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

Abstract

To provide a positive electrode active material that can achieve high density, high capacity, a long-life characteristic, and high energy density, and a positive electrode and a lithium secondary battery to which the positive electrode active material is applied.SOLUTION: A positive electrode active material according to an embodiment includes: a first positive electrode active material containing layered lithium nickel-manganese complex oxide and having a secondary particle mode in which a plurality of primary particles are aggregated; a second positive electrode active material in a mono-particle state containing layered lithium nickel-manganese oxide and having an average particle diameter (D50) smaller than that of the first positive electrode active material; and a third positive electrode active material in a mono-particle state containing lithium-manganese-rich complex oxide in which the mole ratio of lithium to the entire metals except lithium is 1.1 to 3 and the content of manganese per 100 mol% of the entire metals except lithium is 60 mol% or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a positive electrode active material, a positive electrode containing the same, and a lithium secondary battery. [Background technology]

[0002] Lithium secondary batteries, which have high energy density yet are easy to carry, are widely used as power sources for mobile information terminals such as mobile phones, laptops, and smartphones. Recently, active research has been conducted into using high-energy-density lithium secondary batteries as power sources for hybrid and electric vehicles or as power storage sources.

[0003] Various positive electrode active materials have been investigated to realize lithium secondary batteries suitable for these applications. Among these, lithium nickel oxide, lithium nickel manganese cobalt composite oxide, lithium nickel cobalt aluminum composite oxide, and lithium cobalt oxide are commonly used as positive electrode active materials. However, while demand for large-sized, high-capacity, or high-energy density lithium secondary batteries has recently increased rapidly, the supply of positive electrode active materials containing the rare metal cobalt is expected to be in short supply. That is, because cobalt is expensive and its remaining reserves are limited, there is a need to develop positive electrode active materials that are free of cobalt or have a reduced cobalt content. Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention provides a positive electrode active material that can achieve high density, high capacity, long life characteristics, and high energy density, and a positive electrode and a lithium secondary battery using the same. [Means for solving the problem]

[0005] In one embodiment, a first positive electrode active material includes a layered lithium nickel-manganese composite oxide and is in the form of secondary particles formed by agglomeration of a plurality of primary particles; a second positive electrode active material includes a layered lithium nickel-manganese composite oxide and has an average particle size (D 50 and a third positive electrode active material in the form of a single particle, the third positive electrode active material comprising a lithium-manganese-rich composite oxide in which the molar ratio of lithium to all metals excluding lithium is 1.1 to 3 and the manganese content relative to 100 molar percent of all metals excluding lithium is 60 molar % or more.

[0006] In another embodiment, a positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, the positive electrode active material layer including the positive electrode active material.

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

[0008] The positive electrode active material according to one embodiment maximizes capacity while minimizing production costs, ensures long-life characteristics, and improves high-voltage characteristics and high-temperature storage characteristics. A lithium secondary battery using the positive electrode active material exhibits high initial charge / discharge capacity and efficiency even under high-voltage driving conditions, and can achieve high energy density due to its high pellet density and 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 cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 3] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 4] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 5] 1 is a scanning electron microscope (SEM) image of a first positive electrode active material prepared in Example 1. [Figure 6] 1 is a scanning electron microscope (SEM) image of a first positive electrode active material prepared in Example 1. [Figure 7] 1 is a SEM image of a second positive electrode active material prepared in Example 1. [Figure 8] 1 is a SEM image of a second positive electrode active material prepared in Example 1. [Figure 9] 1 is a SEM image of a third positive electrode active material prepared in Example 1. [Figure 10] 1 is a SEM image of a third positive electrode active material prepared in Example 1. DETAILED DESCRIPTION OF THE INVENTION

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

[0011] The terms used herein are merely used to describe exemplary embodiments and are not intended to limit the present invention. The singular expressions include the plural expressions unless the context clearly indicates otherwise.

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

[0013] It should be understood that the terms "comprise," "include," "comprise," or "have" are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, but do not preclude the possible presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0014] In the drawings, the thickness of various layers and regions is exaggerated for clarity, and similar parts are designated by the same reference numerals throughout the specification. When a layer, film, region, plate, or other part is said to be "on" or "above" another part, this includes not only the case where it is "directly on" another part, but also the case where there is another part between them. Conversely, when a part is said to be "directly on" another part, it means that there is no other part between them.

[0015] Here, the term "layer" includes not only a shape formed on the entire surface when observed in a plan view, but also a shape formed on a part of the surface.

[0016] The average particle size can be measured by a method well known to those skilled in the art, for example, by using a particle size analyzer or by using a transmission electron microscope image or a scanning electron microscope image. Alternatively, the average particle size can be calculated by measuring using a dynamic light scattering method, counting the number of particles for each particle size range, and then calculating the average particle size. Unless otherwise defined, the average particle size is the diameter (D) of particles whose cumulative volume is 50% by volume in the particle size distribution. 50 ) unless otherwise defined, the average particle size is the diameter (D) of the particle that makes up 50% of the cumulative volume in the particle size distribution obtained by measuring the size (diameter or length of the major axis) of 20 or more particles randomly selected in a scanning electron microscope image. 50 ) may be taken as the average particle size.

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

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

[0019] positive electrode active material In one embodiment, a first positive electrode active material includes a layered lithium nickel-manganese composite oxide and is in the form of secondary particles formed by agglomeration of a plurality of primary particles; a second positive electrode active material includes a layered lithium nickel-manganese composite oxide and is smaller in average particle size (D 50 and a third positive electrode active material in the form of a single particle, the third positive electrode active material comprising a lithium-manganese-rich composite oxide in which the molar ratio of lithium to all metals excluding lithium is 1.1 to 3 and the manganese content relative to 100 molar percent of all metals excluding lithium is 60 molar % or more.

[0020] The cathode active material contains no or only a small amount of expensive cobalt and contains low-cost manganese, thereby reducing costs and increasing mass productivity. It also has excellent high-voltage characteristics, achieving high density and further increasing capacity. The cathode active material has the advantage of achieving high pellet density and high capacity, thereby maximizing the energy density of the battery. Because this cathode active material is low-cost yet satisfies high capacity, high voltage, and high density characteristics, lithium secondary batteries incorporating this material can enable long-distance driving when installed in electric or hybrid vehicles.

