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: The present invention relates to: a positive electrode active material that includes core particles containing a layered lithium nickel-manganese-based composite oxide having a nickel content of greater than or equal to 60 mol% based on 100 mol% of a total metal amount excluding lithium, and a coating layer located on a surface of the core particles and including Al and P; a preparation method thereof; a positive electrode including the positive electrode active material; and a lithium secondary battery.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 having 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 these, 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. By the way, recently, while the demand for large-sized, high-capacity, or high-energy density lithium secondary batteries has been rapidly increasing, the supply amount of positive electrode active materials containing rare metal cobalt is expected to be extremely insufficient. That is, since cobalt is expensive and the remaining reserves are not large, there is a need 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] As a positive electrode active material containing a lithium nickel-manganese-based composite oxide, by introducing an optimal coating layer, the performance of the lithium secondary battery at high temperature and high voltage is improved, and the capacity characteristics, initial charge-discharge efficiency, and high-temperature life characteristics are improved.

Means for Solving the Problems

[0005] In one embodiment, a core particle containing a layered lithium nickel-manganese composite oxide in which the nickel content is 60 mol% or more with respect to 100 mol% of the total metal excluding lithium, and a coating layer containing Al and P located on the surface of the core particle are provided as a positive electrode active material.

[0006] In another embodiment, (i) a core particle containing a layered lithium nickel-manganese composite oxide in which the nickel content is 60 mol% or more with respect to 100 mol% of the total metal excluding lithium is prepared, (ii) an aluminum raw material is introduced into an aqueous solvent and mixed to prepare a coating solution, (iii) the core particle is introduced into the coating solution and mixed to produce a first mixed solution, (iv) a phosphorus-based raw material is introduced into the first mixed solution and mixed to produce a second mixed solution, and (v) after removing the aqueous solvent from the mixed solution, the obtained product is dried and heat-treated to obtain a positive electrode active material, and a method for producing a positive electrode active material is provided.

[0007] In another embodiment, a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector are provided, and the positive electrode active material layer contains the positive electrode active material described above.

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

Advantages of the Invention

[0009] The positive electrode active material according to one embodiment maximizes the capacity while minimizing the production cost, ensures long-life characteristics, and improves characteristics at high voltages and high-temperature characteristics. The lithium secondary battery applying the positive electrode active material can exhibit high initial charge-discharge capacity and efficiency, and can realize excellent high-temperature life characteristics and high-temperature storage characteristics.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, specific embodiments will be described in detail so that those skilled in the art can easily implement them. However, the present invention can be implemented in various different forms and is not limited to the embodiments described herein.

[0012] The terms used herein are used only to describe exemplary embodiments 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] Here, terms such as "comprising", "including", or "having" are intended to specify the presence of implemented features, numbers, steps, components, or combinations thereof, and should be understood not to preclude in advance the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0015] For the purpose of clearly showing various layers and regions in the drawings, the thickness is enlarged, and the same drawing reference numerals are assigned 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] Also, here, the "layer" includes not only the shape formed on the entire surface but also the shape formed on a part of the 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 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, data analysis is performed to count the number of particles for each particle size range, and then the average particle size value can be obtained based on this. Unless otherwise defined, the average particle size can be the diameter D 50 of the particle at which the cumulative volume is 50% by volume in the particle size distribution. Also, unless otherwise defined, the average particle size can be obtained by randomly measuring the sizes (diameter or major axis length) of more than 20 particles from a scanning electron microscope image to obtain a particle size distribution, and taking the diameter D 50 of the particle at which the cumulative volume is 50% by volume in the said particle size distribution as the average particle size.

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

[0019] "Metal" is interpreted as a concept that includes common metals, transition metals, and metalloids.

[0020] Positive electrode active material In one embodiment, provided is a positive electrode active material including core particles containing a layered lithium nickel - manganese - based composite oxide in which the content of nickel is 60 mol% or more with respect to 100 mol% of the total metal excluding lithium, and a coating layer containing Al and P and located on the surface of the core particles.

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

[0022] In one embodiment, in order to improve the surface stability of a layered nickel-manganese-based cathode active material in a high-voltage region, a coating layer containing Al and P is introduced to strengthen the surface of the particles and form a coating layer having a structurally 3D lithium channel, thereby proposing a solution that can improve not only the high-voltage high-temperature life characteristics and high-temperature storage characteristics but also the initial charge-discharge efficiency.

[0023] core particle The core particles contain a lithium nickel-manganese-based composite oxide. The nickel content is 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%, based on 100 mol% of the total metal excluding lithium in the lithium nickel-manganese-based composite oxide. When the nickel content satisfies the above range, a high capacity can be realized, and the structural safety can be enhanced even when the cobalt content is decreased.

[0024] The manganese content may be 15 mol% or more, for example, 15 mol% to 40 mol%, 15 mol% to 35 mol%, 15 mol% to 30 mol%, or 20 mol% to 30%, based on 100 mol% of the total metal excluding lithium in the lithium nickel-manganese-based composite oxide. When the manganese content satisfies the above range, the cathode active material can achieve a high capacity and improve the structural stability.

[0025] The lithium nickel-manganese composite oxide may 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 removed from the structure. The content of aluminum relative to 100 mol% of the lithium nickel-manganese-aluminum composite oxide may be 0.1 mol% or more, 0.5 mol% or more, or 1 mol% or more. For example, it may be 1 mol% to 3 mol%, 1 mol% to 2.5 mol%, 1 mol% to 2 mol%, or 1.5 mol% to 2.5 mol%. When the aluminum content satisfies the above range, a stable layered structure can be maintained even when cobalt is removed, 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.

[0026] According to one embodiment, the concentration of aluminum in the core particles can be uniform. That is, it means that aluminum is evenly dispersed in the core particles without having a concentration gradient from the center to the surface direction within the core particles, or without the aluminum concentration being higher or lower outside than inside within the core particles. 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 additionally doping aluminum during the synthesis process of the core particles. The core particles may be in the form of secondary particles in which a plurality of primary particles are aggregated, but it can also be said that the aluminum content inside the primary particles is the same or similar regardless of the position of the primary particles. That is, when a primary particle is selected at an arbitrary position in the cross-section of the secondary particle and the aluminum content inside the primary particle but not at the interface of the primary particle is measured, the aluminum content can be expressed as being 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, and no aluminum by-products or aluminum aggregates are generated, so that the capacity, efficiency, and life characteristics of the positive electrode active material can be improved simultaneously.

