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

Abstract

The invention relates to a positive electrode active material, a method of preparing the same, and a positive electrode and a rechargeable lithium battery including the same. Provided is a positive electrode active material including a core particle, the core particle including a zirconium-doped layered lithium nickel manganese aluminum-based composite oxide, in which the core particle is a secondary particle formed by aggregating a plurality of primary particles, the secondary particle has an average particle diameter (D50) of about 10 [mu] m to about 25 [mu] m, and in the zirconium-doped layered lithium nickel manganese aluminum-based composite oxide, the average particle diameter (D50) of the secondary particle is about 10 [mu] m to about 25 [mu] m. The zirconium content is from about 0.2 mol% to about 0.8 mol% based on 100 mol% of the total metal other than lithium. The positive electrode active material according to some embodiments may maximize capacity while minimizing production costs to ensure long cycle life characteristics and improve high voltage characteristics and high temperature characteristics. If the positive electrode active material is used in a rechargeable lithium battery, high initial charge / discharge capacity and efficiency can be achieved under high voltage operating conditions, and long cycle life characteristics can be achieved under high voltage conditions and high temperature conditions.

Description

Technical Field

[0001] There are disclosed a positive electrode active material, a method for preparing the same, a positive electrode including the same, and a rechargeable lithium battery. Background Art

[0002] Portable information devices (such as cellular phones, laptop computers, smart phones, etc.) and / or electric vehicles have used rechargeable lithium batteries having high energy density and easy portability as a driving power source. Recently, active research has been conducted to use rechargeable lithium batteries having high energy density as a driving power source or a power storage source for hybrid vehicles or electric vehicles.

[0003] Various positive electrode active materials have been studied to realize various applications of rechargeable lithium batteries for these uses. Among them, lithium nickel-based oxides, lithium nickel manganese cobalt-based composite oxides, lithium nickel cobalt aluminum-based composite oxides, and lithium cobalt-based oxides are mainly used as positive electrode active materials. However, although the interest in large-sized, high-capacity, and / or high-energy density rechargeable lithium batteries has rapidly increased recently, the supply of positive electrode active materials including rare metal cobalt is expected to be severely insufficient. In other words, since cobalt is expensive and the remaining reserves are not much, it is necessary to develop positive electrode active materials that exclude cobalt or reduce its content. Summary of the Invention

[0004] Some embodiments of the present disclosure provide a positive electrode active material including a zirconium-doped layered lithium nickel manganese aluminum-based composite oxide (hereinafter, may be simply referred to as "layered lithium nickel manganese aluminum-based composite oxide" or "lithium nickel manganese aluminum-based composite oxide") having economic feasibility, high capacity, and long cycle life characteristics, as well as improved high voltage characteristics and high temperature characteristics, a method for preparing the same, a positive electrode including the same, and a rechargeable lithium battery.

[0005] In some embodiments, the positive electrode active material includes core particles including a zirconium-doped layered lithium nickel manganese aluminum-based composite oxide, wherein each of the core particles is a secondary particle formed by aggregating a plurality of primary particles, and the average particle diameter (D 50 ) is about 10 μm to about 25 μm, and in the zirconium-doped layered lithium nickel manganese aluminum-based composite oxide, based on the total metal other than lithium in 100 mol% of the zirconium-doped layered lithium nickel manganese aluminum-based composite oxide, the zirconium content is about 0.2 mol% to about 0.8 mol%.

[0006] In some embodiments, a method for preparing a positive electrode active material includes: mixing a nickel-manganese-aluminum composite hydroxide, a zirconium raw material, and a lithium raw material together and performing a heat treatment to obtain a zirconium-doped layered lithium nickel-manganese-aluminum composite oxide, wherein based on 100 mol% of the total metals of the nickel-manganese-aluminum composite hydroxide and zirconium of the zirconium raw material, the zirconium content of the zirconium raw material is about 0.2 mol% to about 0.8 mol%.

[0007] In some embodiments, a positive electrode includes a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector, wherein the positive electrode active material layer includes the aforementioned positive electrode active material.

[0008] Some embodiments provide a rechargeable lithium battery including the aforementioned positive electrode, negative electrode, and electrolyte.

[0009] The positive electrode active material according to some embodiments can maximize or increase the capacity while minimizing or reducing the production cost to ensure long cycle life characteristics and improve high voltage characteristics and high temperature characteristics. If the positive electrode active material is applied to a rechargeable lithium battery, high initial charge / discharge capacity and efficiency can be achieved under high voltage operating conditions, and long cycle life characteristics can be achieved under high voltage conditions and high temperature conditions. Description of the Drawings

[0010] The accompanying drawings, together with the specification, illustrate embodiments of the subject matter of the present disclosure, and the accompanying drawings, together with this description, are used to explain the principles of the embodiments of the subject matter of the present disclosure.

[0011] Figure 1 A schematic diagram showing a rechargeable lithium battery according to some embodiments.

[0012] Figure 2 A cross-sectional view schematically showing a rechargeable lithium battery according to some embodiments.

[0013] Figures 3 to 4 A schematic diagram showing a rechargeable lithium battery according to some embodiments.

[0014] Figure 5 An SEM-EDS image of the surface of the final positive electrode active material prepared in Example 1.

[0015] Figures 6 to 7 An SEM image of the surface of the positive electrode active material prepared in Example 1.

[0016] Figures 8 to 9 An SEM image of the surface of the positive electrode active material prepared in Example 2.

[0017] Description of the Reference Numerals

[0018] 100: Rechargeable lithium battery 10: Positive electrode

[0019] 11: Positive electrode lead tab 12: Positive electrode terminal

[0020] 20: Negative electrode 21: Negative electrode lead tab

[0021] 22: Negative electrode terminal 30: Separator

[0022] 40: Electrode assembly 50: Housing

[0023] 60: Sealing member 70: Electrode tab

[0024] 71: Positive electrode tab 72: Negative electrode tab Detailed implementation mode

[0025] Hereinafter, example implementation modes will be described in more detail so that those of ordinary skill in the art can easily implement them. However, the subject matter of the present disclosure can be implemented in many different forms and should not be construed as limited to the example implementation modes stated herein.

[0026] The terms used herein are only for describing the implementation modes and are not intended to limit the present disclosure. Singular expressions include plural expressions unless the context clearly indicates otherwise.

[0027] As used herein, "a combination thereof" means a mixture, laminate, composite, copolymer, alloy, blend, reaction product, etc. of components.

[0028] In this document, it should be understood that terms (such as "comprises", "includes" or "have") are intended to indicate the presence of the implemented features, quantities, steps, elements or combinations thereof, but do not exclude the possibility of the presence or addition of one or more other features, quantities, steps, elements or combinations thereof.

[0029] In the drawings, for clarity, the thickness of layers, films, panels, regions, etc. may be enlarged, and throughout the specification, the same reference numerals denote the same elements. It will be understood that if an element (such as a layer, film, region or substrate) is referred to as "on" another element (such as a layer, film, region or substrate), it may be directly on the other element (such as a layer, film, region or substrate), or there may also be intervening elements. In contrast, if an element (such as a layer, film, region or substrate) is referred to as "directly on" another element (such as a layer, film, region or substrate), there are no intervening elements.

[0030] A "layer" herein may include not only the shape on the entire surface when viewed from a plan view, but also the shape on a partial surface.

[0031] The average particle size can be measured by any suitable method commonly used in the art (e.g., by a particle size analyzer and / or by transmission electron microscope images and / or scanning electron microscope images). In an embodiment, the average particle size value can be obtained by measuring using the dynamic light scattering method, performing data analysis, counting the number of particles in each particle size range, and calculating therefrom. Unless otherwise defined, the average particle size (D 50 ) can refer to the diameter of the particle with a cumulative volume of 50% by volume in the particle size distribution. As used herein, if no other definition is provided, the average particle size (D 50 ) means the diameter of the particle with a cumulative volume of 50% by volume in the particle size distribution obtained by randomly measuring the sizes (diameter or major axis length) of about 20 particles in the scanning electron microscope image.