[0021] The first positive electrode active material may be included in an amount of 30 wt% to 90 wt%, for example, 35 wt% to 75 wt% or 40 wt% to 60 wt%, based on a total of 100 wt% of the first, second, and third positive electrode active materials. The second positive electrode active material may be included in an amount of 5 wt% to 40 wt%, for example, 10 wt% to 30 wt% or 20 wt% to 26 wt%, and the third positive electrode active material may be included in an amount of 5 wt% to 30 wt%, for example, 7.5 wt% to 25 wt% or 10 wt% to 20 wt%. When mixed in these ratios, high capacity can be achieved while maximizing energy density.

[0022] Lithium nickel-manganese composite oxide The recent surge in the price of the rare metal cobalt has prompted demand for the development of cobalt-free or reduced-content cathode active materials. Among these, cathode active materials with an olivine-based crystal structure, such as lithium iron phosphate (LFP), lithium manganese phosphate (LMP), and lithium manganese iron phosphate (LMFP), or a spinel-based crystal structure, such as lithium manganese oxide (LMO), have limited capacity due to the limited amount of lithium available within their structures. Layered lithium nickel-manganese cathode active materials offer excellent capacity and efficiency characteristics due to their ability to increase the amount of lithium within their structures, making them suitable for high-capacity batteries. However, the removal of cobalt, which plays a key role in the layered structure, reduces structural stability, increases resistance, and hinders long-life performance. Furthermore, the removal of cobalt accelerates side reactions between the cathode active material and electrolyte under high-voltage and high-temperature conditions, resulting in increased gas generation and reduced lifespan.

[0023] Therefore, in one embodiment, a method is proposed for improving the capacity and life characteristics at high voltage of a positive electrode active material by appropriately adjusting the ratio of nickel to manganese in a lithium nickel-manganese composite oxide, introducing other elements such as aluminum in addition to nickel and manganese, or introducing a uniform coating layer by applying an appropriate coating method.

[0024] In the layered lithium nickel-manganese composite oxide, the nickel content may be 60 mol% or more relative to 100 mol% of all metals excluding lithium, for example, 60 mol% to 80 mol%, 65 mol% to 80 mol%, 70 mol% to 80 mol%, 60 mol% to 79 mol%, 60 mol% to 78 mol%, or 60 mol% to 75 mol%, etc. When the nickel content satisfies this range, high capacity can be achieved, and structural stability can be improved even when the cobalt content is reduced.

[0025] The manganese content may be, for example, 15 mol % or more relative to 100 mol % of all metals excluding lithium in the layered lithium nickel-manganese composite oxide, such as 15 mol % to 40 mol %, 15 mol % to 35 mol %, 15 mol % to 30 mol %, or 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.

[0026] For example, the lithium nickel-manganese composite oxide may be a lithium nickel-manganese-aluminum composite oxide containing aluminum in addition to nickel and manganese. When the composite oxide contains aluminum, it is advantageous for maintaining a stable layered structure even when cobalt is excluded from the structure. The aluminum content relative to 100 mol% of the lithium nickel-manganese-aluminum composite oxide may be 0.1 mol% or more, 0.5 mol% or more, or 1 mol% or more, for example, 1 mol% to 3 mol%, 1 mol% to 2.5 mol%, 1 mol% to 2 mol%, or 1.5 mol% to 2.5 mol%. When the aluminum content satisfies the above 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.

[0027] According to one embodiment, the aluminum concentration within the particles containing the lithium nickel-manganese composite oxide may be uniform. This means that the aluminum concentration is not gradient from the center to the surface within the particle, nor is the aluminum concentration higher or lower at the outside than at the inside of the particle, but is uniformly dispersed within the particle. This structure can be achieved by synthesizing the composite oxide using nickel-manganese-aluminum hydroxide as a precursor by using an aluminum raw material in the precursor preparation without additional aluminum doping during the synthesis of the lithium nickel-manganese composite oxide. The particles may be in the form of secondary particles formed by agglomeration of multiple primary particles, and the aluminum content within the primary particles may be the same or similar regardless of the position of the primary particles. That is, by selecting a primary particle at any position in the cross-section of the secondary particle and measuring the aluminum content within the primary particle (not at the interface), the aluminum content can be expressed as the same / similar / uniform regardless of the position of the primary particle, i.e., whether the primary particle is near the center or the surface of the secondary particle. In this structure, a stable layered structure can be maintained even when cobalt is absent or present in only a small amount, and aluminum by-products and aluminum aggregates are not generated, thereby improving the capacity, efficiency, and life characteristics of the positive electrode active material simultaneously.

[0028] The layered lithium nickel-manganese composite oxide can be specifically represented by the following chemical formula 1. [Chemical formula 1] Li a1 Ni x1 Mn y1 Al z1 M 1 w1 O 2-b1 X b1

[0029] 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 1is 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.

[0030] 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. 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.

[0031] 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.

[0032] As an example, the layered lithium nickel-manganese composite oxide may not contain cobalt or may contain a small amount of cobalt, and the content of cobalt based on 100 mol% of the total metal excluding lithium may be 0 mol% to 0.01 mol%.

[0033] The particles containing the layered lithium nickel-manganese composite oxide may be in the form of secondary particles formed by agglomeration of multiple primary particles, or single particles, or a combination thereof. The secondary particles and single particles may be spherical, ellipsoidal, polyhedral, or irregular in shape, and the primary particles that make up the secondary particles may be spherical, ellipsoidal, plate-shaped, or a combination thereof.

[0034] Coating layer The first positive electrode active material and / or the second positive electrode active material may include core particles containing a layered lithium nickel-manganese composite oxide, and a coating layer located on the surface of the core particles and containing Al, B, Mg, Ti, V, W, Y, Zr, or a combination thereof.

