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

Abstract

To provide a positive electrode active material including a lithium nickel-manganese complex oxide, in which the characteristics of high capacity and high energy density are secured while reducing the price of a positive electrode material, the side reaction with an electrolyte at high voltage is suppressed, and the high-voltage performance is improved, a positive electrode including this positive electrode active material, and a lithium secondary battery.SOLUTION: A positive electrode active material includes: a first positive electrode active material containing a lithium nickel-manganese complex oxide in which the content of nickel is 60 mol% or more relative to 100 mol% of the entire metals excluding lithium and in a mode of a secondary particle formed by aggregation of a plurality of primary particles, the average particle diameter (D50) of the secondary particle is 10 μm to 20 μm; a second positive electrode active material containing a lithium nickel-manganese complex oxide in which the content of nickel is 60 mol% or more relative to 100 mol% of the entire metals excluding lithium and in a monoparticulate mode, the average particle diameter (D50) of the monoparticle is 2 μm to 8 μm; and a third positive electrode active material in a particulate form containing a lithium transition metal phosphorus oxide.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 and 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 extremely short. In other words, because cobalt is expensive and its remaining reserves are limited, there is a need to develop positive electrode active materials that exclude 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 containing a lithium nickel-manganese composite oxide, which ensures high capacity and high energy density characteristics while drastically reducing the price of the positive electrode material, and has improved high voltage performance due to suppression of side reactions with electrolytes at high voltages. The present invention also provides a positive electrode and a lithium secondary battery containing the same. [Means for solving the problem]

[0005] In one embodiment, the present invention comprises a lithium nickel-manganese composite oxide in which the nickel content is 60 mol % or more relative to 100 mol % of all metals excluding lithium, and the secondary particles are formed by agglomeration of a plurality of primary particles, and the average particle size (D 50 ) of 10 μm to 20 μm, and a lithium nickel-manganese composite oxide in which the nickel content is 60 mol % or more relative to 100 mol % of all metals excluding lithium, and the single particles are in the form of single particles. 50 and a third positive electrode active material in the form of particles containing a lithium transition metal phosphate.

[0006] In another embodiment, a positive electrode is provided, comprising 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 comprising the positive electrode active material described above.

[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 cathode active material according to one embodiment maximizes capacity while minimizing production costs, ensures long-life characteristics, and suppresses side reactions with the electrolyte at high voltages. A lithium secondary battery using the cathode active material can exhibit high initial charge / discharge capacity and efficiency even under high-voltage driving conditions, and achieve long-life characteristics. [Brief explanation of the drawings]

[0009] [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 a first positive electrode active material of Example 1. [Figure 3] 1 is an SEM image of a second positive electrode active material of Example 1. [Figure 4] 1 is an SEM image of a third positive electrode active material of Example 1. [Figure 5] 10 is an SEM image of the third positive electrode active material of Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0010] Although the present invention may be embodied in many different forms, it is not intended to be 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," "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, thicknesses are exaggerated to clearly show multiple layers and regions, and similar parts are designated by the same reference numerals throughout the specification. When a part such as a layer, film, region, or plate is said to be "on" another part, this includes not only the case where it is "directly on" the other part, but also the case where there is another part between them. Conversely, when a part is said to be "directly on" the other part, it means that there is no other part between them.

[0015] Here, the term "layer" 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.

[0016] The average particle size can be measured by methods 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, it can be measured using dynamic light scattering, and data analysis can be performed to count the number of particles in each particle size range, and then the average particle size can be calculated based on this. 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 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 to obtain a particle size distribution, and then calculating the diameter (D 50 ) can be taken as the average particle size.

[0017] Here, "or" is not to be construed as exclusive; 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 (semimetals).

[0019] positive electrode active material In one embodiment, the present invention comprises a lithium nickel-manganese composite oxide in which the nickel content is 60 mol % or more relative to 100 mol % of all metals excluding lithium, and the secondary particles are formed by agglomeration of a plurality of primary particles, and the average particle size (D 50 ) of 10 μm to 20 μm, and a lithium nickel-manganese composite oxide in which the nickel content is 60 mol % or more relative to 100 mol % of all metals excluding lithium, and the single particles are in the form of single particles. 50and a third positive electrode active material in the form of particles containing a lithium transition metal phosphate.

[0020] The recent surge in the price of the rare metal cobalt has led to demand for the development of cathode active materials that exclude cobalt or contain reduced amounts. Among these, cathode active materials with a spinel crystal structure, such as lithium manganese oxide (LMO), have limitations in achieving high capacity due to the limited amount of lithium that can be utilized within the structure. Layered nickel-manganese cathode active materials can increase the amount of lithium within the structure, making them suitable for high-capacity batteries with excellent capacity and efficiency characteristics. However, the removal of cobalt, which plays a key role in the layered structure, reduces structural stability, increases resistance, and makes it difficult to ensure long life. Furthermore, the exclusion of cobalt accelerates side reactions between the cathode active material and the electrolyte under high voltage and high temperature conditions, increasing gas generation and reducing life.

[0021] In one embodiment, a first positive electrode active material containing a lithium nickel-manganese composite oxide and in the form of secondary particles of 10 μm to 20 μm in size is mixed with a second positive electrode active material in the form of single particles of 2 μm to 8 μm in size, and then a third positive electrode active material containing a lithium transition metal phosphate, which is a low-cost material, is mixed with this to propose a positive electrode active material that achieves high capacity and high energy density, long life characteristics, and improved high-voltage performance.

[0022] The average particle size (D 50 ) is the average particle size (D 50 ) or larger. In this case, the first positive electrode active material can be expressed as large grains or large particles, and the second positive electrode active material can be expressed as small grains or small particles. The average particle size (D 50 ) is the average particle size (D 50) or larger. By appropriately mixing large secondary particle-type particles and small single particle-type particles as the lithium nickel-manganese oxide and additionally mixing lithium transition metal phosphate, it is possible to maximize the capacity and energy density and improve the high voltage characteristics.

[0023] Here, the average particle size is determined by measuring the size (diameter or length of the major axis) of 20 or so particles randomly in a scanning electron microscope image of the positive electrode active material to obtain a particle size distribution, and then determining the diameter (D 50 ) can be taken as the average particle size.

[0024] The average particle size (D 50 The average particle size (D ) of the single particles of the second positive electrode active material may be, for example, 10 μm to 18 μm, or 12 μm to 16 μm. 50 The particles of the third positive electrode active material may be a type of primary particle, and their average particle size (D 50 ) may be, for example, 10 nm to 2 μm, e.g., 50 nm to 1.5 μm, 100 nm to 1.0 μm, 100 nm to 900 nm, or 100 nm to 600 nm. When the average particle size of each positive electrode active material satisfies the above range, high capacity can be achieved and energy density can be maximized.

[0025] The first positive electrode active material may be included in an amount of 60% to 90% by weight, the second positive electrode active material may be included in an amount of 5% to 35% by weight, and the third positive electrode active material may be included in an amount of 5% to 35% by weight, based on a total of 100% by weight of the first, second, and third positive electrode active materials. Specifically, the first positive electrode active material may be included in an amount of 60% to 85% by weight, the second positive electrode active material may be included in an amount of 10% to 25% by weight, and the third positive electrode active material may be included in an amount of 5% to 20% by weight. When the mixing ratio of each positive electrode active material satisfies the above range, the energy density can be further increased while increasing the capacity.

