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

Abstract

To provide a positive electrode active material in which economical efficiency, high capacity and long life characteristics are secured, and high voltage characteristics and high temperature characteristics are improved, a method for producing the same, and a positive electrode and a lithium secondary battery including the same.SOLUTION: The positive electrode active material includes core particles containing a layered lithium-nickel-manganese-based composite oxide, and an yttrium-containing coating layer positioned on surfaces of the core particles, wherein a yttrium content on surfaces of the positive electrode active material measured by energy profiling energy dispersive spectrometry (EP-EDS) is 0.1 at% to 5.0 at% with respect to 100 at% of all metals excluding lithium. A lithium secondary battery to which the positive electrode active material is applied may exhibit high initial charge and discharge capacity and efficiency even under high voltage driving conditions, may implement long-life characteristics, and may effectively suppress a gas generation problem due to high voltage and high temperature driving.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

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

[0003] Various positive electrode active materials have been investigated to realize lithium secondary batteries suitable for these applications. Among these, lithium nickel oxide, lithium nickel manganese cobalt composite oxide, lithium nickel cobalt aluminum composite oxide, and lithium cobalt oxide are commonly used as positive electrode active materials. However, while demand for large-sized, high-capacity, and high-energy density lithium secondary batteries has rapidly increased in recent years, the supply of positive electrode active materials containing the rare metal cobalt is expected to be in short supply. In other words, because cobalt is expensive and its remaining reserves are limited, there is a need to develop positive electrode active materials that do not contain cobalt or that have a reduced cobalt content. Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention provides a cathode active material containing a lithium nickel-manganese composite oxide, which is economical, has high capacity, and has long life characteristics, and has improved high-voltage characteristics and high-temperature characteristics; a method for producing the cathode active material; and a cathode and a lithium secondary battery including the cathode active material. [Means for solving the problem]

[0005] In one embodiment of the present invention, there is provided a cathode active material including: core particles containing a layered lithium nickel-manganese composite oxide; and an yttrium-containing coating layer located on the surface of the core particles; wherein the yttrium content on the surface of the cathode active material, as measured by energy profiling energy dispersive spectroscopy (EP-EDS), is 0.1 at% to 5.0 at% relative to 100 at% of all metals excluding lithium.

[0006] In another embodiment of the present invention, there is provided a method for producing a cathode active material, including: (i) preparing core particles containing a layered lithium nickel-manganese composite oxide; (ii) adding an yttrium raw material to an aqueous solvent and mixing them to prepare a coating solution; (iii) adding the core particles to the coating solution and mixing them to prepare a mixed solution; and (iv) removing the aqueous solvent from the mixed solution, drying the resultant, and heat-treating it to obtain a cathode active material.

[0007] In yet another embodiment of the present invention, there is provided a positive electrode including a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector, the positive electrode active material layer including the above-described positive electrode active material.

[0008] In yet another embodiment of the present invention, there is provided a lithium secondary battery comprising the above positive electrode, negative electrode, and electrolyte. [Effects of the Invention]

[0009] The positive electrode active material according to one embodiment of the present invention minimizes production costs, maximizes capacity, ensures long life characteristics, and improves high voltage and high temperature characteristics. A lithium secondary battery using the positive electrode active material can exhibit high initial charge / discharge capacity and efficiency even under high voltage driving conditions, and achieves long life characteristics. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 2] 1 is a 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 microscopy (SEM) image of the positive electrode active material of Comparative Example 1. [Figure 6] 1 is a scanning electron microscopy (SEM) image of the positive electrode active material of Comparative Example 1. [Figure 7] 10 is an SEM image of the positive electrode active material of Comparative Example 2. [Figure 8] 10 is an SEM image of the positive electrode active material of Comparative Example 2. [Figure 9] 1 is an SEM image of the positive electrode active material of Example 3. [Figure 10] 1 is an SEM image of the positive electrode active material of Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0011] Although the present invention may be embodied in many different forms, it is not limited to the embodiments set forth herein.

[0012] The terms used herein are merely used to describe exemplary embodiments and are not intended to limit the present invention. The singular expressions include the plural expressions unless the context clearly indicates otherwise.

[0013] As used herein, "combinations thereof" refers to mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0014] It should be understood that the terms "comprise," "include," "comprise," or "have" are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, but do not preclude the possible presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0015] In the drawings, thicknesses of various layers and regions are exaggerated for clarity, and similar parts are designated by the same reference numerals throughout the specification. When a layer, film, region, plate, or other part is said to be "on" or "above" another part, this includes not only the case where it is "directly on" another part, but also the case where there is another part between them. Conversely, when a part is said to be "directly on" another part, it means that there is no other part between them.

[0016] 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.

[0017] 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 or a scanning electron microscope. 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 through data analysis, 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 ) and, unless otherwise defined, the average particle size is determined by measuring the size (diameter or length of the major axis) of 20 or more particles randomly selected from a scanning electron microscope image to obtain a particle size distribution, and then calculating the diameter (D 50 ) can be taken as the average particle size.

[0018] 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.

[0019] Here, the term "metal" is interpreted as a concept including general metals, transition metals, and metalloids (semimetals).

[0020] positive electrode active material In one embodiment, the present invention provides a cathode active material comprising: core particles containing a layered lithium nickel-manganese composite oxide; and an yttrium-containing coating layer located on the surface of the core particles; wherein the yttrium content on the surface of the cathode active material, as measured by energy profiling energy dispersive spectroscopy (EP-EDS), is 0.1 at% to 5.0 at% relative to 100 at% of all metals excluding lithium.

