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 price of a positive electrode material is reduced, the characteristics of high capacity and high energy density are secured, 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 existing in a mode of a secondary particle formed by aggregation of a plurality of primary particles, and a second positive electrode active material in a monoparticulate form containing the similar complex oxide as above. The second positive electrode active material exists on a surface of a monoparticle, and includes a coating layer containing aluminum and yttrium. The content of aluminum in the coating layer is 0.1 to 2 mol% and the content of yttrium is 0.1 to 1 mol% relative to 100 mol% of the entire metals excluding lithium in the second positive electrode active material.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-ion batteries, which offer high energy density while remaining portable, are primarily used as power sources for mobile information terminals such as mobile phones, laptops, and smartphones. Recently, research has been actively conducted on using high-energy-density lithium-ion batteries as power sources or energy storage sources for hybrid and electric vehicles.

[0003] To realize lithium secondary batteries that meet these applications, a variety of positive electrode active materials are being considered. Among them, lithium nickel oxides, lithium nickel manganese cobalt composite oxides, lithium nickel cobalt aluminum composite oxides, and lithium cobalt oxides are mainly used as positive electrode active materials. However, in recent years, while the demand for large, high-capacity, or high-energy-density lithium secondary batteries has surged, the supply of positive electrode active materials containing cobalt, a rare metal, is expected to be extremely insufficient. In other words, because cobalt is expensive and its remaining reserves are not large, there is a need to develop positive electrode active materials that either exclude cobalt or reduce its content. [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] The present invention provides a positive electrode active material comprising a lithium nickel-manganese composite oxide, which revitalizes the cost of the positive electrode material while ensuring high capacity and high energy density characteristics, suppressing side reactions with the electrolyte at high voltages, and improving high-voltage performance, as well as a positive electrode containing the same and a lithium secondary battery. [Means for solving the problem]

[0005] In one embodiment of the present invention, a first positive electrode active material contains a lithium nickel-manganese composite oxide in which the nickel content is 60 mol% or more based on 100 mol% of the total metal excluding lithium, and is in the form of secondary particles formed by aggregation of a plurality of primary particles. And a second positive electrode active material contains a lithium nickel-manganese composite oxide in which the nickel content is 60 mol% or more based on 100 mol% of the total metal excluding lithium, and is in the form of single particles. The second positive electrode active material includes a coating layer located on the surface of the single particle and containing aluminum and yttrium. With respect to 100 mol% of the total metal excluding lithium in the second positive electrode active material, the aluminum content of the coating layer is 0.1 mol% to 2 mol%, and the yttrium content of the coating layer is 0.1 mol% to 1 mol%. A positive electrode active material is provided.

[0006] In another embodiment of the present invention, a positive electrode is provided that includes a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector, and the positive electrode active material layer includes the positive electrode active material described above.

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

Effects of the Invention

[0008] The positive electrode active material according to one embodiment of the present invention minimizes production cost and maximizes capacity, ensures long-life characteristics, and suppresses side reactions with the electrolyte at high voltages. The lithium secondary battery to which the positive electrode active material is applied can exhibit high initial charge and discharge capacity and efficiency even under high voltage driving conditions, and can realize long-life characteristics.

Brief Description of the Drawings

[0009] [Figure 1] It is a cross-sectional view schematically showing a lithium secondary battery according to one embodiment. [Figure 2] It is a scanning electron microscopy (SEM) image of the first positive electrode active material of Example 1. [Figure 3] This is an SEM image of the second positive electrode active material in Example 1. [Modes for carrying out the invention]

[0010] The following describes specific embodiments in detail so that they can be easily implemented by those with ordinary skill in the art. However, the present invention can be realized in various different forms and is not limited to the embodiments described herein.

[0011] The terms used herein are for illustrative purposes only and are not intended to limit the invention. Unless otherwise clearly stated in the context, singular expressions include plural expressions.

[0012] Here, "these combinations" refers to mixtures of components, laminates, composites, copolymers, alloys, blends, reaction products, etc.

[0013] Here, terms such as “include,” “equip,” or “possess” are intended to specify the existence of a particular feature, number, stage, component, or combination thereof, and should be understood not to preemptively exclude the existence or possibility of adding one or more other features, numbers, stages, components, or combinations thereof.

[0014] To clearly represent various layers and regions in the drawings, thicknesses are shown enlarged, and similar parts are given the same drawing reference numerals throughout the specification. When a layer, film, region, plate, or other part is said to be "on top of" or "on" another part, this includes not only when it is "directly on top of" another part, but also when there is another part in between. Conversely, when a part is said to be "directly on top of" another part, it means that there is no other part in between.

[0015] Furthermore, the term "layer" here includes not only the shapes formed on the entire surface when observed in a plan view, but also the shapes formed on a portion of the surface.

[0016] The average particle size can be measured by methods widely known to those skilled in the art, for example, by a particle size analyzer, or by a transmission electron microscope image or scanning electron microscope image. Alternatively, it can be measured using dynamic light scattering, and after performing data analysis to count the number of particles for each particle size range, the average particle size value can be calculated from this. Unless otherwise defined, the average particle size means the diameter (D50) of the particle whose cumulative volume in the particle size distribution is 50% by volume. Or, unless otherwise defined, the average particle size may be obtained by measuring the size (diameter or length of the major axis) of more than 20 random particles from a scanning electron microscope image to obtain a particle size distribution, and then taking the diameter (D50) of the particle whose cumulative volume in the said particle size distribution is 50% by volume as the average particle size.

[0017] Here, "or" is not interpreted in an exclusive sense; for example, "A or B" is interpreted as including A, B, A+B, etc.

[0018] The term "metal" is interpreted as a concept that includes general metals, transition metals, and metalloids (metallic semi-metals).

[0019] positive electrode active material One embodiment of the present invention provides a positive electrode active material comprising: a first positive electrode active material in the form of secondary particles formed by the aggregation of a plurality of primary particles, which contains a lithium nickel-manganese composite oxide in which the nickel content is 60 mol% or more per 100 mol% of the total metal excluding lithium; and a second positive electrode active material in the form of single particles, which contains a lithium nickel-manganese composite oxide in which the nickel content is 60 mol% or more per 100 mol% of the total metal excluding lithium. The second positive electrode active material includes a coating layer located on the surface of the single particle and containing aluminum and yttrium, wherein the aluminum content of the coating layer is 0.1 mol% to 2 mol% and the yttrium content of the coating layer is 0.1 mol% to 1 mol% per 100 mol% of the total metal excluding lithium in the second positive electrode active material.

[0020] In recent years, with the sharp rise in the price of cobalt, a rare metal, there has been a demand for the development of cathode active materials that either exclude cobalt or reduce its cobalt content. Among these, cathode active materials with olivine-based crystal structures such as lithium iron phosphate (LFP), lithium manganese phosphate (LMP), and lithium iron manganese phosphate (LMFP), or spinel crystal structures such as lithium manganese oxide (LMO), have limitations in achieving high capacity because the amount of lithium that can be utilized within the structure is small. Layered nickel-manganese cathode active materials can have a high lithium content within the structure, resulting in excellent capacity and efficiency characteristics, making them suitable as materials for high-capacity batteries. However, the removal of cobalt, which plays a core role in the layered structure, leads to a decrease in structural stability, an increase in resistance, and difficulty in ensuring long life characteristics. In addition, because cobalt is removed, side reactions between the cathode active material and electrolyte accelerate under high voltage and high temperature conditions, increasing gas generation and reducing life characteristics.