[0026] The lithium nickel-manganese composite oxide of the first positive electrode active material and the lithium nickel-manganese composite oxide of the second positive electrode active material may be the same or different. The nickel content in each lithium nickel-manganese composite oxide is 60 mol% or more relative to 100 mol% of all metals excluding lithium in the lithium nickel-manganese composite oxide, and may be, for example, 60 mol% to 80 mol%, 65 mol% to 80 mol%, 70 mol% to 80 mol%, 60 mol% to 79 mol%, 60 mol% to 78 mol%, or 60 mol% to 75 mol%, etc. When the nickel content satisfies this range, high capacity can be achieved and structural safety can be improved even when the cobalt content is reduced.

[0027] The manganese content may be, for example, 10 mol % to 40 mol % relative to 100 mol % of all metals excluding lithium in the lithium nickel-manganese composite oxide, such as 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 %, 20 mol % to 30 mol %, etc. When the manganese content satisfies this range, the positive electrode active material can achieve high capacity while improving structural stability.

[0028] The lithium nickel-manganese composite oxide in each of the first and second positive electrode active materials 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 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 mol% to 1.9 mol%. When the aluminum content is within this range, a stable layered structure can be maintained even when cobalt is excluded, preventing the problem of structural collapse during charge and discharge, and achieving long-life characteristics for the positive electrode active material.

[0029] The lithium nickel-manganese composite oxide of the first positive electrode active material and the lithium nickel-manganese composite oxide of the second positive electrode active material can each be independently represented by Chemical Formula 1 below.

[0030] [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; 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, Y, and Zr, and X is one or more elements selected from F, P, and S.

[0031] In Chemical Formula 1, 0.9 ≤ a1 ≤ 1.5 or 0.9 ≤ a1 ≤ 1.2 may hold. Also, 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.

[0032] In 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 hold; 0.1 ≤ y1 ≤ 0.35, 0.1 ≤ y1 ≤ 0.30, 0.1 ≤ y1 ≤ 0.29, 0.15 ≤ y1 ≤ 0.39, or 0.2 ≤ y ≤ 0.3 may hold; 0.01 ≤ z1 ≤ 0.025, 0.01 < z ≤ ≤ 0.02, or 0.01 < ≤ z1 ≤ 0.019 may hold; 0 ≤ w1 ≤ 0.28, 0 ≤ w1 ≤ 0.27, 0 ≤ w1 ≤ 0.26, 0 ≤ ≤ w1 ≤ 0.25, 0 ≤ w ≤ 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 hold.

[0033] The lithium nickel - manganese composite oxide may be a cobalt - free compound that does not contain cobalt or contains a very small amount of cobalt. That is, the lithium nickel - manganese composite oxide of the first positive electrode active material and the lithium nickel - manganese composite oxide of the second positive electrode active material may each independently have a cobalt content of 0 mol% to 0.01 mol% based on 100 mol% of the total metal excluding lithium.

[0034] First positive electrode active material According to one embodiment, the aluminum concentration may be uniform within the secondary particles of the first positive electrode active material, excluding the coating layer. This means that there is an aluminum concentration gradient from the center to the surface within the particle, or that the aluminum concentration is neither higher nor lower at the outside than at the inside of the particle, and that the aluminum is uniformly dispersed within the particle. This can be said to be a structure obtained by synthesizing a composite oxide using a nickel-manganese-aluminum hydroxide as a precursor by using an aluminum raw material in the preparation of a precursor without additional aluminum doping during the synthesis of the positive electrode active material. In other words, the aluminum content within the primary particles can be said to be the same or similar regardless of the position of the primary particles. If a primary particle is selected at 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 this structure, a stable layered structure can be maintained even when cobalt is absent or present in a very small amount, and aluminum by-products and aluminum aggregates are not generated, so the capacity, efficiency, and life characteristics of the positive electrode active material can be improved simultaneously.

[0035] According to an embodiment, the first positive electrode active material may further include a coating layer containing aluminum and zirconium located on the surface of the secondary particles. By including the aluminum-zirconium-rich layer on the surface of the first positive electrode active material, side reactions with the electrolyte at high voltages may be effectively suppressed, thereby improving capacity and life characteristics at high voltages.

[0036] The aluminum content of the coating layer may be 0.1 mol% to 2 mol%, and the zirconium content of the coating layer may be 0.05 mol% to 1 mol%, relative to 100 mol% of the total metals excluding lithium in the first positive electrode active material. The aluminum content of the coating layer of the first positive electrode active material 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%. The aluminum and zirconium contents in the coating layer may 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 thin and uniform coating layer can be formed, and side reactions with the electrolyte can be effectively suppressed without increasing the resistance of the positive electrode active material, thereby improving the life characteristics of lithium secondary batteries at high voltages.

[0037] The zirconium content of the coating layer of the first positive electrode active material may be, for example, 0.1 mol% to 1 mol%, 0.1 mol% to 0.9 mol%, 0.1 mol% to 0.8 mol%, or 0.1 mol% to 0.6 mol%. When the zirconium content is within this range, the positive electrode active material forms a good coating layer without decreasing capacity or increasing resistance, effectively suppressing side reactions with the electrolyte, and further improving capacity characteristics and life characteristics under high voltage driving conditions.

[0038] The coating layer of the first positive electrode active material may further contain yttrium in addition to aluminum and zirconium. In this case, the content of yttrium may be 0.1 mol % to 1 mol % relative to 100 mol % of the total metals excluding lithium of the first positive electrode active material.

[0039] The coating layer of the first positive electrode active material may be in the form of a film that continuously surrounds the surfaces of the secondary particles, for example, in the form of a shell that surrounds the entire surfaces of the secondary particles. This is distinct from a structure in which only a portion of the surfaces of the secondary particles is partially coated. According to one embodiment, the coating layer may be formed to completely surround the surfaces of the secondary particles, but with a very thin and uniform thickness. As a result, the positive electrode active material may exhibit improved structural stability without increasing resistance or decreasing capacity, effectively suppress side reactions with the electrolyte, reduce gas generation under high voltage and high temperature conditions, and achieve long-life characteristics.

[0040] The thickness of the coating layer of the first positive electrode active material may be 30 nm to 500 nm, for example, 30 nm to 450 nm, 30 nm to 400 nm, 30 nm to 350 nm, 30 nm to 300 nm, 30 nm to 250 nm, 30 nm to 200 nm, 30 nm to 150 nm, 50 nm to 500 nm, 80 nm to 500 nm, or 100 nm to 500 nm. When the coating layer satisfies this 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 may be measured, for example, by TOF-SIMS, XPS, or EDS analysis, and the thickness range of the coating layer may be measured by TEM-EDS line profile analysis.