[0032] As used herein, "or" is not construed in an exclusive sense. For example, "A or B" is construed to include A, B, A + B, etc.

[0033] "Metal" is construed to include the concepts of common metals, transition metals, and metalloids (semi-metals).

[0034] Positive electrode active material

[0035] In some embodiments, the positive electrode active material includes a core particle, the core particle includes a layered lithium nickel manganese aluminum composite oxide doped with zirconium, wherein the core particle is a secondary particle formed by aggregating a plurality of primary particles, and the average particle size (D 50 ) of the secondary particle is about 10 μm to about 25 μm, and in the layered lithium nickel manganese aluminum composite oxide doped with zirconium, based on the total metals other than lithium in 100 mol% of the layered lithium nickel manganese aluminum composite oxide doped with zirconium, the zirconium content is about 0.2 mol% to about 0.8 mol%.

[0036] Since the price of the rare metal cobalt has recently increased sharply, there has been an interest in developing cathode active materials that exclude cobalt or reduce its content. Among them, cathode active materials having an olivine crystal structure (such as lithium iron phosphate (LFP), lithium manganese phosphate (LMP), lithium manganese iron phosphate (LMFP), etc.) or cathode active materials having a spinel crystal structure (such as lithium manganese oxide (LMO), etc.) have limitations in achieving high capacity due to the small amount of available lithium in the structure. Due to the high amount of available lithium in the structure, layered lithium nickel manganese aluminum-based cathode active materials have excellent capacity and efficiency characteristics, making them suitable as materials for high-capacity batteries. However, when cobalt, which plays a key role in the layered structure, is removed, the structural stability decreases, the impedance (e.g., resistance) increases, and it becomes difficult to ensure long cycle life characteristics. The cobalt-excluded layered lithium nickel manganese aluminum-based cathode active materials may have a problem of accelerated side reactions with the electrolyte under high-voltage conditions and high-temperature conditions, resulting in an increase in the amount of gas generation and deterioration of the cycle life characteristics.

[0037] Accordingly, in order to maintain a stable layered structure even when the cobalt element is excluded from the structure of the layered lithium nickel manganese aluminum-based cathode active material, and in order to improve the stability in the high-voltage region, in some embodiments, the hetero element zirconium is doped into the layered lithium nickel manganese aluminum-based cathode active material to improve not only the high-voltage and high-temperature cycle life characteristics but also the initial charge and discharge efficiency.

[0038] Core particle

[0039] The core particle includes a zirconium-doped layered lithium nickel manganese aluminum-based composite oxide.

[0040] Based on the total metals other than lithium in 100 mol% of the cathode active material (e.g., zirconium-doped layered lithium nickel manganese aluminum-based composite oxide), the nickel content in the zirconium-doped layered lithium nickel manganese aluminum-based composite oxide may be greater than or equal to about 60 mol%, for example, about 60 mol% to about 80 mol%, about 65 mol% to about 80 mol%, about 70 mol% to about 80 mol%, about 60 mol% to about 79 mol%, about 60 mol% to about 78 mol% or about 60 mol% to about 75 mol%. If the nickel content in the zirconium-doped layered lithium nickel manganese aluminum-based composite oxide satisfies the above range, high capacity can be achieved even when the cobalt content is reduced, and the structural stability can also be increased. Nickel is included in the core particle but may move to some coatings during the coating process, so the nickel content may refer to the nickel content included in the entire cathode active material.

[0041] Based on the total metals other than lithium in 100 mol% of the positive electrode active material (e.g., zirconium-doped layered lithium nickel manganese aluminum composite oxide), the manganese content in the zirconium-doped layered lithium nickel manganese aluminum composite oxide can be, for example, greater than or equal to about 10 mol%, for example, about 10 mol% to about 40 mol%, about 10 mol% to about 39 mol%, about 10 mol% to about 38 mol%, about 15 mol% to about 35 mol%, about 15 mol% to about 30 mol% or about 20 mol% to about 30 mol%. If the manganese content in the zirconium-doped layered lithium nickel manganese aluminum composite oxide satisfies the above range, the positive electrode active material can improve the structural stability while achieving a high capacity. Manganese is included in the core particles but can move to some coatings during the coating process, so the manganese content can refer to the manganese content included in the entire positive electrode active material.

[0042] Based on the total metals other than lithium in 100 mol% of the positive electrode active material (e.g., zirconium-doped layered lithium nickel manganese aluminum composite oxide), the aluminum content in the zirconium-doped layered lithium nickel manganese aluminum composite oxide can be greater than or equal to about 0.1 mol%, greater than or equal to about 0.5 mol% or greater than or equal to about 1 mol%, for example, about 1 mol% to about 3 mol%, about 1 mol% to about 2.5 mol%, about 1 mol% to about 2 mol% or about 1 mol% to about 1.9 mol%. Here, the aluminum content refers to the content of aluminum present in the core particles. If the aluminum content satisfies the above range, even if cobalt is excluded from the core particles, a stable layered structure can be maintained, the problem of structural collapse due to charge and discharge can be suppressed or reduced, and the long cycle life characteristics of the positive electrode active material can be achieved.

[0043] According to some embodiments, the concentration of aluminum in the core particles can be uniform (or substantially uniform). In an embodiment, the foregoing means that there is no aluminum concentration gradient from the center to the surface of the core particles, or the aluminum concentration in the inner part of the core particles is neither higher nor lower than that in the outer part of the core particles, and the aluminum is uniformly (or substantially uniformly) distributed within the core particles. This can be a structure obtained by using aluminum raw materials during the production of the precursor and not doping aluminum additionally during the synthesis of the core particles, and thus synthesizing a composite oxide using a nickel manganese aluminum hydroxide as the precursor. The core particles can be in the form of secondary particles in which a plurality of primary particles are aggregated, and the aluminum content within the primary particles can be the same or similar, regardless of the position of the primary particles. For example, if primary particles are selected at random positions in the cross-section of the secondary particles and the aluminum content is measured inside the primary particles rather than at their interfaces, the aluminum content is the same / similar / uniform, regardless of the position of the primary particles (e.g., whether the primary particles are close to the center or the surface of the secondary particles). In this 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 cycle life characteristics of the positive electrode active material can be improved simultaneously (or substantially simultaneously).

[0044] Based on the total metals other than lithium in the positive electrode active material (e.g., a layered lithium nickel manganese aluminum composite oxide doped with zirconium) of 100 mol%, the zirconium content in the layered lithium nickel manganese aluminum composite oxide doped with zirconium can be about 0.2 mol% to about 0.8 mol%, for example, about 0.2 mol% to about 0.7 mol%, about 0.2 mol% to about 0.6 mol%, or about 0.2 mol% to about 0.5 mol%. If the zirconium content in the layered lithium nickel manganese aluminum composite oxide doped with zirconium satisfies the above range, even if cobalt is excluded, a stable layered structure can be maintained, the problem of structural collapse due to charging and discharging can be suppressed or reduced, long cycle life characteristics of the positive electrode active material can be achieved, and for example, the initial discharge capacity and initial charge / discharge efficiency (hereinafter, may be simply referred to as "efficiency") under high voltage driving conditions can be improved, and the high temperature cycle life characteristics can be improved.

[0045] The lithium nickel manganese aluminum composite oxide can be represented, for example, by Chemical Formula 1.

[0046] Chemical Formula 1

[0047] Li a1 Ni x1 Mn y1 Al z1 Zr v1 M 1 w1 O 2-b1 X b1

[0048] In Chemical Formula 1, 0.9 ≤ a1 ≤ 1.8, 0.6 ≤ x1 ≤ 0.8, 0.1 ≤ y1 ≤ 0.38, 0.01 ≤ z1 ≤ 0.03, 0.002 ≤ v1 ≤ 0.008, 0 ≤ w1 ≤ 0.2, 0.9 ≤ x1 + y1 + z1 + v1 + 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 Zn, and X is one or more elements selected from F, P, and S.