[0035] Lithium nickel-manganese composite oxides are susceptible to chemical attack from components in the electrolyte when the battery is operated under high voltage or high temperature conditions, and side reactions with the electrolyte can occur frequently. This can result in a large amount of gas generation, which can reduce the battery life and safety. However, by introducing a coating layer according to one embodiment, this problem can be solved.

[0036] Layered lithium nickel-manganese composite oxides have significantly different residual lithium content on the particle surface than oxides of other compositions, such as lithium nickel-cobalt-manganese composite oxides, lithium nickel-cobalt-aluminum composite oxides, and lithium cobalt-based oxides. This difference in surface properties makes it difficult to form a uniform, well-formed coating layer using existing coating methods. Therefore, in one embodiment, a uniform coating layer can be formed on the first and / or second cathode active material by (i) first preparing a coating solution in which salt is completely dissolved by adding and mixing coating materials into an aqueous solvent using a salt-dissolution method, (ii) adding and mixing core particles into this coating solution, and (iii) subsequently removing the solvent, drying, and heat-treating the solution. Although this is a salt-dissolution wet coating method, it can also be considered a pre-addition method in which the salt, the coating material, is first completely dissolved and then the active material particles are added. This method successfully forms a uniform, thin coating layer on the surface of the layered lithium nickel-manganese composite oxide.

[0037] This coating method can further increase the content of coating elements on the surface of the active material compared to conventional dry methods or post-addition wet methods. For example, the coating content on the surface of the first positive electrode active material and / or the second positive electrode active material, as measured through EP-EDS analysis, may be 5 at% to 35 at% relative to 100 at% of the total metals excluding lithium on the surface, e.g., 5 at% to 30 at%, 5 at% to 25 at%, or 10 at% to 20 at%. Within this content range, the coating layer can effectively improve high-voltage characteristics without increasing the resistance of the positive electrode active material.

[0038] For example, the coating layer may be in the form of a film that continuously surrounds the surface of the core particle, or in the form of a shell that surrounds the entire surface of the core particle. This is different from a structure in which only a portion of the surface of the core particle is partially coated. According to one embodiment, the coating layer may be formed to completely surround the surface of the core particle, but with a very thin and uniform thickness. As a result, the cathode active material does not increase in resistance or decrease in capacity, improves structural stability, effectively suppresses side reactions with the electrolyte, reduces gas generation under high voltage and high temperature conditions, and achieves long-life characteristics.

[0039] According to the method, the thickness of the coating layer of the first positive electrode active material and / or the second positive electrode active material may be 5 nm to 200 nm, e.g., 5 nm to 150 nm, 5 nm to 100 nm, 5 nm to 80 nm, 5 nm to 50 nm, or 10 nm to 50 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 can be measured, for example, by SEM, TEM, TOF-SIMS, XPS, or EDS analysis, for example, by EDS line profile analysis of a cross section of the positive electrode active material.

[0040] According to one embodiment, the coating layer has a 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 cathode active material particle may be 20% or less, 18% or less, or 15% or less. Here, the coating thickness deviation refers to the thickness of the coating layer within a single cathode active material particle. For example, the coating thickness deviation may be calculated by measuring the thickness at approximately 10 points in an electron microscope image of the cross section of a single cathode active material particle, calculating the arithmetic mean, and then dividing the absolute value of the difference between one data point and the arithmetic mean value by the arithmetic mean value and multiplying the result by 100. Having the thickness deviation or standard deviation of the coating layer within the above range indicates that a uniformly thick coating layer is formed on the surface of the cathode active material particle in a good shape. This improves the structural stability of the cathode active material, effectively suppresses side reactions with the electrolyte, and minimizes resistance increases and capacity reductions due to the coating.

[0041] The content of the coating element relative to 100 mol% of all metals excluding lithium in the entire first positive electrode active material and / or second positive electrode active material varies depending on the type of coating element, but may be approximately 0.01 mol% to 5 mol%, for example, 0.05 mol% to 3 mol%, or 0.1 mol% to 2 mol%.

[0042] For example, when an Al coating layer is introduced, the Al content of the coating layer may be 0.1 mol % to 3.0 mol % relative to 100 mol % of all metals excluding lithium in the entire first positive electrode active material and / or second positive electrode active material, such as 0.1 mol % to 2.0 mol %, 0.5 mol % to 1.5 mol %, or 0.7 mol % to 1.3 mol %.

[0043] When an Al coating layer is introduced, the coating layer may include, for example, a layered aluminum compound, such as aluminum oxide, lithium aluminum oxide, or a combination thereof, and may include, for example, LiAlO2.

[0044] First positive electrode active material In one embodiment, the first positive electrode active material includes the layered lithium nickel-manganese composite oxide, characterized in that it has a secondary particle form formed by agglomeration of a plurality of primary particles, where the secondary particles may be spherical, ellipsoidal, polyhedral, or irregular in shape, and the primary particles may be spherical, ellipsoidal, plate-shaped, or a combination thereof.

[0045] The average particle size (D 50 The average particle size (D) may be 10 μm to 25 μm, for example, 11 μm to 20 μm, or 12 μm to 18 μm. 50 ) may be obtained by measuring the sizes (diameter or length of the major axis) of 20 or more particles randomly selected in a scanning electron microscope image of the positive electrode active material to obtain a particle size distribution, and taking the diameter of particles whose cumulative volume is 50% by volume in the particle size distribution as the average particle size.

[0046] The first positive electrode active material may include a core particle in the form of a secondary particle formed by aggregating a plurality of primary particles, and a coating layer disposed on the surface of the core particle and containing Al, B, Mg, Ti, V, W, Y, Zr, or a combination thereof.

[0047] For example, the coating layer of the first positive electrode active material may include Al, Zr, or a combination thereof, and the coating layer of the first positive electrode active material may include Al, and the Al content of the coating layer may be 0.5 mol% to 2 mol% relative to 100 mol% of all metals excluding lithium in the first positive electrode active material. This is an optimal coating component for the first positive electrode active material, and can further improve capacity characteristics and life characteristics at high voltages.