[0027] The lithium nickel-manganese-based composite oxide is specifically represented by the following Chemical Formula 1. [Chemical Formula 1] Li a1 Ni x1 Mn y1 Al z1 M 1 w1 O 2-b1 X b1

[0028] 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 B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, and Zr, and X is one or more elements selected from F, P, and S.

[0029] In Chemical Formula 1, 0.9 ≤ a1 ≤ 1.5, or 0.9 ≤ a1 ≤ 1.2 may be satisfied. Also, Chemical Formula 1 may contain aluminum, and in this case, 0.6 ≤ x1 ≤ 0.8, 0.1 ≤ y1 ≤ 0.39, 0.01 ≤ z1 ≤ 0.03, and 0 ≤ w1 ≤ 0.29 can be satisfied. For example, 0.6 ≤ x1 ≤ 0.8, 0.1 ≤ y1 ≤ 0.39, 0.01 < z1 ≤ 0.03, and 0 ≤ w1 ≤ 0.29 can be satisfied.

[0030] 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 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 be satisfied, 0.01 ≤ z1 ≤ 0.025, 0.01 < z1 ≤ 0.02, or 0.01 < z1 ≤ 0.019 may 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 be satisfied.

[0031] As an example, the lithium nickel - manganese - based composite oxide may not contain cobalt or may contain a small amount of cobalt, and the content of cobalt relative to 100 mol% of the total metal excluding lithium may be 0 mol% to 0.01 mol%.

[0032] The core particles may be in the form of secondary particles formed by aggregation of a plurality of primary particles. The secondary particles may be spherical, ellipsoidal, polyhedral, or irregular in shape, and the primary particles may be spherical, ellipsoidal, plate-shaped, or a combination thereof.

[0033] Since the core particles are liable to be chemically attacked by components in the electrolyte during the driving of the battery under high voltage or high temperature conditions, many side reactions with the electrolyte may occur, resulting in a large amount of gas generation, thus causing problems such as a decrease in battery life and safety. However, by introducing a coating layer according to an embodiment described later, such problems can be solved.

[0034] coating layer The positive electrode active material according to one embodiment includes a coating layer containing Al and P and located on the surface of the core particles. Such a coating layer not only improves the structural stability of the core particles containing a layered lithium nickel-manganese composite oxide, but also effectively suppresses the side reaction between the positive electrode active material and the electrolyte, and promotes the conduction of lithium ions to reduce the resistance, thereby increasing the initial discharge capacity and charge-discharge efficiency of the lithium secondary battery, and simultaneously improving the high-temperature life characteristics and high-temperature storage characteristics.

[0035] The presence of Al and P in the coating layer can be grasped through analyses such as SEM-EDS and XPS. The coating layer may include, for example, one or more of P-O bonds, P=O bonds, Al-O bonds, Al=O bonds, and P-O-Al bonds. The coating layer may include, for example, aluminum phosphate, and more specifically, may include aluminum oxide and aluminum phosphate. As an example, the coating layer may include lithium-aluminum oxide and aluminum phosphate, and may include, for example, Al2O3, LiAlO2, and / or AlPO4.

[0036] In one embodiment, the positive electrode active material may include a first coating layer containing aluminum oxide, which is located on the surface of the core particles, and a second coating layer containing aluminum phosphate, which is located on the first coating layer. That is, the positive electrode active material may include a coating layer having a double-layer structure. The first coating layer may include aluminum oxide, lithium-aluminum oxide, or a combination thereof, and for example, may include LiAlO₂. The second coating layer contains both Al and P, and for example, may include AlPO₄.

[0037] In one embodiment, by the manufacturing method described below, the core particles are put into an aluminum-containing coating solution and mixed to perform Al coating first, and then a phosphorus-based coating raw material is put in and mixed to form a P coating layer on the Al coating layer. According to such a method, a positive electrode active material can be provided in which a first coating layer containing Al or containing aluminum oxide is formed on the core particles, and a second coating layer containing P, specifically, containing aluminum phosphate, is formed on the first coating layer. Different from one embodiment, when coating with P first, for example, PO₄ 3- ions may react with the Li + ions of the core particles to generate lithium phosphates such as Li₃PO₄, and as a result, a problem may occur in that the surface structure of the positive electrode active material changes and the reversible capacity decreases. However, when coating is performed in the order according to one embodiment, the structural stability of the core particles is further enhanced, the conduction of lithium ions is promoted, the resistance is reduced, the reversible capacity is increased, and it is confirmed that the life characteristics and high-temperature characteristics are improved. According to the method according to one embodiment, the positive electrode active material may contain aluminum oxide, lithium-aluminum oxide, aluminum phosphate, or a combination thereof on the surface, but may not contain lithium phosphate in some cases.

[0038] In the coating layer, the content of Al may be 0.5 mol% to 3 mol%, for example, 0.5 mol% to 2.5 mol%, 0.5 mol% to 2 mol%, or 0.5 mol% to 1.5 mol% with respect to 100 mol% of the total elements other than lithium and oxygen in the positive electrode active material. Also, in the coating layer, the content of P may be 0.1 mol% to 2 mol%, for example, 0.1 mol% to 1.5 mol%, 0.1 mol% to 1 mol%, 0.1 mol% to 0.9 mol%, or 0.1 mol% to 0.5 mol% with respect to 100 mol% of the total elements other than lithium and oxygen in the positive electrode active material. When the contents of Al and P satisfy the respective ranges, the structural stability of the layered lithium nickel-manganese composite oxide is improved, the conduction of lithium ions is promoted, and the initial discharge capacity, charge-discharge efficiency, high-temperature life characteristics, and high-temperature storage characteristics of the lithium secondary battery can be simultaneously improved.

[0039] Also, the Al content with respect to 100 at% of the total elements other than lithium on the surface of the positive electrode active material measured by scanning electron microscope energy dispersive spectroscopy (SEM-EDS) may be 5 at% to 35 at%, for example, 5 at% to 30 at%, 5 at% to 25 at%, 6 at% to 20 at%, or 7 at% to 15 at%. Also, the P content with respect to 100 at% of the total elements other than lithium on the surface of the positive electrode active material measured by SEM-EDS may be 0.1 at% to 8 at%, for example, 0.5 at% to 7 at%, 1 at% to 6 at%, or 2 at% to 5 at%. The total elements may be, for example, Li, Ni, Mn, Al, Ti, O, and C. When the respective contents of Al and P on the surface of the positive electrode active material satisfy the above ranges, the initial charge-discharge capacity, initial charge-discharge efficiency, high-temperature life characteristics, and high-temperature storage characteristics of the lithium secondary battery to which this is applied can be simultaneously improved.

