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

Abstract

To improve the performance of a lithium secondary battery at high temperatures and high voltages and improve the capacity characteristics, initial charge / discharge efficiency, and high-temperature life characteristics thereof, by introducing an optimal coating layer, as a positive electrode active material including a lithium nickel-manganese-based composite oxide.SOLUTION: There is provided a positive electrode active material that includes core particles including a layered lithium nickel-manganese-based composite oxide, and a coating layer located on a surface of the core particles and containing aluminum and zinc. The positive electrode active material minimizes a production cost, maximizes capacity and ensures long life characteristics, and improves characteristics at high voltage and high-temperature characteristics. A lithium secondary battery to which the positive electrode active material is applied can exhibit high initial charge / discharge capacity and efficiency even under high-voltage driving conditions, and can achieve long life characteristics under high-voltage and high-temperature conditions.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 Art

[0002] Lithium secondary batteries having a high energy density and being easy to carry are mainly used as driving power sources for mobile information terminals such as mobile phones, notebook computers, and smartphones. Recently, research has been actively conducted on using lithium secondary batteries with a high energy density as driving power sources or power storage power sources for hybrid vehicles and electric vehicles.

[0003] In order to realize a lithium secondary battery suitable for such applications, various positive electrode active materials have been studied. Among them, lithium nickel-based oxides, lithium nickel manganese cobalt composite oxides, lithium nickel cobalt aluminum composite oxides, lithium cobalt oxides, etc. are mainly used as positive electrode active materials. However, in recent years, while the demand for large-sized, high-capacity, or high-energy density lithium secondary batteries has increased rapidly, the supply of positive electrode active materials containing cobalt, which is a rare metal, is expected to be extremely insufficient. That is, since cobalt is expensive and the remaining reserves are not large, it is necessary to develop a positive electrode active material that excludes cobalt or reduces its content.

Summary of the Invention

Problems to be Solved by the Invention

[0004] The present invention provides a positive electrode active material containing a lithium nickel-manganese-based composite oxide, which improves the performance of a lithium secondary battery at high temperature and high voltage by introducing an optimal coating layer, and improves the capacity characteristics, initial charge-discharge efficiency, and high-temperature life characteristics.

Means for Solving the Problems

[0005] In one embodiment of the present invention, there is provided a positive electrode active material including: core particles containing a layered lithium nickel-manganese composite oxide; and a coating layer containing aluminum and zinc and located on the surface of the core particles.

[0006] In another embodiment of the present invention, there is provided a method for manufacturing a positive electrode active material, including: (i) preparing core particles containing a layered lithium nickel-manganese composite oxide; (ii) preparing a coating solution by adding and mixing an aluminum raw material and a zinc raw material in an aqueous solvent; (iii) producing a mixed solution by adding and mixing the core particles into the coating solution; and (iv) removing the aqueous solvent from the mixed solution, and then drying and heat-treating the obtained product to obtain a positive electrode active material.

[0007] In 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, wherein the positive electrode active material layer contains the positive electrode active material described above.

[0008] In another embodiment of the present invention, there is provided a lithium secondary battery including the positive electrode, a negative electrode, and an electrolyte.

Advantages of the Invention

[0009] The positive electrode active material according to one embodiment of the present invention minimizes the production cost and maximizes the capacity, ensures long-life characteristics, and improves characteristics at high voltage and high temperature. The lithium secondary battery applying the positive electrode active material can exhibit high initial charge-discharge capacity and efficiency even under high-voltage driving conditions, and can realize long-life characteristics under high-voltage and high-temperature conditions.

Brief Description of the Drawings

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Best Mode for Carrying Out the Invention

[0011] Hereinafter, specific embodiments will be described in detail so that those having ordinary knowledge in this technical field can easily implement them. However, the present invention can be realized in various different forms and is not limited to the embodiments described herein.

[0012] The terms used herein are for illustrative purposes only and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

[0013] Here, "these combinations" means a mixture, laminate, composite, copolymer, alloy, blend, reaction product, etc. of components.

[0014] The terms such as "comprising", "including", or "having" are intended to specify the presence of implemented features, numbers, steps, components, or combinations thereof, and it should be understood that they do not preclude the presence or addition of one or more other features, numbers, steps, components, or combinations thereof in advance.

[0015] For the sake of clearly expressing various layers and regions in the drawings, the thickness is enlarged and shown, and the same reference numerals are given to similar parts throughout the specification. When a part such as a layer, film, region, or plate is "on" or "above" another part, this includes not only the case where it is "directly above" the other part but also the case where there are other parts in between. Conversely, when a part is "directly above" another part, it means that there are no other parts in between.

[0016] Here, "layer" includes not only the shape formed on the entire surface but also the shape formed on a partial surface when observed in a plan view.

[0017] The average particle size can be measured by methods widely known to those skilled in the art. For example, it can be measured with a particle size analyzer, or it can also be measured from a transmission electron microscope image or a scanning electron microscope image. As another method, it can be measured using the dynamic light scattering method, and after performing data analysis to count the number of particles for each particle size range, the average particle size value can then be calculated therefrom. Unless otherwise defined, the average particle size refers to the diameter (D 50 ) of the particles with a cumulative volume of 50% by volume in the particle size distribution. Also, unless otherwise defined, the average particle size is obtained by measuring the sizes (diameter or major axis length) of more than 20 randomly selected particles from a scanning electron microscope image to obtain a particle size distribution, and taking the diameter (D 50 ) of the particles with a cumulative volume of 50% by volume in the said particle size distribution as the average particle size.

[0018] Here, "or" is not construed in an exclusive sense. For example, "A or B" is construed to include A, B, A + B, etc.

[0019] "Metal" is construed as a concept including common metals, transition metals, and metalloids (semi-metals).

[0020] Positive electrode active material In one embodiment, a positive electrode active material is provided that includes core particles containing a layered lithium nickel-manganese composite oxide; and a coating layer located on the surface of the core particles and containing aluminum and zinc.

[0021] In recent years, as the price of cobalt, a rare metal, has skyrocketed, there has been a demand for the development of cathode active materials that exclude cobalt or reduce its content. Among them, cathode active materials with an olivine crystal structure such as lithium iron phosphate (LFP), lithium manganese phosphate (LMP), and lithium manganese iron phosphate (LMFP), or a spinel crystal structure such as lithium manganese oxide (LMO) have limitations in achieving high capacity because the amount of lithium that can be utilized within the structure is small. Layered lithium nickel-manganese-based cathode active materials can increase the amount of lithium in the structure, so they are excellent in terms of capacity and efficiency characteristics and are suitable as materials for high-capacity batteries. However, when cobalt, which plays a core role in the layered structure, is removed, the structural stability decreases, the resistance increases, and it becomes difficult to ensure long-life characteristics. In addition, in order to exclude cobalt, there is a problem that the side reaction between the cathode active material and the electrolyte accelerates under high voltage and high temperature conditions, increasing the gas generation amount and deteriorating the life characteristics.

[0022] In one embodiment, by introducing a coating layer containing both aluminum and zinc on the surface of core particles containing a layered nickel-manganese-based composite oxide, while strengthening the particle surface, a coating layer having a 3D lithium channel structurally is formed, thereby proposing a method that can improve not only the high voltage and high temperature life characteristics but also the initial charge-discharge efficiency.