[0021] In one embodiment, a positive electrode active material is provided that contains a lithium nickel-manganese composite oxide and is provided in a form in which a first positive electrode active material in the form of secondary particles and a second positive electrode active material in the form of single particles are mixed, and a specific coating agent is applied to each in a specific amount, thereby achieving high capacity and high energy density, long life characteristics, and improved high voltage performance.

[0022] The average particle size (D) of the secondary particles of the first positive electrode active material. 50 ) is the average particle size (D) of the single particles of the second positive electrode active material. 50 ) may be larger than ). In this case, the first positive electrode active material can be described as large grains or large particles, and the second positive electrode active material can be described as small grains or small particles. By appropriately mixing large particles in secondary particle form and small particles in single particle form, the capacity and energy density of the nickel-manganese positive electrode can be maximized, improving its lifetime characteristics and durability.

[0023] Here, the average particle size is determined by obtaining a particle size distribution by randomly measuring the size (diameter or length of the long axis) of more than 20 particles in a scanning electron microscope image of the positive electrode active material, and the diameter (D) of the particle whose cumulative volume in the particle size distribution is 50% by volume. 50 ) may be used as the average particle size.

[0024] The average particle size (D) of the secondary particles of the first positive electrode active material. 50 The average particle size (D) of the single particles of the second positive electrode active material may be, for example, 10 μm to 20 μm, 10 μm to 18 μm, or 12 μm to 16 μm. 50 The particle size of each positive electrode active material may be, for example, 0.5 μm to 8 μm, 1 μm to 7 μm, 1.5 μm to 6 μm, or 2 μm to 5 μm. When the average particle size of each positive electrode active material satisfies the above range, high capacity and high energy density can be achieved.

[0025] The first positive electrode active material is present in an amount of 60% to 95% by weight relative to 100% by weight of the combined total of the first and second positive electrode active materials, for example, 70% to 90% by weight. The second positive electrode active material is present in an amount of 5% to 40% by weight relative to 100% by weight of the combined total of the first and second positive electrode active materials, for example, 10% to 30% by weight. When the mixing ratio of the first and second positive electrode active materials satisfies the above range, the energy density can be increased while maximizing 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 from each other. The nickel content of each lithium nickel-manganese composite oxide satisfies 60 mol% or more relative to 100 mol% of the total metal 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%. When the nickel content satisfies the above range, high capacity can be achieved and structural safety can be improved even if the cobalt content is reduced.

[0027] The manganese content may be, for example, 10 mol% to 40 mol% based on 100 mol% of the total metals excluding lithium in the lithium nickel-manganese composite oxide, and may be, for example, 10 mol% to 39 mol%, 10 mol% to 35 mol%, 10 mol% to 30 mol%, 10 mol% to 29 mol%, 15 mol% to 39 mol%, 20 mol% to 39 mol%, 20 mol% to 30%, etc. When the manganese content satisfies the above range, the positive electrode active material can improve the structural stability while realizing a high capacity.

[0028] In each of the first positive electrode active material and the second positive electrode active material, the lithium nickel-manganese composite oxide may be a lithium nickel-manganese-aluminum composite oxide further containing aluminum in addition to nickel and manganese. When aluminum is contained in the composite oxide, it is advantageous for maintaining a stable layered structure even when the cobalt element is excluded from the structure. The aluminum content based on 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, and may be, 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 satisfies the above range, a stable layered structure can be maintained even when cobalt is excluded, the problem of the structure collapsing due to charge and discharge can be suppressed, and the long-life characteristics of the positive electrode active material can be realized.

[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 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

[0030] 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, where M 1 is one or more elements selected from Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr, 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 also be satisfied. Further, Chemical Formula 1 may contain aluminum, and 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 also 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 also be satisfied; 0.01 ≤ z1 ≤ 0.025, 0.01 < z1 ≤ 0.02, or 0.01 < z1 ≤ 0.019 may also be satisfied; 0 ≤ w1 ≤ 0.28, 0 ≤ w1 ≤ 0.27, 0 ≤ w1 ≤ 0.26, 0 ≤ w1 ≤ 0.25, 0 ≤ w1 ≤ 0.24, 0 ≤ w1 ≤ 0.23, 0 ≤ w1 ≤ 0.22, 0 ≤ w1 ≤ 0.21, 0 ≤ w1 ≤ 0.2, 0 ≤ w1 ≤ 0.15, 0 ≤ w1 ≤ 0.1, or 0 ≤ w1 ≤ 0.09, etc., may also be satisfied.

[0033] The lithium nickel-manganese composite oxide may be a cobalt-free compound that does not contain cobalt or contains only a very small amount of cobalt. In other words, 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 contain 0 mol% to 0.01 mol% cobalt relative to 100 mol% of the total metal excluding lithium.

[0034] First positive electrode active material According to one embodiment, the concentration of aluminum may be uniform within the secondary particles of the first positive electrode active material, excluding the coating layer. This means that there is no concentration gradient of aluminum within the particles from the center to the surface, nor is the aluminum concentration higher or lower outside the particles than inside, but rather that the aluminum is uniformly dispersed within the particles. This structure is obtained by synthesizing a composite oxide using nickel-manganese-aluminum hydroxide as a precursor by using an aluminum raw material during the precursor manufacturing process, without further doping with aluminum in the synthesis process of the positive electrode active material. In other words, the aluminum content inside the primary particles may 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 particles and the aluminum content is measured inside the primary particle rather than at the interface, it can be said that the aluminum content is the same / similar / uniform regardless of the position of the primary particle, i.e., whether the primary particle is close to the center or surface of the secondary particle. In such a structure, a stable layered structure can be maintained even if cobalt is absent or present in very small amounts, preventing the generation of aluminum by-products and aluminum aggregates, and simultaneously improving the capacity, efficiency, and lifetime characteristics of the positive electrode active material.

[0035] In one embodiment, the first positive electrode active material is located on the surface of the secondary particles and may further include a coating layer containing aluminum and zirconium. By including an aluminum-zirconium-rich layer on its surface, the first positive electrode active material effectively suppresses side reactions with the electrolyte at high voltages, improving its capacity and lifespan characteristics at high voltages.

[0036] For the first positive electrode active material, the aluminum content of the coating layer is 0.1 mol% to 2 mol% relative to 100 mol% of the total metal excluding lithium, and the zirconium content of the coating layer may be 0.05 mol% to 1 mol%. The aluminum content of the coating layer in 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 content of aluminum, zirconium, etc., in the coating layer can be measured, for example, by SEM-EDS analysis of the surface or cross-section of the positive electrode active material. When the aluminum content in the coating layer satisfies the above range, it is possible to form a uniform and thin coating layer, the resistance of the positive electrode active material does not increase, side reactions with the electrolyte are effectively suppressed, and the life characteristics of the lithium secondary battery at high voltage can be improved.