[0040] On the surface of the positive electrode active material, the ratio of the Al content to the P content (Al / P) may satisfy 2 or more, for example, it may be 2 to 10, 2 to 8, 2 to 6, 2 to 4, or 2 to 3. When the ratio is satisfied, the initial charge-discharge capacity, initial charge-discharge efficiency, high-temperature life, and high-temperature storage characteristics of the lithium secondary battery can be improved simultaneously.

[0041] The coating layer according to one embodiment may be, for example, in the form of a film that continuously surrounds the surface of the core particles, and may 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, the coating layer can be formed in a form that entirely surrounds the surface of the core particles and can be formed to have a very thin and 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 can be effectively suppressed, and the gas generation amount under high voltage and high temperature conditions can be reduced to realize long-life characteristics.

[0042] The thickness of the coating layer may be 5 nm to 500 nm, for example, 5 nm to 400 nm, 5 nm to 300 nm, 5 nm to 200 nm, 5 nm to 100 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, and the structural stability of the positive electrode active material can be improved to effectively suppress side reactions with the electrolyte. The thickness of the coating layer may be measured, for example, through SEM, TEM, TOF-SIMS, XPS, or EDS analysis, etc. As an example, it may be measured through EDS line profile analysis of the cross-section of the positive electrode active material.

[0043] The coating layer according to one embodiment is characterized by being thin at the level of several tens to several hundreds of nanometers in thickness and having a uniform thickness. For example, the deviation in the thickness of the coating layer within one positive electrode active material particle may be 20% or less, or may be 18% or less, or 15% or less. Here, the deviation in the thickness of the coating layer is 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 can be, 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, calculating the arithmetic mean, dividing the absolute value of the difference between one data and the arithmetic mean value by the arithmetic mean value, and multiplying by 100. 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. Thereby, 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 can be minimized.

[0044] In addition to aluminum, the coating layer may further contain nickel, manganese, or a combination thereof.

[0045] The average particle diameter D of the positive electrode active material according to one embodiment 50 is not particularly limited, and may be, for example, 1 μm to 25 μm, 5 μm to 25 μm, 10 μm to 25 μm, 11 μm to 20 μm, or 12 μm to 18 μm. The average particle diameter is obtained by randomly measuring the sizes (diameter or major axis length) of more than 20 particles in a scanning electron microscope image of the positive electrode active material to obtain a particle size distribution, and taking the diameter D of the particle with a cumulative volume of 50% by volume in the particle size distribution 50 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, which is advantageous for forming the coating layer according to one embodiment.

[0046] In another embodiment, the other positive electrode active material is characterized by not containing sodium. Generally, sodium ions may be used in the manufacturing process of the positive electrode active material. However, according to the manufacturing method described later, a core particle with a stable structure and a coating layer with a uniform thickness can be formed without using sodium ions.

[0047] On the other hand, the positive electrode active material according to an embodiment may contain a sulfur (S) component on its surface, which may be due to the coating raw material described later.

[0048] Method for manufacturing positive electrode active material In one embodiment, a method for manufacturing a positive electrode active material is provided, which includes: (i) preparing core particles containing a layered lithium nickel-manganese composite oxide in which the content of nickel is 60 mol% or more with respect to 100 mol% of the total metal excluding lithium; (ii) preparing a coating solution by adding and mixing an aluminum raw material into an aqueous solvent; (iii) adding and mixing the core particles into the coating solution to produce a first mixed solution; (iv) adding and mixing a phosphorus-based raw material into the first mixed solution to produce a second mixed solution; and (v) removing the aqueous solvent from the mixed solution, and then drying and heat-treating the obtained product to obtain a positive electrode active material. The positive electrode active material described above can be manufactured through the above method.

[0049] First, as an example, the layered lithium nickel-manganese composite oxide may be manufactured by mixing a lithium nickel-manganese 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. The nickel-manganese-aluminum composite hydroxide may be manufactured by a general coprecipitation method.

[0050] A nickel-manganese composite hydroxide, wherein the nickel content satisfies 60 mol% or more, based on 100 mol% of the total metal, and for example, may be 60 mol% to 80 mol%, 65 mol% to 80 mol%, 70 mol% to 80 mol%, 60 mol% to 79 mol%, 60 mol% to 78 mol%, or 60 mol% to 75 mol%. When the nickel content satisfies the above range, high capacity can be achieved, and even if the cobalt content is reduced, the structural safety can be enhanced.

[0051] A nickel-manganese composite hydroxide, wherein the manganese content may be 15 mol% or more, based on 100 mol% of the total metal, and for example, may be 15 mol% to 40 mol%, 15 mol% to 39 mol%, 15 mol% to 35 mol%, 15 mol% to 30 mol%, 20 mol% to 30%, etc.

[0052] Further, when the nickel-manganese composite hydroxide further contains aluminum, the aluminum content may be 0.1 mol% or more, 0.5 mol% or more, or 1 mol% or more, based on 100 mol% of the total metal, and for example, may be 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 contents of manganese and aluminum in the composite hydroxide satisfy the above ranges respectively, high capacity can be achieved, the structural safety of the positive electrode active material can be enhanced, and the production cost can be reduced to improve the economic efficiency.

[0053] The method for manufacturing a positive electrode active material according to an embodiment may use a nickel-manganese-aluminum composite hydroxide in which aluminum is evenly dispersed in the structure as a precursor by using an aluminum raw material during the production of the precursor without additionally doping aluminum during the production of the core particles. 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 since aluminum by-products and aluminum aggregates are not formed, the capacity, efficiency characteristics, and life characteristics of the positive electrode active material can be improved.

[0054] In the nickel-manganese composite hydroxide, the cobalt content may be 0.01 mol% or less, 0.005 mol% or less, or 0.001 mol% or less with respect to 100 mol% of the total metal. Such a nickel-manganese composite hydroxide can avoid the increase in unit price due to cobalt and is economical, and it can be said that the capacity is maximized and the structural stability is improved.

[0055] 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

[0056] 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, Y, and Zr.