[0049] In the above Chemical Formula 1, 0.9 ≤ a1 ≤ 1.5, or 0.9 ≤ a1 ≤ 1.2. In an embodiment, 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 ≤ 0.29, or 0.2 ≤ y1 ≤ 0.3; 0.01 ≤ z1 ≤ 0.025, 0.01 < z1 ≤ 0.02, or 0.01 < z1 ≤ 0.019; 0.002 ≤ v1 ≤ 0.007, 0.002 ≤ v1 ≤ 0.006, or 0.002 ≤ v1 ≤ 0.005; and 0 ≤ w1 ≤ 0.15, 0 ≤ w1 ≤ 0.1, or 0 ≤ w1 ≤ 0.09.

[0050] The lithium nickel manganese aluminum composite oxide may be a cobalt-free compound that does not include cobalt or includes a very small amount of cobalt, and has a cobalt content of about 0 mol% to about 0.01 mol% based on 100 mol% of the total metals other than lithium in the zirconium-doped layered lithium nickel manganese aluminum composite oxide. In an embodiment, based on 100 mol% of the total metals other than lithium in the zirconium-doped layered lithium nickel manganese aluminum composite oxide, the zirconium-doped layered lithium nickel manganese aluminum composite oxide may have a cobalt content of 0 mol%.

[0051] The core particles may be in the form of secondary particles made by aggregating a plurality of primary particles. The secondary particles may be spherical, ellipsoidal, polyhedral, and / or irregular in shape, and the primary particles may be spherical, ellipsoidal, plate-like, or a combination thereof. The average particle size (D 50 ) may be about 10 μm to about 25 μm, for example, about 11 μm to about 20 μm or about 12 μm to about 18 μm. As used herein, if no other definition is provided, the average particle size (D 50It refers to the diameter of the particles with a cumulative volume of 50% by volume in the particle size distribution obtained by randomly measuring the sizes (diameter or major axis length) of about 20 particles in the scanning electron microscope image of the positive electrode active material. If the average particle size of the core particles meets the above range, high capacity and long cycle life can be achieved, and it is suitable or desirably formed into a coating according to some embodiments.

[0052] If the battery operates under high voltage or high temperature conditions, the core particles are vulnerable to chemical erosion by the components in the electrolyte, so many side reactions can occur with the electrolyte, resulting in an increase in the amount of gas generated, thereby deteriorating the battery cycle life and safety. However, these problems can be solved by introducing a coating according to some embodiments, which will be further described below.

[0053] Coating

[0054] The positive electrode active material according to some embodiments includes: core particles including a zirconium-doped layered lithium nickel manganese aluminum composite oxide; and a coating on the surface of the core particles and including aluminum (hereinafter, may be simply referred to as "aluminum-containing coating" or "coating"), wherein the core particles are secondary particles formed by aggregating a plurality of primary particles, and the average particle size (D 50 ) is about 10 μm to about 25 μm, and in the zirconium-doped layered lithium nickel manganese aluminum composite oxide, based on the total metals other than lithium in 100 mol% of the zirconium-doped layered lithium nickel manganese aluminum composite oxide, the zirconium content is about 0.2 mol% to about 0.8 mol%. The core particles have been described above, so the description thereof will not be repeated here and the coating will be described.

[0055] Based on the total metal other than lithium in 100 mol% of the positive electrode active material, the aluminum content in the coating can be from about 0.5 mol% to about 1.5 mol%, for example, from about 0.5 mol% to about 1.3 mol%, from about 0.6 mol% to about 1.1 mol%, or from about 0.7 mol% to about 0.9 mol%. The aluminum content of the coating only refers to the aluminum content included in the coating, without considering the aluminum included in the core particles. The aluminum content in the coating of the entire positive electrode active material can be measured, for example, by scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) analysis of the surface or cross-section of the positive electrode active material. If the aluminum content in the coating meets the above range, the coating can have a uniform (or substantially uniform) and thin thickness, which does not increase the impedance (e.g., resistance) of the positive electrode active material and effectively suppresses or reduces side reactions with the electrolyte, thereby improving the cycle life characteristics of the rechargeable lithium battery under high voltage conditions and high temperature conditions. For example, if the aluminum content of the coating is too high, a uniform coating may not be formed, or the impedance (e.g., resistance) may increase, which can reduce the charge / discharge efficiency and cycle life characteristics. And if the aluminum content of the coating is too low, a coating with an appropriate or suitable thickness may not be formed, and the effect of suppressing or reducing side reactions with the electrolyte may be reduced.

[0056] According to some embodiments, the coating can be in the form of a film continuously surrounding the surface of the core particles, or can be in the form of a shell surrounding the entire surface of the core particles. This is different from the structure in which only a part of the surface of the core particles is coated. According to some embodiments, the coating can be formed to completely cover the surface of the core particles and can be formed to have a very thin and uniform (or substantially uniform) thickness, so that the positive electrode active material does not (or substantially does not) increase the impedance (e.g., resistance) or does not (or substantially does not) reduce the capacity, improves the structural stability, effectively suppresses or reduces side reactions with the electrolyte, reduces the amount of gas generated under high voltage conditions and high temperature conditions, and achieves long cycle life characteristics.

[0057] For example, the coating can include a fibrous shape (e.g., a mesh shape and / or a spider web shape). The mesh-like coating can be formed on the entire surface of the core particles, so it can be understood that the coating surrounds the entire surface of the core particles. This is different from the structure in which only a part of the surface of the core particles is coated. The coating can be formed to have a very thin and uniform (or substantially uniform) thickness while having a fibrous shape. As a result, the positive electrode active material does not (or substantially does not) increase the impedance (e.g., resistance) or does not (or substantially does not) reduce the capacity, improves the structural stability, effectively suppresses or reduces side reactions with the electrolyte, reduces the amount of gas generated under high voltage conditions and high temperature conditions, and achieves long cycle life characteristics.

[0058] According to some embodiments, the coating may have a thickness of about 30 nm to about 500 nm (such as about 30 nm to about 450 nm, about 30 nm to about 400 nm, about 30 nm to about 350 nm, about 30 nm to about 300 nm, about 30 nm to about 250 nm, about 30 nm to about 200 nm, about 30 nm to about 150 nm, about 50 nm to about 500 nm, about 80 nm to about 500 nm or about 100 nm to about 500 nm). If the coating meets the above thickness range, the structural stability of the positive electrode active material can be improved without increasing the impedance (e.g., resistance) or reducing the capacity due to the coating, and the side reactions with the electrolyte can be effectively suppressed or reduced. The thickness of the coating can be measured by, for example, time-of-flight secondary ion mass spectrometry (TOF-SIMS), X-ray photoelectron spectroscopy (XPS) or energy-dispersive X-ray spectroscopy (EDS) analysis, and the thickness range of the coating can be measured by a transmission electron microscope-energy-dispersive X-ray spectroscopy (TEM-EDS) line profile.

[0059] The coating according to some embodiments is characterized by a thin and uniform (or substantially uniform) thickness at the level of several tens of nanometers to several hundreds of nanometers. For example, the deviation of the coating thickness in one positive electrode active material particle may be less than or equal to about 20%, less than or equal to about 18% or less than or equal to about 15%. Herein, the deviation of the coating thickness refers to the deviation of the coating thickness within one positive electrode active material particle. For example, the deviation of the coating thickness can be calculated by measuring the thicknesses of about 10 points in the electron microscope image of the cross-section of a single positive electrode active material particle to calculate the arithmetic mean, and then dividing the absolute value of the difference between one measurement data and the arithmetic mean by the arithmetic mean and multiplying by 100%. The fact that the deviation or standard deviation of the coating thickness meets the above range means that the coating with a uniform (or substantially uniform) thickness is formed on the surface of the positive electrode active material particles in the form of a good film. Accordingly, the structural stability of the positive electrode active material is improved, the side reactions with the electrolyte can be effectively suppressed or reduced, and the increase in impedance (e.g., resistance) or the decrease in capacity caused by coating can be minimized or reduced.

[0060] The coating may include, for example, a layered aluminum compound, such as aluminum oxide, lithium aluminum oxide (e.g., LiAlO2) or a combination thereof.