[0041] The coating layer of the first positive electrode active material is characterized by its thin yet uniform thickness, ranging from several tens to several hundreds of nanometers. For example, the thickness deviation of the coating layer within a single positive electrode 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 positive electrode active material particle. For example, the coating thickness deviation may be calculated by measuring the thickness at approximately 10 points in an electron microscope image of the cross section of a single positive electrode active material particle, calculating the arithmetic average, and then dividing the absolute value of the difference between one data point and the arithmetic average by the arithmetic average and multiplying the result by 100. A coating thickness deviation or standard deviation within the above range indicates that a uniformly thick coating layer is well formed in the form of a film on the surface of the positive electrode active material particle. This improves the structural stability of the positive electrode active material, effectively suppresses side reactions with the electrolyte, and minimizes resistance increases and capacity reductions due to the coating.

[0042] Meanwhile, aluminum may diffuse into the secondary particles during the formation of the coating layer. Therefore, according to an embodiment, the positive electrode active material may further include a grain boundary coating region containing aluminum located on the surface of the primary particle within the secondary particle. 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, extending up to approximately 60% of the radius. The grain boundary coating region is a concept distinct from the coating layer on the surface of the secondary particle, and refers to a coating region formed on the surface of the primary particle located within the secondary particle. 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 may further stabilize the structure of the positive electrode active material, thereby improving its lifespan.

[0043] 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.

[0044] Meanwhile, the aluminum content of the coating layer of the first positive electrode active material may be higher than the aluminum content of the coating layer of the second positive electrode active material (described later). For example, the aluminum content of the coating layer of the first positive electrode active material and the aluminum content of the coating layer of the second positive electrode active material may be 5:1 to 2:1, or 4:1 to 2:1, in molar ratio. In this case, the aluminum in the coating layers of the first and second positive electrode active materials does not act as a resistor, improving the structural stability of each material and maximizing the capacity and life characteristics at high voltage.

[0045] Second positive electrode active material A single particle of the second positive electrode active material means that the particle exists independently without a grain boundary and is made up of a single particle. It may refer to a single particle, a monolith structure, a single body structure, or a non-aggregated particle in which the particles are morphologically present in an independent phase and do not aggregate with each other, for example, a single crystal.

[0046] The second positive electrode active material may further include an aluminum-containing coating layer located on the surface of the single particle, which may improve initial discharge capacity and life characteristics at high voltage.

[0047] The aluminum content in the coating layer of the second positive electrode active material may be 0.1 mol% to 2 mol%, for example, 0.2 mol% to 1.9 mol%, 0.3 mol% to 1.8 mol%, 0.5 mol% to 1.5 mol%, or 0.8 mol% to 1.3 mol%, based on 100 mol% of the total metals (excluding lithium) in the second positive electrode active material. This refers to the aluminum content in the coating layer, separate from the aluminum contained within the individual particles. The aluminum content in the coating layer can be measured, for example, by SEM-EDS analysis of the surface or cross-section of the positive electrode active material. When the aluminum content in the coating layer satisfies this range, a thin and uniform coating layer can be formed, and side reactions with the electrolyte can be effectively suppressed without increasing the resistance of the positive electrode active material, thereby improving the life characteristics of lithium secondary batteries under high-voltage and high-temperature conditions. 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.

[0048] The coating layer of the second positive electrode active material may further include yttrium, which may more effectively suppress side reactions between the positive electrode active material and the electrolyte at high voltages, thereby improving life characteristics. The yttrium content in the coating layer may be 0.1 mol% to 1 mol% relative to 100 mol% of the total metals (excluding lithium) in the second positive electrode active material, e.g., 0.1 mol% to 0.9 mol%, 0.1 mol% to 0.8 mol%, 0.1 mol% to 0.6 mol%, 0.1 mol% to 0.4 mol%, or 0.1 mol% to 0.3 mol%. When the yttrium content satisfies this range, the positive electrode active material forms a good coating layer without a decrease in capacity or an increase in resistance, effectively suppressing side reactions with the electrolyte and effectively reducing gas generation under high voltage and high temperature conditions.

[0049] The coating layer of the second positive electrode active material may be in the form of a film that continuously surrounds the surface of the single particle, for example, in the form of a shell that surrounds the entire surface of the single particle. This is distinct from a structure in which only a portion of the particle surface is partially coated. According to one embodiment, the coating layer may be formed to completely surround the surface of the single particle, but with a very thin and uniform thickness. As a result, the positive electrode active material may have improved structural stability without increasing resistance or decreasing capacity, and side reactions with the electrolyte may be effectively suppressed, thereby achieving long-life characteristics at high voltages.

[0050] The thickness of the coating layer of the second positive electrode active material may be 30 nm to 500 nm, for example, 30 nm to 450 nm, 30 nm to 400 nm, 30 nm to 350 nm, 30 nm to 300 nm, 30 nm to 250 nm, 30 nm to 200 nm, 30 nm to 150 nm, 50 nm to 500 nm, 80 nm to 500 nm, or 100 nm to 500 nm. When the coating layer satisfies this 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 may be measured, for example, by TOF-SIMS, XPS, or EDS analysis, and the thickness range of the coating layer may be measured by TEM-EDS line profile analysis.

[0051] The coating layer of the second positive electrode active material is characterized by its thin yet uniform thickness, ranging from several tens to several hundreds of nanometers. For example, the thickness deviation of the coating layer within a single positive electrode 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 positive electrode active material particle. For example, the coating thickness deviation may be calculated by measuring the thickness at approximately 10 points in an electron microscope image of the cross section of a single positive electrode active material particle, calculating the arithmetic average, and then dividing the absolute value of the difference between one data point and the arithmetic average by the arithmetic average and multiplying the result by 100. A coating thickness deviation or standard deviation within the above range indicates that a uniformly thick coating layer is well formed in the form of a film on the surface of the positive electrode active material particle. This improves the structural stability of the positive electrode active material, effectively suppresses side reactions with the electrolyte, and minimizes resistance increases and capacity reductions due to the coating.

[0052] In the coating layer of the second positive electrode active material, aluminum may exist in the form of a continuous film, and yttrium may exist in the form of islands, depending on the characteristics of each element.

[0053] In one embodiment, aluminum and yttrium may be mixed in one coating layer, and in this case, aluminum may be present in the form of a continuous film, and yttrium may be present in the form of islands, but the forms are not limited thereto.

[0054] In another embodiment, aluminum and yttrium may form separate layers. For example, the second positive electrode active material may include a first coating layer containing aluminum located on the surface of the single particle, and a second coating layer containing yttrium located on the first coating layer. Aluminum may first adhere to or be absorbed onto the surface of the single particle to form a thin first coating layer, and then yttrium may be coated on top of that to form the second coating layer. While aluminum and yttrium may be mixed in the first and second coating layers, the first coating layer may be an aluminum-rich coating layer primarily composed of aluminum, and the second coating layer may be an yttrium-rich coating layer primarily composed of yttrium. In this case, yttrium may exist in the second coating layer in the form of islands, but this is not particularly limited.

