[0061] A lithium nickel-manganese composite oxide can be obtained through the first heat treatment. In the obtained lithium nickel-manganese composite oxide, the nickel content, relative to 100 mol% of all metals excluding lithium, can be 60 mol% to 80 mol%, the manganese content can be 10 mol% or more, the aluminum content can be 0 mol% to 3 mol%, and the cobalt content can be extremely small, ranging from 0 mol% to 0.01 mol%. This composite oxide has a significantly different residual lithium content on the particle surface from oxides of other compositions, such as lithium nickel-cobalt-manganese composite oxide, lithium nickel-cobalt-aluminum composite oxide, and lithium cobalt-based oxide, resulting in various different surface characteristics. Therefore, it is impossible to form a uniform, well-formed coating layer using existing coating methods.

[0062] Therefore, in the method for manufacturing a positive electrode active material according to an embodiment, steps (ii) and (iii) include preparing an aluminum coating solution in which salt is completely dissolved by a salt-dissolution method by adding and mixing an aqueous solvent and an aluminum raw material, and then adding and mixing core particles into the aluminum coating solution, followed by drying and coating, thereby forming a uniform coating layer on the positive electrode active material.

[0063] Although it is a salt-dissolution wet coating method, it can be considered a pre-addition method in which the coating raw material salt is first completely dissolved and then the active material particles are added. This method can successfully form a uniform, thin coating layer on the surface of the layered lithium nickel-manganese composite oxide. This coating method can further increase the content of coating elements on the active material surface compared to general dry methods and post-addition wet methods.

[0064] The aqueous solvent may include distilled water, an alcoholic solvent, or a combination thereof. The aluminum source may be, for example, aluminum sulfate. Aluminum sulfate is an optimal source for forming a uniform aluminum coating layer on the layered lithium nickel-manganese composite oxide.

[0065] The aluminum content in the aluminum raw material may be 0.1 mol% to 3.0 mol%, for example, 0.1 mol% to 2.0 mol%, 0.5 mol% to 1.5 mol%, or 0.7 mol% to 1.3 mol%, based on a total of 100 mol% of all metals excluding lithium in the core particle and the aluminum in the aluminum raw material. By designing the aluminum coating content within this range, a coating layer with a uniform thickness of tens to hundreds of nanometers can be formed, reducing the amount of gas generation in the lithium secondary battery under high-voltage or high-temperature operating conditions and improving its high-capacity and long-life characteristics.

[0066] The aluminum raw material is added to the aqueous solvent and mixed for approximately 1 to 60 minutes, e.g., 3 to 30 minutes, or 5 to 10 minutes. The mixing speed may be 100 to 800 rpm, e.g., 200 to 600 rpm, or 250 to 500 rpm. Under these mixing conditions, the aluminum raw material is completely dissolved in the aqueous solvent to produce a colorless and transparent coating solution. Using this coating solution, a uniform coating layer according to one embodiment can be effectively formed. The pH of the coating solution after mixing may be, for example, 1.5 to 4, e.g., 2.0 to 3.5, 2.5 to 3.3, 2.7 to 3.3, or 2.9 to 3.2.

[0067] The core particles are added to the prepared coating solution, and the coating solution is stirred while the core particles are added, thereby improving the coating quality.

[0068] Furthermore, the time required for adding core particles to the coating solution may be 30 seconds / 500g to 2 minutes / 500g, for example, 30 seconds / 500g to 1.5 minutes / 500g. By appropriately adjusting the rate at which the core particles are added, the pH of the supernatant after coating is completed can be appropriately adjusted, thereby effectively forming a uniform coating layer according to one embodiment. If the rate at which the core particles are added is too slow, the reaction rate per particle may change, preventing the formation of a uniform coating layer. If the rate at which the core particles are added is too fast, the pH may change too quickly, preventing the formation of a uniform coating layer.

[0069] The time for stirring after all the core particles have been added to the coating solution may be approximately 15 to 60 minutes, for example, 20 to 50 minutes, or 30 to 45 minutes. The time from the start of adding the core particles to the coating solution to the end of stirring, i.e., the coating reaction time, can be appropriately adjusted to approximately 1 hour or less.