[0061] In an embodiment, in addition to aluminum, the coating may further include nickel, manganese or a combination thereof. Nickel and manganese may be included in the core particles and may be introduced during the coating formation process, and their contents are not particularly limited. The coating according to some embodiments includes aluminum and optionally includes nickel and manganese, and is formed to have a thin and uniform (or substantially uniform) thickness, thereby improving the high-voltage characteristics of the positive electrode active material and improving the cycle life characteristics.

[0062] On the surface of the positive electrode active material according to some embodiments, based on the total metal other than lithium in 100 wt% of the positive electrode active material, the Al content may be about 45 wt% to about 55 wt%, and by coating Al at such a high content, the structural stability of the positive electrode active material can be further improved. The Al content on the surface of the positive electrode active material can be measured, for example, by energy dispersive X-ray spectroscopy (EDS).

[0063] In an embodiment, in addition to aluminum, the coating may further include sulfur. Sulfur can be introduced during the process of adding aluminum sulfate in the aluminum raw material for forming the aluminum coating, and its content is not particularly limited. The coating according to some embodiments includes aluminum and optionally includes sulfur, and can improve the high-voltage characteristics and cycle life characteristics of the positive electrode active material.

[0064] Based on the total metal other than lithium in 100 mol% of the positive electrode active material, the cobalt content in the positive electrode active material according to some embodiments can be, for example, less than or equal to about 0.01 mol%, less than or equal to about 0.005 mol% or less than or equal to about 0.001 mol%, for example, about 0 mol% to about 0.01 mol%, about 0 mol% to about 0.005 mol% or about 0 mol% to about 0.001 mol%.

[0065] In some embodiments, the positive electrode active material may not include sodium. Generally, sodium ions can be used in the preparation process of the positive electrode active material, but according to the preparation method further described below, core particles with a stable structure and a uniform (or substantially uniform) thickness coating can be formed without using sodium ions.

[0066] Method for preparing positive electrode active material

[0067] In some embodiments, the method for preparing a positive electrode active material includes: mixing a nickel-manganese-aluminum composite hydroxide, a zirconium raw material, and a lithium raw material together, and performing heat treatment, wherein based on 100 mol% of the total metal of the nickel-manganese-aluminum composite hydroxide and the zirconium of the zirconium raw material, the zirconium content of the zirconium raw material is about 0.2 mol% to about 0.8 mol%.

[0068] The nickel-manganese-aluminum composite hydroxide can be a precursor of the core particles, can be in the form of secondary particles in which a plurality of primary particles are aggregated, may not include cobalt or may include a very small amount of cobalt, and can be, for example, a cobalt-free nickel-manganese-aluminum composite hydroxide. The nickel-manganese-aluminum composite hydroxide can be prepared by a conventional co-precipitation method.

[0069] Based on 100 mol% of the total metal in the nickel-manganese-aluminum composite hydroxide, the nickel content in the nickel-manganese-aluminum composite hydroxide can be greater than or equal to about 60 mol%, and for example, is about 60 mol% to about 80 mol%, about 65 mol% to about 80 mol%, about 70 mol% to about 80 mol%, about 60 mol% to about 79 mol%, about 60 mol% to about 78 mol%, or about 60 mol% to about 75 mol%. If the nickel content in the nickel-manganese-aluminum composite hydroxide satisfies the above range, high capacity can be achieved even when the cobalt content is reduced, and the structural stability can be increased.

[0070] Based on 100 mol% of the total metal in the nickel-manganese-aluminum composite hydroxide, the manganese content in the nickel-manganese-aluminum composite hydroxide can be greater than or equal to about 10 mol%, for example, is about 10 mol% to about 40 mol%, about 15 mol% to about 35 mol%, about 15 mol% to about 30 mol%, or about 20 mol% to about 30%. If the manganese content in the nickel-manganese-aluminum composite hydroxide satisfies the above range, high capacity can be achieved, while the structural stability of the positive electrode active material can be increased, and the production price can be reduced to increase economic benefits.

[0071] Based on 100 mol% of the total metal in the nickel-manganese-aluminum composite hydroxide, the aluminum content in the nickel-manganese-aluminum composite hydroxide can be greater than or equal to about 0.1 mol%, greater than or equal to about 0.5 mol%, or greater than or equal to about 1 mol%, for example, is about 1 mol% to about 3 mol%, about 1 mol% to about 2.5 mol%, about 1 mol% to about 2 mol%, or about 1 mol% to about 1.9 mol%. If the aluminum content in the nickel-manganese-aluminum composite hydroxide satisfies the above range, high capacity can be achieved, while the structural stability of the positive electrode active material can be increased, and the production price can be reduced to increase economic benefits.

[0072] In a method for preparing a positive electrode active material according to some embodiments, when preparing the core particles, aluminum is not doped additionally, but an aluminum raw material can be used to prepare the precursor, so a nickel-manganese-aluminum composite hydroxide (wherein aluminum is uniformly (or substantially uniformly) dispersed in the structure) is used as the precursor. If such a precursor is used, the positive electrode active material can stably maintain a layered structure without cobalt even though charging and discharging are repeated, and no aluminum by-products and / or aluminum aggregates are formed, thereby improving the capacity and efficiency characteristics and the cycle life characteristics of the positive electrode active material.

[0073] In the nickel-manganese-aluminum composite hydroxide, based on 100 mol% of the total metals in the nickel-manganese-aluminum composite hydroxide, the cobalt content can be less than or equal to about 0.01 mol%, less than or equal to about 0.005 mol% or less than or equal to about 0.001 mol%. Such nickel-manganese-aluminum composite hydroxide can be economical because it avoids the increase in unit cost caused by cobalt, maximizes or increases the capacity, and improves the structural stability.

[0074] For example, the nickel-manganese-aluminum composite hydroxide can be represented by Chemical Formula 2.

[0075] Chemical Formula 2

[0076] Ni x2 Mn y2 Al z2 M 2 w2 (OH)2

[0077] In Chemical Formula 2, 0.6 ≤ x2 ≤ 0.8, 0.1 ≤ y2 ≤ 0.4, 0 < z2 ≤ 0.03, 0 ≤ w2 ≤ 0.2, 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 Zn.

[0078] In Chemical Formula 2, for example, 0.6 ≤ x2 ≤ 0.8, 0.1 ≤ y2 ≤ 0.39, 0.01 ≤ z2 ≤ 0.03, and 0 ≤ w2 ≤ 0.19.

[0079] The nickel-manganese-aluminum composite hydroxide is in particulate form, and the average particle size (D 50 ) can be about 10 μm to about 25 μm, about 11 μm to about 20 μm, or about 12 μm to about 18 μm.

[0080] For example, the zirconium raw material can be zirconium oxide.

[0081] The nickel-manganese-aluminum composite hydroxide and the zirconium raw material can be mixed together at a molar ratio of about 1:0.001 to 1:0.1 (for example, about 1:0.001 to 1:0.01).

[0082] The heat treatment can be carried out in an oxygen atmosphere, for example, in a temperature range of about 750 °C to about 950 °C, about 780 °C to about 900 °C, or about 810 °C to about 890 °C for about 2 hours to about 20 hours or about 4 hours to about 12 hours. Through the above heat treatment, a zirconium-doped layered lithium nickel manganese aluminum composite oxide can be obtained. Based on the total metals other than lithium in 100 mol% of the zirconium-doped layered lithium nickel manganese aluminum composite oxide, the obtained zirconium-doped layered lithium nickel manganese aluminum composite oxide can include about 0.2 mol% to about 0.8 mol% of zirconium and about 60 mol% to about 80 mol% of nickel, and does not include cobalt or includes a very small amount of cobalt less than or equal to about 0.01 mol%. Since the zirconium-doped layered lithium nickel manganese aluminum composite oxide can have significantly different residual lithium contents and different various properties on the particle surface from oxides with different compositions (for example, other nickel-based oxides, such as lithium nickel cobalt manganese composite oxides, lithium nickel cobalt aluminum composite oxides, etc.), it is impossible to use a conventional coating method to form a suitable or satisfactory coating in the form of a uniform film. In one or more embodiments, a method for improving high-voltage characteristics and high-temperature characteristics is proposed by uniformly (or substantially uniformly) forming a coating with a very thin thickness on the surface of a lithium nickel manganese aluminum composite oxide including a very small amount of cobalt and having a nickel content greater than or equal to about 60 mol%.