[0037] The zirconium content of the coating layer in 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 satisfies the above range, the positive electrode active material can form a good coating layer without a decrease in capacity or an increase in resistance, effectively suppressing side reactions with the electrolyte, and further improving capacity characteristics and lifetime 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 yttrium content may be 0.1 mol% to 1 mol% relative to 100 mol% of the total metal content of the first positive electrode active material excluding lithium.

[0039] The coating layer of the first positive electrode active material may be in the form of a film that continuously surrounds the surface of the secondary particles, or, for example, in the form of a shell that surrounds the entire surface of the secondary particles. This is distinct from a structure in which only a part of the surface of the secondary particles is partially coated. According to one embodiment, the coating layer can be formed in a form that completely surrounds the surface of the secondary particles and is very thin and uniform in thickness, thereby improving the structural stability of the positive electrode active material without increasing resistance or decreasing capacitance, effectively suppressing side reactions with the electrolyte, reducing gas generation under high voltage and high temperature conditions, and achieving 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 the above thickness range, the structural stability of the positive electrode active material can be improved without increasing resistance or decreasing capacitance due to the coating, and side reactions with the electrolyte can be effectively suppressed. The thickness of the coating layer can be measured by, for example, TOF-SIMS, XPS, or EDS analysis, and the thickness range of the coating layer may be measured by TEM-EDS line profile.

[0041] The coating layer of the first positive electrode active material is characterized by being thin and uniform in thickness, typically in the range of tens to 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 thickness deviation of the coating layer refers to the thickness of the coating layer within a single positive electrode active material particle. The thickness deviation of the coating layer is calculated, for example, by measuring the thickness at more than 10 points in an electron microscope image of the cross-section of a single positive electrode active material particle, calculating the arithmetic mean, then dividing the absolute value of the difference between one data point and the arithmetic mean by the arithmetic mean and multiplying by 100. When the thickness deviation or standard deviation of the coating layer satisfies the above range, it means that a coating layer of uniform thickness has been successfully formed in film form 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 increase and capacity decrease due to the coating.

[0042] On the other hand, during the coating layer formation process, aluminum can diffuse into the secondary particles. As a result, the positive electrode active material in one embodiment may be located on the surface of the primary particles inside the secondary particles and may further include a grain boundary coating region containing aluminum. The interior of the secondary particle can mean the entire interior excluding the surface of the secondary particle, or it can mean the region from the surface of the secondary particle to approximately 60% of the radius in the direction toward the center of the secondary particle. 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 particles located inside the secondary particle. The presence of the grain boundary coating region can be confirmed by SEM-EDS analysis of the cross-section of the positive electrode active material. The formation of the aluminum grain boundary coating region further stabilizes the positive electrode active material structurally and improves its lifetime characteristics.

[0043] The aluminum content within the grain boundary coating is not particularly limited; for example, the aluminum content within the grain boundary coating may be less than the aluminum content within the coating layer.

[0044] On the other hand, the aluminum content of the coating layer of the first positive electrode active material may be greater than the aluminum content of the coating layer of the second positive electrode active material, as 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, and the capacitance and lifetime characteristics at high voltage can be maximized while improving the structural stability of each.

[0045] Second positive electrode active material A single particle of the second positive electrode active material means that it exists independently without grain boundaries within the particle and consists of a single particle. It can mean a single particle existing in an independent phase where particles do not aggregate morphologically, a monolithic structure, a single-body structure, or a non-aggregated particle, and may be a single crystal as an example.

[0046] The second positive electrode active material is located on the surface of the single particle and includes a coating layer containing aluminum and yttrium, wherein the aluminum content of the coating layer is 0.1 mol% to 2 mol%, and the yttrium content of the coating layer is 0.1 mol% to 1 mol%. When the coating layer of the second positive electrode active material contains both aluminum and yttrium, and each satisfies the above content range, the initial discharge capacity and lifetime characteristics of the positive electrode active material at high voltage according to one embodiment can be maximized.

[0047] The aluminum content in the coating layer of the second positive electrode active material is characterized by being 0.1 mol% to 2 mol% relative to 100 mol% of the total metal excluding lithium in the second positive electrode active material, and may be, for example, 0.2 mol% to 1.9 mol%, 0.3 mol% to 1.8 mol%, 0.5 mol% to 1.5 mol%, or 0.8 mol% to 1.3 mol%. This refers only to the aluminum content contained in the coating layer, separate from the aluminum contained within the single particles. The aluminum content in the coating layer can be measured, for example, by SEM-EDS analysis of the surface or cross-section of the positive electrode active material. When the aluminum content in the coating layer satisfies the above range, it is possible to form a uniform and thin coating layer, the resistance of the positive electrode active material does not increase, side reactions with the electrolyte are effectively suppressed, and the life characteristics of the lithium secondary battery under high voltage and high temperature conditions can be improved. For example, if the aluminum content of the coating layer is too high, a uniform coating layer may not be formed, or the resistance may increase, reducing the charge-discharge efficiency and lifespan characteristics. Conversely, if the aluminum content of the coating layer is too low, a coating layer of the appropriate thickness may not be formed, reducing the effect of suppressing side reactions with the electrolyte.

[0048] The yttrium content in the coating layer of the second positive electrode active material is characterized by being 0.1 mol% to 1 mol% relative to 100 mol% of the total metal excluding lithium in the second positive electrode active material. For example, it may be 0.1 mol% to 0.9 mol%, 0.1 mol% to 0.8 mol%, 0.1 mol% to 0.6 mol%, 0.1 mol% to 0.4 mol%, or 0.1 mol% to 0.3 mol%. When the yttrium content satisfies the above range, a good coating layer is formed in the positive electrode active material 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 second positive electrode active material is characterized by having both aluminum and yttrium included in the coating layer, which improves capacitance characteristics and lifetime characteristics at high voltages compared to cases where only one of the two is included.

[0050] The coating layer of the second positive electrode active material may be in the form of a film that continuously surrounds the surface of a single particle, or, for example, in the form of a shell that surrounds the entire surface of a single particle. This is distinct from a structure in which only a part of the particle surface is partially coated. According to one embodiment, the coating layer can be formed to surround the entire surface of a single particle while being very thin and of uniform thickness. As a result, the structural stability of the positive electrode active material is improved without an increase in resistance or a decrease in capacitance, side reactions with the electrolyte are effectively suppressed, and long-life characteristics at high voltages can be achieved.

[0051] 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 the above thickness range, the coating can improve the structural stability of the positive electrode active material and effectively suppress side reactions with the electrolyte without increasing resistance or decreasing capacitance. The thickness of the coating layer can be measured by, for example, TOF-SIMS, XPS, or EDS analysis, and the thickness range of the coating layer may be measured by TEM-EDS line profile.

[0052] The coating layer of the second positive electrode active material is characterized by being thin and uniform in thickness, ranging from tens to 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 thickness deviation of the coating layer refers to the content of the thickness of the coating layer within a single positive electrode active material particle. The thickness deviation of the coating layer can be, for example, calculated by measuring the thickness at more than 10 points in an electron microscope image of the cross-section of a single positive electrode active material particle, calculating the arithmetic mean, and then dividing the absolute value of the difference between one data point and the arithmetic mean by the arithmetic mean and multiplying by 100. When the thickness deviation or standard deviation of the coating layer satisfies the above range, it means that a coating layer of uniform thickness has been successfully formed in film form 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 the increase in resistance and decrease in capacity due to the coating.