[0070] In one embodiment, when the core particles are added to the coating solution and mixing is stopped, i.e., when mixing or coating is completed, the pH of the supernatant may be in the range of 5.5 to 8.5. If the pH of the supernatant is less than 5.5, it may be too acidic and a uniform coating layer may not be formed, and if the pH is more than 8.5, it may be too basic and it may also be difficult to form a uniform aluminum coating layer.

[0071] After removing the aqueous solvent from the mixed solution, the resulting product can be dried, for example, at 40°C to 240°C, 100°C to 220°C, or 150°C to 200°C, for example, under vacuum conditions, and such conditions can produce a good coated product.

[0072] The product obtained after removing the aqueous solvent from the mixed solution and drying can be referred to as a coated product. The coated product includes core particles and an aluminum-containing coating layer located on the surface of the core particles. For example, the coating layer can have a fibrous shape, such as a mesh or spider web shape. Such a mesh can be continuously formed over the entire surface of the core particles. The mesh-like coating layer can surround the core particles with a very thin and uniform thickness, thereby strengthening the surface of the positive electrode active material, improving structural stability, and improving high-temperature and high-voltage characteristics.

[0073] In one embodiment of the method for manufacturing a cathode active material, step (iv) involves dry-mixing the coating material and a cobalt raw material and heat-treating the mixture to obtain a cathode active material, where LiAlO2 is formed by coating the core particles with aluminum, and cobalt is diffused into the core particles through the dry coating and coated on the grain boundaries of the primary particles. This results in a surface modification, with the primary particle surfaces coated with cobalt and the secondary particle surfaces coated with aluminum, improving capacity and lifespan characteristics and reducing gas generation during high-temperature storage.

[0074] The cobalt source material may be, for example, cobalt hydroxide (Co(OH)2), cobalt oxide, or a combination thereof. A lithium source material may be additionally mixed during the dry mixing of the coating material and the cobalt source material. In this case, the lithium source material may be, for example, lithium hydroxide (LiOH).

[0075] The cobalt content in the cobalt raw material may be 0.1 mol% to 5.0 mol%, for example, 0.5 mol% to 4.0 mol%, 1.0 mol% to 3.0 mol%, or 2.0 mol% to 3.0 mol%, relative to the total of all metals (excluding lithium) in the core particle and the cobalt in the cobalt raw material (100 mol%). By designing the cobalt content within this range, cobalt can be diffused into the core particle and coated on the grain boundaries of the primary particles, thereby improving life characteristics under high voltage or high temperature operating conditions and initial charge / discharge efficiency.

[0076] In step (iv), the coating material and the cobalt raw material are dry-mixed together, and the zirconium coating can be performed by mixing the lithium raw material and the zirconium raw material together. The zirconium raw material may be zirconium oxide, for example.

[0077] The zirconium content in the zirconium raw material may be 0.01 mol% to 1.5 mol% based on 100 mol% of all metals excluding lithium in the positive electrode active material, and may be designed to be, for example, 0.05 mol% to 1.0 mol%, 0.1 mol% to 1.0 mol%, 0.1 mol% to 0.5 mol%, or 0.1 mol% to 0.4 mol%. By designing the zirconium coating content within this range, a coating layer with a uniform thickness of tens to hundreds of nanometers can be formed, thereby improving life characteristics under high voltage or high temperature operating conditions and initial charge / discharge efficiency.

[0078] If the first heat treatment refers to the heat treatment of the nickel-manganese composite hydroxide and the lithium raw material mixed together, then the second heat treatment refers to the heat treatment of the coated product. The second heat treatment can be understood as the process of forming a coating layer, and can be carried out, for example, in an oxygen atmosphere at temperatures ranging from 700°C to 850°C, 750°C to 840°C, or 800°C to 830°C for 2 to 20 hours or 3 to 10 hours. When the second heat treatment temperature is set within this range, aluminum tends to diffuse less into the interior of the secondary particles and remains primarily on the surface of the secondary particles, simultaneously forming a very thin, uniformly thick shell coating on the surface of the secondary particles.