[0023] Core particles The core particles contain a layered lithium nickel-manganese-based composite oxide.

[0024] The content of nickel with respect to 100 mol% of the total metal excluding lithium in the positive electrode active material is 60 mol% or more, and can be, for example, 60 mol% to 80 mol%, 65 mol% to 80 mol%, 70 mol% to 80 mol%, 60 mol% to 79 mol%, 60 mol% to 78 mol%, or 60 mol% to 75 mol%. When the content of nickel satisfies the above range, high capacity can be achieved, and even if the content of cobalt decreases, the structural safety can be enhanced. Nickel is contained in the core particles, but can move to some coating layers in the coating process. Therefore, the content of nickel means the content of nickel contained in the entire positive electrode active material.

[0025] The content of manganese with respect to 100 mol% of the total metal excluding lithium in the positive electrode active material is 10 mol% or more, and can be, for example, 10 mol% to 40 mol%, 15 mol% to 35 mol%, 15 mol% to 30 mol%, or 20 mol% to 30%. When the content of manganese satisfies the above range, the positive electrode active material can improve the structural stability while achieving high capacity. Manganese is contained in the core particles, but can move to some coating layers in the coating process. Therefore, the content of manganese means the content of manganese contained in the entire positive electrode active material.

[0026] The lithium nickel-manganese composite oxide can be, for example, a lithium nickel-manganese-aluminum composite oxide further containing aluminum in addition to nickel and manganese. When aluminum is contained in the composite oxide, it is advantageous for maintaining a stable layered structure even when the cobalt element is excluded from the structure. The content of aluminum with respect to 100 mol% of the total metal excluding lithium in the positive electrode active material is 0.1 mol% or more, 0.5 mol% or more, or 1 mol% or more, and can be, for example, 1 mol% to 3 mol%, 1 mol% to 2.5 mol%, 1 mol% to 2 mol%, or 1.5 mol% to 2.5 mol%. Here, the aluminum content means the content of aluminum present in the core particles. When the aluminum content satisfies the above range, a stable layered structure can be maintained even when cobalt is excluded from the core particles, the problem of the structure collapsing due to charge and discharge can be suppressed, and the long-life characteristics of the positive electrode active material can be realized.

[0027] According to one embodiment, the concentration of aluminum within the core particles can be uniform. That is, there is no concentration gradient of aluminum from the center to the surface direction within the core particles, or the aluminum concentration inside the core particles is not higher or lower outside than inside, meaning that the aluminum within the core particles is uniformly dispersed. This can be said to be a structure obtained by synthesizing a composite oxide using a nickel-manganese-aluminum-based hydroxide as a precursor by using an aluminum raw material during the production of the precursor without further doping aluminum during the synthesis process of the core particles. The core particles can be in the form of secondary particles aggregated from a plurality of primary particles, but it can be said that the aluminum content within the primary particles is the same or similar regardless of the position of the primary particles. That is, when a primary particle is selected from any position in the cross-section of the secondary particle and the aluminum content inside rather than at the interface of the primary particle is measured, it can be expressed that the aluminum content is the same / similar / uniform regardless of the position of the primary particle, that is, whether the primary particle is close to the center or the surface of the secondary particle. In such a structure, even if cobalt is absent or present in a very small amount, a stable layered structure can be maintained, no aluminum by-products or aluminum aggregates are generated, and the capacity, efficiency, and life characteristics of the positive electrode active material can be improved simultaneously.

[0028] Specifically, the layered lithium nickel-manganese-based composite oxide 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

[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, and M 1is one or more elements selected from Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zr, and Zn, 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 hold. Further, Chemical Formula 1 contains aluminum, and in this case, 0.6 ≦ x1 ≦ 0.8, 0.1 ≦ y1 ≦ 0.39, 0.01 ≦ z1 ≦ 0.03, and 0 ≦ w1 ≦ 0.29 can be satisfied. For example, 0.6 ≦ x1 ≦ 0.8, 0.1 ≦ y1 ≦ 0.39, 0.01 < z1 ≦ 0.03, and 0 ≦ w1 ≦ 0.29 can be satisfied.

[0031] In the Chemical Formula 1, for example, 0.6 ≦ x1 ≦ 0.79, 0.6 ≦ x1 ≦ 0.78, 0.6 ≦ x1 ≦ 0.75, 0.65 ≦ x1 ≦ 0.8, or 0.7 ≦ x1 ≦ 0.79, 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, 0.01 ≦ z1 ≦ 0.025, 0.01 < z1 ≦ 0.02, or 0.01 < z1 ≦ 0.019, 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 and the like can hold.

[0032] The layered lithium nickel - manganese - based composite oxide of the core particles is, 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 can be 0 mol% to 0.01 mol%.

[0033] The core particles may be in the form of secondary particles formed by aggregation of a plurality of primary particles. The secondary particles can be spherical, ellipsoidal, polyhedral, or irregular in shape, and the primary particles can be spherical, ellipsoidal, plate - shaped, or a combination thereof.

[0034] When the battery is driven under high voltage or high temperature conditions, the core particles are vulnerable to chemical attack from the components within the electrolyte, and many side reactions with the electrolyte can occur. As a result, there are problems such as a large amount of gas generation, and a decrease in battery life and safety. However, by introducing a coating layer according to an embodiment described later, such problems can be solved.

[0035] Coating layer The cathode active material according to one embodiment is characterized in that it is located on the surface of the core particles and includes a coating layer containing aluminum and zinc.

[0036] For the cathode active material according to one embodiment, the aluminum content with respect to 100 at% of the total components on the surface of the cathode active material measured by XPS (X-ray photoelectron spectroscopy) is 5 at% to 35 at%, for example, it can be 5 at% to 30 at%, 5 at% to 25 at%, or 10 at% to 20 at%. Also, the zinc content with respect to 100 at% of the total components on the surface of the cathode active material measured by XPS is 0.1 at% to 3.0 at%, for example, it can be 0.3 at% to 2.5 at%, or 0.5 at% to 2.0 at%. This only means the content of aluminum and zinc contained in the coating layer. When the content of aluminum and zinc on the surface of the cathode active material particles satisfies the above range, it is possible to form a uniform and thin coating layer, the resistance of the cathode active material does not increase, side reactions with the electrolyte are effectively suppressed, and the life characteristics of the lithium secondary battery under high voltage and high temperature conditions can be improved.

[0037] The aluminum content in the coating layer with respect to 100 mol% of the total metals excluding lithium in the entire cathode active material is 0.5 mol% to 1.5 mol%, for example, it can be 0.5 mol% to 1.4 mol%, 0.6 mol% to 1.4 mol%, 0.7 mol% to 1.3 mol%. The aluminum content of the coating layer only means the content of aluminum contained in the coating layer regardless of the aluminum contained in the core particles.

[0038] Further, the zinc content in the coating layer with respect to 100 mol% of the total metal excluding lithium in the entire positive electrode active material is 0.01 mol% to 1.5 mol%, and can be, for example, 0.05 mol% to 1.0 mol%, 0.1 mol% to 1.0 mol%, 0.1 mol% to 0.5 mol%, or 0.1 mol% to 0.4 mol%. The zinc content in the coating layer means only the content of zinc contained in the coating layer regardless of the zinc contained in the core particles.