[0048] Second positive electrode active material In one embodiment, the second positive electrode active material includes the layered lithium nickel-manganese composite oxide and has an average particle size (D 50) and is characterized by being in the form of a single particle, wherein the single particle may be spherical, ellipsoidal, plate-shaped, irregularly shaped, or a combination thereof.

[0049] The average particle size (D 50 ) may be 0.5 μm to 8 μm, for example, 1 μm to 7 μm, or 1 μm to 5 μm. 50 ) may be obtained by measuring the sizes (diameter or length of the major axis) of 20 or more particles randomly selected in a scanning electron microscope image of the positive electrode active material to obtain a particle size distribution, and taking the diameter of particles whose cumulative volume is 50% by volume in the particle size distribution as the average particle size.

[0050] The second positive electrode active material may include a core particle in the form of a single particle, and a coating layer located on the surface of the core particle and containing Al, B, Mg, Ti, V, W, Y, Zr, or a combination thereof. For example, the coating layer of the second positive electrode active material may include Al, Y, or a combination thereof. The Al content of the coating layer may be 0.1 mol% to 1 mol% relative to 100 mol% of all metals excluding lithium in the second positive electrode active material, and the Y content of the coating layer may be 0.01 mol% to 0.5 mol% relative to 100 mol% of all metals excluding lithium in the second positive electrode active material. This is an optimal coating component for the second positive electrode active material, and can further improve capacity characteristics and life characteristics at high voltages.

[0051] The first positive electrode active material may be included in an amount of 60 wt% to 95 wt%, or 70 wt% to 90 wt%, and the second positive electrode active material may be included in an amount of 5 wt% to 40 wt%, or 10 wt% to 30 wt%, based on a total weight of the first and second positive electrode active materials (100 wt%). When mixed in these ratios, high capacity can be achieved while maximizing energy density.

[0052] Third positive electrode active material The third positive electrode active material is characterized by comprising a lithium-manganese-rich composite oxide (LMR) having a lithium to total metal excluding lithium molar ratio of 1.1 to 3 and a manganese content of 60 mol% or more relative to 100 mol% of total metal excluding lithium, and is in the form of a single particle, where the single particle may be spherical, ellipsoidal, plate-shaped, irregular, or a combination thereof.

[0053] LMR material is a layered structure cathode active material that contains an excess amount of lithium and a relatively high content of manganese. It not only generates capacity through the oxidation-reduction of existing transition metals, but also applies a new principle of oxygen oxidation-reduction to generate high capacity. At the same time, it has a high proportion of low-cost manganese, making it garnering attention as an ultra-low-cost next-generation cathode active material.

[0054] In the third positive electrode active material, the molar ratio of lithium to all metals excluding lithium is 1.1 to 3, and may be, for example, 1.2 to 2.5, 1.3 to 2.3, or 1.5 to 2.1. Furthermore, in the third positive electrode active material, the content of manganese relative to 100 mol% of all metals excluding lithium may be 60 mol% or more, and may be, for example, 60 mol% to 90 mol%, 60 mol% to 80 mol%, 60 mol% to 75 mol%, 60 mol% to 70 mol%, or 62 mol% to 68 mol%.

[0055] The lithium-manganese-rich composite oxide of the third positive electrode active material can be represented by, for example, the following chemical formula 2. [Chemical formula 2] Li 1+x2 (Ni y2 Mn z2 M 2 1-y2-z2 ) 1-x2 O 2-b2 X b2

[0056] In Chemical Formula 2, 0.04≦x2≦0.5, 0.1≦y2≦0.5, 0.5≦z2≦0.9, and 0≦b2≦0.1; M 2is one or more elements selected from Al, 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.

[0057] In Chemical Formula 2, for example, 0.05≦x2≦0.4, or 0.06≦x2≦0.3 may be satisfied, and 0.2≦y2≦0.4 and 0.6≦z2≦0.8 may be satisfied, or 0.3≦y2≦0.4 and 0.6≦z2≦0.7 may be satisfied.

[0058] The third positive electrode active material is in the form of a single particle, and the average particle size (D 50 ) may be smaller than the average particle size of the second positive electrode active material, for example, 0.1 μm to 5 μm, 0.5 μm to 4 μm, or 1 μm to 3 μm. That is, the positive electrode may be a mixture of the first positive electrode active material, which is a large particle, the second positive electrode active material, which is a medium particle, and the third positive electrode active material, which is a small particle, thereby maximizing the energy density and effectively improving the high voltage characteristics. Here, the average particle size (D 50 ) may be obtained by measuring the sizes (diameter or length of the major axis) of 20 or more particles randomly selected in a scanning electron microscope image of the positive electrode active material to obtain a particle size distribution, and taking the diameter of particles whose cumulative volume is 50% by volume in the particle size distribution as the average particle size.

[0059] In the lithium-manganese-rich composite oxide of the third positive electrode active material, the content of cobalt relative to 100 mol % of all metals excluding lithium may be 0 mol % to 0.01 mol %.

[0060] The third positive electrode active material may have a surface residual lithium content of 0.3 wt% or less, for example, 0.2 wt% or less, 0.1 wt% or less, or 0.001 wt% to 0.1 wt%, which distinguishes it from high-nickel materials with a nickel content exceeding 70 mol%.

[0061] The third positive electrode active material may have an a-lattice constant of 2.865 Å or more, for example, 2.865 Å or more, 2.870 Å or more, or 2.875 Å to 2.885 Å, as determined by X-ray diffraction analysis (XRD). For example, the a-lattice constant of the positive electrode active material may be 2.875 Å or more. The ratio of the c-lattice constant to the a-lattice constant may be 4.968 or less, for example, 4.965 or less, 4.960 or less, or 4.955 to 4.965. When the a-lattice constant and the ratio of the c-lattice constant to the a-lattice constant of the positive electrode active material satisfy the above ranges, the voltage drop problem during charge and discharge caused by the third positive electrode active material can be effectively alleviated, energy density can be improved, and capacity and life characteristics in the high-voltage region can be improved.