[0057] In the above Chemical Formula 2, for example, 6 ≦ x2 ≦ 0.8, 0.1 ≦ y2 ≦ 0.39, 0.01 ≦ z2 ≦ 0.03, 0 ≦ w2 ≦ 0.29 may also be possible.

[0058] The nickel-manganese composite hydroxide is in particulate form, and the average particle size D of the particles 50 may be 1 μm to 25 μm, 5 μm to 20 μm, 10 μm to 20 μm, 11 μm to 18 μm, or 12 μm to 15 μm.

[0059] The nickel-manganese composite hydroxide and the lithium raw material may be mixed in a molar ratio of 1:0.9 to 1:1.8. For example, they may be mixed in a molar ratio of 1:0.9 to 1:1.5 or 1:0.9 to 1:1.2. The first heat treatment may be carried out in an oxygen atmosphere. For example, it may be carried out in a temperature range of 750 °C to 950 °C, or 780 °C to 900 °C, or 810 °C to 890 °C, and may be carried out for 2 hours to 20 hours, or 4 hours to 12 hours. Lithium nickel-manganese composite oxide can be obtained through the heat treatment. The obtained composite oxide is the aforementioned cathode active material and is substantially the same as that described for the core particles.

[0060] The content of residual lithium on the surface of the particles of the layered lithium nickel-manganese composite oxide is quite different from that of oxides with other compositions, such as lithium nickel-cobalt-manganese composite oxide, lithium nickel-cobalt-aluminum composite oxide, lithium cobalt oxide, etc. Different surface characteristics make it impossible to form a good coating layer with a uniform film form by existing coating methods. In one embodiment, a method is proposed that can coat the surface of the particles of the layered lithium nickel-manganese composite oxide with Al and P to a very uniform thickness.

[0061] In one embodiment, an aluminum raw material is put into an aqueous solvent and mixed to first prepare a coating solution, and then core particles are put into this coating solution and mixed. This can be said to be a salt-dissolution wet coating method and a pre-addition method in which the salt of the coating raw material is first completely dissolved and then the cathode active material particles are added.

[0062] The aqueous solvent may contain distilled water, an alcohol-based solvent, or a combination thereof.

[0063] As an example, the aluminum raw material may be aluminum sulfate. Aluminum sulfate can be said to be an optimal raw material for forming a uniform Al coating layer on the layered lithium nickel-manganese composite oxide.

[0064] The Al content in the aluminum raw material may be designed to be 0.1 mol% to 3.0 mol% with respect to the total 100 mol% of the elements excluding lithium and oxygen in the core particles and the aluminum in the aluminum raw material. For example, it may be designed to be 0.1 mol% to 2.0 mol%, 0.5 mol% to 1.5 mol%, 0.6 mol% to 1.4 mol%, 0.7 mol% to 1.3 mol%, or 0.8 mol% to 1.2 mol%. By designing the Al coating content 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, reducing the gas generation amount of the lithium secondary battery under high voltage or high-temperature driving conditions and improving the high-capacity and long-life characteristics.

[0065] The charging and mixing of the aluminum raw material into the aqueous solvent may be carried out for approximately 1 minute to 60 minutes. For example, it may be carried out for 1 minute to 30 minutes, 3 minutes to 30 minutes, or 5 minutes to 10 minutes. Also, the mixing speed may be 100 rpm to 800 rpm. For example, it may be 200 rpm to 600 rpm, or 250 rpm to 500 rpm. Through such mixing conditions, the aluminum raw material can be completely dissolved in the aqueous solvent to produce a colorless and transparent coating solution. By using such a coating solution, a uniform coating layer according to one embodiment can be effectively formed. The pH of the coating solution after mixing completion may be, for example, 1.5 to 4. For example, it may be 2.0 to 3.5, 2.5 to 3.3, 2.7 to 3.3, or 2.9 to 3.2.

[0066] The core particles are introduced into the prepared coating solution. At this time, by introducing the core particles while stirring the coating solution, the coating quality can be improved.

[0067] Also, the time taken to introduce the core particles into the coating solution may be 30 seconds / 500 g to 2 minutes / 500 g, for example, 30 seconds / 500 g to 1.5 minutes / 500 g, etc. By appropriately adjusting the rate of introducing 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 rate of introducing the core particles is excessively slow, the reaction rate for each particle may change and a uniform coating layer may not be formed. Also, if the rate of introducing the core particles is excessively fast, the rate of change of pH may be fast and a uniform coating layer may not be formed.

[0068] The stirring time after all the core particles have been introduced into the coating solution may be approximately 15 minutes to 60 minutes, for example, 20 minutes to 50 minutes, or 30 minutes to 45 minutes. The time from when the introduction of the core particles into the coating solution starts until the stirring is completed, that is, the time to produce the first mixed solution, can be appropriately adjusted within approximately 1 hour.

[0069] In one embodiment, when the introduction and mixing of the core particles into the coating solution are stopped, that is, the pH range of the first mixed solution may be 5.5 to 8.5. If the pH of the first mixed solution is less than 5.5, the acidity becomes strong and a uniform coating layer may not be formed. If the pH exceeds 8.5, the basicity becomes strong and in this case too, it may be difficult to form a uniform Al coating layer.

[0070] (iv) In the step of (iv), a P coating can be performed by adding a phosphorus-based raw material to the first mixed solution and mixing them. Here, the phosphorus-based raw material may be, for example, phosphoric acid (H3PO4). In one embodiment, in the step of (iii), core particles are added to the Al coating solution and mixed to induce an Al coating, and then, in the step of (iv), by adding and mixing the phosphorus-based raw material, a P coating can be induced on the outermost surface of the positive electrode active material. As described above, different from one embodiment, when P is coated first, for example, PO4 3- ions react with the Li + ions of the core particles to form lithium phosphates such as Li3PO4, and as a result, structural variation may occur on the surface of the positive electrode active material, and there may be a problem that the reversible capacity decreases. However, according to one embodiment, when a P coating is performed after an Al coating, the structural stability of the core particles is further enhanced, the conduction of lithium ions is promoted, the resistance is reduced, the reversible capacity is increased, and it is confirmed that the life characteristics and high-temperature characteristics are improved.

[0071] According to the manufacturing method according to one embodiment, a first coating layer containing aluminum oxide, lithium-aluminum oxide, or a combination thereof is formed on the surface of the core particles, and a second coating layer containing aluminum phosphate can be formed on the first coating layer. Since the aluminum oxide, etc. of the first coating layer and the aluminum phosphate of the second coating layer are not well mixed, they may exist as separate layers. Also, since phosphate is in an anionic form, it is expected to exist on the outermost surface of the positive electrode active material rather than diffusing into the core particles.