[0039] Also, the total amount of aluminum and zinc in the coating layer with respect to 100 mol% of the total metal excluding lithium in the entire positive electrode active material is 0.11 mol% to 3.0 mol%, and as an example, can be 0.5 mol% to 1.5 mol%. This means only the content of aluminum and zinc contained in the coating layer regardless of the aluminum and zinc contained in or possibly contained in the core particles. The total metal excluding lithium in the entire positive electrode active material that serves as the reference for the above content range means the total content of the metal excluding lithium present in the entire positive electrode active material particles rather than on the surface of the positive electrode active material.

[0040] The contents of aluminum and zinc in the coating layer in the entire positive electrode active material can be measured, for example, by SEM-EDS analysis of the surface or cross-section of the positive electrode active material. When the contents of aluminum and zinc in the coating layer satisfy the above ranges, it is possible to form a uniform and thin coating layer, the resistance of the positive electrode active material does not increase, side reactions with the electrolyte are effectively suppressed, and the life characteristics of the lithium secondary battery under high voltage and high temperature conditions can be improved. For example, when the contents of aluminum and zinc in the coating layer are too high, a uniform coating layer may not be formed, or the resistance may increase and the charge-discharge efficiency and life characteristics may deteriorate. When the contents of aluminum and zinc in the coating layer are too low, a coating layer with an appropriate thickness may not be formed, and the effect of suppressing side reactions with the electrolyte may decrease.

[0041] On the surface of the positive electrode active material, the ratio of the aluminum content to the zinc content (Al / Zn) can satisfy 2 or more, and can be, for example, 2 to 50, 2 to 40, 2 to 30, 2 to 20, 2 to 10, or 3 to 7. When the above ratio is satisfied, the initial charge-discharge capacity, the initial charge-discharge efficiency, and the life characteristics at high temperature and high voltage of the lithium secondary battery can be improved simultaneously.

[0042] The coating layer according to one embodiment can be in the form of a film that continuously surrounds the surface of the core particles, and can be, for example, in the form of a shell that surrounds the entire surface of the core particles. This is distinguished from a structure that is partially coated only on a part of the surface of the core particles. According to one embodiment, while the coating layer is formed in a form that entirely surrounds the surface of the core particles, it can be formed very thinly and with a uniform thickness. As a result, the positive electrode active material does not have an increase in resistance or a decrease in capacity, the structural stability is improved, side reactions with the electrolyte are effectively suppressed, the gas generation amount under high voltage and high temperature conditions is reduced, and long life characteristics can be realized.

[0043] In the coating layer according to one embodiment, aluminum and zinc are mixed with each other, and zinc is distributed in part or all of the region where aluminum is distributed.

[0044] The thickness of the coating layer according to one embodiment is 5 nm to 200 nm, and can be, for example, 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 the above thickness range, the resistance does not increase or the capacity does not decrease due to the coating, the structural stability of the positive electrode active material can be improved, and side reactions with the electrolyte can be effectively suppressed. The thickness of the coating layer can be measured, for example, by SEM, TEM, TOF-SIMS, XPS, or EDS analysis, and as an example, it can be measured by EDS line profile analysis of the cross-section of the positive electrode active material.

[0045] The thickness of the coating layer according to one embodiment is thin at the level of several tens to several hundreds of nanometers and has a uniform thickness. For example, the deviation in the thickness of the coating layer within one positive electrode active material particle is 20% or less, and can be 18% or less, or 15% or less. Here, the deviation in the thickness of the coating layer refers to the content with respect to the thickness of the coating layer within one positive electrode active material particle. The deviation in the thickness of the coating layer means that, for example, after measuring the thicknesses at more than 10 points in an electron microscope image of a cross-section of one positive electrode active material particle and calculating the arithmetic mean, the absolute value of the difference between one data and the arithmetic mean value is divided by the arithmetic mean value and multiplied by 100. The fact that the deviation or standard deviation of the thickness of the coating layer satisfies the above range means that a coating layer with a uniform thickness is formed in a good form on the surface of the positive electrode active material particle. As a result, the structural stability of the positive electrode active material is improved, side reactions with the electrolyte are effectively suppressed, and an increase in resistance and a decrease in capacity due to the coating are minimized.

[0046] On the other hand, the coating layer can further contain nickel, manganese, or a combination thereof in addition to aluminum and zinc. Nickel and manganese are those that were contained in the core particles and flowed in during the formation process of the coating layer, and their contents are not particularly limited. The coating layer according to one embodiment selectively contains nickel and manganese while necessarily containing aluminum and zinc, is thin and formed with a uniform thickness, and can improve the high-voltage characteristics and life characteristics of the positive electrode active material.

[0047] In addition, the coating layer can further contain sulfur in addition to aluminum and zinc. Sulfur is that which flowed in during the process of introducing aluminum sulfate among the aluminum raw materials or zinc sulfate among the zinc raw materials for forming the coating layer, and its content is not particularly limited. The coating layer according to one embodiment selectively contains sulfur while necessarily containing aluminum and zinc, and can improve the high-voltage characteristics and life characteristics of the positive electrode active material.

[0048] The average particle diameter (D 50 ) of the positive electrode active material according to one embodiment is not particularly limited, and can be, for example, 10 μm to 18 μm, 11 μm to 16 μm, or 12 μm to 15 μm. The average particle diameter is obtained by measuring the sizes (diameter or major axis length) of more than 20 particles randomly in a scanning electron microscope image of the positive electrode active material to obtain a particle size distribution, and the diameter (D 50 ) of the particles with a cumulative volume of 50% by volume in the particle size distribution can be taken as the average particle diameter. When the average particle diameter of the positive electrode active material satisfies the above range, high capacity and long life can be realized, and it is advantageous to form a coating layer according to one embodiment.

[0049] The cobalt content in the positive electrode active material according to one embodiment is, for example, 0.01 mol% or less, 0.005 mol% or less, 0.001 mol% or less with respect to 100 mol% of the total metal excluding lithium, and can be, for example, 0 mol% to 0.01 mol%, 0 mol% to 0.005 mol%, or 0 mol% to 0.011 mol%.

[0050] The positive electrode active material according to one embodiment can be characterized by not containing sodium. Generally, sodium ions can be used in the manufacturing process of the positive electrode active material, but according to the manufacturing method described later, core particles with a stable structure and a coating layer with a uniform thickness can be formed without using sodium ions.

[0051] Manufacturing method of positive electrode active material In one embodiment, a method for manufacturing a positive electrode active material is provided, including: (i) preparing core particles containing a layered lithium nickel-manganese composite oxide; (ii) adding an aluminum raw material and a zinc 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, and then drying and heat-treating the obtained product to obtain a positive electrode active material.