[0062] Pellet Density The positive electrode active material according to one embodiment can achieve a high pellet density. For example, the pellet density of the positive electrode active material may be 3.0 g / cc to 3.7 g / cc, e.g., 3.1 g / cc to 3.6 g / cc, 3.1 g / cc to 3.5 g / cc, 3.3 g / cc to 3.7 g / cc, or 3.4 g / cc to 3.6 g / cc. A lithium secondary battery using such a positive electrode active material can achieve a high energy density.

[0063] The pellet density can be measured by the following method. After weighing 3 g of the positive electrode active material, a mold (area: 1.298 cm) was placed in the mold. 2 ) and gradually insert the mold bar into the mold body. The mold set is placed in a hydraulic press and pressed at 4 ton (Metric ton) for 30 seconds, after which the height is measured and the pellet density can be measured.

[0064] positive electrode In one embodiment, a positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, the positive electrode active material layer including the positive electrode active material described above. The positive electrode active material layer may further include other positive electrode active materials in addition to the positive electrode active materials described above. The positive electrode active material layer may also optionally include a binder, a conductive material, or a combination thereof.

[0065] According to one embodiment, the loading level of the positive electrode active material layer is 10 mg / cm 2 ~40mg / cm 2 may be, for example, 10 mg / cm 2 ~30mg / cm 2 or 10 mg / cm 2 ~20mg / cm 2 In addition, the density of the positive electrode active material layer in the final rolled positive electrode may be 3.3 g / cc to 3.7 g / cc, for example, 3.3 g / cc to 3.6 g / cc or 3.4 g / cc to 3.58 g / cc. When using a positive electrode active material according to an embodiment, it is advantageous to achieve such a loading level and positive electrode density, and a positive electrode satisfying the loading level and positive electrode density in the above ranges is suitable for realizing a lithium secondary battery with a high capacity and a high energy density.

[0066] binder The binder serves to firmly adhere the positive electrode active material particles to each other and to firmly adhere the positive electrode active material to the current collector. Representative examples of binders include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, nylon, etc.

[0067] Conductive material The conductive material is used to impart conductivity to the electrode, and any electron-conductive material that does not cause chemical changes in the battery that is constructed can be used. Examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0068] The content of the binder and the conductive material may be 0.5% by weight to 5% by weight, respectively, relative to 100% by weight of the positive electrode active material layer.

[0069] The positive electrode current collector can be made of Al, but is not limited to this.

[0070] Lithium secondary battery In one embodiment, a lithium secondary battery is provided that includes the positive electrode, the negative electrode, and the electrolyte. For example, the lithium secondary battery may include a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte.

[0071] Lithium secondary batteries can be classified into cylindrical, prismatic, pouch, and coin types depending on their shape. FIGS. 1 to 4 are schematic diagrams illustrating a lithium secondary battery according to an embodiment, with FIG. 1 illustrating a circular battery, FIG. 2 illustrating a prismatic battery, and FIGS. 3 and 4 illustrating pouch-type battery shapes. Referring to FIGS. 1 to 4, a lithium secondary battery 100 may include an electrode assembly 40 having a separator 30 interposed between a positive electrode 10 and a negative electrode 20, and a case 50 housing the electrode assembly 40. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte (not shown). The lithium secondary battery 100 may include a sealing member 60 that seals the case 50, as shown in FIG. 1. Also, as shown in FIG. 2, the lithium secondary battery 100 may include a positive electrode lead tab 11, a positive electrode terminal 12, a negative electrode lead tab 21, and a negative electrode terminal 22. As shown in FIGS. 3 and 4, the lithium secondary battery 100 may include electrode tabs 70, i.e., a positive electrode tab 71 and a negative electrode tab 72, which serve as electrical paths for conducting the current generated in the electrode assembly 40 to the outside.

[0072] The lithium secondary battery according to one embodiment is suitable for being rechargeable at a high voltage or being driven at a high voltage, and can be said to be a battery with improved characteristics under high voltage conditions.

[0073] The lithium secondary battery includes a third positive electrode active material that is a lithium-manganese-rich material. To utilize the reversible positive electrode capacity of the third positive electrode active material, the initial charge voltage must be 4.60 V or higher. For example, the initial charge can be performed at 4.65 V. The upper limit voltage for subsequent charges is lower than the upper limit voltage for the initial charge. Since the lithium secondary battery according to an embodiment is designed to operate in a high voltage range, the charge can be performed in a voltage range of 4.45 V or higher. For example, the charge voltage after the second cycle can be 4.45 V or higher, such as 4.45 V to 4.6 V, 4.45 V to 4.55 V, or 4.45 V to 4.50 V. By using the positive electrode active material according to an embodiment, the lithium secondary battery can significantly reduce gas generation even when charged at a high voltage, achieving high capacity and long life characteristics.

[0074] negative electrode The negative electrode may include a current collector and a negative electrode active material layer located on the current collector. The negative electrode active material layer includes a negative electrode active material and may further include a binder, a conductive material, or a combination thereof.

[0075] negative electrode active material The negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, a lithium metal alloy, a material capable of being doped with and dedoped from lithium, or a transition metal oxide.

[0076] The material capable of reversibly intercalating / deintercalating 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 amorphous, plate-like, flake-like, spherical, or fibrous graphite, such as natural graphite or artificial graphite. Examples of the amorphous carbon include soft carbon, hard carbon, mesophase pitch carbide, and calcined coke.

[0077] The lithium metal alloy may be 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.

[0078] As the substance capable of doping and undoping lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used. As the Si-based negative electrode active material, silicon, a silicon-carbon composite, SiOx (0 < x ≦ 2), a Si-Q alloy (where Q is an element selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements (excluding Si), group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof, for example, Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof), or a combination thereof may be used. As the Sn-based negative electrode active material, Sn, SnO2, a Sn alloy, or a combination thereof may be used.