[0072] The phosphorus content of the phosphorus-based raw material may be 0.1 mol% to 2 mol%, for example, 0.1 mol% to 1.5 mol%, 0.1 mol% to 1 mol%, 0.1 mol% to 0.9 mol%, or 0.1 mol% to 0.5 mol% with respect to the total 100 mol% of the elements excluding lithium and oxygen in the core particles and the phosphorus of the phosphorus-based raw material. By designing the P coating content 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, improving the life characteristics under high voltage and high temperature driving conditions and improving the initial charge-discharge efficiency.

[0073] After introducing the phosphorus-based raw material into the first mixed solution, the mixing time is 15 minutes to 60 minutes, for example, 20 minutes to 50 minutes, or 30 minutes to 45 minutes. The time until the second mixed solution is produced can be appropriately adjusted within almost 1 hour. Also, when a phosphorus-based raw material, for example, phosphoric acid, is introduced into the first mixed solution, the pH initially becomes low and acidic, and after mixing for a while, the pH may become high again. The pH range of the second mixed solution at the completion of mixing may be about 5.5 to 8.5. If the pH of the second mixed solution is less than 5.5, the acidity may become strong and a uniform coating layer may not be formed. If the pH exceeds 8.5, the basicity becomes strong and in this case too, it may be difficult to form a uniform coating layer.

[0074] After removing the aqueous solvent with the second mixed solution, drying the product may be performed, for example, at 40°C to 240°C, 100°C to 220°C, or 150°C to 200°C, and as an example, it may be performed under vacuum conditions. Good coated products can be obtained under such conditions.

[0075] After removing the aqueous solvent with the second mixed solution and completing the drying of the product, the resulting state can be referred to as a coated article. The coated article includes core particles and a coating layer located on the surface of the core particles and containing Al and P. As an example, the coating layer may include a fibrous shape, for example, a mesh shape or a spider web shape. Such a mesh may be continuously formed over the entire surface of the core particles. The mesh-shaped coating layer can surround the core particles with a very thin and uniform thickness, thereby strengthening the surface of the positive electrode active material, improving the structural stability, and enhancing the high-temperature and high-voltage characteristics.

[0076] When the mixing and heat treatment of the nickel-manganese composite hydroxide and the lithium raw material described above are expressed as the first heat treatment, the heat treatment of the coated article can be referred to as the second heat treatment.

[0077] In one embodiment, the second heat treatment temperature range may be 730°C to 800°C, for example, 740°C to 800°C, 750°C to 800°C, 750°C to 780°C, or 750°C to 775°C. When the second heat treatment temperature is set within the above range, the tendency of aluminum to diffuse into the secondary particles is reduced, and it mainly remains on the surface of the secondary particles. At the same time, a shell-shaped coating with a very thin and uniform thickness can be formed on the surface of the secondary particles, and the P element or the surface of the secondary particles can be well coated.

[0078] When the second heat treatment temperature exceeds 800°C, the tendency of aluminum to diffuse into the secondary particles increases, and it is difficult to form a high-concentration Al-rich coating layer on the surface. As a result, the initial charge-discharge capacity and efficiency characteristics at high voltage may decrease, and the life characteristics at high voltage and high temperature may also decrease. When the second heat treatment temperature is less than 730°C, some of the aluminum and phosphorus components may aggregate or be unevenly distributed on the surface of the secondary particles, thereby reducing the life characteristics and the initial charge-discharge efficiency under high-temperature and high-voltage conditions.

[0079] The second heat treatment may be performed, for example, in an oxygen atmosphere for 2 to 20 hours, or 3 to 10 hours.

[0080] The obtained positive electrode active material can be said to include core particles containing a layered lithium nickel-manganese composite oxide in which the nickel content is 60 mol% or more with respect to 100 mol% of the total metal excluding lithium, and a coating layer containing Al and P located on the surface of the core particles. At this time, the coating layer may contain a layered aluminum-based oxide and aluminum phosphate.

[0081] Positive electrode In one embodiment, a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector are included, and the positive electrode active material layer provides a positive electrode containing the positive electrode active material described above. The positive electrode active material layer may further contain other types of positive electrode active materials in addition to the positive electrode active material described above. Further, the positive electrode active material layer may selectively further contain a binder, a conductive material, or a combination thereof.

[0082] According to one embodiment, the loading level of the positive electrode active material layer is 10 mg / cm 2 to 40 mg / cm 2 and may be, for example, 10 mg / cm 2 to 30 mg / cm 2 or 10 mg / cm 2 to 20 mg / cm 2 and may be. Also, in the final rolled positive electrode, the density of the positive electrode active material layer may be 3.3 g / cc to 3.7 g / cc, for example, 3.3 g / cc to 3.6 g / cc or 3.4 g / cc to 3.58 g / cc. When 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 and high-energy density lithium secondary battery.

[0083] 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, but are not limited to, 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.

[0084] Conductive material The conductive material is used to impart conductivity to the electrode, and in the battery being configured, any electron conductive material that does not cause a chemical change can be used. 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.

[0085] The contents of the binder and the conductive material may each be 0.5 wt% to 5 wt% based on 100 wt% of the positive electrode active material layer.

[0086] As the positive electrode current collector, Al may be used, but it is not limited thereto.

[0087] Lithium secondary battery In one embodiment, a lithium secondary battery including the positive electrode, negative electrode, and electrolyte described above is provided. As an example, the lithium secondary battery may include a positive electrode, a negative electrode, a separator positioned between the positive electrode and the negative electrode, and an electrolyte solution.

[0088] Lithium secondary batteries can be classified into cylindrical, prismatic, pouch-type, coin-type, etc. according to their form. FIGS. 1 to 4 are schematic views showing a lithium secondary battery according to an embodiment. It can be said that FIG. 1 is circular, FIG. 2 is prismatic, and FIGS. 3 and 4 are pouch-type battery forms. Referring to FIGS. 1 to 4, the lithium secondary battery 100 may 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 impregnated with an electrolytic solution (not shown). The lithium secondary battery 100 may include a sealing member 60 for sealing 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, 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.

[0089] The 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 may be 4.45 V or more, and may be 4.45 V to 4.7 V, 4.45 V to 4.6 V, or 4.45 V to 4.55 V, etc. By applying the 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 realize high capacity and long life characteristics.