[0083] In some embodiments, a coating solution is first prepared by adding an aluminum raw material to an aqueous solvent, adding the obtained zirconium-doped layered lithium nickel manganese aluminum composite oxide and mixing, and then drying and performing a second heat treatment to form a coating according to some embodiments. The foregoing is a wet salt solution coating method and can be called a pre-addition method, in which the salt (which is the coating raw material) is first completely dissolved, and then the core particles of the positive electrode active material (i.e., the zirconium-doped layered lithium nickel manganese aluminum composite oxide) are added.

[0084] The aqueous solvent may include distilled water, an alcohol solvent, or a combination thereof. For example, the aluminum raw material may be aluminum sulfate. Aluminum sulfate may be a suitable or optimal raw material for forming a uniform (or substantially uniform) aluminum-containing coating on the layered lithium nickel manganese aluminum composite oxide. The aluminum raw material is the raw material for forming the coating, and based on the total metal other than lithium in 100 mol% of the finally obtained positive electrode active material, the aluminum content in the aluminum raw material can be designed to be about 0.5 mol% to about 1.5 mol%, for example, about 0.5 mol% to about 1.3 mol%, about 0.6 mol% to about 1.1 mol%, or about 0.7 mol% to about 0.9 mol%. If the aluminum content of the coating raw material is designed within the above range, the coating can be formed to have a thin and uniform (or substantially uniform) thickness of several tens of nanometers to several hundreds of nanometers, reduce the amount of gas generated by the rechargeable lithium battery under high voltage or high temperature operating conditions, and improve the high-capacity and long cycle life characteristics.

[0085] The coating solution obtained by mixing the aluminum raw material in the aqueous solvent may have a pH of about 1.5 to about 3.5 (for example, about 2.0 to about 3.4, about 2.5 to about 3.3, about 2.7 to about 3.3, or about 2.9 to about 3.2).

[0086] Adding the core particles of the positive electrode active material to the coating solution and mixing can be carried out for about 5 minutes to about 80 minutes, about 5 minutes to about 60 minutes, or about 5 minutes to about 40 minutes. The pH of the mixed solution obtained after stirring can be about 4.5 to about 8.5, for example, about 5.0 to about 8.0, about 5.5 to about 7.5, or about 6.0 to about 7.0. If the above conditions are met, it is suitable or desirably to form a coating with a uniform (or substantially uniform) thickness.

[0087] Drying after the mixing process can be understood as a process of removing the solvent, and can be carried out, for example, at about 40°C to about 240°C, about 100°C to about 220°C, or about 150°C to about 200°C.

[0088] If the heat treatment of the mixture obtained by mixing the nickel manganese aluminum composite hydroxide, the zirconium raw material, and the lithium raw material together is denoted as the first heat treatment, then the heat treatment after drying the product obtained by removing the solvent from the mixed solution can be called the second heat treatment. The second heat treatment can be understood as a process of forming the coating. For example, it is carried out in an oxygen atmosphere at a temperature range of about 700°C to about 850°C, about 750°C to about 840°C, or about 800°C to about 830°C for about 2 to about 20 hours or about 3 to about 10 hours. In an embodiment, the second heat treatment temperature can be lower than the first heat treatment temperature, and the second heat treatment time can be the same as or shorter than the first heat treatment time. By carrying out the second heat treatment under the above conditions, a suitable or desired coating can be obtained.

[0089] Positive electrode

[0090] In some embodiments, the positive electrode includes a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector, wherein the positive electrode active material layer includes the aforementioned positive electrode active material. In addition to the aforementioned positive electrode active material, the positive electrode active material layer may further include other types (or kinds) of positive electrode active materials. In an embodiment, the positive electrode active material layer may optionally further include a binder, a conductive material (e.g., a conductivity material), or a combination thereof.

[0091] According to some embodiments, the loading level of the positive electrode active material layer may be about 10 mg / cm 2 to about 40 mg / cm 2 e.g., about 10 mg / cm 2 to about 30 mg / cm 2 or about 10 mg / cm 2 to about 20 mg / cm 2 . In an embodiment, the density of the positive electrode active material layer in the finally pressed positive electrode may be about 3.3 g / cc to about 3.7 g / cc, e.g., about 3.3 g / cc to about 3.6 g / cc or about 3.4 g / cc to about 3.58 g / cc. If the positive electrode active material according to some embodiments is applied, it is beneficial to implement such a loading level and density of the positive electrode active material layer, and the positive electrode in which the loading level and density of the positive electrode active material layer satisfy the above ranges is suitable for implementing a high-capacity, high-energy density rechargeable lithium battery.

[0092] Binder

[0093] The binder improves the adhesion characteristics between the positive electrode active material particles and between the positive electrode active material particles and the positive electrode current collector. Examples of the binder may include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylate esterified styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and nylon, but are not limited thereto.

[0094] Conductive material

[0095] It includes a conductive material to provide electrode conductivity (e.g., electrical conductivity), and any suitable conductive material can be used as the conductive material, unless it causes chemical changes (e.g., undesirable chemical changes in a rechargeable lithium battery). Examples of the conductive material can include: carbonaceous materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, carbon nanotube, etc.; metallic materials including metal powders and / or metal fibers such as copper, nickel, aluminum, silver, etc.; conductive polymers (e.g., electrically conductive polymers) such as polyphenylene derivatives; or mixtures thereof.

[0096] Based on 100 wt% of the positive electrode active material layer, the respective contents of the binder and the conductive material can be about 0.5 wt% to about 5 wt%.

[0097] The positive electrode current collector can include, but is not limited to, Al foil.

[0098] Rechargeable lithium battery

[0099] Some embodiments provide a rechargeable lithium battery, which includes the aforementioned positive electrode, negative electrode, and electrolyte. As an example, the rechargeable lithium battery can include a positive electrode, a negative electrode, a separator between the positive electrode and the negative electrode, and an electrolyte.

[0100] According to the shape, the rechargeable lithium battery can be classified into a cylindrical battery, a prismatic battery, a pouch battery, a coin-shaped battery, etc. Figures 1 to 4 For showing a schematic diagram of a rechargeable lithium battery according to some embodiments, where Figure 1 is a cylindrical battery, Figure 2 is a prismatic battery, and Figures 3 to 4 are each a pouch battery. Referring to Figures 1 to 4 , the rechargeable lithium battery 100 includes: an electrode assembly 40 having a separator 30 between a positive electrode 10 and a negative electrode 20; and a housing 50 that houses the electrode assembly 40. The positive electrode 10, the negative electrode 20, and the separator 30 can be impregnated with an electrolyte. As Figure 1 shown, the rechargeable lithium battery 100 can include a sealing member 60 that seals the housing 50. In Figure 2 , the rechargeable lithium 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 Figures 3 to 4 shown, the rechargeable lithium battery 100 includes an electrode tab 70 ( Figure 4 ), for example, a positive electrode tab 71 and a negative electrode tab 72 ( Figure 3 ), which serves as a circuit path for guiding the current formed in the electrode assembly 40 to the outside.

[0101] According to some embodiments, a rechargeable lithium battery can be rechargeable at a high voltage and / or can be adapted to be driven at a high voltage. For example, the charging voltage of the rechargeable lithium battery can be greater than or equal to about 4.45 V, such as about 4.45 V to about 4.7 V, about 4.45 V to about 4.6 V, or about 4.45 V to about 4.55 V, etc. By applying the positive electrode active material according to some embodiments, even when charged at a high voltage, the rechargeable lithium battery can significantly reduce the gas generation amount and can achieve high capacity and long cycle life characteristics.

[0102] Negative electrode

[0103] The negative electrode may include a negative electrode current collector and a negative electrode active material layer on the negative electrode current collector, and the negative electrode active material layer may include a negative electrode active material and may further include a binder, a conductive material (e.g., a conductive material), or a combination thereof.