[0079] The silicon-carbon composite may be a composite of silicon and amorphous carbon. The average particle size (D 50 ) may be, for example, 0.5 μm to 20 μm. According to one embodiment, the silicon-carbon composite may be in a form in which silicon particles are coated with amorphous carbon on the surface of the silicon particles. For example, it may 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 may also be located between the primary silicon particles, and for example, the primary silicon particles may be coated with amorphous carbon. The secondary particles may exist dispersed in an amorphous carbon matrix.

[0080] The silicon-carbon composite may further contain crystalline carbon. For example, the silicon-carbon composite may include a core containing crystalline carbon and silicon particles and an amorphous carbon coating layer located on the surface of the core. The crystalline carbon may be artificial graphite, natural graphite, or a combination thereof. Examples of the amorphous carbon include soft carbon, hard carbon, mesophase pitch carbide, and calcined coke.

[0081] When the silicon-carbon composite contains silicon and amorphous carbon, the content of silicon may be 10% to 50% by weight based on 100% by weight of the silicon-carbon composite, and the content of amorphous carbon may be 50% to 90% by weight. Also, 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.

[0082] Also, the thickness of the amorphous carbon coating layer may be 5 nm to 100 nm. The average particle size (D 50 ) of the silicon particles (primary particles) may be 10 nm to 1 μm, or 10 nm to 200 nm. The silicon particles may exist alone as silicon, or in the form of a silicon alloy, or in an oxidized form. The oxidized form of silicon can be represented as 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 size (D 50 ) means the diameter of the particle with a cumulative volume of 50% by volume in the particle size distribution.

[0083] The Si-based negative electrode active material or the Sn-based negative electrode active material can be used by mixing with a carbon-based negative electrode active material. When the Si-based negative electrode active material or the Sn-based negative electrode active material and the carbon-based negative electrode active material are mixed and used, the mixing ratio may be 1:99 to 90:10 by weight.

[0084] binder The binder serves to firmly adhere the negative active material particles to each other and to the current collector. The binder may be a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0085] Non-aqueous binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

[0086] The water-based binder may be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0087] When an aqueous binder is used as the negative electrode binder, a cellulose-based compound that can impart viscosity may be further included. The cellulose-based compound may be a mixture of one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or alkali metal salts thereof. The alkali metal may be sodium, potassium, or lithium.

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

[0089] Conductive material The conductive material is used to impart conductivity to the electrode, and any electron-conductive material that does not cause chemical changes in the battery that is constructed can be used. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0090] The content of the negative electrode active material may be 95 wt% to 99.5 wt% relative to 100 wt% of the negative electrode active material layer, and the content of the binder may be 0.5 wt% to 5 wt% relative to 100 wt% of the negative electrode active material layer. For example, the negative electrode active material layer may contain 90 wt% to 99 wt% of the negative electrode active material, 0.5 wt% to 5 wt% of the binder, and 0.5 wt% to 5 wt% of the conductive material.

[0091] 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.

[0092] electrolyte The electrolyte for a lithium secondary battery may be, for example, an electrolytic solution, which may include a non-aqueous organic solvent and a lithium salt.

[0093] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can migrate, and may be a carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based solvent, an aprotic solvent, or a combination thereof.

[0094] Examples of carbonate solvents that can be used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. Examples of ester solvents that can be used include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, caprolactone, etc. Examples of ether solvents that can be used include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran. Examples of ketone solvents that can be used include cyclohexanone. Examples of alcohol solvents that can be used include ethyl alcohol and isopropyl alcohol. Examples of aprotic solvents that can be used include nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, which may contain a double bond, an aromatic ring, or an ether group); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane and 1,4-dioxolane; and sulfolanes.

[0095] The non-aqueous organic solvents can be used alone or in combination of two or more kinds. When two or more kinds are used in combination, the mixing ratio can be appropriately adjusted depending on the desired battery performance, which should be widely understood by those working in the field.

[0096] When a carbonate-based solvent is used, a cyclic carbonate and a chain carbonate can be mixed and used, and the cyclic carbonate and the chain carbonate can be mixed in a volume ratio of 1:1 to 1:9.

[0097] The non-aqueous organic solvent may further include an aromatic hydrocarbon organic solvent. For example, a carbonate solvent and an aromatic hydrocarbon organic solvent may be mixed in a volume ratio of 1:1 to 30:1.

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

[0099] Representative examples of the ethylene carbonate compounds include fluoroethylene carbonate, difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, and cyanoethylene carbonate.

[0100] Lithium salts are substances dissolved in organic solvents and act as a source of lithium ions in the battery, enabling basic lithium secondary battery operation and facilitating the movement of lithium ions between the positive and negative electrodes. Representative examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide; LiFSI), LiC4F9SO3, and LiN(C x F 2x+1 SO2)(C y F2y+1 SO2) (x and y are integers of 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFBOP), and lithium bis(oxalato)borate (LiBOB).

[0101] The lithium salt concentration is preferably within the range of 0.1 M to 2.0 M. When the lithium salt concentration is within this range, the electrolyte has appropriate ionic conductivity and viscosity, thereby exhibiting excellent performance and allowing lithium ions to migrate effectively.

[0102] Separator Depending on the type of lithium secondary battery, a separator may be present between the positive and negative electrodes. Such separators can be made of polyethylene, polypropylene, polyvinylidene fluoride, or multilayer films of two or more of these materials. Of course, mixed multilayer films such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator can also be used.

[0103] The separator may include a porous substrate and a coating layer including an organic material, an inorganic material, or a combination thereof located on one or both sides of the porous substrate.

[0104] The porous substrate may be a polymer membrane formed of any one polymer selected from polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyether ketone, polyaryl ether ketone, polyetherimide, polyamide imide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon (registered trademark), and polytetrafluoroethylene, or a copolymer or mixture of two or more of these.

[0105] The porous substrate can have a thickness of about 1 μm to 40 μm, for example, 1 μm to 30 μm, 1 μm to 20 μm, 5 μm to 15 μm, or 10 μm to 15 μm.

[0106] The organic material may include a (meth)acrylic copolymer including a first structural unit derived from (meth)acrylamide 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.

[0107] The inorganic material may include, but is not limited to, inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof. The average particle size (D 50 ) may be 1 nm to 2000 nm, for example, 100 nm to 1000 nm, or 100 nm to 700 nm.