[0021] As the price of the rare metal cobalt has skyrocketed in recent years, there has been a demand for the development of cathode active materials that either eliminate cobalt or reduce its content. Among these, cathode active materials with olivine-based crystal structures, such as lithium iron phosphate (LFP), lithium manganese phosphate (LMP), and lithium manganese iron phosphate (LMFP), or spinel-based crystal structures, such as lithium manganese oxide (LMO), have limitations in achieving high capacity due to the limited amount of lithium available within their structures. Layered lithium-nickel-manganese cathode active materials offer excellent capacity and efficiency characteristics due to their high lithium content, 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, increasing gas generation and reducing lifespan.

[0022] In one embodiment, a cathode active material is proposed that maximizes capacity and efficiency by coating yttrium at a specific content to form a uniform coating layer, and reduces gas generation even under high voltage and high temperature conditions, thereby achieving long-life characteristics.

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

[0024] The nickel content relative to 100 mol% of all metals excluding lithium in the positive electrode active material may be 60 mol% or more, 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 the above range, high capacity can be achieved and structural stability can be improved even when the cobalt content is reduced. Nickel is contained in the core particles but can migrate to some of the coating layers during the coating process. Therefore, the nickel content refers to the nickel content contained in the entire positive electrode active material.

[0025] The manganese content relative to 100 mol% of all metals excluding lithium in the positive electrode active material may be 10 mol% or more, for example, 10 mol% to 40 mol%, 15 mol% to 35 mol%, 15 mol% to 30 mol%, or 20 mol% to 30 mol%, etc. When the manganese content satisfies the above range, the positive electrode active material can achieve high capacity while improving structural stability. Manganese is contained in the core particles, but can migrate to some of the coating layers during the coating process. Therefore, the manganese content refers to the manganese content contained in the entire positive electrode active material.

[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. The presence of aluminum in the composite oxide is advantageous in maintaining a stable layered structure even when cobalt is excluded from the structure. The aluminum content relative to 100 mol% of all metals (excluding lithium) in the positive electrode active material may be greater than 0 mol%, 0.1 mol% or more, 0.5 mol% or more, or 1 mol% or more. For example, the aluminum content may be greater than 0 mol% and 3 mol% or less, 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 from the core particles, preventing 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 core particle may be uniform. This means that the aluminum concentration gradient within the core particle may be from the center to the surface, or that the aluminum concentration is neither higher nor lower at the outside than at the inside, and the aluminum is uniformly dispersed within the core particle. In this case, the aluminum concentration gradient within the core particle may be 0.05 mol% or less, for example, 0.01 mol% to 0.05 mol%. This structure may be obtained by synthesizing a composite oxide using a nickel-manganese-aluminum hydroxide as a precursor by using an aluminum raw material in the preparation of a precursor without further doping with aluminum during the synthesis of the core particle. The core particle may be in the form of a secondary particle formed by agglomeration of multiple primary particles, and the aluminum content within the primary particle may be the same or similar regardless of the position of the primary particle. In other words, if a primary particle is selected from any position in the cross-section of the secondary particle and the aluminum content is measured within the primary particle, rather than at the interface of the primary particle, the aluminum content can be expressed as the same / similar / uniform regardless of the position of the primary particle, i.e., whether the primary particle is near the center or the surface of the secondary particle. In such a structure, even if cobalt is absent or present in only a very small amount, a stable layered structure can be maintained, and no aluminum by-products or aluminum agglomerates are generated, thereby simultaneously improving the capacity, efficiency, and life characteristics of the positive electrode active material.

[0028] The layered lithium nickel-manganese composite oxide is, for example, represented by the following chemical formula 1.

[0029] [Chemical formula 1] Li a1 Ni x1 Mn y1 Al z1 M 1 w1 O 2-b1 X b1 In Chemical Formula 1, 0.9 ≦ a1 ≦ 1.8, 0.6 ≦ x1 ≦ 0.8, 0.1 ≦ y1 ≦ 0.4, 0 ≦ z1 ≦ 0.03, 0 ≦ w1 ≦ 0.3, 0.9 ≦ x1 + y1 + z1 + w1 ≦ 1.1, and 0 ≦ b1 ≦ 0.1, and M 1 is one or more elements selected from B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, 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, and 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] The layered lithium nickel-manganese composite oxide of the core particles may be, for example, a cobalt-free compound that does not contain cobalt or contains a very small amount of cobalt, and the content of cobalt with respect to 100 mol% of the total metal excluding lithium may be 0 mol% to 1 mol%, 0 mol% to 0.1 mol%, or 0 mol% to 0.01 mol%.

[0033] The core particle may be in the form of a secondary particle formed by aggregating a plurality of primary particles. The secondary particles may be spherical, ellipsoidal, polyhedral, or irregular in shape, while the primary particles may be spherical, ellipsoidal, plate-like, or a combination thereof.

[0034] The core particles are susceptible to chemical attack from components in the electrolyte when the battery is operated under high voltage or high temperature conditions, and may undergo frequent side reactions with the electrolyte, resulting in a large amount of gas generation and reduced battery life and safety. However, these problems can be solved by introducing a coating layer according to one embodiment described below.

[0035] Coating layer According to one embodiment, the cathode active material has an yttrium content of 0.1 at% to 5.0 at% relative to 100 at% of all metals (excluding lithium) on the surface of the cathode active material, as measured by EP-EDS. For example, the content may be 0.2 at% to 4.5 at%, 0.3 at% to 4.0 at%, or 0.4 at% to 3.6 at%. This refers only to the content of yttrium contained in the coating layer. When the yttrium content on the surface of the cathode active material particles satisfies the above range, a uniform and thin coating layer can be formed, the resistance of the cathode active material does not increase, side reactions with the electrolyte are effectively suppressed, and the life characteristics of lithium secondary batteries under high voltage and high temperature conditions can be improved.