[0053] In the coating layer of the second positive electrode active material, due to the properties of each element, aluminum may exist in a continuous film form, while yttrium may exist in an island form.

[0054] In one embodiment, aluminum and yttrium may be mixed within a single coating layer, in which case the aluminum may exist in a continuous film form and the yttrium may exist in an island form, but the form is not limited.

[0055] In another embodiment, aluminum and yttrium can each form separate layers. For example, the second positive electrode active material may include a first coating layer containing aluminum located on the surface of a single particle, and a second coating layer containing yttrium located on the first coating layer. The first coating layer is formed in the form of a thin film as aluminum is first attached to or absorbed onto the surface of the single particle, and the second coating layer is formed as yttrium is coated on top of it. Of course, the first and second coating layers may contain a mixture of aluminum and yttrium, but the first coating layer may be an aluminum-rich coating layer with aluminum as the main component, and the second coating layer may be a yttrium-rich coating layer with yttrium as the main component. In this case as well, the yttrium may exist in island form in the second coating layer, but is not particularly limited.

[0056] The thicknesses of the first and second coating layers 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 the thicknesses of each layer meet the above ranges, the coating improves the structural stability of the positive electrode active material and effectively suppresses side reactions with the electrolyte, thereby improving the lifetime characteristics at high voltages, without increasing resistance or decreasing capacitance.

[0057] The cobalt content in the positive electrode active material according to one embodiment may be, for example, 0.01 mol% or less, 0.005 mol% or less, or 0.001 mol% or less relative to 100 mol% of the total metal excluding lithium, or for example, 0 mol% to 0.01 mol%. The positive electrode active material according to one embodiment may be, for example, a cobalt-free positive electrode active material.

[0058] Furthermore, in one embodiment, the other positive electrode active material may be characterized by not containing sodium. Generally, sodium ions can be used in the manufacturing process of positive electrode active materials, but according to the manufacturing method described later, it is possible to form positive electrode active material particles with a stable structure and a coating layer of uniform thickness without using sodium ions.

[0059] Method for manufacturing positive electrode active material In one embodiment, a method for producing a positive electrode active material is provided, which includes (i) mixing a nickel-manganese composite hydroxide having a nickel content of 60 mol% or more relative to 100 mol% of the total metal with a lithium raw material and heat-treating it to prepare a first positive electrode active material in the form of secondary particles formed by the aggregation of multiple 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 metal with a lithium raw material and heat-treating it to obtain a lithium nickel-manganese composite oxide in the form of single particles; adding the obtained lithium nickel-manganese composite oxide to a solution of aluminum raw material and yttrium raw material mixed in an aqueous solvent and mixing, then drying and reheat-treating it to prepare a second positive electrode active material; and (iii) mixing the first positive electrode active material and the second positive electrode active material. In the preparation process for the second positive electrode active material, the aluminum content in the aluminum raw material is 0.1 mol% to 2 mol% relative to 100 mol% of the total metal excluding lithium in the second positive electrode active material, and the yttrium content in the yttrium raw material is 0.1 mol% to 1 mol% relative to 100 mol% of the total metal excluding lithium in the second positive electrode active material. The above-mentioned positive electrode active material can be manufactured by the above method.

[0060] In the preparation processes for the first and second positive electrode active materials, the nickel-manganese composite hydroxide may contain no cobalt or only a very small amount of cobalt. For example, it may be a cobalt-free nickel-manganese composite hydroxide, or, as another example, a cobalt-free nickel-manganese-aluminum composite hydroxide. The nickel-manganese composite hydroxide can be produced by a general coprecipitation method.

[0061] In nickel-manganese composite hydroxides, the nickel content is 60 mol% or more relative to 100 mol% of the total metal, 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%. When the nickel content meets the above range, high capacity can be achieved, and structural safety can be improved even if the cobalt content is reduced.

[0062] In nickel-manganese composite hydroxides, the manganese content may be 10 mol% to 40 mol% relative to 100 mol% of the total metal, or it may be 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.

[0063] Furthermore, if 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 metal, 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 content of the composite hydroxide each meets the above ranges, it is possible to improve the structural safety of the positive electrode active material while achieving high capacity, thereby lowering production costs and improving economic efficiency.

[0064] In nickel-manganese composite hydroxides, the cobalt content 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 metal. Such nickel-manganese composite hydroxides can avoid the cost increase due to cobalt, are economical, maximize capacity, and improve structural stability.

[0065] Nickel-manganese complex hydroxides are represented, for example, by the following chemical formula 2. [Chemical formula 2] Ni x2 Mny2 Al z2 M 2 w2 (OH)2

[0066] 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 Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr.

[0067] In the aforementioned chemical formula 2, for example, 6≦x2≦0.8, 0.1≦y2≦0.39, 0.01≦z2≦0.03, and 0≦w2≦0.29 may also be used.

[0068] Nickel-manganese composite hydroxides are in particulate form, and the average particle size (D) of these particles is 50 The particle size may be 10 μm to 18 μm, 11 μm to 16 μm, or 12 μm to 15 μm.

[0069] In the preparation process for the first positive electrode active material, aluminum is not further doped in the aluminum. By using aluminum raw materials during the production of the precursor, a nickel-manganese-aluminum composite hydroxide in which aluminum is evenly dispersed within the structure may be used as the precursor. By using such a precursor, a positive electrode active material can be produced that maintains a stable layered structure even after repeated charging and discharging, without containing cobalt. This prevents the formation of aluminum by-products and aluminum aggregates, improving the capacity, efficiency characteristics, and lifespan characteristics of the positive electrode active material.

[0070] In the preparation step for the first positive electrode active material, the nickel-manganese composite hydroxide and the lithium raw material may be mixed in a molar ratio of 1:0.9 to 1:1.8, for example, in a molar ratio of 1:0.9 to 1:1.5 or 1:0.9 to 1:1.2. The heat treatment after mixing can be carried out in an oxygen atmosphere, for example, in a temperature range of 750°C to 950°C, or 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 by heat treatment. The obtained composite oxide contains 60 mol% or more of nickel per 100 mol% of the total metal, for example, 60 mol% to 80 mol%, and may contain no cobalt or only a very small amount of 0.01 mol% or less.

[0071] A method for producing a positive electrode active material according to one embodiment may further include a coating step after obtaining a lithium nickel-manganese composite oxide in the preparation step of the first positive electrode active material. The 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 terms of the residual lithium content on the particle surface, resulting in various differences in surface properties. Existing coating methods cannot form a good coating layer with a uniform film morphology. One embodiment provides a method for improving high-voltage characteristics by forming a very thin and uniform coating layer on the surface of a lithium nickel-manganese composite oxide having a very small cobalt content and a nickel content of 60 mol% or more. For example, a coating layer according to one embodiment can be formed by adding and mixing an aluminum raw material in an aqueous solvent, adding and mixing the lithium nickel-manganese composite oxide, and then drying and reheating the mixture. This may be a wet coating method.