[0052] In the method for manufacturing a positive electrode active material according to an embodiment, the step of preparing core particles containing a layered lithium nickel-manganese composite oxide includes the step of mixing a nickel-manganese composite hydroxide and a lithium raw material 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 in which a plurality of primary particles are aggregated, and may not contain cobalt or may contain a very small amount of cobalt, for example, it may be a cobalt-free nickel-manganese composite hydroxide. The nickel-manganese composite hydroxide can be produced by a normal coprecipitation method.

[0053] In the nickel-manganese composite hydroxide, the content of nickel relative to 100 mol% of the total metal is 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. may be possible. When the content of nickel satisfies the above range, high capacity can be realized, and even if the content of cobalt is decreased, the structural safety can be enhanced.

[0054] In the nickel-manganese composite hydroxide, the content of manganese relative to 100 mol% of the total metal is 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. may be possible. When the content of manganese satisfies the above range, while realizing high capacity, the structural safety of the positive electrode active material can be enhanced, and the production price can be lowered to enhance the economic efficiency.

[0055] Also, when the nickel-manganese composite hydroxide further contains aluminum, the content of aluminum relative to 100 mol% of the total metal is 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% may be possible. When the aluminum content in the composite hydroxide satisfies the above range, while realizing high capacity, the structural safety of the positive electrode active material can be enhanced, and the production price can be lowered to enhance the economic efficiency.

[0056] According to one embodiment, a method for manufacturing a positive electrode active material uses an aluminum raw material during the production of a precursor without further doping aluminum during the production of core particles, so that a nickel-manganese-aluminum composite hydroxide in which aluminum is uniformly dispersed in the structure can be used as the precursor. When using such a precursor, it is possible to manufacture a positive electrode active material in which the layered structure is stably maintained even during repeated charge and discharge without cobalt, and no aluminum by-products or aluminum aggregates are formed, and the capacity, efficiency characteristics, and life characteristics of the positive electrode active material can be improved.

[0057] In the nickel-manganese composite hydroxide, the cobalt content with respect to 100 mol% of the total metal is 0.01 mol% or less, 0.005 mol% or less, 0.001 mol% or less, and can be, for example, 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, is economical, maximizes the capacity, and can improve the structural stability.

[0058] The nickel-manganese composite hydroxide is represented by the following Chemical Formula 2 as an example. [Chemical Formula 2] Ni x2 Mn y2 Al z2 M 2 w2 (OH)2

[0059] 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 Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zr, and Zn.

[0060] In the 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 hold.

[0061] The nickel-manganese composite hydroxide is in particulate form, and the average particle diameter (D 50 ) can be 10 μm to 18 μm, 11 μm to 16 μm, or 12 μm to 15 μm.

[0062] The nickel-manganese composite hydroxide and the lithium raw material can 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.

[0063] The first heat treatment can be carried out in an oxygen atmosphere, for example, in a temperature range of 750 °C to 950 °C, or 780 °C to 900 °C, or 810 °C to 890 °C, and can be carried out for 2 hours to 20 hours, or 4 hours to 12 hours.

[0064] By the first heat treatment, a lithium nickel-manganese composite oxide can be obtained. In the obtained lithium nickel-manganese composite oxide, the content of nickel with respect to 100 mol% of the total metal excluding lithium is 60 mol% to 80 mol%, the content of manganese is 10 mol% or more, the content of aluminum is 0 mol% to 3 mol%, and cobalt can be contained in a very small amount of 0 mol% to 0.01 mol%. Such a composite oxide has a considerably different content of residual lithium on the particle surface and many different surface properties compared to oxides of other compositions, such as lithium nickel-cobalt-manganese composite oxides, lithium nickel-cobalt-aluminum composite oxides, lithium cobalt-based oxides, etc., and it is impossible to form a good coating layer with a uniform film form by existing coating methods. In one embodiment, a method is proposed in which the particle surface of the layered lithium nickel-manganese composite oxide can be coated with aluminum and zinc simultaneously with a very uniform thickness.

[0065] In one embodiment, an aluminum raw material and a zinc raw material are introduced into an aqueous solvent and mixed to first prepare a coating solution. Core particles containing a lithium nickel-manganese composite oxide obtained by a first heat treatment are then introduced and mixed therein, followed by drying and a second heat treatment, whereby a coating layer according to one embodiment can be formed. This is a salt-dissolution wet coating method and can be a pre-addition method in which the salt, which is a coating raw material, is first completely dissolved and then the active material particles are introduced.

[0066] The aqueous solvent can include distilled water, an alcohol-based solvent, or a combination thereof. The aluminum raw material can be, for example, aluminum sulfate. Aluminum sulfate can be an optimal raw material for forming a uniform aluminum coating layer on a layered lithium nickel-manganese composite oxide. The zinc raw material can be zinc sulfate, zinc nitrate, or a combination thereof.

[0067] With respect to the total of 100 mol% of the metals excluding lithium in the core particles, the aluminum in the aluminum raw material, and the zinc in the zinc raw material, the aluminum content in the aluminum raw material can be designed to be 0.5 mol% to 1.5 mol%, for example, 0.5 mol% to 1.4 mol%, 0.6 mol% to 1.4 mol%, 0.7 mol% to 1.3 mol%. By designing the content of the aluminum coating within the above range, a coating layer having a thin thickness on the order of several tens to several hundreds of nanometers and a uniform thickness can be formed, the gas generation amount of the lithium secondary battery can be reduced under high voltage or high temperature driving conditions, and the high capacity and long life characteristics can be improved.

[0068] With respect to the total 100 mol% of the entire metal excluding lithium in the core particles, aluminum in the aluminum raw material, and zinc in the zinc raw material, the zinc content in the zinc raw material can be designed to be 0.01 mol% to 1.5 mol%, for example, 0.05 mol% to 1.0 mol%, 0.1 mol% to 1.0 mol%, 0.1 mol% to 0.5 mol%, or 0.1 mol% to 0.4 mol%. By designing the content of the zinc coating within the above range, a coating layer with a thin thickness of several tens to several hundreds of nanometers and a uniform thickness can be formed, improving the life characteristics under high voltage or high-temperature driving conditions and simultaneously improving the initial charge-discharge efficiency.

[0069] Adding the aluminum raw material and the zinc raw material to the aqueous solvent and mixing them can be carried out for approximately 1 minute to 60 minutes, for example, 3 minutes to 30 minutes, or 5 minutes to 10 minutes. Also, the mixing speed is 100 rpm to 800 rpm, and can be, for example, 200 rpm to 600 rpm, or 250 rpm to 500 rpm. Under such mixing conditions, the aluminum raw material and the zinc raw material can be completely dissolved in the aqueous solvent to produce a colorless and transparent coating solution, and by using such a coating solution, a uniform coating layer according to one embodiment can be effectively formed. The pH of the mixed and completed coating solution is, for example, 1.5 to 4, and can be, for example, 2.0 to 3.5, 2.5 to 3.3, 2.7 to 3.3, or 2.9 to 3.2.

[0070] The core particles are added to the produced coating solution. At this time, the coating quality can be improved by adding the core particles while stirring the coating solution.