[0090] 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 may include a negative electrode active material and may further include a binder, a conductive material, or a combination thereof.

[0091] Negative electrode active material The negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and undoping lithium, or a transition metal oxide.

[0092] Examples of the material capable of reversibly intercalating / deintercalating 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-shaped, 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.

[0093] As the alloy of 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.

[0094] As the material capable of doping and undoping lithium, an Si-based negative electrode active material or an Sn-based negative electrode active material may be used. The Si-based negative electrode active material may be silicon, a silicon-carbon composite, SiOx (0 < x < 2), an Si-Q alloy (where Q is an element selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements (excluding Si), group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof, for example, Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof), or a combination thereof. The Sn-based negative electrode active material may be Sn, SnO2, an Sn alloy, or a combination thereof.

[0095] 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, from 0.5 μm to 20 μm. According to one embodiment, the silicon-carbon composite may be in a form in which silicon particles and amorphous carbon are coated on the surface of the silicon particles. For example, it may include secondary particles (cores) assembled from primary silicon particles and an amorphous carbon coating layer (shell) located on the surface of the secondary particles. The amorphous carbon may also be located between the primary silicon particles, and for example, the primary silicon particles may be coated with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0096] 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.

[0097] When the silicon-carbon composite contains silicon and amorphous carbon, the content of silicon may be from 10% by weight to 50% by weight based on 100% by weight of the silicon-carbon composite, and the content of amorphous carbon may be from 50% by weight to 90% by weight. When the composite contains silicon, amorphous carbon, and crystalline carbon, the content of silicon may be from 10% by weight to 50% by weight based on 100% by weight of the silicon-carbon composite, the content of crystalline carbon may be from 10% by weight to 70% by weight, and the content of amorphous carbon may be from 20% by weight to 40% by weight.

[0098] Also, the thickness of the amorphous carbon coating layer may be from 5 nm to 100 nm. The average particle diameter D of the silicon particles (primary particles) 50may be from 10 nm to 1 μm, or may be from 10 nm to 200 nm. The silicon particles may exist alone as silicon, may exist in the form of a silicon alloy, or may exist in an oxidized form. The oxidized form of silicon can be represented by SiOx (0 < x < 2). At this time, the atomic content ratio of Si:O indicating the degree of oxidation may be from 99:1 to 33:67. In this specification, unless otherwise defined, the average particle size D 50 means the diameter of the particles with a cumulative volume of 50% by volume in the particle size distribution.

[0099] The Si-based negative electrode active material or the Sn-based negative electrode active material may be used in mixture with a carbon-based negative electrode active material. When the Si-based negative electrode active material or the Sn-based negative electrode active material and the carbon-based negative electrode active material are used in mixture, the mixing ratio may be from 1:99 to 90:10 by weight.

[0100] 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 may be used.

[0101] 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.

[0102] The aqueous binder may be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0103] When using an aqueous binder as the negative electrode binder, it may further contain a cellulose-based compound capable of imparting viscosity. As this cellulose-based compound, one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or alkali metal salts thereof may be mixed and used. As the alkali metal, Na, K, or Li may be used.

[0104] The dry binder is a polymer substance capable of being fibrillated, and may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or combinations thereof.

[0105] Conductive material The conductive material is used to impart conductivity to the electrode, and in the configured battery, any electron conductive material that 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, and 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.

[0106] The content of the negative electrode active material may be 95% by weight to 99.5% by weight based on 100% by weight of the negative electrode active material layer, and the content of the binder may be 0.5% by weight to 5% by weight based on 100% by weight of the negative electrode active material layer. For example, the negative electrode active material layer may contain 90% by weight to 99% by weight of the negative electrode active material, 0.5% by weight to 5% by weight of the binder, and 0.5% by weight to 5% by weight of the conductive material.

[0107] Current collector The negative electrode current collector may contain, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or an alloy thereof, and may be in the form of a foil, sheet, or foam. The thickness of the negative electrode current collector may be, for example, 1 μm to 20 μm, or may be 5 μm to 15 μm, or 7 μm to 10 μm.

[0108] Electrolyte The electrolyte for the lithium secondary battery may be, for example, an electrolytic solution, which may contain a non-aqueous organic solvent and a lithium salt.

[0109] 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 may be a carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based solvent, an aprotic solvent, or a combination thereof.

[0110] As carbonate solvents, 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. may be used. As ester solvents, methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, caprolactone, etc. may be used. As ether solvents, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. may be used. Further, as ketone solvents, cyclohexanone, etc. may be used. As alcohol solvents, ethyl alcohol, isopropyl alcohol, etc. may be used, and as aprotic solvents, nitriles such as R-CN (R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may contain a double bond, aromatic ring, or ether group), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, 1,4-dioxolane, sulfolane, etc. may be used.

[0111] The non-aqueous organic solvent may be used alone or in a mixture of two or more. When used in a mixture of two or more, the mixing ratio can be appropriately adjusted according to the intended battery performance, which should be widely understood by those skilled in the art.

[0112] When using a carbonate solvent, a cyclic carbonate and a chain carbonate may be mixed and used, and the cyclic carbonate and the chain carbonate may be mixed at a volume ratio of 1:1 to 1:9.

[0113] The non-aqueous organic solvent may further contain an aromatic hydrocarbon-based organic solvent. For example, the carbonate-based solvent and the aromatic hydrocarbon-based organic solvent may be mixed and used at a volume ratio of 1:1 to 30:1.

[0114] The electrolytic solution may further contain vinyl ethyl carbonate, vinylene carbonate or an ethylene carbonate-based compound in order to improve the battery life.

[0115] 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.

[0116] The lithium salt is a substance that dissolves 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 promotes 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 F 2y+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), and may contain one or more selected therefrom.

[0117] The concentration of the lithium salt is preferably used within the range of 0.1 M to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolytic solution has appropriate ionic conductivity and viscosity, so that excellent performance can be exhibited and lithium ions can move effectively.

[0118] Separator A separator may be present between the positive electrode and the negative electrode depending on the type of the lithium secondary battery. As such a separator, polyethylene, polypropylene, polyvinylidene fluoride or a multilayer film of two or more layers thereof may be used, and it goes without saying that a mixed multilayer film such as a two-layer separator of polyethylene / polypropylene, a three-layer separator of polyethylene / polypropylene / polyethylene, or a three-layer separator of polypropylene / polyethylene / polypropylene may be used.