[0036] The yttrium content in the coating layer relative to 100 mol% of all metals excluding lithium in the entire positive electrode active material may be 0.1 mol% to 3.0 mol%, for example, 0.1 mol% to 2.8 mol%, 0.1 mol% to 2.6 mol%, 0.1 mol% to 2.4 mol%, 0.1 mol% to 2.2 mol%, or 0.2 mol% to 2.0 mol%. When the yttrium content satisfies the above range, the positive electrode active material forms a good coating layer without a decrease in capacity or an increase in resistance, effectively suppresses side reactions with the electrolyte, and effectively reduces the amount of gas generation under high voltage and high temperature conditions.

[0037] According to one embodiment, the coating layer may be in the form of a film that continuously surrounds the surface of the core particle, for example, in the form of a shell that surrounds the entire surface of the core particle. This is distinct from a structure in which only a portion of the surface of the core particle is partially coated. According to one embodiment, the coating layer may be formed to completely surround the surface of the core particle, but with a very thin and uniform thickness. As a result, the cathode active material does not increase in resistance or decrease in capacity, has improved structural stability, effectively suppresses side reactions with the electrolyte, reduces gas generation under high voltage and high temperature conditions, and achieves long-life characteristics.

[0038] According to one embodiment, the thickness of the coating layer 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 does not increase resistance or decrease capacity, but improves the structural stability of the positive electrode active material and effectively suppresses side reactions with the electrolyte. The thickness of the coating layer can be measured, for example, by TOF-SIMS, XPS, or EDS analysis, and the thickness range of the coating layer can be measured by TEM-EDS line profile analysis.

[0039] According to one embodiment, the coating layer has a thin, uniform thickness, ranging from several tens to several hundreds of nanometers. For example, the thickness deviation of the coating layer within a single cathode active material particle may be 20% or less, 18% or less, or 15% or less. Here, the coating thickness deviation refers to the thickness of the coating layer within a single cathode active material particle. For example, the coating thickness deviation may be calculated by measuring the thickness at approximately 10 points on an electron microscope image of a cross section of a single cathode active material particle, calculating the arithmetic mean, dividing the absolute value of the difference between one data point and the arithmetic mean value by the arithmetic mean value, and multiplying the result by 100. Having the coating layer thickness deviation or standard deviation within the above range indicates that a coating layer of uniform thickness is successfully formed in the form of a film on the surface of the cathode active material particle, thereby improving the structural stability of the cathode active material, effectively suppressing side reactions with the electrolyte, and minimizing increases in resistance and decreases in capacity due to the coating.

[0040] Meanwhile, the coating layer may further contain nickel, manganese, or a combination thereof in addition to yttrium. Nickel and manganese are originally contained in the core particles and are introduced during the coating layer formation process, and their contents are not particularly limited. According to one embodiment, the coating layer necessarily contains yttrium and selectively contains nickel and manganese. The coating layer is formed to a thin and uniform thickness, which can improve the high-voltage characteristics and life characteristics of the positive electrode active material.

[0041] The average particle size (D 50 The positive electrode active material may be, for example, large particles in the form of secondary particles, and the average particle size (D 50 ) may be, for example, 2 μm to 18 μm, 11 μm to 16 μm, or 12 μm to 15 μm. The average particle size is determined by measuring the size (diameter or length of the major axis) of 20 or more particles randomly selected in a scanning electron microscope image of the positive electrode active material to obtain a particle size distribution, and calculating the diameter (D) of the particle whose cumulative volume is 50% by volume in the particle size distribution. 50) may be taken as the average particle size. When the average particle size of the positive electrode active material satisfies the above range, high capacity and long life can be achieved, and it is advantageous to form a coating layer according to an embodiment.

[0042] The cobalt content in the positive electrode active material according to one embodiment may be, for example, 1 mol% or less, 0.1 mol% or less, 0.01 mol% or less, 0.005 mol% or less, or 0.001 mol% or less, relative to 100 mol% of all metals excluding lithium, and may be, for example, 0 mol% to 1 mol%, 0 mol% to 0.1 mol%, 0 mol% to 0.01 mol%, 0 mol% to 0.005 mol%, or 0 mol% to 0.011 mol%.

[0043] In addition, the cathode active material according to an embodiment may be characterized by being sodium-free. Although sodium ions are generally used in the manufacturing process of a cathode active material, the manufacturing method described below allows core particles with a stable structure and a coating layer with a uniform thickness to be formed without using sodium ions.

[0044] Method for producing positive electrode active material In one embodiment, a method for producing a positive electrode active material is provided, including: (i) preparing core particles containing a layered lithium nickel-manganese composite oxide; (ii) adding an yttrium raw material to an aqueous solvent and mixing them to prepare a coating solution; (iii) adding the core particles to the coating solution and mixing them to produce a mixed solution; and (iv) removing the aqueous solvent from the mixed solution, drying the resultant, and heat-treating it to obtain a positive electrode active material.

[0045] The yttrium content in the yttrium raw material may be 0.1 mol% to 3.0 mol%, for example, 0.1 mol% to 2.8 mol%, 0.1 mol% to 2.6 mol%, 0.1 mol% to 2.4 mol%, 0.1 mol% to 2.2 mol%, or 0.2 mol% to 1.0 mol%, relative to 100 mol% of all metals in the positive electrode active material excluding lithium. The positive electrode active material described above can be produced by the above method.

[0046] In one embodiment of a method for manufacturing a cathode active material, the step of preparing core particles containing a layered lithium nickel-manganese composite oxide includes a step of mixing a nickel-manganese composite hydroxide and a lithium source and performing a first heat treatment. The nickel-manganese composite hydroxide is a precursor of the core particles and may be in the form of secondary particles formed by agglomeration of a plurality of primary particles. The nickel-manganese composite hydroxide may contain no or only a small amount of cobalt, for example, a cobalt-free nickel-manganese composite hydroxide. The nickel-manganese composite hydroxide may be manufactured by a conventional coprecipitation method.