[0071] Also, the time required to add core particles to the coating solution is 30 seconds / 500 g to 2 minutes / 500 g, and can be, for example, 30 seconds / 500 g to 1.5 minutes / 500 g. By appropriately adjusting the speed of adding the core particles, after the coating is completed, the pH of the supernatant can be appropriately adjusted, thereby guiding to effectively form a uniform coating layer according to one embodiment. If the speed of adding the core particles is too slow, the reaction rate for each particle may change, and a uniform coating layer may not be formed. Also, if the speed of adding the core particles is too fast, the rate of change of pH becomes fast, and a uniform coating layer may not be formed.

[0072] The stirring time after all the core particles are added to the coating solution is approximately 15 minutes to 60 minutes, and can be, for example, 20 minutes to 50 minutes, or 30 minutes to 45 minutes. The time from when the addition of the core particles to the coating solution starts until the stirring is completed, that is, the coating reaction time, can be appropriately adjusted within approximately 1 hour.

[0073] In one embodiment, when the addition and mixing of the core particles to the coating solution is stopped, that is, the pH range of the supernatant at the end of mixing or coating can be 5.5 to 8.5. When the pH of the supernatant is less than 5.5, the acidity becomes strong, and a uniform coating layer may not be formed. When the pH exceeds 8.5, the basicity becomes strong, and in this case, it may also be difficult to form a uniform aluminum coating layer.

[0074] After removing the aqueous solvent from the mixed solution, drying the obtained product can be carried out, for example, at 40°C to 240°C, 100°C to 220°C, or 150°C to 200°C. As an example, it can be carried out under vacuum conditions, and good coated products can be obtained under such conditions.

[0075] After removing the aqueous solvent from the mixed solution and completing the drying of the resulting product, it can be said that the coated product is in a completed state. The coated product includes core particles and a coating layer located on the surface of the core particles and containing aluminum and zinc. As an example, the coating layer can include a fibrous shape and can be, for example, reticular or spider web-like. Such a reticular shape can be continuously formed over the entire surface of the core particles. The reticular coating layer can surround the core particles very thinly and with a uniform thickness, thereby strengthening the surface of the positive electrode active material, improving the structural stability, and improving the high-temperature and high-voltage characteristics.

[0076] Mixing the nickel-manganese-based composite hydroxide and the lithium raw material and heat-treating them as described above is defined as the first heat treatment, and heat-treating the coated product is defined as the second heat treatment. The second heat treatment can be understood as a process for forming the coating layer. For example, it can be carried out in an oxygen atmosphere at a temperature range of 700 °C to 850 °C, 750 °C to 840 °C, or 800 °C to 830 °C for 2 hours to 20 hours, or 3 hours to 10 hours. When the second heat treatment temperature is set within the above range, the tendency of aluminum to diffuse into the interior of the secondary particles decreases and mainly remains on the surface of the secondary particles. At the same time, a very thin and uniform-thickness shell-like coating can be formed on the surface of the secondary particles, and zinc can also be well-coated on the surface of the secondary particles.

[0077] Positive electrode In one embodiment, it includes 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 provides a positive electrode containing the positive electrode active material described above. The positive electrode active material layer can further include other types of positive electrode active materials in addition to the positive electrode active material described above. Also, the positive electrode active material layer can selectively further include a binder, a conductive material, or a combination thereof.

[0078] According to one embodiment, the loading level of the positive electrode active material layer can be 10 mg / cm 2 ~40 mg / cm 2 and can be, for example, 10 mg / cm 2~30 mg / cm 2 or 10 mg / cm 2 ~20 mg / cm 2 It can be. Also, in the final rolled positive electrode, the density of the positive electrode active material layer can 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 applying the positive electrode active material according to one embodiment, it is advantageous to realize such a loading level and positive electrode density, and a positive electrode satisfying the loading level and positive electrode density within the above range is suitable for realizing a high-capacity, high-energy density lithium secondary battery.

[0079] Binder The binder plays a role of making the positive electrode active material particles adhere well to each other and making the positive electrode active material adhere well to the current collector. Representative examples of the binder include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, nylon, etc., but are not limited thereto.

[0080] Conductive material The conductive material is used to impart conductivity to the electrode, and in the configured battery, any electron conductive material can be used as long as it does not cause a chemical change. Examples of the conductive material include carbon-based substances such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, carbon nanotube; metal-based substances in the form of metal powder or metal fiber containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0081] The contents of the binder and the conductive material can each be 0.5% by weight to 5% by weight based on 100% by weight of the positive electrode active material layer.

[0082] As the positive electrode current collector, Al can be used, but it is not limited thereto.

[0083] Lithium secondary battery In one embodiment, a lithium secondary battery including the above-described positive electrode, negative electrode, and electrolyte is provided. As an example, the lithium secondary battery can include a positive electrode, a negative electrode, a separator positioned between the positive electrode and the negative electrode, and an electrolytic solution.

[0084] The lithium secondary battery can be classified into a cylindrical type, a rectangular type, a pouch type, a coin type, etc. according to its form. FIGS. 1 to 4 are schematic views showing a lithium secondary battery according to one embodiment. It can be said that FIG. 1 is a cylindrical shape, FIG. 2 is a rectangular shape, and FIGS. 3 and 4 are pouch-type battery forms. Referring to FIGS. 1 to 4, the lithium secondary battery 100 can include an electrode assembly 40 with a separator 30 interposed between a positive electrode 10 and a negative electrode 20, and a case 50 in which the electrode assembly 40 is incorporated. The positive electrode 10, the negative electrode 20, and the separator 30 may be immersed in an electrolytic solution (not shown). The lithium secondary battery 100 can include a sealing member 60 for sealing the case 50 as shown in FIG. 1. Also, in FIG. 2, the lithium secondary battery 100 can 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 can include electrode tabs 70, that is, a positive electrode tab 71 and a negative electrode tab 72, which serve as an electrical path for guiding the current formed by the electrode assembly 40 to the outside.

[0085] A lithium secondary battery according to an embodiment may be suitable for charging at a high voltage or driving at a high voltage. For example, the charging voltage of the lithium secondary battery is 4.45V or higher, and may be 4.45V to 4.7V, 4.45V to 4.6V, or 4.45V to 4.55V, etc. By applying a positive electrode active material according to an embodiment, the lithium secondary battery can significantly reduce the gas generation amount even when charged at a high voltage, and can achieve high capacity and long life characteristics.

[0086] 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 contains a negative electrode active material and may further contain a binder, a conductive material, or a combination thereof.

[0087] Negative electrode active material The negative electrode active material includes a material capable of reversibly inserting / desorbing lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and dedoping with lithium, or a transition metal oxide.

[0088] Examples of the material capable of reversibly inserting / desorbing the lithium ions include carbon-based negative electrode active materials, which may include, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite. Examples of the amorphous carbon include soft carbon, hard carbon, mesophase pitch carbide, calcined coke, etc.

[0089] As the alloy of the lithium metal, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0090] As the substance capable of doping and undoping lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used. As the Si-based negative electrode active material, silicon, a silicon-carbon composite, SiOx (0 < x < 2), a Si-Q alloy (where Q is an element selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements (excluding Si), group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof, for example, Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof), or a combination thereof can be used. As the Sn-based negative electrode active material, Sn, SnO2, a Sn alloy, or a combination thereof can be used.