[0079] positive electrode In one embodiment, a 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 materials described above. The positive electrode active material layer may also optionally include a binder, a conductive material, or a combination thereof.

[0080] According to one embodiment, the loading level of the positive electrode active material layer is 10 mg / cm 2 ~40mg / cm 2 may be, 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 loading level and positive electrode density in the above ranges is suitable for realizing a lithium secondary battery with a high capacity and a high energy density.

[0081] 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.

[0082] Conductive material The conductive material is used to impart conductivity to the electrode, and any electron-conductive material that 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.

[0083] 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.

[0084] The positive electrode current collector can be made of Al, but is not limited to this.

[0085] Lithium secondary battery In one embodiment, a lithium secondary battery is provided that includes the positive electrode, the negative electrode, and the electrolyte. 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.

[0086] Lithium secondary batteries can be classified into cylindrical, prismatic, pouch, and coin types depending on their shape. FIGS. 1 to 4 are schematic diagrams illustrating a lithium secondary battery according to an embodiment, with FIG. 1 illustrating a circular battery, FIG. 2 illustrating a prismatic battery, and FIGS. 3 and 4 illustrating pouch-type battery shapes. Referring to FIGS. 1 to 4, a lithium secondary battery 100 may include an electrode assembly 40 having a separator 30 interposed between a positive electrode 10 and a negative electrode 20, and a case 50 housing the electrode assembly 40. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with 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, as shown 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.

[0087] The lithium secondary battery according to one embodiment is suitable for being rechargeable at a high voltage or being driven at a high voltage, and can be said to be a battery with improved characteristics under high voltage conditions.

[0088] For example, the upper charging voltage limit may be 4.45 V or higher, such as 4.45 V to 4.6 V, 4.45 V to 4.55 V, or 4.45 V to 4.50 V. By using the positive electrode active material according to an embodiment, the lithium secondary battery can significantly reduce the amount of gas generation even when charged at a high voltage, and can achieve high capacity and long life characteristics.

[0089] 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.

[0090] negative electrode active material The negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and undoping with lithium, or a transition metal oxide.

[0091] Examples of the material capable of reversibly intercalating / deintercalating the lithium ions include carbon-based negative electrode active materials, which may include, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-shaped, flaky, spherical, or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0092] As the alloy of 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.

[0093] As the material capable of doping and undoping with lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used. The Si-based negative electrode active material may be silicon, a silicon-carbon composite, SiOx (0 < x ≤ 2), a Si-Q alloy (where Q is an element selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements (excluding Si), group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof, for example, Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof), or a combination thereof. The Sn-based negative electrode active material may be Sn, SnO2, a Sn alloy, or a combination thereof.

[0094] The silicon-carbon composite may be a composite of silicon and amorphous carbon. 50 ) may be, for example, 0.5 μm to 20 μm. According to one embodiment, the silicon-carbon composite may be in the form of silicon particles and the surfaces of the silicon particles coated with amorphous carbon. For example, it may include secondary particles (cores) formed by granulating primary silicon particles, and an amorphous carbon coating layer (shell) located on the surfaces of the secondary particles. The amorphous carbon may also be located between the primary silicon particles, for example, the primary silicon particles may be coated with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0095] The silicon-carbon composite may further include 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 core surface. The crystalline carbon may be artificial graphite, natural graphite, or a combination thereof. Examples of the amorphous carbon include soft carbon, hard carbon, mesophase pitch carbide, and calcined coke.

[0096] When the silicon-carbon composite contains silicon and amorphous carbon, the silicon content may be 10 wt% to 50 wt% and the amorphous carbon content may be 50 wt% to 90 wt% relative to 100 wt% of the silicon-carbon composite. When the composite contains silicon, amorphous carbon, and crystalline carbon, the silicon content may be 10 wt% to 50 wt%, the crystalline carbon content may be 10 wt% to 70 wt%, and the amorphous carbon content may be 20 wt% to 40 wt% relative to 100 wt% of the silicon-carbon composite.