[0108] The organic material and the inorganic material may be mixed in one coating layer, or may be stacked in a coating layer containing an organic material and a coating layer containing an inorganic material.

[0109] The thickness of each of the coating layers may be 0.5 μm to 20 μm, for example, 1 μm to 10 μm, or 1 μm to 5 μm.

[0110] Examples of the present invention and comparative examples are described below. The following examples are merely illustrative of the present invention, and the present invention is not limited to the following examples. [Example]

[0111] 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 845°C for 8 hours in an oxygen atmosphere to obtain a composition of Li 1.05 Ni 0.75 Mn 0.23 Al 0.02 O2 and the average particle size (D 50 A first lithium nickel-manganese composite oxide in the form of secondary particles having a particle size of about 14 μm was prepared.

[0112] Aluminum sulfate was added to a distilled water solvent and stirred at 350 rpm for 5 minutes to prepare a coating solution. The salt was confirmed to be completely dissolved in the coating solution, making it colorless and transparent. 500 g of the first lithium nickel-manganese composite oxide prepared was added to the continuously stirred coating solution for 1.5 minutes and stirred for approximately 45 minutes. The aluminum content in the aluminum sulfate was designed to be 1.0 mol% relative to 100% by weight of the total metals excluding lithium in the final large particles. The pH of the supernatant after stirring was confirmed to be 5.5. The solvent was removed from the mixed solution using an aspirator and filter press, and the solution was dried in vacuum at 190°C to obtain a coated product.

[0113] The coated product was subjected to a second heat treatment at 750° C. for 8 hours in an oxygen atmosphere to prepare a first positive electrode active material.

[0114] 5 and 6 are SEM images of the first positive electrode active material.

[0115] (2) Preparation of the second positive electrode active material Ni 0.75 Mn 0.23 Al 0.02 (OH)2, LiOH, and Al2O3 were mixed in a molar ratio of 1:1:0.02 and subjected to a first heat treatment at 850°C for 8 hours in an oxygen atmosphere to obtain a LiNi 0.75 Mn 0.23 Al 0.02 O2 and the average particle size (D 50 A second lithium nickel-manganese composite oxide in the form of a single particle having a particle size of about 3 μm was prepared.

[0116] Aluminum sulfate and yttrium nitrate were added to a distilled water solvent and mixed, and then the second lithium nickel-manganese composite oxide was added and mixed for approximately 45 minutes. The aluminum content in the aluminum sulfate was designed to be 0.4 mol% based on 100% by weight of the total metals excluding lithium in the final fine particles, and the yttrium content in the yttrium nitrate was designed to be 0.05 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 positive electrode active material.

[0117] 7 and 8 are SEM images of the second positive electrode active material.

[0118] (3) Production of the third positive electrode active material Ni 0.25 Mn 0.75 (OH)2 and LiOH were mixed so that the molar ratio of Li / (Ni+Mn) was about 1.5, and the mixture was heat-treated in an oxygen atmosphere at 950°C for 24 hours to obtain a lithium-manganese-rich composite oxide (Li 1.5 Ni 0.25 Mn 0.75 O2) and the average particle size (D 50 A third positive electrode active material having a single particle shape and a particle size of about 2 μm was prepared.

[0119] 9 and 10 are SEM images of the third positive electrode active material.

[0120] (4) Production of final positive electrode active material The final positive electrode active material was prepared by mixing 66.5 wt % of the first positive electrode active material, 28.5 wt % of the second positive electrode active material, and 5 wt % of the third positive electrode active material.

[0121] 2. Lithium secondary battery manufacturing 98.5 wt % of the prepared final positive electrode active material, 1.0 wt % of polyvinylidene fluoride binder, and 0.5 wt % of carbon nanotube conductive material were mixed to prepare a positive electrode active material layer slurry, which was then coated on an aluminum foil current collector, dried, and rolled to prepare a positive electrode.

[0122] 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.

[0123] 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.

[0124] Example 2 A cathode active material and a lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that the final cathode active material was manufactured by mixing 63 wt % of the first cathode active material, 27 wt % of the second cathode active material, and 10 wt % of the third cathode active material.

[0125] Example 3 A cathode active material and a lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that the final cathode active material was manufactured by mixing 59.5 wt % of the first cathode active material, 25.5 wt % of the second cathode active material, and 15 wt % of the third cathode active material.

[0126] Example 4 A cathode active material and a lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that the final cathode active material was manufactured by mixing 56 wt % of the first cathode active material, 24 wt % of the second cathode active material, and 20 wt % of the third cathode active material.

[0127] Example 5 A cathode active material and a lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that the final cathode active material was manufactured by mixing 52.5 wt % of the first cathode active material, 22.5 wt % of the second cathode active material, and 25 wt % of the third cathode active material.

[0128] Example 6 A cathode active material and a lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that the final cathode active material was manufactured by mixing 49 wt % of the first cathode active material, 21 wt % of the second cathode active material, and 30 wt % of the third cathode active material.

[0129] Comparative Example 1 A positive electrode active material and a lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that only the first positive electrode active material and the second positive electrode active material were used as the final positive electrode active material.

[0130] Comparative Example 2 A positive electrode active material and a lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that only the third positive electrode active material was used alone as the final positive electrode active material.

[0131] The manufacturing methods of Examples 1 to 6 and Comparative Examples 1 and 2 are summarized in Table 1 below.

[0132] [Table 1]

[0133] Evaluation example 1: Positive electrode mixture density Table 2 shows the mixture density as a function of rolling strength for the positive electrode plates produced in Examples 1 to 6 and Comparative Examples 1 and 2.

[0134] [Table 2]

[0135] Referring to Table 2, it can be seen that the positive electrodes manufactured in Examples 1 to 6 have higher mixture densities than the comparative example.