[0091] The silicon-carbon composite can be a composite of silicon and amorphous carbon. The average particle diameter (D 50 ) of the silicon-carbon composite particles can be, for example, 0.5 μm to 20 μm. According to one embodiment, the silicon-carbon composite can be in a form in which silicon particles and amorphous carbon are coated on the surface of the silicon particles. For example, it can include secondary particles (cores) formed by granulating primary silicon particles, and an amorphous carbon coating layer (shell) located on the surface of the secondary particles. The amorphous carbon can also be located between the primary silicon particles, and for example, the primary silicon particles can be coated with amorphous carbon. The secondary particles may be dispersed and present in an amorphous carbon matrix.

[0092] 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.

[0093] When the silicon-carbon composite contains silicon and amorphous carbon, the content of silicon may be 10% to 50% by weight based on 100% by weight of the silicon-carbon composite, and the content of amorphous carbon may be 50% to 90% by weight. When the composite contains silicon, amorphous carbon, and crystalline carbon, the content of silicon may be 10% to 50% by weight, 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 based on 100% by weight of the silicon-carbon composite.

[0094] In addition, the thickness of the amorphous carbon coating layer may be 5 nm to 100 nm. The average particle diameter (D 50 ) of the silicon particles (primary particles) may be 10 nm to 1 μm, or 10 nm to 200 nm. The silicon particles may exist alone as silicon, or in the form of a silicon alloy, or in an oxidized form. The oxidized form of silicon may be represented by SiO x (0 < x < 2). At this time, the atomic content ratio of Si:O indicating the degree of oxidation may be 99:1 to 33:67. In this specification, unless otherwise defined, the average particle diameter (D 50 ) means the diameter of the particle with a cumulative volume of 50% by volume in the particle size distribution.

[0095] The Si-based negative electrode active material or the Sn-based negative electrode active material can be used by mixing with a carbon-based negative electrode active material. When the Si-based negative electrode active material or the Sn-based negative electrode active material is mixed with the carbon-based negative electrode active material, the mixing ratio may be 1:99 to 90:10 by weight.

[0096] Binder The binder plays a role in making the negative electrode active material particles adhere well to each other and making 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.

[0097] 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.

[0098] The aqueous binder can 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, phenol resin, epoxy resin, polyvinyl alcohol, and a combination thereof.

[0099] When using an aqueous binder as the negative electrode binder, a cellulose-based compound capable of imparting viscosity can be further included. As this cellulose-based compound, carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or an alkali metal salt thereof can be used by mixing one or more of them. As the alkali metal, Na, K, or Li can be used.

[0100] The dry binder is a polymer substance capable of being fibrillated, and can be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride - hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0101] Conductive material The conductive material is used to impart conductivity to the electrode, and in the battery being configured, any material that is an electron - conductive material and does not cause a chemical change can be used. Specific examples include carbon - based substances such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, carbon nanotube; metal - based substances containing copper, nickel, aluminum, silver, etc. in the form of metal powder or metal fiber; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0102] The content of the negative electrode active material is 95% to 99.5% by weight based on 100% by weight of the negative electrode active material layer, and the content of the binder can be 0.5% to 5% by weight based on 100% by weight of the negative electrode active material layer. For example, the negative electrode active material layer can 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.

[0103] Current collector The negative electrode current collector can 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 alloys thereof, and can be in the form of a foil, sheet, or foam. The thickness of the negative electrode current collector is, for example, 1 μm to 20 μm, and can be 5 μm to 15 μm, or 7 μm to 10 μm.

[0104] Electrolyte The electrolyte for the lithium secondary battery can be, as an example, an electrolytic solution, which can contain a non - aqueous organic solvent and a lithium salt.

[0105] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move. The non-aqueous organic solvent can be a carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based solvent, an aprotic solvent, or a combination thereof.

[0106] As the carbonate-based solvent, 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. can be used. As the ester-based solvent, methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, caprolactone, etc. can be used. As the ether-based solvent, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. can be used. Also, as the ketone-based solvent, cyclohexanone, etc. can be used. As the alcohol-based solvent, ethyl alcohol, isopropyl alcohol, etc. can be used, and as the aprotic solvent, nitriles such as R-CN (R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and can contain a double bond, an aromatic ring, or an ether group); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane, 1,4-dioxolane; sulfolanes, etc. can be used.

[0107] The non-aqueous organic solvent can be used alone or in admixture of two or more thereof. When used in admixture of two or more thereof, the mixing ratio can be appropriately adjusted according to the intended battery performance, which can be widely understood by those skilled in the art.

[0108] When using a carbonate solvent, a cyclic carbonate and a chain carbonate can be used in admixture, and the cyclic carbonate and the chain carbonate can be mixed at a volume ratio of 1:1 to 1:9.

[0109] The non-aqueous organic solvent can further contain an aromatic hydrocarbon-based organic solvent. For example, the carbonate solvent and the aromatic hydrocarbon-based organic solvent can be used in admixture at a volume ratio of 1:1 to 30:1.

[0110] The electrolytic solution can further contain vinyl ethyl carbonate, vinylene carbonate or an ethylene carbonate-based compound in order to improve the battery life.

[0111] Typical examples of the ethylene carbonate-based compound include fluoroethylene carbonate, difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate and the like.

[0112] The lithium salt is dissolved in the organic solvent, acts as a source of lithium ions in the battery to enable the operation of a basic lithium secondary battery, and plays a role in promoting the movement of lithium ions between the positive electrode and the negative electrode. Typical examples of the lithium salt include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide; LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F2y+1 SO2) (where x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalate)phosphate (LiDFOB), lithium bis(oxalate)borate (LiBOB), or one or more selected therefrom can be included.

[0113] The concentration of the lithium salt is preferably used in the range of 0.1 M to 2.0 M. If the concentration of the lithium salt is within the above range, the electrolyte has appropriate ionic conductivity and viscosity, so it can exhibit excellent performance and lithium ions can move effectively.

[0114] Separator Depending on the type of lithium secondary battery, there may be a separator between the positive electrode and the negative electrode. As such a separator, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof can be used, and it goes without saying that mixed multilayer films such as a two-layer separator of polyethylene / polypropylene, a three-layer separator of polyethylene / polypropylene / polyethylene, and a three-layer separator of polypropylene / polyethylene / polypropylene can be used.

[0115] The separator can include a porous substrate and a coating layer located on one or both sides of the porous substrate and containing an organic substance, an inorganic substance, or a combination thereof.

[0116] The porous substrate can be a polymer selected from any one of polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyether ketone, polyaryl ether ketone, polyether imide, polyamide imide, polybenzimidazole, polyether sulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon (registered trademark), and polytetrafluoroethylene, or a polymer film formed of a copolymer or mixture of two or more of these.

[0117] The porous substrate can have a thickness of about 1 μm to 40 μm, for example, a thickness of 1 μm to 30 μm, 1 μm to 20 μm, 5 μm to 15 μm, or 10 μm to 15 μm.

[0118] The organic substance can include a (meth)acrylic copolymer containing a second structural unit including at least one of a first structural unit derived from (meth)acrylamide, a structural unit derived from (meth)acrylic acid or (meth)acrylate, and a structural unit derived from (meth)acrylamidosulfonic acid or a salt thereof.