[0072] The aqueous solvent may include distilled water, an alcoholic solvent, or a combination thereof. The aluminum raw material may include, for example, aluminum nitrate, aluminum sulfate, aluminum carbonate, aluminum hydroxide, or a combination thereof. As an example, the aluminum raw material may include aluminum sulfate, in which case it is advantageous to form a coating layer of uniform thickness on the surface of the lithium nickel-manganese composite oxide particles. The aluminum content in the aluminum raw material is 0.1 mol% to 2 mol% relative to 100 mol% of the total metal excluding lithium in the first positive electrode active material, for example, 0.2 mol% to 1.9 mol%, 0.3 mol% to 1.8 mol%, 0.5 mol% to 1.5 mol%, or 0.8 mol% to 1.3 mol%.

[0073] The solution obtained by mixing the aluminum raw material with 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 can be 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. Meeting these conditions is advantageous for forming a coating layer of uniform thickness.

[0074] Reheat treatment is a process for forming a coating layer and can be carried out, for example, in an oxygen atmosphere at a temperature range of 700°C to 850°C, 750°C to 840°C, or 800°C to 830°C for 2 to 20 hours, or 3 to 10 hours.

[0075] In addition to aluminum, the material obtained after the drying process can also be reheated by adding a zirconium raw material to the material coated with zirconium. The zirconium raw material may be, for example, zirconium oxide, and can be added so that the zirconium content is 0.05 mol% to 1 mol% per 100 mol% of the metal excluding lithium in the first positive electrode active material.

[0076] In the preparation step for the second positive electrode active material, the nickel-manganese composite hydroxide and the lithium raw material may be mixed in a molar ratio of 1:0.9 to 1:1.8, or for example, in a molar ratio of 1:0.9 to 1:1.5 or 1:0.9 to 1:1.2. The heat treatment after mixing these can be carried out in an oxygen atmosphere, for example, in a temperature range of 750°C to 950°C, or 780°C to 900°C, or 810°C to 890°C, for 2 to 20 hours, or 4 to 12 hours. The heat treatment can yield a lithium nickel-manganese composite oxide. The obtained composite oxide contains 60 mol% or more nickel per 100 mol% of the total metal, for example, 60 mol% to 80 mol%, and may contain no cobalt or only a very small amount of 0.01 mol% or less. To obtain a single-particle form, the process may further include a grinding step after the production of the lithium nickel-manganese composite oxide.

[0077] Coating the single-particle form of the second positive electrode active material with aluminum and yttrium cannot be done using existing coating methods as is. However, by applying a wet coating method as described in one example, a uniform film-shaped, high-quality coating layer can be formed. Specifically, the second positive electrode active material can be produced by adding the obtained single-particle form of lithium nickel-manganese composite oxide to a solution obtained by mixing aluminum and yttrium raw materials in an aqueous solvent, mixing it, drying it, and then reheating it.

[0078] The details regarding the aqueous solvent and aluminum raw material are as described above. The aluminum content in the aluminum raw material is 0.1 mol% to 2 mol% relative to 100 mol% of the total metal excluding lithium in the second positive electrode active material, for example, 0.2 mol% to 1.9 mol%, 0.3 mol% to 1.8 mol%, 0.5 mol% to 1.5 mol%, or 0.8 mol% to 1.3 mol%. The yttrium raw material may include, for example, yttrium nitrate, yttrium sulfate, yttrium carbonate, yttrium hydroxide, or a combination thereof. The yttrium content in the yttrium raw material is 0.1 mol% to 1 mol% relative to 100 mol% of the total metal 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 including the content of the coating raw material within the above ranges, it is possible to form a coating layer with a thin thickness of tens to hundreds of nanometers and a uniform thickness, thereby reducing the amount of gas generated in lithium secondary batteries under high-voltage driving conditions and improving high capacity and long life characteristics.

[0079] The solution obtained by mixing the aluminum raw material and 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 can be added to the aqueous solvent containing the aluminum raw material and the yttrium raw material and mixed for about 5 to 80 minutes, or 5 to 60 minutes, or 5 to 40 minutes. The pH of the mixed solution after stirring 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.

[0080] Drying after the mixing step is a step to remove the solvent and can be carried out at, for example, 40°C to 240°C, 100°C to 220°C, or 150°C to 200°C. Reheat treatment is a step to form a coating layer and can be carried out at, for example, 2 to 20 hours or 3 to 10 hours 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. The reheat treatment temperature may be lower than the heat treatment temperature mentioned above, and the reheat treatment time may be the same as or even shorter than the heat treatment time mentioned above. By performing reheat treatment under these conditions, the desired coating layer can be obtained. In one embodiment, a dry coating method can be applied to coat the single-particle second positive electrode active material with aluminum and yttrium. The coating materials in this dry coating method may, for example, be aluminum oxide and yttrium oxide.

[0081] The first positive electrode active material and the second positive electrode active material can be mixed in a weight ratio of 60:40 to 95:5, for example, in a weight ratio of 70:30 to 90:10. When mixed in such ratios, it is possible to improve capacity and lifetime characteristics while maximizing energy density.

[0082] positive electrode In one embodiment, the positive electrode includes a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector, wherein the positive electrode active material layer provides a positive electrode containing the positive electrode active material described above. The positive electrode active material layer may further contain other types of positive electrode active materials in addition to the positive electrode active material described above. The positive electrode active material layer may also selectively further contain a binder, a conductive material, or a combination thereof.

[0083] According to one embodiment, the loading level of the positive electrode active material layer is 10 mg / cm³. 2 ~40 mg / cm³ 2 It may also be 10 mg / cm³, for example. 2 ~30 mg / cm³ 2 or 10 mg / cm³ 2~20 mg / cm³ 2 It is also possible that the density of the positive electrode active material layer in the rolled final positive electrode may be 3.5 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 the positive electrode active material according to one embodiment, it is advantageous to achieve such a loading level and positive electrode density, and a positive electrode that satisfies the above range of loading level and positive electrode density is suitable for realizing a high-capacity, high-energy-density lithium secondary battery.

[0084] binder The binder plays a role in ensuring that the positive electrode active material particles adhere well to each other and that the positive electrode active material adheres well to the current collector. Typical examples of binders include, but are not limited to, polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylic styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and nylon.

[0085] conductive material Conductive materials are used to impart conductivity to electrodes, and any electronically 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, Ketjenblack, carbon fibers, carbon nanofibers, and carbon nanotubes; metallic materials containing copper, nickel, aluminum, silver, etc., in the form of metal powders or metal fibers; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0086] The binder and conductive material content may be 0.5% to 5% by weight or 0.5% to 3% by weight, respectively, based on 100% by weight of the positive electrode active material layer.

[0087] Al can be used as the positive electrode current collector, but it is not limited to this.

[0088] Lithium-ion rechargeable battery One embodiment provides a lithium secondary battery including the positive electrode, negative electrode, and electrolyte described above.

[0089] Lithium secondary batteries can be classified into cylindrical, prismatic, pouch-type, coin-type, and other types depending on their form. Figure 1 is a schematic diagram showing a lithium secondary battery according to one embodiment. Referring to Figure 1, the lithium secondary battery 100 may include an electrode assembly 40 with a separator 30 between a positive electrode 10 and a negative electrode 20, 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).

[0090] A lithium secondary battery according to one embodiment may be capable of being charged at a high voltage or suitable for being driven at a high voltage. For example, the charging voltage of the lithium secondary battery may be 4.45V or higher, and may be 4.45V to 4.7V, 4.45V to 4.6V, or 4.45V to 4.55V. By applying the positive electrode active material according to one embodiment, the amount of gas generated can be significantly reduced even when charged at a high voltage, and high capacity and long life characteristics can be achieved.