[0104] Negative electrode active material

[0105] The negative electrode active material may include a material that reversibly intercalates / deintercalates lithium ions, lithium metal, a lithium metal alloy, a material capable of doping / dedoping lithium, and / or a transition metal oxide.

[0106] The material that reversibly intercalates / deintercalates lithium ions may include, for example, crystalline carbon, amorphous carbon, or a combination thereof as a carbon-based negative electrode active material. The crystalline carbon may be irregular and / or flaky, lamellar, spherical, and / or fibrous natural graphite and / or artificial graphite. The amorphous carbon may be soft carbon, hard carbon, a mesophase pitch carbonized product, calcined coke, etc.

[0107] The lithium metal alloy may include 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.

[0108] The material capable of doping / dedoping lithium may be a Si-based negative electrode active material and / or a Sn-based negative electrode active material. The Si-based negative electrode active material may include silicon, a silicon-carbon composite, SiO x(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, such as Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof) or a combination thereof. The Sn-based negative electrode active material can be Sn, SnO x (0 < x ≤ 2, such as SnO2), an Sn alloy, or a combination thereof.

[0109] The silicon-carbon composite can be a composite of silicon and amorphous carbon. The average particle size (D 50 ) can be, for example, from about 0.5 μm to about 20 μm. According to some embodiments, the silicon-carbon composite can be in the form of silicon particles and amorphous carbon coated on the surface of the silicon particles. For example, the silicon-carbon composite can include secondary particles (cores) in which primary silicon particles are aggregated and an amorphous carbon coating (shell) on the surface of the secondary particles. Amorphous carbon can also be between the primary silicon particles. For example, the primary silicon particles can be coated with amorphous carbon. The secondary particles can be dispersed in an amorphous carbon matrix.

[0110] The silicon-carbon composite can further include crystalline carbon. For example, the silicon-carbon composite can include: a core including crystalline carbon and silicon particles and an amorphous carbon coating on the surface of the core. The crystalline carbon can be artificial graphite, natural graphite, or a combination thereof. The amorphous carbon can include soft carbon, hard carbon, mesophase pitch carbonized products, and / or calcined coke.

[0111] If the silicon-carbon composite includes silicon and amorphous carbon, based on 100 wt% of the silicon-carbon composite, the content of silicon can be from about 10 wt% to about 50 wt% and the content of amorphous carbon can be from about 50 wt% to about 90 wt%. In an embodiment, if the silicon-carbon composite includes silicon, amorphous carbon, and crystalline carbon, based on 100 wt% of the silicon-carbon composite, the content of silicon can be from about 10 wt% to about 50 wt%, the content of crystalline carbon can be from about 10 wt% to about 70 wt%, and the content of amorphous carbon can be from about 20 wt% to about 40 wt%.

[0112] In an embodiment, the thickness of the amorphous carbon coating can be from about 5 nm to about 100 nm. The average particle size (D 50) can be from about 10 nm to about 1 μm or from about 10 nm to about 200 nm. The silicon particles can exist as silicon alone, in the form of a silicon alloy, and / or in the oxidized form of silicon. The oxidized form of silicon can be represented by SiO x (0 < x ≤ 2). In an embodiment, the atomic content ratio Si:O indicating the degree of oxidation can be from about 99:1 to about 33:67. As used herein, if no other definition is provided, the average particle size (D 50 ) indicates the diameter of the particles in which the cumulative volume in the particle distribution is about 50% by volume.

[0113] The Si-based negative electrode active material and / or the Sn-based negative electrode active material can be mixed with the carbon-based negative electrode active material. If the Si-based negative electrode active material and / or the Sn-based negative electrode active material are mixed with the carbon-based negative electrode active material and used, the mixing ratio can be a weight ratio of from about 1:99 to about 90:10.

[0114] Binder

[0115] The binder is used to bond the negative electrode active material particles to each other well and is also used to bond the negative electrode active material to the negative electrode current collector. The binder can be a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0116] The non-aqueous binder can include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0117] The aqueous binder can include styrene-butadiene rubber, (meth)acrylate esterified styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, poly(ethylene oxide), polyvinylpyrrolidone, poly(epichlorohydrin), polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, or a combination thereof.

[0118] If the aqueous binder is used as the binder in the negative electrode active material layer, a cellulose-based compound capable of imparting or increasing viscosity can be further included. As the cellulose-based compound, one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, and their alkali metal salts can be mixed and used. The alkali metal can be Na, K, and / or Li.

[0119] The dry binder can be a polymer material capable of becoming fibers (e.g., capable of fibrillating or fibrillation), and can be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, poly(ethylene oxide), or a combination thereof.

[0120] Conductive material

[0121] A conductive material is included to provide electrode conductivity (e.g., electrical conductivity), and any suitable conductive material can be used as the conductive material, unless it causes a chemical change (e.g., an undesired chemical change in a rechargeable lithium battery). Examples of conductive materials include: carbonaceous materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, carbon nanotube, etc.; metallic materials including metal powders and / or metal fibers such as copper, nickel, aluminum, silver, etc.; conductive polymers (e.g., electrically conductive polymers) such as polyphenylene derivatives; or mixtures thereof.

[0122] Based on 100 wt% of the negative electrode active material layer, the content of the negative electrode active material can be about 95 wt% to about 99.5 wt%, and based on 100 wt% of the negative electrode active material layer, the content of the binder can be about 0.5 wt% to about 5 wt%. For example, based on 100 wt% of the negative electrode active material layer, the negative electrode active material layer can include about 90 wt% to about 99 wt% of the negative electrode active material, about 0.5 wt% to about 5 wt% of the binder, and about 0.5 wt% to about 5 wt% of the conductive material.

[0123] Current collector

[0124] The negative electrode current collector can include, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), and / or alloys thereof, and / or can be in the form of a foil, sheet, and / or foam. The thickness of the negative electrode current collector can be, for example, about 1 μm to about 20 μm, about 5 μm to about 15 μm, or about 7 μm to about 10 μm.

[0125] Electrolyte

[0126] For example, the electrolyte for a rechargeable lithium battery can be an electrolyte that can include a non-aqueous organic solvent and a lithium salt.

[0127] The non-aqueous organic solvent serves as a medium for transporting ions participating in the electrochemical reaction of the battery. The non-aqueous organic solvent can include carbonate solvents, ester solvents, ether solvents, ketone solvents, alcohol solvents, aprotic solvents, or combinations thereof.

[0128] Carbonate solvents may include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. Ester solvents may include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, caprolactone, etc. Ether solvents may include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. In an embodiment, ketone solvents may include cyclohexanone, etc. Alcohol solvents may include ethanol, isopropanol, etc., and aprotic solvents may include nitriles (such as R-CN (where R is a C2-C20 straight-chain, branched-chain or cycloalkyl group and may include double bonds, aromatic rings or ether bonds, etc.)); amides (such as dimethylformamide); dioxolanes (such as 1,3-dioxolane, 1,4-dioxolane, etc.); sulfolane, etc.

[0129] The non-aqueous organic solvents may be used alone or in a mixture of two or more types (or kinds), and if two or more types (or kinds) of non-aqueous organic solvents are used in a mixture, the mixing ratio may be appropriately or suitably adjusted according to the appropriate or desired battery performance, which should be readily recognized by those of ordinary skill in the art after reading this disclosure.

[0130] If carbonate solvents are used, the cyclic carbonate and the chain carbonate may be mixed and used together, and the cyclic carbonate and the chain carbonate may be mixed together at a volume ratio of about 1:1 to about 1:9.

[0131] The non-aqueous organic solvents may further include aromatic hydrocarbon organic solvents. For example, the carbonate solvent and the aromatic hydrocarbon organic solvent may be mixed and used together at a volume ratio of about 1:1 to about 30:1.

[0132] The electrolyte may further include vinylene ethylene carbonate, vinylene carbonate and / or ethylene carbonate compounds to improve the battery cycle life.

[0133] Examples of ethylene carbonate compounds may include fluoroethylene carbonate, difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate and cyanoethylene carbonate.