[0047] In the nickel-manganese composite hydroxide, the nickel content relative to 100 mol% of all metals may be 60 mol% to 80 mol%, for example, 65 mol% to 80 mol%, 70 mol% to 80 mol%, 60 mol% to 79 mol%, 60 mol% to 78 mol%, or 60 mol% to 75 mol%, etc. When the nickel content satisfies the above range, high capacity can be achieved, and structural stability can be improved even if the cobalt content is reduced.

[0048] In the nickel-manganese composite hydroxide, the manganese content relative to 100 mol% of the total metals may be 10 mol% or more, for example, 10 mol% to 40 mol%, 15 mol% to 35 mol%, 15 mol% to 30 mol%, or 20 mol% to 30%, etc. When the manganese content satisfies the above range, it is possible to improve the structural stability of the positive electrode active material while realizing high capacity, and it is possible to reduce production costs and improve economic efficiency.

[0049] Furthermore, when the nickel-manganese composite hydroxide further contains aluminum, the aluminum content relative to 100 mol% of the total metals may be 0.1 mol% or more, 0.5 mol% or more, or 1 mol% or more, for example, 1 mol% to 3 mol%, 1 mol% to 2.5 mol%, 1 mol% to 2 mol%, or 1 mol% to 1.9 mol%. When the aluminum content in the composite hydroxide satisfies the above range, it is possible to improve the structural stability of the positive electrode active material while realizing high capacity, and to reduce production costs and improve economic efficiency.

[0050] According to one embodiment, a method for manufacturing a cathode active material may involve using a nickel-manganese-aluminum composite hydroxide as a precursor, in which aluminum is uniformly dispersed within the structure, without further doping aluminum during the preparation of the core particles. Using such a precursor may result in a cathode active material that stably maintains its layered structure even during repeated charge and discharge cycles, even without cobalt, and may improve the capacity, efficiency, and lifespan of the cathode active material by preventing the formation of aluminum by-products or aluminum aggregates.

[0051] In the nickel-manganese composite hydroxide, the cobalt content relative to 100 mol% of all metals may be 1 mol% or less, 0.1 mol% or less, 0.01 mol% or less, 0.005 mol% or less, or 0.001 mol% or less, for example, 0 mol% to 1 mol%, 0 mol% to 0.1 mol%, 0 mol% to 0.01 mol%, 0 mol% to 0.005 mol%, or 0 mol% to 0.001 mol%. Such a nickel-manganese composite hydroxide can avoid the increase in unit price due to cobalt, making it economical, and can maximize capacity and improve structural stability.

[0052] The nickel-manganese composite hydroxide is, for example, represented by the following chemical formula 2.

[0053] [Chemical formula 2] Ni x2 Mny2 Al z2 M 2 w2 (OH)2 In Chemical Formula 2, 0.6≦x2≦0.8, 0.1≦y2≦0.4, 0≦z2≦0.03, 0≦w2≦0.3, and 0.9≦x2+y2+z2+w2≦1.1; and M 2 is one or more elements selected from B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr.

[0054] In Chemical Formula 2, for example, 0.6≦x2≦0.8, 0.1≦y2≦0.39, 0.01≦z2≦0.03, and 0≦w2≦0.29 may be satisfied.

[0055] The nickel-manganese composite hydroxide may be in the form of particles, and the average particle size (D 50 ) may be 10 μm to 18 μm, 11 μm to 16 μm, or 12 μm to 15 μm.

[0056] The nickel-manganese composite hydroxide and the lithium raw material may be mixed at a molar ratio of 1:0.9 to 1:1.8, for example, at a molar ratio of 1:0.9 to 1:1.5 or 1:1 to 1:1.2.

[0057] The first heat treatment can be performed in an oxygen atmosphere, for example, at a temperature range of 750°C to 950°C, or 780°C to 900°C, or 810°C to 890°C, for 2 hours to 20 hours, or 4 hours to 12 hours.

[0058] The first heat treatment allows for the production of a lithium nickel-manganese composite oxide. In the resulting lithium nickel-manganese composite oxide, the nickel content may be 60 mol% to 80 mol%, the manganese content may be 10 mol% or more, the aluminum content may be 0 mol% to 3 mol%, and the cobalt content may be extremely low, ranging from 0 mol% to 1 mol%, relative to 100 mol% of all metals excluding lithium. This composite oxide differs significantly from existing nickel-based oxides of other compositions, such as lithium nickel-cobalt-manganese composite oxide and lithium nickel-cobalt-aluminum composite oxide, in terms of the residual lithium content on the particle surface and many of their surface properties. Therefore, it is impossible to form a uniform, well-formed coating layer using existing coating methods. In one embodiment, we propose a method for forming a very thin, uniform coating layer on the surface of a lithium nickel-manganese composite oxide with an extremely low cobalt content and a nickel content of 60 mol% or more, thereby improving high-voltage and high-temperature properties.

[0059] In one embodiment, a coating layer according to one embodiment can be formed by adding and mixing an yttrium raw material into an aqueous solvent to prepare a coating solution, adding and mixing core particles containing the lithium nickel-manganese composite oxide obtained by the first heat treatment thereto, followed by drying and a second heat treatment. This is a salt-dissolution wet coating method, and can be a pre-addition method in which the salt, which is the coating raw material, is first completely dissolved and then the active material particles are added.