[0091] 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 comprising a negative electrode active material and further comprising a binder, a conductive material, or a combination thereof.

[0092] negative electrode active material The negative electrode active material includes a material capable of reversibly inserting / desorbing lithium ions, lithium metal, an alloy of lithium metal, a material dopable and dedopable with lithium, or a transition metal oxide.

[0093] As the material capable of reversibly inserting / desorbing the lithium ions, a carbon-based negative electrode active material can be used, which can include, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical or fibrous natural graphite, or artificial graphite, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, fired coke, and the like.

[0094] As the alloy of the lithium metal, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al and Sn can be used.

[0095] As the material dopable and dedopable 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 can be silicon, a silicon-carbon composite, SiOx (0 < x < 2), a Si-Q alloy (where Q is an element selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements (excluding Si), Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof, for example, Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof), or a combination thereof. The Sn-based negative electrode active material can be Sn, SnO2, a Sn alloy, or a combination thereof.

[0096] The silicon-carbon composite may be a composite of silicon and amorphous carbon. The average particle size (D) of the silicon-carbon composite particles. 50 The particle size can 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 amorphous carbon coated on the surface of the silicon particles. For example, it may include secondary particles (core) formed by granulating primary silicon particles and an amorphous carbon coating layer (shell) located on the surface 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 the amorphous carbon matrix.

[0097] The silicon-carbon composite may further contain crystalline carbon. For example, the silicon-carbon composite may include a core containing crystalline carbon and silicon particles, and an amorphous carbon coating layer located on the surface of the core. The crystalline carbon may be artificial graphite, natural graphite, or a combination thereof. The amorphous carbon may be soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0098] When the silicon-carbon composite contains silicon and amorphous carbon, the silicon content may be 10% to 50% by weight per 100% by weight of the silicon-carbon composite, and the amorphous carbon content may be 50% to 90% by weight. Furthermore, when the composite contains silicon, amorphous carbon, and crystalline carbon, the silicon content may be 10% to 50% by weight per 100% by weight of the silicon-carbon composite, the crystalline carbon content may be 10% to 70% by weight, and the amorphous carbon content may be 20% to 40% by weight.

[0099] Furthermore, the thickness of the amorphous carbon coating layer may be 5 nm to 100 nm. The average particle size (D) of the silicon particles (primary particles) 50) can be 10 nm to 1 μm, or 10 nm to 200 nm. The silicon particles may exist alone as silicon, or in the form of a silicon alloy, or in an oxidized form. The oxidized form of silicon may be SiO x (0 < x < 2). At this time, the atomic content ratio of Si:O indicating the degree of oxidation can be 99:1 to 33:67. In this specification, unless otherwise defined, the average particle size (D 50 ) means the diameter of the particle with a cumulative volume of 50% by volume in the particle size distribution.

[0100] 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. The mixing ratio 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 mixed and used can be 1:99 to 90:10 by weight ratio.

[0101] Binder The binder serves to well adhere the negative electrode active material particles to each other and to well adhere the negative electrode active material to the current collector. As the binder, a non-aqueous binder, an aqueous binder, a dry binder or a combination thereof can be used.

[0102] 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.

[0103] The aqueous binder may be selected from styrene-butadiene rubber, (meth)acrylicated 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.

[0104] When an aqueous binder is used as the negative electrode binder, it may further contain a cellulosic compound that can impart viscosity. This cellulosic compound can be a mixture of one or more carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose, or alkali metal salts thereof. The alkali metal can be Na, K, or Li.

[0105] The dry binder is a polymeric substance that can be formed into fibers, and may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0106] conductive material Conductive materials are used to impart conductivity to electrodes, and any electronically 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, Ketjenblack, carbon fibers, carbon nanofibers, and carbon nanotubes; metallic materials in the form of metal powders or metal fibers, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0107] The content of the negative electrode active material is 95% to 99.5% by weight relative to 100% by weight of the negative electrode active material layer, and the content of the binder may be 0.5% to 5% by weight relative to 100% by weight of the negative electrode active material layer. For example, the negative electrode active material layer may contain 90% to 99% by weight of the negative electrode active material, 0.5% to 5% by weight of the binder, and 0.5% to 5% by weight of the conductive material.

[0108] Current collector The negative electrode current collector may include, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or alloys thereof, and may be in the form of 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.

[0109] electrolyte The electrolyte for lithium secondary batteries can be, for example, an electrolyte solution, which may contain a non-aqueous organic solvent and a lithium salt.

[0110] Non-aqueous organic solvents act as a medium through which ions involved in the electrochemical reactions of a battery can move. Non-aqueous organic solvents can be carbonate, ester, ether, ketone, or alcoholic solvents, aprotic solvents, or combinations thereof.

[0111] Examples of carbonate-based 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-based solvents that can be used include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, and caprolactone. As ether-based solvents, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran can be used. As ketone-based solvents, cyclohexanone can be used. As alcohol-based solvents, ethyl alcohol and isopropyl alcohol can be used, and as aprotic solvents, nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group with 2 to 20 carbon atoms, and can include double bonds, aromatic rings, or ether groups); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane and 1,4-dioxolane; and sulfolanes can be used.

[0112] Non-aqueous organic solvents can be used alone or in combination of two or more. When used in combination of two or more, the mixing ratio can be appropriately adjusted according to the desired battery performance, which is generally understood by those working in this field.

[0113] When using carbonate-based solvents, cyclic carbonates and linear carbonates can be mixed, and these can be mixed in a volume ratio of 1:1 to 1:9.

[0114] Non-aqueous organic solvents may further include aromatic hydrocarbon organic solvents. For example, carbonate solvents and aromatic hydrocarbon organic solvents can be mixed and used in a volume ratio of 1:1 to 30:1.

[0115] The electrolyte may further contain vinyl ethyl carbonate, vinylene carbonate, or ethylene carbonate compounds to improve battery life.

[0116] Typical examples of the aforementioned ethylene carbonate compounds include fluoroethylene carbonate, difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, and cyanoethylene carbonate.

[0117] Lithium salts dissolve in organic solvents and act as a source of lithium ions within batteries, enabling the operation of basic lithium secondary batteries and facilitating the movement of lithium ions between the positive and negative electrodes. Typical 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 It may contain one or more selected from SO2) (where x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalate)phosphate (LiDFOB), and lithium bis(oxalate)borate (LiBOB).

[0118] The lithium salt concentration is preferably used within the range of 0.1 M to 2.0 M. When the lithium salt concentration falls within this range, the electrolyte has appropriate ionic conductivity and viscosity, resulting in excellent performance and effective lithium ion movement.

[0119] 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 layers of these materials. Mixed multilayer films such as polyethylene / polypropylene two-layer separators, polyethylene / polypropylene / polyethylene three-layer separators, and polypropylene / polyethylene / polypropylene three-layer separators can also be used.

[0120] The separator may include a porous substrate and a coating layer containing organic, inorganic, or a combination thereof located on one or both sides of the porous substrate.