[0119] The separator may include a porous substrate and a coating layer located on one or both surfaces of the porous substrate and containing an organic substance, an inorganic substance, or a combination thereof.

[0120] The porous substrate may 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 a mixture of two or more of these.

[0121] The porous substrate may 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.

[0122] The organic substance 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 (meth)acrylate and a structural unit derived from (meth)acrylamidosulfonic acid or a salt thereof.

[0123] The inorganic substance 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 diameter D of the inorganic particles 50 may be from 1 nm to 2000 nm, for example, from 100 nm to 1000 nm, or from 100 nm to 700 nm.

[0124] The organic substance and the inorganic substance may be present mixed in one coating layer, or may be present in a form in which a coating layer containing the organic substance and a coating layer containing the inorganic substance are laminated.

[0125] The thickness of each coating layer may be from 0.5 μm to 20 μm, for example, from 1 μm to 10 μm, or from 1 μm to 5 μm.

[0126] 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.

[0127] Example 1 1. Manufacture of positive electrode active material Ni 0.75 Mn 0.24 Al 0.01 (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 Li 1.05 Ni0.75 Mn 0.24 Al 0.01 is O2, and a secondary particle form lithium nickel-manganese composite oxide with an average particle size D 50 of about 14 μm was produced.

[0128] 600 g of distilled water and aluminum 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. Subsequently, 500 g of the produced lithium nickel-manganese composite oxide was charged into the continuously stirred coating solution over 1.5 minutes and stirred for about 30 minutes to produce a first mixed solution. At this time, the aluminum content in the aluminum sulfate was designed to be 1 mol% with respect to 100 mol% of the total elements excluding lithium and oxygen in the final cathode active material. The pH of the first mixed solution after completion of stirring was confirmed to be 6.6. Next, H3PO4 was added to the first mixed solution and stirred for about 30 minutes to produce a second mixed solution. The P content in the phosphoric acid was designed to be 0.1 mol% with respect to 100 wt% of the total elements excluding lithium and oxygen in the final cathode active material. The addition of phosphoric acid lowered the pH of the solution, and after stirring, it increased again and maintained about 6.6.

[0129] Thereafter, the solvent was removed from the second mixed solution using an aspirator and a filter press, and vacuum dried at 190 °C to obtain a coated product.

[0130] The second heat treatment was performed on the coated product in an oxygen atmosphere at 750 °C for 8 hours to produce the final cathode active material.

[0131] 2. Manufacture of coin cell 98.5 wt% of the produced cathode active material, 1.0 wt% of a polyvinylidene fluoride binder, and 0.5 wt% of a carbon nanotube conductive material were mixed to produce a cathode active material layer slurry, which was coated on an aluminum foil current collector, dried, and rolled to produce a cathode. At this time, the loading level of the cathode active material layer was 10 mg / cm 2and the density of the rolled final positive electrode is about 3.4 g / cc.

[0132] Using lithium metal as the counter electrode, a polytetrafluoroethylene separator, and an electrolyte 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, a coin cell was fabricated in a conventional manner.

[0133] Example 2 In the production of the positive electrode active material, except that the content of P in phosphoric acid was changed to 0.3 mol% with respect to the total 100% by weight of the elements excluding lithium and oxygen in the final positive electrode active material, the positive electrode active material and the coin cell were produced in substantially the same manner as in Example 1.

[0134] Example 3 In the production of the positive electrode active material, except that the content of P in phosphoric acid was changed to 0.5 mol% with respect to the total 100% by weight of the elements excluding lithium and oxygen in the final positive electrode active material, the positive electrode active material and the coin cell were produced in substantially the same manner as in Example 1.

[0135] Comparative Example 1 In the production of the positive electrode active material, except that no Al, P coating was performed and the lithium nickel-manganese composite oxide itself was used as the positive electrode active material, the positive electrode active material and the coin cell were produced in substantially the same manner as in Example 1.

[0136] Comparative Example 2 Except that no P coating was performed and only Al coating was performed, that is, after filtering and drying the first mixed solution, the second heat treatment was performed to produce the positive electrode active material, the positive electrode active material and the coin cell were produced in substantially the same manner as in Example 1.

[0137] Evaluation Example 1: SEM-EDS analysis Figure 5 is an SEM image of the surface of the positive electrode active material coating product manufactured in Example 3, and Figure 6 is an SEM image of the surface of the positive electrode active material manufactured in Comparative Example 1. Comparing Figure 5 and Figure 6, a kind of mesh-shaped coating is observed on the surface of the coating product of Example 3.

[0138] In addition, SEM-EDS analysis was performed on the surface of the coating product manufactured in Example 3. Figure 7 shows the detection intensity graphs for each of the elements C, O, Mn, Ni, Al, and P, and Figure 8 shows the SEM image (upper left) and the images mapping each of the elements O, Al, Mn, Ni, and P. Referring to Figure 7, it can be confirmed that both Al and P elements are detected on the surface of the positive electrode active material coating product. Referring to Figure 8, it can be confirmed that the Al and P elements are very uniformly distributed on the surface of the positive electrode active material coating product.

[0139] In addition, the content of each element on the surface of the coating product of Example 3 calculated through SEM-EDS analysis is shown in Table 1 below. It can be said that Table 1 shows the content of each element with respect to the total elements excluding lithium on the surface of the positive electrode active material, that is, C + O + Al + P + Mn + Ni 100 at%.

[0140]

Table 1

[0141] Referring to Table 1, the content of Al with respect to the total elements excluding lithium on the surface of the coating product of Example 3 is 7.82 at%, the content of P is 3.46 at%, and the Al / P content ratio is confirmed to be approximately 2.26.

[0142] Evaluation Example 2: Evaluation of initial charge-discharge capacity and efficiency of battery The coin cells manufactured in Examples 1 to 3 and Comparative Examples 1 and 2 were charged at a constant current of 0.2C up to an upper limit voltage of 4.45V at 25°C and then charged at a constant voltage up to 0.05C, and then discharged at 0.2C up to a cut-off voltage of 3.0V to perform initial charge and discharge. The initial charge capacity, the initial discharge capacity, and the ratio of the latter to the former were calculated as efficiency and shown in Table 2 below.

[0143] Evaluation Example 3: Evaluation of high-temperature life characteristics Subsequent to Evaluation Example 2, cycles of charging at 1.0C and discharging at 1.0C were repeated 50 times or more in a voltage range of 3.0V to 4.45V at 45°C, and the ratio of the 50-cycle discharge capacity to the initial discharge capacity was calculated and shown in Table 2 below as the high-temperature life.