[0060] The aqueous solvent may include distilled water, an alcohol-based solvent, or a combination thereof. The yttrium raw material may include, for example, yttrium nitrate, yttrium sulfate, yttrium carbonate, yttrium hydroxide, or a combination thereof. The yttrium raw material is a raw material for forming a coating layer. The yttrium content in the yttrium raw material may be 0.1 mol% to 3.0 mol% relative to 100 mol% of the total metals excluding lithium in the final cathode active material, and may be designed to be, for example, 0.1 mol% to 2.8 mol%, 0.1 mol% to 2.6 mol%, 0.1 mol% to 2.4 mol%, 0.1 mol% to 2.2 mol%, or 0.2 mol% to 2.0 mol%. Designing the content of the coating raw material within the above range allows for the formation of a coating layer with a thin and uniform thickness on the order of tens to hundreds of nanometers, thereby reducing the amount of gas generation from the lithium secondary battery under high-voltage or high-temperature operating conditions and improving its high capacity and long-life characteristics.

[0061] The coating solution obtained by adding the yttrium raw material to the aqueous solvent and mixing it 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.

[0062] The core particles can be added to the coating solution and mixed for about 5 to 80 minutes, 5 to 60 minutes, or 5 to 40 minutes. The pH of the mixed solution after mixing can 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.

[0063] Drying after the mixing step can be understood as a step of removing the solvent, and can be carried out at, for example, 40°C to 240°C, 100°C to 220°C, or 150°C to 200°C.

[0064] The first heat treatment is the process of mixing the nickel-manganese composite hydroxide and the lithium raw material and then heat-treating the mixture, and the second heat treatment is the process of removing the solvent from the mixed solution, drying the resulting mixture, and then heat-treating it. The second heat treatment can be understood as a process of forming a coating layer, and can be performed, for example, in an oxygen atmosphere at a temperature range of 700°C to 850°C or 750°C to 840°C for 2 to 20 hours or 3 to 10 hours. The second heat treatment temperature may be lower than the first heat treatment temperature, and the second heat treatment time may be the same as or even shorter than the first heat treatment time. By performing the second heat treatment under these conditions, a desired coating layer can be obtained.

[0065] positive electrode In one embodiment, the positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, the positive electrode active material layer including the positive electrode active material described above. The positive electrode active material layer may further include other positive electrode active materials in addition to the positive electrode active material described above. The positive electrode active material layer may also optionally further include a binder, a conductive material, or a combination thereof.

[0066] According to one embodiment, the loading level of the positive electrode active material layer is 10 mg / cm 2 ~40mg / cm 2 For example, 10 mg / cm 2 ~30mg / cm 2 or 10 mg / cm 2 ~20mg / cm 2 When applying a positive electrode active material according to an embodiment, it is advantageous to achieve such a loading level, and a positive electrode satisfying the loading level in the above range is suitable for realizing a lithium secondary battery with a high capacity and a high energy density.

[0067] The loading level refers to the weight ratio of the positive electrode active material layer to its area. Generally, electrodes are manufactured by applying a slurry containing an electrode active material to a current collector, drying the slurry, and rolling it. The loading level may be one of the conditions designed during the process of applying the electrode active material slurry to the current collector. For example, the loading level may be calculated as the weight ratio of the electrode active material layer to the cross-sectional area of ​​the electrode active material layer when the electrode slurry is applied to the current collector before drying and rolling the electrode plate. A higher loading level can be understood as a thicker electrode active material layer being applied in greater amounts. Here, the electrode active material slurry includes an electrode active material and a solvent, and may optionally include a binder and / or a conductive material. A positive electrode can also be manufactured by a dry process. In this case, an electrode active material layer is formed on a current collector without using a solvent, and then rolled to form a positive electrode. The loading level refers to the weight ratio of the electrode active material layer to its area before rolling.

[0068] Furthermore, the density of the positive electrode active material layer in the final rolled positive electrode is 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 density of the positive electrode active material layer, and a positive electrode having a positive electrode active material layer density within the above range is suitable for realizing a lithium secondary battery with a high capacity and a high energy density.

[0069] The density of the positive electrode active material layer refers to the ratio of the weight to the volume of the positive electrode active material layer in a rolled positive electrode, and is expressed as composite density or electrode plate density. The density of the positive electrode active material layer can be measured by coating a positive electrode active material slurry on a positive electrode current collector, drying, and rolling it to fabricate a positive electrode, cutting the positive electrode into a size of approximately 30 mm x 30 mm, measuring the thickness and weight of the positive electrode active material layer excluding the positive electrode current collector, multiplying the cross-sectional area and thickness of the positive electrode active material layer to calculate the volume, and then dividing the weight by the volume. The positive electrode active material slurry includes a positive electrode active material and a solvent, and may optionally include a binder and / or a conductive material. For example, drying and rolling the positive electrode active material slurry after coating can involve drying at 80°C and rolling at a pressure of approximately 50 MPa for 3 seconds. Dry-rolling of the electrode plate can also be performed by forming a positive electrode active material layer on a current collector without using a solvent, followed by rolling to produce a positive electrode. The area, thickness, and weight of the positive electrode active material layer in the rolled state can be measured, and the weight can be divided by the volume to determine the electrode plate density. Dry-rolling of the electrode plate can be performed, for example, by rolling at a pressure of about 3 tons for 30 seconds.

[0070] binder The binder serves to firmly adhere the positive electrode active material particles to each other and to firmly adhere the positive electrode active material to the current collector. Representative examples of binders include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and nylon.

[0071] Conductive material The conductive material is used to impart electrical conductivity to the electrode, and any material that is electron-conductive and does not cause chemical changes in the battery that is constructed can be used. Examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0072] 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.

[0073] The positive electrode current collector may be made of Al, but is not limited to this.