[0121] The porous substrate may be a polymer film formed from one polymer selected from polyethylene, polyolefins such as polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyetherketone, polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon®, and polytetrafluoroethylene, or from a copolymer or mixture of two or more of these polymers.

[0122] The porous substrate can have a thickness of approximately 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.

[0123] The organic substance may include a (meth)acrylic copolymer comprising a first structural unit derived from (meth)acrylamide, a second structural unit comprising at least one of a first structural unit derived from (meth)acrylic acid or (meth)acrylate, and a structural unit derived from (meth)acrylamide sulfonic acid or a salt thereof.

[0124] 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) of the inorganic particles is 50 The range is 1 nm to 2000 nm, and can be, for example, 100 nm to 1000 nm or 100 nm to 700 nm.

[0125] The organic and inorganic materials may exist mixed together in a single coating layer, or they may exist in a form in which a coating layer containing organic materials and a coating layer containing inorganic materials are stacked on top of each other.

[0126] The thickness of the coating layer is 0.5 μm to 20 μm, and can be, for example, 1 μm to 10 μm, or 1 μm to 5 μm.

[0127] The following describes examples and comparative examples of the present invention. The following examples are merely illustrative of the present invention and are not limited to the following examples.

[0128] Example 1 1. Manufacturing of positive electrode active material (1) Manufacturing of the first positive electrode active material Ni 0.75 Mn 0.23 Al 0.02 (OH)2 and LiOH are 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, resulting in a composition of Li 1.05 Ni 0.75 Mn0.23 Al 0.02 It is O2 and the average particle size (D 50 A first composite oxide in the form of secondary particles with a diameter of approximately 14 μm was produced.

[0129] After adding aluminum sulfate to distilled water as a solvent, the first composite oxide was added and mixed for approximately 20 to 60 minutes. At this time, the aluminum content of the aluminum sulfate was designed to be 1.0 mol% relative to 100 mol% of the total metal excluding lithium in the final first cathode active material. After removing the solvent from the mixed solution and drying at 190°C, zirconium oxide was added to the obtained material, and a second heat treatment was performed at 825°C for 8 hours in an oxygen atmosphere to produce the first cathode active material. The zirconium content of the zirconium oxide was designed to be 0.2 mol% relative to 100 mol% of the total metal excluding lithium in the final first cathode active material. Figure 2 is a scanning electron microscope image of the produced first cathode active material.

[0130] (2) Manufacturing of the second positive electrode active material Ni 0.75 Mn 0.23 Al 0.02 (OH)2, LiOH, and Al2O3 are mixed in a molar ratio of 1:1:0.02 and heat-treated at 850°C for 8 hours in an oxygen atmosphere, resulting in a composition of LiNi 0.7 Mn 0.2 Al 0.02 It is O2 and the average particle size (D 50 A second composite oxide in single-particle form with a diameter of approximately 3 μm was fabricated.

[0131] The second composite oxide, Al2O3, and Y2O3 were mixed and heat-treated at 825°C for 8 hours in an oxygen atmosphere to produce the second cathode active material. At this time, the final second cathode active material was mixed so that the coating aluminum was 0.4 mol% and the yttrium was 0.1 mol% relative to 100 wt% of the total metal excluding lithium. Figure 3 is a scanning electron microscope image of the produced second cathode active material.

[0132] (3) Manufacturing of the final positive electrode active material The first positive electrode active material and the second positive electrode active material were mixed in a weight ratio of 7:3 to prepare the final positive electrode active material.

[0133] 2. Manufacturing of the positive electrode A cathode active material layer slurry was prepared by mixing 98.5% by weight of the manufactured cathode active material, 1.0% by weight of polyvinylidene fluoride binder, and 0.5% by weight of carbon nanotube conductive material. This slurry was then coated onto an aluminum foil current collector, dried, and rolled to produce the cathode. The density of the final rolled cathode was approximately 3.52 g / cc.

[0134] 3. Manufacturing of lithium-ion batteries A negative electrode active material slurry was prepared by mixing 97.5% by weight of graphite negative electrode active material, 1.5% by weight of carboxymethylcellulose, and 1% by weight of styrene-butadiene rubber in an aqueous solvent. The negative electrode active material slurry was coated onto a copper foil current collector, and the negative electrode was produced by drying and rolling.

[0135] A lithium secondary battery was manufactured using a conventional method with a polytetrafluoroethylene separator and an electrolyte solution prepared by dissolving 1M LiPF6 in a solvent containing a 3:7 volume ratio mixture of ethylene carbonate and dimethyl carbonate.

[0136] Example 2 The positive electrode active material, positive electrode, and lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that the yttrium content in the yttrium oxide coating agent was designed to be 0.2 mol% relative to 100% by weight of the total metal excluding lithium in the final second positive electrode active material.

[0137] Example 3 The positive electrode active material, positive electrode, and lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that the aluminum content in the aluminum oxide coating agent was designed to be 0.2 mol% relative to 100% by weight of the total metal excluding lithium in the final second positive electrode active material.

[0138] Example 4 The positive electrode active material, positive electrode, and lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that the aluminum content in the aluminum oxide coating agent was designed to be 0.6 mol% relative to 100% by weight of the total metal excluding lithium in the final second positive electrode active material.

[0139] Example 5 The positive electrode active material, positive electrode, and lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that the zirconium content in the zirconium oxide coating agent was designed to be 0.1 mol% relative to 100 mol% of the total metal excluding lithium in the final positive electrode active material.

[0140] Example 6 The positive electrode active material, positive electrode, and lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that the zirconium content in the zirconium oxide coating agent was designed to be 0.3 mol% relative to 100 mol% of the total metal excluding lithium in the final positive electrode active material.

[0141] Comparative Example 1 The positive electrode active material, positive electrode, and lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that yttrium oxide, one of the coating agents, was not used in the production of the second positive electrode active material.

[0142] Comparative Example 2 The positive electrode active material, positive electrode, and lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that the yttrium content in the yttrium oxide coating agent was designed to be 1.5 mol% relative to 100% by weight of the total metal excluding lithium in the final second positive electrode active material.

[0143] Comparative Example 3 The positive electrode active material, positive electrode, and lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that aluminum oxide was not used as a coating agent in the production of the second positive electrode active material.

[0144] Comparative Example 4 The positive electrode active material, positive electrode, and lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that the aluminum content in the aluminum oxide coating agent was designed to be 3 mol% relative to 100% by weight of the total metals excluding lithium in the final second positive electrode active material.

[0145] Reference example 1 The first positive electrode active material was manufactured as follows: Ni 0.75 Mn 0.25 (OH)2, LiOH, and Al2O3 are mixed in a molar ratio of 1:1:0.02 and heat-treated at 850°C for 8 hours in an oxygen atmosphere, resulting in a composition of LiNi 0.75 Mn 0.23 Al 0.02 It is O2 and the average particle size (D 50 A first composite oxide in secondary particle form with a particle size of approximately 14 μm was prepared. The first composite oxide was mixed with aluminum oxide powder and zirconium oxide powder and heat-treated in an oxygen atmosphere at 825°C for 8 hours to produce a first cathode active material that was dry-coated with Al and Zr. The cathode active material, cathode, and lithium secondary battery were prepared in substantially the same manner as in Example 1, except that this was used as the first cathode active material.