[0097] The thickness of the amorphous carbon coating layer may be 5 nm to 100 nm. 50) may be 10 nm to 1 μm, or 10 nm to 200 nm. The silicon particles may exist as silicon alone, or in the form of a silicon alloy, or in an oxidized form. The oxidized form of silicon is SiO x (0 < x ≤ 2) can be expressed. 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 size (D 50 ) means the diameter of the particle with a cumulative volume of 50% by volume in the particle size distribution.

[0098] The Si-based negative electrode active material or the Sn-based negative electrode active material can be used by mixing with a carbon-based negative electrode active material. When the Si-based negative electrode active material or the Sn-based negative electrode active material and the carbon-based negative electrode active material are used in combination, the mixing ratio may be 1:99 to 90:10 by weight.

[0099] binder The binder plays a role of well adhering the negative electrode active material particles to each other and well adhering the negative electrode active material to the current collector. As the binder, a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof can be used.

[0100] Examples of the non-aqueous binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene-propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0101] 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.

[0102] 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.

[0103] The dry binder may be a fiberizable polymeric material such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0104] Conductive material The conductive material is used to impart conductivity to the electrode, and any electron-conductive material that does not cause chemical changes in the battery that is constructed can be used. 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.

[0105] The content of the negative electrode active material may be 95 wt% to 99.5 wt% relative to 100 wt% of the negative electrode active material layer, and the content of the binder may be 0.5 wt% to 5 wt% relative to 100 wt% of the negative electrode active material layer. For example, the negative electrode active material layer may contain 90 wt% to 99 wt% of the negative electrode active material, 0.5 wt% to 5 wt% of the binder, and 0.5 wt% to 5 wt% of the conductive material.

[0106] current collector The negative electrode current collector may contain, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or an alloy thereof, and may be in the form of a foil, sheet, or foam. The thickness of the negative electrode current collector may be, for example, 1 μm to 20 μm, 5 μm to 15 μm, or 7 μm to 10 μm.

[0107] electrolyte The electrolyte for a lithium secondary battery may be, for example, an electrolytic solution, which may include a non-aqueous organic solvent and a lithium salt.

[0108] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can migrate, and may be a carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based solvent, an aprotic solvent, or a combination thereof.

[0109] 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.

[0110] The non-aqueous organic solvents can be used alone or in combination of two or more kinds. When two or more kinds are used in combination, the mixing ratio can be appropriately adjusted depending on the desired battery performance, which should be widely understood by those working in the field.

[0111] 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.

[0112] 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.

[0113] The electrolyte may further contain vinyl ethyl carbonate, vinylene carbonate, or ethylene carbonate based compounds to improve battery life.

[0114] 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.

[0115] Lithium salts are substances dissolved in organic solvents and act as a source of lithium ions in the battery, enabling basic lithium secondary battery operation and facilitating the movement of lithium ions between the positive and negative electrodes. Representative examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide; LiFSI), LiC4F9SO3, and LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (x and y are integers of 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFBOP), and lithium bis(oxalato)borate (LiBOB).

[0116] 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 ionic conductivity and viscosity, thereby exhibiting excellent performance and allowing lithium ions to migrate effectively.

[0117] Separator Depending on the type of lithium secondary battery, a separator may be present between the positive and negative electrodes. Such separators can be made of polyethylene, polypropylene, polyvinylidene fluoride, or multilayer films of two or more of these materials. 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 can also be used.

[0118] 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.

[0119] The porous substrate may be a polymer membrane formed from 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.

[0120] 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.

[0121] The organic material may include a (meth)acrylic copolymer including a first structural unit derived from (meth)acrylamide and a second structural unit including at least one of a structural unit derived from (meth)acrylic acid or a (meth)acrylate and a structural unit derived from (meth)acrylamidosulfonic acid or a salt thereof.