[0055] The thicknesses of the first coating layer and the second coating layer are not particularly limited, but the thickness of the first coating layer may be 10 nm to 200 nm, for example, 20 nm to 200 nm, 30 nm to 200 nm, or 30 nm to 180 nm. The thickness of the second coating layer may be 20 nm to 300 nm, for example, 20 nm to 250 nm, 20 nm to 200 nm, 30 nm to 300 nm, or 50 nm to 300 nm. When each thickness falls within the above 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, thereby improving life characteristics at high voltages.

[0056] Third positive electrode active material The lithium transition metal phosphate of the third positive electrode active material can include, for example, lithium iron phosphate, lithium manganese iron phosphate, lithium manganese phosphate, lithium titanium phosphate, or a combination thereof.

[0057] The lithium transition metal phosphate of the third positive electrode active material can be specifically represented by Chemical Formula 3, Chemical Formula 4, Chemical Formula 5, Chemical Formula 6, or Chemical Formula 7.

[0058] [Chemical Formula 3] Li a3 Fe (1-x3) M 3 x3 PO4 In Chemical Formula 3, 0.90 ≤ a3 ≤ 1.5, 0 ≤ x3 ≤ 0.4, and M 3 is Al, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Sn, Sr, V, W, Y, Zn, Zr, or a combination thereof.

[0059] The compound represented by Chemical Formula 3 is lithium iron phosphate. In Chemical Formula 3, for example, 0.90 ≤ a3 ≤ 1.2, or 0.95 ≤ a3 ≤ 1.1, and 0 ≤ x3 ≤ 0.3, 0 ≤ x3 ≤ 0.2, 0 ≤ x3 ≤ 0.1, or 0 < x3 ≤ 0.05. For example, when a3 = 1 and x3 = 0, Chemical Formula 3 can be represented as LiFePO4.

[0060] [Chemical Formula 4] Li a4 Mn x4 Fe (1-x4-y4) M 4 y4 PO4 In Chemical Formula 4, 0.90 ≤ a4 ≤ 1.5, 0.1 ≤ x4 ≤ 0.9, 0.1 ≤ y4 ≤ 0.9, and M 4 is Al, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Sn, Sr, V, W, Y, Zn, Zr, or a combination thereof.

[0061] The compound represented by Chemical Formula 4 is lithium manganese iron phosphate. In Chemical Formula 4, for example, 0.90 ≤ a4 ≤ 1.2, or 0.95 ≤ a4 ≤ 1.1, and 0.2 ≤ x4 ≤ 0.8, 0.3 ≤ x4 ≤ 0.7, or 0.4 ≤ x4 ≤ 0.6. The compound represented by Chemical Formula 4 is, for example, LiMn 0.9 Fe 0.1 PO4, LiMn 0.8 Fe 0.2PO4, LiMn 0.7 Fe 0.3 PO4, LiMn 0.6 Fe 0.4 PO4, LiMn 0.5 Fe 0.5 PO4, LiMn 0.4 Fe 0.6 PO4, LiMn 0.3 Fe 0.7 PO4, LiMn 0.2 Fe 0.8 PO4, or LiMn 0.1 Fe 0.9 It may be PO4 or the like.

[0062] [Chemical formula 5] Li a5 Mn (1-x5) M 5 x5 PO4 In Chemical formula 5, 0.90 ≤ a5 ≤ 1.5, 0 ≤ x5 ≤ 0.4, and M 5 is Al, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Sn, Sr, V, W, Y, Zn, Zr, or a combination thereof.

[0063] The compound represented by Chemical formula 5 is a lithium manganese phosphate oxide. In Chemical formula 5, for example, 0.90 ≤ a5 ≤ 1.2, or 0.95 ≤ a5 ≤ 1.1 may hold, and 0 ≤ x5 ≤ 0.3, 0 ≤ x5 ≤ 0.2, 0 ≤ x5 ≤ 0.1, or 0 < x5 ≤ 0.05 may hold. For example, when a5 = 1 and x5 = 0, Chemical formula 5 can be expressed as LiMnPO4.

[0064] [Chemical formula 6] Li a6 Ti (2-x6) M 6 x6 (PO4)3 In Chemical formula 6, 0.90 ≤ a6 ≤ 1.5, 0 ≤ x6 ≤ 0.4, and M 6 is Al, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Sn, Sr, V, W, Y, Zn, Zr, or a combination thereof.

[0065] The compound represented by Chemical Formula 6 is a lithium titanium phosphate. In Chemical Formula 6, for example, 0.90 ≦ a6 ≦ 1.2, or 0.95 ≦ a6 ≦ 1.1, and 0 ≦ x6 ≦ 0.3, 0 ≦ x6 ≦ 0.2, 0 ≦ x6 ≦ 0.1, or 0 < x6 ≦ 0.05 are possible. For example, when a6 = 1 and x6 = 0, Chemical Formula 6 can be represented as LiTi2(PO4)3.

[0066] [Chemical Formula 7] Li a7 Ti (1-x7) M 7 x7 PO5 In Chemical Formula 7, 0.90 ≦ a7 ≦ 1.5, 0 ≦ x7 ≦ 0.4, and M 7 is Al, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Sn, Sr, V, W, Y, Zn, Zr, or a combination thereof.

[0067] The compound represented by Chemical Formula 7 is a lithium titanium phosphate. In Chemical Formula 7, for example, 0.90 ≦ a7 ≦ 1.2, or 0.95 ≦ a7 ≦ 1.1, and 0 ≦ x7 ≦ 0.3, 0 ≦ x7 ≦ 0.2, 0 ≦ x7 ≦ 0.1, or 0 < x7 ≦ 0.05 are possible. For example, when a7 = 1 and x7 = 0, Chemical Formula 7 can be represented as LiTiPO5.

[0068] As a specific example, the lithium transition metal phosphate of the third positive electrode active material is LiFePO4, LiMn 0.7 Fe 0.3 PO4, LiMn 0.6 Fe 0.4 PO4, LiMn 0.5 Fe 0.5 PO4, LiMn 0.4 Fe 0.6 PO4, LiMn 0.3 Fe 0.7 PO4, LiMnPO4, LiTiPO5, LiTi2(PO4)3, or a combination thereof can be included.

[0069] 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%, based on 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.

[0070] In addition, the cathode active material according to an embodiment may be characterized as being sodium-free. Although sodium ions are typically used in the manufacturing process of a cathode active material, the manufacturing method described below allows for the formation of cathode active material particles with a stable structure and a coating layer with a uniform thickness without using sodium ions.

[0071] Method for producing positive electrode active material In one embodiment, there is provided a method for producing a positive electrode active material, including: (i) mixing a nickel-manganese composite hydroxide having a nickel content of 60 mol% or more relative to 100 mol% of the total metals with a lithium raw material and heat-treating the mixture to prepare a first positive electrode active material in the form of secondary particles formed by aggregation of a plurality of primary particles; (ii) mixing a nickel-manganese composite hydroxide having a nickel content of 60 mol% or more relative to 100 mol% of the total metals with a lithium raw material and heat-treating the mixture to prepare a second positive electrode active material in the form of single particles; (iii) preparing a third positive electrode active material containing a lithium transition metal phosphate; and (iv) mixing the first positive electrode active material with the second positive electrode active material and the third positive electrode active material.