[0134] Lithium salts dissolved in non-aqueous organic solvents supply lithium ions in a battery, ensuring the basic operation of rechargeable lithium batteries and improving the transport of lithium ions between the positive and negative electrodes. Examples of lithium salts may include at least one selected from 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 difluoro bis(oxalate) phosphate (LiDFBOP), and lithium bis(oxalate) borate (LiBOB).

[0135] The concentration of the lithium salt can be in the range of about 0.1 M to about 2.0 M. If the concentration of the lithium salt is within the above range, the electrolyte can have appropriate or suitable ionic conductivity and viscosity, so excellent performance can be achieved and lithium ions can move effectively.

[0136] Separator

[0137] Depending on the type (or kind) of the rechargeable lithium battery, the separator can be between the positive and negative electrodes. The separator can include a polyethylene separator, a polypropylene separator, a polyvinylidene fluoride separator, or a multilayer film of two or more of its layers (such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, a polypropylene / polyethylene / polypropylene three-layer separator, etc.).

[0138] The separator can include a porous substrate and a coating on one or two surfaces (e.g., two opposite surfaces) of the porous substrate, and the coating includes an organic material, an inorganic material, or a combination thereof.

[0139] The porous substrate can be a polymer film including the following: any one polymer selected from polyolefins (such as polyethylene and polypropylene), polyesters (such as polyethylene terephthalate and polybutylene terephthalate), polyacetals, polyamides, polyimides, polycarbonates, polyether ketones, polyarylether ketones, polyetherimides, polyamideimides, polybenzimidazoles, polyethersulfones, polyphenylene ethers, cycloolefin copolymers, polyphenylene sulfides, polyethylene naphthalate, glass fibers, and polytetrafluoroethylene (e.g., Teflon); or a copolymer or mixture of two or more of them.

[0140] The porous substrate can have a thickness of about 1 μm to about 40 μm (e.g., about 1 μm to about 30 μm, about 1 μm to about 20 μm, about 5 μm to about 15 μm, or about 10 μm to about 15 μm).

[0141] The organic material may include a (meth)acrylic copolymer, which includes: 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.

[0142] The inorganic material may include inorganic particles selected from the group consisting of Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof, but is not limited thereto. The average particle size (D 50 ) may be from about 1 nm to about 2000 nm, such as from about 100 nm to about 1000 nm or from about 100 nm to about 700 nm.

[0143] The organic material and the inorganic material may be mixed together in one coating, or a coating including the organic material and a coating including the inorganic material may be stacked.

[0144] The thickness of the coating may be from about 0.5 μm to about 20 μm, such as from about 1 μm to about 10 μm or from about 1 μm to about 5 μm.

[0145] Examples and comparative examples of the present disclosure are described below. However, the following examples are only examples of the embodiments of the present disclosure, and the present disclosure is not limited to the following examples.

[0146] Example 1

[0147] 1. Preparation of the positive electrode active material

[0148] Ni 0.75 Mn 0.24 Al 0.01 (OH)2, LiOH, and ZrO2 were mixed together in a molar ratio of 1:1:0.002, and first heat-treated in an oxygen atmosphere at 845 °C for 8 hours to obtain a lithium nickel manganese aluminum composite oxide having a composition of LiNi 0.748 Mn 0.24 Al 0.01 Zr 0.002 O2 and in the form of secondary particles with an average particle size (D 50 ) of about 14 μm. In the lithium nickel manganese aluminum composite oxide, the zirconium content was designed to be 0.2 mol% based on the total metals other than lithium in 100 mol% of the lithium nickel manganese aluminum composite oxide.

[0149] A coating solution was prepared by adding aluminum sulfate and 600 g of distilled water to a 1 L reactor, and then stirring the resulting mixture at about 350 rpm for about 5 minutes to dissolve the salt (i.e., aluminum sulfate). When the salt was completely dissolved, the resulting coating solution was checked to be colorless and transparent. Subsequently, 500 g of lithium nickel manganese aluminum composite oxide was added to the coating solution, stirred for 1.5 minutes, and then kept stirring for about 30 minutes. Herein, based on 100 mol% of the total metals other than lithium in the final positive electrode active material, the aluminum content of aluminum sulfate was designed to be 0.8 mol%.

[0150] After removing the solvent from the resulting mixed solution by using a suction pump and a filter press, the initial coated product was obtained by vacuum drying at 190 °C.

[0151] The initial coated product was subjected to a second heat treatment at 750 °C for 8 hours in an oxygen atmosphere to obtain the final positive electrode active material.

[0152] 2. Preparation of rechargeable lithium battery cell

[0153] 98.5 wt% of the positive electrode active material, 1.0 wt% of polyvinylidene fluoride binder, and 0.5 wt% of carbon nanotube conductive material were mixed together to prepare a positive electrode active material layer slurry, and the positive electrode active material layer slurry was coated on an aluminum foil current collector, and then dried and pressed to prepare a positive electrode. Herein, the loading level of the positive electrode active material layer was 10 mg / cm 2 , and the density of the positive electrode active material layer in the finally pressed positive electrode was about 3.4 g / cc.

[0154] 97.5 wt% of graphite negative electrode active material, 1.5 wt% of carboxymethyl cellulose, and 1 wt% of styrene-butadiene rubber were mixed together in an aqueous solvent to prepare a negative electrode active material layer slurry. The negative electrode active material layer slurry was coated on a copper foil current collector, and then dried and pressed to prepare a negative electrode.

[0155] Subsequently, the positive electrode was used together with lithium metal as the counter electrode and a polytetrafluoroethylene separator. In addition, an electrolyte prepared by dissolving 1 M LiPF6 in a mixed solvent of ethylene carbonate and dimethyl carbonate with a volume ratio of 3:7 was used to prepare a rechargeable lithium battery cell according to the usual method.

[0156] Example 2

[0157] The positive electrode active material and the rechargeable lithium battery cell were prepared in a manner substantially the same as in Example 1, except that based on 100 mol% of the total metals other than lithium in the final positive electrode active material, the aluminum content of aluminum sulfate was designed to be 1.0 mol%.

[0158] Example 3

[0159] The positive electrode active material and the rechargeable lithium battery cell were prepared in substantially the same manner as in Example 2, except that in the preparation of the positive electrode active material, the zirconium content was designed to be 0.5 mol% based on the total metal other than lithium in 100 mol% of the lithium nickel manganese aluminum composite oxide.

[0160] Example 4

[0161] The positive electrode active material and the rechargeable lithium battery cell were prepared in substantially the same manner as in Example 2, except that in the preparation of the positive electrode active material, the zirconium content was designed to be 0.8 mol% based on the total metal other than lithium in 100 mol% of the lithium nickel manganese aluminum composite oxide.

[0162] Comparative Example 1

[0163] The positive electrode active material and the rechargeable lithium battery cell were prepared in substantially the same manner as in Example 2, except that the positive electrode active material was prepared without adding ZrO2 (i.e., without the zirconium doping process).

[0164] Comparative Example 2

[0165] The positive electrode active material and the rechargeable lithium battery cell were prepared in substantially the same manner as in Example 2, except that in the preparation of the positive electrode active material, the zirconium content was designed to be 0.1 mol% based on the total metal other than lithium in 100 mol% of the lithium nickel manganese aluminum composite oxide.

[0166] Comparative Example 3

[0167] The positive electrode active material and the rechargeable lithium battery cell were prepared in substantially the same manner as in Example 2, except that in the preparation of the positive electrode active material, the zirconium content was designed to be 1.0 mol% based on the total metal other than lithium in 100 mol% of the lithium nickel manganese aluminum composite oxide.

[0168] Evaluation Example 1: Zirconium Doping Analysis in Positive Electrode Active Material

[0169] The zirconium doping state of the positive electrode active material of Example 1 was examined by SEM-EDS mapping. SEM-EDS was analyzed using Philips' FEI Titan 80-300 at an acceleration voltage of 15 kV. Figure 5 is the SEM-EDS image of Zr on the surface of the final positive electrode active material of Example 1. Refer to Figure 5 , zirconium doping was on the entire positive electrode active material, which strengthened the structural stability, thus improving the electrochemical performance at high voltages.