[0119] The inorganic substance can 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, 100 nm to 700 nm.

[0120] The organic matter and the inorganic matter may be present as a mixture in a single coating layer, or may be present in a form in which a coating layer containing the organic matter and a coating layer containing the inorganic matter are laminated.

[0121] The thickness of each of the coating layers is 0.5 μm to 20 μm, and for example, may be 1 μm to 10 μm, or 1 μm to 5 μm.

[0122] Hereinafter, examples and comparative examples of the present invention will be described. The following examples are merely illustrative of the present invention, and the present invention is not limited to the following examples.

[0123] Example 1 1. Production of the positive electrode active material Ni 0.75 Mn 0.23 Al 0.02 (OH)2 and LiOH were mixed at a molar ratio of 1:1.05 and first heat-treated at 845 °C for 8 hours in an oxygen atmosphere to obtain a composition of LiNi 0.75 Mn 0.23 Al 0.02 O2, and a lithium nickel-manganese composite oxide in the form of secondary particles with an average particle diameter (D 50 ) of about 14 μm was produced.

[0124] 600 g of distilled water, aluminum sulfate, and zinc sulfate were charged into a 1 L reactor, and stirred at about 350 rpm for about 5 minutes for salt dissolution to produce a coating solution. It was confirmed that the salt was completely dissolved in the coating solution and was colorless and transparent. 500 g of the produced lithium nickel-manganese composite oxide was charged into the continuously stirred coating solution for 1.5 minutes and stirred for about 30 minutes. At this time, the aluminum content in the aluminum sulfate was designed to be 1.0 mol% with respect to 100 mol% of the total metal excluding lithium in the final positive electrode active material, and the zinc content in the zinc sulfate was designed to be 0.1 mol% with respect to 100 mol% of the total metal excluding lithium in the final positive electrode active material. It was confirmed that the pH of the supernatant after completion of stirring was 8.

[0125] The solvent was removed from the mixed solution using an aspirator and a filter press, and vacuum drying was performed at 190 °C to obtain a coated product.

[0126] The second heat treatment was performed on the coated product in an oxygen atmosphere at 750 °C for 8 hours to produce the final positive electrode active material.

[0127] 2. Manufacture of Lithium Secondary Battery 98.5% by weight of the manufactured positive electrode active material, 1.0% by weight of a polyvinylidene fluoride binder, and 0.5% by weight of a carbon nanotube conductive material were mixed to produce a positive electrode active material layer slurry, which was coated on an aluminum foil current collector and dried and rolled to produce a positive electrode. At this time, the loading level of the positive electrode active material layer was 20 mg / cm 2 and the density of the rolled final positive electrode was about 3.4 g / cc.

[0128] 97.5% by weight of a graphite negative electrode active material, 1.5% by weight of carboxymethyl cellulose, and 1% by weight of styrene-butadiene rubber were mixed in an aqueous solvent to produce a negative electrode active material layer slurry. The negative electrode active material layer slurry was coated on a copper foil current collector and dried and rolled to produce a negative electrode.

[0129] A lithium secondary battery was manufactured in a conventional manner using a polytetrafluoroethylene separator and an electrolytic solution in which 1 M LiPF6 was dissolved in a solvent obtained by mixing ethylene carbonate and dimethyl carbonate at a volume ratio of 3:7.

[0130] Example 2 The positive electrode active material and the lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that in the manufacture of the positive electrode active material, the zinc content in zinc sulfate was designed and mixed to be 0.25 mol% with respect to 100 mol% of the total metal excluding lithium in the final positive electrode active material.

[0131] Example 3 The positive electrode active material and the lithium secondary battery were produced in substantially the same manner as in Example 1, except that in the production of the positive electrode active material, the zinc content in zinc sulfate was designed and mixed to be 0.05 mol% with respect to 100 mol% of the total metal excluding lithium in the final positive electrode active material.

[0132] Example 4 The positive electrode active material and the lithium secondary battery were produced in substantially the same manner as in Example 1, except that in the production of the positive electrode active material, the zinc content in zinc sulfate was designed and mixed to be 0.5 mol% with respect to 100 mol% of the total metal excluding lithium in the final positive electrode active material.

[0133] Comparative Example 1 In the production of the positive electrode active material, aluminum sulfate and zinc sulfate were not added, that is, the coating process of aluminum and zinc was not performed, and the LiNi 0.75 Mn 0.23 Al 0.02 O2 composite oxide itself was used as the positive electrode active material, and the positive electrode active material and the lithium secondary battery were produced in substantially the same manner as in Example 1.

[0134] Comparative Example 2 In the production of the positive electrode active material, zinc sulfate was not added, that is, the zinc coating process was not performed, and the aluminum-coated LiNi 0.75 Mn 0.23 Al 0.02 O2 composite oxide was used as the positive electrode active material, and the positive electrode active material and the lithium secondary battery were produced in substantially the same manner as in Example 1.

[0135] Comparative Example 3 In the production of the positive electrode active material, aluminum sulfate was not added, that is, the aluminum coating process was not performed, and the LiNi coated with 1 mol% of zinc 0.75 Mn 0.23 Al 0.02 O2 composite oxide was used as the positive electrode active material, and the positive electrode active material and the lithium secondary battery were produced in substantially the same manner as in Example 1.

[0136] Evaluation Example 1: Surface Analysis of the Positive Electrode Active Material The positive electrode active materials produced in Example 1, Example 2, and Comparative Examples 1 to 3 were photographed and compared using a scanning electron microscope (SEM). Fig. 5 is an SEM image of the surface of the final positive electrode active material produced in Example 1, and Fig. 6 is an enlarged image thereof. Fig. 7 is an SEM image of the surface of the final positive electrode active material produced in Example 2, and Fig. 8 is an enlarged image thereof. Fig. 9 is an SEM image of the surface of the final positive electrode active material produced in Comparative Example 1, and Fig. 10 is an enlarged image thereof. Fig. 11 is an SEM image of the surface of the final positive electrode active material produced in Comparative Example 2, and Fig. 12 is an enlarged image thereof. Fig. 13 is an SEM image of the surface of the final positive electrode active material produced in Comparative Example 3, and Fig. 14 is an enlarged image thereof. In the case of Comparative Examples 1 to 3 in Figs. 9 to 14, it was confirmed that the surface of the secondary particles was smooth, while in the case of Examples 1 and 2 in Figs. 5 to 8, it was found that aluminum and zinc coating layers were confirmed on the surface of the secondary particles.

[0137] Evaluation Example 2: Analysis of the Contents of Aluminum and Zinc on the Surface of the Positive Electrode Active Material The contents of aluminum and zinc on the surface of the positive electrode active material were confirmed by XPS (X-ray photoelectron spectroscopy) depth profile and peak quantification, and the results are shown in Figs. 15 to 16, and the results of the contents of aluminum and zinc on the surface of the positive electrode active material before the second heat treatment are shown in Figs. 17 to 18. The XPS analysis was performed under the following conditions using an ESCALAB 250Xi apparatus manufactured by Thermo Fisher Scientific. At this time, the contents of aluminum and zinc are the values when the sum of the atomic percentages of all components is set to 100. - X-ray: Al Ka 1486.6 eV - Charge neutralization: Low energy ion & electron - Ar+ Gun: 4000 eV -Ar+ Monatomic Gun

[0138] Referring to FIGS. 15 and 16, when confirmed by XPS, it was confirmed that the coating layer was distributed in the form of a film on the outside because the concentration of aluminum decreased while moving from the surface to the bulk within the range of 5 at% to 35 at%. Also, it was confirmed that the concentration of zinc was formed within the range of 0.1 at% to 3.0 at%.