[0144] Evaluation Example 4: Evaluation of high-temperature storage characteristics In Evaluation Example 1, the battery in the state of being initially charged up to 4.45V was stored at 90°C for 4 hours, and then the amount of gas generated inside the battery was measured and shown in Table 2 below.

[0145]

Table 2

[0146] Referring to Table 2 above, in the case of Examples 1 to 3, the initial discharge capacity was improved compared to Comparative Examples 1 and 2, the initial charge and discharge efficiency was improved, the high-temperature life characteristics were further improved, and it can be seen that the amount of gas generated during high-temperature storage was also further reduced.

[0147] Although the preferred embodiments have been described in detail above, 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 following claims also belong to the scope of the rights of the present invention.

Explanation of Reference Numerals

[0148] 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: Case 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 having a nickel content of 60 mol % or more relative to 100 mol % of all metals excluding lithium; a coating layer containing Al and P and located on a surface of the core particle.

2. The positive electrode active material of claim 1 , wherein the coating layer comprises aluminum phosphate.

3. The positive electrode active material of claim 1 , wherein the coating layer comprises aluminum oxide and aluminum phosphate.

4. 2. The positive electrode active material according to claim 1, comprising a first coating layer located on a surface of a core particle and containing aluminum oxide, and a second coating layer located on the first coating layer and containing aluminum phosphate.

5. The coating layer has an Al content of 0.5 mol % to 3 mol % based on 100 mol % of all elements in the positive active material excluding lithium and oxygen; 2 . The positive electrode active material of claim 1 , wherein the coating layer has a phosphorus content of 0.1 mol % to 2 mol % based on 100 mol % of all elements in the positive electrode active material excluding lithium and oxygen.

6. The aluminum content is 5 at% to 35 at% and the phosphorus content is 0.1 at% to 8 at% based on 100 at% of all elements except lithium on the surface of the positive electrode active material as measured by scanning electron microscope energy dispersive spectroscopy (SEM-EDS); The positive electrode active material according to claim 1 , wherein a ratio of the Al content to the P content (Al / P) on the surface of the positive electrode active material is 2 or more.

7. the coating layer is in the form of a shell that continuously surrounds the surface of the core particle; The thickness of the coating layer is 5 nm to 500 nm; 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.

8. The layered lithium nickel-manganese composite oxide of the core particle has a nickel content of 60 mol% to 80 mol%, a manganese content of 15 mol% or more, and a cobalt content of 0 mol% to 0.01 mol%, based on 100 mol% of all metals excluding lithium; 2. The positive electrode active material according to claim 1, wherein the layered lithium nickel-manganese composite oxide of the core particle further contains aluminum, and the content of aluminum in the core particle is 1 mol % to 3 mol % relative to 100 mol % of all metals excluding lithium.

9. The positive electrode active material according to claim 1, wherein the layered lithium nickel-manganese composite oxide of the core particle is represented by chemical formula 1. [Chemical formula 1] Li a1 Ni x1 Mn y1 Al z1 M 1 w1 O 2-b1 X b1 (In Chemical Formula 1, 0.9≦a1≦1.8, 0.6≦x1≦0.8, 0.1≦y1≦0.4, 0≦z1≦0.03, 0≦w1≦0.3, 0.9≦x1+y1+z1+w1≦1.1, and 0≦b1≦0.1; M 1 is one or more elements selected from B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, and Zr, and X is one or more elements selected from F, P, and S).

10. The core particle is in the form of a secondary particle formed by agglomeration of a plurality of primary particles, The average particle diameter D of the positive electrode active material 50 The positive electrode active material according to claim 1 , wherein the thickness of the first electrode is 10 μm to 25 μm.

11. preparing core particles containing a layered lithium nickel-manganese composite oxide having a nickel content of 60 mol % or more relative to 100 mol % of all metals excluding lithium; The aluminum raw material is mixed with the aqueous solvent to prepare a coating solution. The core particles are added to the coating solution and mixed to prepare a first mixed solution; A phosphorus-based raw material is added to and mixed with the first mixed solution to produce a second mixed solution; and removing the aqueous solvent from the second mixed solution, drying the resulting product, and heat-treating the product 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 15 mol % or more, the aluminum content is 0 mol % to 3 mol %, and the cobalt content is 0 mol % to 0.01 mol %, relative to 100 mol % of all metals excluding lithium.

13. The aluminum source is aluminum sulfate, The phosphorus-based raw material is phosphoric acid, The aluminum content of the aluminum raw material is 0.5 mol % to 3 mol % based on a total of 100 mol % of all metals other than lithium in the core particle and aluminum in the aluminum raw material; The method of claim 11, wherein the phosphorus content of the phosphorus-based raw material is 0.1 mol % to 2 mol % relative to 100 mol % in total of all elements of the core particles and phosphorus of the phosphorus-based raw material.

14. The pH of the coating solution is between 1.5 and 4; The time taken to introduce the core particles into the coating solution is 30 seconds / 500 g to 2 minutes / 500 g; The time for mixing the core particles in the coating solution is 15 to 60 minutes; The method of claim 11, wherein the first mixed solution has a pH of 5.5 to 8.

5.

15. After adding the phosphorus-based raw material to the first mixed solution, the mixing time is 15 to 60 minutes. The method of claim 11, wherein the second mixed solution has a pH of 5.5 to 8.

5.

16. 12. The method of claim 11, wherein the drying of the product after removing the aqueous solvent from the second mixed solution is performed in a vacuum at 40°C to 240°C, and the heat treatment is performed at a temperature in the range of 730°C to 800°C.

17. 12. The method for producing a positive electrode active material according to claim 11, wherein the coating product obtained by removing the aqueous solvent with the second mixed solution and drying the product includes the core particles and a coating layer located on a surface of the core particles and containing Al and P, and the coating layer has a mesh shape or a spider web shape.

18. A positive electrode current collector; 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 claim 1 .

19. The loading level of the positive electrode active material layer is 10 mg / cm 2 to 40 mg / cm 2 and 20. The positive electrode of claim 18, wherein the positive electrode active material layer has a density of 3.3 g / cc to 3.7 g / cc.

20. The positive electrode according to claim 18 ; A negative electrode; An electrolyte. A lithium secondary battery having a charging voltage of 4.45V or more.

Images