[0170] Evaluation Example 2: Surface Analysis of Positive Electrode Active Material

[0171] The positive electrode active materials of Example 1 and Example 2 were compared by taking scanning electron microscope (SEM) images. Figure 6 is an SEM image of the surface of the positive electrode active material prepared in Example 1, and Figure 7 is its enlarged image. Figure 8 is an SEM image of the surface of the positive electrode active material prepared in Example 2, and Figure 9 is its enlarged image. The amount of aluminum coating in Example 2 is greater than that in Example 1, where referring to Figures 6 to 9 , the greater the amount of aluminum coating, the thicker the aluminum coating formed on the surface.

[0172] Evaluation Example 3: Evaluation of Initial Charge / Discharge Capacity and Efficiency

[0173] At 25 °C, the rechargeable lithium battery cells of Example 1 to Example 4 and Comparative Example 1 to Comparative Example 3 were charged at a constant current of 0.2C to an upper limit voltage of 4.45V, and then charged at a constant voltage to 0.05C, and then discharged at 0.2C to a cut-off voltage of 3.0V for initial charge and discharge. In Table 1, the initial charge capacity, the initial discharge capacity, and the ratio of the initial discharge capacity to the initial charge capacity as the efficiency are provided.

[0174] Evaluation Example 4: High-Temperature Cycle Life Characteristics

[0175] After the initial charge and discharge in Evaluation Example 3, at 45 °C, in the voltage range of 3.0V to 4.45V, the battery cells were charged and discharged at 1.0C for 50 cycles or more to calculate the ratio of the discharge capacity of the 50th cycle to the initial discharge capacity (i.e., the high-temperature cycle life), and the results are also shown in Table 1.

[0176] Table 1

[0177]

[0178]

[0179] Referring to Table 1, compared with the examples and other comparative examples, Comparative Example 1 without zirconium doping showed poor high-temperature cycle life characteristics.

[0180] Examples 1 to 4 in which the zirconium content of the lithium nickel manganese aluminum composite oxide is in the range of 0.2 mol% to 0.8 mol% showed improved high-temperature cycle life characteristics compared to Comparative Examples 2 and 3 in which the zirconium content was outside the following range. In addition, Example 1 in which the aluminum content in the coating was 0.8 mol% achieved high initial charge and discharge capacities, high initial charge and discharge efficiencies, and excellent high-temperature cycle life characteristics simultaneously (e.g., synchronously).

[0181] Although the subject matter of the present disclosure has been described in connection with the content of exemplary embodiments currently regarded as practical, it should be understood that the present disclosure is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims and their equivalents.

Claims

1. A positive electrode active material, comprising: A core particle, comprising a layered lithium nickel manganese aluminum composite oxide doped with zirconium, wherein each of the core particles is a secondary particle formed by aggregating a plurality of primary particles, The average particle size D of the secondary particles 50 is 10 μm to 25 μm, and in the layered lithium nickel manganese aluminum composite oxide doped with zirconium, based on 100 mol% of the total metals other than lithium in the layered lithium nickel manganese aluminum composite oxide doped with zirconium, the zirconium content is 0.2 mol% to 0.8 mol%.

2. The positive electrode active material according to claim 1, wherein: in the layered lithium nickel manganese aluminum composite oxide doped with zirconium, based on 100 mol% of the total metals other than lithium in the layered lithium nickel manganese aluminum composite oxide doped with zirconium, the nickel content is 60 mol% to 80 mol%, the manganese content is greater than or equal to 10 mol%, and the aluminum content is 1 mol% to 3 mol%.

3. The positive electrode active material according to claim 1, wherein: the concentration of aluminum in the core particles is uniform.

4. The positive electrode active material according to claim 1, wherein: in the layered lithium nickel manganese aluminum composite oxide doped with zirconium, based on 100 mol% of the total metals other than lithium in the layered lithium nickel manganese aluminum composite oxide doped with zirconium, the cobalt content is 0 mol% to 0.01 mol%.

5. The positive electrode active material according to claim 1, wherein: the layered lithium nickel manganese aluminum composite oxide doped with zirconium is represented by Chemical Formula 1: Chemical Formula 1 Li a1 Ni x1 Mn y1 Al z1 Zr v1 M 1 w1 O 2-b1 X b1 Among them, in Chemical Formula 1, 0.9 ≤ a1 ≤ 1.8, 0.6 ≤ x1 ≤ 0.8, 0.1 ≤ y1 ≤ 0.38, 0.01 ≤ z1 ≤ 0.03, 0.002 ≤ v1 ≤ 0.008, 0 ≤ w1 ≤ 0.2, 0.9 ≤ x1 + y1 + z1 + v1 + 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 Zn, and X is one or more elements selected from F, P, and S.

6. The positive electrode active material according to claim 1, wherein: further comprises a coating on the surface of the core particles and comprising aluminum.

7. The positive electrode active material according to claim 6, wherein: based on 100 mol% of the total metals other than lithium in the positive electrode active material, the aluminum content in the coating is 0.5 mol% to 1.5 mol%.

8. The positive electrode active material according to claim 6, wherein: the coating is in the form of a shell continuously surrounding the surface of the core particles.

9. The positive electrode active material according to claim 6, wherein: the thickness of the coating is 30 nm to 500 nm.

10. The positive electrode active material according to claim 6, wherein: the deviation of the thickness of the coating within one positive electrode active material particle is less than or equal to 20%.

11. A method for preparing a positive electrode active material, comprising: mixing a nickel manganese aluminum composite hydroxide, a zirconium raw material, and a lithium raw material together, and performing heat treatment to obtain a layered lithium nickel manganese aluminum composite oxide doped with zirconium, wherein based on 100 mol% of the total metals of the nickel manganese aluminum composite hydroxide and the zirconium of the zirconium raw material, the zirconium content of the zirconium raw material is 0.2 mol% to 0.8 mol%.

12. The method according to claim 11, wherein: In the nickel-manganese-aluminum composite hydroxide, based on 100 mol% of the total metals in the nickel-manganese-aluminum composite hydroxide, the nickel content is 60 mol% to 80 mol%, the manganese content is greater than or equal to 10 mol%, the aluminum content is 1 mol% to 3 mol%, and the cobalt content is 0 mol% to 0.01 mol%.

13. The method according to claim 11, wherein: The heat treatment is carried out at 750 °C to 950 °C.

14. A method for preparing a positive electrode active material, comprising: (i) preparing a zirconium-doped layered lithium nickel manganese aluminum composite oxide by the method for preparing a positive electrode active material according to any one of claims 11 to 13; (ii) adding an aluminum raw material to an aqueous solvent and mixing to prepare a coating solution; (iii) adding the zirconium-doped layered lithium nickel manganese aluminum composite oxide to the coating solution and mixing them together to prepare a mixed solution; and (iv) removing the aqueous solvent from the mixed solution, drying and heat-treating the resulting product to form a coating on the surface of the zirconium-doped layered lithium nickel manganese aluminum composite oxide.

15. The method according to claim 14, wherein: Based on 100 mol% of the total metals other than lithium in the positive electrode active material, the aluminum content of the coating is 0.5 mol% to 1.5 mol%.

16. A positive electrode, comprising: a positive electrode current collector, and a positive electrode active material layer on the positive electrode current collector, wherein the positive electrode active material layer comprises the positive electrode active material according to any one of claims 1 to 10, the positive electrode active material prepared by the method according to any one of claims 11 to 13, or the positive electrode active material prepared by the method according to any one of claims 14 and 15.

17. The positive electrode according to claim 16, wherein: The positive electrode active material layer has a loading level of 10 mg / cm 2 to 40 mg / cm 2 .

18. The positive electrode according to claim 16, wherein: The positive electrode active material layer has a density of 3.3 g / cc to 3.7 g / cc.

19. A rechargeable lithium battery, comprising: the positive electrode according to any one of claims 16 to 18; a negative electrode; and an electrolyte.

20. The rechargeable lithium battery according to claim 19, wherein: The charging voltage of the rechargeable lithium battery is greater than or equal to 4.45 V.

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