[0146] Reference example 2 The positive electrode active material, positive electrode, and lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that the coating with aluminum sulfate was omitted in the manufacturing of the first positive electrode active material.

[0147] Reference example 3 The positive electrode active material, positive electrode, and lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that the zirconium coating step in the production of the first positive electrode active material was omitted, that is, zirconium oxide was not added during the second heat treatment.

[0148] To aid understanding, the design details of the positive electrode active materials for the examples, comparative examples, and reference examples are briefly shown in Table 1 below.

[0149] [Table 1]

[0150] Evaluation Example 1 The lithium secondary batteries manufactured in the examples, comparative examples, and reference examples were charged at 25°C with a constant current of 0.2C to 4.45V, then with a constant voltage of 0.05C, and finally discharged at 0.2C to a cutoff voltage of 3.0V to perform initial charge and discharge. The initial discharge capacities are shown in Table 1 above.

[0151] Next, the battery was charged to 1.0C and discharged to 1.0C at 45°C in a voltage range of 3.0V to 4.45V, and this cycle was repeated 50 or more times. The ratio of the discharge capacity after 50 cycles to the initial discharge capacity was calculated and is shown in Table 1 above.

[0152] Table 1 also shows the density of the positive electrode mixture in the rolled state for the examples, comparative examples, and reference examples.

[0153] Referring to Table 1, it was found that the examples achieved excellent initial discharge capacity and high cathode density, while also showing further improvements in lifetime characteristics compared to the comparative examples.

[0154] Although preferred embodiments have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art that utilize the basic concepts defined in the claims also fall within the scope of the present invention. [Explanation of Symbols]

[0155] 100 Lithium-ion rechargeable batteries 10 positive electrode 20 negative electrode 30 Separators 40 Electrode assembly 50 cases

Claims

1. A first positive electrode active material containing a lithium nickel-manganese composite oxide in which the nickel content is 60 mol% or more relative to 100 mol% of the total metal excluding lithium, and which is in the form of secondary particles formed by the aggregation of multiple primary particles, and It contains a lithium nickel-manganese composite oxide in which the nickel content is 60 mol% or more relative to 100 mol% of the total metal excluding lithium, and also contains a second positive electrode active material in single particle form. The second positive electrode active material is located on the surface of the single particle and includes a coating layer containing aluminum and yttrium. In the second positive electrode active material, with respect to 100 mol% of the total metal excluding lithium, the aluminum content of the coating layer is 0.1 mol% to 2 mol%, and the yttrium content of the coating layer is 0.1 mol% to 1 mol%. The lithium nickel-manganese-containing composite oxide of the first positive electrode active material and the lithium nickel-manganese-containing composite oxide of the second positive electrode active material are positive electrode active materials in which the cobalt content is 0 mol% to 0.01 mol% relative to 100 mol% of the total metal excluding lithium.

2. The average particle size (D) of the secondary particles of the first positive electrode active material. 50 ) is the average particle size (D) of the single particles of the second positive electrode active material. 50 The positive electrode active material according to claim 1, which is larger than ).

3. The average particle size (D) of the secondary particles of the first positive electrode active material. 50 ) is 10 μm to 20 μm, The average particle size (D) of the single particle of the second positive electrode active material 50 The positive electrode active material according to claim 1, wherein the diameter is 0.5 μm to 8 μm.

4. The positive electrode active material according to claim 1, wherein the first positive electrode active material is present in an amount of 60% to 95% by weight and the second positive electrode active material is present in an amount of 5% to 40% by weight, based on a total weight of 100% by weight of the first positive electrode active material and the second positive electrode active material.

5. The positive electrode active material according to claim 1, wherein the lithium nickel-manganese-containing composite oxide of the first positive electrode active material and the lithium nickel-manganese-containing composite oxide of the second positive electrode active material are the same or different, and each independently has a nickel content of 60 mol% to 80 mol% relative to 100 mol% of the total metal excluding lithium.

6. The lithium nickel-manganese-containing composite oxide of the first positive electrode active material and the lithium nickel-manganese-containing composite oxide of the second positive electrode active material are, independently, lithium nickel-manganese-aluminum-containing composite oxides that further contain aluminum in addition to nickel and manganese. The positive electrode active material according to claim 1, wherein the aluminum content of the lithium nickel-manganese-aluminum-containing composite oxide is 1 mol% to 3 mol% relative to 100 mol% of the total metal excluding lithium.

7. The lithium nickel-manganese-containing composite oxide of the first positive electrode active material and the lithium nickel-manganese-containing composite oxide of the second positive electrode active material are each independently represented by the following chemical formula 1, 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 X is one or more elements selected from Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr, and X is one or more elements selected from F, P, and S.

8. The positive electrode active material according to claim 7, wherein in the chemical formula 1, 0.6 ≤ x1 ≤ 0.8, 0.1 ≤ y1 ≤ 0.39, 0.01 ≤ z1 ≤ 0.03, and 0 ≤ w1 ≤ 0.

29.

9. The positive electrode active material according to claim 1, wherein the first positive electrode active material is located on the surface of the secondary particles and further comprises a coating layer containing aluminum and zirconium.

10. The positive electrode active material according to claim 9, wherein the aluminum content of the coating layer is 0.1 mol% to 2 mol% of the total metal excluding lithium in the first positive electrode active material, and the zirconium content of the coating layer is 0.05 mol% to 1 mol%.

11. The positive electrode active material according to claim 9, wherein the aluminum content of the coating layer of the first positive electrode active material is greater than the aluminum content of the coating layer of the second positive electrode active material.

12. The positive electrode active material according to claim 11, wherein 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 are in a molar ratio of 5:1 to 2:

1.

13. The positive electrode active material according to claim 9, wherein the coating layer of the first positive electrode active material is in the form of a shell that continuously surrounds the surface of the secondary particles.

14. The positive electrode active material according to claim 9, wherein the thickness of the coating layer of the first positive electrode active material is 30 nm to 500 nm.

15. The positive electrode active material according to claim 9, wherein the coating layer of the first positive electrode active material further contains yttrium.

16. The positive electrode active material according to claim 9, wherein the first positive electrode active material further comprises a grain boundary coating portion containing aluminum, located on the surface of the primary particles inside the secondary particles.

17. The positive electrode active material according to claim 1, 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.

18. The positive electrode active material according to claim 1, wherein the thickness of the coating layer of the second positive electrode active material is 30 nm to 500 nm.

19. The positive electrode active material according to claim 1, wherein in the coating layer of the second positive electrode active material, aluminum exists in a continuous film form and yttrium exists in an island form.

20. The positive electrode active material according to claim 1, wherein the second positive electrode active material comprises a first coating layer located on the surface of the single particle and containing aluminum, and a second coating layer located on the first coating layer and containing yttrium.

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

22. Positive electrode current collector, and The positive electrode active material layer located on the positive electrode current collector is included, The positive electrode comprises the positive electrode active material layer according to any one of claims 1 to 21.

23. The positive electrode according to claim 22, wherein the density of the positive electrode active material layer is 3.5 g / cc to 3.7 g / cc.

24. The positive electrode according to claim 22, Negative electrode, and A lithium-ion secondary battery containing an electrolyte.

25. A lithium secondary battery according to claim 24, wherein the charging voltage is 4.45V or higher.

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