[0074] Lithium secondary battery In one embodiment, a lithium secondary battery is provided that includes the positive electrode, the negative electrode, and the electrolyte described above. 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.

[0075] Lithium secondary batteries can be classified into cylindrical, prismatic, pouch, and coin types depending on their shape. FIGS. 1 to 4 are schematic diagrams showing lithium secondary batteries according to an embodiment, with FIG. 1 illustrating a cylindrical battery, FIG. 2 illustrating a prismatic battery, and FIGS. 3 and 4 illustrating pouch battery types. Referring to FIGS. 1 to 4, a lithium secondary battery 100 may include an electrode assembly 40 having a positive electrode 10 and a negative electrode 20 with a separator 30 interposed therebetween, and a case 50 housing the electrode assembly 40. The positive electrode 10, the negative electrode 20, and the separator 30 may be immersed in 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, 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 current generated in the electrode assembly 40 to the outside.

[0076] A lithium secondary battery according to an embodiment may be capable of being charged at a high voltage or may be suitable for being driven at a high voltage. For example, the charging voltage of the lithium secondary battery may be 4.45 V or higher, such as 4.45 V to 4.7 V, 4.45 V to 4.6 V, or 4.45 V to 4.55 V. By using a positive electrode active material according to an embodiment, the lithium secondary battery can significantly reduce gas generation even when charged at a high voltage, thereby achieving high capacity and long life characteristics.

[0077] 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.

[0078] negative electrode active material The negative electrode active material includes a material capable of reversibly inserting / extracting lithium ions, lithium metal, a lithium metal alloy, a material capable of being doped with and dedoped from lithium, or a transition metal oxide.

[0079] As the substance capable of reversibly inserting / desorbing the lithium ions, a carbon-based negative electrode active material may be used, which may include, as examples, 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, calcined coke, and the like.

[0080] 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 may be used.

[0081] As the substance capable of doping and undoping with lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material may be used. As the Si-based negative electrode active material, it may be silicon, a silicon-carbon composite, SiOx (0 < x < 2), a Si-Q alloy (where Q is an element selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements (excluding Si), group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof, for example, Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof), or a combination thereof. As the Sn-based negative electrode active material, it may be Sn, SnO2, a Sn alloy, or a combination thereof.

[0082] The silicon-carbon composite may be a composite of silicon and amorphous carbon. The average particle diameter (D of the silicon-carbon composite particles 50) may be, for example, 0.5 μm to 20 μm. According to one embodiment, the silicon-carbon composite may be in the form of silicon particles, and the surfaces of the silicon particles may be coated with amorphous carbon. For example, it may include secondary particles (cores) formed by granulating primary silicon particles, and an amorphous carbon coating layer (shell) located on the surfaces of the secondary particles. The amorphous carbon may also be located between the primary silicon particles, for example, the primary silicon particles may be coated with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0083] The silicon-carbon composite may further include crystalline carbon. For example, the silicon-carbon composite may include a core including crystalline carbon and silicon particles, and an amorphous carbon coating layer located on the core surface. The crystalline carbon may be artificial graphite, natural graphite, or a combination thereof. Examples of the amorphous carbon include soft carbon, hard carbon, mesophase pitch carbide, and calcined coke.

[0084] When the silicon-carbon composite contains silicon and amorphous carbon, the silicon content may be 10 to 50% by weight and the amorphous carbon content may be 50 to 90% by weight, based on 100% by weight of the silicon-carbon composite.Alternatively, when the composite contains silicon, amorphous carbon, and crystalline carbon, the silicon content may be 10 to 50% by weight, the crystalline carbon content may be 10 to 70% by weight, and the amorphous carbon content may be 20 to 40% by weight, based on 100% by weight of the silicon-carbon composite.

[0085] The thickness of the amorphous carbon coating layer may be 5 nm to 100 nm. 50 ) can be 10 nm to 1 μm, or 10 nm to 200 nm. The silicon particles may be present as silicon alone, in the form of a silicon alloy, or in an oxidized form. The oxidized form of silicon is SiO xIt can be represented by (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 diameter (D 50 ) means the diameter of the particle with a cumulative volume of 50% by volume in the particle size distribution.

[0086] The Si-based negative electrode active material or 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 Sn-based negative electrode active material and the carbon-based negative electrode active material are used in combination, the mixing ratio can be 1:99 to 90:10 by weight ratio.

[0087] Binder The binder serves to make the negative electrode active material particles adhere well to each other and also make the negative electrode active material adhere well to the current collector. As the binder, a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof can be used.

[0088] 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.

[0089] The aqueous binder can be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluorine rubber, polyethylene oxide, polyvinyl pyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene-propylene-diene copolymer, polyvinyl pyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0090] 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.

[0091] The dry binder can be a fiberizable polymeric material such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0092] Conductive material The conductive material is used to impart conductivity to the electrode and can be any material that is electron-conductive and does not cause chemical changes in the battery. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0093] The content of the negative electrode active material may be 95% to 99.5% by weight, and the content of the binder may be 0.5% to 5% by weight, relative to 100% by weight of the negative electrode active material layer. For example, the negative electrode active material layer may contain 90% to 99% by weight of the negative electrode active material, 0.5% to 5% by weight of the binder, and 0.5% to 5% by weight of the conductive material.

[0094] current collector The negative electrode current collector can include, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or an alloy thereof, and can be in the form of a foil, sheet, or foam. The thickness of the negative electrode current collector can be, for example, 1 μm to 20 μm, 5 μm to 15 μm, or 7 μm to 10 μm.

[0095] 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.

[0096] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reactions of the battery can migrate, and can be a carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based solvent, an aprotic solvent, or a combination thereof.

[0097] 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.