[0072] In the respective processes for preparing the first and second positive electrode active materials, the nickel-manganese composite hydroxide may contain no or a very small amount of cobalt, and may be, for example, a cobalt-free nickel-manganese composite hydroxide, such as a cobalt-free nickel-manganese-aluminum composite hydroxide. The nickel-manganese composite hydroxide may be prepared by a common coprecipitation method.

[0073] The nickel content in the nickel-manganese composite hydroxide is 60 mol% or more relative to 100 mol% of the total metals, and can be, for example, 60 mol% to 80 mol%, 65 mol% to 80 mol%, 70 mol% to 80 mol%, 60 mol% to 79 mol%, 60 mol% to 78 mol%, or 60 mol% to 75 mol%, etc. When the nickel content satisfies this range, high capacity can be achieved, and structural safety can be improved even if the cobalt content is reduced.

[0074] The manganese content in the nickel-manganese composite hydroxide may be 10 mol% to 40 mol%, 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%, 20 mol% to 30%, etc., relative to 100 mol% of the total metal.

[0075] Furthermore, when the nickel-manganese composite hydroxide further contains aluminum, the aluminum content may be 0.1 mol% or more, 0.5 mol% or more, or 1 mol% or more, relative to 100 mol% of the total metals, 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 manganese and aluminum contents in the composite hydroxide satisfy the above ranges, high capacity can be achieved while improving the structural safety of the positive electrode active material, and production costs can be reduced, improving economic efficiency.

[0076] The cobalt content in the nickel-manganese composite hydroxide may be 0.01 mol% or less, 0.005 mol% or less, or 0.001 mol% or less, relative to 100 mol% of the total metals. Such nickel-manganese composite hydroxides are economical because they avoid the increase in unit price due to cobalt, and they can be said to maximize capacity and improve structural stability.

[0077] The nickel-manganese composite hydroxide can be represented by, for example, the following chemical formula 2.

[0078] [Chemical formula 2] Nix2 Mn y2 Al z2 M 2 w2 (OH)2 In chemical formula 2, 0.6≦x2≦0.8, 0.1≦y2≦0.40≦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, and Zr.

[0079] 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.

[0080] In the preparation process of the first positive electrode active material, aluminum is not additionally doped, and instead, an aluminum raw material is used in the preparation of the precursor, resulting in a nickel-manganese-aluminum composite hydroxide in which aluminum is uniformly dispersed within the structure. By using this precursor, a positive electrode active material can be produced that stably maintains its layered structure even during repeated charge and discharge, even without cobalt, and the capacity, efficiency, and life characteristics of the positive electrode active material can be improved because aluminum by-products and aluminum aggregates are not formed.

[0081] In the preparation of the first positive electrode active material, the nickel-manganese composite hydroxide and the lithium source material may be mixed in a molar ratio of 1:0.9 to 1:1.8, for example, 1:0.9 to 1:1.5 or 1:0.9 to 1:1.2. Heat treatment after mixing may be performed in an oxygen atmosphere, for example, at a temperature range of 750°C to 950°C, 780°C to 900°C, or 810°C to 890°C, for 2 to 20 hours, or 4 to 12 hours. A lithium nickel-manganese composite oxide can be obtained through the heat treatment. The resulting composite oxide may contain nickel at 60 mol% or more, for example, 60 mol% to 80 mol%, based on 100 mol% of the total metals, and may contain no cobalt or a very small amount of cobalt of 0.01 mol% or less.

[0082] According to one embodiment, a method for manufacturing a positive electrode active material may further include a coating process after obtaining a lithium nickel-manganese composite oxide during the preparation of a first positive electrode active material. Lithium nickel-manganese 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. Because of this difference in surface properties, it is difficult to form a uniform, well-formed coating layer using existing coating methods. In one embodiment, a method is proposed for improving high-voltage characteristics by forming a very thin, uniform coating layer on the surface of a lithium nickel-manganese composite oxide with a minimal cobalt content and a nickel content of 60 mol% or more. For example, a coating layer according to one embodiment may be formed by adding and mixing an aluminum source to an aqueous solvent, adding and mixing the lithium nickel-manganese composite oxide, and then drying and reheating the mixture. This method is referred to as a wet coating process.

[0083] The aqueous solvent may include distilled water, an alcohol-based solvent, or a combination thereof. 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 composite oxide particles. The aluminum content in the aluminum source may be designed to be 0.1 mol% to 2 mol%, for example, 0.2 mol% to 1.9 mol%, 0.3 mol% to 1.8 mol%, 0.5 mol% to 1.5 mol%, or 0.8 mol% to 1.3 mol%, relative to 100 mol% of all metals excluding lithium in the first positive electrode active material.

[0084] The solution obtained by mixing the aluminum raw material with the aqueous solvent may have 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 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 may be 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.

[0085] The reheat treatment can be understood as a process for forming a coating layer, and can be carried out, for example, in an oxygen atmosphere at a temperature range of 700°C to 850°C, 750°C to 840°C, or 800°C to 830°C for 2 hours to 20 hours, or 3 hours to 10 hours.

[0086] In order to coat the product with zirconium in addition to aluminum, a zirconium source may be added to the product after the drying process and then heat-treated again. The zirconium source may be, for example, zirconium oxide, and may be added so that the zirconium content is 0.05 mol% to 1 mol% relative to 100 mol% of the metals excluding lithium in the first positive electrode active material.

[0087] In the preparation of the second positive electrode active material, the nickel-manganese composite hydroxide and the lithium source material may be mixed in a molar ratio of 1:0.9 to 1:1.8, for example, 1:0.9 to 1:1.5 or 1:0.9 to 1:1.2. Heat treatment after mixing may be performed in an oxygen atmosphere, for example, at a temperature range of 750°C to 950°C, 780°C to 900°C, or 810°C to 890°C, for 2 to 20 hours, or 4 to 12 hours. A lithium nickel-manganese composite oxide can be obtained through the heat treatment. The obtained composite oxide may contain nickel at 60 mol% or more, for example, 60 mol% to 80 mol%, based on 100 mol% of the total metals, and may contain no cobalt or a very small amount of 0.01 mol% or less. To obtain a single-particle form, a milling process may be further included after the preparation of the lithium nickel-manganese composite oxide.

[0088] The process for preparing the second positive electrode active material may also further include a process of mixing a nickel-manganese composite hydroxide and a lithium raw material, heat-treating the mixture to obtain single particles containing a lithium nickel-manganese composite oxide, and then coating the single particles. While conventional coating methods cannot be used to coat aluminum on the single-particle second positive electrode active material, a wet coating method, as an example, can be used to form a uniform, well-formed coating layer. Specifically, the second positive electrode active material can be manufactured by adding the obtained single-particle lithium nickel-manganese composite oxide to a solution containing an aluminum raw material mixed with an aqueous solvent, mixing the resulting mixture, drying, and heat-treating the mixture again.