[0122] 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 ) may be 1 nm to 2000 nm, for example, 100 nm to 1000 nm, or 100 nm to 700 nm.

[0123] 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.

[0124] 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.

[0125] 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. [Example]

[0126] Example 1 1. Production of positive electrode active material Ni 0.75 Mn 0.23 Al 0.02 (OH)2 and LiOH were mixed in a molar ratio of 1:1.05 and subjected to a first heat treatment at 845°C for 8 hours in an oxygen atmosphere to obtain a composition of Li 1.05 Ni0.75 Mn 0.23 Al 0.02 O2 and the average particle size (D 50 ) was about 14 μm in size.

[0127] Aluminum sulfate was added to a distilled water solvent and stirred at 350 rpm for 5 minutes to prepare a coating solution. The salt was confirmed to be completely dissolved in the coating solution, making it colorless and transparent. 500 g of the prepared lithium nickel-manganese composite oxide was added to the continuously stirred coating solution for 1.5 minutes and stirred for approximately 25 minutes. The aluminum content in the aluminum sulfate was designed to be 1.0 mol% relative to 100 wt% of the total metals excluding lithium in the positive electrode active material. After stirring was completed, the pH of the supernatant was confirmed to be 5.5. The solvent was removed from the mixed solution using an aspirator and filter press, and the solution was dried in vacuum at 190°C to obtain a coated product.

[0128] The coated product was mixed with cobalt hydroxide (Co(OH)2) and LiOH and subjected to a second heat treatment in an oxygen atmosphere at 825°C for 8 hours to prepare a cathode active material. The cobalt content in the cobalt hydroxide was designed to be 2.0 mol% relative to 100 mol% of the total metals excluding lithium in the cathode active material.

[0129] 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.

[0130] A half-cell was fabricated using the cathode, lithium metal counter electrode, and electrolyte in a conventional manner, using a polytetrafluoroethylene separator and an electrolyte solution of 1M LiPF6 dissolved in a solvent containing ethylene carbonate and dimethyl carbonate in a volume ratio of 3:7.

[0131] Example 2 In preparing the positive electrode active material, zirconium oxide was designed so that the zirconium content in the zirconium oxide was 0.2 mol % relative to 100 mol % of the total metals excluding lithium in the positive electrode active material. The zirconium oxide was mixed with the coating material, cobalt hydroxide (Co(OH)2), and LiOH, and the cobalt content in the cobalt hydroxide was designed so that the cobalt content was 1.0 mol % relative to 100 mol % of the total metals excluding lithium in the positive electrode active material. A positive electrode active material and a lithium secondary battery were prepared in substantially the same manner as in Example 1, except that the zirconium oxide was mixed with the coating material, cobalt hydroxide (Co(OH)2), and LiOH, and the cobalt content in the cobalt hydroxide was 1.0 mol % relative to 100 mol % of the total metals excluding lithium in the positive electrode active material.

[0132] Example 3 A cathode active material and a lithium secondary battery were manufactured in substantially the same manner as in Example 2, except that the cobalt content in the cobalt hydroxide was designed to be 2.0 mol % relative to 100 mol % of the total metals excluding lithium in the cathode active material.

[0133] Example 4 A cathode active material and a lithium secondary battery were manufactured in substantially the same manner as in Example 2, except that the cobalt content in the cobalt hydroxide was designed to be 3.0 mol % relative to 100 mol % of the total metals excluding lithium in the cathode active material.

[0134] 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 in the preparation of the positive electrode active material, cobalt hydroxide (Co(OH)2) and LiOH were not added, and the prepared coated product alone was subjected to the second heat treatment.

[0135] Comparative 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, cobalt hydroxide (Co(OH)2) and LiOH were not added, and the prepared coated product was subjected to a second heat treatment alone, and instead of wet coating using distilled water solvent and aluminum sulfate, aluminum oxide was added to the lithium nickel-manganese composite oxide, and then the resultant was subjected to dry coating, in which heat treatment was performed at 600°C for 5 hours, to coat aluminum.