[0098] The non-aqueous organic solvent may be used alone or in combination of two or more kinds. When a mixture of two or more kinds is used, the mixing ratio may be appropriately adjusted depending on the desired battery performance, which is widely understood by those skilled in the art.

[0099] 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.

[0100] 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.

[0101] The electrolyte may further contain vinyl ethyl carbonate, vinylene carbonate or ethylene carbonate based compounds to improve the battery life.

[0102] 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.

[0103] Lithium salts are substances that dissolve in organic solvents and act as a source of lithium ions within the battery, enabling basic lithium secondary battery operation and facilitating the movement of lithium ions between the positive and negative electrodes. Representative examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide; LiFSI), LiC4F9SO3, and LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (x and y are integers of 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalate)phosphate (LiDFBOP), and lithium bis(oxalate)borate (LiBOB).

[0104] The concentration of the lithium salt is preferably within the range of 0.1 M to 2.0 M. When the concentration of the lithium salt is within this range, the electrolyte has appropriate ion conductivity and viscosity, thereby exhibiting excellent performance and allowing lithium ions to migrate effectively.

[0105] Separator Depending on the type of lithium secondary battery, a separator may be present between the positive and negative electrodes. Such separators may be made of polyethylene, polypropylene, polyvinylidene fluoride, or multilayer films of two or more of these. Of course, mixed multilayer films such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may also be used.

[0106] 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.

[0107] 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 polymers.

[0108] 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.

[0109] 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.

[0110] The inorganic material may include, but is not limited to, inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof. The average particle size (D 50 ) is 1 nm to 2000 nm, and can be, for example, 100 nm to 1000 nm, or 100 nm to 700 nm.

[0111] 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.

[0112] 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.

[0113] 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.

[0114] Example 1 1. Production of positive electrode active material Ni 0.75 Mn 0.24 Al 0.01 (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 0.24 Al 0.01O2 and the average particle size (D 50 A composite oxide in the form of secondary particles with a particle size of about 14 μm was produced.

[0115] A coating solution was prepared by adding 600g of distilled water and yttrium nitrate to a 1L reactor and stirring at 350 rpm for 5 minutes to dissolve the salt. The salt in the coating solution was confirmed to be completely dissolved and colorless and transparent. 500g of the lithium nickel-manganese composite oxide prepared was added to the continuously stirred coating solution over 1.5 minutes and stirred for approximately 30 minutes. The yttrium content in the yttrium nitrate was designed to be 0.2 mol% based on 100% by weight of the total metals excluding lithium in the final cathode active material.

[0116] The solvent was removed from the mixed solution using an aspirator and a filter press, and the mixture was dried in vacuum at 190°C to obtain a coated product.

[0117] The coated product was subjected to a second heat treatment at 750° C. for 8 hours in an oxygen atmosphere to prepare a final positive electrode active material.

[0118] 2. Lithium secondary battery manufacturing 98.5 wt% of the prepared positive electrode active material, 1.0 wt% of polyvinylidene fluoride binder, and 0.5 wt% of carbon nanotube conductive material were mixed to prepare a positive electrode active material layer slurry, which was then coated on an aluminum foil current collector, dried, and rolled to prepare a positive electrode. At this time, the loading level of the positive electrode active material layer was 20 mg / cm. 2 The density of the final rolled positive electrode was about 3.4 g / cc.

[0119] 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.

[0120] 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.

[0121] 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 content of yttrium in yttrium nitrate was designed and mixed to be 0.5 mol % relative to 100 mol % of the total metals excluding lithium in the final cathode active material.

[0122] 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 content of yttrium in yttrium nitrate was designed and mixed to be 1.0 mol % relative to 100 mol % of the total metals excluding lithium in the final cathode active material.

[0123] 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 content of yttrium in yttrium nitrate was designed and mixed to be 2.0 mol % relative to 100 mol % of the total metals excluding lithium in the final cathode active material.

[0124] Comparative Example 1 The positive electrode active material is manufactured without the yttrium coating process. 1.05 Ni 0.75 Mn 0.24 Al 0.01 A positive electrode active material and a lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that the O2 composite oxide itself was used as the positive electrode active material.

[0125] Comparative Example 2 A cathode active material and a lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that in the preparation of the cathode active material, aluminum sulfate was added to a distilled water solvent instead of yttrium nitrate, and the aluminum content in the aluminum sulfate was designed to be 1.0 mol % relative to 100 mol % of the total metals excluding lithium in the final cathode active material.

[0126] Evaluation example 1: Surface analysis of positive electrode active material The cathode active materials prepared in Example 3, Comparative Example 1, and Comparative Example 2 were photographed using a scanning electron microscope and compared. Figures 5 and 6 are SEM images of the particle surfaces of the cathode active material of Comparative Example 1, which was not coated. Figures 7 and 8 are SEM images of the particle surfaces of the cathode active material of Comparative Example 2, which was only aluminum coated. Figures 9 and 10 are SEM images of the particle surfaces of the cathode active material of Example 3. Referring to Figures 5 to 10, it can be seen that the surface shape of the cathode active material of Example 3 is different from that of Comparative Examples 1 and 2.

[0127] Evaluation example 2: Analysis of yttrium content on the surface of positive electrode active material The yttrium content on the surface of the positive electrode active materials prepared in Examples 1 to 3 and Comparative Examples 1 to 4 was analyzed by energy profiling energy dispersive spectroscopy (EP-EDS), and the results are shown in Table 1. EP-EDS (AMETEK Octane Elite) was used under the following conditions: EDS vac: 15 kV, current: 10 μA, live time: 90 seconds.

[0128] [Table 1]

[0129] Referring to Table 1, it can be seen that the positive electrode active materials of Examples 1 to 4 contain yttrium in an appropriate range on the surface of the positive electrode active material.