[0089] The aqueous solvent and the aluminum raw material are as described above. The aluminum content in the aluminum raw material may be designed to be 0.1 mol% to 2 mol%, for example, 0.2 mol% to 1.9 mol%, 0.3 mol% to 1.8 mol%, 0.5 mol% to 1.5 mol%, or 0.8 mol% to 1.3 mol%, relative to 100 mol% of all metals excluding lithium in the second positive electrode active material.

[0090] When adding an aluminum raw material to an aqueous solvent, an yttrium raw material can also be added to coat Al and Y. The yttrium raw material can include, for example, yttrium nitrate, yttrium sulfate, yttrium carbonate, yttrium hydroxide, or a combination thereof. The yttrium content in the yttrium raw material can be designed to be 0.1 mol% to 1 mol% relative to 100 mol% of the total metals excluding lithium in the second positive electrode active material, for example, 0.1 mol% to 0.9 mol%, 0.1 mol% to 0.8 mol%, 0.1 mol% to 0.6 mol%, 0.1 mol% to 0.4 mol%, or 0.1 mol% to 0.3 mol%. By designing the content of the coating raw materials within the above ranges, a coating layer with a thin and uniform thickness of tens to hundreds of nanometers can be formed, reducing the amount of gas generation in lithium secondary batteries under high-voltage operating conditions and improving their high capacity and long life characteristics.

[0091] The solution obtained by mixing the aluminum raw material and optionally the yttrium raw material in an aqueous solvent may have 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 composite oxide is added to the aqueous solvent containing the aluminum raw material and the yttrium raw material and mixed for approximately 5 to 80 minutes, 5 to 60 minutes, or 5 to 40 minutes. The pH value of the mixed solution after stirring may be 4.5 to 8.5, for example, 5.0 to 8.0, 5.5 to 7.5, or 6.0 to 7.0. Meeting these conditions is advantageous for forming a coating layer of uniform thickness.

[0092] Drying after the mixing process can be understood as a process of removing the solvent, and can be performed, for example, at 40°C to 240°C, 100°C to 220°C, or 150°C to 200°C. Reheat treatment can be understood as a process of forming a coating layer, and can be performed, for example, in an oxygen atmosphere at a temperature range of 700°C to 850°C, 750°C to 840°C, or 800°C to 830°C for 2 hours to 20 hours, or 3 hours to 10 hours. The reheat treatment temperature may be lower than the previous heat treatment temperature, and the reheat treatment time may be the same as or shorter than the previous heat treatment time. By performing reheat treatment under these conditions, a desired coating layer can be obtained.

[0093] The first, second, and third positive electrode active materials may be mixed so that, for a total of 100 wt%, the first positive electrode active material is included at 60 wt% to 90 wt%, the second positive electrode active material is included at 5 wt% to 35 wt%, and the third positive electrode active material is included at 5 wt% to 35 wt%. Specifically, the first positive electrode active material may be included at 60 wt% to 85 wt%, the second positive electrode active material is included at 10 wt% to 25 wt%, and the third positive electrode active material is included at 5 wt% to 20 wt%. Mixing the positive electrode active materials in these ratios can maximize energy density while increasing capacity.

[0094] 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 agent, or a combination thereof.

[0095] 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 Furthermore, the density of the positive electrode active material layer in the final rolled positive electrode may be 3.4 g / cc to 3.7 g / cc, for example, 3.5 g / cc to 3.6 g / cc or 3.5 g / cc to 3.58 g / cc. When applying 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 ranges is suitable for achieving a high-capacity, high-energy-density lithium secondary battery.

[0096] binder The binder serves to effectively adhere the positive electrode active material particles to each other and to effectively 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.

[0097] Conductive agent The conductive agent is used to impart electrical conductivity to the electrode, and any electron-conductive material that does not undergo chemical change in the battery that is constructed can be used. Examples of the conductive agent 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 containing copper, nickel, aluminum, silver, etc., in the form of metal powder or metal fiber; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0098] The content of the binder and the conductive agent may be 0.5% by weight to 5% by weight, or 0.5% by weight to 3% by weight, respectively, relative to 100% by weight of the positive electrode active material layer.

[0099] The positive electrode current collector may be made of Al, but is not limited to this.

[0100] 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 agent, or a combination thereof.

[0101] 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.

[0102] 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.

[0103] As the lithium metal alloy, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0104] 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.

[0105] The silicon-carbon composite can be a composite of silicon and amorphous carbon. The average particle diameter (D 50 ) of the silicon-carbon composite particles can be, for example, 0.5 μm to 20 μm. According to one embodiment, the silicon-carbon composite can be in a form in which silicon particles and amorphous carbon are coated on the surface of the silicon particles. For example, it can include secondary particles (cores) formed by granulating primary silicon particles, and an amorphous carbon coating layer (shell) located on the surface of the secondary particles. The amorphous carbon is also located between the primary silicon particles, and for example, the primary silicon particles can be coated with amorphous carbon. The secondary particles can be dispersed and present in an amorphous carbon matrix.

[0106] 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 this 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.

[0107] 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, the content of silicon may be 10% to 50% by weight based on 100% by weight of the silicon-carbon composite, 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.

[0108] 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, in the form of a silicon alloy, or in an oxidized form. The oxidized form of silicon may be represented by SiO x (0 < x < 2). At this time, the atomic content ratio of Si:O indicating the degree of oxidation may be 99:1 to 33:67. In this specification, unless otherwise defined, the average particle diameter (D 50 ) means the diameter of the particle with a cumulative volume of 50% in the particle size distribution.

[0109] 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 ratio.

[0110] binder The binder serves to effectively 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.

[0111] 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.

[0112] 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.

[0113] 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.

[0114] The dry binder is a fiberizable polymeric material, such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0115] Conductive agent The conductive agent is used to impart conductivity to the electrode, and any electron-conductive material that does not undergo chemical change 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.

[0116] 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 agent.

[0117] 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.

[0118] 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.

[0119] 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.

[0120] 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), and butylene carbonate (BC). 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, and caprolactone. 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.

[0121] 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 can be widely understood by those working in the field.

[0122] When a carbonate-based solvent is used, a cyclic carbonate and a chain carbonate may be mixed and used, and the cyclic carbonate and the chain carbonate may be mixed in a volume ratio of 1:1 to 1:9.

[0123] 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.

[0124] The electrolyte may further contain vinyl ethyl carbonate, vinylene carbonate or ethylene carbonate based compounds to improve the battery life.

[0125] 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.

[0126] 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, LiN(C x F 2x+1 SO2)(C y F 2y+1SO2) (x and y are integers of 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFOB), and lithium bis(oxalato)borate (LiBOB).

[0127] The concentration of the lithium salt is preferably within the range of 0.1 M to 2.0 M. When the concentration of the lithium salt is within this range, the electrolyte has appropriate ionic conductivity and viscosity, thereby exhibiting excellent performance and allowing lithium ions to migrate effectively.

[0128] Lithium secondary battery In one embodiment, a lithium secondary battery is provided that includes the positive electrode, negative electrode, and electrolyte described above.

[0129] 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).