[0139] Furthermore, referring to FIGS. 17 and 18, when the active material before the second heat treatment was confirmed by XPS, it was also confirmed that the coating layer was distributed in the form of a film on the outside because the concentration of aluminum decreased while moving from the surface to the bulk within the range of 5 at% to 35 at%. Also, it was confirmed that the concentration of zinc was formed within the range of 0.1 at% to 3.0 at%.

[0140] Evaluation Example 3: Initial Charge-Discharge Capacity and Efficiency Evaluation The lithium secondary batteries manufactured in Examples 1 to 4 and Comparative Examples 1 to 3 were charged at a constant current of 0.2C to an upper limit voltage of 4.45V at 25°C and then charged at a constant voltage to 0.05C, and then discharged at 0.2C to a cut-off voltage of 3.0V to perform initial charge and discharge. The initial charge capacity, initial discharge capacity, and the ratio of the latter to the former are calculated as efficiency and shown in Table 1 below.

[0141] Evaluation Example 4: High-Temperature Life Characteristics Following the initial charge and discharge in Evaluation Example 3, cycles of charging at 1.0C and discharging at 1.0C in the voltage range of 3.0V to 4.45V at 45°C were repeated 50 times or more, and the ratio of the 50-cycle discharge capacity to the initial discharge capacity was calculated and shown in Table 1 below.

[0142]

Table 1

[0143] Referring to Table 1 above, it was confirmed that in the cases of Example 1 and Example 2, it was possible to simultaneously achieve a high initial charge-discharge capacity, an initial charge-discharge efficiency, and excellent high-temperature life characteristics. Compared with Comparative Example 2 in which only aluminum was coated alone at 1.0 mol%, the initial discharge capacity, the initial charge-discharge efficiency, and the high-temperature life characteristics were all improved in Example 1. Also in the case of Example 2, it was found that the initial discharge capacity, the initial charge-discharge efficiency, and the high-temperature life characteristics were all improved compared with Comparative Example 2. Further, compared with Comparative Example 3 in which only zinc was coated alone at 1.0 mol%, the initial discharge capacity and the initial charge-discharge efficiency were improved in Example 1. Also in the case of Example 2, it was found that the initial discharge capacity and the initial charge-discharge efficiency were improved compared with Comparative Example 3.

[0144] It was confirmed that Comparative Example 1 without introducing an aluminum and zinc coating layer was inferior in high-temperature life characteristics and also somewhat decreased in initial discharge capacity and initial charge-discharge efficiency characteristics compared with the examples.

[0145] On the other hand, in the cases of Examples 1 to 3 in which the zinc content in the coating layer was included in the range of 0.1 mol% to 0.4 mol%, compared with the case of Example 4 where it was not so, it was confirmed that the initial discharge capacity, the initial charge-discharge efficiency, and the high-temperature life characteristics were improved and the battery performance was enhanced.

[0146] As described in detail above for the preferred embodiments, the scope of the rights of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concepts defined in the claims also belong to the scope of the rights of the present invention.

Description of Reference Numerals

[0147] 100 Lithium secondary battery 10 Positive electrode 11 Positive electrode lead tab 12 Positive electrode terminal 20 Negative electrode 21 Negative electrode lead tab 22 Negative electrode 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 coating layer located on the surface of the core particle and containing aluminum and zinc; A positive electrode active material comprising:

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

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 is 1 mol % to 3 mol % relative to 100 mol % of all metals excluding lithium.

4. The positive electrode active material according to claim 3 , wherein the aluminum concentration is uniform within the core particle.

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

6. The layered lithium nickel-manganese composite oxide is represented by the following chemical formula 1: [Chemical formula 1] Li a1 Ni x1 Mn y1 Al z1 M 1 w1 O 2-b1 X b1 In Chemical Formula 1, 0.9≦a1≦1.8, 0.6≦x1≦0.8, 0.1≦y1≦0.4, 0≦z1≦0.03, 0≦w1≦0.3, 0.9≦x1+y1+z1+w1≦1.1, and 0≦b1≦0.1; M 1 is one or more elements selected from Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zr, and Zn, and X is one or more elements selected from F, P, and S.

7. 2. The cathode active material according to claim 1, wherein an aluminum content relative to 100 at% of the total components on a surface of the cathode active material is 5 at% to 35 at% and a zinc content relative to 100 at% of the total components is 0.1 at% to 3.0 at% as measured by XPS (X-ray photoelectron spectroscopy).

8. 2. The positive electrode active material according to claim 1, wherein the aluminum content in the coating layer is 0.5 mol % to 1.5 mol % relative to 100 mol % of all metals excluding lithium, and the zinc content in the coating layer is 0.01 mol % to 1.5 mol % relative to 100 mol % of all metals excluding lithium.

9. 2. The positive electrode active material according to claim 1, wherein the ratio of the aluminum content to the zinc content (Al / Zn) on the surface of the positive electrode active material is 2 to 50.

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

11. The positive electrode active material according to claim 1 , wherein the coating layer has a thickness of 5 nm to 200 nm.

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

13. (i) preparing core particles containing a layered type lithium nickel-manganese composite oxide; (ii) preparing a coating solution by adding and mixing an aluminum raw material and a zinc raw material into an aqueous solvent; (iii) adding the core particles to the coating solution and mixing to prepare a mixed solution; and (iv) removing the aqueous solvent from the mixture, drying the resultant, and heat-treating it to obtain a positive electrode active material; A method for producing a positive electrode active material comprising the steps of:

14. The method for producing a positive electrode active material according to claim 13, wherein the aluminum content in the aluminum raw material is 0.5 mol% to 1.5 mol% and the zinc content in the zinc raw material is 0.1 mol% to 0.4 mol% relative to a total of 100 mol% of all metals excluding lithium in the core particles, the aluminum in the aluminum raw material, and the zinc in the zinc raw material.

15. The aluminum source is aluminum sulfate, The method for producing a positive electrode active material according to claim 13, wherein the zinc source is zinc sulfate, zinc nitrate, or a combination thereof.

16. The method for producing a positive electrode active material according to claim 13, wherein the heat treatment is carried out at 700°C to 850°C.

17. 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 12.

18. The loading level of the positive electrode active material layer is 10 mg / cm 2 ~40mg / cm 2 20. The positive electrode of claim 17,

19. 18. The positive electrode of claim 17, wherein the positive electrode active material layer has a density of 3.3 g / cc to 3.7 g / cc.

20. 18. The positive electrode of claim 17 ; A negative electrode; and electrolyte; A lithium secondary battery comprising:

21. The lithium secondary battery according to claim 20, wherein the charging voltage of the lithium secondary battery is 4.45 V or more.

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