[0136] Comparative Example 3 In the production of positive electrode active materials, Ni 0.75 Mn 0.25 (OH)2 with the composition Li 1.05 Ni 0.75 Mn 0.25 A positive electrode active material and a lithium secondary battery were fabricated in substantially the same manner as in Comparative Example 2, except that a lithium nickel-manganese composite oxide (O2) was prepared and used, and aluminum was additionally doped to adjust the aluminum content to 2.0 mol% relative to 100 mol% of the total metals excluding lithium in the positive electrode active material.

[0137] Comparative Example 4 A positive electrode active material and a lithium secondary battery were manufactured in substantially the same manner as in Comparative Example 3, except that the aluminum coating was not performed in the preparation of the positive electrode active material.

[0138] Comparative Example 5 A positive electrode active material and a lithium secondary battery were manufactured in substantially the same manner as in Comparative Example 4, except that aluminum was not additionally doped in the preparation of the positive electrode active material.

[0139] The manufacturing methods of Examples 1 to 4 and Comparative Examples 1 to 5 are summarized in Table 1 below.

[0140] [Table 1]

[0141] Evaluation example 1: Cross-sectional observation of positive electrode active material The state of the aluminum and cobalt coating was confirmed through SEM-EDS mapping of a cross section of the cathode active material prepared in Example 1 cut with a focused ion beam (FIB). Figures 5 and 6 are SEM-EDS images showing aluminum on a cross section of the cathode active material prepared in Example 1. Referring to Figures 5 and 6, it can be seen that an aluminum coating layer with a thickness of approximately 40 nm or less is formed as a uniform film on the surface of the cathode active material, and that some aluminum is also coated on the grain boundaries, which are the boundaries between primary particles inside the secondary particles.

[0142] Additionally, Figure 7 shows an SEM-EDS analysis image of cobalt element mapping on a cross section of the positive electrode active material of Example 1. Referring to Figure 7, it can be seen that cobalt was not formed as a coating layer on the surface of the positive electrode active material, but rather diffused into the interior of the secondary particles and coated on the grain boundaries, which are the boundaries of the primary particles.

[0143] Evaluation example 2: Initial charge / discharge capacity and efficiency evaluation The lithium secondary batteries manufactured in Examples 1 to 4 and Comparative Examples 1 to 5 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, and at a constant voltage of 0.05 C, and then discharged at 0.2 C to an end voltage of 3.0 V. Table 2 below shows the initial charge capacity and initial discharge capacity, as well as the ratio of the latter to the former, calculated as efficiency.

[0144] Evaluation example 3: Life characteristics Following the initial charge and discharge in Evaluation Example 2, the cycle of charging at 1.0 C and discharging at 1.0 C in the voltage range of 3.0 V to 4.45 V at 45°C was repeated 50 times or more, and the ratio of the 50th cycle discharge capacity to the initial discharge capacity was calculated and shown in Table 2 below.

[0145] Evaluation example 4: Evaluation of gas generation rate when stored at 80℃ The lithium secondary batteries manufactured in Examples 1 to 4 and Comparative Examples 1 to 5 were fabricated into 4.4 V class 30 mAh cells and left at 80°C for 30 days. The gas generation amount (ml) on the 30th day was measured using a refinery gas analyzer (RGA) and is shown in Table 2 below.

[0146] [Table 2]

[0147] Referring to Table 1, it can be seen that in Examples 1 to 4, in which cobalt dry coating was performed after aluminum wet coating, the initial efficiency and lifespan characteristics were improved and the amount of gas generated during high-temperature storage was reduced compared to Comparative Examples 1 to 5, in which aluminum wet coating and / or cobalt dry coating was not performed. In particular, it can be seen from Examples 3 and 4 that when the cobalt content was 2 to 3 mol%, the most excellent effects were observed in terms of lifespan characteristics and amount of gas generated during high-temperature storage.