[0130] A lithium secondary battery according to an embodiment may be suitable for being charged at a high voltage or for being driven at a high voltage. For example, the charging voltage of the lithium secondary battery may be 4.3 V to 4.6 V, or 4.40 V to 4.55 V. By using a positive electrode active material according to an embodiment, the lithium secondary battery may significantly reduce the amount of gas generation even when charged at a high voltage, thereby achieving high capacity and long life characteristics.

[0131] Separator Depending on the type of lithium secondary battery, a separator may be present between the positive electrode and the negative electrode. Such a separator may be made of polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film 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 may also be used.

[0132] The separator may include a porous substrate and a coating layer containing an organic material, an inorganic material, or a combination thereof located on one or both sides of the porous substrate.

[0133] The porous substrate may be a polymer membrane formed of any one polymer selected from the group consisting of 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 copolymers, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon (registered trademark), and polytetrafluoroethylene, or a copolymer or mixture of two or more of these polymers.

[0134] 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.

[0135] 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.

[0136] The inorganic substances include Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, and Mg(OH). 2、 The inorganic particles may include, but are not limited to, inorganic particles selected from boehmite and combinations thereof. 50 ) can be 1 nm to 2000 nm, for example, 100 nm to 1000 nm, or 100 nm to 700 nm.

[0137] The organic material and the inorganic material may be mixed in one coating layer, or may be stacked in a form in which a coating layer containing an organic material and a coating layer containing an inorganic material are stacked.

[0138] 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.

[0139] 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.

[0140] Example 1 1. Production of positive electrode active material (1) Preparation of the first 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 850°C for 8 hours in an oxygen atmosphere to obtain a composition of Li 1.05 Ni 0.75 Mn0.23 Al 0.02 O2 and the average particle size (D 50 A first composite oxide in the form of secondary particles having a particle size of about 14 μm was prepared.

[0141] Aluminum sulfate was added to a distilled water solvent, and then the first 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 mol% of the total metals excluding lithium in the final first positive electrode active material. The solvent was removed from the mixed solution, and the mixture was dried at 190°C. Zirconium oxide was then added to the resulting material, and a second heat treatment was performed at 825°C for 8 hours in an oxygen atmosphere to produce the first positive electrode active material. The zirconium content in the zirconium oxide was designed to be 0.2 mol% relative to 100 mol% of the total metals excluding lithium in the final first positive electrode active material. Figure 2 shows an SEM image of the prepared first positive electrode active material. The average particle size (D 50 ) is approximately 14 μm.

[0142] (2) Preparation of the second positive electrode active material Ni 0.75 Mn 0.25 (OH)2, LiOH and Al2O3 were mixed in a molar ratio of 1:1:0.02 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 second composite oxide in the form of single particles having a particle size of about 3 μm was produced.

[0143] Aluminum sulfate and yttrium nitrate were mixed into a distilled water solvent, and then the second composite oxide was added and mixed for 20 to 60 minutes. The aluminum content in the aluminum sulfate was designed to be 0.4 mol% relative to 100% by weight of the total metals excluding lithium in the final second cathode active material, and the yttrium content in the yttrium nitrate was designed to be 0.1 mol%. The solvent was removed from the mixed solution, which was then dried at 190°C and heat-treated in an oxygen atmosphere at 825°C for 8 hours to produce a second cathode active material. Figure 3 shows an SEM image of the produced second cathode active material. The average particle size (D 50 ) is approximately 3.5 μm.

[0144] (3) Production of the third positive electrode active material The average particle size of the primary particles is (D 50 LiFePO4 with a particle size of approximately 200 nm is prepared. Figure 4 shows an SEM image of the third positive electrode active material.

[0145] (4) Production of final positive electrode active material A final positive electrode active material was prepared by mixing 70 wt % of the first positive electrode active material, 20 wt % of the second positive electrode active material, and 10 wt % of the third positive electrode active material.

[0146] 2. Fabrication of the positive electrode 98.5 wt% of the prepared cathode active material, 1.0 wt% of polyvinylidene fluoride binder, and 0.5 wt% of carbon nanotube conductive agent were mixed to prepare a cathode active material layer slurry, which was then coated on an aluminum foil current collector, dried, and rolled to prepare a cathode. The density of the final rolled cathode was approximately 3.46 g / cc.

[0147] 3. Lithium secondary battery manufacturing 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.

[0148] 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.

[0149] Example 2 The third positive electrode active material has an average particle size of primary particles (D 50 ) is about 180 nm 0.6 Fe 0.4 Except for using PO4, a positive electrode and a lithium secondary battery were fabricated in substantially the same manner as in Example 1. FIG. 5 is an SEM image of the third positive electrode active material of Example 2.

[0150] Comparative Example 1 A positive electrode and a lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that the second positive electrode active material was not mixed, and a mixture of 80 wt % of the first positive electrode active material and 20 wt % of the third positive electrode active material was used as the positive electrode active material.

[0151] Comparative Example 2 A positive electrode and a lithium secondary battery were manufactured in substantially the same manner as in Example 2, except that the second positive electrode active material was not mixed, and a mixture of 80 wt % of the first positive electrode active material and 20 wt % of the third positive electrode active material was used as the positive electrode active material.

[0152] Comparative Example 3 A positive electrode and a lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that the third positive electrode active material was not mixed, and a mixture of 70 wt % of the first positive electrode active material and 30 wt % of the second positive electrode active material was used as the positive electrode active material.

[0153] To facilitate understanding, the design details of the positive electrode active materials of the examples and comparative examples are summarized in Table 1 below.

[0154] [Table 1]

[0155] Evaluation example 1 The lithium secondary batteries manufactured in the examples and comparative examples 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 to an end voltage of 3.0 V, and the initial discharge capacity is shown in Table 1. Next, a cycle of charging 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 50-cycle discharge capacity to the initial discharge capacity was calculated and shown in Table 1.

[0156] Table 1 also shows the densities of the positive electrode mixtures in the rolled state for the examples and comparative examples.

[0157] Referring to Table 1, it can be seen that the Examples have a higher positive electrode mixture density than the Comparative Examples, and are therefore superior in capacity and life characteristics when driven at a high voltage of 4.45 V. Comparative Examples 1 and 2 have a lower positive electrode mixture density than the Examples, and are therefore shown to have lower initial discharge capacities when driven at a high voltage.

[0158] 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]

[0159] 100: Lithium secondary battery 10: Positive electrode 20: Negative electrode 30: Separator 40: Electrode assembly 50: Case

Claims

1. The lithium nickel-manganese composite oxide contains 60 mol % or more of nickel relative to 100 mol % of all metals excluding lithium, and is in the form of secondary particles formed by agglomeration of a plurality of primary particles, and the average particle size of the secondary particles (D 50 ) is 10 μm to 20 μm, The present invention relates to a lithium nickel-manganese composite oxide having a nickel content of 60 mol % or more relative to 100 mol % of all metals excluding lithium, and the composite oxide is in the form of a single particle, and the average particle diameter (D 50 ) is 2 μm to 8 μm, and a third positive electrode active material in the form of particles containing a lithium transition metal phosphate; Including, the first positive electrode active material further includes a coating layer located on a surface of the secondary particle and containing aluminum; the second positive electrode active material further includes a coating layer located on a surface of the single particle and containing aluminum; The positive electrode active material includes the first positive electrode active material in an amount of 60% by weight to 90% by weight, the second positive electrode active material in an amount of 5% by weight to 35% by weight, and the third positive electrode active material in an amount of 5% by weight to 35% by weight, relative to a total of 100% by weight of the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material.