[0130] Evaluation example 3: Initial charge / discharge capacity and efficiency evaluation The lithium secondary batteries manufactured in Examples 1 to 4 and Comparative Examples 1 and 2 were initially charged and discharged at 25° C. at a constant current of 0.2 C to an upper limit voltage of 4.45 V, and at a constant voltage of 0.05 C, and then discharged at 0.2 C to an end voltage of 3.0 V. Table 2 below shows the initial charge capacity, initial discharge capacity, and the ratio of the latter to the former calculated as efficiency.

[0131] Evaluation example 4: High temperature life characteristics Following the initial charge and discharge of Evaluation Example 3, a cycle of charging at 1.0 C and discharging at 1.0 C in a voltage range of 3.0 V to 4.45 V at 45°C was repeated 50 times or more, and the ratio of the 50-cycle discharge capacity to the initial discharge capacity was calculated and shown in Table 2 below.

[0132] [Table 2]

[0133] Referring to Table 2, it can be seen that the lithium secondary batteries of Examples 1 to 4 achieved charge / discharge capacity and efficiency characteristics that were higher or equal to those of the comparative example, while also exhibiting improved high-temperature life characteristics.

[0134] In contrast, it can be seen that in the case of Comparative Example 1, where no coating was applied, the life characteristics under high voltage and high temperature conditions are not as good as those in Examples 1 to 4. Also, in the case of Comparative Example 2, where only an aluminum coating was applied, it can be seen that the initial charge / discharge efficiency and life characteristics under high voltage and high temperature conditions are not as good as those in Examples 1 to 4.

[0135] Although the preferred embodiments have been described in detail above, the scope of the present invention is not limited to these, and various modifications and improvements made by those skilled in the art using the basic concepts defined in the claims also fall within the scope of the present invention. [Explanation of symbols]

[0136] 100 Lithium secondary battery 10 positive electrode 11 Positive electrode lead tab 12 Positive terminal 20 negative electrode 21 Negative electrode lead tab 22 Negative terminal 30 Separator 40 Electrode assembly 50 cases 60 Sealing member 70 Electrode tab 71 Positive electrode tab 72 Negative electrode tab

Claims

1. Core particles containing a layered lithium nickel-manganese composite oxide; and a yttrium-containing coating layer located on the surface of the core particle; A positive electrode active material comprising: The positive electrode active material has an yttrium content on the surface of the positive electrode active material measured by energy profiling energy dispersive spectroscopy (EP-EDS) of 0.1 at % to 5.0 at % relative to 100 at % of all metals excluding lithium.

2. 2. The positive electrode active material according to claim 1, wherein in the layered lithium nickel-manganese composite oxide, the nickel content is 60 mol% to 80 mol% relative to 100 mol% of all metals excluding lithium, and the manganese content is 10 mol% or more.

3. 2. The positive electrode active material according to claim 1, wherein the layered lithium nickel-manganese composite oxide further contains aluminum, and the content of aluminum relative to 100 mol % of all metals excluding lithium is greater than 0 mol % and less than or equal to 3 mol %.

4. The positive electrode active material according to claim 3 , wherein the aluminum concentration gradient difference within the core particle is 0.05 mol % or less.

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

6. The layered lithium nickel-manganese composite oxide is the positive electrode active material according to claim 1, which is represented by the following chemical formula 1: [Chemical formula 1] Li ａ１ Ni ｘ１ Mn ｙ１ Al ｚ１ M １ ｗ１ O ２－ｂ１ X ｂ１ In the 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, and Zr, and X is one or more elements selected from F, P, and S.

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

8. The cathode active material of claim 1 , wherein the coating layer has a thickness of 30 nm to 500 nm.

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

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

11. (i) preparing core particles containing a layered lithium nickel-manganese composite oxide; (ii) adding and mixing the yttrium raw material into the aqueous solvent to prepare a coating solution; (iii) adding the core particles to the coating solution and mixing them to prepare a mixed solution; and (iv) removing the aqueous solvent from the mixed solution, and then drying and heat-treating the resultant to obtain a positive electrode active material.

12. 12. The method for producing a positive electrode active material according to claim 11, wherein in the layered lithium nickel-manganese composite oxide, the nickel content is 60 mol% to 80 mol%, the manganese content is 10 mol% or more, the aluminum content is more than 0 mol% and 3 mol% or less, and the cobalt content is 0 mol% to 0.01 mol%, relative to 100 mol% of all metals excluding lithium.

13. 12. The method for producing a positive electrode active material according to claim 11, wherein the yttrium content in the yttrium raw material is 0.1 mol % to 3.0 mol % relative to 100 mol % of all metals excluding lithium in the positive electrode active material.

14. the pH of the solution obtained by mixing the yttrium raw material in the aqueous solvent is 1.5 to 3.5; The method for producing a positive electrode active material according to claim 11, wherein the pH of the mixed solution obtained by adding the core particles to the coating solution and mixing them is 4.5 to 8.

5.

15. The method for producing a positive electrode active material according to claim 11, wherein the heat treatment is carried out at 700°C to 850°C.

16. a positive electrode current collector, and a positive electrode active material layer located on the positive electrode current collector, The positive electrode active material layer comprises the positive electrode active material according to any one of claims 1 to 10.

17. The loading level of the positive electrode active material layer is 10 mg / cm ２ ~40 mg / cm ２ 17. The positive electrode of claim 16, wherein

18. 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.

19. The positive electrode of claim 16 ; a negative electrode; and Electrolyte; A lithium secondary battery comprising:

20. 20. The lithium secondary battery according to claim 19, wherein the lithium secondary battery has a charging voltage of 4.45 V or higher.

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