[0136] Evaluation example 2: Battery performance evaluation The lithium secondary batteries prepared in Examples 1 to 6 and Comparative Examples 1 and 2 were initially charged at 4.65 V, and then the voltage was reduced to 4.45 V and charged. That is, the lithium secondary batteries prepared in Examples 1 to 6 and Comparative Examples 1 and 2 were charged at a constant current of 0.2 C at 25°C to 4.65 V, and then the voltage was maintained until the current value reached 0.05 C, and then discharged at a constant current of 0.2 C to 2.5 V, thereby carrying out a first charge-discharge cycle. Next, the batteries were charged at a constant current of 0.2 C at 25°C to 4.45 V, and then the voltage was maintained until the current value reached 0.05 C, and then discharged at a constant current of 0.2 C to 2.5 V, thereby carrying out a second charge-discharge cycle. The second discharge capacity is shown in Table 3 below as "4.45 V Capacity."

[0137] Next, the cycle of charging at 1.0 C and discharging at 1.0 C in the voltage range of 3.0 V to 4.45 V at 45°C was repeated 50 times or more, and the ratio of the 50th cycle discharge capacity to the second discharge capacity was calculated and shown as "4.45 V life" in Table 3 below.

[0138] Next, the cells were charged and discharged at a rate of 0.2 C / 0.2 C at 25°C in the voltage range of 3.0 V to 4.45 V to calculate the energy density. The energy density was calculated using the formula {average driving voltage (V) × capacity (Ah) / cell weight (kg)}, where capacity is the product of the positive electrode weight (g) and the discharge capacity (mAh / g).

[0139] [Table 3]

[0140] Referring to Table 3, it can be seen that Examples 1 to 6 have the same or improved lifespan characteristics as Comparative Example 1, and have higher energy densities and improved cathode utilization rates. However, Comparative Example 2 has a higher energy density than the Examples, but as described in Evaluation Example 1, Comparative Example 2 has the disadvantage of having a very low composite density. Therefore, it can be seen that the lithium secondary batteries fabricated in Examples 1 to 6 are generally improved compared to the lithium secondary batteries fabricated in Comparative Examples 1 and 2.

[0141] Although the preferred embodiments have been described in detail above, the scope of the present invention is not limited to these, and various modifications and improvements made by those skilled in the art using the basic concepts defined in the following claims also fall within the scope of the present invention. [Explanation of symbols]

[0142] 100: Lithium secondary battery 10: Positive electrode 11: Positive lead tap 12: Positive terminal 20: Negative electrode 21: Negative lead tap 22: Negative terminal 30: Separator 40: Electrode assembly 50: Case 60: Sealing material 70: Electrode tap 71: Positive tap 72: Negative tap

Claims

1. a first positive electrode active material including a layered lithium nickel-manganese composite oxide in the form of secondary particles formed by agglomeration of a plurality of primary particles; The first positive electrode active material contains a layered lithium nickel-manganese composite oxide and has an average particle size (D 50 a second positive electrode active material having a single particle form; and a third positive electrode active material in the form of single particles, comprising a lithium-manganese-rich composite oxide in which the molar ratio of lithium to all metals excluding lithium is 1.1 to 3 and the manganese content is 60 mol % or more relative to 100 mol % of all metals excluding lithium; A positive electrode active material comprising:

2. 2. The positive electrode active material according to claim 1, wherein the first positive electrode active material is included in an amount of 30% by weight to 90% by weight, the second positive electrode active material is included in an amount of 5% by weight to 40% by weight, and the third positive electrode active material is included in an amount of 5% by weight to 30% 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.

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

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

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

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

7. The layered lithium nickel-manganese composite oxide is represented by Chemical Formula 1, and is the positive electrode active material according to claim 1: [Chemical formula 1] Li a1 Ni x1 Mn y1 Al z1 M 1 w1 O 2-b1 X b1 In the above chemical formula 1, 0.9≦a1≦1.8, 0.6≦x1≦0.8, 0.1≦y1≦0.4, 0≦z1≦0.03, 0≦w1≦0.3, 0.9≦x1+y1+z1+w1≦1.1, and 0≦b1≦0.1; M 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.

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

9. The first positive electrode active material comprises a core particle in the form of a secondary particle formed by aggregating a plurality of primary particles; and The positive electrode active material according to claim 1 , further comprising: a coating layer containing Al located on a surface of the core particle.

10. The average particle size (D 50 2. The positive electrode active material according to claim 1, wherein the particle size is 0.5 μm to 8 μm.

11. The second positive electrode active material comprises a core particle having a single particle form; and 2. The positive electrode active material of claim 1, further comprising: a coating layer located on a surface of the core particle, the coating layer comprising Al, Y, or a combination thereof.

12. The positive electrode active material according to claim 1, wherein the lithium-manganese-rich composite oxide of the third positive electrode active material is represented by Chemical Formula 2: [Chemical formula 2] Li 1+x2 (N y2 Mn z2 M 2 1-y2-z2 ) 1-x2 O 2-b2 X b2 In Chemical Formula 2, 0.04≦x2≦0.5, 0.1≦y2≦0.5, 0.5≦z2≦0.9, and 0≦b2≦0.1; 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, Y, and Zr, and X is one or more elements selected from F, P, and S.

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

14. The average particle size (D 50 2. The positive electrode active material according to claim 1, wherein the particle size is 0.1 μm to 5 μm.

15. The average particle size (D 50 ) is the average particle size (D 50 2. The positive electrode active material of claim 1, wherein the σ is less than 0.

16. a positive electrode current collector, and a positive electrode active material layer located on the positive electrode current collector Including, The positive electrode active material layer comprises the positive electrode active material according to any one of claims 1 to 15.

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

18. The positive electrode according to claim 16 . a negative electrode, and electrolyte A lithium secondary battery comprising:

19. The upper limit voltage for the first charge is 4.60 V or more. The lithium secondary battery according to claim 18, wherein the upper limit voltage of subsequent charging is lower than the upper limit voltage of the initial charging and is 4.45 V or higher.

20. 20. The lithium secondary battery of claim 18, wherein the negative electrode comprises a carbon-based negative electrode active material, lithium metal, an alloy of lithium metal, a silicon-based negative electrode active material, or a combination thereof.

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