2. The average particle size (D 50 2. The positive electrode active material according to claim 1, wherein the average particle diameter of the first and second nanoparticles is 10 nm to 2 μm.

3. 2. The positive electrode active material according to claim 1, wherein the lithium nickel-manganese composite oxide of the first positive electrode active material and the lithium nickel-manganese composite oxide of the second positive electrode active material have the same or different compositions, and each independently has a nickel content of 60 mol % to 80 mol % relative to 100 mol % of all metals excluding lithium.

4. the lithium nickel-manganese composite oxide of the first positive electrode active material and the lithium nickel-manganese composite oxide of the second positive electrode active material are each independently a lithium nickel-manganese-aluminum composite oxide further containing aluminum in addition to nickel and manganese, 2. The positive electrode active material according to claim 1, wherein the content of aluminum in the lithium nickel-manganese-aluminum composite oxide is 0.1 mol % to 3 mol % relative to 100 mol % of all metals excluding lithium.

5. 2. The positive electrode active material according to claim 1, wherein the lithium nickel-manganese composite oxide as the first positive electrode active material, the lithium nickel-manganese composite oxide as the second positive electrode active material, and the lithium transition metal phosphate as the third positive electrode active material each independently have a cobalt content of 0 mol % to 0.01 mol % relative to 100 mol % of all metals excluding lithium.

6. The positive electrode active material according to claim 1, wherein the lithium nickel-manganese composite oxide of the first positive electrode active material and the lithium nickel-manganese composite oxide of the second positive electrode active material are each independently 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 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, and Zr, and X is one or more elements selected from F, P, and S.

7. 7. The positive electrode active material according to claim 6, wherein, in Chemical Formula 1, 0.6≦x1≦0.8, 0.1≦y1≦0.39, 0.01≦z1≦0.03, and 0≦w1≦0.29 are satisfied.

8. A positive electrode active material as described in claim 1, wherein the aluminum content of the coating layer is 0.1 mol% to 2 mol% relative to 100 mol% of all metals excluding lithium in the first positive electrode active material.

9. The positive electrode active material of claim 8 , wherein the coating layer further comprises zirconium, yttrium, or a combination thereof.

10. 10. The positive electrode active material of claim 9, wherein the coating layer further contains 0.05 mol % to 1 mol % zirconium and / or 0.05 mol % to 1 mol % yttrium, relative to 100 mol % of metals excluding lithium in the first positive electrode active material.

11. The positive electrode active material of claim 8 , wherein the coating layer of the first positive electrode active material has a shell shape that continuously surrounds the surfaces of the secondary particles.

12. The cathode active material according to claim 8 , wherein the coating layer of the first cathode active material has a thickness of 30 nm to 500 nm.

13. The positive electrode active material of claim 8 , wherein the first positive electrode active material further comprises a grain boundary coating portion located on a surface of the primary particle inside the secondary particle and containing aluminum.

14. A positive electrode active material as described in claim 1, wherein the aluminum content of the coating layer is 0.1 mol% to 2 mol% relative to 100 mol% of all metals excluding lithium in the second positive electrode active material.

15. The positive electrode active material of claim 14 , wherein the coating layer of the second positive electrode active material is in the form of a shell that continuously surrounds the surface of the single particle.

16. The cathode active material of claim 14, wherein the coating layer of the second cathode active material has a thickness of 30 nm to 500 nm.

17. the coating layer of the second positive electrode active material further contains yttrium; 15. The positive electrode active material of claim 14, wherein the yttrium content of the coating layer is 0.1 mol % to 1 mol % relative to 100 mol % of all metals excluding lithium in the second positive electrode active material.

18. 18. The positive electrode active material of claim 17, wherein in the coating layer of the second positive electrode active material, aluminum exists in the form of a continuous film and yttrium exists in the form of islands.

19. 18. The cathode active material of claim 17, wherein the second cathode active material comprises a first coating layer containing aluminum located on a surface of the single particle, and a second coating layer containing yttrium located on the first coating layer.

20. 10. The cathode active material of claim 1, wherein the lithium transition metal phosphate of the third cathode active material comprises lithium iron phosphate, lithium manganese iron phosphate, lithium manganese phosphate, lithium titanium phosphate, or a combination thereof.

21. The positive electrode active material of claim 1 , wherein the lithium transition metal phosphate of the third positive electrode active material is represented by Chemical Formula 3, Chemical Formula 4, Chemical Formula 5, Chemical Formula 6, or Chemical Formula 7: [Chemical formula 3] Li a3 Fe (1-x3) M 3 x3 PO 4 In Chemical Formula 3, 0.90≦a3≦1.5, 0≦x3≦0.4, and M 3 is Al, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Sn, Sr, V, W, Y, Zn, Zr, or a combination thereof; [Chemical formula 4] Li a4 Mn x4 Fe (1-x4-y4) M 4 y4 PO 4 In chemical formula 4, 0.90≦a4≦1.5, 0.1≦x4≦0.9, 0.1≦y4≦0.9, M 4 is Al, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Sn, Sr, V, W, Y, Zn, Zr, or a combination thereof; [Chemical formula 5] Li a5 Mn (1-x5) M 5 x5 PO 4 In Chemical Formula 5, 0.90≦a5≦1.5, 0≦x5≦0.4, and M 5 is Al, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Sn, Sr, V, W, Y, Zn, Zr, or a combination thereof; [Chemical formula 6] Li a6 Today (2-x6) M 6 x6 (PO 4 ) 3 In Chemical Formula 6, 0.90≦a6≦1.5, 0≦x6≦0.4, and M 6 is Al, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Sn, Sr, V, W, Y, Zn, Zr, or a combination thereof; [Chemical formula 7] Li a7 Today (1-x7) M 7 x7 PO 5 In Chemical Formula 7, 0.90≦a7≦1.5, 0≦x7≦0.4, and M 7 is Al, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Sn, Sr, V, W, Y, Zn, Zr, or a combination thereof.

22. The lithium transition metal phosphate of the third positive electrode active material is LiFePO 4 , LiMn 0.7 Fe 0.3 P.O. 4 , LiMn 0.6 Fe 0.4 P.O. 4 , LiMn 0.5 Fe 0.5 P.O. 4 , LiMn 0.4 Fe 0.6 P.O. 4 , LiMn 0.3 Fe 0.7 P.O. 4 , LiMnPO 4 , LiTiPO 5 , LiTi 2 (P.O. 4 ) 3 or a combination thereof.

23. 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 22.

24. 24. The positive electrode according to claim 23, wherein the density of the positive electrode active material layer is 3.4 g / cc to 3.7 g / cc.

25. The positive electrode according to claim 23 . a negative electrode, and A lithium secondary battery containing an electrolyte.

26. The lithium secondary battery according to claim 25, wherein the charging voltage is 4.3V to 4.6V.

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