[0148] Additionally, it can be seen that Comparative Examples 2 and 3, which were coated with aluminum through dry coating, exhibited inferior effects in terms of lifespan characteristics and gas generation rate when stored at high temperatures compared to Comparative Example 1, which was coated with aluminum through wet coating. It can also be seen that Comparative Examples 4 and 5, which were not coated with aluminum, exhibited inferior effects in terms of lifespan characteristics and gas generation rate when stored at high temperatures compared to Comparative Examples 1 to 3, which were coated with aluminum.

[0149] 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 following claims also fall within the scope of the present invention. [Explanation of symbols]

[0150] 100: Lithium secondary battery 10: Positive electrode 11: Positive lead tap 12: Positive terminal 20: Negative electrode 21: Negative lead tap 22: Negative terminal 30: Separator 40: Electrode assembly 50: Case 60: Sealing material 70: Electrode tap 71: Positive tap 72: Negative tap

Claims

1. core particles containing a layered lithium nickel-manganese composite oxide and having a secondary particle form in which a plurality of primary particles are aggregated; an aluminum coating layer located on the surface of the core particle; and a grain boundary coating portion located on the surface of the primary particle and containing cobalt; A positive electrode active material comprising:

2. 2. The positive electrode active material according to claim 1, wherein the layered lithium nickel-manganese composite oxide has a nickel content of 60 mol% to 80 mol% and a manganese content of 15 mol% or more relative to 100 mol% of all metals excluding lithium.

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

4. 4. The positive electrode active material according to claim 3, wherein the aluminum concentration is uniform within the layered lithium nickel-manganese composite oxide.

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

6. The layered lithium nickel-manganese composite oxide is represented by Chemical Formula 1, and is the positive electrode active material according to claim 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≦0.4, 0≦z1≦0.03, 0≦w1≦0.3, 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, Y, Zr, and Zn, and X is one or more elements selected from F, P, and S.

7. 2. The positive electrode active material of claim 1, wherein the aluminum content of the aluminum coating layer is 0.1 mol % to 3.0 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 1 , further comprising a zirconium coating layer on the aluminum coating layer.

9. 9. The positive electrode active material of claim 8, wherein the zirconium content of the zirconium coating layer is 0.1 mol % to 1.5 mol % relative to 100 mol % of all metals excluding lithium in the positive electrode active material.

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

11. The cathode active material of claim 1, wherein the aluminum coating layer has a thickness of 10 nm to 500 nm.

12. 2. The positive electrode active material of claim 1, wherein the cobalt content of the grain boundary coating portion is 0.1 mol % to 5.0 mol % relative to 100 mol % of all metals excluding lithium in the entire positive electrode active material.

13. 2. The cathode active material of claim 1, wherein the content of cobalt on the surface of the core particle is 0 mol % to 0.01 mol % relative to 100 mol % of all metals excluding lithium in the entire cathode active material.

14. The average particle size (D 50 2. The positive electrode active material according to claim 1, wherein the particle size is 10 μm to 25 μm.

15. (i) preparing core particles, which include a layered lithium nickel-manganese composite oxide and are in the form of secondary particles formed by agglomeration of a plurality of primary particles; (ii) preparing an aluminum coating solution containing an aqueous solvent and an aluminum source; (iii) adding the core particles to the aluminum coating solution, mixing them, and then drying them to prepare a coated product; and (iv) dry-mixing the coated product with a cobalt raw material and heat-treating the mixture to obtain a positive electrode active material; A method for producing a positive electrode active material comprising the steps of:

16. 16. The method for producing a cathode active material according to claim 15, wherein the aluminum content of the aluminum raw material is 0.1 mol% to 3.0 mol% and the cobalt content of the cobalt raw material is 0.1 mol% to 5.0 mol% relative to 100 mol% of all metals excluding lithium in the cathode active material.

17. 16. The method of claim 15, wherein in step (iv), the heat treatment is performed at a temperature in the range of 700°C to 850°C.

18. The method of claim 15, wherein in step (iv), when the coating material and the cobalt raw material are dry-mixed, the lithium raw material and the zirconium raw material are mixed together.

19. 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 14.

20. The positive electrode according to claim 19 . a negative electrode, and electrolyte A lithium secondary battery comprising:

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